Anammox granule destruction and reconstruction in a partial nitrification/anammox system under hydroxylamine stress.

Nitrite oxidizing bacteria (NOB) outcompeting anammox bacteria (AnAOB) poses a challenge to the practical implementation of the partial nitrification/anammox (PN/A) process for municipal wastewater. A granules-based PN/A bioreactor was operated for 260 d with hydroxylamine (NH2OH) added halfway through. qPCR results detected the different amounts of NOB among granules and flocs and the dynamic succession during operation. CLSM images revealed a unique layered structure of granules that NOB located inside led to the inhibition effect of NH2OH delayed. Besides, the physical and morphological characteristics revealed that anammox granules experienced destruction. AnAOB took the broken granules as an initial biofilm aggregate to reconstruct new granules. RT-qPCR and high throughput sequencing results suggested that functional gene expression and community structure were regulated for the AnAOB metabolism process. Correspondingly, the rapid proliferation (0.52 â†’ 1.99%) of AnAOB was realized, and the nitrogen removal rate achieved a nearly quadruple improvement (0.21 â†’ 0.83 kg-N/m3·d). This study revealed that anammox granules can self-reconstruct in the PN/A system when granules are disintegrated under NH2OH stress, broadening the feasibility of applying PN/A process.

Continuous plug-flow anammox system for mature landfill leachate treatment: Key zone for anammox pathway.

This study established the one-stage partial nitrification coupled anammox and partial denitrification coupled anammox process in an anoxic/oxic continuous plug-flow system and operated for 465 days to treat mature landfill leachate. 97.9 %-98.1 % of inorganic nitrogen was removed when the nitrogen loading rate was maintained at 0.33-0.36 kg N/m3/d, and a high anammox contribution to nitrogen removal (89.8 %-92.4 %) was achieved. The long-term in-situ free ammonia (FA) anoxic treatment contributed to the stable performances of partial nitrification and in-situ fermentation. The employed integrated fixed-film activated sludge technology favored the enrichment of hzsA, hzsB, hdh, amoA, hao, narG, and napA functional genes. The oxic zone, particularly oxic biofilm, was the key zone for anammox pathway, where Candidatus_Kuenenia (from 1.6 % to 8.3 %) with high tolerance to FA and salinity stress outcompeted Candidatus_Brocadia (from 18.3 % to 0.1 %) as the dominant anammox bacteria. This study could provide guidance for anammox-mediated landfill leachate treatment in practical projects.

Advanced nitrogen removal from mature landfill leachate based on novel step-draining partial nitrification-denitrification and Anammox process: Significance of low volume exchange ratio.

To save external carbon source dosage and simplify NH4+ to NO2- ratio control strategy, this study established a novel step-draining based partial nitrification-denitrification and Anammox (PND-AMX) system for advanced nitrogen removal from mature landfill leachate. Separation of partial nitrification and denitrification was realized based on step-draining, achieving 74.8 % nitrogen removal. 25 % was the optimal volume exchange ratio for synergistic removal of organics and nitrogen, allowing full use of carbon source. NH4+ to NO2- ratio was easily controlled by varying the volume ratio of the first and second effluent of PND reactor. Brocadia, Kuenenia and Jettenia collectively accounted for 13.61 % in AMX reactor, contributing 21.0 % of nitrogen removal. Nitrogen removal efficiency and nitrogen removal rate reached 98.3 ± 1.2 % and 3.07 ± 0.09 kgN/(m3∙d), respectively. Partial Anammox process based on step-draining was easier to realize and of practical significance for application in treatment of landfill leachate.

Anammox-mediated municipal solid waste leachate treatment: A critical review.

