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1. Chemistry of Disinfection By-Product Formation

1. Chemistry of Disinfection By-Product Formation. Introduction Disinfectant + Precursor  DBPs Chemical disinfectants: Cl 2 , NH 2 Cl, O 3 , ClO 2 DBP Precursors: Natural organic matter (NOM), Br - Parameters affecting DBP formation (Singer, 1994) pH Temperature Time Disinfectant dose

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1. Chemistry of Disinfection By-Product Formation

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  1. 1. Chemistry of Disinfection By-Product Formation • Introduction • Disinfectant + Precursor  DBPs • Chemical disinfectants: Cl2, NH2Cl, O3, ClO2 • DBP Precursors: Natural organic matter (NOM), Br- • Parameters affecting DBP formation (Singer, 1994) • pH • Temperature • Time • Disinfectant dose • Residual • DBPs • Halogen substitution by-products • Oxidation by-products

  2. Major DBPs formed during disinfection of drinking water • Trihalomethanes (THMs) • Chloroform CHCl3 • Bromodichloromethane CHBrCl2 • Dibromochloromethane CHBr2Cl • Bromoform CHBr3 • Haloacetic acids (HAAs) • (Mono)chloroacetic acid CH2ClCOOH • Dichloroacetic acid CHCl2COOH • Trichloroacetic acid CCl3COOH • Bromochloroacetic acid CHBrClCOOH • Bromodichloroacetic acid CBrCl2COOH • Dibromochloroacetic acid CBr2ClCOOH • (Mono)bromoacetic acid CH2BrCOOH • Dibromoacetic acid CHBr2COOH • Tribromoacetic acid CBr3COOH • Haloacetonitriles (HANs) • Dichloroacetonitrile CHCl2CN • Trihloroacetonitrile CCl3CN • Bromochloroacetonitrile CHBrClCN • Dibromoacetonitrile CHBr2CN

  3. Major DBPs formed during disinfection of drinking water • Haloketones (HKs) • 1,1-Dichloroacetone(propanone) CHCl2COCH3 • 1,1,1-Trichloroacetone(propanone) CCl3COCH3 • Miscellaneous chlorinated organic compounds • Chloral hydrate CCl3CH(OH)2 • Chloropicrin CCl3NO2 • Cyanogen halides • Cyanogen chloride ClCN • Cyanogen bromide BrCN • Oxyhalides • Chlorite ClO2- • Chlorate ClO3- • Bromate BrO3- • Aldehydes • Formaldehyde HCHO • Acetaldehyde CH3CHO • Glyoxal OHCCHO • Methyl glyoxal CH3COCHO

  4. Major DBPs formed during disinfection of drinking water • Aldoketo acids • Glyoxylic acid OHCCOOH • Pyruvic acid CH3COCOOH • Ketomalonic acid HOOCCOCOOH • Carboxylic acids • Formate HCOO- • Acetate CH3COO- • Oxalate -OOCCOO- • Maleic acids • 2-tert-Butylmaleic acid • Chlorophenols MX (Mutagen X) H O O C C H C O O H C ( C H ) 3 3

  5. Chloramination can minimize THM formation, but increase CNCl levels • Ozonation: aldehydes, aldoketo acids, carboxylic acids, carboxylic acids, and other biodegradable organic matter (BOM) + BrO3-, brominated by-products • Use of ClO2 • Less TOX formed • Chlorite (ClO2-) and chlorate (ClO3-) formed

  6. Chemistry of DBP Formation • Haloform Reaction • Resorcinol-type moiety of fulvic acids (Rook, 1977): p. 31

  7. Chemistry of DBP Formation • Haloform Reaction • Norwood et al. (1980): Cl2 + selected aromatic comps. (resorcinol type – greatest yield) • HOCl  OH- + Cl+ (electrophile) • Electron-rich sites in organic structures (nucleophiles) – base-catalyzed (high pH) • Activated aromatic rings • Aliphatic -dicarbonyls, pyrrole ring – carbanions • Amino nitrogen Ortho position activated

  8. (-Diketone) (DCAA) (TCAA) (CF) • Chemistry of DBP Formation • Haloform Reaction • Reckhow and Singer (1985)

