Depletion rates of O2-naphthenic acids from oil sands process-affected water in wetland microcosms†

Treatment wetland microcosms were constructed to evaluate the fate of O₂-naphthenic acids in microcosm reactors containing OSPW only (i.e., natural attenuation), OSPW with peat soil (sorption and microbial degradation), and cattail microcosm reactors (plant-mediated uptake and biotransformation). Depletion in OSPW occurs by mechanisms of natural attenuation, sorption and microbial degradation, and plant-mediated uptake and biotransformation. The average rate of depletion for O₂-naphthenic acids was 0.005 (SD 0.010) per day in OSPW only, 0.029 (SD 0.013) per day in OSPW with peat soil, and 0.043 (SD 0.013) per day in cattail microcosm reactors. Slow rates of depletion from OSPW by natural attenuation highlight the need to develop effective remediation strategies for OSPW, and the increase in rates of depletion for cattail microcosm reactors highlights the importance of wetland vegetation in supporting naphthenic acid removal from OSPW. Reactors containing OSPW with peat soil showed the greatest increase in rates of O₂-naphthenic acid depletion for lower molecular weight congeners compared to reactors with OSPW only. Cattail microcosm reactors showed the greatest increase in the rates of O₂-naphthenic acid depletion for higher molecular weight congeners compared to reactors with OSPW and peat soil.