Total Nitrogen Removal Efficiency Research Articles

Impact of Dissolved Oxygen on the Performance and Microbial Dynamics in Side-Stream Activated Sludge Hydrolysis Process

Dissolved oxygen (DO) plays an important role in the performance of biological wastewater treatment systems. This study investigated the effect of the DO concentration on nutrient removal performance and microbial community structure in side-stream activated sludge hydrolysis (SSH) and conventional anaerobic/anoxic/aerobic (A2O) processes. The results showed that the change in DO had little effect on the removal performance of chemical oxygen demand (COD), and the removal efficiencies were about 90% for both reactors. Compared with the high DO level (4.1–6.9 mg/L), the A2O and SSH reactors had better nitrogen removal performance at low (0.5–2.2 mg/L) and moderate (2.2–3.9 mg/L) DO levels, with ammonia (NH4+-N) removal efficiencies of 88–89% and 89–91%, respectively, and total nitrogen (TN) removal efficiencies of 74–76% and 75–81%, respectively. Directly reducing the DO concentration from high to low reduced the phosphate removal efficiencies of the A2O and SSH reactors from 80.2% and 86.2% to 63.1% and 70.6%, respectively, while re-elevating the DO concentration to moderate levels significantly improved the phosphate removal efficiencies to 94.6% and 96.0%, respectively. Compared to the A2O reactor, the SSH reactor had more stable and better nutrient removal performance under different DO conditions, partly due to the additional carbon sources produced through the sludge fermentation in the side-stream reactor. The decrease in the DO concentration resulted in a decrease in the relative abundance of Acinetobacter but an increase in the relative abundance of Competibacter, potentially leading to the deterioration in phosphorus removal.

Integrated thiosulfate-driven denitrification, partial nitrification and anammox process in membrane-aerated biofilm reactor for low-carbon, energy-efficient biological nitrogen removal

Combining multiple bioprocesses in a single membrane-aerated biofilm reactor (MABR) unit for wastewater treatment is an emerging research focus. This study investigated the feasibility of coupling thiosulfate-driven denitrification (TDD) with partial nitrification and anammox (PNA) in a MABR for the treatment of ammonium-containing wastewater. The integrated bioprocess was tested over a continuous operation period (>130 d) in two MABRs: one with a polyvinylidene fluoride membrane (MABR-1), and the other with micro-porous aeration tubes covered with non-wovenpolyester fabrics (MABR-2). After start-up, the MABR-1 and MABR-2 based on the TDD–PNA process achieved satisfactory total nitrogen removal efficiencies of 63% and 76%, with maximum oxygen utilisation efficiencies of up to 66% and 80% and nitrogen removal fluxes of 1.3 and 4.7 gN/(m2·d), respectively. Predictions from the AQUASIM-model verified the integrated bioprocess. These lab scale findings confirmed the applicability of MABR technology for simultaneous sulfur and nitrogen removal, promising for pilot-scale application.

A Novel Layered and Advanced Nitrogen Removal Filter with Gravel and Embedded Bio-Organic Carrier Based on Autotrophic and Heterotrophic Pathways

Given increasingly prominent environmental issues, there is a pressing need to satisfy more stringent emission standards for wastewater treatment plants (WWTP) while concurrently prioritizing energy conservation; a new up-flow layered nitrogen removal filter was constructed on a laboratory scale using gravel (for the bottom and top layers) and embedded bio-organic carriers (for the middle layer) containing microorganisms as fillers to treat the secondary effluent by introducing a portion of raw water. This study investigated the nitrogen removal effectiveness and transfer pathways of synthetic wastewater at varying mixing ratios, promoted the enrichment of Anammox Bacteria (AnAOB) by embedding microorganisms, and analyzed the microbial community structure using high-throughput sequencing techniques. The findings showed that the highest total nitrogen (TN) removal efficiency was achieved with chemical oxygen demand (COD), ammonia (NH4+-N), and nitrate (NO3−-N) contents in the mixture at 77, 10, and 8 mg·L−1, respectively, with an average efficiency of 89.42%. NO3−-N was mostly removed through denitrification (heterotrophic), while NH4+-N was eliminated by partial nitrification (PN) and anaerobic ammonium oxidation (Anammox, autotrophic). According to high-throughput sequencing results, denitrifying bacteria such as Thauera (1.30–6.96%), Flavobacterium (0.18–0.40%), and Parcubacteria (0.14–0.32%) were present in all the filter layers, and Anammox bacteria such as Candidatus_Kuenenia were predominant in the middle layer at a 0.88% abundance, with the aid of organic carriers.

