It is the proportion of the aluminium already bound to hydroxide before dosing, typically 40 to 70 percent. Higher basicity means more of the hydrolysis has been done during manufacture, so less alkalinity is consumed in the treated water and pH moves less. Lower basicity retains more charge-neutralising power. The right basicity depends on the raw water and should be specified rather than left generic.
2
Why does PAC work better than alum in cold water?
Because hydrolysis slows markedly as temperature falls, and alum depends on that hydrolysis happening in the water. PAC arrives with the polymeric hydroxide species already formed, so its performance is far less temperature-dependent. That matters in winter operation, where alum dose has to be raised substantially to compensate and floc quality still suffers.
3
Does PAC produce less sludge than alum?
Generally yes. Because the pre-formed polymeric species are more efficient coagulants per unit of aluminium, dose rates are lower, and less added aluminium means less aluminium hydroxide ending up in the sludge. For a works paying to dewater and dispose of sludge, that difference can outweigh the higher unit price of PAC.
4
What pH range does PAC work across?
Typically 5 to 9, considerably wider than alum's narrow effective band around pH 6 to 7. That tolerance means less pH correction chemical, simpler control and more stable performance when raw water quality varies, which is a large part of why PAC has displaced alum at many works.
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Our team is ready to help with any specific enquiries about Polyaluminium Chloride (PAC).