| At present, a lot of urban sewage treatment plants use the A2/O and the modified activated sludge process for nitrogen and phosphorus removal. However, the drawback of such processes is the deviation from the actual operation and requirement for sluge age. Especially under the condition of low temperature. The nitrifying bacteria was more sensitive to temperature and lower growth rate. Therefore, the deviation was larger, which resulted in poor effect of nitrogen removal in the northern area of our country in winter. Reduce the load of sludge, extend solids rentention time and increase the return of sludge and other measures were taken to reinforce the nitrification effect of urban sewage treatment plant in winter. But these may lead to lower process capacity and higher operating costs. The formation of the attached and suspended microorganisms coexistence system can increase the concentration of nitrifying bacteria in the system without extend solids rentention time, can improve nitrification effect with the preservation of phosphorus removal effect by adding suspended carrier to activated sludge system. In recent years, this method has been applied in the upgrade of urban sewage treatment plant gradually, and has achieved a certain effect. However, the nitrification contributions of biofilm and activated sludge was reported seldomly.To study the aerobic tank in A2/O process which added with suspended carrier in Xi’an the Forth Wastewater Teatment Plant on second phase. The change of nitrogen and the maximum specific nitrification rate of biofilm and activated sludge under the condition of summer and winter were monitored. To analyse the propotion of nitrifying bacteria which accounted for biofilm and activated sludge, calculate the nitrification capacity and then investigate the contribution of nitrifying bacteria in the biofilm and activated sludge. Finally, elucidated the growth of biofilm under different SCOD /NH4+-N. The main research results obtained are as follows:(1) In summer, the average temperature of 23.0℃, the ammonia nitrogen in aerobic zone at the end of the third corridor was 3.7 mg/L, which satisfied the level of discharge standard.So aerobic zone had about 2/5 surplus volume in summer. The AUR and NUR of activated sludge was 4.43mgNH4+-N/gVSS·h and 4.73mgNO2--N/gVSS·h, the AUR and NUR of biofilm was 2.95mgNH4+-N/gVSS·h and 3.77mgNO2--N /gVSS·h respectively. The propotion of nitrifying bacteria which accounted for activated sludge was about two times than biofilm’s. This showed that activated sludge play a major role to remove nitrogen in this system in summer.(2) In winter, the average temperature of 14℃. The biomass of biofilm was 3690mg/L(carrier), and the biomass of activated sludge was 3187mg/L, and biofilm thickness was about 130 on the average. There were a large number of protists such as rotifers and epistylis. When the dosage of the carrier accounted for 4.4% of the total volume of aerobic zone, the increased biomass by suspended carrier was 162 mg/L. The AUR and NUR of activated sludge was 3.16mgNH4+-N/gVSS·h and 3.39 mg NO2--N/gVSS·h, the AUR and NUR of biofilm was 3.63mgNH4+-N/gVSS·h and 4.17mgNO2--N/gVSS·h respectively. The propotion of nitrifying bacteria which accounted for biofilm was slightly higher than activated sludge.(3) When the added suspended carriers accounted for 4.4% of the total volume of aerobic zone, the contribution of biofilm to nitrification was 5.5%, while activated sludge was 94.5%.This showed that adding suspended carrier to the system strengthened nitrification effect in a certain extent.(4) The SCOD/NH4+-N along the aerobic zone were 4.8,3.9,3.0,3.0.The SCOD/NH4+-N in the third corridor was 3.0, while the AUR and NUR of biofilm were 3.87mgNH4+-N/gVSS·h and 4.88mgNO2--N/gVSS·h. The biomass of biofilm was 2854mg/L(carrier), the specific nitrification rate of biofilm is highest, which can be considered to change the zone forward the third corridor of aerobic zone. |
PDF Full Text Request