1 / 24

ENVE 201 Environmental Engineering Chemistry 1

ENVE 201 Environmental Engineering Chemistry 1 . CHLORINATION Dr. Aslıhan Kerç. Chlorination. Disinfection of public water supplies and wastewater effluents . To prevent spread of water borne diseases (?) Cholara, typhoid  by contamination of drinking water with wastewater

joben
Download Presentation

ENVE 201 Environmental Engineering Chemistry 1

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. ENVE 201EnvironmentalEngineeringChemistry 1 CHLORINATION Dr. Aslıhan Kerç

  2. Chlorination • Disinfection of publicwatersuppliesandwastewatereffluents. • To prevent spread of water borne diseases (?) Cholara, typhoid  by contamination of drinking water with wastewater ChlorinationformsTHMs

  3. Alternative disinfectants : Chlorine dioxide Ozone Emergency chlorination w/hypochlorites (1850) Continuous chlorination of public water supplies  1904 ( Calcium Hypochloride)

  4. Calcium Hypochloride instable during storage limited usage Development of gaseous chlorine feeding facilities increased use Continual decline of waterborne disease

  5. Current increase in waterborne diseases: • Giardiasis • Cryptosporidium • Infectious Hepatisis ( viral infection ) Protozoa

  6. Chlorine Chemistry Chlorine compound used in disinfection • Chlorine gas Cl2 • Calcium Hypochlorite Ca(OCl)2 • Sodium hypochlorite NaOCl • Chlorine dioxide ClO2 (Cl- is not a disinfectant) For small applications

  7. Cl2 when applied to water  forms hypochlorous acid and hydrochloric acid Cl2 + H2O ↔ HOCl + H+ +Cl- (1) Stability constant for this rxn K = [HOCl][H+] [Cl-] / [Cl2] = 4.5*10 -4 @25 ° C

  8. Ionization : HOCl ↔ H+ + OCl- (2) K = [H+] [OCl-] / [HOCl] = 2.9* 10-8 @ 25 ° C Free available chlorine = [HOCl] + [OCl-] Variable w / temperature

  9. Distribution between these species is important • Killing effiency of HOCl is 40 -80 times larger than OCl - . Lower pH favors HOCl. • HOCl = Hypochlorous acid • OCl - = Hypochloride ion

  10. Percentage distribution of HOCl and OCl - : [HOCl]/ ([HOCl] + [OCl -] = 1 / ( 1+ ([OCl -] / [HOCl] )) = 1 / (1 + (Ki/ [H+] Hypochlorite salts : Ca(OCl)2 + 2H2O ↔ 2HOCl + Ca(OH)2 NaOCl + H2O ↔ HOCl+NaOH

  11. Rxn(1) is dominated by Cl2. Obnoxious comp. NCl3 may form requires high quality water • For Chlorinator feed water use high quality water • To avoid localized low pH  flash mixing

  12. AbovepH4  equilibrium (1) shiftstoright. • Cl2decreasepH • HypochloritesincreasepH Rxns. with impurities in water: • Cl2andHOClreactwithammoniaandhumicmaterial.

  13. Rxns with ammonia : • Ammonium ion is in equilibrium with ammonia and hydrogen ion. NH4+↔ NH3 + H+ • NH3 react with Cl2 or HOCl (hypochlorous acid) • Rxns are dependent on pH , temperature , contact time , and Cl2 /NH3 ratio

  14. Dominant Species : • Monochloramine (NH2Cl) and Dichloramine (NHCl2)  combined available chlorine • Chlorinereadilyreactswithreducingagents. • Fe2+ , Mn 2+ , H2S , organic matter : Chlorine is reduced to Cl. H2S + Cl2 2HCl + S

  15. Thesesubstancesincreasechlorinedemand. Cl2 + Phenols Produce mono-, di-, Trichlorophenols  producetaste , odor • Cl2alsoreactswithotherhalogens Br- + HOCl HOBr + Cl- • HOBr : Hypobromousacid

  16. Cl2andHOBrreactswithhumicsubstance  Halogenated organics. THMs Suspected human carcinogens. • Maximum contaminant level 100 µg/L  80µg/L Alternative disinfectants ?

  17. Cl2 is the only disinfectant producing protective residual within the distribution systems. Factors important in disinfection : • Time to contact • Concentration Kill α Cn * t

  18. Generalized curve obtained during breakpoint chlorination

  19. Break Point Chlorination

  20. Break Point Chlorination • Cl2 /NH3 ratio 1:1 for the formation of mono , dichloroamines. • Further increase in mole ratio  trichloramine, oxidation of part of ammonia to N2 or NO3-. • These rxns. are completed at mole ratio 1.5:1 • Chloramine residuals maximum @1:1mol • Then decline to a minimum till 1,5:1

  21. Breakpoint Chlorination • Chlorination of a water to the extent that all the ammonia is converted to N2 or higher oxidation states. Theoretically 3 mole chlorine  conversion to trichloramine 4 mole chlorine complete oxidation to nitrate 2NH3 +3Cl2N2 +6H++ 6Cl-

  22. Breakpoint chlorination  for better disinfection, required to obtain free chlorine residual , if ammonia is present. • Method of ammonia removal in ww • Combined chlorine residuals  Longer lasting ( final treatment with ammonia ) • Chlorine demand : Amount of chlorine that must be added to reach a desired level of residual.

  23. Chlorine Residual Determination • Old Methods  total chlorine • New Methods  free and combined chlorine Total Chlorine Residual • Measurement depend on measuring the oxidizing power • Other oxidizing agents present may interfere  manganese, nitrites

  24. Starch – Iodide Method : • Oxidizing power of free and combined chlorine to convert iodide to iodine. Cl2 +2I-I2+ 2Cl- I2 + starch blue color • Blue color  shows the presence of free chlorine.

More Related