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Anaerobic ammonia oxidation bacteria (AnAOB) are difficult to cultivate due to their long start-up time and sensitivity to environmental conditions. In this study, anammox granular sludge was cultured with ordinary activated sludge under influent dissolved oxygen concentrations of 6–8 mg/L, successfully enriching AnAOB. The presence of multiple microorganisms in the activated sludge enabled the anammox system to resist the unfavorable influent environment and sustain system stability. The total nitrogen removal rate reached a maximum of 81%, and the TN effective load increased from 0.1 to 1.5 kg N/m3/d. The results showed that the dissolved oxygen present in the influent did not lead to a breakdown in the anammox system. The protein in the sludge extracellular polymeric substances played an important role in the enrichment of AnAOB, and the sludge settling performance at the bottom of the reactor was better than that at the top of the reactor, with protein/polysaccharide in the range of 5–6.3. Candidatus brocadia and Candidatus kuenenia were the main anammox functional bacteria in the system. On 153 d of reactor operation, their relative abundances were 8.51 and 5.68%, respectively. This study shows that microorganisms in activated sludge contribute to the stability of the anammox system when the influent conditions are appropriate. This provides a new idea for the rapid start-up of the anammox system and enrichment of AnAOB. [ABSTRACT FROM AUTHOR]

Aggregation of anammox bacteria is essential to maintain high biomass concentrations and prevent the loss of biomass in anammox processes. PICRUSt (Phylogenetic Investigation of Communities by Reconstruction of Unobserved States) was used in this study to predict the metagenomic potentials and characterize the microbial community structure and functional features in anammox aggregates (e.g., sludge flocs, biofilms, and granules). The results showed that Candidatus Brocadia was the most dominant anammox genera in all aggregates (38.0% in flocs, 69.4% in biofilm, and 52.0% in granules) and the functional gene involved in the anammox process was detected in the highest amount in biofilms, followed by granules and flocs. Furthermore, the anammox microbial aggregation pathway was explored that anammox bacteria have strong motility and high capability for early attachment. Anammox bacteria could produce large amounts of EPS (extracellular polymeric substances) regulated by quinolone and transport to extracellular environment through type II secretion system. The strong ability of c‐di‐GMP (bis‐(3′‐5′)‐cyclic dimeric guanosine monophosphate) synthesis enabled a stable architectural structure of aggregation. This study elucidated the aggregation mechanism of anammox microorganisms at the genetic level to enhance the stability of anammox processes. Practitioner points: Candidatus Brocadia was the most dominant anammox genera in aggregates.Anammox bacteria have strong motility and high attachment capability.Anammox bacteria possess strong EPS synthesis regulated by quinolone.c‐di‐GMP synthesis enables a stable structure of aggregation. [ABSTRACT FROM AUTHOR]

• PDA promotes AnAOB enrichment with abundance increase from 7 × 106 to 3 × 108 copes/gSS. • PNA was achieved in activated sludge system aerobic zone to treat real wastewater. • NER and NRR increased to 95% and 0.12 kgN/m3·d after transforming PDA to PNA. • With the NAR increased from 5.5 to 97.5%, anammox contribution decreased. • PN achievement benefits efficient nitrogen removal and less depend on anammox. Anaerobic ammonium oxidation (anammox) combined with partial nitrification (PN) is expected to achieve energy self-sufficiency in wastewater treatment, while its advantages have not been fully revealed. An anaerobic/aerobic/anoxic (AOA) system was established to treat low chemical oxygen demand (COD)-total inorganic nitrogen (TIN) (C/N) ratio (3.08) municipal wastewater. Anammox bacteria were enriched from 7 × 106 to 3 × 108 copies/gSS during partial denitrification coupling with anammox (PDA) phase. With the PN achievement, the anammox hotspot zone transformed from the anoxic zone through PDA (37%) to the aerobic zone by partial nitrification coupled with anammox (PNA) (12%). As the nitrite accumulation rate increased to 97%, the TIN removal efficiency and rate increased to 95% and 0.12 kgN/(m3·d). Although anammox performance weakened after this transformation, the carbon sources saved by PN drove more nitrogen removal. PNA was beneficial for advanced and efficient nitrogen removal in carbon-limited wastewater treatment and was less dependent on higher anammox contribution. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, enhanced nitrogen removal through in situ enrichment of anammox bacteria was successfully obtained in a full-scale municipal wastewater treatment plant (WWTP). The WWTP was an anaerobic-anoxic-oxic (AAO) process and upgraded by adding moving carriers into the anoxic zone. Enhanced nitrogen removal was obtained during almost two years of operation. The significant nitrogen removal might be associated with the in situ enrichment of anammox bacteria on the adding carriers, as revealed by the comprehensive results of molecular analysis and 15N-stable isotope tracing tests. Quantitative PCR results indicated that anammox bacteria in the anoxic-carrier biofilms presented a higher abundance than flocculent sludge (16S rRNA: P < 0.005; HzsB : P < 0.042). The 16S rRNA amplicon sequencing showed significant differences in the phylum Planctomycetes (P < 0.001) between anoxic-carrier biofilms and flocculent sludge. And metagenomic sequencing analysis further revealed the anammox relative abundance in the anoxic-carrier biofilms was significantly higher than the reported level in the flocculent sludge of conventional WWTPs. In addition, 15N-stable isotope tracing tests showed that anammox could be combined with nitrate reduction by the anoxic-carrier biofilms. Thus, enriched anammox bacteria might contribute to nitrogen loss and lead to improvements in the nitrogen removal, which was also supported by the mass balance analysis of organic carbon, nitrogen, and phosphorus of the WWTP. Overall, this study suggests that anoxic-carrier biofilms might be a candidate to enhance nitrogen removal through partial anammox in municipal WWTPs. Image 1 • The carriers added in the anoxic zone of the municipal WWTP could enhance N-removal. • The anoxic-carrier biofilms enriched with both denitrifies and anammox bacteria. • Anoxic biofilms show comparable AMX activity as denitrification by 15N isotope tracer. • Coupling nitrate reduction with anammox might enhance N-loss via anoxic biofilms. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The feasibility of achieving mainstream EPD-Anammox was first demonstrated. • Around 90% of nitrogen removal was achieved with a low C/N (∼2.9). • Nitrogen removal via anammox accounted for 49.8%, reducing oxygen and carbon demands. • An appropriate NO 2 −-N/NH 4 +-N (∼1.2) was achieved without complex control process. • Denitrifying GAOs (36.6%) were responsible for the high nitrite accumulation. Abstract Successful application of mainstream anammox would be favorable for energy- and resource-efficient sewage treatment. This study presents a new strategy to achieve mainstream anammox, which combined with endogenous partial denitrification (EPD) for treating sewage wastewater. In this EPD-Anammox system, nitrite was stably produced by EPD with a nitrate-to-nitrite transformation ratio of 80%. Through adjusting the volume exchange ratio of EPD-reactor after anaerobic reaction, a suitable NO 2 −-N/NH 4 +-N ratio of ∼1.20 for anammox reaction was achieved. Further, results showed a stable, high nitrogen removal efficiency (90%) with an effluent total nitrogen of 5.8 mg N/L under low C/N (∼2.9). Anammox contributed 49.8% of the overall nitrogen removal owing to the steady nitrite supply from EPD. Denitrifying glycogen-accumulating organisms (GAOs, 36.6%) having potential for endogenous denitrification and Candidatus Brocadia (34.6%) were respectively dominated in the EPD-SBR and anammox-UASB and responsible for the high nitrite accumulation and anammox reaction. [ABSTRACT FROM AUTHOR]

