Reduction of COD and turbidity in leachates through coagulation-adsorption

Department of Civil Engineering, National Institute of Technology, Manipur-795004 Email: albinoiit@gmail.com In this study, aluminium sulphate, ferric chloride and polyaluminium chloride coagulants were employed for reduction of organic colloids through cogulation-floculation and then adsorption using Parkia Speciosa (Petai) pods activated carbon for removal of dissolved ions from leachate. Polyaluminium chloride showed maximum turbidity reduction of 93.25% and 96.80% at optimum pH 4 for fresh and stabilized leachate respectively as compared to that of aluminium sulphate and ferric chloride with turbidity removals ranging from 70% to 91% for both types of leachate. The optimum doses of aluminium sulphate, ferric chloride and polyaluminium chloride for fresh leachate were 8 g/L with corresponding COD removals of 80%, 90% and 75% respectively. However, for stabilized leachate COD reduction, polyaluminium chloride and ferric chloride exhibits the same removals of 77.78% using 4 g/L and 3 g/L respectively against 55.55% by 4g/L aluminium sulphate. As the pre-treated effluents still have COD above the permissible limit, activated carbon derived from Parkia Speciosa pods was used as an adsorbent for further treatment. On the application of the diffusion model for fresh leachate, high R2 values of 0.976 and 0.992 were observed using 10 g/L and 20 g/L adsorbent dose respectively resulting in overall COD removals of 85% and 89.50% respectively. For stabilized leachate, high R2 values of 0.964 and 0.992 were observed for adsorbent doses of 5 g/L and 10 g/L respectively resulting in overall COD removals of 91.67% and 93.33% respectively, confirming the physical diffusion of organics in the adsorbent as the predominant mechanism rather than chemical adsorption