Chitosan modification and its synergism with clay to mitigate harmful algal blooms

Abstract

Chitosan is a natural and eco-friendly material, often used as a flocculant in water purification; however, due to the influences of high salinity and pH, the application of chitosan in seawater has been greatly limited. In this paper, a modified chitosan (3-chloro-2-hydroxypropyl trimethyl ammonium chloride (CTA) chitosan, denoted as CTC) was prepared by chemical modification. This greatly increased the solubility of chitosan both in deionized water and seawater, and solved the technical difficulty of applying chitosan in seawater. The structure of CTC and its solubilization on chitosan in seawater were analyzed by Zeta potential, FTIR, 13C NMR, XRD and SEM. On this basis, CTC modified clay (CTCMC) was further prepared based on the principle of mitigating harmful algal blooms with modified clay. At a CTCMC dosage of 20 mg/L, the removal efficiency of Prorocentrum donghaiense was approximately 80%, while the dosage of traditional modified clay (MCI) was 200 mg/L for the same removal efficiency. The dosage was nearly an order of magnitude less than that of the MCI, suggesting that the novel CTCMC is promising in the mitigation of harmful algal blooms. Further, the flocculation mechanism was determined based upon surface properties, and mechanical and flocculation characteristics.