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4.1. Description of milk processing
4.2. Emissions
4.3. Prevention of waste production

4.1. Description of milk processing

Dairy plants are found all over the world, but because their sizes and the types of manufactured products vary tremendously, it is hard to give general characteristics. The dairy industry can be divided into several production sectors. Each division produces wastewater of a characteristic composition, depending on the kind of product that is produced (milk, cheese, butter, milkpowder, condensate). Figure 4 presents a schematic flow sheet of the main dairy products.

Milk receiving

Irrespective of the product, every factory has a section where milk is delivered and stored.

Liquid milk products

In developed countries (parts of Europe, North-America, Australia etc.), raw milk is decreamed and pasteurised or sterilised. After these steps, several products are made: consumer milk, chocolate milk, custard etc.

In developing countries/regions (Southern and Eastern Africa, the Middle East - Syria and India etc.) boiling but also fermenting may be used as a means to preserve milk in the absence of refrigeration facilities. Usually, as a sanitizing method, the vessels for the storage of milk are smoked. Fermented milk may be used in fermented form but often it is churned so as to produce butter and buttermilk.


There are about 500 varieties of cheese produced throughout the world. These are classified in nine major cheese families. These varieties come about as a result of different types of production processes. The composition of the wastewater of each specific production process varies from variety to variety. For the purpose of discussing the environmental impact, the production of cheese will be related to the production of whey. For hard cheeses (Cheddar cheese, Dutch cheese, etc.), the quantity of whey produced is high and equals more or less the amount of milk used. During the production of other types of cheeses, such as soft types, the whey production is much lower or there is no production of whey at all.


In developed countries, butter is made from cream that has been churned (separation of sweet butter and sweet buttermilk). In developing regions the technology in use for the making of butter and ghee is closely related to the technology to make fermented milk. Traditional butter is made from fully soured whole milk that is churned.

Milk powder

Milkpowder is made from raw milk, skimmilk or sweet buttermilk. After pasteurization, decreaming etc. the water from the milk is removed through evaporation.


For condensed milk and cream, a portion of the water is removed by evaporation. Khoa is a product typically found in India and neighbouring countries. It is produced by thermal evaporation of milk to 65-70% solid state and serves as base material for a variety of Indian sweets.

4.2. Emissions

4.2.1. Solid waste
4.2.2. Wastewater
4.2.3. Air pollution

4.2.1. Solid waste

Hardly any solid waste is produced by the dairy industry. The main solid waste produced by the dairy industry is the sludge resulting from wastewater purification. There are figures available about the amount of sludge production: in aerobic systems the sludge production is about 0.5 kg per kg of removed COD and in anaerobic systems about 0.1 kg per kg of removed COD.

4.2.2. Wastewater

Wastewater from dairy industry may originate from the following sources:

Milk receiving

Wastewater results from tank, truck and storage tank washing, pipe line washing and sanitizing. It contains milk solids, detergents, sanitizers and milk wastes.

Whole milk products

Wastewater is mainly produced during cleaning operations. Especially when different types of product are produced in a specific production unit, clean-up operations between product changes are necessary. In developing countries, the main problem is pollution through spoilage of milk.


Waste results mainly from the production of whey, wash water, curd particles etc. Cottage cheese curd for example is more fragile than rennet curd which is used for other types of cheese. Thus the whey and wash water from cottage cheese may contain appreciably more fine curd particles than that from other cheeses. The amount of fine particles in the wash water increases if mechanical washing processes are used.


Butter washing steps produce wash water containing buttermilk.

Skim milk and buttermilk can be used to produce skimmilk powder in the factory itself or itself or these materials may be shipped to another dairy food plant by tank truck.

The continuous butter production process materially reduces the potential waste load by eliminating the buttermilk production and the washing steps (Harper et. al., 1971).

Milk powder

Environmental problems are caused by high energy consumption (= emission of CO2, CO etc.), by cleaning and by emission of fine dust during the drying process.

Condensed milk/Cream/Khoa

Environmental problems related to the production of condensate and khoa are mainly caused by the high energy consumption during the evaporation process.

