Interpretation of Ultimate Biochemical Oxygen Demand Data via Kinetic Curve Extrapolation Models, 1992 Environmental Conference Proceedings

In this report, we explain the methodology and limitations in the interpretation of Biochemical Oxygen Demand (BOD). Data bases of up to 257 days are employed to yield Ultimate BOD(UBOD) values. Clear separation of the contribution of carbonaceous and nitrogenous BOD is found to be crucial, and procedures to accomplish this are illustrated. Carbonaceous data sets are processed by a non-linear regression program employing either a one or two term first order model. The two term first order model is definitively superior to the one term model. In physical chemical terms, the two term model corresponds to concurrent fast and slow reaction rates.

Subsets of the data reflecting shorter duration experiments are also analyzed. The UBOD values for the two term model remain fairly consistent until the program fails to converge on a UBOD end value. In contrast. the one term model yields UBOD values that fall farther and farther below the best result as shorter data bases are employed. Statistically, the one term model appears to improve at shorter durations, but this is due to a loss of information of the long term characteristics of the BOD curve.