Industrial Wastes
DAIRY INDUSTRY H. A. TREBLER
A~GD H. G. HARDING
National Dairy Research Laboratories, Inc., Baltimore, Md
b b Dairy products are bigbly
Eoneentrated and perishable, and th& wastes h a v e a high, pollution value. The trend in t h e dairy industry is tow& large manufacturing plants, fully equipped to utilize all by-products5 but there .is still a large n u d e r of widely scattered small plants. T h e establishment of more large by-product plants wbich utilize all .available waste products f r o m near-by small plants will do m u c h t o preyent stream pollution. The v i r i o u s types of dairy wastes a n d methods of disposal are discussed. In general, cooling waters should be s w g a t e d , domestic wastes &+d @,to septic tanks
or city sewers; the s t r e n g t h of other wastes sbould b e reduced to a m i n i m u m by improved by-products utilieation, waste saving, and waste prevention within the milk plant; and t h e flow should be aerated and equalized before discharge. Necessary t r e a t m e n t should be given, if possible, in combinationw i t h existing or f u t u r e city waste disposal plant+ If these means are not available, the trend is toward t r e a t m e n t on recirculating tridde filters. Efficient a n d economical contml, maintenance, and supervision of industrial waste disposal plants are needed and m a y have to be met on an industry-wide basis in t h e future.
M
but there has ale0 been an increase in the manufacture of other dairy products except butter, which has shown a marked dec r e w particulssly during the war yertrs. The size of the average dairy p h t has inoreased markedly, although a large number of widely scattered small plants still exists. With improvemeqt in transportation, the tendency is definitely towards larger plants with larger milksheds. Formerly a large part of the milk was s e p a m t d in? cream and skim milk on the farms; the sldm milk was utili5G directly . for stock feed, whereas the cream was either made into butter on the farm or sent to creameries for churning. A considerable paxt of the milk is still utilized in this way, but with the increasing prices of milk+olida-not-fat and with improvement in roads, whole milk is bdng shipped from fmto factories, which. then can evaporate and dry, separate cream &nd churn butter, or produce cheee, according to consumer demand and the sowx Of greShSt profit. Wartime ne& for concentrated dairy products of good keeping quality resulted in the construction of many new milk evaporab ing and drying plants. It slso resulted in the diversion of a great deal of skim milk solids from animalto human consumption. At present there is a revmal of thk trend, but it is difficgt to predict the relative future markets for the various milk products. Considerable effort is being made to obtain a more even milk s ~ p p l yby better feeding during the winter and by better distribution of the calving season, but the industry is s w 1 highly seasonal, with 50% higher average daily milk production during the Iate spring and early summer months when pastures are a v d able for cheap feed. Since demand for fluid milk and cream in urban markets remains fairly uniform throughout the year, large volumes of ~ s mnsb he tramformed into products which seasonal ~ U r p l milk &an he stored for future use and tr&~sported over long distances. Table I lists mme of these products, and the simplified flow sheet of Figure 1sbom their approximate relation to one another. For instance, butter represents the most valuable part of milk in a concentrated farm, which can be kept in refrigerated storage for a long time without serious impairment of qudity. I n butter only the butterfat is preserved; the skim milk and buttermilk must be further praserved by concentration or drying, or they can he used directly for animal feed, or they arc wasted when bot enough stock are available to consume them.
