Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary...

42
SPINOFF ON FRUIT AND VEGETABLE WATER AND WASTEWATER MANAGEMENT ROY E. CARAWAN JAMES V. CHAMBERS ROBERT R. ZALL PROJECT SUPERVISOR ROGER H. WI LKOWSKE EXTENS I ON SPEC I AL REPORT No A"18~ JANUARY, 1979 PREPARED BY: EXTENS I ON SPEC I AL I STS AT : NORTH CAROL I NA STATE UN IVERS I TY CORNELL UN I VERS I TY PURDUE UN I VERS I TY WITH THE SUPPORT OF THE Sc I ENCE AND EDUCAT I ON A D M I N I STRAT I ON-EXTENS I ON USDA - WASHINGTON, D. C.

Transcript of Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary...

Page 1: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

SPINOFF ON

F R U I T A N D V E G E T A B L E W A T E R A N D

W A S T E W A T E R M A N A G E M E N T

ROY E. CARAWAN

JAMES V. CHAMBERS ROBERT R. ZALL

PROJECT SUPERVISOR

ROGER H. WI LKOWSKE

EXTENS ION SPEC I AL REPORT No A " 1 8 ~ JANUARY, 1979

PREPARED BY: EXTENS I ON SPEC I AL I STS AT : NORTH CAROL I NA STATE UN IVERS I TY

CORNELL UN I VERS I TY

PURDUE UN I VERS I TY

WITH THE SUPPORT OF THE

Sc I ENCE AND EDUCAT I ON

ADMI N I STRAT I ON-EXTENS I ON

USDA - WASHINGTON, D. C.

L

Page 2: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

36 F&V SPNOFF/CONTROL OF WATER & WW

methods- for cont ro l l ing water and wastewater i n comnodity-specific processes.

CARROT PROCESS I NG MOD I F I CAT I ONS

Washing s o i l from root vegetables requi res a l o t o f water. One l a r g e f r e s h c a r r o t s u p p l i e r i n C a l i f o r n i a used about 4,000 gal/min of wash water

i n t he cou rse o f p rocess ing 500 T carrots lday the year round. Because o f short supplies of water and expensive waste disposal, wash water recyc l ing

became a t t r a c t i v e . The continuous water recycl ing system i s described below and d e p i c t e d i n F i g u r e 11.

Two s e t t l i n g ponds, each 60' by 150', serve as surge reservo i rs . From here, water i s pumped f o r use i n f l u m i n g t h e c a r r o t s . The flume water i s used- f o r f l u s h i n g t h e c a r r o t s from the t rucks . Th i s f l ush ing removes 90% o f t h e f i e l d s o i l . C a r r o t s go through a brush washer, and then through sor t ing s ta t ions , where small sizes and misshapen c a r r o t s a r e removed as c u l l s . The desired s izes are hydrocooled, then sent through a second brush washer. Po- tab le wa te r i s sp rayed ove r t he ca r ro ts i n t he f i na l sec t i on .

P a r t o f t h e f l u m e w a t e r i s pumped through a pa ten ted , cy l i nd r i ca l , so l - i ds - l i qu id separa to r . Here, water enters an annular space a t the top; f low v e l o c i t i e s decrease as so l i ds a re spun inward th rough o r i f i ces toward the

center, rather than outward as i n conven t iona l cone-shaped cyclone separators. The cleaned water exi ts a t t h e t o p ; s o l i d s s e t t l e t o t h e b o t t o m where they are cont inuously f lushed out and r e t u r n e d t o t h e s e t t l i n g pond. Trash i s screened out through a stat ionary curved screen separator before enter ing

the four cen t r i fuga l separa tors . F low th rough the four separa tors i s 200-300 gpm t o t a l .

ppm. Ch lo r ina t i on of these f lows, which cycle through the ponds, keeps t h e reservoirs, f lumes, and equipment f ree o f bac ter ia l , funga l o r - a lga l g rowth .

Water i n t h e h y d r o c o o l e r s and i n t h e f i n a l sprays i s c h l o r i n a t e d a t 100

The low-cos t se l f - i ns ta l l ed recyc l i ng sys tem j us t desc r ibed , e f fec t i ve l y r e c y c l e s a l l wash and flume water, excepting a small amount sprayed dur ing f i n a l r i n s e , and the water car r ied ou t w i th the p roduc t . The system requ i res no extra energy except that for handl ing a pressure drop o f about 8 p s i t o pump the water through the centr i fugal separators. Separators remove 98% of

Page 3: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

37 F&V SPNOFF/CONTROL OF WATER & WW

CARROTS INTO NYOROCOOl ER

In closed loop system, about 300 gpm is diverted from 2000gpm flume and pumped through a 28”-wide/.06asieve separator. and centrifugal separators. and is used to clean carrots in brush washers above. Centrifugal force slows particles down as they pass through orifices; solids are continuously flushed out at bottom

F i g u r e 11. C a r r o t wash w a t e r r e c y c l i n g system.

Page 4: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

38 F&V SPNOFF/CONTROL OF WATER & WW

t h e s o i l p a r t i c l e s s i z e d 44 microns (325 screen s ize) o r la rger . The best r e s u l t o f a l l i s t h a t t h e r e i s no waste t o t r e a t .

t

IN-PLANT CHANGES RESCUE CARROT PROCESSOR

P lan t "A" processes frozen carrots. The p lant operates on a t y p i c a l

schedule o f 5 days per week, 10 t o 11 months each year. Normal product ion i s s e t f o r two sh i f t s per day w i th add i t iona l c lean-up t ime as needed. Average throughput i s about 8 r a w tons per hour.

Figure 12 shows the t yp i ca l f l ow d iag ram tha t p lan t A fo l lowed before any process modi f icat ions were made. Car ro ts were de l i ve red i n b ins e i t he r

d i r e c t l y f r o m t h e f i e l d s o r f r o m a s o r t i n g shed. They were washed, trimned, convent iona l l y l ye pee led and d iced o r s l i ced . B lanch ing was accomplished i n a water blancher; post blanch cool ing was also accomplished using water.

Water use was high, approaching a d a i l y average consumption o f 1.5 mgd; BOD l e v e l s were correspondingly high, averaging about 2,400 mg/l .

This p lant , landlocked by c i t y growth, was already paying a surcharge f o r i t s e f f l u e n t d i s p o s a l t o t h e m u n i c i p a l w a s t e t r e a t m e n t system. The c i t y recognized that expanded t r e a t m e n t f a c i l i t i e s were needed t o accommodate i n -

dus t r i a l use rs . So, t h e c i t y proposed t e n t a t i v e r e v i s i o n s i n i t s s u r c h a r g e system which i f adopted, would cause monthly rates t o approach $4,000.

A t t h i s p o i n t , p l a n t A ' s managers decided t o i n s t i t u t e changes i n t h e form o f cap i ta l inves tments . When des ign ing the p lan t mod i f i ca t ions , the engineers considered each waste contr ibut ing process wi th in the process ing scheme. Figure 13 shows t h e r e s u l t s o f t h e s e e f f o r t s ; T a b l e 6 records the b e n e f i t s ga i ned .

RROT WASljJJjG

Water used t o wash the incoming carrots had p rev ious l y been combined w i t h t h e m a i n p l a n t e f f l u e n t stream. However, observat ion and t e s t i n g of t h i s s t r e a m i n d i c a t e d t h a t i t s c h i e f components were sand and d i r t , some f i e l d d e b r i s , and occas iona l car ro t par t i c les . Because o f t h e p l a n t ' s l o - cat ion, i t was decided that th is stream should be iso la ted f rom the s t reams with higher waste concentrat ions and discharged separately under an NPDES

permit. A double screening system was i n s t a l l e d ( n o t shown on diagram) t o remove v a r i o u s s o l i d p a r t i c l e s from the waste stream. This not only lower-

ed t h e suspended and s e t t l e a b l e s o l i d s b u t a l s o , i n p a r t , c o n t r i b u t e d t o r e -

ducing the BOD discharge. Freezer defrost water was a l s o d i v e r t e d t o merge

Page 5: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

39 F&V SPNOFF/CONTROL OF WATER & WW

I B I N S I L I Q U I D WPSTE

WASH D I R T , S O L I D S

1 I

S O L I D S , L Y E LYE PEEL "4

?

I

"--

SOL I D S "=p.

J U I C E S D I C E / S L I C E - - -a-

r

WATER BLANCH L

ORGANICS, ""4 S O L I D S

I

ORGAN I C S WATER COOL

I FREEZE C I T Y SEWER

F i g u r e 12. O r i g i n a l flow, car ro t p rocessor "A".

c

Page 6: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

SOLID WASTE

so

D I R T , S O L I D S 1 I

40

F&V SPNOFF/CONTROL OF WATER & WW

~ DS DISPOSAL

t SEPARATE

LIQUID WASTE

I

DISCHARGE

CONDENSATE

BLANCH

I I

CITY SEWER

F igure 13. Modif ied flow, carrot processor "A".

Page 7: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

41 F&V SPNOFF/CONTROL OF WATER & WW

Table 6. Carrot Process "A". Parameter Differences

- - P a r a m e t e r B e f o r e A f t e r

F l o w ( M G D ) 1 . 5 0 . 6 l

F l o w R a t i o ( G a l / T o n )

BOD ( m g / l )

S 1 i c e d R e c o v e r y ( % )

9 3 7 5

2 4 0 0

50

3 7 5 0

1 6 0 0

6 2

D i c e d R e c o v e r y ( % ) 6 5 7 2

M o n t h l y S u r c h a r g e ( 8 ) 4000* 500

* E s t i m a t e d

I 0.35 M G D d i s c h a r q e d u n d e r N P D E S p e r m i t , 0.25 M G D t o c i t y

Page 8: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

42 F&V SPNOFF/CONTROL OF WATER & WW

with this-stream. The effect of this separation should not be underestimated. These two components are responsible for about 60% of the total plant flow - about 350,000 gallons per day. The alternative discharge of this large water volume t o a municipal waste treatment system would have been extremely expen- sive.

PEELING The peeling process was identified as the main source of BOD and SS gen-

eration. The water required for peel removal was a substantial percentage of the plant's to t a l effluent. A new lye peeler ( ferr is wheel type) was pur- chased and installed.

The conventional high-pressure water lye peel removal system was replaced w i t h a Magnuscrubber. The resulting peel waste slurry was pumped directly t o a holding t a n k . Ultimately this waste fraction is disposed of in sanitary landfill.

In a d d i t i o n t o the water use and BOD reductions expected, the equipment modifications just described were responsible for improving finished product recoveries for both sliced and diced carrots, These increased yields were a direct result of the new peel removal system. Plant personnel also noticed a reduction in caustic soda consumption.

The engineers working on process modifications recognized t h a t every attempt should be made t o stop the introduction of solid wastes i n t o the eff- luent stream. The original plant flow allowed for trimmings and solid waste t o be flushed i n t o gutters, followed by final screening before discharge t o the city sewer system. This allowed for additional leaching of soluble sol- ids and was, in par t , responsible for the p l a n t ' s h i g h BOD. problem, a separate series of dry sol ids conveyors were insta port trimming table and other wastes directly t o outside bins gers a1 so made a concerted effort t o instruct plant employees methods of handl ing solid waste.

