Why is aluminum added to drinking water during treatment?
Microorganisms present in drinking water include viruses, bacteria (e.g., E. coli), and protozoa (e.g., Cryptosporidium and the beaver fever causing organism, Giardia). At low levels, these organisms can cause sickness and disease (incl. severe diarrhea) and are generally very difficult to remove from water. The parasites Giardia and Cryptosporidium are very resistant to most types of disinfection, including chlorination. Water treatment with aluminum sulphate is, however, effective at removing these parasites when used in a chemical treatment process called coagulation. Coagulation is a process in which small particles (0.001 to 10 m) bunch together to form large particles (>10 m), which can then be removed by settling or filtration. In natural water, most particles (including microorganisms) have a negative electric charge and, rather than clump together to form larger particles, the particles repel each other. To get the particles in solution to form larger clumps, this negative cha
