A comparative study of sorption of chromium (III) onto chitin and chitosan

0 R. Nagendran National Green Tribunal , Southern zone, TNPCB Building, Arumbakkam, Chennai 600106, India 1 P. Singh (&) Centre for Environmental Studies, Anna University , Chennai 600025, India Heavy metals have always been the most hazardous components in the wastewater of industries like electroplating, automobiles, mining facilities and fertilizer manufacturers. Treatment of heavy metal laden wastewater requires expensive operational and maintenance systems. Food processing industries create a huge amount of shell waste which is sold to poultry farms in powdered form but the quantity thus used is still not comparable to the left over waste. The shell contains chitin which acts as an adsorbent for the heavy metals and can be used to treat heavy metal wastewater. The paper presents a study on the use of chitin and its processed product, chitosan, to remove chromium. Shake flask experiment was conducted to compare the adsorptive capacity of chitin and chitosan for chromium removal from simulated solution and isotherm studies were carried out. The studies showed that the chitosan was a better adsorbent than chitin. Both chitin and chitosan gave best adsorption results at pH 3. Chitin exhibited maximum chromium removal of 49.98 % in 20 min, whereas chitosan showed 50 % removal efficiency at a contact time of 20 min showing higher adsorptive capacity for chromium than chitin. The Langmiur and Freundlich isotherm studies showed very good adsorption capacity and monolayer interaction according to the regression coefficient 0.973 for chitosan and 0.915 for - chitin. The regression coefficient for Freundlich isotherm was 0.894 and 0.831 for chitosan and chitin, respectively. Wastewater Adsorption Chromium Chitin Heavy metals are essential for various biochemical processes but beyond a level they are known to be detrimental to life forms owing to their toxicity, persistent nature and tendency to bioaccumulate (Igwe and Abia 2006). Chromium is one such heavy metal used in electroplating, mining, automobiles, etc., making the effluent generated in these industries extremely harmful if not treated and disposed properly. Though required in trace amounts for biological functions, excess chromium is reported to cause health-related problems like rashes, ulcers, respiratory disorders, alteration in genetic material, cancer (Banerjee et al. 2010) and weakening of immune system (Shrivastava et al. 2002). In aqueous solution Chromium exists in two oxidation states, Cr3? and Cr6? (Mukherjee et al. 2013). Out of the two states Cr6? is more toxic than the other but some strong oxidants can oxidize Cr3? to Cr6? (Zuo and Balasubramanian 2013). Removal of heavy metals requires high operational and maintenance cost and the technologies available are expensive (Opeolu et al. 2010). The employed wastewater treatment methods include reverse osmosis, precipitation, ion exchange and adsorption (Ahalya et al. 2003). Ion exchange, membrane filtration and coagulation are generally used for treating chromium-laden wastewater (Fabbricino et al. 2013). Adsorption is an option which provides benefits such as a clearer effluent and possibility of heavy metal recovery at a low cost (Shankar et al. 2014). Adsorbents commonly used for chromium adsorption include alginate (Navarro et al. 2006) and activated carbon (Mohan and Pittman 2006), imidazole functionalized sol gel (Park and Tavlarides 2008 ), microorganisms like fungi, bacteria and algae, tobacco dust, plant biomass and also agricultural wastes such as rice bran, soybean, cottonseed hulls, coconut shell and chitin(Opeolu et al. 2010). For the adsorption of chromium, aquatic weeds (Elangovan et al. 2008; Yun et al. 2001), short-chain polyaniline synthesized on jute fiber (Kumar et al. 2008), grape stalks and yohimbe bark (Fiol et al. 2008), sugarcane bagasse (Garg et al. 2009) and the fungus Coriolus versicolor (Sanghi et al. 2009), among others, have been used. Trivalent chromium is said to be sorbed onto biosorbents by mechanisms like ion exchange, surface complexation or a combination of both depending on the biosorbent used and the available functional group (Han et al. 2006). India is one of the top ten producers of aquaculture products in the world (Greenfacts 2010). The export of shrimps and crabs is usually done in a canned form for which meat is shelled and processed further. The unused shells sometimes are sold to poultry farms as feed but the quantity thus used is not comparable to tonnes of waste that is generated. Additionally, the disposal of this waste causes environmental problems. This waste in the form of chitin is a potential biosorbent of heavy metals. Chitin, obtained from crustacean shells is the second most abundant natural polysaccharide (Kumar 2000). Chitin contains 58 % of nitrogen in the form of aliphatic amino groups (Dutta et al. 2004). Chitosan is a polymer of glucosamine, found naturally in some fungal cell wall, produced chemically from the deacetylati (...truncated)