[Stable Nitrite Accumulation and Phosphorus Removal from High-nitrate and Municipal Wastewaters in a Combined Process of Partial Denitrification and Denitrifying Phosphorus Removal (PD-DPR)].

In this study, a novel process combining partial denitrification (PD, NO3--N→NO2--N) and denitrifying phosphorus removal (DPR) in an anaerobic-anoxic-aerobic sequencing batch reactor (SBR) was developed. By comprehensively controlling the influent C/N ratio, anaerobic drainage ratio, and anoxic duration, the nitrite accumulation and phosphorus removal performance of a system treating high-strength nitrate and municipal wastewaters was investigated. The results showed that, after 140 days, the nitrate-to-nitrite transformation ratio (NTR) was 80.1%, and PO43--P removal efficiency was 97.64%. In the anaerobic stage (180 min), glycogen-accumulating organisms (GAOs) and phosphorus-accumulating organisms (PAOs) efficiently utilized the carbon source in municipal wastewater to enhance intracellular carbon storage. In the anoxic stage (150 min), denitrifying GAOs (DGAOs) and heterotrophic denitrifying bacteria (DOHOs) carried out endogenous and exogenous short-range denitrification, respectively, to achieve stable nitrite accumulation; simultaneously, denitrifying PAOs (DPAOs) carried out denitrifying phosphorus uptake to achieve efficient phosphorus removal. In the aerobic stage (10 min), without initiating ammonia/nitrite oxidation, PAOs absorbed excessive phosphorus, which improved the phosphorus removal performance of the system. The effluent NO2--N/NH4+-N of a ratio of 1.31:1 (close to the theoretical value of ANAMMOX process, 1.32:1), with little PO43--P and COD (0.30 and 12.94 mg·L-1), meets the requirements for deep-level nitrogen removal by coupling with ANAMMOX process.

[Pilot Study on Start-up and Stable Operation at Low Temperature Based on Denitrifying Phosphorus Removal].

In order to understand the denitrifying and phosphorus removal characteristics of denitrifying phosphate-accumulating organisms (DPAOs), a pilot scale (20 m3) denitrifying and phosphorus removal experiment was carried out using a modified University of Cape Town (UCT) process at low temperatures of (6-16)℃. The test results show that at such temperatures, the hydraulic retention time (HRT) is 20 h and the solids retention time (SRT) is 35 days, and the modified UCT process can start up successfully and run steadily. When running steadily, the system can maintain nitrogen and phosphorus removal rates of 60%±5% and 80%±5%, respectively. The effluent concentrations of chemical oxygen demand (COD), ammonium nitrogen (NH4+-N), total nitrogen (TN), and total phosphorus (TP) were 20, 5, 11, and 0.5 mg·L-1, respectively, which meet the first A emission standard of "Pollutant Discharge Standard for Urban Sewage Treatment Plant" (GB 18918-2002). In order to further investigate the characteristics of nitrogen and phosphorus removal in the system, the reflux ratio from the aerobic tank to the anoxic tank was increased to 150%. After the system was stabilized, it obtained higher nitrogen and phosphorus removal rates of 80%±10% and 90%±5%, respectively. Among them, denitrifying phosphorus removal in the anoxic tank accounted for 80%±4% of the total biological phosphorus removal. The average effluent concentrations of COD, NH4+-N, TN, and TP were 19.55, 0.1, 7.8, and 0.15 mg·L-1, respectively, which meet the Beijing Standard A discharge standard.

[Rapid Cultivation of Anaerobic Ammonium Oxidation Granular Sludge and Inhibition Kinetics of Granular Sludge].

