Quality of waste water, surface water, drinking water is expressed, among many other parameters, by concentration of organic carbon present in it. Decomposition of natural organic matters (humic acid, fulvic acid, amines, urea etc.) and/or synthetic contaminant sources (detergents, herbicides, fertilizers etc.) are the source of organic carbon.
Level of contamination is measured by determination of total organic carbon (TOC) concentration. Monitoring of upstream and downstream from a treatment plant gives an idea on performance of water treatment facilities.
Drinking water treatment process includes steps for microbiological cleaning; generally by using halogens to kill bacteria. Water containing organic carbon in turn becomes water containing THMs after halogen treatment, that is more undesirable because of THMs' carcinogenic nature.
Water not only contains organic but also carbon of inorganic nature, mainly carbonates, coming from dissolution of minerals in the source streams. Then, it is a good idea to review classification of carbon characteristics in water. The terms total carbon (TC), total inorganic carbon (TIC) and total organic carbon (TOC) are the main ones. TC refers to all carbon present in the water including both inorganic and organic. TIC covers carbonates, dissolved carbon dioxide or bicarbonate structures. TOC is the contamination coming from decaying organic sources, bacteria etc. In addition, the terms purgeable organic carbon (POC) and nonpurgeable organic carbon (NPOC) are also used for volatile organic compounds and all carbon present after sample acidification respectively.
TOC analysis consists of three operations: sample treatment, reaction, and detection. Sample treatment covers acidification of the sample with an acid solution, that is not itself a carbon source. This process aims all inorganic carbon to be converted to carbon dioxide, additionally be insoluble and vented with the help of a sparging gas, generally air. Treated sample is then sent to the reaction system for oxidation of organics. Carbon dioxide, the reaction product, is analyzed by non-dispersive infrared (NDIR) and/or conductivity detectors.
For the reaction step, oxidation can be performed by using several processes such as, high temperature oxidation, high temperature catalytic oxidation, photo-oxidation, thermo-chemical oxidation, photo-chemical oxidation and electrolytic oxidation.
High temperature catalytic oxidation offers the capability of determining particulate organic carbons, oxidation of hardly-oxidizable molecules as well as oxidation of nitrogen as well so that TN can be analyzed in the same run just by adding a NO detector after the CO2 detector. Pt dispersed on high-surface-area alumina is generally used as catalyst for HTCO, due to its power in bond breaking of carbonaceous matrixes.
TRL-onlineTOC-B analyzer with its dual zone furnace helps efficient oxidation of even very stable carbon bonds via platinum-based catalyst. Thermal bond breakage offered by high temperature zone decreases the load of catalyst. Reaction products are conditioned by cooling followed by moisture, mist, Cu and Sn traps before the analyzer. The NDIR detector specifically measures carbon dioxide content of the effluent stream. Carbon dioxide rate then converted to TOC concentration in the sample. The built-in communication features offer transmission of results to a central station for further monitoring.
NDIR: Non-dispersive infrared
NPOC: Non-purgeable organic carbon
POC: Purgeable organic carbon
TC: Total Carbon
TIC: Total Inorganic Carbon
TOC: Total Organic Carbon