The very nature of the different operations involved in dairy, irrespective of the products size, generate waste water of different magnitude. The dairy is one of the major contributors among the food industry both in terms of value and effluent. The biggest share comes from cheese and ice cream factories. The relatively high concentration of organic matter in the dairy effluent makes it peculiar in its class and this results in a higher biological oxygen demand (BOD). This kind of effluent should not be allowed to mix up with the municipal waste as it will result in a shock load.

Great care has to be exercised while discharging the dairy waste water into the general pool as they impose relatively high oxygen demand. Lactose is converted into lactic acid resulting in decrease in its concentration, when dissolved oxygen is insufficient for oxidation.

This in turn will lower the pH to a point when casein is precipitated (The isoelectric point of casein is at pH 4.6). Due to economic reasons involved in the effluent treatment, the dairy industry is very slow in taking up the treatment aspects. With increasing social awareness about the environment, the dairy industry is forced to treat its effluents effectively and efficiently before disposal into the public drainage.

Source of dairy waste

The degree of waste produced in a dairy plant varies depending upon the products prepared and the home keeping practices. The dairy waste consists mainly of raw materials lost during handling and processing and cleaning materials carried into the processing water. The composition involves a substantial concentration of fat, milk, protein, lactose, lactic acid, minerals, detergents and sanitizers.

The majority of the pollutants are dissolved in either organic or inorganic form. Equipment cleaning along with whey and butter milk contributes to the majority of the organic load. The unavoidable waste generation process include rinsing, cleaning and sanitizing of pipelines and equipment start up, product change over and shut down of HTST and UHT processes, losses during the filling operations, spill over of lubricants from pipelines, joints, valves and pumps etc.

Composition of waste water / effluent obtained in a dairy plant

S.No Constituents Cheese plant Milk receiving and pasteurization section Casein plant Butter, Butteroil and ghee section Pooled Dairy Effluent
1 Total solids 2250 3620 650 3400 1650
2 Color White White Clear Brown White
3 Chlorides 100 95 70 100 115
4 Volatile solids 25 75 55 65 60
5 Suspended solids 600 1300 100 2200 650
6 Phosphates 12 10 5 2 10
7 pH 6.7 8.2 7.7 7.1 6.1
8 Calcium carbonate 480 500 460 420 530
9 Absorbed oxygen 480 400 10 85 --
10 BOD 2150 1620 200 1250 810
11 COD 3130 2600 370 3200 1340
12 Oil and Grease 520 690 -- 1320 290
13 COD:BOD 1.46 1.43 1.85 2.56 1.65

What are the methods available to treat dairy waste water?

They are classified as physical, chemical and biological methods. The selection of a particular method depends on different factors including the physico-chemical nature of the effluent, biological oxygen demand load, quantum of the effluent to be treated, location of the treatment plant, degree of purification required and the economy of a treatment method adopted.


  • Equalization
  • Neutralization
  • Separation / Clarification


  • Biological Methods

  • Activated sludge process

  • Aerobic process

  • Oxidation ditch / trickling filters

  • Rotating biological discs

  • Anaerobic digestion