A pilot study was performed over 91 days to determine if the activated sludge process could treat a segregated stripped sour water (SSW) stream from a petroleum refinery. The study was performed in two periods. The first period was terminated after 19 days due to excessive sludge bulking. The elimination of sludge bulking during the 70-day second period is attributed to operational changes that included aerating the influent to oxidize reduced sulfur, adjusting the influent pH, and adding micronutrients to satisfy biological requirements. The pilot system was shown to achieve chemical oxygen demand (COD) removal of up to 93 percent. Nitrification was achieved, with effluent ammonia values less than 1 mg-N/L. These results indicate that direct treatment of SSW with the activated sludge process is possible and has direct application to full-scale petroleum refinery wastewater plant upgrades.