The Experimental Study On The Treatment Of The Secondary Biochemical Tailwater By Multi-stages A/O Biological Filter And Miciro-flocculation Filtration

The secondary sewage could damage the self-purification capacity of water,if it was discharged into surface water,due to high emissions,high concentration of nitrogen and phosphorus.The special climatic conditions of the cold and drought in the northwest have made some index of sewage higher than the first B standard of《Urban Sewage Treatment Plants Pollutant Discharge Standard 》(GB18918-2002).Due to the high emission of the secondary sewage,advanced sewage treatment can greatly reduce the possibility of eutrophication and improve secondary utilization of sewage,thus alleviating the pressure of the demand of water.Secondary sewage in the northwest is a typical case of low concentrations of organic and the high concentration of total nitrogen(TN),total phosphorus(TP).This experiment adopts the combination of aeration biological filter and activated sludge process of A/O devicemultistage A/O biological filter combined with miciro-flocculation filtration to process secondary sewage.The removal efficiency of COD,NH4+-N and the circumstance of microorganism and scanning electron microscopy are studied.The optimal operation parameters are determined by the study of the influencing factors of multi-stage A/O biological filter.The coagulant of microflocculation filtration,the corresponding amount and the filtration rate are determined.Finally,the removal of major pollutants in the secondary sewage treated by multi-stages A/O biological filter and miciro-flocculation filtration are studied.The results shows that:(1)The multistage A/O biological filter is activated combined with the inoculation hanging membrane method,the organic load decrement method and the prehanging aerobic membrane method.When system flow distribution ratio,hydraulic load and aerobic column dissolved oxygen is 50%:50%,0.7m3·(m2·h)-1 and 4mg/L,the system needs 57 days to be launched successfully.Biological microscopy revealed a large number of microorganisms.The scanning electron microscopy also showed white bands and spots.Meanwhile,the removal rate of COD is 57%,and the removal rate of the NH4+-N reaches 85%.(2)During stable operation of the multistage A/O biological filter,studying the influence of dissolved oxygen,the flow distribution ratio and the parameters of the hydraulic loading on the COD,NH4+-N,TN removal of sewage.And optimizing the filter parameters: dissolved oxygen is 4 mg/L,the flow distribution ratio is 70%:30%,hydraulic load is 1.2m3·(m2·h)-1.Under the optimal condition,the removal rate of COD,NH4+-N,TN of multistage A/O biological filter is 68.89%,90.6% and 32.53% respectively.COD and NH4+-N index reach theⅢ standard of 《 Surface Water Environment Quality Standard 》(GB3838-2002)and theremoval rate of TP is below 10%,which can not reach the Ⅳ standard of《Surface Water Environment Quality Standard 》(GB3838-2002).TN index reach the first B standard of《Urban Sewage Treatment Plants Pollutant Discharge Standard》(GB18918-2002).(3)A beaker experiment is used to determine the type of coagulant and the dosage of the coagulant,and the PAC is the best coagulant,with 6mg/L as the optimal dosage.Micro flocculation and filtration effect is researched at different filtration velocity.The optimal micro flocculation filter filtration velocity is 8m/h.Under the optimal condition,the TP removal rate can reach more than 70% of all levels,COD removal rate can reach 30%.The results show that TP removal of micro flocculation filtration is good,and removing COD also works.(4)After adding the carbon source,the COD removal rate of multistage A/O biological filter reaches 76.28%,the index reaches the Ⅳ standard of《Surface Water Environment Quality Standard》(GB3838-2002);NH4+-N removal rate reaches 90.44%,the index reaches the Ⅲ standard of《Surface Water Environment Quality Standard》(GB3838-2002).TN removal rate reaches 68%,which is obviously improved comparing not adding the carbon source.The water index is below 10mg/L,the index is far less than the first A standard of《Urban Sewage Treatment Plants Pollutant Discharge Standard》(GB18918-2002).(5)With the multi-stages A/O biological filter and miciro-flocculation filtration treat for the secondary biochemical sewage,COD removal rate reaches 82.42%,the index reaches theⅢ standard of《Surface Water Environment Quality Standard》(GB 3838-2002),NH4+-N removal rate reaches 93.65%,the index reaches the Ⅲ standard of 《 Surface Water Environment Quality Standard》(GB 3838-2002);The removal rate of TN is 70.39% and the effluent concentration is below 9mg/L,which is well below the first A standard of《Urban Sewage Treatment Plants Pollutant Discharge Standard》(GB18918-2002).TP removal rate reaches 73.17%,the index reaches the Ⅳ standard of《Surface Water Environment Quality Standard》(GB 3838-2002).The combined process effluent COD,NH4+-N,TN and TP all meet the water quality indicators for urban reclaimed water use industrial water,urban landscape water use and urban miscellaneous water use.