Nutrient removal efficacy and microbial dynamics in constructed wetlands using Fe(III)-mineral substrates for low carbon-nitrogen ratio sewage treatment.

This study evaluated the roles of two common sources of Fe(III)-minerals-volcanic rock (VR) and synthetic banded iron formations from waste iron tailings (BIF-W)-in vertical flow-constructed wetlands (VFCWs). The evaluation was conducted in the absence of critical environmental factors, including Fe(II), Fe(III), and soil organic matter (SOM), using metagenomic analysis and integrated correlation networks to predict nitrogen removal pathways. Our findings revealed that Fe(III)-minerals enhanced metabolic activities and cellular processes related to carbohydrate decomposition, thereby increasing the average COD removal rates by 10.7% for VR and 5.90% for BIF-W. Notably, VR improved nitrogen removal by 1.70% and 5.40% compared to BIF-W and the control, respectively. Fe(III)-mineral amendment in bioreactors also improved the retention of denitrification and nitrification bacteria (phylum Proteobacteria) and anammox bacteria (phylum Planctomycetes), with increases of 3.60% and 3.20% using VR compared to BIF-W. Metagenomic functional prediction indicated that the nitrogen removal mechanisms in VFCWs with low C/N ratios involve simultaneous partial nitrification, ANAMMOX, and denitrification (SNAD). Network-based analyses and correlation pathways further suggest that the advantages of Fe(III)-minerals are manifested in the enhancement of denitrification microorganisms. Microbial communities may be activated by the functional dissolution of Fe(III)-minerals, which improves the stability of SOM or the conversion of Fe(III)/Fe(II). This study provides new insights into the functional roles of Fe(III)-minerals in VFCWs at the microbial community level, and provides a foundation for developing Fe-based SNAD enhancement technologies.

Migration of microorganisms between nitrification-denitrification flocs, anammox biofilms and blank carriers during mainstream anammox start-up.

To solve the shortage of inoculum, the feasibility of establishing simultaneous partial nitrification, anammox, and denitrification (SNAD) reactor through inoculating nitrification-denitrification sludge, anammox biofilm and blank carriers was investigated. Advanced nitrogen removal efficiency of 91.2 ± 3.6 % was achieved. Bacteria related to nitrogen removal and fermentation were enriched in anammox biofilm, blank carriers and flocs, and the abundance of dominant anaerobic ammonia oxidizing bacteria (AnAOB), Candidatus Brocadia, reached 3.4 %, 0.5 % and 0.3 %, respectively. Candidatus Competibacter and Calorithrix became the dominant denitrifying bacteria (DNB) and fermentative bacteria (FB), respectively. The SNAD system was successfully established, and new mature biofilms formed in blank carriers, which could provide inoculum for other anammox processes. Partial nitrification, partial denitrification and aerobic_chemoheterotrophy were existed and facilitated AnAOB enrichment. Microbial correlation networks revealed the cooperation between DNB, FB and AnAOB that promoted nitrogen removal. Overall, the SNAD process was started up through inoculating more accessible inoculum.

Increasing carbon to nitrogen ratio promoted anaerobic ammonia-oxidizing bacterial enrichment and advanced nitrogen removal in mainstream anammox system.

The effects of fluctuating organic carbon to nitrogen (C/N) ratios on mainstream simultaneous partial nitrification, anammox, and denitrification (SNAD) process were studied over 376-day period. The nitrogen removal efficiency decreased from 85.0 ± 6.6 % to 75.8 ± 2.8 % as C/N ratio decreased (3.4 â†’ 1.7), but increased to 82.0 ± 1.9 % when C/N ratio raised to 2.9 and to 78.4 ± 3.0 % when C/N ratio decreased again (2.9 â†’ 2.1), indicating that high C/N ratios promoted nitrogen removal. As C/N ratio raised (1.7 â†’ 2.9), anaerobic ammonia-oxidizing bacteria (AnAOB) abundance increased from 1.3 × 109 to 2.0 × 109 copies/L, which explained the improved nitrogen removal. With an elevated C/N ratio, partial nitrification and endogenous partial denitrification reactions were enhanced, providing more nitrite for AnAOB. Additionally, the aerobic_chemoheterotrophy function and particle sizes increased, forming more stable anoxic microenvironment for AnAOB. Overall, increasing C/N ratio promoted the stability of mainstream SNAD.

