Biological denitrification in an anoxic sequencing batch biofilm reactor: Performance evaluation, nitrous oxide emission and microbial community

Induced domestication of humic reduction-denitrification coupled bacteria improved treatment of sediment: Performance, remediation effect, and metabolic mechanisms

The high organic matter in river sediment primarily induces black and odorous rebound. Traditional humic-reducing bacteria demonstrate relatively single metabolic functions and restrain the remediation within complex sediment environments. In addition, Ca(NO3)2 is commonly utilized in synergistic with bioremediation to improve the reducing environment of sediments. In this study, a multifunctional bacterial community with humic reduction-denitrification coupled bacteria was domesticated by the step-feeding strategy in an anaerobic baffle reactor (ABR). The performance, remediation effect, and metabolic mechanisms were analyzed. The results indicated that humic-reducing bacteria (HRB) and denitrifying-humic-reducing bacteria (DF/HRB) have quinone-reduction and denitrification capabilities. The synergistic effect of DF/HRBs and Ca(NO3)2 was superior to HRBs and Ca(NO3)2 on the removal of total organic matter(TOM). Microbial community structure analysis revealed an enhanced relative abundance of denitrification and humic-reducing bacteria (e.g., Thauera, Pseudomonas, Sulfurospirillum, Desulfovibrio, Geobacter) in the DF/HRB, resulting in a superior synergistic effect of DF/HRBs with Ca(NO3)2. This work helps to present an innovative approach to domesticate humic-reducing bacteria suited for the remediation environment effectively. It also expands the application of humic-reducing bacteria for in-situ anaerobic remediation of river sediments.

Regulation of ARGs abundance by biofilm colonization on microplastics under selective pressure of antibiotics in river water environment

Interactions of microplastics (MPs) biofilm with antibiotic resistance genes (ARGs) and antibiotics in aquatic environments have made microplastic biofilm an issue of keen scholarly interest. The process of biofilm formation and the degree of ARGs enrichment in the presence of antibiotic-selective pressure and the impact on the microbial community need to be further investigated. In this paper, the selective pressure of ciprofloxacin (CIP) and illumination conditions were investigated to affect the physicochemical properties, biomass, and extracellular polymer secretion of polyvinyl chloride (PVC) microplastic biofilm. In addition, relative copy numbers of nine ARGs were analyzed by real-time quantitative polymerase chain reaction (qPCR). In the presence of CIP, microorganisms in the water and microplastic biofilm were more inclined to carry associated ARGs (2-3 times higher), which had a contributing effect on ARGs enrichment. The process of pre-microplastic biofilm formation might have an inhibitory effect on ARGs (total relative abundance up to 0.151) transfer and proliferation compared to the surrounding water (total relative abundance up to 0.488). However, in the presence of CIP stress, microplastic biofilm maintained the abundance of ARGs (from 0.151 to 0.149) better compared to the surrounding water (from 0.488 to 0.386). Therefore, microplastic biofilm act as abundance buffer island of ARGs stabilizing the concentration of ARGs. In addition, high-throughput analyses showed the presence of antibiotic-resistant (Pseudomonas) and pathogenic (Vibrio) microorganisms in biofilm under different conditions. The above research deepens our understanding of ARGs enrichment in biofilm and provides important insights into the ecological risks of interactions between ARGs, antibiotics, and microplastic biofilm.

A comprehensive literature mining and analysis of nitrous oxide emissions from different innovative mainstream anammox-based biological nitrogen removal processes

The biological nitrogen removal (BNR) process in wastewater treatment plants generates a substantial volume of nitrous oxide (N2O), which possesses a potent greenhouse gas effect. A limited number of studies have systematically investigated the N2O emissions of anammox-based systems with different BNR processes under mainstream conditions. Based on extensive big data statistical analysis, it had been revealed that simultaneous nitritation, anammox and denitrification (SNAD), partial nitritation anammox (PNA) and partial denitrification anammox (PDA), exhibit significantly lower N2O emission factors when compared to traditional BNR processes. The median values for N2O emission factors were determined to be 1.01 %, 1.15 % and 1.43 % for SNAD, PNA and PDA, respectively. Based on nitrogen removal data and N2O emission factors, the N2O emissions from PNA, SNAD and PDA processes were calculated to be 0.016 g·d-1, 0.037 g·d-1 and 0.008 g·d-1, respectively. Furthermore, the machine learning models (SVM and ANN) exhibited excellent predictive performance for N2O emissions in the BNR processes. However, after removing environmental factors, the R2 value of the SVM model sharply decreased. The SHAP feature analysis demonstrated the significant impact of environmental factors on the accuracy of predictive performance in machine learning models. Spearman correlation analysis was employed to investigate the relationship between N2O emissions and operational factors as well as microbial communities. The results demonstrated a negative correlation between HRT, temperature and C/N with N2O emissions. Moreover, strong associations were observed between Nitrosomonas, Nitrospira, Denitratisoma, Thauera species and N2O emissions. The contribution of N2O production via AOB pathways played a key role that was quantitatively calculated to be 93 %, 80 % and 48 % in the PNA, SNAD and PDA processes, respectively. These findings highlight the potential of these innovative BNR processes in mitigating N2O emissions.

Response of partial nitritation and denitrification processes to high levels of free ammonia in a pilot mature landfill leachate treatment system: Stability and microbial community dynamics

The high levels of free ammonia (FA) challenge the application of partial nitritation (PN) and denitrification (DN) in the treatment of ammonia-rich wastewater. This study explored the impact of high levels of FA on the PN and DN stability and microbial community dynamics. By reducing reflux and increasing influent load, the concentrations of FA in PN and DN reactors increased from 28.9 mg/L and 140.0 mg/L to 1099.8 mg/L and 868.4 mg/L, respectively. During this process, the performance of PN and DN remained stable. The microbial analysis revealed that the Nitrosomonas exhibited strong tolerance to high levels of FA, and its relative abundance was positively correlated with amoABC (R2 0.984) and hao (R2 0.999) genes. The increase in microbial diversity could enhance the resistance ability of PN against the FA impact. In contrast, high levels of FA had scant influence on the microbial community and performance of DN.