Municipal solid waste (MSW) leachate treatment through the anaerobic ammonium oxidation (anammox) process has received increasing attention due to less oxygen consumption, carbon source demand, and sludge production. The recent advances in anammox-mediated MSW leachate treatment are systematically reviewed. During MSW leachate treatment, the anammox technology could be flexibly combined with partial nitrification, partial denitrification, fermentation, and methane oxidation. Additionally, this review comprehensively discussed the specific effects on anammox bacteria (AnAOB) of key stressors in MSW leachate such as dissolved organic matters, salinity, and antibiotics, and introduced the corresponding pretreatment methods. The key control strategies focusing on achieving effective AnAOB retention, amelioration of microenvironments, and stable nitrite source were summarized. Moreover, the potential for nitrous oxide emission mitigation in anammox-based MSW leachate treatment systems was evaluated. Finally, this review highlighted the full-scale applications of anammox-mediated MSW leachate treatment and proposed the prospects as well as research gaps in this field.

An Innovative Process for Mature Landfill Leachate and Waste Activated Sludge Simultaneous Treatment Based on Partial Nitrification, In Situ Fermentation, and Anammox (PNFA).

An innovative partial nitrification, in situ fermentation, and Anammox (PNFA) system was developed to achieve mature landfill leachate and waste activated sludge simultaneous treatment. Three separate sequencing batch reactors (SBRs) were used for partial nitrification (PN-SBR), integrated fermentation-denitrification (IFD-SBR), and partial nitrification-Anammox (PNA-SBR). After 200 days of continuous operation, a satisfactory nitrogen removal efficiency (NRE) of 99.2 ± 0.1% was obtained, with an effluent total nitrogen (TN) of 15.2 ± 3.2 mg/L. In IFD-SBR, the volatile fatty acids generated from fermentation drove efficient denitrification, obtaining sludge and nitrogen reduction rates of 4.2 ± 0.7 and 0.61 ± 0.04 kg/m3·day, respectively. Furthermore, unwanted fermentation metabolites (134.1 mg/L NH4+-N) were further treated by PNA-SBR using a combination of step-feed and intermittent aeration strategies. In PNA-SBR, Anammox significantly contributed to 82.1% nitrogen removal, and Anammox bacteria (Candidatus Brocadia, 2.3%) mutually benefited with partially denitrifying microorganisms (Thauera, 4.2%), with 66.3% of generated nitrate reduced to nitrite and then reutilized in situ by Anammox. Compared with the conventional nitrification-denitrification process, PNFA reduced oxygen energy consumption, external carbon source dosage, and CO2 emission by 21.3, 100, and 38.9%, respectively, and obtained 50.1% external WAS reduction efficiency.

Improving stability of mainstream Anammox in an innovative two-stage process for advanced nitrogen removal from mature landfill leachate.

This study presents an innovative mainstream Anammox based on multiple NO2--N supplement pathways to treat actual mature landfill leachate over 180 days. Desirable effluent quality of 11.8 mg/L total nitrogen (TN) and nitrogen removal efficiency of 98.8% were achieved despite fluctuation conditions of 1.5-fold influent substrates and 8.0-fold dissolved oxygen overload. Nitrogen mass balance confirmed Anammox was the dominant nitrogen removal pathway, contributing up to 87.9%. Functional genes of ammonia monooxygenase (amoA), hydrazine synthase (hzsB), and ratio of nitrate/nitrite reductase were highly detected. Anammox genera, Candidatus_Kuenenia (4.1%) and Candidatus_Brocadia (5.3%) were dominant in two functional systems, respectively, due to the different affinity of nitrite, oxygen, and organic carbon. As an economical and sustainable technology, the innovative process enabled a 95.1% decrease in organic carbon demand, a 61.5% reduction in aeration energy consumption, and 77.6% lower biomass production compared with traditional nitrification-denitrification process.

Development of a novel partial nitrification, fermentation-based double denitrification bioprocess (PN-F-Double/DN) to simultaneous treatment of mature landfill leachate and waste activated sludge.

