Summary Besides small amounts of suspended oil, oilfieldproduced water after conventional treatment cancontain dissolved organic and ammonium compounds that may preclude its discharge into the oceanbecause of environmental protection regulations.Two field pilot studies in southern California established the technical feasibility and cost ofremoving these dissolved compounds by biologicaloxidation in a biodisk. Effluent from the two pilot plants complied with all requirements of Californialaw. Introduction Despite the lack of documented adverse effects fromnormal petroleum operations, environmentalprotection regulations have been adopted that limitthe offshore discharge of produced water. The WaterQuality Control Plan for the Ocean Waters ofCalifornia (CWQCP), adopted in 1972 andamended in 1978, regulates all domestic andindustrial wastewaters discharged within California's3-mile (5.5-km) zone. The CWQCP includes effluentlimits on oil and grease, dissolved phenols, dissolvedammonium compounds, and toxicity to marine life.U.S. guidelines proposed in 1975 for the onshore petroleum industry by the Environmental ProtectionAgency would require"zero pollutant discharge"inside the 3-mile (5.5-km) zone by 1983. Previous publications have reported thecompositions of oilfield produced waters. Workdone by Chevron shows that typical produced watersfrom the U.S. west coast and the Gulf of Mexico, after oil removal by gravity separation and/orflotation, have compositions ranging from 20 000 to135 000 g/m3 TDS, 45 to 130 g/m3 ammonia (as N), and 0.1 to 3.0 g/m3 phenols (as C6H5OH). Conventionaloilfield water-separation processes are notdesigned to remove these dissolved compounds, andother treatment processes are needed where disposalrestrictions on such compounds exist. Biological oxidation uses harmless bacteria, algae, fungi, and protozoa to convert dissolved organic andammonium compounds into water plus CO2 andnitrates/nitrites, respectively. A field pilot studyof an aerated lagoon conducted at Carpinteria, CA, demonstrated the feasibility of biological oxidationfor removing dissolved compounds such as ammoniaand phenols from produced waters. This paperdescribes two field pilot studies conducted insouthern California that demonstrated, for the firsttime, the feasibility of another biological oxidationtreatment process - the rotating biological surface(biodisk). JPT P. 1136^