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[Display omitted] • A two-stage process was developed to treat real low C/N municipal wastewater. • Biological P removal and autotrophic N removal occurred in two separate reactors. • Aerobic granulation in both reactors promoted the process efficiency and stability. • Efficient P (91%) and N removal (81%) were achieved under low C/N ratio of 5.4. • The process can recover 33% of influent organic as biogas and 68% of P as struvite. In this study, a novel two-stage aerobic granular sludge (AGS) system was developed to treat municipal wastewater. High removal efficiencies of phosphorus (91%) and nitrogen (81%) were obtained under a low influent carbon/nitrogen ratio of 5.4. The high nutrient removal was attributed to microbial segregation in the two sequencing batch reactors (SBRs). In the first reactor, the high abundance of polyphosphate-accumulating organisms (Candidatus Accumulibacter 15.3%) promoted a high rate of enhanced biological phosphorus removal (EBPR). In the second reactor, residual ammonium was autotrophically removed via partial nitritation/anammox (PN/A). Moreover, granular sludge was maintained in both SBRs with a sludge volume index of 40–80 mL/g, which reduced the settling time and improved the operational stability. Furthermore, batch tests and mass balance analysis revealed that most influent phosphorus (68%) and some organics (33%) were recovered from the waste sludge as struvite and methane, respectively. Overall, this study illustrates that the novel two-stage AGS system integrating EBPR and PN/A is promising for enhancing nutrient removal, as well as resource and bioenergy recovery from municipal wastewater. [ABSTRACT FROM AUTHOR]

[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]

• 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 (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]

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]

A novel two-sludge system of anaerobic anoxic oxic–biological contact oxidation (A 2 /O–BCO) was developed for high-efficiency utilization of influent carbon sources treating wastewater with low carbon/nitrogen (COD/N) ratio. Unlike traditional A 2 /O process, the oxidation of ammonium (NH 4 + -N) in this system mainly took place in the BCO reactor through nitrate (NO 3 − -N) recycling to provide electron acceptors for denitrifying phosphorus removal. The results showed that the A 2 /O reactor achieved the efficient utilization of carbon sources, with 75% chemical oxygen demand (COD) in the anaerobic zone being consumed to synthesize poly-β-hydroxyalkanoates (PHA). The PHA utilization rate in the anoxic zone was more than 70% with the denitrifying phosphorus removal of 97.83%. The batch tests of phosphorus accumulating organisms (PAOs) and denitrifying PAOs (DNPAOs) activities showed that the DNPAOs accounted for 73.80% of the PAOs in the system. The A 2 /O sludge of lower extracellular polymeric substances (EPS) production exhibited a better settling ability than conventional denitrification and phosphorus removal processes. The denitrifying phosphorus removal process of higher phosphorus percentage promoted the formation of granular sludge, which was confirmed by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The fluorescence in situ hybridization (FISH) results showed that PAOs became dominant with low amount of nitrifiers in the A 2 /O reactor, and nitrifiers were enriched in the BCO reactor. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel granulation approach with Thiothrix -hydroxyapatite coupled particles was established. • Mixotrophic denitrification and anammox were integrated in single particle for nitrogen removal. • Coupled particles could effectively cope with low temperatures and organic loading shocks. • Thiothrix produced elemental sulfur as secondary electron donor and energy source. • Coupled particles provided suitable ecological niches for functional microorganisms. Sulfur-driven autotrophic denitrification coupled with anammox (SPDA) is a promising process for autotrophic nitrogen removal, but autotrophic microorganisms are challenging to retain in wastewater treatment units. In this study, a single-stage mixotrophic denitrification coupled with anammox (MDA) process was established in an up-flow anaerobic sludge bed reactor with Thiothrix -hydroxyapatite coupled particles. The advancement of the sludge granulation process effectively strengthened the resistance of the MDA system to environmental stresses, and the SPDA-dominated nitrogen removal process achieved a total nitrogen removal efficiency of 88.6 %, a nitrogen removal rate of 0.432 KgN/m3/d at temperatures as low as 12.8 °C and an organic loading rate of 0.63 KgCOD/m3/d. Interestingly, the ecological niche integration of sulfur oxidizing bacteria (SOB), anammox bacteria and heterotrophic denitrifying bacteria in the granular sludge was observed during long-term operation. The FISH-CLSM results revealed the spatial distribution of functional microorganisms in the granular sludge and the potential pollutant transformation mechanism. The aggressive growth of SOB dominated by Thiothrix constructed a biological wall at the periphery of the granules, which ensured their priority for nitrate acquisition, supplied nitrite to the internal anammox bacteria, and acted as an important barrier against the shock of organic loads. Overall, this study presents a novel granulation approach for the biological treatment of sulfur-containing wastewater, highlighting the efficacy of functional integration within Thiothrix -hydroxyapatite coupled particles as an effective strategy to resist environmental stress. [ABSTRACT FROM AUTHOR]

