Environmental Health Perspectives

Vol. 69, pp. 31-44, 1986

Occurrence of By-Products of Strong

Oxidants Reacting with Drinking Water

Contaminants-Scope of the Problem

by Rip G. Rice* and Maria Gomez-Taylort

This paper describes results of a detailed literature review of the organic and inorganic by-products that

have been identified as being formed in aqueous solution with four of the strong oxidizing/disinfecting

agents commonly employed in drinking water treatment. These agents are: chlorine, chlorine dioxide,

chloramine, and ozone.

Significant findings include the production of similar nonchlorinated organic oxidation products from

chlorine, chlorine dioxide, and ozone. In addition, all three chlorinous oxidants/disinfectants can produce

chlorinated by-products under certain conditions. The presence of chloronitrile compounds in drinking

waters is indicated to arise from reactions of chlorine or chloramine to amine/amide functions in amino

acids or proteinaceous materials, followed by dehydrohalogenation. These nitriles could hydrolyze to

produce the corresponding chloroacetic acids.

It is concluded that to minimize the presence of oxidation by-products in drinking waters, the concentrations of oxidizable organic/inorganic impurities should be lowered before any oxidizing agent is added.

Introduction

This paper is concerned with the by-products of chemical oxidizing agents that are used in the treatment of

drinking water (chlorine, chlorine dioxide, ozone, chloramine), sometimes for disinfection, sometimes for chemical oxidation, and sometimes for both purposes. Most

of the chemicals currently used as disinfectants also are

powerful oxidizing agents, and many times, water treatment processes use these chemical oxidizing agents during pretreatment, rather than during the terminal disinfectant step. For example, potassium permanganate

and ozone are used for iron and manganese or taste and

odor removal. It is thus important for health effects

professionals to recognize that the so-called disinfection

by-products will be present following oxidative pretreatment, even though disinfection may not yet have

been practiced during the water treatment process.

As a result, the water treatment specialist must understand the chemistries involved in the following topics: the by-products of the chemical oxidizing agents as

they are reduced while doing their oxidation/disinfection work during water treatment; reactions of chemical

oxidizing agents with organic materials present at the

point of addition of oxidant/disinfectant, i.e., by-prod-

*Rice International Consulting Enterprises, 1331 Patuxent Drive,

Ashton, MD 20861.

tU.S. Environmental Protection Agency, 401 M Street SW, Washington, DC 20460.

ucts of organic materials; and reactions of chemical oxidizing agents with inorganic materials present at the

point of addition of oxidant/disinfectant, i.e., by-products of inorganic materials.

Objectives

This paper summarizes the most significant findings

of a detailed survey of the literature, funded by the

U.S. Environmental Protection Agency (EPA), Office

of Drinking Water. The objectives of this program were

to survey and analyze the published literature dealing

with known oxidation chemistries of products formed

when various oxidizing agents are used during drinking

water treatment processes. Eight specific oxidizing

agents were studied; first priority was given to chlorine,

chlorine dioxide, ozone, and chloramine; second priority

was given to potassium permanganate, hydrogen peroxide, bromine, and iodine.

The major findings of this study are presented in this

paper for the four first-priority compounds. Each of the

first-priority oxidants will be discussed in terms of the

by-products of the oxidants themselves (e.g., those materials which form from the oxidant as it is reduced),

as well as by-products isolated as a consequence of oxidation of the soluble substrates. In the case of halogen

oxidants, we will also discuss some of the halogenated

materials obtained during treatment of soluble substrates.
RICE AND GOMEZ-TAYLOR

Table 1. Relative oxidation power of various oxidizing species.

Oxidation potential, Relative oxidation

Species at 25°C, Va powerb

Hydroxyl free radical 2.80 2.05

Ozone 2.07 1.52

Hydrogen peroxide 1.77 1.30

Permanganate ion 1.49 1.10

Hypochlorous acid 1.49 1.10

Chlorine 1.36 1.00

Hypobromous acid 1.33 0.98

Chlorine dioxide 1.275 0.94

Monochloramine 1.16 0.85

Hypoiodous acid 0.99 0.73

a Relative to the hydrogen electrode.

bBased on chlorine as reference ( = 1.00).

Chemistry of Oxidants/Disinfectants

Oxidation is defined as a loss of electrons; reduction

as a gain of electrons. During oxidation/reduction reactions, as one component (the soluble substrate = SS)

is chemically oxidized, the oxidizing agent is chemically

reduced. Halogen-containing oxidants/disinfectants

provide an additional complication, however, in that

these materials also can undergo halogenation reactions.

It should be recognized, however, that the halogen

compounds commonly used in drinking water treatment

(particularly chlorine) give rise to both halogenation and

oxidation/reduction reactions and that these reactions

usually occur simultaneously. Furthermore, it has been

estimated that in the case of chlorine added to aqueous

solutions containing soluble organic substrates capable

of being oxidized/chlorinated, only 10% of the chlorine

added results in the production of chlorinated compounds (1,2). Thus 90% of the chlorine added reacts

solely as an oxidizing agent, producing nonchlorinated

organic oxidation products.

Oxidation Potentials

Some measure of the ability of the various oxidants

to oxidize soluble substrates can be gathered from consideration of their relative oxidation potentials, shown

in Table 1 for the oxidants included in this project. However, it should be appreciated that each chemical oxidation reaction proceeds at a specific reaction rate, governed by kinetics, and affected by a variety of factors,

such as concentrations of substrate/oxidant, temperature, pH, the presence of other materials capable of

reacting with the oxidant, and the production of oxidation by-products, many of which also can react with

the oxidant.

It must also be realized that even though some oxidizing agents with high oxidation potentials also are

excellent disinfecting agents (ozone, chlorine, hypochlorous acid, chlorine dioxide), other strong oxidants are

poor disinfectants (permanganate, hydrogen peroxide).

Oxidant Characteristics

Table 2 compares the pertinent attributes of each of

the eight oxidants/disinfectants considered in this study

Table 2. Comparison of relative effectiveness of oxidants/

disinfectants.

Disinfecting Oxidizing Halogenation

Oxidant efficiency efficiency capability

Chlorine High High Low

CGO2 (pure) High High Low

C102 (made High High Variable,

from NaClO2 depending on

+ excess amount of free

chlorine) chlorine

C1NH2 Low Low Low

Ozone High High Zero (except

when bromide is

present)

KMnO4 Low High Zero

H202 Low Moderate Zero

Bromine High Low High

Iodine High Very low Low

in terms of their relative ability to disinfect, to oxidize,

and to halogenate.

By-Products of Strong Oxidants/

Disinfectants

Pertinent literature reports for each of the four primary oxidants/disinfectants (chlorine, chlorine dioxide,

chloramine, and ozone) will be summarized with respect

to their reactions with specific types of organic materials

that are or can be expected to be encountered in drinking water supplies: by-products of the disinfectant itself,

reactions with inorganic substrates, reactions with organic aliphatic substrates, reactions with amino acids,

reactions with organic aromatic substrates, reactions

with heterocyclic substrates, and reactions with humic

and fulvic substrates. However, only the major findings

of the literature study are discussed, particularly as

they relate to drinking water treatment.

