Nitrogen Removal Characteristics Research Articles

Characteristics of Nitrogen Removal from an Integrated Fixed-Film Activated Sludge (IFAS) System and the Relationship Between Activated Sludge and Biofilm Interactions

In order to investigate the enhancement mechanism of modified three-dimensional elastic filler (MTEF) on the nitrogen removal performance of the integrated fixed-film activated sludge (IFAS) process, and to clarify the interactions between competition and synergy between activated sludge and biofilm in the IFAS system, an IFAS reactor (T2) filled with MTEF was employed for the study, while a sequencing batch reactor activated sludge process (SBR) reactor (T1) was utilized for comparison. IFAS and SBR reactors were operated over an extended period at ambient temperature to assess the enhancement of pollutant removal performance with the addition of the filler to investigate the competitive dynamics between activated sludge and biofilm under varying influent water qualities (C/N, N/P, and organic loading), and to analyze the synergistic relationship between activated sludge and biofilm at the microbial level using high-throughput sequencing technology. The results demonstrate that throughout the entire operational phase, reactor T2 exhibited superior pollutant removal efficiency. Compared to reactor T1, reactor T2 achieved an average increase in the removal rates of COD, ammonia nitrogen, and total nitrogen by 13.07%, 12.26%, and 28.96%, respectively. The findings on the competitive dynamics between activated sludge and biofilm indicate that the nitrification volumetric load of the IFAS system is significantly higher than that of a pure activated sludge system, suggesting that the IFAS system possesses enhanced nitrification capabilities. Furthermore, when dealing with wastewater characterized by low C/N ratios and high phosphorus pollution, or under substantial organic loads, the biofilm holds a competitive edge and the IFAS system exhibits improved stability. High-throughput sequencing data reveal that the microbial community structures in activated sludge and biofilm can influence each other, thereby enabling the IFAS system to effectively enrich denitrification-related functional microbial populations. Additionally, the biofilm has a certain enhancing effect on the expression levels of nitrogen metabolism-related functional genes in the activated sludge phase microorganisms, indicating that, in addition to competitive interactions, there is also a synergistic effect between the biofilm and activated sludge.

Potential effects of Cu2+ stress on nitrogen removal performance, microbial characteristics, and metabolism pathways of biofilm reactor

Sequencing batch biofilm reactors (SBBR) were utilized to investigate the impact of Cu2+ on nitrogen (N) removal and microbial characteristics. The result indicated that the low concentration of Cu2+ (0.5 mg L−1) facilitated the removal of ammonia nitrogen (NH4+-N), total nitrogen (TN), nitrate nitrogen (NO3−-N), and chemical oxygen demand (COD). In comparison to the average effluent concentration of the control group, the average effluent concentrations of NH4+-N, NO3−-N, COD, and TN were found to decrease by 40.53%, 17.02%, 10.73%, and 15.86%, respectively. Conversely, the high concentration of Cu2+ (5 mg L−1) resulted in an increase of 94.27%, 55.47%, 22.22%, and 14.23% in the aforementioned parameters, compared to the control group. Low concentrations of Cu2+ increased the abundance of nitrifying bacteria (Rhodanobacter, unclassified-o-Sacharimonadales), denitrifying bacteria (Thermomonas, Comamonas), denitrification-associated genes (hao, nosZ, norC, nffA, nirB, nick, and nifD), and heavy-metal-resistant genes related to Cu2+ (pcoB, cutM, cutC, pcoA, copZ) to promote nitrification and denitrification. Conversely, high concentration Cu2+ hindered the interspecies relationship among denitrifying bacteria genera, nitrifying bacteria genera, and other genera, reducing denitrification and nitrification efficiency. Cu2+ involved in the N and tricarboxylic acid (TCA) cycles, as evidenced by changes in the abundance of key enzymes, such as (EC:1.7.99.1), (EC:1.7.2.4), and (EC:1.1.1.42), which initially increased and then decreased with varying concentrations of Cu2+. Conversely, the abundance of EC1.7.2.1, associated with the accumulation of nitrite nitrogen (NO2−-N), gradually declined. These findings provided insights into the impact of Cu2+ on biological N removal.