Start-up phase optimization of pyrite-intensified hybrid sequencing batch biofilm reactor (PIHSBBR): Mixotrophic denitrification performance and mechanism

Pyrite-based autotrophic denitrification (PAD) is an emerging biological process to diminish nitrate pollution, but the relatively low NO₃^--N removal rate limits its practical application. In this research, a pyrite-intensified hybrid sequencing batch biofilm reactor (PIHSBBR) was designed to treat low C/N ratio domestic wastewater. The results showed that PIHSBBR could achieve optimal removal of COD, NH₄⁺-N, and TN under the aeration rate of 1.0 L/L∙min and the hydraulic retention time (HRT) of 8 h, with removal rates of 69.67 ± 4.37%, 77.04 ± 4.84%, and 63.92 ± 6.66%, respectively. The PAD efficiency in PIHSBBR during the stable operation was not high (13.05-31.01%), and the main nitrogen removal pathway in PIHSBBR, especially in the aerobic zone, was simultaneous nitrification and denitrification (SND). High-throughput sequencing analysis unraveled that Planctomycetota (3.65%) had a high abundance in the anoxic zone of PIHSBBR, implying that anaerobic ammonium oxidation (anammox) might have occurred in the anoxic zone. In addition, the nitrogen cycle function gene with the highest abundance was nirBD, indicating the possible presence of dissimilatory nitrate reduction to ammonium (DNRA) within the system (aerobic and anoxic zones). Our research can provide useful information for the improvement and future application of PIHSBBR.

An alternative approach towards nitrification and bioremediation of wastewater from aquaponics using biofilm-based bioreactors: A review

Aquaponics combines the advantages of aquaculture and hydroponics as it suits the urban environment where a lack of agricultural land and water resources is observed. It is an ecologically sound system that completely reuses its system waste as plant fertilizer. It offers sustainable water savings, making it a supreme technology for food production. The two major processes that hold the system together are nitrification and denitrification. The remains of fish in form of ammonia reach the bio filters where it is converted into nitrite and further into nitrate in presence of nitrifying and denitrifying bacteria. Nitrate eventually is taken up by the plants. However, even after the uptake from the flow stream, the effluent contains remaining ammonium and nitrates, which cannot be directly released into the environment. In this review it is suggested how integrating the biofilm-based bioreactors in addition to aquaculture and hydroponics eliminates the possibility of remains of total ammonia nitrogen [TAN] contents, leading to bioremediation of effluent water from the system. Effluent water after releasing from a bioreactor can be reused in an aquaculture system, conditions provided in these bioreactors promote the growth of required bacteria and encourages the mutual development of plants and fishes and eventually leading to bioremediation of wastewater from aquaponics.

Systematic review: External carbon source for biological denitrification for wastewater

Nitrogen mitigation is serious environmental issue around the globe. Several methods for wastewater treatment have been introduced, but biological denitrification has been recommended, particularly with addition of the best external carbon source. The key sites of denitrification are wetlands; it can be carried out with different methods. To highlight the aforementioned technology, this paper deals to review the literature to evaluate biological denitrification and to demonstrate cost effective external carbon sources. The results of systematic review disclose the denitrification process and addition of different external carbon sources. The online literature exploration was accomplished using the most well-known databases, that is, science direct and the web of science database, resulting 625 review articles and 3084 research articles, published in peer-reviewed journals between 2015 and 2021 were identified in first process. After doing an in-depth literature survey and exclusion criteria, we started to shape the review from selected review and research articles. A number of studies confirmed that both nitrification and denitrification are significant for biological treatment of wastewater. The studies proved that the carbon source is the main contributor and is a booster for the denitrification. Based on the literature reviewed it is concluded that biological denitrification with addition of external carbon source is cost effective and best option in nitrogen mitigation in a changing world. Our study recommends textile waste for recovery of carbon source.

Composition of dissolved organic matter (DOM) in wastewater treatment plants influent affects the efficiency of carbon and nitrogen removal

Wastewater treatment plants (WWTPs) play a critical role in receiving, removing, and discharging dissolved organic matter (DOM) in aquatic systems. To date, understanding the composition and fate of DOM in different WWTPs with various environmental and socioeconomic conditions is limited. This study analyzed DOM components in the influent and effluent samples from 49 WWTPs in China using EEM-PARAFAC and ESI-FT-ICR-MS methods. The influencing factors of DOM components in the influent were also analyzed. Geographic location and GDP showed significant (p < 0.05) correlations with DOM components in the influent. The removal efficiency of DOM in WWTPs was closely related to the DOM compositions, where carbohydrates, lipids, and protein-like components (removal efficiencies > 75 %) were more readily decomposed than the humic-like components, lignin, and tannin. The relative fraction of humic-like compound C3 in the influent was correlated negatively with total nitrogen (TN) and chemical oxygen demand (COD) removal in WWTPs (p < 0.05). Besides, the relative fraction of DOM containing the element sulfur also showed significant negative correlations with the humification of DOM (p < 0.05). The results from EEM-PARAFAC and ESI-FT-ICR-MS methods showed no obvious correlation for the DOM characterizations except for humic-like fluorescent fraction C3 and lignin, while significant positive correlations (p < 0.05) between the aromatic index (AI_mod) from the ESI-FT-ICR-MS analysis and the humification index (HIX) from spectrofluorimetry. This supports the use of these spectral indexes as simple surrogates to represent part chemical compositions in further research.

Iron scraps packing rapidly enhances nitrogen removal in an aerobic sludge system and the mechanism

Simultaneous nitrification and denitrification (SND) has the advantage of energy saving and carbon demand reduction. Here, readily available low-cost iron scraps packing was added to an aerobic sludge system. This successfully enhanced the efficiency of total nitrogen removal from 37.7 ± 13.2 % to 62.7 ± 7.9 % over 2 days. While electrons from iron biocorrosion did not contribute to nitrate reduction, iron promoted heterotrophic denitrification. The iron scraps changed the spatial distribution of the microbial community, where more denitrification bacteria accumulated around the packing and higher denitrification capacity was noted. Metagenomic analysis of the sludge cultured in the presence of iron scraps for 2 days revealed that, with the exception of the enriched amoA/B/C gene expression, the abundance of other key nitrogen removal genes showed little variation. Furthermore, the structure of the microbial community was unchanged probably due to the relatively short culturing period. However, metatranscriptomic analysis indicated that iron increased the abundance of nitrifying bacteria (i.e. unclassified Nitrosomonas, Nitrosomonas sp. Is79A3 and Nitrospira defluvii) and promoted higher expression of nitrification genes. Notably, iron scraps packing decreased the abundance of the key denitrification bacteria Thauera sp. MZ1T from 52.92 to 7.58 %. The expression of napA/B also decreased, while expression of narG/H/I increased by 9 to 23 fold and a 2 to 3 fold over expression was noted for nirS, norB/C and nosZ in the presence of iron scraps. This suggested that aerobic denitrification was inhibited and anaerobic denitrification was promoted. This study has provided in-depth understanding of the influence of iron on SND to improve the application of iron-supported biological processes.