For the rapid cultivation of anaerobic ammonium oxidation (ANAMMOX) granular sludge (AGS), a small amount of flocculent ANAMMOX sludge (FAS) was taken as the research object, and a bio-flow separate ball was used as the filler in an up-flow anaerobic sludge bed (UASB) to rapidly begin ANAMMOX and to cultivate granular sludge. In addition, the substrate inhibition kinetic characteristics of the AGS were investigated by using the Haldane model. The results showed that start-up of the ANAMMOX was successfully achieved. The total nitrogen removal rate was more than 85%, and the volume load of total nitrogen was 0.72 kg·(m3·d)-1. AGS with diameters of 1.0-3.0 mm were cultured within 127 days using the Bio-flow Separate Ball. The kinetic studies showed that the maximum reaction rates for ammonia and nitrite of granular sludge were 1.46 kg·(kg·d)-1 and 1.76 kg·(kg·d)-1, with half inhibition constants of ammonia and nitrite at 852.2 mmol·L-1 and 108.2 mmol·L-1, respectively. Compared with FAS, AGS can withstand higher concentrations of ammonia and nitrite and can maintain a higher reaction rate. The placement of the filler has positive significance for starting ANAMMOX and rapidly culturing AGS.

[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.

[Effect of the Influent C/P Ratio on the Nutrient Removal Characteristics of the SNEDPR System].

This study focuses on the nitrogen (N) and phosphorus (P) removal characteristics in a simultaneous nitrification-endogenous denitrification and phosphorus removal (SNEDPR) system at different influent C/P ratios. An extended anaerobic/low aerobic (dissolved oxygen:0.5-1.0 mg·L-1) sequencing batch reactor (SBR) fed with municipal sewage was studied by adjusting different C/P ratios (10, 15, 20, 30, and 60). The experimental results show that the proper reduction of the influent C/P ratio (C/P ratio reduced from 60 to 30) enhances the competitive advantages of phosphorus-accumulating organisms (PAOs) in the SNEDPR system. The highest phosphorus removal efficiency was achieved at a C/P ratio of 30, with the anaerobic phosphorus release rate (PRR) and aerobic phosphorus uptake rate (PUR, used as P/MLSS) reaching 3.5 mg·(g·h)-1 and 4.2 mg·(g·h)-1 respectively, and an average effluent PO43--P concentration below 0.3 mg·L-1. The percentage of PAOs contributing to the storage of endogenesis carbon (PPAO, An) reached 88.1%. However, a poor phosphorus removal performance was observed with further reduction of the influent C/P ratios to 10; both the PO43--P removal efficiency and PPAO, An decreased from 38.1% and 82.4% to 3.1% and 5.3%, respectively. The PRR and PUR were 0.2 mg·(g·h)-1 and 0.24 mg·(g·h)-1, respectively. The COD removal performance was not affected by the decreasing influent C/P ratios; the average COD removal efficiency stabilized at 85%. In addition, the nitrification performance became worse with decreasing C/P ratios (from 60 to 20) because the effluent NH4+-N and NO2--N concentrations increased from 0 and 6.9 mg·L-1 to 5.1 mg·L-1 and 16.2 mg·L-1, respectively. The nitrificaton performance recovered when the C/P ratios further decreased to 10, but the nitrite accumulation was disturbed as both the effluent NH4+-N and NO2--N concentrations reduced to 0. The effluent NO3--N concentration increased from 0.08 mg·L-1 to 14.1 mg·L-1. The SNED efficiency first decreased from 62.1% to 36.4% and then increased to 56.4%. The advantageous competition of glycogen accumulating organisms (GAOs) improved when the influent C/P ratio was lower than 15. The enhancement of the endogenous denitrification ability of GAOs might explain the recovery denitrification performance of the system when the influent C/P ratios decreased from 20 to 10.

[Effect of Different Sludge Retention Time (SRT) Operations on the Nutrient Removal Characteristics of a SNEDPR System].

