Use of chitosan for the removal of metal ion contaminants and proteins from water

Gamage, Dona Ashoka Sriyani (2003) Use of chitosan for the removal of metal ion contaminants and proteins from water. Masters thesis, Memorial University of Newfoundland.

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Abstract

Chitin is the second most abundant natural biopolymer after cellulose and is distributed in the shells of crustacea and cuticle o f insects and also in the cell wall of some fungi. Chitosan is the deacetylated product of chitin. Chitosan has been used in a number of fields such as agriculture, the food industry and medicine. Both chitin and chitosan are recognized as excellent metal ligands, forming stable complexes with many metal ions. In particular, chitosan is considered one of the best natural chelators for transition metal ions and an effective protein coagulating agent. The processing discards of shellfish pose major technological problems, mainly due to their insolubility in water and resistance to biodegradation. Direct use o f crab processing discards is generally discouraged due to the obnoxious odour of putrefying shells, therefore, value-added utilization of their discards is of paramount importance. In the treatment of crab processing discards to extend their usable shelf-life, five different chemical treatments were used. Fresh samples of crab processing discards were treated by dipping in 1 % formaldehyde, formic acid, acetic acid, sodium bicarbonate or sodium hydroxide solution. Experiments were con.d ucted at two temperatures ranges; 4- 7°C and 20-25°C. The samples were evaluated for sensory characteristics by a seven - membered panel and the results were recorded. Chitin isolated from crab processing discards was deacetylated in order to produce three types of chitosan (Types 1, 2 and 3). Chitosans so prepared were evaluated for their capacity to chelate single metal ion solutions containing Co²⁺, Fe²⁺, Ni²⁺, Cd²⁺, Mn²⁺, Zn²⁺ and Cu²⁺. Then, the three chitosan types were tested for their capacity to chelate metal ions in samples of water obtained from a zinc minining site, Buchans, Newfoundland. Ethylenediaminetetraacetic acid (EDT A) was used as the reference chelating agent. The capacity to chelate single metal ions by chitosan and EDTA was determined by a colourimetric method and metal chelation capacity of wastewater was determined by inductively coupled plasma-mass spectrometry (ICP-MS) at three pH levels (5,6 and 7). Chelation and recovery of metals from aqueous solutions using a column containing chitosan was also determined by ICP MS. Ethylenediaminetetraacetic acid was used to recover metal ions that were chelated by chitosan in the column. Chitosan served as an effective coagulating agent in removing proteins from waste water. Out of the tested treatments, 1 % formaldehyde served best in controlling the foul odour development both at 4-7°C and 20-25°C followed by formic acid. Due to possible carcinogenicity of formaldehyde, formic acid could be best utilized in controlling foul odour of crab wastes. At all pH levels tested, EDTA exhibited the highest chelation capacity. At pH 5, chitosan served best for metal ion chelation and pH 7 was best for metal mixtures in waste water. Metal chelation by a column method for single metal ions showed over 98% chelation both at 50 and 100 ppm except for Co²⁺ while gave a metal recovery of 52-97%. For mixtures of metal ions, except Co²⁺, exhibited 94% chelation and metal recovery was 24-90%. Chitosan Type 1 showed the best protein flocculation ability followed by Types 2 and 3 chitosan. Encouraging results for metal chelation and recovery by the prepared chitosan and protein flocculation reveal that crustacean processing discards can be converted to useful environmentally friendly material for wastewater purification.

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