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

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