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BIOSORPTION: TOOL FOR ENVIROMENTAL CLEANING BY MICROORGANISMS

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The discovery and further development of biosorption phenomena provide a basis for a whole new technology aimed at the removal of various pollutants or the recovery of valuable resources from aqueous systems. Today, biosorption is one of the main
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   1 BIOSORPTION: TOOL FOR ENVIROMENTAL CLEANING BY MICROORGANISMS A TERM PAPER BY NWIYI, I. U.   2 List of Figures Figure 1: Biosorption mechanisms as classified by Veglio and Beolchini …  6 Figure 2: Showing schematic diagram of Mechanism of biosorption …  8 Figure 3: Schematic diagram of bonding in a metal-EDTA complex ion …  9 Figure 4: Phosphodiester structure (circled) …   …   …   …   …  11 Figure 5: Microbial mediated metal transformations. …   …   …   …  12 Figure 6: Schematic diagram of Mechanism of biosorption II …   …  12 List of Tables TABLE 1: Types of native biomass that have been used for preparing biosorbents 6 TABLE 2: Effects of batch processing factors on biosorptive removal of adsorptive pollutants, such as metals or dyes …   …   …   …   …  15 TABLE 3: Modification methods for converting raw biomass into better biosorbents 16 TABLE 4: Desorption methods for regeneration of biosorbenets and recovery of metals or dyes. …   …   …   …  18 TABLE 5: Commercialized biosorbents …   …   …   …  19   3 SUMMARY  The discovery and further development of biosorption phenomena provide a basis for a whole new technology aimed at the removal of various pollutants or the recovery of valuable resources from aqueous systems. Today, biosorption is one of the main components of environmental and bioresource technology. Microbes have been widely used in the process of environmental clean-up and are known as bioremediators. Their ability to absorb metal ions from aqueous solutions either as living or dead biomass as well as derived products has been exploited. Physico-chemical mechanisms of removal, which may be encompassed by the general term ‘biosorption”, include adsorption, ion  exchange and entrapment which are features of living and dead biomass as well as derived products. In living cells, biosorption can be directly and indirectly influenced by metabolism. Biosorption is a process with some unique characteristics. It can effectively sequester dissolved metals from very dilute complex solutions with high efficiency. This makes biosorption an ideal candidate for the treatment of high volume low concentration complex waste-water. Biosorption can be defined as the selective sequestering of metal soluble species that result in the immobilization of the metals by microbial cells. Metal sequestering by different parts of the cell can occur via various processes: complexation, chelation, coordination, ion exchange, precipitation, reduction. Currently, a wide range of microorganisms (bacteria, archaebactreia, yeasts, fungi and algae) and plants are being studied for use in biosorption bioremediation processes. Some of these microorganisms have already been employed as biosorbents of various pollutants. The major advantages of this technology over conventional ones include; low cost, high efficiency, minimization of chemical or biological sludges, the regenerative ability of biosorbents, and the possibility of metal recovery following adsorption.   4 1.0 INTRODUCTION  Pollution may be described as the undesirable change in the environment brought about by man’s activities (Odokuma, 2012).  Pollution of the environment by toxic metals and radionuclides arises as a result of many activities, largely industrial, although sources such as agriculture and sewage disposal also contribute. These pollutants are discharged or transported into the atmosphere and aquatic and terrestrial environments mainly as solutes or particulates and may reach high concentrations, especially near the site of entry. Metallic radionuclides have also entered the environment as a result of weapons-testing and accidents such as Chernobyl (Elstner et al., 1987). The effects of metals on the functioning of ecosystems vary considerably and are of economic and public-health significance. These pollutants interact naturally with biological systems. Uncontrolled, it seeps into any biological entity within the range of exposure. The most problematic contaminants include heavy metals, pesticides and other organic compounds which can be toxic to wildlife and humans in small concentration. There are existing methods for remediation, but they are expensive or ineffective (Ahalya, et al 2003). Consequently environmental awareness is growing among consumers and industrialists and legal constraints on emissions are increasingly strict, leading to a need for cost-effective emission control (Gadd, 1990). Any type of solid material has the capacity to adsorb pollutants to some degree, a number of industrial inorganic wastes, such as ash, or natural inorganic materials like clay, synthetic materials like zeolite, as well as, living or nonliving biomass/biomaterials, have been investigated as cheap adsorbents capable of replacing the well-known, but more expressive ones (Bhatnagar and Minocha, 2006, Ahmaruzzaman 2008, Lin and Juang, 2009). Considering their cost and efficiency, biomass-based adsorbents or biosorbents as they are commonly called, are the most attractive alternatives to ion exchange resins and activated carbons (Vijayaraghavan, and Yun 2008). The use of biosorbents for the removal of toxic pollutants or for the recovery of valuable resources from aqueous wastewaters, is one of the most recent developments in environmental or bioresource technology (Aksu, 2005, Volesky, 2007, Vijayaraghavan, and Yun, 2008). The major advantages of this technology over conventional ones include not only its low cost, but also its high efficiency, the minimization of chemical or biological sludges, the ability to regenerate biosorbents, and the possibility of metal recovery following adsorption (Volesky, 2007). Biosorption has been defined by Volesky, 2007 a pioneer in the field as the property of certain biomolecules (or types of biomass) to bind and concentrate   5 selected ions or other molecules from aqueous solutions. As opposed to a much more complex phenomenon of bioaccumulation based on active metabolic transport, biosorption by dead biomass (or by some molecules and/or their active groups) is passive and occurs  primarily due to the ‘affinity’ between the biosorbent and adsorbate  (Volesky, 2007). Biosorption is a physico-chemical and metabolically-independent process based on a variety of mechanisms including absorption, adsorption, ion exchange, surface complexation and precipitation by different parts of the cell can occur via these various processes (Jianlong, and Chen, 2006, Marina and Gadd, 2013). Immobilization may be the result of more than one mechanism, for example, metal complexation may be followed by metal reduction or metal precipitation. Metabolically active and inactive cells behave in different ways. Thus inactive microbial cells can only immobilize metals by biosorption, whereas active microbial cells may immobilize soluble metal species both by biosorption and by other mechanisms that are part of and/or are due to the microbial metabolism (Hatzikioseyian, et al 2001). Biosorption has also been defined as the selective sequestering of metal soluble species that result in the immobilization of the metals by microbial cells. Metal sequestering by different parts of the cell can occur via various processes: complexation, chelation, coordination, ion exchange, precipitation, reduction (Marios, et al, 2012). This review paper deals with the significance of biosorption using microorganisms, it plays important role in the restoration of pollution from the environment which is an important conservation effort for sustainable development and environmental management. 1.1 BRIEF HISTORY OF BIOSORPTION As early as the 18 th  and 19 th  centuries the ability of living microorganisms to take up metals from aqueous solution was investigated (Modak, and Natarajan 1995), it is only within the last three decades that living or non-living microorganisms have been used as adsorbents for removal and recovery of materials from aqueous solutions. The earliest technological applications of biosorption techniques involved sewage and waste treatment (Donghee, et al 2010). Its use in renovating wastewater generated by the chemical industry was also investigated. Scientists in life sciences primarily focused on the toxicological effects and accumulation of heavy metals in microorganisms, while environmental scientists and engineers used this capability of microorganisms as a means of monitoring heavy metal pollution, as well as, for removal/recovery of metals from metal-bearing wastewaters
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