Pilot-scale Experiement On Treatment Of Non-Point Source Pollution From Agricultural Area In Dianchi Lake Basin With MBR

Recently,with the point source pollution such as industrial sewage,municipal wastewater and others having been gradually controlled,non-point source pollution,especially from agriculture area is becoming the major contributor of water pollution.According to the statistics,Chemical Oxygen Demand,Total Nitrogen,Total Phosphorus respectively accounted for 37%,27%,45% of agricultural non-point source pollution discharged into Dianchi lake each year.At present,sewer interception tunnels and the mixed water purification plants have been built along the east and the south bank of Dianchi Lake.Howerver the area interception system served is so large,and the agricultural ditch distributed in the basin is so extensive that it is more difficult to manage and maintain the system.At the same time,the stability of the mixed water purification plant at the end of the system is influenced greatly by feedwater quality which is farther lower than the design value resulted from the lagging of villages sewage interception system construction and the permeating of groundwater and other factors.In addition,few reference experience of MBR applied to treat non-point source pollution in domestic and overseas.The efficacy of interception systerm and the control of the Dianchi Lake water environment are weaked by all of the above factors.In order to provide the guidance for the operation of the mixed water purification plant,a set of pilot-scale experiement equipment with the same MBR process as that in the real plant was set up to explore optimum operation techniques based on the characteristics of current water quality.The research results are significant to have the interception system in Dianchi Lake basin function effectively,to improve the water environment of the Dianchi Lake and to develop agricultural non-point source pollution treatment technology.The influence of nitrification ratio,sludge reflux ratio,mixed liquid suspended solids and dissolved oxygen on the process efficiency were investigated by single factor test,and the optimum operating values were determined.The effects of the nitrogen and the phosphorus enhanced removal from system by carbon and flocculant addition,operation optimization were analyzed.The effect of membrane contamination and cleaning measures were also discussed and evaluated.The research results are as follows.(1)The optimum operation parameters of the MBR process were nitrification solution ratio 200%,sludge reflux ratio 150%,MLSS 4000 ~ 5000mg/L,DO 1~2mg/L.The removal rates of CODcr,NH3-N,TN and TP were 80.29%,97.95%,27.10%,36.91%,respectively under the optimum condition..(2)With addition of 30mg/L sodium acetate,the removal rate of TN and TP were 40% and 46.42%,respectively.TN concentration in effluent could meet the discharge standard of class A assuringly.It was necessary to remove TP further.(3)With the increase of PAC dosage,the removal of TP was enhanced.The removal rate of TP was about 70% with 20mg/L PAC,and TP concentration in effluent was lower than 0.41mg/L which meets the discharge standard of class A.