Solar photo-Fenton as a pre-oxidation step for biological treatment of landfill leachate in a pilot plant with CPCs

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A solar photo-Fenton process, without iron addition, is proposed for the decontamination of a landfill leachate in a pilot plant with CPCs, after a preliminary pre-treatment in aerated and non-aerated lagoons. The solar photo-Fenton reaction leads to 60% mineralization (DOC final = 1200 mg L −1) and 90% reduction of aromatic content of the leachate after 5 sunny clear days (165 kJ UV L −1), consuming 275 mM of H 2O 2. Photo-Fenton kinetics comprises a “lag period” after the acidification until approximately 68.7 kJ UV L −1 in which less oxidized compounds are converted into more oxidized ones but without significant CO 2 release, followed by a first-order kinetic behaviour ( k = 0.007 L kJ UV −1, r 0 = 20.2 mg kJ UV −1) until 136 kJ UV L −1, with a H 2O 2 consumption rate in both periods of k H 2 O 2 = 2.1 mmol H 2 O 2 k J UV − 1 . According to activated sludge respirometry and Zahn–Wellens biodegradability tests, BOD 5/COD ratio, polyphenols concentration and COS (carbon oxidation state), the biodegradability of the leachate was enhanced during the photo-Fenton treatment. From the kinetic results, the optimal amount of UV solar energy required for photo-treatment to reach a biodegradable effluent is 100 kJ UV L −1 (10.5 h of photo-Fenton at a constant solar UV power of 30 W m −2), consuming 180 mM of H 2O 2 when used in excess, which means almost 40% mineralization of the leachate, 82% reduction of polyphenols concentration and 83% reduction of aromatic content.