0048-9697(85)90338-9] F. Fiessinger; J.J. Rook; J.P. Duguet -- Alternative Methods for Chlorination
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The Science of the Total Enuironment, 47 (1985) 299-315
Elsevier Science Publishers B.V., Amsterdam -Printed in The Netherlands
299
ALTERNATIVE METHOOS FOR CHLORINATION
F. Fiessinger, J.J. R ook and J.P. Ouguet
Laboratoire Central Lyonnaise des Eaux, 78230 Le Pecq (France)
ABSTRACT
Existing disinfectants are oxidative agents which all present negative
effects on subsequent treatment processes. None of them has decisive advantages
over chlorine, althouq h chlorine-dioxide and chloramines migh t at times be
preferable. Optim um treatment practices wil l improve the removal of organic
orecursors before final disinfection which could then consist in a liqh t chlorine
addition. A
philosophy of radical change
in water treatment- technology
encompassing physical treatment without chemicals such as memb rane filtration ,
solid disinfectants is presented.
INTRODUCTION
Since its introduction into water treatment in the begin ning of this century,
chlorine has held a predom inant position as reliab le disinfectant because of its
broad range biocid al effectiveness,
its reasonable persistence in treated waters,
its ease of applica tion and control and its cost effectiveness.
In addition
chlorine is the only chemical agent that is able to oxidize ammonia readily.
Chlorine is also used for controlling the proliferation of algae during the warm
periods in uncovered coagula tion and sedim entation basins. Unfortunately, when
organic m atter is present chlorination results in the formatio n of undesirable
halogenated compounds ; i.e.
total haloge nated compounds (TOX) and more
particularly the Trihalom ethanes (THM).
The use of modern analytical techniques
has led to the identific ation of a large part of them (Christman et al., 1983,
Bruchet et a1.1984, Coleman et al. 1984, Ouguet et al. 1984b) as illustrated in
Figure 1. Som e of these compounds like dichloroaceton itrile, several chlorinated
ketones, chloroform are known to be mutagenic or toxic (Sim mon et al. 1977, Bul l
1980).
The effects of water chlorinatio n on mutagen ic activity have been studied.
Many authors, (Kool, 1984) , conclude that chlorinatio n increases mutagenicity
(see Fig.2) but the nature of organics and chlorinatio n conditions have a great
influence. Thus Cognet (1984) found that during chlorinatio n of treated Sei ne
water, variation of mutagenicity during one year was not statistically
significative.
0048-9697/8 5/$03.30 0 1985 Elsevier Science Publishers B.V.
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[ 78.8 7. MWc1000 1
\
1
- VOLATILE5
I NON VOLATILES
Fig. 1.
Diagram of molecular weigh t distribution of TOX after prech lorination
of a reservoir water (C halet, France) and speciation of the volatile fraction.
I
2 3 4
VOLUME OF WATER
i Ilterl
Fig. 2. Comparison of mutagenic activity on Salmo nella thyphimurium strain
TA'98(-'S9) , before (xl and after prechlorination/Dissoved air flotatio n A
of a surface water (Moul le, France)
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Another risk is related to the direct toxicity of chlorine gas during its
road transport and its storage as liqu id chlorine, in plants located near densely
populat ed areas. This risk can be avoided by using sodium hypochlorite instead
of liqu id chlorine, though at a 20 to 25 % increase in costs (Gomella,198 0). In
situ generation of chlorine, through electrolysis migh t also be appli ed.
ALTERNATIVE DISINFECTANTS
Altho ugh chlorine is a good disinfectant,
the potenti al health risks of
halogen ated by-products formation have caused the entire subject of drinking
water disinfection to be reconsidered. The mai n alternative disinfectants in use
are ozone, chlorine dioxide, chloramines and to a less extend ultraviolet light,
hydrogen peroxide, permanga nate, other halogens an d silver ions. Gom ella (1980)
and Fiessinger (1981) summarized the properties of several disinfectants with
respect to their possible reactivities with water constituents. An extended
summary of oxidant properties based on these surveys is shown in table 1.