To overcome this lled t o trans- . Plant mana- on proper

EilmwME As shown i n Figure 12 , this plant had used a hot water blancher for years.

Water blanchers, however, have been shown t o be major sources of water pol 1 u- t ion. Leaching solids, continuous spillage and overflow, a l l contribute

Page 9: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

43 F&V SPNOFF/CONTROL OF WATER & WW

heavily t o a p lan t ' s BOD and SS loads. The waste stream from the water blan- cher was not only concentrated, b u t was of substantial volume. So, the old water blancher was removed and a steam blancher was ins ta l led . Now the only effluent from this uni t process . is a h igh ly concentrated 1-2 gpm condensate. The e f fec t on to ta l BOD and SS load has been considerably lessened, yet the desirable product quality characteristics have been retained.

CooLING Similarly, post blanch hydrocooling , necessary to prepare carrots for

freezing and t o optimize freezer efficiencies, was found to cont r ibu te to the plant 's effluent load . The conventional hydrocooling system was replaced w i t h an ambient a i r cooler . Working on a fluidized bed pr inciple , the pro- duct leaves the blancher and i s blown and vibrated over perforated screens

. by the action of a i r j e t s blowing through and upward to contact the product. The action of t he a i r and the mechanical vibrations of the screen move the product across the screen d u r i n g which time the required cooling gradient is achieved. Using air e l iminates almost a l l water contact after blanching ex- cept for one or two fine water sprays between the blancher and cooler. Water use a t this stage was estimated a t no more t h a n 2 g a l / m i n .

CAPrTALXNVESTMENT The plant estimated that their total expenditures for a l l the improve-

ments and modifications amounted t o about $90,000. Although no attempt was made to calculate paybacks on investment cap i t a l , i t can be seen i n Table 6 that savings accrued due t o reduced discharged volume and pounds of pollu- tants sent to the c i ty waste treatment system accounts f o r about $42,000 per year. If one were to add a monetary value to the increased yeilds obtained, the investment would become even more a t t r ac t ive . The changes just described were documented i n a study by LaConde and Schmidt (1976).

DRY CAUSTIC PEELING

Of the u n i t operations i n the processing of f r u i t s and vegetables which use water and generate waste, the most notable for magnitude of water use and waste generation is the peeling operation. Whether product peeling is by water, steam, caustic, or a combination of these, the operation has always generated a l iquid waste troublesome because of i t s volume, organic load, and

Page 10: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

I 44

F&V SPNOFF/CONTROL OF WATER & WW

pH value.. For example, approximately 40 percent of the BOD from peach can- ning comes from the peeling operation.

In recent years interest i n dry peeling of f r u i t s and vegetables has increased because of the impact t ha t this process has on reducing water .po l - lut ion. As a result of this interest, equipment manufacturers have explored developing machinery for such peeling processes. This section will present the waste and water reduction results that have been achieved by us ing such processes.

~

Tomatoes, clingstone peaches and potatoes are the principal "target" commodities a t which dry caustic peeling efforts have been aimed. The peel- ing machine i s bas i ca l ly designed to gent ly remove the peel from s o f t fruits and vegetables w i t h o u t us ing water, and to co l lec t the peel waste residue so t h a t i t does not enter the p lan t ' s wastewater effluent. This is done by col- lection, haulage, and separate disposal of concentrated peeling wastes.

To gently wipe away peel softened by caustic, the machine uses very t h i n sof t rubber discs . These rubber discs are placed on rotating cylindrical r o l l s arranged i n a circular revolving cage containing a feed screen through the center. The fruit moves paral le l to the rol l axis and perpendicular t o the surfaces of the roll discs. The so f t , moving disc surfaces provide gen- t l e , thorough scrubbing much l i k e wiping the fruit w i t h the palms of the hands. The feed rate is accurately control1 ed by the central screw conveyor. A f inal r inse to remove the las t t races of peel and caustic is the only fresh water used. During an EPA demonstration grant w i t h the Del Monte Corp., water use i n the peeling operation was reduced from 850 gal water/ton peaches t o 90 gal water/ton peaches by u s i n g the dry peeling process.

In conventional peeling, the peel i s pre-softened by contact w i t h d i - lu te sodium hydroxide and then removed from the peach u s i n g large volumes Of

fresh potable water that comprise high-pressure sprays. Water from this peeling operation therefore contains essentially all of the removed peel.

Dry caustic peeling i n which mechanical r u b b i n g i s used t o remove the softened peel was or iginal ly developed for the potato processing industry; however, peeling softer fruit such a s peaches required the development Of

the new process just described. Peeling is the l a rges t single source of waste from fruit processing,

accounting for as much a s 10 percent of the total wastewater flow and 40

percent of the to ta l biochemical oxygen demand.

Page 11: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

r

c

L

i

45 F&V SPNOFF/CONTROL OF WATER & WW

.The dry caustic peeling process also allows for collection of the peel as a pumpable slurry. This slurry may have potepltial value as an animal supplement or i n reclaiming marginal farm land, Because the peel i s not carried i n the wastewater flow, the total organi.: and suspended solids load- i n g of the wastewater from the peeling process i s reduced by about 60 percent. Peach quality was judged t o be equal t o t ha t of conventionally peeled peaches.

The most striking resu l t of the commercial tests of the dry caustic peeler i s the 90 percent reduction i n water use as compared to the convention- al caustic peeler. Significant pollution parameters.can be reduced by approx- imately 60 percent. Table 7 i l lustrates the average wastewater volumes and pollution loadings for each process, based on 24-hour composite samples taken on each of the 21 days o f the demonstration period.

Table 8 sumarizes the characterist ics of the peach peel so l id wastes. The relat ively h i g h pH of the slurry and the low pH of the rinse water i n d i - ca te tha t most of the caustic i s removed w i t h the peel.

A commercial dry caustic peeler has a l so been operated successfully on freestone peaches. There is additional economic incentive for use on free- stone (as opposed to clingstone) peaches, since the mechanical action of the wiper effect ively removes bruises and decreases the higher cost of hand i n - spection associated w i t h freestone peaches.

After having tested dry caustic peeling on peaches, Magnuson Engineers, Inc. decided to try the process on tomatoes. They established that a dry caustic peeling machine they designed would also very effectively peel caus- t ical ly- t reated tomatoes.

Tomatoes peel very differently from peaches. Much stronger caustic sol- utions are required and caustic-compatible wetting agents must be used. While the tomato surface beneath the skin is a t tacked by the caustic, the skin i t s e l f remains in tac t and dislodges as sheets of t issue. Other types of tomato peelers have d i f f i cu l ty in thoroughly removing this peel t i s sue because i t tends to t ransfer from tomato t o tomato, or from tomato to equip- ment and back to another tomato. Water sprays are generally used t o t r y t o flush away these skins and hand labor i s required t o f inish the skin removal

The dry caustic peeler that has been used on peeling tomatoes removes substant ia l ly 100% of the peel a t capac i t i e s of 8 to 10 tons per hour w i t h - out using any wash water. This method has eliminated nearly all of the hand labor required to remove the peel. About one agal/min of "lubrication" water is used i n the machine.

Page 12: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

Table 8. Composition of Peach Peel Solids

46 FBV SPNOFF/CONTROL OF WATER & WW

Table 7. Comparison of the Average Liquid Eff luent from the Del Monte Dry Caustic Demonstration Project with Conventional Caustic Peeling

A l l units in Ibs'ton of peaches unless otherwise noted

Conventional DrV Caustic Caustic Peeling Peeling

Water usage 850 gals/tonl 90 gals/ton COD 10.8 (1500 ppm) 4.2 (5600 ppm)

Suspended Solids 5.6 (790 ppm) 1.9 (2500 ppm 1 Total Soiids 17.8 (2500 ppm) 4.0 (5300 ppm) pH Range 6-9 4-6

1 Assumes countercurrent rinse. Without a countercurrent rinse, this

BODS 6.7 (940 ppm) 2.8 (3700 ppm)

number could be as high AS 2000 gals.'ton peaches.

( Ibs Total Sluny (Ton Peaches) % Total Solids pH Range

153 7-1 1 9-1 1

Page 13: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

47 F&V SPNOFF/CONTROL OF WATER & WW

"REDUCTION

i

In both the tomato and peach peel ing opel*at ions, the dry caust ic peeler c o l l e c t s and d e l i v e r s a fu l l s t rength, essent . ;a l ly undi lu ted peel waste s ludge. Since the peel waste i s a major source of BOD, i t i s h i g h l y d e s i r a b l e t o keep th is pee l was te ou t o f a plant 's wastewater. Smith (1976) ci ted a 1974 study that d iscovered that peel wastes accounted for 60% o f t h e t o t a l p l a n t BOD load i n a peach cannery and 35% o f t h e t o t a l BOD l o a d i n a tomato cannery. The p lan ts compr is ing tha t s tudy were genera l l y t yp i f ied by Ca l i f o rn ia p ro - cessing methods. Food processors now recognize that removing BOD loads from

wastewater i s very expensive, both i n terms o f the p lan t inves tment fo r was te- wa te r t rea tmen t f ac i l i t i es and t h e f a c i l i t i e s ' o p e r a t i n g c o s t s . It i s now widely acknowledged that prevent ing wastes f rom enter ing the p lant ef f luent i s an e x c e l l e n t method for precluding wastewater t reatment costs. This i s e s p e c i a l l y t r u e i n seasonal operations where expensive wastewater treatment

f a c i l i t i e s would be used f o r o n l y two o r t h r e e months per year.

CREASED PRQRUCT RFCQYERY Smith (1976) also noted that a C a l i f o r n i a tomato processor who was us ing

fou r d ry pee l i ng machines reported an increased product recovery of 2.5 cases

per ton. This product recovery was a t t r i b u t e d t o t h e r e d u c t i o n i n p r o d u c t losses made poss ib le by t h e d r y p e e l i n g u n i t s . The same processor also no- t i c e d a 44.7% r e d u c t i o n i n t h e amount of caustic consumption as a r e s u l t of i ns ta l l i ng t he d ry pee le rs . Such savings were poss ib le because the mechani- ca l w ip ing act ion o f the rubber d iscs can do an e f fec t i ve j ob wh i l e expos ing the tomatoes to l ess caus t i c . Th i s p roduc t sav ings o f cou rse , means l e s s product loss i n the spent caust ic so lu t ion. S imi lar ly , s ince water washing i s n o t used dur ing peel removal , the loss o f tomato so l ids which i n conven- t i ona l pee le rs a re no rma l l y ca r r i ed away by the wastewater, i s e l iminated.

SOMF BY-PRODUCT POSSIBII I T I F S

Now t h a t t h e mechanics o f d r y c a u s t i c p e e l i n g have been proven, much a t ten t i on i s be ing f ocused on the hand l ing and disposal of peel waste s ludge. So f a r , t h i s s l u d g e has been d i sposed o f by spreading on land; sometimes it has been spread on pasture land where ca t t l e a re f eed ing .

