Catalytic Ozonaztion Process With TiO₂ Modified By Graphene For The Advanced Treatment Of Landfill Leachate

Landfill leachate is a kind of refractory organic wastewater,which has the characteristics of complex composition,strong toxicity,high chromaticity,high concentration of pollutants,poor biodegradability and so on.It is difficult to be degraded it completely by the traditional process of"pretreatment+biochemical treatment".In order to meet the emission requirements,it is necessary to carry out advanced treatment.Catalytic ozonation technology has high efficiency of degrading organic pollutants,and it is easy to implement,easy to operate and low cost.Therefore,it has a broad application prospect in the field of advanced treatment of landfill leachate.In this paper,TiO₂ was selected as catalyst and graphene layer was formed on its surface by carbonization pyrolysis to prepare graphene modified TiO₂ catalyst.In addition,in order to solve the problem of immobilization of powder catalyst,graphene modified TiO₂/PTFE composite membrane was prepared by loading modified catalyst on the surface of microfiltration membrane,which was used in catalytic ozonation to degrade landfill leachate.The specific research contents include:（1）the graphene modified TiO₂ catalyst was prepared,and the effects of pyrolysis temperature,carbon source dosage and curing agent dosage on the catalyst activity were investigated,and the catalysts with excellent performance were selected.（2）Compounding catalyst with organic membrane to prepare graphene modified TiO₂/PTFE composite membrane.The micro-morphology,water flux and hydrophilicity of the composite membrane were characterized,and the catalytic ozonation activity of the composite membrane was investigated.（3）The landfill leachate was treated by catalytic ozonation with graphene modified TiO₂/PTFE composite membrane.It investigated that the effects of ozone dosage,p H value of solution and reflux ratio on the treatment efficiency.The fouling of the composite membrane was monitored.The result showed that the preparation conditions such as pyrolysis temperature,carbon source dosage and curing agent dosage all had effects on the catalytic activity of graphene modified TiO₂ catalyst.The graphene modified TiO₂ catalyst had the optimum catalytic activity when the pyrolysis temperature was 700℃,the dosage of glucose was 1.2g and the dosage of curing agent was 0.3g（TiO₂ dosage 3g）.The graphene modified TiO₂ catalysts were characterized by SEM,XRD,Roman,NH3-TPD,BET,p Hzpc and so on.There were proved that the graphene layer was formed on the surface of P25,and the introduction of graphene layer enhanced the surface acidity,specific surface area and isoelectric point of TiO₂ catalyst.The degradation of p-chlorobenzoic acid（p-CBA）in solution by catalytic ozonation of graphene modified TiO₂ followed the pseudo-first-order reaction kinetic law.Increasing the dosage of catalyst and ozone is helpful to promote the degradation of p-CBA.When the solution p H value is in the range of 2 to 10,the catalytic ozonation process had been beneficial to the degradation of p-CBA.The inhibition experiment of tert-butanol and the EPR detection experiment of hydroxyl radical confirmed that graphene modified TiO₂ catalyst could promote the decomposition of ozone and produce hydroxyl radical from an indirect and direct perspectives.Graphene modified TiO₂/PTFE composite membranes were prepared and characterized.From SEM,there were observed that the catalyst particles completely covered the surface of the original microfiltration membrane,and the particles coalesced and densified on the membrane surface with the increase of catalyst loading.The water flux of the composite membrane is lower than that of the original microfiltration membrane,but the hydrophilicity of the composite membrane is obviously improved.The experimental results of catalytic ozonation showed that the composite membrane retained the catalytic activity of graphene modified TiO₂catalyst.The advanced treatment of landfill leachate by composite membrane catalytic ozonation process can effectively reduce the pollution indexes of wastewater,such as chromaticity,turbidity,COD,TOC,UV₂₄₅,etc.,in which the COD value is lower than 100mg/L,reaching the prescribed discharge standard.In addition,after treatment,the number of organic pollutants detected in landfill leachate decreased from 47 to 33.Generally speaking,the catalytic ozonation process of graphene modified TiO₂/PTFE composite membrane has a good effect on advanced treatment of landfill leachate.