Mature landfill leachate is difficult to be treated due to its complex composition, high concentration of ammonia, and low carbon/nitrogen ratio (C/N). Simultaneous partial nitrification, Anammox and denitrification (SNAD) with intermittent aeration was developed to achieve nitrogen removal from mature landfill leachate. An ammonia conversion efficiency of 99.3 ± 0.3% and total nitrogen (TN) removal efficiency of 99 ± 0.1% were obtained under the influent NH 4 + -N , SCOD and TN of 1950 ± 250 mg/L 1900 ± 200 mg/L and 2300 ± 75 mg/L, respectively. Full utilization of carbon source and high efficient Anammox were two significant factors in SNAD process. Based on the nitrogen balance, the nitrogen removal contribution was 77.1% for Anammox, and 15.6% for denitrification. Three dimensional excitation-emission matrix (EEM) fluorescence spectroscopy was used to detect dissolved organic matter (DOM) in a typical operation cycle for the first time, demonstrating that DOM increased during the anoxic phase and facilitated the reduction of excess NO 3 - -N by denitrification. Quantitative polymerase chain reaction (QPCR) analysis revealed dominant bacterial groups, aerobic ammonia-oxidizing bacteria (AOB) and anaerobic ammonia oxidizing bacteria (AnAOB), which accounted for 12.99% and 8.32% of total bacteria respectively. As a whole, in the SNAD process, nitrogen and COD are removed from the wastewater simultaneously. [ABSTRACT FROM AUTHOR]

This study proposed a novel strategy for achievement of partial denitrification driven by endogenous carbon sources in an anaerobic/anoxic/aerobic activated sludge system. Results showed that in the steady-stage, the nitrate-to-nitrite transformation ratio (NTR) was kept at around 87% without nitrate in the effluent. During the anaerobic period, exogenous carbon sources was completely taken up, accompanied by the consumption of glycogen and production of polyhydroxyalkanoates (PHAs). During the anoxic period, nitrate was reduced to nitrite by using PHAs as carbon sources, followed by the replenishment of glycogen. Thus, the phenotype of denitrifying GAOs was clearly observed and endogenous partial denitrification (EPD) occurred. Furthermore, results showed the nitrate reduction was prior to the nitrite reduction in the presence of nitrate, which led to the high nitrite accumulation. [ABSTRACT FROM AUTHOR]

• Improved NRE from 72.2% to 77.2% was firstly achieved as temperature decreases. • More tolerance of PD at low temperature increased nitrite substrates for anammox. • Ca. Brocadia increased by 167% and focused on biofilm (0.27%) at low temperature. • Anammox contribution improved from 41.8% to 60.2% and responsible for better NRE. Low temperature is one of the obstacles in mainstream anammox. This study aimed to evaluate the stability of a step-feed bioreactor dominated by denitratation/anammox (PD/A) for treating municipal wastewater with decrease in temperature (21.5 °C→12.6 °C). During long-term operation, nitrogen removal efficiency (NRE) was improved from 72.2% (21.5 °C→14.9 °C) to 77.2% (stable at 13.9 °C) with influent and effluent total inorganic nitrogen of 44.6 and 10.1 mg N/L. Better low temperature tolerance of nitrate reduction than nitrite reduction enhanced denitratation and increased nitrite substrates for anammox. Microbial structure analysis revealed that Ca. Brocadia increased by 167% and reached 0.27% on biofilm at low temperature. Finally, anammox contribution improved from 41.8% to 60.2%, saving organic carbon for denitrification, which was responsible for better NRE. Moreover, Ferribacterium, Dechloromonas , and Thauera were the major denitrifiers distributed in suspended sludge. Overall, this study provides an optimistic prospect for promoting anammox in mainstream applications at low temperature. [Display omitted] [ABSTRACT FROM AUTHOR]

This study presents a novel process (i.e. PN/SFDA) to remove nitrogen from low C/N domestic wastewater. The process mainly involves two reactors, a pre-Sequencing Batch Reactor for partial nitritation (termed as PN-SBR) and an anoxic reactor for integrated Denitrification and Anammox with carbon sources produced from Sludge Fermentation (termed as SFDA). During long-term Runs, NO 2 − /NH 4 + ratio (i.e. NO 2 − -N/NH 4 + -N calculated by mole) in the PN-SBR effluent was gradually increased from 0.2 to 37 by extending aerobic duration, meaning that partial nitritation turning to full nitritation could be achieved. Impact of partial nitritation degree on SFDA process was investigated and the result showed that, NO 2 − /NH 4 + ratios between 2 and 10 were appropriate for the co-existence of denitrification and anammox together in the SFDA reactor, and denitrification instead of anammox contributed greater for nitrogen removal. Further batch tests indicated that anammox collaborated well with denitrification at low C/N (1.0 in this study). [ABSTRACT FROM AUTHOR]

The recently developed Partial Denitrification/Anammox (PD/A) is an emerging process for simultaneous ammonium and nitrate removal, while the remaining organics from PD may pose an adverse effect on the subsequent anammox process. In this study, a granule-based anammox UASB reactor was developed with receiving municipal wastewater driven PD effluent that contained a certain amount of refractory organic matter, the characterization of different size-fractionated granules on nitrogen removal and microbiological mechanisms were investigated. Anammox activity increased with granule size, while an oversize exceeding 2.5 mm would lead to activity reduction. Significant denitrification activity was detected, it exhibited a contrary relationship with anammox activity. Delightedly, the denitrification was observed to proceed with high nitrite accumulation, especially in smaller granules with nitrate-to-nitrite transformation ratio (NTR) above 84.4%. These results were confirmed by microbial analysis, anammox genus including Candidatus Kuenenia , Brocadia, and Jettenia were identified in all granules, their abundances increased with granule size, and the dominated Kuenenia preferred to grow in larger granule. Various kinds of denitrification bacteria were detected with the relative abundances increased with the decrease in granules size. Particularly, the Thauera that responsible for PD with high nitrite accumulation was revealed to grow in such system, its relative abundance in small-size granules (12.9%, <0.5 mm) was much higher than the large ones (<2.3%). Overall, this study improved our understanding of the synergy of anammox and denitrification bacteria between size-fractionated granules, it provides a guide for system optimization towards great stability by biomass segregation strategy, and sheds new light to develop an efficient anammox coupling with PD process in continuous-flow UASB reactor. • Effect of organics from PD on size-fractionated anammox granules were investigated. • Remaining organics induces the occurrence of PD in anammox reactor. • PD functional bacteria was identified to be much higher in smaller granules. • A one-stage continuous-flow PD/A process was expected to achieve in anammox UASB. [ABSTRACT FROM AUTHOR]