As t h i s s l u d g e m a t e r i a l becomes a v a i l a b l e i n g r e a t e r q u a n t i t i e s , p o s s i - b l e uses f o r it will arise. Brandy manufacture i s one p o s s i b l e o u t l e t .

Tomato peel waste of fers promise for use as a by-product. The peel

Page 14: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

48 F&V SPNOFF/CONTROL OF WATER & WW

waste has a higher solids content than pureed whole tomatoes, because i t i s

made up e n t i r e l y o f m a t e r i a l from t h e o u t e r c e l l w a l l s o f t h e tomatoes. This

ma te r ia l i s t he most h igh l y co lo red po r t i on o f the tomato, so it i s very h igh

i n desirable red pigment. O f course, the mater ia l conta ins caust ic (NaOH), b u t t h i s c a n be neu t ra l i zed w i th hyd roch lo r i c ac id (HC1) and conver ted to

c m o n tab1 e s a l t (NaC1) and water. Sal t i s u s u a l l y added t o tomato products anyway, so i t ' s very l i ke ly tha t the tomato pee l f rac t ion can be processed i n t o h i g h q u a l i t y tomato products for human consumption.

LEAFY-GREENS WASH WATER RECYCLE

Indus t r ies tha t p rocess lea fy vegetab les use la rge volumes o f water, ma in ly dur ing four un i t opera t ions :

4 0 washing

0 b l anc h i ng 0 coo l i ng

t ranspor t ing product .

Three types o f washers a r e most commonly used i n c o m e r c i a l o p e r a t i o n s : im- mersion, spray-belt, and rotary-spray. Est imates of wash water requirements

per un i t weight o f product range f rom 50% o f t h e t o t a l wa te r requirement of 3 t o 5 gal /1 b necessary f o r complete processing, t o 73% o f a t o t a l 1.1 t o

1.5 gal /1 b c i t e d e l sewhere f o r complete processing requirements.

modify the system i n some way t o p e r m i t r e c y c l i n g o f t he wash w a t e r i t s e l f .

Of course the chief concern i s t h a t t h e r e c y c l e d w a t e r be o f good enough qua l i t y th roughout the per iod o f use to insure aga ins t degradat ion of t he product qual i ty beyond acceptable 1 imi t s .

fu l l -scale, immersion-type washers that would permi t wash water recyc l ing

during greens-washing operations, were designed and evaluated i n a study whose desc r ip t i on f o l l ows .

co l la rd g reens were being processed and one when spinach was being processed.

One obvious way t o conserve water i n a greens-washing operation i s t o

To l e a r n more about ef fects of water recycl ing on product qual i ty , two

The washers' performances were monitored during f i v e t r i a l s , f o u r when

L Two washers were designed t o wash 4,000 lbs o f p roduc t pe r hou r . The

bottoms were comprised o f th ree sec t ions , each V-shaped t o f a c i l i t a t e t h e

Page 15: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

49 F&V ‘;PNOFF/CONTROL OF WATER & WW

collection and removal of g r i t when the washers were d ra ined , The maximum depth i n each washing t a n k was 3 f t . , and the ntminal capacity of each was 688 gallons. Water from each washer was recyclcd through separate settling tanks whose nominal capaci t ies were 718 gallons.

Both washers were identical and were operated i n se r ies . Each was equipped a t the i n p u t end w i t h three banks of sprayers (4 nozzles each) ; one bank placed a t water level and two above the incoming product. One of the overhead banks of sprayers was l a t e r taken out of service i n order to main- t a i n h i g h pressure on the nozzles while reducing the overall recirculation ra te from 200 gpm (757 l/min) to about 125 gpm (473 l/min). This change was necessary because i t was discovered that the washer drain system and the re- turn sump-pump could not handle the larger flow.

As product entered, i t was spread out and vigorously agitated by the sprayers, and pushed toward the f i rs t of three center-mounted, paddle wheels covered w i t h f lattened expanded metal. The three revolving paddle-wheel drums propelled the product th rough the washer, a l ternately submerging and releasing i t . . Insects and leaf fragments floated to the surface inside each drum while the product was submerged, while water, forcefully dispensed through a s ta t ionary bank of three spray nozzles (positioned inside each drum) , prevented 1 eaves from becoming entangled i n the expanded metal cover- ing and provided additional cleaning. An ex i t conveyor - - made of an open- mesh, p las t ic b e l t i n g w i t h f l i gh t s every 2 f t - - carried product out of each washer.

Water and f loat ing t rash t h a t collected inside the rotating drums flowed out of the washers through surface side-drains into a trough leading t o a box containing a submersible sump-pump. This pump forced water into the settling tanks through a moving-belt f i l t e r made of polyester screen that trapped trash and carried i t t o a collection box. Streams of compressed a i r a t the end of the conveyor were directed upward t h r o u g h the belt across i t s wid th t o force trash into the collection box. The nominal capacity of each settling t a n k was 718 gal , and provided a detention time o f about 7 min fo r gr i t t o s e t t l e when the recirculat ion ra te was 100 gpm.

Fresh, chlorinated water was added t o the system a t only one point: the second sett l ing tank. The overflow was carried t h r o u g h an H-flume into the f i r s t s e t t l i ng t ank . The volume i n excess of that required t o make up for losses i n each washer, caused by carry-over on the product, was discharged as waste from the f i r s t s e t t l i n g tank through a second H-flume. Flow meters were installed to allow monitoring of fresh-water i n p u t and recirculat ion

Page 16: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

50 F&V SPNOFF/(ONTROL OF WATER & WW

ra tes , .which could be controlled by opening or closing gate valves through each washer-settling tank system. The H-flumes were equipped w i t h continu- ous stage recorders and were calibrated so t h a t d e p t h of flow through the flumes could be converted to volume flow rates .

The researchers concluded that the experimental washing system, as a whole, performed well du r ing the four t r ia l s us ing col lards and the one using spinach. While the quality of the water a s i t was recycled t h r o u g h the washers d i d deter iorate as more and more greens were processed, cleaning o f the greens while they passed through the system was always evident. Re- duction of bacterial population densities on the greens were observed i n a l l f ive t r i a l s , probably because chlorine residuals were maintained a t h i g h levels and because of a detergent action i n the wash water induced by dis- solved organic compounds 1 eached f rom the vegetables.

Conclusions from th i s study were:

Most of the actual cleaning of product occurred i n the f i rs t washer and sett l ing basin; an average of 71% of organic and inorganic wastewater consti tuents were pre- sent i n the. f i r s t washer and sett l ing basin. The sett l ing tanks were effect ive i n removing small par t ic les such as s i l t and fine sand. I n one t r i a l when suff ic ient gr i t for analysis was recovered, 63 percent of the to ta l was found i n s e t t l i ng t a n k No. 1 . Washer No. 1 collected the most of the f ine and medium sand (12 percent o f the total weight of gr i t collected). Differ- ences i n to ta l suspended solids concentrations i n the wash water from the head to the back of a s e t t l i ng tank d i d not accurately reflect the actual solids removal that occurred. There were dis t inct d i f ferences i n f i n a l wash water qual- i t y when different cut t ings of collards were processed, the differences most probably being a function of pro- duct maturity. The water-usage r a t e i n the experimental system, was, on the average, 15.6 gal/min (59.0 l / m i n ) , which i s 77 per- cent less than tha t used by the conventional commercial washers. Water use per u n i t product was an average of only 0.56 gal/lb (4.66 l / k g ) compared t o an estimated usage of 1.5-2.5 gal/lb (12.5-20.8 l/kg) by conventional equipment. The average chemical concentrations of the wash water being discharged from the system a t t h e end of the tri- als were high, both i n organic and inorganic suspended sol ids . When collards were washed, the organic suspen- ded so l ids were concentrated a t 110 mg/l while the i n - organic suspended sol ids were at concentrat ions of 61 mg/l . When spinach was washed, organic suspended sol ids concentrations rose to 632 mg/l, and inorganic suspended

Page 17: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

51 F&V :PNOFF/CONTROL OF WATER & WW

solids concentrations occurred a t concentrations of 57 mg/l. The magnitudes o f the sol ids cancentrations pro- bably ref lect the fact that there was considerable t u r b u - lence in the settling tanks because c f the h i g h recircu- la t ion ra tes w i t h i n the system, and tecause the lighter particulates (clay and small leaf fragments, e.g.) d i d not se t t le wel l .

6 ) The average concentrations of COD and BOD5 i n waste water being discharged from the system a t the end of the t r i a l s were s imilar to those i n weak municipal sewage. When collards were processed, COD values averaged 356 mg/l and BOD values average 80 mg/l . When spinach was washed, COD values averaged 211 mg/l while BOD values averaged 46 mg/l .

7 ) Concentrations of both organic and inorganic compounds i n wash water were much lower than those reported i n another study, a s were the waste loads generated per u n i t weight of product processed. The best agreement o f data between the two studies was for to ta l suspended sol ids. The other study’s values for organic waste loads (COD and BOD, l b / ton) were from 5 to 6 -times higher t h a n those calculated in this study.

8) Recirculation of wash water i n immersion-type, leafy-green washing systems i s a promising modification of existing processing methods fo r reducing water consumption and con- centrating waste loads so that they can be more eas i ly treated.

t

c

c

t

I’

c

c

4

I N D I V I D U A L Q U I C K BLANCHING (IQB)

Preparing vegetables for preservation by canning, freezing, or dehydra- t ion resul ts i n large volumes o f high-strength organic waste streams. For the purpose of reducing total plant effluent and BOD, a t tent ion has been focused on the blanching operation. Blanching serves several purposes i n - c l u d i n g :

0 removing tissue gasses 0 inactivating or activating enzymes 0 reducing microbial load 0 cleaning the product a wil t ing the t i s sue to fac i l i t a te packing.

These objectives are accomplished by heating the vegetables i n ei ther hot water or steam. Both hot water and steam blanching produce liquid wastes h i g h i n BOD, and both resu l t i n loss o f water soluble nutrients, A report based on a study of two Wisconsin canning plants stated that a 90% reduction i n blancher effluent volume would reduce total p l a n t waste flow by 10 t o 201,

Page 18: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

52 F&V SPNOFF/CONTROL OF WATER & WW

and would reduce t o t a l p l a n t BOD product ion by 20 t o 50%. I n an e f f o r t t o

approach these reductions, a study was made to des ign a blanching process which would produce a wastewater f low o f 10% o f that from a comnercial hot

water blancher. The p r o j e c t r e s u l t e d i n a new concept o f h e a t i n g f.oods and the app l i ca t i on t o b lanch ing was demonstrated. The process, ind iv idual quick blanch (IQB), was used as a precanning process, and t h e r e s u l t s of that study are presented here.

