The simulated activated sludge system was set up to treat the oilfield produced water after physical-chemical treatment in this study. The molecular methods such as PCR-DGGE and sequencing were applied to study population dynamics and diversity of yeast during system starting up and running. The result indicated that both in the influent and activated sludge showed higher yeast diversity. And yeast diversity increased during system running. It suggested that yeast would exist in the sludge and contribute to COD removal. And also yeast would perform well in hydrocarbon transformation and pollutant removal.
