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Waste T r e a t m e n t in the Danish D a i r y I n d u s t r y P. RONKILDE POULSEN The Danish Government Research Institute for Dairy Industry Hillerdd, Denmark ABSTRACT The Danish Government Research Institute began research in dairy waste treatment about 40 yr ago. The purpose was to serve the dairy industry continuously with information about progress in methods of waste treatment, and through specialized advisory service to support individual dairy plants in their efforts to keep step with progressive public demands for a better environment. A brief outline of environmental legislation, emphasizing the official guidelines for discharge of waste, will be given together with a brief survey of the load of pollution in Danish dairy effluents. Technical possibilities for restricting unavoidable pollution to a minimum will be mentioned. Recent results from experiments at the research institute with different waste treatment systems will be summarized and their adaptability to dairy waste under prevailing conditions evaluated. In a Danish dairy journal from 1935 the following simple and serious question was raised by a dairy manager. "What is the price for an effluent treatment plant for our dairy, and is it reliable and efficient?" He did not receive an answer. This characterizes the situation in Denmark about 40 yr ago. Knowledge and experience in treatment and neutralizing of dairy effluent was limited because the subject had not been investigated systematically, technologically, and scientifically. However, several waste water treatment plants, set up according to different principles, already had been running for some years. A dairy effluent irrigation plant was built as early as 1883, and a number of septic tank plants were built in the years around 1910. The reason no answer was given to the simple question above was most likely that the practical experience from these plants were widely

Received August 16, 1976.

different, often characterized by fortuitousness and mystery. This was primarily due to inexperience in the function of the plant, lack of measuring methods, and lack of a real basis for evaluating the effect of the plant. Only 3 yr later in 1938, a research program on treatment of dairy effluent was initiated at the Danish Government Research Institute for Dairy Industry. Activities in that field have been part of our research program since. Over the years there has been considerable research activity caused by changes in the structure of the dairy industry and the community as a whole. The actual situation is dominated by the following three aspects: (a) Increased risk of heavier detrimental pollution; (b) Increased sensitivity to the ecological balance, and (c) Increased concern for the environment. Today we have a comprehensive knowledge about the problems of waste water treatment, and I am quite sure that if a question like the one in 1935 by the dairy manager were published in our dairy journal today, the person in question would be overwhelmed with offers and guarantees.

Legislative Aspects As far back as the 17th century Denmark has had special legislation aimed at protecting streams and lakes. In 1949 revised legislation was passed whereby every outlet of waste water must be authorized by special courts of justice. Waste water discharge was not allowed to cause general inconvenience or to disturb the natural state and balance of the streams. From case to case these courts of justice were supported by biologists and other experts. In 1 9 7 4 - 2 5 years l a t e r - a f t e r several years of intense public debate about environmental protection, new legislation was passed dealing with all aspects of environmental pollution. According to this legislation a complete official authorization of every firm, regarding its effluent sources and purifying efforts, is required. The firms have to give a detailed account of all their possible pollution.

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POULSEN

TABLE 1. Officially recommended acceptable limits of pollution for different categories of recipients.

pH Temperature (C) BOD5 (mg/liter) Phosphorus (rag/liter) Ammonia-N (mg/liter)

A Lakes

B Streams

C Inlets

D Sea

6.5-8.5 30 20 1 2

6.5 8.5 30 20 ... . . .

6-9 30 100 1 . .

.

As basis for judgment the standards in Table 1 have been recommended, making allowance for the pollution quantities which can be accepted by the different types of environmental regions. Payment for neutralizing pollution is subject to the basic principle that the one who causes a loss must pay the expenses for treatment. In certain cases the municipality pays 10 to 15%, and sometimes a discount is allowed for severely polluting industries, with a so-called industry tariff for the calculation of the expenses. An example: Industry tariff = normal tariff (i + 200)/600, where i = degree of pollution in the industry effluent (BODs). As effluents from normal households are usually calculated on 300 BODs, this offer to the industry is rather favorable. Since the environmental law-complex was brought into force in 1974, a fixed amount has been granted from the government to be divided as subsidies to activities limiting pollution. The Load of Pollution in Dairy Effluents

The brief statistics in Table 2 give an idea of Danish dairying. TABLE 2. Danish dairying. Number of dairy farms Number of dairy cows Number of cooperative dairies Number of private dairies Total production of (1000 tons) Milk Butter Cheese Market milk Canned milk and milk powder, calculated as milk

Journal of Dairy Science Vol. 60, No. 7

58,000 1,083,000 294 76 4,612 136 151 683 1,057

.

.

3 '5 400 ... .

.