Specific By-Products of Oxidants/

Disinfectants

Chlorine. As is widely understood by water treatment specialists, chlorine gas reacts with water at a pH

value just below 7 to produce hypochlorous acid (HOCI)

and chloride ion (C-):

C12 + H20 -- HOCl + ClAs the pH is raised, hypochlorous acid dissociates to

hypochlorite ion (OCI) -. However, this is an equilibrium

reaction which is controlled entirely by pH:

HOCI + H20 = (OCl)- + H3O

When these species (HOCI, OCI-) oxidize substrates,

the chlorine moieties are chemically reduced to chloride

ion:

HOCl [or (OCl)-] + SS SSOXid + Clwhere SS denotes soluble substrate and SSOxd denotes

oxidized soluble substrate.

32
STRONG OXIDANT BY-PRODUCTS IN DRINKING WATER

Chloride ion cannot be reoxidized by free chlorine,

and, therefore, once formed, it remains as a permanent

by-product.

Chlorine Dioxide. Unlike chlorine, pure chlorine

dioxide (CG02) does not react at significant rates with

water or ammonia at neutral pH ranges. However, because chlorine dioxide usually is generated in drinking

water treatment plants by reaction of chlorine with

chlorite ion, solutions of C102 may contain some amount

of free chlorine. Thus the use of chlorine dioxide might

be expected to produce some of the same chlorination

products as does chlorine, but at much lower concentrations, depending upon how much free chlorine is

present after synthesis of C102.

Photolysis experiments by Zika et al. (3) showed that

C102 decomposes to chlorite ion, C102 . However,

chlorite ion also has a short lifetime in full sunlight (less

than 10 min), decomposing to Cl02 and hypochlorite

anion (OCI-). Therefore, under sunlight conditions,

even pure chlorine dioxide, synthesized to contain no

free chlorine, can photolyze to produce hypochlorite ion.

At acid pH, this reaction will produce HOCI, which can

undergo chlorination reactions.

Zika et al. (3) also showed that the major stable end

products of photolysis of C102 in aqueous solution are

Cl-, chlorate ion (ClO37), and oxygen. The first two

species are produced through hydrolysis of chlorous acid

anhydride (CI203) and the dimeric form of chlorine monoxide (C1202), with C10- and Cl . Free radicals also are

involved in the reaction sequences.

When chlorine dioxide undergoes reaction as a chemical oxidant, it is reduced to chlorite ion. If other strong

oxidizing agents are present in solution (ozone and/or

free residual chlorine, for example) chlorite can be reoxidized back to C102. However, ozone will continue to

oxidize chlorite (or C102) to chlorate ion (C103 ). Thus

when both ozone and chlorite/CI02 are present initially

in aqueous solution, Fiessinger et al. (4) consider C102

to be merely an intermediate reaction product between

chlorite and chlorate ions.

In conducting studies at operating French water

treatment plants, Fiessinger et al. (4) showed that granular activated carbon (GAC) decomposes chlorite ion but

not chlorate ion. Thus, when both Cl02 and ozone are

used in drinking water treatment processes, these researchers recommend either that ozone should be used

and its residual allowed to decay before addition of C102,

or that C102 treatment should be followed by GAC treatment (to decompose chlorite ion) before ozonation.

Monochloramine. Monochloramine can be generated by adding chlorine to a solution containing ammonia, by adding ammonia to a solution containing free

residual chlorine, or by premixing pure solutions of ammonia and chlorine, then adding the preformed chloramine solution to the water to be treated.

Addition of ammonia to a chlorine solution has the

disadvantage of first developing a free chlorine residual,

which will produce many chlorinated and/or oxidation

products initially. Addition of chlorine to an ammonia

Table 3. Major by-products of primary oxidants/disinfectants.

Oxidant/disinfectant Major by-products

Chlorine HOCI, (OCl)-, C1-

Chlorine dioxide (C102) , (Cl03)O , C1-, + chlorine

(if prepared using excess chlorine)

Monochloramine Excess chlorine or ammonia, depending

on method of preparation; hydrolysis to

HOCI/(OCI)-

Ozone Oxygen, (OH)-

solution minimizes development of free residual chlorine, except at the specific point of addition of chlorine.

The third overcomes the disadvantages of the first two

methods.

On the other hand, monochloramine hydrolyzes

slowly in aqueous solution, producing hypochlorite (at

alkaline pH) or hypochlorous acid (at acid pH). This

hydrolysis occurs faster at lower pH levels (5). Thus

the opportunity for chlorination reactions occurring

through hypochlorous acid/hypochlorite always is present, even with preformed monochloramine solutions.

Ozone. Ozone (03) reacts by two different mechanisms in aqueous solution. At low pH (below 6), ozone

reacts directly as the ozone molecule. At high pH (above

8), ozone dissociates into hydroxyl free radicals [(OH)'],

which are the oxidizing species. Between pH 6 and 8,

ozone reacts by either or both pathways, with hydroxyl

free radicals predominating as the pH approaches 8.

Combining ozone with ultraviolet radiation or with

hydrogen peroxide accelerates the production of hydroxyl free radicals from ozone. Hydroxyl free radicals

also are generated from hydrogen peroxide (H202),

which is produced during many ozone oxidations of organic materials, or which can be added during or prior

to ozonation.

The presence of free radical scavengers, particularly

bicarbonate ion, decreases the accelerating effects of

hydroxyl free radicals on oxidation reactions. The major

by-product of the reduction of ozone is oxygen.

Summary. Table 3 shows the major by-products

formed during the reduction of the four primary oxidants/disinfectants.

Reactions of Oxidants with Inorganic

Substrates

Chlorine. Bromide ion, nitrite ion, ammonia, sulfide, iron(II), and manganese(II) are components frequently encountered in drinking water supplies. Each

of these materials is reactive with free chlorine (hypochlorous acid). The divalent metallic ions and sulfide

ion are oxidized to their higher valence states. Nitrite

ion forms nitrate ion, and bromide ion is oxidized to free

bromine. In turn, free bromine hydrolyzes to produce

hypobromous acid and hypobromite ion.

Ammonia reacts with free chlorine to produce monochloramine, dichloramine, and nitrogen trichloride, depending on the stoichiometries of the reactants as well

33
RICE AND GOMEZ-TAYLOR

as on the solution pH. Under proper conditions, monochloramine may be the only product formed. If sufficient excess chlorine is present, all ammonia-nitrogen

can be converted to elemental nitrogen (the breakpoint

chlorination process).

Chlorine Dioxide. Unlike chlorine, there is no more

than slight reaction of pure chlorine dioxide with ammonia or water. Additionally, the reaction of bromide

ion with chlorine dioxide is thermodynamically unfavorable, and does not occur (6).

Aqueous solutions containing 1.5 x 10- M C102 and

exposed to sunlight produced chloride and chlorate ions

as the major ionic products. However, when the solution

also contained 1 x 10-4 M bromide ion, bromate ion

(BrO3 ), was observed as an additional product. Although the Cl02 was photolyzed during the first few

minutes, the concentration of BrO3 increased only

gradually on continued exposure to sunlight.

