Disinfection systems organic acids

Joseph Lister introduced phenol (carbolic acid) as a disinfectant in 1967. It has been the standard disinfectant to which other disinfectants are compared under the same conditions. The result of this comparison is the phenol coefficient. Salmonella typhi, a pathogen of the digestive system, and Staphlococcus aureus, a common wound pathogen, are typically used to determine phenol coefficients. A disinfectant with a phenol coefficient of 1.0 has the same effectiveness as phenol (Dorland s Illustrated Medical Dictionar). A coefficient less than 1.0 means that the disinfectant is less effective than phenol and greater than 1.0 is more effective than phenol. Phenol coefficients are reported separately for the different test organisms. 

Disinfectants are usually only monitored to ensure that disinfection has taken place. Certain disinfectants, such as chlorine, are sometimes monitored at the tap or in the distribution system, as a measure of the quality in distribution. A wide range of potential by-products of disinfection may be formed in treatment, particularly if natural organic matter is present at high concentrations. The most commonly monitored by-products are the trihalomethanes (THMs) formed through chlorination THMs are normally considered to be an adequate marker of the total disinfection by-products from chlorination. Some countries also monitor haloacetic acids, but these are difficult and expensive to analyse because of their high polarity. Bromate is sometimes measured when ozone is used, but its formation relates to bromide concentrations in the raw water and the conditions of ozonation. Analysis can be extremely difficult and monitoring is not usually considered except where standards have been set or on an infrequent basis. 

Phenols (Fig. 17.7) are widely used as disinfectants and preservatives. They have good antimicrobial activity and are rapidly bactericidal but generally are not sporicidal. Their activity is markedly diminished by dilution and is also reduced by organic matter. They are more active at acid pH. The main disadvantages of phenols are their caustic effect on skin and tissues and their systemic toxicity. The... 

In aquatic environments, more research is needed on the chemical speciation of silver to evaluate risk to the organism and its consumers. Most silver criteria formulated for the protection of aquatic life are now expressed as total recoverable silver per liter. But total silver measurements do not provide an accurate assessment of potential hazard. Silver ion (Ag+), for example, is probably the most toxic of all silver chemical species and must be accurately measured in the assessment of silver risks in aquatic environments, perhaps as acid-soluble silver. Little is known of the biocidal properties of Ag + andAg + that are the active ingredients in disinfectants and used increasingly in water purification systems of drinking water and swimming pools. The effects of these silver species on organism health clearly must be researched. Silver interactions with other metals and compounds in solution are not well defined. For example, mixtures of salts of silver and copper markedly increased the survival of oyster embryos, but only when... 

Water natural waters - oxygen and redox chemistry, acid/lDase chemistry and carbonate system drinking water - purification, disinfection, impact of chlorine groundwater - contaminants and remediation wastewater - phosphate, oxygen demand, fate of organic compounds, wastewater treatment (four lectures)... 

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