Nitrogen removal from pharmaceutical wastewater using simultaneous nitrification-denitrification coupled with sulfur denitrification in full-scale system.

Fermentation pharmaceutical wastewater (FPW) containing excessive ammonium and low chemical oxygen demand (COD)/nitrogen ratio (C/N ratio) brings serious environmental risks. The stepwise nitrogen removal was achieved in a full-scale anaerobic/aerobic/anoxic treatment system with well-constructed consortia, that enables simultaneous partial nitrification-denitrification coupled with sulfur autotrophic denitrification (SPND-SAD) (∼99 % (NH4+-N) and ∼98 % (TN) removals) at the rate of 0.8-1.2 kg-N/m3/d. Inoculating simultaneous nitrification-denitrification (SND) consortia in O1 tank decreased the consumed ΔCOD and ΔCOD/ΔTN of A1 + O1 tank, resulting in the occurrence of short-cut SND at low C/N ratio. In SAD process (A2 tank), bio-generated polysulfides reacted with HS- to rearrange into shorter polysulfides, enhancing sulfur bioavailability and promoting synergistic SAD removal. PICRUSt2 functional prediction indicated that bioaugmentation increased genes related to Nitrogen/Sulfur/Carbohydrate/Xenobiotics metabolism. Key functional gene analysis highlighted the enrichment of nirS and soxB critical for SPND-SAD system. This work provides new insights into the application of bioaugmentation for FPW treatment.

Pilot-scale study of step-feed anaerobic coupled four-stage micro-oxygen gradient aeration process for treating digested swine wastewater with low carbon/nitrogen ratios.

This study developed an innovative step-feed anaerobic coupled four-stage micro-oxygen gradient aeration process to treat digested swine wastewater. An anaerobic zone was used for prepositive denitrification; four micro-oxygen reactors (zones O1-O4) were used for simultaneous partial nitrification and denitrification through low-dissolved oxygen gradient control, step-feed, and swine wastewater-digested swine wastewater distribution. The nitrogen-removal efficiency was satisfactory (93 ± 3 %; effluent total nitrogen, 53 ± 19 mg/L). Mass balance coupled with quantitative polymerase chain reaction analysis revealed that simultaneous partial nitrification and denitrification was achieved in four micro-oxygen zones. Zones O1 were the major denitrification zones for nitrogen removal; nitrification was primary happened in zones O2 and O3. Correlation analysis confirmed that low-dissolved oxygen gradient control was the key to achieving efficient nitrogen removal. This study provides a low oxygen energy consumption method to treat digested swine wastewater with a low carbon/nitrogen ratio (<3).

[N2O Emission from the Processes of Wastewater Treatment: Mechanisms and Control Strategies].

As a direct carbon emission source, the amount of nitrous oxide (N2, which is actually caused by AOB denitrification. To control the N2O emission during biological N-removal, complete HND and NO2- accumulation for AOB denitrification should be avoided to a large extent. For this purpose, DO in aerobic tanks should be controlled at a normal level (approximately 2 mg·L-1), and solid retention time (SRT) should be extended, up to 20 d, which would avoid accumulating N2O for AOB denitrification. Additionally, external carbon should be supplemented in time to promote HDN approaching the end, N2. This review summarizes the mechanisms of all the mentioned N2O emission pathways and discusses the control strategies of N2O emission according to the associated mechanisms.

Enhanced aerobic granular sludge by static magnetic field to treat saline wastewater via simultaneous partial nitrification and denitrification (SPND) process.

Saline wastewater poses a threat to biological nitrogen removal. This study investigated whether and how static magnetic field (SMF) can improve the salt-tolerance of aerobic granular sludge (AGS) in two simultaneous partial nitrification and denitrification (SPND) reactors. Results confirmed that the SMF improved the mean size and settleability of granules, stimulated secretion of extracellular polymeric substances with high protein content, in turn enhancing the aerobic granulation. Although high salt stress inhibited functional microorganisms, the SMF maintained better SPND performance with average COD removal, TN removal and nitrite accumulation ratio finally recovering to 100%, 72.9% and 91.1% respectively. High throughput sequencing revealed that functional bacteria evolved from Paracoccus to halotolerant genera Xanthomarina, Thauera, Pseudofulvimonas and Azoarcus with stepwise increasing salinity. The enhanced salt-tolerance may be because the SMF promoted the activity of these halotolerant bacteria. Therefore, this study proposes an economic, effective and environmental biotechnology for saline wastewater treatment.