The I Q B u n i t used i n t h e s t u d y c o n s i s t e d o f two insulated chests, one

heated by d i r e c t steam and the o the r hea ted i nd i rec t l y . The IQB's capac i ty was about 300 lbs /h r . The p roduc t , t aken f rom the p rocess l i ne j us t p r i o r to enter ing the convent ional p ipe b lancher , was d i s t r i b u t e d i n a s i n g l e l a y e r on a mesh b e l t moving through the steam chamber. The residence t ime i n t h e

chamber al lowed the mass average temperature o f t h e p r o d u c t t o r e a c h d e s i r - able blanching temperatures. The product was t h e n t r a n s f e r r e d t o a much slow- e r moving b e l t t r a v e l i n g t h r o u g h t h e second chamber. The product remained the re un t i l b lanch ing was accomplished. The product was then hand-packed

i n t o 303 x 407 cans t o a given fill weight , br ine and hot water were added, and the cans were sealed. Then the cans were i n s e r t e d i n t o t h e p l a n t ' s con-

veying 1 i n e t o go through the cont inuous re tor t process. Prev ious invest igat ions by o ther researchers w i th the I Q B u n i t showed

t h a t t h e r e d u c t i o n i n waste f l o w from blanching was enhancea b y s l i g h t l y d r y - ing the p roduc t p r io r to s teaming. So, some of the exper iments i n t h i s s t u d y were conducted on the product which was d r i e d by a 5 t o 20% weigh t reduc t ion i n an a l ternat ing upf low-downf low hot (160-180OF) a i r d r y e r .

t o t a l s o l i d s , suspended s o l i d s , t o t a l and soluble phosphorus , t o t a l o r g a n i c - The e f f l uen t f rom the I Q B blancher was c o l l e c t e d and analyzed for BOD,

n i t rogen, ammonia-ni t rogen, n i t rate-ni t rogen, and pH.

CONCLUSIONS OF THE IQB STUDY The r e s u l t s o f t h i s s t u d y i n d i c a t e t h a t IQB can be used successfu l ly for

b lanch ing vegetab les p r io r to the i r cann ing . The IQB process resu l ts i n r e - duc t ion o f b lancher e f f luen t by 68 t o 99% whi le ma in ta in ing p roduc t qua l i t y . Spec i f i c resu l t s i nc lude :

1 ) Peas: B lancher e f f luent was reduced a t l e a s t 68% i n t h e IQB process compared t o pipe-blanching. Excessive drying of the peas r e s u l t e d i n s k i n breakage w i t h r e s u l t i n g c loudy br ine and loss o f p roduc t qua l i t y .

Page 19: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

53 F&V S?NOFF/CONTROL OF WATER & WW

Corn: IQB reduced blancher ef f luent between 77 and 99%. There was no product qual i ty loss except under h igh tem- perature pre-dry ing condi t ions where the product was darker i n co lo r than the con t ro l . Green Beans: An 86 t o 95% reduct ion i n b lancher e f f luen t was obtained using IQB. P roduc t qua l i t y was comparable t o pipe-blanched canned product except when pre-dr ied. With pre-drying, sloughing was evident. Lima Beans: Reductions up t o 99% were accomplished i n the b lanching operat ion us ing IQB. Wi th d ry ing , the loss of skins seemed to impa i r p roduc t qua l i t y .

HEAT-COOL SEQUENCE FOR TOMATO PEEL REMOVAL

A new process f o r commercial tomato peeling uses only heat and water, both o f which can be recycled. Conventional peel ing processes use large

.amounts o f heated caust ic ( lye). Caust ic i s expensive and r e q u i r e s l a r g e amounts o f energy f o r i t s p r o d u c t i o n .

The new process involves heat ing tomatoes wi th steam at about 315"C,

then cool ing them i n a water bath or spray. Each s tep lasts about 10 sec- onds, and the heat-cool sequence i s u s u a l l y conducted three t imes for a t o t a l o f 60 seconds. Peels can then be removed mechanical ly.

TOMATO PROCESS I NG

Tchobanoglous e t a l . (1976) s tud ied the e f fec ts o f some in-cannery pro- cess modif icat ions on reducing water use and waste a t H ickmot t Foods, Inc., a sma l l independent tomato cannery. The nature and r e s u l t s o f t h e i r i n - p l a n t wa te r po l l u t i on con t ro l e f fo r t s a re sumar i zed he re .

Hickmott Foods, Inc. cans tomatoes i n an 80-day opera t i ng season du r ing

the months of Ju ly through October . Except for a week o r two a t t h e b e g i n n i n g and end o f t h e season, canning i s a cont inuous, ' round-the-clock operat ion.

To meet waste discharge requirements, the plant undertook a program of waste- water management to c lean- up i t s was tewater d ischarge to the San Joaquin River.

S ign i f i can t reduc t i ons i n the wastewater f low ra te and s t r e n g t h have been

accomplished by modify ing var ious operat ions wi th in the cannery product ion area. These changes and t h e i r i m p a c t a r e d i s c u s s e d i n t h i s f o l l o w i n g s e c t i o n .

-UCTI ON

The two p r i n c i p a l components o f t h e wastewater produced during the 1973

Page 20: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

54 F&V SPNOFF/CONTROL OF WATER & WW

and 1974 tomato canning seasons were the process water and the water f rom the

evaporators and re to r ts (see Tab le 9 ) . Water used in t he p roduc t i on p rocess i s der ived pr imari ly f rom the municipal water supply; the water used to cool

the evaporators and r e t o r t s i s f i l t e r e d San Joaquin River water. Several steps were taken between 1973 and 1974 t o reduce the quant i ty o f

water used by the cannery and t o reduce the wastewater f low rates. The coo l -

ing water was analyzed and found t o be s u i t a b l e f o r d i r e c t d i s c h a r g e t o t h e

r i v e r (COD less than 50 mg/l) a f te r coo l i ng . E l im ina t i ng t he coo l i ng wa te r

f rom the waste stream reduced the f low requir ing t reatment f rom 3.1 m i l l i o n gal/day t o 1.14 mi l l ion ga l /day, whi le cannery product ion increased 20%.

The i n s t a l l a t i o n o f four dry peel removal machines reduced the total water needed fo r pee l ing f rom 306 t o 124 gal/min. The quant i t y o f pee l s ludge produced dropped from 150 t o 25 gal /min whi 1 e cannery production increased 20%. This reduced volume o f pee l ing s ludge made i t p o s s i b l e t o i s o l a t e t h i s m a t e r -

iil and process separately. All low pressure-high volume washdown hoses were removed and a high pres-

sure hose system w i t h n o z z l e s t h a t s h u t o f f upon re lease was i n s t a l l e d . T h i s change r e s u l t e d i n a washdown f l o w r e d u c t i o n o f a t l e a s t 80 gal/min (see Table 9). As low pressure hoses were u s u a l l y l e f t t o r u n on the f loor , the reduc- t i o n was probably somewhat l a r g e r . Some employees ob jec ted t o t he use of t h e high pressure spray as i t was harder to con t ro l , bu t they eventua l l y became accustomed to us ing these nozz les. No degradation i n t h e q u a l i t y o f t h e p r o -

d u c t o r p l a n t s a n i t a t i o n was observed.

Cooling water discharge was reduced by 200 gal/min by r e u s i n g t h e r e t o r t cool ing water for can washing. Besides reducing the amount o f water t o be coo led be fo re d i scha rge t o t he r i ve r , t he amount o f r i v e r water tha t requ i red

f i l t e r i n g and c h l o r i n a t i o n f o r use i n t h e can washing system was a l s o reduced.

1 The quant i ty of raw tomato const i tuents present in the process waste-

water was reduced from the 1973 t o 1974 season by m o d i f i c a t i o n s i n t h e p e e l - ing opera t ion and f l o o r waste management.

Dry Peeling. The i n s t a l l a t i o n o f f o u r d r y p e e l removal machines and mod- i f i c a t i o n s i n t h e o p e r a t i o n o f t h e c a u s t i c p e e l e r s r e s u l t e d i n a reduc t i on i n caustic chemical use and i n t h e q u a n t i t y o f waste generated that required treatment. This was accompl ished wi th no d e t e r i o r a t i o n i n p r o d u c t q u a l i t y . Dry caus t ic pee l ing , us ing ro ta t ing rubber d iscs to mechan ica l l y rub pee l from

Page 21: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

55 FRV !PNOFF/CONTROL OF WATER R WW

Table 9. Daily Water Usage Dur ing 1974 Cjnr i n g Season and Percent Reduction D a t a Over 1973 Canning : easona

- __ -_ ~ - . -

1974 Percent F lowrate, Reduc: ton

gpm ove r 1973 I tem D e s c r i p t i o n o f Source No. "" . . " - .. ." " "" . "

Process was tewa t e r b " "" "- ". - ".

1 2 3 4 5 6 7 8 9

10 11 12

.13 14 15

-

Seals on sump pump ( 1 / 2 " l i n e , 2 @ 8.8 gpm) Bin washing system ( 2 @ 17.5 qpm) Incoming product sprays 2 @ 10 gpm) Small tomato dropout f luming t o p roduc t t ab les Make-up water to l ye pec . le rs ( 2 @ 10 gpm) R inse t anks a f te r pee l i ng ( 2 P 50 gpm i n 1973) Dry scrubbers (4 I? 6 gpm) ( 1 @ 50 gpm i n 1973) Rinse water on r o l l e r washers ( 4 @ 20 gpm) ( 4 @ 35 gpm i n 1973) B e l t l u b r i c a t i o n and c lean ing Can washers, 7 peel ino. 3 product (10 @ 18 gpm) K e t t l e s ( 1 " l i n e , 1 @ 30 gpm) Washdown l ines , low p ressure ( 4 @ 35 gpn i n 1973) Washdown l i n e s , h i g h pressurc (6 @ 10 gpm) Can c o o l i n g , o u t s i d e c o o l e r s ( 7 @ 35 gpn) Coo l ing water . vacuum pumps ( 3 @ 8.8gpm)

TGTAL k ' A S T E k ' i i i E l i G E i i T U k i E D . gpm (1126 gpm i n 1973)

Evaporators L Reto r t s9 .

____ " ___ - 16 Evzporator No. 1 5 55 - 17 Evaporator No. 2 350 - 1 8 Reto r t s 10Oh 69

1,000 - T i "

Fluming Wateri

19 Tomato f l um ing 600 " _ _ _ _ _ ~ 'Based on ind iv idual f lowrate i r ,easuremnts dur ing 1973 and 1974 peak product ion per iods. bAl1 process wastewater must be treated by the w a s t e w a t e r t r e a t m e n t f a c i l i t i e s e x c e p t I t e m 7.

C E l i n i n a t e d f r o m 1973 o p e r a t i o n . dReduced by lower ing spray p ressure . cTo be reduced i n 1975 b y s h o r t e n i n g b e l t runs. fNozzles shut o f f when n o t i n hand o f operator . w a t e r from evspora to rs and re to r t s i s d i s c h a r g e d d i r e c t l y t o r i v e r a f t e r P a s s i n 5 t h r o u g h

hRetor t water i s recovered and used for can washing. iFluming water i s r e c y c l e d i n t e r n a l l y . Make-up wa te r i s o b t a i n e d f r o m Items 3 6 4 .

