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The partial-denitrification-anammox (PdNA) process exhibits great potential in enabling the simultaneous removal of NO 3 - -N and NH 4 + -N. This study delved into the impact of exogenous nano zero-valent iron (nZVI) on the PdNA process. Adding 10 mg L -1 of nZVI increased nitrogen removal efficiency up to 83.12 % and maintained higher relative abundances of certain beneficial bacteria. The maximum relative abundance of Candidatus Brocadia (1.6 %), Candidatus Kuenenia (1.5 %), Ignavibacterium (1.3 %), and Azospira (1.2 %) was observed at 10 mg L -1 of nZVI. However, the greatest relative abundance of Thauera (1.3 %) was recorded under 50 mg L -1 . Moreover, applying nZVI selectively enhanced the abundance of NO 3 - -N reductase genes. So, keeping the nZVI concentration at 10 mg L -1 or below is advisable to ensure a stable PdNA process in mainstream conditions. Considering nitrogen removal efficiency, using nZVI in the PD-anammox process could be more cost-effective in enhancing its adoption in industrial and mainstream settings., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The substantial discharge of ferroferric oxide nanoparticles (Fe 3 O 4 NPs) into sewage threatens the survival of functional microorganisms in wastewater treatment. This study elucidated responses of anaerobic ammonium oxidation (anammox) consortia to inhibition from high Fe 3 O 4 NPs concentration and recovery mechanisms. The nitrogen removal efficiency decreased by 20.3 % and recovered after 55 days under 1000 mg/L Fe 3 O 4 NPs concentration. Toxicity was attributed to reactive oxygen species (ROS) production. The excessive ROS damaged membrane integrity, nitrogen metabolism, and DNA synthesis, resulting in the inhibition of anammox bacteria activity. However, recovery mechanisms of anammox consortia activity were activated in response to 1000 mg/L Fe 3 O 4 NPs. The increase of heme oxygenase-1, thioredoxin, and nicotinamide adenine dinucleotide-quinone oxidoreductase genes alleviated oxidative stress. Furthermore, the activation of metabolic processes associated with membrane and DNA repair promoted recovery of anammox bacteria activity. This study provided new insights into NPs contamination and control strategies during anammox process., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Anaerobic ammonium oxidation (anammox) is an efficient nitrogen removal process; however, nitrate byproducts hampered its development. In this study, extracellular polymeric substances (EPS) were embedded into NH 2 -MIL-101(Fe), creating NH 2 -MIL-101(Fe)@EPS to reduce nitrate. Results revealed that chemical nitrate reduction efficiency of NH 2 -MIL-101(Fe)@EPS surpassed that of NH 2 -MIL-101(Fe) by 17.3 %. After adding 0.5 g/L NH 2 -MIL-101(Fe)@EPS within the anammox process, nitrate removal efficiency reached63.9 %, consequently elevating the total nitrogen removal efficiency to 92.4 %. 16S rRNA sequencing results elucidated the predominant role of Candidatus Brocadia within NH 2 -MIL-101(Fe)@EPS-anammox system. Concurrently, sufficient photogenerated electrons were transferred to microorganisms, promoting the growth of Desnitratisoma and OLB17. Additionally, photogenerated electrons activated flavin and Complex III, thereby up-regulating crucial genes involved in intra/extracellular electron transfer. Subsequently, denitrification and dissimilatory nitrate reduction to ammonium were activated to reduce nitrate. In summary, this study achieved a notable rate of photocatalytic nitrate reduction within anammox process through the NH 2 -MIL-101(Fe)@EPS photocatalysts., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The chemical oxygen demand (COD) in municipal wastewater has become an obstacle for anammox in mainstream applications. In this study, the single chamber microbial fuel cell (MFC) was installed as an influent device for a partial nitrification-sequencing batch reactor (PN-SBR) to realize integrating COD removal and partial nitrification. After 80 days of operation, the nitrite accumulation rate reached 93%, while the COD removal efficiency was 56%. The output voltage and the power density of MFC were 66.62 mV and 2.40 W/m 3 , respectively. The content of EPS, especially polysaccharides in the stable phase, has increased compared with the seed sludge. The most dominant genus in MFC anode biofilm and SBR granular sludge was Thauera, which has organic compounds degradation capacity and could degrade nitrate. This study revealed the microbial interaction between MFC and partial nitrification and provided a new strategy for stable ammonia and nitrite supply for mainstream anammox plants., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

