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Selenium Remediation at Red Rock Ranch (Coalinga, CA)

Last updated on 01/27/2009

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Selenium (Se), a major pollutant in agricultural drainage water of California’s San Joaquin  Valley, imposes an enormous risk to the top predators (waterfowl) inhabiting environments impacted by agricultural drainage. Previous research demonstrated the feasibility of combining harvest of invertebrates with algal volatilization to reduce concentrations of Se in drainage water discharged to a wetland evaporation system at the Tulare Lake Drainage District (TLDD). Our current research adapts and extends this technology for bioremediation of drainage water with substantially higher concentrations of Se and salt, co-contaminated with nitrate, in a unique treatment system. The goal is to optimize and implement an economic and sustainable method, harnessing microalgal selenium volatilization and food chain disruption, to reduce the ecotoxic risk posed by Se-contaminated agricultural drainage water. A secondary goal is to produce economically valuable by-products from the process.

Our project takes place at Red Rock Ranch (RRR), a 600+ acre farm located at Five Points, CA, practices Integrated On-Farm Drainage Management (IFDM). Drainage water resulting from irrigation of standard crops is further recycled through irrigation of a series of salt tolerant crops both to manage drainage water on site and gain additional economic value from the water. The end-result of such intensive use of the water, combined with evaporation, is wastewater contaminated with excessively toxic levels of Se and salt. Such conditions are commonly associated with agricultural production in the southern San Joaquin Valley. The Red Rock Ranch site features a 28,100 gallon, “raceway” configured aquaculture pond. Recent design modifications include sufficient depth to limit evaporation and temperature fluctuations and a paddle wheel to provide adequate water column mixing and aeration.

1)                                                     2)
RRR_research
1) Raceway pond at RRR; 2) dominant microalgae in the pond

Results to date
• Artemia and microalgae strains have adapted to high salt, high Se RRR drainage water.
• Consistent removal of Se has been maintained through one year of evaporation/drainage water addition cycles.
• Iron has been identified as a limiting factor and growth additives have been developed for optimal algal growth and Se volatilization.
• Se volatilization rates and species diversity are dependent on length of light:dark cycle.
• Se volatilization rates are influenced by nitrate concentration.


Benefits
• Economical treatment of Se contaminated drainage water
• Harvest of Artemia as a source of protein and Se to supplement cattle feed
• Harvest of microalgal biomass for biofuel production
• Conversion of pollution into high value products