ILK is an important,, nutritious, and perishable food. Unfortunately the more nutritious and more perishable a food material is, the more its industrial wastes are likely to cause stream pollution. The effectof excessive amounts of dairy wastes on a stream is the same as that of many other strong food wastes; it uses up the dissolved-oxygen, thereby creates objectionable conditions, and makes it impoasihle for fish to live in the stream. as the oxygen content of the water does not go below parts per million (p.p.m.), s d amounts of dairy waste lire actually beneficial to fish life, because dairy waste stimulates the growth of the organisms upon which fish feed. Table, I shows the chief components of milk and some of its important producta and by-produds. The latter never should be wasted to streams or sewem but, unfortunately, sometimes still me. The tahle also shows the pollution factors of these products when discharged t o streams, both as average 5 d a y biochemical oxygen demand (B.O.D.) and as population eflvalent in comparison with average sanitary waste. The latter figuree show how important it is to utilize every pound of.milk solids and to keep them out of plant wastes. The function of the dajr industry is to collect the milk from the farmers, process it, and get the milk and its many by-products to the ultimate consumer in the most economical manum possible and with a minimum amount of waste. A number of peculiar conditions within the i n d u s t r y 4 u e partly to its hiStOnCd development snd rapid growth, partly to the chsmioal nature of milk and its products, and partly to extremely rigid sanitmy requirements-have made efficient waste saving, utilization, and disposal d i f f i d t and costly. Eowever, the industry is becoming more and more conscious of its waste and pollution problems, and is making good progress towards their economical solution. The history of the dairy industry in the United States is similar to that of many other industries in that there has been a gadual development from a home industry to a large factory industry. During the last ten years this development has been seeeded up by several important factors, such as increased demand for pasteurised milk and ice cream and for evaporated and dried milk PIOdUCtS, wbich require a relatively large investment in equipment. During this same period there has been,.@ $he United States, an increase in milk production of 2 billion pounds per year, until a6 present the annual production is about 125 billion. A large part of the increase has gbne into fluid pvteurized milk;
609
INDUSTRIAL A N D ENGINEERING CHEMISTRY Table I.
Approximate Average Composition* of Milk and Dairy Products
-.Protein from Casein and ButterLactalfat. bumin. Whole milkd Evapd. milk 8kim milk Dry skim milk 8weetened skim. mndensed Buttermilk. Whe I ChsBda. cham
Milk Sugar
(Lao-
Aaidity
8".
tose),
erose,
3.2 6.7 3.3 36.9
6.1 10.0 5.3 50.5
0 0 0
10.4 3.4 0.9 26.6 2.2 3.9
16.8 4.3 4.0 1.5 3.0 5.9
%
%
3.9 7.9 0.1 0.9 0.3 0.4' 0.3 35.5 40.0 12.0
%
. P0eulatmn
%
Aah,
Laotio.
0.7
.... _.
. %
a
1.4 0.8 8.1
40
2.5
0
0.7 0.6
0
s
%
...._ . Qii
0.2
Total Solids,
Equiv.' Per
Org.
HunB.O.D.L.
'12.9 2K.9 9.5 96.7
Solids. % 12.2 24.5 8.7 88.6
70.0 9.4 6.9 76.5 45.6 37.7
67.5 8.7 6.3 73.0 46.2 36.9
60.2 7.2 3.5 60.0 39.9
%
%
10.3
20.8
7.2 73.7
d e weight 61 125 43 442 301 43 21 360 139 175
0 3.5 ... 0 0.4 .., ICE WeBm mix 15 0.8 28.2 Averages from varioua sources. 5 Par cant B.O.D. number of ounda of oxygen -d bu 100 pounds of produot in LL stream in$ days at Zoo C. e Population equivalent is bassi on factor of 0.167 pound B.O.D. per person per dn in average,domestm waste. d S h o e the composition of whole milk varies conaidarably beaause Of m a n y facton). tie valves for Individual aamplea may show ooaridenrbla difrerenoe. * Ripened cream buttermilk. I Amerioan oheese whey. Cream
-
.._
In cheese both the fat and the protein parts of the milk are conrentrated together in fnirly nonperishable form for storage and transportation. Cheese whey contains most of the milk sugar and mineral salts and relatively small amounta of fat and protein. Much whey is wasted or used directly for stock feed, but more and more is evaporated and dried to give valuable hyproducts used for human and animal consumption. Table I1 shows the most importan+proceases in the dairy industry and the pounds B.O.D. loss which can be expected from eaoh procese with reaeonably modem equipment and careful operation. These so-cded standard lwea have tentatively been approved by the Dairy Sanitary Engineers Committee in PennsylvlLnia, and &o by the Task Committee on Dairy Waste
Disposal, which is a subeommittee of the Dairy Industries Cornrmttw. T h e latter consisis of representativesof all thedifferent groups in the dairy industry in the United Staka. Waste volume depends entirely on the cost and temperature of the available water supply and on cleaning methods; consequently average figures (M, 24) do not mean much. TYPE8 OF WASTE AND DISPOSAL METHODS
The'dsiry industry has several kinds of waste which frequently are worth while to treat separately. GENEEM,DOMESTICWASTES,such as waste from locker room, lavatories, and laundries, should go to the regular sanitary
PROTElh (CASE1 MI-* SJGAR ILAC
WHOLE MILK
-
1
