Study On The Treatment Characteristics Of Leachate By A Novel Composite Anode Supported Electro-hybrid Ozonation-coagulation(CA-E-HOC) Process

In recent years,the combined treatment process of"anaerobic-anoxic/aerobic MBR biological+nanofiltration and reverse osmosis"has become the mainstream process of leachate treatment in China.However,due to the high concentration of refractory organics and ammonia nitrogen（NH₄⁺-N）in the leachate,which has a strong inhibitory effect on microorganisms,the conventional biological process treatment is not complete.After the effluent from the biological treatment enters the membrane for advanced treatment,the membrane pollution is serious,and the generation of concentrated liquid is large.The accumulation of pollutants caused by the recharging of concentrated liquid continuously deteriorates the effect of treatment process.In response to the above problems,a composite anode supported electro-hybrid ozonation-coagulation（CA-E-HOC）process was constructed to achieve the simultaneous removal of organics and NH₄⁺-N in leachate.The process was applied to the pretreatment and advanced treatment of leachate and supplemented by conventional biological treatment process to solve the problems of low compliance rate and large concentration in the existing treatment process.This study provides a novel theoretical and application basis for the"full quantification"treatment of leachate.The main innovations of the paper are as follows:（1）Aiming at the problems of complex characteristics,high concentration of pollutants and large fluctuation of leachate,this paper systematically studied the water quality characteristics of leachate,clarified the limiting factors of leachate for biological treatment and pointed the objects that should be paid main attention to in the treatment process.Results showed that the main limiting factors of leachate from waste transfer stations（WTSs）and landfill leachate for directly biological treatment were high organic and NH₄⁺-N pollution load,poor biodegradability and low C/N ratio,respectively.It was also pointed out that improving the biodegradability of organics and effectively reducing the concentration of NH₄⁺-N in leachate by effective pretreatment technology are the key to improving the efficiency of subsequent biological treatment.（2）In order to reduce the toxicity of organics and NH₄⁺-N effectively by pretreatment,a CA-E-HOC process was constructed.The core of CA-E-HOC process was the synthesis of electrocatalytic anode and iron powder into composite anode（CA）,and the generation of active chlorine species（RCS）was enhanced in ozone-coagulation integrated reaction system.Results show that the Ti/Ru O₂-Ir O₂ and particle size of iron powder were the most suitable EO tube and iron powder for CA synthesis.The specific surface area,active site and the mass transfer efficiency of CA were improved compared with Fe and Ti/Ru O₂-Ir O₂ anode.The yield of active chlorine was 4～5 times that of conventional Fe electrode with only 23.36%-31.01%total amount of iron produced.The consumption rate of zero valent iron was significantly reduced,the passivation of electrode surface was effectively alleviated,and the removal effect of organic matter and ammonia nitrogen was improved.（3）In order to reduce the impact of leachate on the subsequent biochemical system,a CA-E-HOC process was constructed based on the CA to strengthen the simultaneous removal effect of organics and NH₄⁺-N.In order to reduce the impact of high organics and NH₄⁺-N load on subsequent biochemical system,treatment effect of CA-E-HOC process was evaluated,and the mechanism of pollutant removal was explored.The results show that CA-E-HOC existed the best simultaneous removal effect for organics and NH₄⁺-N removal with the highest ratio of CO₂/H₂O and gaseous nitrogen in the product.During the treatment process,the organics of leachate can be transformed and mineralized,which can improve the biodegradability and reduce the pollution load,respectively.Multiple reactions such as synergistic between ozone and coagulants（SOC）,synergistic oxidation between active chlorine and ozone（SCO）,electrolytic chloride oxidation（ECO）occurred in the CA-E-HOC,resulting in reactive species such as·OH,H₂O₂,HCl O/Cl O^-,Cl O·and Cl·production.The SOC reaction played the domaited role for organics removal and the ECO/SCO reaction domaited NH₄⁺-N removal.Strengthed RCS generation increased the content of coagulants and the proportion of dominant hydrolysis forms in the system through relieving the aging and of coagulants,resulting in more hydroxyl radical（·OH）generation form SOC.The·OH produced by SOC can also activate Cl^-that has not been electrolytically oxidized in the system,increasing the production of RCS.Therefore,the synergistic effects among ozone-coagulation-active chlorine exist in the process.（4）Based on the principle of"full quantification treatment"of leachate,the processing techniques for different sources and processing standards are proposed.Aiming at the management emissions standard of leachate from the WTS,the process of"CA-E-HOC pretreatment+two-stage A/O+MBR biological treatment+CA-E-HOC advanced treatment"was proposed.In view of direct discharge requirements,effluent of CA-E-HOC advanced treatment was introduced into post-A/O-MBR treatment.For the treatment of landfill leachate,a process of"CA-E-HOC pretreatment+two-stage A/O-MBR biological treatment+CA-E-HOC+post-A/O-MBR+ozone biological activated carbon advanced treatment"was recommended.Based on the above process,the corresponding treatment device was developed and applied in the actual leachate treatment project,which verified the reliability and practicability of the treatment process and the developed device.The research results of this paper provide a new technical support for the"full quantification"treatment of leachate.