1. Chemistry of Disinfection By-Product Formation

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

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)

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-trichloroprop
  anone (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