Pilot Study On The Upgrading Of Suzhou Municipal Sewage Treatment Plants

In order to deal with the problems of deterioration of water environment caused by the rapid development of urbanization,improve the discharge standard and sewage treatment efficiency of urban sewage treatment plants,and make urban sewage become a renewable and reused stable resource,the sewage treatment plants in some areas of China are facing a new round of upgrading from"Class-A"standard to"Quasi-Ⅳ"standard.Based on the"Opinions on the High Quality Promotion Plan for the Three-year Action of Urban and Rural Domestic Sewage Treatment"issued by Suzhou government and"Suzhou Special Discharge Standard",the research carried out the analysis of sewage treatment plant,analysis of process in sewage treatment plant and pilot test about upgrading and reconstruction,and explored the difficulties and solutions of the upgrading and reconstruction combined with the experience of upgrading and reconstruction in other regions of China.Sewage treatment process in China is mainly based on the principle of traditional biological nitrogen and phosphorus removal.In order to achieve effective biological treatment,the process has certain requirements for the nutritional structure of raw sewage.Among them,the content of carbon source is a very important constraint in the process of denitrification to remove total nitrogen.Nitrate nitrogen（NO₃^-）is the main component of total nitrogen in the effluent of most sewage treatment plants,and the main reason for its accumulation is the low denitrification rate caused by insufficient carbon source.Through the investigation and analysis of typical AAO Process,it showed that the main factor limiting the total nitrogen removal rate in plug flow activated sludge process with nitrification liquid reflux and sludge reflux is that the contradiction of increasing nitrification liquid reflux to improve denitrification capacity and reducing total nitrogen in tail water,and that the reduction of carbon source concentration in anoxic zone caused by diluting raw water with large amount of reflux liquid,which restricts denitrification.What is more,in the activated sludge process,the effective bacteria in the circulating activated sludge have the alternation process of activation,dormancy and awakening with the change of functional areas,and the effective utilization rate is not high.In view of this problem,this research aims to increase the microbial biomass and improve the living environment of microorganisms,fix and cultivate the microbial flora,and use the new biomass filler as the carrier.The sludge film composite system process and denitrifying active sand filter process were the main pilot research objects.The feasibility and effectiveness of the measures were verified in the small scale and pilot scale study on the enhancement of ordinary AAO Process by using novel biomass filler as biofilm carrier.After two months of adjustment and operation,the effluent COD_Cr,total nitrogen and total phosphorus of the small plant have reached the"Class-A"standard,the ammonia nitrogen has reached the"Suzhou Special Discharge Standard",and it has a certain treatment while reducing the sludge concentration of activated sludge.After six months of regulation and operation,the average removal rates of COD_Cr,ammonia nitrogen,total nitrogen and total phosphorus in the pilot plant were respectively 92.48%,96.18%,75.94%and 93.19%.Even in the early winter,all kinds of water quality can reach the"first class a"standard,while in summer,except for the total phosphorus,all other water quality can reach the"Suzhou Special Discharge Standard",especially the total nitrogen in the effluent was 7.06 mg/L.The average load of sludge on the novel biomass filler was9.4 mg/g.Compared with the single activated sludge system,the sludge membrane composite system was more stable in nitrogen removal,and microbial detection showed that most of the microorganisms in the biofilm were the Caldilineaceae.In addition,the filler itself has a certain adsorption effect on ammonia nitrogen,and the overall strengthening effect on the process is significant.The pilot test of advanced biological treatment process adopted the denitrification filter process with active sand filter as pool type.Its continuous backwashing features are easy to manage,stable to operate,and meet the retention requirements of denitrification filter for biofilm.After three months of commissioning,the average effluent NO₃^-is 5.98 mg/L.The average removal rate was 14.6%,and the total nitrogen in the effluent reached the"Suzhou Special Discharge Standard",but the adjustment of carbon source dosage and stripping amount needed to be strictly controlled to achieve better effect.Taking the opportunity of a new round of upgrading and reconstruction,this project carried out the investigation and analysis of Suzhou sewage treatment plant and typical process,put forward the difficulties and solutions of upgrading and reconstruction,and carried out the necessary pilot test verification,which provided reference and suggestions for upgrading and reconstruction of Suzhou,which was in line with the basic national policy of increasing revenue and reducing expenditure and sustainable development in China,and had a broad application prospect,which was helpful to the development of Suzhou Promote the development of water treatment in China.