Characteristics of Nitrogen Removal and Functional Gene Transcription of Heterotrophic Nitrification-Aerobic Denitrification Strain, Acinetobacter sp. JQ1004

In this study, the heterotrophic nitrification–aerobic denitrification strain JQ1004 was investigated in terms of its nitrogen removal mechanism and kinetic properties, laying the foundation for its application in the field of wastewater treatment. Nitrogen balance analysis revealed that the final metabolic product was N2, and approximately 54.61% of N was converted into cellular structure through assimilation. According to the fitting of the Compertz model, the maximum degradation rates of ammonia and nitrate were 7.93 mg/(L·h) and 4.08 mg/(L·h), respectively. A weakly alkaline environment was conducive to N removal, and the sensitivity of functional genes to acidic environments was amoA > nirS > narG. An appropriate increase in dissolved oxygen significantly enhanced heterotrophic nitrification activity, and notably, the denitrification-related functional gene narG exhibited greater tolerance to dissolved oxygen compared to nirS. The transcription level of amoA was significantly higher than that of narG or nirS, confirming that there might have been direct ammonia oxidation metabolic pathways (NH4+→NH2OH→N2) besides the complete nitrification and denitrification pathway. The annotation of nitrogen assimilation-related functional genes (including gltB, gltD, glnA, nasA, nirB, narK, nrtP, cynT, and gdhA genes) in the whole-genome sequencing analysis further confirmed the high assimilation nitrogen activity of the HN-AD strain.

Nitrogen removal characteristics and Cr(VI) tolerance mechanisms of heterotrophic nitrifying bacterium Pseudomonas putida strain LX1

To solve the severe inhibition effect of nitrification process by heavy metals, necessitating the discovery of heavy metals-resistant nitrifying bacteria. In this study, a highly efficient bacterium, Pseudomonas putida strain LX1, capable of heterotrophic nitrification–aerobic denitrification (HN-AD) and resistant to hexavalent chromium (Cr(VI)) was isolated from activated sludge. Strain LX1 exhibited excellent growth activity and achieved efficient NH4+-N removal rates (94.07%–83.36 %) under 0–25 mg/L Cr(VI) stress. The heterotrophic nitrification ability of strain LX1 was superior to that of aerobic denitrification, and there was no accumulation of nitrite or nitrate during HN-AD process. Moreover, Three-dimensional excitation-emission matrix and Fourier-transform infrared spectroscopy analysis indicated that strain LX1 secreted more extracellular polymeric substances with negatively charged functional groups to bind Cr(VI) and alleviate its toxicity. Enzymatic analysis showed that strain LX1 countered the oxidative damage of reactive oxygen species by promoting the activities of oxidative dismutase and catalase. Furthermore, transcriptomic analyses revealed that the upregulation of genes associated with heavy metal substrate transporter proteins and antioxidant systems in strain LX1 contributed to the resistance against the high biotoxicity caused by Cr(VI). This study is important for understanding the heavy metal response mechanisms of HN-AD strains and its potential application in practical wastewater treatment.

Biological nitrogen removal characteristics and mechanisms of a novel salt-tolerant strain Vibrio sp. LV-Q1 and its application capacity for high-salinity nitrogen-containing wastewater treatment

High concentration of salts in wastewater can adversely affects the metabolic activities and growth of microorganisms, resulting in reduced efficiency of biological nitrogen removal. Screening high-efficiency heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria with salt tolerance is important for the wastewater treatment. In this study, a novel salt-tolerant strain LV-Q1 capable of HN-AD was isolated and identified as Vibrio sp. This strain demonstrates a salinity tolerance range of 0–8 %. Notably, strain LV-Q1 exhibited exceptional nitrogen removal efficiencies (at initial concentrations of 100 mg/L), achieving 97.97 % for NH4+-N, 100 % for NO3--N, and approximately 100 % for mixed nitrogen (NH4+-N and NO3--N) at a salinity of 5 %. Optimal ammonium removal parameters for LV-Q1 were established. The nitrogen removal pathway of LV-Q1 primarily involves direct assimilation of ammonium and its conversion into N2 through HN-AD. Analysis of the salt tolerance mechanism revealed LV-Q1's ability to equilibrate osmotic pressure through the accumulation of amino acids and betaine, production of antioxidative enzymes or extracellular protein, and utilization of its quorum sensing (QS) properties to withstand high-salinity environments. The strain LV-Q1 exhibited strong resistance to salinity shock in bioaugmentation within a moving bed biofilm reactor (MBBR), markedly enhancing nitrogen and carbon removal performance with an improved removal efficiency of 26.74 % and 10.15 % averagely at the end of the reaction at a salinity of 5 %. Moreover, Vibrio sp. LV-Q1 successfully proliferated and dominated, and its relative abundance gradually increased to 59.81 %. This study contributes new insights and resources for the treatment of nitrogen in saline effluents.

