Article

Enhancing recovery of magnesium as struvite from landfill leachate by pretreatment of calcium with simultaneous reduction of liquid volume via forward osmosis

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Abstract

Abstract Landfill leachate contains substances that can be potentially recovered as valuable resources. In this study, magnesium in a landfill leachate was recovered as struvite with calcium pretreatment; meanwhile, the leachate volume was reduced by using a submerged forward osmosis (FO) process, thereby enabling significant reduction of further treatment footprint and cost. Without pretreatment, calcium exhibited strong competition for phosphate with magnesium. The pretreatment with a Ca2 +: CO32– molar ratio of 1:1.4 achieved a relatively low loss rate of Mg2 + (24.1 ± 2.0%) and high Ca2 + removal efficiency (89.5 ± 1.7%). During struvite recovery, 98.6 ± 0.1% of magnesium could be recovered with a significantly lower residual PO43 −-P concentration (< 25 mg L− 1) under the condition of (Mg + Caresidual): P molar ratio of 1:1.5 and pH 9.5. The obtained struvite had a similar crystal structure and composition (19.3% Mg and 29.8% P) to that of standard struvite. The FO process successfully recovered water from the leachate and reduced its volume by 37%. The configuration of calcium pretreatment - FO - struvite recovery was found to be the optimal arrangement in terms of FO performance. These results have demonstrated the feasibility of magnesium recovery from landfill leachate and the importance of the calcium pretreatment, and will encourage further efforts to assess the value and purity of struvite for commercial use and to develop new methods for resource recovery from leachate.

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... Other studies investigated K-struvite recovery from landfill leachates [100,101]. Li et al. [100] used a nanofiltration (NF) membrane separation process coupled with a cation exchange membrane electrolysis (CEME) and a precipitation process to treat landfill leachate. Specifically, 99% of the potassium in the NF concentrate of landfill leachate was transported to the cathode after 8 h. ...
... Wu et al. [101] investigated the recovery of nutrients from landfill leachate after a forward osmosis (FO) process. To study the interference of calcium in the K-struvite formation process, the authors performed tests on raw leachate and after a pretreatment for calcium removal. ...
... After calcium removal, the process resulted in a significant improvement of struvite recovery. In particular, 4.34 kg of struvite and 365.6 kg of water could be recovered from one cubic meter of treated leachate [101]. ...
Article
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A.S.) † These authors contributed equally to this work. Abstract: The definition of technologies capable of removing and recovering nutrients from polluting effluents is a key environmental challenge. Through these technologies, it would be possible to protect aquatic systems and prevent the consumption of natural resources for the production of commercial fertilizers. In this regard, the application of the precipitation processes of struvite-type compounds is an attractive approach. Indeed, these processes are potentially able to remove nutrients from many effluents and produce a precipitate reusable as a slow-release fertilizer. The scientific community has largely focused on the precipitation of magnesium ammonium phosphate (MgNH4PO4·6H2O, MAP), while the recovery of the analogous magnesium potassium phosphate (MgKPO4·6H2O, MPP) has received extensive attention in the last decade. Research on this topic is continuously progressing to improve the precipitation process in different aspects (working conditions, reaction units, interference elimination, etc.). Until now, there has been no paper that comprehensively reviewed the applicability of MPP precipitation for the removal and recovery of nutrients from aqueous waste. To fill this gap, the present paper aimed to provide an exhaustive analysis of the literature reports on MPP processes to help researchers understand the theoretical and applicative aspects, the main problems, and the need for further research. In this regard, the applications in the treatment of various aqueous wastes were considered. The theoretical concepts, the main process parameters, and the effects of inhibiting substances and impurities are presented. Moreover, the development of reactor configurations and their working conditions are evaluated. Finally, the potential use of MPP as a fertilizer and some economic evaluations are reported. On the basis of the conducted analysis, it emerged that the recovery of MPP was mainly affected by the pH, dose, and nature of reagents, as well as the presence of competitive ions. The optimal pH values were reported to be between 9 and 11. Reagent overdoses with respect to the theoretical values improved the process and the use of pure reagents guaranteed superior performance. The stirred-tank reactors and fluidized bed reactors were the most used units with high process yields. The applicability of MPP in agronomic practices appears to be a suitable option.
... CaCl 2 , Ca(NO 3 ) 2 , NaCl and thermolytic solutes based on ammonia and carbon dioxide, similar to NH 4 HCO 3 , are the most DS employed for FO applications (Achilli et al., 2010). At the end of the FO filtration, the DS is recovered and recycled back to the FO unit while the permeate may need further treatment for its direct discharge or reuse (Wu et al., 2018). The energy consumption of FO systems without DS regeneration is notably lower (0.2-0.9 vs 10-14 kWh m −3 ) (Voutchkov and Kaiser, 2020); therefore, from an energy-efficient and resource recovery point of view, the selection of a fertilizer draw solute for FO application can be an attractive strategy. ...
... The proposed system recovered about 4.34 kg struvite and 366 kg of water per m 3 of treated leachate in optimum conditions. The net profit was estimated at 0.80 USD m −3 (Wu et al., 2018). ...
... A1: FO -calcium pre-treatment -struvite precipitation, A2: calcium pre-treatment -FO -struvite precipitation and A3: calcium pre-treatment -struvite precipitation -FO. Reprinted fromWu et al. (2018) with permission from Elsevier (license number: 5121960273804). FO: forward osmosis. ...
Article
Membrane filtration processes have been used to treat landfill leachate. On the other hand, closing the leachate treatment loop and finding a final destination for landfill leachate membrane concentrate (LLMC)-residual stream of membrane systems-is challenging for landfill operators. The re-introduction of LLMC into the landfill is typical; however, this approach is critical as concentrate pollutants may accumulate in the leachate treatment facility. From that, leachate concentrate management based on resource recovery rather than conventional treatment and disposal is recommended. This work comprehensively reviews the state-of-the-art of current research on LLMC management from leachate treatment plants towards a resource recovery approach. A general recovery train based on the main LLMC characteristics for implementing the best recovery scheme is presented in this context. LLMCs could be handled by producing clean water and add-value materials. This paper offers critical insights into LLMC management and highlights future research trends.
... As observed earlier in the equation for struvite formation (Equation (1)), equal molar ratios between the nutrients are needed; therefore, if there is a deficiency in one or more of the nutrients, an external source to provide the missing ion is required [20,23]. In most cases, and since the aim is to recover phosphorus, the limiting nutrient is magnesium [19], and according to multiple studies, Mg is usually supplemented using magnesium chloride or magnesium hydroxide. ...
... The growing population and urbanization have also led to a rapid increase in municipal solid waste (MSW); therefore, sanitary landfills are considered an easy and economical technique for the disposal of MSW. However, the decomposition of landfill waste results in landfill leachate that is rich in a number of valuable minerals, including magnesium [20]. The production of shale oil and gas acts as an alternative energy source, but the produced wastewater from the operation contains organic and inorganic contaminants and is highly saline. ...
... The pH and N:P ratios were varied and 98% of the phosphorus was removed under the optimum conditions of pH 9 and N:P ratio of 2:1. Wu et al. [20] investigated the efficiency of leachate samples collected from a landfill in Virginia, USA as a source of magnesium to recover struvite. Phosphorus was added in the form of phosphoric acid (H 3 PO 4 ) in this study. ...
Article
Full-text available
Citation: Fattah, K.P.; Sinno, S.; Atabay, S.; Khan, Z.; Al-Dawood, Z.; Yasser, A.K.; Temam, R. Impact of Magnesium Sources for Phosphate Recovery and/or Removal from Waste. Energies 2022, 15, 4585.
... Moreover, the composition of real wastewater can impact the longterm stability of granular AMX systems, either due to unbalanced nutrients and/or ions concentrations or for the presence of potential inhibitory compounds. When AMX granular technology is applied to streams prone to mineral precipitation, such as anaerobic digestion supernatant, landfill leachate or in wastewater reuse systems, the implications of mineral formation on process performance and stability should be carefully assessed and controlled [4,5]. Mineral precipitation has been reported to occur in granular biomass systems, either in anaerobic digestion (AD), partial-nitritation/anammox (PN/A), anammox (AMX) and aerobic granular sludge (AGS), both in lab-scale as well as in real-scale applications [4,6,7]. ...
... Water line (blue), gas line (dashed red) and sensors (dotted green). Influent port (1); gas recirculation inlet (2); water-lock and overpressure control(3); moisture trap (4); vacuum pump(5).ammonium and nitrite inlet concentration were 100-200 mgN- ...
Article
When treating wastewaters prone to inert precipitation with granular sludge systems, mineral formation needs to be properly controlled to ensure system’s long-term stability. In this work, an extensive study on mineral precipitation on the surface of anammox granular sludge is presented. A 7-L reactor was inoculated with one-year stored biomass and volumetric load up to 0.48 gN-NO2⁻/l/d were achieved, with nitrite removal above 95% and total nitrogen removal rate of almost 1 gN/l/d. Severe mineral precipitation was observed on the granules’ surface after three months of hard-water feeding and resulted in a dramatic deterioration of reactor performance and biomass activity. Substrate diffusion limitation in the inner layers, insufficient mixing due to higher granule density and biofilm erosion due to shear stress increase were deemed the main mechanisms that lead to progressive process disruption. Gravimetric selection was applied to discard granules affected by precipitation and allowed for process restoration. Microbial community analyses revealed that mineral composition possibly affected competition between “Ca. Brocadia” and “Ca. Kuenenia”. The knowledge gathered in the present study details the dramatic consequences on process performance lead by severe mineral precipitation and it is presented as a warning for full-scale applications treating wastewaters prone to precipitation.
... Another proposed desalination technology for leachate treatment is the combined chemical precipitation method and the FO process. Wu et al. [122] proposed using a pre-treatment strategy involving the addition of carbonate to improve the struvite precipitation and purity, followed by the FO desalination process as presented in Fig. 7. The researchers investigated three aspects to evaluate the performance of the new hybrid system. ...
... The FO process was arranged in three different modes: 1-FOcalcium pretreatment -struvite precipitation (C1), 2-calcium pretreatment -FO -struvite precipitation (C2) and 3-calcium pretreatment -struvite precipitation -FO (C3). Adapted with permission from Wu et al. [122]. [123]. ...
... kg −1 . 44,74 The struvite recovery cost from human urine was reported as $0.31 kg −1 struvite recovered, 75 dairy wastewater as $1.38 kg −1 struvite, 76 and algal biomass as $0.94 kg −1 struvite. 77 Human urine requires the addition of magnesium and phosphorus to enhance the recovery. ...
... Thus, leachate with high Ca 2+ needs an extra step of pre-treatment, which was found to contribute ∼61% of the total struvite recovery cost. 74 Concentrates generated from membrane separation processes, such as nanofiltration and reverse osmosis, can yield greater struvite recovery because of the higher concentration of nutrients. 84−86 A combination of cation-exchange membrane electrolysis and a magnesium potassium phosphate (MgKPO 4 · 6H 2 O, K-struvite) crystallization technique demonstrated the corecovery of gaseous chlorine and hydrogen from leachate concentrate. ...
... Their finding demonstrated that the aquaporin FO membrane was effective to remove the Sb (>99.7% rejection) as well as other inorganic and organic contaminants (90%) during the treatment of real dyeing wastewater. In the context of resource recovery, several works regarding FO application to promote valuable resource recovery from saline wastewater was reported in the literature [43,75,76]. For instance, Wu et al. [75] studied the effect of MgCl 2 as the DS to obtain the struvite from agricultural wastewater (i.e., livestock wastewater) using the FO system. ...
