A simple physical-chemical method was developed as an alternative to the respirometry method for determining the wastewater COD fractions in terms of biodegradability. Wastewater was fractionated into soluble, colloidal, non-settleable and settleable particle components by the physical-chemical method. The COD biodegradability fractions including readily biodegradable COD, slowly biodegradable COD, inert soluble COD and inert particulate COD were determined from the respirometry and modeling method. A conversion matrix was derived that can be used for COD biodegradability fractions conversion from simple physical-chemical analysis. The denitrification experiment indicated that the physical-chemical conversion method can be a valuable tool for wastewater denitrification potential estimation. (C) 2014 Elsevier B.V. All rights reserved.