Deciphering the microbial community and functional genes response of anammox sludge to sulfide stress

Groundwater flow regime shapes nitrogen functional traits by affecting microbial community assembly processes in the subsurface

The complex nitrogen (N) cycle in groundwater systems is affected by both biological and environmental factors. The interactions between hydrogeological conditions and the microbial community assembly processes that impact N-cycling processes remain poorly understood. We explored the assembly patterns of N-cycling microbial communities along the groundwater flow path. The environmental heterogeneity in different hydrological phases increased along the flow path (mean Ed: 0.16-0.49), accompanied by different microbial community assembly patterns. The assembly patterns that engaged in dissimilatory nitrate reduction to ammonium (DNRA) and denitrification changed across the water-sediment phases. Nitrifying microorganisms in the discharge area were mainly influenced by heterogeneous selection (41-69 %), and were closely correlated with dissolved oxygen (DO) concentrations. Homogeneity along flow-through increased stochastic assemblies, such as downstream drift of anammox bacterial (AnAOB) communities. Thus, the N removal pathway changed from "nitrification-denitrification" in the recharge area to "partial nitrification-anammox" in the discharge area. The increasing environmental heterogeneity brought more deterministic assembly patterns of N-cycling communities, linked to higher community turnover along the groundwater flow path. This study indicated that groundwater flow regime determined microbial community assembly patterns, providing valuable insight into the response of N transitions to environmental variations in groundwater systems.

Advanced nitrogen removal of sulfur-driven autotrophic denitrification from landfill leachate after partial nitrification and denitrification pretreatment

Sulfur-driven autotrophic denitrification (S0dAD) was employed to remove residual nitrogen from the biological effluent of landfill leachate after partial nitrification and denitrification pretreatment. The performance of S0dAD were assessed with various NOx--N (NO2--N and NO3--N) loadings over a 185-day operational period. The results demonstrated that a notable NOx--N removal efficiency of 97.8 ± 2.0% was achieved under nitrogen removal rates of 0.12 ± 0.02 kg N/(m3· d), leading to total nitrogen concentrations of 8.6 ± 3.8 mg/L in the effluent. Batch experiments revealed competitive utilization of nitrogenous electron acceptors, with NO2--N demonstrating 2-4 times higher denitrification rates than NO3--N under coexistence conditions. Genus-level microbial community identified that Thiobacillus and Sulfurovum was highly enriched with as key denitrifying bacteria in the S0dAD system. These findings provide insights for advanced nitrogen removal coupling S0dAD with partial nitrification and denitrification process for landfill leachate treatment.

Enhancement of hydrazine accumulation in anammox bioreactors

The role of hydrazine (N2H4) in anammox metabolism has been widely studied; however, studies on N2H4 biosynthesis by anammox bacteria are limited in the literature. In this context, the current research aims to investigate the enhancement of biological N2H4 production in the anammox process in a long-term manner. The experimental studies started with the optimization of the operating conditions to achieve maximum N2H4 accumulation. Under favorable conditions (pH = 8.97 ± 0.08; T = 35.5 ± 0.5 °C; initial hydroxylamine dose = 1.46 ± 0.01 mM), 17.16 ± 0.64 mg L-1 of N2H4 accumulated in the batch systems. The continuity of N2H4 bioproduction was then evaluated by long-term observations. A continuous flow bioreactor was operated in four consecutive manipulated periods under optimized conditions. In the long-term operated bioreactor, 55.10 ± 0.30 mg L-1 N2H4 was accumulated at optimal conditions, which was 2.5 times higher than reported in the literature. Although manipulation of the bioreactor operating conditions initially resulted in a significant increase in N2H4 bioaccumulation, it subsequently caused a severe deterioration in anammox activity. However, this could be mitigated by increasing the biomass concentration in the anammox systems. In addition, the relative abundance of Candidatus Kuenenia decreased by 1.88% throughout the long-term operation.

Sulfur-carbon loop enhanced efficient nitrogen removal mechanism from iron sulfide-mediated mixotrophic partial denitrification/anammox systems

This study successfully established Iron Sulfide-Mediated mixotrophic Partial Denitrification/Anammox system, achieving nitrogen and phosphorus removal efficiency of 97.26% and 78.12%, respectively, with COD/NO3--N of 1.00. Isotopic experiments and X-ray Photoelectron Spectroscopy analysis confirmed that iron sulfide enhanced autotrophic Partial Denitrification performance. Meanwhile, various sulfur valence states functioned as electron buffers, reinforcing nitrogen and sulfur cycles. Microbial community analysis indicated reduced heterotrophic denitrifiers (OLB8, OLB13) under lower COD/NO3--N, creating more niche space for autotrophic bacteria and other heterotrophic denitrifiers. The prediction of functional genes illustrated that iron Sulfide upregulated genes related to carbon metabolism, denitrification, anammox and sulfur oxidation-reduction, facilitating the establishment of carbon-nitrogen-sulfur cycle. Furthermore, this cycle primarily produced electrons via nicotinamide adenine dinucleotide and sulfur oxidation-reduction processes, subsequently utilized within the electron transfer chain. In summary, the Partial Denitrification/Anammox system under the influence of iron sulfide achieved effient nitrogen removal by expediting electron transfer through the carbon-nitrogen-sulfur cycle.

