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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]

An integrated partial nitrification, sludge fermentation and denitrification process in a sequencing batch reactor (PNSFD-SBR), was developed to enhance nitrogen removal from domestic wastewater with low C/N (i.e. SCOD/TN) between 2 to 3 and to reutilize/reduce external waste activated sludge (WAS). Average ammonium removal efficiency of 95.9%, total nitrogen removal efficiency of 93.5%, and external WAS reduction rate of 21.6% was achieved during long-term experiment at 30 ± 1 °C. Real-time pH-DO (dissolved oxygen) monitor and control played an important role in the PNSFD achievement. A batch test indicated that micro-aeration (less than 1 mg/L) sustained partial nitrification, which further facilitated subsequent sludge fermentation and denitrification processes. Moreover, Illumina MiSeq analysis demonstrated the predominant bacteria were Rhodocyclaceae , Anaerolineaceae and Saprospiraceae on family level and they were key to partial nitrification, denitrification and sludge fermentation, by which the feasibility of PNSFD process to achieve simultaneous nitrogen removal and external WAS reutilization/reduction was verified. [ABSTRACT FROM AUTHOR]

[Display omitted] • Proposed a side-stream sludge treatment method for rapid proliferation of GAOs. • Highly enriched GAOs (3.09–18.25%) facilitated ED while DOHOs decreased by 62.78%. • The abundance of PAOs was reduced but didn't deteriorate the phosphorus removal efficiency. • The TIN and PO 4 3−-P in influent and effluent were 71.26, 8.01 mg/L and 6.40, 0.30 mg/L, respectively at C/N of 3.25. Endogenous denitrification (ED) is an effective approach to achieve advanced nitrogen removal for low COD/N (C/N) municipal wastewater, in which internal carbon sources are used for denitrification. However, phosphorus-accumulating organisms (PAOs) and denitrifying ordinary heterotrophic organisms (DOHOs) outcompeting glycogen-accumulating organisms (GAOs) for carbon sources decreases total inorganic nitrogen (TIN) removal efficiency. This study proposed a novel side-stream sludge treatment strategy, i.e., through phosphorus famine, to selectively strengthen GAOs. Two sequencing batch reactors (SBR) were used, with one served as an anaerobic/aerobic/anoxic SBR (AOA-SBR) and the other as a side SBR. Side-stream phosphorus famine treatment was conducted three times during 140 days' experiment, of which 20–30% of the sludge collected from the AOA-SBR was imposed to phosphorus famine condition in the side SBR for 4 days (24 cycles). Results showed that the average TIN and phosphorus removal efficiencies were 88.76% and 95.31%, and the average TIN and phosphorus in the effluent were 8.01 and 0.30 mg/L, respectively, treating low C/N (~3.25) municipal wastewater in the AOA-SBR. The relative abundance of PAOs decreased from 3.23% to 2.15% and that of DOHOs reduced by 62.78%. In contrast, the abundance of GAOs increased from 3.09% to18.25%, which should be the key reason for the improvement of the ED efficiency. Moreover, the enrichment of GAOs promoted ED simultaneously using glycogen and poly-β-hydroxyalkanoates (PHA) as carbon sources. The strategy of side-stream treatment proved the potential of rapid proliferation of GAOs while achieving improved nitrogen removal. [ABSTRACT FROM AUTHOR]

Abstract: The step-feed anoxic/oxic biological nitrogen removal process has been proposed as an attractive alternative for the conventional biological nitrogen removal process for the purpose of enhanced nitrogen removal. For step-feed process, the biological nitrogen removal efficiency is a function of influent flow distribution. In this study, the effects of influent flow rate distribution on the performance of nitrogen removal process were investigated. The effects of influent flow rate distribution on COD, ammonia, total nitrogen removal efficiency, nitrification rate and sludge volume index value were also studied. According to the performance characteristic of the step-feed process, the concept of influent flow rate distribution ratio was firstly introduced. The maximum influent flow distribution ratios (λ max) under the condition of different influent C/N ratios were determined, respectively, by trial and error method. The experimental results showed that high total nitrogen removal efficiency, higher than 95%, could be achieved under certain influent flow rate distribution ratio without internal nitrate cycle or addition of external carbon source. It was obvious that nitrification rate of each stage under different influent flow distributions decreased along with the decreasing of sludge loading and volume loading in each stage, and the degree of reduction rise gradually with the increasing of influent flow distribution ratio. The sludge volume index value would also increase along with the increase of influent flow distribution ratio. [Copyright &y& Elsevier]

