INTEGRATED BLANCHING AND COOLING TO REDUCE PLANT EFFLUENT

John L. Bomben*, George E . Brown*, W i l l i a m C . Die t r ich* , Joyce S. Hudson* and Daniel F. Farkas*

INTRODUCTION

Blanching of vege tab les f o r f r e e z i n g , canning o r dehydrat ion produces a l a r g e po r t ion of t h e t o t a l o rganic s o l i d s i n a p l a n t e f f l u e n t (1). In most cases over 50% of the p l a n t BOD is due t o blanching and cool ing . Reducing t h i s e f f l u e n t would g ive a l a r g e reduct ion i n t h e 800 m i l l i o n pounds of BOD and 392 m i l l i o n pounds of suspended s o l i d s produced by t h e canned and frozen f r u i t s and vegetab le indus t ry .

In recent years t h e Nat iona l Canners Assoc ia t ion has i n v e s t i g a t e d m e a n s of reducing p o l l u t i o n from blanching. The c h a r a c t e r i s t i c s of water, steam, microwave and hot gas blanching w e r e s tud ied ( 2 ) . It w a s found that hot gas blanching gave a system which reduced b lancher e f f l u e n t t o a very low volume f o r some products ( 3 ) . However, ho t gas blanching requi red more energy than convent ional blanching, and it w a s app l i ed only t o canned vegetab les where t h e r e is no need f o r cool ing . Cooling can leach as much, o r more, s o l i d s from t h e products as does blanching ( 4 ) 3

The USDA Western Regional Research Laboratory has conducted research on improving steam blanching s o as t o reduce e f f l u e n t volume and BOD as w e l l as improve product q u a l i t y by reducing over-blanching. This research r e s u l t e d i n t h e development of a hea t ing and hold ing technique c a l l e d Indiv idua l Quick Blanching (IQB) (5). With I Q B t h e product i s heated with steam i n a s i n g l e l a y e r on a conveyor t o a mass average temperature s u f f i c i e n t f o r enzyme i n a c t i v a t i o n , and t h e product is he ld a d i a b a t i c a l l y i n a deep bed on a second conveyor allowing enough t i m e f o r temperature e q u i l i b r a t i o n and enzyme i n a c t i v a t i o n . This method reduces leaching from t h e product and thereby reduces e f f l u e n t BOD because of t h e uniform hea t ing inhe ren t i n a s i n g l e l a y e r as opposed t o the deep bed used i n convent ional steam blanching. i n leaching can be accomplished by prewarming and p a r t i a l l y drying w i t h hot ail: t he feed en te r ing t h e steam h e a t e r ( 4 ) .

:s: ; -:.;

Fur the r reduct ion

Most cooling a f t e r blanching i s done i n flumes o r by water sprays . Both of t hese cause leaching of s o l i d s from t h e product and genera te

* USPA, Western Regional Research Laboratory, Berkeley, C a l i f o r n i a .

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l a r g e volumes of e f f l u e n t . Recently, air cool ing equipment has been i n s t a l l e d i n some f r eez ing p l a n t s (6,7). Water sp rays are used wi th a i r cool ing t o reduce the evapora t ive weight l o s s i n t h e product , and t h e excess w a t e r becomes e f f l u e n t . amount of water needed, e f f l u e n t produced o r product y i e l d when blanched vegetab les are a i r cooled.

A t p re sen t no d a t a are a v a i l a b l e on t h e

The work descr ibed i n t h i s paper w a s done t o demonstrate a means of achieving a blanching and cool ing method t h a t would produce less leaching of s o l i d s from t h e product t o t h e e f f l u e n t stream. conveyors provided a ready means of achieving compact equipment and a design of high h e a t e f f i c i e n c y . descr ibed by Brown, e t a l . (8).

Vibratory

This work is an ex tens ion of t h a t

PILOT PLANT EQUIPMENT

A schematic diagram of t h e equipment used i n t h i s work i s shown i n Figure 1. The equipment c o n s i s t s of t h r e e sec t ions : h e a t e r , ho lder and cooler , The h e a t e r and ho lde r have been completely descr ibed by Brown, e t al . (8), The cooler used i n t h a t earlier work w a s made from a neoprene b e l t conveyor, while i n t h e work descr ibed he re , a v i b r a t o r y conveyor w a s used. Figure 2 is a photograph of t h e assembled blanching- cool ing equipment.