The mechanism and nitrogen removal performance of anammox process under different concentrations of Ca 2+ and Mg 2+ were explored from the perspective of molecular biology analysis based on the metabolic changes of the second messenger cyclic diguanylate (c-di-GMP). After 100-day operation, reactor with 98 mg/L Ca 2+ and 30 mg/L Mg 2+ achieved a higher anammox performance with an average total nitrogen (TN) removal efficiency of 85.8%. Under the Mg 2+ concentration of 30 mg/L, a higher Ca 2+ could accelerate anammox process by promoting the amplification of Candidatus Brocadia (0.62%) and production of Diguanylate cyclase (DGC-s: 6.54 × 10 8 copies/μL DNA) which function was to synthesize c-di-GMP. While under the Ca 2+ concentration of 49 mg/L, Mg 2+ concentration at appropriate rang could promote the degradation process of c-di-GMP. Since Ca 2+ had positive linear relationship with TN removal (R 2  = 0.96), a higher Ca 2+ concentration is recommended in the culture medium. This study provided a potential method for optimization of anammox process., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Anaerobic ammonium oxidation (anammox) process appears a suitable substitute to nitrification-denitrification at a lower C/N ratios. Anammox is a chemolithoautotrophic process, belong to phylum Planctomycetes, and they are slow growing bacteria. Different strategies, e.g., biofilm formation, granulation and gel immobilization, have been applied to maintain a critical mass of bacterial cells in the system by avoiding washout from the bioreactor. Gel immobilization of anammox appears the best alternative to the natural process of biofilm formation and granulation. Polyvinyl alcohol-sodium alginate, polyethylene glycol, and waterborne polyurethane are the most reported materials used for the entrapment of anammox bacteria. However, dissolution of the gel beads refrains its application for long term bioprocess. Magnetic powder could coat on the surface of the beads which may increase the mechanical strength and durability of pellets. Application and problem of immobilization technology for the commercialization of this technology also addressed., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

In this study, acclimation of freshwater nitritation-anammox sludge to remove nitrogen in high saline and hypersaline wastewater was evaluated, during which the microbes activity and microbial community revolution were revealed to understand the fate of a nitritation-anammox process (SNAP) in response to increasing salt stress. By enhanced aeration, the SNAP system can treat saline (3%) ammonium-rich (185 mg/L) wastewater after gradual adaption. Hypersalinity (5%) caused final deterioration of the SNAP system due to a severe inhibition on anammox activity. Genera Kuenenia (anammox), Nitrosomonas (AOB) and Nitrosovibrio (AOB) bacteria were salt adaptable microbes, while genus Nitrospira (NOB) bacteria were sensitive to salinity. Under the enhanced aeration, AOB bacteria could bear 3% salinity with possible enriched ammonia monooxygenase to stimulate the conversion of ammonium to nitrite by producing more intermediate-hydroxylamine, which could alleviate the negative effect of insufficient hydroxylamine oxidase members in AOB bacteria., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

