The A/O+SNAD Process For Municipal Wastewater

Too much N and P nutrients discharged into water can not only cause eutrophication and environmental problems, but also threaten human health seriously. As a consequence, our country strengthens the discharge standard of nitrogen and phosphorus concentrations. Therefore, it becomes an focused issue to research and develop high efficiency and energy saving of biological denitrification and phosphorus removal process.The traditional biological denitrification and phosphorus removal are generally realized in a same sluge system, however, this faces probolems of the competition between phosphorus accumulating bacteria and denitrifying bacteria and causes more oxygen consumption and needs extra organic carbon source,which results in low nitrogen & phosphorus removal efficiency and high energy consumption and the high cost of operation. If N, P can be removed independence and controlled under appropriate operation respectively, the removal of N and P will be efficient.In order to achieve this purpose, this subject adopts A/O and SNAD technology to remove P,N, respectively. A/O biological phosphorus removal process is aimed at removing P through controlling the aerobic pool in the limited filamentous bulking using Phosphorus Accumulating Organisms(PAOs) mainly to remove phosphorus and COD without nitration reaction, maiking for subsequent denitrification provide. SNAD process utilizes nitrosation bacteria, anaerobic ammonia oxidation bacteria and denitrifying bacteria to realize the N and COD removal at the same time. The process mainly uses autotrophic anaerobic ammonia oxidation bacteria. Compared with the traditional biological denitrification process, this process can save oxygen consumption without adding additional organic carbon source and reach high efficiency of N and P removal.This study is divided into three phases. The first stage is start-up of A/O biological phosphorus removal reactor and investigate the influencing factor to the reactor. The main research results are as follows:(1) Start-up and operation effect. In this study, domestic wastewater was taken as raw water. The reactor had been operated under the condition of(30±1)℃,the concentration of DO and pH value was kept between(1.2~1.7) mg/L,6.8~7.4,respectively. After 130 days of operation, the A/O reactor was started up successfully. In the stable operation stage, the average concentration of effluent COD and TP were 43 mg/L and 0.3 mg/L, respectively. The removal rate of COD and TP reached 84% and 92%.(2) The influence of different DO. Under the condition that DO concentration was 0.5~1.0 mg/L,SVI value was 180 ~ 230 mL/g, duing when limited filamentous bulking sludge grown inthe reactor, abundant PAOs could alleviate problem of sludge settling performance which coused by low DO.The second stage is start-up of SNAD reactor and investigate the influencing factor to the reactor. The main research results are as follows:(1) Start-up and operation effect. In the study, artifical wastewater was made as raw water. The reactor had been operated under the condition of(30±1)℃, ammonia concentration was between(36~64) mg/L the concentration of NaHCO3 and pH value was kept between(10~15) mg/L,7.3~7.5,respectively. SNAD reactor start-up was divided into two parts.The first part was the baffled biofilm autotrophic denitrification reactor start-up. After 112 days of operation, the baffled biofilm autotrophic denitrification reactor was started up successfully. In the stable operation stage, the average concentration of effluent NH4+-N and TN were 2.76 mg/L and 11.51 mg/L, respectively. The removal rate of NH4+-N and TN reached 94% and 77%. The nitrongen removal load of the reator was up to 0.23kg/m3·d.The second part was the start-up of SNAD reactor. The elluent was added COD and controlled the concentration was 43~60 mg/L. After 182 days of operation, SNAD reactor was started up successfully. The removal rate of NH4+-N, TN and COD reached 97%, 85% and 97%,respectively.(2) The influence of different C/N to the reactor. When C/N ratio was less than 2, the reactor had no significant effect on anammox bacteria and realized simultaneous partial nitrification, anammox and denitrification in a single reactor. When C/N ratio was more than 2, the rapid growth of the denitrifying bacteria inhibited the activity of anammox bacteria due to the high COD concentration. Thus, the nitrogen removal became worse.The third stage was based on the successful launch and stable opertation of A/O and SNAD reactor. The two reactors was combined to treat domestic sewage was studied.(1) A/O + SNAD combination process. The influent concentrations of TP, TN and COD were 4.3 mg/L, 51 mg/L and 306 mg/L, respectively. the average concentration of effluent TP, TN and COD were 0.14 mg/L, 8.14 mg/L and 16.19 mg/L, respectively, the average removal rate was 97%, 84% and 94%,respectively.(2) The influence of different NH4+-N concentration. When the concentration of NH4+-N rised from 30 mg/L to 100 mg/L gradually, it makes no apparent difference to the removal rate of phosphorus and COD. The average removal rate of TP and COD were 94% and 91%, respectively. When the concentration of NH4+-N was 30 mg/L, NH4+-N removal rate almost reached 100%, TN removal rate reached 87%.When the concentration of NH4+-N reached 100 mg/L, NH4+-N and TN removal rate fell to 78% and 78%, respectively.