Impact of organic carbon on sulfide-driven autotrophic denitrification: Insights from isotope fractionation and functional genes

Additional organics are generally supplemented in the sulfide-driven autotrophic denitrification system to accelerate the denitrification rate and reduce sulfate production. In this study, different concentrations of sodium acetate (NaAc) were added to the sulfide-driven autotrophic denitrification reactor, and the S0 accumulation increased from 7.8% to 100% over a 120-day operation period. Batch experiments revealed a threefold increase in total nitrogen (TN) removal rate at an Ac--C/N ratio of 2.8 compared to a ratio of 0.5. Addition of organic carbon accelerated denitrification rate and nitrite consumption, which shortened the emission time of N2O, but increased the N2O production rate. The lowest N2O emissions were achieved at the Ac--C/N ratio of 1.3. Stable isotope fractionation is a powerful tool for evaluating different reaction pathways, with the 18ε/15ε values in nitrate reduction ranging from 0.5 to 1.0. This study further confirmed that isotope fractionation can reveal denitrifying nutrient types, with the 18ε (isotopic enrichment factor of oxygen)/15ε (isotopic enrichment factor of nitrogen) value approaching 1.0 for autotrophic denitrification and 0.5 for heterotrophic denitrification. Additionally, the 18ε/15ε values can indicate changes in nitrate reductase. There is a positive correlation between the 18ε/15ε values and the abundance of the functional gene napA, and a negative correlation with the abundance of the gene narG. Moreover, 18ε and 15ε were associated with changes in kinetic parameters during nitrate reduction. In summary, the combination of functional gene analysis and isotope fractionation effectively revealed the complexities of mixotrophic denitrification systems, providing insights for optimizing denitrification processes.

Effect of sulfide on the nitrogen removal performance and microbial community of low-substrate Anammox process

Anammox is one of the most innovative nitrogen removal technologies, while its functional bacteria-anaerobic ammonia-oxidizing bacteria (AAOB) is sensitive to the impurities in the wastewater. In this study, the long-term effects of sulfide at different concentrations (0, 5, 10, 20, 30, 50, 25 mg L-1) on low substrate Anammox process were studied. The results showed that when the sulfide was 25-30 mg L-1, AAOB was well coupled with sulfide-denitrifying bacteria and the total nitrogen removal efficiency (TNRE) reached a maximum of 91.0%. The hydroxylamine oxidoreductase activity and Heme-c reached 1.678 EU g-1 SS and 0.0023 mmol g-1 SS, respectively, with the hzo and nosZ gene concentrations as 2.52 × 108 and 4.45 × 107 copies mL-1. 50 mg L-1 sulfide inhibited the nitrogen removal by AAOB, resulting in the TNRE decreasing to 81.7%. The experimental results provide a reference for the practical application of Anammox in treating sulfur-containing wastewater.

Metabolic Profiles and Microbial Synergy Mechanism of Anammox Biomass Enrichment and Membrane Fouling Alleviation in the Anammox Dynamic Membrane Bioreactor

The anammox dynamic membrane bioreactor (DMBR) is promising in applications with enhanced anammox biomass enrichment and fouling alleviation. However, the metabolic mechanism underlying the functional features of anammox sludge and the biofilm membrane is still obscure. We investigated the metabolic networks of anammox sludge and membrane biofilm in the DMBR. The cooperation between anammox and dissimilatory nitrate reduction to ammonium processes favored the robust anammox process in the DMBR. The rapid bacterial growth occurred in the DMBR sludge with 1.33 times higher biomass yield compared to the MBR sludge, linked to the higher activities of lipid metabolism, nucleotide metabolism, and B vitamin-related metabolism of the DMBR sludge. The metabolism of the DMBR biofilm microbial community benefited the fouling alleviation that the abundant fermentative bacteria and their cooperation with the anammox sludge microbial community promoted organics degradation. The intensified degradation of foulants by the DMBR biofilm community was further evidenced by the active carbohydrate metabolism and the upregulated vitamin B intermediates in the biofilms of the DMBR. Our findings provide insights into key metabolic mechanisms for enhanced biomass enrichment and fouling control of the anammox DMBR, guiding manipulations and applications for overcoming anammox biomass loss in the treatment of wastewater under detrimental environmental conditions.

Combination of sulfide-driven partial denitrification with anammox enhanced by zeolite powder for autotrophic nitrogen and sulfide removal from wastewater

Sulfide-driven partial denitrification and anaerobic ammonia oxidizing (anammox) (SPDA) is a high-efficiency technology to achieve simultaneous nitrogen and sulfide removal. Nitrite accumulation from sulfide-driven partial denitrification is the key to achieve SPDA. Zeolite powder was added to strengthen the competition of anammox bacteria against nitrite. The nitrogen removal rate (NRR) and partial denitrification efficiency in reactor was 5.18 kg-N m-3d-1 and 92.3% during 180 days of operation, higher than those without zeolite powder, indicating an improving contribution of zeolite powder. Metabolomics analysis revealed zeolite powder addition enhanced the metabolisms of amino acids, nicotinate and porphyrin through increasing glutamate content, and improved EPS secretion, heme c content and particle size. Besides, high ammonia enriched by zeolite powder was conducive to improve anammox activity and NRR. This study provides the metabolic insights into the mechanism of zeolite powder enhancing SPDA, which is meaningful towards overcoming the limitations in practical application of SDPA.