... However, it shall be noted that the addition of chemical during pre-treatment will increase the ionic concentration in the landfill leachate, thus reducing the osmotic pressure gradient across the FO. Wu et al. [43] investigated the trade-off between water recovery capability and ionic concentration in feed solution as well as the treatment configuration. The lowest water flux (0.05 LMH) was observed after a 60-h operation when the leachate was subjected to calcium pretreatment and struvite precipitation steps before the FO process. ...
Article
The saline wastewater from various sources including agriculture and industrial activities, appears to have high salt concentration, organic content and other pollutants which can harm the environment. Thus, saline waste-water treatment has become one of the major concerns in many countries. Membrane technology offers great potential in saline wastewater treatment due to its high permeate quality, flexibility, and desalination capability. This paper highlights the current development in various types of membrane processes such as pressure driven-based membranes, forward osmosis, membrane distillation, electrodialysis and membrane bioreactor, either as a stand-alone or integrated process for saline wastewater treatment. The membranes performance in terms of water reclamation as well as resource recovery is discussed. Besides, the membrane fouling issue is highlighted, and the efficiency of various fouling mitigation strategies when dealing with real/challenging saline wastewater are reviewed. Finally, the future challenges and outlook in the context of membrane application for saline wastewater treatment are discussed.
... Besides, some pretreatment measures, such as calcium pretreatment and microbial electrolysis cell can also be coupled with FO process and achieved excellent performance in the treatment of landfill leachate [93,94], exhibiting a great potential for resource recovery and sustainable leachate management. In the work by Wu et al. [93] on treatment of landfill leachate, calcium pretreatment was applied, to reduce the competition with Mg 2+ for phosphate during struvite formation process and mitigate membrane fouling in FO process. ...
... Besides, some pretreatment measures, such as calcium pretreatment and microbial electrolysis cell can also be coupled with FO process and achieved excellent performance in the treatment of landfill leachate [93,94], exhibiting a great potential for resource recovery and sustainable leachate management. In the work by Wu et al. [93] on treatment of landfill leachate, calcium pretreatment was applied, to reduce the competition with Mg 2+ for phosphate during struvite formation process and mitigate membrane fouling in FO process. And the subsequent FO dewatering reduced the leachate volume and enhance Mg 2+ concentration, contributing to the reduction of further treatment footprint and reagent dosage. ...
Article
Full-text available
During the last decades, the utilization of osmotic pressure-driven forward osmosis technology for wastewater treatment has drawn great interest, due to its high separation efficiency, low membrane fouling propensity, high water recovery and relatively low energy consumption. This review paper summarizes the implementation of forward osmosis technology for various wastewater treatment including municipal sewage, landfill leachate, oil/gas exploitation wastewater, textile waste-water, mine wastewater, and radioactive wastewater. However, membrane fouling is still a critical issue, which affects water flux stability, membrane life and operating cost. Different membrane fouling types and corresponding fouling mechanisms, including organic fouling, inorganic fouling, biofouling and combined fouling are therefore further discussed. The fouling control strategies including feed pre-treatment, operation condition optimization, membrane selection and modification, membrane cleaning and tailoring the chemistry of draw solution are also reviewed comprehensively. At the end of paper, some recommendations are proposed.
... Sena and Hicks (2018) recently showed the positive aspects of P recovery using struvite precipitation through a detailed life cycle analysis. Due to its chemical composition, it has been proposed to be used as a fertilizer, a fire retardant in fabrics, or as a binding material in cement (Acelas et al., 2015;Kabdas ßl et al., 2009;Huang et al., 2014;Wu et al., 2018). Struvite formation can be expressed as Eq. ...
Article
This manuscript presents an integrated management scheme for leachate which employed struvite precipitation to recover ammonia nitrogen and phosphorus, aerobic granular sludge process for carbon oxidation (in the form of BOD and sCOD) and single stage anaerobic ammonia oxidation (ANAMMOX) for nitrogen management. The influent fed to the integrated treatment scheme was a mixture of anaerobic digester centrate and real leachate in 4:1 ratio. Almost 77% recovery of phosphorus and 25% removal of NH4+-N were accomplished through struvite precipitation at an optimum pH of 9. High pH contributed to free ammonia loss during struvite precipitation experiments. In the aerobic granular sludge reactor overall, BOD5, COD and NH4+-N removal percentages were 74%, 45% and 35% and in the PN/A reactor, overall 35% removal of total inorganic nitrogen (TIN) was observed. More than 80% BOD removal was recorded in the granular reactor with soluble COD (sCOD) removal fluctuating between 28 and 57% depending on the operational phase. High-throughput amplicon sequencing of 16S rRNA gene targeting V4 region revealed a dominance of phylum Planctomycetes, in the PN/A reactor system. Presence of Rhodobacteraceae, Xanthomonadaceae, Flavobacteriaceae in the granular biomass confirmed the defined redox zones inside mature granules indicating simultaneous removal of nitrogen (N) and organics in aerobic granular sludge technology. Exposing the synthetically cultured aerobic granules directly to the mixture of leachate and centrate unveiled an alteration in physical characteristics of granules; however, reactor operational data and microbial community analysis ascertain the effectiveness of the treatment scheme treating two urban waste-streams.
... Forward osmosis (FO), an important technology within MTs, with an extensive low energy consumption has been gaining significant attention in the field of water desalination and wastewater treatment (Ansari et al., 2016;Jang et al., 2018;Li et al., 2011). The performance of the FO process is governed by multiple factors including the characteristic of feed and draw solutions (type of solute, concentration and volume), operational parameters (cross-flow velocity and flow rate) and temperature (Wu et al., 2018). The membrane-like characteristics (area, material type and membrane orientation) and the structural characteristics (porosity, tortuosity and thickness) have also direct effect on the performance of FO process (Pardeshi et al., 2016;Phuntsho et al., 2012;Wilberforce et al., 2019). ...
... Microbial electrochemical cells (MXCs), such as microbial electrolysis cell (MEC), microbial fuel cell (MFC), microbial desalination cell (MDC), are considered as promising bioprocesses for recovery of value-added bioresources (e.g., bio-electricity, H 2 , CH 4 , H 2 O 2 , nutrients, etc.) and simultaneous treatment of waste and wastewater (Al-Mamun et al., 2018;Barua et al., 2019;Ki et al., 2017b;Wu et al., 2018). These systems utilize unique anode-respiring bacteria (ARB) that are capable of facilitating long-distance electron transfer to the anode through extracellular electron transport mechanism (Malvankar et al., 2012;Reguera et al., 2005;Torres et al., 2010). ...
... Compared to pressure-driven membrane processes, FO is less susceptible to fouling and requires significantly less energy, particularly when draw solution regeneration is not required [1,2]. As a novel membrane process, FO has been investigated for the treatment of challenging wastewater [3] and a range of innovative applications including resource recovery [4,5], hypersaline desalination [6,7], and sludge thickening [8,9]. ...
Article
This study elucidates the impact of draw solution chemistry (in terms of pH and draw solute species) and membrane fouling on water flux and the rejection of trace organic contaminants by forward osmosis. The results show that draw solution chemistry could induce a notable impact on both water flux and TrOCs rejection. In addition, the impact was further influenced by membrane fouling. The reverse flux of proton (or hydroxyl) could alter the feed solution pH, which governed the separation of ionisable TrOCs. In addition, charged compounds generally exhibited higher rejections than neutral ones by the clean membrane. Electrostatic interaction, rather than size exclusion, was therefore the dominant rejection mechanism for most compounds. There was also a weak correlation between rejection and molecular sizes of the 43 TrOCs. Compared with Na⁺, Li⁺ with a larger hydrated radius showed a significantly lower reverse salt flux, resulting in a lower ionic strength and therefore a stronger electrostatic interaction. A fouling cake layer consisted of low molecular weight neutral organics could also affect TrOC rejection due to pore blockage and cake-enhanced concentration polarisation.
... This categorization was supported by the high occurrence of keywords related to the study of FO performance and application, as in Cluster 1. For instance, extensive publications have shown the potential of the FO process for wastewater treatment [108], nutrient concentration [109,110], resource recovery [111][112][113], food concentration [114], produced water remediation [115], and desalination [116]. All these topics have appeared as keywords in Fig. 10. ...
Article
Issues of water scarcity and water security have driven the rapid development of various technologies to ensure water sustainability. The forward osmosis (FO) membrane process has been widely recognized as one of the more promising technologies to play an important role in alleviating the issues of water sustainability. Extensive research has been carried out worldwide to explore the potential of FO in desalination, water and wastewater treatment and reclamation. It is of the utmost importance to understand the topics of interest and research trends to further advance the development of FO process technology. In this study, a bibliometric analysis based on the Scopus database was carried out to identify and understand the global research trends of FO process based on 6 main analyses: basic growth trends, journals, countries, institutions, authors, and keywords. A total of 1462 article records published between 1967–2018 were extracted from Scopus and used as the raw data for bibliometric analysis using VOSviewer software. The total number of FO articles has sharply increased since 2009 and stabilized at around 250 publications in the past three years. The increase could be associated with the breakthrough in FO membrane science, where the contributions were from the 5 most productive countries: USA, China, Singapore, Australia, and South Korea. FO research started to diversify after the appearance of commercial FO membranes with improved characteristics, enabling the researchers to employ them for various application studies. Keywords analysis showed that the main directions of FO research could be categorized into three clusters: application of FO, membrane fouling study, and FO membrane synthesis. These bibliometric results provide a valuable reference and information on current research directions of FO for researchers and industry practitioners who are interested in FO technology.
... CaCl2, Ca(NO3)2, NaCl, and thermolytic solutes based on ammonia and carbon dioxide, similar to NH4HCO3, are the most DS employed for FO applications (Achilli et al., 2010). At the end of the FO filtration, the DS is recovered and recycled back to the FO unit while the permeate may need further treatment for its direct discharge or reuse (Wu et al., 2018). The energy consumption of FO systems without DS regeneration is notably lower (0.2─0.9 vs. 10─14 kWh m -3 ) (VOUTCHKOV & KAISER, 2020); therefore, from an energy-efficient and resource recovery point of view, the selection of a fertilize draw solute for FO application can be an attractive strategy. ...
Thesis
Full-text available
The current thesis explores the techno-economic aspects of nanofiltration (NF) and reverse osmosis (RO) processes treating landfill leachate. The management of membrane concentrate streams and related issues are analysed in this context. Experimental landfill cells were constructed to investigate the impacts of concentrate recirculation practice on the leachate quantity, quality, and treatment performance. Data from the 420-day monitoring experiment were analysed using a statistical tool. Membrane-based technologies stand out for their high cost-benefit. NF and RO systems removed organic matter, reported as chemical oxygen demand (COD), absorbance at 254 nm (UV254), and ammonia nitrogen at removal efficiencies higher than 90%.The leachate treatment operating costs ranged from 0.132 to 3.35 USD per m3 of treated leachate. In contrast, the management of the concentrated leachate generated by membrane filtration processes is not considered when the expenses for NF/RO implementation are estimated. Concentrate streams are commonly re-introduced into the landfill without additional cost for landfill managers. However, the consequences of this practice are not well-known, and the literature's findings show contrasting conclusions. Our assessment using simulated landfill cells indicated that membrane concentrate infiltration increases the organic content of methanogenic leachates. The pollution parameters' median values were higher in leachates drained from cells that operated with concentrate recirculation (i.e., 6729 vs 1367 mg L -1 [COD], 33.39 vs 17.39 cm -1 [UV 254 ]; p-value < 0.05). The recalcitrant organics' accumulation impacted the RO treatment efficiency by increasing organic fouling onto the membrane surface. In that direction, greener solutions for the leachate membrane concentrate management are recommended to guarantee the long-term sustainability of the leachate treatment chain. In this scenario, the use of leachate concentrate residue in the pyrolysis process of agroindustrial biomass was investigated to produce add-value products. This resource recovery study showed promising results, which could foster more sustainable strategies to close the landfill leachate treatment loop.
