Pentavalent vanadium and hexavalent uranium removal from groundwater by woodchip-sulfur based mixotrophic biotechnology

Abstract

Mining and smelting of vanadium uranium ore results in the release and coexistence of vanadium and uranium in environment, raising severe risks. The feasibility of synchronous removal of pentavalent vanadium (V(V)) and hexavalent uranium (U(VI)) was investigated in mixotrophic column reactor packed with woodchips and elemental sulfur (S0). The impact of various groundwater chemistry (i.e., elevated V(V) or U(VI)) and hydraulic retention time was investigated. Over the course of the 140-day experiment, the removal efficiencies of U(VI) and V(VI) ranged from 55.1 to 80.7% and 52.2 to 99.5%, respectively. The soluble V(V) and U(VI) were transformed into insoluble V(IV) and U(IV), and further removed in the form of precipitation. Several functional V(V) and U(VI) reducing microorgisms including Azospira, Luteolibacter, Azotobacter, Meniscus, Pseudomonas, Thiobacillus and Bacteroides, were identified and they had close partnerships. Further, the co-occurrence network revealed autotrophic sulfur oxidizing bacteria Thiobacillus was positively correlated with other heterotrophic bacteria. The carbohydrate metabolism and digestive system related genes were enriched in the final stage. Multiple lines of evidence suggested a mixotrophic process occurred in the woodchip- and sulfur-based column reactor, offering promising strategies for synchronous management of V(V) and U(VI) contaminated groundwater via mixotrophic processes.