Deep insights into the population shift of n-DAMO and Anammox in granular sludge: From sidestream to mainstream

Granular sludge combined n-DAMO and Anammox (n-D/A) is an energy-efficient biotechnique for the simultaneous removal of nitrogen and dissolved methane from wastewater. However, the lack of knowledge so far about the metabolic interactions between n-DAMO and Anammox in response to operation condition in granular sludge restrains the development of this biotechnology. To address this gap, three independent membrane granular sludge reactors (MGSRs) were designed to carry out the granule-based n-D/A process under different conditions. We provided the first deep insights into the metabolic interactions between n-DAMO and Anammox in granular sludge via combined metagenomic and metatranscriptomic analyses. Our study unveiled a clear population shift of n-DAMO community from Candidatus Methanoperedens to Candidatus Methylomirabilis from sidestream to mainstream. Candidatus Methanoperedens with relative abundance of 25.2% played the major role in nitrate reduction and methane oxidation under sidestream condition, indicated by the high expression activities of mcrA and narG. Candidatus Methylomirabilis dominated the microbial community under mainstream condition with relative abundance of 32.1%, supported by the high expression activities of pmoA and hao. Furthermore, a transition of Anammox population from Candidatus Kuenenia to Candidatus Brocadia was also observed from sidestream to mainstream. Candidatus Kuenenia and Candidatus Brocadia jointly contributed to the primary anaerobic ammonium oxidation suggested by the high expression value of hdh and hzs. Candidatus Methylomirabilis was speculated to perform ammonium oxidation mediated by pMMO under mainstream condition. These findings might help to reveal the microbial interactions and ecological niches of n-DAMO and Anammox microorganisms, shedding light on the optimization and management of the granule-based n-D/A system.

Electron transfer mechanism of intracellular carbon-dependent DNRA inside anammox bacteria

Generally, anaerobic ammonium oxidation (anammox) converts nitrite (NO2-) and ammonium (NH4+) to nitrogen gas (N2) but generates some nitrate (NO3-) (equivalent to 11% of inlet total nitrogen (TN)). Although it reported that anammox bacteria could degrade NO3- via dissimilatory nitrate reduction to ammonium (DNRA) pathway using the intracellular carbon as the electron donor, it is still unclear the specific electron transfer mechanism in this intracellular carbon-dependent DNRA inside anammox bacteria, and whether the sole anammox bacteria could achieve higher TN removal efficiency more than the theoretical maximum of 89%. In this study, transcriptome analysis and metabolic inhibitor experiments demonstrated that NADH generated from the decomposition of the intracellular carbon (glycogen) supplied electrons for the NO3-conversion; the electrons were transferred from NADH to nitrate reductase (Nar) and nitrite reductase forming ammonium (NrfA) from ubiquinone (UQ) and complex III, respectively. Combining the intracellular carbon-dependent DNRA with normal anammox process, an average TN removal efficiency of 95% was achieved by the sole anammox bacteria in a sequencing batch reactor. Fluorescent in situ hybridization (FISH) images and real-time fluorescence quantitative PCR (qPCR) results illustrated anammox bacteria could survive and proliferate in the SBR. Our work improved the understanding of the electron transfer mechanism inside anammox bacteria, and further exploit its potential in nitrogen pollutants removal.

Impacts of granular sludge properties on the bioreactor performing nitrate/nitrite-dependent anaerobic methane oxidation/anammox processes

In this work, a bioprocess model was applied to first determine the impacts of influent substrates conditions on the granular bioreactor performing nitrate/nitrite-dependent anaerobic methane oxidation (n-DAMO) and anammox integrated processes and then investigate the roles of granular sludge properties in regulating the bioreactor performance and start-up process. The ideal influent substrates conditions were identified at NO2--N/NH4+-N of 1:1 and dissolved CH4 concentration of 85 g COD m-3, which achieved 98.6% total nitrogen removal and 87.7% dissolved CH4 utilization. Under such ideal influent conditions, the initial properties of granular sludge didn't significantly affect the granular bioreactor performance. However, inoculation of granular sludge with a relatively small granular sludge size and a high abundance of n-DAMO archaea or/and anammox bacteria could effectively shorten the bioreactor start-up. Meanwhile, reducing the diffusivity of solutes within granular sludge was also beneficial for expediting the start-up process and promoting dissolved CH4 utilization.

