Sterilization of Empty Containers for Food Industry OZONE CHEMISTRY AND TECHNOLOGY Downloaded from pubs.acs.org by UNIV OF TEXAS AT EL PASO on 10/22/18. For personal use only.
ALFRED TORRICELLI Falkenplatz 7, Berne, Switzerland
A novel method for sterilizing glass containers with ozonized air has been developed. W h e n used to replace a sulfur dioxide sterilization process, it resulted in substantial operating economies. Operation of a fully automatic soft drink plant is described.
A process f o r r a p i d s t e r i l i z a t i o n of t h e i n t e r i o r of e m p t y c o n t a i n e r s , w i t h o z o n a t e d air u n d e r pressure, was tested for t h e first t i m e i n 1952-53. T h e r e s u l t s were s a t i s f a c t o r y , a n d a l a r g e S w i s s f a c t o r y p r e p a r i n g soft d r i n k s w i t h a m i n e r a l w a t e r base h a s since a d o p t e d t h e n e w process f o r s t e r i l i z i n g b o t t l e s p r i o r t o filling. T h i s is t h e p l a n t of t h e Société des e a u x minérales d ' E p t i n g e n a t S i s s a c h , n e a r B a l e , t h e m o s t m o d e r n soft d r i n k f a c t o r y i n S w i t z e r l a n d . P r i o r t o 1954 t h e p l a n t w a s e q u i p p e d w i t h a m o d e r n i n s t a l l a t i o n f o r s t e r i l i z i n g b o t t l e s w i t h s u l f u r d i o x i d e . T h e d r a w b a c k s of t h i s process, a n d p a r t i c u l a r l y t h e h i g h o p e r a t i n g costs, i n s p i r e d t h e c o m p a n y m a n a g e m e n t t o l o o k f o r some o t h e r m e a n s of sterilization. T h e p r e s e n t ozone s t e r i l i z a t i o n i n s t a l l a t i o n a t S i s s a c h , t h e o n l y one of i t s k i n d , w a s p r e c e d e d b y a p i l o t p l a n t t e s t . F o r o v e r h a l f a y e a r t h e r e s u l t s of ozone a n d s u l f u r d i o x i d e s t e r i l i z a t i o n s were c o m p a r e d . F o r r a p i d i t y of s t e r i l i z a t i o n a n d t h e v i g o r of i t s b a c t e r i c i d a l a c t i o n , ozone w a s i n e v e r y w a y e q u a l t o s u l f u r d i o x i d e , e v e n w i t h ozone dosages o n l y one h u n d r e d t h as g r e a t . T h e o p e r a t i n g cost w i t h ozone p r o v e d t o be o n l y a b o u t one t w e n t i e t h t h e cost w i t h s u l f u r d i o x i d e . F i g u r e 1 is a s c h e m a t i c o u t l i n e of t h e p l a n t - s c a l e process, w h o s e a p p l i c a t i o n h a s been c o m p l e t e l y s a t i s f a c t o r y f r o m t h e s t a r t some 2 % y e a r s ago. Sterilization
Apparatus
F i g u r e 1 is a s c h e m a t i c d i a g r a m of t h e p l a n t - s c a l e process. T h e ozonated a i r for t h e s t e r i l i z a t i o n process is p r o d u c e d as follows : C o m p l e t e l y o i l - f r e e a i r is s u p p l i e d b y a compressor specially equipped for the project. T h e c o m p r e s s o r operates i n t e r m i t t e n t l y a n d a u t o m a t i c a l l y , f u r n i s h i n g a i r as r e q u i r e d . A i r p r e s s u r e is m a i n t a i n e d a t 7 1 p . s . i . (5 k g . p e r s q . c m . ) i n a s u p p l y t a n k w h i c h s m o o t h s o u t s u d d e n changes i n p r e s s u r e . O n l e a v i n g t h i s t a n k t h e p u r i f i e d a i r is c o o l e d b y w a t e r coils t o a t e m p e r a t u r e of 15° t o 18° C . T o d r y t h e a i r f o r g e n e r a t i n g o z o n e , a s y s t e m of d e h y d r a t i o n b y c o o l i n g w a s c h o s e n , as p u r e a i r c o m p r e s s e d t o 71 p . s . i . w a s a v a i l a b l e . I t sufficed, a t t h i s p r e s s u r e , t o r e d u c e t h e t e m p e r a t u r e of t h e c o m p r e s s e d a i r t o —35° C . i n o r d e r t o r e d u c e t h e h u m i d i t y t o 375
376
A D V A N C E S IN CHEMISTRY SERIES
WATER-COOLED REFRIGERATOR
OZONE
r-GOMPRESSED AIR 1 TANK (71 RS.I.)
