Transcript 1. Disinfection By-Products: A Historical Perspective

1. Chemistry of Disinfection By-Product Formation
• Introduction
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Disinfectant + Precursor  DBPs
Chemical disinfectants: Cl2, NH2Cl, O3, ClO2
DBP Precursors: Natural organic matter (NOM), BrParameters affecting DBP formation (Singer, 1994)
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pH
Temperature
Time
Disinfectant dose
Residual
– DBPs
• Halogen substitution by-products
• Oxidation by-products
Major DBPs formed during disinfection of drinking water
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Trihalomethanes (THMs)
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CHCl3
CHBrCl2
CHBr2Cl
CHBr3
Haloacetic acids (HAAs)
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Chloroform
Bromodichloromethane
Dibromochloromethane
Bromoform
(Mono)chloroacetic acid
Dichloroacetic acid
Trichloroacetic acid
Bromochloroacetic acid
Bromodichloroacetic acid
Dibromochloroacetic acid
(Mono)bromoacetic acid
Dibromoacetic acid
Tribromoacetic acid
CH2ClCOOH
CHCl2COOH
CCl3COOH
CHBrClCOOH
CBrCl2COOH
CBr2ClCOOH
CH2BrCOOH
CHBr2COOH
CBr3COOH
Haloacetonitriles (HANs)
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Dichloroacetonitrile
Trihloroacetonitrile
Bromochloroacetonitrile
Dibromoacetonitrile
CHCl2CN
CCl3CN
CHBrClCN
CHBr2CN
Major DBPs formed during disinfection of drinking water
• Haloketones (HKs)
– 1,1-Dichloroacetone(propanone)
– 1,1,1-Trichloroacetone(propanone)
CHCl2COCH3
CCl3COCH3
• Miscellaneous chlorinated organic compounds
– Chloral hydrate
– Chloropicrin
• Cyanogen halides
– Cyanogen chloride
– Cyanogen bromide
• Oxyhalides
– Chlorite
– Chlorate
– Bromate
• Aldehydes
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Formaldehyde
Acetaldehyde
Glyoxal
Methyl glyoxal
CCl3CH(OH)2
CCl3NO2
ClCN
BrCN
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ClO2
ClO3BrO3HCHO
CH3CHO
OHCCHO
CH3COCHO
Major DBPs formed during disinfection of drinking water
• Aldoketo acids
– Glyoxylic acid
– Pyruvic acid
– Ketomalonic acid
OHCCOOH
CH3COCOOH
HOOCCOCOOH
• Carboxylic acids
– Formate
– Acetate
– Oxalate
HCOOCH3COO-OOCCOO-
• Maleic acids
HOOC CHCOOH
– 2-tert-Butylmaleic acid
C(CH3)3
• Chlorophenols
OH
Cl
Cl
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Cl2HC
Cl
Cl2HC
Cl
H
HO
Cl
MX (Mutagen X)
O
O
OHC
COOH
• 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 byproducts
• Use of ClO2
– Less TOX formed
– Chlorite (ClO2-) and chlorate (ClO3-) formed
• Chemistry of DBP Formation
– Haloform Reaction
• Resorcinol-type moiety of fulvic acids (Rook, 1977): p.
31
OH
R1
R1
H
R2
OH
R3
HOCl
H2O
COOH
C
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OH
H
C
CCl3
C
R2
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R3
C
Cl
O
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a: T HMs (e.g., chloroform)
b: HAAs (e.g., T CAA) or chloral hydrate [CCl
3CH(OH)2]
c: HKs (haloketones)
Rook, J.J. 1977.Environ. Sci. Technol.
, 11(5): 478.
• 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
N
H
Ortho position activated
• Chemistry of DBP Formation
– Haloform Reaction
• Reckhow and Singer (1985)
(-Diketone)
Fulvic Acid
CHCl2COR
CCl3COR
pH 7
R=OFG R=OFG
CCl3COOH (TCAA)
R'COCH2COR
R=OH
R'COCCl2COR
CHCl2COOH (DCAA)
R=CH3
pH 12
CCl3COCH3
CHCl3
CCl3COCHCl2
(CF)
*OFG = oxidizable functional group.
Chlorination: Chem istry,
In
Reckhow, D.A. and Singer, P .C. 1985. Water
, Vol. 5.
Environm ental Im pact and Health Effects
• 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
O
O
• 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)
• 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
• 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
• 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
• 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
• 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