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Understanding Chlorine Residual Analysis in Water Treatment

Delve into the chemistry, industrial applications, and NJAC regulations of residual chlorine analysis. Learn about dechlorinating agents and methods for accurate testing. Ensure compliance and safety in water treatment processes.

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Understanding Chlorine Residual Analysis in Water Treatment

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  1. Analyze Immediately Residual Chlorine

  2. Topics…. • Background: Chlorine Chemistry • Industrial Application • NJAC Regulations • Summary

  3. Hold Times • 0 - 15 minutes - note time of collection & time of analysis!

  4. Background: • A strong oxidizing agent • …therefore, a very reactive element... • …oxidizes inorganic & organic matter in the water supply & pipe distribution systems...

  5. 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)

  6. 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….

  7. Definition: • Chloramines + other chlorine-nitrogen compounds = “free available chlorine” • “total residual chlorine”(aka, “residual chlorine”) = free available chlorine + combined available chlorine.

  8. 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

  9. 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)

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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 .

  15. 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.

  16. Thank you... ...for your patience, time and attention today!!!

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