CHEMSCAN
  • Applications
    • Municipal Water Monitoring >
      • Ammonia Feed
      • Chloramination Control
      • Chlorination
      • Color Analysis
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      • Ion Exchange Breakthrough
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      • Peak Point Chloramination Control
      • Phosphate Sequesterant Feed Control
      • Reservoir Monitoring
      • Security Monitoring
      • TOC Monitoring in Water
      • Well Blending
    • Wastewater Monitoring and Control >
      • Aeration Control and Energy Cost Reduction
      • Biological Nutrient Removal
      • Biological Phosphorus Removal
      • Chemical Phosphorus Removal
      • Chloramination /Breakpoint Avoidance
      • Chlorination/De-Chlorination
      • De-Nitrification Monitoring
      • Nitrification
      • Nutrient Deficiency Analysis
      • Lagoon Discharge
      • SBR Stage Control
      • TOC Monitoring
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  • Products
    • ChemScan Mini Analyzer >
      • mini oP (Ortho Phosphate)
      • mini oP (Ortho Phosphate) Extended Range
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      • mini LoP (Low Ortho Phosphate)
      • mini UV-254
      • mini LowAm (Low Ammonia)
      • mini Mn (Manganese)
      • mini LowMn (Low Manganese)
      • mini LowChlor (Low Chlorine)
      • mini Sulfite
      • mini Ammonia
      • mini FreeAm (Free Ammonia)
      • mini Fe (Iron)
      • mini Ni (Nickel)
      • mini PAA (Peracetic Acid)
      • mini ChlorAm
    • ChemScan mini Accessories
    • ChemScan Process Analyzers >
      • ChemScan 2150/S Chloramination Analyzer
      • ChemScan 2150/DC Chem Feed Analyzer
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      • ChemScan 2150/NoP Chem Feed Analyzer
      • ChemScan 2150/NHoP Nutrient Analyzer
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      • ChemScan UV-3150 Process Analyzer
      • ChemScan 4100 Nutrient Control
      • ChemScan 6101 Nutrient Control
    • ChemScan Process Analyzers with HMI >
      • ChemScan 2250/S HMI Chloramination Analyzer
      • ChemScan 4200 HMI Analyzer
      • ChemScan 3250 HMI Analyzer
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      • ChemScan 2250/N HMI Analyzer
      • ChemScan 2250 HMI Analyzer
      • ChemScan 6201 HMI Analyzer
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Chlorination Control

Rev. 5/98

Statement of the Problem 

Chlorination of water or wastewater is performed to destroy microbiological organisms and also to oxidize nitrogen or sulphur compounds, metals and organic substances. Chlorine will form hypochlorous acid (HOCl) and hypochlorite ion (OCl-) upon introduction to water. The relative percentage of these forms of free chlorine are pH dependent, as shown in Figure 1.

Apparatus

Although the object of disinfection is the destruction of pathogenic organisms, the dosage of chlorine available for disinfection may be affected by the presence of other oxidizable matter that may exert a demand above the demand from pathogens. 

Surface water treatment plants may experience a variable incoming concentration of natural organic matter (NOM) in the form of organic acids. These organic acids may only be partially removed during the treatment process, leaving a variable concentration in the water entering the primary disinfection process. Flow pacing alone may not assure that the necessary free chlorine residual has been established for the required contact period.

Control Strategy

Analysis of free chlorine in the effluent from the primary chlorine contact basin is one strategy for control. This information is fed back to a controller, which adjusts the chlorine feed rate to maintain a target concentration in the effluent. It is important that the analytical technique be able to detect free chlorine (as opposed to combined chlorine). If there is a long contact time, feed back control may not provide a satisfactory response to variable demand conditions.

Where there is a variable demand from oxidizable material other than pathogens, another strategy is to monitor the incoming concentration of oxidizable material and use this information for feed forward or compound loop control of the chlorine feed rate.

In water, NOM can be detected directly by ChemScan. In wastewater, substantial demand can also be exerted from nitrite (NO2), which is another parameter ChemScan can detect without reagents.
Hypochlorite ion has a strong absorbance signature in the ultraviolet wavelength range with a peak absorbance at 292 nm, while Hypochlorous acid has a weaker absorbance signature with a peak at 236 nm. As the pH of the sample is altered, the absorbance signature will rotate at 254 nm as the form of free chlorine is exchanged between HOCl and OCl- forms, as shown in Figure 2.