• 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]

Graphical abstract Highlights • Effluent TN as low as 4.0 mg N/L was achieved via PD-Anammox process. • Anammox was stable and accounted for 78.2% on nitrogen removal. • Low nitrous oxide (N2O) was produced in PD-Anammox process. • Oxygen consumption, COD demand and sludge production would be largely reduced. • PD-Anammox process can be easily retrofitted from existing plants. Abstract High nitrate (NO 3 −-N) concentration in the effluent of wastewater treatment plants (WWTPs), cannot meet the increasing stringent discharge limits. Hence, the tertiary treatment is necessary to lower the total nitrogen concentration. In this study, an innovative partial denitrification (PD)-Anammox process was applied to remove the nitrate nitrogen (20–40 mg N/L) from secondary effluent. The nitrate wastewater were firstly fed to PD sequencing batch reactor (SBR, 10 L) to produce nitrite along with the low carbon/nitrogen ratio (C/N) municipal sewage (NH 4 + of 57.8 mg N/L, COD of 175.8 mg/L), then the effluent from SBR was pumped to the anaerobic sludge blanket (UASB, 3.2 L) performing anammox for further nitrogen removal. The integrated process was operated for 224 days with the secondary effluent to municipal sewage volume ratio of 2.9–6. The results suggested that an excellent nitrate removal efficiency of 97.9% was achieved, and the mean removal efficiency of NH 4 +-N and COD from municipal sewage were 95.2% and 81.6%, respectively, leading to the total nitrogen and COD concentration in the final effluent as low as 4.0 mg N/L and 30.1 mg/L, respectively. Anammox was the main nitrogen removal pathway with a mean proportion of 78.2%, and Candidatus_Brocadia was identified as the dominating genus. Furthermore, it was found that a minor nitrous oxide (N 2 O) was produced in the integrated process. The PD-Anammox process was verified to be economically and environmentally feasible for retrofitting of existing plants. [ABSTRACT FROM AUTHOR]

Highlights: [•] A prominent ENDPR system was developed and operated with low HRT and low COD/N. [•] DPAOs could be temporarily inhibited under low aeration rate (DO=0.2mgL−1). [•] Lower poly-P accumulated in the sludge was the direct cause of the deterioration of phosphorus removal. [ABSTRACT FROM AUTHOR]

[Display omitted] • Rising NO 2 –-N stress accelerated the growth of NPG with stable NO 2 –-N production. • EPS was stimulated with increasing size and offered supplementary electron donors. • Highly enriched functional bacteria Thauera was evenly distributed around NPG. • Enhanced electron transfer for NO 3 –-N reductase played a key role in efficient NPG. Nitrite-producing denitrification granular sludge (NPG) is emerging as a novel approach to employing anammox for cost-efficient nitrogen removal from high-strength nitrate-containing wastewater. However, the underlying impact of increasing stress of nitrite (NO 2 –-N) accumulation on microbial metabolism and cooperation of denitrifying bacteria and heterotrophs in NPG was still not clear. This study first demonstrated a high-rate NPG system with elevating nitrate (NO 3 –-N) from 52.4 mg/L to 613.2 mg/L. During this operation, a rapid increase in granular size from 322.8 µm to 1124.0 µm was observed with a relatively stable nitrate-to-nitrite transformation ratio (NTR) as high as 83.0 %, and effluent NO 2 –-N of increasing from 16.5 mg/L to 331.9 mg/L. Such an increasing NO 2 –-N stress improved the capability of the TCA cycle with rising intermediates of amino acid metabolism. This further stimulated the production of exocellular organic matter that replenished as electron donors and promoted the growth of granular size. The homogeneously spatial distribution of key bacteria (Thauera) surrounding the NPG with a calcium-dominated inorganic core inside was revealed to play a key role in enhanced substrate transfer capability. Genes nar and nap encoding NO 3 –-N reductase dominated by key species belonging to Thauera showed much higher abundance than that encoding NO 2 –-N reductase, which was the key reason for relatively stable NO 2 –-N accumulation. It illustrated the excellent persistence of NPG to high NO 2 –-N stress with special structure of functional bacteria inside granules, providing a great potential for the treatment of high-strength nitrate-containing wastewater. [ABSTRACT FROM AUTHOR]