Introducing fermentation technology into sewage treatment is a sustainable development concept, but future application still faces many challenges. A novel partial nitrification, fermentation-based double denitrification bioprocess (PN-F-Double/DN) was achieved in three separated SBR type reactors, simultaneously treating high ammonia (1766.6 mg/L) mature landfill leachate and external waste activated sludge (WAS, MLSS = 20.6 g/L). Firstly, NH4+-N was oxidized to NO2--N in partial nitrification reactor (PN-SBR), with nitrite accumulation ratio (NAR) of 96.5%. Next, the PN-SBR effluent (NO2--N = 1529.8 mg/L) coupled with the WAS were introduced to an anoxic reactor for integrated fermentation-denitrification (IFD-SBR). The occurrence of fermentation was mainly attributed to free nitrous acid (FNA, nitrite protonate form) promoting the splitting decomposition of sludge spatial configuration and interfacial forces. The released volatile fatty acids (VFAs) were utilized in situ during the denitrification process (NO2--N→N2), obtaining 0.6 kg/m3•d nitrogen removal rate and 3.3 kg/m3•d sludge reduction rate. Finally, undesirable fermentation by-products from IFD-SBR (NH4+-N = 119.2 mg/L) were further removed in the endogenous post-denitrification reactor (EPD-SBR) through operational strategy of anaerobic/aerobic/anoxic by residual VFAs as the carbon source. In the EPD-SBR, Defluviicoccus (0.9%) and Candidatus Competibacter (5.8%) dominated carbon source storage and nitrogen removal, acting as a typical denitrifying glycogen-accumulating organism (DGAO), with an intracellular carbon storage efficiency of 83.1% and nitrogen removal contribution of 93.7%. After 200 days of operation, the PN-F-Double/DN process provided effluent containing, on average, 1.86 mg/L NH4+-N and 5.5 mg/L NOx--N, with 98.5% TN removal. Compared with traditional bioprocesses, PN-F-Double/DN allowed up to 25% saving in aeration energy consumption, 100% decrease in carbon source demand, and achieve 46.1% external WAS reduction.

Achieving synergetic treatment of sludge supernatant, waste activated sludge and secondary effluent for wastewater treatment plants (WWTPs) sustainable development.

A novel process that combines partial nitrification, fermentation and Anammox-partial denitrification (NFAD) was proposed to co-treat ammonia rich sludge supernatant (NH4+-N = 1194.1 mg/L), external WAS (MLSS = 22092.6 mg/L) and WWTP secondary effluent (NO3--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.

New insights into co-treatment of mature landfill leachate with municipal sewage via integrated partial nitrification, Anammox and denitratation.

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 (SBRPN); meanwhile, organic matter in municipal sewage was partially removed in another reactor (SBROMR); finally, nitrite produced (611.5 ± 28.1 mg N/L) in SBRPN 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 (UASBAD). 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).

Advanced nitrogen removal from mature landfill leachate via partial nitrification-Anammox biofilm reactor (PNABR) driven by high dissolved oxygen (DO): Protection mechanism of aerobic biofilm.

A novel partial nitrification-Anammox biofilm reactor (PNABR) operated under high dissolved oxygen (DO) with pre-anoxic - aerobic - anoxic operational mode was developed for efficient denitrogenation from mature landfill leachate. With DO concentration gradually increasing to 4.03 ± 0.03 mg/L, the ammonia oxidation rate (AOR) was enhanced to 25.8 mgNH4+-N/(L h), while nitrite oxidation bacteria (NOB) was inhibited effectively by alternating free ammonia (FA) and oxygen starvation. DO micro-distribution revealed that estimated 1900 µm of aerobic biofilm could protect anammox biofilm underneath from being inhibited by high DO. qPCR analysis further suggested that ammonia oxidation bacteria (AOB) abundance in whole biofilm was 6.12 × 109 gene copies/(g dry sludge), which was twice than found in the floc. Anammox bacteria accounted for 2.39% of total bacteria in whole biofilm, contributing 90.0% to nitrogen removal. Nitrogen removal rate (NRR) and nitrogen removal efficiency (NRE) finally reached 396.6 gN/(m3 d) and 96.1%, respectively.

