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Core-shell structured poly(vinyl alcohol)/sodium alginate bead for single-stage autotrophic nitrogen removal
Abstract
A core-shell structured poly(vinyl alcohol)/sodium alginate gel bead was fabricated and the thickness of the outer layer was controlled. Immobilized ammonia-oxidizing bacteria (AOB) and ANAMMOX bacteria in outer and inner parts of the beads, respectively, cooperate to perform single-stage autotrophic nitrogen removal (SANR). As a critical designing factor, oxygen penetration depth according to the oxygen concentration in bulk phase and nitrifying biomass concentration in the outer layer were examined to protect strictly anaerobic ANAMMOX bacteria from oxygen inhibition. Oxygen penetrated up to a depth of 2350 ± 360 μm with the lowest nitrifying biomass of 703 mg-VSS/L at a dissolved oxygen concentration of 8 mg/L. However, a thick shell layer of more than 3 mm effectively protected the ANAMMOX bacteria from oxygen inhibition. The applicability of the core-shell structured gel bead for single-stage autotrophic nitrogen removal was validated in batch and continuous modes. A continuous bioreactor with a synthetic ammonia wastewater showed a maximum nitrogen removal efficiency of 80.4 ± 1.20% with a total nitrogen loading rate of 590 ± 12.1 g-N/m³-d. Findings of this study suggest that start-up strategy of SANR using the core-shell structured gel bead can minimize the adaptation period without scarifying the ANAMMOX activity.
... Immobilization affords a high bacterial cell density in the reactor and easy solid-liquid separation in the settling tank. Furthermore, the gel support can improve the bacterial stability against substrate inhibition, as demonstrated in systems constituting anaerobic amSmonia-oxidizing (anammox) bacteria immobilized in polyvinyl alcohol (PVA) cryogel [4] and both AOB and anammox bacteria immobilized in the outer and inner parts, respectively, of the core-shell structured PVA/sodium alginate gel beads [5]. The immobilization techniques include adsorption, covalent attachment, cross linking, and in situ entrapment [6,7]. ...
... In the present study, the main focus is on the in situ entrapment of bacteria within a polymeric gel. In the prior studies reported in literature, nitrifying bacteria [5,[8][9][10] and anammox bacteria [4,5,[9][10][11] were entrapped in gels that were synthesized via free radical polymerization using reagents such as polyethylene glycol and 2,2-bis[4-(methacryloxy polyethoxy) phenyl] propane (BPE) monomer. In our previous study [12], novel millimeter-sized AOB-entrapping composite gel beads were developed using a method involving the preparation of calcium alginate microcapsules entrapping AOB via electrostatic atomization, followed by the free radical polymerization of the droplets of a pre-gel aqueous suspension containing microcapsules, BPE, and other reagents during their descent into silicone oil. ...
... In the present study, the main focus is on the in situ entrapment of bacteria within a polymeric gel. In the prior studies reported in literature, nitrifying bacteria [5,[8][9][10] and anammox bacteria [4,5,[9][10][11] were entrapped in gels that were synthesized via free radical polymerization using reagents such as polyethylene glycol and 2,2-bis[4-(methacryloxy polyethoxy) phenyl] propane (BPE) monomer. In our previous study [12], novel millimeter-sized AOB-entrapping composite gel beads were developed using a method involving the preparation of calcium alginate microcapsules entrapping AOB via electrostatic atomization, followed by the free radical polymerization of the droplets of a pre-gel aqueous suspension containing microcapsules, BPE, and other reagents during their descent into silicone oil. ...
Nitrifying biomass immobilized in a gel has been applied for wastewater treatment, as immobilization results in a high bacterial cell density in the reactor and facilitates easy solid–liquid separation in the settling tank. Herein, the diffusivity, reaction rate, and concentration profile of oxygen in a spherical gel entrapping ammonia-oxidizing bacteria (AOB) are investigated. Calcium alginate gel and 2,2-bis[4-(methacryloxy polyethoxy)phenyl] propane (BPE) gel are used as models to prepare millimeter-sized spherical gels. A novel method involving controlled oxygen transfer into/out of the spherical gel with alternative flow of air and N2 gas, measurement of oxygen concentration at the center of the spherical gel using an oxygen microsensor, and analysis using the Fickian diffusion equation is developed to determine oxygen diffusivity in the gel. Ammonia oxidation in the AOB-entrapping gel is also monitored by measuring the oxygen concentration at the center of the gel using an oxygen microsensor. The oxygen concentration profile in the gel is estimated based on the oxygen diffusivity and pseudo-first-order reaction rate constant determined for suspended AOB cells. The kinetic rate-determining step in the AOB-entrapping gel is identified using the effectiveness factor. The results would be useful for the development of aerobic bacteria-entrapping gels and the design of wastewater treatment processes using these gels.
... Therefore, the concentration of sodium alginate was 0.5% for followup study. Other studies report that dosage of sodium alginate in microbial beads immobilization were 0.8% [45], 0.9% [30] and 2% [44]. As shown in Table 5 and Figure 4, if the concentration of sodium alginate (w/v) is low, the immobilized particles are easy to form pellets. ...
... Therefore, the concentration of sodium alginate was 0.5% for follow-up study. Other studies report that dosage of sodium alginate in microbial beads immobilization were 0.8% [45], 0.9% [30] and 2% [44]. As shown in Table 5 and Figure 4, if the concentration of sodium alginate (w/v) is low, the immobilized particles are easy to form pellets. ...
... Therefore, the concentration of sodium alginate was 0.5% for followup study. Other studies report that dosage of sodium alginate in microbial beads immobilization were 0.8% [45], 0.9% [30] and 2% [44]. It can be seen from Table 6 and Figure 5 that the amount of microbial agent significantly affected the spherification of colloids. ...
In this study, immobilized microbial beads were proposed as a solution for excessive nitrogen concentration of the river sediment. The predominant denitrifying microbes were screened from the river sediment. The optimized production of immobilized microbial beads and long-term nitrogen removal efficiency were investigated. 16S rRNA gene sequencing analysis showed that denitrifying bacteria such as Pseudomonas, Alcaligenes, Proteiniclasticum, Achromobacter and Methylobacillus were dominant microflora in the enriched microbial agent, which accounted for 94.43% of the total microbes. Pseudomonas belongs to Gammaproteo bacteria, accounting for 49.22% and functioned as the most predominant denitrifying bacteria. The material concentration of 8% polyvinyl alcohol, 0.5% sodium alginate and 12.5% microbial biomass were found to be the optimal immobilizing conditions. The NH4+-N and total nitrogen (TN) removal rates in sediment with dosing immobilized microbial beads were estimated as 68.1% and 67.8%, respectively, when compared to the dosing liquid microbial agent were 50.5% and 49.3%. Meanwhile, the NH4+-N and TN removal rates in overlying water went up from 53.14% to 59.69% and from 68.03% to 78.13%, respectively, by using immobilized microbial beads.
... The different raw materials and preparation methods might also contribute Table 1 The common materials and cross-linking method. (Isaka et al., , 2013Kimura et al., 2010Kimura et al., , 2011Qiao et al., 2010;Furukawa et al., 2009;Isaka et al., 2008;Date et al., 2008) PVA (Sitthi et al., 2020;Wisniewska et al., 2021;Yang et al., 2019;Tuyen et al., 2018;Lu et al., 2018;Bae et al., 2017;Ali et al., 2014Zhu et al., 2014;Qiao et al., 2013;Quan et al., 2011;Zhu et al., 2009;Hsia et al., 2008;Wang et al., 2021) Crosslinking ...
... and nitrifying sludge in PVA gel carriers to operate a one-stage PN/A, with a final NRR-C of 0.032 kg-N m −3 -carrier d −1 to treat low-strength NH 4 + -N wastewater (NH 4 + -N ≤ 140 mg L −1 ) after 150 days operation. These studies showed that AOB tended to form a thick biofilm layer on the outer edge of the entrapment carriers after cultivation.Bae et al. (2017) minimized the one-stage PN/A adaptation period by using a synthesized core-shell structure of PVA-SA gel beads to entrap the AOB (outer layer) and AAOB (inner layer) in different spatial distributions, and achieved an NRR-C of 0.039 kg-N m −3 -carrier d −1 in 55 days. Yang et al. ...
Two biomass immobilization techniques; entrapment and carrier-based, attract increasing attention in anammox and partial nitrification/anammox (PN/A) systems. This paper provides a comprehensive review of the advances, outstanding issues, and future research directions in this field. The application of both entrapment and carrier-based biofilm immobilization for reactor start up, improving the nitrogen removal performance, and protecting autotrophic bacteria from environmental fluctuations in anammox and partial nitrification/anammox systems are summarized and discussed. The key characteristics of carriers for biomass immobilization are biocompatibility for supporting microbial growth, permeability for effective mass transfer, and physical/chemical stability for long-term use. Carriers without these characteristics must be improved and re-evaluated for their feasibility in applications. Lab-scale, pilot, and full-scale studies are needed to overcome the potential obstacles of preliminary studies, and to investigate the long-term performance of biomass immobilization techniques, especially using real wastewater as influent, which may introduce more complexity and threaten the carrier's immobilization. In addition, calculating the ‘nitrogen removal rate normalized by the packing ratio of carriers (NRR-C)’ in the immobilization system is strongly suggested to obtain a direct comparison of immobilization performance/limitations from different studies. This review will improve understanding of the major challenges of immobilization technology in anammox and PN/A systems and provide insights into the next-stage of research and full-scale applications.
... Thus, this method of cell immobilization appears extensible to most types of microorganisms and microbial communities 9,[12][13][14] . While polymers such as polyethylene glycol [15][16][17] or cellulose 18 have been investigated for immobilizing nitrifying microorganisms, polyvinyl alcohol is generally preferred [19][20][21][22][23][24] owing to its low toxicity, high porosity, high mechanical stability, low cost, and ease to use 25 . Poly(vinyl alcohol) (PVA) is often used in combination with sodium alginate (SA), together forming a robust gel (PVA-SA hydrogel) that resists shear forces that may occur in continuously mixed systems 26 such as wastewater treatment plants. ...
... So far, applications to wastewater treatment have focused on the immobilization of ammonia-oxidizing bacteria (AOB) from enrichments 21,23,27 or from nitrifying activated sludge, where AOB was paired with anaerobic ammonium oxidizing (Anammox) bacteria [28][29][30][31] for enhanced autotrophic nitrogen removal from warm and ammonia laden sidestream wastewater. Anammox technology can reduce energy requirements by half 32 but the consistent supply of nitrite to Anammox in the dilute mainstream remains a major bottleneck for wider applicability. ...
Ammonia-oxidizing archaea (AOA) are major players in the nitrogen cycle but their cultivation represents a major challenge due to their slow growth rate and limited tendency to form biofilms. In this study, AOA was embedded in small (~2.5 mm) and large (~4.7 mm) poly(vinyl alcohol) (PVA)—sodium alginate (SA) hydrogel beads cross-linked with four agents (calcium, barium, light, or sulfate) to compare the differences in activity, the diffusivity of nitrogen species (NH 4 ⁺ , NO 2 ⁻ , and NO 3 ⁻ ), and polymer leakage in batch systems over time. Sulfate-bound PVA-SA beads were the most stable, releasing the lowest amount of polymer without shrinking. Diffusion coefficients were found to be 2 to 3 times higher in hydrogels than in granules, with ammonium diffusivity being ca . 35% greater than nitrite and nitrate. Despite a longer lag phase in small beads, embedded AOA sustained a high per volume rate of ammonia oxidation compatible with applications in research and wastewater treatment.
... However, it has also been shown that encapsulation immobilization techniques lead to the degradation of performance under long-term reactor operation. Bae et al. showed that a large inactive dead space was formed in the dense gel that initially encapsulated the high concentration of inoculum, limiting the substrate transfer [123]. Synthetic polymer polyvinyl alcohol (PVA) has been used as a conventional encapsulation matrix to form PVA/sodium alginate (SA) gel beads [124]. ...
