Abstract
Hexavalent chromium is a carcinogenic heavy metal that needs to be removed effectively from polluted aquifers in order to protect public health and the environment. This work aims to evaluate the reduction of Cr(VI) to Cr(III) in a contaminated aquifer through the stimulation of indigenous microbial communities with the addition of reductive agents. Soil-column experiments were conducted in the absence of oxygen and at hexavalent chromium (Cr(VI)) groundwater concentrations in the 1000–2000 μg/L range. Two carbon sources (molasses and EVO) and one iron electron donor (FeSO4·7H2O) were used as ways to stimulate the metabolism and proliferation of Cr(VI) reducing bacteria in-situ. The obtained results indicate that microbial anaerobic respiration and electron transfer can be fundamental to alleviate polluted groundwater from hazardous Cr(VI). The addition of organic electron donors increased significantly Cr(VI) reduction rates in comparison to natural soil attenuation rates. Furthermore, a combination of organic carbon and iron electron donors led to a longer life span of the remediation process and thus increased total Cr(VI) removal. This is the first study to investigate biotic and abiotic Cr(VI) removal by conducting experiments with natural soil and by applying biostimulation to modify the natural existing microbial communities.
Highlights
Chromium (Cr) is a heavy metal that occurs in soils, sediments and groundwater through geogenic and anthropogenic sources
Hexavalent chromium (CrO42−, Cr2O72−) is highly soluble, toxic and a well-known carcinogen [13,14], that has been designated by the USEPA as one of seventeen chemicals posing the greatest threat to human health [15]
After the start-up period, both columns were supplied for two weeks via recirculation with a 4L Cr(VI) solution in order to evaluate the reductive capacity of each soil column without the addition of any reducing agent
Summary
Chromium (Cr) is a heavy metal that occurs in soils, sediments and groundwater through geogenic and anthropogenic sources. The main natural sources of Cr in the environment are ophiolithic and serpentine rocks, as well as their weathering products [1,2]. The World Health Organisation has set a limit of 50μg/L for total Cr in drinking water [16]. In several parts of the world reported values for geogenic Cr(VI) in aquifers can exceed that limit by tenths of μg/L, while anthropogenic Cr(VI) concentrations can exceed 10,000 μg/L, such as in the Asopos river basin in Greece [17,18,19,20,21]. It is important to establish adequate treatment methods to rapidly reduce Cr(VI) to Cr(III) in Cr-contaminated aquifers in order to protect the environment and public health
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