The Br- concentration first decreased to 50% of that

added initially, and then increased as the reaction proceeded. This finding was interpreted as showing an initially rapid oxidation of Br- to OBr-, which then reacted photochemically to produce BrO3 and Br-.

Monochloramine. Bromide ion reacts slowly with

monochloramine (NH2CI), producing bromochloramine

(NHBrCl), not hypobromite ion (6). Hypobromite ion

reacts rapidly with NH2CI, probably producing NHBrCl

(7).

Nitrite ion catalyzes the reaction between chloramine

and bromide ion, but is not itself oxidized by NH2C1 (8).

Ozone. As a general rule of thumb, any oxidizable

inorganic material will be oxidized when treated with

ozone. Bromide ion is oxidized with ozone rapidly to

produce hypobromous acid/hypobromite[HOBr/(OBr)].

Hypobromite ion decomposes back to bromide ion.

Therefore, bromide ion can act as a catalyst in the destruction of ozone. Excess ozone oxidizes hypobromite

ion to bromate ion, the reaction proceeding faster with

increasing pH. In the presence of ammonia, bromide is

oxidized by ozone to hypobromite which, in turn, reacts

with ammonia to produce bromamine.

Nitrite ion reacts almost instantaneously with ozone,

forming nitrate ion.

Ozone reacts slowly with hypochlorite ion, producing

77% chloride ion and 23% chlorate ion. The rate of reaction decreases with decreasing pH (as the more stable-to-ozonation HOCI is formed from hypochlorite ion).

Therefore, applying ozone to drinking water containing

free hypochlorite ion destroys both, decreasing the efficiency of both reagents (9).

Because of the low yield of chlorate ion produced during ozone oxidation of hypochlorite ion, significant quantities are not expected to form in drinking water treatment plants. To ensure the total absence of chlorate ion,

however, ozonation should be conducted in the absence

of free residual chlorine.

Ozone reacts with chloramine, producing chloride and

nitrate ions. The reaction is independent of pH and is

about 20% as fast as the reaction of ozone with hypochTable 4. Inorganic oxidation/halogenation products obtained

from the four primary oxidant/disinfectants.

Inorganic Oxidation/halogenation

constituent product Oxidant

Ammonia Chloramines Chlorine

Nitrite ion Nitrate ion Chlorine, ozone

Bromide ion Hypobromite ion CI02,a ozone, Cl2

Hypobromite + bromate C102,a ozone

BrNHCl ClNH2

Hypochlorite ion Chlorate ion (23%) + Ozone

chloride ion (77%)

ClNH2 Chloride + nitrate ions Ozone

Fe 2; Mn 2 Fe 3; Mn 4 C12, C102, ozone

Mn+4 MnO4- (permanganate) Ozone

a In intense sunlight.

lorite ion. Chlorate ion is not produced in this reaction

(9).

Ozone oxidizes bromamine to nitrate and bromide ions

(9).

Ozone does not oxidize chloride ion to chlorine, hypochlorite, or chlorate at any meaningful rate under

drinking water treatment plant ozonation conditions (9).

Ozone oxidizes chlorite ion to chlorine dioxide; in turn

chlorine dioxide is oxidized by ozone to chlorate ion.

Therefore, drinking water ozonation should be conducted in the absence of these two chlorine species

(chlorite ion and chlorine dioxide) (9).

Ferrous iron is oxidized rapidly to ferric ions, which

hydrolyze, producing the insoluble ferric hydroxide.

Manganous ion is oxidized quickly to manganic ion,

which hydrolyzes and precipitates as manganese dioxide. Continued ozonation resolubilizes manganese in the

form of permanganate ion.

Cyanide ion is rapidly oxidized to cyanate by ozone,

which slowly hydrolyzes to nitrogen and CO2. Ozone

oxidizes sulfide ion to free sulfur, then to sulfite ion,

and ultimately to sulfate ion.

Summary. Chlorine can react with ammonia to produce monochloramine, dichloramine, and nitrogen trichloride. Bromide ion is oxidized to hypobromite. Nitrite

ion is oxidized to nitrate, and ferrous and manganous

ions are oxidzed to the ferric and manganic forms, respectively.

Chlorine dioxide does not react with water or ammonia, but does oxidize bromide ion to hypobromite and

bromate, but only in intense sunlight and with high

concentrations of C102.

Chloramine reacts with bromide ion to produce

BrNHCI, not hypobromite. Nitrite ion is not oxidized

to nitrate by monochloramine. Ozone oxidizes nearly

any oxidizable constituent, except ammonia at drinking

water pH ranges. Bromide ion is oxidized to hypobromite, then to bromate ion. Hypochlorite ion is oxidized to

chloride ion (77%) and 23% chlorate ion. Chloramine is

oxidized to chloride and nitrate ions.

Table 4 summarizes the inorganic oxidation/halogenation products that have been obtained from the four

oxidants/disinfectants.
STRONG OXIDANT BY-PRODUCTS IN DRINKING WATER

Reactions of Oxidants/Disinfectants with

Organic Aliphatic Substances

Chlorine. Acyl compounds and 1,3-diketones (and

1,3-dihydroxyaromatic materials) readily undergo the

haloform reaction during aqueous chlorination, producing trihalomethanes (THMs) and nonchlorinated acids

(10). However, THMs also are produced from other precursors (humic and fulvic acids, for example) and by

reaction mechanisms, not yet clearly defined, other than

the haloform reaction.

Aldehydic groups in unsaturated compounds can be

oxidized to acid groups during aqueous chlorination,

without incorporating chlorine into the molecule (11-

13).

In simulating the migration of vinyl chloride monomer

(VCM) from PVC pipes into water, Ando and Sayato

(14) showed that injection of 10 mg/L quantities of VCM

into deionized water, followed by various concentrations

of sodium hypochlorite, converted the vinyl chloride into

chloroacetaldehyde and chloroacetic acid:

H2C = CHC1 + HOCI -1 C1CH2CHO + C1CH2COOH

It may be significant that additional chlorination did not

appear to take place.

During aqueous chlorination, other unsaturated aliphatic compounds appear to add the elements of HOCI

(HO and Cl) across the double bond to form chlorohydrins (15,16):

R-C=C-R' + HOC1-*R-C-C-R'

J

HO C1

These compounds then can react further (15) (1) by dehydrochlorination, i.e., a chlorohydrin can form an epoxide, which itself may further react with water to produce a glycol):

R C- R' R-RHC1R C _C R' +HOH

HO Cl 0

R -C- C -R'

HO OH

(2) by ammoniation; i.e., as in the presence of ammonia,

a chlorohydrin can form aminoalcohols and/or glycols:

R C,-C-R' + NH3

R -C-C-R'and/or R C- R'

HO NH2 HO bH

Carlson and Caple (16) studied the aqueous chlorination of the mono-unsaturated oleic acid over a wide

range of pH values (1.8 to 11.2) and chlorine concentrations (0.51 to 10.2 mg/L) and in the presence of ammonia. They identified a number of the expected products of addition across the double bond, along with a

low yield of the 9,10-epoxystearic acid:

CH3(CH2)7CH - CH(CH2)7COOH

Aliphatic amines react with aqueous chlorine to produce

N-chloroorganic compounds (N-chloroamines). Under

virtually all conditions of temperature and pH encountered in drinking water treatment plants, 99% of the

free available chlorine was found to react within 0.5

second with a variety of commonly present amines and

amino acids to form N-chloroamines and N-chloroamino

acids (17). N-Chloroorganic compounds are even less

bactericidal than monochloramine. Thus the presence

of organonitrogen compounds reduces the effectiveness

of chlorine as a disinfectant.

