Difficulty Analysis Of Standard Improvement For Small Urban Sewage Plant And Scheme Study On The Corresponding Transformation Process

For the deeper implementation of the provincial policy, i.e’five water treatment, pollution control first’, the further reinforcement of water governance in Zhejiang province, thus the comprehensive improvement of water environment and the accelerating of transformation and upgrading, Environmental Protection Department in Zhejiang Province released the policy of’Implementation plans for waste water treatment (from 2014 to 2017)’on April 30,2014. The plan pointed out that the strategy of’one factory, one policy’ should be fulfilled, and standard improvement as well as transformation process for small urban sewage plant should be accelerated, especially for all of those the effluent of which can not meet the level of standard A provided in ’Discharge standards for pollution from urban sewage plant’(GB18918-2002).One plant in a town in Linan, Zhejiang Province, designed with the treatment scale of 5000 tons per day and with the required effluent quality level of standard A provided in’Discharge standards for pollution from urban sewage plant’, employs the treatment process which is a combination of grid, grit chamber, primary sedimentation basin, A2O-SBR and standard discharge well. Yet during the practical operation, the practical water treatment rate ranges from 67% to 92%, meaning that the practical influent load is lower than the desigened one. In the practical enffluent, the water indexs of COD, BOD5 both fulfill the level of standard A while the indexs of SS, TN, and TP can not meet the standard A, simultansously, although they all reach the standard B as expected in the design. As no disinfection device was installed in the previous prject, the standard fulfillment of TN, TP and SS and the disinfection of tail water are the key point and the difficult point for the standard improvement as well as transformation process in this plant.Based on the current situation and operation of this plant, as well as the difficult point for the standard improvement as well as transformation process, the current thesis check the original design parameters, including process flow, structure design, equipment selection, analysising the difficult points for the standard inprovements, and then put forward the corresponding solutions.The current solution is as follows:multiphase polymer-PVA biological packings are set to strengthen the biochemical treatment stage, enhancing biological denitrification efficiency without water outage and mechanical halt; deep treatment technology (coagulation sand filter) is added after biological system, utilizing aluminum sulfate as flocculant and PAM as coagulant aid, to strengthen the phosphorus and suspended solids removal capacity; ultraviolet disinfection is utilized to remove the microbial contamination in tail water, so as to make the indexs of TN, TP, SS, fecal escherichia coli achieve the stability of level of standard A.After the renovation, the receiving water quality can be improved and pollutant emissions can be cut. Pollutant emissions of COD, BOD5, SS each can be reduced by 18.25 tons per year, while NH3-N be reduced by 5.48 tons per year, TN 9.13 tons per year, TP 0.91 tons per year. The project total investment 4.4375 million yuan, the unit cost 887.50 yuan/tons of waste/day, modified some of the new operation cost 0.103 yuan/tons of water, after transforming the total operation cost 0.803 yuan/tons of water.