Enhanced nitrogen removal from rural domestic sewage via partial nitrification-anammox in integrated vertical subsurface flow constructed wetland

This study aimed to improve the removal of nitrogen treating rural domestic sewage by developing a novel strategy for achieving partial nitrification-anammox (PNA) in an integrated vertical subsurface flow constructed wetland (VSFCW). The influent ammonia was oxidized to nitrite in the partial nitrification VSFCW (VSFCWPN), and 5 mg/L of hydroxylamine was added under the appropriate dissolved oxygen concentration level (1.2 ± 0.2 mg/L) to stabilize the average nitrite accumulation rate at 88.24% and maintain the effluent NO2--N/NH4+-N ratio at 1.26 ± 0.15. The effluent from VSFCWPN was introduced to the following chamber (VSFCWAN), where ammonia and nitrite were removed by the autotrophic anammox process. This implementation achieved high removal efficiencies for chemical oxygen demand, total nitrogen, and PO43--P, reaching 86.26%, 90.22%, and 78.94%, respectively, with influent concentrations of 120.75 mg/L, 60.02 mg/L, and 5.05 mg/L. Substrate samples were collected from 10 cm height (PN1, AN1) and 25 cm height (PN2, AN2). Microbial community analysis showed that Nitrosomonas dominated the community composition in VSFCWPN, with an increase from 1.61% in the inoculated sludgePN to 16.31% (PN1) and 12.09% (PN2). Meanwhile, Ca. Brocadia accounted for 44.81% (AN1) and 36.50% (AN2) in VSFCWAN. These results confirm the feasibility of the proposed strategy for establishing PNA and efficiently treating rural domestic sewage in an integrated VSFCW.

Effects of benthic bioturbation on anammox in nitrogen removal at the sediment-water interface in eutrophic surface waters

Anaerobic ammonium oxidation (anammox) significantly contributes to nitrogen loss in freshwater ecosystems. The sediment-water interface (SWI), known as a "hot spot" for anammox, also harbors numerous macroinvertebrates. However, the impact of their bioturbation on anammox has generally been overlooked. This study compared the effects of three representative macroinvertebrates (i.e., Propsilocerus akamusi, Branchiura sowerbyi and Radix swinhoei) with different bioturbation modes on anammox and the N-removal processes at the SWI by using a microcosmic system. The results demonstrated that all three benthic macroinvertebrates promoted anammox in addition to denitrification processes. The highest N-removal was achieved in the presence of P. akamusi considered as a gallery-diffuser, where the relative abundance of Planctomycetes (to which the anammox bacteria belong) increased by 70%. P. akamusi increased the abundance of anammox hzsB gene by 2.58-fold and promoted potential anammox rate by 12.79 nmol N g-1 h-1, which in turn facilitated total N-removal mass increased by 2.42-fold. In the presence of B. sowerbyi and R. swinhoei, the potential anammox rates increased by 4.81 and 5.57 nmol N g-1 h-1, respectively. These results underscore the substantial impact of macroinvertebrates on anammox and N-removal processes, highlighting their crucial role in N pollution control, and sustaining the overall health and stability of eutrophic water bodies.

Defense mechanism of Fe(III)-assisted anammox under salt stress: Performance and microbial community dynamics

