Department of Microbiology, Dr. Ram Manohar Lohia Avadh University, Faizabad, India.
Rev Environ Contam Toxicol. 2012;217:75-140. doi: 10.1007/978-1-4614-2329-4_2.
Bioremediation offers the possibility of using living organisms (bacteria, fungi, algae,or plants), but primarily microorganisms, to degrade or remove environmental contaminants, and transform them into nontoxic or less-toxic forms. The major advantages of bioremediation over conventional physicochemical and biological treatment methods include low cost, good efficiency, minimization of chemicals, reduced quantity of secondary sludge, regeneration of cell biomass, and the possibility of recover-ing pollutant metals. Leather industries, which extensively employ chromium compounds in the tanning process, discharge spent-chromium-laden effluent into nearby water bodies. Worldwide, chromium is known to be one of the most common inorganic contaminants of groundwater at pollutant hazardous sites. Hexavalent chromium poses a health risk to all forms of life. Bioremediation of chromium extant in tannery waste involves different strategies that include biosorption, bioaccumulation,bioreduction, and immobilization of biomaterial(s). Biosorption is a nondirected physiochemical interaction that occurs between metal species and the cellular components of biological species. It is metabolism-dependent when living biomass is employed, and metabolism-independent in dead cell biomass. Dead cell biomass is much more effective than living cell biomass at biosorping heavy metals, including chromium. Bioaccumulation is a metabolically active process in living organisms that works through adsorption, intracellular accumulation, and bioprecipitation mechanisms. In bioreduction processes, microorganisms alter the oxidation/reduction state of toxic metals through direct or indirect biological and chemical process(es).Bioreduction of Cr6+ to Cr3+ not only decreases the chromium toxicity to living organisms, but also helps precipitate chromium at a neutral pH for further physical removal,thus offering promise as a bioremediation strategy. However, biosorption, bioaccumulation, and bioreduction methods that rely on free cells for bioremediation suffer from Cr6 toxicity, and cell damage. Therefore, immobilization of microbial cell biomass enhances bioremediation and renders industrial bioremediation processes more economically viable from reduced free-cells toxicity, easier separation of biosorbents from the tannery effluent, ability to achieve multiple biosorption cycles, and desorption (elution) of metal(s) from matrices for reuse. Thus, microbial bioremediation can be a cost competitive strategy and beneficial bioresource for removing many hazardous contaminants from tannery and other industrial wastes.
生物修复利用活的生物体(细菌、真菌、藻类或植物),主要是微生物,来降解或去除环境污染物,并将其转化为无毒或低毒形式。与传统的物理化学和生物处理方法相比,生物修复具有成本低、效率高、化学品用量少、二次污泥量减少、细胞生物质再生以及回收污染物金属的可能性等优点。皮革工业在鞣制过程中广泛使用铬化合物,将含铬废物排放到附近的水体中。在全球范围内,铬是已知的最常见的地下水无机污染物之一,位于污染危险场所。六价铬对所有形式的生命都构成健康风险。皮革废水中铬的生物修复涉及不同的策略,包括生物吸附、生物积累、生物还原和生物材料的固定化。生物吸附是金属物种与生物物种的细胞成分之间发生的非定向物理化学相互作用。当使用活生物质时,它是代谢依赖的,而在死细胞生物质中是代谢独立的。死细胞生物质比活细胞生物质更有效地吸附重金属,包括铬。生物积累是活生物体中一种代谢活跃的过程,通过吸附、细胞内积累和生物沉淀机制起作用。在生物还原过程中,微生物通过直接或间接的生物和化学过程改变有毒金属的氧化/还原状态。Cr6+还原为 Cr3+不仅降低了铬对生物体的毒性,而且有助于在中性 pH 下沉淀铬,以便进一步进行物理去除,因此作为一种生物修复策略具有很大的前景。然而,依赖游离细胞进行生物修复的生物吸附、生物积累和生物还原方法受到 Cr6 毒性和细胞损伤的影响。因此,微生物细胞生物质的固定化增强了生物修复能力,使工业生物修复过程更具经济可行性,降低了游离细胞毒性,更容易从皮革废水中分离生物吸附剂,能够实现多次生物吸附循环,以及从基质中解吸(洗脱)金属以重复使用。因此,微生物生物修复可以成为一种具有成本竞争力的策略,并且是从皮革和其他工业废物中去除许多危险污染物的有益生物资源。