Response of nitrite accumulation, sludge characteristic and microbial transition to carbon source during the partial denitrification (PD) process

Partial denitrification (PD, nitrate (NO3--N) → nitrite (NO2--N)) as a novel pathway for NO2--N production has been widely concerned, but the specific conditions for highly efficient and stable nitrite maintenance are not yet fully understood. In this study, the effects of carbon sources (acetate, R1; propionate, R2; glucose, R3) on NO2--N accumulation was discussed without seeding PD sludge and the mechanism analysis related to sludge characteristic and microbial evolution were elucidated. The optimal NO2--N, nitrate-to-nitrite transformation ratio (NTR) and nitrite removal efficiency (NRE) reached up to 32.10 mg/L, 98.01 %, and 86.95 % in R1. However, due to the complex metabolic pathway of glucose, the peak time of NO2--N production delayed from 30 min to 60 min. The sludge particle size decreased from 154.2 μm (R1), 130.8 μm (R2) to 112.6 μm (R3) with the increasing extracellular polymeric substances (EPS) from 80.75-85.44 mg/gVSS, 82.68-92.75 mg/gVSS to 106.31-110.25 mg/gVSS, where the ratio of proteins/polysaccharides (PN/PS) was proved to be closely associated with NO2--N generation. For the microbial evolution, Saccharimonadales (70.42 %) dominated the glucose system, while Bacillus (7.42-21.63 %) and Terrimonas (4.24-5.71 %) were the main contributors for NO2--N accumulation in the acetate and propionate systems. The achievement of PD showed many advantages of lower carbon demand, minimal sludge production, lesser greenhouse gas emission and prominent nutrient removal, offering an economically and technically attractive alternative for NO3--N containing wastewater treatment.

Implemented impediment of extracellular electron transfer-dependent anammox process :Unstable nitrogen removal efficiency and decreased abundance of anammox bacteria

The present study investigates the extracellular electron transfer (EET)-dependent anammox process as a promising approach for sustainable wastewater treatment. The study examines the performance and metabolic pathway of the EET-dependent anammox process in comparison to the nitrite-dependent anammox process. The EET-dependent reactor successfully achieved nitrogen removal with a maximum removal efficiency of 93.2%, although it exhibited a lower ability to sustain high nitrogen removal load when compared to the nitrite-dependent anammox process, which poses opportunity and challenge for ammonia-wastewater treatment under applied voltage conditions. Nitrite was identified as a critical factor responsible for the changes in microbial community structure, resulting in a significant reduction in nitrogen removal load in the absence of nitrite. The study further suggests that the Candidatus Kuenenia species could dominate the EET-dependent anammox process, while nitrifying and denitrifying bacteria also contribute to the nitrogen removal in this system.

Sulfate-reducing ammonium oxidation: A promising novel process for nitrogen and sulfur removal

Sulfate-reducing ammonium oxidation (sulfammox), a novel and promising process that has emerged in recent years, is essential to nitrogen and sulfur cycles and offers significant potential for the elimination of ammonium and sulfate. This review discussed the development of sulfammox process, the mechanism, characteristics of microbes, potential influencing factors, applicable bioreactors, and proposed the research needs and future perspective. The sulfammox process could be affected by many factors, such as the NH4+/SO42- ratio, carbon source, pH, and temperature. However, these potential influencing factors were only obtained based on what has been seen in papers studying related processes such as denitrification, sulfate-reduction, etc., and have to be further tested in bioreactors carrying out the sulfammox process in the future. Currently, sulfammox is predominantly used in granular activated carbon anaerobic fluidized beds, up-flow anaerobic sludge blanket reactors, anaerobic expanded granular bed reactors, rotating biological contact reactors, and moving bed biofilm reactors. In the future, the operating parameters of sulfammox should be further optimized to improve the processing performance, and the system can be further scaled up for actual wastewater treatment. In addition, the isolation, identification, and characterization of key functional microbes and the analysis of microbial interrelationships will also be focused on in future studies to enable an in-depth analysis of the sulfammox mechanism.

The rapid start-up of CANON process through adding partial nitration sludge to ANAMMOX system

This study aimed to start up the completely autotrophic nitrogen removal over nitrite (CANON) process after adding partial nitration (PN) sludge to the ANAMMOX reactor, so as to help the rapid start-up and stable operation of the CANON process in practical engineering applications. There were three steps in the research: cultivating the PN sludge, building a reliable ANAMMMOX system, and finally starting and running the CANON process. The PN sludge was successfully cultivated in less than 45 days with around 90% nitrite accumulation rate. The ANAMMOX reactor enriched a significant quantity of red granular sludge within 70 days, achieving the maximum nitrogen removal rate of 1.74 kg/(m³·d). Eventually, the CANON reactor was started up successfully, which achieved 95.08% of average ammonium removal efficiency and 84.51% of average total nitrogen removal efficiency in 60 days. The residual recalcitrant nitrite-oxidizing bacteria in the CANON process was successfully inhibited by intermittent aeration and 12 mg/L free ammonia in UASB reactor. Besides, Candidatus Kuenenia, Candidatus Brocadia and Nitrosomonas were the main functional microorganisms involved in the CANON process.

Performance changes in the anammox process under the stress of rare-earth element Ce(III) and the evolution of microbial community and functional genes

The high Ce(III) content in ionic rare-earth tailings wastewater has hindered the application of anammox process in this field. Here, the effect of Ce(III) on the performance of anammox processes was investigated, and the evolution of microbial communities and functional genes was explored using metagenomic sequencing. The results showed that the reactor nitrogen removal rate decreased when the Ce(III) concentration reached 25 mg/L, although ammonia nitrogen removal (92.31%) and nitrogen removal efficiency (81.33%) remained at a high level; however, both showed a significant decreasing trend. The relative abundance of anammox bacteria increased continuously from P1-P5, reaching 48.81%, whereas the relative abundance of Candidatus jettenia reached 33.71% at P5, which surpassed that of Candidatus brocadia as the most abundant anammox bacteria, and further analysis of functional genes and metabolic pathways revealed that Candidatus brocadia was richer in biochemical metabolic genes, whereas Candidatus jettenia had richer efflux genes.