  9. Chemistry of DBP Formation • Oxidation Reactions • Ozonation (Doré et al., 1988): • Substitution on the aromatic ring  hydroxylation • Reaction on the aliphatic chains  carbonyl • Subsequent reactions  ketones, aldehydes, organic acids, aliphatic compounds, carbon dioxide • Oxidation reactions by O3 and Cl2 • Amino acids  aldehydes (Cloirec and Martin, 1985; p. 35) • ClO2 • With phenols  dicarboxylic acids (e.g., maleic acid, oxalic acid), chlorophenols, p-benzoquinone

  10. Chemistry of DBP Formation • Secondary Effect of Ozonation • Preozonation • Can destroy a portion of the precursors for THMs, TOX, TCAA, and dichloroacetonitrile (DCAN) • However, no net effect on the precursors of DCAA • Increase in the precursors for 1,1,1-trichloropropanone (TCP) • This is caused by the transitory formation of polyhydroxylated aromatic compounds or by the accumulation of methylketone functions that are only slightly reactive with ozone • Ozonation  Chlorination • Acealdehyde  chloroacetaldehyde / chloral hydrate • Scully (1990) • Formaldehyde + chloramine  CNCl (under acidic conditions)

  11. The Effects of DBP Precursors on DBP Formation • The Effects of NOM on DBP Formation • Total organic carbon (TOC) concentration • SUVA (Specific UltraViolet Absorbance): humic content of water • [UV abs (cm-1)  100] / DOC concentration (mg/L) • Humic substances  higher SUVAs and higher DBP formation potential (DBPFP) than the nonhumic fraction • SUVA-to-DOC ratio  a reflection of the aromatic content of the NOM • Positive correlation between TCAA/THM ration and the SUVA • SUVA  degree of conjugation

  12. The Effects of DBP Precursors on DBP Formation • The Effects of Algae on DBP Formation • Both algal biomass and their extracellular products (Hoehn et al., 1990): the latter more formation • Late exponential phase of growth • Algae: a source of amino acids  HANs (e.g., DCAN) • The Effects of Bromide on DBP Formation • Saltwater intrusion, connate (inherent) water, oil-field brines, and industrial and agricultural chemicals • HOCl + Br- HOBr + Cl- • HOCl + HOBr + NOM  DBPs • Increased formation of more brominated DBPs • Increased rate of THM formation • HOBr – more efficient halogenation agent vs. HOCl – more effective oxidant • Ratio of bromide to the average free available chlorine (Cl+) controls bromine substitution: higher ratio – higher content of brominated DBPs

  13. The Effects of Water Quality Parameters on DBP Formation • The Effects of pH and Reaction Time on DBP Formation • Higher pH values • Increased production of chloroform • Decreased formation of nonpurgeable organic chlorine • Decreased formation of TCAA, TCP, and DCAN • Longer reaction time • More formation of THMs • Decreased HAA, chloral hydrate, DCAN, and TCP levels • Result of base-catalyzed hydrolysis of some non-THM DBPs • OH- acts as a nucleophile

  14. The Effects of Water Quality Parameters on DBP Formation • The Effects of temperature and Seasonal Variability on DBP Formation • Seasonal variations: precursors & temperature • Cold (winter): more formation of reactive intermediates (e.g., TCP) • Heavy rainfalls  leaching (discharge) of soil organic matter into water  eutrophic  more precursors • The Effects of Chlorine Dose and Residual on DBP Formation • Higher doses and residuals • More formation of HAAs over THMs • Higher proportion of trihalogenated HAAs • Reduction in the concentration of TCP and DCAN

  15. The Effects of Water Quality Parameters on DBP Formation • The Effects of Water Quality Parameters on DBP Formation Testing • THMFP (or DBPFP) methods • Indirect measurement of the amount of DBP precursors in a water • Seven day incubation • Simulated Distribution System (SDS) testing • Used to predict the actual condition and speciation of DBPs that would form in a distribution system • SDS conditions are site-specific • Uniform Formation Condition (UFC) tests • Stadard temperature • pH 8.0 • Chlorine residual  3 mg/L

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