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Intermittent aeration strategy to enhance organics and nitrogen removal in subsurface flow constructed wetlands
Abstract
In this study, an intermittent-aerated subsurface flow constructed wetland (SFCW) A was set up to assess its performance in decentralized rural sewage treatment. A conventional SFCW B and a subsurface wastewater infiltration system (SWIS C) were also constructed for comparison. Alternate anaerobic and aerobic conditions were well developed by intermittent aeration. High removal of organic pollutants (29.3gm(-2)d(-1)), ammonium nitrogen (3.5gm(-2)d(-1)) and total nitrogen (3.3gm(-2)d(-1)) were obtained simultaneously in SFCW A compared with SFCW B and SWIS C. Fluorescence in situ hybridization analysis proved that the intermittent aeration obviously enhanced the growth of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) in SFCW A. These results suggest that intermittent aeration strategy is reliable to enhance the performance of SFCWs in decentralized rural sewage treatment.
... In recent years, aerated wetlands (AWs) have become wellappreciated worldwide and proved optimal for nitrification (Nivala et al., 2020;Zhou et al., 2018;Masih, 2017a, 2017b;Fan et al., 2013;Hu et al., 2012). However, denitrification is often limited due to unfavorable conditions such as high oxygen concentrations (due to aeration) and lack of soluble as well as biodegradable organic matter (OM). ...
... As a consequence, the removal efficiency of TN is often limited in AWs (Ding et al., 2012b;Uggetti et al., 2016;Khan et al., 2022). Moreover, in previous studies, aeration effects have only been tested in continuous mode (Butterworth et al., 2013;Maltais-Landry et al., 2009;Nivala et al., 2019a) or in time-based aeration (Fan et al., 2013;Hu et al., 2012;Masih, 2017a, 2017b;Zhou et al., 2018) and, mostly synthetic wastewaters were used at low flow rates (X. Chen et al., 2018;Ding et al., 2012;Li et al., 2014;Zapater-Pereyra et al., 2014). ...
... Previous studies (X. Chen et al., 2018;Ding et al., 2012;Fan et al., 2013;Zhuang et al., 2019) have revealed that with the increase in COD/N ratios, AWs showed significantly higher TN removal as compared to non-aerated systems. However, most of the studies were conducted on a small scale and/or in a controlled environment, with longer hydraulic residence time (HRT) and focusing mostly on the secondary treatments. ...
Aerated wetlands (AW) are normally used for high oxygen demand situations and were proven optimal for nitrification. However, denitrification remains a concern in AWs especially due to unfavorable oxygen concentrations and lack of biodegradable organic matter (OM). In this study, a 350 m² aerated horizontal subsurface flow constructed wetland (HSSF CW) treating the effluent of a municipal wastewater treatment plant, was tested in a high hydraulic loading rate situation (0.69 m³.m⁻².d⁻¹, 12 h hydraulic retention time), in combination with external carbon dosing to promote denitrification. Forced bed aeration (FBA™) allowed to independently aerate three equally sized zones along the flow direction, and was controlled by a Dissolved Oxygen (DO) sensor in each zone. Zone 1 was destined for nitrification (DO = 2–3 mg.O2.L⁻¹), zone 2 for denitrification (no aeration) with the addition of a carbon source (Brenntaplus VP-1), and zone 3 was again aerated (DO = 2–3 mg.O2.L⁻¹) to degrade any residual OM. Four different carbon dosages (COD/N 0, 2.0, 3.5 and 4.0) were applied at the start of zone 2, based on online measured nitrate data. The results revealed that nitrification remained optimal (±100%) throughout the experiment despite the lower water temperature (10–15 °C). Total nitrogen (TN) removal increased from 23 to 59% as the COD/N ratio increased from 0 to 4. However, the COD removal efficiency remained moderate during initial dosing (21 and 18% for COD/N = 0 and 2, respectively) and further decreased with higher carbon dosing (no removal for COD/N = 4.0). The outcomes of this study can be helpful for implementing carbon dosing to enhance nitrate removal in full-scale AWs used for tertiary treatment.
... A key research focus for this technology has been the aeration regime [19,20]. So far, most experiments have analyzed the aeration effects in continuous mode [19,21] or time-based intermittent aeration [22][23][24]. Only a few studies [25] applied aeration based on dissolved oxygen (DO) level setpoints. ...
... Similar results were described by Uggetti et al. [25] where the authors obtained 99.9% NH 4 -N removal in both continuous aerations and controlled intermittent aeration mode. Moreover, other studies ( [22]; Lie yu [42]) also proved the positive effect of aeration on ammonium reduction, from 20-24% to 89-93% for non-aerated and intermittently aerated HSSF CWs respectively. The NO 3 -N concentrations in this study provide useful information about nitrate sinks in both CWs. ...
... The results of the COD removal efficiencies in the current study are in accordance with Stefanakis et al. [5], where a continuous AW was investigated for effluent polishing of a municipal WWTP and showed a COD removal of 22.3%. However, these findings are contradictory to other experiments where the effect of varying degrees of aeration was found to be negligible in terms of COD removal [19,22,25,42]. ...
Aerated wetland (AW) technology is typically used in high oxygen demand situations. This study however investigated its applicability for further polishing of effluents of both a municipal and an industrial wastewater treatment plant. Different aeration and pollutant removal strategies were tested, all under high hydraulic loading rate conditions (0.69 m³.m⁻².d⁻¹, 12 hours hydraulic retention time). The experiments were done on two 350 m² horizontal subsurface flow constructed wetlands (HSSF CW), filled with expanded clay aggregates (ArgexTM) and planted with common reed (Phragmites australis). Each CW was divided into three equal zones, each equipped with forced bed aeration (FBATM). For this study, continuous (100% on) and time-based (50%-time on/off) aeration were compared versus set dissolved oxygen levels controlled by oxygen sensors (3-4, 2-3 and 1-2 mgO2.L⁻¹ in each zone, and 2-3 mgO2.L⁻¹ in zone 1 and no aeration in zones 2 and 3, designated as 2-3/0/0). Results showed near 100% nitrification for all aeration regimes. Chemical oxygen demand (COD) removal was between 18-33% during high aeration (100%, 50%, 3-4 and 2-3 mgO2.L⁻¹) but was reduced (1-15%) during the most limiting aeration modes (1-2 and 2-3/0/0 mgO2.L⁻¹). Denitrification was limited for municipal effluent, however, reasonable NO3-N removal (31-72%) was noted for industrial effluent. The optimal balance between removal efficiency and energy consumption was found to be for the 2-3 mgO2.L⁻¹ aeration setting, consuming 6.9 - 11.2 Wh.m⁻³. The outcomes of this study can be helpful for implementing aerated CWs as a tertiary treatment.
... The copy number of the amoA gene was 2.60 to 6.12 times higher than that of nxrA, aligning with the findings of Pelissari et al. [47]. Ammonia-oxidizing bacteria oxidize NH 4 + -N to NO 2 --N, thereby providing substrates for nitrite-oxidizing bacteria to oxidize NO 2 --N to NO 3 − -N [48]. At the rear ends of HSSFCWs, a steady decrease was observed in the disparity between the absolute abundance of amoA and nxrA, indicating that the conversion rate of NH 4 + -N to NO 2 − -N by ammonia-oxidizing bacteria was reduced in the rear ends of HSSFCWs. ...
... times higher than that of nxrA, aligning with the findings of Pelissari et al. [47]. Ammoniaoxidizing bacteria oxidize NH4 + -N to NO2 --N, thereby providing substrates for nitrite-oxidizing bacteria to oxidize NO2 --N to NO3 − -N [48]. At the rear ends of HSSFCWs, a steady decrease was observed in the disparity between the absolute abundance of amoA and nxrA, indicating that the conversion rate of NH4 + -N to NO2 − -N by ammonia-oxidizing bacteria was reduced in the rear ends of HSSFCWs. ...
Nitrogen pollution of surface water is still a critical issue worldwide. In this study, a total of four treatments were conducted in horizontal subsurface flow constructed wetlands (HSSFCWs) to explore the removal rate of nitrogen in the carbon-deficient wastewater, including combination of aeration and external carbon source (CW_CA), external carbon source (CW_C), aeration (CW_A), and control group without aeration and carbon source (CW_CK). Results showed that the removal rates of total nitrogen (TN) in the enhanced treatments were increased compared with CW_CK. The highest removal rates of COD (66.56%), NH4+-N (73.51%), NO3−-N (79.31%), and TN (76.19%) were observed in the CW_CA treatment. The bacterial community structure at the fore and rear ends of HSSFCWs was simultaneously changed in the CW_CA and CW_C treatments, respectively. The highest richness index at both the fore and rear ends of HSSFCWs was found in the CW_CA treatment. The richness and diversity indices of CW_C declined at the fore ends of HSSFCWs, but increased at the rear ends of HSSFCWs. Furthermore, the functional bacteria and genes significantly changed among different treatments. At the fore ends of HSSFCWs, the highest relative abundance of nitrifiers and absolute abundance of amoA and nxrA were obtained in CW_A, and the highest relative abundance of denitrifying bacteria and absolute abundance of nirS, nirK, nosZ were found in CW_C. However, at the rear ends of HSSFCWs, the highest relative abundance of nitrifiers and denitrifying bacteria as well as the absolute abundance of related genes were also observed in the CW_CA treatment. Overall, CW_CA improved the nitrogen removal rate by increasing the abundance of nitrogen-converting functional microbes and the genes associated with nitrification and denitrification.
... Denitrification (i.e. NO 3 − → N 2(g) ) is a beneficial process contributing to total nitrogen (TN) removal in CWs (Fan et al., 2013;Hu et al., 2012;Ong et al., 2010;Wu et al., 2020). Denitrification is an anaerobic process, therefore requiring un-oxygenated regions in the wetland for the process to be completed. ...
... Some studies have found an increase in P removal with increased DO due to greater adsorption and precipitation (Ilyas and Masih, 2018;Li et al., 2021b), whilst other studies showed no significant effects of artificial aeration on the removal of TP (Chyan et al., 2016). Although artificial aeration requires additional energy input, it has been found to be beneficial, especially when the CW is operated at a high HLR, and has the advantage that it can be controlled to achieve desired oxygen outputs (Boog et al., 2019;Fan et al., 2013;Hu et al., 2012;Maltais-Landry et al., 2009;Nivala et al., 2020;Ong et al., 2010;Zhu et al., 2019). Oxygen can be supplied by aerators at different rates, including continuous aeration (CA) (Maltais-Landry et al., 2009) or intermittent aeration (IA). ...
High organic loadings to constructed wetlands can result in water quality issues such as low dissolved oxygen and high ammonium concentrations, with artificial aeration a potential mitigation option. This study compared baseline (no aeration – NA), continuous aeration (CA), and intermittent aeration (IA) conditions to improve water quality in a tertiary treatment free water surface constructed wetland (FWS CW) with night time hypoxia/anoxia, and high nutrient concentrations. The response variables included dissolved oxygen (DO), total nitrogen (TN), ammonium nitrogen (NH4⁺-N), nitrate nitrogen (NO3⁻-N), total phosphorus (TP), phosphate (PO43–-P), and dissolved organic carbon (DOC). In situ aeration and monitoring was performed from April to June 2021 in a large, field-scale FWS CW, the Laratinga wetlands Mount Barker, South Australia.
The results demonstrated that DO increased by an average 2.11 mg L⁻¹ from NA to CA during the night and 1.26 mg L⁻¹ and 1.84 mg L⁻¹ from NA to IA during the night and day respectively when averaging over the basins. The C/N ratio was very low and there was no significant influence of DO on DOC concentrations. There was no significant difference in TN concentrations with the application of aeration aside from a decrease in the channel at night from NA to IA, and an increase in NH4⁺-N resulted under IA compared with NA in Basin 1 and 2 during the day. This implies that the N loadings exceeded the wetland's ability to complete nutrient conversions at a rate that aligns with input rate. The concentrations of NO3⁻-N increased at night under CA and IA treatments suggesting that some nitrification was promoted, or there was inhibition of dissimilatory nitrate reduction to ammonium. The concentrations of TP and PO43–-P significantly increased with the aeration compared with no aeration, however there was no difference between the aeration treatments. This suggested that increased sediment resuspension during aeration increased P in the water. There was no change in DOC with the application of aeration. Overall, the DO increased with aeration application and may be able to better support the wetland ecology; however, the Laratinga wetland is overloaded and the capacity of the wetland to effectively transform and remove nutrients is inhibited, even with the application of artificial aeration.
... DO concentrations (<2 mg/L), particularly in the VSSF, would be caused by the oxygen demands for the organic matter oxidation of (min 1.5 mg/L DO), generating a competition of the DO, thus decreasing the ammonium-oxidizing bacteria's performance and, as a consequence, nitrification [66,67]. According to Liu et al. [67], DO concentrations higher than 1.5 mg/L are needed for nitrification to occur. ...
... The − -N than in the HSSF (up to 97% in autumn), which could have been removed through denitrification under anaerobic conditions [66]. Alternatively, the decrease in NO 3 − -N could also be explained by simultaneous nitrification/denitrification (SND) processes [71]. ...
The aim of this study is to evaluate seasonal enhancement of nitrogen removal on domestic wastewater treatment performance by partially saturated and saturated HBCWs. To achieve this, two HBCWs consisting of a vertical subsurface flow constructed wetland, followed by a horizontal subsurface flow constructed wetland (VSSF-HSSF) were evaluated. Two saturation levels were used: (a) partially saturated HB1:VSSF1 (0.6 m)-HSSF1 (0.15 m), (b) saturated HB2: VSSF2 (0.8 m)-HSSF2 (0.25 m). Each unit was planted with Schoenoplectus californicus and was operated for 297 days. The removal efficiencies in HB1 and HB2 were above 70%, 86%, 77% and 55% for chemical oxygen demand (COD), total suspended solids (TSS), nitrogen as ammonium (NH4+-N), and total nitrogen (TN), respectively. For VSSF, a higher level of saturation (from 0.6 to 0.8 m) meant a decrease of 17% in the TN removal efficiencies, and for HSSF, an increase from 0.15 to 0.25 m of saturation meant a decrease of 11 and 10% in the NH4+-N and TN removal efficiencies, respectively. Thus, the increase of saturation level in HBCWs reduces the transformation and/or removal of components of the wastewaters to be treated, particularly nitrogen. Through this research, the possibility of optimizing the transformation of nitrogen with partially saturated hybrids can be examined.
... Here, we chose input variables with three aspects: influent, operation, and design, based on the understanding of the SCW system and the availability of published data about SCW. The critical factors of SCW have been previously considered, such as plant, wastewater type, HLR, hydraulic retention time, water depth, feeding (Ghosh and Gopal, 2010;Stefanakis and Tsihrintzis, 2012;Wu et al., 2015), C:N ratio (Wang et al., 2020a), and oxygen or air supply (Fan et al., 2013;Ilyas and Masih, 2017;Jia et al., 2018). ...
... (7)) and (Eq. (8)) (Dobson and Barnett, 2008): ...
... Improved agronomic practices, increased N use efficiency, use of diversified cropping systems, adoption of crop cultivars with high harvest index, and the use of soil bioresources such as P-solubilizers and arbuscular mycorrhizal fungi in crop production were reported to lower the average C footprint in semi-arid areas (Gan et al., 2011). The over-exploitation of groundwater by agriculture for irrigation during recent years has lowered aquifer levels in many Asian countries, and pumping water from lower strata in the future would result in a greater use of energy, which is mostly generated by coal combustion, and would therefore result in increased emissions of GHG (Zhang et al., 2013). Improved water use efficiency is likely to become a critical criterion for many grain-producing areas in South Asia, in part due to necessary adaptation to the anticipated adverse effects from climate change (Elliott et al., 2014). ...
