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Chlorine, Is There A Better Alternative?
235
CHLORINE, I S THERE A BETTER ALTERNATIVE? by t h e S t a f f of t h e D r i n k i n g Water R e s e a r c h D i v i s i o n , USEPA, Gordon G . Robeck, D i v i s i o n D i r e c t o r
ABSTRACT
In b r i e f , t h e c u r r e n t s t a t u s of o u r p r e s e n t knowledge r e g a r d i n g a l t e r n a t i v e s t o f r e e c h l o r i n e i s as f o l l o w s : 1.
B i o c i d a l C a p a b i l i t i e s - Ozone i s t h e most p o t e n t b i o c i d e of t h o s e u n d e r
consideration.
C h l o r i n e d i o x i d e i s a b o u t on a p a r w i t h hypochlorous a c i d ,
t h e most e f f i c i e n t form of f r e e r e s i d u a l c h l o r i n e .
Chlorine dioxide, i n
c o n t r a s t t o f r e e r e s i d u a l c h l o r i n e , i n c r e a s e s i n e f f i c i e n c y a s pH i n c r e a s e s above 6.
Chloramine i s a much weaker b i o c i d e t h a n h y p o c h l o r i t e i o n , t h e
least i n e f f i c i e n t form of f r e e r e s i d u a l c h l o r i n e .
2.
Health e f f e c t s
health effects.
-
A l l of t h e p o t e n t i a l a l t e r n a t i v e s may c a u s e some a d v e r s e
C h l o r i t e and c h l o r a t e , two of t h e r e a c t i o n p r o d u c t s of
c h l o r i n e d i o x i d e , have been shown t o c a u s e a s u b c l i n i c a l a p p a r e n t l y compensated h e m o l y t i c anemia i n r a t s .
On t h e o t h e r hand, a c c o r d i n g t o v e r y p r e l i m i n a r y
s t u d i e s , c h l o r i n e and a l l of t h e a l t e r n a t i v e s e x c e p t c h l o r i n e d i o x i d e have been shown t o produce r e a c t i o n p r o d u c t s from s u b s t a n c e s i n water t h a t c a n i n i t i a t e tumors i n mice.
A c t u a l l y , a l l d i s i n f e c t a n t s a r e r e a c t i v e molecules
c a p a b l e of a l t e r i n g t h e c h e m i c a l n a t u r e of o r g a n i c s u b s t a n c e s p r e s e n t i n t h e water.
Thus, t h e a l t e r n a t i v e d i s i n f e c t a n t s q u e s t i o n r e l a t e s t o o t h e r a s p e c t s
of w a t e r t r e a t m e n t p a r t i c u l a r l y t h e u s e of p r o c e s s e s f o r o r g a n i c p r e c u r s o r removal p r i o r t o d i s i n f e c t i o n .
3.
Technology and Economics
-
The s i m p l e s t and most economical c o n v e r s i o n f o r
many u t i l i t i e s , would be t o t h e u s e of c h l o r a m i n e s and t h e most d i f f i c u l t and e x p e n s i v e would be t o t h e u s e of ozone. intermediate i n cost.
C o n v e r s i o n t o c h l o r i n e d i o x i d e would be
INTRODUCTION
The p o t e n t i a l a l t e r n a t i v e s t o f r e e r e s i d u a l c h l o r i n e f o r d r i n k i n g w a t e r d i s i n f e c t i o n t h a t have r e c e i v e d major c o n s i d e r a t i o n i n t h e U n i t e d S t a t e s a r e c h l o r i n e d i o x i d e , ozone, and c h l o r a m i n e s .
A l l of t h e s e have been used e x t e n s i v e l y
i n d r i n k i n g water t r e a t m e n t , ( c h l o r a m i n e s i n t h e U.S.,
c h l o r i n e d i o x i d e and ozone
i n Europe and o t h e r a r e a s ) and t h e r e f o r e a l a r g e background of h i s t o r i c a l i n f o r m a t i o n and e x p e r i e n c e i s a v a i l a b l e .
Two comprehensive r e p o r t s on t h e s e
a l t e r n a t i v e d i s i n f e c t a n t s w e r e p u b l i s h e d w i t h i n t h e l a s t few y e a r s . "An Assessment of Ozone and C h l o r i n e Dioxide '"echnologies Water S u p p l i e s " (EPA 600/2-78/147,
Aug.
1
1978) c o n s i s t s of a s u r v e y of t h e u s e of
ozone and c h l o r i n e d i o x i d e f o r w a t e r t r e a m t e n t i n t h e U.S., The o t h e r i s a S t a t e - o f - t h e - A r t
One e n t i t l e d
f o r Treatment of Municipal Canada, and Europe.
r e p o r t e n t i t l e d "Ozone, C h l o r i n e D i o x i d e and
Chloramines a s A l t e r n a t i v e s t o C h l o r i n e f o r D i s i n f e c t i o n of D r i n k i n g Water." T h i s r e p o r t c o v e r s v a r i o u s a s p e c t s of each of t h e d i s i n f e c t a n t s , i n c l u d i n g g e n e r a t i o n , measurement a n d u s e , b i o c i d a l a s p e c t s , c h e m i s t r y and h e a l t h e f f e c t s of b y p r o d u c t s , and c o s t s .
I t was f i r s t i s s u e d i n November 1977 and was r e p r i n t e d
w i t h u p d a t e d r e f e r e n c e s t o more r e c e n t s t u d i e s i n O c t o b e r 1979.
Much of t h i s
m a t e r i a l i s b e i n g u p d a t e d i n a f o r t h c o m i n g handbook on t h e c o n t r o l of t r i h a l o m e thanes.
3
Many o t h e r d i s i n f e c t a n t s such as i o d i n e , u l t r a - v i o l e t ,
hydrogen p e r o x i d e ,
bromine c h l o r i d e , bromine, p o t a s s i u m permanganate a n d f e r r a t e i o n h a v e been s u g g e s t e d and t r i e d , b u t t h e d i s c u s s i o n i n t h i s p a p e r w i l l be c o n f i n e d t o ozone, c h l o r i n e d i o x i d e and c h l o r a m i n e s .
In b r i e f , t h e c u r r e n t s t a t u s of o u r p r e s e n t knowledge r e g a r d i n g t h e u s e of t h e s e d i s i n f e c t a n t s as a l t e r n a t i v e s t o f r e e c h l o r i n e i s a s f o l l o w s :
1.
Biocidal Activity The primary r e a s o n f o r t h e u s e of d i s i n f e c t a n t s i n t h e t r e a t m e n t of d r i n k i n g
w a t e r i s t o e n s u r e t h e d e s t r u c t i o n of p a t h o g e n i c microorganisms d u r i n g t h e treatment process, water.
t h e r e b y p r e v e n t i n g t h e t r a n s m i s s i o n of d i s e a s e by d r i n k i n g
Secondarily,
t h e p r e s e n c e of a d i s i n f e c t a n t i n t h e water d i s t r i b u t i o n
s y s t e m h e l p s t o m a i n t a i n t h e q u a l i t y of w a t e r by p r e v e n t i n g t h e growth of n u i s a n c e microorganisms. B i o c i d a l a c t i v i t y by c h e m i c a l d i s i n f e c t a n t s h a s f r e q u e n t l y been c o n s i d e r e d a k i n e t i c p r o c e s s s i m i l a r t o a c h e m i c a l r e a c t i o n , t h e microorganism b e i n g c o n s i d e r e d as one o f t h e s u b s t a n c e s i n v o l v e d i n t h e r e a c t i o n .
In c o n s i d e r i n g
t h e e f f e c t i v e n e s s o r e f f i c i e n c y of b i o c i d a l a g e n t s , t h e r a t e a t which t h e r e a c t i o n o r k i l l i n g of t h e m i c r o o r g a n i s m p o p u l a t i o n p r o c e e d s i s of concern.
