A company’s inability to recognize real-time organic loading changes in their wastewater treatment plant could result in excessive charges from the local water utility.
A production facility located in the U.S. Midwest currently controls the organic loading in their wastewater’s chemical treatment based on chemical oxygen demand (COD) testing. The sampling frequency is once per day and is typically taken at the beginning of the first shift.
The COD test is performed in-house and takes approximately 2.5 hours from the time a sample is collected until a final result is determined. Chemical treatment is then adjusted based on the amount of organic loading determined from the COD test.
The company appropriates a significant amount of their budget for fees received from the local utility. These surcharges are due to the excessive organic levels and are accepted as normal operating costs.
To help minimize these surcharges and better treat the wastewater in-house, GE Analytical Instruments was asked to perform an evaluation of the organic loading, using an on-line total organic carbon (TOC) analyzer.
A Sievers InnovOx On-Line TOC Analyzer from GE Analytical Instruments was installed at the facility. For this test, the InnovOx monitored the wastewater coming from the factory into the treatment facility (the influent) and the treated wastewater being released to the local water utility (the effluent).
The influent on-line TOC data showed there was variability in the organic loading throughout the day that was not being captured by the daily COD test. In fact, this organic loading variability could be linked directly to the surcharges coming from the local utility.
The facility’s perceived state of organic loading can be seen by the green line. The blue line, calculated from the InnovOx On- Line TOC Analyzer, shows that the actual variability in organic loading was severely underestimated based on the COD grab samples (red dots).
COD to TOC Correlation
To establish a correlation between COD and TOC, the InnovOx ran for approximately six weeks. During that time, about 23 COD results were reported. A coefficient of determination, or R2 value, of 0.95 was established. The R2 value is an indication of the variance in the correlation, and a value of 0.95 shows a very high correlation.
Applying a correlation factor to the continuous TOC analysis clearly demonstrates that the perceived state of the water quality had been overestimated.
GE Analytical Instruments has made innovative strides in TOC analysis, providing a robust analyzer for the most difficult matrices—the Sievers InnovOx TOC Analyzer. By using an ultra-efficient Supercritical Water Oxidation (SCWO) technique, the InnovOx is able to run thousands of water samples continuously with no recalibration.
The Sievers InnovOx’s principle of operation is based on the wet chemical oxidation technique, which adds an acid and oxidizer to the sample of interest. The inorganic carbon is removed by purging, and the sample is then oxidized with persulfate at elevated temperatures. The resultant carbon dioxide is measured by a nondispersive infrared spectrometer.
The InnovOx elevates the temperature of the sample and reagent mixture to ensure efficient oxidation and to convert the liquid water sample into supercritical water. Once in this phase, a phenomenon called SCWO occurs. This innovation achieves greater than 99% efficient oxidation, resulting in superior accuracy and precision.
The Sievers InnovOx also removes problematic sample matrix contamination at the end of every analysis. As a result, no salt or oxidation byproducts buildup in the reactor, tubing, or valves.
This project demonstrates that COD analysis only shows a snapshot of the organic loading in a treatment process. In fact, many plants use biochemical oxygen demand (BOD) in lieu of COD. The five-day BOD organic loading test shows an even larger disconnect to the real-time plant process.
Implementing on-line TOC analysis gives a clearer and faster check of real-time organic loading over both BOD and COD. With a fast organic measurement like TOC, a plant has the ability to adjust its chemical treatment to avoid expensive surcharges due to high organic levels. The proven Sievers InnovOx On-Line TOC technology can also benefit any plant that is concerned about excessive organic loading in their effluent that is discharged to an external water body or reused in another plant process.
Case study - Cost-saving solutions using Sievers InnovOx TOC analyzers - optimizing organic loading