Nitrate reduction pathways and microbial community to different COD/NO3−-N ratios in mesophilic and thermophilic denitrification systems

Hydrolytic acidification integrated with denitrification (DEN) presents a promising treatment strategy for high-temperature industrial wastewater, such as oil, leather and ethanol wastewater. This study aimed to investigate the synergistic influence of temperature and the COD/NO3−-N ratio on the nitrogen reduction pathway using a series of semi-continuous flow reactors. The results revealed that the optimal total nitrogen (TN) removal performance was achieved under thermophilic (T = 60 °C) and COD/NO3−-N ratio of 37, with the highest TN reduction amount of 594.3 ± 41.8 mg/L. However, under other conditions, the TN removal efficiency reduced due to NH4+-N accumulation. Higher temperature facilitated the nitrogen reduction rate and butyrate yield rate, while inhibiting the dissimilatory reduction to ammonium (DNRA) process to 20.7 %. Furthermore, the higher temperature increased the bacterial diversity and the relative abundances of Clostridium, Acidaminococcus and Ruminococcus, thus, enhancing organic matter hydrolysis and nitrogen removal efficiency. In contrast, Carnobacterium, with percentage account of 34.4 %, was only detected under thermophilic conditions with a low COD/NO3−-N ratio. The COD/NO3−-N ratio only generated a slight effect on the production of volatile fatty acids (VFAs) and nitrogen reduction pathways, but had significant influence on the microbial community. These findings provide novel insight into the implementation of hydrolysis acidification coupled with anaerobic denitrification process in thermophilic wastewater treatment.

Simultaneous removal of refractory organic pollutants and nitrogen using electron shuttle suspended biofilm carriers in an integrated hydrolysis/acidification-anoxic/aerobic process

Azo dyes wastewater contains refractory pollutant and nitrogen, which threatens human health and ecological environment when discharged into environment directly. Electron shuttle (ES) is able to participate in the extracellular electron transfer, and thus enhances the removal efficiency of refractory pollutant. However, the continuous dosing of soluble ES would rise operation cost and cause contamination inevitably. In this study, a type of insoluble ES (carbonylated graphene oxide (C-GO)) was developed and melt blended into polyethylene (PE) to prepare novel C-GO-modified suspended carriers. Compared to those of conventional carrier (31.60%), the surface active sites of novel C-GO-modified carrier increased to 52.95%. An integrated hydrolysis/acidification (HA, filled with C-GO-modified carrier) - anoxic/aerobic (AO, filled with clinoptilolite-modified carrier) process was applied to remove azo dye acid red B (ARB) and nitrogen simultaneously. ARB removal efficiency was significantly improved in the reactor filled with C-GO-modified carriers (HA2) compared to the reactor filled with conventional PE carriers (HA1) or activated sludge (HA0). Total nitrogen (TN) removal efficiency of the proposed process increased by 25.95–32.64% compared to the reactor filled with activated sludge. Moreover, the intermediates of ARB were identified by liquid chromatograph-mass spectrometer (LC-MS), and the degradation pathway of ARB through ES was proposed. C-GO-modified carriers induced ARB-removal-related bacterial enrichment (such as Chloroflexi, Lactivibrio, Longilinea, Bacteroidales and Anaerolineaceae). Besides, the relative abundance of denitrifiers and nitrifiers in the AO reactor filled with clinoptilolite-modified carrier was increased by 11.60% compared with activated sludge. Copy numbers of genes related to membrane transport, carbon/energy metabolism and nitrogen metabolism increased significantly on the surface-modified carriers. This study proposed an efficient approach for simultaneous azo dyes and nitrogen removal, showing potential in actual application.

