Effluent Total Nitrogen Research Articles

Combined heterotrophic and autotrophic system for advanced denitrification of municipal secondary effluent in full-scale plant and bacterial community analysis

Total nitrogen (TN) removal is the major technical challenge for wastewater treatment plants to meet the more stringent discharge standard. In this study, lab- (0.05 m3/d), pilot- (1000 m3/d) and full-scale (10,000 m3/d) combined heterotrophic and autotrophic denitrification reactors (HARs) were designed and operated to treat municipal secondary effluent. During the 110-day stable operation, the effluent TN was reduced below 2.5 mg/L without secondary pollution causing by the excessive addition of organics, close to Class IV of Environmental Quality Standards for Surface Water. The bacterial richness and diversity increased with the expansion of reactor scale. Denitrifying bacteria (DB) dominated in all reactors, however, Thiomonas (12.42%), Methylotenera (6.35%), Thiobacillus (20.62%), Methyloverstatilis (5.44%) and Thauera (8.21%) were the main genera in lab-, pilot- and full-scale reactors respectively. The denitrification efficiency temporarily deteriorated at the later stage, and redundancy analysis (RDA) indicated the obviously increased sulfate reducing bacteria (SRB) and sulfide were main contributors. Sludge supplement rapidly recovered the reactors performance in five days. This study suggests that HARs could be a promising technique for advanced denitrification of the municipal secondary effluent.

Highly efficient and low-energy nitrogen removal of sludge reduction liquid by coupling denitrification- partial nitrification-Anammox in an innovative auto-recycling integration device with different partitions

The denitrification (DN), partial nitrification (PN) and Anammox processes were coupled in an auto-recycling integration device to remove nitrogen from the supernatant of sludge reduction pretreatment. The nitrogen removal performance of the device and the effect of organic matter concentration on the nitrogen transformation were discussed. The results showed that DN, PN and Anammox are well coupled and total nitrogen (TN) removal rate reached 0.85 kg/(m3·d). The pre-DN process can achieve the removal of NO3−-N produced by the back-end PN-Anammox process without the need of reflux pump drive. When the influent NH4+-N concentration was approximately 400 mg/L, the effluent TN concentration was less than 20 mg/L. The fluctuation of organic matter led to changes of nitrogen transformation in the system, and the best ratio of influent CODbio/TN was 0.7–0.9. Nitrosomonas and Candidatus Brocadia played important roles in the nitrogen removal process as the main functional microorganisms of PN and Anammox, respectively.

Achieving stable two-stage mainstream partial-nitrification/anammox (PN/A) operation via intermittent aeration.

The mainstream anammox process has attracted extensive attention recently. Compared to single-stage partial-nitrification/anammox (PN/A) system, two-stage PN/A process was more advantageous for achieving mainstream anammox. However, complex control strategy in partial-nitrification reactor (N-SBR) might not be feasible in practical application. The aim of this study was to provide an easy operation strategy to achieve two-stage PN/A process. Firstly, intermittent aeration was investigated to achieve 100% conversion of ammonium to nitrite in N-SBR. The effluent nitrite concentrations increased from 19.96 to 38.62mg/L when intermittent aeration ratio (IAC) varied from 30min/30min-30min/15min. During 125d's operation of N-SBR, stable partial nitrification performance was obtained through intermittent aeration, without coupling with low dissolve oxygen or short sludge retention time. Then, raw municipal wastewater was directly mixed with N-SBR effluent to provide suitable feed to anaerobic sequencing batch reactor (A-SBR).When the mixture ratio between the raw wastewater and the N-SBR effluent was 2.5, the effluent ammonium and total inorganic nitrogen (TIN) was only 0.97 and 2.52mgN/L, respectively. Additionally, carbon-based pollutants was also removed in the proposed system without any pretreatment, which made the process easier to operate in practice.