[Display omitted] • Anammox contribution to nitrogen removal was robustly maintained at 91.3 ± 6.6 %. • Compared with stable NO 3 – → NO 2 –, NO 2 – → N 2 was sensitive to temperature reduction. • Anammox abundance was increased (0.56% to 1.22%) despite of decreased temperature. • NO 2 – accumulation at lower temperature was unexpectedly helpful to enrich anammox. Effluent quality deterioration caused by seasonal temperature reductions in wastewater treatment systems using partial anammox technology is a challenge that cannot be ignored. Here, relationships of denitrification and anammox under decreasing temperature were investigated in an anoxic moving bed biofilm reactor (MBBR). Compared with stable partial-denitrification (NO 3 – → NO 2 –), the NO 2 – reduction to N 2 was considerably inhibited when the temperature decreased, conversely helping to the competition of NO 2 – for anammox. Namely, this transformation provided sufficient substrates for anammox bacteria. Although the TIN removal decreased slightly, anammox contribution was robustly maintained at 91.3 ± 6.6 %, even increased. High-throughput sequencing results revealed that anammox bacteria were enriched (0.56 % to 1.22 %). Moreover, qPCR results showed that increased ratio of hzsB /(nirK + nirS) further supported anammox gained an enhancement. This study demonstrated partial-denitrification/anammox process using anoxic MBBR could maintain stable autotrophic nitrogen removal contribution when encountering temperature decrease, providing a new perspective on the application of mainstream anammox. [ABSTRACT FROM AUTHOR]

Due to the difficulty in removing nitrogen from landfill leachate, a combined continuous-flow process of nitritation and anammox was applied to process mature leachate. The transformation rate of ammonia and nitrite accumulation ratio in A/O reactor were kept above 95% and 92% respectively through associated inhibition of free ammonia (FA) and free nitrous acid (FNA) to NOB. The total nitrogen volumetric load of anammox in an UASB reactor was brought up from 0.5 kg/(m 3 ·d) to 1.2 kg/(m 3 ·d) by gradually increasing influent substrate concentration and reducing hydraulic retention time (HRT). The results show that COD from mature leachate did not bring obvious inhibition effects to anammox. Under concentrations of influent ammonia and COD which were respectively 1330 mg/L and 2250 mg/L, the removal efficiencies of TN and COD reached 94% and 62% respectively. In the quantitative PCR reactions, the proportions occupied by AOB, NOB and anammox in A/O were 11.39%, 1.76% and 0.05% respectively; and proportions of those in UASB were 0.35%, 4.01% and 7.78% respectively. [ABSTRACT FROM AUTHOR]

This work demonstrates the feasibility of simultaneous nitrogen removal and external waste activated sludge (WAS) reutilization/reduction by using the synergy of sludge fermentation, denitrification and anammox processes in up-flow reactors (SFDA). Pre-treated domestic wastewater and synthetic wastewater (containing nitrite ∼20 mg/L, ammonium ∼10 mg/L in both) were fed to 1# and 2# SFDA, respectively. Long-term operation of 1# SFDA was investigated with achieving the peak ammonium removal rate of 0.021 and nitrite removal rate of 0.081 kg N/(m 3 d) as nitrogen loading rate elevated from 0.075 to 0.106 kg N/(m 3 d). Negative effect of dissolved oxygen on anammox or fermentation in the 2# SFDA was demonstrated negligible due to rapid depletion by microorganisms. Furthermore, a “net” sludge reduction of 38.8% was obtained due to sludge decay and organics consumption by denitrification. The SFDA process was expected to potentially be used for nitrogen removal and WAS reutilization/reduction in full-scale application. [ABSTRACT FROM AUTHOR]

A combined process including a partial nitritation SBR (PN-SBR) followed by a simultaneous sludge fermentation, denitrification and anammox reactor (SFDA) was established to treat low C/N domestic wastewater in this study. An average nitrite accumulation rate of 97.8% and total nitrogen of 9.4 mg/L in the effluent was achieved during 140 days’ operation. The underlying mechanisms were investigated by using Illumina MiSeq sequencing to analyze the microbial community structures in the PN-SBR and SFDA. Results showed that the predominant bacterial phylum was Proteobacteria in the external waste activated sludge (WAS, added to the SFDA) and SFDA while Bacteroidetes in the PN-SBR. Further study indicated that in the PN-SBR, the dominant nitrobacteria, Nitrosomonas genus, facilitated nitritation and little nitrate was generated in the PN-SBR effluent. In the SFDA, the co-existence of functional microorganisms Thauera , Candidatus Anammoximicrobium and Pseudomonas were found to contribute to simultaneous sludge fermentation, denitrification and anammox. [ABSTRACT FROM AUTHOR]

The recently proposed DEnitrifying AMmonium OXidation (DEAMOX) process combined anaerobic ammonia oxidation (ANAMMOX) with denitrification to convert nitrate to nitrite, which was a promising way for treating wastewater containing nitrate and ammonia. This study investigated the feasibility of establishing DEAMOX process by seeding partial denitrification sludge (NO 3 − → NO 2 − ) using sodium acetate as an electron donor in a sequencing batch reactor. Results showed that the DEAMOX process was established successfully and operated stably in 114-days operation. The average effluent total nitrogen concentration was below 5 mg L −1 and TN removal efficiency reached up to 97% at COD/NO 3 − ratio of 3.0 under initial NH 4 + concentration of 25 mg L −1 and NO 3 − of 30 mg L −1 . It suggested that the presence of NO 2 − in the system supplied for ANAMMOX and the relatively long sludge retention time (SRT) for denitrifiers were attributed to commendable coexistence of ANAMMOX and denitrifying bacteria. [ABSTRACT FROM AUTHOR]

Occurrence of anaerobic ammonium oxidation (anammox) in marine and freshwater systems has greatly changed our understanding of global nitrogen (N) cycle and promoted the investigation of the role and ecological features of anammox in anthropogenic ecosystems. This study focused on the spatio-temporal abundance, activity, and biodiversity of anammox bacteria in full-scale municipal wastewater treatment plants (WWTPs) via traditional nitrification/denitrification route with low-strength ammonium loading. The anammox bacteria were detected in all the treatment units at the five WWTPs tested, even in aerobic zones (dissolved oxygen >2 mg L −1 ) with abundance of 10 5 –10 7 hydrazine synthase ( hzs ) gene copies g −1 . The 15 N-isotope tracing technology revealed that the anammox rates in WWTPs ranged from 0.08 to 0.36 μ mol N g −1 h −1 in winter and 0.12–1.20 μ mol N g −1 h −1 in summer with contributions of 2.05–6.86% and 1.71–7.26% to N 2 production, respectively. The diversity of anammox bacteria in WWTPs was distributed over only two genera, Brocadia and Kuenenia . Additionally, the exploration of potential interspecies relationships indicated that ammonia oxidation bacteria (AOB) was the major nitrite-substrate producer for anammox during nitrification, while Nitrospira , a nitrite oxidation bacteria (NOB), was the potential major competitor for nitrite. These results suggested the contribution of N-removal by the widespread of anammox has been overlooked in traditional municipal WWTPs, and the ecological habitats of anammox bacteria in anthropogenic ecosystems are much more abundant than previously assumed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nitritation was stable with NAR always higher than 82% when temperature fluctuated. • Ca. Brocadia was enriched from 0.03% (20.4℃) to 0.24% (12.9℃) in suspended sludge. • Granulation was achieved in domestic wastewater system as temperature dropped. • Average particle size of sludge increased from 128.5 μm to 245.6 μm. • Relative abundance of Ca. Brocadia in granule was as high as 16.09% Low temperature is an important factor affecting the municipal wastewater treatment systems. The aim of this study was tracking the variations in the abundance of anammox bacteria (AnAOB) and the sludge form as the temperature decreased. Mutual boost of granulation and enrichment of AnAOB was achieved even though the temperature dropped from 20.4 °C to 12.9 °C. The average particle size of the sludge increased from 128.5 μm to 245.6 μm. With low dissolved oxygen (DO) aeration (0.2–0.5 mg/L) and short oxic hydraulic retention time (HRT) (5 h), nitritation in the anaerobic/oxic/anoxic (AOA) system was stable enough to provide NO 2 – for AnAOB. Ca. Brocadia , a type of typical AnAOB, was enriched from 0.03% to 0.24% in the suspended sludge and reached 16.09% in the granular sludge. Overall, this study presents the prospects of anammox and granule technologies when treating municipal wastewater at a low temperature. [ABSTRACT FROM AUTHOR]