Enhanced chromium and nitrogen removal by constructing a biofilm reaction system based on denitrifying bacteria preferential colonization theory

Understanding the developmental characteristics of microbial communities in biofilms is crucial for designing targeted functional microbial enhancements for the remediation of complex contamination scenarios. The strong prioritization effect of microorganisms confers the ability to colonize strains that arrive first dominantly. In this study, the auto-aggregating denitrifying bacterial Pseudomonas stutzeri strain YC-34, which has both nitrogen and chromium removal characteristics, was used as a biological material to form a stable biofilm system based on the principle of dominant colonization and biofortification. The effect of the biofilm system on nitrogen and chromium removal was characterized by measuring the changes in the quality of influent and effluent water. The pattern of biofilm changes was analyzed by measuring biofilm content and thickness and characterizing extracellular polymer substances (EPS). Further analysis of the biofilm microbiota characteristics and potential functions revealed the mechanism of strain YC-34 biofortified biofilm. The results revealed that the biofilm system formed could achieve 90.56% nitrate-nitrogen removal with an average initial nitrate-nitrogen concentration of 51.9 mg/L and 40% chromium removal with an average initial hexavalent chromium Cr(VI) concentration of 7.12 mg/L. The biofilm properties of the system were comparatively analyzed during the biofilm formation period, the fluctuation period of Cr(VI)-stressed water quality, and the stabilization period of Cr(VI)-stressed water quality. The biofilm system may be able to increase the structure of hydrogen bonds, the type of protein secondary structure, and the abundance of amino acid-like components in the EPS, which may confer biofilm tolerance to Cr(VI) stress and allow the system to maintain a stable biofilm structure. Furthermore, microbial characterization indicated an increase in microbial diversity in the face of chromium stress, with an increase in the abundance of nitrogen removal-associated functional microbiota and an increasing trend in the abundance of nitrogen transfer pathways. These results demonstrate that the biofilm system is stable in nitrogen and chromium removal. This bioaugmentation method may provide a new way for the remediation of heavy metal-polluted water bodies and also provides theoretical and application parameters for the popularization and application of biofilm systems.

Enhanced nitrate removal efficiency and microbial response of immobilized mixed aerobic denitrifying bacteria through biochar coupled with inorganic electron donors in oligotrophic water

The nitrogen removal characteristics and microbial response of biochar-immobilized mixed aerobic denitrifying bacteria (BIADB) were investigated at 25 °C and 10 °C. BIADB removed 53.51 ± 1.72 % (25 °C) and 39.90 ± 4.28 % (10 °C) nitrate in synthetic oligotrophic water. Even with practical oligotrophic water, BIADB still effectively removed 47.66–53.21 % (25 °C), and 39.26–45.63 % (10 °C) nitrate. The addition of inorganic electron donors increased nitrate removal by approximately 20 % for synthetic and practical water. Bacterial and functional communities exhibited significant temperature and stage differences (P < 0.05), with temperature and total dissolved nitrogen being the main environmental factors. The dominant genera and keystone taxa exhibited significant differences at the two temperatures. Structural equation model analysis showed that dissolved organic matter had the highest direct and indirect effects on diversity and function, respectively. This study provides an innovative pathway for utilizing biochar and inorganic electron donors for nitrate removal from oligotrophic waters.

Nitrogen removal characteristics of novel bacterium Klebsiella sp. TSH15 by assimilatory/dissimilatory nitrate reduction and ammonia assimilation

A novel strain with heterotrophic nitrification and aerobic denitrification was screened and identified as Klebsiella sp. TSH15 by 16S rRNA. The results demonstrated that the ammonia-N and nitrate-N removal rates were 2.99 mg/L/h and 2.53 mg/L/h under optimal conditions, respectively. The analysis of the whole genome indicated that strain TSH15 contained the key genes involved in assimilatory/dissimilatory nitrate reduction and ammonia assimilation, including nas, nar, nir, nor, glnA, gltB, gdhA, and amt. The relative expression levels of key nitrogen removal genes were further detected by RT-qPCR. The results indicated that the N metabolic pathways of strain TSH15 were the conversion of nitrate or nitrite to ammonia by assimilatory/dissimilatory nitrate reduction (NO3−→NO2−→NH4+) and further conversion of ammonia to glutamate (NH4+-N → Glutamate) by ammonia assimilation. These results indicated that the strain TSH15 had the potential to be applied to practical sewage treatment in the future.

