Aluminum sulphate (alum) and polyaluminum chloride (PAC) are types of commonly used coagulants in wastewater treatments. However, these coagulants produce activated sludge which is very hazardous. Hence, it is suggested that a biodegradable coagulant can be a better alternative. Coagulation of residue oil and suspended solid from palm oil mill effluent (POME) an oily effluent using a biodegradable biopolymer, i.e. chitosan was explored in this study using a flocculator. Chitosan is a cationic biodegradable biopolymer produced by the extensive deacetylation of chitin obtained from shrimp shell wastes. The performance of chitosan was compared to alum and PAC. POME contains about 10,000 mg/l of suspended solid and 2000 mg/l of residue oil. The results obtained proved that chitosan was comparatively more efficient and economical to alum and PAC. At the defined optimum experimental conditions (dosage: 0.5 g/l, contact time: 15 min, mixing rate: 100 rpm. sedimentation time: 20 min and pH 4) chitosan showed more than 95% of suspended solid and residue oil removal. For alum and PAC the optimum dosages were 8.0 and 6.0g/l, respectively, 30 min of mixing time at 100 rpm, 50 and 60 min of settling, respectively, and pH of 4.5 to obtain the same percentage of removal as performed by chitosan. (c) 2006 Elsevier B.V. All rights reserved.