Relationship between chemical and theoretical oxygen demand for specific classes of organic chemicals

This study examined the relationship between ThOD and COD for a database of 565 organic chemicals comprising 64 classes. A mixed beta-normal distribution was used to develop a statistically reliable method to estimate COD from ThOD for specific classes of organic chemicals. The data were divided into six groups; (1) well-correlated aromatic chemicals, (2) well-correlated non-aromatic chemicals, (3) potentially well-correlated aromatic chemicals, (4) potentially well-correlated non-aromatic chemicals, (5) other aromatic chemicals, (6) other non-aromatic chemicals. The results show there is 90% statistical confidence that COD will be within the range of: 0.96-1.0 x ThOD (mean equal to 0.98) for the chemical classes in group 1; 0.92-1.0 x ThOD (mean equal to 0.97) for the chemical classes in group 2; 0.80-1.0 x ThOD (mean equal to 0.93) for the chemical classes in group 3; 0.75-1.0 x ThOD (mean equal to 0.92) for the chemical classes in group 4. The COD for chemicals in groups 5 and 6 was either poorly correlated or could not be correlated because insufficient data were available. COD cannot be estimated from ThOD for the 43 chemical classes represented by the 288 chemicals in groups 5 and 6. Caution should be used in applying COD measurements to these chemical classes or to mixtures which consist primarily of chemicals contained in these chemical classes. In addition, a modification of the COD test may be required for individual chemicals contained in this poorly correlated group of chemical classes (e.g., modification For volatile chemicals, C. J. M. Wolff (1975) COD determination of volatile compounds, Water Res. 9, 1015). (C) 1998 Elsevier Science Ltd. All rights reserved.