Study On Optimal Operation Of Step Feed A~2+OSA Process For Low C/N Ratio Wastewater Treatment

The step feed A²/O process is a further optimization of the traditional A²/O process.The anaerobic tank and the anoxic tank are synchronized to feed water,so as to solve the problem of competition between the denitrifying bacteria and the intrinsic matrix of the phosphorus-accumulating bacteria,so that can strengthen the system nitrogen and phosphorus removal efficiency.A²+OSA process based on the step feed A²/O process,adds sludge anaerobic retention tanks to the sludge returning section which constitutes a oxygen-setting-anaerobic nitrogen and phosphorus removal coupling sludge reduction process.In this dissertation,the step feed A²+OSA process and the step feed A²/O process after the expansion of the aerobic pond were restarted and parameters were optimized.Through comparison,the effects of each reaction unit in the two treatment processes on the accumulation of extracellular polymer?EPS?in activated sludge were discussed and analyzed;at the same time,the content of polyphosphorus in EPS in each reaction unit in the two processes was analyzed and discussed.The same laboratory water distribution was used as the study object.The ratio of influent to water in the anaerobic tank and the anoxic tank was 1:1,the reflux ratio of the nitration solution was 250%,and the sludge return ratio was 100%.in the initial start-up phase.The results showed that the removal efficiency of COD and NH₃-N was good in both processes,but the removal efficiency of TN and TP was not very well.The average concentrations of COD,NH₃-N,TN,and TP in the multi-influent A²+OSA process were 15.88mg/L,0.31mg/L,17.33mg/L,and 5.22mg/L The average concentrations of COD,NH₃-N,TN,and TP in the process were 21.75mg/L,0.26mg/L,19.89mg/L,and 5.32mg/L.and the step feed A²+OSA process is superior to the comparative process under the conditions.In the optimization process of step feed A²+OSA process and step feed A²/O process parameters,the NO₃^--N in the process is targeted to reduce the adverse effects of phosphorus removal from the process.The ratio of influent to anaerobic tank and anoxic tank was adjusted to 5:7,7:5 and 1:2,the reflux ratio of nitrified liquid was increased to 350%,400%and 450%,and the influent C/N was adjusted to 12:1,10:1 and8:1.After the process operated stablely,the optimum operating conditions were determined as follows:the influent distribution ratio of anaerobic tank and anoxic tank was 5:7,the ratio of nitrifying liquid reflux was 400%and C/N was 10:1.Under this condition,the average concentrations of COD,NH₃-N,TN and TP in the multi-influent A²+OSA process were 35.29 mg/L,0.32 mg/L,5.95 mg/L and 0.20 mg/L,and the average removal rates were 94.61%,99.40%,91.09%and 97.63%.The average concentrations of COD,NH₃-N,TN and TP in the step feed A²/O process were36.14mg/L,0.33mg/L,8.40mg/L and 0.27mg/L respectively,and the average removal rate was 94.47%,99.38%,87.46%and 97.00%.Under the conditions of stable operation of the two processes,the interaction between EPS and phosphorus removal was studied.The results show that the step feed A²+OSA process have higher EPS accumulation than other process,and the EPS content on the protein content of up to 46.76%⁶0.93%of the total EPS.In each reaction unit,OSA had the highest EPS accumulation,reaching 155.45 mg/g VSS.