ozone chemistry and technology - ACS Publications

Drinking Water Purification ALFRED TORRICELLI

Downloaded by UNIV OF CALIFORNIA SAN FRANCISCO on December 10, 2014 | http://pubs.acs.org Publication Date: January 1, 1959 | doi: 10.1021/ba-1959-0021.ch060

Falkenplatz 7 Berne, Switzerland

A comparison of conventional means of mixing ozone with water for disinfection with two recently developed methods shows that the newer methods permit more effective utilization of ozone. Operating experiences with pilot plants utilizing these systems are described. With the new methods ozone dosage requirements can be reduced by as much as one half, while maintaining full bactericidal efficiency.

France, t h e b i r t h p l a c e of ozone w a t e r t r e a t m e n t , i s t h e o n l y c o u n t r y i n E u r o p e t o r e m a i n f a i t h f u l t h r o u g h h a l f a c e n t u r y t o t h e i d e a of u s i n g ozone t o p u r i f y d r i n k ing water. T h e foremost authorities o n hygiene i n t h a t c o u n t r y , among w h o m were t h e late P r o f e s s o r s R o u x a n d C a l m e t t e of t h e P a s t e u r I n s t i t u t e , h a v e n e v e r ceased t o c o n s i d e r t h e t r e a t m e n t of w a t e r w i t h ozone t o b e t h e b e s t d i s i n f e c t i n g process k n o w n . I t does n o t a d d t o t h e w a t e r a n y i n j u r i o u s f o r e i g n s u b s t a n c e . M o r e o v e r , ozone n e v e r generates u n p l e a s a n t tastes, as c h l o r i n e a n d i t s d e r i v a t i v e s d o ; o n t h e c o n t r a r y , i t c a n d e s t r o y m o s t u n p l e a s a n t tastes a n d o d o r s . C o l o r due to organic decomposition p r o d u c t s i n w a t e r c a n also be r e m o v e d . O z o n e w a t e r p u r i f i c a t i o n p l a n t s c o n s t r u c t e d i n F r a n c e a b o u t t h e b e g i n n i n g of t h e c e n t u r y a r e s t i l l i n o p e r a t i o n . T h o s e w h o m a n a g e t h e m seem a w a r e t h a t ozone is a n i d e a l w a y t o p u r i f y d r i n k i n g w a t e r a n d t h a t t h e r e is n o t h i n g a t p r e s e n t a v a i l able w h i c h c a n replace i t . U n f o r t u n a t e l y , 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 t h e r e a l q u e s t i o n of t h e w h o l e someness of t h e w a t e r s u p p l y i n a l l i t s aspects h a s b e e n t o o o f t e n n e g l e c t e d , w i t h e m p h a s i s o n l y o n t h e p r o b l e m of 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 b a c t e r i a . Though doubtless t h e most i m p o r t a n t , this is n o t t h e o n l y question w h i c h s h o u l d be t a k e n i n t o c o n s i d e r a t i o n . T h e a i m of t h e h y g i e n i s t s h o u l d b e t o assure t h e c o m m u n i t y w a t e r w h i c h i s n o t o n l y safe, b u t also agreeable t o d r i n k . A t p r e s e n t , ozone best meets these r e q u i r e m e n t s . U p t o n o w , o z o n a t i o n of d r i n k i n g w a t e r h a s b e e n c o n s i d e r e d t o o d i f f i c u l t , e s p e cially i n comparison w i t h chlorination. T h e o u t l a y for the relatively expensive i n s t a l l a t i o n s a n d t h e h i g h costs of o p e r a t i o n w e r e o b j e c t i o n a b l e . I n m o s t cases t h e p l a n t s h a v e seemed u n p r o f i t a b l e . I t a p p e a r s , m o r e o v e r , t h a t a l l t h e E u r o p e a n o z o n a t i o n p l a n t s s t i l l e m p l o y w a t e r - t r e a t m e n t processes w h i c h d o n o t p e r m i t p r o p e r u t i l i z a t i o n of a l l t h e ozone p r o d u c e d b y t h e o z o n a t o r s . P e r h a p s 4 0 % of t h e ozone is lost because of t h e d i f f i c u l t y of d i s s o l v i n g t h e gas i n t h e w a t e r w i t h t h e a v a i l a b l e means. O n t h e o t h e r h a n d , t h e r e is n o d o u b t of t h e a c t u a l efficacy of t h e ozone w a t e r treatment i n the F r e n c h plants i n operation. 453

In OZONE CHEMISTRY AND TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1959.

