Impact of substrate concentration on anammox-UBF reactors start-up

Achieving partial nitrification and denitrification coupled with simultaneous partial nitrification, anammox, and denitrification (PND-SNAD) by the inhibition of sulfide to accomplish stabilized nitrogen removal

The simultaneous partial nitrification, anammox, and denitrification (SNAD) process is widely applied for treating high-ammonia wastewater, but its application to low-ammonia organic wastewater has been scarcely explored. In this study, a partial nitrification and denitrification coupled with simultaneous partial nitrification, anammox, and denitrification (PND-SNAD) system was established to treat organic wastewater with low ammonia concentration. Experimental results revealed that sulfide at 5 mg/L selectively inhibited nitrite-oxidizing bacteria (NOB) but had little effect on ammonium-oxidizing bacteria (AOB). Finally, NOB was suppressed in PND system by intermittently adding sulfide to the PND system. The PND system provided nitrite and activated sludge enriched with AOB to the SNAD system during stable operation. The SNAD system demonstrated chemical oxygen demand (COD) and nitrogen removal efficiencies of 89.86 % and 86.45 %. Candidatus Brocadia and Nitrosomonas were the main ammonium oxidizing bacteria (AnAOB) and AOB. The contribution of AOB and denitrifying bacteria (DNB) to nitrogen transformation was 67.15 % and 25.33 % in the PND system. In the SNAD system, the contributions of AnAOB, AOB, and DNB were 34.40 %, 33.59 %, and 27.56 %, respectively. Overall, this study provided a new sustainable strategy for treating organic wastewater with low ammonia concentration.

Enhancing anammox granular sludge for mainstream anammox process by adding iron-loaded diatomite: Performance and intrinsic mechanism

Iron-loaded diatomite (Fe-DE) was developed as the innovative material to enhance anammox granular sludge (AnGS) and mainstream anammox performance. By adding Fe-DE with the Fe:DE ratio of 1:20 and the dosage of 3 g/L, the start-up period of mainstream anammox process was shortened from 29 d to 17 d and its nitrogen removal rate was increased from 0.234 kg N/(m3·d) to 0.437 kg N/(m3·d). AnGS generated more hydrophobic functional groups and redox substances, forming the robust particle structure and improving the electron transfer of anammox reaction. In addition, the key genes PleC, PleD and TrpE/G, related to quorum sensing, increased from 502.69, 91.18 and 18.25 CPM to 532.84, 103.66 and 19.96 CPM. The key genes hzs and hdh related to anammox process also increased by 30.76% and 24.26%. As a result, formation of AnGS was promoted and the enrichment level of Candidatus Brocadia was improved. This study provides a novel insight into the development of innovative material for enhancing mainstream anammox process.

Screening, identification, and application of anaerobic ammonia oxidizing bacteria in activated sludge systems: A comprehensive review

Anaerobic ammonium oxidation (Anammox) has garnered significant attention due to its ability to eliminate the need for aeration and supplementary carbon sources in biological nitrogen removal process, relying on the capacity of anaerobic ammonium oxidizing bacteria (AnAOB) to directly convert ammonium and nitrite nitrogen into nitrogen gas. This review consolidates the latest advancements in AnAOB research, outlining the mechanisms and enzymatic processes of Anammox, and summarizing the molecular biological techniques used for studying AnAOB, such as 16s rRNA sequencing, qPCR, and metagenomic sequencing. Additionally, it also overviews the currently identified AnAOB species and their distinct metabolic traits, while consolidating strategies to improve their performance. It further delineates coupled processes that utilize Anammox technology, offering practical insights for process selection. Eventually, the review concludes by suggesting future research directions and highlighting critical areas for further investigation. This review serves as a theoretical reference for the enrichment and cultivation of AnAOB, environmental impact management, and the selection of effective treatment processes.

Effects of different substrate ratios on the enrichment of anammox bacteria at low substrate concentration

Anammox bacteria (AnAOB) can be easily enriched under high temperatures and high substrate concentrations, while the application of the mainstream anammox process in low substrate municipal sewage is still relatively uncommon. Therefore, this study investigated the enrichment of AnAOB under conditions of low ammonia nitrogen and nitrite concentration at 25 °C. Results showed that using inoculated aerobic sludge, four ASBRs (R1, R2, R3 and R4) were successfully initiated with different influent substrate (NO2--N/NH4+-N) ratios of 1.2, 1.32, 1.4 and 1.5, respectively, with reactor start-up times were 162, 150, 120 and 134 days, respectively. The values of ΔNO2--N/ΔNH4+-N in reactors were stable at 1.17, 1.32, 1.43 and 1.53 respectively. The increase in influent substrate ratios resulted in improved TN removal rates and accelerated consumption of chemical oxygen demand (COD) during the initial start-up stage. The maximum TN removal rates achieved in the four reactors were 76.09%, 79.24%, 82.82% and 82.63%, respectively. The color of sludge gradually changes from yellowish-brown to reddish-brown. Furthermore, the surface of sludge exhibited a porous mineral structure, with crater-like cavities. The dominant anammox species in the system was identified as Candida Brocadia (3.04%). According to qPCR, the abundance of hzsB in the system is 1.65 × 1012 copies/g VSS, confirming the effective enrichment of AnAOB.

Nitrogen removal performance and the biocenosis with microalgae consortium Nitrosifying and anammox bacteria in an upflow reactor

This study introduced an innovative pathway utilizing an algal anaerobic ammonium oxidation (ALGAMMOX) system to treat ammonium wastewater. Lake bottom sludge and anammox sludge were used to cultivate functional microorganisms and microalgae for nitrogen removal in an upflow reactor made of transparent materials. The results showed that the ALGAMMOX system achieved 87.40 % nitrogen removal when the influent NH4 +-N concentration was 100 mg-N/L. Further analysis showed that anammox bacteria Candidatus Brocadia (8.87 %) and nitrosobacteria Nitrosomonas (3.74 %) were crucial contributors, playing essential roles in nitrogen removal. The 16S rRNA gene showed that the anammox bacteria in the sludge transitioned from Candidatus Kuenenia to Candidatus Brocadia. The 18S rRNA gene revealed that Chlamydomonas, Bacillariaceae and Pinnularia were the dominant microalgae in the system at a relative abundance of 7.99 %, 3.64 % and 3.14 %, respectively. This novel approach provides a theoretical foundation for ammonium wastewater treatment.

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.

