Metagenomic insights into the symbiotic relationship in anammox consortia at reduced temperature

Integrating network and in-silico simulation insights into the ecological interactions shaped by carbon sources in partial denitrification and anammox system

The underlying ecological mechanism of microbial communities shaped by carbon source in partial denitrification and anammox (PDA) systems remains poorly understood, despite the potential of multiple carbon sources to support the partial denitrification process. Herein, the integrated network and in-silico simulation methods were used to evaluate the considerable impact of carbon sources on the dynamics of ecological interactions. The fluctuation of carbon source (from acetate to glucose and ethanol) significantly destabilized the performance of PDA system (total nitrogen removal efficiency decreased from 96.8% to 69.1%). Glucose simultaneously altered the composition of denitrifying bacteria, resulting in a significant enrichment of the genus Elstera (from 0% to 12.7%). By contrast, genus Thauera re-dominated for partial denitrification with ethanol as carbon source. Importantly, heterotrophic bacteria (e.g., genus Calditrichia) gradually enriched by utilizing ethanol. The presence of acetate in phase IV further enhanced the competitive advantage of heterotrophic bacteria over denitrifying bacteria, thereby resulting in the deteriorated performance of the PDA system. The in-silico simulation of co-culture further revealed that the overgrowth of auxotrophic species Calditrichia utilized amounts of nutrients and limited other functional bacteria. Additionally, the whole co-occurrence network indicated that positive interactions likely improved the adaptability of anammox bacteria under the unsteady conditions. This study provides profound insights into the ecological interactions shaped by carbon sources in PDA systems and underscores the necessity of comprehensive review of the external carbon source to ensure optimal performance.

Transcriptional and molecular simulation analysis of the response mechanism of anammox bacteria to 3,4-dimethylpyrazole phosphate stress

Anaerobic ammonium oxidation (anammox) and nitrification are two vital biological pathways for ammonium oxidation, pivotal in microbial nitrogen cycling. 3,4-Dimethylpyrazole phosphate (DMPP) is commonly used as inhibitors in agricultural soils to reduce nitrogen losses from farmland, while whether it affect anammox is an open question. Acute inhibition tests revealed that 53.5 mg·L-1 DMPP caused 50 % reduction in anammox bacteria. After 36 days of prolonged exposure to 5 mg·L-1 DMPP, the ammonium(nitrite) removal rate of endnote decreased from 78.39(94.78) to 13.57(15.28) mgN·gVSS-1·d-1. Additionally, the abundance of Ca. Kuenenia decreased from 36.5 % to 6.06 %. Transcriptomic analysis revealed that the mRNA levels of ammonium transport genes (amt_1 and amt_4), and hydrazine synthase (hzs) were significantly downregulated. Molecular docking simulations indicated that DMPP bound with ammonium transport and hydrazine synthesis. This interaction hindered the transcriptional levels of genes encoding ammonium transporters and hzs. The study has guiding value to reduce the nitrogen loss involved in anammox bacteria in agricultural soils under the application of DMPP.

Unravelling the complex influence of dissolved organic matter on microbial diversity in a salinized lake

Ecosystems in cold and arid regions, such as Dai Lake - a typical inland, salinized lake in the semi-arid region of northern China - face severe environmental challenges, including salinization and biodiversity loss. This study investigates the chemical composition of dissolved organic matter (DOM) and the structure of microbial communities in lake water and sediments, offering novel insights into the ecosystem's dynamics. In winter, DOM in the lake water is primarily derived from decaying plant and animal matter, while sediment DOM is predominantly associated with microbial activity. Statistical analyses revealed significant correlations between DOM components and key microbial species, including Firmicutes, Actinobacteria, α-Proteobacteria, and Acidobacteria (p < 0.05), highlighting the critical role of microbial communities in DOM transformation. Partial least squares structural equation modeling (PLS-SEM), a latent variable approach integrating multiple regression analysis, demonstrates that DOM composition, along with environmental factors such as salinity, temperature, and nutrient levels, significantly influences microbial diversity and community dynamics in the lake. These findings highlight the importance of seasonally adjusting management strategies - such as controlling nutrient inputs, monitoring water quality, and managing sediments - to protect key microbial communities and sustain ecosystem health.

Ferrihydrite regulated nitrogen metabolic pathway at biocathode of bioelectrochemical system - Insight into biofilm formation and bacterial composition

To further understand the nitrogen metabolism disrupted by anthropogenic activities, 2.5 g/L of ferrihydrite were added into cathodic chamber of bioelectrochemical system to expediate the nitrogen removal process. It was found that the nitrate removal constant was significantly improved and maintained at around 0.09 h-1 with ferrihydrite addition, while the control group maintained only at around 0.05 h-1. Besides, it seemed that the addition of ferrihydrite lead to less biomass accumulation but higher biofilm viability. Meanwhile, ferrihydrite selectively enriched OTUs capable of participating in both iron and nitrogen metabolism, relative abundance of OTU1631 (Thiobacillus) and OTU1467 (Comamonas granuli) was accordingly upped to 58.75 % and 5.11 %, respectively. Moreover, denitrification related genes were enhanced while genes related to nitrogen fixation, dissimilatory nitrate reduction, assimilatory nitrate reduction and nitrification were downregulated, further confirming the redirected electron transfer for the promotion of denitrification.

Unravelling depth layers of microbial communities, nitrogen transformation rate, and extracellular polymeric substances in anammox granules

Anammox granules harbor a variety of bacteria, with each granule layer providing a niche for bacteria with specific metabolic functions. To investigate microbial distribution, nitrogen transformation rates, and extracellular polymeric substance (EPS) content across the depth layers of anammox granules, granules sized 0.9-2.0 mm were sheared into seven layers. The outer layers exhibited higher anammox bacterial abundance (9.9 %) than the inner layers (8.1 %). In contrast, the abundance of denitrifying bacteria increased from 25.0 % in outer layers to 34.9 % in inner layers. Nitrifying bacteria, along with heterotrophic nitrifying and aerobic denitrifying bacteria, were predominantly found in outer layers. Despite the higher EPS content in inner layers, denitrification rates remained low across all layers, likely due to limited carbon availability from microbial lysis or EPS. These findings offer valuable insights into the niche distribution of microbial communities within anammox granules.

Coupling Thiosulfate-Driven denitrification and anammox to remove nitrogen from actual wastewater

A coupled thiosulfate-driven denitrification and anammox (TDDA) process was established to remove nitrogen from wastewater. It was optimized in an up-flow anaerobic sludge blanket reactor using synthetic wastewater, and its reliability was then verified with actual wastewater. The results demonstrated that nitrate, nitrite, and ammonium could be synergistically removed, and the highest total nitrogen removal efficiency reached 97.8% at a loading of 1.39 kgN/(m3·d). Anammox bacteria, primarily Candidatus_Brocadia, were the main contributors to nitrogen removal, while sulfur-oxidizing bacteria such as Thiobacillus and Rhodanobacter played a supportive role. By optimizing substrate conditions to enhance the anammox process, the coupled system attained higher abundances of functional genes such as napA, nirS, hzs, soxXA, and soxYZ, along with the corresponding microbial species. The data suggested that microbial cross-feeding and self-adaptation strategies were key to efficient nitrogen removal by TDDA.

Recombinant IL-34 alleviates bacterial enteritis in Megalobrama amblycephala by strengthening the intestinal barrier

The potential role of interleukin-34 (IL-34), an important cytokine that regulates intestinal function in mammals, is currently being explored in the context of fish intestinal diseases. In this study, we assessed the preventive potential of recombinant Megalobrama amblycephala IL-34 (rMaIL-34) protein in bacterial enteritis. MaIL-34 exhibited conserved structural and evolutionary features with teleost IL-34 and was found to be involved in the intestinal immune response to Aeromonas hydrophila infection. Furthermore, treatment with rMaIL-34 significantly improved the survival rate of M. amblycephala following A. hydrophila infection and alleviated the symptoms of enteritis in these fish. In vivo, rMaIL-34 enhanced goblet cell proliferation and mucus layer tightness, thereby maintaining mucosal integrity following infection. Additionally, rMaIL-34 attenuated the decrease in ZO-1 expression and inhibited the increase in intestinal permeability caused by A. hydrophila, thereby reducing the concentrations of DAO and D-LAC in the plasma. Furthermore, rMaIL-34 suppressed oxidative stress, apoptosis, and inflammatory responses triggered by A. hydrophila, thereby strengthening the immune barrier. At the microbiological level, rMaIL-34 contributed to improved intestinal microbiota distribution and enhanced the functions of intestinal microbiota in terms of energy metabolism, antibiotic biosynthesis, and oxidative phosphorylation. This study reveals, for the first time, the multiple roles of fish IL-34 in resistance to bacterial enteritis and paves the way for the development of rMaIL-34 as an immunotherapy for bacterial enteritis in fish.