Insights into the reaction of anammox to exogenous pyridine: Long-term performance and micro mechanisms

Some industrial wastewaters contain high amounts of toxic nitrogen-containing heterocyclic compounds, which may inhibit the efficiency of biological treatment. This work systematically investigated how exogenous pyridine affected the anaerobic ammonia oxidation (anammox) system and discussed the microscopic response mechanisms based on genes and enzymes. The anammox efficiency was not seriously inhibited by pyridine less than 50 mg/L. Bacteria secreted more extracellular polymeric substances to resist pyridine stress. After 6 days stress with 80 mg/L pyridine, the nitrogen removal rate of anammox system lost 47.7%. Long-term stress of pyridine reduced anammox bacteria by 7.26% and the expression of functional genes by 45%. Pyridine could actively bind to hydrazine synthase and ammonium transporter. This work fills a research gap in the ongoing threat of pyridines to anammox, and has guiding value for the application of anammox process in the treatment of ammonia-rich wastewater containing pyridine.

Deciphering the role of granular activated carbon (GAC) in anammox: Effects on microbial succession and communication

Anaerobic ammonium oxidation (anammox) offered an energy-efficient option for nitrogen removal from wastewater. Granular activated carbon (GAC) addition has been reported that improved biomass immobilization, but the role of GAC in anammox reactors has not been sufficiently revealed. In this study, it was observed that GAC addition in an upflow anaerobic sludge blanket (UASB) reactor led to the significantly shortened anammox enrichment time (shortened by 45 days) than the reactor without GAC addition. The nitrogen removal rate was 0.83 kg N/m³/day versus 0.76 kg N/m³/day in GAC and non-GAC reactors, respectively after 255 days' operation. Acyl-homoserine lactone (AHL) quorum sensing signal molecule C8-HSL had comparable concentrations in both anammox reactors, whereas the signal molecule C12-HSL was more pervasive in the reactor containing GAC than the reactor without GAC. Microbial analysis revealed distinct anammox development in both reactors, with Candidatus Brocadia predominant in the reactor that did not contain GAC, and Candidatus Kuenenia predominant in the reactor that contained GAC. Denitrification bacteria likely supported anammox metabolism in both reactors. The analyses of microbial functions suggested that AHL-dependent quorum sensing was enhanced with the addition of GAC, and that GAC possibly augmented the extracellular electron transfer (EET)-dependent anammox reaction.

Starting-up performances and microbial community shifts in the coupling process (SAPD-A) with sulfide autotrophic partial denitrification (SAPD) and anammox treating nitrate and ammonium contained wastewater

A novel coupling process (SAPD-A) with sulfide autotrophic partial denitrification (SAPD) (NO₃^--N→NO₂^--N) and anaerobic ammonium oxidation (Anammox) was developed using anaerobic sequencing batch reactor (ASBR) in this work. The integrated process comprised two stages. Firstly, the starting-up of SAPD process succeeded by gradually increasing the influent nitrate and sulfide in 95 days. The average nitrate removal efficiency (NRE) and NO₂^--N accumulation rates were 71.24% ± 0.21% and 46.44% ± 0.53% at SAPD process (days 75-95). Then, successful coupling process (SAPD-A) was implemented in two stages (stage I and stage II of SAPD-A). In stage I, it is feasible to promote the successful construction of SAPD-A process by elevating influent ammonium only based on SAPD system, making the NRE increased from 44.45% ± 0.46% (day 95) to 64.62% ± 0.12% at the end of stage I in SAPD-A system (day 126). Meanwhile, the ammonium nitrogen removal efficiency (ARE) and total nitrogen removal efficiency (TN-RE) also rose up to 42.46% ± 2.02% and 63.28% ± 0.54% respectively. Furthermore, the average ARE, NRE and TN-RE during the stage II in the bioreactor could reach 65.17% ± 1.45%, 74.50% ± 0.81% and 77.81% ± 0.37% by loading some biofilters (with of approximate 10% of the volume of the bioreactor) attached anaerobic ammonium oxidation bacteria (AnAOB). High-throughput sequencing results showed that the dominant genera concerning nitrogen removal were norank_f_norank_o_Fimbriimonadates (with the abundance of 2.88-8.54%), norank_ o_ norank _ c_ OM190 (2.48-4.41%), norank_f_norank_o_norank_c_WWE3 (11.01-17.69%), subgroup_10 (1.97-3.81%), Limnobacter（2.17-3.49%）, norank_f_n orank_ o_norank_ c_OLB14 (2.03-5.23%), norank-f-PHOS-HE36 (2.18-5.5%), Ellin6067 (1.34-2.24%) and Candidatus_ Brocadia (1.95-2.42%) during the whole starting-up period of coupling SAPD-A process. Batch experiments revealed that the sulfide was fully oxidized within 2 h, with the maximum reaction rate of 38.30 ± 1.53 mg (L h)^-1 in the first 1 h. Simultaneously, the concentration of nitrate sharply decreased from 53.08 ± 0.23 mg L^-1 to 24.16 ± 0.42 mg L^-1 with the reaction rate of 66.41 ± 2.12 mg (L h)^-1 in 0.5 h. Also, the ammonium concentration significantly declined from 47.88 ± 0.34 mg L^-1 to 10.98 ± 0.39 mg L^-1 in 8 h. Anammox process was responsible for the dominant nitrogen removal in the coupling SAPD-A system.