231
The c o m p a r a t i v e b i o c i d a l e f f i c i e n c y of d i s i n f e c t a n t s i s f r e q u e n t l y e x p r e s s e d a s t h e r e l a t i v e c o n c e n t r a t i o n (mg/L) of d i f f e r e n t d i s i n f e c t a n t s needed t o o b t a i n e q u i v a l e n t d i s i n f e c t i o n rates o r as t h e r e l a t i v e i n a c t i v a t i o n r a t e s produced by t h e same c o n c e n t r a t i o n of d i f f e r e n t d i s i n f e c t i n g a g e n t s .
Most of t h i s i n f o r m a t i o n
h a s been o b t a i n e d by l a b o r a t o r y e x p e r i m e n t a t i o n u n d e r c a r e f u l l y c o n t r o l l e d c o n d i t i o n s i n " c l e a n " s y s t e m s i n t h e a b s e n c e of e x t r a n e o u s d i s i n f e c t a n t demanding s u b s t a n c e s and u s i n g p u r e c u l t u r e s of t h e m i c r o o r g a n i s m u n d e r s t u d y . The e x p e r i m e n t a l r e s u l t s show t h a t c h l o r i n e d i o x i d e a t pH 7 and c h l o r i n e i n t h e form of h y p o c h l o r o u s a c i d (HOC1) a t pH 6 produce s i m i l a r r a t e s of i n a c t i v a t i o n of
E.
&.
H y p o c h l o r i t e i o n (OCl-)
a t pH 10 was l e s s e f f e c t i v e and monochloramine
a t pH 9 and d i c h l o r a m i n e a t pH 4.5 w a s even l e s s e f f e c t i v e t h a n 0C1- a t pH 10. From t h e d a t a t h e d e g r e e of d i f f e r e n c e i n e f f i c i e n c y between t h e d i s i n f e c t a n t s c o u l d be c a l c u l a t e d and e x p r e s s e d q u a n t i t a t i v e l y , i . e . ,
as e f f e c t i v e a s OC1- a t pH 10.
H O C l a t pH 6 i s 35 t i m e s
H i g h e r d i s i n f e c t a n t c o n c e n t r a t i o n s and l o n g e r
c o n t a c t times i n g e n e r a l , a r e needed f o r i n a c t i v a t i o n of p o l i o v i r u s 1 t h a n € o r
E.
a.The
d i f f e r e n c e s a r e on t h e o r d e r of l e s s t h a n 1 t o 2 o r d e r s of magnitude,
depending on t h e d i s i n f e c t a n t used.
A l s o , t h e d i f f e r e n c e i n e f f i c i e n c y between
H O C l a t pH 6 and OC1- a t pH 1 0 i s o n l y a b o u t f o u r - f o l d
and t h e e f f i c i e n c y o r d e r
of t h e two t y p e s of combined c h l o r i n e i s r e v e r s e d . S i m i l a r s t u d i e s have n o t been done u s i n g ozone as t h e d i s i n f e c t a n t , m a i n l y b e c a u s e ozone i s s u c h a p o w e r f u l and u n s t a b l e d i s i n f e c t a n t t h a t l i m i t a t i o n s on s a m p l i n g t i m e s and ozone measurements make o b t a i n i n g good e x p e r i m e n t a l r e s u l t s difficult.
I n s p i t e of t h i s d i f f i c u l t y , S p r o u l ,
t h a n 99.999 p e r c e n t r e d u c t i o n of ozone c o n c e n t r a t i o n of 0.38 mg/L.
E. &
4 st. showed
that a greater
occurred i n 1 0 seconds a t a n i n i t i a l
S i m i l a r l y , a 99.7 p e r c e n t r e d u c t i o n of
p o l i o v i r u s 1 o c c u r r e d i n 1 0 s e c o n d s a t a n i n i t i a l ozone c o n c e n t r a t i o n of 0.012 mg/L. The d a t a p r e s e n t e d above i n d i c a t e t h e i n f l u e n c e of e n v i r o n m e n t a l f a c t o r s on disinfection.
T h i s means t h a t p r e c i s e r a n k i n g s of t h e t h r e e a l t e r n a t i v e
d i s i n f e c t a n t s , o z o n e , c h l o r i n e d i o x i d e , and c h l o r a m i n e s c a n n o t be made.
In
g e n e r a l , however, ozone and c h l o r i n e d i o x i d e a r e ranked a s s t r o n g d i s i n f e c t a n t s , n e a r l y e q u a l t o o r g r e a t e r t h a n f r e e c h l o r i n e even a t low pH.
Further, i n
c o n t r a s t t o f r e e c h l o r i n e , t h e d i s i n f e c t i n g power of n e i t h e r is reduced by i n c r e a s i n g pH and w i t h c h l o r i n e d i o x i d e t h e o p p o s i t e is t r u e .
Chloramines
a r e g e n e r a l l y ranked a s d i s i n f e c t a n t s t h a t a r e weaker t h a n f r e e c h l o r i n e a t a l l pH v a l u e s , b u t t h e y a r e a d e q u a t e i n many cases, a s some u t i l i t i e s have been s u c c e s s f u l l y u s i n g c h l o r a m i n e s f o r some time.
F u r t h e r , t h e e q u i l i b r i u m between
monochloramine and d i c h l o r a m i n e , which have d i f f e r e n t d i s i n f e c t i n g powers, i s i n f l u e n c e d by pH.
2.
Use of A l t e r n a t i v e D i s i n f e c t a n t s
Although none of t h e u n i t p r o c e s s e s s t u d i e d ( o z o n a t i o n , c h l o r a m i n a t i o n and t h e f e e d i n g of c h l o r i n e d i o x i d e )
produce t r i h a l o m e t h a n e s ,
each d i s i n f e c t a n t
s p e c i f i c a l l y h a s a d v a n t a g e s and d i s a d v a n t a g e s beyond t h e g e n e r a l d i s a d v a n t a g e of o r g a n i c by-product
formation.
Ozone i s a n e x c e l l e n t b i o c i d e and t h e b i o c i d a l a c t i v i t y i s n o t a f f e c t e d by t h e pH of t h e w a t e r . Ozone d o e s n o t prodoce a d i s i n f e c t a n t r e s i d u a l , however, and i f i t were used a l o n e , n o b i o c i d a l a g e n t would be p r e s e n t t h r o u g h o u t t h e d i s t r i b u t i o n system.
Although o v e r 1,000 w a t e r t r e a t m e n t p l a n t s a r o u n d t h e
w o r l d do g e n e r a t e ozone o n - s i t e ,
t h e g e n e r a t i o n equipment r e q u i r e d o n - s i t e i s
more e l a b o r a t e t h a n t h a t r e q u i r e d when c h l o r i n e i s u s e d as t h e d i s i n f e c t a n t . F i n a l l y , r e p o r t s from Europe have i n d i c a t e d t h a t when ozone i s u s e d , t h e o r g a n i c m a t e r i a l s i n t h e w a t e r become more b i o d e g r a d a b l e and t h i s f r e q u e n t l y r e s u l t s i n h i g h e r m i c r o b i o l o g i c a c t i v i t y i n t h e d i s t r i b u t i o n system. Chloramines h a v e t h e a d v a n t a g e of b e i n g e a s y t o g e n e r a t e and f e e d , and do produce a p e r s i s t e n t r e s i d u a l t h a t c a n be m a i n t a i n e d t h r o u g h o u t t h e d i s t r i b u t i o n system.
On t h e o t h e r hand, c h l o r a m i n e s a r e weaker b i o c i d e s , and t h e i r b i o c i d a l
a c t i o n becomes weaker when t h e pH of t h e water i s r a i s e d . Chlorine dioxide has s e v e r a l advantages a s a n a l t e r n a t i v e d i s i n f e c t a n t .
