Influence of a new coagulant aid-Enteromorpha extract on coagulation performance and floc characteristics of aluminum sulfate coagulant in kaolin–humic acid solution treatment

A new coagulant aid, Enteromorpha extract (Ee), was studied to enhance the coagulation performance when it was used together with aluminum sulfate (AS). The dual-coagulant, aluminum sulfate–Enteromorpha extract (AS–Ee), was achieved by dosing Ee 30 s after AS was dosed. AS–Ee and AS were comparatively evaluated regarding their coagulation performance. The results showed that Ee played an important assistant part in the coagulation process. The coagulation effect of AS–Ee was about 10% higher than that of AS with respect to the removal of turbidity, UV254 and DOC. Floc characteristics were also investigated in terms of floc size, strength and recovery ability, with the results indicating that the strength of flocs produced by two coagulants were both enhanced with Al dosage increasing, while the floc recoverability was decreased. Floc produced by AS–Ee had bigger size and faster growth rate than that by AS. Meanwhile, the former was also stronger and had a better recoverability than the latter. The charge neutralization was the dominant mechanism of AS, and Ee had good adsorption bridging effect. Due to the combination of two advantages, coagulation efficiency of the dual-coagulant could be enhanced significantly.