Evolution of particle counts in filtered water from a direct filtration process using aluminum polychloride

This text presents and discusses the performances of direct filtration eval uated by means of particle counts and turbidity of raw water in periods of low and high turbidity. It also deals with the relationships between the re movals of particles measuring from 2 to 150 mu m (total counts) and those o f particles in the other size ranges, which vary from 2 to 5 and from 5 to 15 mu m. The tests were carried out on a pilot plant (20 m(3)/h) that treat s waters from the St. Lawrence River (Canada) using the polyaluminum chlori de (PACl) coagulation method followed by rapid filtration at 10 m/h. The re sults show that when the turbidity of the raw water is low, it is not alway s possible to predict a filter breakthrough based on the turbidity of its e ffluent, whereas it is possible to do so by observing the evolution of the particle counts. There exist good correlations between the removals of the total particle counts (2-150 mu m) and those of the counts of particles in the other size ranges (2-5 and 5-15 mu m). Furthermore, the evolution of al l these ranges of particle size reveals the same tendencies with respect to the quality of the filtered water.