Experimental Study On Electrochemical Treatment Of Rural Agricultural Non-point Source Sewage In Dianchi Basin

During the period from the Ninth Five-Year Plan to the Twelfth Five-Year Plan,an efficient collection and interception system at the front end,a sewage interception and storage system at the middle end and a sewage treatment system at the end of the lake were constructed,which played a significant role in reducing the non-point source pollution load and improving the water environment in Dianchi Lake.In order to solve the problem that the MBR process of a water purification plant in the terminal wastewater treatment system does not meet the standard,the MBR process was fine regulated in the early stage of the project,but the effluent TP can not reach the standard after the regulation.At present,chemical methods are used to strengthen phosphorus removal in the water purification plant to ensure that the effluent phosphorus is stable and up to the standard.However,the cost of chemical phosphorus removal is high,and there is a problem of waste disposal of phosphorus-rich chemical sludge,and the addition of phosphorus removal agent will aggravate the risk of film scaling.In addition,the efficiency of bio-unit treatment in MBR process is still low,and it is difficult to achieve intermittent treatment with open and seasonal?dry and rainy season?.In order to solve the above problems,a set of electrochemical treatment technology was proposed,and an electrochemical pilot-scale system was constructed in the water plant.The two aspects of direct treatment of rural agricultural non-point source sewage and intensive phosphorus removal from MBR effluent were studied.The removal effect of pollutants by electrochemical process and the optimization of electrochemical parameters were discussed.The effects of chemical phosphorus removal,prolonged reaction time?HRT?and electrolyte addition on enhanced nitrogen removal were studied.The parameters of electrochemical deep phosphorus removal were optimized by response surface methodology?RSM?.The economic indexes of chemical enhanced phosphorus removal and electrochemical enhanced phosphorus removal in Waterworks were compared.Through the research,the following conclusions are drawn:1)The removal rates of CODCr,NH₃-N,TN and TP were 65.9%,3.2%,6.7%and79.9%respectively under the conditions of current intensity=5A,plate spacing=7cm,plate number=6 pairs and HRT=6h.TP effluent can discharge much less than 0.3mg/L,but the effect of nitrogen removal is poor.2)The greater the current intensity of electrochemical process,the better the phosphorus removal effect.When the current intensity is equal to 5A and HRT is equal to 2.5h,the effluent concentration of TP can achieve the first-class A discharge standard of urban sewage.The less the number of plates is,the better the phosphorus removal effect is,but the difference is not significant,and the change of plate spacing will not have a significant or almost no effect on TP removal;prolonging HRT and adding NaCl electrolyte can enhance the phosphorus removal efficiency.The removal rates of NH₃-N and TN increased by about 35%when NaCl concentration was equal to 3000 mg/L and HRT was equal to 20 h in the electrochemical reactor.3)Enhanced phosphorus removal from MBR effluent by electrochemical process can meet the first-class A standard requirement when current intensity=5A,plate spacing=7cm,plate number=6 pairs,HRT=3h,and the maximum TP concentration of effluent is only 0.41 mg/L.When HRT=4h,the maximum TP concentration of effluent is only 0.25 mg/L<0.3 mg/L,which can meet the discharge requirement.In RSM parameters optimization,the combination of parameters that can make effluent TP reach the standard and the lowest energy consumption is:current intensity=2.56 A,plate spacing=7 cm,HRT=2.68 H.After optimization,the electrochemical power consumption is about 0.324 yuan/t wastewater,which saves 69%of the power consumption compared with the unoptimized situation.4)The comprehensive specific energy consumption of electrochemical enhanced phosphorus removal is 3334.76*10³ kJ/kg P.Compared with PAC chemical enhanced phosphorus removal,it can save 9.1%.In terms of treatment cost,the cost of electrochemical enhanced phosphorus removal is 253.13 yuan/kg P,which is about 7.7%higher than that of PAC chemical enhanced phosphorus removal.However,magnesium ammonium phosphate can be recovered by electrochemical process to compensate treatment cost.It is expected that it will be returned annually after replacing PAC chemical enhanced phosphorus removal.The yield benefit is 354,000 yuan per year,which can save 192,000 yuan per year compared with chemical phosphorus removal.