Biodegradation of Aromatic Compounds Under Hypersaline Conditions: Comparing Aerobic Biofilm Reactors with Conventional Activated Sludge

Biofilm formation can help to mitigate the stress placed on organisms during biological treatment of high-salinity wastewaters, such as "produced water" resulting from oil and gas extraction. This study investigated the implementation of two different biofilm-based biological reactors, activated carbon as an adsorptive biofilm surface (Bio-GAC) and aerobic granular sludge (AGS), and a conventional activated sludge (CAS) reactor for the treatment of synthetic produced water (PW) under hypersaline conditions (85,000 mg/L NaCl). A mixture of benzyl alcohol, o-cresol, and phenol were used as a carbon source with concentrations of 100, 100, and 250 mg/L, respectively. The performance of Bio-GAC was higher than AGS, with overall removal efficiencies for aromatic compounds of 100% and 93%. The presence of catechol in all three reactors during the reaction cycle confirmed that biodegradation was occurring. The performance of CAS was significantly lower in terms of removal efficiency for aromatic compounds (73%) and resilience to high salinity. Scanning electron microscopy showed that biofilm-based biosystems establish stronger biofilm texture. Microbial community analysis showed that carbon source and biosystem type played a crucial role in selecting for microbiome structure. These findings show that biofilm reactors can be used to successfully biodegrade toxic organic contaminants in a high-salinity environment, and that the hybrid Bio-GAC process is particularly promising for treating PW.