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

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 (DOCfinal = 1200 mg L−1) and 90% reduction of aromatic content of the leachate after 5 sunny clear days (165 kJUV L−1), consuming 275 mM of H2O2.Photo-Fenton kinetics comprises a “lag period” after the acidification until approximately 68.7 kJUV L−1 in which less oxidized compounds are converted into more oxidized ones but without significant CO2 release, followed by a first-order kinetic behaviour (k = 0.007 L kJUV−1, r0 = 20.2 mg kJUV−1) until 136 kJUV L−1, with a H2O2 consumption rate in both periods of kH2O2=2.1   mmol H2O2 kJUV−1.According to activated sludge respirometry and Zahn–Wellens biodegradability tests, BOD5/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 kJUV L−1 (10.5 h of photo-Fenton at a constant solar UV power of 30 W m−2), consuming 180 mM of H2O2 when used in excess, which means almost 40% mineralization of the leachate, 82% reduction of polyphenols concentration and 83% reduction of aromatic content.