Successful establishment of Anammox by cultivating residual sludge and its response to elevated nitrogen loading

Anaerobic ammonia oxidation (Anammox) process was one of the most economical nitrogen removal technology, however, the slow growth rate and the shortage of sufficient seed sludge limit its application. In this study, Anammox was successfully established using residual sludge as seed sludge, and the variation in its nitrogen removal, stability, and microbial characteristics in response to the elevated ammonia and nitrite were explored. The sludge exhibited Anammox activity on day 34, and the system was successfully established on day 67, while the hzo gene expression increased from 1.1 * 104 to 9.4 * 105 copies/mL. The established Anammox system showed good resistance to the high nitrogen shock (200–1000 mg/L), and the relative abundance of Candidatus_Kuenenia notably increased. However, when the total nitrogen in influent reached 1200 mg/L, the nitrogen removal of the Anammox system was suppressed. And Candidatus_Kuenenia abundance significantly decreased while Arenimonas increased. Residual sludge could be adopted for establishing Anammox system, and the system could be used for efficiently treating wastewater with nitrogen lower than 1000 mg/L. The result in the present study has significance to the application of Anammox process and deeply save the economic cost of seed sludge since residual sludge was widely available.

Nitrogen removal characteristics of anammox biofilm and analyses of the dynamic network structure of functional microbes under gradient nitrogen stress

The universal porous gel/vertical fixed bed-anaerobic ammonia oxidation (UPG/VFB-A) is a complex efficient denitrification symbiotic system of microorganisms for leachate. However, the different gradient nitrogen loading lead to dynamic correlation and difference in biofilm formation remain unclear. Therefore, the UPG/VFB-A was operated for 300 days under gradient total nitrogen loading rate (TNLR) conditions, and its biofilm biomass characteristics, bacterial population succession and functional denitrification gene dynamic network were investigated to achieve strong impact resistance and recovery of the reactor for landfill leachate. The results showed that the total nitrogen removal efficiency (TNRE) was 92.4 ± 2.7% and the nitrogen removal (NR) up to 487.0 ± 20.5 mg/L. The system was highly resistant and resilient to high concentrations of FA (11.68 mg/L) and FNA (0.0467 mg/L) with total nitrogen removal rate (TNRR) up to 1.12 kg/m3/d. Candidatus Kuenenia (from 0.09% to 17.2%) with high tolerance to FA and FNA was superior to Candidatus Brocadia (from 9.7% to 4.7%) as the main AnAOB. Meanwhile, the gradient nitrogen had a significant effect on the abundance of genes related to nitrogen conversion, and the relative abundance of typical anammox genes hzs and hdh was highest at a feedwater load of 1.34 kg/m3/d, reaching 20.7% and 16.5%, respectively. This study can provide guidance for anammox treatment of landfill leachate in practical engineering.

Nitrogen removal characteristics of heterotrophic nitrification-aerobic denitrification bacterium Acinetobacter ZQ-A1 and community characteristics analysis of its application in pig farm wastewater.

A heterotrophic nitrifying aerobic denitrifying (HN-AD) strain ZQ-A1 with excellent denitrification performance, identified as Acinetobacter, was isolated from simultaneous nitrification and denitrification (SND) craft. ZQ-A1 was capable of removing NH4+, NO2-, and NO3-; the 21-hour removal rates were 84.84%, 87.13%, and 92.63%. ZQ-A1 has the ability to treat mixed nitrogen sources. In addition, ZQ-A1 can be well applied to actual sewage. According to the analysis of microbial community characteristics, the relative abundance of Acinetobacter in the experimental group increased from 0.06% to 2.38%, which is an important reason for the removal rate of NH4+ exceeding 99% within 30 days. The results of KEGG function prediction showed that with the addition of ZQ-A1, the relative abundance of pathways related to bacterial metabolism, such as tricarboxylic acid cycle metabolism, was higher. The research expanded the thinking of HN-AD bacteria in actual production and laid a foundation for its application in sewage treatment.

