Technological Research And Operation Performance Analysis On Upgrading Andreconstruction Of Urban Sewage Treatment Plant

In recent years,people's demand for environmental quality is getting higher and higher.The effluent from the original sewage treatment plant still has a negative impact on the environment.So more and more urban sewage treatment plants have carried out the upgrading work to meet the required standard.Taking the sewage treatment plant upgrading project of Dalian Lingshuihe as an example,this study carries out the following research and analysis:Firstly,through the investigation and analysis of the operating water volume of sewage treatment plant in recent years.We found that the average daily treatment volume was 64,033m³/d,and the maximum daily treatment water volume was 75,090 m³/d in 2017.The inffluent of the sewage treatment plant has reached the original designed workload,which called an urgent need to expand the treatment scale of the sewage treatment plant.Take this situation into consideration,the new water consumption after the upgrading work of the sewage treatment plant iscalculated to be 80,000 tons per day by utilizing three methods which areper capita comprehensive domestic water consumption index method,comprehensive water consumption index method of urban unit construction land and the index method of land usage.Secondly,through the analysis of water quality indexes?COD,BOD,SS,TN,NH₄⁺-N,TP,C/N?,it shows that neither TN effluent index nor TP effluent index can meet the grade A standard.At the same time,combined with the water quantity and water resistance and the evaluation of activated sludge,it is concluded that the CAST process needs to be modified to enhance the performance of nitrogen and phosphorus removal.In the current widely used nitrogen and phosphorus removal process,CAST,AAO,FCR and MBBR are selected for qualitative and quantitative technical and economic analysis.Then,we determined the biochemical process of the sewage treatment plant.It shows that the most suitable process for the upgrading project is to have the AAO pool capacity at 44,168 m³,sludge age of 14.88 d,unit power consumption of 0.361 degree/m³,the cost of water treatment per ton is 1.49 yuan and also has a certain low C/N ability to remove TN.The transformation of AAO process mainly increases the capacity of sewage treatment plant to remove TN.For the improvement of TP processing capacity,it is necessary to further increase coagulation and other deep processing units.Finally,though the research of reconstruction scheme and the actual operation performance after the reconstruction.During the construction,the use of non-cut water construction,can minimize the pollution to the environment.During the transformation of both the biological pool and the deep treatment unit,each unit is connected to the original sewage treatment system and put into use immediately after the completion of the transformation.After the complete transformation of the biological pool and deep treatment unit,the effluent index can basically be stable at COD 12.52 mg/L,BOD 4.36 mg/L,SS 2.20 mg/L,TN 18.20 mg/L,NH₄⁺-N 1.85 mg/L,TP 0.32 mg/L.For the effluent TN that did not meet the standard immediately,the orthogonal test was carried out during the commissioning stage,and the order of factors affecting the effluent TN was determined as internal reflux ratio>carbon source dosage>dissolved oxygen>external reflux ratio.Finally,the effluent TN reached 13.24 mg/L through the commissioning test,and the discharge reached the standard.At the same time,it is concluded that the order of factors affecting biological phosphorus removal is the treatment volume of a single biological pools>external reflux ratio>anaerobic tank inlet water ratio.It has a certain reference value to optimize the dosage of pharmaceuticals in the actual operation of sewage treatment plants.