Enhanced treatment of a biodiesel effluent using ferrioxalate in a photo-Fenton process based on the use of solar radiation

Abstract Biodiesel effluent demands treatment to enhance their organoleptic properties and to reduce the levels of organic load and toxicity. A step of coagulation-flocculation using 0.50 mmol L −1 Fe(NO 3 ) 3 was applied at the natural pH of the effluent (pH 2.9) removing its turbidity and apparent color. A solar/photo-Fenton process was employed to minimize the chemical oxygen demand – COD, when multiple additions of oxalate were done at intervals of 50 kJ m −2 of accumulated UVA radiation, during the photocatalytic reaction. The best results were achieved using 1.0 mmol L −1 of ferrioxalate, allowing reducing in 72% the COD and in 76% the biochemical oxygen demand of the treated effluent, after 602 kJ m −2 of accumulated dose of UVA radiation. Concomitantly, the acute toxicity to Vibrio fischeri was reduced from 70% to 6%. In view of this, this modality of treatment can be a good alternative for decontamination and detoxification of this kind of wastewater, mainly considering that no further step of neutralization is need once that during the treatment the pH increase up to close 7, and that solar energy can be employed, reducing costs related to energy consumption.