[Display omitted] • Biological nitrate removal with municipal wastewater as co-substrate was demonstrated by CANDAN process; • High-efficient nitrogen removal with NRE and NRR of above 84 % and 0.6 Kg N/m3/d achieved; • Efficient denitratation with NTR above 84.6% always obtained despite increased municipal wastewater; • Increased municipal wastewater did not pose an adversely effect on anammox process; • Stable CANDAN process with dominated anammox sustained in treating nitrate sewage with varying concentrations. The innovative Complete Ammonium and Nitrate removal via Denitratation-Anammox over Nitrite (CANDAN) process represents a promising low-carbon technology for wastewater treatment, has been widely studied in sequential batch reactors (SBRs) treating synthetic wastewaters. This work focuses on the development of the CANDAN process within a continuous-flow Upflow Anaerobic Sludge Blanket (UASB) reactor for nitrate sewage treatment (NO 3 –-N: 100–1000 mg N/L), featuring varying proportions of real municipal wastewater as a co-substrate (61.3 mg NH 4 +-N/L, 191.5 mg COD/L). The results demonstrate consistently high N removal performance, with over 84.0 % of total nitrogen (TN) removed from the mixed wastewaters at a rate of approximately 0.6 Kg N/m3/d. As the proportion of municipal wastewater in the feed increased, the activity of denitrifying microorganisms improved. However, their growth was constrained by exacerbated endogenous respiration resulting from prolonged Hydraulic Retention Time (HRT) under a constant loading rate. The ideal nitrite production with the nitrate-to-nitrite transformation ratio (NTR) of above 84.6 % was always obtained. This sustained the dominance of the anammox pathway at around 80 % throughout the operation, underscoring its pivotal role in supporting the exceptional performance of the CANDAN process within the UASB reactor. Microbial analysis revealed an increase in species richness and diversity with higher proportions of municipal wastewater, while anammox functional bacteria exhibited slight enrichment in the later stages, further emphasizing the sustainability of the CANDAN process even with increased proportions of municipal wastewater. The outcomes of this study provide valuable insights into the successful development of a continuous-flow CANDAN process for highly efficient nitrate sewage treatment by incorporating real municipal wastewater as a co-substrate, advancing the goal of achieving carbon–neutral wastewater treatment practices. [ABSTRACT FROM AUTHOR]

[Display omitted] • Amino-functionalized graphene oxide aerogel (MGOA) was ingeniously synthesized. • The adsorption property of MGOA was studied by static and fix-bed adsorption. • MGOA achieves efficient adsorption towards quinoline in water. • MGOA can be easily separated from liquid phase. • Performance of MGOA was confirmed by both adsorption capacity and PC. The direct emission of quinoline in coking wastewater has great harm to human health and environmental quality. Therefore, it is urgent to develop advanced materials for efficient adsorption of quinoline in wastewater. In this study, a novel three-dimensional amino-functionalized graphene oxide aerogel (MGOA) was prepared by an acid induction strategy, which triggers the esterification and amidation of graphene oxide (GO) nanosheets and ammonium citrate. This strategy not only improves the chemical stability and mechanical strength of as-prepared MGOA, but also provides a large number of effective adsorption sites to achieve the efficient adsorption towards quinoline. MGOA has the advantages of three-dimensional interconnected hierarchical pore structure, large specific surface area, and low density. When the initial quinoline concentration is 50 mg L−1, the adsorption capacity (q e) of MGOA towards quinoline is as high as 103 mg g−1 at 298 K. More importantly, in the column adsorption system, the distribution coefficient (PC) at 10% breakthrough is 14.16 mg g−1 μM−1, which is the highest level yet reported. MGOA exhibits good reusability and outstanding solid-liquid separation advantage during eight adsorption-desorption cycles. Density functional theory and van der Waals surface electrostatic potential were used to investigated the adsorption behavior of quinoline on aerogel. The binding force between MGOA and quinoline molecule is strong, with an adsorption energy up to −78.68 kJ mol−1. Thus, MGOA is considered as a promising candidate for removing quinoline contaminants from aqueous solutions. [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] • Efficient nitrite production with high PD activity was achieved even at an influent nitrate of 800 mg N/L. • P removal initially increased with influent nitrate, but decreased with further increments beyond 400 mg N/L. • High Ca had minor effect on nitrite production, but facilitated P removal with maximum efficiency of 96.9% achieved. • PD-HAP granules tended to disintegrate at nitrate >400 mg N/L, while good settleability still obtained. • Controlling pH levels is expected to enable high-efficiency nitrite production and P removal from high-nitrate wastewater. This study introduces a novel PD-hydroxyapatite (HAP) coupled granular sludge process that efficiently produces nitrite while also addressing the issue of phosphorus (P) removal. Three laboratory-scale sequencing batch reactors (SBRs) were operated with varying calcium (Ca) concentrations, the performance of nitrite production, P removal, and the characteristics of PD-HAP granules under increasing nitrate concentrations (200–800 mg N/L) were investigated. Results demonstrated an increase in nitrite production with influent nitrate, with high PD activity maintained even in the presence of elevated nitrite levels. P removal improved as influent nitrate increased to 400 mg N/L but declined thereafter, likely due to the elevated pH promoting carbonate formation, which competed with phosphate for Ca2+. Supplying a higher Ca2+ concentration improved P removal, with R3 achieving a maximum removal efficiency of 96.9% at an influent nitrate of 400 mg N/L, surpassing R2 (85.7%) and R1 (70.0%). Additionally, it was observed that PD-HAP granules increased in size with higher nitrate concentrations but turned to be disintegrated with small granules formed when nitrate exceeded 400 mg N/L. However, despite this, the granules still maintained good settleability, with only a slight increase in sludge volume index (SVI 5) from 14.8 to 25.9 ml/g MLSS. This study demonstrated the tremendous potential of PD-HAP granular sludge process for treating high-nitrate wastewater in combination with anammox. [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]

