The report gives results of bench-scale biological treatability tests with wastewaters produced from the KRW Energy Systems gasifier process development unit (KRW-PDU). Goals of the tests were to assess the biotreatability of these aqueous wastes and to develop data for correlations to establish a basis for designing a biooxidation process. An autotrophic activated sludge process was developed that utilized a mixed culture of nitrifying and sulfur-oxidizing bacteria for simultaneous thiocyanate biodegradation and nitrification. Elevated concentrations of chloride, fluoride, and boron in experimental wastewaters did not inhibit either nitrifying or sulfur-oxidizing bacteria in the activated sludge process. However, heavy metals were concentrated in the activated sludges, thought to be a consequence of the long sludge ages of the experimental process.