Anaerobic ammonia oxidation (anammox) process is known as a low-energy and environmentally friendly process for treating nitrogen-rich wastewater. Anammox bacteria are the key microorganisms to achieve this biological process. However, the efficient enrichment of anammox bacteria has been a bottleneck for its practical application because of their slow growth and high sensitivity, and no pure culture has been found. Therefore, the development of efficient anammox bacterial enrichment techniques is of great theoretical and application value. Solving the problem of anammox bacterial activity and improving the process denitrification performance is one of the current research hotspots. In this paper, three aspects of anammox bacteria are described in terms of their physiological properties, environmental influencing factors, and short-term starvation tolerance; a systematic review of the latest research progress in accelerating the activity of anammox bacteria using enrichment strategies for process regulation, the construction of granulation models, suspended sludge biomass management, and strain preservation. Finally, the future frontier development of anammox bacteria was discussed and foreseen.
... The immobilization of microorganisms in polymeric matrices, such as hydrogels, is a biotechnological strategy that, compared to suspended biomass systems, addresses technical and economic limitations [34], such as high energy consumption for aeration required for nitrification [35], management of excess biomass [36], and poorly separation of liquid and solid in the sedimentation tank [37]. In contrast, immobilization of microorganisms in hydrogels allows to separate biomass easily [38], provide protection to microorganisms against shear stress and toxic compounds in aqueous media [39], and reduce the cost of aeration while facilitate the mass transfer involved in the removal of conventional contaminants [40]. ...
PFAS have demonstrated to affect some aerobic microorganisms applied for wastewater treatment. This study evaluated the nutrient removal of three types of hydrogels containing a consortium of microalgae-bacteria (HB), activated carbon (HC), or both (HBC) in presence of perfluorodecanoic acid (PFDA). The nutrients evaluated were ammonium nitrogen (NH4–N), nitrate nitrogen (NO3–N), phosphate (PO4), and chemical oxygen demand (COD). Fluorine (F−) concentration and the integrity of HB exposed to PFDA were also determined at the end of experiments to understand the potential sorption and effects of PFDA on hydrogel. The results indicated that the presence of PFDA did affect the nitrification process, 13% and 36% to HB and HBC, respectively. Mass balance confirmed negative impact of PFDA on nitrogen consumption in HB (−31.37%). However, NH4–N was removed by all types of hydrogels in a range of 61–79%, while PO4 was mainly removed by hydrogels containing activated carbon (AC), 37.5% and 29.2% for HC and HBC, respectively. The removal of both NH4 and PO4, was mainly attributed to sorption processes in hydrogels, which was enhanced by the presence of AC. PFDA was also adsorbed in hydrogels, decreasing its concentration between 18% and 28% from wastewater, and up to 39% using HC. Regarding COD concentration, this increased overtime but was not related to hydrogel structure, since Transmission Electron Microscopy imaging revealed that their structure was preserved in presence of PFDA. COD increasement could be attributed to soluble algal products as well as to PVA leaching from hydrogels. In general, the presence of AC in hydrogels can contribute to mitigate the toxic effect of PFDA over microorganisms involved in biological nutrient removal, and hydrogels can be a technique to partially remove this contaminant from aqueous matrices.
... The DO penetration depth inside the PVA/alginate carrier was determined to be as low as 66.7 ± 28.9 μm. In addition, to improve the penetration depth to 966.7 μm, up to 8.0 mgO 2 /L DO is required in bulk liquid [34]. Such a high DO concentration range would not only consume excessive aeration energy, but would also be a difficult operating factor that is difficult to consider in the field. ...
The non-porous structure of the outer layer in the existing polyvinyl alcohol (PVA)/alginate carrier lowered the stability and efficiency of the partial nitritation/anammox (PN/A) process. In this study, these drawbacks could be improved with the addition of a foaming agent, and the effect was evaluated in a two-step PN/A process on a pilot scale. The penetration efficiency for dissolved oxygen was a parameter for determining the optimal content of the foaming agent, and it could be determined as 0.3% w/v. In the pilot PN, the DO diffusion inside the PVA/alginate carrier was effective for selective nitrite oxidizing bacteria (NOB) inhibition. As a result, ammonium oxidation efficiency of 49.3 ± 2.7% was achieved within 20 d of operation, resulting in a NO2⁻-N/NH4⁺-N ratio of 0.92 ± 0.1 in the effluent. In the pilot anammox, the contribution of endogenous denitrification to nitrogen removal (95.6 ± 2.9%) was a major factor inhibiting the physiological activity of anammox. The strategy of decreasing the hydraulic retention time worked effectively in alleviating the negative impact, which improved the contribution of anammox to nitrogen removal. In addition, this strategy was also worked effective in alleviating the effect of inhibitors on anammox activity under field conditions. With stabilization of nitrogen removal by anammox, exogenous denitrification even contributed to improving nitrogen removal efficiency, and a nitrogen removal rate of 1.1 ± 0.1 kg/m³/d was achieved at an influent nitrogen load of 1.4 ± 0.1 kg/m³/d.
... Microbial immobilization technology has excellent performance in increasing cell density and maintaining biomass activity, and at the same time strengthens the resistance of microorganisms to toxic substances or adverse environmental conditions [9,10], which is especially suitable for enrichment culture of slow-growing AnAOB. anammox immobilization technology has been extensively studied at home and abroad [9][10][11]. At present, polyvinyl alcohol-sodium alginate (PVA-SA) gel beads are generally used as immobilized carrier, but there are disadvantages such as difficulty in improving biological activity, insufficient mechanical strength and poor long-term operation stability [12,13]. ...
In view of the problems of slow start, easy loss and sensitive to low temperature environment in the suspension culture of anaerobic ammonia oxidation bacteria (AnAOB) suspension culture, polyvinyl alcohol (PVA) was used to prepare the anaerobic ammonia oxidation (anammox) immobilized filler, so as to realize the rapid start-up and activity improvement of anammox. Meanwhile, the response of nitrogen removal performance of encapsulated biomass to temperature reduction was determine by batch experiment. In addition, changes in the internal structure, flora composition and diversity of the filler were analyzed by scanning electron microscopy (SEM) and high-throughput sequencing. The results showed that the nitrogen removal capacity of the immobilized filler (E1) was significantly higher than that of the suspended sludge contrast system (S1) after 100d enrichment culture. The final nitrogen removal rate reached 1.168kg·(m3·d-1) -1, and the total nitrogen removal efficiency was 92%. The immobilization improved the resistance of AnAOB to low temperature. At 15°C, the effluent ammonia and nitrite of S1 were seriously accumulated, and E1 could maintain a stable nitrogen removal effect under the regulation of HRT. The population diversity was maintained in the immobilized filler, and the functional bacteria of anammox Candidatus Kuenenia was effectively enriched, accounting for 32.55% in E1. The results of this study provide valuable information for the application and popularization of anammox immobilized filler.
... The diffusion coefficient for NH + 4 , O 2 and NO − 2 at 25 • C is around 15-20 × 10 -6 cm 2 /sec [100]. Bae et al. [101] investigated the impact of the bulk liquid DO concentration and thickness of the outer nitrifying biomass layer over the DO penetration depth across the biofilm. They reported that at high DO concentration of 8 mg/L and nitrifying biomass layer thickness of 2.35 + 0.28 mm, the DO penetration depth was 1.85 ± 0.10 mm. ...
Nitrogen removal is an important aspect of wastewater treatment. Conventional biological nitrogen removal process is widely adopted for its reliable and effective nitrogen removal. However, its high operational and capital costs have led to the development of more cost-effective solutions. The discovery of anaerobic ammonium oxidation (ANAMMOX) bacteria and its integration with shortcut nitrogen removal processes has proved to be a sustainable solution. However, the requirement of carbon-free feed and discharge of high nitrate concentration in the effluent limit their practical applications. To overcome these challenges, an innovative nitrogen removal process, the simultaneous partial nitrification, anammox and denitrification (SNAD) process, has been studied. SNAD involves a synergistic relationship among ammonia oxidizing bacteria (AOB), ANAMMOX and denitrifers for high nitrogen removal efficiency. This study provides a focused review of the recent developments in SNAD process, specifically covering the critical process parameters for efficient operation and different reactor configurations. A detailed assessment of the process parameters such as carbon/nitrogen ratio, substrate type, free ammonia, free nitrous acid and hydraulic retention time is provided to identify the factors affecting the SNAD efficiency and required control measures. A comparison of different suspended and attached growth reactor configurations is also provided to understand the process reliability and potential for full-scale operation. This review will provide guidance for future engineering applications for high efficiency and cost-effective nitrogen removal via SNAD process.
... Taken together these simulations suggest that a greater surface area to volume ratio (s/v) would improve oxygen delivery to the encapsulated biomass, and as a result, ammonium oxidation rates. These simulations also provide support for the idea that the low DO zone within the beads could be used for the co-encapsulation of aerobic AOB (predicted to grow near the bead surface) and anaerobic bacteria such as denitrifiers or anammox bacteria (Bae et al., 2017). ...
Encapsulation is a promising technology to retain and protect autotrophs for biological nitrogen removal. One-dimensional biofilm models have been used to describe encapsulated systems; they do not, however, incorporate chemical sorption to the encapsulant nor do they adequately describe cell growth and distribution within the encapsulant. In this research we developed a new model to describe encapsulated growth and activity of Nitrosomonas europaea, incorporating ammonium sorption to the alginate encapsulant. Batch and continuous flow reactors were used to verify the simulation results. Quantitative PCR and cross-section fluorescence in situ hybridization were used to analyze the growth and spatial distribution of the encapsulated cells within alginate. Preferential growth of Nitrosomonas near the surface of the encapsulant was predicted by the model and confirmed by experiments. The modeling and experimental results also suggested that smaller encapsulants with a larger surface area to volume ratio would improve ammonia oxidation. Excessive aeration caused the breakage of the encapsulant, resulting in unpredicted microbial release and washout. Overall, our modeling approach is flexible and can be used to engineer and optimize encapsulated systems for enhanced biological nitrogen removal. Similar modeling approaches can be used to incorporate sorption of additional species within an encapsulant, additional nitrogen-converting microorganisms, and the use of other encapsulation materials.
... It was only speculated that low DO levels less than 2.0 6 mg/L result in insensitive variation of OPD, especially with the high initial concentration of 7 nitrifying activated sludge in the outer layer (2,441 ± 238 mg-VSS/L in this study). Likely, the 8 OPD range of 100~200 μm is frequently reported in various nitrifying and single-stage PN-9AMX processes at limited DO levels less than 2.0 mg/L[38,39].10 For DO levels of 8 and 6 mg/L, the OPD was significantly reduced from 966.7 ± 52.3 to 11 333.3 ± 36.4 and 510.4 ± 14.6 to 286.7 ± 37.1 μm, respectively, after the enrichment. ...
The single-stage configuration of the partial nitritation (PN)–anaerobic ammonium oxidation (AMX) process is preferred due to low pH fluctuation and the low concentration of inhibitory NO2-. The novel core-shell structure integrates ammonia-oxidizing reaction in the outer layer to protect AMX bacteria in the core gel bead from oxygen inhibition and provide NO2-. Here, the initial activity of ammonia-oxidizing bacteria (AOB) in the outer layer was assessed by the specific oxygen uptake rate (OUR). AOB activity was positively correlated with biomass loading in the outer layer. A maximum OUR of 10.5 mg-DO/L∙h was achieved with AOB loading of 0.23 mg-VSS per bead. During AOB enrichment, the NO2- production rate was linearly increased up to 0.65 kg-N/m3-d for 17 days (PVA hydrogel packing ratio=17%). The maximum oxygen penetration depth (OPD) was reduced from 966.7±52.3 μm before enrichment to 333.3±36.4 μm after the AOB enrichment. The liable bacteria were observed within a range of 165 μm of the outer layer using the live and dead cell staining. Based on the OPD and liable cell distribution results, a minimal outer layer thickness of approximately 350 μm was suggested to facilitate a successful PN–AMX process.
... Furthermore, it was also reported that the performance of reactors with entrapped biomass attenuated after long-term operation. In these compact gels, that initially entrapped high concentrated inoculum, it was found that a large inactive dead space was formed that limited mass transfer of substrates (Bae et al., 2017). ...