A distinct shift of bacterial community driven by organic matter (OM) and powder activated carbon (PAC) was discovered in the simultaneous anammox and denitrification (SAD) process which was operated in an anti-fouling submerged anaerobic membrane bio-reactor. Based on anammox performance, optimal OM dose (50 mg/L) was advised to start up SAD process successfully. The results of qPCR and high throughput sequencing analysis indicated that OM played a key role in microbial community evolutions, impelling denitrifiers to challenge anammox's dominance. The addition of PAC not only mitigated the membrane fouling, but also stimulated the enrichment of denitrifiers, accounting for the predominant phylum changing from Planctomycetes to Proteobacteria in SAD process. Functional genes forecasts based on KEGG database and COG database showed that the expressions of full denitrification functional genes were highly promoted in R C , which demonstrated the enhanced full denitrification pathway driven by OM and PAC under low COD/N value (0.11)., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Membrane bioreactor with non-woven fabric membranes (NWMBR) is developing into a suitable method for anaerobic ammonium oxidation (anammox). As a carrier, non-woven fabric membrane divided total biomass into biofilm and suspended flocs gradually. Total nitrogen removal efficiency was maintained around 82.6% under nitrogen loading rate of 567.4mgN/L/d after 260days operation. Second-order substrate removal and Stover-Kincannon models were successfully used to simulate the nitrogen removal performance in NWMBR. High-throughput sequence was employed to elucidate the underlying microbial community dynamics. Candidatus Brocadia, Kuenenia, Jettenia were detected to affirm the dominant status of anammox microorganisms and 98.2% of anammox microorganisms distributed in biofilm. In addition, abundances of functional genes (hzs, nirK) in biofilm and suspended flocs were assessed by quantitative PCR to further investigate the coexistence of anammox and other microorganisms. Potential nitrogen removal pathways were established according to relevant nitrogen removal performance and microbial community., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Reducing activity of commensal bacteria in inocula may enhance anammox bacteria proliferation and realization of anammox process. Fast start-up of anammox process in an UASB reactor was successfully achieved by using autoclaved sludge (anaerobic granular sludge pretreated by autoclaving) and 0.3% active anammox sludge as inoculum. Continuous experiments indicated that R2 (autoclaved sludge addition) could shorten the start-up period from 72days to 63days. The first 50days anammox population specific growth rates (μ) of R1 (the control) and R2 were determined to be 0.014d -1 and 0.045d -1 using q-PCR assays. Analysis of coefficient of variations of nitrogen removal performance during days 96-225 indicated that R2 was more stable than R1. The Illumina MiSeq sequencing showed that autoclaving could decrease microbial diversity of sludge and enhance the abundance of anammox bacteria. Furthermore, PICRUSt community functions forecast and c-di-GMP measure illuminated the result of higher stability in R2., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

A permanent microbial stratified nitrogen removal system coupling anammox with partial nitrification (SNAP) in a sequencing batch biofilter granular reactor (SBBGR) was successfully constructed for the treatment of ammonia-rich wastewater. With a nitrogen loading rate of 0.1kgNm -3 ·d -1 , the maximal ammonia and total nitrogen removal efficiencies could reach up to 96.08% and 84.86% on day 108, respectively. The pH, DO profiles revealed a switch of functional species (AOB and anammox) at a typical intermittent aeration cycle. qPCR and high throughput analyses certified a stable spatial microbial stratified community structure. Although, anammox preferred strict anaerobic environment while AOB needed oxygen, a special stratified community structure contributed to conquer this obstacle. Moreover, Bacteroidet, Chlorobi, OD1, Planctomycetes, and Proteobacteria were the dominant species in the SBBGR. Although we have predicted the possible pathways of nitrogen transformation, further studies are needed to validate the pathways in enzymology., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

