A Correlation Study for Total Organic Carbon and the Five-Day Biochemical Oxygen Demand Test in Water Reclamation Plant Influent and Effluent

Wet Chemistry Automation
Poster Presentation

Presented by T. Pluth
Prepared by T. Bremm Pluth, D. Brose, P. Grunwald, A. Jesernik
Metropolitan Water Reclamation District of Greater Chicago, 6001 W. Pershing Road, Cicero, Illinois, 60804, United States

Contact Information: [email protected]; 708-588-3136


The five-day biochemical oxygen demand (BOD5) test is widely used for monitoring and reporting since it is a surrogate of the degree of organic pollution in water. However, its analysis is long and labor intensive. Total organic carbon (TOC) can be used as a replacement for BOD5 once a long-term correlation between TOC and BOD5 is demonstrated, as stated in the Clean Water Act 40 CFR 133.104(b). TOC has many advantages including its short test time, faster data reporting, reproducibility, and automation. Additionally, the TOC test is more environmentally friendly since it does not require mercury as a reagent. The Metropolitan Water Reclamation District of Greater Chicago (MWRDGC) conducted a one-year study to determine the correlation of TOC with BOD5 and five-day carbonaceous biochemical oxygen demand (CBOD5) for each of its seven water reclamation plants (WRPs) in order to modify National Pollutant Discharge Elimination System permits to include TOC monitoring instead of BOD5 and CBOD5 monitoring. Influent and effluent 24-hour composite samples were collected seven days a week from the MWRDGC’s major WRPs and five days a week from the minor WRPs. Samples were analyzed for BOD5 and CBOD5 following the Standard Method 5210 B. In addition, samples were analyzed for TOC following the Standard Method 5310 B (High-Temperature Combustion Method). Influent and effluent data were compiled, and statistical correlations determined. Linear regression models with logarithmic transformations were observed to best describe the BOD5:TOC and CBOD5:TOC correlations.