Harmful algal blooms mitigation using clay/soil/sand modified with xanthan and calcium hydroxide

Abstract

A method was studied for marine harmful algal blooms (HABs) mitigation using clay, soil, or sand modified with xanthan and calcium hydroxide. Results showed that xanthan could trap and wrap Amphidinium carterae cells via bridging and netting interactions due to its superior salt compatibility in seawater. The maximum cell removal efficiency was 55% when xanthan was used alone. The removal effect of xanthan was enhanced by the addition of appropriate calcium hydroxide that decreased the repulsive interaction between anionic xanthan and negatively charged algal cells. Three kinds of minerals (clays, soils, and sands) were ineffective in removing algal cells before treatment. When xanthan and calcium hydroxide were used together as modifiers, the removal efficiency increased to 83-89% within 30 min using 300 mg L-1 clays, soils, or sands modified with 20 mg L-1 xanthan and 100 mg L-1 calcium hydroxide. After several hours, 95-98% cell removal was achieved and there was no significant difference in the removal efficiencies among clays, soils, and sands after being modified with xanthan and calcium hydroxide. Thus, the method would provide an alternative modification approach to suppress and mitigate HABs using local soils/sands and polymers in marine systems.