... The reason for poor removal efficiency for nitrogen and phosphorus is because SSF-type CWs are anoxic systems with insufficient amount of dissolved oxygen in water (Vymazal, 2014); moreover, the traditional bed materials are not suitable enough to abate phosphorus as they lack sufficient calcium, magnesium, iron and aluminium ions (Vohla et al., 2011). Energy-intensive solutions such as bed aeration (Fan et al., 2013) or influent wastewater aeration (Rossmann et al., 2013) using solar-powered aerators though will compromise the intrinsic operational simplicity of these systems. Such modifications should be limited to sites where skilled supervision is available at a reasonable cost. ...
This book with 13 chapters presents various efforts across India, made by different corporates in collaboration with ICRISAT. It describes how in each location, cutting across the sectors, both the corporate and a research organization have meticulously designed and executed location- specific projects in the interest of enhancing livelihoods and improving natural resource use efficiency. The first chapter sets the stage to understand the CSR path of development, course corrections, policy support from the Government of India, refinements made over the years, key findings of the recent assessments made by leading agencies and critical role played by national-level corporate associations. Chapter 2 presents why holistic solutions are needed to effectively address the issues of increasing land degradation, water scarcity and threat of climate change to bring in sustainable system intensification and diversification to high-yielding, climate-smart and high-value crops. Chapter 3 deals with unabated soil degradation due to low soil organic C levels, multiple nutrient deficiencies including micro and secondary nutrients, rising salinity and soil loss due to erosion which jeopardize food security of swiftly rising global population projected to be 9.7 billion by 2050. Chapter 4 describes the semiarid tropical region as primarily agrarian with the dominance of rainfed traditional agricultural production systems. Chapter 5 explains how water plays an important role in semiarid tropical regions to address water scarcity, land degradation, and crop and livestock productivity which improve the rural livelihood system. Chapter 6 shows the initiative by Asian Paints Limited to improve rural livelihood through integrated watershed development programme in six villages in Patancheru mandal of Medak district, Telangana, covering an area of 7143 ha. Chapter 7 emphasizes the development of the Bundelkhand region of Central India, which is the hot spot of water scarcity, land degradation and poor socioeconomic status. Chapter 8 provides soil health mapping for enhancing water use efficiency in watersheds for sustainable improved livelihoods in Sir Dorabji Tata Trust-supported initiative across 16 districts of Madhya Pradesh and Rajasthan states of India. Chapter 9 describes a scaling-up approach in developing soil test-based fertilizer recommendations at block level, supported by the Sir Ratan Tata Trust in Jharkhand and Madhya Pradesh. Chapter 10 explains innovative model of farmer-centric watershed management in Kurnool district, Andhra Pradesh and Vijayapura district, Karnataka for improving rural livelihoods and reducing degradation of natural resources. Chapter 11 presents the success story the community and farm-based rainwater conservation (supported by RECL) have created a net storage capacity of approximately 18 000 m ³ with total conservation of approximately 50 000 m ³ /year of surface runoff water in Anantapur watershed of Andhra Pradesh and 27 000 m ³ storage capacity with conservation of approximately 54 000 m ³ /year of surface runoff water in Mahabubnagar watershed of Telangana. Chapter 12 demonstrates how improved sanitation and hygiene through proper wastewater management is critical to sustainable growth of rural communities. Chapter 13 summarizes, based on different case studies shown in earlier chapters, livelihood benefits and improved water use efficiency across various CSR sites. Overall, this book provides an excellent insight into the early phase of CSR work undertaken by ICRISAT-led consortium for achieving the impacts and has gathered number of learnings by working in partnership.
... After effective organics oxidation and nitrification by aeration, the carbon source as electron donor was Uncorrected Proof deficient, which led NO À 3 À N as electron accepters to be accumulated and not to be eliminated with a low carbon/nitrogen ratio. The results accorded with the report of Fan et al. (2013). With a carbon/nitrogen ratio of 12 and 16, the average removal efficiencies of TN in IA-SWIS and CA-SWIS were significantly higher than those in NA-SWIS (P , 0.05). ...
This study investigated the influences of aeration mode and influent carbon/nitrogen ratio on matrix oxygen concentration, pollutant removal, greenhouse gas emission, functional gene abundances and bacterial community in subsurface wastewater infiltration systems (SWISs). Intermittent or continuous aeration enhanced oxygen supply at 0.6 m depth in the matrix, which improved organics removal, nitrogen removal, the abundances of bacterial 16S rRNA, amoA, nxrA, narG, napA, nirK, nirS, norB, nosZ genes, bacterial community Alpha diversity, the relative abundances of Actinobacteria at 0.6 m depth, the relative abundances of Chloroflexi, Gemmatimonadetes, Bacteroidetes and Firmicutes at 0.9 and 1.2 m depth and reduced CH4 and N2O conversion efficiencies, the abundance of mcrA gene with carbon/nitrogen ratio of 12 and 16 compared with non-aeration. Increased carbon/nitrogen ratio resulted in higher TN removal efficiencies and lower CH4 and N2O conversion efficiencies in aeration SWISs than those in non-aeration SWIS. Intermittent aeration SWIS obtained high removal efficiencies of 83.2, 85.4 and 90.8% for TN, NH4+ -N and COD and low conversion efficiency of 0.21 and 0.65% for N2O and CH4 with optimal carbon/nitrogen ratio of 12. However, high TN (82.6%), NH4+ -N (84.9%) and COD (92.2%) removal efficiencies and low CH4 (0.67%) and N2O (0.23%) conversion efficiencies were achieved in continuous aeration SWIS with carbon/nitrogen ratio of 16.
... Intermittent aeration is another aeration strategy, which creates alternating aerobic and anoxic environments to simultaneously facilitate nitrification and denitrification for TN removal, while also reducing the overall energy cost 105 . This method drives efficient removal of COD (97%, 29.3 g m −2 d −1 ), NH 4 + -N (95%, 3.5 g m −2 d −1 ) and TN (80%, 3.3 g m −2 d −1 ) in pilot-scale SSFCWs treating domestic wastewater, better than that in conventional CW systems 106 . Moreover, optimal intermittent aeration decreased CH 4 emission by 60% in a field-scale SSFCW 107 and N 2 O emissions by 38% in laboratory-scale SSFCWs 108 . ...
... These COD values are consistent with other studies in Brazil on GW without a kitchen sink fraction [21,34]. Considering the area of the system per person, the present study operated with a superficial area of 0.7 m 2 , which is below the 0.8 to 8 m 2 ·person −1 reported in other studies [35][36][37] of HSSF-CW. Hoffmann et al. [32] recommended that the specific area required should be between 3 and 10 m 2 ·person −1 in warm climates. ...
Surfactants are among the main chemical contaminants in greywater (GW) and can cause severe health issues in humans and aquatic organisms. We assessed the performance of a multistage constructed wetland system (EvaTAC) for GW treatment and capacity of the microbial community in linear alkyl benzene sulfonate (LAS) biodegradation. Physicochemical analyses were performed over 497 d, and biomass samples were collected for high-throughput DNA sequencing. The system was predominated by anaerobic conditions and received an average chemical oxygen demand (COD) and LAS of 374 and 32 mg·L −1 , with removal rates of 66% and 43%, respectively. A positive correlation between COD and LAS suggested COD as a design parameter for LAS removal. We identified microbial genera participating in hydrolysis, fermentation, syntrophy, acetogenesis, methanogenesis, surfactant degradation, and sulphate reduction. Among the 15 surfactant-degrading genera, Pseudomonas was predominant. Community richness and diversity indices were comparable between subsystems, with a slight decrease in diversity observed towards the outlet. Among the LAS degraders, Rhodopseu-domonas palustris had the highest relative abundance of operational taxonomic unit (OTU)s in all samples and the highest richness in the anaerobic chamber. The patterns in microbial community composition and environmental conditions suggest that LAS biodegradation occurred throughout the EvaTAC system.
... It is reported that typical sludge growth yield from the CAS process ranges from 0.3 to 0.5 g dry biomass/g COD removed, which simply states that 1 kg COD elimination generates approximately 0.3-0.5 kg dry biomass (Wan et al., 2016). Due to the activity of chemoheterotrophic bacteria that utilize organic matter and use O 2 as a final electron acceptor (Biddanda et al., 1994;Fan et al., 2013), aeration can affect the accumulation of biomass in the system (Fajri et al., 2018). Consequently, WAS production is inevitably increased from the CAS-based WWTPs causing high energy demands for post-treatment. ...
Despite a quick shift of global goals toward carbon-neutral infrastructure, activated sludge based conventional systems inhibit the Green New Deal. Here, a municipal wastewater treatment plant (MWWTP) for carbon neutrality and energy sustainability is suggested and discussed based on realizable technical aspects. Organics have been recovered using variously enhanced primary treatment techniques, thereby reducing oxygen demand for the oxidation of organics and maximizing biogas production in biological processes. Meanwhile, ammonium in organic-separated wastewater is bio-electrochemically oxidized to N2 and reduced to H2 under completely anaerobic conditions, resulting in the minimization of energy requirements and waste sludge production, which are the main problems in activated sludge based conventional processes. The anaerobic digestion process converts concentrated primary sludge to biomethane, and H2 gas recovered from nitrogen upgrades the biomethane quality by reducing carbon dioxide in biogas. Based on these results, MWWTPs can be simplified and improved with high process and energy efficiencies.
... Similar result was also confirmed by Lai et al. (2020b), who found that the NH 4 + -N mean removal rate of aerated VFCW was 9% higher than that of non-aerated VFCW. Fan et al. (2013b) investigated that NH 4 + -N mean removal rate can achieved 89% in aerated CWs. Compared with VFCW-1, intermittent aeration of VFCW-3 significantly increased the mean removal rate of NH 4 + -N, indicating that nitrification of NH 4 + -N may be inhibited by the lack of dissolved oxygen. ...
Four vertical-flow CWs (VFCWs) with different substrates and aeration conditions were studied on nutrient-removal capacity from synthetic wastewater. Zeolite substrate VFCWs (none-aerated: VFCW-1, aerated: VFCW-3) paralleled with ceramsite (none-aerated:VFCW-2, aerated: VFCW-4) were used to study the removal efficiencies of N and organics, the bacterial community, and the related functional genes. The results indicated that the pollutant removal efficiency was significantly enhanced by intermittent aeration. VFCW-4 (ceramsite with aeration) demonstrated a significant potential to remove NH4+-N (89%), NO3–-N (78%), TN (71%), and COD (65%). VFCW-3 and VFCW-4 had high abundances of Amx, amoA, and nirK genes, which was related to NH4+-N and NO2–-N removal. The microbial diversity and structure varied with aeration and substrate conditions. Proteobacteria, Actinobacteria, Candidatus, and Acidobacteria were the main bacteria phyla, with the average proportion of 38%, 21%, 19%, and 7% in the VFCWs. Intermittent aeration increased the abundance of Acidobacteria, which was conducive to the removal of organic matters. Overall, ceramsite substrate combined with intermittent aeration has a great potential in removing pollutants in VFCWs.
... Studies have shown that appropriate soil dissolved oxygen concentration favors the propagation of anammox bacteria (Planctomyces), but a too high concentration inhibits their growth (Fu et al. 2020). Furthermore, maintaining the appropriate soil dissolved oxygen concentration could also increase the activity of nitrifying bacteria, reduce the activity of anaerobic microorganisms like denitrifying bacteria, and subsequently improve the available N content of rhizosphere soil (Fan et al. 2013;Pan et al. 2015). Additionally, the N fixation process is crucial for maintaining the biological productivity of ecosystems, because it can compensate for the bioavailable N loss caused by anammox and denitrification (Capone and Knapp 2007). ...
The technology for the activation of irrigation brackish water was successful at improving the soil environment and crop yields. However, very few studies have examined how activated brackish water irrigation affects the rhizosphere bacterial communities and network patterns. By combining 16S rRNA high-throughput sequencing, we evaluated the diversity and composition of the rhizosphere bacterial community after being subjected to different types of irrigation with activated brackish water. We also analyzed the correlation and co-occurrence networks among the bacterial diversity, composition, and rhizosphere soil properties. The results showed that compared with brackish water irrigation, the salt content of activated irrigation water significantly decreased by 9.35%, 9.83%, and 12.95%, respectively. Irrigation with different types of activated brackish water had no significant (p > 0.05) effect on the diversity of the rhizosphere bacterial community, but it significantly changed its community composition, which was primarily dominated by soil nutrient indicators. The soil total nitrogen (TN) showed a significant (p < 0.01) negative correlation with the Chao1 index. Additionally, the changes in bacterial communities under different types of activated brackish irrigation water mainly occurred at the genus level. We showed that the rhizosphere soil that had been irrigated with oxygenated brackish water and magnetized brackish water better supported the reproduction of some soil-borne pathogens. Magnetization-oxygenation coupling treatment could significantly reduce the colonization of soil-borne pathogens of the rhizosphere soil, while also favoring the function of functional bacteria involved in soil nutrient transformation. This study highlights the main factors affecting the rhizosphere soil bacterial community structure by activated brackish water irrigation, while also providing new technical support for brackish water irrigation.
... It was noted that the average DO in SSF CW without aeration was about 0.24 mg/L, which was insufficient for nitrification . Fan et al. (2013) assessed, DO concentration in SSF CW with intermittent aeration as 3.40 mg/L and 0.5 mg/L when intermittent aeration was not provided. Intermittent aeration helped in achieving both oxic and anoxic conditions alternatively for higher removal of nitrogen concentration. ...
Fecal sludge and septage (FSS) are more concentrated than domestic wastewater which makes it difficult to treat and requires immediate attention otherwise, it leads towards serious environmental problems. In this review, an attempt has been made to highlight and discuss the various aspects of fecal sludge and septage management (FSSM) like its generation, characterization, containment, transportation, treatment, reuse and disposal. A comparison of existing fecal sludge treatment plants and technologies has been reviewed considering land requirement, capital cost, operation and maintenance cost, advantages and disadvantages. Based on the existing practices and review, a techno-economic treatment scheme is designed and proposed for solid-liquid separation and treatment of FSS with resource-recovery as fertilizer, material for construction, energy and treated effluent. To make FSSM, self-sustainable, a revenue generation model is also delineated for the researchers and decision-makers to evaluate its feasibility and implementation, especially in developing and underdeveloped countries.
... Intermittent aeration helped achieve aerobic and anoxic conditions to achieve higher nitrogen removal concentrations (Liu et al. 2019). According to previous research, intermittent aeration can reduce the photosynthetic process of plants, but 4 h of intermittent aeration per day has very little effect on plants (Fan et al. 2013). Intermittent aeration of 4-6 h per day not only reduces aeration costs, but also improves nitrogen and organic removal efficiency (Shukla et al. 2021). ...
This study focused on the water quality of a river in Wuhan City, China, which is surrounded by ponds that were transformed into a bypass multipond wetland system to improve river water quality. The bypass multipond wetland system included surface-flow artificial wetlands, modified partition ponds, aeration reoxygenation ponds, ecological ponds, and other processes. After the stable operation of the process, the water transparency was higher than 60 cm and the dissolved oxygen (DO) was higher than 5 mg/L, while the ammonia nitrogen (NH3-N) concentration was less than 1.0 mg/L, total phosphorus (TP) was lower than 0.2 mg/L, and chemical oxygen demand (COD) was lower than 20 mg/L, achieving the treatment target. After monitoring the results of each process, the process which best enhanced the water transparency enhancement was the surface-flow of the artificial wetlands and ecological ponds. The aeration reoxygenation pond had the best effect on DO enhancement. The processes that most affected NH3-N and TP removal were the surface-flow artificial wetlands and ecological ponds. The modified parthenogenic pond had the greatest effect on COD removal. The bypass multipond wetland system not only improved the river water quality but also enhanced the river landscape, and can act as a reference for similar river water quality improvement actions.
