Biological treatment and bioremediation

In other studies with arsenic-spiked groundwater, Katsoyiannis and Zouboulis (2004) were able to further optimize arsenic removal with G. ferruginea and L. ochracea. The As(III) concentrations in the groundwater were lowered from 200 pg L-1 to below 10 pg L-1 in the presence of Fe(II) and oxygen. They also confirmed that bacteria catalytically oxidized the Fe(II) to Fe(III) and As(III) to As(V). Oxidation produced iron (oxy)(hydr)oxide precipitates, which removed the As(V) from the water (Katsoyiannis and Zouboulis, 2004). 

Rather than oxidizing As(III), some bacteria precipitate/coprecipitate, sorb, or otherwise directly remove As(III) from water. In their studies, Kostal et al. (2004) overexpressed the ArsR protein in Escherichia coli bacteria cells. The protein has a high affinity for As(III), which allowed the cells to remove nearly 100% of 50pgL 1 of As(III) from water (Kostal et al., 2004 Table 7.1). 

Schwertmannite may also be associated with the biological precipitation and coprecipitation of As(V). Through field and laboratory investigations, Ohnuki et al. (2004) studied the coprecipitafion of As(V) from pH 4.7 mine water by iron-rich bacterial colonies of Gallionella sp. They found that As(V) was associated with iron and sulfur in schwertmannite precipitates within the colonies. 

Phytoremediation with living plants may be improved through genetic engineering and a thorough understanding of arsenic metabolism and detoxification in plants (Montes-Baydn et al., 2004). As an initial step, Montes-Bay on et al. (2004) studied arsenic metabolism in Brassica juncea (Indian mustard). They found that some of the arsenic was associated with thiol groups in the plant. 

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