Grease Recovery in the Meat Packing Industry

E. N. MORTENSON

Chemical Engineer, Research Division Swift & Co.

Chicago, Illinois

The task of finding practicable means to achieve complete recovery of every by-product and utilization of all wastes produced by indus­ trial operations is by no means a simple or easy one. Though there are ways to remove practically every constituent which may be present in the waters discharged from industrial operations, the really big problem we are all wrestling with is how to do the most thorough job of removal in a practicable and economical way. To save and to use every by-product, with sufficient return to make the effort worth­ while, by no means reduces the amount of pollutional material present in the outgoing waste waters enough to obviate the need for some degree of industrial-waste treatment. There are two choices in the manner in which the quality and character of meat industry wastes can be reduced or altered. The first and best way is to minimize losses at the source. If this step proves inadequate, the second recourse is to provide, and to use properly, treatment facilities to recover as much as possible before the waste waters finally leave the plant. Actually, in the meat packing industry we do both. By-product recovery to many of us is synonymous with the meat packing industry. Our complete use of every by-product seems astound­ ing when recounted in full detail to the layman; and he, I believe, appreciates it far more than do we in the meat industry, to whom it seems commonplace. Yet many of us make the mistake of over­ emphasizing in our own minds how well we make use of every by­ product. Often we tend to lull ourselves into the idea that nothing gets away because we do produce a large number of by-products. If we examine very critically every step of the processing of the main products and the by-products, we can readily find many places and ways in which products can be lost.

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It is the purpose of this discussion to re-examine very carefully and critically every possibility where losses of fats, oils, and greases to the waste effluents can occur. Similarly, we wish to consider what can be done to recover these valuable by-product materials in simple and yet effective ways. In considering the industrial wastes which leave meat packing plants, it is readily apparent why the recovery of greases is such an important aspect of the problem. In processing livestock for meat, and for all of the by-products, both edible and inedible, practically every step from the pens to the shipping dock requires water in some amount. Since we have a raw product which contains very appreciable amounts of fat which can get into and be carried away with the water, grease recovery remains an ever-present problem from start to finish. In order that we may have a reasonable perspective of what grease recovery involves and its importance, we should first review some simple facts in regard to the meat business. First of all, it is hard to generalize as to the yields expected of meat, fats, and bones from one particular species of livestock. As an example, consider the fat content in a side of dressed beef of canner quality versus one of choice or prime grade. The canner may have as low as 11 % fat, while a side of choice grade beef may carry over 30%. (1) This is over 250% variation in terms of fat present in the dressed carcass. The actual, rendered fat recovered in the form of edible and inedible tallows from low-grade versus high-grade animals will have a proportionately similar variation. It is equally true that fat yields can vary nearly as much in the other species. Secondly, the volume of livestock processed from day to day and week to week in meat plants has wide variations. There are seasonal flush marketing periods of meat animals similar to flush seasons in other food industries, as in the fruit and vegetable canning field and the milk industry. Along with this variation in volume of raw product rides the equally variable price and demand for the primary product itself and the by-products, the latter oftentimes being in great oversupply with consequently depreciated values. This factor markedly affects the attention which is given to the recovery of such by-products as the inedible tallows and greases. In Table I we have shown published data taken from an Institute of Meat Packing, University of Chicago, publication:(2) 30

TABLE I

PROPORTION OF INCOME FROM BY-PRODUCTS IN THE MEAT INDUSTRY Percentage Percentage from Percentage from from meat by-products hide or pelt Hog 96.6 3.+ Sold with carcass Sheep 81.4 4.1 14.5 Calf 92.8 7.2 Sold with carcass Steer 87.3 4.1 8.6

There is no such a thing as a fixed yield figure which can be used with certainty to determine whether a particular meat packing plant is producing a normal amount of a given by-product. Neverthe­ less, we do use for accounting purposes standard yield figures based on data developed in carefully run tests at representative plants. It is impossible to rely on actual yield data measured against standard yield results' to gauge whether losses to the waste effluents are above or below normal in a particular meat packing plant. The use of account­ ing figures to ascertain if the loss of product to the sewers is high ' only measures the grossest kind of loss. A large percentage of the blood or tank water can be lost before we get significant reductions in the animal-feeds yield per unit of live slaughter which will actually indi­ cate losses above normal. What we must keep out of the sewers rep­ resents such small quantities that they make little difference in the accounting yields. To evaluate the fats, oils, and grease loss situation in the meat packing industry, it is first necessary to point out what the normal yields of these products are. Table II illustrates very briefly what these yields may be. TABLE II