HIGHLIGHTS
Surface flow artificial wetlands use artificial water plants instead of substrate to reduce retrofitting costs.;
Improved parthenogenic pond set up as deep water and shallow water can work better.;
The use of aeration-microbial bacterial agent can remove pollutants better.;
Artificial water plants are used in ecological ponds to provide more attachment sites for microorganisms.;
... A majority of studies on N transforming microbial community in CWs have been carried out for domestic (Bastviken et al., 2003;Criado and Bécares, 2005;Shipin et al., 2005;Truu et al., 2005;Dong and Sun, 2007;Sawaittayothin and Polprasert, 2007;Tietz et al., 2007;Wu et al., 2013;Fan et al., 2016;Li et al., 2020) or synthetic wastewater (Fan et al., 2013b;He et al., 2018;Liu et al., 2018;Sun et al., 2018;Xia et al., 2020). There are limited studies focussing on microbial community in CWs treating stormwater and the influence of wetland design features on N transforming microbes (Kyambadde et al., 2006;Domingos et al., 2011;Bledsoe et al., 2020). ...
Microbial communities play a vital role in nitrogen (N) removal in constructed wetlands (CWs). However, the lack of studies on microbial characteristics of wetland systems designed to treat stormwater demonstrates the importance of comprehensive investigation on microbial response to wetland fluctuations. Moreover, the observed inconsistency in N removal, and detected links between microbial shifts and wetland water level fluctuations is an area of research interest perculiar to stormwater applications. This study surveyed nearly 150 publications to provide a summary and evaluation of N removal efficiency in different types of CWs where microbial communities and their behavior have been correlated to regulating factors. Factors such as flow regime, plants, and physico-chemical properties (e.g., temperature, dissolved oxygen, pH, and nitrogen concentration) were found to significantly influence microbial diversity and composition. Although many studies have analyzed microbial N removal, a majority conducted their studies in bioretention systems. Accordingly, some of the microbial pathways in CWs designed for stormwater treatment have not been investigated. As such, it is suggested that pathways, such as dissimilatory nitrate reduction to ammonium (DNRA) and comammox activity and their changes over dry-wet cycles in stormwater constructed wetlands be investigated. This information could assist engineers to take advantage of the presence of other N transforming communities which could improve microbial diversity within wetland systems. Moreover, it is recommended to track microbial functional genes and their changes over wetland water fluctuation to develop an ecosystem with conditions favorable for microbial pathways with higher N removal potential. In conclusion, the findings of the current literature review reinforce the importance of stormwater runoff treatment and the implementation of new design strategies that are able to enhance microbial activity and diversity leading to a better treatment outcome.
... Generally, the vary biological nitrification and de-nitrification can be considered as the mechanism of nitrogen removal within an ecological treatment of wastewater for example SWWISs and constructed wetlands, where both of them needs environmental conditions such as anaerobic and aerobic, respectively [18,28]. Nevertheless, in common and traditional SWWISs, it is difficult to be simultaneously implemented due to the arrangement limitation [29]. ...
Soil infiltration systems for wastewater treatment require very low energy and maintenance. They are very efficient, cost-effective, low energy consumption, as well as low construction techniques. They have been widely implemented all-over the world particularly for on-site, in remote areas, and in small communities. Currently, groundwater is in concern shortage worldwide due to the significant increasing and continuous withdrawn. It has been proved that soil wastewater infiltration system (SWWIS) is considering as an important on-site wastewater treatment, and as an alternative process for advanced wastewater treatment in terms of efficiency and operation and maintenance. In this systems, wastewater should be treated firstly by conventional physical/chemical or biological treatment followed by infiltration through aerated and unsaturated zone. In these infiltration systems the wastewaters are purified through several steps including physical adsorption, chemical reaction, and biodegradation. SWWIS’s have exhibited an excellent and consistent capacity with respect to decomposing of organic contaminants, as indicated by chemical oxygen demands (COD) and biochemical oxygen demand (BOD5). Meanwhile, it is efficient in removing all the microbial contaminants as well. The challenge factors of the SWWIS are the clogging problem as well as the removal of phosphorous, and the nitrogen.
... Constructed wetlands (CWs) were designed to simulate the natural purification of pollutants by the wetland plants, substrates, and microorganisms (Shen et al. 2018). CWs displayed potential applicability for the treatment of sludge containing heavy metals because of its simple technological process, low operation cost, and good purification capacity (Fan et al. 2013;Zhong et al. 2020). For instance, a sludge treatment wetland with ventilation was conducted by a scholar to analyze the removal and fate of heavy metals from excess sludge (Meng et al. 2020). ...
A microbial fuel cell coupled with constructed wetland (CW-MFC) was built to remove heavy metals (Zn and Ni) from sludge. The performance for the effects of substrates (granular activated carbon (GAC), ceramsite) and plants (Iris pseudacorus, water hyacinth) towards the heavy metal treatment as well as electricity generation was systematically investigated to determine the optimal constructions of CW-MFCs. The CW-MFC systems possessed higher Zn and Ni removal efficiencies as compared to CW. The maximal removal rates of Zn (76.88%) and Ni (66.02%) were obtained in system CW-MFC based on GAC and water hyacinth (GAC- and WH-CW-MFC). Correspondingly, the system produced the maximum voltage of 534.30 mV and power density of 70.86 mW·m⁻³, respectively. Plant roots and electrodes contributed supremely to the removal of heavy metals, especially for GAC- and WH-CW-MFC systems. The coincident enrichment rates of Zn and Ni reached 21.10% and 26.04% for plant roots and 14.48% and 16.50% for electrodes, respectively. A majority of the heavy metals on the sludge surface were confirmed as Zn and Ni. Furthermore, the high-valence Zn and Ni were effectively reduced to low-valence or elemental metals. This study provides a theoretical guidance for the optimal construction of CW-MFC and the resource utilization of sludge containing heavy metals.
... It can be seen that the change trends of BOD 5 concentration in both CWs were similar to COD. Many studies demonstrated that compared with the intermittent aeration mode, using a continuous aeration system could improve the removal effect of organic matter in artificial wetlands (Dong et al. 2012;Fan et al. 2013;). However, this study showed that the increase of aeration frequency did not affect the removal performance of organic matter in both CWs. ...
This study focused on the removal of organic matter and nitrogen and explored the feasible operation strategies to achieve short-cut nitrification and denitrification in two constructed wetlands (CWs), which were designed to treat the actual landfill leachate from a small county in parallel. The two CWs were horizontal sub-surface flow constructed wetlands (HFCW) with partial-area aeration and vertical sub-surface flow constructed wetlands (VFCW) with full-area aeration. The experimental results showed that both CWs could achieve an excellent organic matter and nitrogen removal performance under the conditions of intermittent aeration with high frequency and medium intensity (2 h of aeration and 4 h of rest). The removal efficiencies of COD and total nitrogen by HFCW were 89.08% and 73.22%, and the corresponding values of VFCW were 84.51% and 71.44%, respectively. Meanwhile, the inhibition kinetics model indicated that HFCW with partial-area aeration could enhance the free ammonium (FA) tolerance of ammonium-oxidizing bacteria (AOB) and reduce the conversion percentage of ammonia nitrogen. In addition, the intermittent aeration mode with high frequency and medium intensity could keep the DO concentration below under 0.60 mg L⁻¹ in HFCW, which helped to achieve stable short-cut nitrification and ensure the average nitrite accumulation rate (NAR) reach 50.96%. These results suggested that the intermittent aeration in partial-area could achieve successful short-cut nitrification in HFCW, thereby improving the removal efficiency of nitrogen in landfill leachate.
Graphical abstract
... It was noted that the average DO in SSF CW without aeration was about 0.24 mg/L, which was insufficient for nitrification . Fan et al. (2013) assessed, DO concentration in SSF CW with intermittent aeration as 3.40 mg/L and 0.5 mg/L when intermittent aeration was not provided. Intermittent aeration helped in achieving both oxic and anoxic conditions alternatively for higher removal of nitrogen concentration. ...
Decentralized wastewater treatment has become inevitable as conventional wastewater treatment plants involve huge construction and maintenance costs. One of the most popularly used decentralized wastewater treatments is constructed wetlands. Constructed wetlands are a cost-effective and sustainable treatment method for domestic and industrial wastewater. Over the years, there has been a lot of improvement in the design and process approaches of constructed wetlands. This review paper aims to find the impacts of design processes like artificial aeration, design and flow pattern, effluent recirculation, substrate media, vegetation, and C/N ratio on the treatment performance of constructed wetlands. Based on the review, it is found that intermittent aeration along with recirculation, hybrid constructed wetlands and baffled constructed wetlands are an effective way to remove ammonia and organics from wastewater. Phosphorous removal in constructed wetlands is highly dependent on substrates rather than wetland plants. Further, the paper discusses the future scopes and challenges in terms of improving the efficiency of constructed wetlands, reuse of industrial waste as substrate, solar energy based aeration, etc., to make constructed wetlands a sustainable wastewater treatment technology.
... Constructed wetlands (CWs) were designed to simulate the natural puri cation of pollutants by the wetland plants, substrates and microorganisms (Shen et al. 2018). CWs displayed potential applicability for the treatment of sludge containing heavy metals because of its simple technological process, low operation cost and good puri cation capacity (Fan et al. 2013, Zhong et al. 2020. For instance, a sludge treatment wetland with ventilation was conducted by scholar to analyze the removal and fate of heavy metals from excess sludge (Meng et al. 2020). ...
A microbial fuel cell coupled with constructed wetland (CW-MFC) was built to remove heavy metals (Zn and Ni) from sludge. The performance for the effects of substrates (granular activated carbon (GAC), ceramsite) and plants ( Iris pseudacorus , Water hyacinth ) towards the heavy metal treatment as well as electricity generation were systematically investigated. The CW-MFC systems possessed higher Zn and Ni removal efficiencies as compared to CW. The maximal removal rates of Zn (76.88%) and Ni (66.02%) were obtained in system CW-MFC based on GAC and Water hyacinth (GAC- and WH-CW-MFC). Correspondingly, the system produced the maximum voltage of 534.30 mV and power density of 70.86 mW·m ⁻³ , respectively. Plant roots and electrodes contributed supremely to the removal of heavy metals, especially for GAC- and WH-CW-MFC systems. The coincident enrichment rates of Zn and Ni reached 21.10% and 26.04% for plant roots, 14.48% and 16.50% for electrodes, respectively. A majority of the heavy metals on the sludge surface were confirmed as Zn and Ni. Furthermore, the high-valence Zn and Ni were effectively reduced to low-valence or elemental metals. This study provides a theoretical guidance for the optimal construction of CW-MFC and the resource utilization of sludge containing heavy metals.
... The toxicological effects of these products may appear also in conditions of strong sediment disturbance and secondary intoxication of the reservoir water (Pottinger et al., 20111;. (Singh, 1982;Hamby, 1996;Ruan et al., 2006;Hadad et al., 2006;Chitrakar et al., 2006;Chmielowski & Slizowski, 2008;Juang et al., 2008;Dąbrowska, 2008;Mingjun et al., 2009;Faulwetter et al., 2009;Xiao et al., 2010;Cao et al., 2012;Dong et al., 2012;Gagnon et al., 2012;Sheng et al., 2012;Zhao et al., 2012;Fan et al., 2013;Bartoszek and Koszelnik, 2015;Nasr and Ismail, 2015;Ateia et al., 2016;Mazur et al., 2016;Kaczor et al., 2017;Wsik et al., 2017;Zawadzki et al., 2017;Mazur and Sitarek, 2020;Mazur, 2020;Mazurkiewicz et al., 2020). ...
Aim of the study:
The study aims were to evaluate the aeration process and MBBR bioreactors operation in the bioremediation process of polluted water reservoirs.
Material and methods:
The authors presented a review of water reservoir revitalization methods used in industry practice. Fine and microbubble aeration systems are subject to detailed characteristics. There is described the role of innovative mobile platform systems with MBBR bioreactors in the revitalization of water reservoirs in the article.
Results and conclusions:
Based on the presented scientific information, it has been indicated that the use of effective microaeration and fine bubble aeration systems has a very positive effect on the improvement of the efficiency of revitalization processes. The authors assessed that the indicated methods can only support the main biological method used in the bioremediation of degraded water bodies. The main methods of biological bioremediation was biotechnological methods based on microbiological biopreparations and the formation of eco-barriers (ecotones). A diagram of a prototype rehabilitation platform for water reservoirs is also presented.
In this study, the performance of the Multistage-A/O process in constructed wetland (CW) was compared with A/O/A process in terms of its ability of nitrogen (N) and phosphorus (P) removal...
Biochar has gained global recognition as an effective tool for environmental remediation, and is increasingly being used as an alternative substrate in constructed wetlands (CWs). While, most studies have focused on the positive effects of biochar for the pollutant removal in CWs, less is known about aging and longevity of the embedded biochar. This study investigated the aging and stability of biochar embedded in CWs post-treating the effluent of a municipal and an industrial wastewater treatment plant. Litter bags containing biochar were inserted into two aerated horizontal subsurface flow CWs (350 m2 each), and retrieved on several dates (8-775 days after burial) for assessment of weight loss/gain and changes in biochar characteristics. Additionally, a 525-day laboratory incubation test was conducted to analyze biochar mineralization. The results showed that there was no significant biochar weight loss over time, but a slight increase in weight (2.3-3.0%) was observed at the end, likely due to mineral sorption. Biochar pH remained stable except for a sudden drop at the beginning (8.6-8.1), while the electrical conductivity continued to increase (96-256 μS cm-1) throughout the experiment. The sorption capacity of the aged biochar for methylene blue significantly increased (1.0-1.7 mg g-1), and a change in the biochar's elemental composition was also noted, with O-content increasing by 13-61% and C content decreasing by 4-7%. Despite these changes, the biochar remained stable according to the criteria of the European Biochar Foundation and International Biochar Initiative. The incubation test also showed negligible biochar mass loss (<0.02%), further validating the stability of the biochar. This study provides important insights into the evolution of biochar characteristics in CWs.
In this study, two constructed wetland-microbial fuel cells (CW-MFC), including a closed-circuit system (CCW-MFC) and an open-circuit system (OCW-MFC) with petroleum coke as electrode and substrate, were constructed to explore the effect of multiple key factors on their operation performances. Compared to a traditional CW, the CCW-MFC system showed better performance, achieving an average removal efficiency of COD, NH4+-N, and TN of 94.49 ± 1.81%, 94.99 ± 4.81%, and 84.67 ± 5.6%, respectively, when the aeration rate, COD concentration, and hydraulic retention time were 0.4 L/min, 300 mg/L, and 3 days. The maximum output voltage (425.2 mV) of the CCW-MFC system was achieved when the aeration rate was 0.2 L/min. In addition, the CCW-MFC system showed a greater denitrification ability due to the higher abundance of Thiothrix that might attract other denitrifying bacteria, such as Methylotenera and Hyphomicrobium, to participate in the denitrifying process, indicating the quorum sensing could be stimulated within the denitrifying microbial community.