[Display omitted] • Simultaneous anammox-denitrification is reviewed from fundamentals to implementations. • Biofilm formation are promising for retaining anammox bacteria. • Organic matter limitation plays an important role in denitrifiers' restraint. • Challenges and recent advances in three types of SAD are discussed. • Diverse future aspects of the emerging SAD process were proposed. Simultaneous anaerobic ammonium oxidation (Anammox) and Denitrification (called SAD) holds significant promise for removing nitrogen and organic matter from wastewater. Previous studies have demonstrated the ability of SAD process and its emerging extensions, such as Simultaneous Nitritation, Anammox and Denitrification (SNAD) and simultaneous Anammox, Denitrification and Sludge Fermentation (ADSF), to integrate the nitrogen cycle with the carbon cycle. This study systematically reviews three types of SAD process, in terms of their microbial groups and their relationships. Anammox bacteria and denitrifiers commonly experience a symbiotic and/or competitive relationship when treating real wastewater. Biofilm formation and organic matter limitations are considered the most critical conditions for the co-existence of anammox and denitrification. This study also provides an overview of the research and development of the state-of-the-art processes based on SAD. We conclude that, while the optimized performance of SAD process and its extensions have been largely recognized, there is a need to better understand the mechanics, particularly with respect to a kinetic and stoichiometric analysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • PD/A granules achieved high-rate and enhanced N removal with continuous feeding. • Dynamic migration of anammox bacteria to outer edge of granules was found in CSTR. • Stratified structure benefited for cross-feeding between anammox and denitrifiers. • Versatile metabolism of anammox bacteria for reducing NO 3 −-N was assumed in PD/A process. • Anammox bacteria could be efficiently enriched at cost of decreased PD bacteria. Anammox coupling with denitrification has attracted increasing attention in low-strength wastewater treatment. However, its wide application in continuous-flow process is seriously restricted by insufficient anammox capacity due to the failed biomass retention. The functional capacities of communities inhabiting the fluctuating habitat has been little understood. This study developed a novel granular sludge-based partial denitrification coupling with anammox (PD/A) process with the feeding strategy shifting from sequencing to continuous flow in a Continuous Stirred Tank Reactor (CSTR), treating low-strength wastewater containing ammonia (NH 4 +-N) of 46.1 mg/L and nitrate (NO 3 −-N) of 60.7 mg/L. Significantly enhanced specific anammox activity was demonstrated, attributed to the robust nitrite (NO 2 −-N) generation with NO 3 −-N to NO 2 −-N transformation ratio (NTR) averaged 84.1 %. Remarkable total nitrogen (TN) removal of 95.4 % was thus achieved with anammox pathway contribution as high as 88.3 %. Interestingly, a dynamic and stratified microbial structure was obtained in CSTR, in which anammox migrated to outer layer together with Thauera capable of partial denitrification (PD) in big granules, resulting in more efficient cross-feeding and strengthening the cooperation between anammox and heterotrophic PD bacteria in CSTR. Metagenomic-based metabolic inferences provide first insight into the versatile microbial metabolic potential of anammox bacteria for reducing NO 3 −-N with acetate as electron donor in PD/A process. They were successfully enriched and retained with the relative abundance of 8.4 %, being attributed to the enhanced mass transfer efficiency. On the contrary, dominant denitrifier Thauera decreased sharply to 4.2 %. This study provides a new alternative of anammox coupling with heterotrophics granular sludge for efficient low-strength wastewater treatment under continuous feeding, and open up new perspectives for selecting distinctive communities that stand out by expansive metabolic versatility and excellent microbial collaboration. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel DPR-PDA process was initiated with fully ordinary suspended sludge. • The deep removal of N and P without aeration was achieved under COD/TN of 1.8. • Candidatus_ Brocadia was enriched from 0.01% to 1.86% by prolonging anoxic stage. • The effluent TN and TP were 0.9 and 0.2 mg/L with influent of 106.0 and 1.4 mg/L. Partial Denitrification coupled with Anammox (PDA) process was used as for nitrogen removal from wastewater. However, the phosphate removal still relies on chemical methods in wastewater treatment plants. Denitrifying Phosphorus Removal (DPR) process allows phosphorus uptake under anoxic conditions using nitrate (NO 3 −) as electron acceptor. In this study, the PDA and DPR processes were successfully coupled into a novel integration (DPR-PDA) for co-treatment of simulated domestic wastewater and NO 3 − wastewater to achieve simultaneous nitrogen and phosphorus removal. The effluent TN and TP were 0.9 and 0.2 mg/L during phase Ⅵ (day450-513) under influent COD/TN of 1.8, respectively. Anammox bacteria was self-enriched in this fully suspended sludge system, with abundances increasing from undetected at day19 to 2.0 × 1010 copies/g dry sludge at day468. Anammox bacteria was effectively retained and was responsible for the main nitrogen removal, accompanied by increasing activity up to 3.1 mg N/g VSS/h. Batch tests demonstrated that denitrifying polyphosphate accumulating organisms exhibited DPR capacity immediately after the introduction of NO 3 −, but not after the introduction of nitrite (NO 2 −) only. Candidatus_Competibacter with endogenous denitrification ability was enriched from 13.30 % to 35.42 %, which coexisted with anammox bacteria stably. The novel DPR-PDA process is a promising technology for simultaneous removal of nitrogen and phosphorus with low carbon demand and without aeration. [ABSTRACT FROM AUTHOR]

