Efficient treatment of emulsified oily wastewater by using amphipathic chitosan-based flocculant

Abstract

A series of chitosan-based flocculants have been successfully synthesized by grafting poly(acrylamide) (PAM) or poly(dimethyl acryloyloxyethyl benzyl ammonium chloride) (PDBC) onto chitosan (CS) molecular chain and then characterized by using multiple techniques. The synthesized CS-based flocculants were subsequently used to flocculate the emulsified oil droplets in simulated oily wastewater under various conditions. It was found that the PDBC-grafted CS (CS-g-PDBC) showed better flocculation performance than those of CS and two other commonly used flocculants, i.e. cationic PAM (CPAM) and polyaluminum chloride (PAC). Moreover, the flocculation efficiency of CS-g-PDBC was gradually enhanced with increasing grafting ratio of PDBC, while declined after the introduction of grafted PAM chains. The cationic and hydrophobic groups of PDBC could significantly promote the adsorption of flocculant molecular chains on the negatively charged oil droplets via electrostatic attraction and hydrophobic interaction, thereby facilitating subsequent flocculation process. In addition to the adsorption bridging mechanism, zeta potentials measurements indicated that patching was the dominant mechanism under acidic and neutral conditions, while charge neutralization was the main mechanism under alkaline condition. On this basis, the chosen flocculant CS-g-PDBC was employed to treat the actual oily wastewater. Results showed that the removal ratio of both turbidity and oil exceeded 98%, suggesting that this newly synthesized CS-g-PDBC would be a promising flocculant for emulsified oily wastewater treatment.