Progress 01/01/11 to 12/31/11
OUTPUTS: Nothing significant to report. PI retired. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Nothing significant to report. PI retired.
- No publications reported this period
Progress 01/01/08 to 12/31/08
OUTPUTS: Selenium (Se) contamination of aquatic systems is common throughout the western United States which mainly results from exposure to agricultural drainage water. In order to protect aquatic life, an efficient-feasible treatment system with a low cost is needed for removal of Se from Se-contaminated agricultural drainage water. We investigated the use of non-soluble redox mediators, ZVI, and activated carbon in a biotreatment system in which Se(VI)-reducing bacteria use inexpensive molasses or sucrose to reduce Se(VI) to Se(0) in agricultural drainage water and at the same time accelerate the Se(VI) reduction to Se(0) through redox mediator electron transfer assisted by ZVI. PARTICIPANTS: Dr. Y. Q. Zhang is a postdoctoral scientist working under my (Frankenberger) supervision. Professors Chang and Amrhein are at UCR specializing in water quality. TARGET AUDIENCES: This research will provide solutions to growers in dealing with drainage water in western California and introduce policy makers and legislators to remediation alternatives. PROJECT MODIFICATIONS: Not relevant to this project.
Inexpensive ZVI and activated carbon were used to accelerate Se(VI) reduction to Se(0) by Bacillus RS1 after obtaining a suitable non-soluble redox mediator. ZVI can not only directly remove Se from water and but also indirectly enhance bacterial reduction of Se(VI) to Se(0) by rapidly removing dissolved oxygen from water and rapidly reducing oxidative redox mediators to their reduced forms. Activated carbon served as a carrier of the redox mediators and a support for the Se(VI) reducing bacteria attachment.
- Zhang, Y.Q. C. Amrhein, A. Chang, and W.T. Frankenberger, Jr. 2008. Effect of zero-valent iron and a redox mediator on removal of selenium in agricultural drainage water. Sci.Total Environ. 407:89-96.
Progress 01/01/07 to 12/31/07
OUTPUTS: Acceleration of bacterial reduction of selenate [Se(VI)] to insoluble elemental Se [Se(0)] plays an important role in Se bioremediation. Anthraquinone-2,6-disulfonate (AQDS), a redox mediator, was assessed for its ability to enhance the reduction of Se(VI) (2000 g/L) to Se(0) by Enterobacter taylorae in a mineral medium. The results showed that addition of AQDS did not increase Se(VI) reduction in the medium containing 50 and 250 mg/L of yeast extract, suggesting that E. taylorae cannot directly use anthrahydroquinone-2,6-disulfonate (AHQDS, a reduced form of AQDS) to respire Se(VI). An increase of yeast extract content from 50 to 250 mg/L in the medium dramatically enhanced the AQDS function for rapid reduction of selenite [Se(IV)] to Se(0). During an 8-day experiment, 85-91% of the added Se was reduced to Se(0) in the AQDS amended medium in comparison to formation of 46% of Se(0) in the medium without AQDS. These results show that redox mediators have great application
potential in bioremediation of Se in Se-contaminated water.
TARGET AUDIENCES: Growers, State and County Regulators, News Media
Efficiency and increased reaction rates are important factors considered in the remediation of Se-contaminated agricultural drainage water through bacterial reduction of soluble Se(VI) to insoluble Se(0). Using a redox mediator to enhance Se removal will enhance bacterial treatment in the field.
- Zhang, Y.Q., Zahir, Z. A., Amrhein, C., Chang, A., and Frankenberger, Jr. W.T. (2007). Application of redox mediator to accelerate selenate reduction to elemental selenium by Enterobacter taylorae. J. Agric. Food Chem. 55:5714-5717.
Progress 01/01/06 to 12/31/06
Selecting an inexpensive and effective organic carbon source is the key to reducing the cost in selenium (Se) remediation. Five bacteria were screened based on their ability in using molasses as an organic carbon source to reduce selenate [Se(VI)] in drainage water. Efficiency of Se removal differed in the molasses-added drainage water containing different bacteria, with an order of Enterobacter taylorae > Pantoea sp. SSS2 > Klebsiella sp. WRS2 > Citerobacter freundii > Shigella sp. DW2. By using E. taylorae, 97% of the added Se(VI) (1000 mg/L) was reduced to elemental Se [Se(0)] in an artificial drainage water during an 11-day experiment, and 93% of Se(VI) in a natural agricultural drainage water was reduced to Se(0) and organic Se during a 7-day experiment. E. taylorae also rapidly removed Se(VI) in agar-coated sand columns. During 45 days of the experiment, more than 92% of influent Se was removed from the drainage water with a molasses range of 0.01-0.1%. This
study reveals that molasses may be a cost-effective organic carbon source used by Se(VI)-reducing bacteria to remove Se from agricultural drainage water in field.
The cost of the organic carbon for bacteria to reduce Se(VI) is a key parameter in the economics of the remediation process. Effective usage of organic carbon and selecting inexpensive organic carbon in remediation can significantly reduce the cost, and make bacterial treatment technique practical in the field.
- Zhang, Y. Q. and W. T. Frankenberger, Jr. 2007. Supplementing Bacillus sp. RS1 with Dechloromonas sp. HZ for Enhancing Selenate Reduction in Agricultural Drainage Water. Sci. Total Environ In press.