This study focuses on the nitrogen (N) and phosphorus (P) removal characteristics in a simultaneous nitrification endogenous denitrification and phosphorus removal (SNEDPR) system operating at different sludge retention time (SRT). Four extended anaerobic/low aerobic (dissolved oxygen:0.5-1.0 mg·L-1)-operated sequencing batch reactors (SBRs) fed with municipal sewage were studied at different SRT of 5, 10, 15, and 25 d. The experimental results show that a shorter SRT at an SRT ≥ 10 d enhances the competitive advantage of PAOs in the system and an efficient phosphorus removal performance of the SNEDPR system was achieved at a SRT of 10 d and 15 d. Especially at an SRT of 10 d; the average PPAOs, An was 68.4%, the PRA and PUA reached 31.9 and 34.3 mg·L-1, respectively. The nitrification performance of the system was not affected by SRT changes. The most efficient nitrogen removal performance was achieved at a SRT of 15 d, with a high average TN removal and SNED efficiencies reaching 89.6% and 71.8%, respectively. At a SRT ≥ 10 d, the COD removal performance of the SNEDPR system was also not affected by SRT changes. The COD removal efficiencies were higher than 78%. However, when the SRT was shortened to 5 d, the C, N, and P performances of the system worsened due to the loss of biomass; the SNED and PO43--P removal efficiencies were as low as 5.7% and 0.5%, respectively. In addition, at an SRT=15 d, the sludge-settling performance of the system was the best. The SV and SVI were 20% and 64 mL·g-1, respectively, and the sludge concentration increased with the extension of the SRT. Under long SRT (25 d) operation, the system showed a good resistance to shock loads, but the sedimentation performance of the sludge deteriorated.

[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.

[Characteristics of Ammonia Adsorption and Kinetics by Nitrifying Sludge Immobilized Pellets].

In order to explore the characteristics and mechanisms of ammonia adsorption by both nitrifying sludge waterborne polyurethane (WPU)-immobilized pellets and nitrifying sludge polyvinyl alcohol-sodium alginate (PVA-SA)-immobilized pellets, the ammonia adsorption characteristics of immobilized pellets under different initial ammonia concentrations, and the influences of temperature, pH, and salinity on ammonia adsorption were studied respectively. Moreover, the adsorption isotherms, thermodynamics, and kinetics model analysis were employed to investigate the adsorption process. The adsorption capacity increased as the initial ammonia concentration increased. The optimal pH was 7.0, and salinity and temperature exhibited an inhibitory effect on adsorption. The adsorption capacity for nitrifying sludge-immobilized pellets was higher than the pellets with no sludge; the adsorption capacity of WPU pellets was higher than that of PVA-SA pellets. The thermodynamics demonstrated that the adsorption process was a spontaneous exothermic process and that low temperature favored ammonia adsorption. The process was fitted to the Langmuir and Freundlich isotherm. It exhibited multilevel adsorption at higher energy (Freundlich isotherm) and single adsorption at lower energy by electrostatic force (Langmuir isotherm). Additionally, the process was consistent with the pseudo-second-order kinetic model, as it explained that chemical adsorption was the primary mechanism of ammonia adsorption by immobilized pellets.

[Nitrite Accumulation Characteristics of Partial Denitrification in Different Sludge Sources Using Sodium Acetate as Carbon Source].

In order to explore the characteristics of nitrite accumulation during the operational period of partial denitrification in different sludge sources using sodium acetate as a carbon source, No.1 SBR and No.2 SBR were used to inoculate with surplus sludge taken separately from a secondary sedimentation tank of a sewage treatment plant and simultaneous nitrification and denitrifying phosphorus removal system. By reasonably controlling the initial nitrate concentration and anoxic time, partial denitrification was realized. The carbon and nitrogen removal characteristics under different initial COD and NO3--N concentrations were investigated. The results showed that, using sodium acetate as the carbon source, the partial denitrification process in No.1 SBR and No.2 SBR sludge successfully began in 21 d and 20 d, respectively. The accumulation of NO2--N and nitrite accumulation rate (NAR) in reactors were maintained at high levels (12.61 mg·L-1, 79.76% and 13.85 mg·L-1, 87.60%, respectively). When the initial NO3--N concentration of No.2 SBR was 20 mg·L-1 and the initial COD concentration increased from 60 mg·L-1 to 140 mg·L-1, the operation time for achieving the highest NO2--N accumulation in the system was shortened from 160 min to 6 min. The NO3--N ratio of the denitrification rate (in VSS) increased from 3.84 mg·(g·h)-1 to 7.35 mg·(g·h)-1. Increased initial COD concentration was beneficial to the accumulation of NO2--N during partial denitrification. When the initial COD concentration of No.2 SBR was 100 mg·L-1 and the initial NO3--N concentration increased from 20 mg·L-1 to 30 mg·L-1, NAR was maintained above 90% and up to 100% (the initial NO3--N concentration was 25 mg·L-1). When the initial NO3--N concentration was ≥ 35 mg·L-1, insufficient COD caused NO3--N to be completely reduced to NO2--N. Under different initial COD concentrations (80, 100, or 120 mg·L-1) and different initial NO3--N concentrations (20, 25, 30, or 40 mg·L-1), the nitrogen and carbon removal and partial denitrification performance of the No.2 SBR was better than that of No.1 SBR.

