The effects of powdered activated carbon (PAC) addition to an activated sludge wastewater treatment process for the treatment of oil shale, coal gasification, and tar sands process waters was the primary concern of this research. A total of five retort waters were examined at various concentrations ranging from 6.25% to 100.0%. A manometric technique (Warburg respirometer) was used to determine the oxygen uptake rates of an activated sludge with and without the addition of PAC (100 mg/l) at temperatures of 4°, 15°, 25° and 35°C. It was determined that a PAC-activated sludge treatment process showed substantial increases in specific oxygen uptake rates when the system was subjected to moderately high concentrations of potentially toxic, organic substances as compared to a non-PAC system. Results indicating an optimum level of PAC for the activated sludge system were also noted. The addition of PAC to a conventional activated sludge process significantly improved biochemical oxygen demand (BOD) and chemical oxygen demand (COD) removals as compared to a non-PAC-activated sludge process. These removals compared quite favorably to those found in the literature.