Abstract: This study collected activated sludge samples from biological wastewater treatment systems on sixteen offshore oil platforms located in the Bohai Sea and South China Sea. Through 16S rRNA gene sequencing of the activated sludge samples,the composition and structure of microbial communities in these offshore domestic wastewater treatment systems were investigated by calculating the Observed Species index,Shannon index,and phylogenetic diversity （PD） index. The results reveal that the activated sludge harbors abundant functional bacteria contributing to the removal of chemical oxygen demand （COD）. Slight differences in microbial community composition and structure were observed among different platforms.

Key words: offshore oil platforms, domestic wastewater treatment system, microbial community, 16S rRNA