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