Anammox process has attracted attention due to its excellent nitrogen removal properties in nitrogen-rich wastewater treatment. However, there were some obstacles for the application of anammox to treat high saline wastewater due to its sensitivity to salinity. In this study, Fe(III) addition strategy was developed to assist anammox to adapt high saline surroundings, with the defense mechanism involved in Fe(III)-assisted anammox emphasized. Nitrogen removal performance of anammox was deteriorated at 3.5% salinity, with the average total nitrogen removal rate of 0.85 kg/(m3·d) observed. The continuous addition of Fe(III) could significantly assist anammox to resist high salinity through facilitating the enrichment of anammox species. Candidatus Kuenenia was the main anammox species and outcompeted Candidatus Brocadia under high saline surrounding. The relative abundance of Candidatus Kuenenia increased with increased salinity and reached 41.04% under 3.5% salinity. The synthesis of key enzymes of anammox species were improved through Fe(III) addition and then facilitated the energy metabolism of anammox bacteria under 3.5% salinity. This study provides a new thought in Fe(III)-assisted anammox enhancement technologies and deepens the insight of anammox in high saline wastewater treatment.

Adaptation of anammox process for nitrogen removal from acidic nitritation effluent in a low pH moving bed biofilm reactor

Acidic partial nitritation (PN) has emerged to be a promisingly stable process in wastewater treatment, which can simultaneously achieve nitrite accumulation and about half of ammonium reduction. However, directly applying anaerobic ammonium oxidation (anammox) process to treat the acidic PN effluent (pH 4-5) is susceptible to the inhibition of anammox bacteria. Here, this study demonstrated the adaptation of anammox process to acidic pH in a moving bed biofilm reactor (MBBR). By feeding the laboratory-scale MBBR with acidic PN effluent (pH = 4.6 ± 0.2), the pH of an anammox reactor was self-sustained in the range of pH 5 - 6. Yet, a high total nitrogen removal efficiency of over 80% at a practical loading rate of up to 149.7 ± 3.9 mg N/L/d was achieved. Comprehensive microbial assessment, including amplicon sequencing, metagenomics, cryosection-FISH, and qPCR, identified that Candidatus Brocadia, close to known neutrophilic members, was the dominant anammox bacteria. Anammox bacteria were found present in the inner layer of thick biofilms but barely present in the surface layer of thick biofilms and in thin biofilms. Results from batch tests also showed that the activity of anammox biofilms could be maintained when subjected to pH 5 at a nitrite concentration of 10 mg N/L, whereas the activity was completely inhibited after disturbing the biofilm structure. These results collectively indicate that the anammox bacteria enriched in the present acidic MBBR could not be inherently acid-tolerant. Instead, the achieved stable anammox performance under the acidic condition is likely due to biofilm stratification and protection. This result highlights the biofilm configuration as a useful solution to address nitrogen removal from acidic PN effluent, and also suggests that biofilm may play a critical role in protecting anammox bacteria found in many acidic nature environments.

Permeability decides the effect of antibiotics on sedimentary nitrogen removal in Jiulong River Estuary

Sedimentary denitrification takes place beneath the oxic layer at the sediment-water interface, where nitrate and antibiotics need to diffuse through the overlying water. However, the antibiotics' effect on sedimentary N removal and associated N2O production has not been adequately investigated under in situ conditions. Here, isotope pairing techniques, including slurry incubations (potential) and intact core incubations (in situ), combined with metagenomic analysis were applied to investigate the impacts of two protein-inhibiting antibiotics (oxytetracycline and thiamphenicol) on sediment nitrogen removal in a subtropical estuary. Slurry incubations showed that the two antibiotics significantly inhibited denitrification (67-98%) and anammox (49-99%), while intact core incubations presented no antibiotic effect at upstream but significant inhibition (23%-52%) at downstream. Meanwhile, N2O yields were stimulated up to 20 folds in slurry incubations yet showing insignificant response in intact cores. Such contrasting results between up- and down-stream and between slurry and intact core incubations strongly indicated that permeability, which determines diffusion of antibiotics to microbes, is the key to exert the effect of antibiotics on in situ sedimentary nitrogen removal processes regardless the existence of antibiotics resistance genes. This diffusive obstruction may mitigate the toxic effect of antibiotics on nitrogen removal related microbes in natural environments.

