Use of iron- and manganese-oxidizing bacteria for the combined removal of iron, manganese and arsenic from contaminated groundwater

The problem of groundwater contamination with arsenic has been under extensive discussion, especially in recent years, because of its adverse effects on human health and its widespread presence in groundwater throughout the world. Large drinking water plants in developed countries normally find alternative and arsenic-free water resources, or they apply conventional arsenic removal methods, such as coagulation/filtration, activated alumina and ion exchange. Smaller towns, communities and individual users in rural areas often rely on local water resources and the respective removal methods developed mainly for larger water treatment plants are not easily applicable, because of high operational and capital costs, or they are simply too complicated and their use is sometimes limited by the specific water composition. Consequently, small drinking water systems face the difficult challenge in providing a safe and sufficient supply of drinking water at a reasonable cost. Alternative treatment methods have been developed for application in these cases. In the present paper, the simultaneous removal of arsenic during biological iron and manganese oxidation is reviewed. The method relies on the use of indigenous non-pathogenic iron- and manganese-oxidizing bacteria. Dissolved iron and manganese species often coexist with arsenic in groundwater. Therefore, the application of this method could provide consumers with water of high quality, which is practically free of iron, manganese and arsenic, complying with the respective legislative limits. In this paper the biological oxidation of iron and manganese has been reviewed and recent findings regarding the removal of arsenic have been summarized. Arsenic(RI or V) can be removed efficiently from a wide range of initial concentrations with practically limited operational cost, apart from the capital costs for the installation of treatment units. As a result, the use of chemical reagents for the oxidation of trivalent arsenic can be avoided, because As(III) was efficiently oxidized to As(V) by these bacteria (acting as catalysts) under similar conditions, which are usually applied for the removal of iron and manganese by biological means.