Performance and mechanism of nitrate removal by the aerobic denitrifying bacterium JI-2 with a strong autoaggregation capacity

Here, a new strain JI-2 of the strongly autoaggregating aerobic denitrifying bacteria was screened. The nitrate removal ability and autoaggregation mechanism of JI-2 were analyzed using the nitrogen balance and genomics technology. The nitrate removal rate was 27.05 mg N/(L·h) at pH 9.0 and C/N 8.0. The strain JI-2 removes nitrate via the aerobic denitrification and dissimilation pathways and removes ammonium via the assimilation pathway. 66.81 % nitrate was converted to cellular components under aerobic conditions. Complex nitrogen metabolism genes were detected in strain JI-2. C-di-GMP mediates the motility behavior of JI-2 by binding the FleQ and PilZ proteins, and regulating the expression of PslA. Furthermore, the mechanism of autoaggregation was verified by extracellular polymeric substance analysis. Meanwhile, the nitrate removal rates of strain JI-2 was 11.13-12.50 mg N/(L·h) in wastewater. Thus, strain JI-2 has good prospects for application in the treatment of nitrate wastewater.

Performance of simultaneous nitrification-denitrification and denitrifying phosphorus and manganese removal by driving a single-stage moving bed biofilm reactor based on manganese redox cycling

Simultaneous removal of NH₄⁺-N, NO₃^--N, COD, and P by manganese redox cycling in nutrient wastewater was established with a single-stage moving bed biofilm reactor (MBBR) under low C/N ratio. When sodium succinate replaced the conventional denitrifying carbon source, removal efficiencies of TN, NO₃^--N, NH₄⁺-N, TP, and Mn²⁺ were 65.13 %, 79.63 %, 92.79 %, 51.57 %, and 68.10 %, respectively. Based on modified Stover-Kincannon model, 11.03 and 10.05 mg TN·L^-1·h^-1 of U_max values were obtained with sodium acetate and sodium succinate as substrates. Extracellular polymeric substances were used to evaluate the characteristics of biofilm, and microbial community of biofilm was identified. Transformation processes of NO₃^--N, NH₄⁺-N, Mn²⁺, and P were investigated, suggesting that the main functional groups (e.g., CO, Mn-O, and CN bonds) participated in N, P, and Mn²⁺ removal, and MnO₂ was the main component of biogenic manganese oxides. This study provides a new strategy for nutrients removal by Mn²⁺ driven MBBR.

Nitrous oxide emission mitigation from biological wastewater treatment - A review

Nitrous oxide (N₂O) emitted from wastewater treatment processes has emerged as a focal point for academic and practical research amidst pressing environmental issues. This review presents an updated view on the biological pathways for N₂O production and consumption in addition to the critical process factors affecting N₂O emission. The current research trends including the strain and reactor aspects were then outlined with discussions. Last but not least, the research needs were proposed. The holistic life cycle assessment needs to be performed to evaluate the technical and economic feasibility of the proposed mitigation strategies or recovery options. This review also provides the background information for the proposed future research prospects on N₂O mitigation and recovery technologies. As pointed out, dilution effects of the produced N₂O gas product would hinder its use as renewable energy; instead, its use as an effective oxidizing agent is proposed as a promising recovery option.

Pyrite-Based Autotrophic Denitrifying Microorganisms Derived from Paddy Soils: Effects of Organic Co-Substrate Addition

The presence of organic co-substrate in groundwater and soils is inevitable, and much remains to be learned about the roles of organic co-substrates during pyrite-based denitrification. Herein, an organic co-substrate (acetate) was added to a pyrite-based denitrification system, and the impact of the organic co-substrate on the performance and bacterial community of pyrite-based denitrification processes was evaluated. The addition of organic co-substrate at concentrations higher than 48 mg L^-1 inhibited pyrite-based autotrophic denitrification, as no sulfate was produced in treatments with high organic co-substrate addition. In contrast, both competition and promotion effects on pyrite-based autotrophic denitrification occurred with organic co-substrate addition at concentrations of 24 and 48 mg L^-1. The subsequent validation experiments suggested that competition had a greater influence than promotion when organic co-substrate was added, even at a low concentration. Thiobacillus, a common chemolithoautotrophic sulfur-oxidizing denitrifier, dominated the system with a relative abundance of 13.04% when pyrite served as the sole electron donor. With the addition of organic co-substrate, Pseudomonas became the dominant genus, with 60.82%, 61.34%, 70.37%, 73.44%, and 35.46% abundance at organic matter concentrations of 24, 48, 120, 240, and 480 mg L^-1, respectively. These findings provide an important theoretical basis for the cultivation of pyrite-based autotrophic denitrifying microorganisms for nitrate removal in soils and groundwater.

Enhanced performance and microbial interactions of shallow wetland bed coupling with functional biocathode microbial electrochemical system (MES)

It is essential to remediate the polluted urban river, which endangers the aquatic creatures and affected human body's senses. The treatment wetland combined with microbial electrochemical system (MES) used for the remediation is becoming a new research focus due to its ideal pollutants removal efficiency and small footprint. Here this paper provided a kind of novel shallow wetland bed coupling with close-circuit microbial electrochemical system (WB-CMES) to remove pollutants in surface water. In contrast to the shallow wetland bed coupling with open-circuit MES (WB-OMES) and the shallow wetland bed without MES (WB), the enhancing effects and pollutants removal pathway were evaluated. After 62-day operation, average TN removal efficiency in WB-CMES was 87.7%, which was 19.7% and 13.8% higher than that of WB-OMES and WB respectively. The rate coefficient k of NO₃^--N degradation in WB-CMES was 1.6 and 1.8 times higher than that in WB-OMES and WB. The results of chlorophyll, protein and superoxide dismutase (SOD) in WB-CMES were 27.3%, 44.3% and 12.9% higher than those in WB. The microbial community structure analysis indicated that electroactive bacteria on anode like Desulfobulbus could oxidize organics and generate electrons to compensate cathode, meanwhile, cathode could enrich more species of functional bacteria like Rhodobacter, Pirellula, Hyphomicrobium, Thauera, which had a synergistic effect on oxygen reduction, nitrogen removal and plant growth. The results indicated that oxygen produced by submerged plants could be utilized by the oxygen-reducing functional biocathode of MES and the proper aerobic and anoxic environment might enhance nitrate removal mainly through simultaneous nitrification and denitrification (SND), aerobic denitrification and anammox. This research provided a novel technology with advantages of simple operation, flexible configuration, easy scale-up and low cost for application in remediation of highly polluted surface water.