TABLE 1
Comparis on of Various Disinfectants
cl2 c102 03 KMn04 NH2C1 H2°2
Iron and manganes e
Ammonia
THM formation
THM precursors
removal
Formation of mutagens
or toxic substances
Enhanced biodegrada-
bility
Taste removal
Disinfection
+
it+
ttt
t
+
t
t
it
+
t-
t-
++
+
tt
ttt
tt
t-
t-
++
tt
ttt
+ t
+
? ?
?
t ?
t
t
t- t-
+
- no effect
+ littl e effect
tt
effect
ttt very effectiv e
For the evalu ation of the different properties and effects of an alternative
disinfectant it must be distinguished where it is applied in the treatment
process,(see Fig.31 either in preoxidation,
as an interm ediate step or in post-
disinfection, i.e. before or after the bulk of the organic matter, especially the
trihalomethane formation potential (THMFP) has been removed.
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Fig. 3. Influence of iight on residual Cl02 and chlorite concentration
Fig. 4. Possible positions of oxidation treatments in surface water treatment
process
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Preoxidation
Traditionall y preoxidation is performed,
at the beginning of the treatment
process, to ensure good
hygienic conditions throughout the treatment and to
control alga l growth in flocculation basins. Thus growth can be lim ited by
covering the basins p:‘ovitled
that ammon ia would be removed in subsequent
treatment steps.
Perman ganate. The applica tion of perman ganate in pretreatment oxidizes iron,
manganes e and destroys taste and odor causing substances. It can reduce THMFP but
at the pretreatment dosage usually appl ied the reduction of chloroform formation
is relatively modest (Singer et a1.,1980).
Perman ganate is not a very effective
disinfectant and a possible residual of
manganese precipitation in the
distribution system are two reasons why permang anate is rarely used in water
treatment.
Chlorin e dioxide. The great advantages of the use of chlorine dioxide in
pretreatment are algicidal effect and negligible formation of halogenated by-
products (Stevens 1 982). However, chlorine dioxide produces polar compounds such
as aldehydes,
ketones and acids (Rav Acha, 1984). The mai n inorganic by-products
is chlorite which is reported to be toxic.
Using mouse skin initi ation promoti on essays , amon g mice w hen concentrates
of water disinfected with chlorine dioxide were appli ed, no effect was
observed. However, short term toxicity of chlorine dioxide and more specifically
its inorganic reaction products may present a higher risk than chlorine or ozone
(Bull 19801.
Chlorite (C102-) and chlorate (C103-) in high concentrations (100 mg/l) have
been found to produce methemoglo binemia in animals (Komorita, 1985).
These
uncertainties have made health authorities reluctant to allow the applica tion of
chlorine dioxide in many countries. In some countries standards as low as 0.1
mg/l chlorites have been edicted. In order to main tain these inorganic by-
products at such a low level, the reagents and the by-products concentrations
have to be constantly monitor ed which cause. Many analytical problems are not yet
solved (Masschelein, 1984). The disinfective efficiency of chlorine dioxi de is
reported to be superior to that of chlorine (Hoff, 1981, Longley ,198l). On the
other hand when Cl02 is applied in open basins the photodecomposition of Cl02
necessitates the applica tion of an excessive dose (Fiessinger, 1981) (see Fig.4).
The costs for applying chlorine dioxide are 3 to 4 times than those for
chlorine (Gomella, 1980).
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Ozone. The preozonation of natural organic matter does not lead to its direct
removal as is reflected by nearly unchanged TOC values. The primary effect is to
modify the chemical nature of the molecules towards increase of polarity. The
increased polarity wil l in turn favor adsorbability in subsequent coagulati on
filtration and adsorption processes (Kuehn, 1981). A clear exampl e of improved
turbidity removal induced by oxidative pretreatment was found for preozonated
Sein e water (Fiessinger, 1981) (see Fig. 5). The same improvem ent however, could
be achieved by a slighty increased alum dose, such that in this case prcozonation
was an expensive means for saving on flocculant costs.
Reckhow and Singer (1984) have shown that preozonation of certain lake waters
reduced the formation potentials of THM and TOX significantly (see fig.6). Doses
exceeding 1.2 mg 03 per mg TOC per liter hampere d the removal of THM and TOX
precursors in alum coagulatio n,. Jekel however reported improved removal of
turbidity caused by humic acid coated miner al particles along with improved
particle agglomeration, when preozonation was applied in ratio's below 0.8 mg 03
per mg TOC (Jekel, 1983). Increase of that ratio had no further effect.