NORMAL YIELDS OF FATS AND OILS IN THE MEAT PACKING INDUSTRY From beef slaughter* Edible—oleo oil and stearine 23 lb./M live Non-edible — tallow 5.35 lb./M live From pork slaughter* Edible—lard and pork fat 90 lb./M live Non-edible — greases 15 lb./M live

In view of the tremendous variation in actual fat content that is available from a carcass of poor quality as compared to one of better quality, it must be realized that the data in the foregoing table are only of an approximate character. In handling various steps of the processing there are general prac­ tices that will reduce the loss of fats, oils, and greases to the sewers. Deviation from good salvage practice at the source can be found and corrected by visual inspection. A little common sense in handling product and the exercise of good housekeeping will go a long way toward reducing the losses of fat or fatty tissue. Obviously, visible losses of fatty tissue or rendered fat either on the killing and cutting floors or in processing sections where cooking and rendering is done, can be pointed out and remedied. Proper gratings over floor drains, making it necessary to shovel up small pieces of tissue rather than to let them be washed away during clean-up, are an obvious precaution which should always be insisted upon. Minimizing leaks through pump glands, valves, and gates in the rendering departments is all a part of good housekeeping and will help hold fat losses at a low level. A marked reduction in the fat loss to the sewer can be made by ex­ cluding from the offal washer all hashed product which does not need washing. There is a tendency to overdo the offal washing in many instances. Sufficient rendering equipment to handle adequately the peak volume of fatty material during heavy kills is a very important factor. Good practice in the rendering sections of a meat packing plant will do more to lessen the load of fatty tissue, protein, rendered fats, oils and greases, and intestinal contents to the sewer than can be done by careful handling in all other departments. This section, besides requiring adequate equipment, should (1) keep its water use at a minimum, (2) prevent souring of raw materials, (3) refrain from overloading melters or rendering tanks, (4) maintain machinery in good condition, (5) evaporate all concentrated cook liquors. This last point (5) in the foregoing list raises the question as to why isn't all rendering done on a dry basis so that we won't have large quantities of tank water? There are several reasons why a substantial amount of wet rendering is still done. Prime steam process­ ing has been the generally accepted method of rendering and some trade indicates a preference for prime steam lard over dry-rendered lard. Some few packers have for many years used the dry method. In recent years, and even more so at the present time, many packers are becoming interested in dry rendering but lack of equipment and the generally expensive layout required will no doubt tend to delay a complete changeover to a dry-rendering basis. Regardless of the attention given to good housekeeping and the efforts made to salvage all utilizable material at the source, to the extent consistent with practical operations, every meat packing plant 32 requires efficient and well cared for grease interceptors and catch basins. Practically all references in the literature regarding meat packing plant wastes state simply, "catch basins are employed to sal­ vage grease." Very little specific information as to actual details of construction, operation, or efficiency of these facilities is given. It is true that there are ample data on the fat content of meat packing plant wastes once they leave the plant and enter sewerage systems or treatment plants. A thorough approach to the problem of minimizing the fat con­ tents of these outgoing wastes requires consideration of the loads imposed on the retention facilities. We have shown briefly in Table II the fats, oils, and grease yields on an over-all basis per 1,000 lbs. live weight and mentioned how these yields vary with the class of animal. For instance, in beef opera­ tion, the total fat production, lumping the edible and non-edible portions together, will amount to an average figure of, say, 28 pounds per 1000 pounds of live animal. Likewise, in pork-slaughter operation, the total production of fats, including both edible and non-edible, is some­ what over 100 pounds per 1000 pounds live. You must remember that these are very approximate figures and are given only to show in general the quantities involved. They show an average yield which we could expect from plants handling a composite of various classes of livestock. The loss of fats, oils, and greases will occur in part from each section of processing. The major share will come from the rendering department and the viscera handling. A relatively small proportion is contributed from the actual killing and carcass-dressing floor or the carcass cutting. In beef operations, the amount of inedible tallow which is rendered out of the skimmings taken off an efficient grease separator will vary from a low of Yz lb. per 1000 pounds live slaughtered to a high of perhaps 2 lbs. This represents a yield of only a fraction of a per cent of the actual live weight (0.05% to 0.2%). It is, however, 10% to 40% of the normal inedible tallow production shown in Table II. These yield figures represent that amount of inedible tallow rendered out of the skimmings which will be recovered from efficient grease separators when the plant processing is handled properly with respect to minimizing fat losses at the source. It cannot be said that similar results are typical for every meat packing plant. Where insufficient care is taken to hold down losses at the source, the loss to the final catch basin can be appreciably greater than indicated. This can be an irretrievable loss if the grease separator does not do a good job. 33