BUTTER MILK OR VACUUM
CONDENSED
ill
Figure 1. Simplified Flow Sheet of the Dairy Industry ( N d e r a in BiUion Pounds per Year)
610
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 39, No. 5
cooling ammonia condensers and milk and cream coolers. Where water is cheap, no attempt is made to re-use this n-ater, but ahere it is exA . Drain tube from separator pensive or scarce, cooling towers or spray ponds B . Ohservation glass C. Milk entrainment returning are widely used. There is no objection to the to evaporator discharge of quch clean cooling waterq to streams D.. Tangent milk inlet E . Individually operated streamor to the storm sen-ers in cities. Cooling waters lined coils qhould not go to sanitary sewers; because of their large volume they would require unnecessary pumping and settling capacities. Cooling water should be used for dilution of effluents fiom waste disposal plants. Cooling waters used for vacuum pan condensers usually carry some organic solids. They are also fairly warm (130" to 140" F.). Because of the high initial and maintenance costs of surface condensers and their relatively low efficiency, the evaporators in the dairy industry use, almost exclusively, spray condensers in which the vapors come in direct contact with the cooling water. Consequently it is important that the evaporators be properly designed or supplied with efficient entrainment separators (Figure 2) to prevent undue losses by entrainment or boilover. An electronic foam levelcontrol device w t h a vacuum breaker which automatically lets air, or preferably steam, into the evaporator to kill the foam has been described previously ( 2 1 ) . This has proved to be very helpful. It appears cheaper and more practical to equip the evaporators with efficient F. Air and noncondensahle entrainment separators than to use surface congases t o ejector or dry %acuumpump densers. Furthermore, the entrainment separators C,. Water inlet I € . Air cooling dome are profitable because of the savings in milk solids. 1. W atrr separation disk If proper precautions are taken to prevent J . Water distribution baffles K. Adjustable vapor deflector entrainment and boilover losses, discharging the>e I,. Water outlet through barocondenser waters to city storm sewers or to metric leg or centrifugal streams is alloIvvable; but the high temperature pump may occasionally be objectionable to aquatic life, and then it may become necessary to spray the water along the banks of the stream or on an adjoining field. Cooling naters used in canned evaporated milk sterilizers also may contain some milk solids whenever the device for closing cans and the device for detecting leaky cans are out of order. Usually, hovever, these waters will be clean and hot, and can be discharged to storm sewers or streams Figure 2. Stainless Steel Yacuum Pan with Entrainwithout trouble; however, spraying may become necessary when the high temperature is objecnient Separator and Countcrcurrent Condenser tionable. SPOILEDPRODUCTS are wastcd mostly in the COURTESY ARTHUR H A R R I S & COMPANY summer if farmers fail to cool their milk properly or if the receiving and cooling equipment in a plant is of insufficient capacity to handle the incoming milk before it sours. Spoilage may also occur In wirers in the cities and to a standard septic tank of ample Tize case of pon-er or equipment breakdown. The remedy is more and in the counti y 01 in nonsewered small towns. The effluent from better dairy equipment and personnel, and more provision for septic tanks can be handled in a standard underground drain field, stand-by power and equipment for emergency use. or it can join other daily n astes for further disposal. Disposition of spoiled products sometimes becomes a difficult BOILERBLOW-OFF, n hich is alkaline and hot, is definitely beneproblem; the wastes must not be dumped to clean streams or to ficial to septic tanks used for domestic waste or to digester tanks city seners in small cities. Sometimes the only practical method used for dairy m i t e , and so should be discharged where it can do of disposal is to truck the products out for dumping in some i,othe most good. lated spot Khere no damage can be done. BACKWASH ATD REGCNER~TION RINSE T ~ A T E R S from xvater BY-PRODVCT 'KASTES,such as whey, buttermilk, and excess softeners hare a high salt content and should preferably be disskim milk, are the worst offenders as regards stream pollution. charged directly to streams or to storm sewers in citieq, although These n-astes are due mostly to the fact that many plants are not the quantity is seldom large enough to cause any trouble if it ii fully equipped to utilize these valuable materials, and the local discharged to city sewage or industrial n aste disposal plants. farmers are not alIvaJ3 equipped to take them back or use d l COOLINQ RATERS are used in relatively large quantities for
May 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
