CHAPTER 28FOOD PROCESSING INDUSTRY

Because of its intimate connection with the public health, the food industry hashad a long history of surveillance of its activities by local, state, and federal agen-cies. The U.S. Congress passed the original Food and Drug Act in 1906. That act,with subsequent legislation, controls not only the chemicals that are directlyadded to food—salt, seasonings, and preservatives—but also such chemicals assizing in food wrap that may indirectly become food additives by contacting food.

In addition to the close control of the FDA, additional surveillance is imposedon meat and poultry processing plants through the U.S. Department of Agricul-ture. No chemical can be brought into a meat or poultry processing plant unlessapproved by the USDA for its intended use, such as equipment cleaning or watertreatment.

Because of this close regulation, the choices of chemicals used in water orwastewater treatment may be more limited in the food industry than in othermajor water-consuming industries.

There are many segments of the food processing industry, of which the majorwater-using categories include sugar cane and beet processing, beverage manufac-turing, fruit and vegetable processing, meat and poultry, grain processing, fats andoils, and dairy products. The water consumptions of these segments are shown inTable 28.1.

Although there are wide variations in the process steps in each of these indus-try segments, there are a number of common unit operations. The distribution ofwater in the plant can be put into three categories: process water, cooling water,and boiler feed water. The percentage distribution varies considerably from a highof about 60% used for processing in the meat and poultry industry, to a low ofonly 15% in the sugar industry. However, 75% of the water used in the sugarindustry is for cooling purposes (and later becomes process water), with only 25%being used in the meat and poultry industry. Most food processing plants generatesteam for cooking or processing, and water used for boiler makeup ranges fromabout 6% of the total usage in fruit and vegetable processing, to about 15% in thefats and oils segment.

Process water uses include: washing of raw materials and process equipment;conveying products from one process area to another; dissolving or extracting;and addition to the finished product. Cooling water may be used to operate refrig-eration equipment, to condense steam from evaporators or turbines, or to coolprocess equipment such as compressors, cookers, and engine jackets.

Steam may be generated for cooking, for heating evaporators, or for space heat-ing. In some industries enough steam is required to justify installation of a turbineto extract power from the steam before it is sent to process (cogeneration). If the

* 1972 Census of Manufactures, U.S. Department of Commerce Publication MC72 (SR-4), WaterUse in Manufacturing.

steam can come into direct contact with food, there are strict limits on chemicalsused for both steam and boiler water treatment, and on their maximumconcentrations.

Knowing the processing operations in a food plant is helpful to an understand-ing of water use; water may be used sequentially for several purposes. For exam-ple, in the sugar industry, which has a very high requirement for condenser cool-ing water because of the evaporation and concentration of syrups, this coolingwater is used for washing cane brought in from the fields before it is discharged,and it is categorized as cooling water rather than process water.

Because the problems of cooling water and boiler water treatment in the foodindustry are similar to other industries, this chapter will deal specifically with pro-cess water, with some consideration of its contamination and final treatment fordisposal.

THE SUGAR INDUSTRY

There are many process steps in the sugar industry (some of which are similar tocorn processing). As the largest food processing water user with a variety of pro-cess operations, the sugar processing industry offers a good example of water usein food processing.

Sugar (sucrose), a chemical classified as a disaccharide with the formulaCi2H22O11, is derived from two major crops, sugar cane and sugar beets. Cane iscultivated in tropical and semitropical climates (e.g., Puerto Rico, Florida), whilebeets are raised in temperate climates (Idaho, California). In the United States,about 7 million tons of sugar are produced annually compared to world produc-tion of 75 million tons each year. In the United States the major sugar cane pro-ducers are Louisiana and Florida, with Hawaii and Texas also important contrib-utors. Beet sugar production is principally in the western and northwestern states.Cane exceeds beet sugar production. Because these crops spoil rapidly, they can-not be stored and the production of sugar is seasonal, with a mill operating aproduction campaign of about 120 days geared to the plant harvest.