Revealing the response of community structure and metabolic pathway to varying organic matter stress in a dissolved oxygen-differentiated airlift internal circulation partial nitritation-anammox system

In practice, the influent organic matter is often pre-treated to reduce the impact on partial nitritation-anammox (PNA) process. However, the influent organics may also drive the denitrification process and improve total nitrogen removal efficiency of the PNA process. Thus, we designed and operated a novel dissolved oxygen-differentiated airlift internal circulation PNA (PNA-DOAIC) system in this study at various influent C/N ratios of 0–4.0. Nitrogen removal performance, microbial activity and community, and metabolic pathways in response to varying organic matter stress were investigated via the continuous experiment combined with batch test. The results showed that the optimum influent C/N ratio was 2.0 in this system, and the efficient and stable operation was still maintained at the C/N ratios of 0–3. At this time, the TN removal efficiency and removal rate could reach 95.1 % and 0.93 kg-N/m3/d, respectively, while COD efficiency remained at 95.4 %. Efficient removal performance was achieved via the PNA coupled with denitrification. However, the anammox bacteria (AnAOB) activity and abundance declined persistently as the influent C/N ratio was further raised, and heterotrophic bacteria gradually replaced AnAOB as dominate genus. Meanwhile, metabolic functions involving the material exchange and organic degradation were significantly enhanced. Nitrogen removal pathways changed from PNA to the nitrification-denitrification process. This study provides deep insights into effects of organic matter on the PNA process and can expand the application scope of this novel PNA-DOAIC bioreactor.

Optimization of Simultaneous Nutrients and Chemical Oxygen Demand Removal from Anaerobically Digested Liquid Dairy Manure in a Two-Step Fed Sequencing Batch Reactor System Using Taguchi Method and Grey Relational Analysis.

The technological development for efficient nutrient removal from liquid dairy manure is critical to a sustainable dairy industry. A nutrient removal process using a two-step fed sequencing batch reactor (SBR) system was developed in this study to achieve the applicability of simultaneous removal of phosphorus, nitrogen, and chemical oxygen demand from anaerobically digested liquid dairy manure (ADLDM). Three operating parameters, namely anaerobic time:aerobic time (min), anaerobic DO:aerobic DO (mg L-1), and hydraulic retention time (days), were systematically investigated and optimized using the Taguchi method and grey relational analysis for maximum removal efficiencies of total phosphorus (TP), ortho-phosphate (OP), ammonia-nitrogen (NH3-N), total nitrogen (TN), and chemical oxygen demand (COD) simultaneously. The results demonstrated that the optimal mean removal efficiencies of 91.21%, 92.63%, 91.82%, 88.61%, and 90.21% were achieved for TP, OP, NH3-N, TN, and COD at operating conditions, i.e., anaerobic:aerobic time of 90:90 min, anaerobic DO:aerobic DO of 0.4:2.4 mg L-1, and HRT of 3 days. Based on analysis of variance, the percentage contributions of these operating parameters towards the mean removal efficiencies of TP and COD were ranked in the order of anaerobic DO:aerobic DO > HRT > anaerobic time:aerobic time, while HRT was the most influential parameter for the mean removal efficiencies of OP, NH3-N, and TN followed by anaerobic time:aerobic time and anaerobic DO:aerobic DO. The optimal conditions obtained in this study are beneficial to the development of pilot and full-scale systems for simultaneous biological removal of phosphorus, nitrogen, and COD from ADLDM.

Response of microbial communities to nutrient removal in coastal sediment by using ecological concrete.

Ecological concrete (eco-concrete) is a kind of environment-friendly material with porous characteristics. In this study, the eco-concrete was used to remove the total nitrogen (TN), total phosphorus (TP), and total organic carbon (TOC) in marine coastal sediment. The bacterial communities in sediment and on eco-concrete surface were also investigated by using high-throughput sequencing and quantitative PCR of 16S rRNA gene. We found that the mean removal efficiencies of TN, TP, and TOC in treatment group were 8.3%, 8.4%, and 12.3% after 28days. The bacterial community composition in the treatment group was significantly different from that in the control group on day 28. In addition, the bacterial community composition on eco-concrete surface was slightly different from that in sediment, and the copy numbers of 16S rRNA gene were higher on eco-concrete surface than in sediment. The types of eco-concrete aggregates (gravel, pebble, and zeolite) also had effects on the bacterial community composition and 16S rRNA gene copy numbers. Furthermore, we found the abundant genus Sulfurovum increased significantly on eco-concrete surface in the treatment group after 28days. Bacteria belonging to this genus were found having denitrification ability and were commonly detected in bioreactors for nitrate removal. Overall, our study expands the application scopes of eco-concrete and suggests that the bacterial communities in eco-concrete can potentially enhance the removal efficiency of nutrients in coastal sediment.

