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[Display omitted] • UDB and DB at different pyrolysis temperatures played contrasting roles. • DB800-amended group displayed superior nitrogen removal performance. • DB at lower pyrolysis temperature imposed suppression. • Properties of dissolved organic matter released by DB were tracked at molecular level. Biochar has attracted increasingly attention in the biological wastewater treatment owing to its unique environmental behavior. However, the differential effects of undissolved and dissolved fractions of biochar (hereafter named as UDB and DB, respectively) on the anaerobic ammonium oxidation (anammox) process remain unclear. The study evaluated the nitrogen removal performance of anammox system in response to UDB and DB prepared at different pyrolysis temperatures (300 °C, 550 °C and 800 °C). The DB800-amended group displayed superior nitrogen removal performance with the total nitrogen removal efficiency (TNRE) of 92.8 ± 1.4 %. Compared with CK, TNRE was changed by +5.0 % (UDB300), +0.4 % (UDB550) and −22.3 % (UDB800) for UDB-amended groups, and by −16.0 % (DB300), −9.4 % (DB550), and +9.2 % (DB800) for DB-amended groups, respectively. The differences were closely related to the physicochemical properties of UDB and DB. Particularly, dissolved organic matter released by DB were tracked at molecular level, which revealed that CHO occupied the highest proportion of 70.3 % and lignin-like and carboxylic rich alicyclic molecules were dominant in DB800. This study would facilitate the understanding of the differences between the nitrogen removal performance of UDB and DB-amended anammox, thus providing deeper insights for the comprehensive assessment of the impacts of biochar on the anammox process. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nature based redox materials can serve as electron acceptors and donors. • Complete nitrogen removal based on redox materials. • Emergence of a new pathway for anerobic ammonium oxidation. • Nature-based sustainable solutions for nitrogen management. Complete nitrogen removal depends on the requirement of oxygen as an electron acceptor and organics as electron donors. In the natural environment, these electron acceptors and donors regulate the nitrogen cycle in association with several nature-based processes, such as iron dependent (feammox), sulphur dependent (sulfammox), and nitrite dependent (annamox). These processes represent the latest discoveries in the nitrification part of the nitrogen cycle and provide the electron acceptors for anaerobic ammonium oxidation. Research findings on these processes suggest that a previously undescribed pathway is available for anaerobic ammonium oxidation, which can regulate the nitrogen cycle in natural environments. It has been shown that some redox active materials can serve simultaneously as electron acceptors and donors in the nitrogen cycle. This review provides comprehensive information of the known oxidative processes in the nitrogen cycle and highlights the emergence of a new pathway for anaerobic NH 4 + oxidation, which is dependent on insoluble redox active materials as electron donors and acceptors. This new pathway is not limited to anaerobic NH 4 + oxidation, but it also includes reductive pathways to nitrogen gas, and thus can lead to complete nitrogen removal from nitrogen environments. Recent developments and knowledge advancement in the nitrogen cycle open a new path for nature-based sustainable solutions for nitrogen management. This new knowledge can provide innovative and novel approaches for conventional NH 4 + removal processes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Multiple mediators function as electron shuttles to promote anammox process; • The EET capability of anammox bacteria can be facilitated by external mediators; • The concurrent presence of mediators triggered the activation of essential