See s e c t i o n on Dry Pee l i ng .

coo l ing tower .

Page 22: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

56 F&V SPNOFF/CONTROL OF WATER & WW

tomatoes dipped i n sodium hydroxide, replaced the convent ional water r inse peel ing operat ion. Ef fect ive peel ing was o b t a i n e d w i t h t h i s method w h i l e

reducing the concentrat ion o f caust ic i n the peelers. Through a combination o f reduc ing the pee le r speed ( r e s u l t i n g i n more tomatoes per bucket but a longer contact t ime wi th the caust ic per tomato) and using mechanical peel- i n g s it was p o s s i b l e t o use a caus t i c so lu t i on o f 7 t o 10% i n 1974 as op- posed t o an 18 t o 20% s o l u t i o n i n 1973. Th is opera t ion change r e s u l t e d i n a reduc t ion i n caus t ic use (6 .9 lbs / ton in 1974 as opposed t o 11.7 l b s / t o n prev ious ly ) and reduced o ther chemical requi rements for neutra l izat ion o f t h e r e s u l t i n g wastewater. As discussed la ter , reducing the pH v a l u e o f t h e caust ic s ludge can a1 so make t h e p o s s i b i l i t y of product recovery more prac- t i cab le .

Dry caust ic mechanical peel ing requires about 80 g a l l o n s o f p o t a b l e water per ton o f tomatoes as opposed t o 720 ga l / ton us ing convent iona l meth- ods. The 80 gal / ton which amounted t o 24 gal /min o f caust ic s ludge produced i n t h e o p e r a t i o n i s a small enough volume so t h a t it can be disposed o f i n a land spreading operaf ion. El iminat ing th is s ludge f rom the waste stream re- duced the BOD load on the water po l lu t ion con t ro l p lan t by 46%.

F loor Waste Management. Because tomatoes a r e , f o r t h e most par t , a water so lub le f ru i t , the longer they remain on t h e c a n n e r y f l o o r o r i n a wastewater conveyance f a c i l i t y , t h e g r e a t e r t h e amounts o f tomato sol ids and j u i c e s con- t r i b u t i n g t o t h e s o l u b l e COD and BOD of the wastewater. If processing wastes are picked up i n s o l i d f o r m t h e y c a n be f e d t o l i v e s t o c k o r a t l e a s t d i s p o s e d o f as s o l i d wastes. Manual c o l l e c t i o n o f l a r g e s o l i d t o m a t o p a r t s was s t ress -

ed dur ing the 1974 season. G r a t i n g s c o v e r i n g a l l f l o o r d r a i n s were a l s o b o l - ted down. R e l i a b l e s o l i d waste per ton o f d a t a were n o t a v a i l a b l e f o r t h e 1973 season bu t i t was est imated that cons iderably more s o l i d waste was used f o r c a t t l e f e e d d u r i n g t h e 1974 season. T h i s i s waste that does no t reach t h e t r e a t m e n t f a c i l i t y as f i n e suspended mat te r o r so lub le o rgan ics .

-TS THAT W I I I b~ TO REDUCED WATER USE Because Hickmott Foods no longer processes sweet potatoes and asparagus,

d a i l y w a t e r use could be reduced f u r t h e r by sho r ten ing t he l eng ths o f be l t s on which peeled tomato products must travel. This change would eliminate about 50 ga l /min o f water now used f o r b e l t l u b r i c a t i o n . I n t u r n , t h i s would reduce the peak water use. i n t h e cannery t o between 750 and 800 gal/min. T h i s q u a n t i t y i s c o n s i d e r e d t o be the minimum water use poss ib le fo r ma in ta in -

ing sani tary condi t ions. Heightened concern by the U.S. Department of Agri-

Page 23: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

57 F&V SPNOFF/CONTROL OF WATER & WW

c

i

culture over the issue of machine mold may u l t i m a t e l y r e s u l t i n increased per

ton water use by Hickmott Foods.

IN-PLANT WATER RECYCLE WITH OFF-LINE MUD REMOVAL

With the advent of mechanical harvest ing of tomatoes, tomato processors noted an increase i n the soi l accumulat ions wi th in f luming systems. Most of t h e s o i l a c c u m u l a t e d i n t h e i n i t i a l f l u m e s o r b i n dumps. F l o w v e l o c i t i e s w i t h i n t h e b i n dumps were i n s u f f i c i e n t t o s c o u r s e t t l e d s o i l s o l i d s from the bas?. The r e s u l t i n g a c c u m u l a t i o n o f s o i l i n t h e b i n dump eventual ly impai red p r c l u c t f l o w and required processing downtime t o remove.

There are two widely pract iced procedures for a l leviat ing the accumula- t i o n o f s o i l i n t h e b i n dump. The f i r s t i s t o employ a h i g h o v e r f l o w r a t e f r o n t h e b i n dump, t h i s o v e r f l o w d i s c h a r g i n g t o t h e p l a n t ' s sewer system. The second procedure involves processing downtime t o d r a i n o f f excess l i q u i d s and t o hand shovel the accumulated soi l into an adjacent receptacle.

Severa l -adverse impacts resu l t f rom the cur ren t p rocedure fo r hand l ing b i n dump mud. I n t h e case o f t he h igh ove r f l ow ra tes , t he excess wa te r used adds t o t h e h y d r a u l i c s u r c h a r g e t o t h e sewer system from t h i s seasonal indus- t r y . The h igh so i l load ings d ischarged to mun ic ipa l t rea tment sys tems resu l t i n o p e r a t i o n and maintenance problems. As a consequence o f t h e n e c e s s i t y f o r p e r i o d i c a l l y s h u t t i n g down t h e b i n dump t o remove accumulated s o i l , t h e t i m e requirements for process ing a given tonnage of tomatoes are extended, resul- t i n g i n r e d u c t i o n o f t h e p l a n t ' s p r o d u c t i v i t y . T h i s , i n t u r n , r e s u l t s i n f u r t h e r excess water use through the down-t ime per iod and for the addi t ional required clean-up and washdown.

Dur ing the 1974 processing season, a study by Wilson, e t a l . (1976) was undertaken to eva lua te a l t e rna t i ve wa te r recyc le sys tem con f igu ra t i ons . Bin dump model s tud ies were then undertaken i n t h e s p r i n g o f 1975 t o develop de- sign data on an e f f i c i e n t system f o r i n t e r c e p t i n g s o i l s o l i d s i n t h e b i n dump

and t ranspor t i ng them t o a s o l i d s removal system w i t h o u t i n t e r f e r i n g w i t h product f 1 ow.

The o b j e c t i v e o f t h e '75 season tomato water r e c y c l e p r o j e c t was t o de-

monstrate a water recycle system which when used i n con junc t i on wi th a normal b i n dump operat ion, would s igni f icant ly reduce the adverse impacts associated w i th cu r ren t p rac t i ces . An essent ia l l y c losed loop recyc le sys tem was employ- ed. The recycled water was used to ma in ta in adequate scour ing ve loc i t ies w i t h i n t h e b i n dump w i t h o u t d e t r i m e n t a l l y a f f e c t i n g p r o d u c t f l o w . A s o l i d s

c

Page 24: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

58 F&V SPNOFF/CONTROL OF WATER & WW

removal system was cons t ruc ted w i th in t he c losed l oop t o remove t h e s e t t l e a b l e

s o l i d s and thereby p revent the i r accumula t ion w i th in the b in dump. This recy- c l e system was expected to e l im ina te excess ive water use r e l a t e d t o h i g h b i n dump overf low rates, as w e l l as those ra tes re la ted t o c lean -up down-time and

extended operat ional per iod for processing a given tonnage of tomatoes. The researchers inves t iga ted four modes o f operat ion aimed a t m i n i m i z i n g

wastewater-related costs. These modes comprised the fo l lowing:

0 convent ional c leaning, wi thout water recycle 0 convent ional c leaning with water recyc le 0 d isc c leaner w i th water recyc le

0 d isc c leaner w i th recyc le and chemical coagulation- f l o c c u l a t i o n .

Water consumption and to ta l so l ids ba lances were made on each mode. The con- c lusions of the study are d iscussed below.

CONCLUSIONS Not su rp r i s ing l y , t he da i l y ave rage tonnage o f tomatoes processed increas-

ed s u b s t a n t i a l l y w i t h d i s c c l e a n i n g and water recycle, as compared w i t h t h e conventional system. An inc rease o f 26% i n t h e tonnage o f tomatoes processed

was r e a l i z e d w i t h t h e d i s c c l e a n e r combined w i th water recyc le and chemical f l occu la t i on . These increases i n t h e d a i l y tonnage o f tomatoes processed may be p r i m a r i l y due t o t h e v i r t u a l e l i m i n a t i o n o f s o l i d s accumu:ation i n t h e

dump tank with consequent impaired product f low. No i nc ident o f temporary shutdown o f s h i f t o p e r a t i o n f o r dump tank clean-up was encountered during the modes o f opera t ion w i th water recyc le .

Wi th respect to the water consumpt ion, the fo l lowing f ind ings were estab- l i s h e d i n t h i s study:

1) The m a j o r i t y o f d a i l y w a t e r usage was operational (48-61%), fo l lowed by clean-up (31-44%) and f i l l i n g (6-8%). There were no s i g n i f i c a n t v a r i a t i o n s i n p e r c e n t a g e usage i n t h e var ious modes o f operat ions. I n a l l modes o f opera t ion , approximately 7% was f i l l i n g ; a p p r o x i m a t e l y 55% operat ion- a l ; and approximately 39% clean-up.

rea l i zed when disc c leaner, combined wi th water recycle and c h e m i c a l f l o c c u l a t i o n r e l a t i v e t o t h e c o n v e n t i o n a l system, was appl ied.

3) A decrease i n the average un i t water consumpt ion ra te re l - a t i ve to counter -cur ren t f low convent iona l c lean ing , occur - ed when water recycle measures were appl ied. A 41%

2 ) A 26% decrease i n t h e a v e r a g e t o t a l d a i l y w a t e r use was

Page 25: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

59 F&V SPNOFF/CONTROL OF WATER & WW

decrease i n average uni t water consumpt ion ra te was r e a l - i zed when the d isc c leaner , w i th water recyc le and chemical f l occu la t i on (164 ga l / t on ) , was a p p l i e d r e l a t i v e t o t h e conventional system (278 gal/ ton).

