Predictive model for treatment of phenolic wastes by activated sludge

The current investigation was made to determine whether a model using cell recycle concentration as a major control parameter is applicable to inhibitory substrates such as phenol. Based upon preliminary studies, the Haldane equation was selected to relate specific growth rate and substrate concentration. Seven long-term pilot plant runs were made at different growth rates. Effluent and control parameters were measured frequently. The maintenance constant was obtained from the pilot plant data. The three Haldane equation constants and the true cell yield were estimated from pilot plant and batch data.The model gave satisfactory predictions with respect to biomass production (X and X_w) and effluent COD, based on the ΔCOD method. The predicted phenol concentration, although very low, was higher than the minute levels observed in the pilot plant effluent (±0.1 mg l⁻¹); possible reasons not directly related to growth are explored, e.g. retention of unmetabolized phenol in the sludge.