... Recently, FO has been successfully applied in the direct concentration of the complex and high strength wastewater streams, such as textile wastewater (Han et al., 2016), drilling mud from oil refining (Hickenbottom et al., 2013), landfill leachate (Iskander et al., 2017;Qin et al., 2016), and domestic wastewater (Aftab et al., 2017(Aftab et al., , 2015. FO has also proved its excellent applicability in treating landfill leachate for the recovery of inorganics, the removal of aromatic hydrocarbons, and the water recovery from high saline and biologically treated leachates (Dong et al., 2014;Iskander et al., 2017;Li et al., 2017;Qin et al., 2016;Wu et al., 2018). However, despite a number of such practical applications, no attention has been paid to the organic fouling potential of landfill leachate in FO, which serves as a critical factor to determine the operational cost and water recovery. ...
Article
Forward osmosis (FO) has been adopted to treat complex wastewater such as landfill leachate due to its high rejection of organics. In this study, the in-line adsorptive process using biochar (BC) or powdered activated carbon (PAC) was applied to a cross flow FO system to enhance the mitigation of the FO membrane fouling from landfill leachate. The changes in the leachate composition along the treatments were tracked by excitation emission matrix-parallel factor analysis (EEM-PARAFAC) to identify tryptophan-like (C1), fulvic-like (C2), and humic-like (C3) components. After a single operation of FO, the C1 was found to be the main constituent responsible for membrane fouling irrespective of varying operation conditions regarding draw solute concentrations and flow rates. Both sorbents (i.e., BC and PAC) exhibited the preferential removal behavior towards C1 > C2 > C3, which was well supported by their individual adsorption isotherm model parameters. The addition of in-line adsorption treatment to FO resulted in substantial improvements in the filtered volume (>57%) and the flux recovery (>80%) compared to the single FO operation. Without chemical cleaning of membrane, the flux was fully recovered at a dose of 10 g/L BC or 0.3 g/L of PAC. A significant and negative correlation was found between the flux recovery and the C1 of the feed leachate or the corresponding spectral peak intensity (p < 0.05) for the integrated FO system, suggesting the potential of using on-line fluorescence monitoring for the performance of the integrated system in terms of fouling mitigation. This study provided a new insight into the effectiveness of BC or PAC adsorption as the in-line integration with an FO system for the targeted removal of FO membrane foulants in landfill leachate.
... Struvite or magnesium ammonium phosphate hexahydrate (MgNH 4 PO 4 ·6H 2 O, MAP) precipitation has been highlighted as an innovative, environmentally sound, and profitable physicochemical treatment method for recovery of recyclable constituents from nutrient-laden industrial discharges. In the literature, a substantial number of work has been performed for the removal and/or recovery of ammonium nitrogen (NH + 4 −N) and/ or phosphate phosphorus (PO 3− 4 −P) as struvite from various effluents such as animal waste stream [2,5,[7][8][9][10][11][12][13][14][15][16], anaerobically digested discharge [17][18][19][20][21], synthetic wastewater [22][23][24][25][26][27][28][29][30], industrial effluent [31][32][33][34], landfill leachate [35][36][37], and human urine [38][39][40][41]. As seen from the previous studies that struvite precipitation has been broadly applied as an encouraging physicochemical treatment technique due to its efficacy in eliminating and/or recovering excess nutrients (e.g. ...
Article
Sustainable uses of the struvite (magnesium ammonium phosphate hexahydrate, MgNH4PO4·6H2O, MAP) recovered from the synthetic wastewater, as a high-quality slow-release fertilizer for the growth of nine medicinal plants and a fire-retardant barrier on the flammability of cotton fabric and wooden plate, were explored in this study. The previous experimental results demonstrated that under the optimal conditions, about 98.7% of NH4⁺-N (initial NH4⁺-N = 1000 mg/L) could be effectively and successfully recovered from simulated wastewater in the form of MAP precipitate. Rates of increase in total fresh weights, total dry weights, and fresh heights of plants grown in soil fertilized with the struvite were determined as 67%, 52%, and 12% for valerian; 121%, 75%, and 18% for cucumber; 421%, 260%, and 47% for dill; 314%, 318%, and 27% for coriander; 432%, 566%, and 30% for tomato; 285%, 683%, and 26% for parsley; 200%, 225%, and 9% for basil; 857%, 656%, and 92% for rocket; and 146%, 115%, and 28% for cress, respectively, compared to the control pots. The microstructure, elemental composition, surface area, thermal behavior, and functional groups of the grown crystals were characterized using SEM, EDS, BET, TGA-DTG-DSC, and FTIR analyses, respectively. Flammability tests and thermal analyses concluded that the dried and crumbled/implanted form of struvite used as a fire-retardant barrier demonstrated a remarkable flame-resistant behavior for both cotton fabric and wooden plate. Findings of this experimental study clearly corroborated the versatility of struvite as non-polluting and environmentally friendly clean product for the sustainable usage in different fields.
... In other studies, the elimination of other ions e.g. Ca 2+ by at least 90%, enhanced the recovery of magnessium from leachate (from 65% -98%) through struvite precipitation (Wu et al., 2018). In a bid to lower struvite precipitation costs, the use of waste phosphoric obtained during production of phosphoric acid and low cost magnesium oxide was proposed. ...
Thesis
The generation of landfill leachate is a significant result of landfilling. Because of the high concentrations of pollutants in leachate, disposal of raw or insufficiently treated landfill leachate can cause harm to the environment. Biological processes are inefficient for the treatment of stabilized landfill leachate given the presence of recalcitrant organic compounds and low leachate biodegradability. As such, post-treatment is required to meet discharge standards. Therefore, this PhD thesis focused on the (post)-treatment of raw and biologically treated landfill leachate using four physical-chemical processes, i.e. ozonation, coagulation-flocculation, granular activated carbon (GAC) adsorption, and ion exchange. The aim was obtaining an optimized and cost effective integrated leachate treatment train. The research also used spectral and chemometric techniques to characterize dissolved organic matter (DOM) components in landfill leachate and to monitor how they are removed during treatment. The results show that (post)-treatment of raw and biologically treated leachate with a single physical-chemical step is inefficient as the environmental discharge standards are not met. However, combining coagulation-flocculation or ozonation with GAC adsorption significantly reduces the pollutant concentrations making it possible to meet the discharge standards. Spectral and chemometric analysis show that coagulation as a pre-treatment step removes high molecular weight humic compounds that would otherwise clog the GAC adsorption sites, and that GAC unselectively removes DOM components hereby improving the overall performance. Ion exchange can be used to recover ammonium from the raw landfill leachate with complete removal. Overall, (post)-treatment of raw and biologically treated leachate with coagulation-flocculation + GAC + ion exchange and coagulation-flocculation + GAC, respectively, are shown to be more efficient and cost effective than a treatment train without coagulation-flocculation pre-treatment.
... The low DS/catholyte conductivity would render a lower osmotic pressure gradient (i.e. water migration driving force) between draw and feed solution across the FO membrane, resulting in less water flux [30]. ...
Article
Osmotic microbial fuel cells (OsMFCs) combine the merits of microbial fuel cell (MFC) and forward osmosis (FO) for simultaneous contaminant removal, electricity generation, and high-quality water extraction. As an FO based technology, reverse solute flux (RSF) is one of the key challenges for its operation. Herein, RSF was converted into a positive effect on the system performance by using NaHCO3 solution as a draw solution (DS)/catholyte. It was found that reverse-fluxed NaHCO3 helped buffer the anolyte pH and thus enhance electricity generation, compared to the OsMFC using the NaCl DS/catholyte. At the same concentration, the NaHCO3 DS/catholyte achieved a higher Coulomb production of 1349.2 ± 80.3 C and higher anolyte pH of 6.48 ± 0.19 than those of the NaCl DS/catholyte. At the same conductivity, the NaHCO3 DS/catholyte exhibited better electricity generation performance with a comparable recovered water volume of 417.7 ± 13.7 mL to that of the NaCl DS/catholyte. As the NaHCO3 concentration increased from 0.1 M to 0.75 M, the OsMFC electricity generation was enhanced due to the increased RSF from 19.2 ± 2.3 to 210.8 ± 17.5 mmol m⁻²h⁻¹. In the anode, 92.0 ± 0.8% to 97.1 ± 0.9% of reverse-fluxed NaHCO3 was used to neutralize protons. These results have demonstrated a new strategy that uses the bicarbonate migration driven by both a concentration gradient and electricity generation to successfully raise the alkalinity of the anolyte towards enhancing electricity generation.
... deionized water (DI water), and then dried in the fume hood for further analysis. For physical cleaning and fouling control, the FO membrane was flushed with DI water for 30 min with a recirculation rate of 200 mL min −1 (16.98 cm s −1 ) after each batch test based on previous studies[20,21]. ...
... By concentrating by 3.2 folds through FO, Iskander et al. observed that, by incorporating FO and humic acid recovery into a Fenton's oxidation system, FO could decrease leachate volume, lower reagent requirements, and reduce sludge production by 30% [180]. Even at a moderate concentration rate (1.5 fold), and after calcium pre-treatment, FO was used to successfully precipitate struvite [181]. FO, combined with microbial desalination cells also proved to be feasible to concentrate leachate and recover nitrogen [182,183]. ...
Article
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In the past few years, osmotic membrane systems, such as forward osmosis (FO), have gained popularity as “soft” concentration processes. FO has unique properties by combining high rejection rate and low fouling propensity and can be operated without significant pressure or temperature gradient, and therefore can be considered as a potential candidate for a broad range of concentration applications where current technologies still suffer from critical limitations. This review extensively compiles and critically assesses recent considerations of FO as a concentration process for applications, including food and beverages, organics value added compounds, water reuse and nutrients recovery, treatment of waste streams and brine management. Specific requirements for the concentration process regarding the evaluation of concentration factor, modules and design and process operation, draw selection and fouling aspects are also described. Encouraging potential is demonstrated to concentrate streams more than 20-fold with high rejection rate of most compounds and preservation of added value products. For applications dealing with highly concentrated or complex streams, FO still features lower propensity to fouling compared to other membranes technologies along with good versatility and robustness. However, further assessments on lab and pilot scales are expected to better define the achievable concentration factor, rejection and effective concentration of valuable compounds and to clearly demonstrate process limitations (such as fouling or clogging) when reaching high concentration rate. Another important consideration is the draw solution selection and its recovery that should be in line with application needs (i.e., food compatible draw for food and beverage applications, high osmotic pressure for brine management, etc.) and be economically competitive.
... 1996;Battistoni et al., 1997Battistoni et al., , 2000Ohlinger et al., 1998;Çelen and Türker, 2001;Münch and Barr, 2001;Fattah et al., 2008;Forrest et al., 2008;Uysal et al., 2010; Fig. 3. Characteristics of monovalent ions involved in formation of struvite and its analogues (Tansel, 2012). wastewater and waste generated from animal farms (Bonmati and Flotats, 2003;Nelson et al., 2003;Zeng and Li, 2006;Huang et al., 2011;Rahman et al., 2011;Jordaan, 2011;Ichihashi and Hirooka, 2012), supernatant produced during concentration of wastewater sludge by centrifuge and concentrate from nanofiltration (i.e., seawater as Mg þ2 supplement) (Lahav et al., 2013); leachate from landfills (Li et al., 1999;He et al., 2007;Zhang et al., 2009;Huang et al., 2014;Wu et al., 2018); wastewater from fertilizer industry or in kidneys at body temperature (i.e., struvite based kidney stones) (Johnson, 1959;Frost et al., 2004;K€ onigsberger and K€ onigsberger, 2006). Kataki et al. (2016) evaluated the need for additional chemical inputs, increasing recovery efficiency, and the fertilizer value and economical aspects of the nutrient recovery from struvite. ...