A novel granulation strategy by introducing magnetic nanoparticles (MNPs) into activated sludge system was investigated in this study. The study of the physicochemical characteristics (appearances, sizes, sludge volume index, and chemical oxygen demand) demonstrated that MNPs could decrease the granulation time and improve the retention of biomass, meanwhile enhanced the compact structure of the granules. The secretion and functional groups especially OH and CO of extracellular polymeric substances (EPS) also had significant changes under the long-term influence of MNPs. The contents of proteins (PN) and polysaccharides (PS) in R2 (with MNPs) were 95.7523mg/gVSS and 43.7129mg/gVSS, while in R1 (without MNPs) they were 85.7523mg/gVSS and 32.8632mg/gVSS, respectively. The contact angles of sludge against water dramatically increased with the increase of MNPs concentration, which means that the addition of MNPs could improve the sludge surface hydrophobicity, playing a positive role in the aggregation process., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Both short-term and long-term exposure experiments were carried out to investigate the influence of magnetic nanoparticles (NPs) on activated sludge. The short-term presence of 50-200 mg/L of NPs decreased total nitrogen (TN) removal efficiencies, resulted from the acute toxicity of a shock load of NPs. However, long-term exposure of 50 mg/L magnetic NPs were observed to significantly improve TN removal efficiency, partially due to the self-repair function of activated sludge and magnetic-induced bio-effect. Sludge properties and extracellular polymer substrates secretion were affected. Additional investigations with enzyme and FISH assays indicated that short-term exposure of 50 mg/L magnetic NPs led to the abatement of nitrifying bacteria. However, the activities of the enzyme nitrite oxidoreductase and key denitrifying enzymes were increased after long-term exposure., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The presence of organic matter (OM) is considered to affect anammox process adversely, while practically wastewaters containing ammonia are not free from OM. In this study, the performance of anammox granules in presence of OM was evaluated under different COD to N ratios. Low OM concentration did not affect ammonia and nitrite removal significantly but improved the total nitrogen removal via denitrifiers. High OM could suppress anammox activity, resulting in a lower ammonia removal. PCR tests revealed that there was a reduction in the number of anammox bacteria and denitrifiers quantity increased when 400mg COD/L influent was applied. A COD to N threshold ratio for anammox inhibition, defined when ammonia removal dropped to 80%, was 3.1, higher than that of flocculent sludge. This study revealed that the coexistence of denitrification and anammox was an effective strategy to treat wastewaters containing high levels of nitrogen and OM., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The possibility to introduce the exotic anammox sludge to seed the pilot-scale anammox granular reactor and its fast start-up for treating high nitrogen concentration wastewater were evaluated in this study. The reactor was started up successfully in two weeks; in addition, high nitrogen removal was achieved for a long period. Stoichiometry molar ratios of nitrite conversion and nitrate production to ammonium conversion were calculated to be 1.26±0.02:1 and 0.26±0.01:1, respectively. The Stover-Kincannon model which was first applied in granular anammox process indicated that the granular anammox reactor possessed high nitrogen removal potential of 27.8 kg/m(3)/d. The anammox granules in the reactor were characterized via microscope observation and fluorescence in situ hybridization technique. Moreover, the microbial community of the granules was quantified to be composed of 91.4-92.4% anammox bacteria by real-time polymerase chain reaction. This pilot study can elucidate further information for industrial granular anammox application., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Granular anammox reactors usually adopted anaerobic/aerobic granules as source sludge, in which the washout of other species and enrichment of anammox biomass were very slow because of the competition of the coexisting bacteria. In this study, inactive methanogenic granules were proved to be suitable for rapid anammox granulation under high nitrogen concentrations by investigating their interaction with anammox bacteria. The start-up nitrite concentration was significantly higher than the published toxic level for anammox bacteria and other lab-scale studies. The nitrogen loading rate increased from 141 to 480 mg/L/d in 120 days operation with a total nitrogen removal efficiency of 96.0+/-0.6%. Anammox granules with a diameter of 1.3+/-0.4mm were observed over the course of three months. Molecular analysis showed that over 67% of the cells in the anammox granules were anammox bacteria after 90 days. The accommodations and proliferations of anammox bacteria in the inactive methanogenic granules might be the main reason for the high anammox purity in a short period. The important role of the extracellular polymer in the granule structure was observed via morphological observation., (Copyright 2010 Elsevier Ltd. All rights reserved.)

The anammox non-woven membrane reactor (ANMR) is a novel reactor configuration to culture the slowly growing anammox bacteria. Different mathematical models were used to study the process kinetics of the nitrogen removal in the ANMR. The kinetics of nitrogen gas production of anammox process was first evaluated in this paper. For substrate removal kinetics, the modified Stover-Kincannon model and the Grau second-order model were more applicable to the ANMR than the first-order model and the Monod model. For nitrogen gas production kinetics, the Van der Meer and Heertjes model was more appropriate than the modified Stover-Kincannon model. Model evaluation was carried out by comparing experimental data with predicted values calculated from suitable models. Both model kinetics study and model testing showed that the Grau second-order model and the Van der Meer and Heertjes model seemed to be the best models to describe the nitrogen removal and nitrogen gas production in the ANMR, respectively., ((c) 2010 Elsevier Ltd. All rights reserved.)

An innovative reactor configuration for Anammox enrichment by connecting a non-woven membrane module with an anaerobic reactor was developed in this study. The Anammox non-woven membrane reactor (ANMR) exhibited high biomass retention ability through the formation of aggregates in the reactor and biofilm on the interior surface of the non-woven membrane. No fouling problems occurred on the membrane after the development of mature biofilms. After 8 months of operation, the nitrogen loading rate (NLR) and nitrogen removal rate (NRR) reached 1263 mg N/l/d and 1047.5 mg N/l/d, respectively, with a maximum specific ammonium consumption (SAC) of 51 nmol/mg protein/min. At steady state, the average ammonium and nitrite removal efficiencies were 90.9% and 95.0%, respectively. Morphological observation of Anammox aggregates and biofilm showed a high degree of compactness. Also, enrichment of Anammox bacteria was quantified by real-time polymerase chain reaction (PCR) analysis as 97.7%., (Copyright (c) 2009 Elsevier Ltd. All rights reserved.)