Improved integrated anaerobic–anoxic–oxic system for landfill leachate treatment using domestic wastewater as carbon source: Performance study and optimization

Landfill leachate has been treated by using an anaerobic–anoxic–oxic (A2/O) system at Datansha Wastewater Treatment Plant in Guangzhou, South China for nearly five years. Through the pilot-scale testing and engineering experiments, the impulse loads of the wastewater treatment systems were successfully reduced. The results showed that the highest removal efficiencies of chemical oxygen demand (COD), ammonium-nitrogen (NH4+-N), and total nitrogen (TN) for the combined treatment of domestic wastewater and landfill leachate were achieved under the operating conditions of hydraulic retention time = 11 h, dissolved oxygen = 3 mg/L, mixed liquid return ratio = 200%, and sludge return ratio = 80%. Compared with the data obtained from the previous operating A2/O system, the removal efficiencies of COD, NH4+-N, and TN increased by 5.6%, 9.8%, and 5.3%, respectively, under the optimal operating conditions for one year. The average effluent concentrations of BOD5, COD, NH4+-N, TN, and total phosphorus were 12.4, 29.9, 2.5, 18.0, and 0.5 mg/L, respectively, and these values could be kept below standard discharge limits in China.

A novel Electrolysis-integrated anammox system for intensified nitrogen removal and simultaneous phosphorus recovery as vivianite

A novel electrolysis-integrated anammox (Ele-anammox) process was developed for intensified nitrogen removal and concomitant phosphorus recovery from nutrient-rich wastewater. By conducting a parallel experiment, average removal efficiencies of total nitrogen (TN) and total phosphorus (TP) in Ele-anammox reactor reached 90.69% and 95.02% respectively, showing increases of 7.76% and 79.08%, as compared to the traditional anammox process. Anammox reaction and synergetic denitrification were mainly responsible for the reinforced N-removal. Successions of microbial communities revealed that Candidatus Kuenenia declined markedly while Candidatus Brocadia was enriched in Ele-anammox system, suggesting that electrical environment provided Candidatus Brocadia with a competitive advantage over other anammox bacteria. Based on the proposed current control strategy (the applied current was calculated to match the influent P loading), precise release of soluble Fe2+ could be achieved by anodic oxidation. Various elemental analysis methods, including the standards, measurements and testing (SMT) protocol, energy dispersive X-ray spectroscopy (eSEM-EDX), X-ray fluorescence spectrometry (XRF) and inductively coupled plasma emission spectroscopy (ICP-OES), jointly indicated that the solid phase of Ele-anammox was primarily Fe-P precipitation, which showed a similar Fe:P ratio with vivianite (Fe3(PO4)2·8H2O, 1.5). X-ray diffraction (XRD) analysis further validated the in-situ crystallization of vivianite, and semi-quantification implied a vivianite content of 85%. Mössbauer spectroscopy showed at least 51.48% ∼ 59.11% of iron was bound in vivianite, while impurity occupation and potential oxidization may impair the purity of P-recovery products, which should be concerned in future practice.

Changes of nitrogen and phosphorus removal pattern caused by alternating aerobic/anoxia from the perspective of microbial characteristics.

The purpose of this study was to compare the impact of different numbers of alternating aerobic/anoxic (A/O) cycles on pollutant removal. Three sequential batch reactors (SBRs) with varying numbers of alternating A/O cycles were established. Under the tertiary anoxic operating conditions, the removal efficiencies of chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total nitrogen (TN), and total phosphorus (TP) were 88.73%, 89.56%, 72.15%, and 77.61%, respectively. Besides, alternating A/O affected the dominant microbial community relative abundance (Proteobacteria and Bacteroidetes) and increased microbial richness and diversity. It also increased the relative abundance of aerobic denitrifying, heterotrophic nitrifying, and denitrifying phosphorus removal bacteria to change N and P removal patterns. Furthermore, the abundance of carbohydrate metabolism and amino acid metabolism was improved by alternating A/O to improve organic matter and TN removal.