[Display omitted] • Co-fermentation liquid provided abundant VFAs as carbon source. • Co-fermentation liquid promoted the NAR to 99.07% to notably save energy. • The NRE of the PNED system reached 98.53% by enhancing endogenous denitrification. • The co-fermentation reactor could achieve a sludge reduction ratio of 21.72%. • The cooperative mechanism of HNADB, DGAOs and AOB in the oxic stage was revealed. In mature landfill leachate with high ammonia nitrogen and extremely low biodegradable organic matter, it is difficult to achieve advanced nitrogen removal through traditional nitrification–denitrification processes. In this study, a low- carbon/nitrogen mature landfill leachate treatment process with an anaerobic/oxic/anoxic strategy was constructed by inputting co-fermentation liquid of corn straw and excess sludge. Under the effect of the co-fermentation liquid, partial nitrification was enhanced. Meanwhile, with the cooperation of the heterotrophic nitrification-aerobic denitrification process, the nitrite accumulation ratio and simultaneous nitrification and denitrification ratio reached 99.07 ± 0.52% and 23.26 ± 1.02%, respectively. The carbon source from the co-fermentation liquid was efficiently converted into polyhydroxyalkanoates, which could drive endogenous denitrification to achieve advanced nitrogen removal. The nitrogen removal efficiency in this system reached 98.53 ± 1.21%. In addition to effectively supplying carbon sources, the co-fermentation reactor also achieved a sludge reduction ratio of 24.78 ± 1.68%. Through metagenomic analysis, the cooperative mechanism by which denitrifying glycogen-accumulating organisms, heterotrophic nitrifying-aerobic denitrifying bacteria and ammonia-oxidizing bacteria achieve nitrogen removal and nitrite accumulation in oxic stage was revealed. This study provides a new and efficient treatment process for mature landfill leachate and sludge reduction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Anammox coupled with partial denitrification enhanced to nitrogen removal above 55%. • Ultra-high abundance of Ca. Brocadia (5.5, 6.5%, 5.8%) in connected anoxic biofilms. • Ca. Brocadia sapporoensis is acetate-resistant, explaining its high enrichment in biofilms. • Anammox activity increased with decreasing denitrifying activity along anoxic zones. For municipal wastewater treatment via partial-denitrification/anammox (PD/A) in the anoxic zone, the primary challenge is effective enrichment of anaerobic ammonium oxidation (anammox) bacteria with a stable autotrophic nitrogen removal performance. This long-term study investigated a pure-biofilm anoxic/oxic reactor using real municipal wastewater with an ammonia concentration of 49.1 ± 3.6 mg N/L, achieving a total inorganic nitrogen concentration of 11.2 ± 3.5 mg N/L in the effluent, resulting in a removal efficiency of 77.4 ± 7.2%. Driven by partial denitrification, the anammox contribution to total nitrogen removal represented an ultra-high level over 55%, and was considerable in the first anoxic zone. Candidatus Brocadia, the only anammox genus detected by 16S rRNA gene sequencing, reached robust abundances of 5.46, 6.49 and 5.79% in the three sequentially connected anoxic zones. Metagenomic sequencing further identified that the main species was Ca. Brocadia sapporoensis, which is inhibited by nitrite but not by acetate, supporting its high-level enrichment under acetate conditions in the anoxic zone. Batch tests indicate that heterotrophic denitrification activity decreased while anammox activity increased along the anoxic zones, and that excessive heterotrophic denitrifying activity was not conducive to increasing the anammox contribution. This study achieved robust anammox bacterial abundance using a pure-biofilm system, shedding fresh light on the application of mainstream anammox in municipal wastewater treatment. [ABSTRACT FROM AUTHOR]

