An optimization strategy for highly efficient flocculation and capture of algal cells: Controlling dosing patterns of modified clay

Abstract

Modified clay technology is the most effective emergency treatment method for harmful algal blooms. In this study, a multiple dosing scheme was proposed to control the maximum number of flocculated algal cells in aluminium-modified clay, aiming to enhance the removal efficiency of algal cells by modified clay; simulation experiments were conducted to investigate the effect of dosing frequency on the flocculation and capture of algal cells by modified clay under the same total dosage. The mechanism analysis confirmed that the multiple dosing method maximized the number of algal cells removed per gram of clay, thereby reducing the self-flocculation of the modified clay. Compared with the single-dosing method, multiple dosing can increase the positive charge of the modified clay system by 40% and prolong the growth and residence time of flocs, which can increase the removal efficiency of algal cells by 20%–30%. Response surface methodology (RSM) was used to optimize the range of each controlled operating parameter. The experimental results showed that the maximum removal efficiency of algal cells can be achieved when the dosing frequency is controlled at 3–5 times, where the dosing interval and the concentration of stock solution are the key factors affecting the removal efficiency of algal cells under the multiple dosing method; the optimal interval time was 20–40 min, and the concentration of stock solution was 10-20 g/L. The results of this study provide a methodological reference for further improving the field application efficiency of modified clay.