Page 27 - 5_TOC in daily practice
P. 27
SCA-130-514
■TOC, total organic carbon 2. Example Acetone (C 3H 6O) 1000mg/L
The TOC content is a measure of the COD=2207mg/L
concentration of organically bound carbon TOC= 621mg/L
and is therefore a direct indication of the Correlation COD/TOC= 3,55
pollution levels by organic compounds in
wastewater. For TOC determination, the 3. Example Ethanol (C 2H 6O) 1000mg/L
sample is typically first acidified in order to COD=2087mg/L
convert the inorganic carbonate and TOC= 522mg/L
hydrogen carbonate compounds into carbon Correlation COD/TOC= 4,00
dioxide. The dissolved CO 2 is subsequently
removed from the sample via sparging with a The examples show the diversity of
stream of carrier gas. The remaining organic correlation factors. In addition to the organic
carbon compounds are then converted to compounds, other compounds like nitrites,
CO 2 via high temperature (catalyst) or wet- bromides, iodides, metal ions or sulfur
chemical oxidation. The amount of CO 2 compounds may be oxidized and influenced
obtained is subsequently determined via the factor.
NDIR detection. NDIR is a specific detection Due to this, the correlation factor can be vary
mode that renders TOC determination free between 2,5 and 4 depending of the
from the effects described above when using wastewater.
other parameters. Based on this, the TOC
parameter is used in many environmental In order to simplify the determination of the
regulations. Another advantage is the correlation factor, paragraph 6 of the German
relatively simple conversion of TOC wastewater law (AbwV) of June 17, 2004
measurements into a continuous monitoring includes the following: “One of the values for
procedure. the chemical oxygen demand (COD) as
defined in the wastewater regulatory law is,
■ Correlation between COD and TOC under compliance with paragraph 1, also
In recent years, COD measurements are valid when the four-fold value of the total
increasingly being replaced by TOC analysis. organically bound carbon (TOC) in mg/L,
However, as the threshold values for organic does not exceed this value”.
pollution levels in wastewater are usually
described and determined as COD values, In the European Union, the factor „3“ is used
efforts are underway to find a correlation for conversion of TOC in COD.
between the two parameters.
For single compounds the factor can be The instrument software of Shimadzu TOC
calculated. systems (TOC-L standalone, TOC-Control L,
TOC-4200 standalone) enables the automatic
1. Example Glucose (C 6H1 2O 6) 1000mg/L conversion of measured TOC values into
COD= 1067mg/L COD value (if the correlation is known).
TOC= 400mg/L
Correlation COD/TOC= 2,66