So l id su r face v i b r a t i n g conveyors were chosen as the h e a t t r a n s f e r conveying su r faces i n t h e h e a t e r and cooler . This type of conveyor can be more e a s i l y cleaned than the w i r e mesh b e l t s used i n most steam blanchers . They a l s o provide a very compact design because they can be s tacked c lose toge the r and they do not have t h e r e t u r n s e c t i o n requi red i n a b e l t conveyor. The v i b r a t o r y conveyor a l s o g ives a means of reducing h e a t l o s s e s s i n c e vege tab le p ieces can be used t o form a seal a t t h e en t rance and e x i t . The r e l a t i v e l y s m a l l s i z e of t h e equipment reduces the cos t of i n s u l a t i o n .

Heater

A d e t a i l e d d e s c r i p t i o n of t h e h e a t e r and holder are given by Brown e t a l . (8); t hus only t h e main f e a t u r e s of t h a t equipment i s given here . An e l ec t romagne t i ca l ly dr iven v a r i a b l e amplitude Syntron c i r c u l a r conveyor w a s used i n t h e hea te r . The conveyor operated wi th a motion t h a t impelled the vege tab le p i eces upward and forward a t 3600 s t r o k e s p e r minute. around one t r a y , dropped through an opening and flowed around t h e o t h e r t r a y t o t h e o u t l e t . The res idence time i n t h e heater w a s c o n t r o l l e d by varying t h e feed p o i n t and t h e p o s i t i o n of t h e opening between t h e t r a y s as w e l l as t h e amplitude of v i b r a t i o n . Steam w a s d i s t r i b u t e d above each t r a y through tubes wi th a series of o r f i c e s . i n su la t ed , The feed w a s introduced through a hopper a t t ached t o t h e steam plenum; thus t h e feed formed a seal on one end of t h e h e a t e r and t h e holder formed one a t t h e o the r end (Figure 1).

Two conveyor t r a y s were s tacked so t h a t product flowed

The h e a t e r w a s completely

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Holder

The holder , a t tached t o t h e h e a t e r plenum, w a s an i n s u l a t e d neoprene tube 6 inches i n diameter and 10 inches long (Figure 1 ) . leaving t h e h e a t e r passed over a screen t o s e p a r a t e i t from t h e h e a t e r condensate, and from t h e r e i t dropped i n t o t h e holder . The level of product i n t h e holder w a s measured wi th a d i p s t i c k . The bulk d e n s i t y of t h e vege tab le p i eces , t h e holder c ros s s e c t i o n a l area and t h e feed rate were t h e d a t a used t o c a l i b r a t e t h e d i p s t i c k s e t t i n g f o r t h e res idence t i m e i n t h e holder .

The product

Cooler

The cooler (Figure 1) used i n these experiments w a s made from a s p i r a l v i b r a t i n g e l e v a t o r (Syntron, Model N o . ES-22). I t , l i k e t h e h e a t e r , had a frequency of 3600 cycles/second and gave t h e product an upward-forward impulse which moved the product up t h e s p i r a l . A photograph of t h i s cooler is shown in Figure 3, where t h e surrounding plenum, which d i r e c t e d the a i r flow and confined t h e atomized h e a t e r condensate, has been p a r t i a l l y removed t o show t h e s p i r a l e l eva to r . e l e v a t o r cons is ted of f i v e 4 inch wide f l i g h t s of 14 5/8 inch diameter. The l eng th over which t h e product t r a v e l e d on t h e conveyor w a s 1 7 f e e t . The plenum surrounding t h e conveyor w a s supported independent ly s o i t d id not contac t t he v i b r a t i n g conveyor. The two blowers (1/5 horsepower, s q u i r r e l cage type ) , connected t o t h e plenum, passed 750 cfm of a i r over t h e product co-cur ren t ly . A i r v e l o c i t y , measured wi th a vane anemometer, w a s regula ted by an o r f i c e a t t he e x i t of each blower, and i t w a s kept a t t h e maximum p o s s i b l e without d i s t u r b i n g t h e flow of t h e product on t h e conveyor. Heater condensate w a s atomized i n t o t h e a i r a t each blower.