Sucrose, which constitutes up to 20% of the weight of the cane or beet, is read-ily degraded by bacterial action. The first step in the degradation is the productionof invert sugars, fructose and glucose:

C12H22O11 + H2O - C6H12O6 + C6H12O6 msucrose fructose ~" glucose ^ '

TABLE 28.1 Water Usages in Food Processing*

Industry segment

SugarBeveragesFruit and vegetablesMeat and poultryGrain processingFats and oilsDairy products

Gross use

1061797620458386358218

Water flows, mgd intake

545275348296218107119

Discharge

51822632428819989

111

The second step is the production of lactic acid (C3H6O4) under the conditionsprevailing in beet sugar manufacture, or dextran (C6H10O5) under the conditionscommon in the cane sugar mills. Since this degradation is primarily caused bybacteria, it is important to maintain control of microbial organisms throughoutthe mill to avoid loss of production of sucrose. Microbial activity also causes pro-cessing difficulties, such as filter blinding, slime formation, and odors.

A basic flow diagram applying to cane and beet sugar processing is shown inFigure 28.1.

Water I ; I Wastewater•>• Washing ->

r . .. I Solids toExt rac t ion ^

_"_ I recovery

Juice

Lime I I Solids to process•*> Purification S T r * "

I and disposal

Steam I ~ I Condensate-* I Concentrate |-.- -^^ ^

>—Molasses— ->i

Steam _) Condensate-*• Crysta l l izat ion -^- — —, ^I to recovery

fSugar to market or fur ther refining

FIG. 28.1 Flow sheet of sugar processing.

As the crops arrive at the mill they contain soil and trash accumulated duringthe harvesting operation. In the case of cane sugar harvested by pushers, similarto bulldozers, the refuse may constitute as much as 10 to 25% of the weight ofmaterial delivered to the mill. This is not merely inert material; it represents amajor source of bacterial inoculation since soil organisms are present with appre-ciable fecal matter from birds, rodents, and other small animals that live on thecrop lands. Because of this, washing is a critical operation to the preparation ofraw materials going to further extraction processes. On the other hand, washingshould not be excessive, as this leads to loss of sucrose in the washwater.

After washing, sucrose is extracted from the raw material. In cane sugar mills,this is usually done by crushing and milling the washed, cut cane stalks, producinga juice containing approximately 12 to 15% sucrose. In the beet sugar industry,the beets are sliced into long, narrow pieces (cossettes), and the sucrose extractedby washing with water in diffusers at about 16O0F (7O0C). There is growing interestin the use of diffusers in place of crushers and mills in cane processing to reducemaintenance costs and improve yield.

The cane stalks are pressed after initial crushing and milling to reclaim asmuch sugar as possible, and the remaining solids (called bagasse) are usually

FIG. 28.2 Process flowchart of cane sugar mill. (Courtesy of Rio Grande Valley Sugar Growers, Inc.)

A Molasses B Molasses

TanksTanks

Vacuumpan

Vacuumpan

C Massecuite

Crystal l izers(B)

Centrifugal

Mixer

Syrup

MinglerC Sugar magmafor seed

Commercialsugar

Final molasses

Vacuumpan

Rotary vacuumfilter

Clarifiedjuice

12-167OSoHdSxScums

Press juice( f i l t ra te)

Clanfiers

Weighing

FirstbodyVapor to

heaters

Secondbody

Thirdbody

Fourthbody

Condenser

Tanks

Syrup

•Knives

Mixed raw juice

burned in boilers to generate steam. Bagasse may also be used as a raw materialfor such products as insulation board or acoustical tile. In the beet sugar industry,the beet pulp residue is quite high in protein, and it may be mixed with some ofthe plant production of molasses for cattle feed.

As with most other natural products, there are a variety of chemicals otherthan sucrose in the cane and beets. These must be removed to maximize the yieldof sugar, minimize the production of molasses, and reduce taste-, color-, andodor-producing impurities. Lime is used to precipitate these impurities, and thelime mud is removed by conventional solids/liquid separation devices. The mudis washed to reclaim as much sugar as possible, and it may then be (a) reburnedto produce fresh lime, (b) returned to the fields for its fertilizer value (it oftencontains significant phosphate), or (c) sent to landfill.

