Experimental Study On Treatment Of Nitrogen And Phosphprus In Urine By Eletrolysis

According to the environmental conditions of the place where people live and the differences in food intake habits and quantities,the amount and composition of urine discharge is slightly different.Human urine accounts for 1 percent of urban sewage,but contributes about 80 percent of nitrogen,50 percent of phosphate,10 percent of chemical oxygen demand（COD）and 70 percent of potassium.And a considerable amount of sulfate,potassium,hormones,drugs and their metabolites.At present,the domestic and foreign domestic sewage discharge mode basically adopts the mode of"flushing toilet,sewage pipe network-sewage treatment plant",but there are some disadvantages in this sewage treatment mode.For example,the large amount of water resources,the high cost of investment and operation,the difficult treatment of sludge,the high energy consumption,which are not conducive to the recovery effective resources of nitrogen and phosphorus.Compared with mixed sewage,such as separate collection of fecal and urine with high pollutant concentration but small volume,and reuse of treated water,it will be helpful to reduce the operating load of municipal sewage treatment plant and to improve the quality of effluent at present.based on the idea of energy conservation and automation,more and more experts and scholars from different countries have put forward the effective technology of collecting and treating domestic sewage separately from the source.Compared with traditional urine microbiological treatment technology,the electrochemical technology reactor has the advantages of simple equipment,small area,easy to realize automation,no secondary pollution and so on.It has been successfullyappliedtomostindustrialwastewatertreatment.Mostof ammonia-nitrogen was oxidized to nitrogen,a small part formed nitrate,and the degradable organic matter in solution was mineralized.Based on the previous research and the results of our own experiments,we propose to take simulated human urine and actual urine as research objects,set nitrogen and phosphorus,organic matter as the target pollutant respectively,In-depth exploration of the influence of the factors of electrochemical denitrification,degradation of organic matter and phosphorus removal process.After that,we make a small device to integrate the above process,and optimize the operation parameters.The contents of nitrogen,phosphorus and organic matter in urine are reduces after treatmentd,which provides scientific basis for the subsequent treatment of urine and the treatment of wastewater with high concentration of nitrogen and phosphorus.The main conclusions are as follows:1)Electrolytic treatment of ammonia nitrogen and organic matter in simulated urine.The removal of ammonia nitrogen and organic matter by anode electrode of RuO₂-IrO₂-TiO₂/Ti is better than that of graphite and iron.The influence degree of ammonia nitrogen and organic matter degradation was in the order of:initial pH>current density>plate spacing.The pH of normal human urine remained neutral at room temperature.Considering the removal effect of ammonia nitrogen and COD and the pH of actual urine,the current density of 80 mA/cm²and the polar plate spacing of 2 cm were determined under the optimum experimental conditions,the removal rate of ammonia nitrogen and COD in urine reached 91%and 44%after 180min without adjusting the pH value of urine.Therefore,it is feasible to removal of nitrogen and degradation of organic matter in urine by electric method.2)An experimental study on electrolytic treatment of phosphorus in urine using iron plate electrode as anode material,the cathode material（such as RuO₂-IrO₂-TiO₂/Ti,iron,graphite）has little effect on phosphorus removal in the system.The theoretical optimal combination corresponds to the initial pH,and the current density and plate spacing are 7,40mA/cm²,2cm respectively.And aeration is optimal at 1.0 L air/min·L solution.The effect of electrolytic phosphorus removal in the system was significant:initial pH>current density>plate spacing.Removal of ammonia nitrogen and COD The rate respectively reached 93%and 14%after 90min in actual urine.3)Considering the hydraulic structure,degradation efficiency,energy consumption and economic practicability of the reactor,the electrocatalytic oxidation technology and the electroflocculation technology are integrated.A small device was designed and made including the main structure size of reactor and the time ratio of denitrification,organic degradation and phosphorus removal set as 2:1.The reaction time was 160 min and 80 min respectively.Graphite and stainless steel were selected as electrode materials.Firstly,graphite rod was used as anode and stainless steel as cathode material.The process of denitrification and phosphorus removal was carried out alternately.The exchange time of the electrode was 40^thmin,80^thmin,160^thmin,200^thh min,respectively.4)The simulated urine was treated by the integrated small device.The final removal rate of ammonia nitrogen,COD,total phosphorus was 83%,51%,92%,respectively.Taking the actual pure urine collected by the male toilet on the 5th floor of Ruizhi Building of Chongqing Technology and Business University as the research object,and the treatment capacity is 1L.The highest removal rate of ammonia nitrogen,COD,total phosphorus was 82%,38%,90%respectively,without the pH of urine adjusted.The electrode polarity was changed intermittently and there was no obvious passivation on the surface of stainless steel electrode.Therefore,the degradation of ammonia nitrogen,COD,total phosphorus in urine is feasible.Due to the limitation of experimental conditions and time,in this paper,the removal of ammonia nitrogen and total phosphorus in urine is limited to laboratory stage.The physical and chemical reaction process of electrolysis is complex.On the other hand,involving many factors in the experiment,such as complex urine ingredient and obvious individual differences,unstable physicochemical properties,there are shortcomings inevitably and need further in-depth study.The mechanism and the practical application of urine electrochemical method need to be further studied in the future.