Advantages of Polyaluminium coagulants on basicity/alkalinity than alum

An important property of polyaluminium coagulants is their basicity. This is the ratio of hydroxyl to aluminium ions in the hydrated complex and in general the higher the basicity, the lower will be the consumption of alkalinity in the treatment process and hence impact on pH.

Various suppliers of ACH and PACI in Australia express the basicity of their product as a percentage e.g. Omega MEGAPAC-23 (40.2% w/w aluminium chlorohydrate) has a basicity of 82% (Omega Chemicals, 2000).

The polyaluminium coagulants in general consume considerably less alkalinity than alum.

They are effective over a broader pH range compared to alum and experience shows that PACI works satisfactorily over a pH range of 5.0 to 8.0.

Another important advantage of using polyaluminium coagulants in water treatment processes is the reduced concentration of sulphate added to the treated water. This directly affects SO4 levels in domestic wastewater.

A raw water with a sulphate level of 3 to 5 mg/L will typically have a SO4 concentration of 15 to 25 mg/L following treatment with alum. The amount of soluble sulphate present in domestic wastevater is now also significanly increased and this can result in elevated hydrogen sulphide production in the sewerage system, leading to odour and corrosion problems.

The advantages of using PACI in regard to the effect on treated water TDS and sulphate levels are apparent. Note also a small improvement in the CCPP value of the treated water when using PACI.

The chemical doses predicted when using PACI compare very well with actual requirements at some Water Filtration Plants.

Keywords: Water Treatment, PAC, Poly aluminum Chloride, poly aluminium chloride, Polyaluminum Chloride, PACL, Coagulant, Flocculant, Yellow PAC, Yellow polyaluminum chloride, White PAC, White polyaluminum chloride, PolyDADMAC, DADMAC, PDADMAC, Polydmdaac, polyelectrolyte

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