Metabolomics uncovers adaptation discrepancy among anammox granular sludge with different granule size: Metabolic pathway regulation by consortia cooperation

The relationship between granular size and anaerobic ammonium oxidation (anammox) performance in the anammox granular sludge (AnGS) system has been extensively observed. However, the metabolic pathways regulated by communication and cross-feedings among anammox consortia remain unclear. The reactor operation and metabolomics analyses were combined to explore the influence of microbiota cooperation on metabolic pathways and granule properties under low temperature (18 °C) and nitrite inhibition. Anammox activity was sustained under challenging circumstances by active quorum sensing among anammox consortia in AnGS with diameters larger than 1.4 mm, which promoted nucleotide metabolism. Cross-feedings among anammox consortia increased the levels of molybdopterin cofactor and folate meanwhile decreasing the cost of carbon fixation metabolism, which supported anabolism and maintained the content of heme c and extracellular polymeric substance. These metabolic insights into the AnGS system provide a new view for anammox process overcoming the low temperature and nitrite stress.

Role of quorum sensing-based regulation in development of anaerobic ammonium oxidation process

Shortage of anaerobic ammonium oxidation (anammox) sludge greatly limits the extensive full-scale application of anammox-based processes. Although numerous start-up strategies have been proposed, the interaction among microbial consortia and corresponding mechanism during the process development remain unknown. In this study, three reactors were established based on different seed sludges. After 27 days, the anammox process inoculated with anammox granules and activated sludge (1:5) was firstly achieved, and the highest nitrogen removal rate was 1.17 kg N m^-3 d^-1. Correspondingly, the anammox activity and abundances of related functional genes increased. Notably, the dominant anammox bacteria shifted from Candidatus Kuenenia to Candidatus Brocadia. Metagenomic analysis indicated that quorum sensing-based regulation mainly contributed to the proliferation and accumulation of anammox bacteria. This work provides an insight into the quorum sensing (QS)-regulated microbial interactions in the anammox and activated sludge consortia during the process development.

Microbial dynamics reveal the adaptation strategies of ecological niche in distinct anammox consortia under mainstream conditions

The feasibility of anammox-based processes for nitrogen-contained wastewater treatment has been verified with different anammox bacteria, however, the ecological niche of anammox bacteria under mainstream conditions is still elusive. In this study, six sludge samples collected from different habitats were utilized to culture anammox bacteria under mainstream conditions, and two distinct anammox genera (Ca. Kuenenia and Ca. Brocadia) with a relative abundance of 6.31% (C1) and 3.09% (C3), respectively, were identified. Notably, the microbial dynamics revealed that anammox bacteria (AMX), ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB), Chloroflexi bacteria (CFX), and heterotrophic denitrification bacteria (HDB) were the core members in anammox consortia. However, Ca. Kuenenia and Ca. Brocadia occupied different ecological niches in anammox consortia. The dissolved oxygen and microbial structures of the anammox-continuous stirred tank reactor systems were the main factors to affect their niche differentiation. Meanwhile, comammox might exist in the systems and occupy the ecological niche of AOB in nitrogen cycling. The network analysis suggested that Ignavibacterium could be the associated bacteria in Ca. Kuenenia-dominated consortia, while Ca. Nitrotoga was that in the Ca. Brocadia-dominated consortia. Our findings reveal a valuable reference for the observation of distinct anammox genera under mainstream conditions, which provides theoretical guidance for the engineering application of mainstream anammox-based processes.

Small biochar addition enhanced anammox granular sludge system for practical wastewater treatment: Performance and microbial community

Anaerobic ammonium oxidation (Anammox) granular sludge (AnGS) has poor strength and is prone to disintegration under complex environmental conditions, especially in the presence of complex organic carbon, which renders the Anammox process instable. Herein, with a mixture of landfill leachate and domestic sewage as wastewater, the effect on the properties of AnGS with two small particle size (0.1-0.2 mm) biochars (coconut and peach biochars) addition were investigated at different COD concentrations (150 mg·L^-1, 200 mg·L^-1, and 250 mg·L^-1), as well as at different BOD/TN (B/N) (0.3 and 0.5). Results showed that the nitrogen removal efficiencies decreased from 89 % to 72 % as the COD concentration increased by 100 mg·L^-1, while peach biochar reactor had better nitrogen removal performance. Excessive organic carbon supply inhibits AnAOB proliferation and B/N had the most significant effect on AnAOB (p < 0.05). The Polymerase Chain Reaction (PCR) indicated peach biochar reactor get higher activity of anammox-related functional genes (hzsA, hdh).

Nitrite accumulation, denitrification kinetic and microbial evolution in the partial denitrification process: The combined effects of carbon source and nitrate concentration

The combined effects of carbon source (HAc, HPr, Glu, Glu + HAc) and nitrate concentration (40, 80 mg/L labeling as R₄₀, R₈₀) on partial denitrification (PD) were discussed at C/N ratio of 2.5 (COD = 100, 200 mg/L). The optimal NO₂^--N and NTR reached to 67.03 mg/L, 99.14% in HAc-R₈₀ system, and denitrification kinetics revealed the same conclusion, corresponding to higher COD utilization rate (CUR: 58.46 mgCOD/(gVSS·h)), nitrate reduction rate (N_aRR: 29.94 mgN/(gVSS·h)) and nitrite accumulation rate (N_iAR: 29.68 mgN/(gVSS·h)). The preference order was HAc > HPr > Glu + HAc > Glu in both R₄₀ and R₈₀ systems due to different metabolic pathways, however, the NO₂^--N accumulation and kinetic parameters of R₈₀ group were dramatically higher than those in R₄₀ for the same carbon source. The R₈₀ group facilitated more concentrated biodiversity (607-808 OTUs) with Terrimonas and norank_f_Saprospiraceae responsible for high NO₂^--N accumulation in HAc and HPr served systems, while norank_f_norank_o_Saccharimonadales and OLB13 dominated the Glu containing systems.