Granule-based immobilization of anammox biomass assisted by polyvinyl alcohol/chitosan (PVA/CS) and PVA/CS/Fe gel beads was studied, via the operation of three identical up-flow reactors (R1 without gel beads, R2 with PVA/CS, R3 with PVA/CS/Fe) for 203 days. In the end, the nitrogen removal rates (NRR) were 5.3 ± 0.4, 10.0 ± 0.3 and 13.9 ± 0.5 kg-N m⁻³ d⁻¹ for R1, R2 and R3, respectively. The porous PVA/CS and PVA/CS/Fe created a suitable eco-niche for anammox bacteria to grow and attach, thus being retained in the reactor. The EPS entangles newly grown cells within the gel beads, resulting in compact aggregation. The interaction between Fe ions added to PVA/CS/Fe gel beads and negatively charged EPS groups strongly promoted granule strength and compactness. The immobilization method proposed by this study was found to effectively improve biomass retention in the reactors, which is promising for advanced anammox process applications.
Sodium‐alginate‐based aerogels possess wide prospects in the fields of packaging, aerospace, industrial construction and transportation because of their environmental compatibility and thermal insulation, but it is still a challenge to obtain a sodium alginate‐based aerogel with high flame retardancy and good thermal insulation. Herein, a sodium‐alginate‐based aerogel with high flame retardancy, thermal insulation and good hydrophobic properties was prepared by two‐step crosslinking strategy of phytic acid and metal ions and liquid phase deposition of trans‐cinnamic acid. As a result, the prepared SA/PA Mn⁺ aerogels obtained excellent flame retardancy (UL‐94 V‐0, LOI 50.1%) and rapid self‐extinguishing, and SA/PA Mn⁺ aerogels obtained good hydrophobic ability (CA = 134.2°). In addition, the mechanical properties of SA/PA Mn⁺ aerogels have also been improved, the compressive modulus increased from 0.66 to 6.37 MPa, and the specific modulus increased from 15.7 to 140.2 MPa cm ⁻³ g⁻¹. This research broadens the application of bio‐based flame‐retardant aerogels in the fields of packaging, aerospace, industrial construction and transportation.
Polyethylene glycol beads encapsulating anaerobic microbes developed for on-site food and beverage wastewater treatment.
Hydrogels immobilizing nitrifying bacteria with different thicknesses of 0.55 and 1.13 cm (HG-0.55 and HG-1.13, respectively) were produced. It was recognized that the thickness of media is a crucial parameter that affects both the stability and efficiency of wastewater treatment. Batch mode experiments were conducted to quantify specific oxygen uptake rate (SOUR) values at various total ammonium nitrogen (TAN) concentrations and pH levels. In the batch test, HG-0.55 exhibited 2.4 times higher nitrifying activity than HG-1.13, with corresponding SOUR values of 0.00768 and 0.00317 mg-O2/L mL-PVA min, respectively. However, HG-0.55 was more susceptible to free ammonia (FA) toxicity than HG-1.13, resulting in a reduction of 80% and 50% in SOUR values for HG-0.55 and -1.13, respectively, upon increasing the FA concentration from 15.73 to 118.12 mg-FA/L. Continuous mode experiments were conducted to assess the partial nitritation (PN) efficiency in practical applications, where continuous wastewater inflow maintains low FA toxicity through high ammonia-oxidizing rates. With step-wise TAN concentration increases, HG-0.55 experienced a gentler increase in FA concentration compared to HG-1.13. At a nitrogen loading rate of 0.78–0.95 kg-N/m³ day, the FA increase rate for HG-0.55 was 0.0179 kg-FA/m³ day, while that of HG-1.13 was 0.0516 kg-FA/m³ day. In the batch mode, where wastewater is introduced all at once, the high accumulation of FA posed a disadvantage for the FA-susceptible HG-0.55, which made it unsuitable for application. However, in the continuous mode, the thinner HG-0.55, with its larger surface area and high ammonia oxidation activity, proved to be suitable and demonstrated its effectiveness. This study provides valuable insights and a framework for the utilization strategy of immobilized gels in addressing the toxic effects of FA in practical processes.
The novel partial denitrification-driven anammox (PD/A) is an energy-efficient method for nitrogen removal from wastewater. However, its stability and efficiency are impeded by the competition between heterotrophic denitrifying bacteria and relatively slow-growing anammox bacteria. In this study, a PD/A granular sludge system was developed, which achieved a nitrogen removal efficiency of 94% with 98% anammox contribution, even as the temperature dropped to 9.6 °C. Analysis of bacterial activity in aggregates of different sizes revealed that the largest granules (>2.0 mm) exhibited the highest anammox activity, 2.8 times that of flocs (<0.2 mm), while the flocs showed significantly higher nitrite production rates of PD, more than six times that of the largest granules. Interestingly, fluorescent in situ hybridization (FISH) combined with confocal laser scanning microscopy (CLSM) revealed a nest-shaped structure of PD/A granules. The Thauera genus, a key contributor to PD, was highly enriched at the outer edge, providing substrate nitrite for anammox bacteria inside the granules. As temperature decreased, the flocs transformed into small granules to efficiently retain anammox bacteria. This study provides multidimensional insights into the spatiotemporal assembly and immigration of heterotrophic and autotrophic bacteria for stable and high-rate nitrogen removal.
Hydrogels immobilizing nitrifying bacteria with different thicknesses of 0.55 and 1.13 cm (HG-0.55 and HG-1.13, respectively) were produced. It was recognized that the thickness of media is a crucial process parameter that affects both the stability and efficiency of wastewater treatment. Batch mode experiments were conducted to quantify specific oxygen uptake rate (SOUR) values at various total ammonium nitrogen (TAN) concentrations and pH levels. In the batch test, HG-0.55 exhibited 2.4 times higher nitrifying activity than HG-1.13, with corresponding SOUR values of 0.00768 and 0.00317 mg-O 2 /L·mL-PVA·min, respectively. However, HG-0.55 was more susceptible to free ammonia (FA) toxicity than HG-1.13, resulting in a reduction of 80% and 50% in SOUR values for HG-0.55 and − 1.13, respectively, upon increasing the FA concentration from 15.73 to 118.12 mg-FA/L. Continuous mode experiments were conducted to assess the partial nitritation (PN) strategy's efficiency in practical applications, where continuous wastewater inflow maintains low FA toxicity through high ammonia-oxidizing rates. With step-wise TAN concentration increases, HG-0.55 experienced a gentler increase in FA concentration compared to HG-1.13. At a nitrogen loading rate of 0.78–0.95 kg-N/m ³ ·day, the FA increase rate for HG-0.55 was 0.0179 kg-FA/m ³ ·day, while that of HG-1.13 was 0.0516 kg-FA/m ³ ·day. Despite its sensitivity to FA toxicity, the thinner HG-0.55 can enhance PN performance owing to its higher ammonia-oxidizing activity. FA susceptibility depends on hydrogel thickness in batch and continuous modes, with continuous mode favoring thin gel with high ammonia-oxidizing activity due to the decrease in FA accumulation.
An anaerobic ammonia oxidation (anammox) and denitrifying immobilized filler coupling reactor (RAD) was established to systematically evaluate its performance for enhancing nitrogen removal using endogenous soluble microbial products (SMPs) in the absence of exogenous COD, and was compared with the coupling mode with exogenous COD addition. The results showed that compared with independent anammox reactor (RA), the RAD can effectively use SMPs to reduce the NO3⁻–N yield and improve the total nitrogen removal efficiency. The NO3⁻–N yield of the RAD decreased over time during the cycle, decreasing by up to 70 % compared to the RA. 3D-excitation emission matrix showed that from the beginning to the end of the cycle, the SMP components changed from available tryptophan to difficult-to-use humic acids. In addition, the temperature and reaction cycle affected NOx⁻–N transformation, while low temperature and a long cycle were not conducive to the complete reduction of NO3⁻–N, leading to the accumulation of NO2⁻–N. In contrast, adding exogenous COD accelerated NO3⁻–N removal by the enhancing denitrification activity, but posed a potential threat to anammox activity. High-throughput sequencing analysis showed that Candidatus Kuenenia and Halomonas were the dominant species of the anammox and denitrifying immobilized fillers, respectively, which supported good coupling effect. These results provide valuable information for the optimization of anammox systems and the reduction of organic carbon consumption.
Media-supported biofilm is a powerful strategy for growth and enrichment of slow-growing microorganisms. In this study, a single-stage nitritation-anammox process treating low-strength wastewater was successfully started to investigate the biofilm development on porous polyurethane hydrogel carrier. Suspended biomass migration into the carrier and being entrapment by its internal interconnected micropores dominated the fast initial colonization stage. Both surface-attached growth and embedded growth of microbes occurred during the following accumulation stage. Fluorescence in situ hybridization analysis of mature biofilm indicated that ammonium-oxidizing bacteria located at the outer layers featured a surface-attached growth, while anammox microcolonies housed in the inner layers proliferated as an embedded-like growth. In this way, the growth rate of anammox bacteria (predominated by Candidatus Kuenenia) could be 0.079 d⁻¹. The anammox potential of the biofilm reactor reached 1.65±0.3 kg/m³/d within two months. This study provides novel insights into nitritation-anammox biofilm formation on the porous polyurethane hydrogel carrier.
Current gel entrapment technology has certain advantages for the enrichment of anammox sludge. In this study, the optimal preparation conditions and cultivation equipment of Ca-alginate cell beads for the culturing anammox sludge were proposed. The preparation parameters of the Ca-alginate cell beads were as follows: 3% sodium alginate, 4% CaCl2, VSA:Vcell = 1:1, a drop height of 9 cm, stirring speed of 300 rpm, and cross-linking time of 24 h. The prepared cell beads were regular spheres with a uniform size and hard texture. Throughout the 9 days of cultivation, the number of anammox bacteria in the Ca-alginate cell beads was 4.3 times that of the initial sludge, and the color of the cell beads changed from yellowish-brown to reddish-brown. Scanning electron microscopy (SEM) analysis showed that the SA gel beads had a good microporous structure. The fluorescence in situ hybridization (FISH) results illustrated that the bacteria were mostly dispersed inside the Ca-alginate cell beads. Additionally, the qPCR results implied that only a relatively small amount of anammox biomass (2.74×106 copies/gel-bead) was required to quickly start the anammox process. The anammox bacteria in the Ca-alginate cell beads grew with a fast growth rate in a short period and exhibited high activity due to diffusion limitations. In addition, the anammox bacteria cultivated in the Ca-alginate cell beads could adapt to the increase in substrate concentration in a short period. The optimal incubation time of this gel entrapment method for anammox sludge was no more than 17 days under the experimental conditions of this work. Therefore, this simple and practicable gel entrapment method may serve as a suitable pre-culture means for the rapid enrichment of anammox bacteria.
The anaerobic ammonium oxidation (ANAMMOX) process was proposed as the most promising nitrogen removal process. Biofilm carriers were demonstrated to effectively enhance the anaerobic ammonium oxidating bacteria (AnAOB) retention. This paper reviews the effect of carrier properties on the AnAOB biofilm development according to the biofilm development process and the application state-of-art of three major kinds of conventional carriers, organic-based, inorganic-based carriers, and gel carriers, from the view of system performance and functional microorganisms. The carrier modification methods and purpose are thoroughly summarized and classified into three categories corresponding to various carrier defects. Four important aspects of the desirable carrier for the mainstream ANAMMOX process were proposed, including providing spatial configuration, enhancing the biomass retention, reinforcing the activity, and improving the growth environment, which needs to combine the advantages of organic and inorganic materials. Eventually, the future application directions of novel carriers for the ANAMMOX-based process were also highlighted.