ADVANCES

454

IN CHEMISTRY SERIES

T h e a u t h o r h a s b e e n o c c u p i e d w i t h t h e p r o b l e m of t h e best u t i l i z a t i o n of ozone f o r t h e p u r p o s e of r e d u c i n g t h e c o n s u m p t i o n of t h e gas t o a m i n i m u m w h i l e e n d e a v o r i n g t o o b t a i n m a x i m u m b a c t e r i c i d a l a c t i o n . A s a r e s u l t of t h i s r e s e a r c h , a n e w w a t e r t r e a t m e n t process f u l f i l l i n g t h e d e s i r e d o b j e c t i v e w a s i n t r o d u c e d f o r t h e first t i m e a t B e r n e i n 1951.


A t p r e s e n t i n E u r o p e , w a t e r is t r e a t e d w i t h ozone a c c o r d i n g t o t h e o l d O t t o process o r t h e V a n d e r M a d e process. A s f a r as i s k n o w n , o t h e r processes h a v e n o t b e c o m e e s t a b l i s h e d . T h e s e t w o a r e t h e o r i g i n a l s y s t e m s p r o p o s e d b y those w h o i n t r o d u c e d ozone i n t o F r a n c e . RAW WATER INLET

I EMULSEUR DESATURATOR ASPIRATED OZONE INLET"

, W / / ////*.

m

STERILIZED ~—WATER OUTLET

-SELF-CONTACT COLUMN TUBE FOR DISSOLVING UNDER PRESSURE

V T77

Figure 1.

v

; ; ν/ /

Schematic section of Otto apparatus for ozonating water

F i g u r e 1 is a s c h e m a t i c s e c t i o n of t h e O t t o s t e r i l i z a t i o n a p p a r a t u s , t h e m o s t c o m m o n l y u t i l i z e d . I t is u s e d g e n e r a l l y i n c o m b i n a t i o n w i t h O t t o p l a t e o z o n a t o r s . T h e w a t e r t o b e t r e a t e d comes u n d e r p r e s s u r e t o t h e émuiseur, a s o r t of w a t e r j e t p u m p . T h e v a c u u m p r o d u c e d b y t h e w a t e r i s sufficient t o s u c k i n t h e o z o n a t e d a i r f r o m t h e o z o n a t o r , a n d t h e m i x t u r e of t h e t w o fluids i s c a r r i e d t o t h e b o t t o m of t h e s e l f - c o n t a c t c o l u m n , w h i c h is a t o w e r 5 m e t e r s (16 feet 4 i n c h e s ) i n d e p t h . T h e w a t e r f a l l s f r e e l y f r o m a w e i r a t t h e t o p of t h e t o w e r , w h e r e m o s t of t h e gas escapes. T h e r e t e n t i o n t i m e i n t h e t o w e r is 8 t o 10 m i n u t e s . F o r e a c h c u b i c m e t e r of w a t e r t o be t r e a t e d , 300 t o 600 l i t e r s of o z o n a t e d a i r a t a c o n c e n t r a t i o n of 2 t o 3 m g . p e r l i t e r are r e q u i r e d ( a dosage of 0.6 t o 1.8 p . p . m . ) . T h e d i s i n f e c t i o n is excellent as l o n g as excess ozone is i n t r o d u c e d i n t o t h e émuiseur. L o s s of ozone w h i c h c a n n o t be d i s s o l v e d i n t h e w a t e r is c o n s i d e r a b l e . T h i s m e t h o d of w a t e r t r e a t m e n t is n o t e c o n o m i c a l w h e n e l e c t r i c i t y m u s t be purchased. I t is suitable for m o u n t a i n districts where the water arrives n a t u r a l l y u n d e r p r e s s u r e a t t h e p l a c e w h e r e i t is t o be t r e a t e d . T h e n t h e cost of e l e c t r i c i t y t o o p e r a t e a p u m p f o r t h e émuiseur is a v o i d e d , a n d excess w a t e r p r e s s u r e also c a n b e u s e d t o generate t h e e l e c t r i c i t y necessary f o r t h e o z o n a t i o n . B u t s u c h f a v o r a b l e c o n d i t i o n s a r e r a r e , e s p e c i a l l y f o r l a r g e centers of p o p u l a t i o n . F i g u r e 2 is a s c h e m a t i c s e c t i o n of t h e s t e r i l i z a t i o n a p p a r a t u s g e n e r a l l y u t i l i z e d w i t h V a n der M a d e ozonators. I t is a simple ozonation tower i n w h i c h the water t o be


