Enhanced Nitrogen With The Patternof Grade Use Of Carbon Resource To Deep Denitrification

The problem of low carbon resource existing in city wastewater treatment is the key problem waiting to be resolved. The new process of enhanced nitrogen removal with the pattern of grade use of carbon resource to deep denitrification is designed by our group. First, the carbon resource is absorbed by phosphorus accumulating bacteria in anaerobic tank. Second, carbon resource is used by denitrifying bacteria in the first denitrification phase. After these phases, readily biodegradable substances is used up. However, hydrolytic acidification phase will then transform the residual carbon resource to readily biodegradable before flowing into the second denitrification phase which will make enhanced denitrification reliable. At the same time, denitrification and phosphorus removal bacteria in th is phase will uptake phosphorus and denitrify using carbon resource existing in the cells. In this case, denitrification and phosphorus removal happen simultaneously. This new process not only can resolve the problem of lack of carbon resource, but also resolve the problem of competition between heterotrophic bacteria and autotrophic bacteria in the aerobic phase.Two separate sludge recycling system containing aerobic nitrification and anaerobic-anoxic denitrifying phosphorus sludge was designed as a two-sludge system to assure that function flora could display their respective advantages. The reactor was start-up and conducted at room temperature, and the operating parameters including the nitrifying effluent bypass ratio(R), the sludge bypass ratio(r) and the hydraulic retention time(HRT) were adjusted and optimized to determine the optimal conditions of system operation.The results showed that the removal efficiency of COD, TP and TN increased with continually increasing R2, and reached maximum ratios of 78.8%, 88.0%, and 80.5% at R2=160%, respectively. But when R2=200%, lower COD utilization in anaerobic tank might induce the release of phosphorus and seriously affect the removal efficiency of nitrogen and phosphorus in the entire system. When r was under 80%, the removal efficiency of COD, TP and TN increased with increasing r and reached maximum ratios of 82.4%, 90.8%, and 83.7% at r=80%, respectively. Whereas when r=100%, the actual HRT shortened and the high concentration of sewage sludge deposited which also seriously affected the removal efficiency of nitrogen and phosphorus in the entire system. But HRT shortened from 24.00 h to 16.00 h, the removal rates of TP and TN were 80.7% and 84.6%, which indicated that the system still reached a good removal efficiency of nitrogen and phosphorus. However, when HRT shortened to 12.00 h, the amount of releasing phosphorus in the anaerobic tank and the denitrifying removal efficiency of phosphorus in the second anoxic tank both declined, and the effect of nitrification in aerobic tank becomes worse, hence, the removal rates of TP and TN were only 45.3% and 70.7%. Therefore, the optimal operating conditions of the system were R1=40%, R2=160%, r=80%. For HRT, it may be considered to be shortened at 1.50 h in the anaerobic tank, 2.00 h in the first anoxic tank, 5.50 h in the hydrolytic acidification tank, 3.00 h in the second anoxic tank, and 4.00 h in the contact oxidation tank.