The purified juice must be concentrated to produce a thick syrup, the form ofsugar often used by the beverage industry, or to produce a crystalline product.The juice is concentratd by evaporation. Since it contains calcium from the limetreatment, a common problem in the industry is the formation of scale in the pans(simple steam-jacketed evaporators) or in the multiple effect evaporators.Another common problem is foaming as the juices become concentrated duringevaporation.

The flow sheet of a cane sugar mill producing raw sugar is shown in Figure28.2. There is widespread use of steam throughout the plant, so the boiler houseis a significant factor in economical production of sugar. Many sugar mills operateintermediate pressure boilers and produce electric power through turbo genera-tors, taking extraction steam from the turbines for operation of pans, evaporators,and crystallizers, and in many cases taking part of the steam through the turbineto a condenser. Cooling water from both turbine and evaporator condensers maythen be used as process water.

Because the operation of a multiple effect evaporator produces more water ascondensate than it consumes as steam, there is usually an excess of condensateavailable as boiler feed water. This condensate often presents special problems inthat it is likely to be high in ammonia, and it may periodically contain sucrose orinvert sugar. The introduction of sugar into the boiler quickly produces an acidcondition, so careful monitoring of the condensate system for sugar content isimportant to the protection of the boiler system.

The pollution control problems of the sugar mills are unusual because of theseasonal nature of the industry. The campaign is usually during the dry months,when streams cannot assimilate any excess organic loading. So the mills minimizedischarge flows by recycling as completely as possible, and the wastewaters aretreated biologically and impounded for solar evaporation or controlled dischargewhen stream flows return to acceptable rates.

THE BEVERAGE INDUSTRY

This segment of the food industry is another major consumer of water, some ofwhich becomes part of the final product. The balance is used for washing of bot-tles and containers, cooling of compressors and refrigeration equipment, andmakeup to boilers producing steam used for cooking, evaporation, heating of pas-teurizers, and space heating.

The water used in the product must, of course, be potable; in addition, thereare standards within the industry related to the effect of water quality on the taste

of the finished beverage. In the soft drink industry, for example, it is common tolime soften the water for hardness and alkalinity reduction, since alkalinitydestroys the flavor of acidic fruit extracts. In the lime softeners, breakpoint chlo-rination is also practiced. The finished water is filtered and then passed throughactivated carbon as a final precaution for the removal of chlorine and any residualtastes or odors. Most soft drink bottling plants have hot water boilers to providethe heat required for bottle and can washing.

Breweries and distilleries, on the other hand, operate their own steam plantsbecause steam is required for cooking and for the operation of evaporators. Inmany of these plants, steam passes through turbines to generate power, exhaustingto lower pressures for process operations. The unit operations in these plants arequite similar to those found in the chemical industry in principle, but specialdesigns enable the equipment to be readily cleaned to prevent microbial contam-ination of the product and to avoid risks to the public health.

FIG. 28.3 A filter installation typical of the food and bev-erage industry practices. Note the use of special stainless-steel piping and fittings. (Courtesy of Cross-ReynoldsEngineering Company, Inc.)

Special designs of piping and fittings, such as long-sweep pipe elbows, are usedthroughout the food industry because of this need for sanitation (Figure 28.3).Highly polished stainless-steel, monel, or chrome-plated steel eliminatesscratches, nicks, and crevices which could offer a home for bacterial growths. The

careful cleaning of equipment after each use creates a special problem of pollutioncontrol in that spent chemical cleaners, especially those containing biocides, ofteninterfere with the performance of pollution control equipment.

Two water-using systems are unique to the food industry and require specialattention to water quality: these are the bottle and container washing systems andthe pasteurizer.

In the bottle washing operation, both cleaning and sterilization are required,so detergents and biocides are applied to match the severity of the problem. If thebottle washer is handling returnable bottles, since there is no way of knowing whatmight have been in the bottles when in the hands of the public, it is important touse effective cleaning chemicals. These are quite alkaline. Because of this, it isbeneficial to have zeolite-softened water for washing and rinsing as this reducesthe demand for detergents and also greatly facilitates the drainage of the bottleafter rinsing for spot-free surfaces.

When strongly alkaline cleaners are used, these provide a biocidal effect thatdepends both on the length of time the chemical is in contact with the bottle, andthe causticity of the cleaning solution. Even with this protection, however, chlo-rine is often applied to the final rinse water to ensure sterility.