[Effect of Influent C/N Ratio on the Nutrient Removal Characteristics of SNEDPR Systems].

To determine the performance of nitrogen and phosphorus removal within a simultaneous nitrification endogenous denitrification system (SNEDPR), an extended anaerobic/low aerobic (dissolved oxygen:0.5-2.0 mg·L-1)-operated sequencing batch reactor (SBR) was fed with simulation wastewater. The SBR was initiated under a constant influent C/N ratio of 10, with the simultaneous enrichment of polyphosphate-accumulating organisms (PAOs). It was then investigated at different influent C/N ratios of 10, 7.5, 5, and 2.5. The experimental results indicated that, when the influent C/N ratio was 10, SNEDPR could be successfully started up. The effluent PO43--P and total nitrogen (TN) concentrations were 0.1 mg·L-1 and 8.1 mg·L-1. PO43--P efficiency, TN efficiency, and SNED efficiency were 99.79%, 89.38%, and 58.0%, respectively. When the influent C/N ratio increased from 5 to 10, the nitrogen and phosphorus removal performance of the system improved with PRA, and SNED efficiency increased from 16.0 m·L-1 and 48.0% to 24.4 mg·L-1 and 69.2%, respectively. When the C/N ratio was 10, the TN and PO43--P removal efficiencies increased to 94.5% and 100%, respectfully. When the C/N ratio was decreased to 2.5, the nitrogen and phosphorus removal performance of the system decreased. The PRA and SNED efficiencies were only 1.36 mg·L-1 and 10%, respectively. During the stable phase of the system (C/N ratio were 10, 7.5 and 5), SNED efficiency reached to 85.9%, with the average effluent concentration of NH4+-N, x--N, and PO43--P being 0.0, 8.1, and 0.1 mg·L-1, respectively.

[Operating Characteristics of a DPR-SNED System Treating Low C/N Municipal Wastewater and Nitrate-containing Sewage].

In order to realize the simultaneous treatment of low C/N municipal wastewater and high nitrate wastewater, a sequencing batch reactor (SBR), inoculated with activated sludge, was used to initiate the denitrifying phosphorus removal coupled with simultaneous nitrification and endogenous denitrification (DPR-SNED). The anaerobic/anoxic/hypoxic durations and dissolved oxygen (DO) concentration were appropriately controlled, and the nitrogen and phosphorus removal characteristics were examined. The experimental results demonstrated that, in the anaerobic/hypoxia operation mode, with an anaerobic duration of 3 h and DO concentration of 0.5-1.0 mg·L-1, the simultaneous nitrification of phosphorus removal (SNEDPR) system successfully began in 60 d. The effluent PO43--P concentration was below 0.5 mg·L-1, the nutrient and COD removal efficiencies were stably maintained above 90% and 80%, respectively, and the SNED efficiency and CODins efficiency reached 70% and 95%, respectively. When the operation mode was anaerobic/anoxic/hypoxic and nitrate-containing sewage was added at the beginning of the anoxic stage, DPR-SNED was achieved with the effluent PO43--P concentration<0.5 mg·L-1, nutrient and COD removal efficiencies above 88% and 90%, respectively, and SNED efficiency and CODins efficiency maintained at 62% and 90%, respectively. After the successful initiation of DPR-SNED, enhanced intracellular carbons storage was achieved by phosphorus-and glycogen-accumulating organisms using the limited carbons in raw municipal wastewater to provide sufficient carbon sources for subsequent nutrient removal. In addition, the endogenous partial denitrification ensured the efficient nitrogen removal performance of the DPR-SNED system at low C/N conditions (average 4).

