Chitosan, a biodegradable compound, is used as an eco-friendly coagulant in water and wastewater treatment to avoid production of the large amounts of sludge using conventional chemical coagulants. Conditioning of chitosan using four different salts (Na2SO4, NaHSO4, (NH4)ZSO(4), and KHSO4) along with H2SO4 and treatment condition optimization were investigated to enhance coagulating efficiency for bentonite suspension. Chitosan dissolved in acetic acid was used for coagulation of 5 g/I bentonite suspension. The optimum concentration of chitosan required for maximum coagulation of bentonite suspension was 5 mg/l. Among the five additives used for conditioning, NaHSO4, at all concentrations. was found to be the most effective for enhancing the coagulating efficiency of chitosan and it was at its maximum when conditioned by 0.05 mM NaHSO4, NaHSO4 conditioned chitosan showed better coagulating efficiency than unconditioned chitosan at all pHs (3-8) tested in this study. The coagulation of bentonite by chitosan was found to decrease with increase in pH of the suspension. Using 5 mg/l of NaHSO4 conditioned chitosan at pH 6, the removal percentage of bentonite was increased from 76% to 88% compared to unconditioned chitosan. (c) 2008 Elsevier B.V. All rights reserved.