455

TORRICELLI—DRINKING WATER PURIFICATION


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.COMPRESSED OZONE INLET 1

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Figure 2 .

Schematic section of V a n der M a d e apparatus for ozonating water

t r e a t e d enters a t t h e b o t t o m a n d leaves a t t h e t o p . T h e o z o n a t e d a i r is i n j e c t e d a t t h e b o t t o m t h r o u g h p o r o u s diffusers, w i t h t h e a i d of a c o m p r e s s o r p l a c e d b e t w e e n t h e o z o n a t o r a n d t h e o z o n a t i o n t o w e r . T h e ozone dosages a p p r o x i m a t e those of t h e O t t o process a n d t h e losses a r e l i k e w i s e c o n s i d e r a b l e . I n these t w o processes t h e o z o n a t i o n c o n d i t i o n s a r e s u c h t h a t efforts t o d i s s o l v e t h e ozone i n t h e w a t e r a t a h i g h r a t e e n c o u n t e r g r e a t difficulties. T h e ozone c o n t e n t of t h e w a t e r reaches i t s m a x i m u m a t t h e b o t t o m of t h e t o w e r , a n d t h e r a t i o t h e n d i m i n i s h e s as t h e o z o n a t e d a i r , m e a n w h i l e l o s i n g i t s ozone, sweeps t h e w a t e r t o w a r d t h e e x i t a t t h e t o p of t h e t o w e r . A t t e m p t s h a v e b e e n m a d e t o i m p r o v e t h e V a n d e r M a d e process b y r e c o v e r i n g t h e ozone w h i c h escapes f r o m t h e t o p of t h e o z o n a t i o n t o w e r b y p a s s i n g i t t h r o u g h a dryer a n d recycling i t t h r o u g h the ozonator. T h i s scheme h a s p r o d u c e d r e s u l t s of d u b i o u s v a l u e a n d a p p a r e n t l y is s e l d o m u s e d , b u t i t is a n i n d i c a t i o n of t h e i m p o r t a n c e a t t a c h e d t o l i m i t i n g t h e ozone losses, w h i c h a r e of i m p o r t a n t e c o n o m i c consequence. S i n c e 1947 a n effort h a s b e e n m a d e t o s t i m u l a t e i n t e r e s t i n S w i t z e r l a n d i n f a v o r of u s i n g ozone t o t r e a t d r i n k i n g w a t e r . D u r i n g t h i s p e r i o d s e v e r a l s m a l l i n s t a l l a t i o n s f o r o z o n a t i n g w a t e r h a v e a p p e a r e d i n S w i t z e r l a n d . M o s t of these were soon a b a n d o n e d because of defects a n d g e n e r a l inefficiency. U n f o r t u n a t e l y , i l l - c o n c e i v e d efforts s u c h as these h a v e c r e a t e d i n d e c i s i o n a n d h e s i t a t i o n a m o n g those w h o m i g h t h a v e b e e n i n c l i n e d t o a d o p t ozone. Processes D e m o n s t r a t e d a t B e r n e I n 1951 t h e p r o p e r t r e a t m e n t of w a t e r w i t h ozone w a s u n k n o w n i n S w i t z e r l a n d . Officials of t h e B e r n e W a t e r B u r e a u a c c e p t e d t h e p r o p o s a l t o c o n s t r u c t n e a r t h e Kônizberg reservoir a pilot p l a n t equipped w i t h a W e l s b a c h C - 4 ozonator to s u p p l y ozone t o t h e t w o w a t e r t r e a t m e n t s y s t e m s b y w h i c h t h e w a t e r w a s t o b e c o m p l e t e l y and economically purified. T h e t w o w a t e r t r e a t m e n t processes i n c l u d e d one u s e d i n t h e U n i t e d S t a t e s b y W e l s b a c h C o r p . , P h i l a d e l p h i a , P a . , a n d a n e w process of t h e a u t h o r ' s i n v e n t i o n , w h i c h