Bottleneck issues such as difficult biofilm culturing, time-consuming granular formation and excessive nitrate production, always limited the application of anammox processes. By using the common but meaningful suspended activated sludge instead of biofilm or granule activated sludge, a combined anammox process, simultaneous partial nitrification, anammox and denitrification (SNAD), was established in a sequencing batch reactor (SBR) in this study to treat real domestic sewage and was operated for 300 days. Results indicated that a high ammonia removal rate and nitrogen removal rate (1.1 and 1.03 (kgN/(m 3 ·d)), respectively) were achieved during the baseline phase treating high ammonia wastewater (350–550 mg/L). During the experimental phase treating domestic sewage with a C/N of 3–3.5, 86.1% of total nitrogen removal efficiency was achieved and only 1.02 mg/L of nitrate concentration was detected in the effluent with an averagely 64.6 mg/L of ammonium in the influent. Nitrogen mass balance analysis demonstrated that about 89% of total nitrogen (TN) was removed by anammox and the remaining 11% of TN was removed by denitrification. Bacterial abundance of Candidatus Brocadia and Thauera increased from 0.02% to 0.5% and 0.39% to 2.24% (from baseline phase to experimental phase), respectively, which made an essential contribution to the nitrogen removal. The advanced nitrogen removal performance reached in the SNAD process showed the possibility of using suspended sludge as a substitute of biofilm and granule sludge concerning anammox, and the process could treat real domestic sewage with a C/N of 3–3.5 without pretreatment of chemical oxygen demand (COD). [ABSTRACT FROM AUTHOR]

A novel post-endogenous denitrification and phosphorus removal (post-EDPR) system was developed by enriching denitrifying glycogen accumulating organisms (DGAOs) and phosphorus accumulating organisms (PAOs) to treat low carbon/nitrogen (C/N) wastewater (C/N = 4.4). The unique feature of the post-EDPR system was the continuous alternating anaerobic/oxic/anoxic zone (3.1 h/3.9 h/7 h) with suspended biofilm carriers in oxic zone. The 132-day test results showed that extended anaerobic and anoxic stage strengthened the intracellular carbon storage and endogenous denitrification. Low dissolved oxygen (DO) concentration (1–2 mg/L) in oxic zone promoted the simultaneous nitrification and denitrification (SND) and saved aeration energy, nitrifiers were enriched with the biofilm carriers and nitrification performance was strengthened, so oxic hydraulic retention time (HRT) could be shortened to avoid excessive polyhydroxyalkanoate (PHA) consumption which would be used for the latter anoxic denitrification. In a steady state, the system achieved advanced nitrogen and phosphorus removal (TIN (total inorganic nitrogen) ≤3 mg/L, PO 4 3−  − P ≤ 0.2 mg/L) with a high removal efficiency of 92.15% and 92.67%, respectively, and PHA played a major role for P-uptake and endogenous denitrification. Microbial community analysis demonstrated that PAOs and GAOs were enriched and performed aerobic P-uptake and anoxic endogenous denitrification, respectively. [ABSTRACT FROM AUTHOR]

