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

Abstract 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 (240 mg Fe 3+ /L, at pH 4.2) and a photo-oxidation through a photo-Fenton (PF) reaction (60 mg Fe 2+ , at pH 2.8) combining solar and artificial light. The ASBO process applied to a leachate after aerobic lagooning, with high organic and nitrogen content (1.1–1.5 g C/L; 0.8–3.0 g N/L) and low biodegradability (BOD 5 /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 419 mg DOC/L after coagulation, would have to be photo-oxidized until DOC 2 O 2 and 10.4 kJ/L of accumulated UV energy, to achieve an effluent that can be biologically treated in compliance with the COD discharge limit (150 mg O 2 /L) into water bodies. The biological process downstream from the photocatalytic system would promote a mineralization > 60%. The PF step cost to treat 100 m 3 /day of leachate was 6.41 €/m 3 , combining 1339 m 2 of CPCs with 31 lamps.