- Biological degradation of a synthetic mixture of several phenolic compounds typically found in coal conversion wastes was investigated in the sequencing batch reactor (SBR). The mixture contained phenol; 0-, m-, and p-cresols; and 2,3-and 3,4-dimethylphenols and had a total chemical oxygen demand (COD) concentration of 7750 mg/L. A variety of aerobic and anoxic control strategies were tested. A strategy that included an extended anoxic period resulted in the accumulation of byproducts that adversely affected removal efficiency and overall performance. In general, however, COD removal efficiencies were greater than 99%, with effluent COD concentrations averaging between 30 and 52 mg/L. Overdesign of the SBR (that is, hydraulic retention times in excess of that required for COD removal) resulted in the development of filamentous bacteria and poor settling characteristics in the reactor. This problem was eliminated or controlled either by introducing a short anoxic fill period or increasing the organic load. Removal patterns indicative of diauxic growth were observed. Conventional design approaches based on overall COD removal patterns and organic load must be applied cautiously and in conjunction with the removal patterns for individual components when used to design facilities that treat multicomponent toxic wastes.