Powdered activated carbon combined with biological treatment to remove organic matter containing cresols and xylenols

Abstract

This study focused on the effectiveness of powdered activated carbon (PAC) on the reduction of inhibition caused by cresols, xylenols and phenol in a joint biological treatment of waste water from an integrated oil refinery and a concentrated stream generated by a gasoline washery from the same industrial complex. The average phenolic concentration in the influent was from 90 to 130 mg/L, and included 20% xylenols, 40% cresols, 35% phenol and other phenolic compounds. The study of removal mechanisms in the PAC‐activated sludge process was performed on an experimental pilot system and showed that 30% of the total organic matter was removed by stripping, 17% was adsorbed on PAC and 28% was biodegraded; the effluent contained a residual organic concentration of 25% of the concentration in the influent. Adsorption experiments showed that 90% of the xylenols and 70% of the cresols, the most inhibitory compounds, were rapidly adsorbed by the PAC. The high adsorption efficiency, as well as the probably low desorption and low biore‐generation of these methylphenols on PAC, enabled an improvement in the biodégradation of the other organic compounds. No improvement in the settling characteristics of the mixed liquid suspended solids could be observed after the PAC addition.