ORGANIC-CARBON AND NITROGEN REMOVAL IN MOVING-BED BIOFILM REACTORS

Pilot moving-bed biofilm reactors (MBBRs), fed on primary settled wast ewater, were used in order to study organic carbon removal and nitrifi cation. Nitrate uptake rate (NUR) tests were performed by feeding sodi um acetate and potassium nitrate to a bench-scale moving-bed batch bio film reactor. In both experiments the same polyethylene biofilm carrie rs were used. Both particulate and filtered COD removal rates appear t o be proportional to the corresponding loading rates. Particulate COD removal is the net effect of adsorption onto and release from the biof ilm surface. Filtered COD removal is the sum of the influent filtered COD removal and the removal of hydrolysed colloidal GOD. Filtered COD removal rates could not be evaluated with a kinetic expression because back-diffusion from biofilm is not always negligible. Nitrification t ests, performed at oxygen limiting conditions, show that the reaction rare was nearly first order with respect to dissolved oxygen due to li quid film diffusion. Denitrification batch tests showed denitrificatio n rates very close to other reported data. Since the process proved re liable and easy-to-operate, it is suitable for application to small WW TPs, either in designing new plants or in upgrading existing overloade d activated sludge systems. (C) 1997 IAWQ. Published by Elsevier Scien ce Ltd.