Chlorine Dioxide. C102 generally produces more

oxidation and less chlorination of organic materials than

does HOCI. Saturated aliphatic hydrocarbons are neither oxidized nor chlorinated by C102. Aliphatic alcohols

can be oxidized with C102 to allphatic acids,which generally are stable to further oxidation by C102.

Unsaturated aliphatic acids (e.g., oleic acid) produce

a variety of compounds during treatment with C102.

These compounds include ketones alpha to the point of

unsaturation; chloroketones at the originally unsaturated carbon atoms; chlorohydrins; dichloro addition

products; and the epoxide. This last type of compound

probably is formed by addition of HOC1 across the double bond, forming the chlorohydrin, which then dehydrochlorinates to form the epoxide. Formation of this

epoxide from oleic acid treated with C102 has been observed by two teams of investigators (18,19).

CH3 -(CH2)7 -CH = CH - (CH2)7 -COOH + C102

-CH -CH - HCL> -CH CHPrimary aliphatic amines are essentially unreactive

with C102. Secondary aliphatic amines react very

slowly. Tertiary aliphatic amines react rapidly to produce aldehydes and secondary allphatic amines, without

forming N-oxides. However, amines which cannot give

up an a-hydrogen atom during oxidation (such as in

quinuclidine) do produce N-oxides during treatment

with C102.

Chloramine. Aldehydes and ketones produce

amides or chloroimines when treated with monochloramine (20,21). Chloroimines derived from aldehydes can

produce nitriles, probably by undergoing dehydrohalogenation (21).

R - CHO + NH2Cl°CI R -CH= N -C HC1

aldehyde chloroimine

R-C N

nitrile

Some olefins react with NH2Cl by adding the - Cl and

35
RICE AND GOMEZ-TAYLOR

- NH2 moieties across the double bond, producing chloroamines (22).

H H

R-CH=CH-R' + NH2C1- R-I - -R'

Cl NH2

Oleic acid plus chlorine in the presence of ammonia produces the same two 9,10-chlorohydrins isolated from

chlorine alone; however, the 9,10-glycol and the 9,10-

epoxystearic acid also are obtained (16).

CH3 -(CH2)7 -CH = CH - (CH2)7 -COOH + HOCI +

NH3 ---CH -CH- + -CH H +

O1OH OHi I

-CH -CH- + - CH- HOH H O

Chlorine transfer from the monochloramine-nitrogen

atom to the nitrogen atom of amines, amino acids, and

peptides, occurs readily in aqueous solution over the pH

range 2-10. This transfer occurs both indirectly by hydrolysis of NH2Cl to produce HOCl, as well as by a

direct reaction of NH2Cl. Reaction products are organic

N-chloro derivatives, or organochloroamines (17).

Ozone. Ozone oxidations of aliphatic compounds

proceed through organic ozonides, peroxides, diperoxides, triperoxides, hydroalkyl peroxides, and peroxyacids. These types of intermediates are readily isolated

in nonaqueous solvents. In aqueous solvents, however,

these intermediates are unstable, decomposing rapidly

to form simpler products (aldehydes, ketones, carboxylic acids, and H202).

Although ozone is capable of oxidizing many organic

compounds completely to CO2 and water, this conversion normally requires large doses of ozone (> 3 moles

O3/mole of organic compound) and long reaction times

(sometimes hours). Under drinking water treatment

plant ozonation conditions (1 to 5 mg/L applied ozone

dosage; 5 to 20 minutes contact time), organic compounds more often are only partially oxidized. The oxidized organic materials usually are more polar, of lower

molecular weight, more biodegradable, and more readily removed from solution by chemical treatment and

filtration.

Oxalic acid (HOOC-COOH) is commonly found as a

"final" oxidation product of many aliphatic (and aromatic

and heterocyclic) organic materials, because of its very

slow rate of oxidation with ozone. Acetic acid is another

"final" oxidation product which also is resistant to further oxidation with ozone.

Formic acid and formaldehyde also are formed in the

later stages of oxidation of many organic materials.

However, these two organic compounds are rapidly oxidized to CO2 and water upon continued ozonation.

Ozone oxidation rates of intermediate organic oxidation products usually are slower than the oxidation

rates of the original compounds.

In general, ozonation of aliphatic unsaturated compounds results in cleavage of the double bond(s), producing aldehydes, ketones, and/or carboxylic acids. Formation of the latter compounds results in a decrease in

pH values. Ozonation of oleic acid has produced small

quantities of the same epoxide isloated during chlorination of oleic acid (16).

Hydrocarbons also have been isolated during ozone

oxidation of unsaturated aliphatic compounds, although

in minor amounts. The longer length of the carbon

chains in these hydrocarbon products suggests cleavage

of the double bond, followed by formation of a hydrocarbon free radical, then coupling of two hydrocarbon

free radicals.

Chlorinated aliphatic compounds are oxidized by

ozone more slowly than are the corresponding nonchlorinated materials. Ozonation or UV/ozonation ruptures

carbon-chlorine bonds, forming chloride ion and the

same aldehydes, ketones, and/or carboxylic acids produced by ozonation of their nonchlorinated analogues.

The following aliphatic compounds have been shown

to be unreactive to ozone, under drinking water treatment plant conditions: oxalic acid, acetic acid, glycerol,

urea, saturated aliphatic and alicyclic hydrocarbons, pelargonic acid, hexanoic acid, octanoic acid, and the explosive RDX (cyclonite).

Discussion. HOCl adds across the double bond of

oleic acid to produce the corresponding chlorohydrins

and small amounts of the epoxy derivative. Chlorine

dioxide produces the same chlorohydrins, the vic-dichloro derivative, and the epoxide. Chloramine forms the

chlorhydrins, the vic-glycol, and small amounts of the

epoxide. Ozone produces small amounts of the epoxide.

Chlorine, ozone, and C102 produce higher yields of compounds in which the original oleic double bond was ruptured.

Chlorine dioxide with aliphatic compounds generally

produces more oxidation products than chlorination

products, particularly if it has been generated to be free

of residual chlorine.

Amine and amido functions react rapidly with free

chlorine (99% in about 0.5 sec), forming N-chloro derivatives, which are even less bactericidal than monochloramine. More importantly, when free ammonia and

an organic amine or amide are present, added chlorine

reacts preferentially with the organic nitrogen before

it reacts with the ammonia to form chloramines.