a
-Mi
BOTTLES TO BE STERILIZED
EVACUATED
AIR
VACUUM OF 26 AIR COMPRESSOR
REFRIGERATIVE AIR DRIERS
FREON COMPRESSOR
@
WELSBACH C-102 OZONATOR
«FLOW D R Y AIR TMETER
VALVE REDUCING^ PRESSURE TO 16 R S J COMPRESSED OZONE DISTRIBUTION TANK-*
EVACUATED OZONE STERILE AIR
MAXIMUM PRODUCTION CAPACITY: 16,000 1-LITER OR 25,000
6-DECILITER BOTTLES PER HOUR
STERILIZED BOTTLES TO THE REFILLING MACHINE
OZONE PRODUCTION: 475 GRAMS PER HOUR AVERAGE OZONE CONCENTRATION: 30mg. PER LITER NORMAL STERILIZATION PERIOD: 15 TO 20 SECONDS ORGANISMS
-M3
DESTROYED: BACTERIA, MOLDS, AND YEASTS
M2-M3=SEITZ STERILIZING MACHINES
Figure 1.
Schematic diagram of installation for a utomatic sterilization of empty bottles with ozone
a b o u t 3 0 m g . p e r c u b i c m e t e r of free a i r , c o r r e s p o n d i n g t o a d e w p o i n t t e m p e r a t u r e of -50° C. T h e a i r - d r y i n g installation comprises t w o identical d r y i n g towers. E a c h tower is sufficient t o ensure d r y i n g of t h e a i r f o r 1 d a y b y m e a n s of a r e f r i g e r a t i o n m a c h i n e . T h e t o w e r u s e d f o r d r y i n g t h e a i r t h e p r e v i o u s d a y is d e f r o s t e d b y t h e h u m i d a i r b e f o r e t h e a i r passes t h r o u g h t h e t o w e r o n s t r e a m , i n w h i c h t h e t e m p e r a t u r e is f u r t h e r r e d u c e d t o less t h a n — 3 5 ° C . T h e p r e s s u r e of t h e d r y a i r l e a v i n g t h e c o o l i n g t o w e r is t h e n r e d u c e d b y a v a l v e t o 16 p.s.i., so t h a t ozone is finally a v a i l a b l e a t t h e s t e r i l i z i n g m a c h i n e a t a p r e s s u r e of a t least 14 p . s . i . T h e a i r is o z o n i z e d a t t h e d e s i r e d p r e s s u r e a n d c o n c e n t r a t i o n b y a W e l s b a c h C-102 industrial ozonator. T h e s t e r i l i z a t i o n process i t s e l f is b a s e d o n t h e f o l l o w i n g p r i n c i p l e : T h e bottles t o be sterilized, h a v i n g been freshly washed, rinsed, a n d d r a i n e d for a b o u t 3 0 seconds, a r e b r o u g h t c o n t i n u o u s l y o n t h e c h a i n c o n v e y o r , ab, t o t h e S e i t z s t e r i l i z i n g m a c h i n e , c o n v e r t e d t o t h e use of ozone. T h e f a c t o r y h a s t h r e e s t e r i l i z i n g m a c h i n e s , d e s i g n a t e d i n F i g u r e 1 as M M , a n d M . T w o of these m a c h i n e s were p r e v i o u s l y used for sterilization w i t h sulfur dioxide. T h e y have been converted b y t h e m a n u f a c t u r e r . T h e t h i r d is n e w ; i t w a s s p e c i a l l y c o n s t r u c t e d f o r use w i t h ozone i n a c c o r d a n c e w i t h e x p e r i m e n t s m a d e d u r i n g t h e tests. A s soon as i t a r r i v e s (c) i n t h e r o t a t i n g s t e r i l i z i n g m a c h i n e , t h e b o t t l e is a u t o m a t i c a l l y c o n n e c t e d t o a p u m p w h i c h i n d u c e s a v a c u u m i n t h e b o t t l e of a b o u t 26 inches of m e r c u r y . T h e a i r is e v a c u a t e d i n a b o u t 1 s e c o n d . D u r i n g t h e n e x t second t h e v a c u u m p u m p is a u t o m a t i c a l l y d i s c o n n e c t e d ( a t d) t o a l l o w t h e o z o n a t e d