of the availablq s ~ p p l yfor stock feed, Also many small plants do not have su5cient amounts .of by-products to justify investment in evaporating or drying equipment. Under no CUCUraStanCeS should these sbmng wastes be dumped to the sewers in s d cities or to small clean streams. Consequently there remains the difficult problem of what to do with these by-products when the volume is too small to justify the installation of evaporating equipment and yet is too large for removal by local farmem. It is feasible but not economical to attempt to handle these Strong waste products in either city or private industrial sewage disposal plants. Tbia might n m i t a t e the wns t ~ c t i o nof disposal plants at costs far out of proportion to the Casts of the milk plants themselves. A sufficient number of large by-product plants should therefore be strategically looated to pick up the available wsste produds from small plants within a given area. This would accomplish more toward elimination of pollution due to dairy waste than any other single method. Time is needed to rectify this situation completely, but p r o p s s is being made every year, WASTBF ~ Dmps M AND LEAKSshould not occur in well managed dairy plants. However, since all dairy eqFpment has to be taken apart every day for cleaning and since, for sanitary reasons, ground joints are preferred to gasket joints, some leaks are almost unavoidable. Figure 3. S~naleserdceDaDer gaskets are b o Dreferred to rubber gaskets. Good preventi,ve k n t e n a n c e will reduce drips and leab to a minimum, and it is alwap possible t o catch occssional leaks with drip pans and to dispose of them along with rinsings from equipment mentioned later. Accidentaloverllow of dump vats, storage tanks, cooler troughs, and similar equipment can be practically eliminated bx using automatic level controls,'pump stops, and level alarms. Modem airtight separators and clarifiers should replace old style centrifugd cream separatom .pd ~larifiers,which usually cause exceasive foaming and loss of foam to the floor. The accidental boilover of hot wells and vats can be eliminated by the use of automatic temperature controls. The drips from milk cans should be collected after they are dumped into the weigh can and before they go into ,the canwashing w h i n e . These drips can be utilized for animal feed. It is also possible to install a small extra prerinse which will remove almost all milk from the cam and still not increase the volume of the drips too much for convenient handling and utilization. All other dairy equipment should also be given a prerinse with a small volume of water after use and before washing. These rinsings can sometimes be utilised in manufactured products, but mostly they are used directly for animal feed. WASHWATERSfrom cans, equipment, and floors will contain relatively little milk solids if all by-products are properly wllected and utilized, and if all possible savings are msrle,by the use of drip pans, prerinses, etc. However, in large plan& the wastes may still require some kiml of treatment before they are .die chssged to a small clean StreSm. T h e degree of required treatment depends on the svailable dilution in the streem and on the rate of reaeration. In this COMeCtiOn Phelps (18) reported: "Maximum utilize tion of dl Stream wets is essentially conservation to the oldfashioned end of the greatest good to the greatesb number. In our own field of sewage and waste disposal we utilize the assets of the oxygen bslance and the natural powers of the stream to
611
Continuous Automatic Sampler and Hook Gage Installed in a 90' Weir Box dissolve oxygen from the air and, with the aid of the hackrial and other life of,the stream, to oxidize and eventually dispose of organic pollution. There is no more economicdprooeasof disposal." Phelps also stated (19): "We are happily passing out of that primitive period during which it was popular to enact laws calling for a given standard of treatment-generally a very high onethroughout the state regardless of the character or use of the stream. Our present purpose is, and must increasingly become, an attempt to fit the design of .the works to the design of the stream with all that this implies. Only in this way a h d l we achieve a true conservation of a natural resource." SAMPLING AND FLOW MEASUREMENT
The first and most important step in deciding on the degree of required treatment is to 8~ that the plant has reliable methoda of reducing waste to a minimum and of utiliaing all. by-products. The next step is to provide a reliable method for flow measurement and sampling, separately if possible, for fl?or washings and cooling watera. Very small waste &WS can be measured hy timing (for instance, every 15 miitutes) the filling of a 5- or 10-gallon container, and then sampling in proportion to the flow by meaSuring out, for example, 1ml. for a flow of 1 gallon per minute at the time of sampling. This method is cumbemonk; it is considerably more convenient to build a box with a 90" triangular weir, measure t h e level of the liquid every 15 minutes with a float gage or a hook gage (Figure 3), and read off tbe flow from a weir table. Sampling can then be done again by &king, for instance, 1 ml. for each gallon per minute flow at the time of sampling. Since sampling in this m e r is time consuming and since ly a simple, eontinuous, autodairy waste flows are ~ s ~ a lirregular, matic Sampling device has been developed (Figure 3) which takes smnpks (for instance, every 4 minutes) exactly in proportion to the flow over a 90' weir. The sampler consists of a rotating flab
612
Figure 4.
