Page 26 - 5_TOC in daily practice

Sum parameter – Total Organic Carbon

Comparison of different sum parameters –
COD, BOD and TOC

SCA-130-514

Identification of organic pollutants in obtained are therefore not useful for
wastewater is essential for performance monitoring and controlling of wastewater
evaluation, construction and operation of a treatment procedures. For continuously
wastewater treatment plant. Several operated BOD analyzers, determination
parameters are currently used in wastewater within 5 -15 minutes has been attempted.
analysis applications. Some of these are
based on oxygen demand, for instance BOD ■ COD (Chemical Oxygen Demand)
(biochemical oxygen demand), COD The COD value indicates the amount of
(chemical oxygen demand and TOD (total oxygen needed to chemically oxidize organic
oxygen demand). Using TOC analysis, compounds present in wastewater. A
however, the total organic carbon content is chemical oxidizing agent is added to the
determined directly so the method is relatively sample and its consumption is subsequently
free from matrix effects. The advantages of measured. In addition to the organic
TOC analyses are apparent especially during compounds, other compounds (nitrites,
continuous monitoring. bromides, iodides, metal ions and sulfur
compounds) present in the water sample can
also be oxidized and have an influence on the
measuring value.
The COD determination is a subject of critical
discussion due to the use of environmentally
hazardous substances such as mercury and
chromium compounds.

■ TOD (Total Oxygen Demand)
This rather seldom parameter evolved from
the idea that chemical oxidation via COD
could be replaced by thermal oxidation,
whereby the amount of oxygen required for
■ BOD (Biochemical Oxygen Demand) high-temperature combustion of all
The BOD value indicates the amount of contaminants is determined. This reduces the
oxygen in water needed for biological measuring time when compared with COD
decomposition of organic compounds determination. However, during TOD
dissolved in wastewater. For BOD measurements, non-carbon containing
determination, microorganisms are added to compounds, for example sulfur and nitrogen
the water sample. After a predefined time compounds, are also oxidized. This is
interval, usually five days, the oxygen probably the reason why this parameter is not
consumed by bacteria during decomposition used by most well-known regulatory
of organic compounds in the water sample is agencies.
determined. The BOD5 test is much too slow
to provide suitable information and the results