= "justify"> 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 1 presents a schematic flow sheet of the main dairy products [33]. br/>
.1 A schematic flow sheet of the main dairy products
3. Dairy industry products. Emissions
3.1 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 wastage and in anaerobic systems about 0.1 kg per kg of removed wastage [41]. br/>
3.2 Wastewater. Whole milk products
Wastewater from dairy industry may originate from the following sources: 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 [1]. br/>
3.3 Cheese/Whey/Curd
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 [9]. br/>
3.4 Butter/Ghee
Butter washing steps produce wash water containing buttermilk.milk and buttermilk can be used to produce skim milk powder in the factory itself or these materials may be shipped to another dairy food plant by tank truck.continuous butter production process materially reduces the potential waste load by eliminating the buttermilk production and the washing steps [14].
3.5 Milk powder
Environmental problems are caused by high energy consumption (= emission of CO 2 , CO etc.), by cleaning and by emission of fine dust during the drying process.