Anammox process in anaerobic baffled biofilm reactors with columnar packings: Characteristics of flow field and microbial community

The enrichment of anammox bacteria is a key issue in the application of anammox processes. A new type of reactor － anaerobic baffle biofilm reactor (ABBR) developed from anaerobic baffle reactor (ABR) was filled with columnar packings and established for effective enrichment of anammox bacteria. The flow field analysis showed that, compared with ABR, ABBR narrowed the dead zone so as to improve the substrate transferring performances. Two ABBRs with different types of columnar packings (Packings 1 and Packings 2) were constructed to culture anammox biofilms. Packings 1 consisted of the single-form honeycomb carriers while Packings 2 was modular composite packings consisting of non-woven fabric and honeycomb carriers. The effects of different types of columnar packings on microbial community and nitrogen removal were studied. The ABBR filled with Packings 2 had a higher retention rate of biomass than the ABBR filled with Packings 1, making the anammox start-up period be shortened by 21.28%. The enrichment of anammox bacteria were achieved and the dominant anammox bacteria were Candidatus Brocadia in both R1 and R2. However, there were four genera of anammox bacteria in R2 and one genus of anammox bacteria in R1, and the cell density of anammox bacteria in R2 was 95% higher than that in R1. R2 has the advantage of maintaining excellent and stable nitrogen removal performance at high nitrogen loading rate. The results revealed that the packings composed of two types of carriers may have a better enrichment effect on anammox bacteria. This study is of great significance for the rapid enrichment of anammox bacteria and the technical promotion of anammox process.

Optimization of up-flow anaerobic sludge blanket second-layer influent distribution structure

ABSTRACTA parametric model of the second-layer influent distributor is proposed to increase the reaction efficiency of the up-flow anaerobic sludge blanket. The impacts on the flow efficiency of the main parameters, including the length of distribution pipe, that is, the cylinder radius r1, the eccentricity of the nozzle e, and the number of nozzles n1, are investigated. The optimal parameter combination of the second-layer influent distributoris obtained by single factor analysis and orthogonal analysis. Then the two-layer distributor combination model, including the bottom influent distributor and the second-layer influent distributor, is established and the simulations are conducted to study the effect of the two-layer distributor on flow inside the reactor. The simulation results show that the proposed two-layer distributor can achieve a higher mixture efficiency than the single distributor.

Unraveling potential mechanism of different metal ions effect on anammox through big data analysis, molecular docking and molecular dynamics simulation

Heavy metals (HMs) have been widely reported to pose an adverse effect on anaerobic ammonia oxidation (anammox) bacteria, yet the underlying mechanisms remain unclear. This study provides new insights into the potential mechanisms of interaction between HMs and functional enzymes through big date analysis, molecular docking and molecular dynamics simulation. The statistical analysis indicated that 10 mg/L Cu(II) and Cd(II) reduced nitrogen removal rate (NRR) by 85% and 43%, while 5 mg/L Fe(II) enhanced NRR by 29%. Additionally, the results of molecular simulations provided a microscopic interpretation for these macroscopic data. Molecular docking revealed that Hg(II) formed a distinctive binding site on ferritin, while other HMs resided at iron oxidation sites. Furthermore, HMs exhibited distinct binding sites on hydrazine dehydrogenase. Concurrently, the molecular dynamics simulation results further substantiated their capacity to form complexes. Cu(II) displayed the strongest binding affinity with ferritin for -1576 ± 79 kJ/mol in binding free energy calculation. Moreover, Cd(II) bound to ferritin and HDH for -1052.67 ± 58.49 kJ/mol, -290.02 ± 49.68 kJ/mol, respectively. This research addressed a crucial knowledge gap, shedding light on potential applications for remediating heavy metal-laden industrial wastewater.

Quantitative effect of adding percentages of anammox granules on the start-up process and microbial community analysis

The anaerobic ammonium oxidation (anammox) process is challenging due to its long start-up duration and high demand for mature anammox seed sludge. However, adding a small amount of anammox sludge to the inoculum can be a reasonable solution. This study investigated the effect of adding percentage of anammox granules (0, 1, 2, 4, and 8%) in the seed sludge on the anammox start-up process. The anammox process was achieved in all five reactors after 55, 6, 5, 3 and 0 days. Increasing the adding percentage effectively shortened the duration of lag phase and cell lysis, but had little effect on the final nitrogen removal performance, except for 4% adding percentage. Families of Brocadiaceae, Burkholderiaceae, Ignavibacteriaceae, SJA-28, and Rhodocyclaceae were dominant, with a core microbiota of eight operational taxonomic unites (OTUs), and Candidatus Brocadia fulgida became the dominant anammox species. Seven synergistic members with anammox bacteria were identified by correlation network analysis. Major potential functional groups involved in C and N cycle were also observed by FAPROTAX. Together with the qPCR and sequencing results, it was suggested that more than 2% of adding percentages would result in a short lag phase, rapid growth rate in elevation stage, high final performances, and anammox bacteria abundance comparable to that in the anammox seed sludge. This crucial finding indicated the feasibility of economical and rapid start-up of the anammox process with a minimum amount of anammox seed sludge.

Fate of iron nanoparticles in anammox system: Dissolution, migration and transformation

Iron nanoparticles (FeNPs) are commonly used in various industrial processes, leading to their release into the environment and eventual entrance into wastewater treatment plants (WWTPs). FeNPs undergo dissolution, migration, and transformation in WWTPs, which can potentially affect the stable operation of anaerobic ammonia oxidation (anammox) systems and may be discharged with wastewater or biomass. To better understand the fate of FeNPs in anammox systems, exposure experiments were conducted using anammox granular sludges (AnGS) and FeNPs. Results demonstrated that FeNPs released Fe2+ upon contact with water, with a portion being bound to functional groups in extracellular polymeric substances (EPS) and the rest entering the bacteria to form highly absorbable substances. A significant amount of FeNPs was observed to cover the surface of AnGS or aggregate and deposit at the bottom of the reactor, eventually converting into Fe3O4 and stably existing within the anammox system. The findings of this study clarify the fate of FeNPs in anammox systems and provide important insights into the stable operation of anammox systems under FeNPs exposure.

Model-based assessment of mainstream nitrate/nitrite-dependent anaerobic methane oxidation and Anammox process in granular sludge at low temperature

The process of nitrate/nitrite-dependent anaerobic methane oxidation (n-DAMO) coupled with anaerobic ammonium oxidation (Anammox) is one of groundbreaking discoveries for nitrogen removal and methane emission reduction from wastewater simultaneously. Yet its treatment of mainstream wastewater at low temperature is still a major challenge. In this work, a one-dimensional granular sludge model incorporating Arrhenius conversion for temperature effects was constructed to depict the relationships among n-DAMO microorganisms and Anammox. The model framework was successfully evaluated with 380 days measurement data from a membrane granular sludge reactor (MGSR) operated at temperature of 20-10 °C and fed with ammonium and nitrite. The model could satisfactorily predict the kinetics of nitrogen removal rates, effluent nitrogen concentrations and biomass fractions in MGSR at varying temperatures. Despite the decrease in microbial activity of functional microorganisms, the coupled n-DAMO and Anammox process based on granule system in mainstream wastewater treatment achieved a TN removal efficiency of about 98 % and a stable nitrogen removal rate of 0.55 g L-1 d-1. The model developed is expected to facilitate fundamentally understanding the underlying mechanisms of the coupled process and provide proposals for its practical engineering application in wastewater treatment plants.