Enhanced simultaneous partial nitrification and denitrification performance of aerobic granular sludge via tapered aeration in sequencing batch reactor for treating low strength and low COD/TN ratio municipal wastewater.

The aerobic granular sludge simultaneous partial nitrification, denitrification and phosphorus removal (AGS-SPNDPR) process was carried out via tapered aeration in sequencing batch reactor (SBR) for treating low strength and low COD/TN ratio municipal wastewater. The results showed that aerobic granular sludge was successfully cultivated with good sedimentation performance when treating the municipal wastewater. Meanwhile, the median granule size increased to 270 (R1) and 257 (R2) µm on day 80. The excellent removal performance of COD (92%) and NH4+-N (95%) were achieved under different aeration modes, while the higher TN removal efficiency (76%) was achieved by tapered aeration. The accumulation of NO2--N in R2 indicated that the tapered aeration was beneficial to achieve simultaneously partial nitrification and denitrification. Meanwhile, the high-efficiency phosphorus (95%) removal was realized via additional carbon source, and SPNDPR process was formed under tapered aeration. The bacterial community analysis indicated denitrifying glycogen-accumulating organisms (DGAOs) Candidatus_Competibacter and ammonia-oxidizing bacteria (AOB) Nitrosomonas were more effectively enriched via tapered aeration, while phosphorus-accumulating organisms (PAOs) Candidatus_Accumulibacter were effectively enriched under additional organic carbon. AOB, denitrifying bacteria and PAOs were simultaneously enriched by tapered aeration and additional carbon source, which was beneficial to nutrients removal. This study might be conducive to the application of AGS-SPNDPR system for treating low strength and low COD/TN ratio municipal wastewater under tapered aeration.

Rapidly achieving and optimizing simultaneous partial nitrification denitrification and anammox integrated process by hydroxylamine addition for advanced nitrogen removal from domestic wastewater.

The achievement and stable maintenance of partial nitrification and partial anammox process for municipal sewage is a challenging research topic at present. In this study, a novel strategy of hydroxylamine (NH2OH) addition under low DO condition was adopted for rapidly achieving simultaneous partial nitrification denitrification and anammox process (SPNDA) to deal with domestic wastewater, the nitrite accumulation ratio (NAR) increased from 1% to 82% in the first 4 days. After the addition of NH2OH was stopped, the PN effect of SPNDA process remained relatively stable within 100 days. During the stable operation period with aerobic HRT of 5 h, the nitrogen removal efficiency was 87.9 ± 4.2%. Moreover, the abundance of denitrifying bacteria and Candidatus Brocadia increased from 1.79% and 0.062% to 22.49% and 0.38% respectively, which promoted nitrogen removal effect. Overall, this study provided a quickly way for achieving the cost-effective SPNDA process to enhance nitrogen removal with NH2OH addition.

Optimization of nitrogen and carbon removal with simultaneous partial nitrification, anammox and denitrification in membrane bioreactor.

In this study, a membrane bioreactor (MBR) was used to achieve both nitrogen and carbon removal by a simultaneous partial nitrification, anammox and denitrification (SNAD) process. During the entire experiment, the intermittent aeration (non-aerobic time : aeration time, min min-1) cycle was controlled by a time-controlled switch, and the aeration rate was controlled by a gas flowmeter, and the optimal operating parameters as determined by response surface methodology (RSM) were a C/N value of 1.16, a DO value of 0.84 mg l-1 and an aerobic time (T ae) of 15.75 min. Under these conditions, the SNAD process achieved efficient and stable nitrogen and carbon removal; the total inorganic nitrogen removal efficiency and chemical oxygen demand removal efficiency were 92.31% and 95.67%, respectively. With the formation of granular sludge, the membrane fouling rate decreased significantly from 35.0 Pa h-1 at SNAD start-up to 19.9 Pa h-1 during stable operation. Fluorescence in situ hybrid analyses confirmed the structural characteristics and the relative ratio of aerobic ammonia-oxidizing bacteria, anaerobic ammonia-oxidizing bacteria and denitrifying bacteria in the SNAD system.