The polymerizing effect of ozone on smal l sized micropollutan ts may present
more interesting possibilities. Duguet and a1.(1985a)) using a dichlorop henol
synthetic organic compounds found that ozonation induced polymerizatio n to
hexamers and insoluble polymers, which will improve removal in coagulation
filtration.
As with other oxidants, ozonation also leads to formatio n of organic by-
products mostly aldehydes, ketones and carboxylic acids (Mal leviall e, 1980)
Especially aldehydes have been quantif ied (Van Hoof et al., 1985) .
Ozonation by-products may also induce mutagenicity in the treated water which
can be effectively removed by activated carbon (Van Hoof,1983). It is also
possible to dimi nish the production of mutagens duri ng ozonation by prolonged
contact time or dosage (Duguet et a1.,1984a) (see Fig.7). Ozonation of organic
matter will naturally increase biodegradability,(Peel and Benedek, 1983) which
can be considered (see Fig. 8) as an advantage as wel l as an disadvantage. This
mater ial must be removed biologic ally before the water leaves the treatment
plant since it may interfere with post disinfection. A principle disadvantage of
the biodegr adation taking place in biologi cally operated carbon filters is that a
complete ecology of higher plankton wil l develop and foul the filters. Practical
experience has shown that the filtered waters may contain heavy loads of
zooplankton during summer periods (Rook, 1983).
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1000
I
‘A
I
TA 98 - S9
.”
<
3
z
>
:
400
\
/
I ‘\
\
\
?, /
\
\I
\
d
200
t
‘h lOOmI
H20
Fig. 7. Effect of ozonation conditions on mutagenic activity of a ground
water at three sample volumes (Le Pecq, France)
30-
20-
lo-
0-
m..:A+-
.:.
. --
J/.-;”
,’
MAY JUL S EPT OCl
Fig. 8. Effects of ozone dose (00) and contact time (TC) on the biodegra dability
of a filtered water (SFW)
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In our view the full advantage of preoxidation can only be obtaine d when used
in combi nation with an effective means of removing biodeg radable subtances, such
as slow sand filtration . Walker observed in a comparative study (1984) of
preozonated slow sand filters a doubl ed removal of TOC, 35 % of the init ial 3.7
mg/l TOC versus 16 % in the non-ozonated control filter.
Post Disinfection
The reason for the use of disinfectants after the complete water treatment is
to kill or inactivate microorganisms still present to protect the distribution
system from regrowth and safeguard hygienic quality. This necessity is even more
pronounced if prechlorination is abandone d. In this case post-disinfection may be
the only hygienic barrier. The choice of disinfectant must be made on the basis
of germic idal activity and persistence for main taini ng a residual in the network
to prevent any further contam ination.
Experimental data show the following order
of decreasing germic idal efficiency 03 'Cl02 'HOC1 >OCl- > NHC12" NH2C l. Ozone
is the best disinfectant but its half life is not sufficient to mai ntain a
residual (see Fig. 9).
Moreover the applica tion of ozone may produce some
biodeg radable matter resulting in regrowth.
For chlorine dioxide this proble m exists to a less extent. Besides it has the
advantage of its long half life ensuring a residual throughout the network. At
the final point of the treatment
organic matter is at minim um. The formation of
chlorite by the organic matter reduction of Cl02 is than lim ited such that the
acute toxicity may be considered to be less significant.
Som e combinatio ns of oxidants like chloramin e + hydrogen peroxide have been
shown to improve control of bacterial regrowth in a treated surface water for
which chlorine disinfection was insufficient (Germonpre, 1985).
More studies
should be done to verify the efficencies of such combination s (H20,
03 + H202 +
UV, 03 t UV). Disinfection using UV involves different mechanisms such as direct
UV action and formation of high energetic radicals which have short half lifes,
but the problem of persistence remains.
This short survey shows that replacement
of chlorine by another disinfectant is not quite an easy task.
The ideal
disinfectant may have four mai n properties :
- germic idal effect
- persistent residual
- no precursor of toxic by-products
- low cost.