A D V A N C E S IN CHEMISTRY SERIES

456

w a s b e i n g t r i e d f o r t h e first t i m e . T h e l a t t e r i n v o l v e d t h e use of W e l s b a c h o z o n a t o r s , w h i c h h a d been f o u n d s u i t a b l e f o r t h i s a p p l i c a t i o n . E a c h o f t h e t w o o z o n a t i o n a p p l i c a t i o n s y s t e m s w a s c o n s t r u c t e d of c o n c r e t e a n d designed t o t r e a t 2 5 c u b i c m e t e r s (6600 g a l l o n s ) of w a t e r p e r h o u r . T h e y were s e r v e d a l t e r n a t e l y b y t h e single o z o n e - g e n e r a t i n g p l a n t w h i c h r a n c o n t i n u o u s l y d a y a n d n i g h t f o r n e a r l y 8 m o n t h s b e g i n n i n g O c t o b e r 1951, t o t h e c o m p l e t e s a t i s f a c t i o n of t h e B e r n e W a t e r B u r e a u as w e l l as o u r s e l v e s .


T h e first s y s t e m , a p p l y i n g t h e process u s e d b y W e l s b a c h C o r p . a t t h e P h i l a d e l p h i a p l a n t , i s d e s i g n a t e d t h e W e l s b a c h s y s t e m ( W ) . I t p e r m i t s o z o n a t i o n of w a t e r u n d e r c o n d i t i o n s m u c h s u p e r i o r t o t h e k n o w n E u r o p e a n processes. T h e s y s t e m i s d e p i c t e d s c h e m a t i c a l l y i n F i g u r e 3. F o r a n h o u r l y w a t e r flow of 25 c u b i c m e t e r s , a r e i n f o r c e d c o n c r e t e t o w e r of 9 0 - c m . i n s i d e d i a m e t e r is u s e d . T h e

GAS INTO THE WATER

Figure 3 .