Promoted aerobic denitrification through denitrifying fungal communities: Co-occurrence patterns and treatment of low C/N micro-polluted water

Despite the growing interest in using mixed-culture aerobic denitrifying fungal flora (mixed-CADFF) for water remediation, there is limited research on their nitrogen removal performance in low C/N polluted water bodies. To address this knowledge gap, we isolated three mixed-CADFFs from overlying water in urban lakes to evaluate their removal performance. The total nitrogen (TN) removal efficiencies were 93.60 %, 94.64 %, and 95.18 %, while the dissolved organic carbon removal efficiencies were 96.64 %, 95.12 %, and 96.70 % for mixed-CADFF LN3, LN7, and LN15, respectively in the denitrification medium under aerobic conditions at 48 h cultivation. The three mixed-CADFFs could utilize diverse types of low molecular weight carbon sources to drive the aerobic denitrification processes efficiently. The optimal C/N ratio for the mixed-CADFFs were C/N = 10, and then C/N = 15, 7, 5, and 2. The high-throughput sequencing analysis of three mixed-CADFFs indicated that Eurotiomycetes, Cystobasidiomycetes, and Sordariomycetes were the dominant class in the communities at class level. The network analysis showed that the rare fungal species, such as Scedosporium dehoogii Saitozyma, and Candida intermedia presented positively co-occurred with the TN removal and organic matter reduction capacity. Immobilization mixed-CADFFs treatment raw water experiments indicated that three mixed-CADFFs could reduce nearly 62.73 % of TN in the low C/N micro-polluted raw water treatment. Moreover, the cell density and cell metabolism indexes were also increased during the raw water treatment. This study will provides new insight into resource utilization of the mixed-culture aerobic denitrifying fungal community in field of environment restoration.

Improving stability and nitrogen removal performance of pilot-scale autotrophic process for mature landfill leachate treatment utilizing in-situ organics

This study established a stable and efficient pilot-scale denitrification (DN) and partial nitritation (PN) combined with autotrophic nitrogen removal process for mature landfill leachate treatment. A total inorganic nitrogen removal efficiency (TINRE) of 95.3% was achieved without any external carbon source input, including 17.1%, 1.0% and 77.2% of nitrogen removal contributed by the DN, PN and autotrophic processes, respectively. ANAMMOX genus, Ca_Anammoxoglobus (19.4%) was dominant in autotrophic reactor. Moreover, denitrifying bacteria could utilize in-situ organics, including poorly degradable organics, to enhance the nitrogen removal performance of autotrophic process, contributing 3.4% of TINRE. This study provides new insights for the economical, low-carbon, and efficient treatment of mature landfill leachate.

The enhancement of nutrients removal performance in a vertical up-flow constructed wetland system using iron-carbon substrates

The reclaimed water was usually further treated by the constructed wetland (CW) to remove nitrogen and phosphorus before it was discharged to water bodies. In this work, the iron-carbon (Fe-C) substrate and plant-based carbon source were added to the vertical up-flow CWs to enhance the denitrification of reclaimed water. It was found that the removal efficiency of nitrate (NO3--N), total nitrogen (TN) and total phosphorus (TP) in the Fe-C amended CWs were significantly increased by 20–35%, 10–25%, and 10–35%. Moreover, the plant-based carbon source also contributed to TN and TP removal. The additional substrates also reduced the emission of NO2 and CH4 from the CWs. Finally, the microbial community was analyzed to disclose the mechanism involved in the enhanced performance of CWs. The enriched hydrogenotrophic and heterotrophic denitrifiers by the Fe-C substrates and pine bark contributed to the enhanced nitrification.