Sludge alkaline fermentation enhanced anaerobic- multistage anaerobic/oxic (A-MAO) process to treat low C/N municipal wastewater: Nutrients removal and microbial metabolic characteristics

This study aimed to present a strategy that utilizing semi-continuous flow primary sludge fermentation liquor as carbon source for anaerobic- multistage anaerobic/oxic (A-MAO) process to treat low chemical oxygen demand (COD) and total nitrogen (TN) (C/N) ratio municipal wastewater. The results showed that adding fermentation liquor resulted in average TN and total phosphorus (TP) concentration in effluent decreased from 33 and 2.80 mg L−1 to 9.2 and 0.23 mg L−1, respectively, which met wastewater discharge standard. High-throughput sequencing results indicated that bacterial richness increased and diversity decreased with fermentation liquor adding, and the dominant genera varied from Methylophilaceae and Methylotenera to unclassified_f_Rhodocyclaceae, noran k_f__env.OPS_17, and Azospira. Meanwhile, the abundance of metabolism and organismal systems in A-MAO process rose from 48.42% and 0.74% to 49.52% and 0.78%. The improvement of nitrogen and phosphorus removal with fermentation adding was based on the increment of enzyme coding genes in nitrogen and phosphorus pathway.

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 ± 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 ± 6014 mg/L) were introduced to an anoxic reactor for integrated fermentation and denitrification (IFD-SBR). Finally, ammonia (101.4 ± 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.

Effect of hydraulic retention time on pollutants removal from real ship sewage treatment via a pilot-scale air-lift multilevel circulation membrane bioreactor

Developing a real ship sewage treatment system that not only satisfies the requirement of small space onboard but also meets the latest emission standards of International Maritime Organization (IMO) is still a challenging task for ship industry. To overcome these problems, in this study, a novel pilot-scale air-lift multilevel circulation membrane bioreactor (AMCMBR) was used to explore the effect of hydraulic retention time (HRT) on effluent chemical oxygen demand (COD) and total nitrogen (TN) while treating real ship sewage. Results indicated that the satisfactory removal efficiencies of COD and TN was achieved in the former stages (Re(COD) = 91.57% and 87.82%; Re(TN) = 77.17% and 81.19%). When HRT decreased to 4 h, the removal efficiencies of COD and TN was 86.93% and 70.49% respectively, which still met the strict IMO discharge standards. This mainly because the biofilm-assistant membrane filtration lead to the increase of physical removal rate. The high ratio of mixed liquor volatile suspended solids (MLVSS)/mixed liquid suspended solids (MLSS) (i.e. 0.75) indicated a high biomass content in the attached sludge and resulted into perfect pollutants removal effort. The compliance rate of COD and TN was 100% and 89%, respectively, which indicated stable operation of the pilot-scale AMCMBR throughout the whole experiment. Fluorescence in situ Hybridization (FISH) analysis revealed that the abundance of β-Proteobacteria was a key microbial reason for TN removal. In addition, wavelet neural network (WNN) model was proved to be suitable to simulate and predict the COD and TN removal. These conclusions indicated that the pilot-scale AMCMBR technology is an effective way for real ship sewage treatment.

Effective nitrogen removal in a two-stage partial nitritation-anammox reactor treating municipal wastewater – Piloting PN-MBBR/AMX-IFAS configuration

A novel partial nitritation-anammox (PNA) reactor configuration was piloted for 250 days. Primary effluent from full-scale municipal wastewater treatment plant was treated in a two-stage biofilm system incorporating innovative process control for cold partial nitritation. Partial nitritation was combined with carbon removal in a moving bed biofilm reactor (MBBR) to achieve high-rate treatment and nitritation was obtained with dissolved oxygen to total ammonium nitrogen (DO/TAN) ratio control and free ammonia (FA) for inhibition of nitratation. Effluent from MBBR was directed to an integrated fixed-film activated sludge (IFAS) reactor where nitrogen was removed via anammox. MBBR achieved partial nitritation at 2.0 ± 0.3 g-N m−2 d−1 and nitrogen removal in the IFAS reactor reached 0.45 ± 0.1 g-N m−2 d−1 (55 g-N m−3 d−1). The process performed well at 19 ± 3 °C with an average effluent total inorganic nitrogen (TIN) concentration of 11 ± 4 mg L−1.

Effect of pH on Pollutants Removal of Ship Sewage Treatment in an Innovative Aerobic-Anaerobic Micro-Sludge MBR System