Effects of co-occurrence of PFASs and chlorinated aliphatic hydrocarbons on microbial communities in groundwater: A field study

The effects of per- and polyfluoroalkyl substances (PFASs) and chlorinated aliphatic hydrocarbons (CAHs) co-contamination on the microbial community in the field have not been studied. In this study, we evaluated the presence of PFASs and CAHs in groundwater collected from a fluorochemical plant (FCP), and carried out Illumina MiSeq sequencing to understand the impact of mixed PFASs and CAHs on the indigenous microbial community. The sum concentrations of 20 PFASs in FCP groundwater ranged from 2.05 to 317.40 μg/L, and the highest PFOA concentration was observed in the deep aquifer (60 m below ground surface), co-contaminated by dense non-aqueous-phase liquid (DNAPL). The existence of PFASs and CAHs co-contamination in groundwater resulted in a considerable decrease in the diversity of microbial communities, while the abundance of metabolisms associated with contaminants biodegradation has increased significantly compared to the background wells. Furthermore, Acinetobacter, Pseudomonas and Arthrobacter were the dominant genera in PFASs and CAHs co-contaminated groundwater. The presence of high concentrations of PFASs and CAHs has been positively associated with the genus of Citreitalea. Finally, geochemical parameters, such as ORP, sulfate and nitrate were the key factors to shape up the structure of the microbial community and sources to rich the abundance of the potential functional bacteria.

Understanding Responses of Soil Microbiome to the Nitrogen and Phosphorus Addition in Metasequoia glyptostroboides Plantations of Different Ages

Nitrogen (N) and phosphorus (P) have significant effects on soil microbial community diversity, composition, and function. Also, trees of different life stages have different fertilization requirements. In this study, we designed three N additions and three P levels (5 years of experimental treatment) at two Metasequoia glyptostroboides plantations of different ages (young, 6 years old; middle mature, 24 years old) to understand how different addition levels of N and P affect the soil microbiome. Here, the N fertilization of M. glyptostroboides plantation land (5 years of experimental treatment) significantly enriched microbes (e.g., Lysobacter, Luteimonas, and Rhodanobacter) involved in nitrification, denitrification, and P-starvation response regulation, which might further lead to the decreasing in alpha diversity (especially in 6YMP soil). The P addition could impact the genes involved in inorganic P-solubilization and organic P-mineralization by increasing soil AP and TP. Moreover, the functional differences in the soil microbiomes were identified between the 6YMP and 24YMP soil. This study provides valuable information that improves our understanding on the effects of N and P input on the belowground soil microbial community and functional characteristics in plantations of different stand ages.

Modeling nitrous oxide emissions in membrane bioreactors: Advancements, challenges and perspectives

Membrane bioreactors (MBRs) have become a well-established wastewater treatment technology owing to their extraordinary efficiency and low space advantage over conventional activated sludge processes. Although the extended activated sludge models can predict the general trend of nitrous oxide (N₂O) emissions in MBRs, the simulation results usually deviate from the actual values. This review critically evaluates the recent advances in the modeling of N₂O emissions in MBRs, and proposes future directions for the development and improvement of models that better match the MBR characteristics. The quantitative impact of MBR characteristics on N₂O emissions is identified as a key knowledge gap demanding urgent attention. Accurately clarification of the N₂O emission pathways governed by MBR characteristics is essential to improve the reliability and practicability of existing models. This article lays a momentous foundation for the optimization of N₂O models in MBRs, and proposes new demands for the next-generation model. The contents will assist academics and engineers in developing N₂O production models for accurate prediction.

Temporal changes of microbial community structure and nitrogen cycling processes during the aerobic degradation of phenanthrene

Phenanthrene (PHE) is frequently detected in worldwide soils. But it is still not clear that how the microbial community succession happens and the nitrogen-cycling processes alter during PHE degradation. In this study, the temporal changes of soil microbial community composition and nitrogen-cycling processes during the biodegradation of PHE (12 μg g^-1) were explored. The results showed that the biodegradation of PHE followed the second-order kinetics with a half-life of 7 days. QPCR results demonstrated that the bacteria numbers increased by 67.1%-194.7% with PHE degradation, whereas, no significant change was observed in fungi numbers. Thus, high-throughput sequencing based on 16 S rRNA was conducted and showed that the abundances of Methylotenera, Comamonadaceae, and Nocardioides involved in PHE degradation and denitrification were significantly increased, while those of nitrogen-metabolism-related genera such as Nitrososphaeraceae, Nitrospira, Gemmatimonadacea were decreased in PHE-treated soil. Co-occurrence network analysis suggested that more complex interrelations were constructed, and Proteobacteria instead of Acidobacteriota formed intimate associations with other microbes in responding to PHE exposure. Additionally, the abundances of nifH and narG were significantly up-regulated in PHE-treated soil, while that of amoA especially AOAamoA was down-regulated. Finally, correlation analysis found several potential microbes (Methylotenera, Comamonadaceae, and Agromyces) that could couple PHE degradation and nitrogen transformation. This study confirmed that PHE could alter microbial community structure, change the native bacterial network, and disturb nitrogen-cycling processes.

Advances in Studies on Microbiota Involved in Nitrogen Removal Processes and Their Applications in Wastewater Treatment

The discharge of excess nitrogenous pollutants in rivers or other water bodies often leads to serious ecological problems and results in the collapse of aquatic ecosystems. Nitrogenous pollutants are often derived from the inefficient treatment of industrial wastewater. The biological treatment of industrial wastewater for the removal of nitrogen pollution is a green and efficient strategy. In the initial stage of the nitrogen removal process, the nitrogenous pollutants are converted to ammonia. Traditionally, nitrification and denitrification processes have been used for nitrogen removal in industrial wastewater; while currently, more efficient processes, such as simultaneous nitrification-denitrification, partial nitrification-anammox, and partial denitrification-anammox processes, are used. The microorganisms participating in nitrogen pollutant removal processes are diverse, but information about them is limited. In this review, we summarize the microbiota participating in nitrogen removal processes, their pathways, and associated functional genes. We have also discussed the design of efficient industrial wastewater treatment processes for the removal of nitrogenous pollutants and the application of microbiome engineering technology and synthetic biology strategies in the modulation of the nitrogen removal process. This review thus provides insights that would help in improving the efficiency of nitrogen pollutant removal from industrial wastewater.

