Total Organic Carbon in Water

FIGURE 18.15 Total organic carbon analyzer employing ultraviolet-promoted sample oxidation. 

After oxidation is complete, the CO2 is sparged from the system and measured with a gas chromatographic detector or by absorption in ultrapure water followed by a conductivity measurement. 

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X.L. Su, L.H. Nie, S.Z. Yao, A novel gas-diffusion/flow-injection system coupled with ahulk acoustic wave impedance sensor for total inorganic carbonate and its application to determination of total inorganic and total organic carbon in waters, Anal. Chim. Acta 349 (1997) 143-151. 

Y.S. Fung, Z. Wu, and K.L. Dao. Determination of total organic carbon in water by thermal combustion-ion chromatography. Anal. Chem., 68 2186-2190,1996. 

I. Gacs and K. Payer. Determination of total organic carbon in water in the form of carbamate by means of a simple denuder/electrolytic conductivity flow ceU system. Anal. Chim. Acta,... 

GEODE [General Electric organic destruction] A development of the Ultrox process in which a combination of ozone and ultraviolet radiation is used to oxidize traces of organic compounds in water. Developed by the General Electric Company and demonstrated at the Commonwealth Edison nuclear power plant at Dresden, IL, in 1989. The requirement was to reduce the concentration of total organic carbon in the process and makeup waters to the low parts-per-billion range. 

A review committee set up under the auspices of the North Atlantic Treaty Organization in 1979 listed 744 chemical contaminants that had been identified in the drinking water of 14 countries (I). Since then, more have been found. However, it has been estimated that more than 80 of the total organic carbon in the drinking water still remains uncharacterized. This growing number of organic chemicals identified in drinking water supplies led to public concern and debate about the potential risks to health. 

Dissolved organic carbon is defined operationally as the fraction of the total organic carbon in the water phase that will pass through a 0.45 pm filter. Assuming illustrative values for ( )p of 10 7 kg/L and (% of 10 7 kg/L, it follows that a chemical with a log Kow of 5 will have Fdw of 99.6%, whereas a chemical with a log Kow of 8 will have a FDW of only 18%. 

Fung et al. [15] have discussed a thermal combustion-ion chromatographic method for the determination of total organic carbon in industrial and potable waters. This method utilises a tube furnace and readily... 

Edwards A. C. and Cresser M. S. (1987) Relationships between ultraviolet absorbance and total organic carbon in two upland catchments. Water Res. 21, 49-56. 

As mentioned earlier, TOC is another important water quality parameter. TOC is equal to the total concentration of organic carbon in water and is reported as milligrams carbon/liter (mg C/L). It serves as a general indicator of the overall quantity of carbon-based matter contained in water. TOC frequently correlates to BOD and COD but is not necessarily always a reliable measure. If a repeatable empirical relationship is established between TOC and BOD or TOC and COD for a particular wastewater, TOC can be used as an estimate of the corresponding BOD or COD. The theoretical TOC (ThCOD) can be calculated stoichiometricaly in similar manner to the ThCOD. 

In some instances the method for carbon determination has to be modified, e.g., the determination of trace amounts of what is referred to as dissolved organic carbon in water after inorganic carbon has been removed. This type of carbon determination involves wet oxidation activated by silver ions in a solution of potassium persulphate in sulphuric acid. The oxidation of organic compounds gives carbon dioxide, which is adsorbed by molecular sieves. The molecular sieves are then heated in a flow of helium to desorb the carbon dioxide, the amount of which is measured by a TCD. The lowest concentration of organic carbon that can be measured in water is 0.2—2ppm [55]. The application of chromatographic elemental analysis to the determination of the total carbon content in water has been described [56]. 

Sharp, I.H., 1973a. Total organic carbon in sea water — comparison of measurements using persulphate oxidation and high temperature combustion. Mar. Chem., 1 211— 229. 

Kawamura K., Kobayashi M., Tsubonuma N., Mochida M., Lee M. and Lee G. (2002) Water-soluble dicarboxyUc acids and total organic carbon in the Asian aerosols results from Cheju and Hokkaido Islands during the ACE-Asia campaign. Sixth International Aerosol Conference, September 8-13, 2002, Taipei, Taiwan, Abstract, pp. 9-10. 

BCFtotai (free and bound (= total) PAH in water) = [Tissue]/[WatertotJ DOC is dissolved organic carbon in water (usually in mg/L or ppm), flip is the fraction of tissue that is lipid (usually in dry weight), foe is the fraction of sediment that is organic carbon (usually in dry weight). 

As summarised in Table 3.4, some electroanalytical methods have been certified by standardisation bodies for the chemical characterisation of ambient water samples, mostly in the class of inorganic substances. Conductometric detection is used in direct method for ionic constituents and also as chromatographic detector for individual cations and anions. Total, inorganic and organic carbon in water can be also assayed by conductometric detection. Amperometric detection has been certified for dissolved oxygen and cyanide. ISE potentiometry is used for standardised measurements of a set of ions and also for the evaluation of water oxidation-reduction potential. Voltammetric detection is the base for diverse methodologies oriented to the determination of trace elements including the most relevant elemental pollutants. 

Several methods have been developed to estimate the oxygen demand in waste water treatment systems. Commonly used laboratory methods are biochemical oxygen demand (BOD), chemical oxygen demand (COD), total oxygen demand (TOD), total organic carbon (TOC), and theoretical oxygen demand (ThOD). 

Organic Carbon. The total organic carbon (TOC) in a water sample is determined by injecting a microliter sample into a heated, packed tube in a stream of oxygen. The water is vapori2ed and carbon is converted to carbon dioxide, which is detected with a nondispersive infrared analy2er. 

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