The gold standard for disinfection of water systems has for a long time been the use of free chlorine, usually provided by hypochlorite / DICD or similar product, at a concentration and duration prescribed by BS 6700 (the British Standard for Designing, Installing, Testing and Maintaining Water Systems). The standard details the use of 50 mg/l (ppm) for a contact time of 1 hour after which the level should be retested, with a minimum of 30 mg/l (ppm) indicating successful disinfection, and under 30 mg/l requiring a repeat dose. The majority of contract specifications for routine disinfection work / tank cleaning identify chlorine as the preferred disinfectant.
BS 6700 also refers to �approved disinfectants other than chlorine� and in recent years the use of biocides containing a blend of hydrogen peroxide and silver ions has increased dramatically. Benefits, amongst others, are said to include;
Safe use
Eco friendly
Efficacy against a wide range of bacteria (including Legionella pneumophila)
Removal of biofilm
Cost effective
One of the major benefits to both the client and water treatment contractor is that such biocides do not require neutralizing. Once the chemical is dosed at the required level it can be left in the system, is not harmful if ingested and breaks down to harmless environmentally friendly by products. This reduces disruption to site (less time without water) and reduces the overall amount of water wasted in the disinfection process.
A word of warning, there is only limited peer reviewed evidence on the long term effectiveness of such chemicals, it�s approval for use in public supplies has recently been reviewed and silver has been implicated in a small number of cases where treated water has been used for medical procedures and silver has entered the blood stream.
For more information please see the Tank Cleaning Services section on Nemco�s Website www.nemco-utilities.co.uk
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http://www.articlecity.com/articles/health/article_12456.shtml
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