Schematic section of Welsbach apparatus for ozonating water

tower is open a t t h e t o p , a n d t h e water t o be treated moves slowly f r o m t o p t o b o t t o m , just the opposite of t h e F r e n c h systems where t h e water moves concurrently w i t h t h e b u b b l e s of ozone. T h e d e p t h of t h e w a t e r i n t h e o z o n a t i o n t o w e r i s 5 m e t e r s . T h e a v e r a g e c o n t a c t t i m e of t h e w a t e r a n d gas i n t h e t o w e r is a b o u t 8 m i n u t e s . T h e o z o n a t e d gas, i n t h e f o r m of fine b u b b l e s , i s i n j e c t e d u n d e r p r e s s u r e t h r o u g h a p o r o u s gas diffuser i n t o t h e b o t t o m of t h e t o w e r , a n d t h e b u b b l e s of o z o n a t e d a i r rise c o u n t e r c u r r e n t t o t h e flow o f w a t e r . T h e o z o n a t e d w a t e r leaves t h e t o w e r a t t h e b o t t o m ; a c h a n n e l b r i n g s i t t o t h e l e v e l of t h e i n t a k e so as t o m a i n t a i n a c o n s t a n t l e v e l of w a t e r i n t h e t o w e r . A c e r t a i n n u m b e r of v a l v e s f o r t a k i n g w a t e r s a m p l e s a r e a r r a n g e d a t t h e p r i n c i p a l p o i n t s o f t h e s y s t e m , so as t o enable o n e t o f o l l o w t h e changes w h i c h o c c u r i n t h e w a t e r d u r i n g t r e a t ment. These water-sampling points correspond to various accurately determined water-ozone contact times. T h e second s y s t e m f o r w a t e r t r e a t m e n t , s h o w n s c h e m a t i c a l l y i n F i g u r e 4, d e p i c t s t h e a p p l i c a t i o n of t h e n e w process, c a l l e d t h e T o r r i c e l l i ( T ) process. T h e i n s t a l l a t i o n is c h a r a c t e r i z e d b y a n o z o n a t i o n c h a m b e r h y d r a u l i c a l l y closed b y t h e p r e s s u r e of t h e w a t e r t o b e t r e a t e d , w h i c h flows t h r o u g h i t . F o r these d e m o n s t r a t i o n s , t h e o z o n a t i o n c h a m b e r w a s c o n t a i n e d i n a r e i n f o r c e d c o n c r e t e c y l i n d e r 125 c m . i n i n s i d e d i a m e t e r a n d 2 3 0 c m . i n i n s i d e h e i g h t . I t w a s c o m p a r t m e n t e d as i n d i c a t e d i n F i g u r e 4. T h e w a t e r enters t h e o z o n a t i o n c h a m b e r b y a v e r t i c a l d e s c e n d i n g c h a n n e l 3 5 c m . i n d i a m e t e r a n d leaves b y a n a s c e n d i n g c h a n n e l . I t m o v e s t h r o u g h t h e s y s t e m u n d e r its o w n h e a d , a c c o r d i n g t o t h e p r i n c i p l e of c o m m u n i c a t i n g vessels. T h e loss of p r e s s u r e


457


RESIDUAL AIR

t

— . P U R E WATER ζΞΓ OUTLET

RAW WATER T — j j J a J INLET ^=^1


CHANNEL FOR RECOVERING OZONE FROM THE OZONAT ION CHAMBER FOR P R E OZONATION

* § - O U T L E T CHANNEL FOR T H E WATER β PRESSURE REGULATOR FOR OZONAT ION CHAMBER

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/-INJECTION OF GAS

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H22 0' (MIN.-SEC.)

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H24 H25 4'-12" 0-19" 0.23

H26 Γ-34" 0.19

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H 27 H 28 H*30 2-49" 3-26" 4-12" 0.23 0.20 020

H3I 7^4"

Figure 7. Rate of destruction of β. coli in Torricelli apparatus with 0.25 gram of ozone injected per cubic meter of water under head of 10 meters H. T. O.

Kônizberg pilot plant at Berne, June 1952 Sampling valves Intervals of time Ozone content of water, mg. per liter Bacteriological test on at least 2 X 100 ml. of water


461



T h e p r e o z o n a t i o n of t h e w a t e r b y m e a n s of excess ozone f r o m t h e o z o n a t i o n c h a m b e r has b e e n i n t r o d u c e d c h i e f l y t o u t i l i z e a l l t h e ozone i n j e c t e d i n t o t h e o z o n a t i o n c h a m b e r w a t e r . I n e l i m i n a t i n g ozone losses, t h e first c o n c e r n w a s t o r e d u c e t h e o p e r a t i n g a n d i n s t a l l a t i o n costs a p p r e c i a b l y . B u t i t was also d e s i r e d t o see i f , b y s a t i s f y i n g p a r t of t h e ozone d e m a n d of t h e w a t e r b e f o r e t h e a c t u a l d i s i n f e c t i o n o p e r a t i o n b y m e a n s of t h e r e c o v e r e d ozone, i t w o u l d be p o s s i b l e t o o b t a i n a s u b s e q u e n t l y m o r e p o w e r f u l b a c t e r i c i d a l a c t i o n w i t h s m a l l e r ozone dosages. T h e o b j e c t has b e e n a t t a i n e d . W h i l e t h e p u r p o s e of t h e p r e o z o n a t i o n b e f o r e t h e w a t e r enters t h e o z o n a t i o n c h a m b e r is n o t t o d e s t r o y t h e b a c t e r i a , i t was n e v e r t h e l e s s i n t e r e s t i n g t o c o n s i d e r t h e possible b a c t e r i c i d a l effect i n i t i a t e d d u r i n g p r e o z o n a t i o n . F i g u r e 7 shows t h a t t h e r e s i d u a l ozone f r o m t h e o z o n a t i o n c h a m b e r , w h e n t h e ozone dosage is o n l y 0.25 g r a m p e r c u b i c m e t e r of w a t e r , has n o b a c t e r i c i d a l effect w h a t e v e r .