enzymes; • The application perspective should focus on the EET-enhanced anammox optimization. The anaerobic ammonium oxidation (anammox) process, transforming ammonia into nitrogen gas in oxygen-free environments using nitrite as an electron acceptor, is increasingly recognized for its potential in treating ammonium-rich wastewater. A major challenge for widespread application of this technology is the limited presence of nitrite in most wastewaters. The intrinsic electroactivity of anammox bacteria implies that the introduction of exogenous additives through the extracellular electron transfer (EET) process could effectively stimulate ammonia oxidation even in the absence of nitrite. This comprehensive review consolidates various approaches to enhance EET-dependent anammox, including the utilization of carbonaceous materials, metal ions, and humic substances. Molecular mechanisms involved in enhancing nitrogen removal performance based on extracellular electron transfer capacity are expounded. The co-occurrence of electron acceptors and exogenous electron shuttles is proposed to increase the activity of c-type cytochromes (c -Cyts) and N-acyl-homoserine lactones (AHLs) in extracellular polymeric substances (EPS), as well as enzymes such as hydrazine synthase (HZS) and hydrazine dehydrogenase (HDH), leading to stable a nitrogen removal performance. This review presents novel insights into the engineering of the EET-enhanced anammox process, providing a theoretical framework for its advancement and optimization. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A biofilm-CANON system was kept robust by adjusting aeration time and frequency. • NO 2 − accumulation at the end of each non-aeration stage should be <6 mg N/L. • DO microelectrode measurements provided a basis for regulating aeration. • Decrease in temperature and NH 4 + concentration stimulated DO diffusion into biofilm. • NOB were successfully controlled (<0.25%) during the entire operational period. Abstract Dissolved oxygen (DO) is an important parameter for regulation of "completely autotrophic nitrogen removal over nitrite" (CANON) systems, but effective strategies for regulating DO and the mechanisms of its effects remain unclear. Here, DO microelectrode and nitrite accumulation monitoring were to develop an intermittent aeration regime for a biofilm-CANON system with decreasing influent ammonia and temperature. With high ammonium concentration (185 ± 31 mg N/L in the bioreactor) at 35 °C (Phase I) and 20–23 °C (Phase II), three repeats of 40/80 min aeration/non-aeration per reaction cycle enabled the biofilm-CANON to achieve optimal total nitrogen removal rates (TNRR) of 0.35 ± 0.03 and 0.29 ± 0.04 kg N/m3/d, respectively. The nitrite accumulation threshold at the end of each non-aeration period was 6 mg N/L. When the ammonium concentration was decreased to 35.6 ± 4.5 mg N/L (in the bioreactor) at 20–23 °C (Phase III), five repeats of 8/32 min aeration/non-aeration per reaction cycle ensured a stable TNRR of 0.18 ± 0.02 kg N/m3/d. Micro-profile measurements showed that the penetration of DO into the biofilms increased with decreasing temperature and ammonia, to 400, 600 and 1300 μm in Phases I, II and III, respectively, at 0.6 mg O 2 /L, confirming the need to reduce aeration time when temperature and influent ammonia decreased. High-throughput sequencing showed that nitrite oxidizing bacteria were <0.25% of total bacteria during the whole operation. Nitrosomonas -affiliated ammonium oxidizing bacteria (inhabiting both flocs and biofilms) and anammox bacteria Candidatus Kuenenia (mainly inhabiting the biofilms) were consistently the dominant functional bacteria. DO microelectrode provided comprehensive insights into the effects of decreasing temperature and influent ammonia on DO penetration and was valuable in the development of more sophisticated aeration regulation of biofilm-CANON systems. [ABSTRACT FROM AUTHOR]

