Detoxification Of Chromium-contaminated Soil With Anaerobic Digestion Sludge

China is one of the major countries which produce chromium salt. Due to thelimits of economy and technology, the vast majority of chromium slag was piledwithout any protective measures. The dissolvable hexavalent chromium，which rangesfrom0.3%-1.5%in chromium slag, can lead severe contamination to the envrionmentby flowing into soil, surface water and ground water with rainfall. As a result, theremediation of chromium-contaminated soil draws more and more attention.Compared with traditional methods, biological remediation has someadvantages，such as low investment, function expense and various of treatmentmethods. In this paper，detoxification of chromium-contaminated soil by anaerobicdigestion sludge and the feasibility of this idear was studied. The influencing factorsthat initial concentration of Cr(VI), moisture content, temperature, initial pH arestudied. The morphological change of chromium before and after the reaction wasanalyzed. We also focus on the mechanism of Cr(VI) removal. The chromiumcontaminated soil, the compound of chromium contaminated soil and anaerobicdigestion sludge were characterized by using XPS and FTIR. The main results arelisted as follows:(1) The method that anaerobic digestion sludge detoxifying chromiumcontaminated soil is feasible and the process mainly consists of two first orderreaction which have different rate. Studies showed that the reduction rate decreasewith the increase of initial concentration of Cr(VI), moisture content and initial pHand with a decrease of temperature. At an initial concentration of Cr(VI) of1108.9mg/kg, the concentration of water soluble hexavalent chromium can be reduced to3.88mg/kg and the reduction rate can reach99.7%.(2) In chromium polluted soil, Cr mainly existes in water soluble form andresidual fraction form. After the treatment of anaerobic digestion sludge, most watersoluble chromium and weak acid extractable chromium transform to reduciblechromium and oxidizable chromium, while a small amount transform into residual form. The mobility of chromium in environment was greatly reduced.(3) After the detoxification of anaerobic digestion sludge, Cr(VI) was reduced toCr(III) and mainly in the form of Cr(OH)3. Hydroxyl group, carboxyl group, aminogroup of sludge organic and anaerobic microorganisms are the key drivers of Cr(VI)reduction.