Residual chlorine levels

If the water is found fit for consumption, with respect to both its mineral and biological content, the problem of sanitization can still arise. Public supply invariably has a very small residual chlorine level. This suppresses biological growth and maintains water quality even when the line is stagnant. As with other forms of treatment, the scale of private supply is usually too small to allow good control of chlorinating equipment. 

Sodium hypochlorite and chlorine gas are the most common agents for treating the water supply itself, and the concentration employed depends both upon the dwell time and the chlorine demand of the water. For most purposes a free residual chlorine level of 0.5-5 ppm is adequate. For storage vessels, pipelines, pumps and outlets a higher level of 50-100 ppm may be necessary, but it is usually necessary to use a descaling agent before disinfection in areas where the water is hard. Distilled, deionized and RO systems and pipelines may be treated with sodium hypochlorite or 1% formaldehyde solution. With deionized systems it is usual to exhaust the resin beds with brine before sterilization with formaldehyde to prevent its inactivation to... 

The % available chlorine from calcium hypochlorite by definition includes CI2, HCIO, and OCl (but not Cl ), is 99.2%, or nearly the same effectiveness on a weight for weight basis as treating with elemental chlorine [9]. As long as the residual chlorine level used with hypochlorite salt disinfections is the same as with chlorine gas, there is no difference in relative effectiveness. 

Preuse validation of deionizing systems used to produce purified water should include consideration of such factors as microbial quality of feed water (and residual chlorine levels of feed water where applicable), surface area of ion-exchange resin beds, temperature range of water during processing, operational range of flow rates, recirculation systems to minimize intermittent use and low flow, frequency of use, quality of regenerant chemicals, and frequency and method of sanitization. 

Effect of bleaching agents Chlorinated oxidizing agents carmot be used in enzymatic HDDs, even in the prewash cycle. The residual chlorine level in the washing bath is enough to quickly destroy the enzyme activity. For example, the activity of Novo s protease Alcalase disappears after 5 min at 38°C (100 F) at about 2 ppm available chlorine [10]. 

High residual chlorine levels. Above 2 or 3 ppm is considered excessive. Occasionally shocking the tower with chlorine is common practice, but should be done less than once per week. 

NHCI2 + HOCl iVC/3 (nitrogen trichloride) + H2O The fraction of each type of chloramines present is dqtendent on the chlorine to ammonia ratio as well as the pH. Ehie to taste and odor issues with dichloramine and nitrogen trichloride, monochloramine is typically the prominent species present for chloramines disinfection [5]. The maximum EPA residual chlorine level is 4 ppm with actual usage levels typically much lower. 

Industrial Hquid chlorine is routinely analy2ed for moisture, chlorine, other gaseous components, NCl, and mercury foUowing estabHshed procedures (10,79). Moisture and residue content in Hquid chlorine is determined by evaporation at 20°C foUowed by gravimetric measurement of the residue. Eree chlorine levels are estimated quantitatively by thiosulfate titration of iodine Hberated from addition of excess acidified potassium iodide to the gas mixture. 

Fig. 7. Toxicity of chlorine to aquatic organisms, (a) Time-dependent mortaUty (50%) of four example species in various levels of total residual chlorine in the laboratory, where for A, A.losa aestivalis and B, Salmogairdnerii r (correlation coefficient of the curve) = —0.96 and for C, P/euroneetesplatessa and D, Salmo trutta r = —0.98. (b) A summary of chlorine toxicity to freshwater species, indicating overall no-effect thresholds for acute and chronic exposures. Numbers indicate where more than one test yielded the same result. A different summary figure appHes to marine organisms because of differences in the...

Please indicate which six of the following issues are the most important when considering the comfort and well-being of users and staff. (Air temperature, bacteria, chloramine levels in the water, chlorinous smells, clear water, fresh air, humidity, pH, residual disinfectant level, trihalomethanes, water temperature, water balance)... 

Wong [8] reported that the losses of chlorine are not related to the formation of iodate by the oxidation of iodide by hypobromite. The presence of iodate in seawater may cause significant uncertainty in the determination of small quantities of residual chlorine in water. Determinations of residual chlorine at the 0.01 mg/1 level are of questionable significance. 

When chlorine is used as an oxidant, sodium bisulphite can be used for dechlorination. However, even after the process of dechlorination, free residual chlorine (FRC) may be present in the discharge. The sodium bisulphite used for dechlorination may also cause low levels of dissolved oxygen in the concentrate. For processes which use ozone, not only must it be removed to prevent damage to oxidant sensitive membranes, but also to prevent the formation of bromate, a known carcinogen, in waters containing bromide (Greenlee et al. 2009). 