This study examined the pre-oxidation of ammonium using a nanofiltration (NF) hollow fiber membrane module to provide an alternative to conventional partial nitrification preceding Anammox. A permeability study showed that NF membranes were suitable for use in the pre-oxidation of ammonium due to high ammonium fluxes across the membrane (low rejection of ammonium), while most COD (in the form of glucose) was retained inside the bulk phase (high rejection of glucose-COD). In pre-oxidation, ammonium oxidizing bacteria (AOB) grown in the shell-side of the membrane module could oxidize the ammonium diffusing from the tube side mainly to nitrite, which then diffused back into the tube side, resulting in a mixture of ammonium and nitrite in the exit stream in an approximately equimolar ratio. This would meet the requirement for the Anammox process as suggested by previous reports. The application of a membrane process for the pre-oxidation of ammonium was found to be promising at a laboratory-scale, and practically viable at a scale similar to a full-scale reactor (Whitlingham STC, Norwich, UK) based on an estimate of the number of HF modules needed. However, a proper optimization study of the process is strongly recommended so that its feasibility could be further examined at a larger scale linking both nitritification and Anammox together. [ABSTRACT FROM AUTHOR]

Under starvation conditions, bacteria could consume intracellular macromolecules, which deteriorates the performance of the bioreactor. However, the fundamental endogenous metabolism of anaerobic ammonium oxidation (anammox) bacteria is poorly understood. Here, we describe the endogenous metabolism of anammox bacteria biomass under short-term anaerobic and anoxic starvation stress (4.5 d and 40 h, respectively) by protein, mRNA and biochemical analyses. The live/dead staining results showed negligible cell death rates. The activity decay rates (decrease in specific activity of active bacteria) were 0.128 d −1 and 0.629 d −1 under anaerobic and anoxic starvation conditions, respectively. The degradation rates of extracellular polymeric substances (EPS) and hydrazine dehydrogenase protein (HDH) were approximately 4- and 5-fold higher under anoxic starvation than under anaerobic starvation tests, suggesting the electron-donor roles for EPS and HDH in denitrification. The greater consumption of intracellular macromolecules during anoxic starvation corresponded with the greater decrease in anammox activities under this condition. Under both starvation conditions, the mRNA decay rates of nirS , hzsA , and hdh mRNA (representing metabolic stability) of anammox bacteria decreased from their normal levels. Such control of specific mRNAs is important for economizing protein synthesis and aids the cells’ recovery after starvation stress. These identified endogenous characteristics of anammox bacteria provide new insights into starvation stress responses at the transcriptional and translational levels, and will assist the optimization of anammox processes in bioreactors, which frequently experience starvation conditions. [ABSTRACT FROM AUTHOR]

Co-occurrence of organic matter (OM) and nitrogen in industrial and domestic wastewaters is a major obstacle in field scale application of anammox process- a novel technology for biological nitrogen removal. This study explored a new symbiosis amongst different consortium i.e., denitrifiers, anammox and anaerobes, which together minimized the inhibition caused due to OM through its concurrent utilization via other metabolic pathways. This symbiosis was achieved by seeding anaerobic granular sludge in existing anammox hybrid reactors at different seed ratios, i.e., 0.2, 0.4, 0.6 and 0.8. COD/TN and seed ratio played a vital role in controlling the overall dynamics of the three different pathways, i.e., denitrification, anammox and anaerobic degradation. The seed ratio of 0.6 was found ideal for synergistic removal of both OM (95.4%) and nitrogen (97.4%). At higher COD/TN ratio, anaerobes were more prevalent and outcompeted anammox bacteria which showed predominance at lower COD/TN ratio. The process performance data were analysed using multi-linear regression (MLR) and non-linear regression models. Biasness of the models were analysed using t -test which dictated MLR model was unbiased and statistically more precise than non-linear regression model. A new mathematical model coceptualised on the mass balance of substrate predicted N 2 and biogas with least error of precision. [ABSTRACT FROM AUTHOR]

