Impact of salinity on the population dynamics of microorganisms in a membrane bioreactor treating produced water

Biomass characteristics may change subject to a salinity increase when treating high strength wastewater. In this study, the impact of salinity in a membrane bioreactor (MBR) was investigated for the treatment of produced water (PW). MBR was operated as a pre-treatment prior to nanofiltration (NF) and reverse osmosis (RO). Mixed PW, that was originated from different oil, gas, and oil-gas wells, were subjected to pre-treatment for 146 days including three different operational phases: Low-salinity (~10 mS/cm), gradual increased salinity (10–40 mS/cm) and high salinity (~40 mS/cm). The results of this study showed that microorganisms could adapt using real wastewater and treat PW up to a certain level of the salinity. At high salinity levels of PW, the floc structure started to be disrupted and membrane fouling was accelerated. PCR-DGGE analysis confirmed the changes in microbial communities' composition in relation with high salinity. The results of the final treatment experiments presented that NF and RO treatment produced high-quality effluents that could be suitable for reuse. [Display omitted] •Produced water (PW) was subjected to biological pre-treatment for 146 days by MBR.•NF and RO treatment produced high-quality effluents for discharge and reuse.•Microorganisms could adapt and treat PW up to a certain level of the salinity.•At high salinity, the floc structure was disrupted and membrane was fouled.•PCR-DGGE analysis indicated changes in the microbial communities' composition.