Supplementing Bacillus sp. RS1 with Dechloromonas sp. HZ for enhancing selenate reduction in agricultural drainage water.

Cost and efficiency are two important factors considered in the remediation of Se-contaminated agricultural drainage water through bacterial reduction of soluble Se(VI) to insoluble Se(0). Bacillus sp. RS1 isolated from rice straw was assessed for its ability to use inexpensive molasses to reduce Se(VI) in agricultural drainage water containing NO3- levels of 0, 50, 100, 250, and 500 mg/L. The results showed that Se(VI) (1000 microg/L) was almost entirely reduced to Se(IV) (62.7%) and Se(0) (36.4%) by Bacillus sp. RS1 in synthetic agricultural drainage (SAD) water without the presence of NO3-. The reduction Se(VI) to Se(0) was limited in the SAD water with NO3- levels of 100, 250, and 500 mg/L. The addition of Dechloromonas sp., a NO3- reducer, to the SAD water not only increased NO3- removal, but also enhanced Se(VI) reduction by Bacillus sp. RS1. During an 8-day experiment, 98-99% of the added Se(VI) was reduced to Se(0) with small amounts of Se(IV) and Se(-II) in the SAD water containing 100 and 250 mg/L NO3-. The addition of Dechloromonas sp. HZ to the natural agricultural drainage water also significantly increased the reduction of Se(VI) (748 microg/L) by Bacillus sp. RS1, with a production of Se(0) (65%) and Se(-II) (32%). These results suggest that a combination of Bacillus sp. RS1 with Dechloromonas sp. HZ has great potential with the use of inexpensive molasses to remediate Se-contaminated agricultural drainage water containing relatively high NO3- levels.