[Enhanced Nitrogen and Carbon Removal Performance of Simultaneous ANAMMOX and Denitrification (SAD) with Trehalose Addition Treating Saline Wastewater].

Enhanced nitrogen and carbon removal performance of simultaneous ANAMMOX and denitrification (SAD) process with trehalose addition treating saline wastewater was investigated in a sequencing batch reactor (SBR). The optimal nitrogen removal was achieved at 0.25 mmol·L-1 trehalose, during which NH4+-N, NO2--N, NO3--N, and COD could be completely removed. Compared to no addition of trehalose, ammonium removal efficiency (ARE), nitrite removal efficiency (NRE) and total nitrogen removal efficiency (TNRE) increased by 50%, 43% and 46%. Ammonium removal rate (ARR) and nitrite removal rate (NRR) increased by 81.25% and 75%, respectively. With increasing concentration of trehalose to 0.5 mmol·L-1, ARE was only 58.82% and the effluent concentration of NH4+-N was 33.25 mg·L-1. Compared to the Haldane model and the Aiba model, the Luong model was the most suitable to simulate the nitrogen removal performance of SAD with trehalose addition treating saline wastewater. The NRRmax, KS, Sm, and n fitted from Luong model were 0.954 kg·(m3·d)-1, 0 mg·L-1, 184.785 mg·L-1, and 0.718, respectively. Compared to the modified Logistic model and the modified Boltzman model, the modified Gompertz model was the most suitable to describe the degradation of a substrate in a single cycle.

[Characteristics and Performance of Embedded ANAMMOX Bacteria in Treating Saline Wastewater].

In order to improve the mechanical stability of the material, the embedded raw material combination was studied in the experiment, and seawater was added to optimize the performance of the material. The results indicated that the optimal material ratio was polyvinyl alcohol (PVA 125 g·L-1)-alginate sodium (SA 20 g·L-1)-activated carbon (40 g·L-1). The curing time was 18 h. After adding seawater, the beads were found to have larger pore sizes inside, and the pores were distributed unevenly because of the Hofmeister effect. At the same time, the mechanical stability and biological capacity were found to be significantly higher than those of the fresh water group. The Raman spectra analysis showed that the addition of seawater made the-OH on PVA have greater crosslinking reactions with the crosslinker. The activated sludge was used to treat wastewater containing sea water, and after an operation of 21 d, the removal rate of NH4+-N was about 90%, and the stoichiometric ratio of △NH4+-N:△NO2--N:△NO3--N was stable at 1:(1.04±0.1):(0.17±0.02). From the 21st day to the 46th day, the reactor was run in a steady state. When the nitrogen load rate doubled, the ammonia nitrogen removal rate and stoichiometry had little variations. The total nitrogen removal rate was about 85%, and the total nitrogen removal load rate was 0.2 kg·(m3·d)-1.

[Enhanced Nitrogen Removal of ANAMMOX Treating Saline Wastewater With Betaine Addition].

High salt content could result in the inhibition of microbes and affect biological treatment processes. At present, an important research topic is how to improve the efficiency of biological treatments. The anaerobic ammonia oxidation (ANAMMOX) process was used to treat high saline wastewater. Nitrogen removal performance with betaine was studied by analyzing the ANAMMOX activity, and ammonia nitrogen and nitrate nitrogen removal. The results showed that:① It has obvious improvement when betaine concentration was 0.1-0.4 mmol·L-1. It alleviated the salt stress on bacteria growth inhibition of ANAMMOX, and also promoted the growth of denitrifying bacteria. When betaine concentration was 0.4-0.5 mmol·L-1, denitrifying bacteria was found to have grown greatly. When betaine concentration was greater than 0.5 mmol·L-1, it was unable to alleviate the salt stress inhibiting denitrification efficiency. As a result, betaine concentration of 0.8 mmol·L-1 completely inhibited bacteria. ② When concentration of betaine was 0.3 mmol·L-1, the optimal nitrogen removal efficiency was achieved. NH4+-N and NO2--N increased by 16% and 32%, respectively. Nitrogen removal rate (NRR) increased by 26.8%. ③ At the end of the recovery experiment, with the decreasing concentrations of betaine, NH4+-N was 50.6%, NO2--N was 63.7%, and NRR was 0.65 kg·(m3·d)-1, so the nitrogen removal efficiency underwent fast recovery.

