Fixed film (rotating biological contactor, RBC) and suspended growth (activated sludge) biological treatment processes were used to treat gasification wastewater from the Great Plains Gasification Plant. This report contains the results of the study, including a comparison of the two processes. The wastewater used was a condensate from Lurgi dry-ash gasification of lignite. The condensate was pretreated at Great Plains by solvent extraction and steam stripping to reduce phenols and ammonia, respectively. This pretreated wastewater is known as stripped gas liquor (SGL). At the University of North Dakota Energy Research Center, this wastewater was treated by both methods at the process development unit (PDU) scale. The RBC was a three stage unit that was tested at four organic loadings, ranging from 0.9 to 3.4 lbs BOD/1000 ft/sup 2/-day. The activated sludge treatment was a completely mixed system with the following operating parameters: a hydraulic retention time of 1 to 4 days, solids retention times of 2 to 13.6 days, and flow rates from 170 to 1500 liters per day (45 to 405 gpd). Process performance data were obtained and the kinetics of treatment were estimated for both treatment units. This report also includes preliminary design data for the RBC and activated sludge processes at the design wastewater flow rate for the Great Plains Gasification Plant. This comparison indicates that for a single process, the activated sludge would probably be the most cost effective. However, the advantages inherent in each process can be realized using the RBC as a pretreatment and the activated sludge process as the polishing step. 22 refs., 36 figs., 17 tabs.