Evaluation of advanced oxidative processes in biodiesel wastewater treatment

[Display omitted] •Systemic study of AOP viability to treat highly organic loaded wastewater from biodiesel production.•Photo-Fenton and solar photolysis reduced organic content most, with solar photolysis having lowest toxicity in final residues.•Approximately 6–8% of residue composition non-treatable.•Large-scale solar treatment is a viable alternative for biodiesel wastewater treatment with solar photolysis easiest to accomplish. In biodiesel production by alkaline transesterification, a large amount of wastewater containing a very high amount of organic matter is generated. In spite of this, biodiesel wastewater is a neglected residue, which very often does not receive the correct treatment. In this work, we have evaluated the potential of advanced oxidative processes (AOP) in biodiesel wastewater treatment. The efficacy of four AOP, namely Fenton, photo-Fenton, solar photo-Fenton and solar-photolysis, was tested measuring the total organic carbon removal from this residue. As well, the toxicity of the treated residue was investigated by fish embryo tests (FET). Photo-Fenton, solar photo-Fenton and solar photolysis led to similar organic load reduction, but solar photolysis (8 h of solar exposure) was considered the best treatment, due to the important organic load reduction reached (more than 92%) associated with an ease of operation and a 100% reduction in toxicity for Zebrafish embryos in the dilution range studied. In the best cases, approximately 6–8% of the organic content in biodiesel wastewater is recalcitrant.