To control eutrophication in aquatic ecosystems, enhancing nitrogen removal in the constructed wetland (CW) by upgrading conventional CW to aeration CW is commonplace. However, regulatory efforts have only focused on reducing dissolved inorganic nitrogen (DIN) discharge and disregarding dissolved organic nitrogen (DON). Here, we used experimental mesocosms to investigate the effect of aeration mode on the characteristics of effluent DON in CW. The results showed that intermittent aeration is prone to introduce large amounts of DON and bioavailable DON (ABDON) in the effluents, although it greatly decreases effluent total nitrogen (TN). Analysis of DON fluorescent components and molecular characteristics indicated that suddenly shifting the environment from anoxic condition to aerobic condition in the intermittent aeration CW (IACW) would stimulate microorganisms to release tryptophan and simple aromatic proteins-like substances, which does not occur in the limited continuous aeration CW (CACW). Consequently, the abundance of DON resembling lipids, proteins/amino sugars, and carbohydrates-like molecules in IACW were about 2.1 times higher than that in CACW. Bioassay results showed that Selenastrum capricornutum and Microcystis aeruginosa incubated with effluent from IACW both generate larger phytoplankton biomass than that with CACW effluent, even though IACW effluent contains less TN than its counterpart. Moreover, Microcystis aeruginosa can simultaneously utilize DON and DIN, while Selenastrum capricornutum seem to utilize the DON only when DIN was not available. This result implies that increasing DON discharge may also influence phytoplankton composition and stimulate harmful phytoplankton species. Overall, this study indicates that upgrading CW solely depending on DIN removal level cannot ensure a mitigation of nitrogen-related eutrophication, and more efforts should be paid to curb DON discharge.
Substrate clogging is one of the major operation challenges of subsurface flow constructed wetlands (SSF-CWs). And the phosphorus (P) removal performance and stability of P accumulation of SSF-CWs would be varied with the development of substrate clogging. In this study, three horizontal SSF-CWs microcosms with different clogging degrees were conducted to explore the mechanism of P accumulation behavior influenced by substrate clogging. Increase in clogging degree resulted in hydraulic retention time (HRT) diminution and adsorption sites increase, which jointly led to reduced P removal efficiency at low clogging degree (L-CW), however, higher P removal efficiency was obtained as adsorption sites increase offset HRT diminution at high clogging degree (H-CW). Substrate adsorption was the primary removal pathway in all SSF-CW systems. It accounted for 77.86 ± 2.63% of the P input in the H-CW, significantly higher than the control (60.08 ± 4.79%). This was attributed to a higher proportion of Fe/Al–P accumulated on the substrate of H-CW, since clogging aggravated the anaerobic condition and promoted the generation of Fe ions. The increase in clogging degree also elevated the release risk of the accrued P in SSF-CWs, since Fe/Al–P was considered bioavailable and readily released under environmental disturbance. The obtained results provide new insights into the P transport and transformation in SSF-CWs and would be helpful to optimize substrate clogging management.
Intermittent feeding method and continuous feeding method were adopted in two experimental form ecological soil wastewater infiltration systems (ESWISs), respectively. The results showed that COD, NH 4 ⁺ and TN removal efficiencies were enhanced from 81.8%, 70.5% and 45.8% in continuous feeding ESWIS to 90.0%, 88.5% and 72.7% in intermittent feeding ESWIS. The same TP removal efficiency was achieved in two feeding mehtods. Matrix oxidation reduction potential (ORP) was enhanced through the intermittent feeding ESWIS, especially above 60 cm depth of the matrix, which encouraged nitrification. The metabolic activity and reproduction of microbes were improved by intermittent feeding method, such as actinomyces, bacteria, nitrifying bacteria, fungus. Meanwhile, denitrifying bacteria and nitrate reductase (NR), nitrite reductase (NIR) activities were also increased. PCR-DGGE analysis confirmed that intermittent feeding method improved bacterial diversity. These results suggest that intermittent feeding method is viable to heighten the performance of ESWISs in sewage treatment.
Mariculture wastewater poses potential risks to the sustainability of the coastal environment. In this study, different types of constructed wetland-microbial fuel cells (CW-MFC), including up-flow CW-MFC (UCW-MFC), down-flow CW-MFC (DCW-MFC), and hybrid up-flow/down-flow CW-MFCs (HCW-MFC) were constructed to evaluate their efficiency to treat mariculture wastewater containing heavy metals (Cu and Zn). The results showed that both the UCW-MFC and DCW-MFC operated with aeration demonstrated better removal performance for conventional pollutants. The presence of heavy metals in wastewater reduced the removal of NH4⁺-N and total inorganic nitrogen, but had no significant effect on the removal of chemical oxygen demand (COD) and total phosphorus (TP). The HCW-MFC had better removal performance than the UCW-MFC and DCW-MFC, especially when treating heavy metal containing wastewater. All systems had excellent removal performance for (Cu²⁺ and Zn²⁺), resulting in concentrations below the first discharge standard. All the systems produced S²⁻, which could react with Cu²⁺/Zn²⁺ to form CuS/ZnS, leading to the removal of heavy metals from the systems. The average output voltage of the three systems was 561.64±16.64 mV for UCW-MFC, 634.73±9.33 mV for DCW-MFC, and 1074.88±49.90 mV for HCW-MFC, respectively. In addition, the maximum power density (PAmax) increased by 160.81% and 44.16% in HCW-MFC compared to those of UCW-MFC and DCW-MFC systems, respectively. Further, connecting the three systems successfully derived a light-emitting diode to emit light, which indicated that CW-MFC systems have promising application prospects for both pollutant removal as well as energy recycling.
The limitation of oxygen and carbon source restricted the TN removal in constructed wetland (CW). Algal pond (AP) could produce oxygen and fix CO2 to improve C/N ratio in water. Therefore, an AP-CW system was established under laboratory conditions to deeply explore the effect of nutrient load distribution and microalgae addition in CWs on pollutant removal. This study showed that AP-CW could remove 49.7% TN and 90.0% TP with no carbon addition in CWs. The significant removal of NH4-N by AP advanced the location of denitrification in CWs. To enhance TN removal, different dosage of microalgae were intermittently added at 20 and 10 cm respectively below the inlet of the vertical flow CW1 and CW2, where the rest NH4-N has been almost oxidized into nitrate. The addition of microalgae influenced the microflora and effluent quality. Microalgae dosage in denitrification area significantly increased the absolute abundance of Σnir. The best TN removal of AP-CW could reach 91.3% when 8 g (dry weight) microalgae was added. However, unlike previous knowledge, microalgae as an organic carbon source would also release N and P during decomposition, leading to increased nutrients in the effluent. The optimal dosage of microalgae was 1 g/5 d in this study. The position and amount of microalgae addition in CWs should be adjusted based on water property and element flow to achieve the best pollutant removal and biomass harvest.
The lack of dissolved oxygen and weak substrate removal capacity in constructed wetlands (CW) leads to terrible removal of nitrogen and polycyclic aromatic hydrocarbons (PAHs). In this study, automatic tidal flow CW microcosms were constructed by improving the oxygen environment (siphon and air-duct) and substrate (magnetite) to enhance purification performance and the mechanism was explored. The results showed that the addition of air-duct could improve the oxygen collection and thus improved the NH4⁺ removal efficiency. Additionally, nitrogen removal was improved greatly due to the simultaneous nitrification and denitrification in aerobic layer with the addition of magnetite. Mass balance indicated the microbial degradation dominated (32–62%) the removal of PAHs. Metagenomic analysis proved the existence of magnetite enhanced the number of PAHs-degrading bacteria, functional groups and metabolic pathways and thus greatly improved the microbial degradation of PAHs. Furthermore, Fe²⁺ /Fe³⁺ cycle played an important role in promoting the anaerobic degradation of PAHs, which might be served as an electron conduit to establish the direct interspecies electron transfer between iron-reducing bacteria (e.g. Deltaproteobacteria bacterium) and Anaerolineae bacterium to degrade PAHs efficiently. This study provided better understanding of the simultaneous removal of PAHs and nitrogen in tidal flow CWs.
Agricultural biomass waste in rural areas has been identified as an economical solid carbon sources in constructed wetlands (CWs) for treating low C/N ratio domestic sewage. However, little information is available regarding its optimal utilization as a media amendment for enhancing nitrogen removal in CWs. In this study, vertical flow CWs with different walnut peel amendment proportions (0%, 25%, 50%, 75%) were developed to explore the effects of biomass dosage on the treatment performance, nitrous oxide (N2O) emission and microbial metabolites. Results showed that the addition of biomass significantly enhanced the denitrification performance in all CWs, and the higher total nitrogen (TN) removal efficiency (91.14–97.16%) was achieved in CWs with the optimal dosage of 25%. While the addition of biomass resulted in a slight increase in N2O emission (20.56–270.13 μg m⁻² h⁻¹) compared with control systems. Additionally, the biomass addition increased the accumulation of extracellular polymeric substances (EPS) by facilitating microbial processes. Higher total EPS production was observed in CW with 25% biomass, and the proportion of tightly bound EPS (48%) dominated in the total EPS in different CWs.
Transient organic load shocks have an important influence on the removal of pollutants and the content and composition of extracellular polymeric substances (EPS). This study was based on a micro-pressure reactor (MPR) with the influent COD concentration as the variable, while different operating conditions were controlled by adjusting the aeration rate. The effect of single-cycle transient organic loading shocks on EPS and pollutant removal and the correlation between their changes were investigated. The results showed that COD removal was unaffected under the shock, and the effect of nitrogen and phosphorus removal decreased. As the incoming carbon source increased, the EPS content at shock increased, with the polysaccharide (PS) content being the most affected. As aeration increased, the effect of organic load shock on EPS and pollutant removal decreased. Under different aeration conditions, PS contributed to denitrification and anaerobic phosphorus release during transient organic load shocks, and protein (PN) contributed to aerobic phosphorus uptake. The reduction in PS and PN relative to the pre-shock caused by the shock resulted in the EPS exhibiting a favourable effect on COD removal and an inhibitory effect on the effectiveness of nitrogen and phosphorus removal.
Vertical flow constructed wetlands (VFCWs) have been widely applied worldwide due to their small footprint and large hydraulic load, however, its sustainable operation and application is still challenging because of the unsatisfactory nitrogen removal. This study developed a novel CW coupled with a magnetic field for treating simulated wastewater, and investigated the effects of magnetic field on enhancing treatment performance and responses of wetland plants and microbial community. The results showed that the magnetic field (average 110 mT) had a significantly intensifying effect on organics and nitrogen removal. The removal efficiencies of NH4⁺-N and TN in CW exposed to magnetic field (MF-CW) were 10.14% and 9.16% higher than those in control CW (C-CW), and an increased COD removal was also found in MF-CW. Biochemical characteristics of plants indicated that the MF did not cause a severe stress for wetland plants, while MF application shifted significantly the microbial community in CWs. Relative abundances of nitrifying bacteria such as Nitrospira (2.36%), Dokdonella (0.27%) and Nitrosomonas (0.17%) had been significantly promoted due to MF exposure, and nitrification-related microbial enzyme (AMO) activity was also increased by 63%. It can be concluded that introducing MF into CWs could intensify organics and nitrogen removal via the biological process, which would contribute to a better understanding of magnetic coupling mechanism.
Knowing the effluent quality of treatment systems in advance to enable the design of treatment systems that comply with environmental standards is a realistic strategy. This study aims to develop machine learning - based predictive models for designing the subsurface constructed wetlands (SCW). Data from the SCW literature during the period of 2009–2020 included 618 sets and 10 features. Five algorithms namely, Random forest, Classification and Regression trees, Support vector machines, K-nearest neighbors, and Cubist were compared to determine an optimal algorithm. All nine input features including the influent concentrations, C:N ratio, hydraulic loading rate, height, aeration, flow type, feeding, and filter type were confirmed as relevant features for the predictive algorithms. The comparative result revealed that Cubist is the best algorithm with the lowest RMSE (7.77 and 21.77 mg.L−1 for NH4–N and COD, respectively) corresponding to 84% of the variance in the effluents explained. The coefficient of determination of the Cubist algorithm obtained for NH4–N and COD prediction from the test data were 0.92 and 0.93, respectively. Five case studies of the application of SCW design were also exercised and verified by the prediction model. Finally, a fully developed Cubist algorithm-based design tool for SCW was proposed.
To understand the denitrification performance and microbial community of two-stage vertical flow constructed wetlands (TS-VFCWs) with iron ore/manganese ore and wood chips, COD and nitrogen removal were investigated under pollution load and salinity shock. High removal of COD (87%), NH4+-N (97%), and NO3--N (98%) were achieved with increasing load, but the high pollutant load inhibited the denitrification performance in TS-VFCW with iron ore and wood chips. TS-VFCW with iron ore and wood chips showed good recovery potential with decreasing load. High NH4+-N removal was observed in TS-VFCW with manganese ore and wood chips. Treatment with 3% salinity decreased COD and NH4+-N removal but improved NO3--N removal, maintaining relatively good nitrogen removal. The addition of iron ore and manganese ore enriched nitrifying bacteria Flavobacterium and autotrophic denitrifying bacteria, while wood chips promoted heterotrophic denitrification and organic degradation. In addition, ubiquitous denitrifying bacteria under salinity ensured excellent denitrification performance.
The nitrate reduction contributions of denitrification, anaerobic ammonium oxidation (anammox) and dissimilatory nitrate reduction to ammonium (DNRA) remain largely unknown especially in the context of river remediation. In this research, the quantitative differentiation of these three nitrate-reduction processes with different remediation conditions was done by the joint use of microbial analysis and nitrogen isotope-tracing.
The experiments were done in simulated river systems with 100-day operations. The results of isotope-tracing showed that the respective N-removal contribution of denitrification was 85.88%–92.46% and 83.49%–84.73% in urban river with aeration and addition of Ca(NO3)2, whereas anammox became the same important (contribution of 49.35%–57.85%) with denitrification for nitrogen removal at a high C/N (Chemical oxygen demand/total nitrogen) ratio of 20. Besides, DNRA only occurred at a C/N ratio of 10 with high-level ammonium accumulation (11.20 ± 0.61 mg/L). Microbial analyses indicated that Ca(NO3)2 injection could promote not only the relative abundance of Proteobacteria (from 47.66% to 59.52%) but also the abundance of hzsB (from (4.66 ± 0.40) × 10⁴ copies·g⁻¹ to (2.66 ± 0.12) × 10⁵ copies·g⁻¹). Moreover, Ca(NO3)2 injection showed significantly positive correlation with Candidatus Jettenia of hzsB and Thiobacillus of all the denitrification functional genes including narG, norB, nosZ and nirS. The C/N ratio showed significantly positive correlation with Azoarcus of nirS (r = 0.941, p < 0.01) and Alloactinosynnema of hzsB (r = 0.941, p < 0.01). It was worth noting that Thiobacillus dominated in N-transformation processes, which underlined the need for the coupling of N transformation with other elements such as sulfur for better understanding and manipulating N cycling in urban rivers.
Previously an enhanced nitrogen removal process, i.e., intermittent Modified Ludzack-Ettinger (iMLE), was developed by incorporating intermittent aeration into the MLE process. In this research, a field demonstration of iMLE process on enhancing nitrogen removal was conducted in Shenzhen Guangming Wastewater Treatment Plant (WWTP) at a daily treatment capacity of 25,000 m³/d. Results indicated that, when operating the iMLE process with dissolved oxygen (DO) based control mode, its effluent chemical oxygen demand (COD) and ammonia concentrations were consistently less than 30 mg/L and 1.5 mg/L, respectively, similar to the original two-stage Anoxic/Oxic (A/O) process with continuous aeration. Even though the influent had insufficient organic matter (BOD5/TN = 2.5), the effluent TN concentration in the iMLE was still consistently below the new limit of 10 mg-N/L, with an average and removal rate of 6.1 ± 1.0 mg-N/L and 78%, respectively. This performance was similar to that in the two-stage A/O process equipped with step feed and external carbon addition. Without the addition of external carbon in the iMLE process, it saved approximately 0.16 Chinese yuan for one cubic meter of wastewater treated. In addition to eliminating external carbon addition, the iMLE process decreased the air consumption by 20–30%, which would also reduce operation cost. Therefore, the iMLE process operated with appropriate DO control could reduce chemical cost and aeration energy use synergistically, which provides a cost-effective approach for WWTP upgrade.