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DECR EASE IN RESIDUAL OZONE WITH TIME - SEINE WATER
o.51
.4-
;;i
E
\
; 0.3-
z
::
0
< 02
2
z
: O.l-
0
0 5
10 15
T (mid
Fig. 9. Decrease in residual ozone with time (Seine water, France)
Fig. 10. Chloroform formation during conventinal breakpoint chlorinatio n curve
0
TOC : 12mg/I
l- l
NH
4
:2gmg/l
”
\
2
-1000
2
%
E
h
T
RATIO Cl/N
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Chlorin e still remains the best availa ble means of disinfection. However
optimal
conditions for its applica tion must be determi ned with respect to a
min imiz ing by-product formation to ensure hygienic safeguard.
It is still
preferable to reduce the amm onia content by biolo gical treatment in order to
avoid high chlorine demands.
ALTERNATIVE STRATEGIES FOR A BETTER USE OF CHLORINE
With the objective to reduce haloge nated compounds such as THM's,
two
treatment strategies can be follow ed :
the chloramination and the use of chlorine
after a maxi mal reduction of organics and specifically mainly the precursors of
chlorinated compounds. The developm ent of new adsorbents such as activated
alum ina and resins may further improve the removal of precursors
Chloramination
As illustrated in figure 10 in natural water containing ammonia, the
trihalome thanes are formed at a chlorine dose corresponding to the destruction of
chloramines of free appearance of free chlorine.
Althou gh the chloramines are weak disinfectants they have alga l inhib iting
properties. With the objective to reduce haloge nated compounds, the pretreatment
may be realized with chloramines. In this case, the chlorine dose must be
adjusted to the maximum of chloramine with or without addition of ammonia. On
line measurem ent of chloramines is not easy and the process control is difficult
to realize.
The mai n problems related to chloramines are tastes and odors a nd some health
effects.
Although monochloramine is the predominant form at a pH of 8, the
correlated traces of di an trichloramines have offensive odors as found by
Krasner (1984) (Table 2).
TABLE 2
Sensory Threshold Values
Compou nds Threshold (mg/l as Cl21
Aroma Flavor
Hypochlorous acid 0.28 0.24
Hypochlorite ion 0.36 0.30
Monochloramine 0.65 0.48
Dichlor amine 0.15 0.13 (from : Krasner 1984)
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The health effects of chloramines and the knowledge of by-products formed
(organic chloramines . ..) need more research,
thus chloramines have recently
been found to cause hemolytic anem ia in patients undergo ing kidney dialysis
(Komorita, 1985).
To solve the problems of taste, odors and health effects
chloram ination may be follow ed by a chloram ine removal from water by reduction on
activated carbon which should be carefully monitor ed to produce a water of
desired quality. This alternative chlorination has a promisin g developm ent; thus
one of the largest water utiliti es
in the USA has changed from chlorine to
chloramines for the control of THM formation.
This control may be also realized by the use of chlorine after the reduction
of organics to a great extent.
OPTIMIZATION OF ORGANICS REMOVA L BEFORE CHLORINATION
As illustrated by figure 11 the use of chlorine only at the end of the water
treatment permits a great reduction of THM formation.
A low THM level may be
obtaine d by the optim ization of each treatment step. Coagulants such as A13+ and
Fe3+ remove significant concentrations of TOC and THM precursors which, in actual
practice tends to range from about 40 % to 70 %. Singer (1983 ) found that the
removals of THMFP concentrations tend to be higher than the corresponding
reduction in TOC. Some improvements in the utilization of metal coagulants can
result in a better reduction of precursors but the comb ination of ozone with an
ddsorbant like activated carbon can retain a large part of
organics from
clarified water. This unil operation is already used routinely in drinking water
production in Europe. However, activated carbon is a rather non specific
adsorbant which whil e a good principle, frequently leaves a fraction of organics
in the water which may give rise to haloge nated compounds during post-
chlorination . Improvements of the yield of the adsorption wil l be feasible by a
research of new adsorbants of different nature combine d with an optimiz ed
oxidation like e.g. ozone coupled with
hydrogen
peroxide (Ouguet et al,
1985b) (see Fig. 12). Ozonation in all cases produces polar products which are
less adsorbable by activated carbon. This is illustrated by shifts in the
adsorption isotherms shown in Figure 13. In a study reported by Duguet et al.