On the pork side we can expect a recovery from a final grease separator in the form of actually rendered grease in amounts of from 2 pounds per 1000 pounds live animal, where the plant operations consist only of carcass dressing and offal processing, to an average figure of 6 pounds, in a plant with complete by-product operations. It may run considerably higher, but with reasonable care at the source should not exceed 8 to 10 lbs./M lbs. live. In both beef and pork operations the actual grease separator yields will depend on the grade of animal. Extremely fat hogs or prime grade beef will yield somewhat more than indicated in the foregoing average figures. Having mentioned briefly the amount of grease or inedible tallow which will be recovered from the grease separators where losses from the operations are held to a minimum and efficient retention, units are used to catch that part which does escape, it is well to consider just what constitutes an efficient grease separation and what important factors are involved. First of all, we must consider what part of the plant waters should be diverted through grease-retention facilities. This oftentimes involves complexities due to the physical layout of the plant. Often it may be expedient to have separate intermediate retention units serving only one particular department, such as the rendering section, the sausage kitchen, or the oil house. These units may serve as depart­ mental grease interceptors. Such units usually provide for intermediate retention and the effluents from them get further settling in the one or more larger final catch basins. For large plants where various grades of inedible tallows or greases are produced, this use of departmental grease separators will justify the added expense in maintenance by producing skimmings which yield a higher-grade grease. However, when only one grade of inedible tallow or grease is produced in a plant, the increase in quality by extensive use of departmental grease inter­ ceptors is rarely enough to make a significant difference.

For grease separators to serve their purpose, of course, all fat- bearing wastes must go through them. It would seem that such a simple fact would not have to be stated at all. Nevertheless, in plants which have grown in size, where new by-product operations have been started that were not in the original layout, where old plants have been revamped, new sewers put in, old floor drains replaced, newer types of machinery installed, it is very important to reiterate and to reemphasize that all fat-bearing wastes must go through well-designed grease separators. Likewise, in order to avoid contamination of the 34 salvaged grease and to have adequate detention, all non-fat-bearing wastes should be excluded from the retention unit. These wastes are:

(1) Clear condenser waters. (2) Engine room drainage, garage wastes, and trolley washings. (3) Boiler blow-down. (4) Waste condensates. (5) Hide-cellar drainage. (6) Sanitary wastes. . (7) Storm water and roof drains. (8) Paunch and stomach contents where hand opened. (9) Livestock pen and drive drainage.

Sometimes it is not physically possible to exclude all condenser wastes, and in such cases a larger volume of flow must be handled in a separator of proportionately larger size. Condensing waters from barometrics and suction tees used on rendering equipment and oil de­ odorizer vacuum systems require separate hot wells so designed as to retain entrainment losses or trap heavy carry-over in case of over­ loading, or surges from fractious materials. With reasonable care in product handling, such discharge should never occur. Yet, the in­ surance should be provided by installing hot wells with 10- to 15- minute detention periods, and baffles should be so arranged as to hold fairly deep layers of skimmings if surge losses occur. Complete exclusion of engine room drainage, garage wastes, and trolley washings from the grease recovery basins is absolutely neces­ sary to keep out mineral oil. Salvage of this material must be done separately, for its presence in the recovered skimmings seriously im­ pairs the subsequent value of the grease in view of the increase in the unsaponifiable matter. The mineral oil can be retained in properly baffled catch basins installed on sewer lines from the sections con­ tributing such waste material. The volumes to be handled are usually small. Sanitary wastes and process wastes are never discharged in com­ mon lines prior to grease recovery facilities of the establishment. Wastes carrying large amounts of solids both dissolved and sus­ pended and free from grease, such as boiler blowdown, hide-cellar drainage, storm flows, paunch and stomach contents, do not necessarily have to be completely kept out. They do, however, decrease the separator efficiency and by the effect of the solids impair the quality of the salvaged grease, not to mention increasing the separator volume needed to effect maximum recovery. 35