The implementation of the latest International Maritime Organization (IMO) emission standard has raised stringent requirements for marine domestic sewage discharge. In this study, a novel aerobic-anaerobic micro-sludge membrane bioreactor (O-AMSMBR) was used to analyze the effect of pH variation on the effluent chemical oxygen demand (COD) and total nitrogen (TN) for marine domestic sewage. Results showed that the novel MBR achieved better COD and TN removal efficiency (Ravg(COD) = 87.77% and Ravg(TN) = 91.01%). In acid environment (pH = 5), anaerobic micro-sludge MBR technology can enhance the pollutants removal efficiency under pH shock. These two findings indicated that anaerobic micro-sludge membrane bioreactor (MBR) technology has great potential in acidity or alkalinity wastewater treatment. The activity of six different enzymes was analyzed in this study. The results showed that nitrate reductase and nitrite reductase can serve as special indicating factors for anaerobic micro-sludge MBR technology on domestic ship sewage. Moreover, wavelet neural network (WNN) and back-propagation neural network (BPNN) were used to simulate the effect of pH on reactor performance. The order of relative importance inculcated that pH is the key factor to consider for biodegradation of organic matter in O-AMSMBR system. The outcomes of this study suggest that post-anaerobic integrated with micro-sludge methods can play a vital role in keeping good pollutant degradation in ship wastewater treatment under pH shift.

Advanced nitrogen removal without addition of external carbon source in an anaerobic/aerobic/anoxic sequencing batch reactor.

Advanced nitrogen removal without the addition of external carbon source is challenging in the conventional biological nitrogen removal processes. This study presented a novel anaerobic/aerobic/anoxic sequencing batch reactor (A/O/A SBR) based on endogenous nitrate (NO3--N) respiration to enhance nitrogen removal. The mean effluent total nitrogen (TN) in the A/O/A SBR could be reduced to as low as 3.5mg/L, when the average influent TN and chemical oxygen demand (COD) were 52.7 and 235.4mg/L, respectively. This advanced nitrogen removal was attributed to the post-denitrification, since 82.7% of TN removal was achieved in the post-anoxic stage. The post-denitrification rate with nitrite (NO2--N, 0.59mg NO2--N/gMLVSS/h) was higher than that with NO3--N (0.35mg NO3--N/gMLVSS/h). Therefore, the post-anoxic time could be further optimized by achieving denitrification via NO2--N. The A/O/A SBR has good potential in achieving advanced nitrogen removal, especially in nitrogen-sensitive rural areas.

Biological denitrification in an anoxic sequencing batch biofilm reactor: Performance evaluation, nitrous oxide emission and microbial community

The present study evaluated the performance of biological denitrification in an anoxic sequencing batch biofilm reactor (ASBBR) and its nitrous oxide (N2O) emission. After 90 days operation, the effluent chemical oxygen demand and total nitrogen removal efficiencies high of 94.8% and 95.0%, respectively. Both polysaccharides and protein contents were reduced in bound EPS (TB-EPS) and loosely bound EPS (LB-EPS) after biofilm formation. According to typical cycle, N2O release rate was related to the free nitrous acid (FNA) concentration with the maximum value of 3.88 μg/min and total conversion rate of 1.27%. Two components were identified from EEM-PARAFAC model in soluble microbial products (SMP). Protein-like substances for component 1 changed significantly in denitrification process, whereas humic-like and fulvic acid-like substances for component 2 remained relatively stable. High-throughput sequencing results showed that Lysobacter, Tolumonas and Thauera were the dominant genera, indicating the co-existence of autotrophic and heterotrophic denitrifiers in ASBBR.

Comparison of nitrate-removal efficiency and bacterial properties using PCL and PHBV polymers as a carbon source to treat aquaculture water

Nitrate (NO3−) accumulation in recirculating aquaculture systems (RASs) with high stocking densities presents a problem for reared animals and the environment. The use of a biodegradable polymer as organic carbon for heterotrophic denitrification exhibits good performance for NO3− removal from wastewater. A comparison of NO3−–N removal efficiency and bacterial properties using polycaprolactone (PCL) and poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) as carbon sources to treat aquaculture water was conducted for a 102-day period. The results indicated that the NO3−–N removal rates of 0.27 ± 0.07 and 0.19 ± 0.05 g/L per day, respectively, could be achieved with influent concentrations ranging from 81.1 to 132.75 mg/L and a flow rate of 1 L/h. The removal of NO3−–N versus consumed PCL (1:1 w/w) was significantly higher than that versus consumed PHBV (0.3:1 w/w) (P < 0.05). The concentrations of effluent nitrite-nitrogen and total ammonium nitrogen were maintained at an acceptable level. The bacterial community structures between the two types of reactors varied significantly. Acidovorax and Denitratisoma were the top two genera of the bacterial community in the biofilm in the PCL beads with a dominance of 26.83% and 6.67%, respectively. In the PHBV beads, Acidovorax at 17.95% and Bdellovibrio at 6.37% were the top two genera. The PCL-denitrification reactor developed in this study showed better potential than the PHBV-denitrification reactor in removing NO3− from aquaculture water.