Enzyme immobilization technology has a key role in improving the stability of enzyme reaction systems and biocatalyst utilization rates. In this study, polyvinyl alcohol/sodium [email protected]3O4 (PVA/[email protected]3O4) magnetic immobilized-enzyme hydrogel beads were prepared. Their structure and morphology were characterized by scanning electron microscopy, surface area and porosity analyses, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and a vibrating sample magnetometer. The capability of PVA/[email protected]3O4 to adsorb neutral protease was investigated with variations in composition, temperature, pH, stirring speed, enzyme concentration, and crosslinking concentration. The optimal parameters of the immobilization process were determined by response surface methodology (3% neutral protease, 4% crosslinking at 200 rpm, 45 °C and pH 7.2), under which an immobilization rate of 41.98 mg/g was obtained. The thermal stability, acid-base stability, and reusability of the immobilized enzyme were improved significantly. After seven cycles, the immobilized enzyme activity remained at 30.8% that of the initial enzyme activity. The results indicate that the immobilization of NP onto magnetic PVA/[email protected]3O4 hydrogel beads improves enzyme efficiency, giving this process potential industrial applications.
The treatment performance of anaerobic ammonia oxidation (anammox) immobilized filler on different proportions of domestic wastewater was evaluated. The results showed that, in comparison to synthetic wastewater, 50% domestic wastewater promoted the anammox reaction of immobilized filler, while 100% domestic wastewater had no significant effect on the anammox activity of immobilized filler but the total nitrogen removal efficiency (TNRE) was improved through enhanced denitrification. The TNRE of the immobilized filler was 82.5%, which was significantly higher than that of AnGS (69.7%), and its average anammox contribution rate was more than 90%. This was because the encapsulated anammox biomass could better maintain competitive advantages and coordinate the symbiotic relationship with denitrifying bacteria. Moreover, lower NH4⁺-N concentration resulted in greater influence of C/N ratio on anammox performance than COD concentration, while the opposite was true at high NH4⁺-N concentration. This study verified that anammox immobilized filler is effective for mainstream applications.
This study examined the feasibility of using a three-layered polyvinyl alcohol (PVA) gel cube for low-strength ammonium wastewater (<50 mg-NH4⁺-N/L) treatment in a single reactor. The outer layer of this three-layered PVA gel cube was composed of immobilized nitrifying bacteria, while the inner layers were composed of anaerobic ammonium oxidation (anammox) bacteria. A single-stage autotrophic nitrogen removal (SANR) reactor containing these three-layered PVA gel cubes was operated at 35 °C for 197 days, with intermittent aeration. Although the activity of nitrite-oxidizing bacteria (NOB) was incompletely inhibited under a narrow range of dissolved oxygen (DO) concentrations (0.1–1.1 mg-O2/L), a nitrogen removal efficiency (NRE) of 71.9% was achieved at 35 °C. At this temperature, the high NRE was achieve due to the coexistence of anammox and denitrifying bacteria. After decreasing the temperature to 20 °C, the NRE was maintained at a similar level (69.8%) for 53 days. The change in the structure of the bacterial community was insignificant with decreasing temperature. The 16 S rRNA high-throughput sequencing analysis revealed that Planctomycetes (46.8–53.4%) was the most abundant phylum, wherein anammox bacteria accounted for 45.4–51.9% of the relative biodiversity abundance. Candidatus Jettenia asiatica disappeared for the operation of 187 days, while Candidatus Brocadia sinica was abundant. After 220 days, the relative abundances of ammonium-oxidizing bacteria (AOB) and NOB doubled and tripled, respectively. The abundant AOB were Nitrosomonas aestuarii and Nitrosomonas ureae, while the dominant NOB was Nitrospira moscoviensis. Nitrates produced by undesirable NOB activity were converted to nitrite by Denitratisoma oestradiolicum, which led to the abundance of anammox bacteria.
Novel sandwich-structured carriers were developed for fast immobilizing anammox sludge, with which a fixed-film membrane bioreactor was further established for treating municipal wastewater. Results showed that fast start-up of the fixed-film reactor with anammox bacteria could be achieved without lag phase, indicated by the respective nitrogen removal efficiency and rate of 70.58±0.66% and 0.12 g N/(L·d). Meanwhile, low membrane fouling 0.0017 bar/hour was also observed. The activity of anammox sludge fixed in the novel carriers gradually stabilized at the level of 6.59 mg N/(g VSS·h), while Candidatus Kuenenia as the dominant anammox bacteria were enriched from the initial abundance of 15.16% to 39.12% after a long-term operation. Consequently, it was demonstrated that the sandwich-structured carriers developed in this study could offer a promising alternative for fast immobilization and start-up of mainstream anammox process.
Although water is essential for global health and the socio-economic development of modern society, providing fresh water universally in a sustainable and affordable manner, for both developing and industrialized communities, is challenging. Polymeric hydrogels have recently drawn increasing interest as promising material platforms to sustainably enhance global water security. This review aims to provide a consolidated overview of polymeric hydrogels as an enabling agent in various water treatment technologies. First, a summary of the different approaches for the preparation of hydrogels with tailored chemistry, morphology, structure, and functions that enable the multifaceted requirements of different water technologies to be met is presented. Then, a set of properties unique to hydrogels, which gives them competitive advantages compared to other materials in the context of water treatment, is presented and discussed. This is followed by a comprehensive review of the applications of hydrogels in different water technologies. Their performance is correlated to their unique properties in order to gain an in-depth mechanistic understanding of how hydrogels can lead to impressive performance and technological innovation. The authors conclude with some proposed solutions and recommendations for prospective research directions to address the remaining challenges specific to each hydrogel-enabled water technology.
Advances in polymers have made significant contribution in diverse application oriented fields. Multidisciplinary applicability of polymers generates a range of strategies, which could pertinent in a wide range of fields. Blends of natural and synthetic polymers have spawned a different class of materials with synergistic effects. Specifically, poly (vinyl alcohol) (PVA) and alginate (AG) blends (PVAG) have demonstrated some promising results in almost every segment ranging from biomedical to industrial sector. Combination of PVAG with other materials, immobilization of specific moieties and physical and chemical crosslinking could result in amendments in the structure and properties of the PVAG matrices. Here, we provide an overview of the recent developments in designing PVAG based matrix and complexes with their structural and functional properties. The article also provides a comprehensive outline on the applicability of PVAG matrix in wastewater treatment, biomedical, photocatalysis, food packaging and fuel cells and sheds light on the challenges that needs to be addressed. Finally, the review elaborates the future prospective of PVAG blends in other unexplored fields like aircraft industry, nuclear science and space exploration.
Low carbon/nitrogen ratio (C/N) wastewater is widespread and difficult to treat. To find a resolution to this issue, this study systematically evaluated the constituents of composite solid carbon (i.e., skeletons, carbon sources and crosslinking agents), and proposed a new multi-carbon source composite S1 (MCSC.S1). The effects on nitrogen removal were further determined through a sequencing batch moving bed biofilm reactor (SBMBBR). The results showed that MCSC.S1, which was composed of polyvinyl alcohol-sodium alginate (PVA-SA), corncob + poly (R-β-hydroxybutyrate) (CC + PHB), and H3BO3-4% CaCl2+Na2SO4 had high stability and absorption. With MCSC.S1, total nitrification removal was enhanced by more than 48.56% through releasing carbon and absorbing the attached denitrifying bacteria. In addition, it was found that MCSC.S1 can simulate the simultaneous nitrification and denitrification (SND) process and contribute to 29.85% of the total nitrogen removal. 16S gene-based analysis attributed this supplementary nitrogen removal to the enrichment of nitrification (i.e., Proteobacteria, Actinobacteria and Chloroflexi), denitrification of associated bacteria (i.e., Nitrospirota) in MCSC.S1 added reactor, and the increase in nitrogen recycling associated genes. These findings collectively demonstrate that the new MCSC.S1 could effectively enhance nitrogen removal efficiency in low C/N ratio wastewater.
Anaerobic ammonium oxidation (ANAMMOX) represents an efficient, cost-effective, but sensitive nitrogen removal process for wastewater treatment. Different reactor configurations have been used in full-scale applications but each configuration has unique characteristics, which could influence process performance and community dynamics. The objective of this study is thus to analyze the impact of mixing conditions on nitrogen removal and community structures in a hybrid up-flow anaerobic sludge blanket reactor (H-UASB), moving bed biofilm reactor (MBBR) and gas-lift reactor (GLR). Community dynamics were studied through shotgun sequencing, while concentrations of NH4⁺, NO3⁻ and NO2⁻ were determined colorimetrically. During the study, MBBR displayed the highest average nitrogen removal efficiency (NRE) (67%) followed by H-UASB (63%), and then GLR (54%). The relative abundance of AMX in the suspended biomass was consistently higher in H-UASB than in MBBR and GLR, while that of nitrite-oxidizing bacteria (NOB) and complete ammonia-oxidizing bacteria (CMX) was higher in MBBR than in GLR and H-UASB. It was observed that the relative abundance of ammonia-oxidizing bacteria (AOB) in the suspended biomass fluctuated across the reactors. The relative abundance of CMX and Nitrospira in the biofilms in H-UASB and GLR was higher than in the suspended biomass, while comparable abundance was observed in MBBR. On the contrary, the relative abundance of AMX in the suspended biomass in H-UASB and MBBR was higher than in the biofilms, whereas it was comparable in the GLR. It was thus concluded that the mixing conditions in the three reactors influenced process performance and community dynamics.
A novel absorbent, PVA/SA-CFZ, was developed by jointly enveloping nanostructured hydrated ferric-zirconium binary oxide and clinoptilolite in the cross-linking of polyvinyl alcohol (PVA)/sodium alginate (SA). As a result, the cation exchange capacity of clinoptilolite and electrostatic attraction capacity of hydrated ferric-zirconium binary oxide can be integrated for the simultaneous removal of nitrogen and phosphorus from wastewater. The adsorption behavior of PVA/SA-CFZ for the co-existing ammonium and phosphate was primarily investigated by batch experiments. Over a wide pH range (4∼11), PVA/SA-CFZ always showed the excellent adsorption performance both for the low-concentration ammonium (<5 mg/L) and phosphate (<0.5 mg/L), which reflected the well adaptability towards unfavorable environmental conditions. The kinetic analysis indicated that the pseudo-second-order kinetic model could quantitatively describe the adsorption process optimally. The mechanistic investigation revealed that ammonium was captured through the cation exchange reaction with clinoptilolite. The electrostatic attraction, inner sphere complexation with Fe/Zr-O-OH groups, and formation of phosphate precipitation jointly contributed to the fixation of phosphate by PVA/SA-CFZ. Generally, it is believed that PVA/SA-CFZ can serve as a promising composite absorbent for the simultaneous deep removal of nitrogen and phosphorus, and support for the advanced treatment of wastewater containing low-level nutrients.
Encapsulating microorganisms is promising to enhance biological nitrogen removal (BNR) in wastewater, with benefits of increased efficiency, reduced inhibition, and improved stability. Encapsulation technology has advanced, with recent findings in...
The characteristics of anammox granular sludge (AnGS) based on color differentiation, and the regulation mechanism of immobilized fillers in the system were investigated. The results showed that biomass content, EPS and activity of red AnGS (R1) were higher than those of brown AnGS (R2). Moreover, R1 showed nitrification, while R2 showed denitrification. Filamentous bacteria constituted the granule skeleton of R1, while R2 mainly constituted inorganic nucleation and granulation. Additionally, immobilization improved the contribution rate of Anammox, and involved different regulatory mechanisms. High-throughput sequencing analysis showed that R1 encapsulation biomass eliminated miscellaneous bacteria and established specific flora, while mixed encapsulated biomass of R1 and R2 re-formed a functional bacterial network, which strengthened interspecies cooperation. The R2 encapsulated biomass and AnAOB copy numbers were inferior and the interspecific cooperation was weak, resulting in an unsatisfactory nitrogen removal performance. These results can strengthen the understanding and optimization of AnGS and its immobilization system.
