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TRIHALOMETHANES

TRIHALOMETHANES. “TRI”= MEANING THREE SITES. “HALO” = FROM THE HALOGEN GROUP. “METHANE” = DERIVED FROM METHANE. H. CL. c. C. CL. H. H. CL. H. TRIHALOMETHANE. METHANE. TRIHALOMETHANES. ORGANICS IN THE SOURCE WATER SUPPLY THE METHANE GROUP

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TRIHALOMETHANES

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  1. TRIHALOMETHANES “TRI”= MEANING THREE SITES “HALO” = FROM THE HALOGEN GROUP “METHANE” = DERIVED FROM METHANE H CL c C CL H H CL H TRIHALOMETHANE METHANE

  2. TRIHALOMETHANES • ORGANICS IN THE SOURCE WATER SUPPLY THE METHANE GROUP • HALOGENS SUCH AS CHLORINE OR BROMINE ARE STRONG OXIDANTS • THE HALOGENS REPLACE THE HYDROGENS ON THE METHANE PORTION OF THE ORGANIC

  3. THE FOUR MOST COMMON THM’S • CHLOROFORM - CHCL3 • BROMOFORM - CHBr3 • BROMODICHLOROMETHANE – CHBrCL2 • DIBROMOCHLOROMETHANE - CHBr2CL

  4. TOTAL TRIHALOMETHANES MCL IS 0.10 mg/l (ppm) OR 100 ug/l (ppb) SUM OF THE CONCENTRATIONS OF THE FOUR THM’S

  5. TRIHALOMETHANES • THINK OF ORGANICS AS A “TEA BAG” IN HOT WATER • THE CHLORINE FROM DISINFECTION OR NATURALLY OCCURRING BROMIDE REACTS WITH THE ORGANICS-REPLACING THE HYDROGEN ATOMS WITH CHLORINE AND/OR BROMINE ATOMS • TRIHALOMETHANES ARE VOLATILE - LIKE GASOLINE VAPORS

  6. TEMPERATURE-HIGHER TEMP’S. FORM THM’S FASTER CONTACT TIME-THE LONGER THE OXIDANT (CL,BR) IS IN CONTACT,THE GREATER THE THM’S (THEY INCREASE IN DEAD END MAINS,ETC.) PH –THE HIGHER THE PH , THE FASTER THE PRODUCTION OF THM’S THE TYPE AND CONCENTRATION OF PRE-CURSORS (ORGANICS) IS IMPORTANT THM FORMATION IS AFFECTED BY:

  7. ALTERNATIVE DISINFECTANTS: NO FREE CHLORINE=NO THM’S • OZONE • CHLORINE DIOXIDE • CHLORAMINES

  8. TREATMENT OF FORMED THM’S • OXIDATION – HAS NOT BEEN VERY SUCCESSFUL. OZONE/U.V. MAY HELP-BUT IS EXPENSIVE. • AERATION –THIS WORKS SINCE THM’S ARE VOLATILE. FORCED TYPE AERATION WORKS BEST. • ADSORPTION – CAN BE ATTACHED TO THE SURFACE OF ACTIVATED CARBON. CHLOROFORM IS DIFFICULT TO REMOVE IN THIS MANNER.

  9. REMOVAL OF THM PRECURSORS • AERATION-DOES NOT WORK ON PRE-CURSORS-THEY ARE NOT VOLATILE (FORMED THM’S ARE) • CLARIFICATION-WORKS IF CHLORINATION IS DONE AFTER CLARIFICATION • ADSORPTION-GRANULATED ACTIVATED CARBON WORKS BUT IS EXPENSIVE • ION EXCHANGE-EXCHANGE RESINS WORK BUT ARE EXPENSIVE

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