a i r u n d e r p r e s s u r e of 14 p . s . i . t o e n t e r t h e b o t t l e . T h e o z o n a t e d a i r i s f e d t h r o u g h a p n e u m a t i c storage a n d d i s t r i b u t i o n t a n k w h i c h s u p p l i e s one o r s e v e r a l m a c h i n e s . T h e bottle, r e filled w i t h o z o n a t e d a i r u n d e r p r e s s u r e , f o l l o w s t h e r o t a t i o n of t h e m a c h i n e a l o n g p a t h def d e s i g n a t e d as t h e s t e r i l i z a t i o n c y c l e . A t / t h e c o m p r e s s e d ozone i s f r e e d f r o m t h e b o t t l e a n d escapes t h r o u g h a v e n t . S t e r i l e a i r a t a t m o s p h e r i c p r e s s u r e replaces t h e ozone. T h e sterile b o t t l e leaves t h e s t e r i l i z i n g m a c h i n e a t g o n a c h a i n c o n v e y o r w h i c h b r i n g s i t t o t h e filling m a c h i n e . O n i t s w a y f r o m g t o h a p r o t e c t i v e screen of u l t r a v i o l e t r a y s p r o t e c t s t h e m o u t h of t h e b o t t l e f r o m r e i n f e c t i o n . 1}
y
2
3
377
TORRICELLI—STERILIZATION OF EMPTY CONTAINERS
T h e r e p l a c e m e n t of t h e o z o n a t e d a i r w i t h s t e r i l e a i r a t t h e e x i t of t h e s t e r i l i z i n g m a c h i n e is d e s i r a b l e t o a v o i d t h e presence of ozone i n t h e a t m o s p h e r e of t h e p l a n t . T h e n o r m a l c o n c e n t r a t i o n o f ozone i s a b o u t 3 0 m g . p e r l i t e r of c o m p r e s s e d g a s . T h i s c o n c e n t r a t i o n is sufficient t o ensure s t e r i l i z a t i o n a t t h e e n d of t h e c y c l e , w h i c h lasts 15 t o 2 0 seconds, a c c o r d i n g t o t h e speed of t h e m a c h i n e . T h e p r o d u c t i o n c a p a c i t y of t h i s i n s t a l l a t i o n i s 16,000 1-liter b o t t l e s o r 25,000 6 - d l . b o t t l e s p e r h o u r . A t t h i s r a t e of o u t p u t t h e ozone c o n s u m p t i o n i s 4 7 5 g r a m s . T h e speed of s t e r i l i z a t i o n is a n e c o n o m i c a l l y i m p o r t a n t f a c t o r . T h e same p r o d u c t i o n r h y t h m m u s t b e m a i n t a i n e d w i t h t h e s t e r i l i z i n g m a c h i n e s w h e n ozone i s u s e d as w h e n s u l f u r d i o x i d e i s u s e d . A n y u n d u e p r o l o n g a t i o n of t h e s t e r i l i z a t i o n c y c l e w o u l d r e q u i r e t h e c o n s t r u c t i o n of l a r g e r m a c h i n e s f o r t h e s a m e o u t p u t . Discussion F o r t h e success of r a p i d s t e r i l i z a t i o n w i t h ozone, t h e b o t t l e s s h o u l d c o n t a i n n o water i n the bottom. T h e i n s i d e w a l l of t h e b o t t l e is c o v e r e d w i t h o n l y a t h i n f i l m of w a t e r , w h i c h is sufficient t o ensure i n s t a n t a n e o u s h u m i d i f i c a t i o n of t h e d r y o z o n a t e d a i r t h e m o m e n t i t enters t h e b o t t l e . B e c a u s e s t e r i l i z a t i o n w i t h o z o n a t e d w a t e r w o u l d be s l o w e r , i t is necessary t o h a v e t h e b o t t o m of t h e b o t t l e d r y . T h e f o r m a t i o n of a t h i n m i s t i n t h e b o t t l e i n d i c a t e s a n a d e q u a t e h u m i d i f i c a t i o