[Start-up and Process Characteristics of Simultaneous ANAMMOX and Denitrification (SAD) in a Pilot-scale Anaerobic Sequencing Batch Reactor (ASBR)].

A pilot scale anaerobic sequencing batch reactor (ASBR, working volume 530 L), inoculated by anaerobic sludge from an A2O process, was developed to investigate the start-up of anaerobic ammonia oxidation (ANAMMOX) and its combination with denitrification for deep-level nitrogen removal from saline wastewater. Simultaneously, the flora structure was analyzed. Results showed that under the conditions of temperature 35℃±1℃ and reaction time 14 h, ANAMMOX was successfully started-up after 160 days of operation. During the stabilized operation stage, ANAMMOX coupled with denitrification (SAD) led to a total nitrogen (TN) removal efficiency and removal rate of 91.1% and 0.45 kg·(m3·d)-1, respectively. The successful cultivated sludge formed granules and presented as a light red color, with the main bacteria genus being Candidatus Brocadia (10.6%). Additionally, high efficiency nitrogen and organic carbon removal (COD and TN removal efficiency of 93.2% and 90.0%, respectively) from wastewater simulating desulfurization and denitrification tailings with high salinity (Cl- concentration of 8000 mg·L-1) was achieved in the SAD system by gradually increasing the salinity gradient. Moreover, the denitrification in SAD was mostly NO3--N→N2, with partial denitrification (NO3--N→NO2--N) accounting for only 30.3%.

[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.

[Effect of Salinity on Nitrogen Removal Performance of a Pilot-scale Anaerobic Ammonia Oxidation Process and Its Recovery Kinetics].

The denitrification characteristics of anaerobic ammonia oxidizing bacteria (AnAOB) treating high salinity wastewater were investigated in an pilot-scale anaerobic sequencing batch reactor (ASBR, 530 L) by gradually increasing the Cl- concentration. The results showed that AnAOB can adapt to the high salinity (Cl- concentration of 10000 mg·L-1) environment for high-efficiency denitrification by means of gradual salinity acclimation and total nitrogen (TN) removal rate of up to 92.3%. In particular, the denitrification performance was influenced by two gradients of Cl- concentrations, namely 6000 mg·L-1 and 10000 mg·L-1, but it could be gradually recovered as the acclimatization process continued. The modified Boltzmann model accurately fit the activity recovery process of AnAOB after being inhibited by the different salinities, and the correlation coefficient R2 was above 0.96. The fitted recovered median values tc for Cl- concentrations of 6000 mg·L-1 and 10000 mg·L-1 were 28.765 d and 44.495 d. NRRmax for these concentrations was 0.145 kg·(m3·d)-1 and 0.212 kg·(m3·d)-1, and NRRmin was 0.021 kg·(m3·d)-1 and 0.085 kg·(m3·d)-1, respectively. After salinity acclimation, the dominant bacteria of AnAOB were Candidatus Brocadia and Candidatus Jettenia (the abundances were 14.76% and 2.7%, respectively), the granulation degree and sludge density increased to varying degrees, and the sludge color was reddish brown.

[Suppression and Recovery Characteristics of Pilot-scale ANAMMOX-ASBR System Treating Desulfurization and Denitrification Tailings from Thermal Power Plant].