Enhancing start-up strategies for anammox granular sludge systems: A review

The anaerobic ammonium oxidation (anammox) process has been developed as one of the optimal alternatives to the conventional biological nitrogen removal process because of its high nitrogen removal capacity and low energy consumption. However, the slow growth rate of anammox bacteria and its high sensitivity to environmental changes have resulted in fewer anammox sludge sources for process start-up and a lengthy start-up period. Given that anammox microorganisms tend to aggregate, granular-anammox sludge is a frequent byproduct of the anammox process. In this study, we review state-of-the-art strategies for promoting the formation of anammox granules and the start-up of the anammox process based on the literature of the past decade. These strategies are categorized as the transformation of alternative sludge, the addition of accelerators, the introduction of functional carriers, and the implementation of other physical methods. In addition, the formation mechanism of anammox granules, the operational performance of various strategies, and their promotion mechanisms are introduced. Finally, prospects are presented to indicate the gaps in contemporary research and the potential future research directions. This review functions as a summary guideline and theoretical reference for the cultivation of granular-anammox sludge, the start-up of the anammox process, and its practical application.

Promotion of nitrogen removal in a denitrification process elevated by zero-valent iron under low carbon-to-nitrogen ratio

The nitrogen removal efficiency and distribution of microbial community in a denitrification process aided by zero-valent iron (ZVI) under low carbon-to-nitrogen ratio (C/N) were assessed in this study. Experimental results demonstrated that the nitrogen removal efficiency (TNRE) increased to 96.4 ± 2.72% and 63.3 ± 4.02% after continuous addition of ZVI with molar ratio of ZVI to nitrate (NO3--N) (ZVI/N) of 6 at C/N of 3 and 2, respectively, which was 4% and 7.7% higher than the blank one. Meanwhile, extracellular polymeric substance (EPS) could be used as electron transfer medium and endogenous carbon source for denitrification system and also the production of which increased by 28.43% and 53.10% under ZVI stimulation compared to the control group. Finally, a symbiotic system composed by autotrophic and heterotrophic denitrification bacteria was formed by aid of ZVI. This study proposed new insights into denitrification process improved by ZVI.

Enhancement of nitrogen removal in coupling Anammox and DAMO via Fe-modified granular activated carbon

Anaerobic ammonium oxidation (Anammox) coupled with Denitrifying anaerobic methane oxidation (DAMO) is an attractive technology to simultaneously remove nitrogen and mitigate methane emissions from wastewater. However, its nitrogen removal rate is usually limited due to the low methane mass transfer efficiency, low metabolic activity and slow growth rate of functional microorganisms. In this study, GAC and Fe-modified GAC (Fe-GAC) were added into Anammox-DAMO process to investigate their effects on nitrogen removal rates and then reveal the mechanism. The results showed that after 80-day experiments, the total nitrogen removal rate was slightly improved in the presence of GAC (3.94 mg L^-1·d^-1), while it reached high as 16.66 mg L^-1·d^-1 in the presence of Fe-GAC, which was ca.17 times that of non-amended control group (0.96 mg L^-1·d^-1). The addition of Fe-GAC stimulated the secretion of extracellular polymeric substance (EPS), improved the electron transfer capability and promoted the production of Cytochrome C. Besides, the key functional enzyme activities (HZS, HDH and NAR) were highest in the Fe-GAC group, which were approximately 1.06-1.56 times higher than those of GAC-amended and blank control groups. Microbial community analysis showed that the abundance of the DAMO archaea (Candidatus Methanoperedens) and Anammox bacteria (Candidatus Brocadia) were remarkably increased with the addition of Fe-GAC. Functional genes associated with nitrogen removal and methane oxidation in Fe-GAC system were up-regulated. This study provides a promising strategy for achieving high rate of nitrogen removal upon Anammox-DAMO process.

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

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

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.

Surface-layer protein is a public-good matrix exopolymer for microbial community organisation in environmental anammox biofilms

Extracellular polymeric substances (EPS) are core biofilm components, yet how they mediate interactions within and contribute to the structuring of biofilms is largely unknown, particularly for non-culturable microbial communities that predominate in environmental habitats. To address this knowledge gap, we explored the role of EPS in an anaerobic ammonium oxidation (anammox) biofilm. An extracellular glycoprotein, BROSI_A1236, from an anammox bacterium, formed envelopes around the anammox cells, supporting its identification as a surface (S-) layer protein. However, the S-layer protein also appeared at the edge of the biofilm, in close proximity to the polysaccharide-coated filamentous Chloroflexi bacteria but distal to the anammox bacterial cells. The Chloroflexi bacteria assembled into a cross-linked network at the edge of the granules and surrounding anammox cell clusters, with the S-layer protein occupying the space around the Chloroflexi. The anammox S-layer protein was also abundant at junctions between Chloroflexi cells. Thus, the S-layer protein is likely transported through the matrix as an EPS and also acts as an adhesive to facilitate the assembly of filamentous Chloroflexi into a three-dimensional biofilm lattice. The spatial distribution of the S-layer protein within the mixed species biofilm suggests that it is a "public-good" EPS, which facilitates the assembly of other bacteria into a framework for the benefit of the biofilm community, and enables key syntrophic relationships, including anammox.

Membrane-aerated biofilm reactor (MABR): recent advances and challenges

Membrane-aerated biofilm reactor (MABR) has been considered as an innovative technology to solve aeration issues in conventional bioreactors. MABR uses a membrane to supply oxygen to biofilm grown on the membrane surface. MABR can perform bubbleless aeration with high oxygen transfer rates, which can reduce energy requirements and expenses. In addition, a unique feature of counter-diffusion creates a stratified biofilm structure, allowing the simultaneous nitrification–denitrification process to take place in a single MABR. Controlling the biofilm is crucial in MABR operation, since its thickness significantly affects MABR performance. Several approaches have been proposed to control biofilm growth, such as increasing shear stress, adding chemical agents (e.g., surfactant), using biological predators to suppress microorganism growth, and introducing ultrasound cavitation to detach biofilm. Several studies also showed the important role of membrane properties and configuration in biofilm development. In addition, MABR demonstrates high removal rates of pollutants in various wastewater treatments, including in full-scale plants. This review presents the basic principles of MABR and the effect of operational conditions on its performance. Biofilm formation, methods to control its thickness, and membrane materials are also discussed. In addition, MABR performance in various applications, full-scale MBRs, and challenges is summarized.