This study investigated a combined partial nitritation and anammox process for treating low-strength ammonia synthetic wastewater (~50 mg-NH4⁺-N/L) at 20°C. The nitrifying bioreactor consisted of immobilized nitrifying bacteria in poly(vinyl alcohol) gel beads, which was operated under limited dissolved oxygen (DO) concentrations of 0.3–0.5 mg-O2/L to suppress nitrite-oxidizing bacteria (NOB) activity. The temperature in the nitrifying bioreactor decreased from 35 to 20°C, and the hydraulic retention time (HRT) was shortened from 6 h to 3 h. The limited DO concentration enabled partial oxidation of ammonia to nitrite (55.8%), but an undesired nitrite oxidation rate of 31.5% was observed at 20°C. The changes in bacterial community structure in response to the different operating conditions were observed by high-throughput 16 S rRNA gene sequencing analysis. The lowered temperature resulted in a significant shift in the bacterial community structure, while the effect of HRT was negligible. Nitrosomonas ureae and Nitrospira moscoviensis played critical roles in nitrification at low DO concentrations. Interestingly, a high nitrogen-removal efficiency of 71.4% was achieved in the integrated nitrifying bioreactor and anammox at 20°C despite incomplete NOB suppression in the nitrifying bioreactor. Denitratisoma oestradiolicum and Petrimonas sp., which are capable of nitrate reduction, were dominant in the anammox reactor, which might allow the provision of additional nitrite for the anammox reaction. The number of Candidatus Jettenia asiatica decreased in response to the lowered temperature, while the population of Candidatus Brocadia sinica increased.
ANAMMOX (anaerobic ammonium oxidation) represents an energy-efficient process for biological nitrogen removal, particularly from wastewater streams with low chemical oxygen demand (COD) to nitrogen (C/N) ratios. Its widespread application, however, is still hampered by a lack of access to biomass-enriched with ANAMMOX bacteria (AMX), slow growth rates of AMX, and their sensitivity to inhibition. Although the coupling of ANAMMOX processes with partial nitrification is already widespread, especially for sidestream treatment, maintaining a functional population density of AMX remains a challenge in these systems. Therefore, strategies that maximize retention of AMX-rich biomass are essential to promote process stability. This paper reviews existing methods of biomass retention in ANAMMOX-mediated systems, focusing on (i) granulation; (ii) biofilm formation on carrier materials; (iii) gel entrapment; and (iv) membrane technology in mainstream and sidestream systems. In addition, the microbial ecology of different ANAMMOX-mediated systems is reviewed.
This study investigated the ability of dual crosslinked interpenetrating polymer network (IPN) blend beads (DIN:SA/PVA-beads), composed of sodium alginate (SA) and poly (vinyl alcohol) (PVA), as a base-triggered carrier for the controlled release of dinotefuran (DIN) in Spodoptera litera midgut. The blend beads were characterized for morphology, encapsulation efficiency, swelling degree, and in vitro release of the blend beads were characterized. The results revealed that the double-crosslinked gel beads had a tightly interpenetrating network structure and exhibited a satisfactory embedding effect for DIN. The maximum of the DIN loading capacity was approximately 1.01%, with a high encapsulation efficiency of 83.19%. The triggered release of DIN from the blend beads was studied in deionized water (pH 3.0–11.0) via high-performance liquid chromatography (HPLC); it was found that the release rate was higher in alkaline pH conditions than in acidic and neutral conditions. An in vivo dynamics and degradation study also demonstrated that the excellent release characteristics of DIN:SA/PVA-beads in the midgut of S. litera. This study provides a promising controlled-release form of dinotefuran that is more effective and can be used for the targeted control of pests with alkaline midgut.
This study investigates the effect of physicochemical conditions on the partial nitritation and anammox treatment by immobilized ammonia oxidizers under ammonium-deplete conditions. The impact of oxygen and temperature was studied by measuring the activity of immobilized aerobic and anaerobic ammonia-oxidizing organisms (Ammonia-oxidizing bacteria (AOB) and archaea (AOA), and Anammox bacteria) embedded in polyvinyl alcohol – sodium alginate (PVA-SA) beads and in thin layer poly-ethylene glycol hydrogels. Beads and flat hydrogels were incubated in a fluidized bed reactor (FBR) and in two flow cells, respectively. Both systems were fed with synthetic wastewater (15 mg N–NH4⁺/L) at different temperatures (20 °C and/or 30 °C) and different dissolved oxygen (DO) concentrations (0.1, 0.3, 0.5 and/or 1 mg/L) over 152 and 207 days, respectively. The FBR system had a maximum removal rate of 1.7 g-N/m³/d at 0.1 mg O2/L, corresponding to 80% removal efficiency, while a high aerobic ammonia-oxidizing activity but a partial oxygen inhibition of Anammox bacteria were observed at higher DO concentrations. In both flow cells, nitrogen removal efficiency was highest (80%) at 30 °C and 1 mg O2/L while removal was less favorable at lower DO and lower temperature. Our results indicate a potential use of hydrogel beads for an energy efficient technology with reduced aeration demand for treating low ammonia wastewater, while layered hydrogels are a possible first step for biological treatments of wastewater using tangential flow. In addition, we provide blueprint drawings of the flow cells, which may be used to 3D-print the apparatus for other applications.
The main aim of this work was to test in-situ sediment remediation of a polluted river bed by the addition of biologically activated beads. The factors influencing the bioremediation performance were analyzed and compared in four experimental devices (D1: 230 g beads without microbes; D2: 230 g detached microbes (20%); D3: 230 g microbial beads; and D4: 230 g activated carbon and microbes). Device 3 (microbial beads) showed the best pollutant removal performance for NH4⁺-N: 76.3%, TN: 93.3% and COD: 92.8%, respectively, in the overlying water. The TOC, TN, heterotrophic and sulfide oxidizing bacteria removal rates reached were 61.9%, 58.0%, 45%, and 90%, respectively.
Granule-base immobilization of biomass is a potential method for a decent quality granular sludge cultivation. In this study, 3D polyvinyl alcohol (PVA) gel beads were chemically cross-linked via a simple NaOH-titration method. The PVA gel beads’ porous morphology was characterized using scanning electron microscope (SEM) and Brunauer–Emmette–Teller (BET), and their mechanical properties were evaluated by swelling rate and compressive stress tests. When cross-linking time was 10 min, high quality gel beads (P10) were synthesized, which demonstrated a homogeneous porous structure, good swelling rate, and high compressive strength. A mechanism for synthesis of the gel beads was proposed based on the results of Fourier transform infrared (FTIR) and X-ray diffractometer (XRD) analysis. Briefly, the intermolecular hydrogen bonds of PVA were firstly broken by NaOH to generate active bond of O–Na, which easily reacted with B(OH)4⁻ to produce the PVA-boric acid gel beads. P10 showed excellent biocompatibility for anaerobic ammonia oxidation (anammox) biomass’ immobilization. After incubation for three months, well granule-base immobilized sludge on P10 was developed in up-flow reactor. The sludge had high abundance of anammox biomass and was in balance with other functional bacteria. This work provides a simple method for the rapid preparation of 3D PVA gel beads and verifies their potential in granule-base immobilization of biomass.
To improve stability of nitrogen removal in partial nitritation (PN)-anammox process, flat-type cryogel films using poly (vinylalcohol) named as FT-CPVAF were applied in continuous reactors. Stable PN operation was maintained with short acclimation of 8 days and ammonium oxidation rate of 1.68 ± 0.12 kg N m-3 d-1 comparatively higher than previous studies. The nitrogen removal, initially inhibited by an oxygen shock, was immediately reactivated with short lag-period by immobilization of anammox bacteria in FT-CPVAF. A novel two-stage PN-anammox process was operated in a continuous flow using FT-CPVAF for treatment of ammonium-rich synthetic wastewater (influent 315 mg NH4+-N L-1) showing 89.6 ± 0.76% of nitrogen removal at short hydraulic retention time (7.7 h). The use of FT-CPVAF enhanced selective enrichment of AOB and anammox bacter ia confirmed by high-throughput sequencing of i.e., relative abundances of Nitrosomonas europaea C-31 (37.14% in PN reactor) and ‘Candidatus Jettenia caeni’ (34.36% in anammox reactor).
In order to reduce the loss of anaerobic ammonia oxidation (anammox) sludge and stabilize the reaction microenvironment, polyvinyl alcohol - polypropylene (PVA-PP) was used to encapsulate anammox bacteria on a filler. The influence of different inoculation amounts (2, 4, 6 and 8%) on the overall nitrogen removal process was first compared and then the anammox characteristics of the immobilized filler under the influence of different environmental factors were evaluated through batch experiments. The results show that the biomass only affected the growth rate of the activity during the logarithmic phase, while the total nitrogen removal rate (NRR) tended to be similar after 99 d of culture. The NRR reached 1.83 kg·(m3·d)-1 on day 140, which was 9.4 times that of suspended sludge before encapsulation, and the structure of embedding filler was complete without shedding. Scanning electron microscopy (SEM) showed that the internal porous network structure formed channels and a large number of anammox bacteria were observed around. Microbial community analysis of the 16S rDNA gene showed that the diversity was maintained in the entrapped carrier. Furthermore, the effective enrichment of the anammox functional bacteria Candidatus Kuenenia (AF375995.1) increarsed from 11.06% to 32.55%. The PVA-PP immobilized filler fit well with the biological nitrogen removal kinetic model and could also achieve coupling of anammox and denitrification. The inhibition effect of the organic carbon source interference and starvation on anammox bacteria was significantly weakened.
Diclofenac sodium (DS) is an emerging contaminant that is toxic and remains at high concentrations in natural aquatic environments. The aim of this study was to fabricate a novel spherical polymeric adsorbent composed of cross-linked chitosan beads grafted by polyethylenimine (PEI) to remove DS from water. The adsorbents were thoroughly characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, elemental analyses, and X-ray photoelectron spectroscopy. A cross-linking step was expected to enhance adsorption. The experimental data obtained from a series of adsorption experiments were fit well by the Langmuir isotherm model and pseudo-second-order model. The epichlorohydrin-PEI adsorbent (EPCS@PEI) showed a maximum adsorption capacity of 253.32 mg/g and removal efficiency of nearly 100% for the DS in the initial 50 mg/L solution. Therefore, EPCS@PEI is proposed as a potential adsorbent for DS removal, where these initial findings are expected to promote further design and fabrication of effective adsorbents for practical applications.
A porous solid carbon source was prepared by semen litchi (SL), poly(vinyl alcohol) (PVA) and sodium alginate (SA) in aqueous. The effect of SL content on structures and denitrification performance of the porous solid carbon source in simulated mariculture wastewater was investigated. The SL/PVA/SA beads showed a network structure with a wide range of macropores. Compared with blank beads, the SL/PVA/SA beads showed a increased rough surface and hole distribution on the surface with the increase of SL. In addition SL/PVA/SA beads has more uniform pore size, but the porosity of SL/PVA/SA beads was decreased with the increase of SL. The porosity of the beads was 83.24%, 74.24%, 71.48% and 71.29% for blank beads and SL/PVA/SA beads contained 30%, 40% and 50% SL. When it was used as a solid carbon source for denitrification. Owing to its good porosity and biocompatibility, SL/PVA/SA beads had shorter acclimation time. Nitrate removal rate could reach up to 100% after two days adaptation. After the exhaustion of carbon sources, nitrate removal rate less than 50% occurred at the 9th, 10th and 11th day for SL/PVA/SA beads contained 30%, 40% 50% SL respectively. The beads contained 50% SL exhibited longer lifetime during the denitrification reaction and denitrification rate could reach to 243.5 ± 7.08 mg N (L·d)⁻¹. It could be used as an economical and effective carbon source for denitrification in mariculture wastewater.
The research on biocompatible ionic liquids is triggering a great interest in cholinium-based solvents, due to their alleged biocompatibility and biodegradability. However, the screening for choline degraders among different microbial sources from extreme locations revealed the suitability of just one halophilic strain (Halomonas sp. LM1C) to efficiently remove high choline concentrations from aqueous streams. An entrapment-based microbial immobilization technique in hydrogel spheres (agar, alginate and alginate-polyvinyl) is evaluated in order to ease process scale up. The mass transfer resistance of the selected hydrogels during cholinium chloride (N1112OHCl) diffusion was evaluated by determining the external mass transfer (k) and diffusion coefficients (De). The results revealed the absence of significant diffusion problems for alginate and alginate-polyvinyl, while the agar-based matrix led to significant cell leakage. Given the superior mechanical performance of alginate-polyvinyl support, this was selected to implement the process at fixed-bed bench-scale bioreactor, leading to a complete contaminant remediation.
