Editor choice

TOC or COD, that is the question

Which parameter is the correct one for measuring the organic load in the wastewater of the food industry?

Manufacturing milk products, beer, mustard, ketchup and similar products generate a large amount of water, some of which has a high organic load. As a result, the chemical oxygen demand (COD) must be determined before industrial wastewater from factories in food and beverage is discharged into the municipal wastewater system. This value specifies the amount of oxygen required to break down the oxidisable substances contained in the water. Accordingly, for over 30 years now, the COD has been the basis for calculating wastewater charges. This makes it the critical parameter of industrial wastewater. But there is a catch. In recent years, no device was available that could measure the COD value directly. Though there is an optical method for measuring COD, it frequently shows only a trend display — and even that is only possible with high error rates. In addition, it can be used only under certain conditions and only when calibrated to a currently running process or a current mixing ratio. As soon as the situation changes, the method no longer permits even a simple yes/no statement about the COD value.

TOC measurement

The total organic carbon (TOC for short) has been determined as an alternative in many cases. The advantage of the TOC measurement is that the value can be determined quickly, the analysers used for this purpose work with environmentally friendly reagents and map the trend of the process with high accuracy. However, the TOC analysers do not always provide the result determined in the lab, which resulted in frequent debates about which measured value was the “correct” one. Service team members often had to take part in these debates when they visited customers on site for after-sales support. When we ask customers what their expectations are for an instrument that measures the organic load of their wastewater, the answer is usually that it should determine the value online and not require any maintenance. However, the desire for a device that measures quickly and can map all changes of the sample composition is not easily fulfilled. The TOC analyser is often used for this reason. It provides fast measuring values, but they do not always match the laboratory values. A different solution is now available when measuring values that can be verified in the laboratory are required.

COD measurement

Most food and beverage companies now have in-house wastewater treatment plants to minimise costs for wastewater charges. These plants usually have a dwell time of two to six hours. This is plenty of time to determine the COD value online in time increments of about an hour. The measurements of the new Liquiline System CA80COD accurately map customer processes. The integrated dilution module enables it to cover a very broad measuring range. In the lower measuring range, we have no need to shy away from the competition. Unlike the old CA71COD, the measured values of the new CA80COD can be confirmed in the laboratory with cell tests. This makes debates about deviating measured values a thing of the past. The new COD analyser adds to our product range such that we can offer customers exactly the parameter and measured value they need to sparkle in the eyes of the water authority.

In the outlet:

  • When an upstream biological cleaning process is in place, the Viomax CAS51D makes it easy to measure a trend for the carbon load in the wastewater (with a matrix that stays approximately the same).
  • The CA80COD is ideal when real COD comparison values are required in the laboratory.

In the inlet:

In wastewater treatment plants in the food industry, it is frequently necessary to process greatly fluctuating carbon loads.

  • Optical measuring systems like Viomax CAS51D brush up against their limits quickly, depending on the composition of the wastewater. Only a test measurement can provide certainty here.
  • A TOC analyser such as the CA72TOC measures quickly, but the measurement results can deviate from laboratory values.
  • The CA80COD offers an advantage in that its measuring values can be verified in the laboratory. However, a longer analysis time is required than for other measurement methods. If necessary, the time can be shortened since wastewater from the food industry can usually be oxidised very quickly.

For more information, please visit: https://eh.digital/2xnH4R9

For more information, please contact:

Jan Swart

Product Manager: Analytics

Tel: (011) 262 8000

jan.swart@za.endress.com


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Farmers Review Africa
Farmers Review Africa
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