Treatment of oil sands process-affected waters using a pilot-scale hybrid constructed wetland

Constructed wetland treatment systems (CWTSs) could provide a passive, low-energy strategy for mitigating risks associated with oil sands process-affected waters (OSPWs). Due to the large volumes (over 975 million m3), heterogeneous composition, and acute and chronic toxicity of OSPW, passive and efficient treatment to decrease risks to biota will be necessary once operators obtain regulatory permission to discharge into aquatic receiving systems. The research objective was to design, assemble, and measure performance of a pilot-scale hybrid CWTS for treatment of OSPW. Constituents of concern (COCs) identified in OSPW included NAs, oil and grease, As, B, Cu, Pb, and Zn. Oxidizing conditions (net sediment redox > −50 mV) were promoted to allow aerobic degradation of organic constituents, and co-precipitation of arsenic with iron oxyhydroxides. Treatment of Cu, Pb, and Zn was targeted through precipitation with sulfides in reducing “micro-environments” in wetland sediments. Solar photocatalytic reactors (hybrid components) were used to remove recalcitrant organics. Performance was assessed using rates and extents of removal of COCs and changes in toxicity as indicated by Ceriodaphnia dubia. Mean total naphthenic acid fraction compound concentrations decreased from approximately 43 mg/L in untreated OSPW to 10 mg/L following a 16-d retention time in the hybrid CWTS. Mean As and Zn concentrations decreased from 0.026 mg/L and 0.129 mg/L in untreated OSPW to 0.011–0.014 mg/L and 0.052–0.062 mg/L in wetland outflows, respectively. Cu and Pb mass decreased by 13–26% in the CWTS; however, evaporative concentration masked removal (in terms of total metal concentrations). Toxicity (in terms of C. dubia survival and reproduction) of OSPW was eliminated following treatment. Results demonstrate that hybrid CWTSs can effectively degrade NAs and alleviate toxicity associated with metals and organics in OSPW.

Supplemental Information

A list of acronyms can be found in Data Resources.

Oil sands process-effected water sourced from the Athabasca Oil Sands region in Alberta, Canada. Hybrid CWTS performance was measured in Series A and B for three experiments (Experiments 1, 2, and 3) between October 2016 and January 2017.

Joint Canada-Alberta Oil Sands Monitoring (JOSM)

The Governments of Canada and Alberta have committed to implementing scientifically rigorous, comprehensive, integrated and transparent environmental monitoring of the oil sands region to ensure this important national resource is developed in a responsible way. Working together, the implementation of monitoring enhancements will ensure installation of necessary infrastructure and appropriate integration with existing monitoring activities in the region. The efforts contribute to an improved understanding of the long-term cumulative effects of oil sands development.

Since 2012, the governments of Alberta and Canada have worked to implement an environmental monitoring program for the oil sands, which integrates air, water, land, and biodiversity. The intent is to improve the characterization of the state of the environment and enhance understanding of the cumulative effects of oil sands development activities in the oil sands area. To date, the Joint Canada-Alberta Oil Sands Monitoring Program has significantly improved the ability to track low-level contaminants by increasing the geographic coverage of monitoring efforts—nearly doubling the number of sites monitored, increasing the frequency of sampling, sampling for more compounds and with more sensitive detection methods, and integrating results (https://www.canada.ca/en/environment-climate-change/news/2017/12/canada-alberta_oilsandsenvironmentalmonitoring.html).

For more information on the JOSM, please visit https://www.canada.ca/en/environment-climate-change/services/oil-sands-monitoring.html