Partial S(0)-driven autotrophic denitrification process facilitated the quick natural enrichment of anammox bacteria at room temperature

Anaerobic ammonium oxidation (anammox) is well-known to be an environmental and promising biotechnology. However, the natural enrichment of anammox bacteria is still a challenging topic. In this study, partial S(0)-driven autotrophic denitrification (PSAD) was developed to stably supply nitrite, and natural enrichment of anammox bacteria was rapidly realized in a single sequencing moving bed biofilm reactor at room temperature. With the initiation of PSAD, anammox bacteria spontaneously emerged within 12 days, and PSAD-anammox coupling system was realized successfully. And then, the influent concentration of ammonium continuously increased to the same concentration as the nitrate, and the mean total nitrogen removal efficiency reached 92.77 %, which was mainly contributed by anammox. Moreover, the coupling of PSAD and anammox reduced the risk of sulfate emissions. cDNA high throughput sequencing revealed that the relative abundance of Candidatus Brocadia and Thiobacillus reached 39.03 % and 13.48 % at the 88th day. Oligotyping analysis illustrated that GATTTAAT and GTCCCA were the dominant Ca. Brocadia and Thiobacillus oligotypes in PSAD-anammox coupling system, respectively. DNA-based stable isotope probing further deciphered that Thiobacillus was the actual performer of PSAD and supported the nitrite for anammox bacteria in PSAD-anammox coupling system. Overall, this work provided a new strategy to naturally enrich anammox bacteria.

Simultaneous methanogenesis and denitrification coupled with nitrifying biofilm for high-strength wastewater treatment: Performance and microbial mechanisms

A combined system consisting of an upflow blanket filter (UBF) and a moving-bed biofilm reactor (MBBR) was developed for the simultaneous removal of organic matters and ammonia from high-strength wastewater. With a constant COD of approximately 2000 mg/L and ammonium nitrogen in a series of concentrations (e.g., 50, 200 and 400 mg/L in stages I to III) of the influent wastewater, the removal efficiencies of COD, ammonium nitrogen and total nitrogen reached 96.10%-98.19%, 100%, and 79.12%-82.15%, respectively. With the increase of influent ammonia nitrogen concentration, the specific methanogenic activity of the UBF granules decreased significantly, while the specific denitrification rates of the UBF granules and specific nitrification rates of the MBBR biofilms increased significantly. Microbial community analysis showed that Methanobacterium and Methanosaeta were the dominant methanogens in the UBF granules, while Candidatus Competibacter, Thauera and Acinetobacter were identified as dominant denitrifiers. In addition, nitrifiers were enriched in MBBR biofilms at 11.33% and 13.87% of the average abundance of Nitrosomonas and Nitrospira, respectively, at stage III (influent ammonium at 400 mg/L, COD/NH₄⁺-N =  5). The ecological network analysis, including full-networks and sub-networks, indicated that the interactions between methanogens and denitrifiers in the UBF granules were strong when the influent ammonium concentration reached 400 mg/L. No intensive interactions were observed among the functional bacteria in the MBBR biofilms over the entire operation. Overall, this study provides a new strategy for the application and construction of efficient biological processes to achieve simultaneous removal of organic matter and nitrogen for high-strength wastewater treatment.

The effects of salinity changes on anammox performance: The response rule and tolerance mechanism

Some wastewaters contain high concentrations of ammonia coexisting with large amounts of salt, which might negatively affect the anaerobic ammonium oxidation (anammox) process. In this study, the performance of the anammox process under different saline conditions was investigated using an upflow anaerobic sludge bed-anammox system. After long-term operating for 275 days, the results indicated that the nitrogen removal efficiency remained high under the 0-40 g NaCl/L, and low salinity (15 g NaCl/L) substantially promoted specific anammox activity. Affected by the saline environment, the appearance, color, and shape of sludge notably changed, and the amount of extracellular polymeric substances gradually increased with increasing salinity, which might be one of the reasons for the strong salt tolerance of the system. Chloroflexi and Planctomycetes were the dominant strains under long-term salinity, and Brocadiaceae_g_ unclassified exhibited halophilic characteristics. The redundancy analysis results showed that the concentration of influent NH₄ ⁺ -N and salinity were the main environmental factors affecting the microbial community of the system. PRACTITIONER POINTS: Provides data to support the maximum value for salinity wastewater treatment with anammox processes' tolerance of 40 g NaCl/L. EPS changes may be responsible for the response to salinity challenges and provide direction for high salinity wastewater treatment. Brocadiaceae_g_ unclassified exhibited a halophilic quality. And it can be focused on to improve treatment efficiency.

Initiating an anaerobic ammonium oxidation reactor by inoculation with starved anaerobic ammonium oxidation sludge and modified carriers

Prolonged starved anammox sludge (SAS) obtained during initial rejuvenation was inoculated into a reactor together with activated sludge (AS), anaerobic granular sludge (AGS) and modified carriers consisting of honeycomb carrier with high biological interception and activated carbon carrier with high adsorption performance. SAS accounted for 5% of the inoculated sludge. The anammox process was started and operated at around 25℃. After 160 days, the nitrogen loading rate and nitrogen removal rate reached 1.12 kgN·m^-3·d^-1 and 0.97 kgN·m^-3·d^-1, respectively. Obvious red anammox biofilms were observed on the modified carriers. Microbial community analysis showed that the relative abundance of anammox bacteria increased from < 0.1% to 22.96%. Candidatus Jettenia and Candidatus Brocadia were the dominating anammox species. This work demonstrates the potential to reuse SAS to improve the start-up efficiency of anammox reactors, which makes good economic sense.

