Study on the flocculation performance of composite coagulant PAC-CTS on low-temperature and low-turbidity drinking water source

Polyaluminum chloride (PAC) and chitosan (CTS) were combined in a volume ratio of 0.5 %,1 % and 1.5 % to synthesize PAC-CTS 0.5 ,PAC-CTS 1.0 and PAC-CTS 1.5 coagulants to treat the drinking water source of the Pihe river under low-temperature and low-turbidity conditions. The effects of CTS volume percentage, coagulation stirring speed, changes in raw water pH, and coagulant dosage on the removal of turbidity, chromaticity, and organic matter were investigated through the coagulation beaker experiment. Finally, analysis of structural characterization was performed using electric potential (ZETA) and scanning electron microscopy (SEM). The results showed that when CTS accounted for 1 % of the volume in PAC-CTS, turbidity, chromaticity, and UV 254 removal efficiency was the best. When the mixing speed is constant, flocculation stirring speeds that are too high and too low are not conducive to the coagulation effect. The optimal flocculation stirring speed is 80 rpm. The pH of raw water has the greatest impact on turbidity, followed by UV 254 , whereas it has almost no effect on chromaticity. The range of optimal pH is 7–8. The effect of PAC-CTS 1.0 shows an increasing trend followed by a decreasing trend with increasing dosage, with the recommended dosage being 9 mg.L −1 . Finally, the SEM images showed that PAC and CTS formed a new structure after forming a composite, with a raised and loose morphology and a certain flocculent structure. When combined with ZETA, it was demonstrated that the electrical neutralization and bridging ability of the composite coagulant were further enhanced, resulting in an improved coagulation effect.