[Bacterial Community Shifts and Nitrogen Removal Characteristics for a SNAD Process Treating Anaerobic Digester Liquor of Swine Wastewater (ADLSW) in a Continuous-Flow Biofilm Reactor (CFBR)].

To realize a simultaneous partial nitrification, ANAMMOX (anaerobic ammonium oxidation), and denitrification (SNAD) process treating anaerobic digester liquor of swine wastewater (ADLSW) in a continuous-flow biofilm reactor (CFBR), we first gradually increased the influent ammonium (NH4+-N) concentration, and then enhanced the ADLSW ratio in the influent during operation; dissolved oxygen (DO) was controlled at (0.4±0.1) mg·L-1 by adjusting the air flow rate, and the temperature was kept at (30±1)℃. Meanwhile, high-throughput sequencing and quantitative PCR (polymerase chain reaction) techniques were used to analyze the bacterial community shifts and the amount of dominant nitrogen removal bacteria. The results demonstrated that a successful start-up of the SNAD process was accomplished in 150 d, and replacement of the actual biogas slurry was completed in 298 d. The effluent (NO3--N+NO2--N)/ΔNH4+-N value was less than 0.11, and the average removal rates of NH4+-N and TN (total nitrogen) increased to 63.26% and 55.71%, respectively. Moreover, high-throughput sequencing results demonstrated that the dominant microbial populations at phylum level were Chloroflexi (with a relative abundance of 50.78%), Proteobacteria (13.34%), and Planctomycetes (9.26%). The relative abundance of Nitrosomonas increased from 1.55% to 1.98%. In addition, the relative abundance of Candidatus_Brocadia and Candidatus_Kuenenia increased from 0.01% and (<0.01%) to 4.66% and 4.18%, respectively, and the relative abundance of Denitratisoma increased from (<0.01%) to 2.06%. Meanwhile, qPCR analysis showed that the amounts of ammonia-oxidizing bacteria, ANAMMOX, and denitrifying bacteria increased significantly compared with the inoculated sludge. An efficient and stable nitrogen removal rate can be achieved, and the follow-up processing cost can be reduced, by application of the SNAD treatment process for ADLSW.

Enhanced nutrient removal of simultaneous partial nitrification, denitrification and phosphorus removal (SPNDPR) in a single-stage anaerobic/micro-aerobic sequencing batch reactor for treating real sewage with low carbon/nitrogen.

The feasibility of simultaneous partial nitrification, denitrification and phosphorus removal (SPNDPR) process was investigated in a single-stage anaerobic/micro-aerobic sequencing batch reactor for treating real sewage. Partial nitrification was maintained with average nitrite accumulation ratio of 90.3% during 266 days' operation. Removal efficiencies for NH4+-N (96.3%), total inorganic nitrogen (81.4%), and phosphorus (91.0%) were stably obtained when treated real sewage with low carbon/nitrogen (3.4), with simultaneous partial nitrification and denitrification efficiency of 73.1%. The mechanism analysis revealed that denitrifying glycogen-accumulating organisms (DGAOs) and denitrifying polyphosphate-accumulating organisms (DPAOs) played the main roles in N-removal and P-removal, respectively. Nitrite pathway and optimized use of the organic carbon available in the sewage were keys for the successful performance. Further microbial community illustrating that DGAOs Candidatus_Competibacter, DPAOs Dechloromonas, and ammonia-oxidizing bacteria Nitrosomonadaceae were main functional groups. Notably, sludge granulation was formed under long-term synchronous low dissolved oxygen and low sludge loading conditions, avoiding sludge bulking.

[Effects of Intermittent Starvation on the Operation of the SNAD Process].

