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.

PRETREATMENTS

Equalization
Neutralization
Separation / Clarification

SECONDARY TREATMENTS

Biological Methods
Activated sludge process
Aerobic process
Oxidation ditch / trickling filters
Rotating biological discs
Anaerobic digestion