[Display omitted] • Domestic sewage & PNA-treated reject water are polished to 4.5 mg/L by anoxic PDA. • External COD supply is finally canceled profiting by enhanced sewage utilization. • Clustered anammox bacteria in compact granule strengthen performance and robustness. • Uronic acid and special protein in EPS promote granulation and pollutant adsorption. • Orderly activated Thauera , Brocadia , Competibacter in PDA cycle coordinate N removal. Partial denitrification/anammox (PD/A) has been recently applied to co-treat domestic wastewater and nitrate-containing anammox effluent. However, studies regarding its performance without external organic supplement, spatial characteristics within sludge aggregates, and chronological changes of active microorganisms along PD/A cycle have rarely been reported. Herein, one-stage PD/A unit extremely and simultaneously polished anammox-pretreated reject water (NH 4 +-N: 65.4 ± 5.7 mg/L, COD: 199.7 ± 23.2 mg/L) and domestic wastewater (NO 3 −-N: 81.6 ± 7.8 mg/L, TN: 85.8 ± 8.9 mg/L, COD: 338.2 ± 29.0 mg/L) to 4.5 ± 2.1 mg/L without external organic carbon supply. Protective "granules-in-granule" aggregates with densely clustered anammox bacteria embedded in homogeneous denitrifying Thauera prevailed in PD/A system, surviving disadvantages from complex wastewater. Uronic acids and β-sheet proteins in outer extracellular matrix facilitated granulation and pollutants adsorption, while tryptophan- and aromatic-like proteins with tighter secondary structure in inner extracellular matrix maintained granular robustness. Importantly, succession of active microorganisms along the PD/A cycle was revealed by transcript-level analysis for the first time. In PD-period, stimulated Thauera contributed to rapid nitrite accumulation. In subsequent anammox-period, Ca.Brocadia was activated to conduct advanced nitrogen removal, which accompanied the timely nitrate-to-nitrite reduction by Thauera and Ca.Competibacter. Elusimicrobia was active throughout the PD/A cycle, which is conducive to eliminate the dependence of PD process on external carbon source by decomposing complex organics in actual wastewater. Protective granular structure, orderly activation and harmonious cooperation of functional consortia facilitated practical nitrogen removal rate of 0.6 ± 0.1 kg-N/m3/d under anoxic condition, which sheds light on engineering application of anammox technology. [ABSTRACT FROM AUTHOR]