Diversified metabolism makes novel Thauera strain highly competitive in low carbon wastewater treatment

Thauera, as one of the core members of wastewater biological treatment systems, plays an important role in the process of nitrogen and phosphorus removal from low-carbon source sewage. However, there is a lack of systematic understanding of Thauera's metabolic pathway and genomics. Here we report on the newly isolated Thauera sp. RT1901, which is capable of denitrification using variety carbon sources including aromatic compounds. By comparing the denitrification processes under the conditions of insufficient, adequate and surplus carbon sources, it was found that strain RT1901 could simultaneously use soluble microbial products (SMP) and extracellular polymeric substances (EPS) as electron donors for denitrification. Strain RT1901 was also found to be a denitrifying phosphate accumulating bacterium, able to use nitrate, nitrite, or oxygen as electron acceptors during poly-β-hydroxybutyrate (PHB) catabolism. The annotated genome was used to reconstruct the complete nitrogen and phosphorus metabolism pathways of RT1901. In the process of denitrifying phosphorus accumulation, glycolysis was the only pathway for glycogen metabolism, and the glyoxylic acid cycle replaced the tricarboxylic acid cycle (TCA) to supplement the reduced energy. In addition, the abundance of conventional phosphorus accumulating bacteria decreased significantly and the removal rates of total nitrogen (TN) and chemical oxygen demand (COD) increased after the addition of RT1901 in the low carbon/nitrogen (C/N) ratio of anaerobic aerobic anoxic-sequencing batch reactor (AOA-SBR). This research indicated that the diverse metabolic capabilities of Thauera made it more competitive than other bacteria in the wastewater treatment system.

Treatment of municipal wastewater by employing membrane bioreactors combined with efficient nitration microbial communities isolated by Isolation Chip with Plate Streaking technology

In this research, we developed a method so-called Isolation Chip with Plate Streaking (ICPS) to selectively enrich nitrifying microbial consortium for treating municipal wastewater. In batch experiment, these bacterial communities were able to remove NH₃ -N in 72 h with an efficiency of 96%. Firmicutes, Bacteroidetes, and Proteobacteria species are dominant bacteria in these communities. When the bacterial communities were used in the membrane bioreactor under typical condition, the removal efficiency was 81.0%. In contrast, under the actual wastewater condition, the efficiency could reach 91.2%. All above results showed clearly that the consortium selected by our ICPS method could achieve high-efficient NH₃ -N removal, thus offering a reliable technique for screening functional microorganisms in the field of water treatment. PRACTITIONER POINTS: ICPS technology was designed and used for screening specialized NH₃ -N-removing isolates. The screening process benefited the growth of the dominant nitrifying bacteria Firmicutes and Bacteroidetes. When the functional bacteria applied into the MBR, the NH₃ -N removal efficiency was 91.2% under actual wastewater conditions.

Comprehensive evaluation of manganese oxides and iron oxides as metal substrate materials for constructed wetlands from the perspective of water quality and greenhouse effect

Manganese oxides and iron oxides have been widely introduced in constructed wetlands (CWs) for sewage treatment due to their extensiveness in nature and their ability to participate in various reactions, but their effects on greenhouse gas (GHG) emissions remain unclear. Here, a set of vertical subsurface-flow CWs (Control, Fe-VSSCWs, and Mn-VSSCWs) was established to comprehensively evaluate which are the better metal substrate materials for CWs, iron oxides or manganese oxides, through water quality and the global warming potential (GWP) of nitrous oxide (N₂O), methane (CH₄), and carbon dioxide (CO₂). The results revealed that the removal efficiencies of chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) in Mn-VSSCWs were all higher than that in Fe-VSSCWs, and manganese oxides could almost completely suppress the CH₄ production and reduce GWP (from 8.15 CO₂-eq/m²/h to 7.17 mg CO₂-eq/m²/h), however, iron oxides promoted GWP (from 8.15 CO₂-eq/m²/h to 10.84 mg CO₂-eq/m²/h), so manganese oxides are the better CW substrate materials to achieve effective sewage treatment while reducing the greenhouse gas effect.

Calcium modified basalt fiber bio-carrier for wastewater treatment: Investigation on bacterial community and nitrogen removal enhancement of bio-nest

Modified basalt fiber (MBF) is a sustainable material studied as novel wastewater treatment bio-carrier recently. This work studied the effects of calcium modification on the bacterial affinity of modified fiber (Ca-MBF), bacterial community, and nitrogen removal performance. Results showed that Ca-MBF with hydrophilic (62.66°) and positively-charged (7.80 mV) surface accelerated bacterial attachment. Volatile suspended solids on Ca-MBF (5.46 g VSS/g fiber) were increased by 2.61 times after modification, with high bacterial activity when bio-carriers were cultured in activated sludge. Extracellular polymeric substances on Ca-MBF was 4.35 times higher and consisted of more protein. Bio-nests with unique aerobic/anaerobic structure formed on the ultrafine carriers in bioreactor. Ca-MBF bioreactor exhibited total nitrogen removal efficiency above 72.2% and COD removal efficiency above 94.2% with more stable performance than unmodified carrier in long-term treatment using synthetic domestic wastewater.16S rRNA gene sequencing revealed enhanced abundance of nitrifying and denitrifying bacteria in Ca-MBF bio-nest.

Pseudomonas stutzeri GF2 augmented the denitrification of low carbon to nitrogen ratio: Possibility for sewage wastewater treatment

A denitrifying strain with high efficiency at low carbon to nitrogen (C/N) ratio of 2.0 was isolated and characterized. It belongs to the genus Pseudomonas. Scanning electron microscopy (SEM) showed that GF2 was rod-shaped. The nitrate removal efficiency reached up to 92.41% (1.85 mg L^-1 h^-1) with the C/N ratio of 2.0 and the nitrite accumulation eventually decreased to 0.88 mg L^-1. By response surface method (RSM) method, three reaction conditions of strain GF2 were optimized, including pH, C/N ratio, and nitrate concentration. Nitrogen balance and gas detection revealed that 88.03% of nitrogen was removed in gaseous form (included 98.80% nitrogen gas), which confirmed its efficient denitrification ability and pathway. 3D fluorescence spectrum (3D-EEM) manifested that in the absence of organic matter, strain GF2 can utilize extracellular polymeric substance (EPS) as carbon source for efficient denitrification. This research strived to provide new research ideas for low C/N ratio sewage treatment.

Fungal pellets immobilized bacterial bioreactor for efficient nitrate removal at low C/N wastewater

In this study, fungal pellets immobilized denitrifying Pseudomonas stutzeri sp. GF3 was cultivated to establish a bioreactor. The denitrification effect of fixed bacteria with fungal pellets was tested by response surface methodology (RSM). Analysis of the bioreactor showed that the denitrification efficiency reached 100% under the optimal conditions and the denitrification efficiency of the actual wastewater treatment in the stable phase reached 95.91%. Moreover, the organic matter and functional groups in the bioreactor under different C/N conditions were analyzed by fluorescence excitation-emission matrix (EEM) spectra and Fourier transform infrared spectroscopy (FTIR), which revealed that metabolic activities of denitrifying bacteria were enhanced with the increase of C/N. The morphology and structure of bacteria immobilized by fungal pellets explored by scanning electron microscope (SEM) showed the filamentous porous fungal pellets loaded with bacteria. Community structure analysis by high-throughput sequencing demonstrated that strain GF3 might was the dominant strain in bioreactor.

