Efficient removal of algae and turbidity from water by a composite coagulant composed of a cationic starch and attapulgite

Algae and suspended colloidal particles produced high turbidity in water, weakened water purification, and threatened the safety of the water supply. In this study, a series of composite coagulants (atp-st-CTA) composed of a cationic starch (st-CTA) and attapulgite (ATP) with different fed mass ratios were fabricated by a simple method to coagulate kaolin suspension with initial turbidity of 80.0 NTU and Chlorella suspension with 0.25 mg/L of chlorophyll a ( chla ), respectively. Fourier transform infrared spectroscopy and scanning electron microscopy investigated the structural characteristics of atp-st-CTA. The maximum turbidity and chla removal rates of atp-st-CTA were 92.2% and 100.0%, respectively, at natural pH conditions. The effects of the fed mass ratio of st-CTA to ATP in the composites, dose, pH, and coexisting humic acid on the coagulation performance of atp-st-CTA were comprehensively investigated. Based on the apparent coagulation behaviors, the zeta potentials of the supernatants after coagulation, and the flocs properties, the coagulation mechanisms of atp-st-CTA were discussed in detail. The complete charge neutralization due to st-CTA and the enhanced sedimentation by ATP synergistically removed turbidity and algae from the water efficiently. In short, atp-st-CTA as a talented material has a notable prospect in applications of water treatment owing to its advantages of environmental friendliness, low cost, and high efficiency.