Comparison of methods for estimating carbonaceous BOD parameters

The performance of seven different methods (Differential, Fujimoto, Thomas, Graphical, Integral, Log-Difference, and Nonlinear Regression) for estimat ing first-stage, carbonaceous biochemical oxygen demand (CBOD), curve param eters, namely k and L-0 were compared using synthetic data generated by Mon te Carlo simulation technique. The comparison of the methods was made based on their efficiency in retrieving the original values of k and L-0 which w ere selected to generate the synthetic data. In the first part of the study , five sets of "true" data (without error substitution) with different k an d L-0 value pairs, (k (d(-1))-L-0 (mg l(-1)): 0.23-10,000; 0.23-250; 0.23-5 0; 0.10-250; and 0.50-250) were used to obtain information about the effect of different k-L-0 combinations and of using 5-day and 20-day CBOD data on the performance of the methods. In the second part, the same methods were used to calculate k and L-0 for ten sets of synthetic data with log-normall y distributed random errors at the coefficient of variation (COV) levels of 0.1, 0.2, and 0.3 for a single k-L-0 value pair, (0.23 d(-1); 250 mg l(-1) ). The results indicated that: (1) different combinations of k-L-0 values h ad no significant effect on the performance of CBOD curve parameter estimat ion methods with the "true" data; (2) use of CBOD20, data, i.e., CBOD data collected for 20 days, provided better estimates fork and L-0; (3) the Inte gral and Nonlinear Regression techniques were found to be the most reliable methods for the estimation of CBOD curve parameters among the other method s considered in this study.