The anammox (anaerobic ammonium oxidation) process has attracted much attention for its cost-saving. However, excess nitrate is usually produced which should be further treated. In this study, an innovative process combined anammox with partial denitrification (nitrate → nitrite) was proposed for advanced nitrogen removal in two sequencing batch reactors (SBRs). The nitrate produced in anammox-SBR (ASBR) was fed into partial denitrification-SBR (DSBR), in which the nitrate was reduced to nitrite, and then removed by backflow of the nitrite to ASBR for secondary anammox process. Results showed that ∼80% nitrate in the effluent of previous anammox was converted to nitrite in DSBR. And the maximum nitrogen removal efficiency (NRE) of 94.06% was obtained with total nitrogen (TN) in the effluent of 10.98 mg/L in average. It indicated that desired effluent quality could be achieved, and the advanced nitrogen removal performance was attributed to the successful achievement of partial denitrification. [ABSTRACT FROM AUTHOR]

• THP-AD filtrate was effectively polished by double-line anammox to TN of 8.8 mg/L. • Inhibition of complex organics can be alleviated with enrichment of Anaerolineae. • Enhanced organic degradability facilitated the external C/N decrease to 0.3 in PDA. • Increasing abundance of Ca.Brocadia and improved anammox activity was obtained. Anammox process has been widely regarded as an energy-efficient method for sludge digestion filtrate treatment. However, the complex high-strength organics in the filtrate, especially of Anaerobic Digestion after Thermal Hydrolysis Pretreatment (THP-AD), brings serious threat to anammox bacteria, and the high nitrate residue in effluent remains another significant barrier in operation. In this study, a novel double-line anammox-mediated system, integrating the Partial Nitrification/Anammox (PNA) with Partial Denitrification/Anammox (PDA) processes in separately sequencing batch reactors (SBRs), was developed to polish the THP-AD filtrate. When the real THP-AD filtrate (1946.5 mg NH 4 +-N/L, 2076.0 mg COD/L) was fed to the front PNA reactor (SBR PNA) with 5-fold dilution, effluent total nitrogen (TN) remained at 93.0 mg/L. Notably, the final effluent TN was effectively polished to as low as 8.8 mg/L by the following PDA reactor (SBR PDA), which was fed with the SBR PNA effluent and real domestic wastewater (71.0 mg NH 4 +-N/L, 209.1 mg COD/L). More severe inhibition on anammox activity was observed in SBR PNA rather than SBR PDA by refractory organics in filtrate. Fortunately, it could be alleviated with the enhanced degradability of particulate organics and aromatic protein-like compounds, attributed to the enrichment of class Anaerolineae in both SBR PNA and SBR PDA. This further stimulated the electron donor supply for PDA process with much lower external carbon source demand. 16S rRNA sequencing analysis revealed that Candidatus Brocadia as dominant anammox bacteria were efficiently enriched in both SBR PNA and SBR PDA , indicating its unexpected toughness and adaptability to the complex organic compounds in THP-AD filtrate. Overall, this study suggested that the novel double-line anammox would be a promising alternative for cost-efficient nitrogen removal from high-strength wastewater containing complex organic matter. [Display omitted]. [ABSTRACT FROM AUTHOR]

The enhancement effect of compatible solutes on anammox activity under salinity stress was investigated. Glycine betaine (GB) was the most effective in alleviating salt toxicity, although all the compatible solutes (GB, trehalose and ectoine) were found to be valid. Acclimation potential of anammox biomass under salinity of 30 g/L increased significantly with GB addition. The recovery time in the reactor with GB addition (RB) (49 days) accompanied by a more stable stoichiometric ratio was 2.65 times shorter than in the control reactor (RC) (130 days). After 49 days, the extracellular polymeric substances and the tetrazolium chloride-dehydrogenase activity were 217.9 mg/gVSS and 38.7 μg TF/gVSS/h in RB, 1.86 times lower and 3.17 times higher than the levels in RC, respectively. RB possessed evident superiority in the aspects of microbial population proportion. And thus, compatible solutes addition was regarded as one of the feasible solution to counteract saline inhibition on anammox. [ABSTRACT FROM AUTHOR]

Highlights: [•] A simultaneous Anammox and denitrification was achieved in the SBR system. [•] The Anammox biomass aggregated as wall growth in SBR. [•] The maximum nitrogen removal efficiency of 97.47% was realized at C/N of 2. [•] The Anammox activity recovered rapidly after suppression of high organic matter concentration. [Copyright &y& Elsevier]

Ammonia oxidation is a central step in the global nitrogen cycle that involves several different-conditions and metabolic bioprocesses, including aerobic versus anaerobic ammonia oxidation, and autotrophic versus heterotrophic ammonia oxidation. With the development and application of metagenomics and other modern molecular approaches, some new organisms (particularly ammonia-oxidizing archaea) and novel pathways related to ammonia oxidation have been identified. Consequently, the understanding of nitrogen cycling processes and the microorganisms that mediate them have been greatly improved. Here the authors summarize the biochemistry, microbiology, and ecophysiology of these organisms (including autotrophic ammonia-oxidizing bacteria, heterotrophic nitrifying bacteria, anaerobic ammonia-oxidizing bacteria, and ammonia-oxidizing archaea) and discuss the current knowledge and important concepts associated with their corresponding pathways. Factors influencing their distribution, abundance, community structure and potential ammonia oxidation rates in natural and engineered ecosystems are also addressed. Furthermore, the mechanism of nitrous oxide emission during these processes and the specific control strategies are explained or proposed. The significant roles of these organisms in novel biological wastewater treatment processes are also evaluated. Finally, several urgent issues and significant perspectives related to these novel pathways and players have been addressed to evoke the involvement of researchers in broadening future studies. [ABSTRACT FROM AUTHOR]

[Display omitted] • Anammox contributed over 70% to N-removal with salinity of 0, 0.4, 0.7, and 1.0%. • Highest NRE of 81.2% and anammox contribution of 76.5% was achieved at 1.0%. • Salinity intensifies nitritation and denitratation processes further enhancing anammox. • Ca. Brocadia enriched on biofilms while Nitrosomonas enriched in suspended sludge. Saline wastewater present in municipal pipe networks poses challenges to biological nitrogen removal due to its inhibition on microorganisms. This study focuses on the effects of low salinity (0.0%, 0.4%, 0.7% and 1.0%) on a system featuring a combination of nitritation/anammox in oxic stage and denitratation/anammox in anoxic stage (double-anammox) in a step-feed SBR for municipal wastewater over a period of 130 days. The results showed that a maximum nitrogen removal efficiency of 81.2% was achieved at a salinity of 1.0% with anammox contribution of 76.5%. Analysis of anammox contribution and sludge activities discovered that low salinity promoted both nitritation and denitratation, further enhancing the coupling with anammox. Further, microbial analysis confirmed that Ca. Brocadia was enriched on biofilms from 0.21% to 0.51% and Nitrosomonas was enriched in flocs from 0.50% to 1.04%. Overall, the double-anammox process appears to be a promising method for the treatment of saline wastewater. [ABSTRACT FROM AUTHOR]