Novel insights into integrated fermentation and nitrogen removal by free nitrous acid (FNA) serving as treatment method.

Free nitrous acid (FNA) has only been studied as the pretreatment of waste activated sludge (WAS). Integrated fermentation and nitrogen removal using FNA as a primary means of treatment are seldom investigated. WAS fermentation was characterized under various FNA concentration. The production of COD, protein, and carbohydrate increased with FNA concentration (in the range of 0.197-1.97 mg/L) before the denitrification process. Volatile fatty acids (VFA) were only produced after complete denitrification. Potential FNA impact on fermentation step found FNA facilitated both solubilization and hydrolysis but inhibited acidification, acetogenesis, and methanogenesis processes. The types of fermentation were determined using threedimensional excitation-emission matrix (EEM) fluorescence spectroscopy. Protein-like substances and Tyrosine/Tryptophan were the most dominant dissolved organic matters (DOMs). The cell decay rate increased from 0.044 to 0.102/d based on the nonlinear fitting for the FNA concentration of 0.197-1.97 mg/L. The microbial biomass mortality reached 92.7% when the FNA in tight extracellular polymeric substances (T-EPS) exceeded 0.04 mg/L. In addition, the microbial diversity and microbial structure were substantially reduced by FNA during long-term operation, while the bacterial abundance associated with hydrolysis and acidification increased significantly.

A continuous-flow combined process based on partial nitrification-Anammox and partial denitrification-Anammox (PN/A + PD/A) for enhanced nitrogen removal from mature landfill leachate.

A novel continuous-flow combined process of partial nitrification, Anammox (PN/A) and partial denitrification-Anammox (PD/A) was established to achieve enhanced nitrogen removal from landfill leachate. The NH4+-N transformation rate and NO2--N accumulation rate in the PN reactor reached 93.4% and 91.5%, respectively. The nitrite generated from the PN reactor was combined with influent (38%) and fed into the Anammox reactor. The nitrate produced in the Anammox reactor was then discharged to PD/A reactor, where nitrate was transformed to nitrite and removed via Anammox. Under a COD/NO3--N ratio of 4.0, the NO3--N-to-NO2--N transformation ratio (NTR) and Anammox contribution rate reached 60.4% and 57.1% in PD/A reactor. The final effluent TN concentration was 15.7 mg/L, and the efficiency of TN removal could reach 98.8%. By combining PN/A with PD/A, enhanced nitrogen removal from landfill leachate was achieved successfully with an external carbon source addition (COD/NH4+-N) of 0.28.

Nitrite accumulation in comammox-dominated nitrification-denitrification reactors: Effects of DO concentration and hydroxylamine addition.

In this study, nitrite accumulation was investigated under different DO conditions and different hydroxylamine addition methods during the domestic wastewater treatment. Two sequencing batch reactors in parallel were operated under cyclic aerobic and anoxic conditions with the DO concentration of 2.0 and 4.0 mg/L in aerobic phase. The nitrite accumulation rate during high DO conditions increased to 44.8 and 66.7% in 20 days. During hydroxylamine addition, the NAR increased over 90% under the continuous and intermittent hydroxylamine addition. Continuous hydroxylamine addition could result in a more efficient and rapid nitrite accumulation. The findings suggested that comammox could be the main reason for the failure of partial nitrification in a low DO environment (< 0.5 mg/L). The nitrogen variation during typical cycles showed that the continuous hydroxylamine addition suppressed the activity of NOB and the ammonia oxidation rate. Further, the qPCR results indicated that the abundance of comammox amoA (ranged from 6.25 × 107 to 4.16 × 108 copies/g VSS) was higher than those of AOB amoA and Nitrobacter in sludge samples. The findings from the current study may enrich our understanding of partial nitrification and its control strategy.

Simultaneous Ammonium oxidation denitrifying (SAD) in an innovative three-stage process for energy-efficient mature landfill leachate treatment with external sludge reduction.

