Removal of phenol in high salinity media by a hybrid process (activated sludge + photocatalysis)

The degradation of phenol by a hybrid process (activated sludge + photocatalysis) in a high salinity medium (50 g L−1 of chloride) has been investigated. The sludge used from a municipal wastewater facility was adapted to the high salt concentrations prior to use. The photocatalytic conditions were optimized by means of a factorial experimental design. TiO2 P25 from Degussa was used as the photocatalyst. The initial phenol concentration was approximately 200 mg L−1 and complete removal of phenol and a mineralization degree above 98% were achieved within 25 h of treatment (24 h of biological treatment and 1 h of photocatalysis). From HPLC analyses, five hydroxylated intermediates formed during oxidation have been identified. The main ones were catechol and hydroquinone, followed by 1,2,4-benzenetriol, 2-hydroxy-1,4-benzoquinone, and pyrogallol, in this order. No formation of organochlorine compounds was observed. Therefore, the proposed hybrid process showed itself to be suited to treat phenol in the presence of high contents of salt.