Sustainable, quality biofertilizer produced from Nile perch (Lates niloticus) wastewater using three Bacillus species: Demonstration in barley hydroponics

Although substantial quantities of Nile perch waste/wastewater are generated in Northeastern and Central Africa, only a small fraction of Nile perch waste is reutilized, with the resultant environmental pollution threatening aquatic life. Therefore, it was investigated whether Nile perch wastewater (NPWW) can be processed to produce a quality biofertilizer and thus completely reused. To achieve this purpose, NPWW degradation was conducted in a 1 L flask for 72 h using a microbial consortium of three Bacillus species. After 72 h biodegradation, the number of viable cells was 5.6 × 107 CFU/mL, the degree of protein hydrolysis was 48.7%, and the removal efficiency of chemical oxygen demand concentration and total nitrogen in NPWW was 52.5% and 44.0%, respectively, with C/N ratios of 5.5−6.4. Small molecules resulting from biodegradation comprised 52.9% hydrophilic amino acids and exhibited 73.9%, 98.9%, and 93.3% of free radical-scavenging activity for DPPH, ABTS, and OH-, respectively. The resultant biofertilizer was non-phytotoxic beyond a 50-fold dilution, and a 1000-fold dilution of the biofertilizer in barley hydroponics resulted in significantly higher stem and leaf growth than the control and commercial fertilizer. The biofertilizer-fed barley leaves exhibited a higher production of photosynthetic pigments and significantly higher antioxidant activity (92.5% for DPPH and 91.8% for ABTS) than the leaves in the control and commercial fertilizer groups. These findings indicate that the biodegraded NPWW rich in small molecules can be used as a biostimulant for sustainable agriculture.

Deciphering the effect of temperature reduction on the biofilm in partial nitritation-anammox system: Insights from microbial community to metabolic pathways

The concept of partial nitritation-anammox (PN/A) process has been proposed for many years, however seasonal temperatures and low ammonia concentrations under mainstream conditions always challenge the application in practical engineering. Thus, we operated a PN/A moving bed biofilm reactor (PN/A-MBBR) for treating 50 mg-NH4/L wastewater at various temperatures of 35 °C, 25 °C, and 15 °C. The effect of temperature reduction on biofilm system was investigated from process performance, microbial community and activity, to metabolic pathways. The results showed that total nitrogen removal efficiency declined from 76.6 % to 48.6 % as the temperature was reduced from 35 °C to 15 °C, while nitrogen removal rate decreased to 0.28 kg-N/m3/d. Low temperature stimulated the secretion of polysaccharide in loosely bound-EPS and protein in tightly bound-EPS. Meanwhile, specific activity of anammox declined from 1.53 to 0.56 g-N/g-VSS/d, and the relative abundance of Candidatus Brocadia dropped from 20.1 % to 9.4 %. Temperature reduction had significant effect on the expression of functional genes (hzsA and hdh) for anammox reaction. Nitrification-denitrification process was enhanced during low temperatures and recovery phases. Biofilm system might respond to temperature reduction by the decline of substance transport and energy consumption, as well as the enhancement of biofilm formation and diversity of nitrogen removal pathways. The findings of this study provide a deep insight into the effect of temperature reduction on PN/A process, also promote the practical applications of mainstream PN/A in the future.

Treatment performance of multistage active biological process (MSABP) reactor for saline sauerkraut wastewater: acclimatization, optimization and improvement.

The wastewater with a high concentration of organics and salt is a major contaminant in the production of sauerkraut. In this study, a multistage active biological process (MSABP) system was constructed to treat sauerkraut wastewater. The key process parameters of the MSABP system were analyzed and optimized by response surface methodology. The optimization results indicated that the most optimal removal efficiencies and removal loading rates of chemical oxygen demand (COD) and NH4+-N were 87.9%, 95.5%, 2.11kg·m-3·d-1 and 0.12kg·m-3·d-1, respectively, with hydraulic retention time (HRT) of 2.5 d and pH of 7.3. Meanwhile, this system could also be improved for the further treatment of COD and total nitrogen by effluent recycle and ozone oxidation. The COD and total nitrogen removal efficiencies of the modified MSABP system were 99.9% and 60.2%, respectively. In addition, the modified system could also reduce the potential harm from high concentrations of NO2--N.

