Treatability of phenol-production wastewater: Rate constant and pathway of dimethyl phenyl carbinol oxidation by hydroxyl radicals.

Phenol-production wastewater is difficult to treat biologically by aerobic processes to meet the effluent standard COD of 120 mg L-1 because it contains several highly refractory aromatic pollutants, particularly dimethyl phenyl carbinol. Pretreatment revealed that dimethyl phenyl carbinol was slowly oxidized by molecular ozone; however, it readily reacted with hydroxyl radicals to yield acetophenone as a primary product. Acetophenone was further oxidized, first through five different pathways to form benzoic acid, phenyl glyoxalic acid, 4-4'-diacetyl biphenyl, and several hydroxylated aromatic compounds, and later to aliphatic carboxylic acids via ring cleavage. Regardless of system configuration (homogeneous vs heterogeneous), operating mode (batch vs continuous), and chemical concentration, the average intrinsic rate constants were 1.05 × 1010 and 9.29 × 109 M-1 s-1 for dimethyl phenyl carbinol and acetophenone, respectively.