The combined anammox (anaerobic ammonium oxidation) and autotrophic desulfurization–denitrification (AADD) process represents a promising innovative technology for biological nitrogen and sulfur removal. In this study, an up-flow anaerobic sludge blanket reactor, which was started with anammox and methanogenic granules, was operated for 245 days to evaluate the co-treatment of wastewater containing nitrogen and sulfur. The reactor demonstrated good performance in terms of nitrogen and sulfide removal and exhibited excellent behavior for removal of NH 4 + -N, NO 2 − -N and S 2− -S exceeding 252, 333 and 330 mg L −1 , respectively. The highest nitrogen removal rate and sulfide removal rate attained were 4.00 kgN m −3 d −1 and 2.39 kgS m −3 d −1 , respectively, which were also the highest reported values for a coupling-system. The influent NH 4 + -N:S 2− -S and NO 2 − -N:S 2− -S ratios set at 1.74 and 2.20–2.27 are suitable for maintaining system stability. The specific activities of anammox and autotrophic desulfurization–denitrification (SAA and SADD), extracellular polymeric substance (EPS), heme c (an important cofactor of some anammox bacterial enzymes) and the diversity of anammox and autotrophic desulfurization–denitrification (ADD) bacteria were investigated during the operation. The SAA and SADD are regarded as key factors for high efficiency. The granules contained many EPS (128.4–204.5 mg g −1 VSS) and minor heme c content (1.17 μmol g −1 VSS). The dominant bacteria belonged to members of Brocadiaceae and Hydrogenophilaceae , a majority of which were anammox bacteria and ADD bacteria, respectively. These observations suggest a new removal process for ammonia, nitrite and sulfide utilizing an uncommon mechanism involving simultaneous anammox and ADD. [ABSTRACT FROM AUTHOR]

In this study, a lab-scale CANON bioreactor was operated for 260 days, decreasing operational temperature from 35 °C to 15 °C and from 466 to 100 mg-N L −1 ammonium. This was done in order to check the feasibility of the acclimation of CANON biomass treating anaerobic digestion supernatant to B-stage influent wastewater operational conditions. Results showed that decrease in temperature posed an impact over the performance of the CANON bioreactor as well as over its bacterial assemblage. Nitrogen removal efficiency showed a moderate decrease when the system was acclimated from 35 °C to 25 °C, but it decreased dramatically in the acclimation from 25 °C to 15 °C. The decrease in temperature and influent ammonium concentration posed an impact over the bacterial community structure of the system. Ammonium oxidizing bacteria changed from Nitrosomonas , Nitrosospira or Nitrosovibrio genera at high temperature and influent ammonium to Prosthecobacter at low temperature and low ammonium. As well, dominant anammox bacteria genus changed from Candidatus Brocadia to Candidatus Anammoxoglobus during acclimation. Proliferation of nitrite oxidizing bacteria only occurred under low temperature and influent ammonium conditions with growth of Rhodanobacter genus. [ABSTRACT FROM AUTHOR]

Anaerobic ammonium oxidation (anammox) is a novel wastewater treatment process. The intrinsic nature of anammox bacteria makes their traditional isolation from a consortium impossible. This study presents a detailed assessment of different pretreatments for percoll density gradient centrifugation (PDGC) to purify anammox bacteria and proposes that the extraction of extracellular polymeric substances (EPS) could significantly increase the purification performance. The results demonstrate that both EPS extraction using cation exchange resin for 2 h and mild ultrasound at an optimal power of 7.2 kJ were suitable pretreatments to increase the purification efficiency in comparison to PDGC performed directly from an original consortium (optimal conditions identified as 8000 rpm, 30 min). Importantly, the implementation of EPS extraction before ultrasound was verified to have the capacity to further increase the purification efficiency up to 95%, which demonstrates the prominent effects of EPS extraction on the PDGC performance. Compared to the previous report, EPS extraction was applied instead of the first centrifugation prior to PDGC to remove large flocs, which correspondingly increased the purified amounts. To clarify the involved mechanism, the bacteria aggregating behaviors before and after EPS extraction over time were visually tracked using a particle size analyzer. The results of this study help to obtain large amounts of anammox bacteria and elucidate the anammox characteristics and communities in both natural and engineered systems. [ABSTRACT FROM AUTHOR]

Quorum sensing (QS) is a microorganism communication system. This study verified the potential existence of the QS system among ANaerobic AMMonium OXidation (anammox) bacteria. The release of three Acyl Homoserine Lactones (AHLs; C 6 -HSL, C 8 -HSL, C 12 -HSL) by anammox culture was confirmed. By conducting series of batch test, the introduction of exogenous C 6 -HSL and C 8 -HSL could significantly increase activity of anammox bacteria, and meanwhile, C 6 -HSL significant increased the growth rate, finally resulting in the increased ammonium nitrogen removal performance of 35% and 20%, respectively, whereas the exogenous C 12 -HSL apparently promoted the growth of heterotrophic bacteria in the community. To further identify how exogenous signal molecular affects anammox culture, analyses of anammox culture supernatant and biomass extraction revealed that these additional signal molecules activated bacteria by inducing the production of endogenous signal molecular by anammox culture. This study might open a new window to overcome the disadvantage of the long-start-up period of anammox reactor restricting the development of current anammox process. [ABSTRACT FROM AUTHOR]

