A powerful arsenite-oxidizing biofilm bioreactor derived from a single chemoautotrophic bacterial strain: Bioreactor construction, long-term operations and kinetic analysis.

Microbial oxidation of As(III) by biofilm bioreactors followed by adsorption is a promising and environment friendly approach to remediate As(III) contaminated groundwater; however, poor activity, stability and expandability of the bioreactors hampered their industrious applications. To resolve this issue, we constructed a new biofilm bioreactor using a powerful chemoautotrophic As(III)-oxidizing bacterium Rhizobium sp. A219. This strain has strong ability to form biofilms and possesses very high As(III)-oxidizing activities in both planktonic and biofilm forms. Perlites were used as the biofilm carriers. Long-term operations suggest that the bioreactor has very high efficiency, stability and scalability under different geochemical conditions, and it is cheap and easy to construct and operate. During the operations, it is only required to supply air, nothing else. All the common contaminants in groundwater slightly affected the bioreactor As(III)-oxidizing activity. The common contaminants in groundwater can be largely removed through assimilation by the bacterial cells as nutrition. The bioreactor completely oxidize 1.0, 5.0, 10.0, 20.0 and 30.0 mg/L As(III) in 12, 18, 20, 25 and 30 min, respectively. Approximately 18, 18, 12, 12 and 21 min were needed to oxidize 1.1 mg/L As(III) at 20, 25, 30, 35 and 40 °C, respectively. The bioreactor works well under the pH values of 5-8, and the most optimal was 7.0. The data suggest that this bioreactor possesses the highest efficiency and stability, and thus has the great potential for industrial applications among all the described As(III)-oxidizing bioreactors derived from a single bacterium.