Wolfratshausen, February 2019
The TOC value
In addition to many individual values, the TOC value is an important parameter. The Total Organic Carbon value is an indication of the pollution of water with organic substances, regardless of whether, for example, bacteria, pesticides, or benzene.
The COD value
In wastewater technology, there is another critical sum parameter, the COD, as it serves, among other things, as guideline for controlling the biological degradation stage in sewage treatment plants. After determining the conversion factor, it was relatively easy to replace the COD by the TOC.
But the Chemical Oxygen Demand is a parameter that has to be determined in the laboratory and is in any case related to the current probe.
Additionally the manual determination is time consuming, 0,5 until 2,5 hours depending of the analytical method employed and produces highly toxic by-products.
The new TOC / TOD analyzer
The analytical problem
The conversion factor is only stable as long as the composition of the wastewater does not change. But there are many different branches of industry, which at different times, from different processes, introduce different wastewater.
This poses new, more difficult challenges for wastewater treatment plants, as the conversion factor TOC / COD can vary between 2 and 4, depending on the wastewater matrix. This makes it indispensable, for example, in wastewater treatment plants with problematic dischargers and in the wastewater control of various industrial parks to measure COD.
What customers want
Many of our customers who know the reliability of our TOC equipment came to us and asked for a device that allows them to permanently capture the COD value online, without a laboratory and without poisoning the environment.
The challenge was
to find an approved measuring method that could also be used online. An older American standard, the ASTM D 6238-98, describes a measurement method for measuring Total Oxygen Demand (TOD).
Here, it is described, how the combustion of a liquid sample, with the involvement of catalysts, the determination of the oxygen reduction leads to Total Oxygen Demand (TOD).
After lengthy research and testing, we succeeded in developing a true online measuring instrument which does not require high-purity cylinder gas and nevertheless measures the oxygen depletion with high precision on the principle of comparative measurement. Of course, TOC measurements are also possible at the same time.