Efficient biological nitrogen removal from high salinity wastewater has been focused recently. The present study comparatively investigated the effects of temperature, salinity and calcium concentration on the performance of anaerobic ammonium oxidation (anammox) processes using anammox granular sludge to treat synthetic wastewater. Four upflow anaerobic sludge blanket reactors were operated in parallel at ambient temperatures evolving from 25 to 9 °C (reactor R 1 ) and thermostatic room temperatures of 35 ± 2 °C (reactors R 2 , R 3 and R 4 ). The results demonstrated that low ambient temperature and high sodium levels impair the nitrogen removal performance of anammox granular sludge. The anaerobic ammonium-oxidizing bacteria gradually adapted to a salt concentration of 15 g L −1 at low ambient temperature, and a nitrogen removal rate of 1.34 ± 0.12 kg N m −3 d −1 was achieved. A nitrogen removal rate of 1.90 ± 0.01 kg N m −3 d −1 in R 4 was achieved at a salt concentration of 15 g L −1 . Moreover, 152 mg L −1 calcium relieved the high salinity inhibition of anaerobic ammonium-oxidizing bacteria. Furthermore, the fractal dimension and permeability of anammox granules were also investigated with settling experiment, which indicated that the anammox granules were porous and permeable. [ABSTRACT FROM AUTHOR]

Anaerobic ammonium-oxidizing (anammox) is a novel wastewater treatment process, which can realize efficient nitrogen removal with low operational cost. The anammox process is usually executed at 35 °C by heating devices. The potential effects of overheating on anammox culture are still remained as an open question. In this study, we share experiences about behavior detection and activity recovery of damaged anammox culture after accidental overheating. When anammox culture suffered 48 °C for 1 h, flocculating and deflocculating occurred, resulting in the suspended culture and the settled. Fluorescence in situ Hybridization, Flow Cytometry and Non-invasive Micro-test Technique showed that the settled culture contained more anammox bacteria than the suspended, leading to its higher death probability as time course, higher bulk liquid H + flux rate and faster activity restoration for nitrogen removal after overheating. The autofluorescence of Candidatus Brocadia fulgida varied during this process and could be considered as a characteristic fingerprint for these anammox bacteria. Experimental results also indicated the shear force produced by 150 rpm stir would contribute to the further damage of the heated bacteria. Reducing shear stress by low stirring rates and static cultivation might potentially be used as effective strategies in the repair of damaged anammox culture. [ABSTRACT FROM AUTHOR]

The performance and hydrodynamic features of a staged up-flow ANAMMOX (anaerobic ammonium oxidation) sludge bed (SUASB) reactor was evaluated. When the reactor was at steady-state conditions, the nitrogen loading rate (NLR) and nitrogen removal rate (NRR) were 5.63 and 4.82 kg N m-3 d-1, respectively. The reactor could withstand a 1.5-fold substrate or hydraulic shock. The modified Stover-Kincannon model was used for the kinetic analysis, and the saturation value (KB) and maximum total substrate utilization rate (Umax) were 14.5 and 14.8 kg N m-3 d-1, respectively. Moreover, the C(t)-Θ curve showed the existence of dead zones in the SUASB at the hydraulic retention times (HRTs) of 3 and 12 h, and the flow pattern performance of the SUASB fell between those of a continuous stirred tank reactor (CSTR) and a plug flow reactor (PFR). [ABSTRACT FROM AUTHOR]