[Display omitted] • Complete nitrogen removal was achieved treating actual low C/N (2.8) sewage. • The double nitrite shunt from PN and EPD guaranteed the thorough anammox reaction. • ED and DPR pathways jointly contributed 37% to TIN removal via nitrate respiration. • Coexistence of enriched AnAOB, GAOs and DPAOs favored co-metabolism stability. • Directional transfer of electrons and substrates radically supported superior performance. Autotrophic nitrogen removal processes based on anammox are facing huge challenges of high effluent quality in wastewater treatment. In this study, a novel hybrid system of anammox coupled with heterotrophic endogenous metabolisms was developed in a single-stage bioreactor to treat real domestic wastewater. Complete nitrogen removal was achieved at a low carbon to nitrogen (C/N) ratio of 2.8 and more than 95.2% nitrogen removal was maintained under an extremely low C/N ratio of 1.9. The nitrite shunt supplied by dual partial pathways (partial nitritation and endogenous partial denitratation) guaranteed the anammox activity with a high contribution to nitrogen removal above 60%. While endogenous denitrification (ED) and denitrifying phosphorus removal (DPR) both participated in nitrate respiration, contributing more than 28% and 9% to nitrogen removal, respectively. The coexistence and enrichment of anammox bacteria (Ca. Brocadia, 0.9%), glycogen accumulating organisms (Ca. Competibacter, 6.4%) and phosphorus accumulating organisms (Dechloromonas , 3.9% and Ca. Accumulibacter, 0.7%) contributed to the co-metabolism of carbon, nitrogen and phosphorus. The functional genes encoding the above metabolism were highly correlated with the dominant strains, indicating that the multiple pathways of carbon and nitrogen metabolism supported the continuous supply of electrons required for nitrogen removal. This study puts forward a novel complete nitrogen removal process by successfully coupling autotrophic and endogenous heterotrophic metabolism. [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] • Anammox-based process achieved highest NRE of 81.2% at salinity of 2.0%. • With real municipal sewage, influent and effluent TIN are 44.5 and 8.2 mg N/L. • Increased salinity inhibited NOB, nitrite reduction bacteria, and AOB by order. • Enhanced nitrite production and biofilm formation ensure high anammox contribution. • Anammox bacteria occupied 1.07% maximally and has strong adaptability to salinity. Nitrogen removal from saline municipal wastewater has recently attracted attention; thus, developing energy-efficient technology such as anaerobic ammonium oxidation (anammox) for advanced nitrogen removal of hypersaline wastewater is significant. In this study, the long-term salt adaptation and evolution mechanisms of an anammox-based process driven by both nitritation (NH 4 +→NO 2 —, PN) and denitratation (NO 3 —→NO 2 —, PD) were investigated under salinities ranging from 1.0% to 3.0% (10–30 g NaCl/L). At 1.0% salinity, PN evolved into the major nitrite production pathway with thorough suppression of nitrite oxidation. At 1.5% salinity, nitrite reduction was inhibited along with suspended sludge loss due to poor sludge settleability. Under 2.0% salinity with only-biofilm, the highest nitrogen removal efficiency (81.2%) was observed with influent and effluent total inorganic nitrogen concentrations of 44.5 and 8.2 mg N/L, respectively. Notably, results showed that anammox bacteria occupied up to 1.07% of the microbial community (qPCR: 1.14×1011 copies/(g dry sludge)) and has strong adaptability to salinity. With salinity increases, anammox contribution kept over 85% and Ca. Kuenenia (0.57%→0.22%) was more tolerant than Ca. Brocadia (0.46%→0.02%). Metagenomic sequencing revealed that the multiple nitrite substrates production by Nitrosomonas (amoA -enriched), Denitratisoma and Denitromonas (narG -enriched) guaranteed the high anammox contribution. This study provides a multifaceted understanding of the anammox-based process, which can enable improved application in real saline wastewater treatment. [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]

[Display omitted] • Graphitic support dimension of ZIF8@C have key influences on phosphate removal. • 2D graphene provides more efficient SSA for ZIF8 anchoring than that of 1D SCNT. • The maximum phosphate adsorption of 491.2 mg g−1 is obtained for ZIF8@rGO-20. • Nanohybrids with a ratio of metal: −OH ≈ 1: 2 afford the highest phosphate removal. • Suppression of SO 4 2− on P adsorption verify the ligand exchange between P and MOF@C. Developing metal–organic framework-incorporated carbon heterostructure (MOF@C) adsorbents with advanced phosphate removal capability is of remarkable significance in satisfying the increasingly stringent wastewater discharge criteria. Nevertheless, the tailored synthesis of MOF@C architectures and related structure-performance modulation remains elusive to date. Herein, we report on the dimensional engineering of MOF@C to prepare ZIF8@single-walled carbon nanotube (SCNT) and ZIF8@reduced graphene oxide (rGO) heterostructures with satisfactory phosphate removal efficiency. The maximum phosphate adsorption capacity of ZIF8@rGO is 491.2 mg g−1, with the largest partition coefficient value of 1900 mg g−1 μM−1 and an initial concentration of 2 mg L−1 under a neutral condition; thus, the prepared heterostructures evidently surpass state-of-the-art adsorbents. The high adsorption capacity is attributable to the two-dimensional graphene support, which provides a more effective surface area for ZIF8 anchoring than that of one-dimensional CNT. Furthermore, phosphate removal on these dimension-engineered MOF@C is examined as a function of pH, system temperature, and coexisting anions. The underlying mechanism is further elucidated via X-ray photoelectron spectroscopy/X-ray diffraction analysis and density functional theoretical simulation; enhanced phosphate removal by ZIF8@rGO is mainly attributable to the ligand exchange between the phosphates and the adsorbent. Our findings can aid the design of multifunctional MOF@C adsorbents for efficient phosphate removal from contaminated waterbodies. [ABSTRACT FROM AUTHOR]

