The effectiveness of chitosan as a coagulant flocculant in surface water treatment has been studied. Tests were carried out in laboratory on treated and raw water. The treated water was mixed with high and low concentrations of bentonite to simulate turbid water. This treated water provides from water treatment plant of Algiers (Boudouaou site) which is supplied by both dams of Keddara and Beni Amrane. The raw water comes directly from these two dams. Chitosan with 85% degree of deacetylation and derived from crab chitin has been used. The performance of coagulation flocculation process has been assessed by measuring the supernatant turbidity for different doses of chitosan, initial turbidity, water quality and pH. The obtained results show that chitosan can be used in a large pH range. Chitosan is effective for coagulation of bentonite suspension and for raw water with high initial turbidity. Otherwise, chitosan is inefficient for raw water with very low initial turbidity. In this case, the use of chitosan as aid coagulant with aluminium sulfate (main coagulant) allows more effectiveness in removing turbidity.
Keywords: Bentonite, chitosan, coagulation flocculation, raw water, turbidity