Biochar (BC) has been widely utilized in constructed wetland (CW) for intensifying the removal of pollutants from low carbon/nitrogen (C/N) wastewater. However, there are knowledge gaps about the optimal proportion of BC as an external carbon substrate. This study developed four sets of aerated vertical flow (VF) CWs with different BC amendment proportions (0%, 25%, 50%, 75%) to explore the influence of BC dosage on the treatment performance, enzyme activity and microbial community. The results showed that all CWs achieved better COD (above 90%) and NH4+-N (above 99%) removal due to adequate oxygen supplement, while the best TN removal (67%) was obtained in CW with 50% BC addition. TP removal ascended gradually with the increasing BC amendment proportion. The activity of enzymes and the proportion of Proteobacteria and Patescibacteria at the phylum level were appreciably enhanced with the addition of BC.
Subsurface constructed wetland (SCW) appears to be an economical and environmental-friendly practice to treat nitrogen-enriched (waste) water. Nevertheless, the removal mechanisms in SCW are complicated and rather time-consuming to conduct and assessment the efficiency of new experiments. This work mined data from literature and developed the machine learning models to elucidate the effect of influent inputs and predict ammonium removal rate (ARR) in SCW treatment. 755 sets and 11 attributes were applied in four modelled algorithms, including Random forest, Cubist, Support vector machines, and K-nearest neighbors. Six out of ten input features including ammonium (NH4), total nitrogen (TN), hydraulic loading rate (HLR), the filter height (i.e., Height), aeration mode (i.e., Aeration), and types of inlet feeding (i.e., Feeding) have posed pronounced influences on the ARR. The Cubist algorithm appears the most optimal model showing the lowest RMSE i.e., 0.974 and the highest R² i.e., 0.957. The contribution of variables followed the order of NH4, HLR, TN, Aeration, Height and Feeding corresponding to 97, 93, 71, 49, 34, and 34%, respectively. The generalization ability to forecast ARR using testing data achieved the R² of 0.970 and the RMSE of 1.140 g/m.2d, indicating that Cubist is a reliable tool for ARR prediction. User interface and web tool of final predictive model are provided to facilitate the application for designing and developing SCW system in real practice.
This study investigated the feasibility of combining natural ventilation and animal disturbance in constructed wetlands (CWs) and the joint effects on oxygen transfer, microbial activity, organics, and nitrogen removal. The results showed that natural ventilation extended the habitat depth of earthworms by approximately 10 cm by significantly improving oxygen transfer in CWs; in turn, the earthworms slightly promoted the addition of oxygen inside CWs through burrowing activity. Therefore, the interaction between natural ventilation and animal disturbance in CWs mutually reinforced oxygen transfer, enzymatic activity, and the ammonification, nitrification, and aerobic degradation of organics. Additionally, the combination of natural ventilation and animal disturbance in CWs promoted the oxygen transfer rate by 42.1%–68.2%; promoted catalase, urease, and dehydrogenase activity by 19.3%–24.8%, 17.4%–22.3%, and 18.1%–25.6%, respectively; and promoted COD and NH3–N removal loads by 48.6%–74.2% and 94.9%–135.3%, respectively. To achieve higher total nitrogen removal, moderate wind speeds (≤1 m/s in this study) are recommended to simultaneously create aerobic and anoxic/anaerobic conditions. Although natural ventilation reduced the microbial diversity in CWs by promoting the abundance of aerobes, the combination of natural ventilation and animal disturbance was generally conducive to improving microbial diversity. The relationship between wind speed and oxygen transfer rate and COD and NH3–N removal loads in naturally ventilated CWs conformed to cubic equations.
Oxygen and carbon source supply are usually insufficient in subsurface flow constructed wetlands. Simultaneous removal of organic pollutants and nitrogen in five batch-operated vertical flow constructed wetlands under different operating conditions was investigated. Alternate aerobic and anaerobic regions were created well with intermittent aeration. Four-month experiments showed that the wetland-applied intermittent aeration combined with step feeding strategy (reactor E) greatly improved the removal of organics, ammonium nitrogen (NH(4)-N), and total nitrogen (TN) simultaneously, which were 97, 96, and 82 %, respectively. It was much better than non-aerated reactors A and B and outperformed intermittently aerated reactor D without step feeding. Continuous aeration (reactor C) significantly enhanced the organics removal and nitrification, but it limited the TN removal (29 %) seriously as a result of low denitrification level, and the high operation cost remained a question. The effect of plants was confirmed in this study, and the monitoring data showed that the plants could grow normally. Intermittent aeration as well as step feeding had no obvious influence on the growth of wetland plants in this study.
Since the mid 1990s, constructed wetlands have been increasingly used as a low-energy ‘green’ technique, in the treatment of wastewater and stormwater, driven by the rising cost of fossil fuels and increasing concern about climate change. Among various applications of these wetlands, a significant area is the removal of nitrogenous pollutants to protect the water environment and to enable effective reclamation and reuse of the wastewater. This paper provides a review of the current state of nitrogen removal technology, focusing on existing types of wetlands, the mechanisms of nitrogen removal, major environmental factors relative to nitrogen removal, and the operation and management of the wetlands.
The influences of intermittent operation and different length of drying time on contaminant removal as well as wetland plant growth in vertical flow constructed wetlands (VFCWs) were investigated in this study. Microcosm wetlands planted with Phragmites australis were subjected to a 4-month experiment involving different operations (continuously and intermittently flood) and time ratios of flood to drain (F/D) with the hydraulic loading of 0.10 m3/m2/batch. It was found that the intermittent operation promoted a lower level of COD and TP removal. The intermittent operation caused more oxidizing conditions in the microcosm wetlands and thus greatly enhanced the removal of ammonium, and the removal efficiency was more than 90%. However, the intermittent operated wetlands had lower TN removal efficiencies the flooding system. With different lengths of drying time, the COD and TP removal were similar. The removal of ammonium was enhanced at a lower level with the prolongation of drying time. Contrarily, the TN removal was lower at F/D = 1:2 (46.86%) than at F/D = 2:1 (56.32%). The detected results of photosynthetic rate of Phragmites australis showed that the intermittent operation had no harmful effect on the wetland plant and the plant could grow normally.
Wetland plants release oxygen through the aerenchyma system to the roots, providing oxic habitats in the rhizosphere. The consumption of the oxygen during the night establishes a diurnal fluctuation of the redox conditions (−320 mV to +300 mV) that explains the coexistence of aerobic and anaerobic microorganisms in the rhizosphere. The redox fluctuation and its effect on the activity of rhizosphere microorganisms were investigated by RNA-based fingerprinting techniques in a laboratory scale reactor planted with Juncus effusus. The denaturing gradient gel electrophoresis (DGGE) patterns of 16S rRNA obtained with “universal” primers were very similar regardless of the time of sampling, indicating that the overall ribosome level of the predominantly active members did not change significantly. The amoA transcript DGGE patterns showed moderate diurnal dynamics with specific bands observed either in day or night samples. However, the majority of amoA genes were continuously expressed, indicating that the activity of functional genes may only partly be a measure sensitive enough for tracing the physiological activity on a short time scale. The results indicate that loose regulation of functional genes can be the main strategy for accommodation to fluctuating environmental conditions. The spatial separation of microbial activities as a result of diurnal fluctuating oxygen availability probably contributes to niche differentiation in the rhizosphere but this is difficult to track it at transcriptome level.
The effects of major operational factors on the performance of vertical-flow pilot-scale constructed wetlands (VFPCWs) were examined in parallel experiments. Experiments were conducted for one year in eight VFPCWs, the main substrate of which consisted of river sand at four of the wetlands, or a mixture of sand and dolomite (10:1 weight ratio) at the other four wetlands. Medium-strength synthetic sewage was applied as influent. A Latin square (balanced for carryover effects) split-plot experimental design was used. The ANOVA statistical model was applied to analyze the relationships between the main operational factors and the effluent COD, NO2-N, NO3-N, TN and PO4-P concentrations. It was found that the effluent concentrations of these parameters were related to the examined factors, as well as to the combined effects of certain influencing factors. The results demonstrated that the VFPCWs operating with relatively small hydraulic load per batch (0.08 m3 m−2), and applied on the wetlands with low batch frequency (two times per week), could result in high COD removal (more than 92%) and sufficient nitrification (more than 60% of TN was transformed to NO3-N). However, the addition of dolomite in the substrate did not significantly affect the overall phosphorus removal, which remained in the range of 39–64%.
Partial nitrification of ammonium to nitrite under oxic conditions (nitritation) is a critical process for the effective use of alternative nitrogen removal technologies from wastewater. Here we investigated the conditions which promote establishment of a suitable microbial community for performing nitritation when starting from regular sewage sludge. Reactors were operated in duplicate under different conditions (pH, temperature, and dilution rate) and were fed with 50 mM ammonium either as synthetic medium or as sludge digester supernatant. In all cases, stable nitritation could be achieved within 10 to 20 days after inoculation. Quantitative in situ hybridization analysis with group-specific fluorescent rRNA-targeted oligonucleotides (FISH) in the different reactors showed that nitrite-oxidizing bacteria of the genus Nitrospira were only active directly after inoculation with sewage sludge (up to 4 days and detectable up to 10 days). As demonstrated by quantitative FISH and restriction fragment length polymorphism (RFLP) analyses of the amoA gene (encoding the active-site subunit of the ammonium monooxygenase), the community of ammonia-oxidizing bacteria changed within the first 15 to 20 days from a more diverse set of populations consisting of members of the Nitrosomonas communis and Nitrosomonas oligotropha sublineages and the Nitrosomonas europaea-Nitrosomonas eutropha subgroup in the inoculated sludge to a smaller subset in the reactors. Reactors operated at 30 degrees C and pH 7.5 contained reproducibly homogeneous communities dominated by one amoA RFLP type from the N. europaea-N. eutropha group. Duplicate reactors at pH 7.0 developed into diverse communities and showed transient population changes even within the ammonia oxidizer community. Reactors at pH 7.5 and 25 degrees C formed communities that were indistinguishable by the applied FISH probes but differing in amoA RFLP types. Communities in reactors fed with sludge digester supernatant exhibited a higher diversity and were constantly reinoculated with ammonium oxidizers from the supernatant. Therefore, such systems could be maintained at a higher dilution rate (0.75 day(-1) compared to 0.2 day(-1) for the synthetic wastewater reactors). Despite similar reactor performance with respect to chemical parameters, the underlying community structures were different, which may have an influence on stability during perturbations.
The processes that affect removal and retention of nitrogen during wastewater treatment in constructed wetlands (CWs) are manifold and include NH(3) volatilization, nitrification, denitrification, nitrogen fixation, plant and microbial uptake, mineralization (ammonification), nitrate reduction to ammonium (nitrate-ammonification), anaerobic ammonia oxidation (ANAMMOX), fragmentation, sorption, desorption, burial, and leaching. However, only few processes ultimately remove total nitrogen from the wastewater while most processes just convert nitrogen to its various forms. Removal of total nitrogen in studied types of constructed wetlands varied between 40 and 55% with removed load ranging between 250 and 630 g N m(-2) yr(-1) depending on CWs type and inflow loading. However, the processes responsible for the removal differ in magnitude among systems. Single-stage constructed wetlands cannot achieve high removal of total nitrogen due to their inability to provide both aerobic and anaerobic conditions at the same time. Vertical flow constructed wetlands remove successfully ammonia-N but very limited denitrification takes place in these systems. On the other hand, horizontal-flow constructed wetlands provide good conditions for denitrification but the ability of these system to nitrify ammonia is very limited. Therefore, various types of constructed wetlands may be combined with each other in order to exploit the specific advantages of the individual systems. The soil phosphorus cycle is fundamentally different from the N cycle. There are no valency changes during biotic assimilation of inorganic P or during decomposition of organic P by microorganisms. Phosphorus transformations during wastewater treatment in CWs include adsorption, desorption, precipitation, dissolution, plant and microbial uptake, fragmentation, leaching, mineralization, sedimentation (peat accretion) and burial. The major phosphorus removal processes are sorption, precipitation, plant uptake (with subsequent harvest) and peat/soil accretion. However, the first three processes are saturable and soil accretion occurs only in FWS CWs. Removal of phosphorus in all types of constructed wetlands is low unless special substrates with high sorption capacity are used. Removal of total phosphorus varied between 40 and 60% in all types of constructed wetlands with removed load ranging between 45 and 75 g N m(-2) yr(-1) depending on CWs type and inflow loading. Removal of both nitrogen and phosphorus via harvesting of aboveground biomass of emergent vegetation is low but it could be substantial for lightly loaded systems (cca 100-200 g N m(-2) yr(-1) and 10-20 g P m(-2) yr(-1)). Systems with free-floating plants may achieve higher removal of nitrogen via harvesting due to multiple harvesting schedule.
The sequencing of 16S and 23S ribosomal RNA (rRNA) molecules is currently the gold standard for the classification of new microbial isolates. Comparative analyses of these sequences are for the first time in the history of microbiology facilitating the reconstruction of universal phylogenetic trees [38]. Among many other important findings the work of Carl Woese and his colleagues demonstrated that only certain (by far not all) phenotypic/physiological groups of micro-organisms are monophyletic (e.g., methanogenes, cyanobacteria, spirochetes). About 10 years ago it has been proposed to use an rRNA approach for studies in microbial ecology [21]. The microbial diversity should be analyzed in a cultivation-independent way by direct rRNA sequence retrieval, whereas nucleic acid probes complementary to rRNA or rRNA genes should be the tools to monitor population dynamics in the environmental samples. By their own nature rRNA-targeted probes track genotypes which are not necessarily linked to one phenotype. Microbial ecologists who want to apply this approach to investigate correlations between community structures and functions should be aware of this fact and design or apply rRNA-targeted probes accordingly.
A stormwater wetland treating non-point source pollution (NPS) from a 64 ha agricultural watershed was monitored over a period of five months. The results indicated that pH and dissolved oxygen (DO) were increased in the wetland due to the algal growth. The highest total suspended solids (TSS) concentration was observed in the aeration pond due to the resuspension of solids, decreased in the wetland. The respective decreases in total nitrogen (TN) and total kjeldahl nitrogen (TKN) were 15.9% and 28.7% on passing through the wetland. The nitrate and ammonia were increased by 45.4% and decreased by 79.9%, respectively. These variations provided strong evidence for the existence of nitrification. The total phosphorus (TP) and phosphate had respective reductions of 52.3% and 58.2% over the wetland. The total chemical oxygen demand (TCOD) and soluble chemical oxygen demand (SCOD) were also decreased. Generally, the TN, TP and phosphate removal efficiencies were positive. These positive removal efficiencies were mainly due to microbial activities, uptake by plants, and chemical precipitation at high pH. Negative removal efficiencies can be caused by continuous rainfall activities, with short antecedent dry days (ADDs) and unstable hydraulic conditions, some other biogeochemical transformations and algal growth also being important parameters.
Nitrification and denitrification have been proved to be the main pathways for nitrogen removal in constructed wetlands (CWs), but they usually could not occur in a single wetland unit simultaneously due to conflicting oxygen demand. In this study, we employed two artificial aeration modes including continuous aeration (CA) and intermittent aeration (IA) in lab-scale vertical flow constructed wetlands (VFCWs) to investigate the nitrogen removal performance with different influent COD/N ratios. The artificial aeration significantly enhanced NH4+-N removal, especially for the wetland units with higher COD/N ratios. The variations of aeration modes and COD/N ratios also had a great effect on nitrogen removal. The IA units had a better performance on nitrogen removal compared to CA units when the COD/N ratio ranged from 5 to 10. Plant biomass and nitrogen accumulation by plant were also studied. It was observed that plants in IA and CA had less biomass and nitrogen uptake at lower COD/N ratios, but plants in IA could achieve a better performance with higher COD/N ratios.
