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.

Automated summary

In this study, a series of composite coagulants (atp-st-CTA) composed of a cationic starch (st-CTA) and attapulgite (ATP) were fabricated to effectively coagulate kaolin and Chlorella suspensions. The coagulation mechanisms of atp-st-CTA were investigated and it was found that the complete charge neutralization due to st-CTA and the enhanced sedimentation by ATP synergistically removed turbidity and algae from the water efficiently. This talented material has great potential in water treatment applications due to its advantages of environmental friendliness, low cost, and high efficiency.