Any FRC that may be present in the concentrate is known to be toxic, and can have severe impacts on marine hfe. However, following dechlorination with sodium bisulfite, the level of free residual chlorine in the concentrate is often quite low, and quickly decreases after discharge as it dissipates and degrades (Lattemann and Hopner 2008). Chlorine also has potential to form halogenated compounds, and although these can be dangerous to marine life, their concentrations are often well below the FRC concentrations, and hence considered less toxic (Lattemann and Hopner 2008). 

Chlorine Inorganic chemicals Maximum residual disinfectant level (MRDL) 4.0 mg/L Eye/nose irritation, stomach discomfort... 

OSHA regulates the level of chlorine dioxide in workplace air. The occupational exposure limit for an 8-hour workday, 40-hour workweek is 0.1 parts per million (0.28 milligrams per cubic meter [mg/m ]). The EPA has set a maximum contaminant level of 1 milligram per liter (mg/L) for chlorite in drinking water and a goal of 0.8 mg/L for both the maximum residual disinfectant level for chlorine dioxide and the maximum contaminant level for chlorite in drinking water treated with chlorine dioxide as a disinfectant. 

As regulated by EPA (as of January 1, 2002), the maximum residual disinfectant level (MRDL) for chlorine dioxide is 0.8 mg/L (EPA 2002g) the maximum contaminant level (MCE) for its oxidation product, chlorite ion, in drinking water is 1.0 mg/L (EPA 2002e). The levels of chlorite ion in distribution system waters have been reported as part of the Information Collection Rule (ICR), a research project used to support the development of national drinking water standards in the United States (EPA 2002d). 

Quentel F, Elleouet C, Madec C. 1994. Electrochemical determination of low levels of residual chlorine dioxide in tap water. Anal Chim Acta 295 85-91. 

Use of the resins with samples containing free chlorine residual is not recommended. Cheh (35) suggested that chlorine may produce mutagenic artifacts on XAD-4. Our experiment with 2-mg/L chlorine residual appeared to promote the release of irreversibly adsorbed spiked standards Six model compounds were recovered at levels several times higher than those observed in normal blank runs. In addition, many resin artifacts were eluted after exposure to this chlorine level, primarily aromatic and aliphatic acids, aldehydes, and ketones. Stoichiometric dechlorination (ferrous ion) is therefore recommended in order to avoid cross contamination between samples and inclusion of undesirable resin artifacts in the residue to be bioassayed. 

UV can also be used in water reclamation and reuse. An example is the reclamation of swimming pool water. Usually, the swimming pool water reuse process includes coagulation, filtration, clarifier, disinfection, and pH adjustment. The conventional swimming pool disinfection chemical is chlorine however, high concentrations of residual chlorine can be harmful to human health. The UV technology can be placed between the filters and chlorine disinfection unit as a pre-disinfection unit and remove pathogens. Hence, much less amount of chlorine (compared with the process without UV unit) is needed for residue disinfectant level. 

Low levels of residual chlorine may be regarded as a biostat, i.e. preventing colonisation or restricting biofilm development. In a particular laboratory experiment [Kaur et al 1988] chlorine levels as low as 0.2 - 0.6 mg/l inhibited biofilm attachment and growth. The effect of flow velocity and chlorine concentration are shown on Fig. 14.14. 

Holmes [1970] showed that water velocity had an effect on mussel removal. Chlorine residuals of 0.5 mg/l at water velocities in excess of 1.5 m/s accomplished effective mussel removal. With chlorine levels below 0.5 mg/l the critical velocity requirements is in excess of 1.5 m/s. Holmes [1970] suggested that the... 

The chronological pattern of decrease in levels of NDELA might parallel those reported for the decrease in levels of arsenic and DDT in tobacco (and its smoke) when arseni-cals and DDT were no longer used on tobacco in the United States. For example, in 1952, arsenicals were removed from the list of recommended and permissible insecticides for tobacco. By 1968, the arsenic content of U.S.-grown tobacco had decreased to 0.5-1.0 pg/g from the 1951 level of about 50 pg/g of tobacco (1870, 4005) arsenic levels reported in 1975 by Griffin et al. (1391) were 0.5 to 0.9 pg/g of tobacco. Similarly, discontinuance of the use of chlorinated insecticides such as DDT in U.S. tobacco culture in the late 1960s resulted in a gradual and substantial reduction of DDT residues in leaf tobacco. Between 1968 and 1974, the residual DDT level in American flue-cured tobacco decreased rapidly and substantially (1870,4005) from 52 pg/g in 1968 to 6 pg/g in 1970, and to 0.23 pg/g in 1974. 

However, it should be noted that the use in tobacco culture of chlorinated insecticides such as DDD and DDT in the United States was discontinued in the late 1960s. For example, between 1968 and 1974, the residual DDT levels per gram of U.S. flue-cured tobacco decreased rapidly and substantially (over 200-fold) as follows 1968, 52 pg/g 1970, 6 pg/g 1974, 0.23 pg/g [USPHS (4005), lARC (1870)]. 

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