Chemical chlorine demand

Chemical Chlorine Demand or Chlorine Binding Capacity... 

The following formula is used to calculate the chemical chlorine demand, or the chlorine binding capacity ... 

The chemical method for the determination of the chemical oxygen demand of non-saline waters involves oxidation of the organic matter with an excess of standard acidic potassium dichromate in the presence of silver sulfate catalyst followed by estimation of unused dichromate by titration with ferrous ammonium sulfate. Unfortunately, in this method, the high concentrations of sodium chloride present in sea water react with potassium dichromate producing chlorine ... 

Consequently the consumption of dichromate is many times higher than that due to organic material in the sample. To complicate matters, any amines in the sample consume and release chlorine in a cyclic process, leading to high chemical oxygen demands. 

Iron ammonium sulfate is an analytical reagent in titrations and colorimetric measurements to measure oxidizing substances, such as chlorine, or to measure the chemical oxygen demand in waste water. The compound is used to prepare Fe(II) standard solution for these analyses. It also is a cahbration... 

Fig. 26.6. U.S. chlorine demand in 2004. (With permission from Chemical Market Associates, Inc.)...

The use of Fenton s reagent for waste water treatment is relatively new compared to its use in mechanistic investigations in organic chemistry.13-15 Fenton s reagent is able to destroy phenols (Figure 5.2), chlorinated phenols and herbicides in water media, as well as reducing chemical oxygen demand in municipal waste. 

Dechlorination is the process of converting highly reactive chlorine from these waters into less reactive chloride ions prior to disposal into receiving streams. Various chemical and nonchemical techniques are currently used for disposal of chlorinated waters by water and wastewater agencies. For example, wastewater treatment plants use sulfur dioxide gas or sodium metabisulfate to dechlorinate treated effluent prior to release into receiving streams. Many water utilities often use passive, non-chemical methods such as discharge to sanitary sewers for disposal of chlorinated waters. Impurities such as organics, iron, and sulfide in the sanitary sewer exert a chlorine demand and neutralize chlorine in the released water. 

The chlorine concentration in stored water gradually decreases with time due to aeration, reaction with sunlight, and reaction with surfaces of holding tanks. A number of utilities store filter backwash water and main disinfection water in holding tanks to allow for residual chlorine decay. On some occasions the chlorine demand of the water is reduced by retention in a holding tank for some time, prior to dechlorination using chemicals. 

When no dechlorination chemical was added, the chlorine concentration decreased from 1.05 to 0.95 mg/L after 1000 feet (Fig. 2). This indicated that only a small amount (0.1 mg/L) of the chloramines dissipated through chlorine demand of paved surfaces. Sodium bisulfite, sodium sulfite, ascorbic acid, and sodium ascorbate neutralized all detectable chlorine to below 0.1 mg/L within 2 ft downstream of the mixing hose (approx 2 s). Sodium thiosulfate neutralized more than 80% of the chlorine within 2 ft. However, chlorine concentrations decreased below 0.1 mg/L (the discharge limit in most states) after about 500 ft (elapsed time 3 min, 2 s). Calcium thiosulfate neutralized 60% of the chlorine within 2 ft and neutralized 90% of the chlorine after 1000 ft (elapsed time 7 min, 10s). 

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