Wi th respec t to the to ta l so l ids ba lances , ;he fo l low ing conc lus ions were drawn:

With the water recyc le measures implemented, t h e s o i l sol- i d s removed from the dump tank per tonnage o f tomatoes processed were s i g n i f i c a n t l y reduced; t h e s o i l s o l i d s l o s t t o t h e sewer per tonnage o f tomatoes processed were reduced s u b s t a n t i a l l y . The es t ima ted so i l so l i ds i ncoming t o t he p lan t pe r un i t weight of tomatoes processed ranged from 10 t o 20 lbs/ ton, and averaged 13 l b s s o i l s o l i d s p e r t o n o f tomatoes pro- cessed. The t o t a l s o i l l o a d e d was est imated f rom the sum o f s o i l s o l i d s w h i c h were co l lec ted f rom the dump tank, l o s t t o t h e sewer, and removed from the s ludge th ickener. It appeared t h a t t h e amount o f s o i l r e a c h i n g t h e p l a n t varied considerably, depending on t h e t y p e o f s o i l i n which the tomatoes were grown, the mo is tu re con ten t o f t h e s o i l i n w h i c h t h e tomatoes were harvested, and the method o f tomato harvesting. E f f i c i e n t c l a r i f i c a t i o n o f t h e t h i c k e n e r o v e r f l o w r e - qu i red su r face l oad ing ra tes o f l ess t han 1,000 gpd/ f t2 . A p p r o x i m a t e l y o n e - h a l f o f t h e g r a v i t y s e t t l e a b l e s o i l so l ids over f lowed f rom the th ickener a t sur face loading r a t e s o f 2,000 gpd/ f t2 .

Using performance parameter values found i n t h i s study, i t was demon-

s t r a t e d t h a t i n s t a l l a t i o n and operat ion o f an i n -p lan t wa te r recyc le system w i t h o f f - l i n e mud removal, would r e s u l t i n about a 50% savings i n t h e t o t a l annual wastewater-related costs. For the 35 tons tomatoes/hr p lant evaluated i n t h i s study, annual savings would amount t o about $47,000.

Page 26: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

60 F&V SPNOFF/CONTROL OF WATER & WW

References

Liptak, B. 6. Food Processing Wastes. Environmental Engineer's Handbook. Volume I - Water Pollution. 1974. Loehr, R. C. Agricultural Waste Management, Problems, Processes, Approa- ches. 1974. LaConde, K. V. and C. 3. Schmidt. In-Plant Control Technology for the Fruits and Vegetables Processing Industry. Proceedings Seventh National Symposium on Food Processing Wastes. EPA-600/2-76-303. December, 1976. Robe, K., associate editor. Low-cost, total recycling of wash water. Food Processing . December, 1977. Dry Caustic Peeling of Clingstone Peaches. Capsule Report. U.S. Environ- mental Protection Agency Industrial Demonstration Grant with Del Monte Corporation. EPA Technology Transfer. Smith, T. J . Dry Peeling o f Tomatoes and Peaches. Proceedings of the S i x t h National Symposium on Food Processing Wastes. EPA-600/2-76-224. December, 1976. Hoehn, R. C. e t a l . Changes i n Organic and Inorganic Constituents of Wash Water Upon Recycle in a Prototype Leafy-Greens Washer. Proceedings of the Seventh National Symposium on Food Processing Wastes. EPA/600-2- 76-304. December, 1976. Heat-cool sequence for tomato peel removal. Picks and Packs. Technical Notes for the California Fruit and Vegetable Processing Industry. Coop- erative Extension, University of California. March, 1978. Tchobanoglous, G. Wastewater Management a t Hickmott Foods, Inc. Pro- ceedings of the S i x t h National Symposium on Food Processing Wastes. EPA-600/2-76-224. December, 1976. Wilson, G. E. e t a l . Tomato Flume Water Recycle w i t h Off-Line Mud Re- moval. Proceedings of the Seventh National Symposium on Food Processing Wastes. EPA-600/2-76-304. December, 1976. Liquid Wastes from Canning and Freezing Fruits and Vegetables. U.S. Environmental Protection Agency Water Pollution Control Research Series 12060 EDK 08/71. August, 1971. Mercer, W. A. Conservation and Recycling of Water and Other Materials. Food Industry Week Conference. Proceedings Waste Management and Po l lu t ion Control. 1971. Kamn, R. e t a l . Evaluating New Business Opportunities from Food Wastes. Food Technology, June, 1977.

Page 27: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

I

61 F&V SPNOFF/RECYCLING & REUSE OF FD PROC WW

R E C Y C L I N G A N D R E U S E O F P R O C E S S I N G W A S T E W A T E R S

Sources of Potable Water

Water can be obtained from two sources, surface reservoirs or streams, and underground rservoirs or streams. These sources can be tapped by a municipality or by a private party. I f a food processor's water comes from a municipal supply system, the water's q u a l i t y is the responsibility of the municipal ity. B u t , a food processor who suppl ies his own potable water comes directly under the provisions of the Safe Drinking Water Act.

Food processing plants must use water t h a t is of potable quality. Potable water must also be used for cleaning a l l equipment which contacts the foods. Water must meet Federally established quality standards in order t o be classified as potable. However, the standards set by any given state may be even more s t r ic t t h a n the Federal standards. For this reason, a food processor must know exactly what qualities the state expects of a processing p lan t ' s water supply. Please turn t o Chapter 5 of the Core Manual entitled By-products, Reuse and Recycling for more information on this topic. However, in some cases, i t is possible t o have multiple-use or reuse of water as discussed i n the fo l l owing.

I n t r o d u c t i o n t o Recycling a n d Reuse

This section explores several aspects of recycl i ng and reusing food processing wastewaters. I t is meant t o give you an overview of the factors affecting wastewater reuse and recycling.

Keep the following basic concept i n mind w i t h regard t o reusing wastewater. Reusing wastewater basically involves collecting the effluent from one or more u n i t processes, and then using t h a t effluent as the

- influent for other unit processes. The key t o wastewater reuse lies in matching the effluent from one u n i t process w i t h the influent requirements of another unit process. The "matchmaker" must be careful t o take into account the effluent I s quant i ty and qual i t y when examini ng the source requirements of prospect i ve processes.

Page 28: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

62

F&V SPNOFF/RECYCLING & REUSE OF FD PROC WW

Legal Aspects o f Water Reuse

Water r i g h t s and re la ted laws dre under nationwide review. Scien- t i s t s , economists and lawyers are evaluating current and fu tu re use of out water resources; const i tu t ional r ights as we l l as ind iv idual s ta te laws may be invo l ved before the present systems of water regulat ions can be appl i e d t o m u l t i p l e - u s e water.

Reusing water i s not a new concept. Published data estimate that 60

percent of the populat ion presently reuses water. The intake water supply p i p e o f one c i t y i s o f t e n downstream from the discharge sewage p ipe o f another metropolis, and coas ta l mun ic ipa l i t ies have no choice but to com- mingle supply and wastewaters when t i d a l c o n d i t i o n s r e t u r n t h e sewage ef f luents in to the water supply s torage reservo i r . The use o f i n t e r s t a t e streams i s not only subjected to the laws of each use r s ta te bu t i s a l so under regulat ions and con t ro l by federa l author i t ies .

Two basic systems of water law in t he Un i ted S ta tes i nc lude r i pa r ian

and appropriat ion. General ly, those areas with abundant water supplies use the common-law doc t r i ne o f r i pa r ian r i gh ts . Areas sparse i n water re- sources found the f i r s t users and s t a t u t o r y p r i o r a p p r o p r i a t i o n d o c t r i n e more su i tab le. Unfor tunate ly , ther are a lso some s ta tes tha t use combina- t i o n s of both systems wi th reg ional spec ia l in terpretat ions.

P o l l u t i o n abatement programs have genera l l y c lass i f ied s ta te waters according t o use and thus have establ ished s tandards o f qual i ty i n accor- dance with these object ives. It seems only prudent that the processor shou ld consu l t the s t ream c lass i f i ca t ions and standards that govern water

p u r i t y i n t h e s t a t e w i t h i n which wastewater i s t o be reused.

Publ ic Heal th Aspects o f Wastewater Reclamation Decis ion to reuse renovated wastewater for human consumption o r i n

processes that normally require potable water ( i .e., food processing), must be equated w i th po ten t i a l hea l th r i sk and hazards. The U.S. Publ ic Heal th Service i n a pol icy statement bel ieves that renovated wastewater i s not su i tab le f o r d r i nk ing wa te r when other sources are avai lable.

Reclamation Methods Water i s a b s o l u t e l y necessary i n food processing, and by p r a c t i c i n g

conservation, reuse and recyc l ing , the amount o f l i q u i d waste and conse-

Page 29: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

63

F&V SPNOFF/RECYCLING & REUSE OF FD PROC WW

i

quent ly the po l lu t ion load f r o m food processing operations can be reduced. Reduction o f water use through reuse of the same water can pay s i g n i f i c a n t dividends i n improving a waste disposal situation. Water reuse i s bene- f i c i a l because water i s no longer a free commodity; it costs money t o procure water; it costs money t o pump water; and it costs money t o dispose o f water.

Food processing waters cannot be reused ind isc r im ina te ly . The i r rec i r cu la t i on i n con tac t w i th f ood p roduc ts must a l low sat is factory product and p lant sani ta t ion. To o f f e r more spec i f i c gu idance i n t he use o f reclaimed waters, NCA o f fe red the fo l low ing recommendations:

O The water should be free of microorganisms of publ ic heal th s ign i f i cance.

O The water should contain no chemicals i n concen t ra t i ons t ox i c o r otherwise harmful to man, and no chemical content of the water should impose t h e p o s s i b i l i t y o f chemical adul terat ion o f the f ina l product.

O The water should be f r e e o f any mater ia ls o r compounds which could impar t d isco lo ra t ion , o f f - f lavor , o r o f f -odor to the p roduc t , o r o therw ise adverse ly a f fec t i t s qua l i t y .

O The appearance and content of the water should be acceptable from an aesthetic viewpoint.

A s an example o f the poss ib i 1 i t i e s f o r water reuse, a survey was made i n a tomato and vegetable packing plant. The ef fect of water reuse was measured i n terms of the percent reduct ion i n water use per ton of product processed. With no water reuse i n can cooling, product washing, o r other operations, water use t o t a l e d 3,340 gal / ton of product. When product wash waters were reci rculated, water use was reduced by 16%. Rec i r cu la t i on o f can cool ing water added a 22% reduc t ion . In the case of vegetable pro- cessing these water reuses allowed a t o ta l wa te r use reduc t ion o f 38%. When tomatoes were being processed, reuse o f the excess water from the

evaporative condenser system t o wash product a1 lowed a t o t a l o v e r a l l

r educ t i on o f 45% i n water use/ton of product. Water i s best saved by reducing i t s r a t e o f consumption. I ndus t r i es

tha t rou t i ne l y mon i to r t he i r wa te r usage and t h e i r waste e f f l uen t f l ows have been a b l e t o reduce the in-house uses of water by as much as 50%.

Unfor tunate ly , some water managers consider renovatd wastewater t o be acceptable only as a l a s t r e s o r t a l t e r n a t i v e . Such at t i tudes obscure the

Page 30: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

64

F&V SPNOFF/RECYCLING & REUSE OF FD PROC WW

real importance of wastewater as being potent ia l l y the rllost economical choice avai lable as a source o f water.

Wastewater treatment and renovation can e x i s t i n v a r i e d forms. D i r e c t

reuse occurs i n canneries when counterflow untreated streams are used

stepwise. Clean water i s piped into the cooking areas where, f o l l ow ing use, it f l ows t o b lanch ing ope ra t i ons . Hav ing f u l f i l l ed i t s se rv i ce here,

i t discharges t o water-conveying canals and f i n a l l y t o incoming washing troughs where i t removes f i l e d d e t r i t u s f r o m f r u i t s and vegetables.