... PTEs such as Zn, Pb, Cu, and Cd are accumulated in the MSWI FA particles, which are regarded as secondary resources (Burlakovs et al., 2018;Geng et al., 2020a;Quina et al., 2018). Resources recovery technologies for the MSWI FA have developed in recent years to alleviate environmental concerns and provide mineral resources (Funari et al., 2015;Meylan and Spoerri, 2014;Wu et al., 2018). Three major recovery technologies included thermal separation, hydrometallurgical methods (i.e., chemical extraction, bioleaching), and electrochemical processes (Geng et al., 2020a). ...
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Municipal solid waste incineration (MSWI) fly ash is considered as a hazardous waste that requires specific treatment before disposal. The principal treatments encompass thermal treatment, stabilization/solidification, and resource recovery. To maximize environmental, social, and economic benefits, the development of low-carbon and sustainable treatment technologies for MSWI fly ash has attracted extensive interests in recent years. This paper critically reviewed the state-of-the-art treatment technologies and novel resource utilization approaches for the MSWI fly ash. Innovative technologies and future perspectives of MSWI fly ash management were highlighted. Moreover, the latest understanding of immobilization mechanisms and the use of advanced characterization technologies were elaborated to foster future design of treatment technologies and the actual-ization of sustainable management for MSWI fly ash.
... Mg/Ca ratios of >4 were not considered since they would only marginally improve struvite production selectivity while significantly increasing the processing costs. 23,44,46,47 Seeding is usually required when crystallization occurs at a supersaturation level lower than that at which spontaneous nucleation occurs. 48 Indeed, no struvite crystal seeds were added into the HTL-APs since the high supersaturation level provided by the alkaline pH (8−9), and the sufficient agitation speed (200 rpm) in this study caused struvite crystal nucleation to be spontaneous. ...
Article
Struvite (MgNH 4 PO 4 ·6H 2 O), a mineral containing bioavailable phosphorus and nitrogen, is a solid slow-release fertilizer that can be produced from the aqueous-phase coproduct of hydrothermal liquefaction (HTL-AP). However, if the struvite crystallization process is carried out at nonoptimal conditions, then the P in the HTL-AP can crystallize with Ca, forming an undesirable hydroxyapatite (Ca 10 (PO 4) 6 (OH) 2) solid byproduct that also acts as an adsorbent for potentially phytotoxic organics. To maximize struvite yield and purity, a deeper understanding of struvite and hydroxyapatite crystallization as well as organics adsorption onto hydroxyapatite is critical. In this study, crystallization experiments varying temperature, time, pH, and Mg/Ca ratio were carried out. The experimental results informed a supersaturation-based reversible crystallization model for struvite and hydroxyapatite while the adsorption of organics was satisfactorily described by the classical Ritchie's and Langmuir equations. The Arrhenius and van 't Hoff equations were applied to describe the thermodynamics and kinetics of these processes. Struvite yield and purity are maximized at 25°C, pH 8, and Mg/Ca ratio of 4, with a P-recovery rate of >90%. A less alkaline pH and higher Mg/Ca ratios maximize the reactivity among NH 4 + , HPO 4 2− , and Mg 2+ , which increases struvite selectivity over hydroxyapatite and reduces organic physisorption onto hydroxyapatite by suppressing organics deprotonation. Lower temperatures reduce struvite endothermic dissolution and organics endothermic adsorption and favor hydroxyapatite exothermic dissolution. The thermodynamics and kinetics data and models from this study are useful in designing a more sustainable and economically feasible HTL-AP valorization route.
... However, concentration of impurities, especially calcium, has a large impact on struvite production [68], a fact that was ignored. Calcium impurities can be precipitated out from mixed wastewater as CaCO3 and reduced to great effect in under 5 min by the pre-treatment addition of NaCO3, resulting in a higher purity struvite product [70]. The efficiency of pH correction and potential decrease in membrane fouling by sparging air within the reactor, should be subject to further study, in combination with the effects of calcium removal. ...
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Industrial wastewater and other trade wastes are often sources of pollution which can cause environmental damage. However, resource recovery approaches have the potential to lead to positive environmental outcomes, profits, and new sources of finite commodities. Information on these waste sources, and the valuable components which may be contained in such waste is increasingly being made available by public, academic and commercial stakeholders (including companies active in meat processing, dairy, brewing, textile and other sectors). Utilising academic and industry literature, this review evaluates several methods of resource recovery (e.g., bioreactors, membrane technologies, and traditional chemical processes) and their advantages and disadvantages in a trade waste setting. This review lays the groundwork for classification of waste and resource recovery technologies, in order to inform process choices, which may lead to wider commercial application of these technologies. Although each waste source and recovery process is unique, membrane bioreactors show promise for a wide range of resource recovery applications. Despite interest, uptake of resource recovery technologies remains low, or not widely championed. For this to change, knowledge needs to increase in several key areas including: availabilities and classification of trade wastes, technology choice processes, and industrial viability.
... Struvite (MgNH 4 PO 4 ⋅6H 2 O) is formed by bonding between magnesium, ammonium, and phosphate ions (Eq. (1)) under favorable conditions (Wu et al., 2018). ...
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The alarming decline in phosphate raw materials and increase in eutrophication has escalated interest in struvite research. This manuscript presents scientometric analysis on struvite for fertilizing applications to comprehend the evolution and transformation of the field, investigate the existing challenges, research gaps, and developments to gain insights on the emerging trends for further studies. A total of 1550 scientific documents, between the years 1999–2020, were collected from Scopus® and PubMed® using an appropriate trail of keywords and analyzed using CiteSpace 5.7. R2. Ten attributes such as annual publication output and types, co-authorship network, co-occurring author keywords, the network of authors’ countries and institutions, author co-citation network, document co-citation network, journal co-citation network, and co-occurring subject categories were investigated. Based on the distinct network patterns generated by the software, progress of the field, paradigm shifts, knowledge gaps, and scientific frontiers were identified and mapped. The literature on struvite research was found to have bloomed in the early 2000s and accelerated significantly until now, with maximum contribution from China and United States. Journal of cleaner production ranks 5th with 3.35% share of the total contribution according to journal co-citation analysis. Cluster analysis of co-occurring author keywords revealed the research progression through the expanse, knowledge gaps, disciplinary and inter-disciplinary advancements, and future exploration trends. The research has evolved from evaluating the process influencing parameters and developing suitable reactor designs to installation of pilot-scale plants for commercialization. However, lack of experiments on real-time wastewater, plant growth studies and the underlying nutrient uptake mechanisms persist as major research gaps. Focussing on these aspects along with integrated advanced technologies such as microbial fuel cells, microbial electrolysis cells, electrochemical precipitation of struvite and wider application of struvite can pave way for enormous progress of this field.
... Moreover, membrane wetting is the key factor to determine whether MD can maintain the long-term operation. To address these challenges, developing highperformance membrane materials and coupling with other processes have been investigated [12][13][14]. So far, however, a comprehensive review of the applications of MD in wastewater treatment and the obstacles and solutions has not been undertaken. ...
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Water serves as an indispensable part of human life and production. On account of the overexploitation of traditional water sources, the demand for wastewater recycling is expanding rapidly. As a promising water treatment process, membrane distillation (MD) has been utilized in various wastewater treatments, such as desalination brine, textile wastewater, radioactive wastewater, and oily wastewater. This review summarized the investigation work applying MD in wastewater treatment, and the performance was comprehensively introduced. Moreover, the obstructions of industrialization, such as membrane fouling, membrane wetting, and high energy consumption, were discussed with the practical investigation. To cope with these problems, various strategies have been adopted to enhance MD performance, including coupling membrane processes and developing membranes with specific surface characteristics. In addition, the significance of nutrient recovery and waste heat utilization was indicated.
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Surface modification with advanced nanomaterials (i.e., 2D nanosheets) can be used to strategically tailor the membrane properties, conferring improved solute permselectivity to targeted molecules. Especially, 2D graphite-like carbon nitride (g-C3N4) nanosheets show a promising alternative for membrane modification, due to the exceptional physico-chemical properties and facile synthesis. Herein, high-flux nanofiltration (NF) membranes were designed using bio-inspired co-deposition of hydrophilic g-C3N4 nanosheets with a polydopamine (PDA)/polyethylenimine (PEI) layer onto porous ultrafiltration (UF) substrates. The g-C3N4 nanosheets created additional nano-channels in the PDA/PEI layer to facilitate water molecule transport, resulting in high permeability (28.4±1.2 L·m-2·h-1·bar-1). Particularly, the bio-inspired layer structure was tailored from UF to NF (592 Da) scale by incorporating g-C3N4 nanosheets, thereby breaking through the permeability-selectivity trade-off effect. The tailored NF membrane enabled ultrahigh retention of three reactive dyes (610 - 630 Da, >99.3%) and low salt rejection (2.9% for NaCl; 7.6% for Na2SO4), significantly promoting the fractionation of dyes and salts for dye desalination. Additionally, the hydrophilic g-C3N4 nanosheets with oxygen plasma treatment further enhanced the wettability of the membrane surfaces, resulting in a superior antifouling performance. This study indicates the promise of g-C3N4 nanosheets to engineer high-flux NF membranes with desirable fractionation performance for sustainable treatment of highly saline wastewater.
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Nitrogen and phosphorus levels in livestock manure and digestive fluid are high, posing a threat to soil and water quality and necessitating nutrient removal and recovery. Phosphorus recovery has the potential to alleviate the global phosphorus resource crisis. This study proposed a magnesium anode constant voltage electrolysis method to crystallise struvite (magnesium ammonium phosphate hexahydrate, MgNH4PO4·6H2O) from anaerobically digested chicken manure slurry using reaction kinetics at variable constant voltages ranging from 2 V to 12 V. The recovery of nitrogen and phosphorus was shown to be effective over a wide initial pH range (3.00 ± 0.03–7.90 ± 0.10) using synthetic digestion fluids. Moreover, the pH gradually increased during the reaction without any external chemical adjustments. The phosphorus recovery rates conformed to the first-order kinetic model, with a maximum rate constant of 2.13 h⁻¹. When the best voltage of 2 V was used at 25 ± 1 °C, the recovery rate reached 5.24 mg P h⁻¹cm⁻² in the synthetic digestion fluids during 90 min and 4.60 mg P h⁻¹cm⁻² in the anaerobically digested chicken manure slurry. The crystalline products recovered were identified as high-purity struvite by XRD and XPS. The purity of recovered struvite with an initial pH of 3.00 and 7.90 was 96.5% and 98.9%, respectively. These results demonstrated that the magnesium electrode could rapidly react with nitrogen and phosphorus to generate high-purity struvite.
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ABSTRCTThis study aimed to investigate pollutant concentration and nitrogen interception characteristics of a forward osmosis (FO) process for concentrating black odorous water. The membrane cell was operated in active layer facing feed solution (AL-FS) mode with aquaporin (AQP) as the membrane material and NaCl solution as the draw solution (DS). The organic pollutants (COD), TP, NH+ 4-N, NO- 3-N, TN, Fe and Mn in black odorous water were concentrated non-intermittently for 24 hours, and their interception characteristics were investigated. The results showed that the average interception rates of COD, TP, NO- 3-N, TN, Fe and Mn were 97.2%, 98.0%, 58.7%, 54.3%, 61.8% and 60.0%, respectively, while the average interception rate of NH+ 4-N was only 1.27%-3.47%. To explore the characteristics of nitrogen interception, a comparison was conducted between AQP membrane and thin film composite (TFC) membrane. Because the surface electronegativity of AQP membrane was stronger than that of TFC, the effect of cation exchange on ammonia nitrogen interception was more serious with AQP membrane. With NaCl solution as DS, the reverse osmosis flux of Na+ was (0.53 ± 0.02 mol·m-2·h-1), which was significantly higher than that of Cl- (0.29 ± 0.03 mol·m-2·h-1) (P < 0.05). The interception effect of AQP membrane on TN was related to the proportion of NH+ 4-N in TN. The pretreatment of black odorous water by aeration could transform part of NH+ 4-N into NO- 3-N, and reduce the negative effect of cation exchange effect on nitrogen interception. The TN interception rate increased from 54.3% to 66.1%.