Poly (vinyl alcohol) (PVA)/alginate gel beads were fabricated to entrap ammonia-oxidizing bacteria. The PVA/alginate gel beads were prepared in different conditions to investigate the effects of the fabrication procedures on the mechanical strength and the initial ammonia-oxidizing activity. For the mechanical strength, the optimal conditions were analyzed using response surface analysis (RSA) considering the inter-correlated effects of the reaction times of cross-linking and phosphorylation. For RSA, nine trials resulted in a partial cubic polynomial equation, which best predicted the amount of residual debris after homogenization. In the model, the optimum conditions of 3.5 h of cross-linking and 5.6 h of phosphorylation were estimated to ensure the maximum mechanical strength. The initial ammonia-oxidizing activity was significantly affected by the cross-linking due to the highly acidic environment of pH 3.3, but it was not affected by the phosphorylation in pH 4.2. Batch experiments to measure the bioactivity showed that only 34.0% of the initial activity survived the fabrication procedure of the 4 h reaction in B(OH)3 in comparison to the 1 h reaction. The lower initial ammonia-oxidizing activity contributed to the delayed acclimation period to achieve ammonia removal of more than 1 kg N/m3 d, but the inhibitory effects were fully recovered in 5 d.
In this work, nitrification and changes in the composition of the total bacterial community under inorganic carbon (IC)-limited conditions, in a nitrifying moving bed biofilm reactor, was investigated. A culture-independent analysis of cloning and sequencing based on the 16S rRNA gene was applied to quantify the bacterial diversity and to determine bacterial taxonomic assignment. IC concentrations had significant effects on the stability of ammonia-oxidation as indicated by the reduction of the nitrogen conversion rate with high NH4+-N loadings. The predominance of Nitrosomonas europaea was maintained in spite of changes in the IC concentration. In contrast, heterotrophic bacterial species contributed to a high bacterial diversity, and to a dynamic shift in the bacterial community structure, under IC-limited conditions. In this study, individual functions of heterotrophic bacteria were estimated based on taxonomic information. Possible key roles of coexisting heterotrophic bacteria are the assimilation of organic compounds of extracellular polymeric substances produced by nitrifiers, and biofilm formation by providing a filamentous structure and aggregation properties.
Partial nitritation/anammox (PN/A) has been one of the most innovative developments in biological wastewater treatment in recent years. With its discovery in the 1990s a completely new way of ammonium removal from wastewater became available. Over the past decade many technologies have been developed and studied for their applicability to the PN/A concept and several have made it into full-scale. With the perspective of reaching 100 full-scale installations in operation worldwide by 2014 this work presents a summary of PN/A technologies that have been successfully developed, implemented and optimized for high-strength ammonium wastewaters with low C:N ratios and elevated temperatures. The data revealed that more than 50% of all PN/A installations are sequencing batch reactors, 88% of all plants being operated as single-stage systems, and 75% for sidestream treatment of municipal wastewater. Additionally an in-depth survey of 14 full-scale installations was conducted to evaluate practical experiences and report on operational control and troubleshooting. Incoming solids, aeration control and nitrate built up were revealed as the main operational difficulties. The information provided gives a unique/new perspective throughout all the major technologies and discusses the remaining obstacles.
Poly(vinyl alcohol) (PVA) has been utilized as a support material for the immobilization of nitrifying bacteria without the comprehensive survey of partial nitritation. In the present study, the activities of nitrifiers and the maximum nitrogen conversion rate of partial nitritation with PVA sponge-cubes were specified according to different conditions. The selective enrichment of ammonia-oxidizing bacteria (AOB) on PVA sponge-cubes was achieved by the competition between AOB and nitrite-oxidizing bacteria for dissolved oxygen. The efficiency of ammonia oxidation was proportional to the concentration of HCO3
− with the molar ratio of HCO3
−-C/NH4
+-N = 1.91 and a half of the ratio was applied to the further experiments to ensure stable partial nitritation. The maximum nitrogen conversion rate of partial nitritation was dependent on the volume, not the size of sponge-cubes. The partial nitritation showed the superior rate performance of 3.09 kg N/m3 day with the packing ratio of 32 % of 5 × 5 × 5 mm3 PVA sponge-cubes.
Currently available microbiological techniques are not designed to deal with very slowly growing microorganisms. The enrichment
and study of such organisms demands a novel experimental approach. In the present investigation, the sequencing batch reactor
(SBR) was applied and optimized for the enrichment and quantitative study of a very slowly growing microbial community which
oxidizes ammonium anaerobically. The SBR was shown to be a powerful experimental set-up with the following strong points:
(1) efficient biomass retention, (2) a homogeneous distribution of substrates, products and biomass aggregates over the reactor,
(3) reliable operation for more than 1 year, and (4) stable conditions under substrate-limiting conditions. Together, these
points made possible for the first time the determination of several important physiological parameters such as the biomass
yield (0.066 ± 0.01 C-mol/mol ammonium), the maximum specific ammonium consumption rate (45 ± 5 nmol/mg protein/min) and the
maximum specific growth rate (0.0027 · h−1, doubling time 11 days). In addition, the persisting stable and strongly selective conditions of the SBR led to a high degree
of enrichment (74% of the desired microorganism). This study has demonstrated that the SBR is a powerful tool compared to
other techniques used in the past. We suggest that the SBR could be used for the enrichment and quantitative study of a large
number of slowly growing microorganisms that are currently out of reach for microbiological research.
A dynamic model describing integrated nitrification and denitrification by Nitrosomonas europaea and Pseudomonas sp. co-immobilized in the separate layers of double-layer gel beads is presented. The model describes diffusion of components, substrate utilization, and growth, all occurring simultaneously in the beads. Both internal and external mass transfer resistance are accounted for. The model predicts biomass and solute bulk concentrations, substrate consumption rates, product formation rates, and biomass and solute concentration profiles within the beads as a function of time. Fluctuations in substrate load, dilution rates, or mass transfer parameters can be accommodated as well. Intrinsic kinetic parameters of the microorganisms, internal and external mass transfer coefficients, initial conditions, bead concentration, and particle diameters are the input parameters. The model was evaluated by comparing experimental and predicted bulk concentrations and macroscopic consumption (production) rates in air-lift loop reactors containing double-layer gel beads. The reactors were run under both steady and dynamic operating conditions. Nitrification rates were determined by daily analysis of influent and effluent ammonia and nitrite concentrations, and denitrification rates were calculated from molecular nitrogen production rates measured by head-space analysis. Model predictions agreed reasonably well with the experimental results. Fluctuations in dilution rates and influent substrate concentrations were adequately described. Although further validation is still required, the model presented here has shown to describe satisfactorily the proposed system.
The physiology of anaerobic ammonium oxidizing (anammox) aggregates grown in a sequencing batch reactor was investigated quantitatively. The physiological pH and temperature ranges were 6.7 to 8.3 and 20 to 43 degrees C, respectively. The affinity constants for the substrates ammonium and nitrite were each less than 0.1 mg of nitrogen per liter. The anammox process was completely inhibited by nitrite concentrations higher than 0.1 g of nitrogen per liter. Addition of trace amounts of either of the anammox intermediates (1. 4 mg of nitrogen per liter of hydrazine or 0.7 mg of nitrogen per liter of hydroxylamine) restored activity completely.
Forward osmosis (FO) and biological nitrification processes were integrated in this study. High strength ammonia wastewater of 2500 mg-N/L was partially nitrified at an ammonia conversion rate of 1.34 ± 0.25 kg-N/m3-day under the limitation of an acidification buffer, i.e., HCO3--C/NH4+-N = 1, as a control factor. Direct contact between the biomass and cellulose triacetate FO membrane was avoided by employing PVA/alginate-immobilized nitrifiers in the bioreactor. The simultaneous FO process concentrated the wastewater at concentration factors (CFs) of up to 2.34 during the partial nitritation (PN) reaction. As a result, the concentration of total dissolved solids (TDS) ranged from 13.6 g/L to 35.7 g/L. It was found that salinity higher than 17 g-TDS/L inhibited the activity of the nitrite-oxidizing bacteria, but not the ammonia-oxidizing bacteria. Scanning electron microscopy and fluorescence excitation–emission matrix and liquid chromatography-organic carbon detection analysis revealed the existence of hydrophilic organic fouling including biopolymers and low molecular weight neutrals on the surface of the FO active layer. However, the FO fouling was successfully controlled by air scouring for 15 min.
The performance of four identical sequencing biofilm batch reactors (SBBR) for autotrophic nitrogen removal was investigated with 2000 mg/L ammonia-containing mature landfill leachate at 30 °C. The main objective of this study was to evaluate the effects of dissolved oxygen (DO) on the performance and microbial community of single-stage nitrogen removal using anammox and partial nitritation (SNAP) system. At an applied load of 0.5 kg N m⁻³ d⁻¹, average total nitrogen removal efficiency (TNRE) above 90% was long-term achieved with an optimal DO concentration of 2.7 mg/L. The microelectrode-measured profiles showed the microenvironments inside the biofilms. 16S ribosomal Ribonucleic Acid (rRNA) amplicon pyrosequencing and denaturing gradient gel electrophoresis (DGGE) were used to analyze the microbial variations of different DO concentrations and different positions inside one reactor.
Polyvinyl alcohol (PVA) immobilized nitrifier was adopted to enhance the treatment of wastewater containing rich ammonia nitrogen (NH4-N) in constructed wetlands (CWs). NH4-N removal in immobilized nitrifier biofortified constructed wetlands (INB-CWs) was positively correlated with the dosage of PVA pellets. INB-CWs planted with Canna indica L. exhibited removal efficiencies of 46% NH4-N, 43% total nitrogen and 65% COD, which are significant higher than control. INB-CWs outperformed the unplanted and non-immobilized constructed wetland or nitrifier suspension system. The ideal reaction conditions for treating synthetic wastewater containing 200 mg L−1 NH4-N were obtained as follows: pH, 8.5; dissolved oxygen, 4.0 mg L−1; temperature, 30 °C and PVA pellets dosage, 60 g L−1. In addition, degradation of PVA pellets accelerated nitrification. Results indicated that the PVA immobilized nitrifier had great potential applications for treating wastewater containing rich ammonia nitrogen in CWs.
The inoculation of conventional activated sludge is a prospective option against transferring anaerobic ammonium oxidation (ANAMMOX) biomass from a currently existing ANAMMOX process in places where large amounts of ANAMMOX biomass are not available. In this study, poly(vinyl alcohol)/sodium alginate gel beads were utilized as an immobilization system to entrap activated sludge. Despite the longer start-up periods than those in previous examples using the ANAMMOX inoculum, the acclimation of ANAMMOX bacteria in the gel beads was successful. The maximum nitrogen removal rate of 1.12 kg N/m3-day was established at a nitrogen loading rate of 1.26 ± 0.04 kg N/m3-day with a total nitrogen removal efficiency of 88.9%. The exponential growth rate in the initial phase was enhanced by a higher nitrogen loading rate. The area-to-volume ratio of the gel beads was the significant control factor for the lag period, showing an inverse relationship due to the internal mass transport limitation. Based on the 16S rRNA gene, a sharp increase in the amount of ANAMMOX bacteria was identified along with an increase in the nitrogen removal rate. The responsible ANAMMOX bacteria were the species related to Candidatus ‘Brocadia sinica’.
The mechanism of significant nitrogen loss in an aerobic rotating biological contactor (RBC) treating ammonium-rich waste water could be identified with the aid of batch experiments, mathematical modeling and microbial analysis. It turned out that the aerobic ammonium and nitrite- oxidizing organisms (nitrosomonas and nitrobacter clusters) are dominant in the upper aerobic 100-200 μm of the biofilm. It is assumed that nitrite, appearing as an intermediate product close to the surface of the aerobic biofilm layer, diffuses into deeper anoxic layers of the biofilm. It is reduced anaerobically there in parallel with ammonium oxidized as described in the Anammox (anaerobic ammonium oxidation) process. This was confirmed in an anoxic batch test with suspended biofilm removed from the RBC. Unknown micro-organisms were detected, some of them similar to the Anammox organisms. A mathematical model which describes the kinetics of the aerobic ammonium- oxidizing, aerobic nitrite-oxidizing and anoxic ammonium-oxidizing micro- organisms was formulated and fitted into the AQUASIM biofilm compartment. The distribution of the populations within the biofilm as well as the ammonium, nitrite and nitrate degradation along the RBC in a steady state and during short-term experiments were modeled and compared with the experimental data.