Light-Driven Electron Uptake from Nonfermentative Organic Matter to Expedite Nitrogen Dissimilation by Chemolithotrophic Anammox Consortia

Nonphotosynthetic microorganisms are typically unable to directly utilize light energy, but light might change the metabolic pathway of these bacteria indirectly by forming intermediates such as reactive oxygen species (ROS). This work investigated the role of light on nitrogen conversion by anaerobic ammonium oxidation (anammox) consortia. The results showed that high intensity light (>20000 lx) caused ca. 50% inhibition of anammox activity, and total ROS reached 167% at 60,000 lx. Surprisingly, 200 lx light was found to induce unexpected promotion of the nitrogen conversion rate, and ultraviolet light (<420 nm) was identified as the main contributor. Metagenomic and metatranscriptomic analyses revealed that the gene encoding cytochrome c peroxidase was highly expressed only under 200 lx light. 15N isotope tracing, gene abundance quantification, and external H2O2 addition experiments showed that photoinduced trace H2O2 triggered cytochrome c peroxidase expression to take up electrons from extracellular nonfermentative organics to synthesize NADH and ATP, thereby expediting nitrogen dissimulation of anammox consortia. External supplying reduced humic acid into a low-intensity light exposure system would result in a maximal 1.7-fold increase in the nitrogen conversion rate. These interesting findings may provide insight into the niche differentiation and widespread nature of anammox bacteria in natural ecotopes.

Novel insight into the inhibitory effects and mechanisms of Fe(II)-mediated multi-metabolism in anaerobic ammonium oxidation (anammox)

Fe(II) participates in complex Fe-N cycles and effects on the microbial metabolism in the anaerobic ammonium oxidation (anammox) dominated system. In this study, the inhibitory effects and mechanisms of Fe(II)-mediated multi-metabolism in anammox were revealed, and the potential role of Fe(II) in the nitrogen cycle was evaluated. The results showed that the long-term accumulation of high Fe(II) concentrations (70-80 mg/L) led to a hysteretic inhibition of anammox. High Fe(II) concentrations induced the generation of high levels of intracellular ·O2-, whereas the antioxidant capacity was insufficient to eliminate the excess ·O2-, thus causing ferroptosis to anammox cells. In addition, Fe(II) was oxidized via nitrate-dependent anaerobic ferrous-oxidation (NAFO) process, and mineralized to coquimbite and phosphosiderite. They formed crusts on the surface of the sludge, leading to mass transfer obstruction. The results of the microbial analysis showed that the addition of appropriate Fe(II) increased the abundance of Candidatus Kuenenia, and served as a potential electron donor to enrich Denitratisoma, promoting anammox and NAFO coupled with nitrogen removal, while high Fe(II) concentrations reduced the enrichment level. In this study, the understanding of Fe(II)-mediated multi-metabolism in the nitrogen cycle was deepened, providing the basis for the development of Fe(II)-based anammox technologies.

Metabolic insights into the interaction between nitrogen removal and 4-chlorophenol reduction of anammox consortia

The response characteristic and performance stabilization of anammox process under the stress of the potential organic pollutants support the application of ammonia-nitrogen wastewater treatment. In the present study, nitrogen removal performance was significantly suppressed with the addition of 4-chlorophenol. The activity of anammox process was inhibited by 14.23% (0.1 mg/L), 20.54% (1 mg/L) and 78.15% (10 mg/L), respectively. Metagenomic analysis revealed a significant decrease in the abundance of KEGG pathways associated with carbohydrate and amino acid metabolism with increasing 4-chlorophenol concentration. Metabolic pathway profiles suggest that putrescine is down-regulated at high 4-chlorophenol stress due to inhibition of nitrogen metabolism processes, while it is up-regulated to reduce oxidative damage. In addition, the presence of 4-chlorophenol induced an enhancement of EPS and bacterial debris decomposition, and a partial conversion of 4-chlorophenol to p-nitrophenol. This study unravels the mechanism of effect on anammox consortia in response to 4-CP, which could provide supplementary to facilitate its full-scale application.

