Treatment of wastewater from oil manufacturing plant by yeasts
Nine strains of yeasts capable of decomposing oil were isolated in order to directly treat wastewater from oil manufacturing plants with no pretreatment. The oil decomposing ability of these yeast strains was evaluated in terms of lipase activity and β-oxidation activity. Since the mixture of the isolated yeasts was superior to any single strain in the oil removal rate, a pilot plant utilizing the mixed strains was operated at the soybean oil factory. Following a one year pilot plant operation, it was found that 10,000 mgℓ−1 of hexane extracts in the raw wastewater could be reduced by yeast treatment to a concentration of about 100 mgℓ−1. This concentration was further treated by the activated sludge process to 2 mgℓ−1. The dominant yeasts in the pilot plant were found to form mycelial or pseudomycelial pellets and have low fermenting ability.