To achieve advanced nitrogen removal from municipal sewage with a low carbon/nitrogen (C/N) ratio, a novel Sludge Double Recirculation- Anaerobic/Aerobic/Anoxic process (SDR-AOA) was developed in a continuous-flow reactor. Low C/N (3.19 in average) sewage with the chemical oxygen demand (COD) concentration of 180.14 mg/L and the total nitrogen (TN) concentration of 56.19 mg/L was applied for long-term treatment in the SDR-AOA process. Results showed that, the average nitrite concentration in the effluent of the aerobic zone was increased from 0.15 mg/L (phase 1) to 16.46 mg/L (phase 3), and the nitrite accumulation ratio (NAR) remained between 85.87% and 94.85% in phase 3, for which the TN removal efficiency was increased from 91.40% (C/N: 5.14) to 95.60% (C/N: 3.19), and the low effluent TN concentrations was as low as 2.47 mg/L. The inhibitory effect of anoxic disturbance on nitrite oxidizing bacteria (NOB) might contribute to the effectiveness of partial nitrification, with the percentage of NOB accounting for total bacteria being declined from 4.66% (day 79) to 1.51% (day 135) on the genus level. Nitrogen mass balance analysis demonstrated that 27.77% of TN was removed through simultaneous nitrification and denitrification in the aerobic zone, while the remaining TN (62.25%) was removed through endogenous denitrification in the post-anoxic zone. Further Illumina MiSeq sequencing analysis demonstrated that the predominant bacteria were Rhodocyclaceae , Saprospiraceae and Comamonadaceae on the family level, and they were the key to nitrogen removal processes. In the end, the advanced nitrogen removal was realized in the SDR-AOA process for treating low C/N municipal sewage through the successful achievement of partial nitrification and endogenous denitrification. [ABSTRACT FROM AUTHOR]

The mainstream anaerobic ammonium oxidation (anammox) has attracted extensive attention recently, particularly due to its potential of transforming current wastewater treatment plants from energy consuming to energy neutral or positive. However, the presence of biodegradable chemical oxygen demanding (COD, 20–80 mg COD L −1 ) in the mainstream anammox reactor stimulates the growth of heterotrophic bacteria, which would compete for oxygen with ammonia-oxidizing bacteria (AOB) and for nitrite with anammox bacteria, thus interfering with the autotrophic nitrogen removal process. In the present work, with consideration of granule size distribution, a one-dimensional model describing the mainstream simultaneous partial nitrification, anammox and denitrification (SNAD) in a granule-based reactor was established, calibrated and validated, based on the long-term experimental results. Through applying the verified model, simulation studies were conducted and the results showed that the effluent total nitrogen concentration of <5 mg N L −1 could be achieved at C/N ratio of 0.2–0.6, DO concentration of 0.2–0.4 mg L −1 and granule radius of 300–600 μm. The combined effects indicated that the SNAD process with TN removal efficiency >90% was obtained at C/N ratio and DO concentration of 0.2–1.0 and 0.2–0.4 mg O 2 L −1 respectively. Finally, the various granule size distribution patterns were simulated, which confirmed that the size distribution needed to be incorporated in the model to accurately describe the granular anammox system, considering a model based on a uniform granule size does not reflect the real situations. These results provide guides to optimize the operation of mainstream granular autotrophic nitrogen removal process. [ABSTRACT FROM AUTHOR]