It i s
a good b i o c i d e and t h e b i o c i d a l a c t i v i t y i s c o n s i s t e n t o v e r t h e pH range u s u a l l y o c c u r r i n g i n w a t e r t r e a t m e n t and t h u s i t is u s e f u l i n most systems.
Chlorine
d i o x i d e c a n r e a d i l y be g e n e r a t e d and f e d , a l t h o u g h c a r e i s needed t o m a i n t a i n a low c o n c e n t r a t i o n of c h l o r i n e i n t h e g e n e r a t e d c h l o r i n e d i o x i d e .
Further,
c h l o r i n e dioxide produces a r e s i d u a l t h a t can p e r s i s t throughout t h e d i s t r i b u t i o n system.
F i n a l l y , a n o t h e r a d v a n t a g e of c h l o r i n e d i o x i d e i s t h a t i s d o e s n o t
r e a c t w i t h ammonia, a n d t h e r e f o r e , t h e d i s i n f e c t a n t demand f o r c h l o r i n e d i o x i d e may be somewhat l e s s t h a n f o r c h l o r i n e i n t h e same water.
A major disadvantage
of u s i n g c h l o r i n e d i o x i d e a s a d i s i n f e c t a n t a l t e r n a t i v e t o c h l o r i n e i s t h e p r o d u c t i o n of c h l o r a t e and c h l o r i t e which may be of h e a l t h s i g n i f i c a n c e when i n g e s t e d r e g u l a r l y . Summary of Treatment Approaches Although some p r o c e s s e s are e f f e c t i v e f o r t r i h a l o m e t h a n e removal, t h e f o r m a t i o n of o t h e r c h l o r i n a t i o n by-products
and t h e c o n t i n u e d f o r m a t i o n of some t r i h a l o -
methanes a f t e r t r e a t m e n t i f f r e e c h l o r i n e c o n t i n u e s t o be u s e d , may r e s u l t i n a t r i h a l o m e t h a n e problem r e m a i n i n g even a f t e r t r e a t m e n t .
The u s e of ozone,
chlorine dioxide o r chloramines as alternative disinfectants will reduce the trihalomethane problem remaining even after treatment. The use of ozone, chlorine dioxide o r chloramines as alternative disinfectants will reduce the trihalomethane concentration in drinking water substantially when replacing free chlorine, however, other problems may be created through their use, such as the formation of other organic by-products besides trihalomethanes.
Thus, lowering the concentration
of precursor materials in water is a more direct way of reducing any disinfectant by-products.
Of couse, there are several treatment alternatives for reducing
trihalomethane precursor concentrations.
Therefore, removal of trihalomethane
precursors may be the preferred way to reduce trihalomethanes o r other by-products instead of changing disinfectants. 3.
Health Effects The following, taken from Attachment 7 of the USEPA Trihalomethane Regulation,
summarizes the pertinent data on the toxicity of chloroform and the other trihalomethanes.
People are exposed to chloroform in the air they breathe and
the food they eat.
Analysis of the relative contribution of chloroform in
drinking water, air and food assumed various levels of exposure based on monitoring studies.
Drinking water may contribute from zero to more than 90
percent of the total body intake. Chloroform has been shown to be rapidly absorbed on oral and intraperitoneal administration and subsequently metabolized to carbon dioxide, chloride ion, phosgene and other unidentified metabolites.
The metabolic profile of chloroforn
in animal species such as mice, rats and monkeys is qualitatively similar to that in humans. Mammalian responses to chloroform exposure inclnde:
central nervous system
depression, hepatoxicity, nephrotoxicity, teratogenicity and carcinogenicity. These responses are discernible in mammals after oral and inhalation exposures to high levels of chloroform ranging from 30-350 mg/kg, the intensity of response being dependent upon the dose.
Although less toxicologic information is available
f o r the bromine-containing trihalomethanes, mutagenicity and carcinogenicity
have been detected in some test systems.
Physiological activity is thought to
be greater for the bromine-containing trihalomethanes than for chloroform. Although short-term toxic responses to trihalomethanes in drinking water are not documented, the potential effects of chronic exposures to trihalomethanes should be a matter of concern.
Prolonged administration of chloroform at relatively
high dose levels, 100 to 133 mg/kg, to rats and mice manifested oncogenic effects. Oncogenic effects were not observed at the lowest dose levels, 17 mg/kg, in three
experiments.
Because methods d o n o t now e x i s t t o e s t a b l i s h a " t h r e s h o l d no
e f f e c t " l e v e l of e x p o s u r e t o c a r c i n o g e n s , t h e p r e c e d i n g d a t a do n o t imply t h a t a " s a f e " l e v e l of e x p o s u r e c a n be e s t a b l i s h e d f o r humans. Human e p i d e m i o l o g i c e v i d e n c e i s i n c o n c l u s i v e , a l t h o u g h p o s i t i v e c o r r e l a t i o n s w i t h some c a n c e r s i t e s have been found i n s e v e r a l s t u d i e s .
Eighteen r e t r o s p e c t i v e
s t u d i e s t h a t h a v e i n v e s t i g a t e d some a s p e c t of a r e l a t i o n s h i p between c a n c e r m o r t a l i t y o r m o r b i d i t y and d r i n k i n g w a t e r v a r i a b l e s have been conducted.
Because
of v a r i o u s l i m i t a t i o n s i n t h e e p i d e m i o l o g i c methods, d i f f i c u l t i e s w i t h t h e w a t e r q u a l i t y d a t a and problems w i t h t h e i n d i v i d u a l s t u d i e s , t h e p r e s e n t e v i d e n c e c a n n o t l e a d t o a f i r m c o n c l u s i o n c o n c e r n i n g t h e e x i s t e n c e of a n a s s o c i a t i o n between c o n t a m i n a n t s i n d r i n k i n g w a t e r and c a n c e r m o r t a l i t y o r m o r b i d i t y .
Causal
r e l a t i o n s h i p s c a n n o t be proven on t h e b a s i s of r e s u l t s from e p i d e m i o l o g i c s t u d i e s . When viewed c o l l e c t i v e l y , however, t h e e p i d e m i o l o g i c s t u d i e s p r o v i d e s u f f i c i e n t e v i d e n c e f o r m a i n t a i n i n g t h e h y p o t h e s i s t h a t a h e a l t h r i s k may be o c c u r r i n g and t h a t t h e p o s i t i v e c o r r e l a t i o n s may be r e f l e c t i n g a c a u s a l a s s o c i a t i o n between c o n s t i t u e n t s of d r i n k i n g w a t e r and c a n c e r m o r t a l i t y . Using d i f f e r e n t models, p r e l i m i n a r y r i s k a s s e s s m e n t s made by t h e S c i e n c e Advisory Board, The N a t i o n a l Academy of S c i e n c e s and USEPA's C a r c i n o g e n Assessment Group have e s t i m a t e d t h e i n c r e m e n t a l r i s k s a s s o c i a t e d w i t h t h e e x p o s u r e from c h l o r o f o r m i n d r i n k i n g w a t e r .
The e x p o s u r e t o c h l o r o f o r m from a i r and
f o o d have n o t been i n c l u d e d i n t h e s e c o m p u t a t i o n s .
The r i s k e s t i m a t e s a s s o c i a t e d
w i t h t h e Maximum Contaminant L e v e l of 0.10 mg/L a r e e s s e n t i a l l y t h e same from t h e N a t i o n a l Academy of S c i e n c e s and t h e C a r c i n o g e n Assessment Group c o m p u t a t i o n s , i.e.,
a b o u t 3 t o 4 p e r s o n s would d e v e l o p c a n c e r per 10,000 p o p u l a t i o n consuming
two l i t e r s of w a t e r c o n t a i n i n g 0.10 mg/L c h l o r o f o r m d a i l y f o r 7 0 y e a r s .
