Does polyaluminum chloride coagulate with hydrolyzed coagulants?

Coagulation with hydrolyzing coagulants has been studied thoroughly, but the coagulation behavior of pre-hydrolyzed coagulants such as polyaluminum chloride (PACl), especially the coagulation mechanisms at various coagulant dosages and pH values of raw water, has not been systemically investigated and not been well understood , .

What is the difference between Alum and PACL coagulation?

The restabilization zone of PACl coagulation disappears at a higher final pH value than that of alum coagulation. Moreover, the charge neutralization and sweep coagulation zones of PACl are broader in the ranges of coagulant dosage (as Al) and pH value than those of alum.

Is polyaluminium chloride better than polyelectrolyte – alum-based coagulation?

At the Barekese Water Treatment Plant in Ghana, an alternative, the polyelectrolyte – polyaluminium chloride (PAC) is also used in coagulation but limited information is available on the operating conditions required to achieve better performance than alum-based coagulation.

What is the optimal pH range for Pac coagulation?

The optimal pH range for PAC coagulation performance was 7.5 to 8.0. The coagulation process in conventional water treatment could be enhanced and the ensuing water pH decline reduced appreciably by applying the right dosage of polyaluminium chloride and appropriate process conditions of pH, fluid mixing speed matrix and residence time.

Why is polymeric PACL a less pH-sensitive coagulant?

Polymeric PACl, which contains cationic species like Al 2 O 2 (OH) + and Al 3 O 4 + , is among the least pH-sensitive coagulants because of (i) the high charge neutralization capacities of cationic alumina species and (ii) faster hydrolysis kinetics at a low and high alkalinity/basicity levels (% = 100/3 × [OH]/ [Al]) .

What is the optimal coagulation mechanism at final pH 7.0?

The optimal mechanism at final pH < 7.0 is charge neutralization. Satisfactory coagulation efficiency could be obtained with either charge neutralization coagulation or sweep coagulation at the final pH values from 7.0 to 10.0. The coagulation process of PACl and the formation of PACl precipitates have the same optimal pH value.