The Tolerance of Anoxic-Oxic (A/O) Process for the Changing of Refractory Organics in Electroplating Wastewater: Performance, Optimization and Microbial Characteristics

In order to investigate the tolerance of an anoxic-oxic (A/O) process for the changing of refractory organics in electroplating wastewater, optimize the technological parameters, and reveal the microbial characteristics, a pilot-scale A/O process was carried out and the microbial community composition was analyzed by high-throughput sequencing. The results indicated that a better tolerance was achieved for sodium dodecyl benzene sulfonate, and the removal efficiencies of organic matter, ammonia nitrogen (NH4+-N), and total nitrogen (TN) were 82.87%, 66.47%, and 53.28% with the optimum hydraulic retention time (HRT), internal circulation and dissolved oxygen (DO) was 12 h, 200% and 2–3 mg/L, respectively. Additionally, high-throughput sequencing results demonstrated that Proteobacteria and Bacteroidetes were the dominant bacteria phylum, and the diversity of the microbial community in the stable-state period was richer than that in the start-up period.

Coupling of nitrifying granular sludge into microbial fuel cell system for wastewater treatment: System performance, electricity production and microbial community shift

A novel electrochemical system coupling of nitrifying granular sludge (NGS) into microbial fuel cell (MFC) system was conducted for simultaneous electricity production and wastewater treatment under sequencing batch mode. After 60 days operation, the contaminants of organic and NH₄⁺-N removal efficiencies of the system were high of 95.43% and 98.55%, respectively. The maximum output voltage and power density of the MFC were average at 170 mV and 33.24 mW/m², respectively. According to EEM-PARAFAC model, the soluble microbial products (SMP) released from anode and cathode chambers could be identified two fluorescence components. Additionally, the fluorescence score of protein-like substances changed more obvious than those of humic-like and fulvic acid-like substances. Geobacter and Nitrospiraceae were the dominant functional populations in the anode and cathode chambers, respectively. The result could provide a potential application technology based on NGS-MFC for simultaneously treatment of organic matter and ammonia.

Biological fixed-film systems

The technical papers published in 2019 regarding wastewater treatment and microbial films were classified into two categories: biofilm and biofilm reactors. The biofilm category includes biofilm formation, biofilm consortia, bacterial signals, biofouling, extracellular polymeric substances, and biofilm membrane bioreactors. The biofilm reactors category provides recent information on rotating biological contactors, fluidized-bed biofilm reactors, integrated fixed-film activated sludge, moving-bed biofilm reactors, packed-bed biofilm reactors, sequencing biofilm batch reactors, and trickling filters.

Biologically mediated release of endogenous N2O and NO2 gases in a hydrothermal, hypoxic subterranean environment

The migration of geogenic gases in continental areas with geothermal activity and active faults is an important process releasing greenhouse gases (GHG) to the lower troposphere. In this respect, caves in hypogenic environments are natural laboratories to study the compositional evolution of deep-endogenous fluids through the Critical Zone. Vapour Cave (Alhama, Murcia, Spain) is a hypogenic cave formed by the upwelling of hydrothermal CO₂-rich fluids. Anomalous concentrations of N₂O and NO₂ were registered in the cave's subterranean atmosphere, averaging ten and five times the typical atmospheric backgrounds, respectively. We characterised the thermal conditions, gaseous compositions, sediments, and microbial communities at different depths in the cave. We did so to understand the relation between N-cycling microbial groups and the production and transformation of nitrogenous gases, as well as their coupled evolution with CO₂ and CH₄ during their migration through the Critical Zone to the lower troposphere. Our results showed an evident vertical stratification of selected microbial groups (Archaea and Bacteria) depending on the environmental parameters, including O₂, temperature, and GHG concentration. Both the N₂O isotope ratios and the predicted ecological functions of bacterial and archaeal communities suggest that N₂O and NO₂ emissions mainly depend on the nitrification by ammonia-oxidising microorganisms. Denitrification and abiotic reactions of the reactive intermediates NH₂OH, NO, and NO₂^- are also plausible according to the results of the phylogenetic analyses of the microbial communities. Nitrite-dependent anaerobic methane oxidation by denitrifying methanotrophs of the NC10 phylum was also identified as a post-genetic process during migration of this gas to the surface. To the best of our knowledge, our report provides, for the first time, evidence of a niche densely populated by Micrarchaeia, which represents more than 50% of the total archaeal abundance. This raises many questions on the metabolic behaviour of this and other archaeal phyla.

Nitrate Removal and Dynamics of Microbial Community of A Hydrogen-Based Membrane Biofilm Reactor at Diverse Nitrate Loadings and Distances from Hydrogen Supply End

The back-diffusion of inactive gases severely inhibits the hydrogen (H2) delivery rate of the close-end operated hydrogen-based membrane biofilm reactor (H2-based MBfR). Nevertheless, less is known about the response of microbial communities in H2-based MBfR to the impact of the gases’ back-diffusion. In this research, the denitrification performance and microbial dynamics were studied in a H2-based MBfR operated at close-end mode with a fixed H2 pressure of 0.04 MPa and fed with nitrate (NO3−) containing influent. Results of single-factor and microsensor measurement experiments indicate that the H2 availability was the decisive factor that limits NO3− removal at the influent NO3− concentration of 30 mg N/L. High-throughput sequencing results revealed that (1) the increase of NO3− loading from 10 to 20–30 mg N/L resulted in the shift of dominant functional bacteria from Dechloromonas to Hydrogenophaga in the biofilm; (2) excessive NO3− loading led to the declined relative abundance of Hydrogenophaga and basic metabolic pathways as well as counts of most denitrifying enzyme genes; and (3) in most cases, the decreased quantity of N metabolism-related functional bacteria and genes with increasing distance from the H2 supply end corroborates that the microbial community structure in H2-based MBfR was significantly impacted by the gases’ back-diffusion.