New insights into pollutants removal, toxicity reduction and microbial profiles in a lab-scale IC-A/O-membrane reactor system for paper wastewater reclamation

In this study, an internal circulation-anoxic/aerobic (IC-A/O) process followed by ultrafiltration (UF) and reverse osmosis (RO) system was applied for paper wastewater reclamation. The IC-AO system presented a stable and efficient performance, achieving high removal of chemical oxygen demand (COD), total organic carbon (TOC) and total nitrogen (TN) with methane production rate of 132.8 mL/d. Acute toxicity to Daphnia magna (D. magna) was reduced significantly (83.2%) and the spearman's rank correlation analysis indicated that the toxicity of effluents from each reactor were positively correlated with COD and TOC. Hexadecanoic acid, octadecanoic acid and benzophenone were the main toxic contributors for biological effluent. Microbial community revealed that Anaerolinea was significantly related with organic pollutants. The UF-RO system further removed pollutants and toxicity with the final effluent COD, TOC, ammonium nitrogen (NH4+-N) and TN of 32.6, 18.8, 0.3 and 9.2 mg/L, respectively, which proved that it was feasible for paper wastewater reuse. This study presented an efficient, practical and environmentally competitive system, and paved a foundation for the treatment and reuse of paper wastewater.

Pre-precipitation of Sewage-SNAD Granular Sludge Process Test

Using artificial water, the simultaneous partial nitrification, ANAMMOX (anaerobic ammonium oxidation), and denitrification (SNAD) granular sludge process was started in a sequencing batch reactor (SBR), and then the ammonia concentration in the influent was reduced gradually. After stable operation for a period of time under the low ammonia concentration, sewage treated by a pre-precipitation process was used as a substrate to investigate the performance and stability of the SNAD granular sludge process. The results show that after the SNAD process was successfully started, the ammonia removal rate was greater than 98%, and total the nitrogen removal rate was about 89%. As the influent ammonia concentration decreased, the nitride-oxidizing bacteria (NOB) activity was increased and the total nitrogen removal rate gradually decreased to 75%. When the pre-precipitated domestic sewage (NH4+-N 52-63 mg·L-1, COD 99-123 mg·L-1) was used as the inflow, the average effluent removal rate of the total effluent was 73.2%, the effluent COD concentration was below 35 mg·L-1, and the maximum effluent ammonia nitrogen and total nitrogen concentration were 0.7 mg·L-1 and 12.8 mg·L-1. The ammonia and total nitrogen concentration in the continuous 30 day effluent reached the 1A level of the integrated discharge standard of water pollutants for municipal wastewater treatment, indicating that the removal of organics and nitrogen from domestic sewage was achieved efficiently and synchronously.

Analysis of Causal Relationships for Nutrient Removal of Activated Sludge Process Based on Structural Equation Modeling Approaches

The removal process of activated sludge in sewage treatment plants is very nonlinear, and removal performance has a complex causal relationship depending on environmental factors, influent load, and operating factors. In this study, how causal relationships are expressed in collected data was identified by structural equation modeling. First, path modeling was attempted as a preliminary step in structural equation model (SEM) construction and, as a result, the nutrient-removal mechanism could not be sufficiently represented as a direct causal relationship between measured variables. However, as a result of the deduced SEMs for effluent total nitrogen (T-N) and total phosphorus (T–P) concentrations, accompanied by exploratory factor analysis to extract latent variables, a causal network was formed that describes the direct or indirect effect of the latent factors and measured variables. Hereby, this study suggests that it is possible to construct an SEM explaining the nutrient-removal mechanism of the activated-sludge process with latent variables. Moreover, nonlinear features embedded in the mechanism could be represented by SEM, which is a model based on linearity, by including causal relations and variables that were not derived by path analysis. This attempt to model the direct and indirect causalities of the process could enhance the understanding of the process, and help decision making such as changing the driving conditions that would be required.

