Study On The Urine Purification And Electricity Generation By Photoelectrochemical Method

Urine is a major nitrogen and COD source and threatens the aqueous environment,leading to eutrophication and energy consumption.However,the conventional technologies encounter the bottleneck due to the high load of nitrogen and organics in urine.Here we propose an innovative idea for complete transformation of urea-nitrogen to N₂ and simultaneous degradation of organics to CO₂ with the assistance of chlorine and hydroxyls radicals（Cl·and HO·）in photoelectrochemical cell system.This idea reveals circulation process of these two radicals:photoexcited holes from WO₃ anode oxidize chloride and hydroxyl ions to Cl·and HO·radicals under illumination,these radicals convert urea-nitrogen to N₂ or slight nitrate,and then slight nitrate is selectively reduced to N₂ on a novel Pd/Au modified porous metallic sheet.TN analysis of a simulated urea solution of 30 mg L^-1 demonstrated that N₂and CO₂ are the primary oxidation products of the urea,and the urea-N was completely stripped（99.45%）in 90 min.Meanwhile,with the detection of EPR spectrum,organics can be transformed to CO₂ by OH·in this cyclic system.Significantly,the feasibility of actual urine treatment was also investigated,indicating great denitrification efficiency（99.37%）and TOC removal efficiency（50.91%）,respectively.On the other hand,urine is a major biomass resource,and its excessive discharge would lead to serious aquatic nitrogen pollution and even eutrophication.In this study,we designed an innovative denitrified fuel cell（DFC）to purify urine and convert its chemical energy into electricity.The central ideas include the following:1)on the anode,chlorine radicals（Cl·）and hydroxyl（HO·）radicals were induced to react with amine or ammonia in urine into N₂,and to mineralize organics into CO₂,respectively;2)on the cathode,NO₂^-or NO₃^-generated in the cell was selectively reduced to N₂ and tiny NH₄⁺by Pd/Au/NF;3)NH₄⁺was further oxidized to N₂ by Cl·according to process 1),then the total nitrogen（TN）was ultimately removed by a continuous redox loop between anode and cathode;4)the separation and migration of charges were strengthened by a self-bias poly-Si/WO₃ photoanode.The DFC showed an efficient electricity yield and almost completely N-removing properties:power density of 2.24 mW cm^-2,total nitrogen and total organic carbon（TOC）removal efficiency,respectively 99.02%and 50.76%for artificial urine;and power density of 2.51 mW cm^-2,TN and TOC removal efficiency,respectively 98.60%and 54.55%for actual urine.In this paper,the photocatalytic electrolysis cell and urine fuel cell were constructed to effectively transform the chemical energy of pollutants and electric energy into each other,so as to remove TN and TOC in urine.The study proposes a potential and environment-friendly approach by using novel DFC to purify urine and generate electricity.