The main suspended solids mentioned in the literature are coagulated milk and fine particles of cheese curd.

Table 18 gives an overview of the waste production data for the dairy industry.








Waste water prod.


100 - 12400


100 - 7100



0.2 - 71.2


0.2 - 7.1



(0.06 - 10.8)



(0.002 - 0.43)



(0.007 - 0.16)

(1): Taiganides (1987), refering to EPA (1971).

(2): Barnes et al (1984), refering to EPA (1971) and Kearney (1973). Values between brackets are recalculated, assuming 2400 kg waste water/ton milk processed, thereby overestimating the range to some extent.

Table 18 confirms that it is hard to give general characteristics of dairy plants. This is, as mentioned before, caused by the variation in the sizes of the plants and variation in types of product manufactured. The effect of the type of product produced is illustrated in Table 19.

Type of product

Wastewater volume









100 - 5400


0.20 - 7.8

Condensed milk


1000 - 3000


0.20 - 13.3






1500 - 5900


0.02 - 4.6

Cottage cheese


800 - 12400


1.30 - 71.2


Milk (canned)

320 - 1870

0.02 - 1.13

Condensed milk

800 - 7290

0.17 - 1.48


800 - 6550

0.19 - 1.91

Natural cheese

200 - 5850

0.30 - 4.04

Cottage cheese

830 - 12540

1.30 - 42



0.2 - 4.0







(1): Taiganides (1987), refering to EPA (1971).
(2): Middlebrooks (1979), refering to EPA (1974).
(3): RIVM (1993): Dutch situation in 1990.

The ranges in Table 19 also indicate that the production of wastewater is highly influenced by management practices (see next paragraph). It is not possible to identify particular waste producing practices. The way in which the water consuming and operation processes are carried out is indicative of the management quality. The major contribution to he waste load comes from cleaning operations, which take place throughout the production process. Only in the production process of (hard) cheese, is whey sewering one of the main contributors to the waste load.

Waste generating processes of major significance include:

- Washing, cleaning and sanitizing of pipelines (metals), pumps, processing equipment, tanks, tank, trucks and filling machines (high N load);

- Start-up, product change over and shut down of HTST and UHT pasteurizers;

- Breaking down of equipment and breaking of packages resulting in spilling during filling operations;

- Lubrication of casers, stackers and conveyors

4.2.3. Air pollution

In dairy plants air pollution is mainly caused because of the need for energy. In the process gasses may be discharged such as CO2, CO, NOx and SO2.

Table 20 gives the emissions into the air as a result of gas- and oil-combustion. No figures are available about the emissions into the air resulting from the use of electricity.

Emissions of CFC’s and NH3 into the air may come about as a result of leakage and stripping of chilling machines when out of use.


Air emission (kg/ton processed milk)

Heating by burning gas or oil









Producing milkpowder

Fine dust:





4.3. Prevention of waste production

The waste load, expressed as BOD depends to a large degree on the style of management. Table 21 gives an example of the relationship between management practices and waste production in terms of BOD and the amount of wastewater produced. The table shows that a large quantity of processed milk does not necessarily lead to higher waste loads or to higher levels of wastewater production.

Management practices cover a wide range of water consumption and process operation activities. Well controlled processes reflect good management qualifications, while bad practices are a reflection of poor management. Table 21 shows the relationships. The qualification “fair” signifies that good as well as bad practises occur. With good management practices, values of BOD 1 kg/ton and produced wastewater below 1 kg/kg may be reached. Poor management will result in values greater than 3 kg/ton resp. 3 kg/kg.

