An innovative multistage treatment system for sanitary landfill leachate depuration: Studies at pilot-scale

In this work, an innovative methodology for the treatment of landfill leachates, after aerobic lagooning, is proposed and adjusted at pilot-scale. This methodology involves an aerobic activated sludge biological pre-oxidation (ASBO), a coagulation/sedimentation step (240mgFe³⁺/L, at pH4.2) and a photo-oxidation through a photo-Fenton (PF) reaction (60mg Fe²⁺, at pH2.8) combining solar and artificial light. The ASBO process applied to a leachate after aerobic lagooning, with high organic and nitrogen content (1.1-1.5gC/L; 0.8-3.0gN/L) and low biodegradability (BOD₅/COD =0.07-0.13), is capable to oxidise 62-99% of the ammonium nitrogen, consuming only the affluent alkalinity (70-100%). The coagulation/sedimentation stage led to the humic acids precipitation, promoting a marked change in leachate colour, from dark-brown to yellowish-brown (related to fulvic acids), accompanied by a reduction of 60%, 58% and 88% on DOC, COD and TSS, respectively. The PF system promoted the degradation of the recalcitrant organic molecules into more easily biodegradable ones. According to Zahn-Wellens biodegradability test, a leachate with 419mg DOC/L after coagulation, would have to be photo-oxidized until DOC <256mg/L, consuming 117mM of H₂O₂ and 10.4kJ/L of accumulated UV energy, to achieve an effluent that can be biologically treated in compliance with the COD discharge limit (150mg O₂/L) into water bodies. The biological process downstream from the photocatalytic system would promote a mineralization >60%. The PF step cost to treat 100m³/day of leachate was 6.41€/m³, combining 1339m² of CPCs with 31 lamps.