Insight into the role of biogenic manganese oxides-assisted gravity-driven membrane filtration systems toward emerging contaminants removal

Effective water purification technologies are required to remove emerging contaminants (ECs) and prevent their extensive occurrence in rural areas. In this work, coupling gravity-driven membrane (GDM) filtration with biogenic manganese oxides (BioMnOx) in the biofouling layer was utilized for treating water containing SMX. Comparisons between BioMnOx-GDM (with BioMnOx) and Control-GDM (without BioMnOx) indicated that BioMnOx could significantly promote the removal of DOC, NH₄⁺-N, and fluorescent pollutants due to its strong oxidating capacity and high biological activity. The formation of BioMnOx increased the abundance of SMX-degrading bacteria, enriched the metabolic pathway and mineralization rate of SMX, and effectively promoted the remove of SMX. More importantly, BioMnOx facilitated the removal of antibiotic resistance genes (ARGs) in the GDM, because it increased the link between microorganisms and reduced the concentration of SMX, thus reduced the expression of ARGs. LB-EPS played an important role in the membrane fouling. Compared with the Control-GDM, the concentration of LB-EPS in BioMnOx-GDM decreased, which was beneficial to alleviate membrane fouling. Although a thicker biofouling layer (1774.88 μm vs.775.54 μm) was formed in BioMnOx-GDM, the biofilm with higher porosity (64.93% vs. 41.24%) had a more positive effect on the flux. Overall, BioMnOx could improve the pollutant removal and stable flux level of the GDM system. BioMnOx-GDM effectively avoided the risks brought by ECs and ensured water safety in rural areas.

Toward emerging contaminants removal using acclimated activated sludge in the gravity-driven membrane filtration system

The occurrence of emerging contaminants is attracting widespread attention due to its potential threat to aquatic organisms and public health. Gravity-driven membrane (GDM) filtration can effectively eliminate water contamination with pathogenic microorganisms in rural areas while being challenged by various micro-pollutants (MPs). This study investigated the removal and transformation of sulfamethoxazole (SMX) in GDM for the first time, and pre-adding acclimated activated sludge was proposed to improve the removal of MPs. More rapid and higher SMX degradation was observed with pre-adding domestication sludge, and the system had better tolerance to SMX shocks. Besides, in the presence of domesticated sludge, more SMX metabolic pathways and better mineralization rates were obtained, which was related to more SMX-resistant bacteria and easier biodegradable carbon sources in the system. Pre-adding sludge also increased the richness and diversity of bacterial community, which provided higher removal efficiencies of conventional pollutants. Thus, the removal rates of DOC (14.7%), NH₄⁺-N (5.6%) and fluorescent substances were obviously improved compared with the control group. In this study, the crisis of MPs was tackled and the removal of conventional pollutants was enhanced by pre-adding domesticated sludge in GDM, which ensured the water quality in rural areas.

The effects of magnetite on anammox performance: Phenomena to mechanisms

Low temperature is adverse to anaerobic ammonium oxidation (anammox) reaction while proper Fe addition can enhance anammox performance. Therefore, batch assays were conducted to investigate the potential effects of magnetite (100 μm, 20 μm and 200 nm) on anammox performance which were achieved from the reactor operated at 10-25 °C. After 3 runs, the results indicated that nano-scale magnetite improved the nitrogen elimination significantly. The specific anammox activity (SAA) of the group with nano-magnetite amendments was greater than the other groups after 3 runs (13.5, 12.9, 14.3, 15.4 and 15.7 mgTN/(gVSS·h)), reaching 18.0 mgTN/(gVSS·h). The distribution of magnetite in the granules were then analyzed using X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). The results indicated that nano-magnetite was more feasible to attached to the surface of the granules which might accelerate the release of Fe(II) or Fe(III) to enhance anammox performance.

Operational mode affects the role of organic matter in granular anammox process

In the presence of organic matter, the granular anammox system under sequencing batch mode showed more robust anammox performance than that under completely mixed mode, which was attributed to the better biomass retention with high settling ability and stability of granular sludge. Based on the specific anammox activity test, stratified and mixed distribution of heterotrophic bacteria was found under completely mixed and sequencing batch mode, respectively. The stratified microbial distribution resulted in low enzyme activity of anammox bacteria and sludge disintegration by hindering substrate transfer with a large accumulation of EPS on the granular surface. Whereas the heterotrophic bacteria mixed in granules (mixed microbial distribution) act as a "skeleton", which increased the particle size, density, and stability of granular sludge. Compared with biokinetic-based selection, diffusion-based selection with high substrate penetration depth more likely resulted in the mixed granular structure and strong resistance to organic inhibition under sequencing batch mode.

Comparison of the dynamic responses of different anammox granules to copper nanoparticle stress: Antibiotic exposure history made a difference

Two types of anaerobic ammonium oxidation (anammox) seed sludge were selected to evaluate their responses to copper nanoparticles (CuNPs) exposure. Antibiotic-exposed anammox granules (R₁) were more likely to be inhibited by 5.0 mg L^-1 CuNPs than the normal anammox granules (C₁). The nitrogen removal efficiency (NRE) of C₁ decreased by 9.00% after two weeks of exposure to CuNPs, whereas that of R₁ decreased by 20.32%. Simultaneously, the abundance of Candidatus. Kuenenia decreased by 27.65% and 36.02% in C₁ and R₁ under CuNPs stress conditions, respectively. Generally, R₁ was more susceptible to CuNPs than C₁. The correlation analysis indicated that the horizontal transfer of antibiotic resistance genes and copA triggered by intI1 facilitated the generation of multiresistance in the anammox process. Moreover, the potential multiresistance mechanism of anammox bacteria was hypothesized based on previous results. The results will generate new ideas for the treatment of complex wastewater using the anammox process.