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Electrolytic metal manganese residue leachate (EMMRL) was produced from long-term deposition of electrolytic metal manganese residue. EMMRL contains huge amount of manganese and ammonia nitrogen which could seriously damage the ecological environment. In this study, a chemical equilibrium model-Visual MINTEQ was used to simultaneously optimize removal of manganese and ammonia nitrogen from EMMRL with chemical precipitation methods. In the laboratory experiment, the effect of different N: P ratios and pH were investigated, and the characterization of the precipitates was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM). The results showed that over 99.9% manganese and 96.2% ammonia nitrogen were simultaneously removed, respectively, when molar ratio of N:P was 1:1.15 at pH 9.5. Moreover, the experimental results corresponded well with the model outputs with respect to ammonia nitrogen and manganese removal. Manganese was mainly removed in the form of MnHPO4·3H2O and manganite, and ammonia nitrogen was mainly removed in the form of struvite. Economic evaluation indicated the chemical precipitation methods can be applied in the factory when the price of precipitation was higher than 0.295 $/kg.
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Struvite crystallization is an interesting method for the recovery of phosphorus (P) from wastewater. However, the struvite crystals obtained are small, which makes them difficult to separate from wastewater. A continuous reactor for enlarging struvite crystals was developed. Batch-scale experiments were conducted to investigate the optimum factors for the enlargement of struvite crystals. The results of pH experiments showed that P recovery efficiency increased with an increase of pH values (7.6 to 10), while the size of struvite crystals decreased. The results of the Mg:P ratios found that the maximum P recovery efficiency occurred at the maximum ratio of Mg:P. The sizes of struvite crystals were not significantly different. For the variation of temperature values, the results showed that P recovery efficiency and crystal sizes decreased when temperature values increased. Therefore, the optimized conditions for P recovery efficiency and enlargement of struvite crystals for the continuous reactor were pH 8.5 and an Mg:P ratio of 1.2:1 at 30 °C (room temperature). The treated swine wastewater and seawater were continuously fed in at the bottom of the reactor. After 30 days, the size of struvite crystals had increased from 125 μm to 0.83 mm (seven times).
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Investigations of the microbial community structures, potential functions and polycyclic aromatic hydrocarbon (PAH) degradation-related genes in PAH-polluted soils are useful for risk assessments, microbial monitoring, and the potential bioremediation of soils polluted by PAHs. In this study, five soil sampling sites were selected at a petrochemical landfill in Beijing, China, to analyze the contamination characteristics of PAHs and their impact on microorganisms. The concentrations of 16 PAHs were detected by gas chromatography-mass spectrometry. The total concentrations of the PAHs ranged from ND to 3166.52 μg/kg, while phenanthrene, pyrene, fluoranthene and benzo[ghi]perylene were the main components in the soil samples. According to the specific PAH ratios, the PAHs mostly originated from petroleum wastes in the landfill. The levels of the total toxic benzo[a]pyrene equivalent (1.63–107.73 μg/kg) suggested that PAHs might result in adverse effects on soil ecosystems. The metagenomic analysis showed that the most abundant phyla in the soils were Proteobacteria and Actinobacteria, and Solirubrobacter was the most important genus. At the genus level, Bradyrhizobium, Mycobacterium and Anaeromyxobacter significantly increased under PAH stress. Based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) annotations, the most abundant category of functions that are involved in adapting to contaminant pressures was identified. Ten PAH degradation-related genes were significantly influenced by PAH pressure and showed correlations with PAH concentrations. All of the results suggested that the PAHs from the petrochemical landfill could be harmful to soil environments and impact the soil microbial community structures, while microorganisms would change their physiological functions to resist pollutant stress.
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Struvite crystallization has been so far proved to be a potential technology for nitrogen and phosphorus recovery from nutrient-rich wastewater. However, humic acid (HA) among organic matters in nutrient-rich wastewaters would inevitably exert an adverse impact on the crystallization. Therefore, in the present study, we innovatively propose a process monitor chart to accurately differentiate and quantify the nucleation and crystal growth of struvite crystallization by means of constant composition technique, thereby probing the effect of HA on the nucleation and growth kinetics of struvite. Moreover, the mechanism underlying the interaction between HA and struvite crystals was also explored by FTIR and XPS analysis. The results indicated that HA not only significantly prolonged the induction time, but also decreased the growth rate of struvite crystals. This can be explained by the fact that HA is prone to complex with the reactant, and its subsequent adsorption on the surface of struvite crystals performs during the crystallization process. Consequently, the crystal morphology initially varied from rod-like shape to trapezoidal prism, and ultimately to triangular prism, as HA concentration gradually increased from 0 to 100 mg/L. Interestingly, the interaction between HA and struvite crystals is likely to be triggered by the formation of amide, HA-Mg²⁺ complex and phosphate ester on the crystal surface. These findings herein put forward an innovate method to elucidate the inhibitory effect of organic matter on the nucleation and growth kinetics of struvite, which can provide a theoretical basis for understanding the interference of organic pollutants with struvite crystallization.
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Unconventional oil and gas industries generate huge amounts of produced water (PW) containing high concentrations of potentially hazardous organic and inorganic contaminants. This study demonstrated the feasibility of simultaneously recovering NH4⁺, K⁺ and Mg²⁺ from PW by struvite precipitation after calcium pretreatment with Na2CO3 addition or CO2 stripping. Without pretreatment, calcium exhibited strong competition for phosphate through the formation of Ca3(PO4)2 precipitate. The pretreatment with a Ca²⁺:CO3²⁻ molar ratio of 1:1.2 achieved a relatively low loss rate of Mg²⁺ (31.3%) and high Ca²⁺ removal efficiency (95.9%). The results also revealed that the Mg/N/P molar ratio and solution pH had a remarkable effect on the struvite precipitation, while the seeding dosage and Na⁺ slightly influenced struvite formation. The combination of pH = 9.5 & Mg/N/P molar ratio = 1.5:1:1.5 was ideal for struvite recovery from PW, resulting in NH4⁺, K⁺ and Mg²⁺ recovery efficiencies of 85.9%, 24.8% and 96.8%, respectively. The results of X-ray diffraction and scanning electron microscopy further confirmed that the precipitates generated at this optimal condition were orthorhombic struvite. Moreover, along with the struvite recovery, no accumulation of heavy metals and organic contaminants was observed, indicating that the struvite quality was sufficient for field application. Furthermore, struvite recovery process was able to reduce the Microtox toxicity of PW towards Vibrio fischeri by 60%. Considering the low cost and relatively simple technology, struvite precipitation process has the potential to be used for large-scale applications for produced water treatment and resource recovery.
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Anthropogenic contamination, including the adaptation of sophisticated agricultural methodologies, has rendered a steep decline in the water and soil quality across the globe. This, in turn, has adversely affected the crop productivity. Hence, to utilize water from a source, a review assessment regarding the water suitability is essential. The present study proposes a new irrigation-based water quality index (IWQI), integrating statistics; hierarchical cluster analysis (HCA) and principal component analysis (PCA), to specific water use. Twenty-three sampling locations were chosen for analyses of 13 water quality parameters from October 2017 to February 2019 from Deepor Beel, Assam, to determine the efficacy of the proposed water quality index. HCA divided the 23 locations into 3 clusters, after which, PCA for each independent cluster provided component scores. These component scores were then used to estimate weights for each parameter for all the 23 locations. The IWQI categorized all the sampling locations as “Very Good”, thereby rendering them fit for irrigation. This was validated through the use of various irrigation parameters, such as sodium adsorption ratio (SAR), Kelly’s ratio (KR), soluble sodium percentage (SSP), residual sodium carbonate (RSC), permeability index (PI), and magnesium adsorption ratio (MgR). USSL and Wilcox plots were also considered for the correlation. IWQI was observed to provide an excellent association with all the parameters. Thus, the study would prove fruitful in establishing long-term and extensive management plans to the conservation of natural water resources.
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Forward osmosis (FO) is considered as an energy-efficient process for numerous applications. Although its performance is determined by the spatially varied operation factors and the length of the channel, most of the reported simulation studies rely on length-averaged lumped models. Here, we introduce a one-D model based on heat and mass transfer and transport behavior for both bulk draw and feed channel flows. We find prediction results to be in good agreement with two different experimental results at inlet feed temperatures below 25 °C. However, the difference of water flux (Jw) and reverse salt flux (RSF) between measured and predicted data increases when both feed and draw temperatures also increase. Our theoretical simulation study first reveals that the feed temperature near the membrane active layer surface is the main factor for improving water and salt permeabilities. We find that, with a channel width of 0.3 m and a channel length of 2.5 m, Jw and RSF calculated using the length-averaged based lumped model are overestimated by 13.01% and 13.12%, respectively, compared to those obtained using our new spatial variation model. Our study demonstrates that the length-averaged based lumped model is not an appropriate simulation model to predict the performance of large-scale FO modules at lower inlet velocities.
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Nowadays, sanitary landfilling is the most common approach to eliminate municipal solid waste, but a major drawback is the generation of heavily polluted leachates. These leachates must be appropriately treated before being discharged into the environment. Generally, the leachate characteristics such as COD, BOD/COD ratio, and landfill age are necessary determinants for selection of suitable treatment technologies. Rapid, sensitive and cost-effective bioassays are required to evaluate the toxicity of leachate before and after the treatment. This review summarizes extensive studies on leachate treatment methods and leachate toxicity assessment. It is found that individual biological or physical-chemical treatment is unable to meet strict effluent guidelines, whereas a combination of biological and physical-chemical treatments can achieve satisfactory removal efficiencies of both COD and ammonia nitrogen. In order to assess the toxic effects of leachate on different trophic organisms, we need to develop an appropriate matrix of bioassays based on their sensitivity to various toxicants and a multispecies approach using organisms representing different trophic levels. In this regard, a reduction in toxicity of the treated leachate will contribute to assessing the effectiveness of a specific remediation strategy.
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The removal of nitrogen and phosphorus from wastewater developed with established struvite (magnesium ammonium phosphate; MAP) production technology is the best alternative to newly produced or freshly degraded phosphate fertilizers. However, the production of struvite from domestic wastewater is not used extensively as initially expected in India because of the poor quality of production technology, competitive prices, and consumer acceptance as a fertilizer. Against this background, the present study aims to expand struvite production from phosphorus-rich wastewater, and bittern waste materials as a secondary source of magnesium in an inverse fluidized bed reactor by investigating their hydrodynamics characteristics. The study examined the influence of hydrodynamic parameters such as minimum fluidization velocity, bed expansion and pressure drop with polypropylene beads of different density under an optimized Mg/P ratio of 1.0. The O-phosphate recovery efficiency of over 95% was achieved by reaching the minimum fluidization velocity at a bed height of 45 cm, with a polypropylene bead with a diameter of 5 mm and a density of 836 kg/m3. The yield of struvite in a day for ten cycles for 30 days was estimated to be about 30–35 kg with 92% phase purity (XRD pattern of crystal). The cost economics suggested that the full-scale IFBR operation for struvite crystallization would be helpful for the community wastewater treatment plant.
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Forward osmosis (FO) has shown advancement towards recovery of useful water from various waste streams. A major issue that arises is the accumulation of salts due to reverse solute flux (RSF) from a draw solution into a feed solution that can result in several negative effects such as decreased water flux and inhibiting biological activities. This paper aims to provide a concise discussion and analysis of methods that can help to alleviate the effects of solute build up. New parameters, solute removal/recovery rate (SRR) and removal/recovery ratio (ReR), are proposed to help better define the performance of reducing solute buildup and employed in case studies to evaluate the selected reduction methods. Solute removal can be accomplished by physical separation, chemical precipitation, and biological removal. Recovery of solutes, one step beyond removal, is discussed and demonstrated by using bioelectrochemical systems and electrodialysis as examples. This work has highlighted the concerns associated with solute buildup and encouraged further exploration of effective tools to mitigate solute buildup for improved performance of FO-based water/wastewater systems.