Chlorine dioxide does not react with primary amines,

reacts very slowly with secondary amines, and with

tertiary amines ClO2 produces secondary aliphatic

amines, without forming N-oxides. With aldehydes and

ketones, monochloramine produces chloroimines, which

(from aldehydes) decompose to produce nitriles. NH2Cl

adds across olefinic double bonds to produce chloroamines. The chlorine atom in monochloramine transfers

rapidly to the nitrogen function in amines, amino acids,

and peptides, producing N-chloro derivatives. These

36
STRONG OXIDANT BY-PRODUCTS IN DRINKING WATER

react further to produce nitriles (see next section for

details).

Ozone generally is not reactive with saturated aliphatic hydrocarbons. However, other types of aliphatic

compounds, particularly olefins, are readily oxidized

through ozonides, peroxides, and hydroperoxide intermediates to form aldehydes, ketones, and acids. A byproduct of all organic oxidations with ozone is hydrogen

peroxide. In the presence of more ozone, however, the

H202 is decomposed into hydroxyl free radicals, which

are more powerful oxidizing agents than the ozone molecule.

Reactions of Oxidants/Disinfectants with

Amino Acids

Amino acids are liberated by microorganisms in natural media and are found in raw water supplies in concentrations of 5 to 2,000 ,ug/L, either in the free state

or combined as peptides, nucleic acids, purines, pyrimidines, and proteins (23). Flocculation/decantation does

not necessarily remove amino acids during water treatment, and they can be present at the final disinfection

stage. These nontoxic materials can be changed structurally upon treatment with oxidizing (disinfection)

agents.

Chlorine. Amino acids react with aqueous chlorine

to form N-mono- or N,N-dichlorinated derivatives, depending on whether chlorine is added in excess. Subsequent decomposition of these compounds is affected

by the nature of the original amine group. If it was a

primary amine, the decomposition products are aldehydes, ketones, carbonic acid, chloride ion, and ammonia. If it was a secondary amino group, the same

products are formed, except that the corresponding

amine replaces the ammonia (24).

Trehy and Bieber (25) identified dichloroacetonitrile

as a product of chlorination of tyrosine in water:

p-HOC6H4 - CH2CH(NH2)COOH + HOCI -1 C12CH - CN

tyrosine dichloroacetonitrile

Sakuri and Sawamura (26) found that monochloroglycine, formed in the first stage of the reaction of glycine

with hypochlorite, was further chlorinated to give dichloroglycine by the action of excess hypochlorite. The

formed dichloroglycine underwent decarboxylation and

dehydrochlorination to form HCN, which then was

chlorinated by chlorine or by excess hypochlorite to

form cyanogen chloride, C1CN. One mole of glycine required three moles of hypochlorite for the formation of

the equivalent CICN.

H2NCH2COOH HOCY Cl NHCH2COOH -C C12NCH2COOH

glycine chloroglycine dichloroglycine

HCN C

C1CN

cyanogen

chloride

Qualls and Johnson (27) showed that the rate of chlorination of ammonia was considerably slower than the

rate of chlorination of glycylglycine. This peptide outcompeted ammonia for the available HOCI until an excess of HOCI was added beyond that required to form

N-chloroglycylglycine.

Le Cloirec et al. (28) isolated the following compounds

from the chlorination of alanine [CH3CH (NH2)COOH]

using chlorine/amino acid ratios (x) between 0.5 and 6:

NH2Cl (chloramine), NHCl2 + NCl3 (dichloramine +

nitrogen trichloride), CH3CHO (acetaldehyde), CH3CN

(acetonitrile), CH3CH = NH (acetimine), and

CH3COOH (traces) (acetic acid). Alanine was totally

destroyed when x was equal to or greater than 2. Dichloramine and nitrogen trichloride appeared at x = 1 and

increased when x was above 2.5. Both acetaldehyde and

acetonitrile were present in solution, the concentration

of acetaldehyde peaking at almost the original alanine

concentration when x approached 1.5. The concentration of acetonitrile increased rapidly as the concentration of acetaldehyde decreased, peaked when x = 4,

and then decreased only slowly afterward.

These observations indicated that acetaldehyde may

be an intermediate in the formation of acetonitrile. To

verify this hypothesis, a solution was prepared containing acetaldehyde and the chloramines formed by the

action of NaOCl on NH4' under the same conditions.

Acetonitrile formed at essentially the same rate as during the chlorination of alanine and at the expense of

acetaldehyde.

Chlorine Dioxide. Allphatic amino acids oxidize

slowly in the presence of C102 free of residual chlorine

and form nonchlorinated oxidation products. Glycine

produced formaldehyde and CO2. Phenylalanine produced small quantities of benzylic acid, benzoic acid,

mandelic acid, and traces of phenylacetaldehyde.

Sulfur-containing amino acids (cystine and methionine) oxidize at the S-atoms to produce bisulfoxide and

sulfonic acid derivatives.

Monochloramine. In the presence of amines, amino

acids, and/or peptides, chloramine is even less effective

as a disinfectant, because of its tendency to form Norganochloramines by chlorine transfer, with concomitant destruction of NH2Cl. For example, with small

amounts of glycine (0.1-0.25 mg/L) present in ammoniated water, the addition of chlorine forms N-chloroglycine preferentially to forming NH2C1 (29).

N,N-Dichloro-a-amino acids decompose rapidly,

forming uitriles, CO2, and chloride ion. This reaction is

at least one order of magnitude faster than the corresponding decomposition of N-monochloro-a-amino acids

(30). This is a second pathway to the production of nitriles in chlorinated waters.

Peptides form N-chloro derivatives with monochloramine only at the terminal - NH2 groups. Amide nitrogen atoms in the body of the peptide chains are unreactive to NH2Cl (30).

Ozone. The amino acid alanine is decomposed readily by ozonation liberating all of the organic nitrogen as

both ammonium and nitrate ions (31). No acetonitrile is

37
RICE AND GOMEZ-TAYLOR

formed by ozonation of alanine (28). Phenylalanine is

less readily decomposed by ozone, and 30% to 75% of

the organic nitrogen remains combined in the organic

oxidation products (31).

Small amounts (but larger than trace quantities) of

polymeric materials (molecular weight 500 to 70,000)

are produced during ozonation of phenylalanine, indicating that it is possible to synthesize polymeric materials by ozonation of this type of difunctional monomeric compound (28).

Discussion. When amino acids or proteinaceous materials (peptides) are treated with chlorine, N-monochloro and/or N,N-dichloro derivatives are produced

rapidly. Even when ammonia is present, these N-chloroamino derivatives are produced selectively over the

formation of monochloramine. Upon further reaction of

these chlorinated compounds, nitriles, hydrogen cyanide, and cyanogen chloride have been identified, particularly when the molar ratio of chlorine to amino acid

(alanine) is as high as 4.

The decomposition rate of N,N-dichloro-a-amino

acids is at least one order of magnitude faster than that

of the corresponding N-monochloro-a-amino acid.

It has been proven that acetaldehyde produces acetonitrile in the presence of the intermediate chlorinated

amino acids. This leads to speculation that other aldehydes may also be nitrile precursors in the presence of

chlorinated amino acids. More studies are required to

confirm this hypothesis.