In the pasteurizing operation, as practiced in breweries, the bottled product ismoved through the pasteurizer, passing first through a chilling zone to halt thegrowth of specific spoilage organisms. A controlled temperature water bath thenslowly brings the beverage to approximately 16O0F (7O0C) and holds it for the timerequired to ensure that the entire contents of the bottle have been pasteurized.Usually two heating stages are used to prevent thermal shock and bottle breakage.The bottle is then moved into a chilling compartment before leaving the pasteur-izer for packaging. It is useful to have zeolite-softened water for this operationalso, to avoid spotting the bottles or cans. The temperature in the pasteurizingsection is maintained by circulating hot water; and the chilling sections (alsostaged to avoid thermal shock) may be tied into a cooling tower and supple-mented with a closed chilled-water system (Figure 28.4), although once-throughcooling water is still widely used.

In the event of bottle breakage, these water systems are inoculated withnutrients (the beverage), and microbial activity may quickly get out of hand. Bio-cides or chlorine-biodispersant treatments are used to keep this under control.

For the most part, beverage industry wastewaters are handled by municipalsewage systems. This may require the plant to install equilization facilities tounify the composition and flow rate. In-house handling of strong wastes, such aschemical cleaners, may also be necessary to make the equalization programeffective.

A number of large distilleries provide their own independent waste treatmentfacilities, usually conventional biological treatment.

FRUIT AND VEGETABLE PROCESSING

Just as with fluming of sugar beets in the sugar industry, traditionally, water hasbeen the media of in-plant conveyance of most fruits and vegetables in this indus-try segment. Not only has this choice been economical, but also it provides addi-tional benefits in prewashing and cooling. However, because of the pollution loadthat results from fluming, new methods of conveyance (air, vacuum, and mechan-ical) are now becoming more common, so washing and rinsing, which mayrequire as much as 50% of the total water used in process operations, is a separate

FIG. 28.4 The flow of product and water through a pasteurizer for careful control of beverage temperatures.Flows are cascaded for energy recovery. (Courtesy of Barry- Wehmiller Company.)

TIME-TEMPERATURE CURVE

LEGENDSPRAY TEMPERATURE

OFFAL TEMPERATURE

BEER TEMPERATURE

BEER OUT

TEMPERATURE0F

BEER IN

MFEED

FLOATVALVE

OVERFLOW

WATCHCHILUNO FUEHEAT

FKOCESS TIME - MINUTES

HEATWM FASTEORIZWIO FRECOOL

FLOATVALVE

OVERFLOW

2ND COOL 3RD COOLSERVICEWATER CHILLED WATER

DISCHARGE

OVERFLOW

REFRIGERATEDWATERSTEAM

SERVICE WATER

step. Grading and sizing are sometimes accomplished simultaneously withwashing.

After the fruits and vegetables are washed, peels are removed in a variety ofways. Steaming or soaking in caustic solutions are the most common, but air andmechanical peeling are also used. Dry caustic peeling of potatoes is gaining accep-tance within the industry as a means of greatly reducing pollution loads.

Water blanching is generally used for vegetable processing to remove air andto leach solubles before canning. Steam blanching of vegetables is usually used todestroy enzymes before freezing or dehydration. The blanching effluent streamcontributes a signficant portion of the total pollution load in canning operations.

In most canneries, the cans are filled with uncooked food and then passedthrough a steam exhaust box to eliminate air preceding the can sealing operation.The food is then cooked in the cans by direct contact of steam in retorts, whichare pressure cookers in which cans are stacked in racks. After cooking, large vol-umes of water are required to cool the cans as they pass through cooling watercanals. For continuous production, horizontal rotary cookers may be used inplace of retorts and cooling canals, with steam cooking in the first cylindrical shelland water cooling in the second. Even larger continuous units are available toprocess up to 50,000 cans on a 2-h cycle including preheat, steaming, cascadecooling, and final cooling.

A number of food products are cooked before they are bottled or canned, andmany of these, such as catsup, require concentration through evaporation of waterfrom the juice. So, there are many varieties of processing units used in the fruitand vegetable processing industry, including jacketed cookers and evaporators.All of this food processing equipment must be kept clean, usually by sanitizingwith chlorinated water or detergents.