Salinity effect on an anaerobic methane- and ammonium-oxidising consortium: Shifts in activity, morphology, osmoregulation and syntrophic relationship

Nitrate-dependent anaerobic methane oxidation (AOM) is a microbial process of both ecological significance for global methane mitigation and application potential for wastewater treatment. It is mediated by organisms belonging to the archaeal family 'Candidatus Methanoperedenaceae', which have so far mainly been found in freshwater environments. Their potential distribution in saline environments and their physiological responses to salinity variation were still poorly understood. In this study, the responses of the freshwater 'Candidatus Methanoperedens nitroreducens'-dominated consortium to different salinities were investigated using short- and long-term setups. Short-term exposure to salt stress significantly affected nitrate reduction and methane oxidation activities over the tested concentration range of 15-200‰ NaCl, and 'Ca. M. nitroreducens' showed the higher tolerance to high salinity stress than its partner of anammox bacteria. At high salinity concentration, near marine conditions of 37‰, the target organism 'Ca. M. nitroreducens' showed stabilized nitrate reduction activity of 208.5 µmol day-1 gCDW-1 in long-term bioreactors over 300 days, in comparison to 362.9 and 334.3 µmol day-1 gCDW-1 under low-salinity conditions (1.7‰ NaCl) and control conditions (∼15‰ NaCl). Different partners of 'Ca.  M. nitroreducens' evolved in the consortia with three different salinity conditions, suggesting the different syntrophic mechanisms shaped by changes in salinity. A new syntrophic relationship between 'Ca. M. nitroreducens' and Fimicutes and/or Chloroflexi denitrifying populations was identified under the marine salinity condition. Metaproteomic analysis shows that the salinity changes lead to higher expression of response regulators and selective ion (Na+/H+) channeling proteins that can regulate the osmotic pressure between the cell and its environment. The reverse methanogenesis pathway was, however, not impacted. The finding of this study has important implications for the ecological distribution of the nitrate-dependent AOM process in marine environments and the potential of this biotechnological process for the treatment of high-salinity industrial wastewater.

Hydrodynamic controls on nitrogen distribution and removal in aquatic ecosystems

The impact of nitrogen (N) on water eutrophication is well-known, but the specific influence of hydrodynamic factors on N occurrence in aquatic systems has remained unclear. This lack of understanding has hindered our ability to assess the self-purification function of aquatic ecosystems and address water pollution problem. Here, we collected overlying water and sediment samples from different aquatic ecosystems (ditch, pond, river, and reservoir) in the Danjiangkou Reservoir area and compared the variation characteristics of various N components, and further conducted an incubation experiment to investigate the rate of N removal. We found that the concentration of total N and its N components decreased from ditches and ponds to rivers and reservoirs, indicating that N removal occurred during water flow, with up to 43% of total N concentration reduction rate. Additionally, we observed higher heterogeneity in eco-stoichiometric characteristics of N components in ditches and ponds compared to rivers and reservoirs. Interestingly, the ditches and ponds exhibited stronger interactions between overlying water and sediment, with higher rates of denitrification and anaerobic ammonium oxidation (anammox). Our findings highlight the need to focus on the upper reaches of agricultural catchments, such as ditches and ponds, for N removal and emphasize the importance of developing region-specific conservation strategies to mitigate N pollution and protect water resources.

Effect of salinity stress on nitrogen and sulfur removal performance of short-cut sulfur autotrophic denitrification and anammox coupling system

The effects of salinity on anaerobic nitrogen and sulfide removal were investigated in a coupled anammox and short-cut sulfur autotrophic denitrification (SSADN) system. The results revealed that salinity had significant nonlinear effects on the nitrogen and sulfur transformations in the coupled system. When the salinity was <2 %, the anammox and SSADN activities increased with increasing salinity, and the total nitrogen removal rate, S⁰ production rate, and nitrite production rate were 0.41 kg/(m³·d), 0.37 kg/(m³·d), and 0.28 kg/(m³·d), respectively. With continuous increase of salinity, the performances of the anammox and SSADN gradually decreased, and the three indicators decreased to 0.14 kg/(m³·d), 0.22 kg/(m³·d), and 0.14 kg/(m³·d) at 5 % salinity, respectively. When the salinity reached 5 %, the nitrogen removal contribution of anammox decreased to 68.4 %, while the contribution of the sulfur autotrophic denitrification increased to 31.6 %. The coupled system recovered in a short time after alleviation of the salinity stress, and the SSADN activity recovery was faster than anammox. The microbial community structure and functional microbial abundance in the coupled system changed significantly with increasing salinity, and the functional microbial abundance after recovery was considerably different from the initial state.