Removal of nitrate nitrogen by Pseudomonas JI-2 under strong alkaline conditions: Performance and mechanism

The nitrate nitrogen removal characteristics of Pseudomonas JI-2 under strong alkaline conditions and the composition and functional groups of extracellular polymeric substance were analyzed. Furthermore, nontargeted metabonomics and bioinformatics technology were used to investigate the alkaline tolerance mechanism. JI-2 removed 11.05 mg N/(L·h) of nitrate with the initial pH, carbon to nitrogen ratio and temperature were 11.0, 8 and 25 °C respectively. Even when the pH was maintained at 11.0, JI-2 could still effectively remove nitrate. JI-2 contains a large number of Na+/H+ antiporters, such as Mrp, Mnh (mnhACDEFG) and Pha (phaACDEFG), which can stabilize the intracellular acid–base environment, and SlpA can enable quick adaptation to alkaline conditions. Moreover, JI-2 responds to the strong alkaline environment by secreting more polysaccharides, acidic functional groups and compatible solutes and regulating key metabolic processes such as pantothenate and CoA biosynthesis and carbapenem biosynthesis. Therefore, JI-2 can survive in strong alkaline environments and remove nitrate efficiently.

Nitrogen removal performance and microbial community of a novel combined electrochemical biofilter for treating a mixture of raw sewage and secondary effluent

A nitrogen removal biofilter coupled with electrode plates was established to treat a mixture of raw sewage and secondary effluent. The nitrogen removal characteristics and microbial community of the combined electrochemical biofilter (CEBF) and quartz sand biofilter (QSBF) were investigated. The results showed that when the influent concentrations of NH4+-N, NO3−-N, and COD were 10, 8, and 60 mg/L, respectively, the average NH4+-N removal rate in CEBF (5.03 mg/(L·d)) was higher than that in QSBF (4.28 mg/(L·d)). The carbon source had a greater impact on denitrification performance than the electrochemical system when the influent C/N ratio was 4.28. When the influent C/N ratio was 3.67, specific anammox rates of CEBF and QSBF increased to 2.67 mg/(g·h) and 2.87 mg/(g·h), respectively. Furthermore, the successful construction of the electrochemical system was confirmed by the enrichment of electrochemically active bacteria on the anode plate, including Geobacter (33.73 %) and Desulfuromonas (10.44 %). The relative abundance of denitrifying bacteria (DNB) on the carriers' biofilm was lower in CEBF compared to QSBF. Anammox bacteria (AnAOB) Candidatus_Kuenenia in CEBF (0.06 %) was higher than that in QSBF (0.02 %). This study provided a reference for the application of electrochemical biofilter in nitrogen removal of WWTPs under low C/N.

Nitrogen Removal Characteristics and Metabolism Mechanism of High-Efficiency Cold-Tolerant Heterotrophic Nitrification-Aerobic Denitrification Bacterium Glutamicibacter sp. WS1 for Various Nitrogen Sources at Low Temperature

For resolving the problems of poor nitrogen removal efficiency and substandard effluent quality in wastewater treatment plants during winter, a cold-tolerant strain Glutamicibacter sp. WS1, with heterotrophic nitrification-aerobic denitrification ability, was isolated from activated sludge. The functional genes for nitrogen conversion of strain WS1 were amplified by PCR, and the nitrogen removal characteristics of the strain were verified under different nitrogen sources at 15℃. In addition, the effects of environmental factors on the aerobic denitrification performance of the strain were explored at low temperature. Finally, a reasonable nitrogen metabolism pathway of strain WS1 was resolved based on functional genes and nitrogen balance analysis. The results showed that strain WS1 contained functional genes related to nitrogen conversion, including amoA, napA, nirS, and nirK genes. Notably, nirS and nirK genes coexisted in the strain. At the low temperature of 15℃, with NH4+-N, NO3--N, NO2--N+NO3--N, and NH4+-N+NO3--N as nitrogen sources, the corresponding removal efficiencies of strain WS1 were 100%, 98.10%, 99.87%+100%, and 100%+94.92%, respectively. The optimal denitrification performance of the strain was achieved with sodium citrate as the carbon source, C/N of 16, pH of 8, DO of 4.5-6.8 mg·L-1, and temperature of 30℃. In addition, the NO3--N removal efficiency of strain WS1 reached 92.50% under low temperature (15℃) and low C/N (10) conditions. Based on the results of PCR amplification and nitrogen balance analysis, heterotrophic nitrification-aerobic denitrification/aerobic denitrification and assimilation were the main pathways for nitrogen substrate removal by strain WS1, in which most of the inorganic nitrogen (47%-56%) was converted to gaseous nitrogen through heterotrophic nitrification-aerobic denitrification/aerobic denitrification. Strain WS1 has broad application prospects in the treatment of low-temperature nitrogenous wastewater.

