Chitosan and carboxymethyl chitosan are used as flocculant adsorbents. Chitosan is a linear high molecular polymer. Due to the presence of free amino groups in its molecules, it is protonated in dilute acids, thereby making the chitosan molecular chain carry a large number of positive charges, becoming a typical cationic flocculant. It has the dual functions of electric neutralization and adsorption flocculation, which can attract colloidal particles with negative charges, reduce their surface potential, compress the spreading electric double layer on the particle surface, thereby destabilizing the colloidal particles, and generating flocculation precipitation through the adsorption, bonding and bridging effects of chitosan polymer chains.
Chitosan acetic acid solution has been used to remove inorganic and organic suspended solids, clarify beverages, deacidify and decolorize fruit juices, treat food production wastewater and oily wastewater, etc. It can also effectively remove organic pesticides (such as DDT) and heavy metals from wastewater. Chitosan has a strong flocculating effect on organic substances such as proteins and starches, and can recover proteins and starches from wastewater such as food processing for use as feed.
Chitosan has a good affinity for dyes and is used for decolorization and COD removal of dye wastewater. Most of the organic dyes used in the printing and dyeing process are water-soluble and generally refractory organic compounds. Microorganisms in conventional activated sludge cannot phagocytose and degrade them, and the effect of ordinary chemical degradation is also poor, making it difficult to meet the discharge standards. Traditional inorganic flocculants have high decolorization efficiency for hydrophobic dyes and dyes with large molecular weights, but poor decolorization effect for dyes with excellent water solubility and small molecular weights, and the treatment cost is high.
Decolorization experiments on water-soluble dyes were carried out with carboxymethyl chitosan. 5mL of carboxymethyl chitosan with a concentration of 10% was used to act on 500mL of five dye solutions with a concentration of 50mg/L: Direct Fast Blue (B-2V), Direct Deep Blue (B-2G1), Direct Scarlet (B-3G), brown and tan dyes. At pH=3, after stirring for 20min and standing for 6h, the decolorization rates were 97.9%, 75.5%, 61.4%, 92.2% and 68.5% respectively.
Under the respective optimal pH values and the same other conditions, decolorization comparison experiments were carried out with carboxymethyl chitosan, polyaluminum, and 4 kinds of flocculant adsorbents, and their decolorization rates were 98.2%, 89.4%, 80.5% and 13.2% in turn. Under the condition of the same addition amount, the decolorization effect of carboxymethyl chitosan and chitosan is better than that of traditional polyaluminum and polyacrylamide. The isotherms of carboxymethyl chitosan adsorbing and flocculating 5 kinds of dyes all conform to the Freundlich formula. Carboxymethyl chitosan and chitosan have the advantages of adsorption, flocculation, and easy biodegradation by microorganisms, so they are more suitable for advanced decolorization treatment of dye wastewater.
