Study On Diagnosis And Optimal Operation Of Denitrification Process For Municipal Wastewater Treatment Plant

With the improvement of urban sewage discharge standards, upgrading of many old sewage treatment plants is imperative because the original design of these plants did not consider the removal of nitrogen and phosphorus.Taking a Handan sewage treatment plant as the research object, through analysis of the plant's actual operating results, the main indicators of SS, BOD, COD, TP can achieve the first-class B standard, but total nitrogen and ammonia nitrogen in effluent don't meet discharge standards. Combination the basic theory of biological denitrification, the main factors, including water quality (organic carbon concentration and types), dissolved oxygen, alkalinity and pH, hydraulic retention time and sludge characteristics (sludge concentration, sludge age and sludge reflux ratio) are on-site monitored. The results show that sufficient carbon, suitable alkalinity and pH, too high sludge concentration and low dissolved oxygen are the main factors affecting denitrification effect.The improved ASM Bio-P model is established based on ASM Bio-P model at considering of autotrophic bacteria and phosphorus effecting on the hydrolysis process, organic carbon concerntion affecting on the growth of nitrifying bacteria, nitrate of return sludge affecting on PHA storage of phosphorus bacteria, at the same time the temperature changes effecting on biological reaction process embedded in the mode.The oxidation ditch process equations are solved by Matlab program, and simulation results show that measured values and simulated values are basically consistent and average relative errors of COD, TN, NH3-N and TP are 11.21%, 8.01%, 7.48% and 69.22%,respectively.In order to improve the plant's denitrification function, optimal operation of the plant is done by using mathematical simulation program. The results show that in summer the best operating conditions are the ratio of aerobic zone to anoxic zone of 3:1, dissolved oxygen concentration of 1mg/L in aerobic zone, SRT of 15d, sludge reflux ratio of 100%,in winter the best operating conditions are the ratio of aerobic zone to anoxic zone of 3:1, dissolved oxygen concentration of 3mg/L in aerobic zone, SRT of 20d, sludge reflux ratio of 50% and water quality basically meet the emission standards.It is recommended that the sewage treatment plant should increase the volume of aerobic zone, making the volume ratio of aerobic zone to anoxic zone controlled at about 3:1,improve dissolved oxygen concentration of aerobic zone, controlling at 1mg/L in summer and 3mg/L in winter; appropriately lower the sludge age to 15d in summer, and appropriately raise the sludge age to 20d in winter; sludge reflux ratio should be lowered to 50% in winter.