A pilot-scale anaerobic sequencing batch reactor (ASBR, working volume 530 L), inoculated with oxygen-segmented sludge in an oxidation ditch process, was developed to investigate the start-up of anaerobic ammonium oxidation (ANAMMOX) and its combination with denitrification for deep-level nitrogen removal from desulfurization and denitrification tailings of a thermal power plant. The results showed that, under conditions with a temperature of (35±1)℃and reaction time of 20 h, ANAMMOX was successfully started up after 180 days. During the stable operations phase, total nitrogen (TN) removal rate and removal efficiency reached 91.1% and 0.3 kg·(m3·d)-1, respectively. During the activity suppression stage of the ANAMMOX-ASBR treating real desulfurization and denitrification tailings, the recovery of its activity could be achieved in 93 days by removing inhibitory factors (Cl- concentration) and reducing the concentration of influent substrate. In addition, by gradually increasing the addition ratio of desulfurization and denitrification tails (30%, 70%, and 100%), the coupling of ANAMMOX and denitrification was achieved in the ASBR to ensure stable effluent TN removal rate and COD concentrations below 92% and 88.5 mg·L-1, respectively. The modified logistic model was more suitable for the NRR recovery process after ANAMMOX was impacted by desulfurization and denitrification tailings. The NRR recovery delay time λ was 17.777 cycles, the and R2 was 0.92948.

[Nitrogen Removal Performance of ANAMMOX with Different Organic Carbon Sources].

Anaerobic ammonium oxidation (ANAMMOX) has been regarded as an efficient process to treat high-strength wastewater without organic carbon source. To investigate the nitrogen removal performance of ANAMMOX in the presence of organic carbon source can broaden its application in organic wastewater treatment. In this work, an anaerobic sequencing batch reactor (ASBR) was used to study the effect of organic carbon source on ANAMMOX process. The experimental results indicated that the activity of anaerobic ammonia oxidizing bacteria (AAOB) decreased by 84.2% when 200 mg·L-1 COD of glucose was added. When sodium acetate was added, the activity of AAOB was affected little. Besides, it even promoted the activity with COD less than 120 mg·L-1. The effect of sucrose on ANAMMOX process was similar to that of sodium acetate and the maximum specific ANAMMOX activity (SAA) increased by 25.0% with 80 mg·L-1 COD. When citric acid was added, the maximum SAA peaked with 80 mg·L-1 COD. The order of ANAMMOX promotion resulted from organic carbon source was sucrose, sodium acetate, citric acid and glucose. With addition of organic carbon source, nitrate could also be removed through the synergy of ANAMMOX and denitrification, and the total nitrogen removal efficiency increased.

[Substrate Inhibition and Kinetic Characteristics of Marine Anaerobic Ammonium Oxidizing Bacteria Treating Saline Wastewater].

An anaerobic sequencing batch reactor (ASBR) was used to study substrate inhibition and kinetic characteristics of marine anaerobic ammonium oxidizing bacteria (MAAOB) treating saline wastewater. The results indicated that when ammonia increased to 1200 mg·L-1, the MAAOB still maintained good nitrogen removal capability, though there was a slight inhibitory effect. At the same time, nitrite nitrogen removal efficiency was stable at about 80.70%. When nitrite increased to 265.6 mg·L-1, the MAAOB were inhibited obviously, and ammonia nitrogen removal efficiency decreased to about 63.01%. When influent nitrite concentration increased to 305.6 mg·L-1, the removal rate of ammonia nitrogen further decreased to 43.93%. The kinetic characteristics resulting from inhibition of the MAAOB were simulated by the Haldane model and Aiba model. Three parameters, TNRRmax, KS, and Ki, and the relationship between effluent substrate concentration and total nitrogen loading (TNRR) were evaluated. Based on further analysis, the Haldane model was more suitable for describing dynamic characteristics resulting from NH4+-N inhibition, while the Aiba model was more suitable for describing the dynamic characteristics resulting from NO2--N inhibition. The predicted effluent inhibitory concentrations of NH4+-N and NO2--N were 3893.625 mg·L-1 and 287.208 mg·L-1, respectively. The results could provide a theoretical basis for saline wastewater treatment by MAAOB.