Partial-denitrification (PD, NO 3 − -N → NO 2 − -N) has been successfully developed to produce nitrite (NO 2 − ) with acetate as the sole carbon source. In this study, a PD sequencing batch reactor (SBR) fed with high-nitrate (NO 3 − : 1000 mg N/L) was firstly developed with carbon source obtained from domestic wastewater (NH 4 + : 59.3 mg N/L, chemical oxygen demand (COD): 186.6 mg/L) as well as a small quantity of external organic matter. The results showed that PD was not degenerated with domestic wastewater addition, and a high nitrite production was still achieved with the nitrate-to-nitrite transformation ratio (NTR) maintained at 90% in the 173-days operation period. By optimizing the nitrate and domestic wastewater feeding volume as well as external carbon dosage, the PD effluent was suitable for ANAMMOX process with a NO 2 − -N/NH 4 + -N of 1.46 and COD/NO 2 − -N of 1.32 obtained under the influent volume of domestic wastewater of 2.8 L, as well as nitrate of 0.4 L, and the external carbon demand was reduced to COD/NO 3 − -N of 1.7. Nitrate reduction rate was fit to Monod kinetics, with a maximum specific NO 3 − -N reduction rate of 4.56 g N/g VSS/d and nitrate half-saturation constant of 6.9 mg N/L, respectively. High-throughput sequencing analysis revealed that the diversity of microbial communities was increased with the domestic wastewater added, but the denitrifiers of Thaura genus that was responsible for high nitrite production was still dominant in PD reactor with a percentage of 54.9–72.9%. This study indicated that the high-nitrate and domestic wastewater could be simultaneously treated via the novel PD-ANAMMOX process in a cost-effective way. [ABSTRACT FROM AUTHOR]

[Display omitted] • EPD can synergize with PNA or even provide NO 2 − alone during PN deterioration. • The EPD capability of GAOs can further benefit the stabilization of PNA process. • Anammox contributed 80% to the excellent nitrogen removal of 92% with all NO 2 − supplied by EPD. • Outstanding anammox stability was obtained via a flexible NO 2 − supply by EPD. • Coexistence of enriched GAOs (6.0%, EPD) and anammox bacteria (1.5%) favored anammox stability. The application of partial nitritation-anammox (PNA) process suffers severe obstacles due to the instability of partial nitritation (PN) process. This study sought to evaluate the feasibility of endogenous partial denitratation (EPD) as a remediation or alternative to supply nitrite for the unstable PNA process. A novel strategy of optimal organics utilization through pre-anaerobic carbon storage and post-anoxic endogenous denitrification coupled with anammox was developed in a single-stage bioreactor treating actual municipal wastewater with low C/N (∼3.2). Specifically, the undesired NO 2 −/NH 4 + ratio (2.4 to 0.04) and nitrate accumulation were obtained by increasing the aeration rate (0.6 to 1.8 L/min) to simulate the PN instability. Delightedly, advanced nitrogen removal efficiency (92.1%) was maintained despite a dramatic decrease in nitrite accumulation ratio from 97.6% to 2.6%. This was attributed to the significant increase in anammox contribution to total nitrogen removal from 30.2% to 80.5%. The steady nitrite flux supplied from EPD coupled with PN (EPD contribution increased from 0 to 97.0%) was assumed to be the main reason for the continually increasing abundance and bioactivity of anammox bacteria. Both the anammox bacteria (1.5%, Ca. Brocadia) and glycogen accumulating organisms (6.0%, responsible for EPD) were enriched and coexisted stably in the single reactor. Our study confirms that coupling EPD with anammox has great potential as a remediation for the unstable mainstream PNA process. [ABSTRACT FROM AUTHOR]

