Page 28 - 5_TOC in daily practice

Sum parameter – Total Organic Carbon

COD and TOC correlation factor – Conversion
examples

SCA-130-515

The determination of the chemical oxygen ■ Theoretical COD/ TOC factor
demand (COD) is time-consuming and If the TOC is used as an analytical parameter
complex. After the sample has been mixed to calculate the COD, a conversion factor is
with various reagents, it is left to boil at 120°C required. The AbwV specifies the factor 4. A
(according to DIN regulation) under reflux (air theoretical factor is derived from the reaction
cooler), subsequently an aliquot of the ratios between C and O 2:
mixture is back-titrated or photometrically
measured (rapid test). � � � � ��
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In addition, environmentally hazardous
substances, such as a mercury-containing As the COD corresponds to the required
sulfuric acid and a potassium-dichromate oxygen amount, the O 2 consumption
solution are used. corresponds to the COD value – C represents
to the TOC value.
The determination of TOC (Total Organic
Carbon), on the other hand, is fast and easy Since the COD or the TOC concentrations
to perform. In addition, less than 1 mL of a must be expressed in terms of mass
diluted hydrochloric acid solution is used for concentration, the molar masses of the two
each analysis. reactants are used here for the conversion.
The ratio of carbon concentration to oxygen
■ COD and TOC in the German Waste concentration corresponds to the TOC/COD
Water Ordinance (AbwV) correlation. Based on the reaction equation
For decades, there have been efforts to above, this means
replace the COD by the TOC parameter.
However, to date the COD is laid down in the for C: 1000 �� ∶ 12 � � 83.33 ����
German Waste Water Ordinance. In order to � ��� �
still use the TOC parameter, Article 6
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“Compliance with the requirements” of the for O 2: 1000 � ∶ 32 ��� � 31.25 �
German Waste Water Ordinance states the
following: The COD factor is derived from the molar
(3) “With due regard for paragraph (1) above, ratio of C to O 2:
a chemical oxygen demand (COD) level
specified in the water discharge permit shall ���� ���� � 2.667
also be deemed to have been met provided 88.33 � ∶ 31.25 �
the quadruple amount of total organically
bonded carbon (TOC), specified in milligrams In this case, the conversion from TOC to
per liter, does not exceed this level.” COD is as follows:

��� �� � � �� � � ��� � �� � ∗ 2.667
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