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... • …oxidizes inorganic & organic matter in the water supply & pipe distribution systems...
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)
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….
Definition: • Chloramines + other chlorine-nitrogen compounds = “free available chlorine” • “total residual chlorine”(aka, “residual chlorine”) = free available chlorine + combined available chlorine.
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
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)
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.
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.
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.
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.
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 .
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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