Research Of Activated Carbon Catalyzed Wet Air Oxidation Of The Fulvic Acid In Landfill Leachate

With the growing of the population, the creation of municipal solid waste ofChina is increasing every day. Landfilling is the most widely used method to copewith the municipal solid waste. Landfill leachate produced during the landfill processcan influence the environment and threaten body health. Biological method iscommonly used to treat the landfill leachate. However, because of the existence ofrefractory pollutant such as Fulvic acid (FA), stabilized landfill leachate is hardlybiodegraded. In this work, the catalytic wet air oxidation of refractory organicpollutant FA was studied, with activated carbon as the catalyst and potassiumpersulfate as the promoter. This method provides a promising pretreatment approachfor bio–treatment of landfill leachate.Firstly, hydroquinone (HQ), as the model pollutant of FA, was degraded as thetarget organic by potassium persulfate (K2S2O8) promoted activated carbon (AC)system, and the free radical reaction mechanism was studied primarily. Underoptimum conditions, HQ after catalytic wet air oxidation (CWAO) was analyzed usingGC–MS. Ethanol and tert-butyl alcohol were used as free radical scavenger to conductexperiments to investigate the free radicals produced during oxidation process. Theresults of GC–MS analysis showed that the main degradation products were somesmall easily biodegradable organic acids and alcohols such as succinic acid,1,5-hexanediol, adipic acid phthalic acid. OH and SO4were believed to havepositive effect to degrade HQ, which was shown by scavenger experiments.Then, CWAO of FA (400mg L-1) was studied. The effects of the amounts ofcatalyst and promoter and temperature on the FA degradation in the persulfatepromoted AC-catalyzed system were investigated. Nitrogen adsorption and desorptionwas used to determin the microporous structure of AC before and after reaction toinvestigate the free radical mechanism involved in the present CWAO system for FAdegradation. Results indicated that, under optimum conditions, almost100%FAconversion and77.8%COD removal were achieved after4h of treatment. Meanwhile,the biodegradability of BOD5/COD ratio was increased from0.13to0.95after CWAO.The formation of oxygen-containing functional groups (–OH groups and carboxylstructures) on the AC surface would contribute to the formation of free radicals toimprove the degradation of FA, while the disadvantageous reconfiguration of AC surface might decrease the removal efficiency of FA to some extent. AC exhibitedgood stability in the catalytic wet oxidation of FA: when AC was used for the fourthtime, the FA conversion was still over60%. Radical mechanism was studied byscavenger experiments. Results indicated that hydroxyl radical (OH) and sulfuricradical (SO4) played a major role in the FA degradation.