Fast formation of anammox granules using a nitrification-denitrification sludge and transformation of microbial community

A lengthy start-up period has been one of the key obstacles limiting the application of the anammox process. In this investigation, a nitrification-denitrification sludge was used to start-up the anammox EGSB process. The transformation process from nitrification-denitrification sludge to anammox granule sludge was explored through the aspects of nitrogen removal performance, granule properties, microbial community structure, and evolution route. A successful start-up of the anammox process was achieved after 94 days of reactor operation. The highest nitrogen removal rate (NRR) obtained was 7.25±0.16 gN/L/d at a nitrogen loading rate (NLR) of 8.0 gN/L/d, and the corresponding nitrogen removal efficiency was a high 90.61±1.99%. The results of the microbial analysis revealed significant changes in anammox bacteria, nitrifying bacteria, and denitrifying bacteria in the sludge. Notably, the anammox bacteria abundance increased from 2.5% to 29.0% during the operation, and Candidatus Kuenenia and Candidatus Brocadia were the dominant genera. Distinct-different successions on Candidatus Brocadia and Candidatus Kuenenia were also observed over the long-term period. In addition, the settling performance, anammox activity and biomass retention capacity of the granules were significantly enhanced during this process, and the corresponding granule evolution route was also proposed. The results in this study indicate the feasibility of using available seed sludge source for the fast-transformation of anammox granules, it is beneficial to the large-scale application of anammox process and the utilization of excess sludge.

Nitrogen removal performance of anammox immobilized fillers in response to seasonal temperature variations and different operating modes: Substrate utilization and microbial community analysis

Four anaerobic ammonium oxidation (anammox) immobilized filler reactors (R1: 33 °C-normal, R2: seasonal temperature-normal, R3: seasonal temperature-feast, R4: seasonal temperature-starvation) were established to study the response of anammox immobilized fillers to seasonal temperature changes and different operating modes. The results showed that the anammox immobilized filler could better adapt to the seasonal temperature drop and maintain the activity potential by adjusting the hydraulic retention time (HRT). During the temperature rise phase, R2 activity increased rapidly with the highest nitrogen removal rate reaching 1.26 kgN·(m³·d)^-1, which was equivalent to control sample R1 (1.33 kgN·(m³·d)^-1). However, feasting and famine conditions severely impaired anammox performance and changed stoichiometric ratios; feasting, in particular, significantly lowered the nitrogen removal potential of R3. The specific anammox activity of R2, R3 and R4 was 92.2%, 52.6% and 67.9%, respectively, that of R1, respectively, where the accumulation of functional bacteria was the reason for the higher activity of R2. Degradation kinetics and NO₂^--N inhibition curves showed that R3 was less sensitive to high concentrations of NH₄⁺-N, while R4 responded earlier to low concentrations of NH₄⁺-N, and the reduction of IC50 at low temperature was the reason for the inhibition of R3 activity. Furthermore, seasonal temperature fluctuations had little effect on the microbial community structure but had a considerable impact on bacteria abundance. The anammox functional bacteria Candidatus Kuenenia was found to be the dominant genus in R1-R4; however, the relative abundance of most bacteria, including anammox bacteria, decreased in R3, while the proportion of fermentation bacteria and denitrifying bacteria increased in R4. These findings highlight the necessity of rational regulation of HRT for the adaptation of anammox immobilized fillers to seasonal temperature changes, which could enhance our understanding of the synergistic effect of seasonal temperature changes and different operating modes on nitrogen removal.

The performance and microbial communities of Anammox and Sulfide-dependent autotrophic denitrification coupling system based on the gel immobilization

Anammox and sulfide-dependent autotrophic denitrification (ASDAD) coupling system can improve the nitrogen removal, but high sulfide concentration will affect the activity of anaerobic ammonia-oxidizing bacteria (AnAOB). Gel immobilization technology can enhance the survivability of microorganisms in unsuitable environments. Therefore, in this investigation, gel immobilization technology was applied into the ASDAD coupling system to explore the removal performance and microbial communities. The results showed that the optimal S^2-/NO₃^- was 0.6, under which the best TN removal efficiency was 85.69%. The removal performance of ASDAD coupling system was stable under rapid variations of nitrogen loading rate and sulfide loading rate. Immobilized sludge cubes could attenuate the effects of temperature on AnAOB and sulfide-oxidizing bacteria. Observations of SEM and stereoscope suggested that AnAOB was more likely to exist on the surface of the sludge cubes. Thiobacillus, Candidatus Brocadia, and Candidatus Kuenenia were the main functional bacteria in the coupling system.

A comprehensive root cause analysis of anammox bioreactor performance decline

The cultivation of anaerobic ammonia oxidizing bacteria (anammox) has gained enormous awareness over the last few decades. Although numerous studies focus massively on successfully growing these anammox to different enrichment environments, in reality, the failure rates are somewhat comparable to the reported success rates. This study combines a variety of measurement techniques to observe and monitor the sequence of a bioreactor performance decline following elevated influent substrate concentration. After attaining stable substrate removal throughout a nitrogen loading rate (NLR) range of 0.691 to 1.669 kg-N·m^-3·d^-1, the performance of the lab-scale anammox-sequencing batch reactor (SBR) abruptly broke down as the NLR reached 2.01 kg-N·m^-3·d^-1. The gathered information showed that the increased NLR firstly caused a significant and unfavorable change in the free ammonia (FA) and free nitrous acid (FNA) concentration in the bioreactor. A subsequent drop in N₂ production and a decline from a peak high of 0.381 to a low of 0.012 kg-N·kg-VSS^-3·d^-1 of the specific nitrogen removal rate (SNRR) led to an 82% absurd decline in microbial cellular energy production. Prior to these anammox switching to survival mode and secreting larger quantities (32% higher) of extracellular polymeric substances (EPS), the activity of syntrophic decomposers increased substantially leading to the internal production of excess CO₂ in the bioreactor and thereby diverging the bioreactor pH to lower levels. The purposes of this study are to understand the reason an anammox process shows different signals during a decline phase and to enable immediate response to performance deterioration.

Nitrogen Removal from Mature Landfill Leachate via Anammox Based Processes: A Review

Mature landfill leachate is a complex and highly polluted effluent with a large amount of ammonia nitrogen, toxic components and low biodegradability. Its COD/N and BOD5/COD ratios are low, which is not suitable for traditional nitrification and denitrification processes. Anaerobic ammonia oxidation (anammox) is an innovative biological denitrification process, relying on anammox bacteria to form stable biofilms or granules. It has been extensively used in nitrogen removal of mature landfill leachate due to its high efficiency, low cost and sludge yield. This paper reviewed recent advances of anammox based processes for mature landfill leachate treatment. The state of the art anammox process for mature landfill leachate is systematically described, mainly including partial nitrification–anammox, partial nitrification–anammox coupled denitrification. At the same time, the microbiological analysis of the process operation was given. Anaerobic ammonium oxidation (anammox) has the merit of saving the carbon source and aeration energy, while its practical application is mainly limited by an unstable influent condition, operational control and seasonal temperature variation. To improve process efficiency, it is suggested to develop some novel denitrification processes coupled with anammox to reduce the inhibition of anammox bacteria by mature landfill leachate, and to find cheap new carbon sources (methane, waste fruits) to improve the biological denitrification efficiency of the anammox system.

