Disinfection disadvantages

Potassium peroxymonosulfate, introduced in the late 1980s, is finding increasing use as an auxiUary oxidant for shock treatment and oxidation of chloramines. Sodium peroxydisulfate is also being sold for shock treatment, however, it is less reactive than peroxymonosulfate. Mixtures of sodium peroxydisulfate and calcium hypochlorite can be used for shock treatment (28). Disadvantages of peroxymonosulfate and peroxydisulfate are they do not provide a disinfectant residual and peroxymonosulfate oxidizes urea and chloramines to nitrate ion, which is a nutrient for algae. 

The Kelsey-Sykes (KS) test. Having regard to the many disadvantages alleged against the RW and CM tests, attempts were made and published in the early 1960s to find improved test methods. The foundations for the new test were laid by Kelsey et al. in 1965, and with the collaboration of the late G. Sykes and ofisobel M. Maurer, the Kelsey-Sykes test was evolved. This test embodied several principles. Firstly, it was a capacity test. Here a bacterial inoculum was added to the disinfectant in three successive lots at 0, 1 and 5 minutes. This is the principle of a capacity test where the capacity or lack of capacity ofthe disinfectant to destroy successive additions of a bacterial culture is tested. 

Table 20.2 Alternative disinfection methods with their advantages and disadvantages...

Compare the advantages and disadvantages of chlorine gas and ozone gas as disinfectants for municipal water supplies. 

Chlorine was first used to disinfect water in Britain in 1904, after a typhoid epidemic. (Typhoid is a water-borne, contagious illness that is caused by a species of Salmonella bacteria.) Strict limits are necessary because chlorine is ineffective when its concentration is less than 0.1 mg/L. It gives water an unpleasant taste at concentrations above 1.0 mg/L. Chlorine has a disadvantage, however. It can react with other chemicals in the water to form poisonous compounds, such as chloroform, CHCI3. These chemicals may remain in solution even after the entire treatment process. 

The EPA Surface Water Treatment Ruse (SWTR) requires public water supplies, under the direct influence of surface water, to be disinfected. Some disinfectants produce chemical by-products SWTR requires that their concentration remain within the MCL. Currently, one such by-product is trihalomethanes. Water disinfection is effective when combined with conventional treatment, such as coagulation, flocculation, sedimentation, and filtration. The latter is accomplished by sand or diatomaceous earth. The effectiveness of disinfection is evaluated by determining total coliform bacteria which are not pathogenic, but their presence suggests that certain pathogens may have survived. The various chemicals commonly used as disinfectants are presented below and some of their advantages and disadvantages are listed. 

Ionizers, Ionizers generate small concentrations of copper and silver ions (by electrochemical dissolution of a copper—silver electrode) that function as algicide and bactericide, respectively (10). Although the concentration of copper (. 3 ppm) is adequate, the concentration of silver, a poor disinfectant, is very low (<50 ppb). Consequendy chlorine sanitizers are necessary not only for effective disinfection but also for oxidation of swimming pool contaminants. Another disadvantage is that copper and silver ions form colored insoluble precipitates, which can cause staining. 

HOCl is highly effective as an oxidant and as a disinfectant (rapid rate of microbial kill). Disadvantages arise from the nonselectivity. Organic matter is oxidized and HOCl participates in substitution reactions yielding organo chlorine compounds such as chlorophenols and trihalomethanes (e.g., chloroform, CHCI3). In order to circumvent this problem partially, ammonium may be added, to form chloramines ( combined chlorine ), which are less reactive. 

The disadvantages of mercurials for antiseptic and disinfectant uses far outweigh any pos.siblc advantages that they might have. Hence, other more effective and lc.ss potentially toxic agents are preferable. 

US Environmental Protection Agency has compared ultraviolet radiation with other disinfection processes in terms of their technological status (Table 5), disinfectant production (Table 6), operation and maintenance (Table 7), process advantages and disadvantages (Table 8), and applicahon points (Table 9). 

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