The main cause of taste and odor in drinking water can be attributed to the microbial production of geosmin and MIB, tertiary alcohols produced by members of certain groups of benthic and pelagic aquatic microorganisms. Geosmim and MIB are found in source waters such as lakes, reservoirs and running water like streams and rivers. Cyanobacteria, also called blue-green algae, are some of the major producers of these compounds. The concentration of these compounds in parts per trillion will cause an earthy musty odor.
Cyanobacteria are a photosynthetic nitrogen-fixing bacteria that survive in a wide variety of habitats, soils and water. The photosynthetic pigments in cyanobateria are cyanophycin, allophycocyanine and erythrophycocyanine. Their thalli vary from unicellular to filamentous and filamentous heterocystous. They fix atmospheric nitrogen in aerobic conditions by heterocyst, specialized cells, and in anaerobic conditions.
Post-treatment production of geosmin due to biological activities can result in odor issues downstream of water treatment and throughout the distribution system. Geosmin and 2-MIB are stable compounds and persist in open water in a dissolved form for extended periods of time. The stability of these compounds makes it difficult for conventional filtration to oxidize and eliminate the problem. Early detection can allow treatment and intake modification to eliminate or reduce the intensity of the problem.
Method 6040E is used to analyze taste and odor compounds inclusive of MIB and geosmin. The method consists of three primary steps: a microextraction procedure, followed by the separation and then mass identification of the compounds.
The compounds are volatilized and collected using solid-phase microextraction (SPME) fiber. The fiber is coated with divinylbenzene-carboxen-polydimethylsiloxane cross-link. It is then placed in the headspace above the sample in a closed vessel. This allows the fibers to equilibrate with the aqueous sample.
Sample Separation and Identification
The fiber is then removed from the headspace and inserted directly into the heated injection port on the gas chromatograph (GC). This allows the analytes to desorb into the GC column. The column provides the separation of the analytes of interest from background interferences. Once this is complete, the compounds will be identified. A mass spectrometer is used to identify the compounds.
This technique allows the RWA Lab to be extremely accurate in the determination of the analytes and highly precise in the concentration of each compound.