Deciphering anammox response characteristics and potential mechanisms to polyethylene terephthalate microplastic exposure

Microplastics (MPs) are frequently detected in the wastewater. Herein, the short-term and long-term effects of polyethylene terephthalate (PET) MPs on anammox granular sludge were investigated and the potential response mechanisms were analyzed. Results showed that although short-term exposure of anammox granular sludge to PET-MPs induced a stress response, the nitrogen removal performance was not significantly affected. By contrast, long-term exposure to PET-MPs inhibited nitrogen removal performance with increased exposure time and PET-MP concentration. The total nitrogen removal efficiency (TNRE) decreased by 28.7 % when sludge was exposed to 200 mg/L of PET-MPs. However, the anammox activity recovered with prolonged operation time, and approximately 87 % of the initial TNRE was recovered after three months. Microbial community evolution and metabolic exchange variations were the potential response mechanisms of anammox granular sludge to PET-MP exposure, with PET-MP exposure decreasing the anammox bacteria growth rate and relative symbiotic bacterial abundance in the anammox consortia and hindering cross-feeding pathways. The findings of this study provide novel insight into anammox behavior when treating wastewater containing PET-MPs.

Responses of suspended sludge and biofilm in a SNAD system under C/N elevation: Microbial activity, nitrogen conversion flux and molecular ecological network

The simultaneous partial nitrification, anammox and denitrification (SNAD) process had received widespread attention as an advanced wastewater treatment process. In this study, the SNAD mainstream nitrogen removal process with the incorporation of polyurethane sponge packing under different C/N conditions was investigated. Results showed that the highest nitrogen removal efficiency of the system was achieved at the C/N of 2.0, while the high C/N (3.5) significantly deteriorate the nitrogen removal efficiency. Meanwhile, high C/N (3.5) significantly inhibited the activity and abundance of anammox bacteria (mainly Candidatus_Kuenenia), resulting in the decreased contribution of anammox (from 63.14 % to 48.09 %). The significant divergence of microbial interactions in the suspended sludge and biofilm was observed with increasing C/N. Compared with suspended sludge, biofilm facilitated higher abundance and activity of anammox bacteria, and the molecular ecological network of biofilm displayed better stability and more efficient mass transfer efficiency between microorganisms. The C/N of 3.5 simplified the subnetworks of Chloroflexi and Proteobacteria but increased the positive interactions between Planctomycetota and other microbes. Anammox bacteria were found as keystone species only in biofilm system. This study provided a theoretical basis and technical guidance for the application of SNAD process in municipal wastewater treatment.

Two-stage partial nitrification-denitrification and anammox process for nitrogen removal in vacuum collected toilet wastewater at ambient temperature

Vacuum collected toilet wastewater (VCTW) contains high and fluctuating contents of organics and nitrogen, which exerts technological challenges to biological treatment processes. A partial nitrification-denitrification and anammox (PND-AMX) process was developed in sequencing batch reactor (SBR) and moving bed biofilm reactor (MBBR) to achieve effective nitrogen removal in VCTW at low ambient temperature. Stable PND was achieved, and nitrogen removal efficiency in SBR could be manipulated by adjusting influent COD/N ratios. As temperature ≥18 °C, 91.0% nitrogen was removed in PND-AMX process. In spite of the decreased anammox activity at 13-18 °C, more than 90% nitrogen removal could be obtained by adjusting SBR influent COD/N to 2.43 ± 0.32 with methanol. In MBBR reactor, Candidatus Kuenenia was the dominant anammox bacteria and contributed to more than 90% nitrogen removal capacity. Co-existing anammox and denitrifying bacteria synergistically contributed to the removal of ammonium, nitrite, nitrate, and COD in MBBR.

Enhancing nitrogen removal from digested swine wastewater by anammox with aeration optimization coupling real-time control strategy

The nitrogen removal of anaerobically digested swine wastewater (ADSW) through partial nitritation and anammox is hindered by the challenge of balancing aeration between ammonia oxidizing bacteria (AOB) and anammox bacteria (AnAOB). This study focused on optimizing aeration through a real-time control strategy in an integrated fixed-film activated sludge reactor for treating ADSW. The system implemented a dual aeration mode that included both low dissolved oxygen (DO) (< 0.4 mg/L) and short-term high DO (0.6-1.2 mg/L), with pH, oxidation-reduction potential, and NH4+-N electrode values as real-time control parameters. NH4+-N removal rate increased from 3.37 to 12.82 mgN/(gVSS·h), and total nitrogen (TN) removal rate enhanced from 0.14 to 0.25 kgN/(m3·d). Increasing DO stimulated AOB activity by 31 % and provided sufficient NO2--N for AnAOB. The r-strategist AnAOB (Candidatus Kuenenia) proliferated well in the biofilm (0.25 % in flocs vs. 1.86 % in biofilm). The enrichment of denitrifiers improved organic matter and TN removal.

Adjusted bacterial cooperation in anammox community to adapt to high ammonium in wastewater treatment plant

Bacterial cooperation is very important for anammox bacteria which perform low-carbon and energy-efficient nitrogen removal, yet its variation to adapt to high NH4 +-N concentration in actual wastewater treatment plants (WWTPs) remains unclear. Here, we found wide and varied cross-feedings of anammox bacteria and symbiotic bacteria in the two series connected full-scale reactors with different NH4 +-N concentrations (297.95 ± 54.84 and 76.03 ± 34.01 mg/L) treating sludge digester liquor. The uptake of vitamin B6 as highly effective antioxidants secreted by the symbiotic bacteria was beneficial for anammox bacteria to resist the high NH4 +-N concentration and varied dissolved oxygen (DO). When NH4 +-N concentration in influent (1785.46 ± 228.5 mg/L) increased, anammox bacteria tended to reduce the amino acids supply to symbiotic bacteria to save metabolic costs. A total of 26.1% bacterial generalists switched to specialists to increase the stability and functional heterogeneity of the microbial community at high NH4 +-N conditions. V/A-type ATPase for anammox bacteria to adapt to the change of NH4 +-N was highly important to strive against cellular alkalization caused by free ammonia. This study expands the understanding of the adjusted bacterial cooperation within anammox consortia at high NH4 +-N conditions, providing new insights into bacterial adaptation to adverse environments from a sociomicrobiology perspective.

Effects of low temperature on the microbial community of MBBR filler biofilm

Moving bed biofilm reactors can purify urban domestic sewage through microbial biodegradation. High-throughput sequencing was used to study the response mechanism of the biofilm microbial community to temperature. The effluent quality of the reactor declined with the decrease in temperature. Proteobacteria, Bacteroidota, and Nitrospirota were the dominant bacteria, accounting for 59.2, 11.9, and 9.4%, respectively. Gammaproteobacteria (38.3%), Alphaproteobacteria (23.2%), and Bacteroidia (12.4%) were the dominant bacteria at the class level. Low temperature had an obvious directional domestication effect on microbial flora, and the composition of the bacterial community was more similar. Pseudomonas was one of the dominant bacterial groups at 5 °C. Nitrospira (p < 0.001) and Trichococcus (p < 0.05) were significantly negatively correlated with effluent ammonia nitrogen and significantly positively correlated with NO3- (p < 0.05) at low temperature. Functional bacteria related to chemoheterotrophy (25.88%) and aerobic_chemoheterotrophy (21.56%) accounted for a relatively high proportion. The bacteria related to nitrate reduction only accounted for 2.62%. Studies have shown that low temperatures can inhibit the growth of nitrogen-cycling bacteria, and few domesticated and selected nitrogen-cycling bacteria play a major role in the removal and transformation of ammonia nitrogen. The degradation of chemical oxygen demand can still be achieved through the adsorption and degradation of dominant functional bacteria.

