Cleaner Production in Dairy Processing
Dairy processing varies from country to country. In less developed nations milk is sold directly to the public whereas it is sold on wholesale basis in the greatest part of the countries. Especially in the United States of America, Europe, Australia and New Zealand have large [diary process plants].
The milk product industry is separated into two main production areas:
- 1. Primary production of milk on farms: These mainly apply keeping of animals like cows, goats, sheep etc for producing milk for human consumption
- 2. Processing of milk: The objective is entering a new market for milk and its products. It is achieved by heat treatment (make the products safe for humans consumption) and preparing various dehydrated and semi-dehydrated products like butter, hard cheese and milk powder which can be stored.
The life cycle of milk and milk products commences with the production of fresh milk on dairy farms. Then it is pasteurised and homogenised for getting market milk, butter, cheese, cream, yogurt etc or it is preserved and processed to long life, condensed, evaporated and powdered milk products. Then products and milk are packaged and sent out to retail outlets. After use by consumers packaging is discarded or recycled.
The dairies are located next to urban area if they produce short- shelf life products like cream or yogurt because of the short distance to the market. If a dairy produces products with longer shelf life it is often located in rural areas closer to the milk supply.
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Figure 1: Input and Output in dairies
3. Environmental impacts
- Water consumption:
The greatest part is used for cleaning the equipment and the work areas. The rates depend on the scale of the plant, of the type and the age of processing, if we have batch or continuous processing etc. An average data for consumed water is 1,3 – 2,5 lwater/kgmilk intake. By implementing CP strategies it can be lowered to 0,8 – 1 lwater/kgmilk intake.
- Effluent discharge:
In dairies water becomes mainly polluted after consuming, so there is a large quantity of effluent. It mainly contains of milk and milk products which are lost from different processes, detergents acidic and caustic cleaning agents. The rate of product loss can be 3-4% of the total rate and depends amongst others on the cleaning practices, process type (batch or continuous) etc. Whey which is produced during cheese production can also be discharged with other wastewater and can affect a load increase of the effluent. How dairies handle the problem with effluent discharge depend amongst others on their place of location. If the dairy is located next to urban centres effluent is discharged to sewage treatment systems. Sometimes effluent contains such a high level of pollutants that it can load the sewage system plants seriously. If the diary is located in a rural area effluent is often used for irrigation of the land. Disadvantages are that dissolved salts can cause salinity and that contaminates can end up in the underlying groundwater. Sometimes effluent is directly discharged into water bodies where they often have a negative impact to the water quality because of the high level of organic matter and the resulting low level of oxygen.
- Energy consumption:
Around 80 % of a plants need of energy is met by the combustion of fossil fuels to generate steam and hot water. The other 20 % are met by electricity to run electrical motors, refrigeration, ventilation and lightening. The total energy consumption causes on the age and the scale of plant, on the automation level and the range of produced products. A typical range for energy consumption is 0,5 – 1,2 MJ/kgmilk intake. Implementing CP strategies the range can decrease to 0,3 MJ/kgmilk intake. However the consumption of different types of energy causes air pollution and green house gas emissions.
By- products can cause problems if they are not handling correctly such as whey which is the most significant product generated from cheese production. Untreated whey contains a high concentration of organic matter and can so pollute rivers and streams and can cause bad odours. Therefore it is tried to sold whey as a by- product. For recovery and use of the lactose and protein content of whey already many opportunities exist.
- Solid wastes:
Types of packages for various products are shown in the table below.
|Yogurt, milk, cream||Plastic lined paperboard carton, plastic bottles and cups, plastic bags, reusable glass bottles|
|Butter, cheese||Wrapped into foil, plastic film, small plastic containers|
|Milk powder||Multi- layer kraft paper sacs, tinned steel cans|
|Other products (condensed milk)||Cans|
Packages mistakes can not be avoid totally. It is tried to recycle as much material as possible but still most of it is discard.
- Air emissions:
They are caused by consumption of energy as said before. Steam is normally generated in on- site boiler, electricity is get from the grid. For both types combustion of fuels is obligatory and involves pollution of environment. Discharges of milk powder for example can deposit on the surfaces in the surrounding. If they become wet they become acidic and can affect in most serious cases corrosion.
Some processes like the production of dried casein with hammer mills or heat treatment with steam injection can generate compulsive or constant noise. This fact has to be observed when the diaries place of location is determined.
Refrigerant systems often use chlorofluorocarbons (CFCs). If they are released to the atmosphere they have a serious effect on the environment. Therefore the systems are often replaced by non- or reduced CFC- systems.
- Hazardous wastes:
They often consist of oily sludge from gearboxes of machines, laboratory waste, batteries, cooling agents etc. Sometimes (especially in Western Europe) it is collected by Waste Companies but still much of it is dumped.
4. Cleaner Production opportunities
The processes of producing dairy products can have serious impacts on the environment if they are not handling correctly. Therefore implementing of CP in this part of life cycle is required.
- Water consumption:
First step is to make an analysis of water use pattern with water meters. The data should be discussed and weak points should be identified. Then a fix minimum rate of water has to be specified to assure the hygiene standards and undisturbed process operations. There is also the possibility to reuse water. Maybe wastewater of one production sector could be used in another one. Evaporator condensate for instance can be reused as cooling water or as boiler feed water. But it has to be assured that the reuse of wastewater does not compromise product quality and hygiene.
Figure 2: Checklist of water saving ideas
- Effluent discharge:
It is closely linked to “water consumption”. Main objective is to avoid the loss of products and raw materials to effluent stream. Therefore it is necessary to avoid spills, to capture the material before it enter the drains and to avoid the contact of fresh water and redidues.
Figure 3: Checklist of ideas for reducing effluent loads
- Energy consumption:
Often no capital investment is necessary and simple better housekeeping and optimisation of existing problems is enough to lower energy consumption. Especially processes involving concentration and drying like the production of milk powder are very energy intensive.
Figure 4: Checklist of energy saving ideas
- case studies
Reference: Cleaner Production Assessment in Dairy Processing; prepared by COWI, Denmark for UNEP and Danish Environmental Protection Agency, Denmark, 2000