Alleviating the nitrite stress on anaerobic ammonium oxidation by pyrolytic biochar

The nitrite (NO₂^-) inhibition in anaerobic ammonium oxidation (anammox) process is widely reported. Here, the effects of three pyrolytic biochars (CS300, CS550 and CS800) were investigated to alleviate NO₂^- stress on anammox process under exposure of varied NO₂^--N concentrations (70, 200, 400 and 600 mg L^-1). No nitrite inhibition was observed at 70 mg N L^-1. However, the total nitrogen removal efficiency (TNREs) decreased with NO₂^--N concentration increased, while the biochar-amended groups achieved higher TNREs than the control (CK). At 200 mg N L^-1, the TNREs were 60.2%, 99.0%, 98.5% and 86.6% for CK, CS300, CS550 and CS800, respectively. At 400 mg N L^-1, the TNREs were 23.3%, 56.0%, 37.1% and 29.7% for CK, CS300, CS550 and CS800, respectively. At 600 mg N L^-1 in which severe inhibition was observed, the TNREs were increased by 231% (p = 0.002), 149% (p = 0.014), and 51.0% (p = 0.166) for CS300, CS550 and CS800, respectively, as compared to CK, with the corresponding specific anammox activity increased by 3.1-, 2,0- and 1.1-folds, respectively. CS300 enriched the relative abundance of Candidatus Kuenenia and increased the gene copies of functional genes (hzsA, hdh, nirS and nirK). Besides, CS300 effectively alleviated the suppression of three membrane-associated enzyme complexes for anammox electron transport chain, indicating the possible contribution of redox-active moieties of CS300 to energy conversion metabolism for mitigating the NO₂^--N inhibition. This study provided an effective strategy for alleviating NO₂^--N stress by applying an environmentally compatible material (biochar) on anammox process.

Response of anammox granules to the simultaneous exposure to macrolide and aminoglycoside antibiotics: Linking performance to mechanism

Antibiotic pollution is becoming increasingly severe due to its extensive use. The potential application of the anaerobic ammonium oxidation (anammox) process in the treatment of wastewater containing antibiotics has attracted much attention. As common antibiotics, spiramycin (SPM) and streptomycin (STM) are widely used to treat human and animal diseases. However, their combined effects on the anammox process remain unknown. Therefore, this study systematically evaluated the response of the anammox process to both antibiotics. The half maximal inhibitory concentrations of SPM and STM were determined. The continuous-flow anammox system could adapt to SPM and STM at low concentrations, while antibiotics at high concentrations exhibited inhibitory effects. When the concentrations reached 5 mg L^-1 SPM and 50 mg L^-1 STM, the nitrogen removal efficiency dramatically decreased and then rapidly recovered within 8 days. Correspondingly, the abundances of dominant bacteria and genes also changed with antibiotic concentrations. In general, the anammox process showed a stable performance and a high resistance to SPM and STM, suggesting that acclimatization by elevating the concentrations was beneficial for the anammox process to obtain resistance to different antibiotics with high concentrations. This study provides guidance for the stable operation of anammox-based biological treatment of antibiotics containing wastewater.

Performance and microbial community structure of a full-scale ANITATMMox bioreactor for treating reject water located in Finland

The aim of this work was to study the operational performance and the microbial community dynamics during the start-up of ANITA^TMMox technology implemented at full-scale wastewater treatment plant in Finland to treat reject water from anaerobic digesters. The average ammonium removal in the studied setup reached around 90%, withstanding ammonium loads up to 0.13 g N m^-2h^-1. The nitrite concentration in the effluent did not exceed 10 mg L^-1, and there was a slight accumulation of NO₃^--N during the operation which was controlled. Thus, the result showed a robust success to high ammonium loading in presence of organic matter. The sequencing showed a heterogeneous microbial population where Methanosaeta, WCHA1-57 genus, Sphingobacteriia, Chlorobia and diverse unknown fungi were found as dominant phylotypes. Moreover, members of the Brocadiaceae family were dominant in the adhered biomass, mostly represented by Candidatus Scalindua, rarely reported in WWTPs. Overall, the results demonstrated a drastic effect of region-specific operational conditions on carrier biofilm microbial communities as it was demonstrated by the microbial studies.

A novel SAD process: Match of anammox and denitrification

Anammox biotechnology has been widely applied for its attractive advantages, but its application has been seriously limited due to the instinctive drawback of nitrate production. In this work, a novel Sequential Anammox and Denitrification (SAD) system was developed for the advanced nitrogen removal by using solid carbon source (SCS) and coupling anammox with denitrification. The long-term operation results demonstrated that the SAD system could remove the total nitrogen (TN) efficiently, with the effluent TN concentration of 1.4 ± 0.5 mg N/L, the TN removal efficiency (NRE) of 99.3 ± 0.2%, and the TN removal rate (NRR) of 1.7 ± 0.1 kg/(m³·d). The determination results showed that SCS had a good property for sustained release of COD, with a dissolved organic yield (by COD) of 1.1 g-COD/g-rice. When the addition rate was set at 6 g-rice/7-days, the COD release rate of 0.9 kg-COD/(m³·d) from SCS matched the nitrate production rate of 1.2 × 10^-1 kg-N/(m³·d) from anammox with consumption ratio of 7.5. The analysis on the microbial community revealed that Candidatus_Brocadia and Denitratisoma were the dominant functional bacteria for anammox and denitrification, which contributed to about 92.7% and 6.6% of the total nitrogen removal, respectively. This work is helpful for the innovation and application of anammox-based technology.