In summary, on t h e b a s i s of t h e a v a i l a b l e t o x i c o l o g i c d a t a , c h l o r o f o r m h a s been shown t o be a c a r c i n o g e n i n m i c e and rats a t h i g h d o s e l e v e l s .
Because
i t s m e t a b o l i c p a t t e r n i n a n i m a l s i s q u a l i t a t i v e s i m i l a r t o t h a t i n humans, c h l o r o f o r m s h o u l d be s u s p e c t e d of b e i n g a human c a r c i n o g e n . s t u d i e s a l s o s u g g e s t a human r i s k .
Epidemiologic
Although d o c u m e n t a t i o n of t h e i r t o x i c i t y i s
n o t so w e l l e s t a b l i s h e d , o t h e r t r i h a l o m e t h a n e s s h o u l d be s u s p e c t e d of p o s i n g similar risk.
Because of t h e s e s u s p e c t e d h e a l t h e f f e c t s , t h e t r i h a l o m e t h a n e
r e g u l a t i o n was promulgated on November 29, 1979. T h e r e i s some e v i d e n c e t o s u g g e s t t h a t d i s i n f e c t a n t a l t e r n a t i v e s t o c h l o r i n e may c a u s e some a d v e r s e h e a l t h e f f e c t s t o o .
F o r example, c h l o r i t e and c h l o r a t e ,
two of t h e r a c t i o n p r o d u c t s of c h l o r i n e d i o x i d e , h a v e been shown t o c a u s e a s u b c l i n i c a l a p p a r e n t l y compensated h e m o l y t i c anemia i n r a t s .
On t h e o t h e r hand,
a c c o r d i n g t o v e r y p r e l i m i n a r y s t u d i e s , c h l o r i n e and a l l of t h e a l t e r n a t i v e s e x c e p t c h l o r i n e d i o x i d e h a v e been shown t o produce r e a c t i o n p r o d u c t s from s u b s t a n c e s
i n w a t e r t h a t c a n i n i t i a t e tumors i n mice. A l l of t h e s e f i n d i n g s are based on l i m i t e d s t u d y a n d f u r t h e r i n v e s t i g a t i o n s a r e underway t o d e t e r m i n e t h e s i g n i f i c a n c e of t h e s e r e s u l t s .
Actually, a l l
d i s i n f e c t a n t s a r e r e a c t i v e m o l e c u l e s c a p a b l e of a l t e r i n g t h e c h e m i c a l n a t u r e of o r g a n i c s u b s t a n c e s p r e s e n t i n t h e water.
These r e a c t i o n s may a c t t o e i t h e r
i n c r e a s e o r d e c r e a s e t h e h a z a r d s posed depending on t h e o r g a n i c s u b s t a n c e s present.
Thus, t h e a l t e r n a t i v e d i s i n f e c t a n t s q u e s t i o n r e l a t e s t o o t h e r a s p e c t s
of w a t e r t r e a t m e n t , p a r t i c u l a r l y t h e u s e of p r o c e s s e s f o r o r g a n i c p r e c u r s o r removal p r i o r t o d i s i n f e c t i o n .
4.
Technology a n d Economics
-
Technology f o r g e n e r a t i o n , a p p l i c a t i o n , and
measurement of a l l of t h e a l t e r n a t i v e s i s a v a i l a b l e .
R e s e a r c h on more e f f i c i e n t
mixing and c o n t a c t i n g d e v i c e s f o r ozone i s i n p r o g r e s s .
The s i m p l e s t and most
economical c o n v e r s i o n f o r many u t i l i t i e s , would be t o t h e u s e of c h l o r a m i n e s and t h e most d i f f i c u l t and e x p e n s i v e would be t o t h e u s e of ozone. C o n v e r s i o n t o c h l o r i n e d i o x i d e would be i n t e r m e d i a t e i n c o s t . T a b l e 1 p r e s e n t s c o m p a r a t i v e c o s t s f o r t h e a l t e r n a t i v e s and c h l o r i n e as t h e y might be t y p i c a l l y used.
Because most p l a n t s w i t h a problem p r e s e n t l y u s e c h l o r i n e ,
some c h a n g e s , such a s a d d i n g ammonia, may be a r e l a t i v e l y small i n c r e m e n t a l cost.
242
TABLE 1 E s t i m a t e d Treatment C o s t f o r A l t e r n a t i v e D i s i n f e c t a n t s b Treatment Capacitya m3/day (mgd) 37,800 (10)
378,000 (100)
T o t a l T r e a t m e n t Cost Process
Key Assumption
ChlorinationC
2 mg/L Dose
With c o n t a c t chamber
( 2 0 minutes)
Without c o n t a c t chamber
6/m3
~/IOOOg a l
6/12 m o o o
0.4
1
0.2
0.7
0.3
0.8
>0.1
0.4
0.4
1.6
0.2
1
0.4
1.1
>0.1
0.6
1 mg/L Dose
Chlorine Dioxide W i t h c o n t a c t chamber
(20 minutes)
Without c o n t a c t chamber
98 p e r c e n t r e d u c t i o n i n InstTHM c o n c e n t r a t i o n
E s t i m a t e d Performance
1 mg/L Dose
Ozone With c o n t a c t chamber
(10 m i n u t e s )
0.6
2.2
0.4
1.3
100 p e r c e n t r e d u c t i o n i n InstTHM c o n c e n t r a t i o n
E s t i m a t e d Performance
3 mg/L n o s e
Chloramines With c o n t a c t chamber
( 2 0 minutes)
Without c o n t a c t chamber E s t i m a t e d Performance
0.7
2.7
0.4
1.7
0.7
2.4
0.4
1.5
99 p e r c e n t r e d u c t i o n i n InstTHM c o n c e n t r a t i o n
a = Operating a t 7 0 p e r c e n t c a p a c i t y on t h e average. b = I n l o c a t i o n s where c l a r i f i c a t i o n p l a n t s a l r e a d y e x i s t , t r e a t m e n t c o s t s f o r improving t r i h a l o m e t h a n e p r e c u r s o r removal by c l a r i f i c a t i o n would o n l y i n v o l v e small changes i n c h e m i c a l c o s t , t h e r e f o r e t o t a l t r e a t m e n t c o s t s would be v e r y low.
Moving t h e p o i n t of c h l o r i n a t i o n from t h e s o u r c e water t o
l a t e r i n t h e t r e a t m e n t t r a i n may a c t u a l l y r e d u c e c h e m i c a l c o s t s and t h e r e f o r e t o t a l treatment costs. c = For c o m p a r a t i v e p u r p o s e s .
gal
243 REFERENCES
1 "An Assessment of Ozone and Chlorine Dioxide Technologies for Treatment of Municipal Water Supplies," Project document put out by U.S. EPA, Number: 2 3
4
EPA 6 0 0 / 2 - 7 8 / 1 4 7 , Aug. 1 9 7 8 , Cincinnati, Ohio 4 5 2 6 8 . "Ozone, Chlorine Dioxide and Chloramines a s Alternatives t o Chlorine for Disinfection of Drinking Water," U.S. EPA Report, 1977, Cincinnati, Ohio 4 5 2 6 8 (out of print). "Treatment Techniques for Controlling Trihalomethanes in Drinking Water," U.S. EPA Research Report, Cincinnati, Ohio 4 5 2 6 8 . Foster, D.M., Emerson, M.A., Buck, C.E., Walsh, D.S. and Sproul, O.J. "Ozone Inactivation of Cell and Fecal Associated Viruses and Bacteria." J. Water Poll. Cont. Fed., Vol. 52, Aug. 1980.
