Transformation of bitumen-derived naphthenic acid fraction compounds across surface waters of wetlands in the Athabasca Oil Sands region.

Bitumen is extracted from oil sands in the Athabasca Oil Sands region (AOSR) of Alberta, Canada. Much of the bitumen-derived toxicity in mine waste is attributable to naphthenic acid fraction compounds (NAFCs). Mines in the AOSR are required to be returned to a natural state after closure; thus, cost-effective strategies are needed to reduce toxicity from NAFCs. Previous studies have demonstrated the capability of constructed wetlands to attenuate NAFCs. However, the capacity of wetlands in the natural environment to degrade and transform NAFCs to less toxic components is poorly understood. To better understand the spatial distribution and fate of NAFCs in natural wetlands, samples were collected across the surfaces of two mature opportunistic wetlands near active oil sands mines. The first wetland has a well-defined surface flow pathway and inflows affected by overburden containing lean bitumen ore. The second wetland, in contrast, is a stagnant water body with raw bitumen visible along its edges. For the wetland with a well defined flow path, NAFCs decreased in concentration down gradient, while oxidized NAFCs constituted a greater proportion of NAFCs with increase in flow path. Likewise there was a decrease in the molecular weights of NAFCs, similar to trends observed in constructed wetland treatment systems. In comparison, NAFCs were more uniformly distributed across the relatively stagnant wetland. Overall, these data provide new evidence that mature opportunistic wetlands in the AOSR can promote the degradation and oxidation of bitumen-derived naphthenic acids into less toxic compounds.

Treatment of oil sands process affected waters by constructed wetlands: Evaluation of designs and plant types.

Constructed wetland treatment systems (CWTS)s can be used to treat various wastewaters. The main constituent in oil sands process-affected water (OSPW) with uncertain treatment by CWTS are naphthenic acid fraction compounds (NAFC)s. The NAFCs are also among the primary contributors of toxicity to aquatic organisms. While there is preliminary evidence that some CWTSs are capable of treating OSPW for future potential discharge, there is little information comparing the effectiveness and efficiencies of different CWTS designs. Obtaining large volumes of OSPW for testing can be difficult, and while it is known that synthetic NAFCs are simpler and have different toxicity than OSPW-NAFCs, it is unknown whether they could serve as a proxy for optimization of CWTS design and operation. This study presents a comprehensive comparison of CWTS performance operated with both synthetic OSPW and OSPW for four CWTS designs differing in plant type, aeration, flow path, water depth, and substrate type. This study evaluated the potential biodegradation of NAFCs including: (1) decrease in total NAFC concentration, (2) shifts in Ox-NAFC fractions from O2- to O3-, O4-, and O5-NAFC, (3) decrease in carbon number, (4) decrease of the double bond equivalencies (DBE), and (5) change in toxicity of the waters to test organisms. CWTS planted with Sedge achieved the greatest extent of NAFC treatment and detoxification regardless of design. Although CWTSs planted with Cattail and Bulrush also degraded NAFCs and decreased toxicity, a greater hydraulic retention time was required, and the total extent of treatment was less than the CWTSs planted with Sedge. While synthetic OSPW was more toxic and experienced faster degradation rates, it showed similar trends to OSPW in terms of CWTS design efficiencies and function. Although synthetic OSPW would not be appropriate for modelling or scaling of CWTSs, it can be useful for testing designs and operating conditions.

Direct analysis of naphthenic acids in constructed wetland samples by condensed phase membrane introduction mass spectrometry.

The application of direct mass spectrometry techniques to the analysis of complex samples has a number of advantages including reduced sample handling, higher sample throughput, in situ process monitoring, and the potential for adaptation to on-site analysis. We report the application of a semi-permeable capillary hollow fibre membrane probe (immersed directly into an aqueous sample) coupled to a triple quadrupole mass spectrometer by a continuously flowing methanol acceptor phase for the rapid analysis of naphthenic acids with unit mass resolution. The intensity of the naphthenic acid-associated peaks in the mass spectrum are normalized to an internal standard in the acceptor phase for quantitation and the relative abundance of the peaks in the mass spectrum are employed to monitor compositional changes in the naphthenic acid mixture using principle component analysis. We demonstrate the direct analysis of a synthetic oil sands process-affected water for classical naphthenic acids (CnH2n+zO2) as they are attenuated through constructed wetlands containing sedge (Carex aquatilis), cattail (Typha latifolia), or bulrush (Schoenoplectus acutus). Quantitative results for on-line membrane sampling compare favourably to those obtained by solid-phase extraction high-resolution mass spectrometry. Additionally, chemometric analysis of the mass spectra indicates a clear discrimination between naphthenic acid-influenced and natural background waters. Furthermore, the compositional changes within complex naphthenic acid mixtures track closely with the degree of attenuation. Overall, the technique is successful in following changes in both the concentration and composition of naphthenic acids from synthetic oil sands process-affected waters, with the potential for high throughput screening and environmental forensics.