Abstract
Previous studies have indicated aquifer heterogeneity has an important influence on the removal of Cr(VI) in groundwater, but little attention is paid to the effects of aquifer heterogeneity during the process especially under conditions like actual groundwater temperature and hydraulic gradient in the field. Thus, in this study, in situ remediation of Cr(VI)-contaminated shallow groundwater in a sandbox was conducted, and the influences of the heterogeneous aquifer composed of coarse, medium, and fine sand on Cr(VI) diffusion and removal before and after emulsified vegetable oil (EVO) injection were investigated, under the conditions of 19±0.5 °C and hydraulic gradient 3‰. The results show that Cr(VI) diffused consistently with groundwater from top left to bottom right; Cr(VI) spread faster in the horizontal direction than in vertical direction, and the horizontal diffusion of Cr(VI) in coarse, medium, and fine sand was 0.054 m/day, 0.036 m/day, and 0.018 m/day, respectively; a high performance of EVO toward Cr(VI) removal by over 95% was mainly because different concentrations of microorganisms migrated among heterogeneous aquifers vertically and horizontally; compared with coarse and medium sand, fine sand, with a better adsorption capacity and a lower permeability, retained relatively more microorganisms, providing favorable conditions during the remediation; a stable and unified effective removal zone, similar to the shape of Ʃ (approximately 1357.87 cm2), was ultimately formed downstream of the injection well.
Highlights
Chromium is one of the most frequently detected heavy metals in groundwater, surface waters and industrial sites, which has been considered as one of the top 20 contaminants on the superfund priority list of hazardous substances for the past 15 years (Grabarczyk et al 2006)
The results indicate the orange zone (OZ) usually diffused from the upper left corner to the lower right corner along the direction of the groundwater flow
The results show that the groundwater flow field has an important effect on the spatial distribution of the ERZ, and a stable ERZ could be established in the entire heterogeneous aquifer downstream of the injection well 18 days following emulsified vegetable oil (EVO) injection under the experimental conditions
Summary
Chromium is one of the most frequently detected heavy metals in groundwater, surface waters and industrial sites, which has been considered as one of the top 20 contaminants on the superfund priority list of hazardous substances for the past 15 years (Grabarczyk et al 2006). Numerous industrial applications, such as production of alloys and mainly steel production, metal finishing, electroplating, leather tanning, textile synthesis, wood treatments and coal mining, usually cause chromium contaminated groundwater (Guo et al 2011, Sahinkaya &Kilic 2014, Yoon et al 2011). Cr(VI) is highly toxic to humans, animals, plants and microorganisms and is associated with the development of various chronic health disorders including organ damage, dermatitis and respiratory impairment (Xu et al.2004), which has been classified as a Group A human carcinogen by the U.S
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