New insight into the irreversible membrane fouling in different pore-sized ultrafiltration ceramic membrane bioreactors (UCMBRs) for high-strength textile wastewater treatment

Despite great achievements in ceramic membrane bioreactor applications, membrane fouling, which decreases the permeability and separation performance of bioreactors and is associated with increased operational costs and energy consumption, remains a problem. The aim of this study was to expand our understanding of the fouling behavior in the long-term performance of ultrafiltration ceramic membrane bioreactors (UCMBRs) for high-strength textile wastewater reclamation. Using real textile wastewater effluent, the effects of ultrafiltration (UF) membrane pore sizes, cleaning strategies, and foulant distribution were systematically evaluated over more than three months of continuous operation. The results showed that UCMBR system achieved chemical oxygen demand and total nitrogen removal efficiencies as high as 91–95% and 39–43%, respectively. The high PN concentration can easily increase the viscosity of mixed liquor samples, contributing to a fouling layer on the membrane surface. In addition, the fouling layer formed on the surface of small-pore-sized ceramic UF membranes was not completely reversible but was difficult to eliminate by simple physical cleaning. Soluble extracellular polymeric substances, especially proteins and low molecular weight neutrals, remained, resulting in irreversible fouling on the UF membrane. However, saturated CO2 backwash showed great potential for enhancing the system through efficient fouling control without using environmentally unfriendly cleaning chemicals. The cake-intermediate and complete-standard models were suitable for explaining the fouling mechanism in the large- and small-pore-sized UF membranes, respectively.

Effective removal of nitrogen and phosphorus from a black-odorous water by novel oxygen-loaded adsorbents

Black-odorous water, caused by hypoxia and overloading of nitrogen and phosphorus, is ubiquitous in global urban rivers. In this study, we developed oxygen-loaded adsorbents by loading oxygen into activated carbon, Attapulgite, Phoslock, and Muscovite via vacuum-pressure swing method, and investigated their aeration and removal efficiency of phosphate, ammonia nitrogen, and total nitrogen in black-odorous water. Results showed that the addition of oxygen-loaded coal-based columnar activated carbon (OCC) or oxygen-loaded Muscovite (OM) alone could increase the dissolved oxygen (DO) concentration at the sediment–water interface to more than 6 mg·L-1 on the first day, and OCC could maintain the high level of oxidation–reduction potential (ORP) (up to + 327 mV) for 15 days. Most oxygen-loaded adsorbents remarkably reduced phosphate in water, essentially from 0.27 mg·L-1 to < 0.05 mg·L-1. Additionally, ammonia nitrogen and total nitrogen were reduced by more than 50 % by adding materials after oxygen loading treatment. The 16 s RNA results showed that Dechloromonas was dominant in abundance, and the reduction of nitrogen was mainly affected by microbial activity. Our results provided a series of oxygen-loaded adsorbent materials with potential engineering applications for rapid treatment of urban black-odorous water.

Effect of plant-self debris on nitrogen removal, transformation and microbial community in mesocosm constructed wetlands planted with Myriophyllum aquaticum

Aquatic macrophytes debris decomposition could release pollutants and nutrients into the water of constructed wetlands (CWs), but their role in nitrogen removal and transformation remains poorly understood. The present study investigated the effects of plant-self debris on nitrogen removal and microbial communities in mesocosm CWs planted with Myriophyllum aquaticum. During the 68-day operation, the plant debris addition did not change the mean removal efficiency of ammonium (NH4+-N) and total nitrogen (TN) of CWs but showed significant differences over the operation time. The NH4+-N and organic nitrogen released from the plant debris decomposition affected the nitrogen removal. The plant debris decreased the effluent nitrate concentration and N2O emission fluxes of the CWs with the increased abundance of denitrifying bacterial genera, indicating that plant debris decomposition increased the denitrification activities via dissolved organic carbon release. High-throughput sequencing indicated that the plant debris altered the distribution and composition of the microbial community in the sediments. Proteobacteria was the dominant phylum (28–52%), and the relative abundance of denitrifying bacteria genera was significantly higher in the sediments with debris addition (37–40%) than in the non-addition (6.6–7.7%). The present study provided new insights into the role of macrophytes in pollutant removal and the plant management strategy of CWs.