Evaluating the Potential Use of Polyaluminium Chloride in the Water Treatment Processes in Mauritius

Abstract

In Mauritius, surface waters harnessed to cater for domestic uses are either treated by the slow sand  filtration method or by the rapid sand filtration method. Chemical treatment in plants working with rapid  sand filtration units use the chemical, Aluminium Sulphate, commonly known as alum. Alum is one of the world’s oldest chemical used in water treatment. However, one of its disadvantages is that it operates over a limited range of pH. Recently, polyaluminium chloride (PACI) has come on the market and due to the various  advantages, many countries have shifted to the use of PACI. At La Nicolière water treatment plant, due to changes in landuse and construction of a reservoir upstream, an increase in pH was observed in the incoming raw water. This resulted in an increase in the amount of alum and lime to be used in the coagulation process, and consequently, an increase in the risk of levels of residual aluminium higher than permissible levels.The potential of PACI was evaluated and results indicated that PACI is highly effective in lowering turbidity levels and colour. It also operates over a larger range of pH, yielding lower residual aluminium levels. Moreover, it produced lower volume of sludge.

Keywords: water treatment, alum, PACI, polyalumnium chloride, aluminium sulphate, coagulation