I
I N D U S T R I A L AND E N G I N E E R I N G C H E M I S T R Y
Dairy-Waste FLOW Equdieing and Aeration Tank Vank in Ground)
scoop whose bottom curvature is developed mathematically from the formula for the flow over a 90' weir. This tool has proved extremely useful both in controlling waste from dairy plants and for determining the treatment efficiency of industrial dispxal units (21).
1
TREATMENT PLANTS
.
After sampling has been carefully done, after all possible sayin@ have been made by the use of drip pans, prerinses. entrainment Separators, level controls, etc., and after all possible efforts have been made to utilize by-products, it may appear necessary to provide further waste treatment. A number of alternatives are available for partial or complete treatmcut. Since milk waste is chemically similm to domestic waste, dl standard chemical and biochemical sewage treatment methods are applicable to milk wastes. Somewhat contrary to popular belief, milk waste is not particularly difficultto treat by standard methods. The strength of municipal sewage is fairly lowabout 100-300 p.p.m. B.O.D. for comhined sanitary and storm sewers and about 12o-400 p.p.m. B.O.D. for separate sanitary sewers-whereas dairy wastes are much highe-bout 500-13W ~.~.m.B.O.D.andoccssiond~ . ~eaterth3MX)p.p.m.inpoorly .~ .. operated plaute. If trouble is encountered. usually it is due to the fact that, with careless milk plant operation, the-waste is very strong, and CODsequently the capxity of the disposal plant may be entirely insuftioieut to handle the load. On the other hand, if a milk plant practices rigomus waste saving and waste utihation, there is no objection to the handling of the remaining milk plant wash watem in regulsr city & p a l plants which have adequate capacity for the additional load. Combined industrial and city waste dispasal plants are preferred for d k waste, but the milk plant should pay ite fair share of the treatment cost. There must be cooperation 80 that, if an accident ~ c c u l gin the milk plant, extra dih~tionor recirculation can be provided in the disposal plant; then strong milk wastes
Vol. 39, No. S
can be pulihed through the primary treatment.before tlrc waste sours rurd cliuaes trouble. Both wheu dairy waste is discharged to a stream and when it @ discharged to a relatively s m d city disposal plant, an aerated RowCqUUhZhg tank (Figure 4) can be useful h c a w : (a) It will pmduec wme B.O.D. reduction by biochemical oxidation (14, 173, especially if the tank is large enough always to re& a quarter to a half full. (b) It will distribute the B.O.D. load to a dispasal plant or to a stream. This is important, since the maximum csparity for biochemical oxidation of 0-io loads, both in stream and io disposal plants, is obtained with completely equalired organic loading. It appears that, iI the waste now from B dairy plant is free fmm Bettleable matter and if thc discharge period is doubled-for example, fmm 12 to 24 how-thia actually comwpourLs to a B.O.D. reduction of S O ~ &as far as the pollution effect of the waste is concerned. This may f q u e n t l y moan the differencebetweon a S h a m ' s not being able to handle the waste withuut difficulty and ita being able to handle it in a satisfactory m e r . (c) It will be an important protection against accidental overloading of streams or dbposal unita due to aecidenta in the milkplant, sincc,if any sudden discharge of milk or dairy pmducta should take place, at least it would be well mixed with a fairly large amount of partly oxidized wastc and then gradually d i e charged to the receiving stream or plaut. Consequently it looks as if aimple, serated Bow-equalising tanks may well prove to be eEeetive and economical wade treat. meot units in tho dairy industry. Where a good job ia dune of waste saving and of by-product utilisation, an equalizing tank may prove to he the only thing needed to prevent pollution difficulties, and the only thing that is economicdy justified, at least for S d plants. Any possible odor from these tsds can easily be controlled by addition of nitrates. The nitrate addition w i l l also reduce the B.O.D.