Figure 8. Rate of destruction of B. coli in the Torricelli apparatus with 0.50 gram of ozone injected per cubic meter of water under a head of 10 meters Kônizberg pilot plant at Berne, June 1952 H.

Sampling values

T. O. *

Intervals of time Ozone content of water, mg. per liter Bacteriological test on at least 2 X 100 ml. of water

O n t h e o t h e r h a n d , F i g u r e 8 shows a p e r c e p t i b l e b a c t e r i c i d a l effect i n t h e p r e o z o n a t e d w a t e r w h e n 0.5 g r a m o f ozone p e r c u b i c m e t e r o f w a t e r h a s b e e n i n j e c t e d i n t o t h e o z o n a t i o n c h a m b e r . M o r e t h a n 9 9 . 9 % of t h e B. coli has b e e n d e s t r o y e d b y t h e r e s i d u a l ozone b e f o r e e n t e r i n g t h e o z o n a t i o n c h a m b e r . T h e r e s u l t s d e m o n s t r a t e r e m a r k a b l e p r o g r e s s i n t h e field of ozone t r e a t m e n t of d r i n k i n g w a t e r . T h e y s h o w t h a t s m a l l e r dosages a n d s h o r t e r r e t e n t i o n t i m e s a r e p o s s i b l e , a l l o w i n g s u b s t a n t i a l r e d u c t i o n i n costs. Processes C u r r e n t l y U s e d in

Berne

Plant

T h e e x t r a o r d i n a r i l y favorable results obtained w i t h the pilot p l a n t described above have not prevented the Berne W a t e r B u r e a u f r o m adopting, after a long wait, water t r e a t m e n t s y s t e m s of i t s o w n d e s i g n . D e s p i t e t h e r e c o m m e n d a t i o n n o t t o m o d i f y thf»


A D V A N C E S IN CHEMISTRY SERIES


462

n e w T o r r i c e l l i process, w h i c h h a d a r o u s e d p e r c e p t i b l e i n t e r e s t , t h e b u r e a u c o m b i n e d t h e process, u s i n g t h e o z o n a t i o n c h a m b e r u n d e r h y d r a u l i c p r e s s u r e w i t h some s p e c i a l systems for introducing the ozonated a i r into the water. Y e t , while conserving the p r i n c i p l e of t h e p r e s s u r e c h a m b e r of t h e process, t h e y d i d n o t use t h e r e s i d u a l ozone from the ozonation chamber. T h e f u l l - s c a l e B e r n e o z o n a t i o n p l a n t has been o p e r a t i n g since t h e s p r i n g of 1955. C o n s t r u c t e d t o t r e a t a m a x i m u m of 1000 c u b i c m e t e r s (264,000 g a l l o n s ) of w a t e r p e r h o u r , i t i s d i v i d e d i n t o t w o i n s t a l l a t i o n s able t o f u n c t i o n i n d e p e n d e n t l y . T h e c a p a c i t y of e a c h i s 500 c u b i c m e t e r s of w a t e r p e r h o u r . O n e o f t h e i n s t a l l a t i o n s i s f e d f r o m W e l s b a c h o z o n a t o r s , t h e o t h e r f r o m V a n de M a d e ozonators. E a c h i n s t a l l a t i o n h a s a c o m p a r t m e n t e d o z o n a t i o n c h a m b e r closed h y d r a u l i c a l l y u n d e r a p r e s s u r e of a b o u t 7 m e t e r s of w a t e r . B u t t h e s y s t e m f o r e x h a u s t i n g r e s i d u a l gas f r o m t h e c h a m b e r u n d e r p r e s s u r e is c h a n g e d , so t h a t i t n o l o n g e r serves its original purpose. T h e t w o systems for disinfecting water are depicted schematically i n Figures 9 a n d 10. I n t h e first s y s t e m ( I ) t h e o z o n a t e d gas is i n j e c t e d a t t h e b o t t o m of t h e first - WATER P R E S S U R E FOR T H E INJECTOR = 1.2 K 3 / c m (17 PSI) 2

