Study On The Pd/XC-72R And Cheap Metal Electrode For Electrochemical Simultaneous Nitrogen And Phosphorus Removal

At present,the secondary effluent of municipal wastewater treatment plants in China is generally facing the problem of excessive total nitrogen concentrations.The municipal wastewater has low C/N.According to the traditional biological process,a number of additional carbon sources need to be added to achieve the discharge of total nitrogen.At the same time,the removal of total phosphorus also needs to add a amount of flocculant,which leads to a substantial increase in the operating cost of the municipal wastewater treatment plant.This paper intends to adopt an electrochemical method to combine the electroreduction and electroflocculation processes to achieve the simultaneous removal of nitrogen and phosphorus in wastewater.In this study,two types of electrochemical methods,ie,self-made carbon-loaded palladium(Pd/XC-72R)cathode,cheap metal iron anode,and cheap metals(iron and aluminum)as cathodes and anodes,were used to deeply remove nitrogen and phosphorus,the feasibility of nitrogen and phosphorus removal and the main factors were investigated,and the mechanism of nitrogen and phosphorus removal was discussed and analyzed.Studies have shown that the crystal structure of the Pd/XC-72R catalyst prepared by the ethylene glycol reduction method was dominated by the Pd(111)crystal plane.The electrolytic system composed of Pd/XC-72R cathode and iron anode was feasible for the removal of nitrogen and phosphorus in wastewater.The presence of Na Cl in the solution inhibited the reduction of nitrate,but promoted the conversion of ammonia to nitrogen.The reduction rate of nitrate was positively related to the current density applied between the two plates.When the current density was 8 m A/cm~2,the reduction rate of nitrate was 100%.Throughout the test,100%phosphate removal was achieved.The Pd/XC-72R electrode has high electrochemical stability.In the cheap metal electrode system,the simultaneous removal of nitrogen and phosphorus from the secondary treatment effluent was feasible.It could achieve 81%total nitrogen removal and 100%phosphate precipitation.After 1.5 h of electrolysis at a current density of 8 m A/cm~2,the reduction rate of nitrate was 93.65%.At this time,the concentrations of nitrite and ammonia were 0.13 mg/L and3.47 mg/L,respectively.The selectivity of nitrogen gas was as high as 90.76%.Compared to iron,aluminum electrode was more suitable as electrode material for denitrification and dephosphorization,which not only had less losses,but also produced more nitrogen in the product of reducing nitrates.Studies had shown that electroreduction of nitrate was carried out in steps.Phosphate was removed by co-precipitation.When using aluminum as cathode and anode to remove nitrogen and phosphorus from the effluent of the secondary sedimentation tank of a municipal wastewater treatment plant in Beijing,under the condition of electrolysis time was 1.5 h and current density of 8 m A/cm~2,the effluent quality conformed to the Class A of pollutant discharge standard of the municipal wastewater treatment plant(GB18918-2002).The energy consumption of the electrochemical method for nitrogen and phosphorus removal was 0.54 KWh/m~3,and the electrode loss was 0.105 g/m~3.