FIG. 28.5 Spray distribution of food processing wastes to sloped grassland withcollection of treated runoff. This system is very efficient in temperate cli-mates. (Courtesy of U.S. Environmental Protection Agency.)

Like most food industries, the fruit and vegetable processors are trying toadopt dry cleaning methods to reduce the pollutant loading on effluent water. Thispollution loading varies enormously from one type of product to another. Forexample, in the processing of asparagus, the BOD and suspended solids are usu-ally below 100 mg/L, whereas in the production of whole kernel corn, the BODand suspended solids may be several thousand milligrams per liter. The solidwastes also vary considerably from one material to another.

Slope 2 -6%

Spray appl icat ion Evaporation

Grass and vegeta t ive l i t ter

Sheet f lowRunoffco l lect ion

Perc°/o//on

Although many canneries are served by municipal sewage systems, many alsooperate their own waste treatment facilities. Those in farm areas where land isavailable have been successful in using spray irrigation as a means of disposal,often accomplishing as high as 99% BOD removal. One reason spray irrigationhas been effective in the canning industry is because of the seasonal nature of itsoperations, permitting discharge during dry weather and avoiding the problemsof freezing that would occur with a year-round operation of spray facilities in coldclimates. A flow diagram of such a facility is shown in Figure 28.5.

Although activated sludge is an effective treatment process, strong waste fromfood processing may be fermented prior to final aerobic digestion to improveoverall BOD reduction. This is especially useful in handling fruit processingwastes because anaerobic fermentation proceeds rapidly and greatly reduces theload on the aerobic polishing unit.

MEA T AND POUL TRY

A generation ago, Carl Sandburg called Chicago "hog butcher for the world";today its great stockyards are almost empty. Economics and environmental con-trol problems have moved the meat industry closer to the animals' grazing landsand feedlots. There, the packinghouses purchase live animals, weigh them, andkeep them for several hours or overnight in "cow palaces," or holding pens, forprocessing.

The diverse steps in meat processing are shown by the flow sheet in Figure28.6. Poultry processing is illustrated by Figure 28.7.

In the first step of meat processing, animals are stunned by electrical, mechan-ical, or sometimes chemical means before slaughter. Large packinghouses canslaughter over 300 cattle or almost 1000 hogs per hour, while giant poultry pro-cessors can kill almost 500 broilers per minute. Water is used sparingly on the killfloor; there are two separate drains so that the blood can be reclaimed for furtherprocessing without being diluted by cleanup water.

Blood is either processed on-site or sold to Tenderers for processing. This con-sists of evaporating the water from the colloidal solids by "dry cooking" in asteam-jacketed vessel or by direct steam contact. The coagulated blood solids arethen dewatered to about 57% moisture either by solids/liquid separation or fur-ther evaporation. The water from this process (serum water) carries a heavy pol-lutant load. Blood processing is a heavy contributor to air pollution also. The finalproduct, blood meal, rich in amino acids, is sold as a nutrient to poultry and hogfeeders.

Cattle hides are removed from carcasses, and these "green hides" are usuallycured on-site by salting and stacking for 14 days or by soaking in a brine solution,which takes about 18 h. The brine solution is filtered for recycle to remove hornand flesh particles, hair and other solids, and discarded after a few days use. Aftercuring and sorting, the hides are sent out for tanning.

Most hogs are processed without skinning; hair is removed by soaking in 14O0Fwater, usually containing a surfactant, and then processing through a dehairer, adevice using rubber hair scrapers with copious sprays of hot water. A gas singerburns remaining hair from the carcass before further processing.

Hair is usually further processed by a caustic soak followed by steam cookingto produce a high-protein animal feed supplement called hair meal.

FIG. 28.6 Flowchart for a packinghouse. (EPA Contract No. 68-01-0031.)