Metabolic evolution and bottleneck insights into simultaneous autotroph-heterotroph anammox system for real municipal wastewater nitrogen removal

When biological nitrogen removal (BNR) systems shifted from treating simulated wastewater to real wastewater, a microbial succession occurred, often resulting in a decline in efficacy. Notably, despite their high nitrogen removal efficiency for real wastewater, anammox coupled systems operating without or with minimal carbon sources also exhibited a certain degree of performance reduction. The underlying reasons and metabolic shifts within these systems remained elusive. In this study, the simultaneous autotrophic/heterotrophic anammox system demonstrated remarkable metabolic resilience upon exposure to real municipal wastewater, achieving a nitrogen removal efficiency (NRE) of 82.83 ± 2.29 %. This resilience was attributed to the successful microbial succession and the complementary metabolic functions of heterotrophic microorganisms, which fostered a resilient microbial community. The system's ability to harness multiple electron sources, including NADH oxidation, the TCA cycle, and organics metabolism, allowed it to establish a stable and efficient electron transfer chain, ensuring effective nitrogen removal. Despite the denitrification channel's nitrite supply capability, the analysis of the interspecies correlation network revealed that the synergistic metabolism between AOB and AnAOB was not fully restored, resulting in selective functional bacterial and genetic interactions and the system's PN/A performance declined. Additionally, the enhanced electron affinity of PD increased interconversion of NO3--N and NO2--N, limiting the efficient utilization of electrons and thereby constraining nitrogen removal performance. This study elucidated the metabolic mechanism of nitrogen removal limitations in anammox-based systems treating real municipal wastewater, enhancing our understanding of the metabolic functions and electron transfer within the symbiotic bacterial community.

Nitrate formation in anammox process: Mechanisms and operating conditions

Anaerobic ammonium oxidation (anammox) is an energy-efficient technology for wastewater nitrogen removal. However, the byproduct nitrate has hindered development and application of anammox process. Meanwhile, the knowledge of nitrate formation during anammox process is insufficient, which prohibits high nitrogen removal. This review firstly summaries and discusses valuable findings on nitrate formation, including molecular mechanism of nitrate production, microbial pathway of nitrate reduction and its net formation. Specially, influences of operating conditions on mechanisms and patterns of nitrate formation are analyzed. Then, based on nitrate formation mechanism, current strategies of nitrate removal from anammox process are reevaluated. Finally, the key knowledge gaps and further process development are presented. Overall, this review sheds light on the understanding of nitrate formation of anammox process, which would further facilitate and optimize the process design and operation for high performance nitrogen removal.

Arginine enhances activity of anammox consortia and process stability with increased nitrogen loading

Cross-feeding based on amino acids metabolism is an important strategy by which anammox bacteria and the co-existing heterotrophs facilitate their own growth and survival. Arginine is one of the necessary amino acids required for bacterial protein biosynthesis but whether adding arginine could benefit growth of anammox bacteria remains unknown. In this study, arginine was supplemented at dose of 5 mg·L-1 to promote the nitrogen removal performance of anammox bioreactors under varied loading rates. The results showed that nitrogen removal efficiency increased by 10.2 % under higher loading rates. Arginine addition substantially simulated the secretion of extracellular proteins and polysaccharides within anammox consortia as a strategy against unfavorable conditions. Canditatus Kuenenia dominated the anammox consortia and their 16S rRNA abundance and anammox-related functional genes were significantly increased by up to 0.42 times and 5.81 times, respectively. The findings of this study provided a feasible strategy to improve the performance of anammox reactors with arginine supplementation.

Research on intensive nitrogen removal of municipal sewage by mainstream anaerobic ammonia oxidation process

The anaerobic ammonia oxidation (anammox) process is a pivotal nitrogen removal technique, playing a significant role in the field of wastewater treatment. The paper commences by delineating the merits of the anammox process in comparison to conventional nitrification-denitrification techniques. Subsequently, it delves into the characteristics of different sludge morphologies process of the behavior of anammox bacteria and their reactions to environmental factors. Revising the issues associated with managing urban sewage in mainstream areas., it discusses the issues faced by the anammox process under reduced nitrogen loads, such as restricted activity due to decreased the levels of ammonia nitrogen and nitrite concentrations, as well as the impact of environmental factors like low temperature, organic matter, and sulfur ions. Following this, a comprehensive review of various types of coupled anammox processes is provided, highlighting the advantages and characteristics of partial nitrification (PN), partial denitrification (PD), methane-dependent nitrite/nitrate reduction (DAMO), sulfur-driven autotrophic denitrification (SAD), iron ammonia oxidation (feammox) and algae photoautotrophy coupling techniques, emphasizing their significance in system stability and resource utilization efficiency. Future research directions include exploring the applicability of the anammox process under various temperature conditions and addressing NO3--N issues in effluent. The findings from these studies will offer valuable insights for further enhancing the optimization of the anammox process in mainstream urban wastewater treatment.

Insights into the carbon and nitrogen metabolism pathways in mixed-autotrophy/heterotrophy anammox consortia in response to temperature reduction

While the multi-coupled anammox system boasts a substantial research foundation, the specific characteristics of its synergistic metabolic response to decreased temperatures, particularly within the range of 13-15 °C, remained elusive. In this study, we delve into the intricate carbon and nitrogen metabolism pathways of mixed-autotrophy/heterotrophy anammox consortia under conditions of temperature reduction. Our macrogenomic analyses reveal a compelling phenomenon: the stimulation of functional genes responsible for complete denitrification, suggesting an enhancement of this process during temperature reduction. This adaptation likely contributes to maintaining system performance amidst environmental challenges. Further metabolic functional recombination analyses highlight a dramatic shift in microbial community composition, with denitrifying MAGs (metagenome-assembled genomes) experiencing a substantial increase in abundance (up to 200 times) compared to autotrophic MAGs. This proliferation underscores the strong stimulatory effect of temperature reduction on denitrifying species. Notably, autotrophic MAGs play a pivotal role in supporting the glycolytic processes of denitrifying MAGs, underscoring the intricate interdependencies within the consortia. Moreover, metabolic variations in amino acid composition among core MAGs emerge as a crucial adaptation mechanism. These differences facilitate the preservation of enzyme activity and enhance the consortia's resilience to low temperatures. Together, these findings offer a comprehensive understanding of the microbial synergistic metabolism within mixed-autotrophy/heterotrophy anammox consortia under temperature reduction, shedding light on their metabolic flexibility and resilience in dynamic environments.

Efficient alleviation granular sludge floatation in a high-rate anammox reactor by dosing folate

Although granular floatation has been recognized as a significant issue hindering the application of high-rate anammox biotechnology, limited knowledge is available about its causes and control strategies. This study proposed a novel control strategy by adding folate, and demonstrated its role in the granular floatation alleviation through long-term operation and granular characterizations. It was found that the floatation of anammox granular sludge was obviously relieved with the decreased sludge floatation potential by 67.1% after dosing with folate (8 mg/L) at a high nitrogen loading rate of 12.3 kg-N/(m3·d). Physiochemical analyses showed that the decrease of extracellular polymeric substances (EPS) content (mainly protein), the alleviation of granular surface pore plugging in conjunction with the smooth discharge of generated nitrogen gas were collectively responsible for efficient floatation control. Moreover, metagenomic analysis suggested that the synergistic interactions between anammox bacteria and their symbionts were attenuated after dosing exogenous folate. Anammox bacteria would reduce their synergistic dependence on the symbionts, and decline the supply of metabolites (e.g., amino acids and carbohydrates in EPS) to symbiotic bacteria. The declined EPS excretion contributed to the alleviation of granular floatation by dredging pores blockage, thus leading to a stable system performance. The findings not only offer insights into the role of microbial interaction in granular sludge floatation, but also provide a feasible approach for controlling the floatation issue in anammox granular-based processes.