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A graphene oxide membrane (GOM) has the potential to be used in forward osmosis (FO) because it has a high water permeability and low reverse salt flux. To explore suitable applications, we initiated the investigation of the forward solute transport through a freestanding GOM in FO. Both uncharged solutes (PEG 200 and PEG 1000) and charged solutes (NaCl, MgSO4, and MgCl2) were investigated, and the forward solute flux in FO was tested. The Donnan steric pore model (DSPM) was utilized to calculate the forward solute flux of the freestanding GOM in FO when discussing diffusion, convection, and electromigration. Our results showed that the freestanding GOM has a better separation performance for multivalent ions than the monovalent ions in the FO mode. We found an information gap between the calculated and experimental forward solute flux values, especially when charged solutes were used in the feed solution and the electrical double layer (EDL) was thick. We propose that the EDL inside the GOM has a screening effect on the forward ion transport during FO, even in the presence of relatively high water flux. According to our analysis, the forward solute transport for charged solutes is governed by steric exclusion and interfacial Donnan exclusion as well as EDL screening along the nanochannels inside the membrane. Our study provides guidance for the future use of the freestanding GOM during FO for water and wastewater treatment.
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Forward osmosis (FO)-membrane distillation (MD) process was integrated with anaerobic fluidized bed bioreactor (AFBR) to advance wastewater treatment. Low removal efficiency of nutrients such as ammonia nitrogen was improved significantly by combining FO-MD process with AFBR. The MD membrane was applied to concentrate the draw solution (DS) which can be diluted by FO filtration. By using 1 M of NaCl as DS, about 80% of ammonia nitrogen was further removed by the FO membrane while the phosphorous was removed almost completely (99%). However, the accumulation of ammonia nitrogen in DS and the reverse salt flux through the FO membrane was unavoidable. Nevertheless, combining MD membrane produced excellent removal efficiency yielding only 4 and 5.6 mg/L of ammonia nitrogen and chemical oxygen demand (COD) in MD permeate, respectively at 15 ℃ of transmembrane temperature. Alternatively, there is the possibility that the FO-MD process can be superior to concentrate resources such as nitrogen and phosphorous present in AFBR. The reverse salt flux from DS into AFBR bulk suspension did not show adverse effects on the performances of bioreactor with respect to COD removal efficiency, conductivity and methane production during operational period. Deposit of the fouling layer on FO membrane was also observed, but the fouling on MD membrane was not severe probably because crystallization rate could be retarded by diluting the DS during FO filtration.
Article
Hybrid osmotic membrane bioreactor (OMBR) takes advantage of the cooperation of varying biological or desalination processes and can achieve NEWS (nutrient-energy-water-solute) recovery from wastewater. However, a lack of universal parameters hinders our understanding. Herein, system configurations and new parameters are systematically investigated to help better evaluate recovery performance. High-quality water can be produced in reverse osmosis/membrane distillation-based OMBRs, but high operation cost limits their application. Although bioelectrochemical system (BES)/electrodialysis-based OMBRs can effectively achieve solute recovery, operation parameters should be optimized. Nutrients can be recovered from various wastewater by porous membrane-based OMBRs, but additional processes increase operation cost. Electricity recovery can be achieved in BES-based OMBRs, but energy balances are negative. Although anaerobic OMBRs are energy-efficient, salinity accumulation limits methane productions. Additional efforts must be made to alleviate membrane fouling, control salinity accumulation, optimize recovery efficiency, and reduce operation cost. This review will accelerate hybrid OMBR development for real-world applications.
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Socioeconomic development and new technological advancements have greatly increased the demand for metals, minerals and nutrients. Thus, substantial interest in developing technologies to recover these commodities from seawater, various brines and wastewater streams (industrial and domestic) has emerged. Less explored and innovative membrane processes including membrane crystallization (MCr), forward osmosis (FO) and membrane capacitive deionization (MCDI) are gaining interest in this regard. The current study provides a critical review of the current trends in applying MCr, FO and MCDI for recovery of metals, minerals and nutrients from various streams. The processes are compared in terms of types of fouling, energy consumption, overall composition of suitable feed solutions, feasible concentration ranges and potential to recover the targeted metal from a multi-component solution. The ultimate objective is to establish future research directions for further improvement of each process and to identify which of the processes is more suitable under a given scenario.
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Since the last decade, microbial-induced carbonate precipitation has been proposed as an environmentally friendly technique to improve the engineering properties of soil. Despite the considerable progress on ureolytic bio-cementation, one of the major concerns that has not been solved yet is related to the production of ammonium. This study aimed to manage ammonium ions to attain a sustainable pathway for bio-cementation treatment. To this end, a two-stage treatment including rinsing of ammonium from soil combined with a recovery of ammonium was considered herein for the first time. In the rinsing process, the followings were studied to optimize ammonium removal from soil: the effects of pH, concentration, and the single salts of the rinse solution. In the subsequent ammonium recovery process, the effects of phosphate source, pH, molar ratio, and Ca2+ ions were extensively investigated. The results revealed that at neutral pH conditions, ammonium removal was the lowest (68.82%). The MgCl2 solution was found to have the greatest ability to remove ammonium followed by CaCl2, NaCl, and distilled water (98.54%, 96.47%, 89.95%, and 74.77%, respectively). The ammonium recovery results showed that 86.8% of ammonium ions could be recovered as a high purity struvite (~ 94%), and that the optimum recovery was achieved at the following conditions: Na2HPO4 as a phosphate source, the Mg2+:NH+4:PO3−4 molar ratio of 1.2: 1: 1, and a pH of 8.5. Overall, it was demonstrated that the proposed method could be an effective way for sustainable ammonium by-products management.
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Reusing produced water (PW) as the subsequent hydraulic fracturing fluid is currently the most economical and dominant practice in the shale oil and gas industry. However, high Ca²⁺ present in PW needs to be removed prior to reuse to minimize the potential for well clogging and formation damage. In this study, the microbially induced calcite precipitation (MICP), as an emerging biomineralization technique mediated by ureolytic bacteria, was employed to remove Ca²⁺ and toxic contaminants from hypersaline PW for the first time. Batch and continuous studies demonstrated the feasibility of MICP for Ca²⁺ removal from hypersaline PW under low urea and nutrient conditions. Throughout the continuous biofiltration operation with biochar as the media, high removal efficiencies of Ca²⁺ (∼96%), organic contaminants (∼100%), and heavy metals (∼100% for As, Cd, Mn and Ni, 92.2% for Ba, 94.2% for Sr) were achieved when PW co-treated with synthetic domestic wastewater (SDW) under the condition of PW:SDW = 1:1 & urea 4 g/L. Metagenomic sequencing analysis showed that a stable ureolytic bacterial consortium (containing Sporosarcina and Arthrobacter at the genus level) was constructed in the continuous biofiltration system under hypersaline conditions, which may play a crucial role during the biomineralization process. Moreover, the combination of the MICP and ammonium recovery could significantly reduce the acute toxicity of PW towards Vibrio fischeri by 72%. This research provides a novel insight into the biomineralization of Ca²⁺ and heavy metals from hypersaline PW through the MICP technique. Considering the low cost and excellent treatment performance, the proposed process has the potential to be used for both hydraulic fracturing reuse and desalination pretreatment on a large scale.
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Little information is available regarding the kinetics, products, and pathways of simultaneous SMX degradation and Cd(II) immobilization from wastewater. In this study, a novel bacterium (Achromobacter sp. L3) with SMX degradation and Cd(II) immobilization capabilities was isolated. The boundary conditions of SMX degradation were as follows: initial pH 6–8, temperature 25–30 °C, and SMX concentration 10–40 mg/L⁻¹. The boundary conditions of Cd(II) immobilization were as follows: initial pH 7–9, temperature 25–35 °C, and SMX concentration 10–30 mg/L⁻¹. The maximum SMX degradation and Cd(II) removal were 91.98% and 100%, respectively. The SMX degradation and Cd(II) immobilization data fitted well with the pseudo-first-order kinetic model, indicating that the two pollutants conform to the same degradation rule. Moreover, the microbial degradation, sediment adsorption, and intermediates identified in the experiments were used to explore the mechanisms of SMX and Cd(II) removal. These results indicate that microbial removal and sediment adsorption play equally important roles in Cd(II) immobilization; however, microbial degradation plays a decisive role in SMX degradation. Furthermore, the relationship between aerobic denitrification, SMX degradation, and Cd(II) immobilization was proposed. These results may provide valuable insights for treatment of wastewater polluted by antibiotics and heavy metals.
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Struvite is a solid phosphorus fertilizer that can be recovered easily from source-separated urine by dosing it with a soluble form of magnesium. The process is simple and low-cost, however, previous studies have shown that the cost of magnesium in low-income countries is crucial to the viability and implementation of struvite precipitation. Literature has proposed producing inexpensive magnesium locally by making magnesium oxide from magnesite. This paper aimed to investigate whether process requirements, costs, and environmental impacts would make this process viable for magnesium production in decentralized settings. Magnesite samples were calcined at temperatures between 400°C and 800°C and for durations between 0.5h and 6h. The release of magnesium was tested by dissolution in phosphate-depleted urine. The optimal processing conditions were at 700°C for 1h: magnesite conversion was incomplete at lower temperatures, and the formation of large crystallites caused a decrease in solubility at higher temperatures. The narrow optimal range for magnesium production from magnesite requires reliable process control. Cost estimations for Nepal showed that using local magnesite would provide the cheapest source of magnesium and that CO2 emissions from transport and production would be negligible compared to Nepal's overall CO2 emissions.
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Ammonia and sulfate, which are prevalent pollutants in agricultural and industrial wastewaters, can cause serious inhibition in several biological treatment processes, such as anaerobic digestion. In this study, a novel bioelectrochemical approach termed bipolar bioelectrodialysis was developed to recover ammonia and sulfate from waste streams and thereby counteracting their toxicity during anaerobic digestion. Furthermore, hydrogen production and wastewater treatment were also accomplished. At an applied voltage of 1.2 V, nitrogen and sulfate fluxes of 5.1 g NH4(+)-N/m(2)/d and 18.9 g SO4(2-)/m(2)/d were obtained, resulting in a Coulombic and current efficiencies of 23.6% and 77.4%, respectively. Meanwhile, H2 production of 0.29 L/L/d was achieved. Gas recirculation at the cathode increased the nitrogen and sulfate fluxes by 2.3 times. The applied voltage, initial (NH4)2SO4 concentrations and coexistence of other ions were affecting the system performance. The energy balance revealed that net energy (≥16.8 kWh/kg-N recovered or ≥4.8 kWh/kg-H2SO4 recovered) was produced at all the applied voltages (0.8-1.4 V). Furthermore, the applicability of bipolar bioelectrodialysis was successfully demonstrated with cattle manure. The results provide new possibilities for development of cost-effective technologies, capable of waste resources recovery and renewable energy production. Copyright © 2015 Elsevier Ltd. All rights reserved.
