Degradation Of Methylene Blue In Water By Biochar/H₂O₂ Fenton-like Processes

Dye wastewater is common industrial wastewater.China discharges a lot of dye wastewater every year.The wastewater is extremely harmful and the water quality is unstable and difficult to handle.Fenton method has been commonly used to treat dye wastewater.Fenton reaction can react faster,and has high efficiency and easy operation.However,its pH value is strict.It is required that the pH must be kept at around 3 in the whole reaction,and the catalyst Fe²⁺is not easy to be reused,which will cause iron pollution.Moreover,its cost is also high.Therefore,in order to reduce costs and avoid secondary pollution,it is of great significance to seek a more economical and environmentally friendly non-metal Fenton reagent.In this paper,biochar was prepared by pyrolysis of bagasse,and it was used as an activator for the activation of H₂O₂ to generate hydroxyl radicals in the Fenton-like reaction.The oxidative degradation of simulated methylene blue dye wastewater was studied.In the biochar/H₂O₂ Fenton-like system,the optimum operating conditions for the removal of methylene blue are 90 mg/L for biochar,0.1 ml for 30wt%hydrogen peroxide,3 for initial pH,and 48 h for reaction time.Under these conditions,the effects of decoloriation rate and TOC removal rate on simulated printing and dyeing wastewater were 99.99%and 41.32%,respectively.In order to improve the TOC removal rate and the reaction time,we improved the Fenton method and put the reaction system into the ultrasonic environment to carry out the reaction.The TOC removal rate of the final reaction reached 71.41%.Moreover,the reaction time is also shortened to 8h,and the amount of materials used in the experimental reagents is less than that when no ultrasound is added,which greatly saves the cost.The mechanism of action was analyzed by the test results.It is believed that the degradation of dyes during the action is mainly due to the action of sulfhydryl radicals and transition metal elements on the surface of biochar,which can activate hydrogen peroxide to generate hydroxyl radicals and degrade methylene blue molecules.In addition,for the actual treatment of printing and dyeing wastewater,we applied the analytic hierarchy process to thethreetechnologies,whichwerebiochar/H₂O₂Fentontechnology,biochar/H₂O₂/ultrasound Fenton technology and Fe²⁺/H₂O₂ Fentontechnology.And three aspects were evaluated that were environment,economy and technology.Finally,the order of the technical solutions was obtained through comprehensive evaluation:biochar/H₂O₂Fenton technology>biochar/H₂O₂/ultrasound Fenton technology>Fe²⁺/H₂O₂ Fenton technology.Therefore,the biochar-based Fenton–like method is feasible for the treatment of methylene blue wastewater and has great potential value.