High-loaded ammonia and low-strength organics mature landfill leachate is not effectively treated by conventional biological processes. Herein, an innovative solution was proposed using a three-stage Simultaneous Ammonium oxidation Denitrifying (SAD) process. Firstly, ammonia (1760 ±â€¯126 mg N/L) in wastewater was oxidized to nitrite in a partial nitrification sequencing batch reactor (PN-SBR). Next, 93% PN-SBR effluent and concentrated external waste activated sludge (WAS; MLSS = 23057 ±â€¯6014 mg/L) were introduced to an anoxic reactor for integrated fermentation and denitrification (IFD-SBR). Finally, ammonia (101.4 ±â€¯13.8 mg N/L) released by fermentation in the IFD-SBR and residual 7% nitrite in the PN-SBR were removed through the anaerobic ammonium oxidation (anammox) process in the SAD up-flow anaerobic sludge bed (SAD-UASB). In addition, NO3--N generation during the anammox process could be reduced to nitrite by partial denitrification (PD) and reused as substrate for anammox. A satisfactory total nitrogen (TN) removal efficiency (98.3%), external sludge reduction rate (2.5 kg/m3 d) and effluent TN concentration (16.7 mg/L) were achieved after long-term operation (280 days). The IFD-SBR and SAD-UASB contributed to 81.9% and 12.3% nitrogen removal, respectively. Microbial analysis showed that anammox bacteria (1.5% Candidatus Brocadia) cooperated well with partial denitrifying bacteria (4.3% Thauera) in SAD-UASB, and average nitrogen removal contribution were 83.1% during significant stability of anammox and 9.2% during the denitrification process, respectively. The three-stage SAD process provides an environmental and economic approach for landfill leachate treatment since it has the advantage of 25.4% less oxygen, 100% organic matter savings and 47.9% less external sludge than traditional biological processes.

High-efficient nitrogen removal from mature landfill leachate and waste activated sludge (WAS) reduction via partial nitrification and integrated fermentation-denitritation process (PNIFD).

Biological nitrogen removal from mature landfill leachate is ineffective due to the extremely low carbon/nitrogen (C/N) ratio. Moreover, a large amount of waste activated sludge (WAS) is inevitably generated from WWTPs during the municipal sewage treatment process. In this study, an innovative process was developed to enhance nitrogen removal from low C/N (1:1) mature landfill leachate and to reduce the WAS during a 300-day operation. Two sequencing batch reactors (SBRs) were involved in this process. Firstly, the mature landfill leachate was pumped into an aerobic reactor to undergo partial nitrification (PN-SBR). Then, the PN-SBR effluent and WAS were pumped into an anoxic reactor to undergo integrated fermentation and denitritation (IFD-SBR). The pH profile was treated as a real-time parameter to precisely control the duration of the PN and IFD processes. Partial nitrification and integrated fermentation-denitritation (PNIFD) system achieved a total nitrogen removal efficiency of 95.0% and an average nitrogen removal rate (NRR) of 0.63 kg/m3·d during the last operational phase. Due to a variety of refractory contaminants, the effluent COD concentration was 1865.9 mg/L and a 19.7% COD removal efficiency was obtained under an influent concentration of 2324.5 mg/L. Compared with the traditional nitrogen removal process, PNIFD not only decreased requirements for oxygen by 25% and the external organic carbon by 100%, but also achieved simultaneous reduction of external WAS. More than 53.7% of the external sludge was reduced during the IFD-SBR operational cycle, with an average external sludge reduction rate (SRR) of 5.09 kg/m3·d. Fermentation/denitritation related microorganisms, such as Anaerolineaceae, Acidimicrobiaceae and Thauera, accounted for up to 41.5% of the total abundance in the IFD-SBR. Based on the long and stable operation, this study provides a simple and promising approach for synchronous nitrogen removal and WAS reduction.

Enhanced nitrogen removal from nitrate-rich mature leachate via partial denitrification (PD)-anammox under real-time control.