We report on and discuss the effects of intermittent starvation on the operation of the simultaneous partial nitrification, ANAMMOX, and denitrification (SNAD) process. The SNAD process was carried out in a sequencing batch reactor (SBR) at room temperature (22℃±3℃), and the intermittent starvation was achieved by periodically extending the hydraulic retention time (HRT) of the system. The results showed that after the operation of intermittent starvation, the NO3--N concentration at the end of the aerobic phase decreased to 8.72 mg·L-1 and the NO2- accumulation percentage reached 83.18%, which indicated that the nitrite oxidizing bacteria (NOB) activity was effectively inhibited and that the nitritation performance improved. After the operation of the intermittent starvation, the ratio of NO2- to NH4+-N at the end of the aerobic phase was adjusted to provide more suitable substrates for the subsequent ANAMMOX process, such that the concentration of NH4+-N in the effluent fell below 1.0 mg·L-1. At the same time, due to the decrease of the NO3- concentration, the total N removal rate reached 92.07%, which indicated that the treatment performance improved. By determining the activity of the functional bacteria, we found that the main reason for the improvement in the nitritation performance after starvation was that the decay rate of the ammonia oxidizing bacteria (AOB) activity during the starvation period was lower than of the decay rate of the NOB activity, and that the recovery rate of the AOB activity during the recovery period was significantly higher than that of the NOB.

[Effects of Different Intermittent Aeration Strategies on the Start-up of SNAD Process].

In this experiment, two reactors, R1 and R2, were inoculated with anaerobic ammonium oxide sludge at room temperature (20℃±3℃). R1 employed intermittent constant aeration while R2 employed intermittent gradient aeration to start up the SNAD granular sludge process, to study the effects of different intermittent aeration ways. The results showed that the time for R2 to stabilize the performance in each stage was shorter, and the actual start-up speed was faster; after successful startup, the eigenvalues of R1 and R2 were 6.46 and 10.34, respectively. The suppression effect for NOB is better in R2; the DO fluctuation in a typical cycle was stable in R2 while the DO in R1 gradually rose overall and reached over 0.5mg·L-1 by the end of the cycle. R2 can maintain low DO more stably and inhibit NOB proliferation; after successful startup, the PN/PS values in the R1 and R2 reached 2.745 and 2.823, respectively, and the particle size reached 365.8 µm and 402.1 µm, respectively. The stability and sedimentation of the particles in R2 were stronger and the particle size increased faster.

Achieving deep-level nutrient removal via combined denitrifying phosphorus removal and simultaneous partial nitrification-endogenous denitrification process in a single-sludge sequencing batch reactor.

The feasibility of coupling denitrifying phosphorus removal (DPR) with simultaneous partial nitrification-endogenous denitrification (SPNED) was investigated in a single-sludge sequencing batch reactor for deep-level nutrient removal from municipal and nitrate wastewaters. After 160-day operation, the DPR process simultaneously reduced most PO43--P and NO3--N anoxically, and the SPNED process achieved further total nitrogen (TN) removal at low dissolved oxygen condition with TN removal efficiency of 90.8%. The effluent NH4+-N, PO43--P and TN concentrations were 1.0, 0.1 and 7.2 mg/L, respectively. Microbial analysis revealed that Dechloromonas (6.7%) dominated DPR process, whereas the gradually enriched Nitrosomonas (4.5%) and Candidatus Competibacter (6.8%) conducted SPNED process accompanied with sharply eliminated Nitrospirae (1.4%). Based on these findings, a novel strategy was proposed to achieve further nutrient removal in conventional treatment through integrating the DPR-SPNED process. As a result, ∼100% of extra carbon and ∼10% of oxygen consumptions would be reduced with satisfactory effluent quality.

[Nitrogen and Phosphorus Removal from Low C/N Municipal Wastewater Treated by a SPNDPR System with Different Aeration and Aerobic Times].