Layered inoculation of anaerobic digestion and anammox granular sludges for fast start-up of an anammox reactor

Layered inoculation of anaerobic digestion (AD) and anammox granular sludges was performed for fast start-up of anammox using an expanded granular sludge bed (EGSB) reactor (R1) with the cell lysis phase and the lag phase being shortened. The maximum nitrogen loading rate (NLR) and nitrogen removal rate (NRR) of R1 were 11 kg N/m³ d and 9.9 kg N/m³ d on day 42, respectively. The domesticated AD granular sludge on the upper layer was collected to another EGSB reactor (R2) to investigate its anammox activity. The results showed that AD granular sludge in R1 had anammox activity and could be cultured into anammox granular sludge. Adsorption, interception and domestication enhanced the biomass of anammox bacteria in R1, accelerating the start-up of the reactor. The findings of this work were expected to solve the problem of fast start-up of an anammox reactor with insufficient anammox seeding sludge in industrial application.

Enhancement of Anammox performances in an ABR at normal temperature by the low-intensity ultrasonic irradiation

A lab-scale ultrasound enhancing Anammox reactor (ABR_U) was established and irradiated once a week by ultrasound with the optimal parameter (frequency of 25.0 kHz, intensity of 1.00 W cm^-2 and exposure time of 36.0 s) obtained by response surface methodology (RSM). ABR_U and the controlled Anammox reactor (ABR_C) without ultrasonic treatment were operated in parallel. The start-up time of Anammox process in ABR_U (59 d) was shorter than that in ABR_C (69 d). At the end of the nitrogen load-enhancing period, NLR (0.500 kg N m^-3 d^-1) and NRR (0.430 kg N m^-3 d^-1) in ABR_U were both higher than NLR (0.400 kg N m^-3 d^-1) and NRR (0.333 kg N m^-3 d^-1) in ABR_C. The results of RTQ-PCR demonstrated that the specific low-intensity ultrasound irradiation improved the enrichment levels of AnAOB in mature sludge. SEM images and the observation of the macroscopic morphology of mature sludge showed that the ultrasound irradiation strengthened the formation of Anammox granular sludge, thereby improved the interception capacity and impact load resistance of the reactor, and enhanced the nitrogen removal performance in ABR_U. The ultrasonic enhanced Anammox reactor based on an ABR with the optimal parameters can promote the rapid start-up and efficient and stable operation of the Anammox process at normal temperature (around 25.0 °C).

Decomposition process of cefotaxime sodium from antibiotic wastewater by Up-flow Blanket Filter (UBF) reactor: Reactor performance, sludge characteristics and microbial community structure analysis

In this study, a novel Up-flow Blanket Filter (UBF) reactor was applied to the degradation of antibiotic wastewater. The experiments showed that when the hydraulic retention time (HRT) was 24 h and the ratio of volatile fatty acids (VFA) to alkalinity (ALK) was 0.3, the best removal efficiency was achieved in the combined packing UBF reactor, and the COD removal efficiency reached 80.1%-84.6%, exhibiting a significant difference in reaction performance from the other two reactors (P < 0.05) and a good efficiency of cefotaxime sodium removal. Moreover, the microstructure and surface characteristics of the reactor fillers were studied through scanning electron microscope (SEM) analysis, which showed that three fillers all had biofilm adhesion, but the combined packing gave best performance. Energy dispersive spectrometer (EDS) tests indicated abundant element components in the combined packing. The particle size distribution of sludge was also considered in the experiment, and the result showed the particle size of sludge increased with the operation of the reactor. In addition, microbial community structures of sludge and biofilm with the combined packing were analyzed. High-throughput sequencing confirmed the existence of Pseudomonas, which had good adaptability to antibiotic wastewater and became the dominant bacteria. Decomposition process of cefotaxime sodium after hydrolysis and anaerobic treatment was analyzed through Fourier transform infrared spectroscopy (FTIR). The reactor, which is economical, exhibited favorable performance in degrading the pollutions in the antibiotic wastewater.

Effects of vibration on anammox-enriched biofilm in a high-loaded upflow reactor

An upflow biofilm reactor was operated for 211 days to investigate the effects of vibration on anammox treatment performance. With vibration, the highest nitrogen removal rates (20 kg-N·m^-3·d^-1) were obtained on day 180. Since the vibration could directly applied on the biofilm, it could release the dinitrogen gas accumulated in the biofilm timely and reduce the internal mass transfer resistance sharply. The specific anammox activity increased by more than 3 times with a higher vibration intensity. Meanwhile, the unique random motion caused by mechanical vibration promotes the production of extracellular proteins. Moreover, the VSS reached 20.97 g·L^-1 which was 1.6 times higher than the control reactor. Such enrichment method resulted in a hard and thick anammox biofilm with a special granular morphology, and the nitrite tolerance concentration could reach 500 mg-N·L^-1. Operated with an adequate vibration intensity could maintain the biofilm thickness and conducive to improve the stability of the reactor. In addition, this technique also allowed the microorganisms inside the biofilm and those on the surface to reach the same culture conditions. Base on the batch experiments, intermittent vibration caused a decrease in energy consumption from about 7.757 (kW·h)·(kg-N)^-1 in group 0-Lv7(60-60) to 0.912 (kW·h)·(kg-N)^-1 in group 0-Lv7(5-60). Compared to the internal recycle without vibration, the energy consumption fell by a slice over 65%. Furthermore, the high-throughput sequencing results showed that the relative abundance of Candidatus Kuenenia in reactor 1 increased from 13.2% to 43.9%.

Accelerated start-up, long-term performance and microbial community shifts within a novel upflow porous-plated anaerobic reactor treating nitrogen-rich wastewater via ANAMMOX process

The anaerobic ammonium oxidation (anammox) process has gained much popularity in recent years following its success in nitrogen removal. However, not much has been reported on techniques to promote anammox bacteria immobilization and associated microbial community evolution. In this study, a novel upflow porous-plate anaerobic reactor (UPPAR) was developed and explored to promote biomass (anammox) retention and growth. To comprehend the performance of the UPPAR, its nitrogen removal efficiencies, as well as the microbial community dynamics involved in the nitrogen removal process, was evaluated and reported. When NLR ranging 0.98-1.08 kg m-3 d-1 was introduced at various stages of the UPPAR operation, a rapid start-up was achieved in 63 d, and the overall nitrogen removal rate could reach 90-95%. By the end of the start-up period, it was revealed that Proteobacteria abundance had reduced by 43.92% as opposed Planctomycetes which increased from 2.95% to 43.52%. Conversely, after the UPPAR had been operated for 124 d, thus at steady-state, the most pronounced phylum observed was Planctomycetes (43.52%) followed by Proteobacteria (26.63%), Chloroflexi (5.87%), Ignavibacteriae (5.55%), and Bacteroidetes (4.9%). Predominant genera observed included Candidatus Kuenenia - (25.46%) and Candidatus Brocadia - (3.15%), an indication that nitrogen removal mechanism within the UPPAR was mainly conducted via autotrophic anammox process. Scanning electron microscopy (SEM) revealed that sludge samples obtained at steady-state were predominantly in granular form with sizes ranging between 2 mm to 5 mm. Granules surfaces were dominated with normal to coccoid-shaped cells as revealed by the SEM.

