Efficiency Of Micro-electrolysis And Deep-bed Filter Combined Process For Treating Secondary Effluent Of Wastewater Treatment Plant

To further enhance the environmental quality of water,the parts of the sewage plant effluent contaminant standards increased from class A to quasi-class IV.In the standard,the effluent concentration of COD was less than 30 mg L^-1,TP was less than 0.3 mg L^-1,TN was less than 10 mg L^-1,NH₄⁺-N was less than 1.5 mg L^-1,respectively.Therefore,the secondary effluent of sewage treatment plants need to be deeply treated in order to achieve high standard discharge.The micro-electrolysis can simultaneously remove organic matter and phosphorus.However,the systematic research on secondary effluent treatment is insufficient.In addition,it is often suitable for acidic conditions,and its processing capacity is limited under neutral conditions.Therefore,improving packing performance and optimizing operating conditions are particularly critical to improving processing capacity.Moreover,it has weakly effect on nitrate removal,unless it combine with a deep-bed filter.In this paper,by preparing the micro-electrolysis packing that can efficiently remove pollutants under neutral conditions and optimizing the operating conditions of the micro-electrolysis filter,to tap the potential of the micro-electrolysis filter column.Simultaneously,by combining the deep-bed filter to achieve in-depth control of organic matter and nitrogen and phosphorus,and to analyze the microbial community and pollutant removal mechanism characteristics.Optimize the filler preparation components and conditions,a micro-electrolytic filler suitable for simultaneous removal of COD and TP from the secondary effluent is prepared.The optimal conditions for preparing the components were as follows.Set iron-to-carbon mass ratio as 2,used ammonium chloride as pore former and the addition ratio was 2%,bentonite as binder optimal and addition ratio was 10%,copper as catalyst and iron-copper-carbon mass ratio was 2:0.5:1,respectively.Calcination temperature of the filler was 600 degrees Celsius and the roasting time was 0.5 hours.Characterization of the filler found that it owned developed pores which diameter 2 nm to 10 nm as mesoporous.The main components exist in the form of elemental form and were stable.Carry out continuous flow experiment with the best prepared packing,and optimize the operating parameters of the micro-electrolysis filter.When the ratio of air to water ratio was 15,the best empty bed contact time was 105 minutes,and the backwash cycle was set to 12 hours,the COD concentration of the effluent water was less than 30 mg L^-1and the TP concentration was less than 0.30 mg L^-1.It met the requirements of"Quasi-Class IV"discharge standard except TN.The effluent concentration of TN was more than10 mg L^-1.The removal mechanism of pollutants in micro-electrolysis was explored.The result showed that the humic acid-like organics in the effluent was significantly reduced and high molecular weight organics were gradually decomposed.And the phosphate was removed by the Fe²⁺and Fe³⁺by forming Fe₄（PO₄）OH₃ and Fe₃（PO₄）₂ produced in the system.Deep-bed filter was coupled to achieve deep denitrification.The optimal conditions were sodium acetate as external carbon sources,C/N ratio of 5 plus minus 0.5,the empty bed contact time of 45 minutes,and the backwash cycle was 72 hours.On this basis,combine micro-electrolysis and deep-bed filter to investigate the continuous operation efficiency.The result showed the effluent concentration of COD,TP,TN and NH₄⁺-N all met the requirements of the standard.The microbial community structure of the coupled process.It found that the micro-electrolysis column was dominated by heterotrophic denitrifying phosphorus accumulating bacteria and some nitrate-type iron oxidizing bacteria.Chemical denitrification and biological denitrification took place in the system,and a certain amount of nitrogen was removed.In the deep-bed filter column,the microorganisms were mainly heterotrophic nitrifying-aerobic denitrifying bacteria and other denitrifying and denitrifying bacteria.