Rural domestic wastewater treatment in constructed ditch wetlands: Effects of influent flow ratio distribution

Constructed wetlands (CWs) are a sustainable technology used to remove pollutants from wastewater; however, their low total nitrogen (TN) removal efficiency remains a pressing issue. Constructed ditch wetland systems (CDWs) differ from CWs in being narrow and shallow. This study observed the performance of CDWs throughout their operational period and investigated the causes of their low TN removal rates. To enhance TN removal, we propose an approach where the inflow is divided into two parts with different influent flow ratios. Four systems were trialed in parallel to examine the effects of the influent flow ratio distribution on organics removal and nitrogen transformation. A flow ratio of 1:2 was considered optimal following comparison of the four experimental CDWs. The removal efficiencies of chemical oxygen demand (COD) and TN in the control CDW (influent flow ratio 3:0) during winter were 91.15% and 25.87%, respectively, whereas the removal efficiencies of the best-performing CDW (influent flow ratio 1:2) were 91.59% and 50.40%, respectively. Based on an analysis of nitrogen transformation, a model of effluent TN and nitrate nitrogen concentration in the four CDWs was constructed.

Wastewater nitrogen budgets can be resolved by complementary functional gene and physicochemical methods

A nitrogen budget for wastewater stabilisation ponds in tropical northern Australia indicated a deficit between influent and effluent Total Nitrogen of ≈46.5%. Stable nitrogen isotope ratios in pond waters and gas emission measurements showed that the deficit was a result of loss of mainly dinitrogen gas while emissions of nitrous oxide and ammonia were minor. We explored spatial and temporal patterns of nitrogen cycling across the pond system by analysing diversity and function of denitrification (nosZ) and Anammox (hzsA) genes known to be responsible for nitrogen gas emission. The relative gene abundance and activity supported the physicochemical evidence that the budgetary nitrogen deficit was largely due to dinitrogen gas emission. Contrary to expectation, most of the dinitrogen gas emissions appeared to occur after the first facultative pond despite nosZ genes being abundant and active. This suggests that other barriers to effective denitrification existed in the facultative pond. The dominant abundance and activity of hzsA genes in the final maturation pond indicated that dinitrogen gas emissions from this pond were likely associated with the Anammox process.

Sources of anammox granular sludge and their sustainability in treating low-strength wastewater

Anaerobic ammonium oxidation (anammox) has been widely applied in the treatment of high-strength nitrogen wastewaters. However, few engineering practices were reported to treat low-strength nitrogen wastewaters. In this study, three types of anammox granular sludge (GS) were separately collected from the expanded granular sludge bed (EGSB) reactors treating nitrogen wastewaters at high (H-), moderate (M-) and low (L-) nitrogen loading rates (NLRs), and employed for the treatment of low-strength nitrogen wastewater in sequencing batch advanced nitrogen removal (ANR) systems. The ANR system with M-GS (namely M-ANR system) was most useful. At the initial biomass concentration of 2.43 g-VSS·L−1, cycle length of 8 h and influent total nitrogen (TN) concentration of less than 15 mg·L−1, the performance data were as follows: effluent TN of less than 1 mg·L−1, TN removal efficiency of more than 92.8%, the nitrogen removal rate (NRR) of 0.039 kg-N·m−3·d−1. The efficient performance lasted as long as 46 cycles, indicating the sustainability of the M-ANR system. The advanced microscopic analysis and metagenomic analysis were applied to reveal the successful but non-permanent treatment by the M-ANR system. The long-time lag between biomass decay and sludge activity decay provided a window period for the good performance of M-ANR system. However, the weak support of oligotrophic habitat for anaerobic ammonium oxidizing bacteria community was doomed to the degradation of anammox GS, resulting in gradual loss of their activities. A periodic addition of fresh M-GS or a periodic rejuvenation cultivation in the eutrophic habitat is necessary to achieve a permanent performance.

Nitrogen removal from coke making wastewater through a pre-denitrification activated sludge process

Under the Industrial Emissions Directive (IED), coke production wastewater must be treated to produce an effluent characterised by a total nitrogen (TN) <50 mg/L. An anoxic-aerobic activated sludge pilot-plant (1 m3) fed with coke production wastewater was used to investigate the optimal operational requirements to achieve such an effluent. The loading rates applied to the pilot-plant varied between 0.198–0.418 kg COD/m3.day and 0.029–0.081 kg TN/m3.day, respectively. The ammonia (NH4+-N) removals were maintained at 96%, after alkalinity addition. Under all conditions, phenol and SCN− remained stable at 96% and 100%, respectively with both being utilised as carbon sources during denitrification. The obtained results showed that influent soluble chemical oxygen demand (sCOD) to TN ratio of should be maintained at >5.7 to produce an effluent TN <50 mg/L. Furthermore, nitrite accumulation was observed under all conditions indicating a disturbance to the denitrification pathway. Overall, the anoxic-aerobic activated sludge process was shown to be a robust and reliable technology to treat coke making wastewater and achieve the IED requirements. Nevertheless, the influent to the anoxic tank should be monitored to ensure a sCOD:TN ratio >5.7 or, alternately, the addition of an external carbon source should be considered.