The 36 inch high

EXPERIMENTAL METHODS

Most of t h e opera t ing d a t a on t h i s equipment w a s ob ta ined wi th green beans (1/2 inch c ross c u t , mixed sieves s i z e Galagreen v a r i e t y ) . Washed and screened green beans were obtained i n 400 l b l o t s from P a t t e r s o n Frozen Foods, Pa t t e r son , Ca l i fo rn ia . They w e r e mixed wi th ice , t r ans - por ted i n in su la t ed con ta ine r s and used 24 t o 96 hours later. Since c a r r o t d i c e were found t o be t h e most d i f f i c u l t t o convey, uniformity of flow i n the coo le r was t e s t e d wi th c a r r o t d i c e as descr ibed by Brown et a l . (8) . Ca r ro t s were topped, diced without pee l ing and screened t o remoye f i n e s . Raw and blanched b r o c c o l i spea r s and cau l i f lower w e r e a l s o t e s t e d on the cooler t o observe i f t hese could be conveyed.

An experimental run cons is ted of blanching and cool ing approximately 50 l b . of r a w vegetable . The feed, cooled product and e f f l u e n t w e r e weighed. Samples of coo le r e f f l u e n t were r e f r i g e r a t e d f o r l a te r a n a l y s i s . Samples of t h e feed and cooled product , taken during t h e run, w e r e frozen.

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Samples of feed, product and e f f l u e n t w e r e analyzed f o r t o t a l s o l i d s by AOAC method 20.010 (9) . Chemical oxygen demand (COD) of t h e e f f l u e n t samples w a s es t imated using a Beckman To ta l Carbon Analyzer (Model 915) (10) . Peroxidase and chlorophyl were measured according t o t h e methods descr ibed by D i e t r i c h and Neumann (11).

RESULTS

Table 1 summarizes t y p i c a l opera t ing condi t ions used i n t h e s e experiments.

Table 1. Typical opera t ing condi t ions

Heating Holding Feed R a t e Excess Cooling Cooler T i m e T i m e ( l b s / h r ) Steam* Time Product (set> (set) (8 (sec) Temp. (OF)

Green Beans 45 45 19 0 12 45 100

Carro ts 25 60 145 24 60 105

* Equals percent over t h e o r e t i c a l steam consumption. Theore t i ca l steam consumption f o r 60°F i n i t i a l temperature and a 195°F f i n a l m a s s average temperature i s 13.8 lb/100 l b feed.

Table 2 g ives t h e y i e l d of cooled green beans obta ined wi th t h e above opera t ing condi t ions as compared t o convent ional blanching and cool ing . It a l s o shows the e f f l u e n t s o l i d s l o s s , which measures t h e amount of s o l i d s l o s t from t h e feed t o t h e e f f l u e n t .

Table 3 g ives t h e amount and COD of t h e e f f l u e n t from the coo le r . These are compared t o those obtained under convent ional blanching condi t ions .

DISCUSSION OF RESULTS

The v i b r a t o r y s p i r a l conveyor used i n t h e coo le r conveyed both t h e c a r r o t s and t h e green beans uniformly and cont inuously. When t h e con- veyor w a s t r i e d wi th c u t cau l i f lower and b r o c c o l i spea r s , t h e 4 inch conveyor w a s too narrow t o convey these vege tab les w e l l , bu t they d i d move up t h e l eng th of t h e s p i r a l .

It w a s found t h a t t h e s p i r a l conveyor requi red a product v e l o c i t y of approximately 17 feet /min. t o g ive a uniform s teady flow of product. This product v e l o c i t y gave a res idence time of only 1 min. w i t h green beans and c a r r o t d i ce . The r e s u l t i n g product temperature of 100-105°F i s h igher

12 3

than t h e 70-80'F usua l ly achieved before f r eez ing i n a commercial process. A conveyor twice as long would provide a 2 min. res idence t i m e , which would g ive adequate cool ing (8).