It thus would appear that to minimize the formation

of nitriles, HCN, and cyanogen compounds, the formation of N,N-dichloroamino acids should be avoided,

or at least minimized. This can be accomplished either

by removing the amino acids before chlorine is added,

or by avoiding the addition of large quantities of chlorine

(i.e., breakpoint chlorination). Since amino acids are

ubiquitous in raw water supplies, treatment conditions

should be developed for their removal, or at least for

rupturing the carbon-nitrogen bond to eliminate the

organic amine functional group, before addition of chlorine.

Neither chlorine dioxide nor ozone produces N-chlorinated derivatives of amino acids. In fact, both oxidants

decompose many amino acids and peptides, although

C102 appears to be unreactive with many amino acids.

With alanine, for example, C102 is unreactive, but ozone

converts all the organic nitrogen to ammonium and nitrate ions. This would suggest that preozonation of raw

water supplies could be used to destroy amino acids,

prior to chlorination or chloramination.

However, phenylalanine is not as easily oxidized,

even with ozone; some 30 to 75% of the organic nitrogen

remains bound in the organic oxidation products. As

before, more studies should be conducted to confirm

these potentials.

Reactions of Oxidants/Disinfectants with

Organic Aromatic and Cyclic Compounds

The three strong oxidants (chlorine, chlorine dioxide,

ozone) act similarly as chemical oxidizing agents with

respect to phenols, aromatic amines and amino acids,

and pesticides. That is, aromatic rings are hydroxylated

in a first step, then quinones are produced as initial

reaction intermediates. With higher dosages and/or

longer reaction times, ring rupture generally occurs,

leading to the formation of aliphatic mono- and di-acids.

Chlorine also produces chlorinated aromatic materials, which lead to chlorinated aliphatic compounds

upon ring rupture. Yields of ring-chlorinated products

are higher at low molar ratios of chlorine to phenol. At

higher ratios, ring-ruptured products predominate.

Pure chlorine dioxide behaves more like chlorine than

ozone with respect to phenol, in that similar products

are obtained as with the use of HOCI. This statement

applies, however, only if the concentration of phenol is

in stoichiometric excess over that of the C102. When

chlorine dioxide is present in excess, p-benzoquinone

and aromatic carboxylic acids are produced (32). On the

other hand, aromatic amino acids undergo oxidation reactions, rather than chlorination, with pure C102.

Chlorine produces small yields of nonchlorinated

epoxy derivatives from abietic acid and cholesterol.

Ozone also produces the same epoxy compounds from

cholesterol and abietic acid (15,16), and from acenaphthylene as well (33).

Ozone (34) and chlorine dioxide (35) have been shown

to oxidize the pesticides Parathion and Malathion initially to the more toxic intermediates, paraoxon and

malaoxon, respectively. Continued ozonation has been

shown to destroy these intermediates, producing simpler decomposition products. Hoffmann and Eichelsdorfer (36) showed that ozonation of heptachlor produced a quantitative yield of heptachlor epoxide, which

itself is stable to further decomposition by ozone.

A number of pesticides are resistant to chemical oxidation, even by ozone. If these pesticides are present

in water supplies, procedures other than chemical oxidation must be used for their removal.

Ozonation of phenol can produce resorcinol, which is

a know THM precursor. The initial rate of oxidation of

phenolic materials with ozone is very fast, reflecting the

ease of oxidation of these materials. During continued

ozonation, however, their rates of oxidation slow considerably, reflecting the slower oxidizability of their oxidation products.

Ozonation of chlorinated aromatic compounds ruptures the carbon-chlorine bonds, producing chloride

ions and ring-ruptured, aliphatic products. Aniline produces the same oxidation products as phenol during

ozonation, plus nitrate ions and ammonia (37,38).

Some oxidative coupling of phenolic materials has

been observed as a result of ozonation, producing higher

molecular weight materials (39). This behavior might

partially explain the ability of ozone to microflocculate

soluble impurities in water supplies.

The ratio of the concentration of 5-day biochemical

oxygen demand to total organic carbon concentration

(BOD5/TOC) increases upon ozonation and increases

faster after ring rupture has occurred (37). This shows

that some biorefractory compounds can be partially ox38
STRONG OXIDANT BY-PRODUCTS IN DRINKING WATER

idized during ozonation to produce organic materials

which are more easily biodegradable.

Polycycic aromatic compounds and some pesticides

(40) have been shown to be readily adsorbed by humic

materials and soil particles, which provide a shielding

effect toward ozonation.

Monochloramine in the presence of excess ammonia

reacts with some aromatic hydrocarbons (benzene, toluene, o-, m-, and p-xylene, and naphthalene) to produce

cyanogen chloride (41,42). With phenol, p-aminophenol

is produced initially, and chlorophenols are identified

after the solution has stood for several days (43-45).

Aromatic acids, which are normally THM precursors,

do not produce THMs with chloramine, but rather form

the corresponding chlorophenolic aromatic acids (46).

Reactions of Oxidants/Disinfectants with

Heterocyclic Compounds

Amino acids, nucleic acid bases, purines, and pyrimidines have been identified in surface water supplies,

particularly when algae levels in the raw water supplies

are high (23). Purines and pyrimidines also are components of nucleic acids in bacteria and are known to

produce mutagens upon chlorination. These materials

may be precursors for nitriles and chloroform (47).

Chlorine. 5-Chlorouracil and 5-chlorocytosine were

identified in the acid hydrolysates of the nucleic acids

separated from bacteria after parts-per-million (ppm)

chlorine disinfection of water supplies (48). Patton et

al. (49) and Gould et al. (50,51) confirmed that cytosine

and uracil react with HOCI in aqueous solution to produce the 5-chloro derivatives. 5-Chlorouracil has been

shown to be mutagenic.

Franssen and van der Plas (52) isolated 5-monochloroand 5,5-dichlorobarbituric acids from the chlorination of

barbituric acid and its derivatives.

Chlorine Dioxide. Nitrogen heterocycles generally

produce oxidation products rather than chlorination

products upon treatment with C102.

Chloramine. Lin and Carlson (53) studied the reaction of a number of environmentally significant heterocycles with aqueous chlorine, chlorine dioxide and

chloramine. Chloramine generally was quite unreactive

with these heterocycles, except at low pH, where hydrolysis to form a significant amount of HOCI occurred,

yielding increased amounts of chlorinated products. In

general, chloramine required much longer reaction

times to produce > 95% reaction than did hypochlorite

or C102 at pH 7.0.

Summary. Chlorination of uracil and cytosine produces the mutagenic 5-chloro derivatives. Chlorine

dioxide generally produces oxidation products rather

than chlorinated derivatives. Chloramine reacts very

slowly, if at all, with heterocyclic materials, except at

low pH ranges (-3), where hydrolysis to HOCl occurs,

allowing chlorination to occur. Ozone produces a variety

of nonchlorinated heterocyclic oxidation products.