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Pollution caused by landfill leachates is one of the main problems of urbanised areas, on account of their chemical composition, which turn in an ineffective treatment. A characterisation of leachates, which takes into account chemical, ecotoxicological and mycological aspects, is basilar for the evaluation of environmental impact of leachate and the development of suitable treatment techniques. In this study, the toxicity of a raw leachate and an effluent coming from traditional wastewater treatment plant was assessed by means of 4 ecotoxicological assays. Both the samples exceed the legal threshold value according to all the tested organisms, indicating the ineffectiveness of activated sludge treatment in the reduction of toxicity. The autochthonous mycoflora of the two samples was evaluated by filtration. The fungal load was 73CFU for leachate and 102CFU for the effluent. Ascomycetes were the dominant fraction (81% and 61%, for leachate and effluent respectively), followed by basidiomycetes (19% and 39%, respectively). Most of them were potential emerging pathogens. A decolourisation screening with autochthonous fungi was set up towards both samples in the presence or absence of glucose. Eleven fungi (basidiomycetes and ascomycetes) achieved up to 38% decolourisation yields, showing to be promising fungi for the bioremediation of leachates. Further experiment will be aimed to the study of decolourisation mechanism and toxicity reduction.
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Fulvic acid (FA) is known to be present at high concentration in leachates from “mature” and “old” landfills. In this work, the catalytic wet air oxidation (CWAO) of FA as a model of refractory organics of stabilized leachate was studied with activated carbon (AC) as catalyst and potassium persulfate (K2S2O8) as promoter. The effect of temperature and the amount of AC and K2S2O8 on the degradation of FA were investigated. Results revealed that FA could be efficiently degraded in the K2S2O8/AC system. At 150 °C and 0.5 MPa oxygen pressure, almost complete FA conversion and 77.8% COD removal were achieved after 4 h of treatment. The biodegradability of BOD5/COD ratio increased from 0.13 of raw FA solution to 0.95 after CWAO. AC exhibited good stability in the catalytic wet oxidation of FA. When AC was used for the fourth time, the FA conversion was still over 60%. Additionally, radical mechanism was studied and three radical scavengers (methanol, tert-butyl alcohol, sodium bromide) were used to determine the kind of major active species taking part in the degradation of FA. It was assumed that hydroxyl radical (OH) and sulfate radical (SO4-) played a major role in the FA degradation.
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Landfilling of municipal waste is still a major issue of the waste management system in Europe. The generated leachate must be appropriately treated before being discharged into the environment. Technologies meant for leachate treatment can be classified as follows (i) biological methods, (ii) chemical and physical methods. Here we review briefly the main processes currently used for the landfill leachates treatments.
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Water scarcity and pollution rank equal to climate change as the most urgent environmental issue for the 21st century. To date, the percolation landfill leachate into the groundwater tables and aquifer systems which poses a potential risk and potential hazards towards the public health and ecosystems, remains an aesthetic concern and consideration abroad the nations. Arising from the steep enrichment of globalization and metropolitan growth, numerous mitigating approaches and imperative technologies have currently drastically been addressed and confronted. Confirming the assertion, this paper presents a state of art review of leachate treatment technologies, its fundamental background studies, and environmental implications. Moreover, the key advance of activated carbons adsorption, its major challenges together with the future expectation are summarized and discussed. Conclusively, the expanding of activated carbons adsorption represents a potentially viable and powerful tool, leading to the superior improvement of environmental conservation.
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This paper reports results of laboratory studies on two pretreatment methods, struvite precipitation using aeration with H(3)PO(4) and Fenton oxidation. These methods utilized specific properties of the leachate: high magnesium content (172 mg L(-1)) for struvite precipitation and a high iron concentration (56 mg L(-1)) for Fenton treatment. Struvite precipitation (H(3)PO(4), 700 mg L(-1)) removed 36% of NH(3)-N and 24% of SCOD. Fenton treatment (at pH 3.5) required 650 mg L(-1) of H(2)O(2) and removed 66% of SCOD. The effect of each pretreatment on the returned activated sludge (RAS) was evaluated using respirometry. Both methods reduced the inhibitory effect of the leachate and substantially increased biokinetic parameters. The BOD(5)/SCOD ratio increased from 0.63 for raw leachate to 0.82 (struvite) and 0.88 (Fenton). Estimation of capital and operational costs of the total leachate treatment indicated that aeration with struvite precipitation, followed by biological treatment, would be the preferred option.
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Clogging of leachate collection systems within municipal solid waste landfills can result in greater potential for contaminants to breach the landfill barrier system. The primary cause of clogging is calcium carbonate (CaCO3(s)) precipitation from leachate and its accumulation within the pore space of the drainage medium. CaCO3(s) precipitation is caused by the anaerobic fermentation of volatile fatty acids (VFAs), which adds carbonate to and raises the pH of the leachate. An important relationship in modeling clogging in leachate collections systems is a yield coefficient that relates microbial fermentation of VFAs to precipitation of calcium carbonate. This paper develops a new, mechanistically based yield coefficient, called the carbonic acid yield coefficient (Y(H)), which relates the carbonic acid (H2CO3) produced from microbial fermentation of acetate, propionate, and butyrate to calcium precipitation. The empirical values of Y(H) were computed from the changes in acetate, propionate, butyrate, and calcium concentrations in leachate as it permeated through gravel-size material. The theoretical and empirical results show that the primary driver of CaCO3(s) precipitation is acetate fermentation. Additionally, other non-calcium cations (e.g., iron and magnesium) precipitated with carbonate (CO3(2-)) when present in the leachate. A common yield between total cations bound to CO3(2-) and H2CO3 produced, called the calcium carbonate yield coefficient (Yc), can reconcile the empirical yield coefficient for synthetic and actual leachates.
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In this work, a low-cost alternative approach (i.e., adding aged refuse (AR) into waste activated sludge) to significantly enhance anaerobic digestion of sludge was reported. Experimental results showed that with the addition dosage of AR increasing from 0 to 400 mg/g dry sludge soluble chemical oxygen demand (COD) increased from 1150 to 5240 mg/L at the digestion time of 5 d, while the maximal production of volatile fatty acids (VFA) increased from 82.6 to 183.9 mg COD/g volatile suspended solids. Although further increase of AR addition decreased the concentrations of both soluble COD and VFA, their contents in these systems with AR addition at any concentration investigated were still higher than those in the blank, which resulted in higher methane yields in these systems. Mechanism studies revealed that pertinent addition of AR promoted solubilization, hydrolysis, and acidogenesis processes and did not affect methanogenesis significantly. It was found that varieties of enzymes and anaerobes in AR were primary reason for the enhancement of anaerobic digestion. Humic substances in AR benefited hydrolysis and acidogenesis but inhibited methanogenesis. The effect of heavy metals in AR on sludge anaerobic digestion was dosage dependent. Sludge anaerobic digestion was enhanced by appropriate amounts of heavy metals but inhibited by excessive amounts of heavy metals. The relative abundances of microorganisms responsible for sludge hydrolysis and acidogenesis were also observed to be improved in the system with AR addition, which was consistent with the performance of anaerobic digestion.
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For the successful completion of a risk analysis process, its foundation (i.e. a baseline study) has to be well established. For this purpose, a baseline study needs to be more integrated than ever, particularly when environmental legislation is increasingly becoming stringent and integrated. This research investigates and concludes that no clear evidence of computer models for baseline study has been found in a whole-system and integrated format, which risk assessors could readily and effectively use to underpin risk analyses holistically and yet specifically for landfill leachate. This is established on the basis of investigation of software packages that are particularly closely related to landfills. Holistic baseline study is also defined along with its implications and in the context of risk assessment of landfill leachate. The study also indicates a number of factors and features that need to be added to baseline study in order to render it more integrated thereby enhancing risk analyses for landfill leachate.
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Recovery of nutrients, water, and energy from high-strength sidestream centrate offers benefits such as reusable resource, minimized discharge and cost-savings in mainstream treatment. Herein, a microbial electrolysis cell - forward osmosis (MEC-FO) hybrid system has been investigated for integrated nutrient-energy-water (NEW) recovery with emphasis on quantified mass balance and energy evaluation. In a closed-loop mode, the hybrid system achieved recovery of 54.2 ± 1.9% of water (70.4 ± 2.4 mL), 99.7 ± 13.0% of net ammonium nitrogen (8.99 ± 0.75 mmol, with extended N2 stripping), and 79.5 ± 0.5% of phosphorus (as struvite, 0.16 ± 0.01 mmol). Ammonium loss primarily from reverse solute flux was fully compensated by the reclaimed ammonium under 6-h extended N2 stripping to achieve self-sustained FO process. The generated hydrogen gas could potentially cover up to 28.7 ± 1.5% of total energy input, rendering a specific energy consumption rate of 1.73 ± 0.08 kWh m−3 treated centrate, 0.57 ± 0.04 kWh kg−1 COD, 1.10 ± 0.05 kWh kg−1 removed NH4+-N, 1.17 ± 0.06 kWh kg−1 recovered NH4+-N, or 5.75 ± 0.54 kWh kg−1 struvite. Recycling of excess Mg2+ reduced its dosage to 0.08 kg Mg2+/kg struvite. These results have demonstrated the successful synergy between MEC and FO to achieve multi-resource recovery, and encouraged further investigation to address the challenges such as enhanced hydrogen production, reducing nutrient loss, and optimizing MEC-FO coordination towards an energy-efficient NEW recovery process.
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Abstract Forward osmosis (FO) is an alternative approach for treating landfill leachate with potential advantages of reducing leachate volume and recovering high quality water for direct discharge or reuse. However, energy consumption by FO treatment of leachate has not been examined before. Herein, the operational factors such as recirculation rates and draw concentrations were studied for their effects on the quantified energy consumption by an FO system treating actual leachate collected from two different landfills. It was found that the energy consumption increased with a higher recirculation rate and decreased with a higher draw concentration, and higher water recovery tended to reduce energy consumption. The highest energy consumption was 0.276 ± 0.033 kW h m−3 with the recirculation rate of 110 mL min−1 and 1-M draw concentration, while the lowest of 0.005 ± 0.000 kW h m−3 was obtained with 30 mL min−1 recirculation and 3-M draw concentration. The leachate with lower concentrations of the contaminants had a much lower requirement for energy, benefited from its higher water recovery. Osmotic backwashing appeared to be more effective for removing foulants, but precise understanding of membrane fouling and its controlling methods will need a long-term study. The results of this work have implied that FO treatment of leachate could be energy efficient, especially with the use of a suitable draw solute that can be regenerated in an energy efficient way and/or through combination with other treatment technologies that can reduce contaminant concentrations before FO treatment, which warrants further investigation.
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Municipal solid wastes incineration (MSWI) flue gas was employed as the carbon source for in-situ calcium removal from MSWI leachate. Calcium removal efficiency was 95-97% with pH of 10.0-11.0 over 100 min of flue gas aeration, with both bound Ca and free Ca being removed effectively. The fluorescence intensity of tryptophan, protein-like and humic acid-like compounds increased after carbonation process. The decrease of bound Ca with the increase of precipitate indicated that calcium was mainly converted to calcium carbonate precipitate. It suggested that the interaction between dissolved organic matter and Ca²⁺ was weakened. Moreover, 10-16% of chemical oxygen demand removal and the decrease of ultraviolet absorption at 254 nm indicated that some organics, especially aromatic compound decreased via adsorption onto the surface of calcium carbonate. The results indicate that introduce of waste incineration flue gas could be a feasible way for calcium removal from leachate.
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Forward osmosis (FO) has been widely studied for desalination or water recovery from wastewater, and one of its key challenges for practical applications is reverse solute flux (RSF). RSF can cause loss of draw solutes, salinity build-up and undesired contamination at the feed side. In this study, in-situ electrolysis was employed to mitigate RSF in a three-chamber FO system (“e-FO”) with Na2SO4 as a draw solute and deionized (DI) water as a feed. Operation parameters including applied voltage, membrane orientation and initial draw concentrations were systematically investigated to optimize the e-FO performance and reduce RSF. Applying a voltage of 1.5 V achieved a RSF of 6.78 ± 0.55 mmol m−2 h−1 and a specific RSF of 0.138 ± 0.011 g L−1 in the FO mode and with 1 M Na2SO4 as the draw, rendering ∼57% reduction of solute leakage compared to the control without the applied voltage. The reduced RSF should be attributed to constrained ion migration induced by the coactions of electric dragging force (≥1.5 V) and high solute rejection of the FO membrane. Reducing the intensity of the solution recirculation from 60 to 10 mL min−1 significantly reduced specific energy consumption of the e-FO system from 0.693 ± 0.127 to 0.022 ± 0.004 kWh m−3 extracted water or from 1.103 ± 0.059 to 0.044 ± 0.002 kWh kg−1 reduced reversed solute. These results have demonstrated that the electrolysis-assisted RSF mitigation could be an energy-efficient method for controlling RSF towards sustainable FO applications.