Highly efficient and robust treatment of low C/N actual domestic sewage via integrated fermentation, partial-nitrification, partial-denitrification and anammox (IFPNDA)

For achieving efficient and robust treatment of domestic sewage with C/N around 2.8, this study innovatively developed an integrated fermentation, partial-nitrification, partial-denitrification and anammox (IFPNDA) process based on the Anaerobic Baffled Reactor and Continuous-flow Stirred Tank Reactor (ABR-CSTR) bioreactor. Desirable N-removal efficiency of 87.5 ± 2.1% was obtained without external organics, correspondingly effluent total nitrogen (TN) concentration reached 6.1 ± 0.7 mg/L. The N-removal stability was greatly facilitated by the effective linkage between partial nitrification (PN) process and partial denitrification (PD) process in emergency. Highly enriched hydrolytic bacteria (6.9%) and acidogenic bacteria (5.7%) in A1, especially Comamonas (2.8%) and Longilinea (3.5%), induced the significant increase of volatile fatty acids (VFAs) in domestic sewage. Thauera (6.1%) in A2 and Nitrosomonas (5.4%) in A3 acted as the dominant flora of nitrite supplies for anammox in IFPNDA process. Candidatus_Brocadia (2.4%) dominated the advanced nitrogen removal. The IFPNDA process exhibited much potential for achieving energy neutrality during wastewater treatment.

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.

Enhanced sludge settlement of two stage PN/Anammox for reject water treatment with respective diatomite addition

The present study investigated the potential of diatomite addition in enhancing sludge settlement of two-stage PN/Anammox for real reject water treatment, with a focus on sludge settling velocity, nitrogen removal capacity, sludge morphological features, and microbial community changes. The study found that diatomite addition significantly improved the sludge settleability of the two-stage PN/A process, resulting in a decrease in sludge volume index (SVI) from 70 to 80 mL/g to about 20-30 mL/g for both PN and Anammox sludge, although the sludge-diatomite interaction differed between the two types of sludge. In the PN sludge, diatomite acted as a carrier, while in the Anammox sludge, it acted as micro-nuclei. The addition of diatomite also increased the biomass amounts in the PN reactor, with a 5-29 % improvement attributed to its role as a biofilm carrier. The effects of diatomite addition on sludge settleability were more prominent at high mixed liquor suspended solids (MLSS), where sludge characteristics were deteriorated. Furthermore, the settling rate of the experimental group consistently exceeded that of the blank group after diatomite addition, with a significant decrease in SV. The relative abundance of Anammox bacteria was improved, and sludge particle size decreased in the diatomite-added Anammox reactor. Diatomite was effectively retained in both reactors, with less loss observed for Anammox than PN due to its more tightly wrapped structure, resulting in a stronger sludge-diatomite interaction. Overall, the results of this study suggest that diatomite addition has potential in enhancing the settling properties and performance of two-stage PN/Anammox for real reject water treatment.

Mitigating mechanism of nZVI-C on the inhibition of anammox consortia under long-term tetracycline hydrochloride stress: Extracellular polymeric substance properties and microbial community evolution