Secondarytreatment

Final eff luent Waste f lowProcess f l o w

Solid wastecomposting

land fill

Manuretrap

Processing:

GrindingCuringPicklingSmokingCookingCanning

Grease trapor

f lo ta t ion unit

Meat products

Edible renderingLardEdible tallow

Cut meatCutting,

deboning

Cooling

Inedible renderingByproducts

Carcasses

TripeViscera handling

Eviscerating,trimming

Hide removal

Hog dehairing

Hide processing

Hog hair recovery

LiverHeartKidneys

HidesHog hair

Dried bloodBlood processingKill ing

Livestock pens

Animals

Waste

Solid Liquid Primary Secondary

Products

••̂ •̂ Product >» Potable water> Wastewate r

> By-product > Process water

FIG. 28.7 Flowchart of poultry processing plant. (Courtesy of U.S. Environmental ProtectionAgency.)

Large volumes of water are used as the cattle and hog carcasses are cut andprocessed. Viscera are removed and conveyed by water to edible and inedibleproduct processing.

Federally inspected and approved fat removed from the meat is rendered tomake fine cosmetics and lard. This process of edible rendering is a "wet process."Live steam is injected into a pressure vessel and the fat is released to float on the

Potablewater

Emptycoops

Truck-bornecoops

a. Receivingarea

b. Ki l l ingstation

d. Scalding

t Defeathermg

g. Whole birdwashing

h. Ev i sce ra t i on

i. Finalwashing

k. Chi l l ing

I. Grad ing,weighing,packing

Refr igerateddel ivery t rucks

Sewer

m. Final was te watercol lect ion and control

c. Bloodrecovery

Blood

Feather

f l o w away

f. Featherrecove ry

Feathers

j . O f f a lrecovery

O f f a l

FIG. 28.8 Meat processing waste treatment, (a) Flow schematic; (b] aerial view. (From EPA625 I 3-74-003, Water Treatment: Upgrading Meat Packing Facilities to Reduce Pollution, October1973, U.S. Environmental Protection Agency, Technology Transfer.)

FLOTATION UNIT BAR SCREEN 8RARSHALL FLUME

LIFT STATION

ANAEROBICLAGOON ANAEROBICLAGOON

AEROBICLAGOON AEROBICLAGOON

SECONDARYAEROBIC LAGOON

EFFLUENT

condensate (stick water). The stick water is high in BOD and extractables, andconstitutes a high loading on the waste treatment plant.

Most inedible rendering is accomplished dry. Ground offal is introduced intoa steam-jacketed vessel, where water is evaporated under a slight vacuum. Thecooked products are tallow and bone meal.

In basic operations, poultry and hog processing are similar. Scalding tanks areused to enhance feather removal; and the production of feather meal is similar tohair meal. Large amounts of water are used throughout the process.

Because of the high BOD of meat processing wastes, water pollution control issomewhat unusual in that anaerobic digestion is frequently used prior to aerobicdigestion. A crust develops on the anaerobic lagoon which normally controls theodors often associated with anaerobic fermentation. Pretreatment by equaliza-tion, screening, and flotation is essential to good control of the operation. Thedigester loading is typically about 0.2 Ib BOD/day per cubic foot of digester vol-ume. The wastewater is usually warm, about 80 to 10O0F (27 to 380C), which isbeneficial, as anaerobic digestion is greatly hindered at low temperatures. Deten-tion may be 12 to 24 h. This combination of anaerobic-aerobic digestion followedby sedimentation usually results in 90% BOD reduction in the first stage and over98% overall (Figure 28.8).

Many packing plants discharging to city sewage plants are required to providepretreatment (equalization, screening, grease removal) to reduce the load andequalize the composition of wastes to avoid upsetting the municipal plantoperations.

SUGGESTED READING

Lund, H. F., (ed.): Industrial Pollution Control Handbook McGraw-Hill, New York, 1971.Shreve, R. N.: Chemical Process Industries, 3d ed., McGraw-Hill, New York, 1967.U.S. Environmental Protection Agency: Development Document for Beet Sugar, EPA-440/

1-74-002-b, March 1974.U.S. Environmental Protection Agency, Development Document for Cane Sugar Refining,EPA-440/ 1-74-002-c, March 1974.

U.S. Environmental Protection Agency: Development Document for Red Meat Processing,EPA-440/1 -74-012-a, March 1974.

U.S. Environmental Protection Agency, Development Document for the Apple, Citrus andPotato Processing Segment, EPA-440/ 1-74-027-a, March 1974.