A Coordinated Approach to Achieving NPDES Permit Compliance for Mercury and Selenium in a Refinery Effluent

To implement water quality standards, selenium and mercury limits were established in the National Pollutant Discharge Elimination System (NPDES) permit issued to Suncor Energy's Commerce City, Colorado, refinery. Before the permit issuance, and as water-quality-based limits became law, the refinery initiated a coordinated approach to capitalize on stakeholder engagement, dialogue, and cooperation with regulatory agencies while assessing future limits, applicable technologies, and compliance options. Selenium concentrations in the sour water stripper bottoms suggested segregated waste stream treatment, while the presence of mercury in nearly all refinery wastewater streams suggested end-of-pipe treatment. Through bench- or pilot-scale studies, Suncor evaluated numerous selenium-removal technologies, including iron co-precipitation, anoxic biological treatment, and reverse osmosis. Because mercury occurred primarily in particulate form, treatment focused on filtration processes. Subsequently, integrated treatment to remove selenium and mercury, while positioning for future zero liquid discharge (ZLD), was identified as a potentially cost-effective solution.