Components of Oils Sands Process Water Involved in Toxicity, Estrogenicity and Biodegradation

Abstract

To process one m3 of oil sands, four m3 of oil sands process wastewater (OSPW) is produced. OSPW is a mixture of compounds including hundreds of different naphthenic acids (NAs) which are considered to the major toxicity contributor of OSPW. Effect-directed analysis was used to establish the link between toxicity/estrogenicity and components in OSPW. OSPW and biologically treated OSPW were separated by solid phase extraction and reverse phase HPLC into “toxic and nontoxic” or “estrogenic and nonestrogenic” fractions as detected by the Microtox® and a yeast estrogenic screening assay respectively. The composition of fractions was determined by ultrahigh resolution mass spectrometry. Multivariate statistical methods were used to analyze the relationship between composition and toxicity/estrogenicity. C15-C18 O2-NAs (CnH2n+zO2) with a double bond equivalent (DBE) of 4, as well as C14-C17 with DBE=3 were found to be the most likely contributors to toxicity, while O2 (CnH2n+zO2), O3 (CnH2n+zO3) and O4 (CnH2n+zO4) C17 to C20 compounds with a DBE 6-10 likely cause estrogenicity. From these studies, the exact formulae and masses of possible estrogenic/toxic compounds in OSPW were identified. These findings will help to focus study on the most environmentally significant components in OSPW. In an earlier published study, OSPW was treated with an immobilized soil bioreactor (ISBR) at a 7 day residence time, which achieved NA reduction by 30-40%. The present study compared untreated and ISBR-treated OSPW, which showed that while DBE=3, 4 were the most recalcitrant NAs and DBE=5 were biodegradable NAs. The presence of aromatic and diamondoid NA structures was confirmed by tandem MS. These results may help to better understand NA biodegradation, the recalcitrant components and improve ISBR performance. Bacteria belonging to the Ochrobactrum, Brevundimonas and Bacillus genera were isolated from the ISBR and tested for their biodegradation of aliphatic, cyclic and aromatic NA surrogates in 96-well plates by tetrazolium redox dyes as the metabolic activity indicator. Ochrobactrum grew best on the most surrogates and both Ochrobactrum and Bacillus were found to degrade recalcitrant tricyclic NAs. This approach can be used to understand the role of individual microorganisms in the mixed microbial population that are involved in the NAs biodegradation in the ISBR.