CHLORINE, I S THERE A BETTER ALTERNATIVE? by t h e S t a f f of t h e D r i n k i n g Water R e s e a r c h D i v i s i o n , USEPA, Gordon G . Robeck, D i v i s i o n D i r e c t o r
ABSTRACT
In b r i e f , t h e c u r r e n t s t a t u s of o u r p r e s e n t knowledge r e g a r d i n g a l t e r n a t i v e s t o f r e e c h l o r i n e i s as f o l l o w s : 1.
B i o c i d a l C a p a b i l i t i e s - Ozone i s t h e most p o t e n t b i o c i d e of t h o s e u n d e r
consideration.
C h l o r i n e d i o x i d e i s a b o u t on a p a r w i t h hypochlorous a c i d ,
t h e most e f f i c i e n t form of f r e e r e s i d u a l c h l o r i n e .
Chlorine dioxide, i n
c o n t r a s t t o f r e e r e s i d u a l c h l o r i n e , i n c r e a s e s i n e f f i c i e n c y a s pH i n c r e a s e s above 6.
Chloramine i s a much weaker b i o c i d e t h a n h y p o c h l o r i t e i o n , t h e
least i n e f f i c i e n t form of f r e e r e s i d u a l c h l o r i n e .
2.
Health e f f e c t s
health effects.
-
A l l of t h e p o t e n t i a l a l t e r n a t i v e s may c a u s e some a d v e r s e
C h l o r i t e and c h l o r a t e , two of t h e r e a c t i o n p r o d u c t s of
c h l o r i n e d i o x i d e , have been shown t o c a u s e a s u b c l i n i c a l a p p a r e n t l y compensated h e m o l y t i c anemia i n r a t s .
On t h e o t h e r hand, a c c o r d i n g t o v e r y p r e l i m i n a r y
s t u d i e s , c h l o r i n e and a l l of t h e a l t e r n a t i v e s e x c e p t c h l o r i n e d i o x i d e have been shown t o produce r e a c t i o n p r o d u c t s from s u b s t a n c e s i n water t h a t c a n i n i t i a t e tumors i n mice.
A c t u a l l y , a l l d i s i n f e c t a n t s a r e r e a c t i v e molecules
c a p a b l e of a l t e r i n g t h e c h e m i c a l n a t u r e of o r g a n i c s u b s t a n c e s p r e s e n t i n t h e water.
Thus, t h e a l t e r n a t i v e d i s i n f e c t a n t s q u e s t i o n r e l a t e s t o o t h e r a s p e c t s
of w a t e r t r e a t m e n t p a r t i c u l a r l y t h e u s e of p r o c e s s e s f o r o r g a n i c p r e c u r s o r removal p r i o r t o d i s i n f e c t i o n .
3.
Technology and Economics
-
The s i m p l e s t and most economical c o n v e r s i o n f o r
many u t i l i t i e s , would be t o t h e u s e of c h l o r a m i n e s and t h e most d i f f i c u l t and e x p e n s i v e would be t o t h e u s e of ozone. intermediate i n cost.
C o n v e r s i o n t o c h l o r i n e d i o x i d e would be
INTRODUCTION
The p o t e n t i a l a l t e r n a t i v e s t o f r e e r e s i d u a l c h l o r i n e f o r d r i n k i n g w a t e r d i s i n f e c t i o n t h a t have r e c e i v e d major c o n s i d e r a t i o n i n t h e U n i t e d S t a t e s a r e c h l o r i n e d i o x i d e , ozone, and c h l o r a m i n e s .
A l l of t h e s e have been used e x t e n s i v e l y
i n d r i n k i n g water t r e a t m e n t , ( c h l o r a m i n e s i n t h e U.S.,
c h l o r i n e d i o x i d e and ozone
i n Europe and o t h e r a r e a s ) and t h e r e f o r e a l a r g e background of h i s t o r i c a l i n f o r m a t i o n and e x p e r i e n c e i s a v a i l a b l e .
Two comprehensive r e p o r t s on t h e s e
a l t e r n a t i v e d i s i n f e c t a n t s w e r e p u b l i s h e d w i t h i n t h e l a s t few y e a r s . "An Assessment of Ozone and C h l o r i n e Dioxide '"echnologies Water S u p p l i e s " (EPA 600/2-78/147,
Aug.
1
1978) c o n s i s t s of a s u r v e y of t h e u s e of
ozone and c h l o r i n e d i o x i d e f o r w a t e r t r e a m t e n t i n t h e U.S., The o t h e r i s a S t a t e - o f - t h e - A r t
One e n t i t l e d
f o r Treatment of Municipal Canada, and Europe.
r e p o r t e n t i t l e d "Ozone, C h l o r i n e D i o x i d e and
Chloramines a s A l t e r n a t i v e s t o C h l o r i n e f o r D i s i n f e c t i o n of D r i n k i n g Water." T h i s r e p o r t c o v e r s v a r i o u s a s p e c t s of each of t h e d i s i n f e c t a n t s , i n c l u d i n g g e n e r a t i o n , measurement a n d u s e , b i o c i d a l a s p e c t s , c h e m i s t r y and h e a l t h e f f e c t s of b y p r o d u c t s , and c o s t s .
I t was f i r s t i s s u e d i n November 1977 and was r e p r i n t e d
w i t h u p d a t e d r e f e r e n c e s t o more r e c e n t s t u d i e s i n O c t o b e r 1979.
Much of t h i s
m a t e r i a l i s b e i n g u p d a t e d i n a f o r t h c o m i n g handbook on t h e c o n t r o l of t r i h a l o m e thanes.
3
Many o t h e r d i s i n f e c t a n t s such as i o d i n e , u l t r a - v i o l e t ,
hydrogen p e r o x i d e ,
bromine c h l o r i d e , bromine, p o t a s s i u m permanganate a n d f e r r a t e i o n h a v e been s u g g e s t e d and t r i e d , b u t t h e d i s c u s s i o n i n t h i s p a p e r w i l l be c o n f i n e d t o ozone, c h l o r i n e d i o x i d e and c h l o r a m i n e s .
In b r i e f , t h e c u r r e n t s t a t u s of o u r p r e s e n t knowledge r e g a r d i n g t h e u s e of t h e s e d i s i n f e c t a n t s as a l t e r n a t i v e s t o f r e e c h l o r i n e i s a s f o l l o w s :
1.
Biocidal Activity The primary r e a s o n f o r t h e u s e of d i s i n f e c t a n t s i n t h e t r e a t m e n t of d r i n k i n g
w a t e r i s t o e n s u r e t h e d e s t r u c t i o n of p a t h o g e n i c microorganisms d u r i n g t h e treatment process, water.
t h e r e b y p r e v e n t i n g t h e t r a n s m i s s i o n of d i s e a s e by d r i n k i n g
Secondarily,
t h e p r e s e n c e of a d i s i n f e c t a n t i n t h e water d i s t r i b u t i o n
s y s t e m h e l p s t o m a i n t a i n t h e q u a l i t y of w a t e r by p r e v e n t i n g t h e growth of n u i s a n c e microorganisms. B i o c i d a l a c t i v i t y by c h e m i c a l d i s i n f e c t a n t s h a s f r e q u e n t l y been c o n s i d e r e d a k i n e t i c p r o c e s s s i m i l a r t o a c h e m i c a l r e a c t i o n , t h e microorganism b e i n g c o n s i d e r e d as one o f t h e s u b s t a n c e s i n v o l v e d i n t h e r e a c t i o n .
In c o n s i d e r i n g
t h e e f f e c t i v e n e s s o r e f f i c i e n c y of b i o c i d a l a g e n t s , t h e r a t e a t which t h e r e a c t i o n o r k i l l i n g of t h e m i c r o o r g a n i s m p o p u l a t i o n p r o c e e d s i s of concern.
