Removal of the Colloidal Suspension from Dam Water Using Mineral Coagulants Prepared by Co-Precipitation

Abstract

In this work, we were interested in eliminating the organic and mineral compounds that pose problems in obtaining drinking water using the method of coagulation. These substances are stable in the medium due to their colloidal sizes and surface loads, which require appropriate treatment. For this purpose, we explored the removal of colloidal suspension using a coagulant formed by co-precipitation of AlCl3.6H2O in an alkaline medium. This practice leads to the formation of polymeric species mixtures such as Al45O45(OH)45Cl and Al2O3.H2O after washing. The removal efficiency of mineral and organic matter is evaluated by measuring the turbidity and permanganate index by varying the concentration of the coagulant from 0.04 to 0.4 g.1−1. It has been shown that the effectiveness of the treatment had been increased in parallel with the concentration. The preliminary hydrolysis of aluminium leads to a fixation of the pH throughout the concentration range. This character had solved the problem of direct use of aluminium salts (conventional method) resulting in a modification of the pH and subsequently, variable efficiency. The refined coagulant (after washing) reaches the removal of 97% turbidity and almost all oxidisable matter using only a mass of 0.08 g.1−1. However, using the crude coagulant (without washing) containing a significant amount of NaCl requires 0.4 g.1−1 to reach only 87% removal of turbidity as well as 35% of oxidisable matter, with an increase of conductivity compared with that of the refined coagulant.