n of t h e o z o n a t e d a i r . E v a c u a t i o n of t h e a i r before i n t r o d u c t i o n of t h e ozone u n d e r p r e s s u r e a l l o w s a h i g h c o n c e n t r a t i o n of ozone t o b e r e a c h e d q u i c k l y i n t h e b o t t l e . T h e r e s u l t i s a n a p p r e c i a b l e r e d u c t i o n i n t h e s t e r i l i z a t i o n c y c l e . F i g u r e 2 i l l u s t r a t e s t h e difference b e t w e e n s t e r i l i z i n g w i t h o u t first e v a c u a t i n g t h e a i r , a n d s t e r i l i z a t i o n a c c o r d i n g t o t h e m e t h o d a t p r e s e n t u s e d . C u r v e Β i l l u s t r a t e s t h e process e m p l o y e d a t S i s s a c h . I t i n d i c a t e s t h e v a r i a t i o n s of ozone c o n c e n t r a t i o n i n t h e b o t t l e d u r i n g t h e s t e r i l i z a t i o n c y c l e , e x p r e s s e d i n p e r cent of t h e m a x i m u m c o n c e n t r a t i o n r e c o r d e d a t t h e e n d of t h e o p e r a t i o n . A t t h e e n d of t h e second second of t i m e , t h e b o t t l e c o n t a i n s a c o n c e n t r a t i o n e q u a l t o 8 0 % of t h e c o n c e n t r a t i o n r e c o r d e d a t t h e e n d o f t h e o p e r a t i o n . W h e n p r e l i m i n a r y e v a c u a t i o n does n o t t a k e p l a c e , t h e c o n c e n t r a t i o n o f ozone i n
Ο
I
2
3
4
STERILIZATION
Figure 2 .
5
6
7
8
CYCLE IN THE STERILIZING
9
ΙΟ
II
12
13
MACHINE, SECONDS
Effect of evacuating air from bottle before introduction of ozone
Relative ozone content of bottles during operation under pressure of 14.7 p.s.i.
A D V A N C E S IN CHEMISTRY SERIES
378
t h e b o t t l e increases m u c h m o r e s l o w l y , a n d a t t h e e n d a t t a i n s a m a x i m u m of o n l y 8 0 % of t h e c o n c e n t r a t i o n o b t a i n e d b y t h e p r e l i m i n a r y e v a c u a t i o n process ( c u r v e A). Thus, i f t h e a i r i s n o t p u m p e d o u t of t h e b o t t l e , a c o n s i d e r a b l e e x t e n s i o n of t h e s t e r i l i z a t i o n cycle is necessary. D u r i n g e x p e r i m e n t s w h i c h p r e c e d e d t h e a d o p t i o n of t h e n e w ozone process, t h e r e s u l t s of s t e r i l i z a t i o n w i t h s u l f u r d i o x i d e w e r e c o m p a r e d w i t h t h e r e s u l t s of ozone sterilization (with preliminary evacuation). T a b l e I is b a s e d o n d a t a f r o m a r e p o r t
T a b l e I. Comparative Results of Sterilization in Two Automatic Sterilizing Machines* Processes Sulfur dioxide Ozone (10-second cycle) (13-second cycle) Maximum Amount of Sterilizing Agent in Flask, M g . per Liter Control Flasks
+++ +++ +++ +++ +++ +++ ++ +++ +++ ++ +++ ++ +++ +++ +++
3000 to 3500
+ +
— — — — + 4— —
++ + ++
b
35
— — — — — — — — — — — — — — —
— — — — — — — — — — — — — —
+
» + + + = strongly infected (more than 1000 organisms per flask). + + = moderately infected (100 to 1000 organisms per flask). + = slightly infected (1 to 100 organisms per flask). — = sterile. Double series. b