231
The c o m p a r a t i v e b i o c i d a l e f f i c i e n c y of d i s i n f e c t a n t s i s f r e q u e n t l y e x p r e s s e d a s t h e r e l a t i v e c o n c e n t r a t i o n (mg/L) of d i f f e r e n t d i s i n f e c t a n t s needed t o o b t a i n e q u i v a l e n t d i s i n f e c t i o n rates o r as t h e r e l a t i v e i n a c t i v a t i o n r a t e s produced by t h e same c o n c e n t r a t i o n of d i f f e r e n t d i s i n f e c t i n g a g e n t s .
Most of t h i s i n f o r m a t i o n
h a s been o b t a i n e d by l a b o r a t o r y e x p e r i m e n t a t i o n u n d e r c a r e f u l l y c o n t r o l l e d c o n d i t i o n s i n " c l e a n " s y s t e m s i n t h e a b s e n c e of e x t r a n e o u s d i s i n f e c t a n t demanding s u b s t a n c e s and u s i n g p u r e c u l t u r e s of t h e m i c r o o r g a n i s m u n d e r s t u d y . The e x p e r i m e n t a l r e s u l t s show t h a t c h l o r i n e d i o x i d e a t pH 7 and c h l o r i n e i n t h e form of h y p o c h l o r o u s a c i d (HOC1) a t pH 6 produce s i m i l a r r a t e s of i n a c t i v a t i o n of
E.
&.
H y p o c h l o r i t e i o n (OCl-)
a t pH 10 was l e s s e f f e c t i v e and monochloramine
a t pH 9 and d i c h l o r a m i n e a t pH 4.5 w a s even l e s s e f f e c t i v e t h a n 0C1- a t pH 10. From t h e d a t a t h e d e g r e e of d i f f e r e n c e i n e f f i c i e n c y between t h e d i s i n f e c t a n t s c o u l d be c a l c u l a t e d and e x p r e s s e d q u a n t i t a t i v e l y , i . e . ,
as e f f e c t i v e a s OC1- a t pH 10.
H O C l a t pH 6 i s 35 t i m e s
H i g h e r d i s i n f e c t a n t c o n c e n t r a t i o n s and l o n g e r
c o n t a c t times i n g e n e r a l , a r e needed f o r i n a c t i v a t i o n of p o l i o v i r u s 1 t h a n € o r
E.
a.The
d i f f e r e n c e s a r e on t h e o r d e r of l e s s t h a n 1 t o 2 o r d e r s of magnitude,
depending on t h e d i s i n f e c t a n t used.
A l s o , t h e d i f f e r e n c e i n e f f i c i e n c y between
H O C l a t pH 6 and OC1- a t pH 1 0 i s o n l y a b o u t f o u r - f o l d
and t h e e f f i c i e n c y o r d e r
of t h e two t y p e s of combined c h l o r i n e i s r e v e r s e d . S i m i l a r s t u d i e s have n o t been done u s i n g ozone as t h e d i s i n f e c t a n t , m a i n l y b e c a u s e ozone i s s u c h a p o w e r f u l and u n s t a b l e d i s i n f e c t a n t t h a t l i m i t a t i o n s on s a m p l i n g t i m e s and ozone measurements make o b t a i n i n g good e x p e r i m e n t a l r e s u l t s difficult.
I n s p i t e of t h i s d i f f i c u l t y , S p r o u l ,
t h a n 99.999 p e r c e n t r e d u c t i o n of ozone c o n c e n t r a t i o n of 0.38 mg/L.
E. &
4 st. showed
that a greater
occurred i n 1 0 seconds a t a n i n i t i a l
S i m i l a r l y , a 99.7 p e r c e n t r e d u c t i o n of
p o l i o v i r u s 1 o c c u r r e d i n 1 0 s e c o n d s a t a n i n i t i a l ozone c o n c e n t r a t i o n of 0.012 mg/L. The d a t a p r e s e n t e d above i n d i c a t e t h e i n f l u e n c e of e n v i r o n m e n t a l f a c t o r s on disinfection.
T h i s means t h a t p r e c i s e r a n k i n g s of t h e t h r e e a l t e r n a t i v e
d i s i n f e c t a n t s , o z o n e , c h l o r i n e d i o x i d e , and c h l o r a m i n e s c a n n o t be made.
In
g e n e r a l , however, ozone and c h l o r i n e d i o x i d e a r e ranked a s s t r o n g d i s i n f e c t a n t s , n e a r l y e q u a l t o o r g r e a t e r t h a n f r e e c h l o r i n e even a t low pH.
Further, i n
c o n t r a s t t o f r e e c h l o r i n e , t h e d i s i n f e c t i n g power of n e i t h e r is reduced by i n c r e a s i n g pH and w i t h c h l o r i n e d i o x i d e t h e o p p o s i t e is t r u e .
Chloramines
a r e g e n e r a l l y ranked a s d i s i n f e c t a n t s t h a t a r e weaker t h a n f r e e c h l o r i n e a t a l l pH v a l u e s , b u t t h e y a r e a d e q u a t e i n many cases, a s some u t i l i t i e s have been s u c c e s s f u l l y u s i n g c h l o r a m i n e s f o r some time.
F u r t h e r , t h e e q u i l i b r i u m between
monochloramine and d i c h l o r a m i n e , which have d i f f e r e n t d i s i n f e c t i n g powers, i s i n f l u e n c e d by pH.
2.
Use of A l t e r n a t i v e D i s i n f e c t a n t s
Although none of t h e u n i t p r o c e s s e s s t u d i e d ( o z o n a t i o n , c h l o r a m i n a t i o n and t h e f e e d i n g of c h l o r i n e d i o x i d e )
produce t r i h a l o m e t h a n e s ,
each d i s i n f e c t a n t
s p e c i f i c a l l y h a s a d v a n t a g e s and d i s a d v a n t a g e s beyond t h e g e n e r a l d i s a d v a n t a g e of o r g a n i c by-product
formation.
Ozone i s a n e x c e l l e n t b i o c i d e and t h e b i o c i d a l a c t i v i t y i s n o t a f f e c t e d by t h e pH of t h e w a t e r . Ozone d o e s n o t prodoce a d i s i n f e c t a n t r e s i d u a l , however, and i f i t were used a l o n e , n o b i o c i d a l a g e n t would be p r e s e n t t h r o u g h o u t t h e d i s t r i b u t i o n system.
Although o v e r 1,000 w a t e r t r e a t m e n t p l a n t s a r o u n d t h e
w o r l d do g e n e r a t e ozone o n - s i t e ,
t h e g e n e r a t i o n equipment r e q u i r e d o n - s i t e i s
more e l a b o r a t e t h a n t h a t r e q u i r e d when c h l o r i n e i s u s e d as t h e d i s i n f e c t a n t . F i n a l l y , r e p o r t s from Europe have i n d i c a t e d t h a t when ozone i s u s e d , t h e o r g a n i c m a t e r i a l s i n t h e w a t e r become more b i o d e g r a d a b l e and t h i s f r e q u e n t l y r e s u l t s i n h i g h e r m i c r o b i o l o g i c a c t i v i t y i n t h e d i s t r i b u t i o n system. Chloramines h a v e t h e a d v a n t a g e of b e i n g e a s y t o g e n e r a t e and f e e d , and do produce a p e r s i s t e n t r e s i d u a l t h a t c a n be m a i n t a i n e d t h r o u g h o u t t h e d i s t r i b u t i o n system.
On t h e o t h e r hand, c h l o r a m i n e s a r e weaker b i o c i d e s , and t h e i r b i o c i d a l
a c t i o n becomes weaker when t h e pH of t h e water i s r a i s e d . Chlorine dioxide has s e v e r a l advantages a s a n a l t e r n a t i v e d i s i n f e c t a n t .
