Is polyaluminium chloride safe for treatment of potable water

Polyaluminum chlorides and polyaluminum chlorosulfates are widely used across the world.  Hundreds of  municipalities have been using polyaluminum chlorides and chlorosulfates for over 2 decades. The American Water Works Association has done studies many years ago but since the products are in such wide use they have not done any concerning the safety of these products recenty. The key to determining water safety, is analyzing the water after treatment.  Criteria such as Total Organic Carbon(TOC), Aluminum,  heavy metals, and turbidity are widely used to evaluate water quality and safety. How you achieve water quality is not relevant unless you leave a residue or change the chemistry of the impurities in the water. Both alum and polyaluminum chloride form various forms of aluminum hydroxide polymers. Polyaluminum chlorides have a tendency to form more of an Al13 polymer which works more efficiently in removing impurities in water. Polyaluminum chlorides attach to impurities in the water and filtered out. Alum treated waters can contain higher levels of aluminum, turbidity and sulfate; polyaluminum chloride treated waters can contain higher levels of chloride and lower levels of  aluminum and turbidity. Since the salinity of drinking water varies widely, the impact of additional chloride is minimal compared to the salinity of different waters. There are studies about chloride to sulfate ratios in water concerning corrosion and leaching lead and copper.  These studies are based on the finished water and the method of teatment is not relevant.

The Advantages of PAC Used as Water Treatment Chemical

1. Using PAC as flocculant, the speed of flocs forming and settling is quick. Flocs formed is easy to filter

2. Comparing to aluminium sulfate flocculant, the quality of water treated with PAC is better; the total cost reduced by 15%~30%, and the solubility is better.

3. It can be applied to water with broad pH range. The floc function valid in water of pH 5 to pH 9.

4. Comparing to inorganic flocculants, PAC is suitable for water of broad temperature, and is functional in low temperature water. It reduces less basicity less, so less or no basifier needed.

5. There is fewer salts in water treated with PAC, this is good for high purity water purifying and ion-exchange treatment

6. The corrosivity of PAC is lower, easy to transfer, handle and operate.

Polyaluminum chloride (PACl) is a well-established coagulant in water treatment with high removal efficiency for arsenic. A high content of Al(30) nanoclusters in PACl improves the removal efficiency over broader dosage and pH range. In this study we tested PACl with 75% AL(30) nanoclusters (PACl(Al30)) for the treatment of arsenic-contaminated well water by laboratory batch experiments and field application in the geothermal area of Chalkidiki, Greece, and in the Pannonian Basin, Romania. The treatment efficiency was studied as a function of dosage and the nanoclusters' protonation degree. Acid-base titration revealed increasing deprotonation of PACl(Al30) from pH 4.7 to the point of zero charge at pH 6.7. The most efficient removal of As(III) and As(V) coincided with optimal aggregation of the Al nanoclusters at pH 7-8, a common pH range for groundwater.