Table 11. Standard Milk Pmcess Losses Lb. B.O.D./IO OW Lb. B.O.D.'/10~000 Lb. Milk for &.ah Lb. Milk or Milk 10,000 Lb. over
Equiv. for 1st 50.000 ProLb. Handled 7 Receiving and Coding milk Tank truok delivery to and fmm plant 1 storing in tanlis 1 Evaporating whole milk Floor waste
50.W Lb. Handled 6
1 1
Cream paateurisstion, aooling. and can 4 4 fillin 16 16 Cottare L e m s E V (abo ossein) American a h m e mahng 10 8 Unssashad mrd 16 14 Wsdhed ourd Skim aondenaing Plain Floor 'li*llte Entrainment loss Swaataned 8 8 Floor wwte 3 a Entrainment loaa 12 12 Superh+sted SEm *ng 20 Roll 4 spray w h e y aondensing sweet ' 8 16 Floor weate 4 4 Entrainment loss Acid 12 8 Floor wasto 3 3 Entrainment loss 10 6 Whey drying 12 , 8 Butterrmlk aondenaing , M i k pasteurization, ooobng, and bottling IOB ormm mix making, pan Ice aream mix making, vat Ice o w m fresdn$ Cultured buttsrrmlk maldpg Bvttor churmng nnd washins 0 One ound of B.O.D. ia equivalent I O 1.2 pounds of phola milk solid., 1.1 p o u g uf skim milk aolids. or 2 2 pound8 of lahey aohds. The 8'1ersm aasrefromonehvvlanissqualro0.17 poundB.0.D. perday.
Y
May 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
In large plants which are located on small clean streams and which have no opportunity to utilize present or future city disposal plants for their wastes, it may become necessary to provide further treatment. In those cases one- or two-stage recircuIating, high-rate trickle filters have been widely used and still appear to be the most economical. A number of other treatment methods have been tried from time to time, such as broad irrigation, lagooning, digestion in heated tanks, chemical precipitation (1, 2, 4, 5 ) , activated sludge (3, I d , le), and various combination processes, such as the Guggenheim (6, 8, I d , 22) and the Mallory ( I O , 11, 16) processes. Some of these, such as broad irrigation and lagooning, can be used to advantage under certain special climatic and soil conditions. Again the addition of nitrates will help control odors (80, 26). The other methods mentioned can also be made to perform satisfactorily, but a t present it appears that the continuous, high-rate recirculating type of trickle filter ( 7 , 9, 13, 23, 85) is preferred in the dairy naate field. Recirculating trickle filters are relatively low in initial and operating costs and appear relatively foolproof and immune to disturbances due to occasional overloading. Even so, there is still a scarcity of reliable esperimental data on which to base a good standard design for a dairy waste disposal unit. Most engineers seem to agree that very coarse trickler media (3-4.5 inch size) should be used. Also, in spite of the fact that experimental trickle filters have been operated with high loadings, engineers agree it is better to be on the safe side and not build commercial units with less than 1 cubic yard of trickler medium per pound B.O.D. per 24 hours, if raw wastes run much over 1000 p.p.m. and if effluents with less than 60 p.p.m. B.O.D. are to be obtained consistently. To people not familiar with the industrial waste field, this may not seem like very good performance. However, this figure probably represents a 90 to 9770 reduction in B.O.D.; this is contained in R relatively small volume, and sufficient cooling water is usually available to produce a mixed plant effluent of about 10 to 30p.p.m. B.O.D. If the B.O.D. loading applied to the disposal unit is equalized over 24 hours, the loading per cubic yard of trickler medium per day can be greatly increased, probably more than doubled. One great difficulty in obtaining good performance and reliable design data is that all available dairy waste disposal plants have a tremendous variation in load (Figure 5) and flow from hour to hour, day to day, and season to season (23). To our knowledge none of the plants has yet found it economically possible to run daily analyses of both raw xvaste and effluent as a regular routine. Results based on grab sampling or even continuous sampling in proportion to the flow for only a few days must, of necessity, be unreliable for such an irregular waste. If the use of aerated equalizing tanks becomes common, it will undoubtedly be easier to obtain the missing data regarding the most economical capacity and type of construction of tricklers, clarifiers, and digesters for adequate treatment of dairy waste alone or in combination with city wastes. MAINTENANCE AND SUPERVISION O F TREATMEKT PLAKTS
All waste disposal plants, except possibly the old-fashioned home septic tanks, need constant supervision and preventive maintenance in order to perform satisfactorily. This poses a problem both in city and industrial waste disposal plants n-hich are small, because the salary of even a part-time qualified operator becomes a financial burden. This is one of the very important reasons why city and industrial waste treatment should be combined in one plant. In other cases arrangements might be made with a qualified operator in a neighboring city to pay at least a weekly visit to the plant. I t may be more economical for the industry to employ a qualified sanitary engineer who can supervise all dairy waste saving and disposal activities in a given territory.