Molecular Characteristics of Catalytic Nitrogen Removal from Coal Tar Pitch over γ-Alumina-Supported NiMo and CoMo Catalysts.

The removal of nitrogen from coal tar pitch (CTP) through the hydrodenitrogenation (HDN) of CTP and its molecular behavior were evaluated in the presence of NiMo/γ-alumina and CoMo/γ-alumina catalysts. Fourier transform ion cyclotron resonance mass spectrometry with atmospheric pressure photoionization was used to analyze the complicated chemical classes and species of CTP and the treated products at the molecular level. Nitrogen species were qualitatively analyzed before and after hydrotreatment. A single-stage hydrotreatment with an HDN catalyst resulted in a high sulfur removal performance (85.6-94.7%) but a low nitrogen removal performance (26.8-29.2%). Based on relative abundance analyses of nitrogen and binary nitrogen species, CcHh-NnSs was the most challenging species to remove during HDN treatment. Furthermore, prior hydrodesulfurization was combined with HDN treatment, and the dual hydrotreatments yielded a significantly improved nitrogen removal performance (46.4-48.7%).

Improving anammox activity and reactor start-up speed by using CO2/NaHCO3 buffer

Anammox bacteria grow slowly and can be affected by large pH fluctuations. Using suitable buffers could make the start-up of anammox reactors easy and rapid. In this study, the effects of three kinds of buffers on the nitrogen removal and growth characteristics of anammox sludge were investigated. Reactors with CO2/NaHCO3 buffer solution (CCBS) performed the best in nitrogen removal, while 4-(2-hydroxyerhyl)piperazine-1-ethanesulfonic acid (HEPES) and phosphate buffer solution (PBS) inhibited the anammox activity. Reactors with 50 mmol/L CCBS could start up in 20 days, showing the specific anammox activity and anammox activity of 1.01±0.10 gN/(gVSS·day) and 0.83±0.06 kgN/(m3·day), respectively. Candidatus Kuenenia was the dominant anammox bacteria, with a relative abundance of 71.8%. Notably, anammox reactors could also start quickly by using 50 mmol/L CCBS under non-strict anaerobic conditions. These findings are meaningful for the quick start-up of engineered anammox reactors and prompt enrichment of anammox bacteria.

Response of granular anammox process under mainstream conditions to continuous and transient organic loads

Even small fluctuations in the amount of organic matter in wastewater significantly affect the structure and function of anammox microbial communities under mainstream conditions with low ammonium concentrations, because a high organic C/N ratio causes heterotrophic denitrifying bacteria to outcompete anammox bacteria. This paper presents a comprehensive investigation of the effects of different levels of continuous and transient organic loads on nitrogen removal and sludge characteristics in upflow granular anammox reactors under mainstream conditions. Continuous organic load at 30 mg chemical oxygen demand (COD)/L influent improved nitrogen removal efficiency without compromising anammox performance. However, exposure to higher levels of continuous organic load (≥60 mg COD/L) caused significant inhibition of anammox activity (complete inhibition at 150 mg COD/L). The performance degradation was accompanied by the destabilization of anammox granular sludge, with a decrease in tightly bound protein and increase in loosely bound polysaccharide contents in the sludge extracellular polymeric substances. Further, DNA sequencing analysis showed that heterotrophic denitrifying Rhodocyclaceae and Pseudomonadaceae bacteria collectively accounted for 36.8–61.3% of the total bacterial reads. These bacteria emerged and outcompeted anammox Ca. Brocadiaceae (accounting for less than 8.4% of the total reads) with increasing organic load, resulting in a significant decrease in anammox activity. Meanwhile, the inhibitory effect of transient organic load (one-day shock loading) was fully reversed within one day at both 150 and 300 mg COD/L shock levels, although the latter caused a sudden fall in anammox performance. The overall results suggest that loading an appropriately low amount of organic matter can provide a means to improve the nitrogen removal performance of anammox granular sludge without sacrificing anammox activity and granule stability under mainstream conditions.

