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Water pollution due to ejection of toxic heavy metals from various types of industries, such as textile, metal finishing, electroplating, painting, dyeing, photography, surface treatment, is a worldwide major environmental concern (Namasivayam and Ranganathan, 1993). Chromium exists in two stable oxidation states, Cr (III) and Cr (VI). Trivalent chromium is an essential trace element for maintaining glucose, cholesterol, and fatty acid metabolism; its toxicity is relatively low. Hexavalent chromium (VI) has been major focused in water and waste water treatment due to its carcinogenic and mutagenic properties which inflict many health problems like allergic contact dermatitis and other immunomodulatory diseases (IARC, 1982). The effluent discharged from various industries may consist of concentration range from tens to hundreds of mg/L. For example, the untreated effluent from electroplating industry contains approximately 100 mg/L Cr (VI), which is higher than the permissible limit of 0.05-1 mg/L (De Filippis and Pallaghy, 1994). Thus, removal of hexavalent Cr (VI) is one of the indispensable processes in waste water treatment. Treatment methods to remove Cr (VI) from water and wastewater include chemical precipitation, ion exchange, membrane separation (Juang and Shiau, 2000), electro-coagulation, solvent extraction, reverse osmosis and reduction. Adsorption is economical and applicable in large-scale treatment of effluents by using non-expensive adsorbate. It is also a useful and simple technique and allows kinetic and equilibrium measurements without any highly sophisticated instruments. Consequently, various potential adsorbents have been implemented for removal of heavy metals from water. Research was going strong to develop more suitable, efficient, cheap and easily accessible type of adsorbents. A large amount of work was carried out using peat, sugar cane bagasses, algae, ash, and de-oiled soy for removal of various heavy metals from aqueous solution. The maximum metal ion uptake and the affinity of absorbent for a metal are important parameters of the biosorption process. These characteristics can be obtained from the representation of sorption isotherms. The Freundlich and Langmuir isotherm is the most used in simple systems (Volesky, 2003).
Living or dead forms of microbial cells, bacteria, fungi and algae have been used as biosorbents in (Volesky, 1990). Biosorption using algae is an alternative process for the removal of metals from the effluents. It is defined as the passive binding of metals or other compounds on a biosorbent (biomass) containing chemically active sites or functional groups (Volesky, 2003). Dead biomass has higher metal uptakes and the process is nutrient independent (Mehta and Gaur, 2005). Biosorbents are prepared from the naturally abundant or waste biomass either by washing biomass with acids or bases, or even both, before final drying and granulation or powdered. The aim of the present study is to determine sorption capacity of naturally available filamentous algae as a biosorbent for removal of Cr (VI) from aqueous solution. The effects of biomass dosage, contact time, solution pH, metal ion concentration and temperature on biosorption process were evaluated.
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