Volatilization of selenium from a dewatered seleniferous sediment: A field study

Summary One of the major concerns in central California (San Joaquin Valley) is the level of selenium (Se) in evaporation ponds containing agricultural drainage water. The objective of this work was to determine if volatilization of Se could be used as a bioremediation program to detoxify a saline seleniferous sediment of a dewatered evaporation pond. The dewatered sediment was rototilled, divided into subplots, and amended with various organic materials including citrus (orange) peel, cattle manure, barley straw and grape pomance. Some of the subplots were fertilized with nitrogen (NH₄)₂SO₄] and zinc (ZnSO₄). Selenium volatilization was monitored in the field with a flux chamber system utilizing alkaline peroxide to trap the gas. Overall, the greatest emission of gaseous Se was recorded in the summer months and the lowest emission during the winter months. The background emission of volatile Se averaged 3.0 g Se h^–1 m^–2. The most effective organic amendment was cattle manure with an avg. Se emission of 54 g Se h^–1 m^–2. Composite soil samples from each subplot (upper 15 cm) were analyzed for total Se on a monthly interval during the course of this field study. After 22 months, the application of water plus tillage alone removed 32.2% of the Se content while the cattle manure treatment removed 57.8%. Among the parameters which enhanced volatilization of Se were an available C source, aeration, moisture, and high temperatures. This field study indicates promising results in detoxifying seleniferous sediments via microbial volatilization once environmental conditions have been optimized.