Separate or simultaneous treatment of nitrate and uranium in groundwater via bioremediation: Review and prospect

Abstract

This review starts with the issue of groundwater contamination in uranium mining areas using acid leaching methods which is threatening drinking water safety, and provides a comprehensive overview of biological remediation technologies for nitrate and uranium contamination in groundwater. Bacterial genera with remediation potential is summarized and theoretical support for applying microorganisms to remove uranium and nitrate simultaneously is discussed comprehensively. Denitrification is the primary mechanism for nitrate removal from groundwater, dual benefits of agricultural waste utilization and environmental pollution control could be achieved by using lignocellulosic waste (e.g. agricultural waste) as a carbon source. Hydrogen is a clean and ideal electron donor for autotrophic denitrification, and removal rate of autotrophic denitrification could be well enhanced via membrane biofilm reactor (MBR) as well as preventing hydrogen leakage. Compared to biosorption and/or biomineralization, stimulating microorganisms to reduce U(VI) to U(IV) is also a promising pathway. Bioelectrochemical systems (BES) could play a supportive role in biological remediation. Clostridium sp. PXL2 could remove U(VI) and nitrate simultaneously from groundwater, while Hydrogenophaga and Thiobacillus genera show satisfied remediation effects in autotrophic denitrification and uranium reduction processes. Uranium exists in the form of crystalline UO2 within the pH range of 0–7 and Eh range of −0.4 to 0 V. Therefore, this review proposes a brand-new methodology for autotrophic denitrification and uranium reduction by utilizing hydrogen as sole electron donor, with pH and Eh regulation through the control of hydrogen and autotrophic denitrification, and maintaining the U-C-O-H system under reduction conditions. There is a reason to believe that this will be a promising environmentally friendly and effective biological remediation method if implemented successfully.