Study On The Treatment Of Membrance Concentrated Leachate By Coagulation Combined With Advanced Oxidation Technology

In recent years,under the promotion of the Chinese government,municipal solid waste treatment mode is gradually transforming from sanitary landfill to incineration.Like sanitary landfill treatment,incineration also has the problem of large leachate production and difficult treatment.Membrane separation technology is often set in the last link of the leachate treatment system,which will produce a lot of concentrated membrane leachate with high organic matter concentration,heavy metal and salt content and poor biodegradability,so it must be properly treated.Because it is difficult to treat concentrated leachate efficiently with single technology,this paper adopts"coagulation combined with advanced oxidation technology"to treat concentrated leachate.Chemical coagulation and electrocoagulation were used as the pretreatment methods for concentrated leachate.Then advanced oxidation treatment of the coagulated effluent was carried out by zero-valent iron Fenton-like,electrochemical oxidation and their combined processes.Firstly,the concentrated leachate was pretreated by chemical coagulation and electrocoagulation.Best treatment results of chemical coagulation were obtained under conditions of 2.0 g L^-1 polymeric ferric sulfate（PFS）,20 mg L^-1 polyacrylamide（PAM）and initial pH 6,the removal of TOC,UV₂₅₄ and CN were 71.46%,79.07%and 92.43%.Best treatment results of electrocoagulation were obtained under conditions of aluminum anode,20 m A cm^-2 current density,1.5 cm electrod gap,electrolysis time 15 min and initial pH 4,the removal of TOC,UV₂₅₄ and CN were55.90%,68.91%and 85.64%.By comparison,it can be seen that the removal effect of chemical coagulation on organic matter is significantly higher than that of electrocoagulation,so chemical coagulation was selected as the pretreatment method.The coagulated effluent of concentrated leachate was further treated by zero-valent iron Fenton-like,electrochemical oxidation and their combined processes.Results of zero-valent iron Fenton-like process showed that the initial pH had the most significant effect on organics removal.When the initial pH value was 3,the dosage of Fe⁰ was 0.4 g L^-1,the dosage of H₂O₂ was 4 m L L^-1,and the reaction time was 60 min,the removal of TOC,UV₂₅₄ and CN were 45.64%,61.27%and 89.77%.Electrochemical oxidation results showed that anode material,current density and initial pH had significant effects on the treatment effect.Using Ru-Ir/Ti as anode,the removal of TOC and CN were 41.63%and 98.69%,when the initial pH value was 7,the current density was 40 m A cm^-2,and the electrolysis time was 60 min.Zero-valent iron Fenton-like combined with electrochemical oxidation process could maximize the removal of organic matter in the coagulated effluent.Under the optimal conditions,the removal of TOC and CN could achieve 66.96%and 98.91%,after 60 min of zero-valent iron Fenton-like reaction and 30 min of electrochemical oxidation.Three-dimensional fluorescence spectrum analysis showed that the degradation of humus in coagulated effluent by electrochemical oxidation was better than that by zero-valent iron Fenton technology.Zero-valent iron Fenton-like showed efficient removal of fulvic-like substances,but there were still some undegraded humic-like substances in the coagulated effluent.Electrochemical oxidation could degrade almost all fulvic-like and humic-like substances into small molecules.In the Zero-valent iron Fenton-like system,organics removal is mainly through the advanced oxidation of homogeneous Fenton reaction and heterogeneous Fenton reaction of iron oxides（Fe₂O₃,Fe₃O₄ and Fe OOH）.The electrochemical oxidation process mainly degrades organic matter efficiently through anodic direct oxidation,and indirect oxidation of Cl₂,HClO and ClO^-produced in the electrolytic process.