Accomplishing a N-E-W (nutrient-energy-water) synergy in a bioelectrochemical nitritation-anammox process

This study reports an investigation of the concept, application and performance of a novel bioelectrochemical nitritation-anammox microbial desalination cell (MDC) for resource-efficient wastewater treatment and desalination. Two configurations of anammox MDCs (anaerobic-anammox cathode MDC (AnA_moxMDC) and nitration-anammox cathode MDC (NiA_moxMDC)) were compared with an air cathode MDC (CMDC), operated in fed-batch mode. Results from this study showed that the maximum power density produced by NiA_moxMDC (1,007 mW/m³) was higher than that of AnA_moxMDC (444 mW/m³) and CMDC (952 mW/m³). More than 92% of ammonium-nitrogen (NH₄⁺-N) removal was achieved in NiA_moxMDC, significantly higher than AnA_moxMDC (84%) and CMDC (77%). The NiA_moxMDC performed better than CMDC and AnA_moxMDC in terms of power density, COD removal and salt removal in desalination chamber. In addition, cyclic voltammetry analysis of anammox cathode showed a redox peak centered at -140 mV Vs Ag/AgCl confirming the catalytic activity of anammox bacteria towards the electron transfer process. Further, net energy balance of the NiA_moxMDC was the highest (NiA_moxMDC-0.022 kWh/m³ >CMDC-0.019 kWh/m³ >AnA_moxMDC-0.021 kWh/m³) among the three configurations. This study demonstrated, for the first time, a N-E-W synergy for resource-efficient wastewater treatment using nitritation-anammox process.

Difference of respiration-based approaches for quantifying heterotrophic biomass in activated sludge of biological wastewater treatment plants

Estimation of heterotrophic biomass concentration in activated sludge is essential to the design, operation and management of activated sludge process for wastewater treatment plants (WWTPs), and many methods have been developed for such a purpose. In this study, three respiration-based methods: the Exponential-growth-rate-based method (Exp-M), the Maximum-respiration-rate-based method (Max-M) and the Endogenous-respiration-rate-based method (End-M), which are frequently used for determining kinetic parameters in activated sludge models, were comparatively examined using experimental results from both full-scale municipal WWTPs and laboratory-scale reactors. Our study revealed the pros and cons of each method, which is valuable for method selection in different applications. The End-M can estimate all the fraction of biomass. However, the proper control of measuring condition is of great challenge. The Exp-M can only determine the exponential growth part of biomass as conditions employed during measuring may make a considerable part of biomass in a nongrowth status, resulting underestimation or even failure of calculation. The Max-M can determine the viable biomass including the nongrowth part, and it is recommended for rapid assessment of biomass. The Max-M was modified after the introduction of a coefficient SOUR_SRT=0 (the specific oxygen utilization rate when the sludge retention time was assumed zero) and was validated by using the experimental results reported in previous studies. Because of its simplicity and much improved accuracy, the modified Max-M method is able to provide more useful information about activated sludge compositions and has a promising application potential in wastewater treatment plants.

Long-term operation and autotrophic nitrogen conversion process analysis in a biofilter that simultaneously removes Fe, Mn and ammonia from low-temperature groundwater

One lab-scale biofilter that simultaneously removes Fe, Mn and ammonia from 4 °C groundwater was established to investigate the nitrogen conversion process. The results showed that 333 days were needed to achieve the required standards for Fe, Mn and ammonia under a filtration rate of 3 m/h. Effluent nitrite concentration was the key factor determining the final operation parameters. Both nitrification and anaerobic ammonium oxidation (ANAMMOX) contributed to nitrogen conversion. The calculation results demonstrated that autotrophic nitrogen removal proportion was about 15.92% in steady operation period. Meanwhile, 7 genera of Mn oxidizing bacteria (MnOB) were detected; Candidatus Brocadia was the only detected ANAMMOX genera. The corresponding functional oxidizing bacteria could be acclimated sufficiently in biofilter treating low-temperature groundwater.

Start-up and operational performance of Anammox process in an anaerobic baffled biofilm reactor (ABBR) at a moderate temperature

A lab-scale anaerobic baffled biofilm reactor (ABBR) was used as a novel reactor to start up Anammox process at a moderate temperature around 20 °C and an innovative filling module was adopted as support material. Quick start-up of Anammox process from the aerobic activated sludge was achieved after 47 days operation. The max nitrogen loading rate and nitrogen removing rate attained 1.00 kg N m^-3 d^-1 and 0.90 kg N m^-3 d^-1 after 161 days operation. Scanning electron microscope photographs showed that the structure as well as the states of the micro-aggregates (micro-aggregates sticking on a non-woven fiber, entangling non-woven fibers and enwrapped by non-woven fibers) enhanced biomass retention for Anammox bacteria. Microbial community analysis showed that Anammox bacteria were effectively enriched with Candidatus Brocadia, Candidatus Jettenia and Candidatus Kuenenia being the main Anammox species in the mature biofilms. This contributed to the excellent Anammox operation performance at the moderate temperature.

Effect of external hydrazine addition on anammox reactor start-up time

Hydrazine is an intermediate product of the anaerobic ammonium oxidation (Anammox) process where both ammonium and nitrite in wastewater are converted to nitrogen gas by bacteria. In this study the effect of external hydrazine addition (5, 10, 15, and 20 mg/L) on the start-up period of the Anammox process was studied using sequencing batch reactors (SBRs). The SBR with an addition of 10 mg/L hydrazine took only 7 weeks to stabilize and achieve the maximum removal of ammonium and nitrite, whereas the SBR without the addition of hydrazine took 12 weeks. The amount of Heme C extracted from the biomass indicated that externally added hydrazine accelerated the growth of Anammox bacteria and reduced the release of nitrous oxide gas from the reactors.

