Free chlorine residuals

Continuous chlorination - free residual Most effective Most costly Not always technically or economically feasible due to high chlorine demand... 

Intermittent chlorination - free residual Often effective Less costly than continuous chlorination... 

Bromine free residual measurements. Chlorine and bromine can be detected and differentiated using the DPD test with the addition of 10% glycine. Because most samples will contain a mixture of both free chlorine and free bromine, both species must be measured. Follow the DPD procedure for chlorine free residuals. Perform the test twice, adding glycine to the second sample. The first measurement will provide a total free residual, a mixture of free chlorine and free bromine. The second measurement will consist of free bromine only. Subtract the second measurement from the first to obtain the amount of free chlorine in the sample. 

Continuous chlorination of a cooling water system often seems most pmdent for microbial slime control. However, it is economically difficult to maintain a continuous free residual in some systems, especially those with process leaks. In some high demand systems it is often impossible to achieve a free residual, and a combined residual must be accepted. In addition, high chlorine feed rates, with or without high residuals, can increase system metal corrosion and tower wood decay. Supplementing with nonoxidizing antimicrobials is preferable to high chlorination rates. 

Water from cooling tower pump suction, pH 8.6-8.8, pressure 20-30 psi (140-210 kPa), flow 2-5 ft/s (0.2 to 1.5 m/s). Dispersant, 1-3 ppm tolyltriazole, sodium hypochlorite 2 hr/day to 0.8 free residual chlorine 0.6-0.8 ppm total zinc and 0.1-0.2 ppm soluble zinc. Free chlorine maintained at 1 ppm for 5 consecutive days/month during the summer. Chemical treatment started after 2 years of no treatment. Water conductivity -612 ( imhos/cm), turbidity 27 NTU (nephelometric turbidity units), chloride 110 ppm, sulfate 50 ppm, carbonate alkalinity (CaCOa) 27 ppm, bicarbonate alkalinity (CaCOs) 118 ppm... 

Environment Water treatment was chrome-zinc for the first 6 years and orthophosphate for the next 5 years. Free residual chlorine 0.1-0.3 ppm filtered orthophosphate 10-17 ppm, 6-8 cycles calcium <200 ppm, 200°F (93°C), pressure 50 psi (0.3 MPa). 

Water chlorination is carried out by using both free and combined residuals. The latter involves chlorine application to produce chloramine with natural or added ammonia. Anhydrous ammonia is used if insufficient natural ammonia is present in the wastewater. Although the combined residual is less effective than free chlorine as a disinfectant, its most common application is as a post-treatment following free residual chlorination to provide initial disinfection. 

The sum of hypochlorous acid and hypochlorine ion is what is measured as free residual chlorine. The hypochlorous acid is a 20 times stronger biocide that the OCl-form. 

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). 

The surveyed data also indicate that there were net increases in all of the following compounds total dissolved solids, total suspended solids, total organic carbon, total residual chlorine, free available chlorine 2,4-dichlorophenol, 1,2-dichlorobenzene, phenolics, chromium, lead, copper, mercury, silver, iron, arsenic, zinc, barium, calcium, manganese, sodium, methyl chloride, aluminum, boron, and titanium. 

Site number Date sampled Type of source Source-water quality Chlorine Free chlorine Residual (mg/L) Plant Finish Water concentration ( g/L) ... 

Free residual chlorine concentration leaving the treatment plant as finished water. 

Most commonly, gaseous chlorine is added daily to large cooling systems, whereupon it combines with all possible reactants, as measured by the chlorine demand. When this demand has been satisfied, the breakpoint is reached, and a continuous free residual of chlorine is then permitted to... 

Intermittent free residuals may exist at levels of 0.3 to 1.0 ppm, depending on the particular cooling system dynamics, which, as has been said previously, may present additional corrosion risks if the free reserve is too high. Good control of chlorine is essential ... 

The first is that the oxidation mechanism of organics in WEO occurs directly at the electrode surface, without evolving intermediate reactions that form chlorinated compounds, and that can be supported by the fact that free residual chlorine is not detected in the effluent samples for all electrolysis conducted at temperatures higher... 

