PILOT-SCALE SELENIUM BIOREMEDIATION OF SAN-JOAQUIN DRAINAGE WATER WITH THAUERA-SELENATIS

This report describes a simple method for the bioremediation of seleni um from agricultural drainage water. A medium-packed pilot-scale biolo gical reactor system, inoculated with the selenate-respiring bacterium Thauera selenatis, was constructed at the Panoche Water District, San Joaquin Valley, Calif, The reactor was used to treat drainage water ( 7.6 liters/min) containing both selenium and nitrate. Acetate (5 mM) w as the carbon source-electron donor reactor feed, Selenium oxyanion co ncentrations (selenate plus selenite) in the drainage water were reduc ed by 98%, to an average of 12 +/- 9 mu g/liter. Frequently (47% of th e sampling days), reactor effluent concentrations of less than 5 mu g/ liter were achieved, Denitrification was also observed in this system; nitrate and nitrite concentrations in the drainage water were reduced to 0.1 and 0.01 mM, respectively (98% reduction), Analysis of the rea ctor effluent showed that 91 to 96% of the total selenium recovered wa s elemental selenium; 97.9% of this elemental selenium could be remove d with Nalmet 8072, a new, commercially available precipitant-coagulan t. Widespread use of this system (in the Grasslands Water District) co uld reduce the amount of selenium deposited in the San Joaquin River f rom 7,000 to 140 Ib (ca, 3,000 to 60 kg)/year.