Study on the removal of hexavalent chromium from contaminated groundwater using emulsified vegetable oil

Abstract

Emulsified vegetable oil (EVO) is an oil-in-water emulsion that could serve as a slowly released electron donor. In this work, column experiments were conducted to elucidate feasibility of EVO for removing hexavalent chromium from groundwater, and to investigate the influences of adding acetate and Mg(OH)2 as amendment. Results showed that a one-time EVO injection stimulated a depletion of terminal electron acceptors, such as O2, Fe(III), and released aqueous Fe(II), generating reducing conditions and resulting in a drastic decrease in Cr(VI) concentration. EVO and amended EVO is feasible to remove Cr(VI) from groundwater. EVO added columns (EVO, EVO + acetate, EVO + Mg(OH)2) retained and removed Cr(VI) contamination in simulated groundwater for 177, 191 and more than 240 days, respectively. Cr(VI) was completely removed from simulated groundwater and XPS characterization confirmed that it was stably immobilized in sediments as Cr(III) compounds. In addition, the amendment of EVO with acetate and Mg(OH)2 facilitated EVO performance on Cr(VI) removal by enhancing the bioreduction of Fe(III). Microbial community structure analysis revealed that EVO injection cause decline in microbial community richness and diversity while induced accumulation of microbes related to organic fermentation and iron reduction, showing potential for further Cr(VI) removal.