An anaerobic (180 min)/aerobic operated sequencing batch reactor (SBR) fed with urban sewage was optimized by regulating the aeration quantity to investigate the deep-level nitrogen (N) and phosphorus (P) removal. The amount of aeration was regulated by adjusting the volume of gas per unit volume of reactor passed in unit time, when the unit is L·(min·L)-1, from 0.125 L·(min·L)-1 gradually to 0.025 L·(min·L)-1, and aerobic times from 3 h to 6 h. The experimental results show that the effluent NH4+-N, NO2--N, NO3--N, and PO43--P concentrations of the optimized SPNDPR system were 0, 8.62, 0.06, and 0.03 mg·L-1. The effluent TN concentration was about 9.22 mg·L-1, and the TN removal efficiency was up to 87.08%. When the aeration quantity was decreased from 0.125 L·(min·L)-1 to 0.100 L·(min·L)-1; then decreased to 0.075 L·(min·L)-1, the nitrification rate of the system recovered and stabilized at 0.16 mg·(L·min)-1. However, when the aeration quantity continuously decreased to 0.050 L·(min·L)-1 and then to 0.025 L·(min·L)-1, the nitrification rate decreased to 0.09 mg·(L·min)-1 and 0.06 mg·(L·min)-1. With reduction of the aeration quantity[from 0.125 L·(min·L)-1 to 0.100, 0.075, 0.050 and 0.025 L·(min·L)-1] and extension of aerobic time (from 3 h to 6 h), the TN removal efficiency increased gradually from 62.82% to 87.08%, and the SND efficiency increased from 19.57% to 72.11%. It was proven that reducing the aeration quantity can enhance the SPND function and deep denitrification by the system was realized. By enhancing the anaerobic intracellular carbon storage and aerobic phosphorus uptake, denitrifying phosphorus removal, partial nitrification, and endogenous nitrification were achieved. The SPNDPR system, after reducing aeration and prolonging aerobic time, was able to realize deep-level denitrification and dephosphorization using low C/N urban sewage.

[Denitrification and Phosphorus Removal from Low C/N Urban Sewage Based on a Post-Partial Denitrification AOA-SBR Process].

This study focuses on the investigation of the nitrogen (N) and phosphorus (P) removal characteristics of a combination of enhanced phosphorus removal (EBPR) with simultaneous partial nitrification endogenous denitrification (SPND) and post-partial denitrification process. An anaerobic/aerobic/anoxic (A/O/A) operated sequencing batch reactor (SBR) fed with urban sewage was optimized by regulating the aeration rate and anoxic time. Based on this optimization, deep-level nitrogen and phosphorus removals from low C/N urban sewage could be realized. The experimental results show that the effluent PO43--P concentration decreased from 0.06 mg·L-1 to 0 mg·L-1, the effluent NH4+-N, NO2--N, and NO3--N concentrations gradually decreased from 0.18, 18.79, and 0.08 mg·L-1 to 0, 16.46, and 0.05 mg·L-1, respectively, and the TN removal efficiency increased from 72.69% to 77.97% when the aeration rate decreased from 1.0 L·min-1 to 0.6 L·min-1 and the anoxic duration was 180 min. With the reduction of the aeration rate, the SPND phenomenon became notable and the SND rate increased from 19.18% to 31.20%. When the anoxic duration was extended from 180 min to 420 min, the effluent PO43--P, NH4+-N, and NO3--N concentrations stabilized at~0, 0, and 0.03 mg·L-1, respectively. The effluent NO2--N concentration was as low as 3.06 mg·L-1, the SND rate was~32.21%, the TN removal performance gradually improved, and the TN removal efficiency was as high as 99.42%. Thus, deep-level nitrogen and phosphorus removals could be realized with the SPNDPR-PD system.

[Startup Strategies for the SNAD Granular Sludge Process at Low Temperature].

