Characterization of sludges produced when using polyaluminum chloride coagulants

The dewatering characteristics of polyaluminum chloride (Hyper⁺Ion 1050A) sludges were investigated using lab-scale tests including specific resistance to filtration (r*), capillary suction time (CST), and sludge pH. The effects of chemical conditioning (lime and cationic polymer) and mixing intensity (Gt) upon the sludge dewatering characteristics in a pilot-scale plate and frame press were also studied.

The dewatering characteristics of the Hyper⁺Ion sludges were found to be dependent upon the influent water turbidity conditions; specifically, the ratio of aluminum coagulant to total dry solids in the sludge. Lime was an effective conditioner for doses that produced a sludge pH value in the range of 11.5 to 11.8 which, again, was a direct function of the aluminum coagulant fraction in the sludge. Cationic polymer and a combination of lime and polymer were also effective conditioning schemes when the appropriate dose and mixing intensity were applied.