Fe(II)-dosed ceramic membrane bioreactor for wastewater treatment: Nutrient removal, microbial community and membrane fouling analysis

Ferrous dosing is used to reduce phosphorus concentration and alleviate polymeric membrane fouling in membrane bioreactor (MBR). However, limited studies have been conducted to investigate the impacts of ferrous dosing on ceramic membrane fouling, nutrient removal efficiency and microbial community. Accordingly, the aim of this study was to investigate the effect of intermittent ferrous dosing with Fe/P molar ratios of 2 and 1 (with a dosing frequency of every two days) on the overall nutrient removal, functional microbial changes and membrane fouling in ceramic membrane bioreactors (CMBR) in treatment of wastewater. TP concentration of 10 mg/L in influent decreased to 1.94 ± 0.62 mg/L (control), 0.38 ± 0.22 mg/L (Fe/P = 1) and 0.31 ± 0.18 mg/L (Fe/P = 2) in the effluent, respectively. Meanwhile, the effluent total nitrogen (TN) concentrations with Fe/P = 1 treatment (6.80 ± 2.02 mg/L) and Fe/P = 2 treatment (5.12 ± 2.28 mg/L) were lower than that of the control (7.72 ± 2.36 mg/L). Compared to Fe/P = 1, the TN removal performance was better for Fe/P = 2 mainly due to the increased abundance of denitrifying bacteria (Zoogloea and Acinetobacter). In addition, excess iron dose might have toxic effects on bacterial physiology, however the Fe concentrations that cause cell damage vary for different bacteria. The relative abundance of Zoogloea (aerobic denitrifying bacteria) continuously increased with ferrous addition (Fe/P = 2), while other bacteria including Dechloromonas, Hyphomicrobium and Thauera (anoxic denitrifying bacteria), Nitrospira (nitrifying bacteria) and Candidatus Accumulibacter (phosphorus accumulating organism) decreased sharply. Furthermore, membrane fouling was effectively moderated by ferrous dosing and Fe/P = 1 treatment showed improved membrane fouling mitigation than Fe/P = 2. Overall, intermittent ferrous addition in CMBR with Fe/P molar ratio of 1 was beneficial to the removal of nutrients (TP, TN and organics), enhanced succession of microbial community and membrane fouling mitigation.

Enhanced nitrogen removal and in situ microbial community in a two‐step feed oxic/anoxic/oxic‐membrane bioreactor (O/A/O‐MBR) process

AbstractBACKGROUNDThe carbon in raw sewage can be reclaimed to reduce nitrate for the advanced denitrification in municipal wastewater treatment plants. A novel two‐step feed oxic/anoxic/oxic‐membrane bioreactor (O/A/O‐MBR) process was proposed to improve carbon‐use efficiency.RESULTSThe flow distribution ratio (FDR), aeration mode and hydraulic loading were optimized to minimize the effluent total nitrogen (TN) concentration. When the FDR was 1:1, the intermittent aeration mode was 4 min air‐on/6 min air‐off and the influent flow was 5 L h−1, the nitrate removal efficiency in the post‐denitrification tank rose to 87.0% and the effluent TN concentration decreased below 15.0 mg L−1. The intermittent aeration strategy in the post oxic‐membrane tank effectively promoted TN loss. The 15N‐DNA based stable isotope probing experiment illustrated that Proteobacteria (35.09%), Actinobacteria (20.56%) and Chloroflexi (16.67%) dominated the intermittently aerated biofilm, and Nitrospira (9.06%) was the major nitrite oxidizing bacteria rather than Nitrobacter, representing a dominant simultaneous nitrification and denitrification pathway for nitrogen removal.CONCLUSIONThe integration of autotrophic nitrifying bacteria and heterotrophic denitrifying bacteria enhances the terminal TN removal under intermittent aeration mode. The two‐step feed O/A/O‐MBR process has the potential to solve carbon limitation in sewage wastewater treatment. © 2018 Society of Chemical Industry