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Analyze Immediately. Residual Chlorine. Topics…. Background: Chlorine Chemistry Industrial Application NJAC Regulations Summary. Hold Times. 0 - 15 minutes - note time of collection & time of analysis!. Background:. A strong oxidizing agent …therefore, a very reactive element...

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Analyze immediately l.jpg

Analyze Immediately

Residual Chlorine


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Topics….

  • Background: Chlorine Chemistry

  • Industrial Application

  • NJAC Regulations

  • Summary


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Hold Times

  • 0 - 15 minutes - note time of collection & time of analysis!


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Background:

  • A strong oxidizing agent

  • …therefore, a very reactive element...

  • …oxidizes inorganic & organic matter in the water supply & pipe distribution systems...


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Chlorine Chemistry

  • Chlorine gas hydrolyzes in water

    to form hypochlorous acid (HOCl):

    Cl2 + H2O  HOCl + H+ + Cl-

  • H+ ions released in the reaction cause a reduction in pH. (sample is more acidic)


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More Chemistry!!!!

  • Hypochlorous form of chlorine is prime disinfecting agent

  • “free available chlorine” or “free chlorine” refers to both HOCl (hypochlorous acid) & OCl- (hypochlorite ion) - ( portions present in the water.

  • If chlorine added to water containing ammonia, chloramines will form….


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Definition:

  • Chloramines + other chlorine-nitrogen compounds = “free available chlorine”

  • “total residual chlorine”(aka, “residual chlorine”) = free available chlorine + combined available chlorine.


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Chlorine Produced Oxidants(CPO)

  • Synonym for total residual chlorine (TRC)

  • In 1992, NJDEP established reporting level for wastewater

  • The enforceable level for permittees with TRC or CPO effluent limits below 0.1 mg/L is 0.1 mg/L


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Dechlorinating Agents

  • Disinfectant water must be neutralized before release into stream

  • Common dechlorinating agents:

    sulfur dioxide (SO2) sodium bisulfite (NaHSO3)

    sodium sulfite (Na2SO3)

    sodium thiosulfate (Na2S2O3)


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Dechlorinating Agents

  • Sodium thiosulfate (Na2S2O3) - frequently used dechlorinating agent

  • Excessive use of other dechlorinating agents (sodium sulfite or sodium bisulfite) can cause low O2 levels in waterways.


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NJAC Regulations

  • Methods: EPA 330.1 - 5, SM 4500-CL B through G.

  • new calibration curve prepared intially or quarterly

  • 1 reagent blank & 5 stds.

  • calibration coefficient >0.995.


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NJAC Regulations

  • Lab shall verify the calibration curve with the calibration check std.(CCS), daily or after every 20 samples, whichever is more frequent

  • CCS must have a concentration at or near the middle of the concentration range of the calibration curve.


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NJAC 7:18-5.5(c)4

  • Lab must record all data used in determining the calibration curve

  • Signed by analyst

  • Record:

    -date of calibration

    -ID of standards. -standard conc.


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Caveats

  • When using chlorine kits…

  • measuring free chlorine - 1 minute test….

  • Versus a 2 - 3 minute test for measuring total chlorine (follow mfg. instructions)

  • Wastewater reporting limit (RL) < 0.1ppm, per NJDEP 1992 letter to permittees .


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Summary

  • Chlorine is useful in:

    * water treatment - to maintain a residual to kill bacteria

    * waste water treatment plants - chlorine is used to destroy pathogens, then chlorine is removed from water prior to discharge into waterway

  • Measurement of residual chlorine gives a snapshot of the chlorine present in water, which can act as an oxidant & which can be hazardous to aquatic life.


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Thank you...

...for your patience, time and attention today!!!


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