It is difficult to achieve high standard effluent through conventional nitrification-denitrification process treating mature leachate and the advanced treatment is usually required. This study proposed an economical process for enhancing nitrogen removal from nitrate-rich leachate which combined partial-denitrification and anammox (PD/A) in a SBR. Under the concentration of influent ammonia and nitrate of 47.5 mg/L and 93.7 mg/L on average, TN removal efficiency of 84.8% was obtained with the effluent TN less than 20 mg/L. It was found that enhanced nitrogen removal of mature landfill leachate through PD-anammox was estimated to save 40% organic carbon addition and reduce the cost of sludge treatment in this study. Moreover, the ORP and pH could potentially be used as control parameters to maintain the stability of combined process.

Efficient step-feed partial nitrification, simultaneous Anammox and denitrification (SPNAD) equipped with real-time control parameters treating raw mature landfill leachate.

An innovative step-feed partial nitrification, simultaneous Anammox and denitrification (SPNAD), equipped with real-time control parameters, achieved efficient nitrogen removal from raw mature landfill leachate. The variables pH and ORP served as real time on-line parameters to flexibly control the durations of aerobic and anoxic. A nitrogen removal efficiency (NRE) of 98.7% and nitrogen removal rate (NRR) of 0.23 kg m-3d-1 were obtained at the influent NH4+ -N, SCOD and total nitrogen (TN) of 1000 ± 250 mg L-1, 1100 ± 200 mg L-1, and 1300 ± 75 mg L-1, respectively. Mass balance research demonstrated that Anammox contributed 69.3% to nitrogen removal and denitrification contributed 15.7%. A significant change in the Anammox community structure occurred (ca. Brocadia from 0.26% to 2.13%, ca. Kuenenia from 0.29% to 0.02%). This change is mainly attributed to different kinetic strategies (R-strategist of ca. Brocadia and K-strategist of ca. Kuenenia). Further study revealed the co-existence of functional microorganisms Nitrosomonas (3.0%), Cadidatus-Brocadia (2.13%), and Thauera (25.3%).

Continuous-flow combined process of nitritation and ANAMMOX for treatment of landfill leachate.

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 0.5kg/(m(3)·d) to 1.2kg/(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 1330mg/L and 2250mg/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.

Effect of carbon source type on intracellular stored polymers during endogenous denitritation (ED) treating landfill leachate.

Glycogen accumulating organisms (GAOs) capable of storing organic compounds as polyhydroxyalkanoate (PHA) have been used for endogenous denitritation (ED), but the effect of carbon sources type on nitrogen removal performance of GAOs treating landfill leachate is unclear. In this study, a successful ED system treating landfill leachate (COD/NH4(+)-N (C/N): 4) without external carbon source addition was applied. The mature leachate with C/N of 1 was used as the feeding base solution, with acetate, propionate, and glucose examined as the carbon sources, and their effects on yields and compositions of PHA produced by GAOs were determined and associated with nitrogen removal performance. In the case of sole carbon source, acetate was much easier to be stored than propionate and glucose, which led to a higher nitrogen removal efficiency. Glucose had the lowest amount of PHA storage and led to the lowest performance. In the case of composite carbon sources (two scenarios: acetate + propionate; acetate + propionate + glucose), GAOs stored sufficient PHA and exhibited similar nitrogen removal efficiencies. Moreover, type of carbon source influenced the compositions of PHA. The polyhydroxybutyrate (PHB) fraction in PHA was far more than polyhydroxyvalerate (PHV) in all tests. PHV was synthesized only when acetate existed in carbon source. The microbial diversity analysis revealed that Proteobacteria was the most abundant phylum. Among the 108 genera detected in this ED system, the genera responsible for denitritation were Thauera, Paracoccus, Ottowia and Comamonadaceae_unclassified, accounting for 46.21% of total bacteria. Especially, Paracoccus and Comamonadaceae_unclassified transformed the carbon source into PHA for denitritation, and carried out endogenous denitritation.