To study the effect of the startup strategies on the simultaneous partial nitrification, ANAMMOX, and denitrification (SNAD) granular sludge processes, these processes were initiated by starting the completely autotrophic nitrogen removal over nitrite (CANON) process and anaerobic ammonia oxidation-denitrification (SAD) process at 12.7℃ and 18.3℃, respectively. The results show that the ammonia nitrogen was almost completely removed and the total nitrogen removal rate reached 86.7% after the R1 reactor was successfully started. When the ammonia concentration was low, the total nitrogen removal rate in the effluent decreased to 75.3%, the total nitrogen concentration in the effluent was~10 mg·L-1, and excessive proliferation of the NOB was observed. The total nitrogen concentration in the effluent exceeded the 1A level of the integrated discharge standard of water pollutants applied in Beijing City. After the R2 reactor was successfully started, the effluent contained almost no ammonia nitrogen and the total nitrogen removal rate was~89.1%, that is, slightly higher than that of the R1 reactor. When the ammonia concentration was low, the concentration of ammonia nitrogen in effluent was less than 1.0 mg·L-1 and the total nitrogen concentration in the effluent was less than 6 mg·L-1. The concentrations of ammonia nitrogen and total nitrogen in the effluent reached the 1A level of the integrated discharge standard of water pollutants applied in Beijing City. First, the startup of the SAD process gradually eliminated the NOB from the system through anaerobic operation in the initial stage of the startup, maintained the stability of the system, provided a good basis for the subsequent aeration to start the SNAD process, maintained the stable operation of the reactor, and the long-term discharge of total nitrogen reached the standard.

[Simultaneous Nitrogen and Phosphorus Removal Characteristics of An Anaerobic/Aerobic Operated SPNDPR System Treating Low C/N Urban Sewage].

This study focused on the nitrogen (N) and phosphorus (P) removal performance optimization of simultaneous partial nitrification-endogenous denitrification and phosphorus removal (SPNDPR) systems. An anaerobic (180 min)/aerobic operated sequencing batch reactor (SBR) fed with domestic wastewater was used for investigating the startup and optimization of SPNDPR by regulating the aeration rate and aerobic duration time. The experimental results showed that at an aerobic aeration rate of 0.8 L·min-1 and aerobic duration time of 150 min, the effluent PO43--P concentration was about 1.5 mg·L-1, with the effluent NH4+-N and NO3--N concentrations gradually decreasing from 10.28 and 8.14 mg·L-1 to 0 and 2.27 mg·L-1, respectively, and effluent NO2--N concentration increasing to 1.81 mg·L-1. When the aeration rate was increased to 1.0 L·min-1 and the aerobic duration time was shortened to 120 min, the phosphorus removal and partial nitrification-endogenous performance of the system gradually increased, but the total nitrogen (TN) removal performance initially decreased and then gradually increased. The final effluent PO43--P and NH4+-N were stably below 0.5 and 1.0 mg·L-1, respectively, aerobic nitrite accumulation and simultaneous nitrification-endogenous denitrification (SND) efficiencies were 98.65 and 44.20%, respectively, and TN removal efficiency was 79.78%. The concurrence of aerobic phosphorus absorption, denitrifying phosphorus removal, partial nitrification, and nitrification-endogenous in the aerobic stage of the SPNDPR system ensured the simultaneous removal of N and P from low C/N wastewater.

[Lab-scale SNAD Process in Wastewater Treatment Plant].

Outside the municipal waste water treatment plant(WWTP) which located in Mentougou District, Beijing, the effluent of the anoxic/oxic(A/O) phosphorus removal process served as the substrate to operate a completely autotrophic nitrogen removal over nitrite(CANON) filter reactor.. After the reactor was successfully activated, glucose was added to the influent as the organic carbon source. The simultaneous partial nitrification, anaerobic ammonium oxidation (ANAMMOX), and denitrification (SNAD) process was started to study the effect of SNAD filter on sewage treatment. The results showed that from 119 d to 128 d, the ammonia removal rate of the CANON process was more than 95%, and the maximum total nitrogen concentration in the effluent was 13.0 mg·L-1. Total nitrogen concentration surpassed the 1A level of the Integrated Discharge Standard of Water Pollutants applied in Beijing City. The SNAD process was started by adding glucose to the influent at 129 d. The total nitrogen removal rate of this process was about 85% at 133-187 d, and the total nitrogen concentration in the effluent was 5.5-7.3 mg·L-1. The filter plugged up at 195 d, and backwash was utilized at 196 d. During the subsequent 30 d, the total nitrogen removal rate of the reactor was greater than 85%, and the total nitrogen concentration in the effluent remained at 6.2-7.2 mg·L-1. Compared with the CANON process, the SNAD process improved the total nitrogen removal rate and reduced the total nitrogen concentration of the effluent by 6 mg·L-1. The ammonia and total nitrogen concentrations in effluent satisfied the 1A level of the Integrated Discharge Standard of Water Pollutants.