In this study, activated carbon-loaded nano-zero-valent iron (nZVI-C) composites were added to anaerobic ammonium oxidation bacteria (AnAOB) to overcome the inhibition of tetracycline hydrochloride (TCH). Results showed that 500 mg L^-1 nZVI-C effectively mitigated the long-term inhibition of 1.5 mg L^-1 TCH on AnAOB and significantly improved the total nitrogen removal efficiency (TNRE) (from 65.27% to 86.99%). Spectroscopic analysis revealed that nZVI-C increased the content of N-H and CO groups in EPS, which contributed to the adsorption of TCH. The accumulation of humic acid-like substances in EPS was also conducive to strengthening the extracellular defense level. In addition, TCH-degrading bacteria (Clostridium and Mycobacterium) were enriched in situ, and the abundance of Ca. Brocadia was significantly increased (from 10.69% to 18.59%). Furthermore, nZVI-C increased the abundance of genes encoding tetracycline inactivation (tetX), promoted mineralization of TCH by 90%, weakening the inhibition of TCH on microbial nitrogen metabolism. nZVI-C accelerated the electron consumption of anammox bacteria by upregulating the abundance of electron generation genes (nxrA, hdh) and providing electrons directly.

Multi-chambers of pilot-scale reactor enhanced partial nitritation performance

Nowadays, applying anammox to treat high nitrogenous side-stream wastewater has taken a step forward. However, the partial nitritation process is sensitive to the ammonium concentration and the nitrogen loading rate, which significantly influences the nitrogen removal performance. This study investigated the performance of a novel nitritation pilot-scale reactor which was divided into four chambers. The nitrite accumulation efficiency reached more than 90 % in the rural wastewater treatment process. As the reactor was divided into four chambers, the comprehensive statistical results showed that the concentration of free ammonium in the front chambers had been effectively improved. The proportion of free ammonium concentration (>0.1 mg NH₃·L^-1), which could inhibit the activity of nitrite oxidizing bacteria, in first chamber (PN1) was 2 times higher than in the last chamber (PN4). Meanwhile, Nitrosomonas, responsible for ammonium oxidation to nitrite, was highly enriched in the first two chambers even though the dissolved oxygen was maintained at 1.5 ± 0.3 mg·L^-1. Compare to conventional reactor, the resistance of the novel reactor to volumetric shock loading has been enhanced. Even though the ammonium loading rate fluctuated greatly, the effluent was still stable and could meet the demand following the anammox process. This study demonstrated that the reactor with multi-chambers could effectively improve the nitrite accumulation efficiency in the partial nitritation process and thus provide a new perspective on the partial nitritation process in a single reactor and further promote the anammox performance in the wastewater treatment process.

Biological carbon promotes the recovery of anammox granular sludge after starvation

This article adopts the strategy of adding biochar and increasing HRT to accelerate the performance and particle morphology recovery of anaerobic ammonia oxidation granular sludge stored at room temperature for 68 days. The results showed that biochar accelerated the death of heterotrophic bacteria, shortened the cell lysis and lag period of the recovery process by 4 days, and it only took 28 days for the nitrogen removal performance of the reactor to recover to the original level, and 56 days for re-granulation. Biochar promoted the secretion of EPS (56.96 mg gVSS^-1), and the sludge volume and nitrogen removal performance of the bioreactor remain stable. Biochar also accelerated the growth of Anammox bacteria. The abundance of Anammox bacteria in the biochar reactor reached 38.76% on the 28th day. The high abundance of functional bacteria and the optimized community structure of biochar made system (Candidatus_Kuenenia: 38.30%) more risk-resistant than control reactor.

Rapid start-up and long-term stable operation of the anammox reactor based on biofilm process: Status, challenges, and perspectives

Anammox-biofilm processes have great potential for wastewater nitrogen removal, as it overcomes the slow growth and easy loss of AnAOB (anaerobic ammonium oxidation bacteria). Biofilm carrier is the core part of the Anammox-biofilm reactor and plays a key role in the start-up and long-term operation of the process. Therefore, the research on the biofilm carrier of Anammox-based process was summarized and discussed in terms of configurations and types. In the Anammox-biofilm process, fixed bed biofilm reactor is a relatively mature biofilm carrier configuration and has advantages in terms of nitrogen removal and long-term operational stability, while moving bed biofilm reactor has advantages in terms of start-up time. Although the long-term operational stability of fluidized bed biofilm reactor is good, its nitrogen removal performance needs to be improved. Among the different biofilm carrier categories, the inorganic biofilm carrier has an advantage in start-up time, due to the enhancement of the growth and metabolic of AnAOB by inorganic materials (such as carbon and iron). Anammox-based reactors using organic biofilm carriers, especially suspension carriers, are well-established and more stable in long-term operation. Composite biofilm carriers combine the advantages of several materials, but their complex preparation procedures lead to high costs. In addition, possible research directions for accelerating the start-up and keeping the long-term stable operation of Anammox reactor by biofilm process were highlighted. It is hoped to provide a possible pathway for the rapid start-up of Anammox-based process, and references for the optimization and promotion of process.

