Biofiltration of oil sands process water in fixed-bed biofilm reactors shapes microbial community structure for enhanced degradation of naphthenic acids.

Naphthenic acids (NAs) are a complex mixture of carboxylic acids present in oil sands process water (OSPW). Their recalcitrant nature makes them difficult to be removed from the environment using conventional remediation strategies. This study hypothesized that, upon continuous operation, biofiltration of OSPW in fixed-bed biofilm reactors would allow the development of NA-degrading microbial community within the biofilter following successful removal. Both raw and ozonated OSPW were treated in the biofilters and changes in microbial community were tested via 16S/18S amplicon sequencing and metatranscriptomics. Through switch from suspended growth to attached growth, a shift in indigenous microbial community was seen following by an increase in alpha diversity. Concomitantly, improved degradation of NAs was monitored, i.e., 35.8% and 69.4% of NAs were removed from raw and ozonated OSPW, respectively. Metatranscriptomics analysis suggested the presence of genes involved in the degradation of organic acids and petroleum-related compounds. Specifically, functional abundance of aromatic compounds' metabolism improved from 0.05% to 0.76%; whereas abundance of benzoate transport and degradation pathway increased from 0.04% to 0.64%. These changes conclude that continuous operation of OSPW in the bioreactors was in favor of shaping the overall microbiome towards better NA degradation.