Effects of priozonation on the methanogenic toxicity of 2,5-dicholorophenol

Ozone pretreatment of a refractory phenolic compound, 2,5-dichlorophenol (DCP), was conducted to determine the biodegradability and toxicity of the reaction products under methanogenic conditions. Two types of batch studies, the biochemical methane potential (BMP) and the anaerobic toxicity assay (ATA), were performed on samples with and without preozonation. The reaction products of 100 mg/L 2,5-DCP were easily biodegraded to methane after a dose of 2.5 g O₃/g 2,5-DCP. Glyoxylic acid, oxalic acid, propionic acid, acetic acid, and formic acid were the oxidation products identified. The reaction products formed in the basic pH range were less inhibitory than those formed in the acid pH range. The toxicity of 2,5-DCP was reduced with increasing doses of ozone. Half-toxicity of 2,5-DCP was reduced with increasing doses of ozone. Half-toxicity-reduction doses of ozone were estimated to be less than 0.8 g O₃/g 2,5-DCP.