About 20 yr ago there were approximately 1500 dairy plants in Denmark--most of them relatively small, with an average milk intake of 3 to 10 million kg per year. As their production pattern was rather uniform, pollution from effluent could with a fair approximation be estimated from milk intake. Today the number of dairy plants has been reduced to less than 400 due to centralization and rationalizing efforts of the dairy industry. This means that the annual milk intake per plant now is about 20 to 50 million kg, and at the same time the production of the dairies has become specialized. Two years ago the Danish Government Research Institute for Dairy Industry analyzed the effluent from 34 dairy plants. The results (Fig. 1) show the relationship between annual milk intake and actual pollution in the effluent. This relationship, however, is not clear and for several reasons could hardly be expected to be. Cheese production accounts for the heaviest pollution compared with other dairy products. The reason is that cheese whey is a cheap by-product and often is handled carelessly. Special attention should be paid to the final pressing of cheese from which whey most often goes directly into the sewer. Another critical point in cheese production is washing, normally carried out before waxing. Table 3 shows the order of pollution from these two sources. The total effluent pollution from cheese production easily sums up to 4 g BOD per kg milk treated. In view of expenses of effluent treatment, pollution of this order is not acceptable. According to our experiences it can be reduced greatly by carefully avoiding waste of whey during drainage of the cheese vat and by collecting the whey from cheese presses. In our detailed studies of the origin of

OUR INDUSTRY TODAY

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400 300

200

100 80

/

66

40 30

20

/"

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reduce the waste to about half this figure. For milk collecting and separating plants we have found pollution small, i.e., about .5 g BOD per kg milk received. In proportion to the amount of milk treated our observations show that the heaviest pollution in dairy effluent comes from small plants and big factories. Apparently dairies of medium s i z e - a b o u t 10 to 20 million kg milk per y e a r - w i t h a limited staff-seem to have the best possibilities of controlling their production and are most capable of keeping product losses and pollution of the effluent within reasonable limits. The extent of measures taken to avoid waste during production is of utmost importance as well as skill and conscientiousness of the personnel working in the dairy industry. Experience with Different Treatment Methods for Dairy Waste

3

a

6

8

10

20

30

40

M I L L I O N KG (m~k year)

FIG. 1. Relation between size of dairy factories and their effluent pollution.

pollution in dairy effluents we also generally confirmed that emptying milk tanks, pipelines, and equipment prior to rinsing causes considerable pollution. Some sort of initial sprinkling and collection of this waste is recommended for further treatment for fodder. In butter production attention is drawn to the drainage of buttermilk as the most critical point. On an average the handling of liquid milk and manufacture of butter result in pollution of 2.0 to 2.5 g BOD per kg milk treated. However, we found it possible by simple measures to

Dairy waste has had a bad reputation, not only among worshippers of nature and anglers but also among engineers and builders of effluent treatment plants. Directly dumped into lakes and streams it was considered to act like poison, and ill effects were said to be found when dairy effluents were discharged into plants constructed for domestic sewage. Thanks to intensive studies of the distinctive character of dairy waste, we now know why and how it should be handled. Specialized research into treatment of dairy waste was first of all to prove that a complete biological purification of dairy effluent is possible and secondly to point out the most suitable methods of treatment. It is fair to add that perhaps the most important effect of this research has been the changes in public opionion about dairy waste and improvement of relations between the dairies and the public administration, including the staff of engineers and technicians, con-

TABLE 3. Pollution from pressing and washing cheese. 30,000 kg milk daily converted to 3,200 kg cheese Eq. persons kg BOD/day number kg/day Whey from cheese pressing Effluent from cheese washing

500-1,000 4,500

25-50 20-25

400-800 300-400

Journal of Dairy Science Vol. 60, No. 7

o -q

g

< o

X XXX XXX XXX X XX

Complete treatment A c t i v a t e d sludge t r e a t m e n t Short time aeration Long time aeration Extended long time aeration Spray irrigation Stabilizing ponds A l t e r n a t i n g d o u b l e t r i c k l i n g filters

X = Small, XX = M o d e r a t e , X X X = High.

XX XX XX XX

XX XX XXX X

X XX XX XXX XX XX

X

X

N

Pre-treatment Equalizing tanks R e c i r c u l a t i o n on t r i c k l i n g filters Filter medium: hrocken stones F i l t e r m e d i u m : plast balls F i l t e r m e d i u m : F l o c n r etc. Chemical precipitation

BOD

E f f i c i e n c y r e d u c t i o n in

T A B L E 4. C h a r a c t e r i s t i c s of d i f f e r e n t t r e a t m e n t m e t h o d s for d a i r y e f f l u e n t s ,

X X X XXX X XX

XX XX XX XXX

X

P

X XX XXX XXX XXX XX

XX X X X

X

Space requirements

XX XX XXX X X XXX

XX XX XX XX

X

Investment

Expenses

XX XX XX XX X XX

XX XX XX XX

X

Operation costs

t~

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",O O

OUR INDUSTRY TODAY cerned with and responsible for municipal sewage systems. I estimate that today about 90% of the Danish dairies are connected with municipal sewage systems. Personnel from the government institute are advising the dairies as well as the municipal authorities to bring about reasonable technical and economic arrangements for joint waste treatments. During the past years several different treatment systems have been investigated at the Danish Government Research Institute for Dairy Industry, and the results and conclusions have been published in our bulletins. It might be relevant to distinguish between the following two different aims of treatment,

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pretreatment and complete treatment of waste. In the first category are tanks or basins for equalizing the effluent from the dairy over 24 h, recirculation on trickling filters, followed by a tank for sedimentation and chemical precipitation. In the second category are the activated sludge treatment plant with different aeration activity and treatment periods, varying from 6 h to several days, and also the spray irrigation of dairy effluents. To this c a t e g o r y - b u t of minor importance in Denmark-also belong the waste stabilization ponds and the alternating double trickling plants. In Table 4 is a simplified outline of the results of our experience with the different types of treatment.

Journal of Dairy Science Vol. 60, No. 7