Constructed wetlands (CWs) have been used in ecological engineering for more than two decades, since 1990. In order to understand the present application and trend of CWs in China, this paper summarized the status quo, prospect and influencing factors in CWs construction, technology application and operation management in China, according to the data obtained by literature survey. Results of the systematic survey showed that CWs technology achieved gradual perfection under pushes of national policies, market demand and technical feasibility, with the capacity of wastewater treatment increasing year by year. However, there were still some problems concerning engineering operation and management. Moreover, the results demonstrated that limited by the economic level, the degree of industrialization and urbanization, climatic conditions as well as land availability, CWs were distributing predominately in the region of 20°13′N–35°20′N in China, where covered the central areas with a subtropical monsoon climate and southern or central areas at province level. In these areas, there were more than 40 plant species, which accounted for 57.14% of the total number of common wetland plants. Most of the CWs composted series or parallel combination forms of the vertical flow and free water surface flow CWs units, and they were suitable to treat more than 20 different types of wastewater. For these CWs, the effluent chemical oxygen demand (COD), biological oxygen demand (BOD), total nitrogen (TN) and total phosphorous (TP) reached in the ranges of 20–60 mg/L, 4–20 mg/L, 1–20 mg/L and 0.2–1 mg/L, respectively. The effluents from CWs were reused in more than eight ways, such as for agricultural irrigation, supplying surface water, green belt sprinkling, etc.
Horizontal subsurface flow constructed wetland (SSF CW) provides good conditions to denitrification but the ability of this system to nitrify NH4+–N is limited. The performance response of SSF CW to simulated wastewater with different COD/N (chemical oxygen demand: TN in influent) ratios was studied during an 8-month period in greenhouse conditions to improve the removal of NH4+–N. In this study, several wetland litters were hydrolyzed to get relevant carbon extracting solution, which was applied to the wetland systems. During the nitrification process, the variation of dissolved oxygen (DO) with COD/N ratios had a significant effect on the removal of NH4+–N. It was found that the total nitrogen (TN) removal efficiency increased with COD/N ratios. Appropriate control of the carbon or nitrogen source concentration and the COD/N ratio in the influent could achieve the optimal nitrogen removal.
The treatment of domestic sewage from a university campus area with diurnally and seasonally variable loading rates was investigated using a pilot-scale subsurface wastewater infiltration (SWI) system operated from January to August 2010. Operating conditions including hydraulic loading rate (HLR) and pollutant loading rate (PLR) were varied during the operation to investigate their impacts on overall treatment performance. The variation values were 0.040, 0.065, 0.081 and 0.125 m3/m2·d for HLR, 6.71, 9.30, 16.80 and 20.00g BOD/m2·d for PLR. The results showed that although the influent loading rates were highly variable, including sudden sharp increases in organic matter concentrations, the SWI system performed well throughout its operation. Taking the hydraulic and treatment efficiencies into consideration, HLR of 0.081 m3/m2·d and PLR of 16.80g BOD/m2·d were recommended. Under this condition, purification processes in the SWI system were gradually established over three weeks, after which the removal efficiencies for chemical oxygen demand (COD), total phosphorus (TP), total nitrogen (TN) and ammonia nitrogen (NH3-N) were 87.5±1.6, 91.8±0.7, 80.1±1.1 and 86.9±2.0%, respectively. Overall, eight months of pilot-scale tests indicated the robustness of SWI system in terms of achieving very high quality of treated water under HLR (0.040 to 0.081 m3/m2·d) and PLR (6.71 to 16.80g BOD/m2·d). This study will guide the decision on a full-scale SWI application in the campus area.
Nitrogen removal and transformations were studied in two pilot-scale combinations of a special configuration of a subsurface wastewater infiltration system with vertical flow named symbiotic treatment®. Both pilot-scale combinations operated in parallel and each one consists of four stages in series, one of them with a vertical distribution of stages and the other one with a horizontal distribution. The main differences between them were the separation between stages (presence (the horizontal distribution)/absence (the vertical distribution) of filtration between steps), the hydraulic load (0.113m3/m2h and 0.082m3/m2h for the horizontal and the vertical distribution, respectively) and the depth of the soil filters (1m each stage in the horizontal distribution whereas the depths in the vertical distribution ranges from 20cm to 40cm). Results of both configurations showed elevated dissolved oxygen concentration, and high removal of organic matter and total suspended solids (with mean removal values of 96% for COD for both plants and 90% and 98% for TSS for the vertical and the horizontal distribution, respectively). High total Kjeldahl nitrogen removals were obtained in both configurations (mean removals of 70% and 90% for the vertical and the horizontal distribution, respectively). Whereas the nitrification potential was higher in the configuration with horizontal distribution which includes pumping and filtering between stages and higher depth of the soil filters, both tested configurations showed promise for nitrification of wastewater, ammonia nitrogen was efficiently transformed to nitrate.
As part of a three year study of the use of reed beds for the treatment of wastewater, two pilot scale constructed wetlands (30m × 5m), one planted with Phragmites australis and the other serving as an unplanted control, were used to treat primary domestic sewage. This paper describes an experiment conducted to test the hypothesis that increasing available oxygen by aeration of the wastewater in the treatment beds could increase nitrification, and hopefully nitrogen removal rates. Prior to aeration, the influent nitrogen load in the wastewater passing through the beds was reduced by approximately 45% and 10% in the planted and control beds respectively. With aeration of the wastewater as it passed through each bed, nitrogen removal was approximately 51% and 20% for the planted and control beds respectively. High rates of nitrification were recorded for the planted bed with aeration, but removal of nitrogen by denitrification was limited, probably because of the absence of a suitable carbon source (indicated by low BOD5 concentrations). High nitrification rates were not recorded in the unplanted control bed. The higher BOD5 concentration measured in this bed may have caused increased competition for available oxygen between heterotrophic bacteria and the relatively slow-growing nitrifying bacteria, resulting in lower rates of nitrification but more efficient denitrification.
The Authors.- Preface.- Introduction.- Transformation Mechanisms Of Major Nutrients And Metals In Wetlands.- Wetland Plants.- Types Of Constructed Wetlands For Wastewater Treatment.- Horizontal Flow Constructed Wetlands. Types Of Wastewater Treated In HF Constructed Wetlands.- The Use Of HF Constructed Wetlands In The World.- References.-Suggested Reading.- Subject Index.
Three pilot subsurface wastewater infiltration systems filled with the same mixed matrix made of 80% brown soil and cinder at a weight of 20% were constructed in the laboratory. All systems worked successfully in the intermittent feeding mode with total hydraulic loading of 4 m3/(m2 d) for over 2 months, with the optimal parameters of shunt ratio of 1:1 and shunt position at the depth of 0.7 m was achieved on the basis of large amounts of experimental data. The experiment results showed that shunt distributing wastewater could significantly improve the nitrogen removal in the subsurface infiltration system and the average removal rates of TN and NH4-N increased by 10% and 5.67%, respectively. Shunt distributing wastewater had little influence on the removal rates of COD and TP. The results suggested that shunt distributing wastewater was simple and effective for nitrogen removal.
To assess the role of plants for oxygen offering in constructed wetlands, this study experimentally evaluated the amount of root oxygen release rate using mass balance method. The mass balance calculation is based on the following components: respiratory oxygen consumption of the roots; oxygen required for degradation of the organic matters; oxygen required for nitrification; and the amount of dissolved oxygen in the influent, effluent and substrate water. Experimental results have demonstrated that the root oxygen release rate was ranged from 20.3 to 58.3 gO2/m2 d with average value of 38.4gO2/m2 d, which was affected dramatically by light intensity. Only 35% and 9% of the oxygen released by roots were used in the degradation of organic matters and nitrogen-nitrification, respectively, while 56% was used for roots respiration with little to be released to the surrounding medium. The results also showed that diurnal fluctuation of oxygen release and light intensity followed unimodal distribution. Meanwhile, a better understanding of the DO (dissolved oxygen) budget was proposed. Root oxygen release rate could be described by two fractions. One is “net specific oxygen release rate” and the other is “dischargeable oxygen release rate”.Research Highlights► We evaluate the diurnal changes of oxygen consumption by organic matter or nitrogen. ► We evaluate the amount of root oxygen release rate using mass balance method. ► Root oxygen release rate could be described by two fractions. ► The daily changes of oxygen release followed unimodal distribution.
The performances of filter systems that use earthworms and plants, combined with earthworm eco-filter (EE) systems in treating synthetic domestic sewage (SDS) with different C/N ratios, were investigated for a 9-month period.
The effects of the combination of filters, earthworms, plants, as well as the combination of earthworms and plants on SDS nutrient removal efficiency were separately investigated to select the optimum system for treating SDS. The results of the current study could be used to determine how treatment performance responds to different C/N ratios and to explain and predict the performance of an operating EE system.
EE systems with earthworms and plants (EP groups) consistently performed better than the other types of systems (CK, E, and P; that is, without earthworms and without plants, with earthworms and without plants, and without earthworms and with plants, respectively) under all C/N ratios. The highest removal efficiencies of chemical oxygen demand, total nitrogen, total phosphorus, and total organic carbon were achieved under C/N ratios of 6:1, 6:1, 6:1, and 9:1, respectively. The optimum nutrient removal efficiency was achieved at C/N = 6, and the contribution order for nutrient removal was EP > P > E > CK.
Influent C/N ratios, the time of year, and the synergetic effects of earthworm behavior and microorganisms significantly affected nutrient removal efficiencies. Considering the removal of all nutrients, EE systems with plants and earthworms achieved optimum removal effects in July when the influent C/N ratio was controlled at 6. Appropriate control of carbon and nitrogen source concentrations permitted the achievement of optimal nutrient removal effects.
Constructed wetlands (CWs) are efficient at removing excessive nutrients from wastewaters. However, this removal often results in the flux of important greenhouse gases (GHG), such as nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) that could mitigate the environmental benefits of CWs. We studied the efficiency of artificial aeration and 2 different macrophyte species (Phragmites australis, Typha angustifolia) on the removal and transformations of nitrogen and GHG gas flux using CW mesocosms supplied with 60 L m−2 d−1 of wastewater. Removal of total nitrogen (TN) and dissolved organic nitrogen (DON) was generally high in all beds but resulted in a net production of oxidized nitrogen (NOy) in aerated CW mesocosms as compared to ammonium (NH4+) in non-aerated units. Aerated units emitted less N2O when planted with P. australis or left unplanted. Aerated beds and planted mesocosms had lower CH4 fluxes than non-aerated units and unplanted beds, respectively. Our study suggests that planted systems with artificial aeration have the overall best performances in that they lead to a reduction of GHG flux and promote the release of NOy over NH4+ in their effluents.
The effect of hydraulic loading rate (HLR; 5 to 20 cm day−1) and carbon addition (1-6 g dried plant material per week) was determined at two temperatures (28°C and 35°C) in 18 flow-through sediment-water wetland microcosms that were fed nitrate-contaminated water (30 mg N L−1). Nitrate removal efficiencies varied from 8% to >95%, decreasing with increasing HLRs and increasing with increasing carbon addition rates. The effect of HLR and carbon addition rate were integrated into the C:N ratio, which alone was highly predictive of nitrate removal efficiency. As nitrate removal efficiencies increased, dissolved organic carbon in the effluent also increased, as did chloroform formation potential. Nitrate-treatment wetlands may be a feasible method of remediating nitrate-contaminated groundwater.
A pilot subsurface wastewater infiltration system filled with a mixed soil of red clay + 25% cinder was constructed in a village located in Dianchi valley in south west China to treat rural sewage. At first, the system was continuously fed with rural sewage at a hydraulic loading of 2 cm d−1 for over 4 months. The removal of COD, T-P, NH4+-N, and T-N over the operation period was achieved at average rates of 82.7, 98.0, 70.0, and 77.7%, respectively. Compared to T-P removal, the lower nitrogen removal rates were attributed to reductive soil condition in the system, which was unfavorable for the nitrification process. An intermittent operation was adopted to improve nitrogen removal. The same performances of COD and T-P removal were achieved in the intermittent operation mode. NH4+-N removal was increased from 70% in the continuous feeding mode to over 90%, and T-N removal rate was elevated over 80% even with the average hydraulic loading as high as 8 cm d−1. Nitrogen balance calculation suggested that nitrification–denitrification was the main mechanism of nitrogen removal that eliminated 57–76% of the fed T-N. Soil redox potential measurement showed that the oxidative environment was increased through intermittent operation, encouraging nitrification. Correspondingly, soil nitrification potential was increased from less than 0.8 mg-N kg−1 h−1 in the continuous feeding mode to about 1.6 mg-N kg−1 h−1 in the intermittent operation mode.
Nitrification, an aerobic microbial process, is generally considered to be the rate-limiting step for N removal in subsurface-flow (SSF) constructed wetlands treating organic wastewaters. SSF wetland nitrogen (N) processing gradients were investigated using cascade mesocosms comprised of five planted (Schoenoplectus tabernaemontani), gravel-filled tanks operated in series, in order to determine the effects of organic substrate availability (measured as chemical oxygen demand, COD) and partial pre-nitrification on rates of N removal. Duplicate sets of cascades supplied with 23 mm d−1 of four different organic wastewaters provided COD:N ratios of ∼2–15 (<1–30 in individual tanks) and a range of N species balances (34–88% ammoniacal-N, NH4-N; <1–40% oxidised N, NOx-N). Mass balances for organic N (Org-N), NH4-N and NOx-N, and COD removal were calculated for each tank of the cascades. Concurrent measurements were made of plant growth and N uptake, sediment N accumulation and selected biogeochemical indicators (redox potential, pH, and CO2 and CH4 emissions). Using a simplified model of sequential N transformations and sinks, average net rates of N mineralisation ranged from 0.22 to 0.53 g m−2 d−1, nitrification from 0.56 to 2.15 g m−2 d−1, denitrification from 0.47 to 1.99 g m−2 d−1 (60–84% of measured N removal) and plant assimilation from 0.28 to 0.47 g m−2 d−1 in the cascade tanks. Nitrification and denitrification occurred concurrently with COD removal, even in the upstream stages of cascades receiving the higher-strength wastewaters. Surprisingly, neither net areal nitrification rates, nor first order nitrification rate constants (kA) were correlated with COD removal rates (as a measure of heterotrophic oxygen demand). Nitrification rates were correlated with average NH4-N concentrations in the cascade tanks, and were closely paralleled by net denitrification rates. Although kA for N mineralisation, nitrification and total N removal were highest for the partially pre-nitrified wastewater tested, considerably higher areal mass removals were achieved in the cascades receiving more concentrated ammonium-rich wastewaters. The oxygen demand required to support full nitrification of ammonia and mineralised Org-N in the cascades (without accounting for competitive heterotrophic oxygen demand) was in the upper range of that expected to be able to be supplied through surficial and plant-mediated oxygen transfer. Implications for understanding the nature of coupled nitrification–denitrification and COD removal in SSF treatment wetlands are discussed.