Abstract: An integrated approach to enhance and maintain high anammox activity and abundance in an upflow anaerobic sludge blanket (UASB) treating low strength wastewater under moderate and low temperatures was developed. A quantitative PCR assay showed the abandance of anammox bacteria to be 1.68±0.08×109 copies/ml in mixed liquor when the temperature was 30°C and was maintained at the level of 1.93±0.41×109 copies/ml in mixed liquor at 16°C. A nitrogen removal rate (NRR) of up to 5.72kgN/m3/d was achieved with a hydraulic retention time (HRT) of 0.12h at 30°C, while nitrite and ammonium removal efficiencies were 94.35% and 92.81%, respectively. NRR decreased with a decrease in temperature and was maintained at 2.28kgN/m3/d with an HRT of 0.28h when at 16°C, while nitrite and ammonium removal efficiencies were 92.31% and 78.45%, respectively. The emission rate of the greenhouse gas N2O was below 0.006% of the NRR in the anammox UASB reactor treating low strength wastewater. [Copyright &y& Elsevier]

[Display omitted] • An ultra-low energy consumption bioprocess was firstly developed for decentralized sewage treatment. • High-efficient nitrogen removal efficiency of 93.7% with 6.7 mg/L in effluent TN was obtained. • Anammox contributed a significance nitrogen removal of 88.1% and 7.6% for denitrification. • UEFC saved 100% mechanical aeration, 100% external carbon dosage. An ultra-low energy consumption continuous flow (UECF) process was used for enhanced nitrogen removal from rural sewage. The ammonia in sewage was first oxidized to nitrite in a bio trickling filter (BTF PN) supplemented with natural oxygen. A stable nitrite accumulation ratio (NAR) of 93.2% was maintained by adding 5 mg/L NH 2 OH every seven days. BTF PN effluent was then combined with certain portion of rural sewage (1:1.2 to 1:1.5) and introduced to an upflow anaerobic sludge blanket reactor, where the nitrogen-containing pollutants were removed by Anammox process (UASB AMX). Effluent total nitrogen (TN) of 6.7 mg/L and a TN removal efficiency of 93.7% were obtained when influent chemical oxygen demand (COD), NH 4 +-N and TN were 321.9, 74.2 and 82.7 mg/L, respectively. Advanced nitrogen removal, based on the desirable cooperation between Anammox bacteria (Ca. Brocadia , 2.3%) and partial denitrification bacteria (Thauera , 4.2%), was achieved over 300 days of stable operation. Considering the nitrogen balance, 57.9% of nitrate generated in Anammox was reduced to nitrite by partial denitrification, and Anammox contributed 88.1% of nitrogen removal and 7.6% of denitrification. Compared with conventional nitrification and denitrification processes, UECF requires no mechanical aeration, no external carbon, produces 76.6% less external sludge, and reduces CO 2 emissions by 92.3%. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel PNA-PDA process was developed for high-level sidestreams treatment. • Desirable polishing treatment of PNA effluent was achieved via PDA approach. • TN removal maintained as high as 98.4% even at low temperature of 13.0 ℃. • Domestic wastewater could be simultaneously treated without aeration. Anaerobic ammonium oxidation (anammox) has been widely accepted as an energy-efficient approach for nitrogen removal from high-strength sidestreams. However, insufficient nitrogen removal due to the excessive NO 3 –-N residue represents the major challenge, especially at low temperature. In this study, highly efficient and synchronous nitrogen removal from ammonia-rich wastewater and real domestic wastewater was achieved via a novel anammox-mediated treatment by coupling with double-nitrite-shunt process in two-stage sequencing batch reactors. Stable partial nitrification/anammox (PNA) was successfully developed, while the total nitrogen (TN) removal efficiency was limited to 86.9 % due to excessive NO 3 –-N accumulation. Significantly, integration with partial denitrification (NO 3 –-N → NO 2 –-N) coupling anammox (PDA) process offered an efficient solution, which transformed the overproduced NO 3 –-N of PNA to NO 2 –-N and subsequently completely removed with NH 4 +-N via anammox pathway by mixing with real domestic wastewater (NH 4 +-N of 69.0 mg/L, COD of 203.6 mg/L). Excellent nitrogen removal performance with average TN removal efficiency of 98.4 % and high-quality effluent with average TN of 4.9 mg/L was maintained despite the temperature dropping to 13.0 ℃. 16S rRNA gene sequencing unveiled the different community of anammox bacteria cooperating stably with AOB and denitrifiers in the two systems. Compared with conventional nitrification/denitrification methods, the novel PNA-PDA process not only enabled 60% saving in aeration energy and 95.5% saving in organic carbon for ammonia-rich wastewater treatment, but also required no aeration energy for domestic wastewater treatment. Overall, this study provides a promising application with simple-control strategy for cost-effective and synchronous nitrogen removal from sidestreams and mainstreams. [ABSTRACT FROM AUTHOR]

[Display omitted] • PN/A-PD/A was efficiently realized in typical UCT process to treat municipal sewage. • TIN in influent and effluent were 51.3 and 11.0 mg/L even with COD/TIN ratio of 2.9. • Anammox activity improved from 6.52 to 9.68 mg NH 4 +-N/gMLSS/d with abundance raised. • Anammox contributed 47% for NRE with two coupled ways for continuous supply of NO 2 –. Improving contribution and nitrogen removal efficiency (NRE) of partial anammox in municipal wastewater is a researching hotspot. This study developed an innovative PN/A-PD/A process with fixed biocarriers in anaerobic/anoxic chambers for actual sewage treatment in a typical step-feed reactor over 390 days. Two coupled pathways providing continuous NO 2 – (partial nitrification in oxic chambers and partial denitrification in anaerobic/anoxic chambers) for anammox were introduced to the process, achieving 47% nitrogen loss by anammox in stable phase. The influent and effluent total inorganic nitrogen (TIN) were 51.3 and 11.0 mg/L, respectively, even with chemical oxygen demand (COD)/TIN ratio of 2.9. Anammox activity improved from 6.52 to 9.68 mg NH 4 +-N/gMLSS/d and abundance on the biocarriers raised to 3.16 × 1010 gene copies/g dry sludge. Overall, this study confirmed partial anammox, spatially coupled with partial nitrification and partial denitrification via oxic/anoxic distribution with step feed mode, as an alternative for application of mainstream anammox. [ABSTRACT FROM AUTHOR]

[Display omitted] • TIN removal reached 92.06% by PN/A process and no external carbon need. • Pre-anaerobic treatment enhanced partial nitrification start-up (NAR > 90%). • The total aerobic HRT was only 5.7 h and the DO was as low as 0.5–1.0 mg/L. • Ca. Brocadia was enriched and the abundance increased from 0.02% to 0.23%. A modified two-stage partial nitrification/anammox (PN/A) process with short aerobic HRT of 5.7 h was established and realized advanced nitrogen removal from domestic wastewater. The first process was partial nitrification in the PN-SBR, the initiation and stable maintenance of partial nitrification was achieved by pre-anaerobic treatment without inoculation or addition of inhibitor, nitrite accumulation rate was over 90% and maintained over 200 days, meanwhile pre-anaerobic improved the storage of endogenous carbon sources to enhance the nitrogen removal efficiency. The second process was anammox in the AMX-SBR, which was fed with the effluent of PN-SBR, the effluent total inorganic nitrogen was below 5 mgN/L, nitrogen removal efficiency reached 92.06%. Furthermore, Candidatus-Brocadia was enriched after treating domestic sewage with low ammonia from 0.02% to 0.23%.This study demonstrated the feasibility of starting and maintaining partial nitrification by pre-anaerobic treatment and the feasibility of nitrogen removal by coupling simultaneous-nitrification–denitrification with anammox to treat actual municipal sewage. [ABSTRACT FROM AUTHOR]