The ChemScan Process Analyzer uses multiple wavelength light absorbance data to characterize the concentration of free chlorine in a sample of known or stable pH. If the pH is not known or is variable, sample pH can be adjusted to the 4-5 range, where HOCl is 100% of the form or to the 10+ range where OCl- is 100% of the form.

Multiple wavelength absorbance can also be used to measure organics, nutrients or metals that may be present in the influent to chlorination process in order to calculate the effect that these constituents may have on the chlorination process.

Chlorination Control, Copyright ChemScan, Inc.​

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ChemScan, Inc.
2325 Parklawn Dr., Suite I, Waukesha, Wisconsin, USA 53186
​Phone: 262-717-9500
Toll Free: 800-665-7133
  • Applications
    • Municipal Water Monitoring >
      • Ammonia Feed
      • Chloramination Control
      • Chlorination
      • Color Analysis
      • Distribution Monitoring
      • Ion Exchange Breakthrough
      • Natural Organic Matter (NOM) Removal
      • Peak Point Chloramination Control
      • Phosphate Sequesterant Feed Control
      • Reservoir Monitoring
      • Security Monitoring
      • TOC Monitoring in Water
      • Well Blending
    • Wastewater Monitoring and Control >
      • Aeration Control and Energy Cost Reduction
      • Biological Nutrient Removal
      • Biological Phosphorus Removal
      • Chemical Phosphorus Removal
      • Chloramination /Breakpoint Avoidance
      • Chlorination/De-Chlorination
      • De-Nitrification Monitoring
      • Nitrification
      • Nutrient Deficiency Analysis
      • Lagoon Discharge
      • SBR Stage Control
      • TOC Monitoring
      • UV Disinfection Control
    • Industrial Water Treatment >
      • Boiler Water Analysis
      • Cooling Water Analysis (Closed Loop)
    • Industrial Process Monitoring >
      • Electroless Plating
    • ASA Technical Papers (ALL)
    • ChemScan Installation Photos
    • Success Stories
    • ChemScan Webinars
  • Service
    • Contact Service Request Form
    • ChemScan Service Team
    • MSDS
    • Communication Protocols
    • Software Utilities
    • Service Videos
  • Parts
  • Company
    • Terms and Conditions
    • Contact Form (General Inquiry)
    • Contact Service
    • Application Data Sheet
    • Employment Opportunities
    • ChemScan Representatives and Distributors
  • Products
    • ChemScan Mini Analyzer >
      • mini oP (Ortho Phosphate)
      • mini oP (Ortho Phosphate) Extended Range
      • mini Cu (Copper)
      • mini LoP (Low Ortho Phosphate)
      • mini UV-254
      • mini LowAm (Low Ammonia)
      • mini Mn (Manganese)
      • mini LowMn (Low Manganese)
      • mini LowChlor (Low Chlorine)
      • mini Sulfite
      • mini Ammonia
      • mini FreeAm (Free Ammonia)
      • mini Fe (Iron)
      • mini Ni (Nickel)
      • mini PAA (Peracetic Acid)
      • mini ChlorAm
    • ChemScan mini Accessories
    • ChemScan Process Analyzers >
      • ChemScan 2150/S Chloramination Analyzer
      • ChemScan 2150/DC Chem Feed Analyzer
      • ChemScan 2150/N Aeration Rate Analyzer
      • ChemScan 2150/NoP Chem Feed Analyzer
      • ChemScan 2150/NHoP Nutrient Analyzer
      • ChemScan 2150 Process Analyzer
      • ChemScan UV-3150 Process Analyzer
      • ChemScan 4100 Nutrient Control
      • ChemScan 6101 Nutrient Control
    • ChemScan Process Analyzers with HMI >
      • ChemScan 2250/S HMI Chloramination Analyzer
      • ChemScan 4200 HMI Analyzer
      • ChemScan 3250 HMI Analyzer
      • ChemScan 2250/NoP HMI Analyzer
      • ChemScan 2250/NHoP HMI Analyzer
      • ChemScan 2250/N HMI Analyzer
      • ChemScan 2250 HMI Analyzer
      • ChemScan 6201 HMI Analyzer
    • ChemScan Analyzer Accessories
    • ChemScan Sensor Family