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 (240 mg Fe³⁺/L, at pH 4.2) and a photo-oxidation through a photo-Fenton (PF) reaction (60 mg Fe²⁺, 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 (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 419 mg DOC/L after coagulation, would have to be photo-oxidized until DOC < 256 mg/L, consuming 117 mM of H₂O₂ 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 O₂/L) into water bodies. The biological process downstream from the photocatalytic system would promote a mineralization > 60%. The PF step cost to treat 100 m³/day of leachate was 6.41 €/m³, combining 1339 m² of CPCs with 31 lamps. - Highlights: • Multistage treatment strategy for mature leachate from municipal sanitary landfill. • Integration of bio-oxidation/coagulation/photo-Fenton/bio-oxidation. • The pre-treatments led to a photo-oxidation 4 × faster, with less energy and H₂O₂. • The full combined treatment allows to obtain a total mineralization above 90%. • The photo-Fenton cost was predicted in 6.4 €/m³, using artificial/solar radiation.