Experimental Study Of The Process Scheme On Upgrading Reconstruction Of Xi’an Fourth WWTP

The study was based on upgrading reconstruction of Xi’an fourth municipal wastewater treatment plant. After the investigation and analysis of the operation situation, the paper discussed the enhanced biological denitrification of the bio-fill added in A/O reactor which was followed by primary sedimentation. Also, the TP, SS and COD removal efficiency was investigated in the advanced wastewater treatment reactor of the "coagulation-sedimentation-filtration" which was followed by secondary sedimentation. The study provide a reasonable design parameters for the upgrading reconstruction.The main findings showed:(1) Xi’an fourth municipal wastewater treatment plant was designed reasonable and operated stable. The average removal rates of COD, NH3-N, TN and SS were92.65%,95.53%,83.63%and99.86%. TN sometimes slightly higher than the first class A criteria, because the hydraulic retention time of anoxic and anaerobic is short. TP can not meet the first class B criteria.(2) It is indicated that under the premise of NH3-N to achieve the first class A criteria, at least20%surplus volume of aerobic zone can be adjusted to the anoxic and anaerobic zone after the analysis of the removal effects of NH3-N in summer and winter (13℃) in biochemical reaction tank of fourth wastewater treatment plant which provided favorable conditions for the upgrading reconstruction. There was no use to build new bioreactor only relying on existing bioreactor to enhance nitrogen and phosphorus removal.(3) The analysis of the comparison test of the pilot plant A/O reactor showed that, while the proportion of carriers was30%, the average removal rate of COD, TN, NH3-N were90%,55%and97.7%, respectively. In comparison, the average removal rate of the without adding carriers reactor were86%,40%and83.8%, respectively, which were relatively low. While the proportion of carriers was30%, the average nitrification rate of reactor was increased by35%, the biomass was increased by1700mg/L. Reviewing the aerobic volume, adding carrier to upgrading reconstruction do not need to increase the volume of aerobic zone of the bioreactor, and the surplus capacity of aerobic zone is about17960m3.(4) The results of advanced wastewater treatment test show that, while the dosage of PAC was0.3g/L, the SS and TP removal efficiency were more obvious, the average effluent concentration were1.84mg/L and0.26mg/L, the average removal rate were84.05%and87.96%. The average effluent concentration of COD was19.65mg/L, the average removal rate was36.39%. The effluent of "coagulation-sedimentation filtration" device which used for treatment of secondary sedimentation effluent met the first class A criteria.