Now that we have detailed what should and what should not pass through the basin installed for grease recovery, how large should it be and how should it be designed? As to size, it is first necessary to know what volume of fat-bearing wastes will normally leave a meat packing plant. The variation in flow from plant to plant depends on (1) the general availability and cost of water; (2) the type of plant, whether a slaughter house or a complete meat packing plant with balanced by-product production or one handling extra by-product material from outside units; (3) the species slaughtered; (4) type of rendering equipment, wet or dry; (5) offal handling. Our experience indicates that for a plant handling all species, that is, mixed kill, and having balanced by-product operation, the volume of fat-bearing wastes will vary from a low of 0.5 gallon to a high of 1 gallon per pound live weight plant-slaughtering capacity. When new recovery facilities are being considered for a plant already in operation, it is, of course, a fairly simple matter to make the necessary surveys to check the actual volumes of waste to be handled in the grease separator. With this latter information from surveys during maximum slaughter opera­ tions, or using the maximum estimated value of one gallon per pound live, the basin should be built large enough to provide a capacity equivalent to one hour of average daytime flow. Normally 75-80% of the fat-bearing wastes leave the plant during the daytime period from 7 A.M. to 7 P.M. with plant and kill operations on an eight-hour basis from 7 A.M. to 3 :30 P.M. and clean-up operations practically fin­ ished by 7 P.M. If the maximum live weight slaughter capacity, on an eight-hour basis, is of the order of 200,000 pounds per day, we would anticipate a fat-bearing waste flow of 200,000 gallons of which approxi­ mately 160,000 gallons will leave the plant during the 12 hours from 7 A.M.-7 P.M. This will give an average hourly flow of 13,500 gallons. For this plant, we would then recommend installing a grease separator having 13,500 gallons capacity. To gauge accurately the size of retention unit needed at any plant there is no substitute for thorough survey data of the fat-bearing-waste volumes. Also, there is no ab­ solutely hard or fast rule which necessitates making the basin no larger than indicated in the foregoing illustration. If the quantity of highly emulsified fat-bearing wastes seems to warrant it, detention periods greater than 60 minutes might be necessary. Wastes which carry only separate fatty tissue, such as those from killing floor operations and cutting rooms and no cook waters, float off what is recoverable in detention periods as short as 30 minutes or less.

Detention periods, of course, don't mean much. It's the flow ve­ locity reduction over a given period of time that counts in settling. 36

Grease recovery is merely settling whereby the salvageable material, the grease, comes to the surface. The more quiescent or still the liquid remains, the more readily a given fatty particle or droplet of oil can rise to the surface. Yet, there has been a tendency and general practice in vogue since 'way back when the first grease trap was built to expect greater recovery of floatable material by the introduction of needless overflow and underflow baffles, which tend to create excessive turbulence. Old-style catch basins were ordinarily quite shallow and narrow, having liquid depths of from two to four feet and were not over six to eight feet wide. The skimming was usually done by hand, with a long handled dipper. For this reason numerous underflow baffles were installed to help corral the ever-elusive skimmings. To help chase the little grease particles to the surface, it was reasoned that the more times they passed over and under a baffle, the quicker they would get to the top and be recoverable. Reasonable design today calls for a basin with sufficient cross- section to keep the flow-through velocities below theoretical rates of one to two feet per minute. Baffling should be at a minimum. It is essential, however, to provide an underflow baffle close to the inlet end in order to dissipate as much as possible the inlet .flow velocity; and, of course, we cannot leave out the final underflow baffle at the out­ let, to which the scum trough is attached. Following that, a final over­ flow weir, extending the full length of the basin, should be used. The skimmings themselves should be removed by continuously operating skimmer flights on large units, where such mechanisms are well justi­ fied, while smaller grease separators can be handled readily by inter­ mittently operating skimming mechanisms powered by hand winches. In brief, a good grease separator for handling the main plant fat- bearing wastes can best be a well-designed preliminary settling basin as normally used in waste-treatment or sewage plants, with emphasis on adequate and sturdy skimming facilities. Normally the depth of tank required will not be quite as great as that considered most practical from the standpoint of good suspended-solids removal. It is important to provide means to discharge the settled solids from whatever type of unit is built. Where provision for such removal is provided at a treatment plant, and permanent removal is not required at the packing plant, the settled solids which accumulate in the grease separator normally are not discharged from basins with continuously operating collector flights. They are usually flushed out after a thor­ ough skimming of the grease separator. This operation is usually done 37 late in the evening. If continuous sludge-removal equipment is in­ stalled, the discharged sludge can either be screened as discharged from the separator or fed back into the basin overflow and be handled at a treatment plant. Continuous mechanical removal of the settled sludge has the advantage that the grease separator never needs dewatering ex­ cept for repair purposes.