Table 2. Comparison of Yields and So l ids Loss i n E f f luen t f o r Green Beans Between Combined Blanching and Cooling vs Conventional Blanching and Flume Cooling

Ef f luen t Gross Yield* So l ids Loss** Reference

(X) (XI

Combined Vibratory B 1 an ch- C o o 1 88

Conventional Steam Blanch

Conventionnl Water Blanch

Flume Cool 95

Flume Cool 96

* W t . of cooled product

** % s o l i d s i n e f f l u e n t X w t . o f e f f l u e n t

W t . of feed t o b lancher Gross Yield =

X w t . of feed Ef f luen t So l ids Loss = % solids in feed

Table 3. Comparison of E f f luen t from Green Beans f o r Combined Blanching and Cooling and Conventional Blanching and Flume Cooling

Ef f luen t COD (lb/lOO l b feed) (lb/lOO l b feed) Reference

Combined Vibratory B l a n ch-Coo 1 7.0 0.17 This work

Conventional Steam Blanch

Conventional Water Blanch

Flume Cooling 500

Flume Cooling 520

0.35 (2

0.32 (2

The lower gross y i e l d of green beans f o r combined blanch-cooling as shown i n Table 2 is c h a r a c t e r i s t i c of a i r cool ing (8). The condensate sprayed on t h e product is only p a r t i a l l y reabsorbed, and i t does no t

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completely compensate f o r evaporat ion of moisture i n t o t h e a i r stream. In flume cool ing t h e r e i s no evapora t ive weight l o s s , b u t t h e h ighe r y i e l d i s accompanied by twice as much s o l i d s l o s t from the product . Since frozen vegetab les are s o l d on t h e b a s i s of weight , a lower y i e l d means less product ion and can be j u s t i f i e d economically only i f t h e va lue of l o s t product is balanced by t h e c o s t of increased waste d i sposa l .

The r e s u l t s i n Table 3 show t h e l a r g e d i f f e r e n c e i n volume of e f f l u e n t between convent ional processing and the combined blanch-cooling. Most of t h i s volume (96%) i s due t o the flume cooling. Assuming a product temperature out of t h e blancher of 195°F and cool ing water temperature of 60"F, i t r equ i r e s 5.8 l b of water p e r l b of product t o o b t a i n an 80°F product temperature. This amount of flume water when added t o the blancher e f f l u e n t r e s u l t s i n twice t h e amount of COD and 70 t i m e s t he volume of e f f l u e n t from combined blanching and cool ing.

I f no change is made i n t h e way f rozen vegetab les are marketed, then a i r cool ing of any kind s u f f e r s a l a r g e c o s t disadvantage. gives a comparison of t h e approximate opera t ing c o s t s of t h r e e d i f f e r e n t k inds of blanching. The b a s i s f o r t h i s cos t estimate is taken from Brown e t a l . (8). It must be emphasized t h a t these c o s t s are approximate, and they are shown merely t o make a comparison. It is obvious t h a t t he c o s t of l o s t green beans (a t $0.20/lb) due t o reduced y i e l d is overwhelming i n comparison t o o t h e r cos t s . Even though t h e combined v i b r a t o r y blanch-cooler can g ive s u b s t a n t i a l savings i n steam and e f f l u e n t c o s t s , and a product wi th more r e t a i n e d s o l i d s , t hese w i l l no t ba lance t h e cos t of product l o s t through evaporat ion.

Table 4

Design of Large Scale Vibratory Blanch-Cooler

To eva lua te f u l l y t h e t echn ica l f e a s i b i l i t y of t h e combined blanch-cooling approach t o processing f rozen vegetab les i t is necessary t o work wi th l a r g e r scale equipment. Figure 4 i s a schematic diagram showing the conf igura t ion and the dimensions of a 1 ton/hr . v i b r a t o r y blanch-cooler. The h e a t e r and coo le r would have a d j u s t a b l e feed po in t s t o accomodate t h e d i f f e r e n t res idence t i m e s needed f o r d i f f e r e n t products . The holder would be a l i ve bottom b i n wi th an automatic level c o n t r o l , which could be ad jus ted t o maintain d i f f e r e n t ho lde r res idence t i m e s .

The coo le r would use t h e same type of conveyor as i n t h e h e a t e r , b u t the c e n t r a l column of t h e s p i r a l could be used t o d i r e c t t he a i r flow. The coo le r s p i r a l conveyor would have t o be much longer t o accomodate up t o 5 min. res idence t i m e f o r l a r g e vege tab les such as b r o c c o l i and Brussels sprouts .

