Dairy industry wastewater constituent
In many countries, the dairy industry is widely regarded as the major contributor to food processing effluent.
As the necessity of enhanced wastewater treatment standards becomes more widely recognized, process requirements have become increasingly severe.
Although the dairy industry is not typically linked with serious environmental issues, it must constantly evaluate its environmental impact, especially since dairy pollutants are primarily of organic origin.
Because of the highly diverse nature of this industry, numerous product processing, handling and packing processes generate wastes of varying quality and quantity, which if not managed, could result in increasing disposal and serious pollution problems.
Wastes from the dairy processing industry, in general, contain high concentrations of organic material such as proteins, carbohydrates, and lipids, high concentrations of suspended solids, high biological oxygen demand (BOD) and chemical oxygen demand (COD), high nitrogen concentrations, high suspended oil and/or grease contents, and large pH variations, necessitating “specialty” treatment to prevent or minimize environmental problems.
Before evaluating the techniques of treatment of dairy processing wastewater, it is necessary to be familiar with the numerous production processes involved in dairy product manufacturing, as well as the contamination potential of multiple dairy products (Table 1.)
Table 1: Reported BOD and COD Values for Typical Dairy Products and Domestic Sewage
| Product | BOD5 (mg/L) | COD (mg/L) |
| Whole milk | 104,000- 120,000 | 183,000-190,000 |
| Skim milk | 67,000-90,000 | 120,000-147,000 |
| Buttermilk | 61,000-75,000 | 110,000-134,000 |
| Cream | 400,000 | 750,000-960,000 |
| Evaporated milk | 208,000-271,000 | 378,000 |
| Whey | 34,000-45,000 | 65,000-80,000 |
| Ice cream | 292,000 | |
| Domestic sewage | 300 | 500 |
BOD, biochemical oxygen demand; COD, chemical oxygen demand.
Sources of dairy industry wastewater
Because of its volume and pollutant load, wastewater generation is the dairy industry’s most serious environmental challenge (primarily organic). A dairy plant produces between 2 and 6 liters of effluent per liter of milk produced.
Table 2: Volume of wastewater created by different Processes
| MAIN ACTIVITY | VOLUME OF WASTEWATER* |
| Production of butter | 1-3 |
| Production of cheese | 2-4 |
| Processing of fresh milk (pasteurization and sterilization) | 2.5 – 9 |
* Liters of wastewater/liter of milk.
The wastewater generated by a dairy firm can be classified in terms of its source: processes and cleaning or refrigeration.
Table 3: Wastewater created by a dairy firm.
| ORIGIN | DESCRIPTION | CHARACTERISTICS | VOLUME |
| Cleaning and processing | Cleaning of surfaces pipes, tanks, and equipment.
Loss of product, whey, brine, ferments, etc. |
Extreme pH, high organic content (BOD and COD), oils and fats, suspended solids | 0.8 – 1.5 |
| Refrigeration | Water from cooling towers, condensation, etc. | Variations in temperature, conductivity | 2 – 4 |
| * Volume is expressed in liters of wastewater/processed milk (Source: E. Spreer, 1991). | |||
The effluent of wastewater
The volume, concentration, and composition of the effluents arising in a dairy plant are dependent on the type of product being processed, the production program, operating methods, the design of the processing plant, the degree of water management applied and the amount of water that is conserved.
Dairy industry wastewater may be divided into three major categories:
Processing water, which includes water used in the cooling and heating processes.
These effluents are often free of pollutants and can be reused or simply discharged into the stormwater system, which is typically utilized for rain runoff water.
Cleaning wastewater are mostly generated by cleaning equipment that has come into contact with milk or milk products, spills of milk and milk products, whey, pressings, and brines CIP cleaning alternatives, and waters caused by equipment faults and even operational errors.
Milk, cheese, whey, cream, separator, and clarifier dairy waters, as well as dilute yogurt, starter culture, and dilute fruit and stabilizing chemicals, may all be included in this wastewater stream.
Sanitary wastewater, is normally piped directly to sewage works.
Dairy washing waters may also contain sterilizing agents and acid and alkaline detergents. As a result, the pH of the wastewater can vary greatly depending on the cleaning approach used.
The most commonly used CIP chemicals are caustic soda, nitric acid, phosphoric acid, and sodium hypochlorite; these all significantly impact wastewater pH.
Other concerns about CIP and sanitizing strategies include biochemical oxygen demand (BOD) and chemical oxygen demand (COD) contributions (typically 10% of total BOD concentration in plant wastewater), phosphorus contribution from phosphoric acid and other phosphorus-containing detergents, high water volume usage for cleaning and sanitizing (as much as 30% of total water discharge), and general concerns about the impact of detergents.
Dairy industry wastewaters are generally produced intermittently; thus, the flow and characteristics of effluents could differ between factories depending on the kind of products produced and the methods of operation.
This also influences the choice of the wastewater treatment option, as specific biological systems have difficulties dealing with wastewater of varying organic loads.
COD and BOD on dairy industry wastewater
Published information on the chemical composition of dairy industry wastewater is scarce.
Milk has a BOD content 250 times greater than that of sewage.
As a result, dairy wastewaters are likely to have quite high organic loads, with lactose, lipids, and proteins (mostly casein) being the main contributors, as well as high amounts of nitrogen and phosphorus associated with milk proteins.
The COD and BOD levels in whey, for example, have been determined to be between 35,000-68,000 mg/L and 30,000-60,000 mg/L, respectively, with lactose accounting for 90% of the COD and BOD contribution.
In general, liquid waste in the dairy industry presents the following characteristics:
Due to the presence of milk components, there is high organic content.
The typical COD of dairy wastewater is between 1,000 and 6,000 mg BOD/liter.
High levels of nitrogen and phosphorous, mainly because of the use of cleaning and disinfection.
Significant pH changes, waste of acidic and alkaline solutions, typically from cleaning operations, with a pH ranging from 2 to 11.
High conductivity (especially for cheese producers because of sodium chloride waste from the salting of the cheese); Temperature variations (caused by the water used for refrigeration).
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