OZONATED AIR FROM OZONATOR 0.57g/m FILTERED_ RAW WATER

3

WATER(=100%)

T A S P I R A T O R FOR OZONATED AIR C=CHLORATOR MIXING CYLINDER WITH B A F F L E S Ρ = W A T E R P R E S S U R E PUMP R= EVACUATION OF RESIDUAL GAS R s

3

α

GREATER PART OF WATER FOR TREATMENT

τ-,-Ι

WASTE

0Z0NE=l6%r

X

PU R E _ WATER TANK

(4/5 TO 9/10) r*-WATER E F F L U E N T

PIPING FOR INJECTION OF O Z O N A T E D ' AIR WITH 1/5 TO l/IO O F TOTAL WATER

Figure 9.

PIPING

D I S S O L V E D OZONE = 52.6 % OF QUANTITY INTRODUCED TWO COMPARTMENT OZONATION CHAMBER UNDER PRESSURE

Berne ozonation plant treatment apparatus, Installation I

To disinfect 500 cubic meters of water per hour (132,000 gallons) Ozone generation by Welsbach ozonators (max. 320 grams of O3 per hr.) Water treatment system. Chlorator combined with ozonation chamber (Torricelli process modified by Scheller) Normal ozone dosage per cubic meter of water, 0.4 gram Ozone concentration in air. 10 grams per cubic meter Retention time of water in ozonation chamber, about 10 minutes

under

hydraulic

pressure

c o m p a r t m e n t of t h e o z o n a t i o n c h a m b e r b y m e a n s of C h l o r a t o r émuiseur i n j e c t o r s a c t i v a t e d b y w a t e r u n d e r p r e s s u r e . F o r t h i s i n j e c t i o n of gas, one s i x t h t o one f o u r t h of t h e t o t a l q u a n t i t y of w a t e r t o be t r e a t e d is u s e d . T h e gas t h u s i n t r o d u c e d i n t o t h e o z o n a t i o n c h a m b e r i m m e d i a t e l y m i x e s a t one e n d of t h e c h a m b e r w i t h t h e r e m a i n i n g r a w w a t e r w h i c h a r r i v e s t h r o u g h a d e s c e n d i n g v e r t i c a l c h a n n e l . T h e u n d i s s o l v e d gas h e l d u n d e r p r e s s u r e a t t h e t o p of t h e o z o n a t i o n c h a m b e r is n o t u s e d t o p r e o z o n a t e t h e w a t e r ; i t i s s i m p l y e v a c u a t e d t h r o u g h a p i p e w h i c h discharges i n t o t h e a s c e n d i n g c h a n n e l t h r o u g h w h i c h t h e w a t e r leaves t h e o z o n a t i o n c h a m b e r . T h e a d v a n t a g e s of t h e T o r r i c e l l i process a r e c o n s e q u e n t l y a p p r e c i a b l y r e d u c e d ; t h e r e s i d u a l ozone f r o m t h e o z o n a t i o n c h a m b e r c a n n o t c o n t r i b u t e t o r a i s i n g t h e r a t i o of d i s s o l v e d ozone i n t h e w a t e r o f t h e o z o n a t i o n c h a m b e r , w h i c h is one of t h e objects of p r e o z o n a t i o n . I n t h e s e c o n d s y s t e m ( I I ) t h e r e i s a c o m p a r t m e n t e d o z o n a t i o n c h a m b e r closed h y d r a u l i c a l l y u n d e r p r e s s u r e . B u t here t h e o z o n a t e d a i r does n o t c o m e i n t o c o n t a c t w i t h


463

TORRICELLI—DRINKING WATER PURIFICATION OZONATED AIR FROM OZONATOR(UNDER

PRESSURE)

0 . 5 7 ^ / m WATER (100 °/

ozone chemistry and technology - ACS Publications

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