Granular Activated Carbon Supported Iron As A Heterogeneous Persulfate Catalyst For The Pretreatment Of Mature Landfill Leachate

Persulfate advanced oxidation technology is a hotspot of advanced oxidation process（AOPs）, recently. Duiring this process, sulfate radical（SO₄^-?） generated by persulfate activation is used to oxidate organic pollutants, make macromolecular organic matter break down to particle matters or inorganic matters and achieve the effect of degradation of pollutants. Under conventional conditions, very little sulfate radical is generated from persulfate, but a large amounts of sulfate radical can be generated under catalytic conditions（UV, heat, transition metals, etc.）.The mature landfill leachate is generated by landfills which are put into use for more than 10 years. Compared with young landfill leachate, the biodegradability of mature leachate declines as the sanitary landfill age increases. Otherwise mature leachate also contains high concentration ammonia and heavy metal, which makes that single biochemical method is unable to deal them. In order to reach the discharge standard, physical or chemical method before biochemical method is required. Advanced oxidation technology has been applied to deal with various types of refractory organic matter, and achieved good results. So persulfate advanced oxidation technology was selected for the degradation of mature leachate in this paper. And the effect of operation parameters such as p H, Fe²⁺ concentration and persulfate concentration on the performance is investigated.Granular activated carbon（GAC） has a large surface area, strong adsorption capacity and other characteristics, so it is used as the supporter of divalent iron（Fe（Ⅱ）） to activate persulfate and produce more sulfate free radicals.In this paper, we first studied the effect of calcination temperature on Fe（Ⅱ） /GAC catalysts. The ESEM and BET technology were applied to analyze the shape and size of catalysts and ICP was applied to analysis Fe（Ⅱ） content in Fe（Ⅱ） /GAC catalysts. The experinmental results showed that the best calcination temperature is 550℃. Then the effect of p H, Fe²⁺ concentration and persulfate concentration on the degradation of mature leachate was investigated. The chemical oxygen demand（COD） of mature leachate measured by microwave digestion method was chose as the performance index during the experiments. In single factor experiments, maximal COD removal rate is 76.3% of p H 3, 66.8% of Fe²⁺ concentration 127mg/L and 66.2% of persulfate concentration 0.5mol/L, respectively. The synthetic experimental results showed that the COD removal rate exceeded 87.8% when the reaction conditions were controlled as Fe²⁺ dosage of 127 mg/L, persulfate concentration of 0.5 mol/L and initial p H of 3.0, simultaneously.Fe（Ⅱ） /GAC catalyst as heterogeneous catalyst has the advantages of reuse. The catalytic efficiency of Fe（Ⅱ） /GAC catalyst reduced to approximately 50% after recycling for three times. Three dimensional excitation-emission matrix（3DEEM） fluorescence was applied to discuss the mechanism of persulfate degradation of mature leachate in this paper and found sulfate radicals can easily degrade the humic matters in mature leachate.