Remediation of Selenium in Salton Sea

SE water remediation

The Salton Sea, the largest inland lake in California, is an important habitat for fish, birds and other wildlife. It serves as a major stop-over for migratory birds traveling the Pacific Flyway. Because of diminishing water supplies and increasing salinity, the Salton Sea ecosystem is in danger of collapse. To compensate for the loss of wetland habitat, the state of California has proposed to construct a Species Conservation Habitat (SCH). The water needed to support the SCH could be obtained from rivers that discharge into the south end of the Salton Sea, that is, the New River and/or the Alamo River. However, these rivers contain significant levels of selenium (Se), fertilizer nutrients (e.g., N and P), and other contaminants, mainly from agricultural irrigation water that drains into the rivers. High concentrations of Se in drainage water have been linked to mortality, developmental defects, and reproductive failure in fish and waterfowl. The overall goal of our research is to develop a cost-effective method for removing Se and other contaminants from these river waters so that they may be used to safely support the SCH.
Of all the technologies compared for Se removal, constructed wetland approaches have the lowest construction and operation costs for contaminant removal. Earlier research from our laboratory has shown that constructed wetlands were able to remove up to 90% of the inflow Se from oil refinery wastewater. Constructed wetlands have also been shown to remove significant amounts of Se from waters contaminated with agricultural irrigation drainage water. Selenium levels that exceed the U.S. EPA surface water criterion of 5 μg Se/L may pose an ecotoxic risk to wildlife including fish, which is of particular concern with respect to the piscivorous birds foraging in the proposed SCH. Unfortunately, very few wetland treatment systems have been able to reduce Se in the outflow to <5 μg Se/L. Because the Alamo and New Rivers typically contain 5 to 7 μg Se/L, with occasional spikes to >10 μg Se/L, the technology of constructed-wetland water treatment systems (CWTS) needs to be improved to reduce Se in the outflow to <2 μg Se/L so as to minimize Se ecotoxicity for wildlife foraging on the proposed SCH.