Nitrogen removal processes were investigated at three frequencies of water level fluctuation, static, low and high (0, 2 and 6 d−1), in duplicate gravel-bed constructed wetland mesocosms (0.145 m3) with and without plants (Schoenoplectus tabernaemontani). Fluctuation was achieved by temporarily pumping wastewater into a separate tank (total drain time ∼35 min). Intensive sampling of the mesocosms, batch-fed weekly with ammonium-rich (∼100 g m−3 NH4-N) farm dairy wastewaters, showed rates of chemical oxygen demand (COD) and total Kjeldahl nitrogen (TKN) removal increased markedly with fluctuation frequency and in the presence of plants. Nearly complete removal of NH4-N was recorded over the 7 day batch period at the highest level of fluctuation, with minimal enhancement by plants. Redox potentials (Eh) at 100 mm depth rose from initial levels of around −100 to >350 mV and oxidised forms of N (NO2 and NO3) increased to ∼40 g m−3, suggesting conditions were conducive to microbial nitrification at this level of fluctuation. In the unplanted mesocosms with low or zero fluctuation, mean NH4-N removals were only 28 and 10%, respectively, and redox potentials in the media remained low for a substantial part of the batch periods (mid-batch Eh ∼+100 and −100 mV, respectively). In the presence of wetland plants, mean NH4-N removal in the mesocosms with low or zero fluctuation rose to 71 and 54%, respectively, and COD removal (>70%) and redox potential (mid-batch Eh>200 mV) were markedly higher than in the unplanted mesocosms. Negligible increases in oxidised N were recorded at these fluctuation frequencies, but total nitrogen levels declined at mean rates of 2.4 and 1.8 g m−2 d−1, respectively. NH4-N removal from the bulk water in the mesocosms was well described (R2=0.97–0.99) by a sorption-plant uptake-microbial model. First-order volumetric removal rate constants (kv) rose with increasing fluctuation frequency from 0.026 to 0.46 d−1 without plants and from 0.042 to 0.62 d−1 with plants. As fluctuation frequency increased, reversible sorption of NH4-N to the media, and associated biofilms and organic matter, became an increasingly important moderator of bulk water concentrations during the batch periods. TN mass balances for the full batch periods suggested that measured plant uptake estimates of between 0.52 and 1.07 g N m−2 d−1 (inversely related to fluctuation frequency) could fully account for the increased overall removal of TN recorded in the planted systems. By difference, microbial nitrification-denitrification losses were therefore estimated to be approximately doubled by low-level fluctuation from 0.7 to 1.4 g N m−2 d−1 (both with and without plants), rising to a maximum rate of 2.1 g N m−2 d−1 at high fluctuation, in the absence of competitive uptake by plants.
Official guidelines for the on-site treatment of domestic sewage have recently been published by the Danish Ministry of Environment as a consequence of new treatment requirements for single houses and dwellings in rural areas. This paper summarises the guidelines for vertical constructed wetland systems (planted filter beds) that will fulfil demands of 95% removal of BOD and 90% nitrification. The system can be extended with chemical precipitation of phosphorus with aluminium polychloride in the sedimentation tank to meet requirements of 90% phosphorus removal. The necessary surface area of the filter bed is 3.2 m2/person equivalent and the effective filter depth is 1.0 m. The filter medium must be filtersand with a d10 between 0.25 and 1.2 mm, a d60 between 1 and 4 mm, and a uniformity coefficient (U = d60/d10) less than 3.5. The sewage is, after sedimentation, pulse-loaded onto the surface of the bed using pumping and a network of distribution pipes. The drainage layer in the bottom of the bed is passively aerated through vertical pipes extending into the atmosphere in order to improve oxygen transfer to the bed medium. Half of the nitrified effluent from the filter is recirculated to the first chamber of the sedimentation tank or to the pumping well in order to enhance denitrification and to stabilise the treatment performance of the system. A phosphorus removal system is installed in the sedimentation tank using a small dosing pump. The mixing of chemicals is obtained by a simple airlift pump, which also circulates water in the sedimentation tank. The vertical flow constructed wetland system is an attractive alternative to the common practice of soil infiltration and provides efficient treatment of sewage for discharge into the aquatic environment.
Wetlands have been intensively studied in the Czech Republic for more than 30 years, but the first full-scale constructed wetland (CW) for wastewater treatment was built in the Czech Republic in 1989. By the end of 1999, about 100 CWs were put in operation. The majority of the systems are horizontal subsurface flow (HSF) CWs and are designed for the secondary treatment of domestic or municipal wastewater. The size of CWs ranges between 18 and 4500 m2 and between 4 and 1100 population equivalent (PE). Most frequently used filtration media are gravel and crushed rock with size fractions of 4/8 and 8/16 mm and Phragmites australis is the most commonly used plant. The treatment efficiency is high in terms of BOD5 (88.0% for vegetated beds) and suspended solids (84.3% for vegetated beds). The removal of nutrients is lower for vegetated beds, and averages 51 and 41.6% for total phosphorus and total nitrogen, respectively.
This paper characterizes the spatial distribution of major microbial populations in a well established subsurface horizontal flow constructed wetland (CWL) that has been in operation for 7 years. The CWL receives partially treated municipal wastewater with an average COD and TSS of 430 and 130 mg L−1, respectively. Results from the seventh year of operation at a loading rate of 11 g-BOD m−2 d−1 show 60% and 70% COD and BOD reduction, respectively. Low oxygen concentrations, typical to subsurface horizontal CWLs, resulted in almost no nitrification. Major microbial groups were characterized by fluorescent in situ hybridization (FISH) at the beginning, center and end of the CWL and at different depths including the root zone. Relatively uniform microbial population distribution was observed, with some evidence for oxygen translocation by plants to the root zone at areas closer to the CWL outlet. Further, depth was found to have a somewhat higher effect on the distribution of the major microbial groups than distance from the inlet. Eubacteria dominated the microbial population at all points consisting almost always more than 85% of the population. About 50% of the Archaea present in the CWL were methane producers. Sulfate-reducing bacteria were observed in significant numbers with low vertical and longitudinal variations. Nitrifying bacteria were present only sparsely (1–3%), while methanotrophic bacteria were found in higher numbers (∼10% of the population).
A compact suspended carrier biofilm reactor (SCBR) was developed for simultaneous nitrification and denitrification (SND) in a single reactor and the performance of nutrient removal was investigated. Microbial community structure response to different ratio of carbon to nitrogen (C/N) was determined by denaturing gel gradient electrophoresis (DGGE) profiles of 16S rDNA V3 region and amoA gene amplifications. In addition, the population dynamics of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were estimated by fluorescence in situ hybridization (FISH) with 16S rDNA-targeted oligonucleotide probes. Results showed that the compact SCBR was efficient in nutrient removal with CODCr removal efficiency over 90% and SND efficiency (ESND) about 83.3%. The diversity of microbial community structure was positively correlated with C/N ratio, while the three communities of amoA gene were relativity homogenous. The population of nitrifiers was in inverse proportions to C/N ratio with the average fraction of AOB and NOB to all bacteria 5.4, 4.8, 3.1% and 4.6, 3.5, 2.7% respectively as C/N ratio changing from 3:1, 5:1 to 10:1. Therefore we could reach a conclusion that the compact SCBR was practical to treat municipal wastewater and the shift of microbial community monitored by molecular technologies could offer guidance to the process optimization in engineering.
In developing countries, the wise use of natural and artificial wetlands for water purification is particularly valuable and exploitable for the protection of water quality in catchments, rivers and lakes. Constructed wetlands are potentially good, low-cost, appropriate technological treatment systems for domestic wastewater in rural areas. Better still, they can be integrated into agricultural and fish production systems where the products are useable and/or re-cycled for optimal efficiency. However, currently, constructed wetlands are rarely installed. The reasons for this are discussed drawing attention to the limitations of aid programmes from donor countries and the need for in-house research, training and development. Recommendations for the development and wider use of constructed wetlands in developing countries are made.
Efforts to protect watercourses, especially sources of drinking water, particularly in rural areas, are now underway in China. Nitrogen present in wastewater, due to its role in eutrophication and potential toxicity to aquatic species, is a focus of primary concern. Constructed wetlands (CWs), a simpler, less costly treatment alternative, have been used to treat domestic wastewater for small communities. Although showing great promise for removing carbonaceous materials from wastewater, wetland systems have not been successful in removing nitrogen mainly due to lack of dissolved oxygen (DO). To enhance nitrogen removal, a novel CW configuration with three stages, towery hybrid constructed wetland (THCW), was designed. The first and third stages were rectangle subsurface horizontal flow CWs, and the second stage was a circular three-layer free-water flow CW. Increased DO by passive aeration of a tower type cascade overflow from the upper layer into the lower layer in the second stage of the wetland enhanced nitrification rates. Denitrification rates were also improved by additional organic matter supplied as a result of bypass influent directly into the second stage. Evergreen tree Pond Cypress (Taxodium ascendens), industrial plants Mat Rush (Schoenoplectus trigueter) and Wild Rice shoots (Zizania aquatica), ornamental floriferous plants Pygmy Waterlily (Nymphaea tetragona) and Narrow-leaved Cattail (Typha angustifolia) were planted in the wetland. The average percentage of removal was 89%, 85%, 83%, 83% and 64% for total suspended solid, chemical oxygen demand, ammonia nitrogen, total nitrogen and total phosphorus, respectively. There was no significant difference (p < 0.05) at low and high hydraulic loads (16 cm/d and 32 cm/d) for performance of THCW. Nitrifying and denitrifying bacteria as well as potential nitrification activity and potential denitrification rates measured have shown that nitrification–denitrification is the main mechanism for nitrogen removal in the wetland. THCW also provided additional aesthetic benefits.
A new development on treatment wetland technology for the purpose of achieving high rate nitrogen removal from high strength wastewater has been made in this study. The laboratory scale alum sludge-based intermittent aeration constructed wetland (AlS-IACW) was integrated with predenitrification, intermittent aeration, and step-feeding strategies. Results obtained from 280 days of operation have demonstrated extraordinary nitrogen removal performance with mean total nitrogen (TN) removal efficiency of 90% under high N loading rate (NLR) of 46.7 g N m(-2) d(-1). This performance was a substantial improvement compared to the reported TN removal performance in literature. Most significantly, partial nitrification and simultaneous nitrification denitrification (SND) via nitrite was found to be the main nitrogen conversion pathways in the AlS-IACW system under high dissolved oxygen concentrations (3-6 mg L(-1)) without specific control. SND under high dissolved oxygen (DO) brings high nitrogen conversion rates. Partial nitrification and SND via nitrite can significantly reduce the demand for organic carbon compared with full nitrification and denitrification via nitrate (up to 40%). Overall, these mechanisms allow the system to maintaining efficient and high rate TN removal even under carbon limiting conditions.
Ten pilot-scale, cylindrical, vertical flow constructed wetland units, of diameter 0.82 m and height 1.5 m, were designed, constructed, and operated treating a simulated municipal wastewater in parallel experiments. The operation scheme was 2 days feeding and 6 days resting. The 10 wetland units had various porous media materials (i.e., carbonate material, material from river bed, zeolite, and bauxite), two vegetation types (i.e., common reeds and cattails), and three total thicknesses of the porous media (i.e., 50, 80, and 90 cm). Water quality samples were collected at the inlet and the outlet of each unit, and were analyzed in the laboratory for BOD5, COD, TKN, ammonia nitrogen, nitrate, nitrite, TP, and ortho-phosphate. This article presents the results obtained after operation of these systems for one full year. Organic matter removal proved to be very good in all 10 units, since it reached on the average 71.1% and 66.9% for BOD5 and COD, respectively. Nitrogen removal was also satisfactory (47.1% for TKN and 42.2% for NH4+—N). TP and ortho-phosphate retention rates reached about 36.9% and 37.9%, respectively.
The aim of this investigation was to evaluate the influence of batch versus continuous flow on the removal efficiencies of chemical oxygen demand (COD), nitrogen (N) and total phosphorus (TP) in tropical subsurface flow constructed wetlands (SSF CW). The quantitative role of the higher aquatic plants in nutrient removal in these two operational modes was also investigated. Results indicated no significant difference (p > 0.05) in COD removal between batch and continuous flow modes for either the planted or unplanted treatments. Furthermore, the batch-loaded planted wetlands showed significantly (p < 0.05) higher ammonium removal efficiencies (95.2%) compared with the continuously fed systems (80.4%), most probably because the drain and fill batch mode presented systematically more oxidized environmental conditions. With respect to TP removal, for both planted and unplanted beds, there was significant enhancement (p < 0.05) in batch flow operation (69.6% for planted beds; 39.1% for unplanted beds) as compared to continuous flow operation (46.8% for planted beds; 25.5% for unplanted beds). In addition, at a 4-day hydraulic retention time (HRT), the presence of plants significantly enhanced both ammonia oxidation and TP removal in both batch and continuous modes of operation as compared to that for unplanted beds. An estimation of the quantitative role of aeration from drain and fill operation at a 4-day HRT, as compared to rhizosphere aeration by the higher aquatic plant, indicated that drain and fill operation might account for only less than half of the higher aquatic plant's quantitative contribution of oxygen (1.55 g O2 per m2 per day for batch flow versus 1.13 g O2 per m2 per day for continuous flow).
The objectives of this study are to compare the performance of newly developed baffled and conventional horizontal subsurface-flow (HSF) constructed wetlands in the removal of nitrogen at the hydraulic retention times (HRT) of 2, 3 and 5 days and to evaluate the potential of rice husk as wetland media for wastewater treatment. The results show that the planted baffled unit achieved 74%, 84% and 99% ammonia nitrogen (NH(4)(+)-N) removal versus 55%, 70% and 96% for the conventional unit at HRT of 2, 3 and 5 days, respectively. The better performance of the baffled unit was explained by the longer pathway due to the up-flow and down-flow conditions sequentially thus allowing more contact of the wastewater with the rhizomes and micro-aerobic zones. Near complete total oxidized nitrogen was observed due to the use of rice husk as wetland media which provided the COD as the electron donor in the denitrification process.
This study investigated three lab-scale hybrid wetland systems with traditional (gravel) and alternative substrates (wood mulch and zeolite) for removing organic, inorganic pollutants and coliforms from a synthetic wastewater, in order to investigate the efficiency of alternative substrates, and monitor the stability of system performance. The hybrid systems were operated under controlled variations of hydraulic load (q, 0.3-0.9 m3/m2 d), influent ammoniacal nitrogen (NH4-N, 22.0-80.0 mg/L), total nitrogen (TN, 24.0-84.0 mg/L) and biodegradable organics concentration (BOD5, 14.5-102.0 mg/L). Overall, mulch and zeolite showed promising prospect as wetland substrates, as both media enhanced the removal of nitrogen and organics. Average NH4-N, TN and BOD5 removal percentages were over 99%, 72% and 97%, respectively, across all three systems, indicating stable removal performances regardless of variable operating conditions. Higher Escherichia coli removal efficiencies (99.9%) were observed across the three systems, probably due to dominancy of aerobic conditions in vertical wetland columns of the hybrid systems.
The objective of present study was to assess the simultaneous removal of organic pollutants and nutrients by five laboratory scale up-flow constructed wetlands (UFCWs). Aerobic and anaerobic regions were well developed at the upper and lower beds, respectively, in the UFCW reactors with supplementary aeration. The emergent plants employed were Phragmites australis and Manchurian wild rice. The COD, T-N, T-P, NH(4)-N and NO(3)-N removal efficiencies for the UFCW reactors were in the range of 90-94%, 69-92%, 29-52%, 59-98% and 45-100%, respectively. The organic matter and NH(4)-N removal efficiencies in the aerated wetland reactors were better than the non-aerated wetland reactors. The supplementary aeration has enhanced the aerobic biodegradation of organic matter and nitrification. The Manchurian wild rice outperformed P. australis in the removals of T-P, T-N and NH(4)-N.
