This study aims at studying physico-chemical treatment as a method of treatment of effluent generated from an engine manufacturing industry. The effluent mostly comprises of machining coolant and hence contains high level chemical oxygen demand (COD). Experiments were carried out using poly aluminum chloride (PAC), ferric chloride (FeCl3) aided by anionic polyelectrolyte as the coagulant aid to determine the effectiveness of coagulation method for removal of COD. The results obtained prove that PAC was found comparatively more effective in removing COD as compared to FeCl3. At optimum pH and coagulant dose, PAC shows COD reduction by 89.2 % while FeCl3 shows COD reduction by 81.9 %.