Performance Of The Bioburden Testing Clarified
TVC Stands for ‘total viable count’, a lab test that indicates the degree of heterotrophic organisms within a sample. Heterotrophs are a large group of organisms which can be further divided into parasites, yeasts, bacteria and molds. Hence, the results of a TVC test may give an indicator into the ‘general level’ of contamination in a system. Heterotrophic organisms use organic carbon for propagation and Proliferation which supports the rationale for the selected growth media used in the lab –‘yeast extract agar’. Due to the diverse selection of organisms which may be cultured on this sort of growth media, these evaluations are called ‘on-selective’. Conversely, those used for the culture and enumeration of certain pathogenic bacteria like Pseudomonas aeruginosa and Legionella species require using ‘selective media’ and methodology.
These selective methods are developed to encourage the growth of bioburden testing. The target organism and discourage the development of ‘on-target’ organisms. The number of heterotrophic organisms may give an indication of changes in water quality and as such the amount of these organisms is contained in the Water Supply Water Quality Regulations as one of many ‘index parameters. The Drinking Water Inspectorate DWI advice on ‘wholesomeness’ that accompanies the Regulations provides an indication of the standing of the parameters If an index parameter fails it’s given value, water companies have to investigate the cause and take any remedial action required to make certain that the water supply isn’t, or dAAS not become, unwholesome. TVC Samples could be incubated at different temperatures depending on the environment sampled for example; it is normal to incubate samples from potable water systems in 22˚C or 37˚C.
Whereas the prescribed method for incubating samples from washer disinfector final rinse waters is 30˚C based on the requirements of HTM 01-06. 30˚C is also the prescribed temperature for samples obtained from cooling tower systems according to A Cop L8, HSG 274 Part 1 since it is the temperature that best represents the favourable growth conditions within these risk systems. Since 2016 the 37°C evaluation was dropped from the Water Supply Water Quality Regulations list of indicator parameters, primarily geared toward the drinking water supply business, but the evaluation remains a relevant indicator of water quality in building water systems.