Experimental Study On The Treatment Of Low C/N Wastewater By "Bypass Carbon Supplement" Process

With the increasingly stringent sewage discharge standards,it was a key problem to be solved urgently to ensure that the sewage treatment plant has a better denitrification and phosphorus removal effect.Due to the impact of insufficient carbon source and carbon source competition,the A²/O process,which is currently the most widely used in sewage treatment plants,has poor denitrification and phosphorus removal at the same time.A new biological nitrogen and phosphorus removal process of"bypass carbon supplementation"was proposed,which solves this problem to a certain extent.In this study,the actual low C/N ratio wastewater was taken as the treatment object,and the method of combining simulation simulation and small test was used for research.Finally,the corresponding kinetic model of the new process was deduced and verified.The main conclusions are as follows:（1）Simulation study.In the influent component parameters,the proportion of rapidly degradable COD in total COD,Fbs,is 0.20,the proportion of ammonia nitrogen in total Kjeldahl nitrogen,Fna,is 0.74,and the proportion of dissolved phosphorus in total phosphorus,Fpo₄,is 0.73.Then the Biowin software was applied to carry out simulation and comparative analysis,and it was found that the COD_Cr removal rate of the"bypass carbon supplement"process was increased by 1.8%compared with the A²/O process;the removal rate of TP was increased by 6.7%compared with the A²/O process.It shows that the"bypass carbon supplement"process has certain feasibility（2）Small test test verification.The single factor test results of split ratio,mixed liquor reflux ratio and sludge reflux ratio shows that:the optimal split ratio of the new process was 7:3,and the removal rate of COD_Cr,TP and the content of aerobic available PHAs of the new process increased by 2.19%,4.17%and 12.11%,respectively,compared with A²/O process（that is,when the shunt ratio was no split）;the optimal mixed liquor reflux ratio of the new process is 250%,the denitrification effect and the denitrifying phosphorus removal effect were both enhanced in the process of increasing the mixed liquor reflux ratio from 100%to 250%;The optimal sludge return ratio of the new process is 70%,properly increasing the sludge return ratio can improve the removal rate of TN but reduce the storage of anaerobic PHAs,thus affecting the removal effect of TP.Finally,the average removal rates of COD_Cr,TP,NH₄⁺-N and TN in the system were 91.67%,92.17%,90.32%and 79.05%,respectively.The average effluent concentrations were 33.05 mg/L,0.34 mg/L,4.08 mg/L and 12.19 mg/L,respectively.The effluent COD_Cr,TP,NH₄⁺-N and TN all reached the national First-class A discharge standard stably,indicating that the simultaneous nitrogen and phosphorus removal effect of the system was good.（3）Dynamic model discussion.According to the operating data under the optimal operating parameters,the COD_Cr removal kinetic model,nitrogen removal kinetic model,phosphorus removal kinetic model and PHAs conversion kinetic model of the new process were deduced and verified,which provided technical support for engineering design.