TOC Correlation to BOD or COD
Challenge: Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) are traditional parameters analyzed in the laboratory to determine organic matter in water and wastewater. Wastewater facility operators need to have constant data to monitor their discharges and optimize treatment processes (biological treatment, chemical dosing, etc). The requirements of BOD and COD analysis prevent them from being implemented as control parameters, however. The BOD five-day analysis time requirement does not allow an operator to use the data for process optimization and. although COD requires less time than the BOD, its analysis includes the use of hazardous chemicals and has no constant analysis capability.
GE Analytical Instruments' InnovOx On-Line Total Organic Carbon (TOC) Analyzer provides a continuous analysis of TOC. The TOC values can be correlated with BOD or COD values, and provide the opportunity to use the regulatory data requirement for process optimization. In addition, the operator can retain, divert, or dilute discharges prior to causing damage.
Industry and Regulatory Guidance
The TOC and BOD or COD correlation procedure has been becoming commonly accepted protocol in wastewater operations. In January 2013, the Instrumentation Testing Association (ITA) published the study. Addressing BOD limitations through Total Organic Carbon Correlations: A
Five Facility International Investigation, to promote the protocol development. In recent years, TOC analysis has been gaining recognition internationally, particularly in European communities, as a substitute for BOD and COD analysis in regulatory requirements [e.g. The Council of European Communities Directive 91/271 EEC dated May 21,1991, and the German Wastewater Law (AbwV) dated June 17, 2004
To help demonstrate the effectiveness of constant TOC monitoring, Figure 1 shows the calculated COD values taken from the InnovOx TOC Analyzer and the actual COD measurements made by an engineer in a US wastewater facility. The fluctuations in the day-to-day (or even hour-to-hour) operation are not being properly tracked. The green overlaid line shows what the facility perceives as the current state. The blue line represents the actual influent which needs additional treatment. From this data, it is apparent that several events are unknowingly entering this treatment facility and ultimately being discharged to the municipality. This shows that continuous TOC monitoring can provide valuable insight on organic loading fluctuation and optimize the treatment performance.