Department of Environmental Engineering and Soil Environment Research Center, Chonbuk National University, Jeonju, Jeollabukdo 57896, Republic of Korea.
K-WATER, Water Quality Center, Daejeon 34350, Republic of Korea.
Environ Pollut. 2019 Oct;253:231-238. doi: 10.1016/j.envpol.2019.07.026. Epub 2019 Jul 8.
Employing biochar for environmental remediation has been widely practiced. Nonetheless, the reduction mechanisms of hexavalent chromium (Cr(VI)) in the presence of biochar have not been fully elucidated (i.e., direct or indirect reduction of Cr(VI) by biochar). In particular, the effect of light on Cr(VI) reduction by biochar was rarely reported. Thus, to clarify the reduction mechanisms of Cr(VI) by biochar at the fundamental level, this study laid great emphasis on the photo-induced reduction of Cr(VI) in the application of biochar. Biochar releases dissolved organic matter (DOM), the DOM can extract Fe(III) from soil by complexation, and the complexes can be photo-reacted under the light. In these respects, Fe(II) formed by the photo-induced reaction of DOM-Fe(III) was particularly evaluated in this study. To evaluate that, three biomass samples (rice straw, granular sludge from an up-flow anaerobic sludge blanket, and spent coffee ground) were torrefied to biochar. To circumvent the adsorption of Cr(VI) onto biochar, biochar extractives (served as a source for DOM) and Fe(III) solution were tested with/without UV light to prove Fe(II) formation. This study experimentally proved that the more Fe(II) under the UV radiation was formed in the co-existence with biochar extractives and Fe(III). All experimental data from three biochar samples were indeed very similar. Cr(VI) reduction by Fe(II) from GB, RB, and CB reached up to 96, 79, and 100%, respectively. The different reduction efficiency signified that the low molecular weight of organic acids, such as oxalate, were more sensitive to the UV light, thereby resulting in the enhanced Fe(II) formation. Such Fe(II) formation subsequently led to the high reduction efficiency of Cr(VI).
采用生物炭进行环境修复已经得到广泛应用。然而，生物炭存在时六价铬（Cr(VI)）的还原机制尚未完全阐明（即生物炭对 Cr(VI)的直接或间接还原）。特别是，生物炭对 Cr(VI)还原的光效应很少有报道。因此，为了从根本上阐明生物炭还原 Cr(VI)的机制，本研究特别强调了生物炭应用中 Cr(VI)的光诱导还原。生物炭会释放出溶解的有机物（DOM），DOM 可以通过络合作用从土壤中提取 Fe(III)，而这些络合物可以在光照下发生光反应。在这些方面，本研究特别评估了 DOM-Fe(III)光诱导反应形成的 Fe(II)。为了评估这一点，三种生物质样品（稻草、上流式厌氧污泥床的颗粒污泥和用过的咖啡渣）被热解为生物炭。为了避免 Cr(VI)吸附到生物炭上，生物炭提取物（作为 DOM 的来源）和 Fe(III)溶液在有无紫外光的情况下进行了测试，以证明 Fe(II)的形成。本研究通过实验证明，在生物炭提取物和 Fe(III)共存的情况下，在紫外辐射下形成的 Fe(II)越多。来自三种生物炭样品的所有实验数据实际上非常相似。GB、RB 和 CB 中的 Fe(II)还原 Cr(VI)分别达到了 96%、79%和 100%。不同的还原效率表明，低分子量的有机酸，如草酸盐，对紫外光更敏感，从而导致 Fe(II)的形成增强。这种 Fe(II)的形成随后导致 Cr(VI)的高还原效率。