Nitrogen utilization efficiency assessment during bioremediation of petroleum-contaminated loess soils: insights from metagenomic analysis

Nitrogen addition is commonly used to remediate total petroleum hydrocarbons (TPH) in petroleum-contaminated soils. However, acceptable exogenous nitrogen dosages and their utilization efficiency for the degradation of hydrocarbons in oil-polluted soils are not well understood. This study compared the hydrocarbon bioremediation capacity by applying different doses of NH4Cl as a stimulant in soils contaminated with TPH at 8553 and 17090 mg/kg. The results showed acceptable exogenous nitrogen levels ranging from 60 to 360 mg N/kg soil, and the optimal nitrogen dosage for TPH remediation was 136 mg N/kg in soils with different TPH concentrations. The nitrogen availability efficiency (NAE) and nitrogen polarization factor availability (NPFA) in the 136 mg N/kg addition treatments were 6.69 and 20.47 mg/mg in 8533 mg/kg TPH-polluted soil, and 6.03 and 31.11 mg/mg in 17090 mg/kg TPH-polluted soil, respectively. Metagenomic analysis revealed that the application of 136 mg/kg nitrogen facilitated ammonia oxidation and nitrite reduction to nitric oxide, and induced soil microorganisms to undergo regulatory or adaptive changes in energy supply and metabolic state, which could aid in restoring the ecological functions of petroleum-contaminated soils. These findings underscore that 136 mg/kg of nitrogen dosage application is optimal for remediation of petroleum-contaminated soils irrespective of the TPH concentrations. This exogenous nitrogen application dosage for TPH remediation aligns with the nitrogen requirements for crop growth in agriculture.

Quorum sensing mediated response mechanism of anammox consortia to anionic surfactant: Molecular simulation and molecular evidence

The widespread use of surfactants raise challenges to biological wastewater treatment. Anaerobic ammonium oxidation (anammox) process has the potential to treat wastewater containing anionic surfactants, but the response of anammox consortia at the molecular level under long-term exposure is unclear. Using high-throughput sequencing and gene quantification, combined with molecular docking, the effect of sodium dodecyl sulfonate (SDS) on anammox consortia were investigated. Levels of reactive oxygen species (ROS) might be lower than the threshold of oxidative damage, while the increase of lactate dehydrogenase (LDH) represented the cell membrane damage. Decreased abundance of functional genes (hdh, hzsA and nirS) indicated the decrease of the anammox bacterial abundance. Trace amounts of N-acyl homoserine lactone (AHL, C6-HSL, C8-HSL and C12-HSL) contained in influent could induce endogenous quorum sensing (QS), which could regulate the correlation between functional bacteria to optimize the microbial community and strengthen the resistance of anammox consortia to SDS. In addition, the proliferation of disinfectant resistance genes might increase the environmental pathogenicity of sewage discharge. This work highlights the potential response mechanism of anammox consortium to surfactants and provides a universal microbial-friendly bioenhancement strategy based on QS.

Rapid start-up and stable operation of pilot scale denitrification-partial nitritation/anammox process for treating electroplating tail wastewater

This study explored a novel economical and efficient process for treating actual low-ammonia nitrogen electroplating tail wastewater. A pilot scale system of denitrification-partial nitrification/anaerobic ammonium oxidation (DN-PN/A) was constructed and operated for 190 days. The partial nitrification (PN) reactor, filled with zeolite, increased free ammonia concentration beyond the nitrite oxidizing bacteria threshold and successfully supplied NO2--N, with nitrite accumulation rate exceeding 90 %. Over 109 days, the total nitrogen removal rate achieved was 80.2 ± 7.41 %, and the chemical oxygen demand removal rate reached 79.68 ± 9.53 %. The dominant functional bacteria were Nitrosomonas (5.45 %) and Candidatus Anammoxoglobus (28.84 %) in PN reactor and anaerobic ammonium oxidation (Anammox) reactor. This process, characterized by rapid start-up, strong shock resistance, and low cost, alleviates the pressure of ammonium pollution control, promotes the sustainable development of the electroplating industry and has the potential for application in the treatment of other industrial wastewater.

Enhanced and robust nitrogen removal using an integrated zeolite and partial denitrification anammox process

Anammox has received increased attention due to its enhanced and cost-efficient approach to nitrogen removal. However, its practical application is complicated by strict influent NO2--N to NH4+-N ratio demands and an 11% nitrate production from the anammox process. This study was the first known research to propose and verify a system of zeolite integrated with partial denitrification and anammox (Z-PDA) in an up-flow anaerobic sludge bed (UASB) reactor. The enhanced and robust nitrogen removal resulted in an ultra-high nitrogen removal efficiency (NRE, 93.0 ± 2.0%). Zeolite adsorption and biological desorption of ammonium contributed to robust nitrogen removal with fluctuating influent NO2--N to NH4+-N ratios. Applying 16S rRNA gene sequencing found that Candidatus Brocadia and Thauera were the key bacteria responsible for anammox and partial denitrification (PD), respectively. Zeolite also acted as a biological carrier. This significantly enriched anammox bacteria with a higher relative abundance of Candidatus Brocadia, reaching 49.2%. Metagenomic analysis demonstrated that the multiple functional genes related to nitrogen removal (nrfA/H, narG/H/I) and the metabolic pathways (Biosynthesis of cofactors, the Two-component system, the Biosynthesis of nucleotide sugars, and Purine metabolism) ensured the resilience of the Z-PDA system despite influent fluctuations. Overall, this study provided novel insights into the impacts of zeolite in the PDA system. It described the fundamental mechanism of zeolite based on adsorption and biological desorption, and demonstrated a meaningful application of the anammox process in sewage treatment.

Deciphering the adaptation mechanism of anammox consortia under sulfamethoxazole stress: A model coupling resistance accumulation and interspecies-cooperation

Sulfamethoxazole (SMX) is frequently detected in wastewater where anammox applications are promising. While it has been demonstrated that anammox consortia can adapt to SMX stress, the underlying community adaptation strategy has not yet been fully addressed. Therefore, in this study, we initially ascertained anammox consortia's ability to co-metabolize SMX in batch tests. Then, a 200-day domestication process of anammox consortia under SMX stress was carried out with community variations and transcriptional activities monitored by metagenomic and metatranscriptomic sequencing techniques. Despite the initial drop to 41.88 %, the nitrogen removal efficiency of the anammox consortia rebounded to 84.64 % post-domestication under 5 mg/L SMX. Meanwhile, a 4.85-fold accumulation of antibiotic resistance genes (ARGs) under SMX stress was observed as compared to the control group. Interestingly, the anammox consortia may unlock the SMX-inhibited folate synthesis pathway through a novel interspecies cooperation triangle among Nitrospira (NAA), Desulfobacillus denitrificans (DSS1), and the core anammox population Candidatus Brocadia sinica (AMX1), in which the modified dihydropteroate synthase (encoded by sul1) of NAA reconnected the symbiotic cooperation between AMX1 and DSS1. Overall, this study provides a new model for the adaptation strategies of anammox consortia to SMX stress.

Metagenomic unveils the promotion of mainstream PD-anammox process at lower nZVI concentration and inhibition at higher dosage

The partial-denitrification-anammox (PdNA) process exhibits great potential in enabling the simultaneous removal of NO3--N and NH4+-N. This study delved into the impact of exogenous nano zero-valent iron (nZVI) on the PdNA process. Adding 10 mg L-1 of nZVI increased nitrogen removal efficiency up to 83.12 % and maintained higher relative abundances of certain beneficial bacteria. The maximum relative abundance of Candidatus Brocadia (1.6 %), Candidatus Kuenenia (1.5 %), Ignavibacterium (1.3 %), and Azospira (1.2 %) was observed at 10 mg L-1 of nZVI. However, the greatest relative abundance of Thauera (1.3 %) was recorded under 50 mg L-1. Moreover, applying nZVI selectively enhanced the abundance of NO3--N reductase genes. So, keeping the nZVI concentration at 10 mg L-1 or below is advisable to ensure a stable PdNA process in mainstream conditions. Considering nitrogen removal efficiency, using nZVI in the PD-anammox process could be more cost-effective in enhancing its adoption in industrial and mainstream settings.