[Display omitted] • Stable partial nitrification was achieved in continuous–flow EBPR system. • NAR reached 99.4%, and the removal efficiency of PO 4 3−–P reached 100%. • Effluent concentration of TIN was lower than 2 mg/L without adding external carbon. • Analysis of transcriptional level revealed the mechanisms of partial nitrification. • Fermentation by Tetrasphaera caused cell lysis and reduction of sludge discharge. Simultaneous partial nitrification, biological phosphorous removal and sludge fermentation in continuous–flow system faced many challenges in wastewater treatment plants (WWTPs). In this study, a novel process was developed to achieve partial nitrification, enhanced biological phosphorus removal and in–situ fermentation (PNPRF) in continuous–flow system dominated by Tetrasphaera treating low carbon/nitrogen ratio (COD/N) real domestic wastewater. After 80 days of operation, no external carbon was added into the influent. Nitrite accumulation ratio (NAR) reached 99.4% and removal efficiency of PO 4 3−–P was 100%. The effluent concentration of total inorganic nitrogen (TIN) was lower than 2 mg/L. Compared with traditional biological nitrogen and phosphorus removal processes, the daily sludge discharge in continuous–flow PNPRF decreased by 61.9%. DNA concentration of the sludge supernatant after anaerobic zone was 2.26-fold of that before anaerobic zone, and percentages of intact cells decreased by 6.9% and necrotic cells increased by 8.3%, indicating that cell lysis caused the reduction of sludge discharge. The negative effect of prolonged anaerobic phase on transcriptional response of nxrB gene was more significant than that of amoA and hao gene, which resulted in stable partial nitrification. The activities of ammonium–oxidizing bacteria (AOB) were higher than that of nitrite–oxidizing bacteria (NOB), and reverse transcriptional PCR (RT–PCR) showed that RNA expression of AOB was higher than that of NOB. Achieving partial nitrification, enhanced biological phosphorus removal and in–situ fermentation in continuous-flow system dominated by Tetrasphaera solved the problems of carbon source deficiency and large amount of sludge discharge in treating real domestic wastewater process. [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]

[Display omitted] • Synthesis of wettability UV switchable adsorbent for a selective phenol adsorption. • Synergy of photosensitive TiO 2 with hydrophobic crosslinker to reverse wettability. • Extremely high phenol adsorption capacity of 8.24 mg-phenol/m2-adsorbent. • Easy recovery of 98% phenol from the saturated adsorbent. • Robust regeneration performance of the adsorbent upon cyclic testing. Here we report the design and synthesis of a novel surface imprinted adsorbent, with an UV-switchable wettability towards an efficient and highly selective phenol recovery from wastewater. The high selectivity of phenol is achieved through surface molecularly imprinted cavities featuring a smart phenol identification function, whilst the UV-switchable wettability is accomplished by the co-loading of nano-sized, photosensitive TiO 2 and hydrophobic 3-(trimethoxysilyl) propyl methacrylate imprinted layer. Through numerous adsorption experiments and extensive characterizations including FESEM, TEM, FT-IR, BET, XRD, XPS, and synchrotron NEXAFS, it is confirmed that upon a prior 0.5 h - long UV irradiation, the imprinted surface of the as-synthesized adsorbent can be switched from hydrophobic to hydrophilic, which in turn results in an equilibrated adsorption capacity of 8.24 mg-phenol/m2-adsorbent that are superior over all the reported values. More intriguingly, with the progress of the adsorption in the dark, the surface of the adsorbent can be gradually reversed to hydrophobic. This in turn enhances the repulsion of particles from the aqueous phase, leading to a quick self-agglomeration and precipitation of the spent adsorbent for an easy recovery. Moreover, 98% of the adsorbed phenol can be recovered via a subsequent washing by methanol, and the regenerated adsorbent is also confirmed to exhibit a nearly stable adsorption capacity upon five cycles. [ABSTRACT FROM AUTHOR]