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.

Decryption for nitrogen removal in Anammox-based coupled systems: Nitrite-induced mechanisms

This study investigated the effects of NO₂^- on synergetic interactions between Anammox bacteria (AnAOB) and sulfur-oxidizing bacteria (SOB) in an autotrophic denitrification-Anammox system. The presence of NO₂^- (0-75 mg-N/L) was shown to significantly enhance NH₄⁺ and NO₃^- conversion rates, achieving intensified synergy between AnAOB and SOB. However, once NO₂^- exceed a threshold concentration (100 mg-N/L), both NH₄⁺ and NO₃^- conversion rates decreased with increased NO₂^- consumption via autotrophic denitrification. The cooperation between AnAOB and SOB was decoupled due to the NO₂^- inhibition. Improved system reliability and nitrogen removal performance was achieved in a long-term reactor operation with NO₂^- in the influent; reverse transcription-quantitative polymerase chain reaction analysis showed elevated hydrazine synthase gene transcription levels (5.00-fold), comparing to these in the reactor without NO₂^-. This study elucidated the mechanism of NO₂^- induced synergetic interactions between AnAOB and SOB, providing theoretical guidance for engineering applications of Anammox-based coupled systems.

Anammox bacteria adapt to long-term light irradiation in photogranules

Photogranules composed of algae, nitrifiers, and anammox bacteria are promising for nitrogen removal from wastewater with reduced aeration and carbon emissions. However, it is difficult to be achieved as the potential inhibition of anammox bacteria by light. In this study, a syntrophic algal-partial nitrification/anammox granular sludge process was developed, with a nitrogen removal rate of 294.5 mg N/(L·d). We found the symbiosis in the community promoted the adaptation of anammox bacteria under light, and cross-feeding played an important role. Microalgae in the outer layers of photogranules sheltered most of the light and supplied cofactors and amino acids to promote nitrogen removal. In particular, Myxococcota MYX1 degraded the extracellular proteins produced by microalgae, providing amino acids to the entire bacterial community, which helped anammox bacteria save metabolic energy and adapt to light. Notably, the anammox bacteria Candidatus Brocadia exhibited unique light-sensing potential and adaptations to light irradiation compared with Candidatus Jettenia, including diverse DNA repair, scavenging of reactive oxygen species, cell movement. The phytochrome-like proteins encoded by Candidatus Brocadia further facilitated their spatial positioning and niche partitioning in photogranules. This study provides insights into the response of anammox bacteria in the algae-bacteria symbiosis system and suggests its potential application for carbon-negative nitrogen removal.

Integration of the sulfate reduction and anammox processes for enhancing sustainable nitrogen removal in granular sludge reactors

The Anammox and Sulfate Reduction Ammonium Oxidation processes were compared in two granular sequencing batch reactors operated for 160 days under anammox conditions. It was hypothesized that increasing the concentration of SO₄^2- may positively influence the rate of N removal under anaerobic conditions and it was tested whether SO₄^2- reduction and anammox occur independently or are related to each other. The cooperation of N-S cycles by increasing the concentration of influent SO₄^2- to 952 mg S/L in the second reactor, a higher ammonium utilization rate and sulfate utilization rate was achieved compared to the first reactor, i.e., 2.1-fold and 15-fold, respectively. Nitrosomonas played the dominant role in the N metabolism, while Thauera - in the S metabolism. This study highlights the benefits of linking the N-S cycles as an effective approach for the treatment of NH₄⁺ and SO₄^2- - rich wastewater, including lower substrate removal cost and reduced energy consumption.