[Display omitted] • NFAD treated sludge supernatant, WAS, and secondary effluent simultaneously. • Satisfactory NRE of 98.7% and SRE of 44.6% were obtained. • Anammox contributed up to 84.1% nitrogen removal in AD-UASB. • In-situ fermentation contributed 13.3% electronic donor for partial denitrification. A novel process that combines partial nitrification, fermentation and Anammox-partial denitrification (NFAD) was proposed to co-treat ammonia rich sludge supernatant (NH 4 +-N = 1194.1 mg/L), external WAS (MLSS = 22092.6 mg/L) and WWTP secondary effluent (NO 3 –-N = 58.6 mg/L). Three separated reactors were used for partial nitrification (PN-SBR), integrated fermentation and denitrification (IFD-SBR) and combined Anammox-partial denitrification (AD-UASB), respectively. The process resulted in excellent nitrogen removal efficiency (NRE) of 98.7%, external sludge reduction efficiency (SRE) of 44.6% and external sludge reduction rate of 4.1 kg/m3 after 200 days of continuous operation. IFD-SBR and AD-UASB contributed towards 89.4% and 9.2% nitrogen removal, respectively. In AD-UASB, cooperation between Anammox bacteria (4.1% Candidatus Brocadia) and partial denitrifying bacteria (3.2% Thauera) resulted in significant stability of Anammox pathway, which contributed up to 84.1% nitrogen removal in the combined Anammox-partial denitrification process. NFAD saved up to 100% organic resource demand and 25% of aeration consumption compared with the traditional nitrification–denitrification process. [ABSTRACT FROM AUTHOR]

As a low consumption and high efficiency process, Partial Nitrification-Anammox/denitratation (PNAD) was applied to co-treat mature landfill leachate with municipal sewage for 300 days. Specifically, ammonia (670.2 ± 63.7 mg N/L) contained in mature landfill leachate was firstly oxidized to nitrite (611.5 ± 28.1 mg N/L) in sequence batch reactor (SBR PN); meanwhile, organic matter in municipal sewage was partially removed in another reactor (SBR OMR); finally, nitrite produced (611.5 ± 28.1 mg N/L) in SBR PN and ammonia (53.1 ± 6.4 mg N/L) residing in pretreated municipal sewage were simultaneously degraded through combined Anammox-denitratation process in an up-flow anaerobic sludge bed (UASB AD). A satisfactory effluent quality of 10.3 mg/L TN was obtained after long-term operation, with Anammox and denitrification contributing to 86.2% and 5.8% nitrogen removal efficiency, respectively. Mass balance confirmed 67.2% nitrate generated from Anammox could be reduced to nitrite and in-situ reused. Anammox bacteria genes and nitrate reductase/nitrite reductase ratio were highly detected, accelerating combined Anammox-denitratation. Further, Ca. Brocadia triumph among various Anammox bacteria groups, increasing from 1.2% (day 120) to 3.6% (day 280). [Display omitted] • PNAD process was proposed to cotreat mature landfill leachate and municipal sewage. • Anammox and denitrification contributed to 86.2% and 5.8% nitrogen removal efficiency. • Candidatus. Brocadia was dominant genus (1.2-3.6%) among various Anammox bacteria groups. • PNAD process saved 25% aeration energy consumption and 100% carbon source demanding than traditional bioprocess. [ABSTRACT FROM AUTHOR]

• The NRE reached 77.8 ± 4.3% even COD/TIN ratio at 2.9 during 548 days of study. • The effect of PD/A will be enhanced after the added anammox biocarriers adapted. • Anammox bacteria abundance on biocarriers remained stable and was higher than WWTPs. • PD/A contributed about 32–47% nitrogen loss in hypoxic zones in step-feed AAO reactor. The application of partial denitrification coupling with anammox (PD/A) in municipal sewage treatment is one of the most promising research field, and it has just begun. In 548 days of experiment treating real domestic sewage, the continuous flow reactor was started up by adding biocarriers containing anammox bacteria and operated stably after acclimatization. The PD/A was successfully achieved in the step-feed AO system. Furthermore, mass balance of ammonium revealed that anammox could contribute 32–47% to nitrogen loss. Compared with no biocarriers addition phase, the nitrogen removal efficiency (NRE) increased to 77.8 ± 4.3% and the effluent total inorganic nitrogen (TIN) decreased to 11.0 ± 2.1 mg/L at the COD/TIN ratio of 2.9 from day 428 to day 548 under the condition of anammox biocarriers addition and without external carbon source. Quantitative polymerase chain reaction (qPCR) and high-throughput sequencing analysis showed that anammox bacteria on the biological carrier accounted for 3.06% of the total bacteria in the stable phase, which was much higher than the reported <0.003% in wastewater treatment plants (WWTPs). After 247 days of operation with anammox biocarriers addition, the abundance of anammox bacteria on the carriers tended to be stable at 3.36 × 1010 gene copies g−1 dry sludge. The activity of anammox decreased and maintained at 13.14 g NH 4 +-N m−3 d−1 under the biocarriers-only condition, while increased from 11.71 g NH 4 +-N m−3 d−1 to 25.65 g NH 4 +-N m−3 d−1 in the hybrid condition of biocarriers and flocs. This study indicated that PD/A is effective to strengthen nitrogen removal with low COD/TIN ratio. [ABSTRACT FROM AUTHOR]

• Anammox was stably enriched on treating municipal wastewater over 500 days' tests • Partial-denitrification/anammox contributed 29.2±6.7% of nitrogen removal • The Ca. Brocadia (4.34%) dominated in the anoxic-carrier biofilms rather than flocs • The Ca. Brocadia was key narG contributor to NO 3 − → NO 2 − in anoxic-carrier biofilms This study proposes a novel strategy of stably enriching anammox in mainstream, based on the competitive difference to NO 2 − between anoxic biofilms and suspended sludge. A modified anaerobic-anoxic-oxic (A2/O) process run for 500 days with actual municipal wastewater. Microbial analysis revealed that anoxic-carrier biofilms had a significantly higher abundance of anammox (qPCR: 0.74% – 4.34%) than suspended sludge (P< 0.001). Batch tests showed that anammox within anoxic-carrier biofilms contributed to significant nitrogen removal, coupled with partial-denitrification (NO 3 − → NO 2 −). The anammox genus, Ca. Brocadia, was highly enriched when suspended sludge was accidentally lost. Further batch tests found that reducing suspended biomass helped anammox enrichment in anoxic-carrier biofilms, because the suspended sludge had strong NO 2 − competition (NO 2 − → N 2) with anammox (increased nirK). Metagenomic sequencing revealed that Ca. Brocadia dominates in the anoxic-carrier biofilms, and is the most important narG contributor to NO 3 − → NO 2 −, which could have promoted the competition of NO 2 − with heterotrophic bacteria. For this A2/O process, the low effluent total nitrogen (8.9 mg ± 1.0 mg N/L) was attributed to partial-denitrification coupling with anammox, demonstrating that this process is applicable to the general influent N-concentration range (30 mg – 50 mg NH 4 +-N/L) of municipal wastewater treatment plants (WWTPs). Based on the special competitive preference of anammox for NO 2 −, this study provides a promising and practical alternative for enriching anammox bacteria in municipal WWTPs. [Display omitted] [ABSTRACT FROM AUTHOR]

