Fate of dissolved organics and generated sulfate ions during biofiltration of oil sands process water pretreated with sulfate radical advanced oxidation process

Fate of dissolved organics and sulfate ions was studied in fixed bed biofilters (FBBs) treating pre-treated oil sands process water (OSPW) in the presence of industrially relevant substrates namely petroleum coke (PC) and sand. For pre-treatment, the solar-activated sulfate radical advanced oxidation process (SR-AOP) was performed using 2.5 and 5 mM peroxymonosulfate (PMS) as a precursor with solar irradiation of 119.5 W h m(-2). Excellent degradation of naphthenic acids (NAs) was attained by SR-AOP, attaining 88 % and 97 % total NAs after 9 h of treatment at 2.5 and 5 mM of PMS, respectively. However, the treatment increased the toxicity due to byproducts and metabolites following the poor removal of dissolved organics, i.e., 13 % and 21.5 %, respectively. Electron paramagnetic resonance spectrometry (EPR) analysis exhibited that hydroxyl radical (center dot OH) and singlet oxygen (O-1(2)) were the predominant active species produced during SR-AOP. The post-treatment biofiltration improved the mineralization of dissolved organics (45 %) and NAs (99 %) as well as removed the residual toxicity (>80 %). Taxonomy-based transcriptomics analyses (RNA) confirmed the enrichment of microbes involved in the degra-dation of hydrocarbons and carboxylic acids, methylotrophy, and potentially C(1)-sulfur compounds metabolism. Scanning electron microscopy with energy-dispersive X-ray spectroscopy indicated the potential of PC to support sulfur deposition, but at slower rates. This study indicates that the produced water can be efficiently reclaimed by using advanced oxidation and biofiltration approaches.

Automated summary

The fate of dissolved organics and sulfate ions in fixed bed biofilters (FBBs) treating pre-treated oil sands process water (OSPW) in the presence of petroleum coke (PC) and sand was studied. Pre-treatment using solar-activated sulfate radical advanced oxidation process (SR-AOP) achieved excellent degradation of naphthenic acids (NAs) but saw poor removal of dissolved organics and increased toxicity due to byproducts and metabolites. Post-treatment biofiltration improved the mineralization of dissolved organics and NAs and removed residual toxicity, confirming the efficient reclamation of produced water by using advanced oxidation and biofiltration approaches.