Successful bio-electrochemical treatment of nitrogenous mariculture wastewater by enhancing nitrogen removal via synergy of algae and cathodic photo-electro-catalysis

Systems with catalytic cathode in microbial fuel cell can achieve high treatment efficiency enhanced by the cathode. Such bio-electrochemical systems have potential applications in treating high-salinity nitrogenous mariculture wastewater. For sustainable development of the mariculture industry, enhancing inorganic nitrogen removal is of vital importance due to the low carbon to nitrogen (C/N) ratio of wastewater and strict discharge standard. Herein, simulated mariculture wastewater (high salinity, low COD/N ratio of 0.5-1.0) was successfully treated in an integrated self-biased bio-electrochemical system, with catalyst (TiO₂/Co-WO₃/SiC) on the cathode and natural-grown algae in the cathode chamber. Satisfactory nitrogen removal (94.05% NH₄⁺-N and 77.35% inorganic nitrogen) and favorable 76.66% removal of organics (UV₂₅₄) were both achieved, with visible light illumination. The NH₄⁺-N in the effluent was below 2 mg L^-1. The synergy of bacteria, algae and cathode, promoted pollutant removal, and made the system sustainable and efficient in treating mariculture wastewater.

Simultaneous nitrate and dissolved organic matter removal from wastewater treatment plant effluent in a solid-phase denitrification biofilm reactor

In the present study, an up-flow solid-phase denitrification biofilm reactor (US-DBR) was established for simultaneous nitrate and dissolved organic matter (DOM) removal from wastewater treatment plant effluent. After 100 days operation, the nitrate and COD removal efficiencies were high of 97% and 80%, respectively. According to EEM-FRI analysis, aromatic and tryptophan protein-like, humic-like and fulvic acid-like substances were identified in DOM. Additionally, protein-like substances in DOM components were much easier transformed as carbon source for denitrification. Moreover, protein secondary structure of DOM changed significantly due to the biodegradation and microorganisms metabolic process. High-throughput sequencing analysis implied that Simplicispira, Diaphorobacter, Hydrogenophaga, Pseudoxanthmonas and Stenotrophomonas were the dominate genera in the whole of US-DBR, that were responsible for the removal of nitrate, organics and degradation of solid carbon source, respectively. This study provided a further biological basis about practical application of solid-phase denitrification for simultaneously remove nitrate and organic matter.

Influence of chlortetracycline as an antibiotic residue on nitrous oxide emissions from wastewater treatment

Strengthening the removal of antibiotics in wastewater treatment plants is a research focus, but whether antibiotics affect nitrous oxide (N₂O) emissions from wastewater treatment remains to be determined. In this study, the effect of chlortetracycline (CTC) on N₂O emissions in anaerobic/oxic/anoxic sequential batch reactors was investigated. Experimental results show that CTC promotes N₂O emissions during biological nutrient removal. The addition of 0.1 mg/L CTC increased the N₂O emission factor by 41.4% compared to the control. Mechanism exploration shows that CTC stimulates the release of extracellular polymeric substance (EPS) and binds to it, the generated EPS-CTC conjugates hinder or expand the mass transfer channel, which intensifies the electronic competition between oxidoreductases and the substrate competition between microorganisms, resulting in incomplete denitrification and nitrite accumulation, thereby increasing N₂O emissions.

Grain size tunes microbial community assembly and nitrogen transformation activity under frequent hyporheic exchange: A column experiment

Hyporheic zones (HZ) are hotspots for biogeochemical reactions where groundwater and surface water mix. River dam buildings and other hydrologic controls alter the sediment grain size distribution and modify the downstream hyporheic exchange, with cascading effects on geochemical and microbial processes in river corridors. In this lab-scale column experiment, the N transformations in HZ filled with sediments in different grain sizes were investigated with a focus on understanding the interplay among variational hydraulic connectivity, microbial community structure, functional potential under frequent groundwater-surface water exchange. Porosity was identified as the main driver determining bacterial community assembly in HZ sediments. Significant microbial zonation was observed along the columns and the degree of co-occurrence of bacterial communities in the Fine column was lower than that in the Coarse and Mix columns. The Coarse column allowed for almost 2.47 times the exchange flux relative to the Fine column, and generates the fastest DO consumption rate (-6.52 μg O₂/L·s). The enrichment of nitrifiers, i.e., Cytophagaceae and Bacillaceae and nitrification functional genes, i.e., amoA_AOA and amoA_AOB revealed the higher nitrification potential in column filled with coarse sediments. In comparison, the highest NH₄⁺ production rates (2.4 × 10^-3 μg N/L·s) took place in Fine column. The higher abundancies of denitrifiers such as Comamonadaceae and Lysobacter and enrichment of functional genes of nirK and nirS interestingly suggested the elevated denitrification potential in Fine column in a more anaerobic environment. The results implied that variations in microbial functional potential and associated nitrogen transformation may occur in size-fractioned HZ to dynamic hyporheic exchange, which added new knowledge to the underlying biogeochemical and ecological processes in regulated river corridors.

Insight into the mechanisms of biochar addition on pollutant removal enhancement and nitrous oxide emission reduction in subsurface flow constructed wetlands: Microbial community structure, functional genes and enzyme activity

A set of constructed wetlands (CWs) under different biochar addition ratios (0%, 10%, 20%, and 30%) was established to analyze the pollutant removal performance enhancement and nitrous oxide (N₂O) emission reduction from various angles, including microbial community structure, functional genes and enzyme activity. Results revealed that the average removal efficiencies of ammonium (NH₄⁺-N) and total nitrogen (TN) were improved by 2.6%-5.2% and 2.5%-7.0%. Meanwhile, N₂O emissions were reduced by 56.0%-67.5% after biochar addition. Increased nitrogen removal efficiency and decreased N₂O emissions resulted from the increase of biochar addition ratio. Biochar addition changed the microbial community diversity and similarity. The relative abundance of functional microorganisms such as Nitrosomonas, Nitrospira, Thauera and Pseudomonas, increased due to biochar addition, which promoted the nitrogen cycle and N₂O emission reduction. High gene copy number and enzyme activity involved in nitrification and denitrification process were obtained in biochar CWs, moderating N₂O emission.

Effect of temperatures and alternating anoxic/oxic sequencing batch reactor (SBR) operating modes on extracellular polymeric substances in activated sludge

In order to investigate the effect of temperatures and operating modes on extracellular polymeric substances (EPS) contents, three sequencing batch reactors (SBRs) were operated at temperatures of 15, 25, and 35 °C (R_{15 °C}, R_{25 °C}, and R_{35 °C}, respectively), with two SBRs operated under alternating anoxic/oxic conditions (R_A/O and R_O/A, respectively). Results showed that higher contents of tightly bound EPS (TB-EPS) and total EPS appeared in R_{15 °C}, while loosely bound EPS (LB-EPS) dominated in R_{35 °C}. In all three kinds of EPS (LB-EPS, TB-EPS and total EPS) assessed, protein was the main component in R_{15 °C} and R_{25 °C}, while polysaccharides dominated in R_{35 °C}. Moreover, compared with R_O/A, R_A/O was favorable for the production of the three kinds of EPS. Furthermore, three kinds of EPS and their components were augmented during the nitrification process, while they declined during the denitrification process under all conditions except for R_{35 °C}.