Anaerobic ammonium oxidation (anammox) is an energy saving and environmentally friendly technique for wastewater treatment. Sludge adsorption is an important process after organics enter the anammox reactor. The extracellular polymeric substances (EPS) of anammox sludge play a key role on the activity of anammox. This study utilized Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) to investigate molecular-level compositional characteristics of the stratified EPS of the anammox sludge, and to explore the adsorption preference of each EPS layer to refractory dissolved organic matter (DOM) during anammox treatment. Results showed that the adsorbed component by the tightly bound EPS layer was dominantly composed of lipids and proteins, with nearly 80% of formulas being CHO and CHON. The outer layers (slime, loosely bound-EPS) preferentially adsorbed the compounds with comparatively higher aromatic and unsaturated degrees, with S-containing formulas and lignin being the predominant components. The newly produced formulas in the effluent were inferred to be associated with the anammox treatment performance. The refractory DOM, with smaller molecular weight and high reductive degree, seemed to experience a single adsorption by the stratified EPS, and became part of the anammox sludge. • High removal efficiency shows preferential S-compound adsorption by Anammox EPS. • EPS outer layers show greater adsorptive ability for refractory DOM. • Small molecular weight, high saturated degree DOM formulas show environmental risk. [ABSTRACT FROM AUTHOR]

• Anammox (Ca.Brocadia , 0.69%) were enriched in biofilms, markedly higher than flocs. • 15N-isotope tracer tests showed partial denitrification is a prerequisite for anammox. • Anammox contributed to 68% of the nitrogen loss via anoxic biofilms in batch tests. • Nitrogen removal efficiency improved 16.9% by combining denitrification and anammox. • Mainstream partial-anammox might has great potential of engineering application. Introducing anammox technology into low-ammonia sewage treatment offers sustainable nitrogen removal, but there remain challenges to its future applications. Here, anammox bacteria were enriched by integrating into partial denitrification (NO 3 −-N to NO 2 −-N) in the anaerobic/anoxic/oxic (A2/O) reactor with low COD/N ratios (2.7 ± 0.4) sewage. This significantly enhanced nitrogen removal through partial anammox process over stable operation of 300 days. Microbial community analysis showed that the anammox bacteria were enriched in anoxic-carrier biofilms (Ca. Brocadia , 0.69%), and their abundance was significantly higher than the flocculent sludge (16 s rRNA sequencing: P < 0.001; qPCR: P < 0.001). Further activity testing via 15N-isotope tracing revealed that partial denitrification is a prerequisite for in situ occurrence of anammox reaction. Anammox contributed to 68% of the total nitrogen loss via anoxic-carrier biofilms in batch tests. Combining denitrification and anammox, the nitrogen removal efficiency of the A2/O process improved by approximately 16.9% for low COD/N ratios real sewage. [ABSTRACT FROM AUTHOR]

• Novel two-stage process to treat low C/N domestic wastewater. • Successful out-selection of NOB by step-wise DO reduction to 0.1 mg/L. • Stable and high-rate partial nitritation with low-DO conditions (0.1 mg/L). • High activity and abundance of anammox with low influent substrate (<38 mg-N/L). • High TIN removal efficiency of 88.24% with short aerobic HRT of 6.7 h. Simultaneous partial nitritation and denitritation (SPND) coupled with anammox was established in this study to treat domestic wastewater. Two lab-scale bioreactors, namely SPND-SBR and ANA-UASB, were used in the two-stage system. In SPND-SBR, stable nitrogen removal efficiency of 51.1% was achieved with a high ammonia oxidation rate of 0.117 kg N/(m3·d). Besides, successful out-selection of nitrite-oxidizing bacteria (NOB) under low-DO of 0.1 mg/L during the steady period, resulting in an average effluent NO 2 −-N/NH 4 +-N ratio of 1.04. In ANA-UASB, the abundance of Candidatus Brocadia and Candidatus Kuenenia increased from 8.21% and 4.01% to 21.33% and 6.41% with low influent substrate contents of only 38 mg N/L. The effluent total inorganic nitrogen (TIN) was only 8.4 ± 1.1 mg N/L and the nitrogen removal efficiency reached 88.24%. Overall, the study demonstrated that the novel low-DO two-stage process for nitrogen removal is a promising technique for wastewater of low C/N ratio. [ABSTRACT FROM AUTHOR]

• NAR was stabilized at above 95% by low DO combine with aeration time control. • Synergistic nitrogen removal achieved by introducing municipal wastewater. • Partial denitrification was another way to supply nitrite in the SAD system. • The TIN removal efficiency reached 97.1% with a short HRT of 6 h. A modified two-stage anammox process was constructed and achieved advanced nitrogen removal from municipal wastewater. The first stage was Partial Nitrification (PN), in which nitrite accumulation rate was over 95% by controlling dissolved oxygen concentration (<1 mg/L) and aeration time (90–120 min). The second stage was simultaneous anammox and denitrification (SAD), in which the reactor was fed with the effluent of the first stage and a part of raw wastewater. The effluent total inorganic nitrogen (NH 4 +-N, NO 2 −-N and NO 3 −-N) was only 1.6 ± 0.8 mg N/L and the nitrogen removal efficiency reached 97.1%. The proportion of anammox in nitrogen removal was up to 73–82% and Candidatus Brocadia was the main anammox genus accounted for 8.0–2.2%. And partial denitrification occurred with the appearance of Thauera (0–1.0%). The PN-SAD process is an energy-saving treatment for municipal wastewater with a total hydraulic retention time of 6 h. [ABSTRACT FROM AUTHOR]

For achieving energy-efficient wastewater treatment, a novel simultaneous nitrogen and phosphorus removal (SNPR) process, which integrated anammox, endogenous partial-denitrification and denitrifying dephosphatation in a sequencing batch reactor with granular sludge was developed to treat mainstream wastewater. After 200 days of operation, a simultaneous high-level nitrogen and phosphorus removal of 93.9% and 94.2%, respectively was achieved with an average influent C/N ratio of 2.9. Anammox pathway contributed 82.9% of the overall nitrogen removal because of the stable nitrite production from nitrate via endogenous partial-denitrification. In addition, phosphorus was mainly removed via denitrifying dephosphatation utilizing nitrate as the electron acceptor, resulting in a significant saving of carbon sources and oxygen demands. Further, adsorption/precipitation of phosphorus occurred in this novel SNPR process, which displaced the energy source to the metabolism of glycogen accumulating organisms (GAOs) for nitrite production and alleviated competition between phosphorus accumulating organisms (PAOs) and anammox for electron acceptor. Using 16S rRNA gene amplicon sequencing analysis, the study found that anammox bacteria (8.4%), GAOs (1.5%) and PAOs (1.1%) co-existed in this system, potentially resulting in simultaneous endogenous partial-denitrification, anammox and denitrifying dephosphatation. The above results demonstrated that the novel SNPR process is a promising technique for energy-efficient wastewater treatment. Image 1 • Anammox can co-exist with GAOs and PAOs, ensuring the effective SNPR performance. • High-level nitrogen and phosphorus removal (93.9% and 94.2%, respectively) was achieved. • Nitrogen removal via anammox accounted for 82.9%, reducing energy and carbon demands. • Adsorption/precipitation of P were involved and facilitated stable SNPR performance. • The novel SNPR process is promising in energy-efficient wastewater treatment. [ABSTRACT FROM AUTHOR]