The amount of dosage specified is ordinarily determined from the residual in the ozonated water leaving the contact tanks. Residuals are determined by the standard o-tolidine arsenite test (1), as specified for free residual chlorine. Tests are made on the site, immediately on sampling, not after delay due to return to the laboratory. This is very important because of the rapid change in residual. 

Determined by standard o-tolidine-arsenite method for free residual chlorine (I). Determined by counts on agar, at 37° C. for 24 hours. 

Since 1952, application of chlorine before filtration, to reduce the postdosage required to produce free residual in distribution, has made removal figures noncomparable. 

Care should be taken not to exceed chlorine-to-ammonia ratios of 5 to 1. This is the breakpoint curve above which aU ammonia is removed, chloramines are absent, and free residual chlorine is present. 

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... 

Equipment may be sterilized or disinfected by heat, chemical disinfection or a combination of both. Many tanks and reaction vessels are sterilized by steam under pressure, and small pieces of equipment and fittings may be autoclaved, but it is important that the steam has access to all surfaces. Equipment used to manufacture and pack dry powder is often sterilized by dry heat. Chemical disinfectants commonly include sodium hypochlorite and organochlorines at 50-100 ppm free residual chlorine, QACs (0.1-0.2%), 70% (v/v) ethanol in water and 1% (v/v) formaldehyde solution. The... 

Molecular chlorine, CI2, is an ideal chemical for delignification as it is cost-efficient and has reasonable selectivity, well capable of removing 75-90% of the residual lignin in a single stage. However its undesirable effects - waste water with chlorides that is corrosive, and a tiny by-product of chlorinated organic compounds -means that molecular chlorine has been abandoned entirely in some countries and where it is still used this is often in conjunction with chlorine dioxide (D) whose environmental footprint is some 2.6 times smaller. Today, more than 75% of pulps are bleached without any molecular chlorine. These are described as elemental chlorine-free (ECF). Only c. 6% of bleached pulps are total chlorine-free (TCF),... 

All the foregoing precautions in connection with pre-chlorination relate to the practice of free-residual chlorination or superchlorination. When chlorine is applied in combination with ammonia to form chloramines, little or no reaction with carbon occurs. Furthermore, chloramines are less likely to form those chlorinous substances that are difficult to adsorb on carbon. 

Because the chlorine can react with many organic substances found in water systems, there is a "chlorine demand" that will affect the biocidal activity of a particular dose. It is usually necessary to add excess chlorine in order to leave a free residual of chlorine in the system to ensure efficient biocidal action. Some comments on chlorine treatment programmes are contained in Table 14.11 [Betz Laboratories Inc. 1976]. 

A silver distillation flask equipped with a silver dropping funnel is placed in an ice-salt bath. Anhydrous HF (50 g.) is distilled into the flask through the side arm. A copper dryii tube filled with KF is then attached to the side arm, in order to absorb the entrained HF. Then HSO Cl is introduced from the dropping funnel into the flask. The reaction starts immediately and a imiform stream of HCl is given off. After completion of the reaction the excess HF and HCl are removed in a stream of dry air, while slowly heating to 110°C. The residue left in the flask is chlorine-free HSQjF. 

Up to 300 g. of oxychloride-free sublimed ThCU may be reacted at 500°C with vacuum-distilled Na (25% excess) in a welded iron bomb (see method I, section on titanium). The iron crucible should be filled with the reaction mixture in the same way as in the reaction between ZrCU and Na, that is, layer by layer. Following the reaction, the bomb is completely cooled, opened and the reaction product treated, first with alcohol (to remove the excess Na), then with water (always maintaining the solution on the alkaline side). After complete removal of the chlorine, the residue is treated with 2N HNO3 to dissolve any Th(OH)4 which may be present, filtered with suction, thoroughly washed with water, alcohol and ether, and dried in vacuxam at 300°C. The metal yield is 55%, in the form of lead-gray platelets and pellets. The coarsest particles are also the purest and contain 0.1% O (1% ThOs). 

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