Research On Construction Of Metal Anode Battery Electrocoagulation System And Removal Efficiency Of Nitrogen And Phosphorus

With the acceleration of urbanization,the total sewage discharge increases year by year,while the sewage discharge standards are raising stricter.Thus,it is of practical significance to seek"high-efficiency and low-energy consumption"technology for sewage treatment.As an electrochemical wastewater treatment technology,electrocoagulation（EC）technology attracts great attentions due to its wide application range,short reaction time,stable and easy separation of flocs,low sludge yield,non-secondary pollution et.al.However,the high energy consumption and electrodes passivation negatively affect the treatment efficiency and limit its further application.Therefore,this research developed a novel metal-battery electrocoagulation system by applying metal batteries to electrocoagulation technology,and systemically investigated the influence of different process and parameters on the removal of nitrogen,phosphorus,and organic matters in wastewater.The novel metal-battery electro-coagulation system not only achieved efficient removal of nitrogen and phosphorus,more importantly,it generated electricity during operational period,which significantly reduced the overall energy consumption for wastewater treatment.In this study,a single-chamber metal-air battery electrocoagulation system was constructed,the metal anodes were iron mesh and aluminum mesh,and the cathode was typical rolled air cathode.In this system,the flocculants were formed with electeicity generation.In order to meet the discharge standards,using iron mesh as anode achieved98%phosphorus removal with a reaction time of 30 mins,while the aluminum as anode with the reaction time of 50 mins was more than 98%.Meanwhile,the distance of metal anode to air cathode was 2 cm,the external resistance was 10Ω,and the electrolyte concentration was 10 mmol/L of Na Cl.Based on the results,the external resistance and electrolyte conductivity were discerned as the main factors that highly affected the phosphors removal efficiency.Reducing external loading and increasing electrolyte conductivity can improve the circuit current and the flocculants generation rate,which enhanced the phosphorus removal.The initial p H values showed limited effect on the phosphorus removal,indicating that the metal-air battery gained wide range of applicable scenarios on phosphorus removal and realize multiple wastewater treatment and purification.This study further examined the metal-air battery effectiveness in treating practical domestic sewage.When the initial p H was acidic（p H=5）,the reaction time was 60 mins,and the external resistance was 10Ω,the phosphorus removal achieved at 96.6%with an effluent concentration less than 0.5 mg/L,which met the domestic sewage discharge standards.Besides,the COD removal of 55.6%and turbidity removal of 68.5%were achieved.In generally,the efficient phosphorus removal could be achieved when the system was operated under low external loading and high circuit current condition,while increasing stirring rate is also beneficial to the phosphorus removal.In addition,the aluminum-air battery exhibited considerable electricity generation capability,with a generated current of 33.2 m A under the external resistance of 5Ω.In summary,the mechanism of metal-air battery electrcoagulation on phosphorus removal was systematically analyzed in this part,which provided important theoretical basis for its further application.In order to enhance nitrogen removal,this study constructed an electrocoagulation system with iron anodes coupled with nitrification and denitrification biocathode,which took advantage of highly efficient nitrogen removal of biocathode and achieved simultaneous removal of ammonia and phosphorus.From the observations,the nitrification and denitrification biocathodes were successfully combined with metal anode,and the maximum power density of nitrification part and denitrification part reached 6.0 W/m³ and 6.6 W/m³.In addition,97.4±0.6%of phosphorus and 99.2±0.5%of SS（algae）were removed by iron anode coagulation.In the nitrification chamber,95.3±1.4%of ammonia was oxidized within 6.0 hours,the main product was nitrate,while in denitrification chamber,nitrate reduction of 61.0±1.8%and 88.2±2.5%and 88.2±2.5%was achieved within 6.0 hours and 10.0 hours respectively,the main product was nitrogen gas.The iron anode coupled nitrification and denitrification electrocoagulation system simultaneously achieved efficient nitrogen and phosphorus removal.In addition,the composition analysis of microbial communities revealed that the nitrifying bacteria included Acinetobacter sp.,Phycisphaera sp.and Nitrosomonas sp.,and the dominant denitrifiers were Planococcus sp.,Exiguobacterium sp.and Lysinibacillus sp.,which playing important roles on nitrogen removal.Finally,considering the capability of electricity generation and flocculant production of metal-air battery,it was applied as the power source for microbial electrolysis cells（MECs）to obtain the combined treatment for sewage treatment,the metal-air battery improved the effluent quality and achieved energy recovery in form of hydrogen in MEC.In the aluminum-air battery combined MEC system,the MEC could remove 75±1%of COD of synthetic wastewater,and it could be further improved to 82±1%when the effluent from MEC was further treated by aluminum flocculant produced by the battery,while the hydrogen production rate of 0.19±0.01m³H₂/m³/d would be obtained.The iron-air battery-MEC system was constructed to treat swine wastewater,when the produced flocculants from battery were used to pre-treat the swine wastewater,the ammonia removal would be obtained at 54±3%,while that removal of COD,SS,and turbidity were 27±2%,49±1%,and 34±3%,respectively.Furthermore,the COD removal efficiency after MEC treatment was further increased to 98±0.2%,and the hydrogen production rate was gained at0.057m³H₂/m³/d.In summary,the metal battery electrocoagulation system combined microbial electrolysis cells system achieved simultaneously pollutants removal and energy recovery,and realized the goal of“high efficient and low-energy consumption”during sewage treatment process.The application of metal batteries for electrcoagulation resolves the problem of high energy consumption of traditional electrcoagulation system,and provided a novel method for the goal of low-carbon and energy-saving wastewater treatment.