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With the world’s increasing energy crisis, society is growingly considered that the operation of wastewater treatment plants (WWTPs) should be shifted in sustainable paradigms with low energy input, or energy-neutral, or even energy output. There is a lack of critical thinking on whether and how new paradigms can be implemented in WWTPs based on the conventional process. The denitrifying anaerobic methane oxidation (DAMO) process, which uses methane and nitrate (or nitrite) as electron donor and acceptor, respectively, has recently been discovered. Based on critical analyses of this process, DAMO-centered technologies can be considered as a solution for sustainable operation of WWTPs. In this review, a possible strategy with DAMO-centered technologies was outlined and illustrated how this applies for the existing WWTPs energy-saving and newly designed WWTPs energy-neutral (or even energy-producing) towards sustainable operations. Keyword: denitrifying anaerobic methane oxidation, wastewater treatment, denitrification, Candidatas ‘Methylomirabilis Oxyfera’, Candidatus ‘Methanoperedens nitroreducens’
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Synthetic landfill leachate was treated using lab-scale vertical flow constructed wetlands (CWs) in sequencing batch modes to assess heavy metal removal efficiencies. The CWs filled with loamy soil and pumice stone were unplanted or planted with common reed (Phragmites australis) (Reed-CW) or common rush (Juncus effusus) (Rush-CW). Synthetic leachate contained acetate, propionate, humate, ammonium, and heavy metals. Common reed grew almost vigorously but common rush partly withered during the 8-month experiment. The CWs reduced the leachate volume effectively by evapotranspiration and removed easily degradable organic matter, color, and ammonium. Furthermore, the CWs demonstrated high removal amounts for heavy metals such as Zn, Cr, Ni, Cd, Fe, and Pb, but not Mn from leachate. The metal removal amounts in the CWs were low for high-strength leachate (influent concentration increased from one time to three times) or under short retention time (batch cycle shortened from 3 days to 1 day). The Rush-CW showed slightly lower removal amounts for Cr, Ni, Mn, and Cd, although the Reed-CW showed lower Mn removal amounts than the unplanted CW did. However, Cd, Cr, Pb, Ni, and Zn were highly accumulated in the upper soil layer in the planted CW by rhizofiltration with adsorption compared with unplanted CW, indicating that the emergent plants would be helpful for decreasing the dredging soil depth for the final removal of heavy metals. Although the emergent plants were minor sinks in comparison with soil, common rush had higher bioconcentration factors and translocation factors for heavy metals than common reed had.
Article
Nickel (Ni(II)) is commonly present in municipal and industrial wastewaters, and thus its potential toxicity to activated sludge in wastewater treatment plants attracts increasing concerns. Although considerable efforts have been paid to this topic, the potential effect of Ni(II) on biological phosphorus removal has not been reported. In this work, short-term and long-term effects of Ni(II) in the range of 0.1–10 mg·L⁻¹ on enhanced biological phosphorus removal (EBPR) were therefore investigated. Compared with the control, short-term exposure to 1 and 10 mg·L⁻¹ of Ni(II) resulted in the decrease of phosphorus removal efficiency from 99.7% to 38.3% and 0, respectively. The phosphorus removal was unaffected after short-term exposure to 0.1 mg·L⁻¹ of Ni(II), but it was completely collapsed after 30-day exposure. The mechanism studies revealed that the cell membrane of microorganisms in activated sludge was not damaged, though the production of reactive oxygen species increased with the increase of Ni(II) exposure concentration. However, the presence of Ni(II) inhibited the anaerobic release of polyphosphate and the activity of exopolyphosphatase but enhanced the transformations of poly-3-hydroxyvalerate and glycogen. Microbial community investigation with high-throughput sequencing analysis showed that alphaproteobacterial glycogen accumulating organisms instead of polyphosphate accumulating organisms became the predominant microorganisms in EBPR systems after long-term exposure to Ni(II).
Article
For the successful completion of a risk analysis process, its foundation (i.e. a baseline study) has to be well established. For this purpose, a baseline study needs to be more integrated than ever, particularly when environmental legislation is increasingly becoming stringent and integrated. This research investigates and concludes that no clear evidence of computer models for baseline study has been found in a whole-system and integrated format, which risk assessors could readily and effectively use to underpin risk analyses holistically and yet specifically for landfill leachate. This is established on the basis of investigation of software packages that are particularly closely related to landfills. Holistic baseline study is also defined along with its implications and in the context of risk assessment of landfill leachate. The study also indicates a number of factors and features that need to be added to baseline study in order to render it more integrated thereby enhancing risk analyses for landfill leachate.
Article
Using liquid fertilizer as a draw solute in forward osmosis (FO) to extract high-quality water from wastewater is of strong interest because it eliminates the need for regenerating draw solute, thereby requiring less energy input to system operation. However, energy consumption of such an approach has not been evaluated before. Herein, a submerged FO system with all-purpose liquid fertilizer as a draw solute was studied for energy consumption of water recovery from either deionized (DI) water or domestic wastewater. The results showed that a higher draw concentration led to higher water flux and lower energy consumption, for example 0.25 ± 0.08 kWh m⁻³ with 100% draw concentration, but reverse salt flux (RSF) was also more serious. Decreasing the recirculation flow rate from 100 to 25 mL min⁻¹ had a minor effect on water flux, but significantly reduced energy consumption from 1.30 ± 0.28 to 0.09 ± 0.02 kWh m⁻³. When extracting water from the secondary effluent, the FO system exhibited comparable performance of water flux and energy consumption to that of the DI water. However, the primary effluent resulted in obvious fouling of the FO membrane and higher energy consumption than that of the secondary effluent/DI water. This study has provided important implications to proper evaluation of energy consumption by the FO system using liquid fertilizer or other non-regenerating draw solutes.
Article
Waste activated sludge (WAS) is difficult to be dewatered due to the highly water bounded in sludge flocs, and the extracellular polymeric substances (EPS) was the major factor affecting sludge dewatering performance. In this study, the hybrid process of electrolysis/electrocoagulation and zero-valent iron activated persulfate oxidation (EZP) showed a significant synergetic effect in enhancing municipal sludge dewaterability, and has the potential for enhancing industrial sludge dewaterability. The optimal dewatering conditions for municipal sludge were voltage 40 V and 4.15 g/L Na2S2O8 when zero-valent iron induced electrodes were applied. After EZP pretreatment, the municipal sludge specific resistance to filtration (SRF) and capillary suction time (CST) decreased by 87.4% and 49.1% respectively. The effects of EZP pretreatment on zeta potential, EPS property, viscosity and dewaterability of different sludge were analyzed to unravel the underlying mechanism of sludge conditioning. Results showed that the EZP oxidation was capable to effectively disrupt the EPS, crack the entrapped cells, and degrade the protein-like substances, reducing the viscosity and negative zeta potential, releasing bound water inside EPS and cells and thus improving sludge dewaterability. According to the analysis of Three-dimensional excitation emission matrix (3D-EEM), the EZP technology greatly decomposed tryptophan and aromatic protein-like substances in EPS. Scanning electron microscope (SEM) analysis further revealed that the disrupted EPS and cells were coagulated after EZP conditioning and reinforced sludge dewatering. The preliminary economic analysis showed that the optimized EZP was economically favorable.
Article
Using fertilizers as draw solutes in forward osmosis (FO) can accomplish wastewater reuse with elimination of recycling draw solute. In this study, three commercial fast-release all-purpose solid fertilizers (F1, F2 and F3) were examined as draw solutes in a submerged FO system for water extraction from either deionized (DI) water or the treated wastewater. Systematic optimizations were conducted to enhance water extraction performance, including operation modes, initial draw concentrations and in-situ chemical fouling control. In the mode of the active layer facing the feed (AL-F or FO), a maximum of 324 mL water was harvested using 1-M F1, which provided 41% of the water need for fertilizer dilution for irrigation. Among the three fertilizers, F1 containing a lower urea content was the most favored because of a higher water extraction and a lower reverse solute flux (RSF) of major nutrients. Using the treated wastewater as a feed solution resulted in a comparable water extraction performance (317 mL) to that of DI water in 72 h and a maximum water flux of 4.2 LMH. Phosphorus accumulation on the feed side was mainly due to the FO membrane solute rejection while total nitrogen and potassium accumulation was mainly due to RSF from the draw solute. Reducing recirculation intensity from 100 to 10 mL min−1 did not obviously decrease water flux but significantly reduced the energy consumption from 1.86 to 0.02 kWh m−3. These results have demonstrated the feasibility of using commercial solid fertilizers as draw solutes for extracting reusable water from wastewater, and challenges such as reverse solute flux will need to be further addressed.
Article
To address the issues of wastewater treatment and depleting phosphorus (P) resources, the present review focuses on the very wide interest in P recovery from wastewater, with scientific research underway in countries across the globe. The study describes the growing concern for diminishing P resources and then the chemical principle of magnesium ammonium phosphate (MAP) precipitation, factors influencing MAP crystallization, and various developments achieved through bench, pilot and full scale MAP reactors. A brief description is given of MAP purification and dissolution to economically exploit MAP as a phosphate and magnesium source. Experience in re-use of recovered MAP as a sustainable agriculture fertilizer is discussed including pot and field trials. © 2012 Society of Chemical Industry
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This paper presents a study concerning ammonia removal from landfill leachate by struvite precipitation with the use of waste phosphoric acid as the phosphate source. The results indicated that the Al3+ ions present in the waste phosphoric acid significantly affected the struvite precipitation, and a removal ratio of ammonia close to that of pure phosphate salts could be achieved. Nevertheless, large amounts of NaOH were necessary to neutralize the H+ present in the waste phosphoric acid. To overcome this problem, a low-cost magnesium source was proposed to be used as well as an alkali reagent in the struvite precipitation. The ammonia removal ratios were found to be 83%, with a remaining phosphate of 56 mg/L, by dosing the low-cost MgO in the Mg:N:P molar ratio of 3:1:1. An economic analysis showed that using waste phosphoric acid plus the low-cost MgO could save chemical costs by 68% compared with the use of pure chemicals. Post-treatment employment of a biological anaerobic filter process demonstrated that the high concentration of Mg2+ remaining in the effluent of the struvite precipitation has no inhibitory effect on the performance of the biological treatment.
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Research in the field of Forward Osmosis (FO) membrane technology has grown significantly over the last 10 years, but its application in the scope of wastewater treatment has been slower. Drinking water is becoming an increasingly marginal resource. Substituting drinking water for alternate water sources, specifically for use in industrial processes, may alleviate the global water stress. FO has the potential to sustainably treat wastewater sources and produce high quality water. FO relies on the osmotic pressure difference across the membrane to extract clean water from the feed, however the FO step is still mostly perceived as a "pre-treatment" process. To prompt FO-wastewater feasibility, the focus lies with new membrane developments, draw solutions to enhance wastewater treatment and energy recovery, and operating conditions. Optimisation of these parameters are essential to mitigate fouling, decrease concentration polarisation and increase FO performance; issues all closely related to one another. This review attempts to define the steps still required for FO to reach full-scale potential in wastewater treatment and water reclamation by discussing current novelties, bottlenecks and future perspectives of FO technology in the wastewater sector.