Rapid start-up of anaerobic ammonium oxidation (anammox) process in up-flow column reactors was successfully achieved by immobilizing minimal quantity of biomass in polyvinyl alcohol (PVA)-sodium alginate (SA) gel beads. The changes in the reactor performance (i.e., nitrogen removal rate; NRR) were monitored with time. The results demonstrate that the reactor containing the immobilized biomass concentration of 0.33 g-VSS L(-1) achieved NRR of 10.8 kg-N m(-3) d(-1) after 35-day operation, whereas the reactor containing the granular biomass of 2.5 g-VSS L(-1) could achieve only NRR of 3.5 kg-N m(-3) d(-1). This indicates that the gel immobilization method requires much lower seeding biomass for start-up of anammox reactor. To explain the better performance of the immobilized biomass, the biological and physicochemical properties of the immobilized biomass were characterized and compared with the naturally aggregated granular biomass. Effective diffusion coefficient (De) in the immobilized biomass was directly determined by microelectrodes and found to be three times higher than one in the granular biomass. High anammox activity (i.e., NH4(+) and NO2(-) consumption rates) was evenly detected throughout the gel beads by microelectrodes due to faster and deeper substrate transport. In contrast, anammox activity was localized in the outer layers of the granular biomass, indicating that the inner biomass could not contribute to the nitrogen removal. This difference was in good agreement with the spatial distribution of microbes analysed by fluorescence in situ hybridization (FISH). Based on these results, PVA-SA gel immobilization is an efficient strategy to initiate anammox reactors with minimal quantity of anammox biomass.
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In this study, we developed an effective strategy to achieve single-stage autotrophic nitrogen removal by co-immobilizing partial nitrifying and anaerobic ammonia oxidation (anammox) biomass. Batch experiments were carried out to determine the optimum dissolved oxygen concentration of 1.5 mg/L, and the optimum biomass ratio of partial nitrifying biomass versus anammox biomass of 1:2. In continuous experiment, the total nitrogen removal rate reached 1.69 g N/L/d (nitrogen loading rate up to 2.2 g N/L/d). At the stable running stage, the TN average removal efficiency reached 77%. Scanning electron microscopy observations showed microorganisms greatly increased after 80 days cultivating. FISH analysis indicated that most anammox cells agglomerated in groups and ammonia oxidizing bacteria formed a thick layer around anammox cells.
The inhibition of free ammonia (FA) to the granule-based enhanced biological phosphorus removal (EBPR) system and the recoverability from macro- to micro-scale were investigated in this study. FA was found to seriously deteriorate the EBPR performance and sludge characteristic (settleability and morphology). The FA inhibitory threshold of 17.76mgNL(-1) was established. Acclimation phenomenon took place when poly-phosphate accumulating organisms (PAOs) were exposed for long time to constant FA concentration (8.88mgNL(-1)). The repressed polysaccharides excretion could lead to breaking the stability and integrity of the granules. Therefore, the reduced particle size and granule disintegration were observed. The molecular analysis revealed that FA had a significant influence on the microbial communities and FA inhibition may provide a competitive advantage to glycogen accumulating organisms (GAOs) over PAOs. Interestingly, the community composition was found irreversible by recovery (Dice coefficients, 36.3%), although good EBPR performance was re-achieved.
Immobilized yeast was encapsulated with cell-free calciumalginate gel by two-step preparation procedure. The volume of coated film decreased with increasing cell concentration. The encapsulation did not affect ethanol production and could prevent cell leakage from the gels.
This paper describes both qualitative and quantitative aspects of simultaneous autotrophic nitrification and heterotrophic denitrification by, respectively, the nitrifier Nitrosomonas europaea and either of the denitrifiers Pseudomonas denitrificans or Paracoccus denitrificans co-immobilized in double-layer gel beads. The system is based on the establishment of well-defined oxic and anoxic zones within the cell supports and on physical separation of the nitrifying and denitrifying populations. Nitrification and denitrification rates were obtained from measured bulk concentrations and head-space analysis. The latter analyses showed that ammonia was primarily converted into molecular nitrogen. Nitrous oxide was not detected. High nitrogen removal rates (up to 5.1rmmol Nrm-3gelrs-1) were achieved in continuous reactors under aerobic conditions. The overall rate of nitrogen removal was controlled by the nitrifying step. The approach followed is, in principle, also suitable to the coupling of other oxidative and reductive bio-processes having complementary metabolic routes. Two-stage bioconversion processes can be thus conducted as if single-staged, which results in more compact reactor systems.
Polyvinyl alcohol (PVA) as a gel matrix was used to coimmobilize nitrifying and denitrifying bacteria by repeated freezing and thawing. Factors affecting single-stage biodenitrification (simultaneously occurring nitrification and denitrification in a reactor) process such as nitrifying bacteria and denitrifying bacteria ratio, organic carbon source, pH, alkalinity, temperature, dissolved oxygen (DO), and the operational stability of coimmobilized cells were investigated. Besides, the kinetics model of single-stage biodenitrification was studied. The experimental results showed that nitrogen removal rate was most fast when nitrifying to denitrifying bacteria ratio was between 1.5:1 and 3.6:1; in four carbon sources of methanol, ethanol, acetic acid and glucose, nitrogen removal rate was most fast when using ethanol; the optimal values of temperature, pH and DO were 30°C, 8.2 and 2∼6 mg · l−1, respectively; the higher alkalinity to ammonia ratio was, the faster nitrogen removal rate was, while nitrogen removal rate went steady when alkalinity to ammonia ratio is over 9. The continuous operational system remained stable for a period of more then 60 days, and the coimmobilized cells could easily adapt to an increase in loading. The effect of internal diffusion on overall rate could be neglected, and the limiting rate process was biochemical reaction in the single-stage biodenitrification process using coimmobilized cells. The reaction kinetics of coimmobilized cells followed Michaelis-Menten form, and its kinetics constant, Km and vmax were 303.0 mg · l−1 and 0.096 mg · l−1 (immobilized cells) · s−1, respectively. The relative errors of predicted and experimental nitrogen removal rate were almost all less than 10%.
It appears that if suspended biomass washout can be reduced effectively, granule formation will be fastened in fluidized bed. Quicker reactor start-up can be anticipated especially for those system keeping slow growth bacteria such as anammox. A hybrid reactor combined fixed-bed with nonwoven fabrics as biomass carrier and fluidized bed with slow speed mechanical stirring was therefore developed, and its nitrogen removal performances was evaluated experimentally. Only in 38 days, the total nitrogen removal rate (NRR) reached to 1.9 kg(N) m(-3) day (-1) and then doubled within 17 days, with total nitrogen removal efficiency kept above 70%. After 180 days reactor operating, the NRR reached a maximum value of 6.6 kg(N) m(-3) day(-1) and the specific anammox activity was gradually constant in 0.32 kg(N) kg(VSS)(-1) day(-1). Biomass attached on nonwoven fabrics could additionally improve reactor nitrogen removal by 8%. The dominant size of granular sludge reached to 0.78 mm with stirring speed adjusted from 30 to 80 rpm and the hydraulic retention time (HRT) from 8 to 1.5 h during the whole operating time. Scanning electron microscope observation showed especially compact structure of granular sludge. A 70% of anammox bacteria percentage was identified by fluorescence in situ hybridization analysis.
Autotrophic nitrogen removal through sequential partial nitritation and anammox reactions can be achieved in biofilm reactors by controlling the oxygen concentration in the bulk liquid in such a way that nitrite oxidizers are outcompeted by anammox bacteria. In the case of granular sludge reactors, the granule size may influence the optimal range of oxygen concentration, as has been confirmed in the present study by means of numerical simulations. The range of oxygen concentrations for which combined partial nitritation and anammox conversion is established becomes broader for larger particles and with increasing influent ammonium concentrations. At the same time the likelihood of nitrite accumulation in the reactor effluent also increases.
Up-flow oxygen-controlled biofilm reactors equipped with a non-woven fabric support were used as a single reactor system for autotrophic nitrogen removal based on a combined partial nitrification and anaerobic ammonium oxidation (anammox) reaction. The up-flow biofilm reactors were initiated as either a partial nitrifying reactor or an anammox reactor, respectively, and simultaneous partial nitrification and anammox was established by careful control of the aeration rate. The combined partial nitrification and anammox reaction was successfully developed in both biofilm reactors without additional biomass inoculation. The reactor initiated as the anammox reactor gave a slightly higher and more stable mean nitrogen removal rate of 0.35 (±0.19) kg-N m(-3) d(-1) than the reactor initiated as the partial nitrifying reactor (0.23 (±0.16) kg-N m(-3) d(-1)). FISH analysis revealed that the biofilm in the reactor started as the anammox reactor were composed of anammox bacteria located in inner anoxic layers that were surrounded by surface aerobic AOB layers, whereas AOB and anammox bacteria were mixed without a distinguishable niche in the biofilm in the reactor started as the partial nitrifying reactor. However, it was difficult to efficiently maintain the stable partial nitrification owing to inefficient aeration in the reactor, which is a key to development of the combined partial nitrification and anammox reaction in a single biofilm reactor.
The application of microelectrodes to measure oxygen and nitrite concentrations inside granules operated at 20 degrees C in a CANON (Complete Autotrophic Nitrogen-removal Over Nitrite) reactor and the application of the FISH (Fluorescent In Situ Hybridization) technique to cryosectioned slices of these granules showed the presence of two differentiated zones inside of them: an external nitrification zone and an internal anammox zone. The FISH analysis of these layers allowed the identification of Nitrosomonas spp. and Candidatus Kuenenia Stutgartiensis as the main populations carrying out aerobic and anaerobic ammonia oxidation, respectively. Concentration microprofiles measured at different oxygen concentrations in the bulk liquid (from 1.5 to 35.2 mg O(2) L(-1)) revealed that oxygen was consumed in a surface layer of 100-350 microm width. The obtained consumption rate of the most active layers was of 80 g O(2) (L(granule))(-1) d(-1). Anammox activity was registered between 400 and 1000 microm depth inside the granules. The nitrogen removal capacity of the studied sequencing batch reactor containing the granular biomass was of 0.5 g N L(-1) d(-1). This value is similar to the mean nitrogen removal rate obtained from calculations based on in- and outflow concentrations. Information obtained in the present work allowed the establishment of a simple control strategy based on the measurements of NH(4)(+) and NO(2)(-) in the bulk liquid and acting over the dissolved oxygen concentration in the bulk liquid and the hydraulic retention time of the reactor.
The enrichment of anaerobic ammonium oxidizing (anammox) bacteria using an upflow anaerobic sludge bioreactor was successfully conducted for 400 days of continuous operation. The bacterial community structure of anammox bioreactor included Proteobacteria (42%), Chloroflexi (22%), Planctomycetes (20%), Chlorobi (7%), Bacteroidetes (5%), Acidobacteria (2%), and Actinobacteria (2%). All clones of Planctomycetes were affiliated with the anammox bacteria, Planctomycete KSU-1 (AB057453). The presence and diversity of ammonia oxidizing bacteria (AOB) and archaea (AOA) were identified by terminal restriction fragment length polymorphism (T-RFLP) based on the amoA gene sequences. The AOB in anammox bioreactor were affiliated with the Nitrosomonas europaea cluster. The T-RFLP result of AOA showed the diverse microbial community structure of AOA with three terminal restriction fragments (T-RFs).