Anaerobic ammonium oxidizing (anammox) bacteria are widely distributed and contribute significantly to the global nitrogen cycle. Traditionally, identification and quantification based on the 16S rRNA gene were considered not reliable because of low 16S rRNA gene sequence identity within Brocadiales. Here we hypothesize that by using appropriate primers and methodology, 16S-based detection and quantification of anammox bacteria can be accurate. We modified an existing 16S rRNA gene-based primer pair (Amx694F–Amx960R) by changing one nucleotide (Amx694F position 18, G→C) (Amx694PF–Amx960R) so that they match the sequences of most Brocadiales anammox bacteria, and evaluated the modified primer pair with 29 freshwater samples from microcosms, anammox reactors and wastewater treatment plants of various geographical origins. The primer pair showed high specificity in detection and quantification of anammox populations in samples that contained >0.1% anammox bacteria. Quantification of anammox abundance by quantitative real-time PCR and delineation of anammox species by denaturing gradient gel electrophoresis agreed well with amplicon sequencing results. A clear shift of anammox population towards ' Candidatus Kuenenia' was observed under laboratory cultivation conditions. With the help of amplicon sequencing, we demonstrated that 16S rRNA gene-based anammox-specific primers are able to achieve qualitative and quantitative monitoring of anammox communities in wastewater treatment plants and natural freshwater environments.2007;73:5261–7. [ABSTRACT FROM AUTHOR]

Nitrate is a byproduct of the anaerobic ammonium oxidation (anammox) process and is related to its electron transfer. However, little is known about the influence of nitrate on the anammox process. In this work, the biphasic effect of exogenous nitrate on the anammox process was investigated in an upflow biofilter (UBF) reactor with ammonium as the sole electron donor. The responses of anammox to increased nitrate were analyzed by one-way ANOVA test and found to be significantly different under a constant and decreased nitrite condition (p < 0.01). With a single increase in nitrate and constant ammonium and nitrite in the influent, the total nitrogen removal rate (TNRR) of anammox was uninhibited, but stoichiometry deviated and nitrate production always showed a linear decrease. In contrast, anammox exhibited a range of activity with constant ammonium and simultaneously increased nitrate and decreased nitrite in the influent, including a continuous reduction of TNRR, a nonpersistent ammonium overconsumption and a pronounced nonlinear response of nitrate production. Correlation analysis shows that the lack of ammonium overconsumption was accompanied by the disappearance of nitrate underproduction. Kinetic models of product formation were effectively used to explore the nitrate production behavior of anammox subjected to increased nitrate, and the metabolite of nitrate was divided into a growth negative coupling type and growth (partial) coupling type under a constant and decreased nitrite condition, respectively. These findings collectively suggest that nitrate has a biphasic effect on the anammox process and is correlated with the availability of nitrite. Image 1 • Exogenous nitrate was uninhibited and unavailable for anammox bacteria with ammonium as the sole electron donor. • A single increase in nitrate in the influent led to a linear decrease in nitrate production. • Nitrate production returned to normal after the linear decrease, when the influent nitrite dropped below 70%. • The lack of ammonium overconsumption was accompanied by the disappearance of nitrate underproduction. • The process underlying nitrate production was explored using a simplified product formation model. [ABSTRACT FROM AUTHOR]

The challenge of sludge digester liquor treatment is its high ammonium nitrogen (NH 4 +-N) concentration. Early reports found that complete ammonia oxidation (comammox) was not present and anaerobic ammonia oxidation (anammox) was difficult to achieve in most sludge digester liquor treatments. In this study, NH 4 +-N removal by cooperation between partial-nitrification, comammox, and anammox processes was achieved in a sequencing batch reactor (SBR) for sludge digester liquor treatment. The results showed that 2100–2200 mg/L of NH 4 +-N was removed in the SBR with 98.82% removal efficiency. In addition, 55.11% of NH 4 +-N was converted to nitrite nitrogen (NO 2 −-N) by partial-nitrification, 25.43% of NH 4 +-N was converted to nitrate nitrogen (NO 3 −-N) by comammox, and 18.28% of NH 4 +-N was removed by anammox. During the operation, in the SBR, the relative abundance of the dominant ammonia-oxidizing bacteria (Chitinophagaceae) was 18.89%, that of the dominant anammox bacteria (Candidatus Kuenenia) was 0.10%, and that of the dominant comammox bacteria (Nitrospira) was 0.20%. Therefore, the high nitrogen removal efficiency in this system was considered the result of the combination of the three processes. These results showed that comammox and anammox could play very important roles in nitrogen transformation and energy-saving in nitrogen removal systems. Nitrogen removal by co-occurring partial nitrification-anammox and comammox from sludge-digestion liquid. Image 1 • The combined process of partial-nitrification, anammox and comammox to remove nitrogen from the sludge digester liquor was established. • Advanced NH 4 +-N removal efficiency (98.82%) was obtained by partial-nitrification (55.11%), anammox (18.28%), and comammox (25.43%). • Chitinophagaceae (18.89%), Candidatus Kuenenia (0.10%) and Nitrospira (0.2%) all worked together which made the partial-nitrification, anammox and comammox co-occurring. [ABSTRACT FROM AUTHOR]

Anaerobic ammonium oxidation (Anammox) is a cost-effective process for treating highly nitrogenous wastewater. However, the fate of organic nitrogen during Anammox treatment is still unclear, which limits its practical application. In this work, the changes in the quality of dissolved organic nitrogen (DON) in coal liquefaction wastewater (CLW) during Anammox were studied in relation to its chemical composition, which was determined by Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The molecular-level characterization of extracellular polymeric substances (EPS) in the Anammox sludge is also reported for the first time in this paper. The relative contribution of N-containing compounds to the total dissolved organic matter (DOM) determined by summating the normalized intensities exceeded 30%, highlighting the complexity of the nitrogenous compounds in the influent. Additionally, Anammox appeared to be better suited to removing DON compounds with fewer carbonyl or carboxyl groups, more aromatic structures, and higher oxidative properties. Lignin-like substances were verified as the predominant component of N-containing compounds in Anammox EPS, followed by protein and substances with condensed aromatic structures. DON compounds with higher degrees of saturation, lower molecular weight, and higher lignin-like properties were more prone to absorption by Anammox EPS. A series of microbe-mediated pathways were demonstrated to be responsible for DON biodegradation, which revealed the organic and inorganic nitrogen removal mechanisms in the Anammox reactor. The obtained results provide great support to the ongoing efforts to optimize the Anammox process. • Quality change of dissolved organic nitrogen (DON) during Anammox process was investigated by FT-ICR MS • Molecular-level characterization of extracellular polymeric substances (EPS) of Anammox sludge was reported firstly • Anammox EPS mainly composed of lignin, followed by protein and substances with condensed aromatic structures • DON with higher saturation degrees, and higher lignin-like properties were more prone to absorption by Anammox EPS [ABSTRACT FROM AUTHOR]