On BOD tests for the determination of biodegradable COD for calibrating Activated Sludge Model No.1

Application of Activated Sludge Model No. 1 requires an influent characteri sation of COD over the different model COD components. Total biodegradable COD (CODBD) is the most important quantity in this characterisation. The us e and interpretation of BOD tests for the determination of biodegradable CO D were investigated. Of four grab samples, the BOD evolution in time was me asured up to fifteen days, with addition of nitrification inhibitor. From t he BOD curves, total BOD (BODinfinity, or BOD infinite) was estimated with first and second-order models. Parameters were fined with one (or two, for the second-order models) kinetic parameter per individual sample as well as one (two) for all samples together. The BOD curves were adequately describ ed by first-order kinetics. The estimated kinetic parameters showed conside rable variation over the samples from the same wastewater. As a consequence , the ratio BODinfinity/BOD5 was not constant for a given wastewater. The r atio BODinfinity/CODtot on the contrary proved much more constant. Therefor e, the total COD instead of BOD5 is suggested as a basis for determination of biodegradable GOD. The BODinfinity estimated has to be converted to CODB D. The conversion factor was computed by simulating the BOD tests using ASM 1, reduced for aerobic conditions. This approach provides a quantitative ba sis for this conversion factor. The sensitivity of this conversion factor t o model parameter values and COD fractionation was determined, which showed that the conversion has to be adjusted for non-default values of the heter otrophic yield. (C) 1999 IAWQ Published by Elsevier Science Ltd. All rights reserved.