Treatment of reverse osmosis concentrate from sanitary landfill leachate by combined processes: electrocoagulation followed by electro-fenton

Abstract

Municipal solid wastes are increasing worldwide and the most common method to dispose solid residues is landfilling. However, in landfills, there is the formation of a highly contaminated leachate that cannot be discharged directly into the environment due to its high toxicity. Some leachate treatment plants are adopting membrane technologies, but a leachate concentrate that requires posterior treatment is obtained. In this chapter, the results obtained in the oxidation of a concentrate from reverse osmosis (chemical oxygen demand of 10±1 g L-1) of a sanitary landfill leachate are discussed. A combined treatment of electrocoagulation (EC) followed by electro-Fenton (EF) was applied. EC was performed using iron consumable anodes and the influence of the applied current intensity, process duration, initial pH and stirring speed was assessed. The EF experiments of the electrocoagulated samples were performed using a boron doped diamond (BDD) anode and a carbon-felt cathode. Since at the end of the EC assays dissolved iron was not enough to perform EF experiments, extra iron was supplied by anodic dissolution of iron electrodes. For the EF assays, the influence of the initial dissolved iron concentration and of the applied current density were evaluated. The results obtained with EF oxidation were compared with the results achieved by anodic oxidation of similar electrocoagulated samples, performed with a BDD anode and a stainless-steel or a carbon-felt cathode. Specific energy consumptions for the different assays were calculated. Ecotoxicological evaluation was assessed with the model organism Daphnia magna. The combined electrocoagulation and electro-Fenton processes showed to be adequate for the treatment of reverse osmosis concentrate from sanitary landfill leachate since it reduces drastically the organic load of the concentrate, as well as the sludge to be discarded.