Microalgae-based treatment of produced water: A comparison between synthetic and a representative real produced water

• Real-produced water (RPW) is more complex than any synthetic-produced water (SPW) • Very high salinity, lack of essential nutrients, and heavy metals in RPW limit the microalgae's growth • High dilution of RPW (∼50 %) along with supplementation of essential nutrients is required. • Microalgae show bioremediation of RPW after nutrient supplementation and salinity adjustment This work evaluates the potential of microalgae Scenedesmus obliquus to treat different synthetic and real PW of different compositions. Four different synthetic PW (SPWs) were formulated using crude oil, sodium dodecyl sulfate (SDS), and xanthan gum. It was found that S. obliquus could grow in all SPW with low and high salinity tested in this study. The presence of crude oil in synthetic PW hinders the algae's growth. No growth was observed in 100 % real-produced water (RPW) despite supplementation with essential growth nutrients. However, the algae cells could grow in 50 % diluted RPW, supplemented with nutrients. However, the growth of algae in 50 % v/v diluted RPW was the lowest compared to all SPW, despite having the same nutrients and salinity level. These results indicate that the presence of hydrocarbons from crude oil poses a major challenge to algae-based decontamination. Total organic carbon levels increased in all samples during growth, and nitrogen consumption was positively correlated with the algal growth rate. Barium (Ba) and Copper (Cu) metals were removed from RPW during S. obliquus cultivation. Some of the hydrocarbons present in 50 % diluted RPW were removed during cultivation. These findings suggest that the lack of essential nutrients, the complex nature of organics, and the high salinity of RPW limit the potential of microalgae as a bioremediation agent for a real RPW. These findings suggest the RPW is very heterogeneous, and any synthetic or simulated PW, even if prepared using individual major constituents of PW, cannot represent the real PW across the field for bioremediation using microalgae.