Deciphering the anammox microbial community succession with humic acid exposure to optimize large anammox granules for robust nitrogen removal

The robustness of the anaerobic ammonia oxidation (anammox) process in treating wastewater with high concentrations of humic acids (HAs), including landfill leachate and sludge anaerobic digestion liquid, has been paid great attention. This study revealed that the anammox sludge granule size of 1.0-2.0 mm could be robust under the HA exposure with high concentrations. The total nitrogen removal efficiency (NRE) was 96.2% at the HA concentration of 20-100 mg/L, while the NRE was 88.5% at the HA concentration of 500 mg/L, with reduced by 7.7%. The increased extracellular polymeric substances (EPS) content which was stimulated by the HA exposure favored the formation of large granules (1.0-2.0 mm) by enveloping medium and micro granules (0.2-1.0 mm). The abundance of anammox bacteria Candidatus Brocadia was found to be higher (14.2%) in large anammox granules sized 1.0-2.0 mm, suggesting a potentially high anammox activity. However, the abundance of denitrifiers Denitratisoma increased by 4.3% in ultra-large anammox granules sized >2.0 mm, which could be attributed to the high EPS content for heterotrophic denitrifiers metabolism as organic matter. The feedback mechanism of the anammox community for maintaining the ecological function under the HA exposure resulted in a closely related microbial community, with positive and negative correlations in the ecological network increased by 64.3%. This study revealed that the HA exposure of the anammox system resulted in the anammox granules of 1.0-2.0 mm size being the dominant granules with robust nitrogen removal, providing significant guidance for the optimization of anammox granules for an efficient treatment of HA-containing wastewater in anammox applications.

Deciphering the formation of granules by n-DAMO and Anammox microorganisms

Nitrate/nitrite-dependent anaerobic methane oxidation (n-DAMO) process is a promising wastewater treatment technology, but the slow microbial growth rate greatly hinders its practical application. Although high-level nitrogen removal and excellent biomass accumulation have been achieved in n-DAMO granule process, the formation mechanism of n-DAMO granules remains unresolved. To elucidate the role of functional microbes in granulation, this study attempted to cultivate granules dominated by n-DAMO microorganisms and granules coupling n-DAMO with anaerobic ammonium oxidation (Anammox). After long-term operation, dense granules were developed in the two systems where both n-DAMO archaea and n-DAMO bacteria were enriched, whereas granulation did not occur in the other system dominated by n-DAMO bacteria. Extracellular polymeric substances (EPS) measurement indicated the critical role of EPS production in the granulation of n-DAMO process. Metagenomic and metatranscriptomic analyses revealed that n-DAMO archaea and Anammox bacteria were active in EPS biosynthesis, while n-DAMO bacteria were inactive. Consequently, more EPS were produced in the systems containing n-DAMO archaea and Anammox bacteria, leading to the successful development of n-DAMO granules. Furthermore, EPS biosynthesis in n-DAMO systems is potentially regulated by acyl-homoserine lactones and c-di-GMP. These findings not only provide new insights into the mechanism of granule formation in n-DAMO systems, but also hint at potential strategies for management of the granule-based n-DAMO process.

Metagenomic insights into microbial metabolic mechanisms of a combined solid-phase denitrification and anammox process for nitrogen removal in mainstream wastewater treatment

To overcome the significant challenges associated with nitrite supply and nitrate residues in mainstream anaerobic ammonium oxidation (anammox)-based processes, this study developed a combined solid-phase denitrification (SPD) and anammox process for low-strength nitrogen removal without the addition of nitrite. The SPD step was performed in a packed-bed reactor containing poly-3-hydroxybutyrate-co-3-hyroxyvelate (PHBV) prior to employing the anammox granular sludge reactor in the continuous-flow mode. The removal efficiency of total inorganic nitrogen reached 95.7 ± 1.2% under a nitrogen loading rate of 0.18 ± 0.01 kg N·m3·d-1, and it required 1.02 mol of nitrate to remove 1 mol of ammonium nitrogen. The PHBV particles not only served as biofilm carriers for the symbiosis of hydrolytic bacteria (HB) and denitrifying bacteria (DB), but also carbon sources that facilitated the coupling of partial denitrification and anammox in the granules. Metagenomic sequencing analysis indicated that Burkholderiales was the most abundant HB genus in SPD. The metabolic correlations between DB (Betaproteobacteria, Rhodocyclaceae, and Anaerolineae) and anammox bacteria (Candidatus Brocadiac and Kuenenia) in the granules were confirmed through microbial co-occurrence networks analysis and functional gene annotations. Additionally, the genes encoding nitrate reductase (Nap) and nitrite reductase (Nir) in DB primarily facilitated nitrate reduction, thereby supplying nitric oxide to anammox bacteria for subsequent nitrogen removal with hydrazine synthase (Hzs) and hydrazine dehydrogenase (Hdh). The findings provide insights into microbial metabolism within combined SPD and anammox processes, thus advancing the development of mainstream anammox-based processes in engineering applications.

A novel simultaneous short-course nitrification, denitrification and fermentation process: bio-enhanced phenol degradation and denitrification in a single reactor

The feasibility of a simultaneous nitrification, denitrification and fermentation process (SNDF) under electric stirrer agitation conditions was verified in a single reactor. Enhanced activated sludge for phenol degradation and denitrification in pharmaceutical phenol-containing wastewater under low dissolved oxygen conditions, additional inoculation with Comamonas sp. BGH and optimisation of co-metabolites were investigated. At a hydraulic residence time (HRT) of 28 h, 15 mg/L of substrate as strain BGH co-metabolised substrate degraded 650 ± 50 mg/L phenol almost completely and was accompanied by an incremental increase in the quantity of strain BGH. Strain BGH showed enhanced phenol degradation. Under trisodium citrate co-metabolism, strain BGH combined with activated sludge treated phenol wastewater and degraded NO2--N from 50 ± 5 to 0 mg/L in only 7 h. The removal efficiency of this group for phenol, chemical oxygen demand (COD) and TN was 99.67%, 90.25% and 98.71%, respectively, at an HRT of 32 h. The bioaugmentation effect not only promotes the degradation of pollutants, but also increases the abundance of dominant bacteria in activated sludge. Illumina MiSeq sequencing research showed that strain BGH promoted the growth of dominant genera (Acidaminobacter, Raineyella, Pseudarcobacter) and increased their relative abundance in the activated sludge system. These genera are resistant to toxicity and organic matter degradation. This paper provides some reference for the activated sludge to degrade high phenol pharmaceutical wastewater under the action of biological enhancement.

Insights into the response mechanisms of activated sludge system under long-term dexamethasone stress

Dexamethasone (DEX) is a hormone drug that is often detected in wastewater treatment plants, but its impact on activated sludge systems is unknown. This study explored the long-term effects of DEX on nutrient removal, microbial activities, microbial assembly, and microbial interactions in the activated sludge system. During the 90-day DEX exposure experiment, both chemical oxygen demand and total nitrogen removal efficiencies were initially inhibited and then recovered. Microbial activities, i.e., specific oxygen uptake rate and denitrification, did not differ significantly from that of the control reactor (p > 0.05), possibly due to the secretion of extracellular polymers that act as a protective barrier against excess reactive oxygen species induced by DEX. This barrier protects cell membrane integrity and ensures stable treatment performance. Analysis of microbial assembly identified the drift of stochastic processes (from 92.7 % to 51.8 %) and homogeneous selection of deterministic processes (from 1.6 % to 38.7 %) as the main driving forces of microbial community structure succession under long-term DEX stress. Although long-term exposure to 1000 μg/L DEX did not significantly increase the abundance levels of functional bacteria (Nitrosomonas and 996-1) and key genes (AmoCAB and Hao), the ammonia oxidation capacity of the activated sludge system was enhanced. Analysis of microbial interactions indicated that streamlining of functional subnetworks and increased cooperation were the primary reasons. This is the first study to explore the long-term effects of DEX on activated sludge and provide insights into microbial interaction and assembly. Moreover, the findings of this study broaden our knowledge and lay an experimental foundation for reducing risks associated with hormone drugs.

Identification of extracellular polymeric substances layer barrier in chloroquine phosphate-disturbed anammox consortia and mechanism dissection on cytotoxic behavior by computational chemistry

The over-dosing use of chloroquine phosphate (CQ) poses severe threats to human beings and ecosystem due to the high persistence and biotoxicity. The discharge of CQ into wastewater would affect the biomass activity and process stability during the biological processes, e.g., anammox. However, the response mechanism of anammox consortia to CQ remain unknown. In this study, the accurate role of extracellular polymeric substances barrier in attenuating the negative effects of CQ, and the mechanism on cytotoxic behavior were dissected by molecular spectroscopy and computational chemistry. Low concentrations (≤6.0 mg/L) of CQ hardly affected the nitrogen removal performance due to the adaptive evolution of EPS barrier and anammox bacteria. Compact protein of EPS barrier can bind more CQ (0.24 mg) by hydrogen bond and van der Waals force, among which O-H and amide II region respond CQ binding preferentially. Importantly, EPS contributes to the microbiota reshape with selectively enriching Candidatus_Kuenenia for self-protection. Furthermore, the macroscopical cytotoxic behavior was dissected at a molecular level by CQ fate/distribution and computational chemistry, suggesting that the toxicity was ascribed to attack of CQ on functional proteins of anammox bacteria with atom N17 (f-=0.1209) and C2 (f+=0.1034) as the most active electrophilic and nucleophilic sites. This work would shed the light on the fate and risk of non-antibiotics in anammox process.