Partial nitrification to nitrite has been frequently obtained at high temperatures, but has proved difficult to achieve at low temperatures when treating low strength domestic wastewater. In this study, the long-term effects of temperature on partial nitrification were investigated by operating a sequencing bath reactor with the use of aeration duration control. The specific ammonia oxidation rate decreased by 1.5 times with the temperature decreasing from 25 to 15 degrees C. However, low temperature did not deteriorate the stable partial nitrification performance. Nitrite accumulation ratio was always above 90%, even slightly higher (above 95%) at low temperatures. The nitrifying sludge accumulated with ammonia-oxidizing bacteria (AOB), but washout of nitrite-oxidizing bacteria (NOB) was used to determine the short-term effects of temperature on ammonia oxidation process. The ammonia oxidation rate depended more sensitively on lower temperatures; correspondingly the temperature coefficient theta was 1.172 from 5 to 20 degrees C, while theta was 1.062 from 20 to 35 degrees C. Moreover, the larger activation energy (111.5 kJ mol(-1)) was found at lower temperatures of 5-20 degrees C, whereas the smaller value (42.0 kJ mol(-1)) was observed at higher temperatures of 20-35 degrees C. These findings might be contributed to extend the applicability of the partial nitrification process in wastewater treatment plants operated under cold weather conditions. It is suggested that the selective enrichment of AOB as well as the washout of NOB be obtained by process control before making the biomass slowly adapt to low temperatures for achieving partial nitrification to nitrite at low temperatures.
The ability of constructed wetlands with different plants in nitrate removal were investigated. The factors promoting the rates of denitrification including organic carbon, nitrate load, plants in wetlands, pH and water temperature in field were systematically investigated. The results showed that the additional carbon source (glucose) can remarkably improve the nitrate removal ability of the constructed wetland. It demonstrated that the nitrate removal rate can increase from 20% to more than 50% in summer and from 10% to 30% in winter, when the nitrate concentration was 30-40 mg/L, the retention time was 24 h and 25 mg/L dissolved organic carbon (DOC) was ploughed into the constructed wetland. However, the nitrite in the constructed wetland accumulated a little with the supply of the additional carbon source in summer and winter, and it increased from 0.15 to 2 mg/L in the effluent. It was also found that the abilities of plant in adjusting pH and temperature can result in an increase of denitrification in wetlands. The seasonal change may also impact the denitrification.
The performance response of planted and the unplanted wetlands to simulated wastewater with different ratios of carbon to nitrogen (C/N) was studied during a 9-month period in greenhouse conditions. With different C/N ratios for influent water (C/N ratios 2.5:1, 5:1 and 10:1), average removal efficiencies for the unplanted and the planted wetlands were as follows: COD (41-52% and 59-68%), TN (24-48% and 25-62%), TP (35-64% and 59-71%) and TOC (22-37% and 16-33%). At C/N 5:1, both systems performed most efficiently for removal of COD and TP. However, high N removal efficiency only occurred when C/N ratio ranged 2.5-5. Both wetlands exhibited good capabilities of total organic carbon removal at C/N 10:1. Maybe, appropriate control of the carbon or nitrogen source concentration and C/N ratio in the influent can achieve the optimal effect of nutrients removal.
Nitrogen (N) processing in constructed wetlands (CWs) is often variable, and the contribution to N loss and retention by various pathways (nitrification/denitrification, plant uptake and sediment storage) remains unclear. We studied the seasonal variation of the effects of artificial aeration and three different macrophyte species (Phragmites australis, Typha angustifolia and Phalaris arundinacea) on N processing (removal rates, transformations and export) using experimental CW mesocosms. Removal of total nitrogen (TN) was higher in summer and in planted and aerated units, with the highest mean removal in units planted with T. angustifolia. Export of ammonium (NH(4)(+)), a proxy for nitrification limitation, was higher in winter, and in unplanted and non-aerated units. Planted and aerated units had the highest export of oxidized nitrogen (NO(y)), a proxy for reduced denitrification. Redox potential, evapotranspiration (ETP) rates and hydraulic retention times (HRT) were all predictors of TN, NH(4)(+) and NO(y) export, and significantly affected by plants. Denitrification was the main N sink in most treatments accounting for 47-62% of TN removal, while sediment storage was dominant in unplanted non-aerated units and units planted with P. arundinacea. Plant uptake accounted for less than 20% of the removal. Uncertainties about the long-term fate of the N stored in sediments suggest that the fraction attributed to denitrification losses could be underestimated in this study.
Constructed wetlands with horizontal sub-surface flow (HF CWs) have successfully been used for treatment various types of wastewater for more than four decades. Most systems have been designed to treat municipal sewage but the use for wastewaters from agriculture, industry and landfill leachate in HF CWs is getting more attention nowadays. The paper summarizes the results from more than 400 HF CWs from 36 countries around the world. The survey revealed that the highest removal efficiencies for BOD(5) and COD were achieved in systems treating municipal wastewater while the lowest efficiency was recorded for landfill leachate. The survey also revealed that HF CWs are successfully used for both secondary and tertiary treatment. The highest average inflow concentrations of BOD(5) (652 mg l(-1)) and COD (1865 mg l(-1)) were recorded for industrial wastewaters followed by wastewaters from agriculture for BOD(5) (464 mg l(-1)) and landfill leachate for COD (933 mg l(-1)). Hydraulic loading data reveal that the highest loaded systems are those treating wastewaters from agriculture and tertiary municipal wastewaters (average hydraulic loading rate 24.3 cm d(-1)). On the other hand, landfill leachate systems in the survey were loaded with average only 2.7 cm d(-1). For both BOD(5) and COD, the highest average loadings were recorded for agricultural wastewaters (541 and 1239 kg ha(-1) d(-1), respectively) followed by industrial wastewaters (365 and 1212 kg ha(-1) d(-1), respectively). The regression equations for BOD(5) and COD inflow/outflow concentrations yielded very loose relationships. Much stronger relationships were found for inflow/outflow loadings and especially for COD. The influence of vegetation on removal of organics in HF CWs is not unanimously agreed but most studies indicated the positive effect of macrophytes.
In this study, the partial nitrification process was started-up successfully in a membrane bioreactor (MBR). The influence of temperature and DO was investigated by sequencing operation of membrane bioreactor. The preferred values were proved as 35 degrees C and 0.3-0.5mg/L, respectively, and were indicated as indispensable controlling factors. In order to increase the sludge concentration, new seed sludge was added into the reactor, which caused the absolute destruction of the reactor performance. The results of reactor experiments showed that the free ammonia (FA) concentration of 74 mg NH(3)/L, as the influent ammonium concentration of 600 mg N/L, was a useful and effective factor to recover the partial nitrification performance. Fluorescence in situ hybridization analysis indicated that nitrifiers hybridizing with NIT3 and NSR1156 were present and active in MBR, which were then eliminated under high FA concentration. The microbiological community analysis further provided the necessary biological information for the realization of partial nitrification.
The bacterial population in an H2-dependent denitrification system was studied. The laboratory set-up was designed for the treatment of potable water and consisted of an electrochemical cell, where the water to be treated was enriched with H2 prior to entering a bioreactor. Bioreactors (columns packed with granulated active carbon) were inoculated with denitrifying bacterial strains isolated from a previous reactor, then sampled immediately after inoculation, or after 1 or 3 months of continuous operation. Total number of the bacteria and numbers of each different strain were determined at various levels of the bioreactor. The strains present in the inoculum were identified as Ochrobactrum anthropi, Pseudomonas stutzeri, Paracoccus panthotrophus and Paracoccus denitrificans. Numbers of the latter declined markedly with time with the other three strains being responsible for nitrate removal. A correlation was found between the relative abundance of each strain and its specific denitrification activity.
In this study, a multi-cathode biofilm-electrode reactor (BER) combined with microfiltration (MF) was investigated using a laboratory-scale experimental apparatus for treatment of nitrate-contaminated water. The multi-cathode electrodes were composed of multiple-granular activated carbons (GACs). GACs attached to each cathode to enlarge surface area of electrodes and to attach bacteria quickly and firmly. In BER, H2 gas is produced by applying electric current, which serves as an electron donor in biological reduction of nitrate to N2 gas. Since some suspended solids were escaping from BER, MF membrane with plate modules and a pore size of 0.2 microm was placed after BER. Experimental results demonstrated that it was possible to operate the multi-cathode BER with high denitrification rates and hydraulic retention time (HRT) as low as HRT = 20 min. The denitrification rate was enhanced by 3-60 times in comparison with former studies. MF membrane successfully rejected the bacteria escaping from BER, so that the effluent concentration of SS was kept below 1 mg SS/l throughout the experiment. It was also possible to operate MF membrane at flux 2-9 times higher and pressure 2.5-31 times smaller than in former studies. This higher performance was mainly brought about by using biofilm and H2 gas as an electron donor. Also, an economic evaluation of BER/MF was included, showing the feasibility of this process. The present BER/MF process is considered advantageous for the enhanced treatment of nitrate-polluted groundwater.
Nitrification, an oxygen-requiring microbial process, is generally considered the rate-limiting step for N removal in subsurface-flow constructed wetlands treating organic wastewaters. We used a simplified model of sequential N transformations and sinks to infer required rates of oxygen supply at 5 stages along experimental wetland mesocosms supplied with four different organic wastewaters with contrasting ratios of COD: N and forms of N. Mass balances of water-borne organic, ammoniacal and nitrate N, and plant and sediment N uptake showed average net rates of N mineralisation ranging from 0.22-0.53 g m(-2) d(-1), nitrification 0.56-2.15 g m(-2) d(-1), denitrification 0.47-1.99 g m(-2) d(-1) (60-84% of measured N removal) and plant assimilation 0.28-0.47 g m(-2) d(-1). The nitrogenous oxygen demand (NOD) required to support the observed nitrification rates alone was high compared to expected fluxes from surficial and plant-mediated oxygen transfer. In the presence of high levels of degradable organic matter (COD removal rates up to 66 g m(-2) d(-1)), heterotrophs with significantly higher oxygen affinities and energy yields are expected to outcompete nitrifiers for available oxygen. Problems with commonly held assumptions on the nature of coupled nitrification-denitrification in treatment wetlands are discussed.
The filter medium could be selected and the longevity of the filter medium by the phosphorus saturation could be predicted in the constructed wetland system, accordingly proposing the scheme to remove the phosphorus for a long period. The phosphorus adsorption capacities of various filter media were investigated in relation to the size and types of filter media to screen the optimal condition. The objective of this study was to evaluate the constructed wetland longevity by improving P adsorption capacity. The maximum P adsorption capacities of filter media A (4--10 mm), B (2--4 mm), and C (0.1--2 mm) were 7.7, 11.6, and 22.5 mg/kg, respectively, showing that they increased as the filter media size decreased. Among the experimental media, the optimal filter media size was 0.1--2 mm. When Ca, Mg, Al and Fe were added to the filter medium C, which is the optimal filter medium, the addition of Ca improved mostly the P adsorption capacity. In the alternative proposal to use these facts, the oyster shell was added to the filter medium and the P adsorption capacity was examined: adding 2% oyster shell increased the P adsorption capacity from 23 to 36 mg/kg. In the column where the oyster shell was mixed, when the oyster shell content was 5%, 10%, 20%, 40%, 60%, 80%, and 100% in the filter medium C, the respective saturation times of the P adsorption were about 6, 9, 17, 30, 43, 56, and 70 days. When the oyster shell content was 0%, 5%, 10%, 20%, 40%, 60%, 80%, and 100% after 1 month in the column, the P adsorption amount was about 180, 600, 1560, 4280, 6157, 7089, 7519, and 7925 mg/kg, respectively. The increment of the P adsorption amount was small if the oyster shell content was 60% or more, because the filter medium with more than 60% oyster shell content did not approach the saturation time by the P adsorption yet. The P adsorption amount for 60%, 80%, and 100% could be predicted as about 9702, 12,879, and 16,056 mg/kg, respectively. The largest amount of extracted P in the filter media with oyster shell after 30 days of P solution application was bound to Ca, followed by water soluble-P, Al--P, and Fe--P. Therefore, it was concluded that the adsorption amount of the phosphorus could be increased by adding the oyster shell to the filter medium. Also, it was concluded that adding the oyster shell to the filter medium in the constructed wetland was the scheme to extend the longevity of the constructed wetland by the phosphorus saturation, and using the oyster shell would be useful in aspect of economical efficiency and easiness. Especially, it would be the alternative proposal to reduce the environmental pollution in aspect of recycling wastes.
Experiments were conducted to investigate the feasibility of applying constructed wetlands to treat a sanitary landfill leachate containing high nitrogen and bacterial contents. Under a tropical condition (temperature of about 30 degrees C), the constructed wetland units operating at the hydraulic retention time of 8d yielded the best treatment efficiencies with BOD(5), TN and fecal coliforms removal of 91%, 96% and more than 99%, respectively. Cadmium removal in the SFCW bed was 99.7%. Mass balance analysis, based on total nitrogen contents of the plant biomass and dissolved oxygen and oxidation-reduction potential values, suggested that 88% of the input total nitrogen were uptaken by the plant biomass. Fluorescence in situ hybridization results revealed the predominance of bacteria, including heterotrophic and autotrophic, responsible for BOD(5) removal. Nitrifying bacteria was not present in the constructed wetland beds.
Experiments were conducted to investigate the feasibility of applying constructed wetlands (CW) to treat a sanitary landfill leachate containing high nitrogen (TN) and bacterial contents. Under the tropical conditions (temperature of about 30 degres C), the CW units operating at a hydraulic retention time (HRT) of 8 days yielded the best treatment efficiencies with BOD5 removal of 91%, TN removal of 96%, total and fecal coliforms (TC and FC) removal of more than 99%. Cadmium removal in the in the SFCW bed was found to be 99.7%. Mass balance analysis, based on TN contents of the plant biomass and dissolved oxygen (DO) and oxidation - reduction potential (ORP) values, suggested that 88% of the input TN were uptaken by the plant biomass. Fluorescence in situ hybridization (FISH) results revealed the predominance of bacteria including the heterotrophic and autotrophic bacteria responsible for BOD5 removal. Nitrifying bacteria was not found to be present in the SSFCW beds.
The aim of this investigation was to evaluate the effect of continuous and intermittent feeding strategies on contaminant removal efficiency of shallow horizontal subsurface-flow constructed wetlands (SSF CWs). Also it was tested the effect of the presence of plant aboveground biomass on removal efficiency. Two experimental wetlands planted with common reed were subjected to a three-phase, 10-month experiment involving a common source of settled urban wastewater with a hydraulic loading rate of 26 mm/d during the first and second phases and 39 mm/d during the third. In the first and second phases one of the wetlands was fed continuously while the other was fed intermittently. In the third phase both systems were operated intermittently, but in one the macrophyte aboveground biomass was cut in order to study the effect of plant aboveground biomass on the removal efficiency. The intermittently fed system presented systematically more oxidised environmental conditions and higher ammonium removal efficiencies (on average 80 and 99% for the first and the second phases respectively) compared with the continuously fed system (71 and 85%). The mass amount of ammonium removed ranged from 0.58 to 0.67 g N/m2 d for the intermittently fed system and from 0.52 to 0.58 g N/m2 d for the continuously fed system. Sulphate removal was higher in the continuously fed system (on average 76 and 79% for the first and second phases respectively) compared with the intermittently fed system (51 and 58%). In the third phase the wetland that operated with aboveground biomass exhibited more oxidised environmental conditions and better removal efficiencies (on average 81% for COD and 98% for ammonium) than the wetland operated without aboveground biomass (73% for COD and 72% for ammonium). The results of this study indicate that the intermittent feeding strategy improved the removal of ammonium and the presence of aboveground biomass enhanced the removal of COD and ammonium.