Comparision of nitrogen removal characteristic and microbial community in freshwater and marine recirculating aquaculture systems

Recirculating aquaculture system (RAS) has a good prospect in aquaculture, but its nitrogen removal characteristics and microbial community changes in freshwater and marine water remain unclear. In this study, six RAS were designed and divided into freshwater group and marine water group with salinity of 0‰ and 32‰, respectively, and operated for 54 days to test changes in nitrogen (NH4+-N, NO2--N, NO3--N), extracellular polymeric substances and microbial communities. The results showed that ammonia nitrogen was rapidly reduced and almost converted to nitrate nitrogen in the freshwater RAS but to nitrite nitrogen in marine RAS. Compared with freshwater RAS, marine RAS had lower tightly bound extracellular polymeric substances and worse stability and settleability condition. 16S rRNA amplicon sequencing reflected significantly lower bacterial diversity and richness in marine RAS. Microbial community structure at phylum level showed lower relative abundance of Proteobacteria, Actinobacteria, Firmicutes, Nitrospirae, but higher abundance of Bacteroidetes under a salinity of 32‰. High salinity decreased the abundance of funtional genera (Nitrosospira, Nitrospira, Pseudomonas, Rhodococcus, Comamonas, Acidovorax, f_Comamonadaceae), which may account for nitrite accumulation and low nitrogen removal capacity in marine RAS. These findings could provide theoretical and practical basis for improving the start-up speed of high-salinity nitrification biofilm.

Gel-immobilized partial nitritation/anammox achieves reliable nitrogen removal at different concentrations of nitrogen and reactivation processes

A two-stage partial nitritation/anammox process based on microbial encapsulation (PN/A-E) was established. The nitrogen removal characteristics of PN/A-E under high and low ammonia nitrogen and after reactivation following a long-term shutdown were comprehensively investigated and compared with anammox granular sludge (AnGS). The stable PN process did not depend on high ammonia nitrogen, and the nitrite accumulation rate reached 95.2 ± 0.7 %. The overall nitrogen removal rate of encapsulated anammox bacteria was twice that of the AnGS, and it was more tolerant to external interference. Moreover, PN/A-E showed good reactivation performance, and the total nitrogen in the effluent was 10.0 ± 1.4 mg·L-1 when the final hydraulic retention time was 2.18 h. The immobilized fillers support an increase in ammonia-oxidizing bacteria under restricted conditions and were more conducive to the dominance of functional bacteria and the stability of microbial community under low ammonia nitrogen. This study provides a positive method to achieve a reliable PN/A.

Nitrogen Removal Characteristics of a Marine Denitrifying Pseudomonas stutzeri BBW831 and a Simplified Strategy for Improving the Denitrification Performance Under Stressful Conditions.

A marine aerobic denitrifying bacterium was isolated and identified as Pseudomonas stutzeri BBW831 from the seabed silt of Beibu Gulf in China. According to the genome analysis, P. stutzeri BBW831 possessed a total of 14 genes (narG, narH, narI, narJ, napA, napB, nirB, nirD, nirS, norB, norC, norD, norQ, and nosZ) responsible for fully functional enzymes (nitrate reductase, nitrite reductase, nitric oxide reductase, and nitrous oxide reductase) involved in the complete aerobic denitrification pathway, suggesting that it had the potential for reducing nitrate to the final N2. Denitrification results showed that P. stutzeri BBW831 exhibited efficient nitrogen removal characteristics. Within 12h, the NO3--N removal efficiency and rate reached 94.64% and 13.09mg·L-1·h-1 under 166.10 ± 3.75mg/L NO3--N as the sole nitrogen source, and removal efficiency of the mixed nitrogen (50.50 ± 0.55, 62.28 ± 0.74, and 64.26 ± 0.90mg/L of initial NH4+-N, NO3--N, and NO2--N, respectively) was nearly 100%. Furthermore, a simplified strategy, by augmenting the inoculation biomass, was developed for promoting the nitrogen removal performance under high levels of NO2--N and salinity. As a result, the removal efficiency of the initial NO2--N up to approximately 130mg/L reached 99.46% within 8h, and the NO3--N removal efficiency achieved at 59.46% under the NaCl concentration even up to 50g/L. The C/N ratio of 10 with organic acid salt such as trisodium citrate and sodium acetate as the carbon source was most conducive for cell growth and nitrogen removal by P. stutzeri BBW831, respectively. In conclusion, the marine P. stutzeri BBW831 contained the functional genes responsible for a complete aerobic denitrification pathway (NO3--N → NO2--N → NO → N2O → N2), and had great potential for the practical treatment of high-salinity nitrogenous mariculture wastewater.