Shift of bacterial community and denitrification functional genes in biofilm electrode reactor in response to high salinity

High salinity suppresses denitrification by inhibiting microorganism activities. The shift of microbial community and denitrification functional genes under salinity gradient was systematically investigated in a biofilm electrode reactor (BER) and biofilm reactor (BR) systems. Denitrification efficiency of both BER and BR was not significantly inhibited during the period of low salinity (0-2.0%). As the salinity increased to 2.5%, BER could overcome the impact of high salinity and maintained a relatively stable denitrification performance, and the effluent NO₃^--N was lower than 1.5 mg/L. High salinity (>2.5%) impoverished microbial diversity and altered the microbial community in both BER and BR. However, two genera Methylophaga and Methyloexplanations were enriched in BER due to electrochemical stimulation, which can tolerate high salinity (>3.0%). The relative abundance of Methylophaga in BER was almost 10 times as much as in BR. Paracoccus is a hydrogen autotrophic denitrifier, which was obviously inhibited with 1.0% NaCl. The hetertrophic denitrifiers were primarily responsible for the nitrate removal in the BER compared to the autotrophic denitrifiers. The abundance and proportion of denitrifying functional genes confirmed that main denitrifiers shift to salt-tolerant species (nirK-type denitrifiers) to reduce the toxic effects. The napA (2.2 × 10⁸ to 6.5 × 10⁸ copies/g biofilm) and nosZ (2.2 × 10⁷ to 4.4 × 10⁷ copies/g biofilm) genes were more abundant in BER compared to BR's, which was attributed to the enrichment of Methylophaga alcalica and Methyloversatilis universalis FAM5 in the BER. The results proved that BER had greater denitrification potential under high salinity (>2.0%) stress at the molecular level.

Exploring the linkage between free nitrous acid accumulation and nitrous oxide emissions in a novel static/oxic/anoxic process

In this work, four batch tests were conducted to comprehensively explore the effects of free nitrous acid (FNA) accumulation on nitrous oxide (N₂O) emissions in a novel energy-saving and N₂O-reducing static/oxic/anoxic (SOA) process. With the accumulation of FNA, the N₂O emission factor increased from 1.51% to 4.32%, and the N₂O emission ratio contributed by ammonia-oxidizing bacteria (AOB) increased from 74.0% to 78.6%, accordingly. Mechanism studies show that produced FNA and weakened aerobic metabolism bring synergy to competition between reductases. Aeration conditions and FNA cytotoxicity exert a greater impact on nitrite-oxidizing bacteria than on AOB, thus enhancing the potential for nitrite accumulation. Considering the removal of nitrogen and phosphorus and the reduction of N₂O emissions in the SOA process, it is feasible to keep the average dissolved oxygen above 2.0 mg/L under the premise of nitrite accumulation.

Exposure to polyamide 66 microplastic leads to effects performance and microbial community structure of aerobic granular sludge

Microplastic polyamide 66 (PA66) was used to explore its mechanism of influence on the contaminants removal from aerobic granular sludge (AGS) and the corresponding change to the microbial community. Results showed that the removal pollution efficiency of the experimental groups with PA66 were inhibited during the early treatment stage. However, as the experiment progressed, the removal efficiencies of chemical oxygen demand (COD) (92.66%, 93.10%, 93.11%, 93.79%) and ammonia nitrogen (94.25%, 94.58%, 95.61%, 94.73%) were similar in the addition 0 g/L (A), 0.1 g/L (B), 0.2 g/L (C) and 0.5 g/L (D) PA66 beakers at the last 10 days. On the first day, the intensity of fluorescence peaks representing tryptophan protein-like and aromatic protein-like substances of loosely-bound extracellular polymeric substances (LB-EPS) indicated that the PA66 microplastic caused damage to the sludge structure, and the intensity of fluorescence peaks representing fulvic acid-like and humic acid-like substances were stronger than those in the control beaker (A). Microbial community analysis showed that the main phyla were Firmicutes (49.11%, 59.77%, 44.33%, 41.21%), Proteobacteria (26.44%, 11.96%, 31.44%, 19.4%) and Bacteroidetes (9.24%, 13.05%, 11.89%, 14.71%) in the four beakers. According to Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, genes representing [T] Signal transduction mechanisms illustrated that adding PA66 microplastic resulted in more signaling molecules in the AGS.

Performance and microbial communities of different biofilm membrane bioreactors with pre-anoxic tanks treating mariculture wastewater

The performance of pollutant removals, activated sludge characteristics, and microbial communities of two biofilm membrane bioreactors coupled with pre-anoxic tanks (BF-AO-MBRs) (one using fiber bundle bio-carriers (FB-MBR) and the other using suspended bio-carriers (MB-MBR)) were compared at the salinity between zero and 60 g/L. At all salinities, three bioreactors showed good COD average removal efficiencies (>94.1%), and FB-MBR showed the best TN removal efficiency (90.4% at 30 g/L salinity). Moreover, FB-MBR had the faster process start-up time and better salt shock resistance. At high salinities (30-60 g/L), more extracellular polymeric substances were produced by the BF-AO-MBRs to avoid the penetration of salt and protect the bacterial community. Because of the different attachment patterns of biofilms, the microbial community structure in the FB-MBR exposed to 30 g/L salinity had higher nitrite-oxidizing/ammonia-oxidizing bacteria ratio (6.44) with more abundance of denitrifiers, which contribute to higher TN removal efficiency and lower nitrite accumulation.

Integrated effects of temperature and COD/N on an up-flow anaerobic filter-biological aerated filter: Performance, biofilm characteristics and microbial community

The integrated effects of temperature and COD/N ratio on performance, biofilm characteristics and microbial community in up-flow anaerobic filter-biological aerated filters (UAF-BAFs) were investigated. Results indicated that the UAF-BAF system could achieve excellent COD, NH₄⁺-N and TN removal, in which effluent quality well met the Class 1A standard. Biofilm physicochemical characteristics showed that the biomass, biofilm thickness and extracellular polymeric substance (EPS) content in the UAF-BAFs reduced with the decrease in COD/N ratio, but were enhanced under low temperature. The biofilm structure characterized by CLSM in the UAF-BAFs significantly shifted, which was closely correlated with operational conditions. Sequencing analysis revealed that Proteobacteria, Epsilonbacteraeota, Bacteroidetes and Firmicutes were dominant in the UAFs and the abundance of ammonium oxidizing bacteria (AOB) was responsible for nitrification performance in the BAFs. Functions analysis indicated that amino acid metabolism, carbohydrate metabolism, energy metabolism and lipid metabolism were clearly regulated by parameters changes.