Testing Basin Efficiency.—With well-designed grease separators and reasonable salvage at the source, the grease loss in the plant waste should be at a minimum; that is, the loss of floatable fat should be extremely low. It is recognized that there is fat present in the wastes which will neither settle nor float and that there is fat with the solids that settle to the bottom of the basin. It used to be our practice to check grease separator overflow losses and losses during clean-out periods by catching composite samples and analyzing them for the total petroleum ether soluble content. Knowing the volume of waste sampled, as accurately as good weir measurements can provide, and the petroleum ether soluble in parts per million, we had a figure which told us roughly just how much grease the plant was losing. However, it did not tell us what part of this loss was actu­ ally recoverable by flotation under quiescent flow conditions for a given period of time. In general, we used experience as a guide and said that anything over 150 parts per million represented a grease loss that should not occur because it was recoverable. Such an estimate for basis of judg­ ing accurately what a particular grease separator was accomplishing proved entirely unsatisfactory. Instead of trying to ascertain recoverable grease losses in this manner, we worked out a practical method which measures the actually floatable or recoverable grease. In brief, this method consists of catching fairly large samples (5 gal. every 5 minutes) from really turbulent sections of outfalls under con­ sideration. These samples are poured into a 55 gal. drum equipped with an overflow siphon draining from the bottom of the drum (see Figure 1). Sampling is carried on over a period of 10 to 12 hours. At the end of that time the accumulated floatable material is skimmed off and analyzed for grease. Having taken volume readings of the sampled flow and knowing the floatable recovery from a given portion of it, we can calculate fairly closely what the recoverable or floatable losses really are. On the basis of this test, we have a goal which experience shows it is possible to attain or even exceed. We say the loss of floatable grease per 1000 lb. live kill on a plant should not run more than 0.1 lb. On »s®,.

X, metal funnel 8* 1 Inch overflow pipe 3. 50 or 60 gal. steel 4. water level 5. welded nipple 6. 1" x 6" plank with hole for funnel

FIG. 1. SAMPLING BARREL FOR RECOVERABLE FAT.

To Operate:

1. Barrel is first filled with clean water.

2. Gallon samples, drawn at definite intervals, are poured into the funnel.

3. Overflow pipe is adjusted so that water will not spill over the sides of the barrel.

4. At the end of the test, floating solids are skimmed, weighed, and analyzed for fat.

Calculation of Results:

Total volume sampled

Lbs. fat in skimmings X Volume poured through funnel = Lbs. recoverable fat.

38 39 the basis of 1000 gals, of waste water discharged per 1000 lbs. live weight slaughtered, this 0.1 lb. recoverable grease loss represents only 12 parts per million of floatable fat in the outgoing waste. It is obviously impossible to judge whether recoveries at the source are up to the recommended standard based on accounting yields. To be absolutely certain that the loss of grease in the waste effluents is not excessive, thorough recoverable-fat-loss surveys, as described above, should be made at frequent intervals. On the basis of such tests, we can definitely know how good the grease recovery is on a given plant.

REFERENCES

1 "Proximate Composition of American Food Materials," Charlotte Chatfield and Georgian Adams. U.S.D.A. Circular No. 549 (June, 1940).

2 "Readings on By-Products of the Meat Packing Industry—Col­ lected by the Institute of Meat Packing, University of Chicago." (1941.)

3 "American Livestock and Meat Industry," R. A. Clemen (1923) p. 349. Ronald Press.

4 "Pork Operations," 5th Revised Edition (1941), p. 211. The Institute of Meat Packing—University of Chicago.