Sulfate dependent ammonium oxidation: A microbial process linked nitrogen with sulfur cycle and potential application

Sulfate dependent ammonium oxidation (Sulfammox) is a potential microbial process coupling ammonium oxidation with sulfate reduction under anaerobic conditions, which provides a novel link between nitrogen and sulfur cycle. Recently, Sulfammox was detected in wastewater treatments and was confirmed to occur in natural environments, especially in marine sediments. However, knowledge gaps in the mechanism of Sulfammox, functional bacteria, and their metabolic pathway, make it challenging to estimate its environmental significance and potential applications. This review provides an overview of recent advances in Sulfammox, including possible mechanisms, functional bacteria, and main influential factors, and discusses future challenges and opportunities. Future perspectives are outlined and discussed, such as exploration of microbial community structure and metabolic pathways, possible interactions with other microbes, environmental significance, and potential applications for nitrogen and sulfate removal, to inspire more researches on the Sulfammox process.

Exogenous extracellular polymeric substances as protective agents for the preservation of anammox granules

The preservation of anammox granules is of great significance for the rapid start-up of the anammox process and improvement of performance stability. Therefore, it is necessary to explore an economical and stable preservation strategy. Exogenous extracellular polymeric substances (EPS) were used as protective agents for the preservation of anammox granules in this study. In brief, EPS from anammox sludge (A-EPS) and denitrifying sludge (D-EPS) were added to preserve anammox sludge at 4 °C and room temperature (15-20 °C). The results showed that A-EPS addition at 4 °C was the optimal condition for the preservation of anammox granules. After 90 days of preservation, the specific anammox activity (SAA) of the anammox granules remained at 92.7 ± 2.2 mg N g^-1 VSS day^-1 (remaining ratio of 33.4%), while that of the sludge with D-EPS addition at the same temperature was only 77.1 ± 3.2 mg N g^-1 VSS day^-1 (remaining ratio of 27.8%). The nitrogen removal efficiency of the experimental group with D-EPS at room temperature was 85.9%, and that of the A-EPS group reached 90.6% under the same temperature conditions. The abundance of the functional genes hzsA, hdh and nirS of the sludge (4 °C; A-EPS addition) after recovery were 138.5%, 317.1%, and 375.9%, respectively, of those of sludge from the D-EPS-added group at the same temperature. RDA revealed the contribution of proteins to the preservation process. Overall, this study provides an economical and robust strategy for the preservation of anammox granules.

Enhancement of nitrite production via addition of hydroxylamine to partial denitrification (PD) biomass: Functional genes dynamics and enzymatic activities

This study investigated the activity of partial denitrification (PD) biomass/key enzymes, functional gene expressions in response to 0 ~ 50 mg/L hydroxylamine (NH₂OH) addition. Results indicated that NH₂OH contributed to nitrite (NO₂^--N) production, facilitating the maximum increase of nitrate (NO₃^--N) to NO₂^--N transformation ratio to 80.47 ± 2.82%, leading to 2.56-fold NO₂^--N higher than those of control. The observed transient inhibitory effect on NO₃^--N reduction process was attributed by high-level NH₂OH (35 ~ 50 mg/L). Enzymatic assays revealed the enhanced activity of both NO₃^--N and NO₂^--N reductase while the former showed obvious superiority which led to high NO₂^--N accumulation. These results were further confirmed by the corresponding functional genes (narG, napA, nirS and nirK). Besides, negative influence of NH₂OH addition was limited to PD aggregates, due to the increasing secretion of extracellular polymeric substances (EPS) as well as proteins/polysaccharides ratios in tightly-bound structure of EPS.

Nitrogen Removal for Liquid-Ammonia Mercerization Wastewater via Partial Nitritation/Anammox Based on Zeolite Sequencing Batch Reactor

Liquid-ammonia mercerization is commonly used to enhance the quality of cotton fabric in the textile industry, resulting in a large amount of liquid-ammonia mercerization wastewater (LMWW) containing high concentration of ammonia to be disposed of. This study proposes a partial nitritation/anammox (PN/A) process based on stable nitritation by a zeolite sequencing batch reactor (ZSBR) for the nitrogen removal of LMWW. The ZSBR could quickly achieve stably full nitritation with a nitrite accumulation ratio higher than 97% and an ammonia removal rate of 0.86 kg N·m−3·d−1 for the raw LMWW with an ammonia level of 1490 mg/L. In order to avoid anammox inhibition by free nitrous acid, the ZSBR was successfully changed to PN operation with diluted LMWW for effluent meeting anammox requirements. The next anammox reactor (an up-flow blanket filter (UBF)) realized a total nitrogen removal efficiency of 70.0% with a NLR (nitrogen loading rate) of 0.82 kg N·m−3·d−1 for LMWW. High-throughput sequencing analysis results indicated that Nitrosomonas and Candidatus Kuenenia were the dominant bacteria in ZSBR and UBF, respectively. All results revealed that the PN/A process based on ZSBR as the PN pretreatment process was feasible for LMWW, facilitating cost-effective and low-carbon nitrogen removal for LMWW treatment in the textile industry in the future.