Biosorption of Chromium (III) from Aqueous Solution by Water Hyacinth Biomass

Abstract

Water is a basic human need which is well emphasized by the saying “A drop of water is worth more than a sack of gold to a thirsty man”. Though it is an essential commodity, disposal of industrial and urban wastes into them beyond its self cleaning capacity causes serious threat. The most prominent presage to the environment through anthropogenic activities is the heavy metal pollution. Heavy metals are trace metals, known to be most persistent and non biodegradable pollutant emanated from wide range of industries. Among that, chromium contamination is a significant obstacle worldwide due to its multifarious use in industrial processes such as plating, alloying, tanning of hides, metallurgy, refractory, textile dyes, paint, chemical manufacturing and petroleum refining etc., (Avudainayagam et al., 2003). This naturally occurring element has a complex electronic and valence shell chemistry with valence states ranging from -2 to +6 (Shahid et al., 2017). From this, the most environmentally significant forms of Cr are trivalent (Cr III) and hexavalent (CrVI). These two oxidation states differ in their mobility and toxicity. Among them, Cr(VI) is mobile and regarded as carcinogen whereas Cr(III) is relatively immobile and less toxic. The Cr(III) has a significant role in lipid and sugar metabolism and regarded as essential trace element for human and animal health (Eskin, 2016) and not for the plants. Though Cr(III) has its own beneficial role, its uptake in supererogatory amounts causes health effects as well as skin rashes. Since Cr(III) is less toxic and immobile, the environmental conditions and complex of physical, chemical and biological factors have the capability to convert it into Cr(VI). However, there is a statement that, in drinking water all Cr is converted to Cr(VI) by strong oxidants such as chlorine, ozone and permanganate utilized for attaining taste, odour removal and disinfection (Clifford and Chau, 1988). So it needs a necessary relook to sequester Cr(III) before discharge to water bodies. Conventional methods such as membrane filtration, chemical precipitation, reduction, ion exchange, chelation, reverse osmosis and electrodialysis are available for its removal (Khatoon et al., 2013) but their expensive nature, energy requirements and generation of toxic sludge calls for economically sound and ecologically safe technology. Search for technologies directed attention towards biosorption. Biosorption is a physico- chemical process in which biomass concentrate and bind the contaminant onto their cellular structure .