Reactions of Oxidants/Disinfectants with

Humic and Other Natural Materials

Chlorine. From the aqueous chlorination of various

aquatic humic materials, Stevens et al. (54) identified

98 specific organic compounds, including 47 discrete

compounds containing chlorine and 51 discrete compounds that did not contain chlorine. De Leer et al. (55)

identified over 100 different reaction products from the

chlorination of soil humic acid material.

Christman et al. (56) showed that the products of

exhaustive chlorination of aquatic humic materials generally fall into three broad structural categories: nonchlorinated substituted aromatics, chlorinated straightchain acids, and nonchlorinated straight-chain aliphatic

acids. From the aqueous chlorination of humic materials, nonvolatile halogen-containing materials account

for about 43% of the total organic halogen found. Chloroform represents about 95% of the volatile organics

formed. The nonvolatile halogenated fraction is produced in higher yield under acidic conditions compared

to that produced under alkaline conditions.

Seeger et al. (57) showed that at low chlorine dosages,

which are more typical of those conditions found in

drinking water treatment plants and their distribution

systems, a large number of ring-chlorinated aromatic

acids is obtained, in addition to the numerous nonchlorinated aromatic and aliphatic compounds identified by

earlier investigators.

Chlorinated fulvic acid samples contain about 60%

more organic-bound chlorine than do chlorinated humic

acid samples, even when the humic chlorination is conducted over twice the reaction time (58).

The principal chlorinated products formed during

aqueous chlorination of fulvic acids at pH 7 are: trichloroacetic acid, 69%; dichloroacetic acid, 9.5%; chloroform, 19%; and dichlorosuccinic acid, 4.5%. These

compounds represent 53% of the total organic halogen

content, and about 14% of the starting organic materials

(about 4% of the original TOC). Note that the amount

of trichloroacetic acid is more than triple that of chloroform (59).

Cyano-substituted compounds (nitriles) recently have

been identified as products of aqueous chlorination of

humic/fulvic materials (54,55,60). These compounds include: chloroacetonitrile, dichloroacetonitrile, trichloroacetonitrile, dichloropropanenitrile, dichloropropenenitrile, trichloropropenenitrile, 3-cyanobutanoic acid,

and 4-cyanobutanoic acid. It is possible that these compounds arise from reactions of chlorine with amino acids

or proteinaceous materials to form N,N-dichloroamino

acids, followed by dehydrohalogenation to the nitriles.

Chlorinated aliphatic aldehydes also have been identified. These compounds might be precursors of the nitriles, as well as of chlorinated acids, which are logical

hydrolysis/oxidation products of the above nitriles. For

example, di- and trichloroacetaldehydes, and mono-,

di-, and trichloroacetic acids (60) could be formed by

hydrolysis of the corresponding nitriles.

Chloropicrin (Cl3CNO2) has been identified recently

39
RICE AND GOMEZ-TAYLOR

(61), along with other volatile organic chemicals, during

chlorination studies with humic and fulvic materials.

Precursors include aminoacids and nitrite ion. Ammonia

must be absent. Chloropicrin was formed more rapidly

at pH 10 than at pH 7, and the presence of nitrite ion

is essential.

Duguet et al. (62) and Mallevialle et al. (63), isolated

chloropicrin from drinking water supplies that had been

prechlorinated. They also showed that the addition of

reducing agents to chlorinated drinking water supplies

with the objective of destroying excess free residual

chlorine, also converts any chloropicrin present to chloroform:

C13- C - NO2 + reducing agent -> CHC13

In light of this fact, it is not surprising that chloropicrin

has escaped more general detection and reporting in

drinking water supplies. If more than the stoichiometric

amount of sulfite or thiosulfate required to quench free

residual chlorine is added, chloropicrin will be destroyed. Equally significant, however, the amount of

chloroform found will be higher than that actually produced as a result of chlorination.

Chloropicrin also has been identified as a product of

chlorination of resorcinol. Filtration through GAC was

found to destroy chloropicrin (62,63). These authors

suggest that the simplest way to control chloropicrin

formation in water supplies is by abandoning breakpoint

prechlorination.

Chlorine Dioxide. Chlorine dioxide does not produce trihalomethanes with humic materials, except

when free chlorine is present. From pure chlorine dioxide, the following four general classes of oxidation products were obtained at pH 3 and 7.8 (64): benzenepolycarboxylic acids, aliphatic dibasic acids (greater yields

from Cl02 than from Cl2 or KMnO4), carboxyphenylglyoxylic acids, and aliphatic monobasic acids. Compounds identified in these studies were similar to those

identified during experiments using chlorine, ozone, and

potassium permanganate as the oxidants.

Several derivatives of furan and dioxane also were

identified, as well as several chlorinated compounds.

Far fewer chlorinated products are formed by reaction

with Cl02 than with Cl2. An average of 30% of the

original TOC was removed by treatment with C102.

Monochloramine. Chloramination of humic and fulvic materials produced no identifiable chlorination or

oxidation products in diethyl ether extracts, although

the fulvic materials tested exerted a demand for 0.13

mole NH2Cl mole of carbon after 24 hr at pH 9, and the

color of the fulvic material had been bleached. This behavior might be explained by selective addition reactions of NH2Cl across olefinic sites in the fulvic molecules, thus destroying some or all of the chromophoric

moieties (57).

Ozone. Ozonation of natural humic and fulvic acids

released the pesticides Lindane and DDT, along with

iron and manganese cations. With small quantities of

ozone simulating dosages used in drinking water treatment plants (0.1 to 2 mg/L), humic acids depolymerized

and, in the majority of experiments, turbidities increased, and BOD5 increased (65).

Ozonation of humic and fulvic materials cleaves the

polymeric chains (> 1000) and forms lower molecular

weight fragments (< 1000) and aliphatic acids and ketones, phenols, and phthalic acids (66,67).

Higher molecular weight polymeric humic materials

(> 300,000) are decomposed during ozonation into

shorter fragments (< 5,000). In addition, the ozonized

solutions now contain higher concentrations of phenolic

constituents than are present before ozonation. These

phenolic compounds might be liberated by decomposition of iron and manganese complexes (68).

More recent studies have shown that aromatic acids

are virtually eliminated after one hour of ozonation,

which conditions provide much higher dosages of ozone

than normally encountered during drinking water ozonation. In some cases, tetrachloro-, and pentachloro-, and

hexachlorobenzenes have been isolated from solutions

of humic materials ozonized for 1 hr. These chlorinated

compounds probably were present as soil humic contaminants and were released as the humic material decomposed during ozonation (69).

Oxidation of fulvic acids caused depolymerization, and

several fractions of lower molecular weight materials

were isolated. Ozonation produced more low molecular

weight compounds from fulvic acids than did KMnO4

oxidation. Ozone/UV produced fewer low molecular

weight compounds than ozonation alone, probably

caused by more complete oxidation of the carbon to CO2

(70). GAC adsorption rates of ozonized humic acids decrease to a minimum at a range of consumed ozone of

0.13-0.3 mg 03/mg organic C, then increase with increased ozone dosage. At 1.08 mg 03/mg C, the biodegradability of the ozonized solutions quadrupled (71).

