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

• 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

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

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)

Major DBPs formed during disinfection of drinking water

HOOC CHCOOH

C(CH3)3

OH

Cl

Cl

Cl

O O

ClCl2HC

HO

HCl2HC

OHC

Cl

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 by-products

• 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

a: THMs (e.g., chloroform)b: HAAs (e.g., TCAA) or chloral hydrate [CCl3CH(OH)2]c: HKs (haloketones)

OH

R1

R2

R3

OH

HHOCl

H2O

c

b a

ClR3

O

CCl3CCR2

COOHR1

C

COH

-H

+

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

HOrtho position activated

• Chemistry of DBP Formation– Haloform Reaction

• Reckhow and Singer (1985)

(DCAA)

(-Diketone)Fulvic Acid R'COCH2COR R'COCCl2COR

CHCl2COR CHCl2COOHR=OH

CCl3COR CCl3COCH3

CCl3COCHCl2CHCl3CCl3COOH

R=CH3

pH 12

R=OFG R=OFG

pH 7

*OFG = oxidizable functional group.

Reckhow, D.A. and Singer, P.C. 1985. In Water Chlorination: Chemistry,Environmental Impact and Health Effects , Vol. 5.

(TCAA) (CF)

• 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 di

chloroacetonitrile (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 aromati

c 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 i

ndustrial 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 effectiv

e oxidant• Ratio of bromide to the average free available chlorine (Cl+) control

s 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 Fo

rmation• 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 Te

sting• 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 woul

d 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