Spent water hand1 i ng can be simp1 i f i e d by segregating wastes into appropriate categories. The commingling o f f l u i d s i n t o common sewers complicates reuse and reclamation programs. The f i r s t task i n reusing wastewater i s t o e s t a b l i s h t h e o b j e c t i v e s . A water demand inventory should bq taken t o determine usage amounts w i t h q u a l i t y l e v e l s o f p u r i t y . Subtota ls o f depar tmenta l ( indust r ia l p lant sect ions) use should add t o t h e t o t a l documented need requ i red f o r t he s i t e .

The dairy industry (Fig. 14) col lects salvaged condensed m i l k vapors

from vacuum pan evaporators and uses them fo r bo i le r water feed and f o r p lan t c lean ing wash wa te r . I n1 i ne t u rb id i t y me te rs mn i t o r t he sa l vaged condensate and divert contaminated mi lk and water vapors t o t h e sewer i n case o f a malfunction.

Salvageable Food Fract ions Food wastes found i n water can cons is t o f par t i cu la te mat te r , d is -

so lved so l ids and f a t s - e i t h e r as an emulsion or i n a f ree- f loa t ing s ta te . Both the food and the water qua l i t y have an in f luence on deciding whether or not the sa lvaged f ract ions gathered f rom wastewater are su i tab le for human o r animal consumption. I f wastes are channeled i n t o sewer l ines , these mater ia ls become a treatment burden, a t some cos t t o a waste t reat-

ment system. Obviously, processes that reclaim human food-grade materials must meet sanitary standards. By-products for animal foods are continu-

ously being upgraded; thus, it may be prudent to fu rn ish reasonab le d u p l i c a t i o n i n nonhuman food production of those techniques used i n human food processing.

Food as par t i cu la te mat te r i s o f ten separa ted f rom l iqu ids by s e t t l - ing, screening, skimming, o r cen t r i fug ing . Automated continuous processes s u i t a b l e f o r c l e a n i n g i n p l a c e a r e most a t t rac t i ve (as con t ras ted w i th

Page 31: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

65 F&V SPNOFF/RECYCLING & REUSE OF FD PROC WW

COOLING WATER

VAPOR VACUUM SOURCE

CHAt.!BER \ I V I I t-1

G BOILER

Fig. 14. Recovery o f m i l k vapors i n powdered milk production. The m i l k evaporator functions much l i k e steam generaged i n b o i l e r . Because the vacuum pan i s subjected to a h igh vacuum th rough the a i r e jec to r system, m i l k bo i 1s at low temperature that rare ly c l imb h igher than 15OOF. M i l k vapors change back t o water, which col lects against the cold condenser

tubes. Vacuum i n c r e a s e s l i n e a r l y t o maximum with lowest temperature thus

vapors f low from A t o B t o C. Mal func t ion ing mi lk evapora tors tend to foam, carry ing over mi lk so l ids; hence, an i n l i n e t u r b i d i t y meter safeguards the condensate pur i ty fo r the sa lvaged water reuse.

Page 32: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

66 F&V SPNOFF/RECYCLING & IIEUSE OF FD PROC WW

batch methods) fo r bo th shor t - te rm and long-term goals. Careful planning w i th we l l -de f i ned ob jec t i ves i s requ i red t o c rea te reso l r ces f rom wastes. Toward the end o f t h i s t e x t you wi 1 I f i n d a sect ion ent i t l e d "By-Product Recovery Use." This sec t ion ou t l ines some commodity-specific recovery schemes.

Recovery o f Chemicals While cleaning chemicals i n waste matter often cause t o x i c i t y and poor

performance o f t h e b i o l o g i c a l t r e a t i n g processes, they a1 so represent a BOD demand. For example, surfactants or common acid detergents produce 0.65 l b

BOD5/lb o f substance. Table 10 shows the BOD demand of selected substances, cleaners and san i t i zers .

L iqu id de tergents , san i t i zers and other analogous products can be handled i n bulk i n a series of vessels. These mater ia ls may then be piped t o r e s e r v o i r s t h a t can s to re and feed the cleaning solutions. Clean-in- place (C.I.P.) c i r c u i t s can be designed t o reuse f l u ids t ha t a re c i r cu la ted by pumping through p i pe l i nes, bulk tanks, storage reservoirs and other media. F ina l uses o f cap tured l iqu ids inc lude f loor c lean ing o r use as the f l u i d i z i n g l i q u i d i n s l u d g e pumping.

Heat Recovery Flow measurements are also necessary because the temperature alone i s

not adequate t o r e f l e c t t h e magnitude of potent ia l heat recovery. Waste- waters should be grouped according t o p u r i t y and temperature, and t h e hot- test water should be w i thout d i lu t ion to avo id heat d iss ipa t ion . Steam condensate i s r e t u r n e d t o t h e b o i l e r by deaerators because t h e w a t e r i s s o f t as we1 1 as hot.

Sometimes a water demand may be s a t i s f i e d by pre feren t ia l water make-

up, where t h e i d e a i s t o use a1 1 the sa lvage water f i r s t w i th f resh water suppl ied on ly when the other sources are exhausted.

Water Reuse

Water reuse may be adopted w i t h economical advantage when: O t h e r e i s i n s u f f i c i e n t w a t e r a v a i l a b l e l o c a l l y t o m a i n t a i n

an open c i r c u i t system a l l year ' round.

O valuable by-product materials can be economical l y recovered from the t reatment processes.

Page 33: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

67

F&V SPNOFF/RECYCLING & REUSE OF FD PROC WW

Table 10. BOD5 of selected chemicals i n detergents, sanit izers and lubr icants used i n food plants.

Page 34: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

68 F&V SPNOFF/RECYCLING & REUSE OF FD PROC WW

O t rea tment cos t o f recyc l ing water i s less than th? in i t ia l cost o f water, plus the cost incurred i n discharging the e f f l u e n t i n t o t h e sewer.

O c o s t o f t r e a t i n g t h e e f f l u e n t t o a required standard i s such tha t , fo r a l i t t l e e x t r a investment, the water qual i ty can be made su i tab le f o r recyc l i ng .

The pract ice o f water reuse can be div ided into sequent ia l reuse, rec i rcu lat ion wi thout t reatment and rec i rcu la t ion w i th t rea tment . Sequential reuse i s the p rac t ice o f us ing a given water stream for two or

more processes or operat ions before f inal t reatment and disposal , i .e., t o use t h e e f f l u e n t o f one process as the inpu t to another . Rec i rcu la t ion i s t he p rac t i ce o f recyc l i ng t he wa te r w i th in a u n i t process or group of processes. A combination of these practices will probably be required for afi optimum reuse scheme.

Table 11 ind icates some of the cannery operations i n which water may be reused i nd i sc r im ina te l y . I t s rec i r cu la t i on i n con tac t w i th f ood products must a l low for : sat is factory p lant and product sanitat ion.

I n an e f f o r t t o o p t i m i z e i n d u s t r i a l w a t e r use and wastewater manage- ment, emphasis i s now being given to decreasing the quant i t ies of water used and the contaminants introduced during use. A l te rna t i ves ava i l ab le f o r volume and pol lutant reduction include water conservation, good

housekeeping, waste stream segregation, process modification and water reuse.

H i s t o r i c a l l y , l i t t l e c o n s i d e r a t i o n was given to water reuse because Of

i t s abundance i n nature and because it was considered t o be hazardous due to bacter ia l contaminat ion. Contaminat ion potent ia l shows t h a t , i n washing f ru i t , un less 40% o f t h e w a t e r i s exchanged each hour, the growth ra te of bac te r io log i ca l organisms becomes extremely high. I n o r d e r t o overcome th i s , o the r means o f con t ro l , such as ch lo r i na t i on , must be used. When ch lo r ina t ion i s d iscont inued, the bac ter ia l count more than doubles. AS soon as c h l o r i n a t i o n i s resumed, the bacterial counts are again brought under control .

Water conservation can be achieved through counterflow reuse systems. Figure 15 o u t l i n e s a counterf low system f o r reuse of water i n a pea cannery. A t the upper r i g h t , f r e s h w a t e r i s used fo r t he f i na l p roduc t wash before the peas are canned, and from t h i s p o i n t t h e w a t e r i s reused and c a r r i e d back i n successive stages for each preceding washing and fl uming

Page 35: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

I

69 F&V SPNOFF/WATER USE & REUSE

i

c

I

Table 11. Po ten t i a l Po in ts o f Water Reuse i n t h e Food Industry. Or lerat i on Can Can Water from Source o f Water

o f Reserved t h i s Equipment f o r Reuse i n E qui pment Water be Reused E l se- Equi pment O

be Used? where i n P l a n t ?

A c i d d i p f o r f r u i t Washing o f product: A. f i r s t wash fol lowed by

B. f i n a l wash of product F1 umes : A. f l uming o f unwashed or un-

prepared product (peas, pumpkin and so on)

B. f l umi ng p a r t i a l l y prepared product

C. f l uming f u l l y prepared product D. f luming o f wastes Lye Peel i ng Product-holding vats; product

Blanchers - all types: A. o r i g i n a l f i l l i n g water B. replacement or makeup water S a l t b r i ne qual i ty graders

Washing pans and t rays ; A. tank washers - or ig ina l water B. spray or makeup water Lub r i ca t i on o f p roduc t i n

2nd wash

covered with water or brine

fo l lowed by a fresh water wash

machines such as pear peelers, f r u i t s i z e graders, and so on

Washing empty cans Washing cans a f t e r c l o s i n g Br ine and syrup Process ing jars under water

Can coolers: A. cool ing canal s

a. o r ig ina l water b. makeup water

B. cont i nuous cookers where cans a re pa r t i a l l y immersed i n water a. or ig ina l water b. makeup water

C. spray coolers with cans not immersed i n water

D. batchcool ing i n r e t o r t s Cleanup purposes A. p re l im inary wash B. f i n a l wash Box washers

no Can coolers

yeso Can coolers yeso Can coolers

yeso Can coolers

yeso Yes no Any wastewater no Can coolers

no

no no

o n l y i n t h i s equipment

no no

yes O Can coolers no yes O Can coc lers

For processing Can coolers and processing waters

Water from these coolers may be re- used sat i s f a c t o r i l y for cool i ng cans a f te r c i r cu la t i ng ove r coo l - ing towers, i f ca re fu l a t ten t i on i s paid t o proper control of re- placement water and t o keeping down bac te r i a1 count by c h l o r i na- t i o n and frequent cleaning

This water may be reused i n other places as ind ica ted

yes O

no Can coolers

es no Can coolers -A certain-amount of water may be reused’for makeup water and i n preceding operations i f t h e c o u n t e r f l o w p r i n c i p l e i s used w i th the recommended precautions.

Page 36: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

70 F&V SPNOFF/RECYCLING l4 REUSE OF FD PROC WW

WASTED "D- D C -3C

DE "-

F i g . 15. Four-stage counterflow system for reuse o f water i n a pea cannery.