Equipment of t h i s s i z e is a v a i l a b l e from several manufacturers a t an est imated cos t of $60,000. f t . x 15 f t .

It would r e q u i r e a f l o o r area of about 15

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Table 4. An E s t i m a t e of Water, Steam, E f f luen t , E l e c t r i c i t y and Product Loss Costs i n Blanching and Cooling of Green Beans*

Water 6 Eff luen t COD

Vol c o s t Amount Disposal E l e c t r i c i t y Steam Product** To ta l (ga l / ton) ($/ton) ( l b / t o n ) c o s t ($/ton) ($ / ton) l o s s c o s t

($ / ton) ($ / ton) ($/ton)

Combined Vibratory

Conventional S team Blanch

blanch-cool 140 0.06 3 0.06 0.060 0.31 28.00 28.43

flume coo l 1200 0.48 7 0.14 0.007 0.55 0 1.17

flume coo l 12 50 0.50 6.4 0.13 0.007 0.80 0 1.43

P N o\

Conventional Water Blanch

* ** Cost of u t i l i t i e s and waste d i s p o s a l taken from Brown e t a l . (8) .

Frozen green beans a t $0.20/lb (12 ) .

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

NATIONAL CANNERS ASSOCIATION, "Liquid Wastes from Canning and Freezing F r u i t s and Vegetables," Of f i ce of Research and Monitoring, Environmental P ro tec t ion Agency, Washington, D.C. (1971).

FULLS, J. W . , MAAGDENBERG, H. J., YACOUB, N. L. , ZINNECKER, M. E., REIMAN, J . M., KARNATH, H. O. , HOMNICK, D. N . , and MERCER, W. A. Reduced waste genera t ion by alternate vegetab le blanching systems. Proceedings of t h e 3rd Nat ional Symposium on Food Processing Wastes, New Orleans, La., Environmnetal P ro tec t ion Technology Series EPA- R2-72-018, 25 (1972).

RALLS, J. W . , MAAGDENBERG, H. J., YACOUB, N. L., ZINNECKER, M. E., REIMAN, J. M., KARNATH, H. O . , HOMNICK, D. N. , and MERCER, W. A. In-plant hot-gas blanching of vege tab les . Assoc ia t ion Pub l i ca t ion D-2614, (1972).

Nat iona l Canners

BOMBEN, J. L., DIETRICH, W. C. , FARKAS, D. F., HUDSON, J . S., DE MARCHENA, E. S., and SANSHUCK, D. W. P i l o t p l a n t eva lua t ion of Ind iv idua l Quick Blanching (IQB) f o r vege tab les . J. Food Sc i . , 38: 590 (1973).

LAZAR, M. E . , LUND, D. B., and DIETRICH, W. C. IQB: A new concept i n blanching. Food Tech., 25: 684 (1971).

COFFELT, R. J., and WINTER, F. H. Evaporative cool ing of blanched vegetab les . J. Food Sc i . , 38: 89 (1973).

SMITH, W. L. , and ROBE, K. Saves 300-400 gpm water, improves vege tab le q u a l i t y . Food Processing, 34(3) : 36 (1973).

BROWN, G. E., BOMBEN, J . L., DIETRICH, W. C . , HUDSON, J. S., and FARKAS, D. F. A reduced e f f l u e n t blanch-cooling method us ing a v i b r a t o r y conveyor. J. Food Sc i . , ( i n p re s s ) .

AOAC. O f f i c i a l Methods of Analysis , 10 th Ed. Associat ion of O f f i c i a l Agr i cu l tu ra l Chemists, p. 308, Washington, D.C. (1965).

APHA. Standard Methods f o r t h e Examination of Water and Wastewater, 13 th ed., p. 257. American Pub l i c Health Assoc ia t ion , New York (1965).

DIETRICH, W. C . , and NEUMA", H. J. Blanching Brusse l Sprouts. Food Tech., 19 (5) : 150 (1965).

IELMINI, J. P r i v a t e communication on c o s t of green beans. (1974).

Reference t o a company and/or product name does no t imply approval o r recommendation of t h i s product by t h e U.S. Department of Agr icu l ture t o t h e exc lus ion of o t h e r s which may a l s o be s u i t a b l e .

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Figure 4 . ONE TON PER HOUR VIBRATORY BLANCHER COOLER