Enhancement of the biodegradability of model wastewater containing recalcitrant or inhibitory chemical compounds by photocatalytic pre-oxidation.

Abstract

m-Dinitrobenzene, diphenylamine and resorcinol, three aromatic compounds found inhibitory or recalcitrant to biological treatments, were chosen as model chemicals for this study on the integration of photocatalytic-biological treatments. The degradation of each of these compounds was achieved by ultraviolet photocatalytic oxidation, leading to the formation of intermediate compounds. The photocatalytic treatment was performed in a TiO2 slurry reactor containing an aqueous solution of one of the three chemicals. The biodegradability of model wastewater treated photocatalytically was measured in terms of BOD1/TOC. Intermediate compounds that appeared at early stages of the photocatalytic degradation of m-dinitrobenzene or diphenylamine seemed to be more inhibitory than the parent compounds but this was not the case for resorcinol. A substantial improvement in BOD1/TOC could be achieved, but it required the mineralization of at least 80% of the organic carbon originally in the water. Microtox toxicity results confirmed the BOD1/TOC trends for diphenylamine.