Because ozonation increases biodegradability of humic

and fulvic materials, removal of dissolved organic carbon can be improved further by following ozone oxidation with a biological treatment before chlorination

(72).

Four major classes of compounds have been isolated

from ozonized solutions of humic and fulvic acids (57,72):

benzenecarboxylic acids, aliphatic dibasic acids (C4 to

C1o), aliphatic monobasic acids (C2 and higher), and carboxyphenylglyoxylic acids. The nonchlorinated, aromatic, and aliphatic compounds identified are identical

or very similar to those obtained when treating the same

humic or fulvic materials with chlorine, chlorine dioxide,

or potassium permanganate.

Discussion. From the complete chlorination of

humic and fulvic acids, more than 100 discrete compounds have been identified. About half of these are

nonchlorinated, and both classes consist of substituted

aromatic compounds and straight-chain aliphatic

mono-, di-, and polycarboxylic acids. About halfthe total

halogen-containing material is nonvolatile, and chloroform comprises about 95% of the volatile organics produced.

Chlorinated products obtained in highest yield include

trichloroacetic acid (69%), chloroform (19%), dichlo40
STRONG OXIDANT BY-PRODUCTS IN DRINKING WATER

roacetic acid (9.5%), and dichlorosuccinic acid (4.5%).

When chlorination conditions that are closer to those

used in drinking water treatment plants (maximum 20

mg/L chlorine doses) are used, more ring-chlorinated

aromatic compounds can be isolated.

Many nitriles have been isolated from chlorination of

humic/fulvic materials, along with chlorinated aldehydes and chlorinated acids. As discussed in the preceding section dealing with amino acids, aldehydes in

the presence of ammonia and chlorine can be precursors

of nitriles. Furthermore, hydrolysis of chlorinated acetonitriles (which have been identified from the chlorination of humic materials) would be expected to produce

the corresponding chloroacetic acids.

Chlorination of a-terpineol produces a variety of

chlorinated derivatives, plus a nonchlorinated epoxide.

At pH 10, the yield of epoxide is 39%, which decreases

to 1-3% yield at pH 3.

Oxidation of humic and fulvic materials with chlorine

dioxide, ozone, and alkaline permanganate forms nonchlorinated oxidation products, which are similar to

those produced during chlorination. The major classes

obtained from ozonation are benzenecarboxylic acids,

C4-C10 aliphatic dibasic acids, C2 and higher aliphatic

monobasic acids, and carboxyphenylglyoxylic acids.

Ozone oxidation of humic/fulvic materials generally

lowers the molecular weights, and sometimes liberates

entrapped or complexed pesticides (Lindane and DDT)

and heavy metals (iron and manganese). At the same

time, turbidities and BOD5 increases. In some cases,

the BOD5 quadruples. Adsorbability of the ozonized organics can decrease at low levels of ozonation (0.13-0.3

mg ozone consumed/mg organic carbon), but then increases with increasing ozone dosage.

Monochloramine produces no products as yet identified, although humics and fulvics exert strong oxidant

demands. Higher nonpurgeable total organic halogen

concentrations were found (9%-40% higher) with chloramine treatment of fulvic materials than with chlorine.

These materials had higher molecular weights and were

less polar than the same materials produced by chlorination.

Conclusions

At our current state of knowledge with regard to the

chemistries of specific organic materials known to be

contained in raw water supplies with respect to the

oxidants/disinfectants currently available and used in

water treatment, no current water treatment process

appears to be able to guarantee the total absence of

oxidation products.

Reactions of free chlorine and monochloramine with

organonitrogen moieties in amino acids, amines, and

peptides can produce nitriles by formation of N,N-dichloro derivatives, followed by decomposition. Aldehydes in the presence of ammonia and chlorine also have

been shown to produce nitriles through the same mechanism.

In the presence of nitrite ion, amino acids and chlorine

produce chloropicrin (nitrotrichloromethane). Addition

of strong reducing agents converts this material to chloroform. Thus it is possible that many early analyses for

trihalomethanes have not found chloropicrin because of

the prompt addition of thiosulfate to destroy free residual chlorine. If this has occurred, these analyses for

the amount of chloroform produced during chlorination

may have been overstated by the amount of chloropicrin

converted to chloroform.

Since the concentration of amino acids and peptides

is highest in raw drinking water, the preceding conclusions lead to consideration of the recommendation that

breakpoint chlorination of raw waters should be abandoned in favor of other procedures that will remove

these nitrogen-containing materials before chlorine is

added.

To minimize the formation of chlorinated organic materials, as much organic material as possible should be

removed before chlorine is added to the water.

Chlorine dioxide generally produces fewer chlorination products than does free chlorine. Amines, amino

acids, and peptide nitrogen groups do not form N-chloro

derivatives with C102.

Preoxidation of water supplies with ozone or chlorine

dioxide before chlorination produces aldehydes, ketones, and acids. Unless the aldehydes are removed (by

flocculation, adsorption, or further oxidation) before

treatment with ammonia and chlorine, nitriles could be

produced.

Epoxide compounds have been identified in laboratory studies of aqueous solutions of oleic acid, abietic

acid, cholesterol, a-terpineol, and acenaphthylene. The

same nonchlorinated epoxy derivative of oleic acid was

produced by treatment with chlorine, ozone, chlorine

dioxide, and chloramine. Abietic acid and cholesterol

formed the same epoxy derivatives from chlorine and

from ozone (no experiments were conducted with C102).

Chlorination of a-terpineol produced a nonchlorinated

epoxy compound in addition to chlorinated products.

Ozonation of acenaphthylene produced the corresponding epoxy derivative, in addition to the more nornal

oxidation products. Ozonation of heptachlor quantitatively produces heptachlor epoxide which is stable to

further ozonation.

Chlorine dioxide in strong sunlight, and aqueous

chlorine (HOCl) oxidize bromide ion to hypobromite ion.

Ozone also will oxidize bromide ion to hypobromite ion,

and additionally will oxidize bromide/hypobromite ions

to bromate ion. Thus, waters containing bromide ion

will have the potential for producing not only brominated trihalomethanes, but other brominated organic

materials.

Ozone reacts with hypochlorite ions, producing chloride and chlorate ions; with chlorine dioxide to produce

chlorate ion; with chlorite ion to produce C102 and chlorate ion; and with monochloramine to produce chloride

and nitrate ions. Therefore, ozonation processes should

be conducted in the absence of these inorganic materials. Any residual ozone should be destroyed before

41
42 RICE AND GOMEZ-TAYLOR

any of these halogenated materials are added for disinfection.

This literature study was supported by the United States Environmental Protection Agency (EPA), Office of Drinking Water, Criteria and Standards Division under Order Number 4W-2943 NTSX,

issued to Rip G. Rice, Incorporated. It has been subject to the Agency's review, and has been approved for publication as an EPA document. The senior author is particularly grateful to his coauthor for

her able and patient guidance of this project, and for her cooperation

in the writing of this manuscript.

Both authors thank Dr. Joseph A. Cotruvo, Director of the Criteria

and Standards Division, for suggesting and supporting this study.

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