For the evaluation of management practices, the following indicators are useful:

1. Housekeeping practices;

2. Water control practices; frequency with which hoses and other sources of water are left running when not in actual use;

3. Degree of supervision of operations contributing to either the volume of wastewater or to BOD coefficients;

4. Extent of spillage, pipe-line leaks, valve leaks and pump seals;

5. Extent of carton breakage and product damage in casing, stacking and cooler operations;

6. Practices followed during the handling of whey;

7. Practices followed in handling spilled curd particles during cottage cheese transfer and/or filling operations

8. The following of practices that reduce the amount of wash water from cottage cheese or butter operations;

9. Extent to which the plant uses procedures to segregate and recover milk solids in the form of rinses and/or products from pasteurization start-up and product change-over;

10. The procedures used to handle returned products;

11. Management attitude towards waste control.


Milk processed



Management level








excellent: 19, 25, 26




excellent: 19, 21, 26, 27




good: 8, 10, 18, 20




poor: 1

Cottage cheese




good: 8, 15, 16




good: 8, 17




poor: 2

Milk, cottage cheese




good: 2, 19




good: 21, 22




fair: 8, 9




poor: 8, 3, 4

Milk, butter




good: 23, 24, 28

Whey powder




good-fair: 11, 12, 13

Milk powder, butter




fair: 14, 7, 3

Description of management level

Poor = 1. no steps taken to reduce waste, 2. whey included, 3. many drips, leaks, 4. returns included, 5. sloppy operations, 6. spillage leaks, 7. hoses running,

Fair = 8. whey excluded, 9. good water volume control, 10. wash water excluded, 11. no entertainment losses, 12. all powder handled as solid waste, 13. no leaks/drips, 14. continuous churn,

Good = 15. fines screened out, 16. wash water to drain, 17. spilled curd handled as solid waste, 18. rinses segregated, 19. rinses saved, 20. returns to feed use, 21. returns excluded, 22. good water control, 23. buttermilk excluded, 24. few leaks,

Excellent = 25. hoses off, 26. filler drip pans, 27. cooling tower, 28. dry floor conditions

Source: EPA, 1971

In the following a summary is given of suggestions for the prevention of dairy waste. At the same time they are indicative of what is to be understood when speaking about good management of waste control (EPA, 1971):

1. Instruction of plant personnel concerning the proper operation and handling of dairy processing equipment. Major losses are due to poorly maintained equipment and to negligence by inadequately trained and insufficiently supervised personnel.

2. The carrying out of a study of the plant and the development of a material balance to determine where losses occur. Modification and replacement of ill-functioning equipment. Where improper maintenance is the cause of losses, a specific maintenance programme should be set up.

3. The use of adequate equipment for receiving, cooling, storing and processing of milk, so as to take care of the maximum volume of flush production and of special products. All piping, around storage tanks and other areas, should be checked on mis-assembly and damage that may lead to leakage.

4. Accurate temperature control on plate, tubular and surface coolers to prevent freeze-on, which may result in loss of products.

5. Elimination of valves on the outlet sides of internal tubular or plate heaters and coolers and maintenance of plates and gaskets in good repair so as to eliminate waste due to blown or broken gaskets

6. Installation of suitable liquid level controls with automatic pump stops, alarms, and other devices at all points where overflows could occur (storage tanks, processing tanks, filler bowls etc).

7. Keeping in good order of vats, tanks and pipelines so as to eliminate and reduce to a minimum the number of leaky joints, gaskets, packing glands and rotary seals.

8. Proper design and installation of vats and tanks at a level high enough above the floor for easy drainage and rinsing if hand cleaned. Tanks should be pitched to insure draining.

9. Correct connections on plate type heat exchangers so as to avoid milk being pumped into the water side of the exchanger or water being pumped into the milk side.

10. Provision and use of proper drip shields on surface coolers and fillers so as to avoid that products reach the floor. Avoidance of cheese vats, vat processors or cooling tanks being overfilled so that no spillage occurs during product agitation. The liquid level in cheese vats should be at least three inches below the top-edge of the vat.

11. Avoidance of foaming of fluid dairy products, since foam readily runs over processing vats and other supply bowls and contains large amounts of solids and BOD. The use of air tight separators, proper seals on pumps and proper line connections to prevent inflow of air when lines are under partial vacuum, will avoid foam production.

12. Turning off of water hoses when not in use. Use should be made of hoses equipped with automatic shut-off valves so as to avoid excessive water usage.

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