It i s
a good b i o c i d e and t h e b i o c i d a l a c t i v i t y i s c o n s i s t e n t o v e r t h e pH range u s u a l l y o c c u r r i n g i n w a t e r t r e a t m e n t and t h u s i t is u s e f u l i n most systems.
Chlorine
d i o x i d e c a n r e a d i l y be g e n e r a t e d and f e d , a l t h o u g h c a r e i s needed t o m a i n t a i n a low c o n c e n t r a t i o n of c h l o r i n e i n t h e g e n e r a t e d c h l o r i n e d i o x i d e .
Further,
c h l o r i n e dioxide produces a r e s i d u a l t h a t can p e r s i s t throughout t h e d i s t r i b u t i o n system.
F i n a l l y , a n o t h e r a d v a n t a g e of c h l o r i n e d i o x i d e i s t h a t i s d o e s n o t
r e a c t w i t h ammonia, a n d t h e r e f o r e , t h e d i s i n f e c t a n t demand f o r c h l o r i n e d i o x i d e may be somewhat l e s s t h a n f o r c h l o r i n e i n t h e same water.
A major disadvantage
of u s i n g c h l o r i n e d i o x i d e a s a d i s i n f e c t a n t a l t e r n a t i v e t o c h l o r i n e i s t h e p r o d u c t i o n of c h l o r a t e and c h l o r i t e which may be of h e a l t h s i g n i f i c a n c e when i n g e s t e d r e g u l a r l y . Summary of Treatment Approaches Although some p r o c e s s e s are e f f e c t i v e f o r t r i h a l o m e t h a n e removal, t h e f o r m a t i o n of o t h e r c h l o r i n a t i o n by-products
and t h e c o n t i n u e d f o r m a t i o n of some t r i h a l o -
methanes a f t e r t r e a t m e n t i f f r e e c h l o r i n e c o n t i n u e s t o be u s e d , may r e s u l t i n a t r i h a l o m e t h a n e problem r e m a i n i n g even a f t e r t r e a t m e n t .
The u s e of ozone,
chlorine dioxide o r chloramines as alternative disinfectants will reduce the trihalomethane problem remaining even after treatment. The use of ozone, chlorine dioxide o r chloramines as alternative disinfectants will reduce the trihalomethane concentration in drinking water substantially when replacing free chlorine, however, other problems may be created through their use, such as the formation of other organic by-products besides trihalomethanes.
Thus, lowering the concentration
of precursor materials in water is a more direct way of reducing any disinfectant by-products.
Of couse, there are several treatment alternatives for reducing
trihalomethane precursor concentrations.
Therefore, removal of trihalomethane
precursors may be the preferred way to reduce trihalomethanes o r other by-products instead of changing disinfectants. 3.
Health Effects The following, taken from Attachment 7 of the USEPA Trihalomethane Regulation,
summarizes the pertinent data on the toxicity of chloroform and the other trihalomethanes.
People are exposed to chloroform in the air they breathe and
the food they eat.
Analysis of the relative contribution of chloroform in
drinking water, air and food assumed various levels of exposure based on monitoring studies.
Drinking water may contribute from zero to more than 90
percent of the total body intake. Chloroform has been shown to be rapidly absorbed on oral and intraperitoneal administration and subsequently metabolized to carbon dioxide, chloride ion, phosgene and other unidentified metabolites.
The metabolic profile of chloroforn
in animal species such as mice, rats and monkeys is qualitatively similar to that in humans. Mammalian responses to chloroform exposure inclnde:
central nervous system
depression, hepatoxicity, nephrotoxicity, teratogenicity and carcinogenicity. These responses are discernible in mammals after oral and inhalation exposures to high levels of chloroform ranging from 30-350 mg/kg, the intensity of response being dependent upon the dose.
Although less toxicologic information is available
f o r the bromine-containing trihalomethanes, mutagenicity and carcinogenicity
have been detected in some test systems.
Physiological activity is thought to
be greater for the bromine-containing trihalomethanes than for chloroform. Although short-term toxic responses to trihalomethanes in drinking water are not documented, the potential effects of chronic exposures to trihalomethanes should be a matter of concern.
Prolonged administration of chloroform at relatively
high dose levels, 100 to 133 mg/kg, to rats and mice manifested oncogenic effects. Oncogenic effects were not observed at the lowest dose levels, 17 mg/kg, in three
experiments.
Because methods d o n o t now e x i s t t o e s t a b l i s h a " t h r e s h o l d no
e f f e c t " l e v e l of e x p o s u r e t o c a r c i n o g e n s , t h e p r e c e d i n g d a t a do n o t imply t h a t a " s a f e " l e v e l of e x p o s u r e c a n be e s t a b l i s h e d f o r humans. Human e p i d e m i o l o g i c e v i d e n c e i s i n c o n c l u s i v e , a l t h o u g h p o s i t i v e c o r r e l a t i o n s w i t h some c a n c e r s i t e s have been found i n s e v e r a l s t u d i e s .
Eighteen r e t r o s p e c t i v e
s t u d i e s t h a t h a v e i n v e s t i g a t e d some a s p e c t of a r e l a t i o n s h i p between c a n c e r m o r t a l i t y o r m o r b i d i t y and d r i n k i n g w a t e r v a r i a b l e s have been conducted.
Because
of v a r i o u s l i m i t a t i o n s i n t h e e p i d e m i o l o g i c methods, d i f f i c u l t i e s w i t h t h e w a t e r q u a l i t y d a t a and problems w i t h t h e i n d i v i d u a l s t u d i e s , t h e p r e s e n t e v i d e n c e c a n n o t l e a d t o a f i r m c o n c l u s i o n c o n c e r n i n g t h e e x i s t e n c e of a n a s s o c i a t i o n between c o n t a m i n a n t s i n d r i n k i n g w a t e r and c a n c e r m o r t a l i t y o r m o r b i d i t y .
Causal
r e l a t i o n s h i p s c a n n o t be proven on t h e b a s i s of r e s u l t s from e p i d e m i o l o g i c s t u d i e s . When viewed c o l l e c t i v e l y , however, t h e e p i d e m i o l o g i c s t u d i e s p r o v i d e s u f f i c i e n t e v i d e n c e f o r m a i n t a i n i n g t h e h y p o t h e s i s t h a t a h e a l t h r i s k may be o c c u r r i n g and t h a t t h e p o s i t i v e c o r r e l a t i o n s may be r e f l e c t i n g a c a u s a l a s s o c i a t i o n between c o n s t i t u e n t s of d r i n k i n g w a t e r and c a n c e r m o r t a l i t y . Using d i f f e r e n t models, p r e l i m i n a r y r i s k a s s e s s m e n t s made by t h e S c i e n c e Advisory Board, The N a t i o n a l Academy of S c i e n c e s and USEPA's C a r c i n o g e n Assessment Group have e s t i m a t e d t h e i n c r e m e n t a l r i s k s a s s o c i a t e d w i t h t h e e x p o s u r e from c h l o r o f o r m i n d r i n k i n g w a t e r .
The e x p o s u r e t o c h l o r o f o r m from a i r and
f o o d have n o t been i n c l u d e d i n t h e s e c o m p u t a t i o n s .
The r i s k e s t i m a t e s a s s o c i a t e d
w i t h t h e Maximum Contaminant L e v e l of 0.10 mg/L a r e e s s e n t i a l l y t h e same from t h e N a t i o n a l Academy of S c i e n c e s and t h e C a r c i n o g e n Assessment Group c o m p u t a t i o n s , i.e.,
a b o u t 3 t o 4 p e r s o n s would d e v e l o p c a n c e r per 10,000 p o p u l a t i o n consuming
two l i t e r s of w a t e r c o n t a i n i n g 0.10 mg/L c h l o r o f o r m d a i l y f o r 7 0 y e a r s .
