Study On Upgrading Process And Operation Of Municipal Sewage Treatment Plant

Nitrogen and Phosphorus are important factors of eutrophication and it is also difficult problem for most municipal wastewater treatment plants in upgrading and modification.In order to enhance the quality of all effluent index,decrease content of nitrogen and phosphorus in water and improve self-purification ability,therefore,It is necessary for sewage treatment plant to research and develop sewage treatment process with a small area?efficient treatment and low energy consumption in operation.The paper mainly studies post-modification process and operation status of 4^th sewage treatment plant in Xi'an city,All effluent index have been increased to level A criteria specified in the discharge standard of pollutants for municipal wastewater treatment plant?GB18918-2002?by reducing the number of primary sedimentation tank operation?adjusting inverted A²O to traditional A²O process and redividing the volume of the reactor?adding 20%suspended fillers in the Anaerobic and Anoxic tanks and reconstructing rotary fibre cloth filter.In addition,this modification is characterized by low work amount?low cost and full use of previous structures,so as to provide reference for upgrading of similar sewage plants.All indexes of pre-modification influent and effluent were tested by means of the national standard method,COD and NH₃-N meet the first level A criteria completely.However,TN?TP and SS is only 65.3%,33%and 26.7%for level A standard rate.therefore,wastewater treatment plant should attach importance to the removal of nitrogen?phosphorus and suspended solid.During the upgrading and retrofitting,the concentrations of COD?NH₃-N?TN and TP?SS in the effluent were reduced to 25 mg/L?0.28 mg/L?7.21 mg/L and 0.21mg/L?5 mg/L respectively in daily operation,the effluent quality meet the discharge standards.Through the treatment of post-modification sewage treatment system at all levels,it is shown that:1)Reducing the number of primary sedimentation tank operation,the value of effluent COD?NH₃-N?TN and TP increase to 199.01 mg/L?34.7 mg/L?49.82 mg/L and 4.19mg/L respectively.more importantly,the content of COD increase to 199.01 mg/L from about 90mg/L,which provide sufficient carbon source for nitrogen and phosphorus removal by microorganism.2)Redividing the volume of the reactor?decreasing the dissolved oxygen concentration in the Oxic tank?adjusting inverted A²O to traditional A²O process and adding suspended fillers in the Anaerobic and Anoxic tanks,the quantity of MLSS in Anaerobic and Anoxic tank reached5620mg/L and 6200 mg/L respectively,Under the condition of not expand reaction volume,the number of microorganisms achieve a surge,whats more,the concentration of Nitrous Nitrogen in the anaerobic tank decrease to 0.88 mg/L from 3.49 mg/L before,providing a premise for high efficiency of phosphorus absorption.In terms of denitrification,the removal amount of post-modification TN increase to 22.14 mg/L in Anoxic tank,which was improved from pre-modification 15mg/L.In addition,as for the phosphorus removal,the release amount of post-modification phosphorus from 0.67 mg/L to 1.47 mg/L in Anaerobic tank,the uptake amount of phosphorus increase to 2.77 mg/L from about 1.5mg/L than before in Oxic tank.3)Reconstructing rotary fibre cloth filter in depth treatment,The average removal rate of COD?NH₃-N?TN and TP?SS is up to 12.7%?15.2%?11%and 46.9%?35.09%.Achieving removal of TP and SS,which is further to ensure that all effluent indexes meet standard in the future.All stages of the compound treatment process were fitted,it is find that:the first level physical treatment stage has better relation,in which NH₃-N?TN?TP and HNO₃-N have significant correlation.the two stage of biological treatment stage is basically not fitted.in addition,the COD?NH₃-N and TN have also better relation in the depth treatment stage.