Enhancing anammox process with granular activated carbon: A study on Microbial Extracellular Secretions (MESs)

Granular activated carbon (GAC), a porous carbon-based material, provides increased attachment space for functional microorganisms and enhances nitrogen removal by facilitating extracellular electron transfer in the anammox process. This study investigates the effects of GAC on the biosynthesis of microbial extracellular secretions (MESs) and explores the roles of these secretions in anammox activities. Four lab-scale reactors were operated: two downstream UASB reactors (D1 and D2) receiving effluents from the upstream UASB reactors (U1: no-GAC, U2: yes-GAC). Our results indicate that MESs were enhanced with the addition of GAC. The effluent from U2 exhibited a 59.62 % higher amino acid content than that from U1. These secretions contributed to an increase in the nitrogen loading rate (NLR) in the downstream reactors. Specifically, NLR in D1 increased from 130.5 to 142.7 g N/m3/day, and in D2, it escalated from 137.5 to 202.8 g N/m3/day, likely through acting as cross-feeding substrates or vital nutrients. D2 also showed increased anammox bacterial activity, enriched Ca. Brocadia population and hao gene abundance. Furthermore, this study revealed that D2 sludge has significantly higher extracellular polymeric substances (EPS) (48.71 mg/g VSS) and a larger average granule size (1.201 ± 0.119 mm) compared to D1 sludge. Overall, GAC-stimulated MESs may have contributed to the enhanced performance of the anammox process.

Integrative chemical and multiomics analyses of tetracycline removal mechanisms in Pseudomonas sp. DX-21

Tetracycline (TC), widely found in various environments, poses significant risks to ecosystems and human health. While efficient biodegradation removes TC, the mechanisms underlying this process have not been elucidated. This study investigated the molecular mechanisms underlying TC biosorption and transfer within the extracellular polymeric substances (EPS) of strain DX-21 and its biodegradation process using fourier transform infrared spectroscopy, molecular docking, and multiomics. Under TC stress, DX-21 increased TC biosorption by secreting more extracellular polysaccharides and proteins, particularly the latter, mitigating toxicity. Moreover, specialized transporter proteins with increased binding capacity facilitated TC movement from the EPS to the cell membrane and within the cell. Transcriptomic and untargeted metabolomic analyses revealed that the presence of TC led to the differential expression of 306 genes and significant alterations in 37 metabolites. Notably, genes related to key enzymes, such as electron transport, peroxidase, and oxidoreductase, exhibited significant differential expression. DX-21 combated and degraded TC by regulating metabolism, altering cell membrane permeability, enhancing oxidative defense, and enhancing energy availability. Furthermore, integrative omics analyses indicated that DX-21 degrades TC via various enzymes, reallocating resources from other biosynthetic pathways. These results advance the understanding of the metabolic responses and regulatory mechanisms of DX-21 in response to TC.

Temperature-resilient superior performances by coupling partial nitritation/anammox and iron-based denitrification with granular formation

Partial nitritation-anammox (PN/A), an energy-neutral process, is widely employed in the treatment of nitrogen-rich wastewater. However, the intrinsic nitrate accumulation limits the total nitrogen (TN) removal, and the practical application of PN/A continues to face a significant challenge at low temperatures (<15 °C). Here, an integrated partial nitritation-anammox and iron-based denitrification (PNAID) system was developed to address the concern. Two up-flow bioreactors were set up and operated for 400 days, with one as the control group and the other as the experiment group with the addition of Fe0. In comparison to the control group, the experiment group with the Fe0 supplement showed better nitrogen removal during the entire course of the experiment at different temperature levels. Specifically, the TN removal efficiency of the control group decreased from 82.9 % to 53.9 % when the temperature decreased from 30 to 12 °C, while in stark contrast, the experiment group consistently achieved 80 % of TN removal in the same condition. Apart from the enhanced nitrogen removal, the experiment group also exhibited better phosphorus removal (10.6 % versus 74.1 %) and organics removal (49.5 % versus 65.1 %). The enhanced and resilient nutrient removal performance of the proposed integrated process under low temperatures appeared to be attributed to the compact structure of granules and the increased microbial metabolism with Fe0 supplement, elucidated by a comprehensive analysis including microbial-specific activity, apparent activation energy, characteristics of granular sludge, and metagenomic sequencing. These results clearly confirmed that Fe0 supplement not only improved nitrogen removal of PN/A process, but also conferred a certain degree of robustness to the system in the face of temperature fluctuations.

Metagenomic insights into the mechanism for the rapid enrichment and high stability of Candidatus Brocadia facilitated by Fe(Ⅲ)

The rapid enrichment of anammox bacteria and its fragile resistance to adverse environment are the critical problems facing of anammox processes. As an abundant component in anammox bacteria, iron has been proved to promote the activity and growth of anammox bacteria in the mature anammox systems, but the functional and metabolic profiles in Fe(III) enhanced emerging anammox systems have not been evaluated. Results indicated that the relative abundance of functional genes involved in oxidative phosphorylation, nitrogen metabolism, cofactors synthesis, and extracellular polymers synthesis pathways was significantly promoted in the system added with 5 mg/L Fe(III) (R5). These enhanced pathways were crucial to energy generation, nitrogen removal, cell activity and proliferation, and microbial self-defense, thereby accelerating the enrichment of anammox bacteria Ca. Brocadia and facilitating their resistance to adverse environments. Microbial community analysis showed that the proportion of Ca. Brocadia in R5 also increased to 64.42 %. Hence, R5 could adapt rapidly to the increased nitrogen loading rate and increase the nitrogen removal rate by 108 % compared to the system without Fe(III) addition. However, the addition of 10 and 20 mg/L Fe(III) showed inhibitory effects on the growth and activity of anammox bacteria, which exhibited the lower relative abundance of Ca. Brocadia and unstable or even collapsed nitrogen removal performance. This study not only clarified the concentration range of Fe(III) that promoted and inhibited the enrichment of anammox bacteria, but also deepened our understanding of the functional and metabolic mechanisms underlying enhanced enrichment of anammox bacteria by Fe(III), providing a potential strategy to hasten the start-up of anammox from conventional activated sludge.

Temporal differentiation in the adaptation of functional bacteria to low-temperature stress in partial denitrification and anammox system

Despite reliable nitrite supply through partial denitrification, the adaptation of denitrifying bacteria to low temperatures remains elusive in partial denitrification and anammox (PDA) systems. Here, temporal differentiations of the structure, activity, and relevant cold-adaptation mechanism of functional bacteria were investigated in a lab-scale PDA bioreactor at decreased temperature. Although distinct denitrifying bacteria dominated after low-temperature stress, both short- and long-term stresses exerted differential selectivity towards the species with close phylogenetic distance. Species Azonexus sp.149 showed high superiority over Azonexus sp.384 under short-term stress, and long-term stress improved the adaptation of Aquabacterium sp.93 instead of Aquabacterium sp.184. The elevated transcription of nitrite reductase genes suggested that several denitrifying bacteria (e.g., Azonexus sp.149) could compete with anammox bacteria for nitrite. Species Rivicola pingtungensis and Azonexus sp.149 could adapt through various adaptation pathways, such as the two-component system, cold shock protein (CSP), membrane alternation, and electron transport chain. By contrast, species Zoogloea sp.273 and Aquabacterium sp.93 mainly depended on the CSP and oxidative stress response. This study largely deepens our understanding of the performance deterioration in PDA systems during cold shock and provides several references for efficient adaptation to seasonal temperature fluctuation.

