Dynamics of naphthenic acids and microbial community structures in a membrane bioreactor treating oil sands process-affected water: impacts of supplemented inorganic nitrogen and hydraulic retention time

This study was focused on how different operating conditions affected the biodegradation of naphthenic acids (NAs) and the microbial community architectures in an anoxic-aerobic membrane bioreactor (MBR) for oil sands process-affected water (OSPW) treatment. After 442 days of continuous optimization, a supplemented NH4-N concentration of 25 mg L-1 and a hydraulic retention time (HRT) of 12 h demonstrated the best removal rates of total classical NAs (37.6%) and total oxidized NAs (23.9%). Neither higher HRTs nor higher supplemented NH4-N concentrations resulted in a better overall removal of NAs. In addition, NAs with larger carbon numbers were generally better degraded, whereas higher cyclicity tended to lessen the biodegradability of NAs. MiSeq sequencing analysis disclosed that orders under Proteobacteria (i.e., Rhodocyclales, Burkholderiales and Nitrosomonadales), Bacteroidetes (i.e., Cytophagales, [Saprospirales] and Flavobacteriales), and Nitrospirae (i.e., Nitrospirales) were the major microbes over the whole study though their relative abundances varied. The results of this study provide insightful information for future studies and application of biological processes for OSPW treatment on a large scale.