(1985b 1 the k-value of the Freundlich isotherm (TOC) was dimin ished by a factor
3 after preozonation. With activated alum ina, however, an increased adsorption
was observed, enhanced by the combine d action of 03 and H202. This case is an
examp le of an optim ization of organics removal which can lead to more effective
reduction of the formation of toxic compounds during final chlorinatio n.
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S
E
O
I
M
E
N
T
T
G
N
I
1
2
I
o
S
A
N
D
F
T
R
A
T
O
N
/
I
1
\
O
Z
O
N
A
T
O
N
\
\ -
o
G
A
C
F
L
R
A
T
O
N
C
H
L
O
R
I
N
E
D
I
S
I
N
F
C
T
O
N
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312
100
75
3 5c
E
2
2:
(
I 1
I’ o
n_.:_ ChP
I I
/ I
Ce(mg/l)
Fig. 13. Effect of ozonation on the isotherms for adsorption of a lake water
(Chalet) on alum ina and activated carbon.
An addi tiona l advantage of having rem oved organic matter as far as possible
is the reduction of chlorine consumption in the distribution system resulting in
lower doses needed for maintaining a desired residual. Depending on the state of
network mul tiple injections of low doses of chlorine at several crucial points
may be necessary.
CONCLUSIONS
- There is no satisfactory alternative for chlorinatio n:
. Prechlorination should be abandoned
. Alg al growth may be controlled with chloramines, or coverage of open
. sedime ntation basins
. Amm onia can be removed biologically
. Chlori ne dioxide and chloramines may constitute satisfactory interim
alternatives
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. Ozone should be used as a comple ment not for a replacement.
- Com binati on of oxidants migh t present interesting synergistic effects in
particular for oxidation 03 + UV.
- Chlorin e can be main tained as a final disinfectant if organic precursors are
sufficiently removed. Process sequences of oxidation, adsorption and
biodegr adation should be carefully designed.
- Disinfection practices should be revised in the light of new germs, Giardia,
Legionella, . . .
- Disinfection mechanisms should be further investigated.
- Megatrends
. New disinfectants
Immunological applications
Imm obilize d disinfectants, Ag . . .
nascent chlorine, electrical treatment
. Improved removal techniques
micro and ultrafiltratio n
improved coagulants
REFERENCES
Bruchet, A., Tsutsumi, Y.; Duguet, J.P. and Mall evia lle, J., 1984.
Characterization of total haloge nated compounds along various water
treatment processes. Presented to the Fifth Conference on Water
Chlorination.
Environmental Impact and Health
Effects. Williamsburg,
Virginia.
Bull, R.J., 1980.
Health effects of alternate disinfectants and their reaction
products. J. Awwa , 5: 299-303.
Christman, R.F., Norvood, D.L., Mill ingto n, D.S., Johnson J.D. and Stevens, AA
1983. Identificati on and yields of major haloge nated products of aquatic
fulvic acid chlorination . Env. Sci. tech., 17 : 625-628.'
Cognet, L., Duguet, J.P., Courtois, Y., Bordet, J.P. and Mall evial le, J., 1984.
Use of MRR for Ames test in a practical operating system. Congress of the
Division of Environmental Chemistry. ACS. Philadelphia , 26-31.
Colem an. W.E., Munc h. J.W.. Kavlor, W.H.. Streicher, R.P., Rinoha nd, H.P. and
Meier,
J.R. 1984:Gas chromatography/mass spectroscopy analysis of-mutagenic
extracts of aqueous chlorinated humic acid.
A comparison of the by-products
to drinking water contaminants. Env. Sci. Techn., 18: 674-681.
Duguet, J.P., Ellul, A., Brodard, E. and Mallevialle J., 1984a. Evolution de la
mutagenese au tours d'un treitement d'ozonation, IOA Congress, Brussels.
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Van Hoof, F., 1983. Remov al and formatio n of mutagenic activity by ozone. Proc.
ICA Symposiu m, "Environm ental Impact and benefit", Brussels, 410-423.
Van Hoof, F., Wittocx, A., Van Bruggenh out, E. and Janssens, J., 1985.
Determ ination of aliphati c aldehydes in water by high pressure liqu id
chroma tography . (in press).