Effect of biochar on the SPNA system at ambient temperatures

Biochar has been extensively studied in wastewater treatment systems. However, the role of biochar in the single-stage partial nitritation anammox (SPNA) system remains not fully understood. This study explored the impact of biochar on the SPNA at ambient temperatures (20 °C and 15 °C). The nitrogen removal rate of the system raised from 0.43 to 0.50 g N/(L·d) as the biochar addition was raised from 2 to 4 g/L. Metagenomic analysis revealed that gene abundances of amino sugar metabolism and nucleotide sugar metabolism, amino acid metabolism, and quorum sensing were decreased after the addition of biochar. However, the gene abundance of enzymes synthesizing NADH and trehalose increased, indicating that biochar could stimulate electron transfer reactions in microbial metabolism and assist microorganisms in maintaining a steady state at lower temperatures. The findings of this study provide valuable insights into the mechanism behind the improved nitrogen removal facilitated by biochar in the single-stage partial nitritation anammox system.

Synchronous Achievement of Advanced Nitrogen Removal and N2O Reduction in the Anoxic Zone in the AOA Process for Low C/N Municipal Wastewater

Continuous flow processes for the in situ determination of N2O emissions during low C/N municipal wastewater treatment have rarely been reported. The anaerobic/aerobic/anoxic (AOA) process has recently shown promising potential in energy savings and advanced nitrogen removal, but it still needs to be comprehensively explored in relation to N2O emissions for its carbon reduction advantages. In this study, a novel gas-collecting continuous flow reactor was designed to comprehensively evaluate the emissions of N2O from the gas and liquid phases of the AOA process. Additionally, the measures of enhancing endogenous denitrification (ED) and self-enriching anaerobic ammonium oxidation (Anammox) were employed to optimize nitrogen removal and achieve N2O reduction in the anoxic zone. The results showed that enhanced ED coupled with Anammox led to an increase in the nitrogen removal efficiency (NRE) from 67.65 to 81.96%, an enhancement of the NO3- removal rate from 1.76 mgN/(L h) to 3.99 mgN/(L h), and the N2O emission factor in the anoxic zone decreased from 0.28 to 0.06%. Impressively, ED eliminated 91.46 ± 2.47% of the dissolved N2O from the upstream aerobic zone, and the dissolved N2O in the effluent was reduced to less than 0.01 mg/L. This study provides valuable strategies for fully evaluating N2O emissions and N2O reduction from the AOA process.

Predicted metabolic roles and stress responses provide insights into candidate phyla Hydrogenedentota and Sumerlaeota as members of the rare biosphere in biofilms from various environments

Pustular mats from Shark Bay, Western Australia, host complex microbial communities bound within an organic matrix. These mats harbour many poorly characterized organisms with low relative abundances (<1%), such as candidate phyla Hydrogenedentota and Sumerlaeota. Here, we aim to constrain the metabolism and physiology of these candidate phyla by analyzing two representative metagenome-assembled genomes (MAGs) from a pustular mat. Metabolic reconstructions of these MAGs suggest facultatively anaerobic, chemoorganotrophic lifestyles of both organisms and predict that both MAGs can metabolize a diversity of carbohydrate substrates. Ca. Sumerlaeota possesses genes involved in degrading chitin, cellulose and other polysaccharides, while Ca. Hydrogenedentota can metabolize cellulose derivatives in addition to glycerol, fatty acids and phosphonates. Both Ca. phyla can respond to nitrosative stress and participate in nitrogen metabolism. Metabolic comparisons of MAGs from Shark Bay and those from various polyextreme environments (i.e., hot springs, hydrothermal vents, subsurface waters, anaerobic digesters, etc.) reveal similar metabolic capabilities and adaptations to hypersalinity, oxidative stress, antibiotics, UV radiation, nitrosative stress, heavy metal toxicity and life in surface-attached communities. These adaptations and capabilities may account for the widespread nature of these organisms and their contributions to biofilm communities in a range of extreme surface and subsurface environments.

Larger hydroxyapatite aggregation from Ca2+ adhesion in ANAMMOX granular sludge caused by high dissolved oxygen

Anaerobic ammonia oxidation (ANAMMOX), a sustainable biological process, is promising to remove NH4+-N from municipal sewage. In this study, results showed that the anammox granular sludge morphology changes with the alternation of dissolved oxygen (DO), mainly attributing to the adhesion of calcium ions (Ca2+) to the surface of sludge particles. Diverse characterization methods revealed that gray adhesions in the form of hydroxyapatite covered the original holes on the anammox granular sludge surface, including scanning Electron Microscopy (SEM), digital camera images, Energy Dispersive Spectrometer (EDS), and X-ray diffraction (XRD). Ex-situ degradation of NH4+-N and NO2--N yielded diverse outcomes. The protein to polysaccharide ratio (PN/PS) in the total extracellular polymeric substances (EPS) across 4 size groups demonstrated a decrease under O2 exposure. Microbial community analysis indicated norank_f_A4b and Nitrolancea being the most abundant genus under O2 exposure at day 1 and day 100, respectively. These findings offer an effective strategy to prevent size-larger granular sludge from deteriorating through changing DO and Ca2+ in municipal wastewater in ANAMMOX.

Robust rehabilitation of anammox system by granular activated carbon under long-term starvation stress: Microbiota restoration and metabolic reinforcement

This article investigates the buffering capacity and recovery-enhancing ability of granular activated carbon (GAC) in a starved (influent total nitrogen: 20 mg/L) anaerobic ammonium oxidation (anammox) reactor. The findings revealed that anammox aggregated and sustained basal metabolism with shorter performance recovery lag (6 days) and better nitrogen removal efficiency (84.9 %) due to weak electron-repulsion and abundance redox-active groups on GAC's surface. GAC-supported enhanced extracellular polymeric substance secretion aided anammox in resisting starvation. GAC also facilitated anammox bacterial proliferation and expedited the restoration of anammox microbial community from a starved state to its initial-level. Metabolic function analyses unveiled that GAC improved the expression of genes involved in amino acid metabolism and sugar-nucleotide biosynthesis while promoted microbial cross-feeding, ultimately indicating the superior potential of GAC in stimulating more diverse metabolic networks in nutrient-depleted anammox consortia. This research sheds light on the microbial and metabolic mechanisms underlying GAC-mediated anammox system in low-substrate habitats.

Anammox activity improved significantly by the cross-fed NO from ammonia-oxidizing bacteria and denitrifying bacteria to anammox bacteria

Nitric oxide (NO) has been suggested as an obligate intermediate in anaerobic ammonium oxidation (anammox), nitrification and denitrification. At the same time, ammonia-oxidizing bacteria (AOB) and denitrifying bacteria (DNB) are always existed in anammox flora, so what is the role of NO produced from AOB and DNB? Could it accelerate nitrogen removal via the anammox pathway with NO as an electron acceptor? To investigate this hypothesis, nitrogen transforming of an anammox biofilter was analyzed, functional gene expression of anammox bacteria (AnAOB), AOB and DNB were compared, and NO source was verified. For anammox biofilter, anammox contributed to 91.3 % nitrogen removal with only 14.4 % of AnAOB being enriched, while DNB was dominant. Meta-omics analysis and batch test results indicated that AOB could provide NO to AnAOB, and DNB also produced NO via up-regulating nirS/K and down-regulating nor. The activation of the anammox pathway of NH4++NO→N2 caused the downregulation of nirS and nxr in Ca. Kuenenia stuttgartiensis. Additionally, changes in nitrogen transforming pathways affected the electron generation and transport, limiting the carbon metabolism of AnAOB. This study provided new insights into improving nitrogen removal of the anammox system.

Analyzing the nitrogen removal performance and cold adaptation mechanism of immobilized cold-acclimation ANAMMOX granules at low temperatures

To improve the treatment performance of anaerobic ammonium oxidation (ANAMMOX) processes at low temperatures, the immobilized cold-acclimation ANAMMOX granules (R3) were prepared and their low-temperature nitrogen removal ability as well as the cold adaptation mechanism were analyzed. The results indicated that the total inorganic nitrogen (TIN) removal efficiency of R3 was significantly higher than that of R2 (cold-acclimation granules without immobilization) and R1 (common granules), especially at 11 ± 2 and 7 ± 2°C (68% and 54%). These were attributed to the remarkable biomass retention capacity of R3, high up to 4.3-4.9 mg/gVSS even at 5-18°C. Besides, higher protein (PN) content of tightly bound extracellular polymeric substances (TB-EPS) also facilitated microbial aggregation in R3. Meanwhile, R3 granules retained higher ANAMMOX activity and heme c content at 5-25°C. The original dominant ANAMMOX genus (Candidatus Kuenenia) in R3 kept higher abundance (49%-57%) at 23 ± 2 and 16 ± 2°C, whereas Candidatus Brocadia became the dominant ANAMMOX genus (25%-32%) in R3 at 11 ± 2 and 7 ± 2°C. Notably, different ANAMMOX genera in R3 may adapt to cold environment by regulating the expression of cold-stress proteins (CspA, CspB, PpiD, and UspA). PRACTITIONER POINTS: Immobilized cold-acclimation ANAMMOX granules showed higher nitrogen removal efficiency at 23°C → 5°C. Immobilization method effectively retained biomass (Candidatus Kuenenia and Candidatus Brocadia). Immobilization facilitated TB-EPS release and biological aggregation in cold-acclimation granules. Expression of cold-stress proteins in immobilized cold-acclimation granules was more active.

