Chlorine concentration

Toxic or malodorous pollutants can be removed from industrial gas streams by reaction with hydrogen peroxide (174,175). Many Hquid-phase methods have been patented for the removal of NO gases (138,142,174,176—178), sulfur dioxide, reduced sulfur compounds, amines (154,171,172), and phenols (169). Other effluent treatments include the reduction of biological oxygen demand (BOD) and COD, color, odor (142,179,180), and chlorine concentration. 

Internal surfaces were covered by loosely adherent corrosion product and deposit. Much of the corrosion product was cuprous oxide. Substantial amounts of iron, silicon, aluminum, zinc, and nickel were also found. Not unexpectedly, chlorine concentrations up to 2% by weight were present sulfur concentrations of about 1% were also found. 

The toxicity of chlorine residuals to aquatic life has been well documented. Studies indicate that at chlorine concentrations in excess of 0.01 mg/1, serious hazard to marine and estuarine life exists. This has led to the dechlorination of wastewaters before they are discharged into surface water bodies. In addition to being toxic to aquatic life, residuals of chlorine can produce halogenated organic compounds that are potentially toxic to man. Trihalomelhanes (chloroform and bromoform), which are carcinogens, are produced by chlorination. 

A major disadvantage of this system is the limitation of the single-pass gas-chlorination phase. Unless increased pressure is used, this equipment is unable to achieve higher concentrations of chlorine as an aid to a more complete and controllable reaction with the chlorite ion. The French have developed a variation of this process using a multiple-pass enrichment loop on the chlorinator to achieve a much higher concentration of chlorine and thereby quickly attain the optimum pH for maximum conversion to chlorine dioxide. By using a multiple-pass recirculation system, the chlorine solution concentrates to a level of 5-6 g/1. At this concentration, the pH of the solution reduces to 3.0 and thereby provides the low pH level necessary for efficient chlorine dioxide production. A single pass results in a chlorine concentration in water of about 1 g/1, which produces a pH of 4 to 5. If sodium chlorite solution is added at this pH, only about 60 percent yield of chlorine dioxide is achieved. The remainder is unreacted chlorine (in solution) and... 

Figure 2.9. Change of the work function (A) with increasing chlorine concentration on an initially clean Pt(l 11) surface at room temperature.17 Reprinted with permission from Elsevier Science.

Figure 2.10, Increase in work function (AO) with increasing oxygen concentration up to 3.8xl014 O atoms cm 2 (circles) at room temperature. The squares show the change in work function (AO) with increasing total (oxygen plus chlorine) concentration, when chlorine is dosed on the saturated oxygen adlayer at room temperature.37 Reprinted with permission from Elsevier Science.

A methane/chlorine mixture detonates if the chlorine concentration is greater than 20%. 

Figure 10.31 Influence of active chlorine concentration on AOX content and whiteness [247]...

Space time (sec) Effluent chlorine concentration (moles/cm3)... 

In the sodium borate solution containing bromide, when the pH 4 buffer is added before the potassium iodate solution, titrations give low total residual chlorine concentrations. This loss increases with the amount of stirring time between the addition of the reagents. Even for a stirring time of 10 seconds, there is a loss of about 17% of the total residual chlorine. If the solution were stirred for 30 min, 85% of the chlorine would have disappeared. The concentration of total residual chlorine determined by the reference methods does not change throughout the experiment. This implies that this loss of chlorine does not occur in the reaction vessel, but in the titration cell as a result of the analytical procedure. 

If potassium iodide is added first, and then the solution is stirred, acidified and titrated, the loss of residual chlorine is reduced, although still significant. The loss again increases monotonically with stirring for 20 min. However, for a stirring time of 1 minute or less, the loss is not detectable within the uncertainty of the analytical method. There is a loss of chlorine whether the sample is stirred in the titrator or on a stirrer, although the loss seems smaller in the latter case. For a stirring time of 20 min, only 24% of the residual chlorine is lost. Moreover, titrations performed at pH 2 and pH 4 yield the same residual chlorine concentrations. 

The approximate chlorine concentration in the original water sample. 

None No flow -chlorination loop Pump failure. Loss of electric power to pump. No chlorine flow to tower basin. Low chlorine concentration in tower basin. Chlorination pump malfunction alarm. 1 ... 

Here, [HOCl]tot refers to the total reactive chlorine concentration, [Cl2] plus [HOC1]. The three terms in this rate law were attributed to the following three rate-limiting steps ... 

Table 3. Comparison of organo chlorine concentrations (mean and range in parenthesis, p,g/g of wet weight) species in the blubber of male Caspian seals with those in other seals collected in 1980s and 1990s from various areas (Hall et al., 2002). 

Information gathering The town s sewage plant discharge is located near the section of the river could the chlorine concentration from the treatment facility be too high Even low levels can be toxic, not only to fish directly, but also to many organisms lower in the food chain that would ultimately kill the fish. 

Product yields in irradiated hydrogen halides are subject to the elfects of back reactions, particularly those involving the halogen molecules. These effects are most serious in the case of HC1, where a 20 % reduction in yield is observed at chlorine concentrations as low as 0.30 mole %86,88. In the more recent studies of the X- and y-radiolysis of HC1 and HBr percentage conversions were kept below 1 x 10 2 mole%. Under these conditions product yields were dose independent, showing that back reactions were negligible. 

Chromatography High SO brine 0 0 0 Easy operation, removal of chlorate. No chemicals. Restriction of effective chlorine concentration. Caution with heat shock. Large amount of soft water required. 

RNDS fluidised bed adsorption HCI and NaOH High S04, brine 0 0 0 Low S04 level. Low running cost. Restriction of effective chlorine concentration. 

Production of hypochlorite takes place in a two-step absorption unit in which 23% caustic solution is fed counter-currently to the chlorine feed-stream. In the first step -the liquid jet-loop reactor - about 90% of the chlorine is converted to hypochlorite. In step two - a packed column - a very efficient absorption [1-3] is carried out in which the chlorine concentration in the off-gas is reduced to <1 ppm. The operating window of this apparatus with respect to chlorine load is quite large and varies from 100 to 6000 kg h-1 of chlorine. This high capacity is necessary for the consumption of peak loads from the electrolysis plant during short time periods. During start-up or shutdown of one electrolyser the total chlorine peak load can vary from 100 to 300 kg in just a few minutes. 

The hypochlorite produced has an active chlorine concentration of 160-180 g l-1 and a free caustic concentration of 4-8 g l-1. Figure 25.1 illustrates the simplified layout of the two-step chlorine destruction unit. All measurements are carried out under steady-state conditions under different peak loads of chlorine. 

Chlorine dioxide can be formed out of the chlorite by either of the reactions described by Equation 25.3 or 25.8. Equation 25.1 describes the chlorite formation. The chlorine concentration in the liquid is normally very low as the reaction with caustic (Equation 25.4) is very fast. The concentration of chlorine and/or hypo-chlorous acid HOCl can increase on depletion of hydroxide ions in the liquid. As in step two of the hypochlorite unit, the caustic concentration is in the order of 4-10 g l-1 and it is possible to conclude that at the gas-liquid interface the concentration might be quite low owing to the fast reaction with chlorine. 

Figure 25.5 plots the results of the same experiments with a lower active chlorine concentration. Compared to the 170 g L1 of hypochlorite solution, the emission peaks here are lower with a 30% reduction. The same effect is seen with the steady-state emission experiments, with a higher hypochlorite concentration giving higher emission values under the same process conditions. 

A further experiment was performed with an extremely high caustic concentration of 38 g l-1 and an active chlorine concentration of 160 g L1. The results are shown in... 

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