Key: A. F i r s t use of water; B. Second use o f water; C. Thi rd use

o f water; D. Fourth use o f water; E. Concentrated chlorine water.

Page 37: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

71 F&V SPNOFF/RECYCLING & REUSE OF FD PROC WW

operation. As the water f lows countercurrent to the product, the washing

and fluming water can become more contaminated; therefore, it i s extremely important (Fig. 15) t o add c h l o r i n e i n o r d e r t o m a i n t a i n s a t i s f a c t o r y sani ta t ion. A t each stage, suff icient chlorine should be added t o s a t i s f y completely the chlor ine demand of the organic matter i n t h e water. With t h i s arrangement, sa t is fac to ry bac ter io log ica l cond i t ions shou ld ex is t in each phase o f t h e washing and fl uming program.

Water Conservation There may be several operations i n a food processing plant where water

i s wasted continuously, thus causing an over load to subsequent c o l l e c t i o n and treatment systems. Consideration should be g iven to s teps that can be

. t a k e n w i t h i n a p l a n t t o conserve water, thus enabling the l iquid waste disposal system to opera te more e f f i c i e n t l y and thereby reduce water po l l u t i on . As an example of water conservation methods the steps possible i n a food processing plant include 1) using automat ic shutof f valves on a l l water hoses t o prevent waste when hoses are not i n use (a running hose can discharge up t o 300 t o 400 gal lons of water/hour), 2 ) us ing low-volume,

high-pressure nozzles rather than low-pressure sprays for cleanup, 3 ) avoid ing unnecessary water overflow from equipment, espec ia l l y when not i n use, and providing automatic fresh water makeup valves, 4 ) avoid ing us ing water to t ranspor t the p roduc t o r so l id waste when the ma te r ia l can be moved e f f e c t i v e l y by dry conveyors, and 5 ) reducing cool ing water f low t o t h e minimum t o accomplish product cooling.

Recently, it was determined that by c o n t r o l l i n g t h e pH o f f r u i t f luming waters by t h e a d d i t i o n o f c i t r i c a c i d , it was poss ib le to reduce the water use wi thout an increase i n b a c t e r i a l numbers. A pH o f 4 will mainta in optimum c o n d i t i o n s w i t h c u t f r u i t , such as peaches. The system not on ly reduces the to ta l vo l ume of water required and there fore the

amount o f wastewater discharged, but also increased the product y i e l d as a resul t o f decreas ing the loss o f so l ids from leaching of sugar and acids. Consequently, there i s a r e d u c t i o n i n t h e t o t a l pounds of organic po l lu- t a n t s i n t h e wastewater. Another advantage i s improved f l a v o r and c o l o r of t h e canned f r u i t because o f b e t t e r r e t e n t i o n and so lub le so l ids.

Another water conservation method is us ing the c losed loop systems on cer ta in p rocess ing un i ts , such as a hydrostat ic cooker-cooler for canned

Page 38: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

72 F&V SPNOFF/RECYCLING & REUSE OF FD PROC WW

product. The water is reused continuously, fresh makeup water being added only t o offset the minor losses from evaporation. Closed loop systems not only conserve water b u t also reclaim much heat and can result i n signifi- cant economic savings.

inherent in various food processing industries t o reduce water and waste loads while a t the same time maintaining product quality. Many factors determine the f i n a l effectiveness of proper water use. For example, tomatoes spray-washed on a roller belt where they are turned are almost twice as clean as the same tomatoes washed on a belt of wire mesh construc- t ion . Also, warm water is approximately 40 percent more effective i n removing contaminants than the same volume of cold water.

there is no straightforward or simple formula t o obta in the least water use. Each case and each food process has t o be evaluated w i t h the equipment used i n order t o arrive a t a satisfactory procedure i n v o l v i n g water use, ch lor ina t ipn and other factors, such as detergents.

I t is not possible t o describe a l l the concepts and ramifications

A delicate balance exists between water conservation and sanitation.

Elimination of Water Use Eliminating water i n certain u n i t operations i n turn eliminates

attendant problems of treating the wastewaters, which were generated by those operations. Wherever possible, food should be handled by either a mechanical belt or pneumatic dry conveying system. If possible, the food should be cooled by an air system rather t h a n by a water cool i n g system. Recent studies by the National Canners Association i n comparing hot air blanching o f vegetables w i t h conventional hot water blanching show t h a t both product and environmental q u a l i t y were improved by using air. Blanch- i n g , used t o deactivate enzymes, produces a very strong liquid waste. For a pea processing operation, this small volume of wastewater is estimated t o be responsible for 50% of the entire wasteload BOD; for corn, 60%, and for beets w i t h peelings, 80%. Preliminary results show a reduced pollution load , while a t the same time provid ing a product qua l i ty improvement i n terms of nutrients, vitamins and mineral content.

Waste Stream Seqregation

t o their wastewater load. Noncontaminated streams offer the possibility of Waste segregation involves the separation of waste streams according

Page 39: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

73 F&V SPNOFF/RECYCLING & REUSE OF FD PROC WW

being discharged direct ly to receiving bodies of water, whereas contaminat-

ed waste streams have t o be treated. As a general ru le, a l l p lants should be provided with three water

discharge systems, namely 1) storm and coo l ing water, 2 ) san i ta ry waste, and 3 ) i n d u s t r i a l waste.

The stormwater system should receive a1 1 surface and storm runoff. Th is system can a lso be used for discharging uncontaminated waters, such as cool ing waters, that require no treatment pr ior to d ischarge. Al though it

i s d e s i r a b l e t o keep uncontaminated wastewater out o f the t reatment p lant , t he cos t o f i ns ta l l i ng separa te co l l ec t i on systems f o r small , isolated streams may be so high that by-passing the treatment plant becomes uneco- nomical .

The san i ta ry system should c o l l e c t t h e wastewaters from a l l washrooms and shower rooms. For most i ndus t r i a l p lan ts it i s d e s i r a b l e t o send these wastes t o a mun ic ipa l p lan t fo r t rea tment , ra ther than to t rea t them ind i v idua l l y .

Process Modif icat ion One a1 t e r n a t i ve avai 1 ab le fo r e l im ina t ing o r reduc ing the wastes

created dur ing process ing invo lves the modi f icat ion or e l imint ion o f the step or steps which are producing the wastes. For example, s ince the peeling process i s one of the greatest sources of wastes i n most f r u i t and vegetable process ing p lants , e f for ts have been directed toward modifying the peel ing process so t h a t t h e peel waste can be removed without using excessive amounts o f water. One recent process modif icat ion, i s t h e "dry" caust ic peel ing process for potatoes. In convent ional steam o r ho t l ye pee l ing processes, potato peels may cont r ibu te up t o 80 percent o f the t o t a l p l a n t wastewater BOD. The new dry caust ic vegetable peel ing method c o l 1 ects peel s and caust ic as a dry and semidry residue, thus preventing t h e i r entrance into plant wastewaters. Dry caus t ic pee l ing i s d iscussed in more d e t a i l i n Chapter 4.

A Sumnary

Reuse o f wastewater i s t h e u t i l i z a t i o n o f a process waste stream one o r more t imes before it leaves plant boundaries. This can be accomplished by piping the wastewater from one u n i t t o another, by t r e a t i n g o r d i l u t i n g

Page 40: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

74

F&V SPNOFF/RECYCLING & REUSE OF FD PROC WW

effluents before reuse in other units, or by combining a few or a l l efflu- ents, treating them and reusing the water.

Incentives for water reuse invol ves the possibilities of reduction of wastewater treatment costs and raw water costs. Al though lower waste treatment costs currently provide the major savings from reuse, i n some areas the supply o f acceptable raw water is decreasing, the price is rising, and reduced raw water usage may provide a s ignif icant incentive i n the future. The typical p lan t considering reuse seldom plans t o completely eliminate wastewater discharges since this would usually require very extensive modifications. The important standard for economic reuse is t h a t a n unused makeup process water can be replaced by a lower-qual i t y water w i t h o u t harming the process. So, reuse schemes should always be considered i n p l a n n i n g for pollution abatement.

Ultimate requirements for water p o l l u t i o n control may be completely closed systems from which no discharges are permitted, and use of fresh water is only required as makeup for evaporation losses. Closed water systems as the f ina l goal of pol 1 u t ion research has long been an ideal. Even though t o t a l reuse may not be legally required, i t may be a viable a1 ternati ve t o meeting stringent discharge regulations.

Possible steps for proceeding toward an intermediate or t o t a l reuse system are:

Determine the effluent qualities and quantities and makeup requirements for p lan t units. A waste stream survey is a must for such an analysis.

O Study the lowest-cost treatments needed for various effluents t o reach the required qual i t ies of secondary users. Trends have been toward treatment of combined waste streams. Segregation of waste streams may offer better reuse possibilities.

O Reduce wastewater volumes by increased maintenance and equipment modifications can reduce flows significantly.

O Study the effects of reuse on existing treatment equipment because water reuse generally results i n a lower volume, more concentrated waste stream.

Comnitment t o t o t a l reuse requires an economic justification covering the expected future costs of fresh water and ultimate waste disposal. I n some areas of the world, the cost of fresh water is rising

Page 41: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove

i.

75

F&V SPNOFF/RECYCLING & REUSE OF FD PROC WW

and the cost for u l t imate d isposal may gradually decrease as technology improves. The key to inexpens ive reuse i s volume reduction. The t o t a l - reuse wi 11 be able t o economical ly t reat on ly a small waste stream f o r t o t a l removal o f contaminants.

The decis ion o f whether t o implement to ta l reuse will be set by a comparison o f cos ts o f raw water and water t reatments wi th and without discharges. These include: water supply; treatment required before use o f f resh water; waste treatment required before discharge; treatment required f o r use o f reused water; p lant modi f icat ion to accept lower qual i ty or higher temperature reused water; extra piping and contro l va lv ing; loss o f f l e x i b i l i t y due to in tegra ted water system.

A t o t a l reuse plan should begin a t the indiv idual process uni ts, s ince .it will a f f e c t t h e i r o p e r a t i o n . I n c e r t a i n cases it may even be more economical t o modify a process so t h a t it r e q u i r e s l i t t l e o r no water. The economics o f t o ta l reuse will vary from p l a n t t o p l a n t .

R e f e r e n c e s c

1 ) Mercer, W. A. 1971. Conservation and Recycl ing o f Water and Other Mater ia ls. Food Indus t ry Week Conference. Proceedings Waste

c Management and Pol 1 u t i on Control.

2 ) Liptak, B. G. 1974. Environmental Engineer's Handbook. Vo Water Po l lu t ion .

3 ) Morresi , A. C., e t a1 . 1978. Cooling Water and B o i l e r Poss f o r Wastewater Reuse. I n d u s t r i a l Wastes, March/April .

lume I - i b i l i t i e s

c

t

Page 42: Spinoff on Fruit and Vegetable Water and Wastewater Management · screened out through a stationary curved screen separator before entering the four centrifugal separators. ... remove