In summary, on t h e b a s i s of t h e a v a i l a b l e t o x i c o l o g i c d a t a , c h l o r o f o r m h a s been shown t o be a c a r c i n o g e n i n m i c e and rats a t h i g h d o s e l e v e l s .
Because
i t s m e t a b o l i c p a t t e r n i n a n i m a l s i s q u a l i t a t i v e s i m i l a r t o t h a t i n humans, c h l o r o f o r m s h o u l d be s u s p e c t e d of b e i n g a human c a r c i n o g e n . s t u d i e s a l s o s u g g e s t a human r i s k .
Epidemiologic
Although d o c u m e n t a t i o n of t h e i r t o x i c i t y i s
n o t so w e l l e s t a b l i s h e d , o t h e r t r i h a l o m e t h a n e s s h o u l d be s u s p e c t e d of p o s i n g similar risk.
Because of t h e s e s u s p e c t e d h e a l t h e f f e c t s , t h e t r i h a l o m e t h a n e
r e g u l a t i o n was promulgated on November 29, 1979. T h e r e i s some e v i d e n c e t o s u g g e s t t h a t d i s i n f e c t a n t a l t e r n a t i v e s t o c h l o r i n e may c a u s e some a d v e r s e h e a l t h e f f e c t s t o o .
F o r example, c h l o r i t e and c h l o r a t e ,
two of t h e r a c t i o n p r o d u c t s of c h l o r i n e d i o x i d e , h a v e been shown t o c a u s e a s u b c l i n i c a l a p p a r e n t l y compensated h e m o l y t i c anemia i n r a t s .
On t h e o t h e r hand,
a c c o r d i n g t o v e r y p r e l i m i n a r y s t u d i e s , c h l o r i n e and a l l of t h e a l t e r n a t i v e s e x c e p t c h l o r i n e d i o x i d e h a v e been shown t o produce r e a c t i o n p r o d u c t s from s u b s t a n c e s
i n w a t e r t h a t c a n i n i t i a t e tumors i n mice. A l l of t h e s e f i n d i n g s are based on l i m i t e d s t u d y a n d f u r t h e r i n v e s t i g a t i o n s a r e underway t o d e t e r m i n e t h e s i g n i f i c a n c e of t h e s e r e s u l t s .
Actually, a l l
d i s i n f e c t a n t s a r e r e a c t i v e m o l e c u l e s c a p a b l e of a l t e r i n g t h e c h e m i c a l n a t u r e of o r g a n i c s u b s t a n c e s p r e s e n t i n t h e water.
These r e a c t i o n s may a c t t o e i t h e r
i n c r e a s e o r d e c r e a s e t h e h a z a r d s posed depending on t h e o r g a n i c s u b s t a n c e s present.
Thus, t h e a l t e r n a t i v e d i s i n f e c t a n t s q u e s t i o n r e l a t e s t o o t h e r a s p e c t s
of w a t e r t r e a t m e n t , p a r t i c u l a r l y t h e u s e of p r o c e s s e s f o r o r g a n i c p r e c u r s o r removal p r i o r t o d i s i n f e c t i o n .
4.
Technology a n d Economics
-
Technology f o r g e n e r a t i o n , a p p l i c a t i o n , and
measurement of a l l of t h e a l t e r n a t i v e s i s a v a i l a b l e .
R e s e a r c h on more e f f i c i e n t
mixing and c o n t a c t i n g d e v i c e s f o r ozone i s i n p r o g r e s s .
The s i m p l e s t and most
economical c o n v e r s i o n f o r many u t i l i t i e s , would be t o t h e u s e of c h l o r a m i n e s and t h e most d i f f i c u l t and e x p e n s i v e would be t o t h e u s e of ozone. C o n v e r s i o n t o c h l o r i n e d i o x i d e would be i n t e r m e d i a t e i n c o s t . T a b l e 1 p r e s e n t s c o m p a r a t i v e c o s t s f o r t h e a l t e r n a t i v e s and c h l o r i n e as t h e y might be t y p i c a l l y used.
Because most p l a n t s w i t h a problem p r e s e n t l y u s e c h l o r i n e ,
some c h a n g e s , such a s a d d i n g ammonia, may be a r e l a t i v e l y small i n c r e m e n t a l cost.
242
TABLE 1 E s t i m a t e d Treatment C o s t f o r A l t e r n a t i v e D i s i n f e c t a n t s b Treatment Capacitya m3/day (mgd) 37,800 (10)
378,000 (100)
T o t a l T r e a t m e n t Cost Process
Key Assumption
ChlorinationC
2 mg/L Dose
With c o n t a c t chamber
( 2 0 minutes)
Without c o n t a c t chamber
6/m3
~/IOOOg a l
6/12 m o o o
0.4
1
0.2
0.7
0.3
0.8
>0.1
0.4
0.4
1.6
0.2
1
0.4
1.1
>0.1
0.6
1 mg/L Dose
Chlorine Dioxide W i t h c o n t a c t chamber
(20 minutes)
Without c o n t a c t chamber
98 p e r c e n t r e d u c t i o n i n InstTHM c o n c e n t r a t i o n
E s t i m a t e d Performance
1 mg/L Dose
Ozone With c o n t a c t chamber
(10 m i n u t e s )
0.6
2.2
0.4
1.3
100 p e r c e n t r e d u c t i o n i n InstTHM c o n c e n t r a t i o n
E s t i m a t e d Performance
3 mg/L n o s e
Chloramines With c o n t a c t chamber
( 2 0 minutes)
Without c o n t a c t chamber E s t i m a t e d Performance
0.7
2.7
0.4
1.7
0.7
2.4
0.4
1.5
99 p e r c e n t r e d u c t i o n i n InstTHM c o n c e n t r a t i o n
a = Operating a t 7 0 p e r c e n t c a p a c i t y on t h e average. b = I n l o c a t i o n s where c l a r i f i c a t i o n p l a n t s a l r e a d y e x i s t , t r e a t m e n t c o s t s f o r improving t r i h a l o m e t h a n e p r e c u r s o r removal by c l a r i f i c a t i o n would o n l y i n v o l v e small changes i n c h e m i c a l c o s t , t h e r e f o r e t o t a l t r e a t m e n t c o s t s would be v e r y low.
Moving t h e p o i n t of c h l o r i n a t i o n from t h e s o u r c e water t o
l a t e r i n t h e t r e a t m e n t t r a i n may a c t u a l l y r e d u c e c h e m i c a l c o s t s and t h e r e f o r e t o t a l treatment costs. c = For c o m p a r a t i v e p u r p o s e s .
gal
243 REFERENCES
1 "An Assessment of Ozone and Chlorine Dioxide Technologies for Treatment of Municipal Water Supplies," Project document put out by U.S. EPA, Number: 2 3
4
EPA 6 0 0 / 2 - 7 8 / 1 4 7 , Aug. 1 9 7 8 , Cincinnati, Ohio 4 5 2 6 8 . "Ozone, Chlorine Dioxide and Chloramines a s Alternatives t o Chlorine for Disinfection of Drinking Water," U.S. EPA Report, 1977, Cincinnati, Ohio 4 5 2 6 8 (out of print). "Treatment Techniques for Controlling Trihalomethanes in Drinking Water," U.S. EPA Research Report, Cincinnati, Ohio 4 5 2 6 8 . Foster, D.M., Emerson, M.A., Buck, C.E., Walsh, D.S. and Sproul, O.J. "Ozone Inactivation of Cell and Fecal Associated Viruses and Bacteria." J. Water Poll. Cont. Fed., Vol. 52, Aug. 1980.