Removal of cooking oil from the domestic wastewater was carried out by immobilized photosynthetic bacteria, Rhodobacter shaeroide S (S) and R. shaeroides NR-3 (NR-3). The microorganisms were immobilized in sodium alginate (2%) or agar (2%). We treated 50 g of cooking oil suspended in artificial sewage wastewater under anaerobic dark conditions in a 15 l acrylic vessel. Results show that after 6 days of batch treatment, 74.2, 58.2 and 15.8% of oil was removed with the alginate-immobilized S, NR-3, and control, respectively. Relatively larger accumulations of volatile fatty acids such as propionic and acetic acids were observed in the control experiment compared with that in the immobilized cell (alginate and agar) experiment. In addition, continuous treatment of oilcontaining wastewater was carried out with agar-immobilized S at a fixed dilution rate of 0.4/day. These results indicate that 96% of the oil was removed from the wastewater, and the maximum removal rate of oil reached approximately 3.83 kg oil/m 3 /d.

A thermotolerant photosynthetic bacterium NAT identified as Rhodobacter sphaeroides was isolated. When alginate-immobilized cells of strain NAT were used in high-temperature treatment of artificial sewage wastewater containing oil, the chemical oxygen demand (COD) decreased by 80% and 76% of the oil was removed after 96 h of treatment at 55 degrees C. Lipase activity was observed in the culture.

Oil degradation in synthetic sewage wastewater was investigated using a photosynthetic bacterium, Rhodobacter sphaeroides S (S strain). When a pure culture of S strain was prepared with glutamate-malate medium (GM medium) containing a salad oil, about 60 % of the oil was degraded under aerobic-dark conditions at 6 days, while oil degradation was relatively small under anaerobic-light conditions. Lipase hydryzed tri-glycerides to glycerol and fatty acids were observed extracellularly in the aerobic-dark culture. Lipase was produced when the S strain grew up with favorable substrates such as glutamatemalate and glucose in the medium. The lipase activity was quite lower than that of Pseudmonus and Bacillus lipase activities. High cell density enhanced oil degradation rather than lipase production in the liquid. S strain well utilized C12 to C18 fatty acids and glycerol as carbon sources respectively.