The use of double-layer beads can provide a way to immobilize selectively different microbial populations having complementary metabolic pathways, but that would compete for a common substrate if simply coimmobilized as a mixed culture. In this work, several methods are presented to produce double-layer beads for the selective coimmobilization of microbial cells. Coating, encapsulation and bead formation by a double-needle device were studied. Combinations of natural support materials such as carrageenan, alginate and chitosan, synthetic polymers such as polyvinyl alcohol and polyacrylonitrile-dextran copolymer, and preformed sintered glass, silica and celite beads, were investigated. The beads produced were evaluated with respect to their mechanical strength, ease of production, shape and mildness for cell immobilization. Beads having synthetic polymers in their outer layers were the strongest of the biocatalytic particles produced. However, their application to immobilization is limited because neither nitrifying nor denitrifying cells immobilized in these supports show any conversion activity. From the double-layer beads tested, algi-nate/carrageenan beads produced by encapsulation best fulfilled our requirements.
The feasibility of long-term (>3 years), low-temperature (4–15 °C) and anaerobic bioreactor operation, for the treatment of acidified wastewater, was investigated. A hybrid, expanded granular sludge bed–anaerobic filter bioreactor was seeded with a mesophilic inoculum and employed for the mineralization of moderate-strength (3.75–10 kg chemical oxygen demand (COD) m⁻³) volatile fatty acid-based wastewaters at 4–15 °C. Bioprocess performance was assessed in terms of COD removal efficiency (CODRE), methane biogas concentration, and yield, and biomass retention. Batch specific methanogenic activity assays were performed to physiologically characterise reactor biomass.
The simultaneous partial nitrification, ANAMMOX and denitrification (SNAD) process was validated to potentially remove ammonium and COD from wastewater in a single, oxygen-limited, non-woven rotating biological contactor (NRBC) reactor. An ammonium conversion efficiency of 79%, TN removal efficiency of 70% and COD removal efficiency of 94% were obtained with the nitrogen and COD loading rate of 0.69 kgN/m(3)d and 0.34 kg/m(3)d, respectively. Scanning electron microscopy (SEM) observation and fluorescence in situ hybridizations (FISH) analysis revealed the existence of the dominant groups of bacteria. As a result, the aerobic ammonia-oxidizing bacteria (AOB), with a spot of aerobic heterotrophic bacteria were mainly distributed in the aerobic outer part of the biofilm. However, ANAMMOX bacteria with denitrifying bacteria were present and active in the anaerobic inner part of the SNAD biofilm. These bacteria were found to exist in a dynamic equilibrium to achieve simultaneous nitrogen and COD removal in NRBC system.
A new bioreactor for the removal of nitrogen from wastewater is described which consists of a tubular polymeric gel containing Nitrosomonas europaea and Paracoccus denitrificans. The outer surface of the tube is in aerobic contact with wastewater containing ammonia, while the inside of the tube is in anaerobic contact with ethanol flowing through the tube. N. europaea oxidizes ammonia to nitrite in the gel, and then P. denitrificans reduces the nitrite to nitrogen gas in the same gel. This concept would be effective for simplifying nitrogen removal systems requiring aerobic and anaerobic operations.
Anaerobic ammonium oxidation with nitrite to N2 (anammox) is a recently discovered microbial reaction with interesting potential for nitrogen removal from wastewater. We enriched an anammox culture from a rotating disk contactor (near Kölliken, Switzerland) that was used to treat ammonium-rich leachate with low organic carbon content. This enrichment led to a relative population size of 88% anammox bacteria. The microorganism carrying out the anammox reaction was identified by analysis of the 16S rDNA sequence and by fluorescence in situ hybridization (FISH) with 16S-rRNA-targeting probes. The percentage sequence identity between the 16S rDNA sequences of the Kölliken anammox organism and the archetype anammox strain Candidatus Brocadia anammoxidans was 90.9%, but between 98.5 and 98.9% with Candidatus Kuenenia stuttgartiensis, an organism identified in biofilms by molecular methods. The Kölliken culture catalyzed the anaerobic oxidation of ammonium with nitrite in a manner seemingly identical to that of Candidatus B. anammoxidans, but exhibited higher tolerance to phosphate (up to 20 mM) and to nitrite (up to 13 mM) and was active at lower cell densities. Anammox activity was observed only between pH 6.5 and 9, with an optimum at pH 8 and a temperature optimum at 37 degrees C. Hydroxylamine and hydrazine, which are intermediates of the anammox reaction of Candidatus B. anammoxidans, were utilized by the Kölliken organisms, and approximately 15% of the nitrite utilized during autotrophic growth was converted to nitrate. Electron microscopy showed a protein-rich region in the center of the cells surrounded by a doughnut-shaped region containing ribosomes and DNA. This doughnut-shape region was observed with FISH as having a higher fluorescence intensity. Similar to Candidatus B. anammoxidans, the Kölliken anammox organism typically formed homogenous clusters containing up to several hundred cells within an extracellular matrix.
The treatment of ammonium rich wastewater, like sludge digester effluent, can be significantly improved when new biotechnological processes are introduced. In this paper, the combination of a partial nitrification process (SHARON) and anoxic ammonium oxidation (Anammox) process for the treatment of ammonia rich influents is evaluated. Herein the combined process has been studied with sludge recycle liquor from the WWTP Rotterdam-Dokhaven. The SHARON process was operated stably for more than 2 years in a 10ICSTR under continuous aeration with a HRT of 1 day. The ammonia in the sludge liquor was converted by 53% to nitrite only. During the test period no formation of nitrate was observed. The effluent of the SHARON process was ideally suited as influent for the Anammox reactor. The Anammox process was operated as a granular sludge SBR-process. More than 80% of the ammonia was converted into dinitrogen gas at a load of 1.2 kgN/m3 per day. Planctomycete-like bacteria dominated the mixed community of the Anammox reactor, and only a small percentage of the population consisted of aerobic ammonium-oxidizing bacteria. This showed that the ammonium-oxidizers in the effluent of the SHARON process did not accumulate in the SBR. The test period showed that the combined SHARON-Anammox system can work stably over long periods and the process is ready for full-scale implementation.
A mathematical model for nitrification and anaerobic ammonium oxidation (ANAMMOX) processes in a single biofilm reactor (CANON) was developed. This model describes completely autotrophic conversion of ammonium to dinitrogen gas. Aerobic ammonium and nitrite oxidation were modeled together with ANAMMOX. The sensitivity of kinetic constants and biofilm and process parameters to the process performance was evaluated, and the total effluent concentrations were, in general, found to be insensitive to affinity constants. Increasing the amount of biomass by either increasing biofilm thickness and density or decreasing porosity had no significant influence on the total effluent concentrations, provided that a minimum total biomass was present in the reactor. The ANAMMOX process always occurred in the depth of the biofilm provided that the oxygen concentration was limiting. The optimal dissolved oxygen concentration level at which the maximum nitrogen removal occurred is related to a certain ammonium surface load on the biofilm. An ammonium surface load of 2 g N/m2. d, associated with a dissolved oxygen concentration level of 1.3 g O2/m3 in the bulk liquid and with a minimum biofilm depth of 1 mm seems a proper design condition for the one-stage ammonium removal process. Under this condition, the ammonium removal efficiency is 94% (82% for the total nitrogen removal efficiency) (30 degrees C). Better ammonium removal could be achieved with an increase in the dissolved oxygen concentration level, but this would strongly limit the ANAMMOX process and decrease total nitrogen removal. It can be concluded that a one-stage process is probably not optimal if a good nitrogen effluent is required. A two-stage process like the combined SHARON and ANAMMOX process would be advised for complete nitrogen removal.
A mathematical model describing nitrification (nitritification plus nitratification) and anaerobic ammonium oxidation (ANAMMOX) combined in a biofilm reactor was developed. Based on this model, a previously proposed one-reactor completely autotrophic ammonium removal over nitrite (CANON) process was evaluated for its temperature dependency and behaviour under variable inflow. The temperature-dependency of growth rates of the involved organisms is described by an Arrhenius-type equation. If temperature decreases, the activities of the involved organisms decrease. This means that thicker biofilms are needed or the ammonium surface load (ASL) to the biofilm should be decreased to maintain full N-removal at lower temperatures. Although the growth rate of nitrite oxidisers is higher than that of ammonium oxidisers at lower temperatures, these organisms can be effectively competed out due to a lower oxygen affinity. Variable inflow or dissolved oxygen (DO) concentration negatively affect the N-removal efficiency due to an unbalance between applied ASL load and required oxygen concentration. A variation of the dissolved oxygen concentration in a small range (+/- 0.2g O2/m3) has no significant influence on the process performance, which means that requirements on electrode sensitivity and a DO control scheme are not too stringent. A variable ASL has obvious influence on the process performance, at both constant and variable DO. A good adjustment of DO in accordance with the variable ASL is needed to optimise the N-removal efficiency. At T = 20 degrees C, an N-removal efficiency of 88% is possible at ASL = 0.5 g NH4+ - N/mr2 d, in a biofilm of at least 0.7 mm thickness and a DO level of 0.3 g O2/m3 in the bulk liquid.
Biogranulation is a promising biotechnology developed for wastewater treatment. Biogranules exhibit a matrix microbial structure, and intensive research has shown that extracellular polymeric substances (EPS) are a major component of the biogranule matrix material in both anaerobic and aerobic granules. This paper aims to review the role of EPS in biogranulation, factors influencing EPS production, the effect of EPS on cell surface properties of biogranules, and the relationship of EPS to the structural stability of biogranules. EPS production is substantially enhanced when the microbial community is subject to stressful culture conditions, and the stimulated EPS production in the microbial matrix in turn favours the formation of anaerobic and aerobic granules. EPS can also play an essential role in maintaining the integrity and stability of spatial structure in mature biogranules. It is expected that this paper can provide deep insights into the functions of EPS in the biogranulation process.
In the Completely Autotrophic Nitrogen removal Over Nitrite (CANON) process, aerobic and anaerobic ammonia oxidizing bacteria cooperate to remove ammonia in one oxygen-limited reactor. Kinetic studies, microsensor analysis, and fluorescence in situ hybridization on CANON biomass showed a partial differentiation of processes and organisms within and among aggregates. Under normal oxygen-limited conditions ( approximately 5 microM O2), aerobic ammonia oxidation (nitrification) was restricted to an outer shell (<100 microm) while anaerobic ammonia oxidation (anammox) was found in the central anoxic parts. Larger type aggregates (>500 microm) accounted for 68% of the anammox potential whereas 65% of the nitrification potential was found in the smaller aggregates (<500 microm). Analysis with O2 and NO2- microsensors showed that the thickness of the activity zones varied as a function of bulk O2 and NO2- concentrations and flow rate.
The fusion protein of enveloped viruses mediates the fusion between the viral and cellular membranes, allowing the penetration of the viral genomes into the host cell. Many of these proteins share a common fold comprising a central core trimer of anti-parallel coiled-coil heterodimers, which are formed by two discontinuous heptad repeat (HR) motifs located at the ectodomain of the fusion proteins. In this study, we constructed and purified the corresponding regions (HR1 and HR2) of mumps virus fusion protein that are predicted to form coiled coil. The HR1 and HR2 were expressed and purified separately or as a single chain connected by an amino acid linker (HR1-linker-HR2, named 2-Helix). Series of biochemical and biophysical analyses of the expressed proteins have shown that HR1 and HR2 of mumps virus fusion protein share the common features of other enveloped virus fusion proteins. CD spectral results show that HR1 forms an alpha-helical coil structure while HR2 exists as an unstructured monomer in PBS in nature. Mixtures of HR1 and HR2 could form a stable six-helix bundle, indicating the interaction of HR1 and HR2. The 2-Helix protein also shows characteristic properties of the 6-helix bundle. Therefore, mumps virus fusion protein has a common core architecture and its HR regions could be used as a drug target for virus fusion inhibitors.
Mechanical shear contributes to granule formation resulting in quick start-up and stability of a hybrid anammox reactor
- Y Gao
- Z Liu
- F Liu
- K Kurukawa
Y. Gao, Z. Liu, F. Liu, K. Kurukawa, Mechanical shear contributes to granule
formation resulting in quick start-up and stability of a hybrid anammox
reactor, Biodegradation 23 (3) (2012) 363-372.