18
IS
SEPT 1946
20
21
22
23
24
613
25
28
27
28
29
30
I
OCT.
Figure 5. Variation i n Day, S i g h t , and 24-Hour Averages of Raw Dairy Waste Entering Treatment Plant (Tw-o-Stage High-Rate Recirculating Trickle Filter)
One thing is certain: I t is worse than useless to build expensive waste disposal units if no economical way can be found for keeping them in good operating condition, preferably the year around. Fully automatic, absolutely foolproof disposal units have not yet been made to operate without any attention for days or months on end. Until such units are manufactured, the greatest progress in elimination of pollution due to dairy waste will be made by (a) improved vast,esaving devices and improved equipment and waste preventing devices within the milk plants, ( b ) new or improved methods of by-product utilization, and (c) dairy waste flow equalization and admission of dairy waste to city disposal plants. LITERATURE CITED
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(1) Cavanaugh, G. W,, Proc. I n t e r n . Assoc. M i l k Dealers, Plant Sect., 1935, 131-7. (2) Dept. Sci. Ind. Research (Brit.), Water Pollution Research, Tech. P a p e r 8, 17-19 (1941). (3) I b i d . , 8, 58-87 (1941). (4) Elder, A. L., and Stahl, G. W,, IND.ENG. CHEM.,31, 925 (1939). (5) Eldridge, E. F., Mich. Eng. Expt. Sta., Bull. 24, 3-18 (1929). (6) I b i d . , 77, 3-15 (1937). (7) Ibid., 77, 17-28 (1937). (8) I b i d . , 83, 9-14 (1938), (9) I b i d . , 87, 11-14 (1939) (10) Ibid., 94, 1-37 (194%). (11) Eldridge, E. F.; Water H’orks d Stwerage, 88, 457-63 (1941). (12) Hatch, B. F., and Bass, J. H., Ohio Conf. Sewage Treatment, Ann. Rep!. 13, 50-91 (1940). (13) Halverson, H. O., Water E7orks R. Sewerage, 83, 307-13 (1936). (14) Levine, AI., Soppcland, Lulu, and Burke, G. IT., Iowa Eng. Expt. Sta., Bull. 68, 5-39 (1923). (15) Mallory, E. B., Water Works d Sewerage, 88, 333 (1941). (16) Mont,agna, S. D., Sewage W o r k s J . , 12, 108-13 (1940). (17) Muers, >I. &I., J . Soc. Chem. I n d . , 55, 71-77T (1936). (18) Phelps, E. B., “Stream Sanitation”, p. 186, Kew Tork, John X l e y B: Sons, Inc., 1944. (19) Ibid., p. 187. (20) Sanborn, K, H., ISD.ESG. CHEiu., 34, 914 (1942). 121) . , Tiebler. H. A , . Proc. 1st Industrial Waste Ctilization Conf., p. 6-21, Purdue Unir., Kov. 1944. Ernsberger, R. P., and Roland, C. T., Sewage (22) Trebler, H. 8., T o r k s J . , 10, 868-Si (1938). and Harding, H. G., Chem. Eng. Progress, 43, (23) Trebler, H. *4., 255 (1947). (24) V. S.Public Health Service. Ohio River Polluticin Survey, Suppl. D , Appendix 8, “Industrial Waste Guide, Milk”, 1942. (25) Warrick, L. F., Food I n d . , 12, 46-8, 99 (1940). (26) Warrick, L. F., Wisniewski, T.F., and Banborn, N. H., Natl. Canners -4ssoc., BzdZ. 29-L (1945). PRESEXTED before t h e Industrial Waste Symposium a t the 111th llee!irip; of t h e ~ M E R I C A XCHEXICAL SOCIETS,.itlantic City, S . J .
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