Experimental design approach to optimal and kinetic evaluation of coag-flocculation performance of afzelia bella extract in coal washery effluent.

23- central composite design(CCD) optimization and kinetics of coal washery effluent (CWE) coag-flocculation by Afzelia bella seed has been studied at room temperature via standard bench scale jar test. Afzelia bella coag-flocculant (ABC) was produced according to work reported by Ghebremichael. The combined effects of pH, dosage and settling time on the particle removal was studied using surface response methodology. Kinetic data generated were fitted with specified kinetic models for the evaluation of functional coag-flocculation kinetic parameters. The optimal values of pH, dosage and settling time were recorded at 6,300mg/l and 30min,respectively. The results of the major kinetic parameters recorded were 2, 7x10-5 l /mg.min and 1.34min for order of reaction, coag-flocculation reaction rate constant and coagulation period, respectively. The minimum removal efficiency recorded was > 95% at 3 mins of coag-flocculation. The results demonstrated that ABC can be applied as a coag-flocculant in the treatment of water at the conditions of the experiment.