Abundance and diversity of nitrogen-removing microorganisms in the UASB-anammox reactor

Anaerobic ammonium oxidation is considered to be the most economical and low-energy biological nitrogen removal process. So far, anammox bacteria have not yet been purified from cultures. Some nitrogen-removing microorganisms cooperate to perform the anammox process. The objective of this research was to analyze the abundance and diversity of nitrogen-removing microorganisms in an anammox reactor started up with bulking sludge at room temperature. In this study, the ammonia-oxidizing archaea phylum Crenarchaeota was enriched from 9.2 to 53.0%. Nitrosomonas, Nitrosococcus, and Nitrosospira, which are ammonia-oxidizing bacteria, increased from 3.2, 1.7, and 0.1% to 12.8, 20.4, and 3.3%, respectively. Ca. Brocadia, Ca. Kuenenia, and Ca. Scalindua, which are anammox bacteria, were detected in the seeding sludge, accounting for 77.1, 11.5, and 10.6%. After cultivation, the dominant genus changed to Ca. Kuenenia, accounting for 82.0%. Nitrospirae, nitrite oxidation bacteria, decreased from 2.2 to 0.1%, while denitrifying genera decreased from 12.9 to 2.1%. The results of this study contribute to the understanding of nitrogen-removing microorganisms in an anammox reactor, thereby facilitating the improvement of such reactors. However, the physiological and metabolic functions of the ammonia-oxidizing archaea community in the anammox reactor need to be investigated in further studies.

Influence of sulfadimethoxine (SDM) and sulfamethazine (SM) on anammox bioreactors: Performance evaluation and bacterial community characterization

The specific inhibitory effects of sulfonamides on anaerobic ammonium oxidation (anammox) process remain unknown. This study investigated the inhibitory characteristics of sulfadimethoxine (SDM) and sulfamethazine (SM) in two anammox bioreactors with NH₄⁺-N (160 mg/L) and NO₂^--N (210 mg/L) in influent. Results indicate that anammox bacteria in both bioreactors adapted to low antibiotic concentrations (less than 3 mg/L). At concentrations between 5 and 7 mg/L, SDM inhibited the growth of anammox bacteria and resulted in a decrease of Candidatus Brocadia abundance from 2.57% to 0.39%. In contrast, at concentrations of 5-9 mg/L, SM inhibited the denitrification process more severely than SDM, resulting in higher accumulation of nitrite and nitrate. The purpose of this study was to elucidate the inhibitory effects of sulfonamides on the anammox process and to provide a reference for the stable operation of anammox bioreactors for the treatment of sulfonamide-containing wastewater.

Performance and microbial community of anammox in presence of micro-molecule carbon source

Because ammonium (NH₄⁺-N) coexists with organic matter in some wastewaters, the possible adverse influences of organic matter become a major concern in the applications of anaerobic ammonium oxidation (anammox). In this study, the effects of acetate, as a representative of micro-molecule organic matter, on anammox were investigated. Efficient nitrogen removal was realized because denitrifying bacteria and anammox bacteria (AnAOB) had a better synergistic effect under the condition of chemical oxygen demand (COD) concentrations lower than 251 ± 7 mg L^-1. Furthermore, the nitrogen removal efficiency (NRE) decreased to 82.02 ± 3.14% when COD was increased to 730 ± 9 mg L^-1, and effluent free ammonia (FA) reached 21.93 ± 4.71 mg L^-1 might be one of factors leading to inhibition. However, the nitrogen-removal contribution rate of anammox remained steady at 61.97 ± 2.84% at COD of 730 ± 9 mg L^-1, which indicated that anammox was still dominant in the system. AnAOB, such as Ca. Kuenenia and Ca. Jettenia, and denitrifying bacteria, such as Denitratisoma and Thauera, were found to coexist in the reactor. Interestingly, Ca. Kuenenia presented in the trend of first decreased then increased with the increasing of organic matter concentration, which might be one of reasons that anammox played an important role in nitrogen removal at high COD concentration.

A novel anammox process combined with vibration technology

This study investigated a fixed bed anammox bioreactor that uses vibration techniques to treat synthetic inorganic wastewater. Continuous experiments indicated that the activity elevation period could be shorten to one third, when the nitrogen removal rate (NRR) reached 1 kg·N/m³·d with vibration. R2 achieved the maximum NRR of 3.3 kg·N/m³·d under the resonance state, which was 1.8 times higher than the control reactor. Analysis of vibration intensity suggested that anammox activity would be great improved with the increasing vibration. These results indicated that vibration played a key role in system performance. Furthermore, high-throughput sequencing showed that the reactor with the vibration had a higher proportion of anammox bacteria, which increased 7 times than the biofilm formation phase. Meanwhile, the proportion of Proteobacteria and Chloroflexi decreased by 37.1% and 7.78%, respectively. These results suggest that vibration could increase the anammox treatment performance and provide a better condition for the anammox bacteria.

Simultaneous nitrite and ammonium production in an autotrophic partial denitrification and ammonification of wastewaters containing thiocyanate

Various products are observed in biological oxidation and reduction of molecules containing elements of variable valence. The variability is caused by the diversity of microorganisms and their metabolic enzymes, which may develop into novel processes in wastewater treatment. The study aimed to develop a novel denitrification process forming nitrite and ammonium in wastewaters containing thiocyanate. High-efficiency nitrite and ammonium production was observed due to autotrophic partial denitrification and ammonification as a result of nitrate and thiocyanate removal. Nitrite, ammonium and sulfate were observed as the ultimate products. The increased NO₃^--N/SCN^--N ratio in the treated wastewater resulted in the decreased removal efficiency of nitrate, and the increased nitrate-to-nitrite transformation ratio and the ratio of NO₂^--N to NH₄⁺-N. Thiocyanate sulfur was oxidized to sulfate via intermediate elementary sulfur providing electron to nitrate or nitrite. The Thiobacillus genus dominated in the sludge providing ammonium and nitrite as substrate for the potentially anammox process.

Effect of glucose on nitrogen removal and microbial community in anammox-denitrification system

The effect of glucose on nitrogen removal and microbial communities in the anammox-denitrification systems was investigated. The optimal nitrogen removal could be achieved when the influent glucose concentration was 56.4mgL^-1. The influent nitrite to ammonium ratio of 0.95-1.40 would not obviously affect the nitrogen removal due to the coexistence of anammox, denitrification and partial denitrification. The anammox activity was deteriorated with increasing glucose concentration. When the influent glucose concentration was increased to 374.9mgL^-1, the average ammonium removal efficiency decreased from 97% to around 10% and anammox activity was seriously inhibited. The anammox activity quickly recovered with decreasing influent glucose and increasing influent nitrite. High-throughput sequencing analysis suggested that the predominant genus changed from Candidatus Kuenenia to Diaphorobacter with the addition of glucose and then changed to Hydrogenophaga with the decrease of glucose. It indicated that organics concentration had an effect on the microbial communities.