Coupled Heat-Activated Persulfate/Electrochemistry For Catalytic Oxidation Landfill Leachate Concentrates

Landfill leachate concentrates is the waste solution trapped by nanofiltration/reverse osmosis（NF/RO）membrane in the biochemical effluent of landfill leachate.It has high content of salt and dissolved organic matter（DOM）,especially refractory organic matter.Without effective treatment,the landfill leachate concentrates will be discharged directly into rivers,reservoirs and other receiving water bodies,which will seriously damage the ecological environment and pose great potential harm to human health.In this paper,the leachate of a domestic waste incineration power plant in Nanchang city,Jiangxi province was treated by a combined process of"pretreatment+UASB reactor+MBR system+DTNF/RO system",in which the landfill leachate concentrates produced by the DTNF/RO system was taken as the research object.Adopts heat activation persulfate oxidation,Ti/RuO₂-IrO₂ anodic oxidation and heat-activated persulfate/electrochemistry for catalytic oxidation of three oxidation systems disposed of the landfill leachate concentrates,the chroma,COD,ammonia nitrogen and Cl^-removal rates as examining index of oxidation effect,discussed the main factors of different oxidation system of landfill leachate concentrates oxidation effect,and the best experimental conditions before and after the reaction of landfill leachate concentrates on UV-vis spectra,3D-EEMFS and FTIR analysis,respectively.In the heat-activated persulfate oxidation system,under the optimal experimental conditions of initial pH value 7.8,temperature 70℃,PS₀ concentration 10 g/L,reaction 3 h,the chroma,COD and ammonia nitrogen removal rates were 90%,52.3%and 77.5%,respectively.The chroma,COD and ammonia nitrogen removal rates all increased with the increase of reaction time,and then tended to be stable.With the increase of temperature,the chroma,COD and ammonia nitrogen removal rates gradually increase,when the temperature reaches 70℃,continue to increase the temperature,the chroma,COD and ammonia nitrogen removal rates increase little.The concentration of PS₀ increased,and the removal of chroma,COD and ammonia nitrogen first increased and then stabilized.The removal rates of COD and ammonia nitrogen were negatively correlated with initial pH.UV-vis spectrum analysis showed that the aromatization degree and relative molecular mass and polymerization degree decreased of DOM in the landfill leachate concentrates after heat-activated persulfate treatment.3D-EEMFS showed that humic acid was oxidized to humic acid with simpler structure and smaller relative molecular mass in the landfill leachate concentrates after heat-activated persulfate treatment.FTIR analysis showed that the absorption intensity of organic compounds in the landfill leachate concentrates decreased and some organic compounds were oxidized and degraded after heat-activated persulfate treatment.In the Ti/Ru O₂-IRO₂ anodic oxidation system,under the optimal experimental conditions with the initial pH value of 7.8,current density of 8 A/dm²,plate distances of 1 cm,and electrolysis time of 4 h,the chroma,COD,ammonia nitrogen and Cl^-removal rates were 100%,100%,98%and 52%,respectively.UV-vis spectrum analysis showed that the aromatization degree and relative molecular mass and polymerization degree decreased of DOM in the landfill leachate concentrates after electrolysis treatment.3D-EEMFS showed that humic acid was oxidized to humic acid with simpler structure and smaller relative molecular mass and soluble microbial degradation by-products in the landfill leachate concentrates after electrolysis treatment.FTIR analysis showed that the absorption intensity of organic compounds in the landfill leachate concentrates decreased and most organic compounds were oxidized and degraded after electrolysis treatment.The current efficiency and energy consumption showed that the current efficiency was the highest when the current density was 4 A/dm².When the current density was greater than 8 A/dm²,the current efficiency decreases with the increase of the current density.With the extension of electrolysis time,energy consumption increases gradually.After electrolysis for 4 h,energy consumption increases the fastest.There was a negative correlation between energy consumption and current efficiency.Under the optimal experimental conditions,the energy consumption was 80.61 kWh/kg COD.In the heat-activated persulfate/electrochemistry for catalytic oxidation system,under the optimal experimental conditions with the initial pH value of 7.8,current density was 8 A/dm²,plate distance was 1 cm,PS₀ concentration was 10 g/L,the system in 70℃reaction 4 h,the chroma,COD,ammonia nitrogen and Cl^-removal rates were 100%,100%,100%and 64.9%,respectively.It has good removal effect on chroma and ammonia nitrogen,and can be removed completely basically.With the increase of PS₀concentration,the COD removal rate showed an increasing trend,while the Cl^-removal rate first decreased and then increased.With the increase of temperature,COD removal first gradually increases and then tends to be stable,and Cl^-removal rate showed a trend of gradual increase.The plate distances have little effect on chroma,COD and ammonia nitrogen removal rates.After 4 h of reaction,chroma,COD and ammonia nitrogen can be basically completely removed.UV-vis spectrum,3D-EEMFS and FTIR analysis showed that the aromatization degree,humus degree and molecular weight and polymerization degree decreased of DOM in the landfill leachate concentrates after treatment;the humic acid was basically completely oxidized and removed;the absorption intensity of conjugated double bonds,phenolic hydroxyl groups,benzene and C-H on substituted benzene aromatic rings decreased,and most organic compounds were oxidized and degraded.Compared with heat-activated persulfate oxidation system and Ti/Ru O₂-IRO₂ anodic oxidation system,the heat-activated persulfate/electrochemistry for catalytic oxidation system has the best removal effect on chroma,COD and ammonia nitrogen.The comparison between Ti/Ru O₂-IRO₂ anodic oxidation system and heat-activated persulfate oxidation system showed that the chroma and ammonia nitrogen removal rates in the landfill leachate concentrates was mainly due to the high Cl^-concentration in the water sample,the anodic precipitation of Cl₂was dissolved in water to form HCl O,and the strong oxidation of HCl O was used for indirect oxidation.In addition,compared with Ti/Ru O₂-IRO₂ anodic oxidation system and heat-activated persulfate/electrochemistry for catalytic oxidation system,respectively,the COD removal rate of the heat-activated persulfate oxidation system was far lower than that of the other two oxidation systems.This may be because of the high Cl^-concentration in the water sample,and a large amount of the generated SO₄^-·was consumed by Cl^-.In conclusion,the heat activated persulfate oxidation system and Ti/Ru O₂-IRO₂ anodic oxidation system showed a synergistic effect and had certain synergistic effect.