Biodegradation of Chromate‐Contaminated Groundwater by Reduction and Precipitation in Surface Soils

Abstract

A cost‐effective method is needed for removing chromate from cooling water blowdown, wastewater effluent, and contaminated groundwater. Experiments were conducted to determine the effectiveness of treating Cr‐contaminated water by using the water for irrigation, and that reduction of Cr(VI) to Cr(III) would occur in a soil amended with organic matter and irrigated to promote low oxidation/reduction status. The Cr(III) would then precipitate as oxides and hydroxides, and be immobilized and rendered plant unavailable. Samples of a field soil (mixed, thermic Typic Torripsamments) overlying a contaminated groundwater site were placed in pots and irrigated for 20 wk with water containing 1000 µg L−1 Cr(VI). Treatments included plants (alfalfa; Medicago sativa L.) vs. no plants, each at three organic matter Ioadings ‐ 0, 12, and 50 Mg ha−1 dried cattle manure (0, 5.5, and 21.8 g manure kg−1 soil). The drainage waters were collected weekly and analyzed for total Cr, Cr(VI), pH, dissolved O2, dissolved organic C, and electrical conductivity. The removal percentages of Cr(VI) from the enriched water ranged from 51 to 98% and increased with increasing organic matter loading. Chromium concentrations in the drainage water were consistently <50 µg L−1 in the organic‐amended soil. Daily irrigation yielded lower drainage water Cr concentrations than weekly irrigation (at a constant weekly volume) due to increased residence time of the water in the bioactive zone. Chromate adsorption accounted for <1% of the total immobilized Cr and the amount taken up by the alfalfa shoots was <0.5% of the total added. This method shows promise as a cost‐effective treatment for Cr‐contaminated groundwater.

Rendimentos de culturas e alterações químicas do solo tratado com resíduos de curtume e crômio hexavalente

“…A lenta redução do Cr 6+ verificada pelos autores, nas condições de cultivo, comprova que a sua redução à forma trivalente é a reação principal para diminuir seus efeitos tóxicos. Efeitos positivos na redução do Cr 6+ após a aplicação de esterco também foram verificados por Losi et al (1994), James (1994) e Cifuentes et al (1996).…”

Literature review: Phytoaccumulation of chromium, uranium, and plutonium in plant systems

“…Chromium(VI) is not thermodynamically stable in soils except in alkaline, oxidizing environments, and is readily reduced to Cr(III) (Cary et al, 1977b). The transformation of Cr(VI) to Cr(III) in soils is likely to occur as a result of reduction by Fe(II) in solution and at mineral surfaces, reduced sulfur compounds, or soil organic matter (Bartlett, 1991;Charlet and Manceau, 1992;Fendorf, 1995;James and Bartlett, 1983b;Losi et al, 1994). The reduction of Cr(VI) to C r ( m by organic matter is more rapid in acid than in alkaline soils (Cary et al, 1977b).…”

Selected physiological responses of kudzu to different chromium concentrations

“…Hexavalent Cr is much more mobile and toxic than Cr (III) (Katz 1991;Ross et al 1981). As a strong oxidizer, Cr (VI) is reduced by electron donors such as ferrous ions and ferrous oxides and minerals containing silicates Rai 1988, 1989); organic matter (Bartlett and Kimble 1976;Cary et al 1977b); and organic-amended soils at near neutral pH (Losi et al 1994). In addition, low oxygen concentration increases the rate of Cr reduction (Bloomfield and Pruden 1980).…”