In order to treat domestic wastewater with high ammonia but low carbon source (low C/N ratio), a novel two sludge pre-A 2 NSBR system (anaerobic/anoxic/aerobic nitrification) was firstly developed by exchanging the sequence of aerobic nitrification and anoxic phase of the conventional A 2 NSBR process (anaerobic/aerobic nitrification/anoxic). The system was operated for 186 days to treat real domestic wastewater with low carbon/nitrogen (C/N = 4.03). Anoxic duration was adjusted and post-aeration phase was added to enhance nitrogen and phosphorus removal. Results indicate that adding post-aeration phase is indispensable to achieve enhanced phosphorus removal, the pre-A 2 NSBR system achieved a high denitrifying phosphorus removal efficiency of 96.86% with efficient utilization of limited carbon source. Specifically, the ammonia effluent was 0.46 mg/L, which solved the bottleneck problem of high ammonia residues in conventional A 2 NSBR process. The fluorescence in situ hybridization (FISH) results showed that PAOs was enriched and GAOs was inhibited in the A 2 SBR, nitrifiers also became dominant in the N-SBR. Moreover, the profiles variation of real-time online indicator such as pH, ORP and DO were demonstrated closely related with the nutrient removal performance, and based on this, it is possible or expected to establish the real time control strategy in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • Anammox bacteria was more severely inhibited by FA than HA in both PN/A and PD/A. • PD/A was more robust under HA or FA shocks compared with PN/A. • Combined inhibition of HA and FA was additive on PN/A while antagonistic on PD/A. • HA hindered substrate transport while FA inhibited HZS activity in anammox bacteria. • HA and FA inhibition was alleviated in PD/A by partly participating denitrification. Anammox-based technologies hold great advantages in treating ammonia-rich wastewater where humic substances (HSs), mainly including humic acid (HA) and fulvic acid (FA), are ubiquitous and threaten the anammox activity. Here, the individual and combined effects as well as the mechanism of HA and FA on two typical anammox-based systems, partial nitrification/anammox (PN/A) and partial denitrification/anammox (PD/A), were investigated. Anammox activity was inhibited by 50 % with 1811.0 mg/L HA and 769.1 mg/L FA in PN/A system, but much higher level of 11706.0 mg/L HA and 5016.0 mg/L FA in PD/A system. The combined inhibition of HA and FA on anammox activity was additive in PN/A but antagonistic in PD/A. Transcription responses of functional genes (hzsA , hzsB , hdh , nirK , and nirS) suggested HA mainly inhibited the transmembrane transport of NH 4 + and NO 2 –, while FA mostly inhibited the activity of intracellular hydrazine synthase (HZS). Interestingly, the strengthened denitrification alleviated the HSs stress on anammox in PD/A. Moreover, the protective microstructure with anammox bacteria encapsulated within abundant Thauera in PD/A granules further prevented PD/A from HSs shock. This study enables a better understanding of the HSs impacts on anammox-based systems, which is critical to integrating anammox technology into actual wastewater treatment. [ABSTRACT FROM AUTHOR]

Autotrophic denitrification has become the main contributor to the nitrogen removal from wastewater due to its high efficiency, safety and economy. Effect of Fe on sulfur autotrophic denitrification coupled to heterotrophic denitrification was investigated to enhance the nitrogen removal. Under the substrate ratios of S 2 O 3 2-:Fe (II):CH 3 COO– of 1:1:3, 1:3:1 and 3:1:1, the microorganisms were wrapped by Fe minerals, and the normal metabolic pathways were blocked. By adjusting the substrate ratios of S 2 O 3 2-:CH 3 COO– of 1:3, 2:2 and 3:1 without Fe (II), the denitrification recovered with the removal efficiency of NO 3 –-N to 99%. Insufficient addition of S 2 O 3 2- and CH 3 COO– promoted the production of NO 2 –-N and N 2 O with high percentage of N 2 O of 5.70%. When S 2 O 3 2- and CH 3 COO– were sufficient, the nitrogen removal was effective and N 2 O production was low (＜1.35%). Modified Blotzman model and Logistic model were suitable to describe the removal of NO 3 –-N, modified Logistic model was suitable to reveal the generation of SO 4 2-. Dechloromonas acted as denitrifying bacteria in substrate ratios of S 2 O 3 2-:CH 3 COO– of 1:3 and 3:1 up to 58% and 56% at the genus level. Autotrophic Thiobacillus bacteria decreased from 19% (inoculated sludge) to 1% (1:3), 16% (2:2) and 17% (3:1), respectively. Thauera was corresponded to the heterotrophic denitrification which was successfully enriched from 0 (inoculated sludge) to 13% (1:3), 49% (2:2) and 2% (3:1). The different substrate ratios promoted the coexistence of autotrophic and heterotrophic bacteria and cooperated with Fe minerals to improve nitrogen removal from wastewater. [ABSTRACT FROM AUTHOR]