Genotoxic Assessment Of Old Landfill Leachate Prior And After MBR/UF/RO Treatment

The landfill leachate is a kind of high concentration of organic wastewater generated from the process of rubbish disposal in landfill,and ―Older‖ landfill leachate refers to leachate produced by landfill more than 5 years.―Older‖ leachate contains high concentration of ammonia,low concentration of organic pollutants,balanceless of C/N ratio,different kinds of poisonous and harmful substance,which will bring huge harm to ecological environment and human health if discharged directly without treatment.At present,project combined biochemical treatment(mostly used is membrane bioreactor-MBR)and depth treatment(membrane technology)is widely used in domestic landfill leachate,physicochemical indexes of effluent can meet the national standards(GB16889-2008)after treated by the technology,but whether it completely non-toxic and harmless is still unknown.Therefore,synthetically evaluating removal efficiency of pollutants and biological toxicity of effluent combined chemical analyses and biological genetic assessment is of great significance to minimize potential risk of leachate,as well as provide technical basis for the development of pollutant treatment project.This article investigated the removal efficiency of landfill leachate in Guangzhou of China,treated by MBR(denitrification/nitrification and post nitrification-denitrification)UF(ultrafiltration)/RO(reverse osmosis)project,the removal effect of poisonous and harmful pollutants about MBR/UF/RO was evaluated by detecting physical and chemical parameters and genetic toxicity assessment.The main results are as follows:(1)HepG2 cytotoxicity caused by leachates was detected with MTT assay,cells were exposed to different leachates at concentrations of 1.25%,2.5%,5%,10%,20% and 30%(v/v)for 24 h.Results show that raw leachate had high cytotoxicity,and at the highest concentration of 30% cell activity was only 9%.After cells exposed to effluent,the lowest cell activity of was 73.5%,which showed slightly cytotoxicity.MDA content decreased,but biomarker of EROD activity was higher than the control group,which indicating the effluent caused slight oxidative damage,but still showed potential genotoxicity.(2)Using comet assay to investigate the DNA damage effect of leachate on HepG2,results show strong genotoxicity of raw leachate,and DNA damage reached level 1 at concentration of 1.25%,DNA damage of effluent reduced after treatment,but still reached level 1 at concentration of 30%.The results of γH2AX flow cytometry assay showed that leachate samples induced different degrees of DSB damage,DNA damage rate of raw leachate reached 194 cells per million after 3 h exposure,effluent caused DSB damage rate was 28 cells per million at concentration of 30%.(3)DNA-protein cross-links(DPC)coefficient was measured by SDS-KCl assay,results showed that different concentrations of raw leachate can all induce DPC,and DPC coefficient increased with increasing concentrations,reduced with treatment project.After cells exposed to 20-30% concentrations of leachate treated by MBR/UF,DNA strand breaks decreased,and the effects of DPC enhanced,which primary indicated the trend of leachate DNA damage from DNA strand breaks to DPC.DPC coefficient caused by effluent still showed significant difference with control group at concentrations of 10-30%,indicating that MBR/UF/RO project can effectively reduce genotoxicity of leachate but can not completely remove.