- Zhang, Y. Q., B.C. Okeke, and W. T. Frankenberger, Jr. 2007 Bacterial Reduction of Selenate to Elemental Selenium Utilizing Molasses as a Carbon Source. Biores. Technol In press
Progress 01/01/05 to 12/31/05
NON-TECHNICAL SUMMARY Bacterial reduction of selenate to insoluble elemental Se is an important remedial technology to remove selenium (Se) from drainage water. Selecting an inexpensive and effective organic carbon source is the key to reducing the cost in Se remediation. We isolated several selenate reducing bacteria that are capable of using inexpensive molasses as an electron donor and carbon source to effectively reduce soluble selenate to insoluble elemental Se, which is much less bioavailable to aquatic organisms than other Se forms such as selenate, selenite, and organic Se species. OBJECTIVES: The major goal of this work was to screen selenate reducing bacteria isolated from different environments based on their ability in using molasses as an organic carbon source to reduce selenate in drainage water, and to use selected selenate reducing bacteria to remove Se from agricultural drainage water in a flow-through bioreactor system. APPROACH: We conducted the
following experimentation in this project: 1. Conduct laboratory experiments to screen selenate reducing bacteria based on their ability in using molasses as an organic carbon source to reduce selenate in drainage water. These bacteria included Enterobacter taylorae, Pantoea sp., Klebsiella sp., Citerobacter freundii, Shigella sp., and Baciilus sp. 2. Conduct laboratory experiments to evaluate effects of salinity, nitrate, and the amounts of molasses used on the removal Se in drainage water. 3. Conduct experiments to remove Se from drainage water in a flow-through bioreactor KEYWORDS: bioremediation; selenium; selenium speciation; selenate reduction; organic carbon; molasses; drainage water; water contamination; nitrate; bacteria; Enterobacter taylora; Pantoea sp.; Klebsiella sp.; Citerobacter freundii; Shigella sp.; Bacillus sp.; bioreactor. PROGRESS: 2005/01 TO 2005/12 Agricultural drainage water with elevated levels of Se has been reported to cause deformity of waterfowl in the
wetland systems in the western United States. Bacterial reduction of selenate to insoluble elemental Se is an important remedial technology to remove Se from drainage water. The cost of the organic carbon for bacteria to reduce selenate is a key parameter in the economics of the remediation process. We conducted a series of laboratory experiments on the bacterial removal of Se by using inexpensive molasses and zero-valent iron. Results revealed that the combination of a bacterial treatment using inexpensive molasses and ZVI can effectively remove Se from river and drainage waters. In an organic carbon-coated flow-through bioreactor system, selenate reducers attached to organic coatings can effectively reduce soluble selenate to elemental Se when it passed through sand columns. Our work indicates that effective usage of organic carbon and selecting inexpensive organic carbon in bioremediation can significantly reduce the cost, and make bacterial reduction technique practical in the
IMPACT: 2005/01 TO 2005/12 The cost of the organic carbon for bacteria to reduce Se(VI) is a key parameter in the economics of the remediation process. Effective usage of organic carbon and selecting inexpensive organic carbon in remediation can significantly reduce the cost, and make bacterial treatment technique practical in the field.
- PUBLICATIONS: 2005/01 TO 2005/12 Zhang, Y.Q. and W.T. Frankenberger, Jr. 2006. Removal of selenate in river and drainage waters by Citerobacter braakii enhanced with zero-valent iron. J. Agric. Food Chem. 54:152-156.
- Siddiue, T., Y.Q. Zhang, B.C. Okeke, and W.T. Frankenberger Jr. 2005. Characterization of sediment bacterial assemblages involved in selenium reduction. Biores. Tech. 97: 1041-1049.
- Zhang, Y.Q. and W.T. Frankenberger, Jr. 2005. Removal of selenium from river water by Enterobacter taylorae in an organic carbon coated sand column. Sci. Total Environ. 346: 280-285.
- Siddiue, T., B.C. Okeke, Y.Q. Zhang, M. Arshad, and W.T. Frankenberger Jr. 2005. Bacterial diversity in selenium reduction of agricultural drainage water amended with rice straw. J. Environ. Qual. 34: 217-226.
- Zhang, Y.Q., J. Wang, C. Amrhein, and W.T. Frankenberger, Jr. 2005. Effect of arsenate and molebdate on the removal of selenate by zero-valent iron. Sci. Total Environ. 346: 280-285.
- Zhang, Y.Q., J. Wang, C. Amrhein, and W.T. Frankenberger, Jr. 2005. Removal of selenate from water by zero-valent iron. J. Environ. Qual. 34: 487-495.
Progress 01/01/04 to 12/31/04
Bioaccumulation of selenium (Se) in wetlands and evaporation ponds has created serious hazards to fish and waterfowl in the western United States. Agricultural drainage water is the main source for Se contamination in this region. Treatment technologies currently being evaluated to reduce the Se load in agriculture drainage water include physical, chemical and biological methods. We conducted a series of experiments on selenite adsorption and selenate reduction using rice straw as biobarrier. Our work reveals that Se removal from drainage water in the presence of rice straw involves microbial reduction of selenate to selenite and then to colloidal Se. These results indicate that rice straw may be useful in removing Se from drainage water in the field because it is an excellent carrier of Se reducing bacteria and it provides a carbon and energy source.
Biological treatment holds the most promise because of its cost effectiveness and permanent removal of Se. Bacteria, plants, and microalgae active in Se precipitation and volatilization are the most promising players in remediation of agricultural drainage water. Our studies show that in aquatic systems the major mechanism of Se removal is through reductive precipitation.
- Frankenberger, W. T., C. Amrhein, T. W. M. Fan, D. Flaschi, J. Glater, E. Kartinen, K. Kovac, E. Lee, H.M. Ohlendorf, L. Owens, N. Terry and A. Toto. 2004. Advanced treatment technologies in the remediation of seleniferious drainage waters and sediments. Irrigation and Drainage Systems 18:19-41.
- Zhang, Y., Z. A. Zahir, and W. T. Frankenberger. 2004. Fate of colloidal-particulate elemental selenium in aquatic systems. Journal of Environmental Quality 33:559-564.