A comparison of coagulant dosing options for the remediation of molasses process water

Effluents arising from molasses fermentation are highly coloured and carry a large organic load. Existing anaerobic/aerobic biological treatments effectively reduce the biological oxygen demand (BOD), but are unable to decolourise or remove the colour associated chemical oxygen demand (COD) from the wastewaters. This study investigated the remediation efficacy of chemical flocculation and electrocoagulation, the process whereby sacrificial anodes corrode to release active coagulant precursors into solution. The chemical flocculants used Als(SO4)2 and FeCl3 have an optimum dosage concentrations, above and below which they are less effective. Both removed almost 90% of the colour and up to 80% of the COD, although this was dependant on effluent quality. Altering the pH alone was also shown to cause colour removal. Electrocoagulation using sacrificial iron or aluminium anodes was as effective as chemical flocculation in reducing colour and COD. The bubbles of hydrogen from the cathode floated almost all the coagulated material to the surface of the reactor, facilitating separation. Particle size distributions of the treated wastewater were measured by laser diffraction. The volume-based frequency distribution made it clear that both chemical flocculation and electrocoagulation resulted in considerable aggregation. A linear relationship between colour and COD removal was demonstrated.