Metagenomics reveals the microbial community and functional metabolism variation in the partial nitritation-anammox process: From collapse to recovery

Mainstream partial nitritation-anammox (PNA) process easily suffers from performance instability and even reactor collapse in application. Thus, it is of great significance to unveil the characteristic of performance recovery, understand the intrinsic mechanism and then propose operational strategy. In this study, we combined long-term reactor operation, batch tests, and metagenomics to reveal the succession of microbial community and functional metabolism variation from system collapse to recovery. Proper aeration control (0.10-0.25 mg O2/L) was critical for performance recovery. It was also found that Candidatus Brocadia became the dominant flora and its abundance increased from 3.5% to 11.0%. Significant enhancements in carbon metabolism and phospholipid biosynthesis were observed during system recovery, and the genes abundance related to signal transduction was dramatically increased. The up-regulation of sdh and suc genes showed the processes of succinate dehydrogenation and succinyl-CoA synthesis might stimulate the production of amino acids and the synthesis of proteins, thereby possibly improving the activity and abundance of AnAOB, which was conducive to the performance recovery. Moreover, the increase in abundance of hzs and hdh genes suggested the enhancement of the anammox process. Changes in the abundance of key genes involved in nitrogen metabolism indicated that nitrogen removal pathway was more diverse after system recovery. The achievement of performance recovery was driven by anammox, nitrification and denitrification coupled with dissimilatory nitrate reduction to ammonium. These results provide deeper insights into the recovery mechanism of PNA system and also provide a potential regulation strategy for the stable operation of the mainstream PNA process.

Efficient nitrogen removal and substrate usage in integrated fixed-film activated sludge-anammox system under seasonal temperature variation

To elucidate how integrated fixed-film activated sludge (IFAS) system favors nitrogen removal performance under seasonal temperature variations, two push-flow reactors were operated with and without carriers under the same operating conditions. The results show that the IFAS system had significant advantages in shock response and low temperature adaptation, with a nitrogen removal rate of 0.37-0.53 kg-N(m3·d)-1 at the temperature of 8-12 °C. Anammox bacteria on carriers were almost unaffected by temperature variation, and its nitrogen removal contribution rate stabilized at 55 % in the IFAS system. The Haldane model reveals that the specific anammox activity in the IFAS system was 28 % to 49 % higher than that in the control system at 13 °C. Candidatus_Jettenia, with the highest abundance of 45 %, was the dominant species in the IFAS system and preferred to attach to the carriers. This study provides a feasible scheme for the application of anammox process.

Novel insights into carbon nanomaterials enhancing anammox for nitrogen removal: Effects and mechanisms

Carbon nanomaterials (CNMs) possess the properties including large specific surface area, high porosity, and stable chemical structures, presenting significant application advantages in wastewater treatment. Indeed, CNMs are considered to be added to anammox systems to strengthen anammox function, especially to resolve the challenge of anammox technology, i.e., the slow growth rate of anammox bacteria, as well as its high environmental sensitivity. This paper systematically reviews the promotion effects and mechanisms of CNMs on the nitrogen removal performance of anammox system. Among the zero-, one-, and two-dimensional CNMs, two-dimensional CNMs have best promoting effect on the nitrogen removal performance of anammox system due to its excellent conductivity and abundant functional groups. Then, the promotion effects of CNMs on anammox process are summarized from the perspective of anammox activity and bacteria abundance. Furthermore, CNMs not only enhance the anammox process, but also stimulate the coupling of denitrification pathways with anammox, as well as the improvement of system operational stability (alleviating the inhibitions of low temperature and pH fluctuation), thus contributing to the promoted nitrogen removal performance. Essentially, CNMs are capable of facilitating microbial immobilization and electron transfer, which favor to improve the efficiency and stability of anammox process. Finally, this review highlights the gap in knowledge and future work, aiming to provide a deeper understanding of how CNMs can strengthen the anammox system and provide a novel perspective for the engineering of the anammox process.

Responses of microbial interactions and functional genes to sulfamethoxazole in anammox consortia

Sulfamethoxazole (SMX) has been widely detected in various environments and its potential environmental risks have caused great concerns. However, the impact mechanism of SMX on microbial interactions among anammox consortia remain unknown. A long-term exposure experiments (140 d) was carried out to systematically examine the influence of SMX (0-1000 μg/L) on the anammox system, especially microbial network dynamics and variations of key metabolic genes. Results showed that anammox system could adapt to SMX below 500 μg/L and maintain a high nitrogen removal efficiency (NRE) of 85.35 ± 2.42%, while 1000 μg/L SMX significantly decreased the abundance of functional microbes and deteriorated denitrification performance with NRE dropped to 36.92 ± 15.01%. Co-occurrence network analysis indicated that 1000 μg/L SMX decreased the interactions between Proteobacteria and Chloroflexi and limited AnAOB from playing an important role as central nodes in the subnetwork of Planctomycetes. Metagenomics analysis found that genes associated with nitrogen removal (i.e., hdh, hzs, nirS, and hao) showed lower expression level after addition of SMX, while SMX-related ARGs (sul1 and sul2) increased by 1.22 and 2.68 times. This study provided us a relatively comprehensive perspective in response of microbial interactions and metabolic activity to various SMX concentrations.

Insights into the response of anammox process to oxytetracycline: Impacts of static magnetic field

The long-term effects of oxytetracycline (OTC) with a high concentration on the anaerobic ammonium oxidation (Anammox) process were evaluated, and the role of static magnetic field (SMF) was further explored. The stress of OTC at 50 mg/L had little effect on the nitrogen removal of anammox process at the first 16 days. With the continuous addition of OTC and the increase of nitrogen loading, the OTC inhibited the nitrogen removal and anammox activity severely. During the 32 days of recovery period without OTC addition, the nitrogen removal was further deteriorated, indicating the inhibition of OTC on anammox activity was irreversible and persistent. The application of SMF alleviated the inhibition of OTC on anammox to some extent, and the specific anammox activity was enhanced by 47.1% compared to the system without SMF during the OTC stress stage. Antibiotic efflux was the major resistance mechanism in the anammox process, and tetA, tetG and rpsJ were the main functional antibiotic resistance genes. The addition of OTC weakened the metabolic interactions between the anammox bacteria and the symbiotic bacteria involved in the metabolism of cofactors and secondary metabolites, leading to the poor anammox activity. The adaptability of microbes to the OTC stress was improved by the application of SMF, which can enhance the metabolic pathways related to bacterial growth and resistance to environmental stress.

Microbial interactions play a keystone role in rapid anaerobic ammonium oxidation sludge proliferation and biofilm formation

Two mature anaerobic ammonium oxidation (anammox) consortia with high/low relative abundance of anammox bacteria were inoculated for the rapid sludge proliferation and biofilm formation in this study, named up-flow anaerobic sludge blanket reactor (UASB1) (high) and UASB2 (low), respectively. Results showed that the nitrogen removal efficiency of UASB2 reached 90.94% after the 120-day operation, which was 13% higher than that of UASB1. Moreover, its biomass amounts were 22.18% (biofilm) and 40.96% (flocs) higher than that of UASB1, respectively. Ca. Kuenenia possessed relative abundances of 29.32% (flocs), 27.42% (biofilm) and 31.56% (flocs), 35.20% (biofilm) in the UASB1 and UASB2, respectively. The relative abundances of genes involved in anammox transformation (hzs, nir) and carbon metabolism (fdh, lgA/B/C, acs) were higher in the UASB2, indicating that Ca. Kuenenia might produce acetate and glycogen to enhance microbial interactions. These findings emphasized the importance of microbial interactions in anammox sludge proliferation and biofilm formation.

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.