Disinfecting, with chlorine

D. Nelson, Swimming Pool Disinfection with Chlorinated-s-tria nerione Products, Special Report 6862, Monsanto Co., St. Louis, Mo., revised May 1975. 

Disinfection The process designed to kill most microorganisms in wastewater, including essentially all pathogenic (disease-causing) bacteria. There are several ways to disinfect, with chlorine being the most frequently used in water and wastewater treatment plants. 

Chlorine dioxide and chlorite usually enter the body when people drink water that has been disinfected with chlorine dioxide. It is not likely that you would breathe air containing dangerous levels of chlorine dioxide, but if you did, it could be absorbed across your lungs. You are not likely to encounter chlorite in the air you breathe. It is not known whether chlorine dioxide or chlorite on your skin would be absorbed to any great extent. 

Kallen and Robert (2000) found no adverse effects on congenital malformations, childhood cancer, infant mortality, low Apgar score, neonatal jaundice, or neonatal hypothyroidism among infants and children who lived in areas where drinking water was disinfected with chlorine dioxide, compared to controls living in... 

Cowley G. 2000. Disinfection with chlorine dioxide. J New Engl Water Works Assoc 114(4) 264-270. 

Disinfection with Chlorine and Chlorine Dioxide. The comparison of the mutagenic activity of the DCM extract before and after disinfection treatment was studied by the Wilcoxon test. No statistical conclusions on disinfection effects can be drawn. However, the MeOH extract showed a significant decrease in mutagenic activity for the line 2 chlorine treatment. Comparison of the two disinfection treatments for the nonozonated GAC filtered water (treatment line 4) shows that chlorine disinfection yields greater mutagenic activity of the DCM extract than chlorine dioxide (Table V). 

Disinfection with chlorine dioxide treatment of nonozonated GAC-filtered water was less mutagenic than chlorine treatment. 

Here is an example of a use objective. Drinking water is usually disinfected with chlorine, which kills microorganisms. Unfortunately, chlorine also reacts with organic matter in water to produce disinfection by-products —compounds that might harm humans. A disinfection facility was planning to introduce a new chlorination process and wrote the following analytical use objective ... 

The flux of DOC from terrestrial landscapes to surface runoff has wide-ranging consequences for aquatic chemistry and biology. DOC affects the complexation, solubility, and mobility of metals (Perdue et al., 1976 Driscoll et al., 1988 Martell et al., 1988 see Chapter 8) as well as the adsorption of pesticides to soils (Senesi, 1992 Worrall et al., 1997). Formation of trihalomethanes when drinking water is disinfected with chlorine, a worldwide threat to water supplies, is also linked to DOC concentrations (Siddiqui et al., 1997). DOC attenuates ultraviolet-B (UV-B) radiation and thus provides some protection to aquatic biota from exposure to harmful UV radiation (e.g., Williamson and Zagarese, 1994). Finally, DOC affects the heat balance and thus stratification in lakes, which is an important constraint for aquatic organisms with limited habitats (Schindler et al., 1996, 1997). 

Several operations may be employed to treat water prior to use. Aeration is used to drive off odorous gases, such as H2S, and to oxidize soluble Fe2+ and Mn2+ ions to insoluble forms. Lime is added to remove dissolved calcium (water hardness). A12(S04)3 forms a sticky precipitate of Al(OH)3, which causes very tine particles to settle. Various filtration and settling processes are employed to treat water. Chlorine, Cl2, is added to kill bacteria. Formation of undesirable byproducts of water chlorination may be avoided by disinfection with chlorine dioxide, C102, or ozone, 03. 

Since the discovery by Rook (1974) that chloroform and other halogenated organic compounds are generated when natural waters are disinfected with chlorine, the reactions of DOM with chlorine and other disinfectants have been studied extensively. Many disinfection by-products have now been identified (e.g., Christman et al., 1983 Kronberg et al., 1991 Becher et al., 1992), their concentrations in municipal water systems have been measured (Krasner et al., 1989), THMFP has been measured for many sources of DOM (Jolley et al., 1983 Collins et al., 1986 Reckhow et al., 1990 Owen et al., 1993 Krasner et al., 1996 Minear and Amy, 1996), and adverse elfects on health and reproduction have been investigated (Graves et al., 2001). 

Chlorine in its free state (HOCl + OCl ) is an effective disinfectant and inactivates most microorganisms in a matter of minutes. However, effective disinfection with chlorine requires careful attention to the following factors. 

Consumption of drinking water is the most probable route of exposure to chlorine dioxide and its by-products. Patients undergoing hemodialysis may be directly exposed to chlorine dioxide through dialysis water disinfected with chlorine dioxide. Chlorine dioxide is a gas therefore, inhalation is also an exposure pathway. 

Drinking water has been disinfected with chlorine for approximately 100 years to protect against waterborne infectious diseases. In addition to chlorination, other methods of drinking water disinfection include the use of chlorine dioxide (either alone or in combination with chlorine), the addition of ammonia to chlorine to form chloramines, ozone treatment, oxidation with potassium permanganate, and ultraviolet radiation. Chlorination, however, is by far the most widely used method. Treatment with chlorine has virtually eliminated cholera, typhoid, dysentery, hepatitis A, and other waterborne diseases)54 ... 

As seen from the data, water disinfected with chlorine can have a complex mixture of lipophiles and hydrophiles. The lipophilic THMs can facilitate the absorption of the hydrophilic haloacetic acids, haloace-tonitriles and haloketones. An analogy between the reproductive toxicity and carcinogenicity of DBPs can be drawn. Though no single chlorinated byproduct studied appears to be carcinogenic, there is evidence from animal studies that DBP mixtures are carcinogenicJ4°l... 

Technical solutions have been developed to a number of important environmental problems. One of the most important contributions to human health has been the chemical purification of drinking water, which has nearly eliminated water-borne diseases in developed countries.2 Disinfection with chlorine and ozonation have been used to eliminate pathogens, and advances in membrane science have enabled removal of various substances from water. Many of the technical solutions have been developed in response to unexpected problems created by other technical advances. 

The behavior of MTBE during chlorination has not been studied in literature so far. However, the detection of MTBE in finished drinking water implies that no elimination occurs during conventional disinfection with chlorine [25,60-62]. The only reference of MTBE in combination with chlorine observed a possible interference of residual free chlorine with the analysis of MTBE with SPME and GC/MS detection [63]. 

Balatonfured is located on the north side of Lake Balaton thus the major source raw water is surface water. It is disinfected with chlorine-dioxide. Particularly in the summertime, the water supplier supplements drinking water with untreated karstic water because of higher consumption. The mixing occurs in the pipework, but near the feedstock features of one or the other type of water are dominant. 

Before leaving this sub-section on chlorine as a disinfectant, we should note that the majority of the Asian cities still do use chlorine to disinfect drinking water. The benefits in term of protection from water-borne diseases in Asia far overweigh the possible hazard from, for example, 10 or 20 ppb of trihalomethanes. Disinfection with chlorine may possibly pose a cancer risk in old age no disinfection in the Asian region does mean a substantial chance of dying from typhoid fever or cholera as a child or young adult. However, as we have seen in Table 1, there are different methods of disinfection and we consider some of these alternatives to chlorination. 

Drinking water is often disinfected with chlorine gas, which hydrolyzes to form hypochlorous acid (HCIO), a weak acid but powerful disinfectant ... 

---