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

Abstract

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(2)O(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) = 20.2mgkJ(UV)(-1)) until 136 kJ(UV) L(-1), with a H(2)O(2) consumption rate in both periods of k(H2O2) = 2.1 mmol H(2)O(2) kJ(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 Wm(-2)), consuming 180 mM of H(2)O(2) when used in excess, which means almost 40% mineralization of the leachate, 82% reduction of polyphenols concentration and 83% reduction of aromatic content.