b y t h e l a b o r a t o r y of t h e I n s t i t u t e of H y g i e n e a n d B a c t e r i o l o g y of t h e U n i v e r s i t y of B e r n e . T h e t a b l e p r e s e n t s t h e r e s u l t s of s t e r i l i z a t i o n o b t a i n e d w i t h flasks s t r o n g l y infected w i t h yeasts, molds, spore-forming bacteria, a n d other c o m m o n bacteria. M o s t of t h e c o n t r o l flasks c o n t a i n e d a c o n s i d e r a b l e n u m b e r of b a c t e r i a , e s t i m a t e d a t s e v e r a l t h o u s a n d p e r flask. O f t h e 15 flasks t r e a t e d w i t h s u l f u r d i o x i d e , o n l y s i x c a m e o u t of t h e m a c h i n e s t e r i l e . I n t h e t w o b a t c h e s of 30 flasks t r e a t e d w i t h ozone, o n l y one flask still contained three live bacteria. T h e s u p e r i o r i t y of ozone o v e r s u l f u r d i o x i d e i s u n d e n i a b l e , even c o n s i d e r i n g t h e different l e n g t h s of t h e s t e r i l i z a t i o n c y c l e s (10 seconds f o r s u l f u r d i o x i d e a n d 13 seconds f o r o z o n e ) . T h e o z o n e dosage u s e d w a s o n l y one h u n d r e d t h of t h a t of s u l f u r d i o x i d e . A l t h o u g h excellent r e s u l t s a r e o b t a i n e d b y o z o n e s t e r i l i z a t i o n i n 13 t o 15 seconds, i t i s r e c o m m e n d e d t h a t t h e s t e r i l i z a t i o n c y c l e b e m a i n t a i n e d i f p o s s i b l e a t n o less t h a n 18 seconds. F i g u r e s 3 a n d 4 s h o w v a r i o u s p a r t s of t h e S i s s a c h s t e r i l i z a t i o n i n s t a l l a t i o n . F i g u r e 3, A, shows t h e a i r c o m p r e s s o r i n s t a l l a t i o n , a n d a d j a c e n t t o i t , t h e t w o v a c c u m p u m p s f o r e m p t y i n g t h e b o t t l e s . A t t h e r i g h t is t h e t a n k h o l d i n g c l e a n a i r c o m p r e s s e d t o 71 p . s . i . F i g u r e 3, B, shows t h e i n s t a l l a t i o n f o r d r y i n g a i r b y r e f r i g e r a t i o n . F i g u r e 4, A, shows t h e W e l s b a c h C - 1 0 2 ozone g e n e r a t o r w i t h t h e i n d i c a t i n g a n d a u t o m a t i c c o n t r o l p a n e l f o r t h e e n t i r e ozone g e n e r a t i n g i n s t a l l a t i o n . O n t h e l e f t i s t h e c o m p r e s s e d ozone d i s t r i b u t i o n t a n k f r o m w h i c h t h e ozone i s p i p e d t o t h e t h r e e s t e r i l i z i n g m a c h i n e s . F i g u r e 4, B, i s of t h e S e i t z s t e r i l i z i n g m a c h i n e . T h i s f i r s t p l a n t f o r d i r e c t s t e r i l i z a t i o n of e m p t y b o t t l e s w i t h o z o n a t e d a i r o p e n s t h e w a y t o n e w i n d u s t r i a l a p p l i c a t i o n s i n t h e f o o d field. A s t u d y i s c u r r e n t l y i n p r o g r e s s
TORRICELLI—STERILIZATION OF EMPTY CONTAINERS
Figure 3 .
O z o n e sterilization installation at Sissach, Switzerland
379
A D V A N C E S IN
380
Figure 4 .
CHEMISTRY SERIES
O z o n e sterilization installation at Sissach
to a d a p t t h e process t o t h e m i l k i n d u s t r y f o r s t e r i l i z i n g b o t t l e s w h i c h w i l l be filled w i t h a b s o l u t e l y s t e r i l e m i l k p r e p a r e d b y a n e w process. A l a r g e Swiss m i l k c o m p a n y h a s been operating a pilot p l a n t for m o r e t h a n a year. RECEIVED for review June 6 , 1 9 5 7 .
Accepted June 19, 1957.
