Dairy Processing

Dairy processors handle large volumes of milk which is converted into fluid milk, butter, cheeses, yoghurts, and many other products. The dairy waste consists primarily of wastewater. Little solid waste is generated during dairy processing. Wastewater which consists of solid waste and liquids are mainly of raw materials lost during handling and processing and cleaning materials carried into the processing water. Wastewater composition involves a substantial concentration of milk constituents: fat, soluble proteins, milk sugars, milk salts, along with cleaners and sanitizers. Table 1 shows a profile of wastewater characteristics for a fluid milk facility. Before being discharged this wastewater would need additional treatment to reduce regulated components (e.g., TSS, FOG, COD, TKN, Total Phosphorous) by 10 to 100 times. Dairy wastewaters vary widely depending in process operations, more so than other food waste. For example, compared to fluid milk wastewater, as shown below, wastewater from a cheese manufacturing plant may have a COD > 100,000 mg/L and a pH around 3.4. In general, dairy wastewater requires greater levels of treatment than other food waste streams because of the high levels of minerals, soluble solids, and fat. Disposing of dairy wastewater generally requires permits from state and federal environmental agencies to ensure minimal environmental impact.

Permits required for dairy processing vary with the type of manufacturing (fluid milk, cheese, butter, ice cream, etc.). The wastewater permit may be a municipal permit for those discharging into a publicly owned treatment works (e.g., city or municipality) or a National Pollution Discharge Elimination System (NPDES) permit if the facility treats its own wastewater and directly discharges into the environment. These permits specify maximum allowable limits for discharge parameters such as total flow, BOD₅, COD, FOG, TKN, and Total Phosphorous. These limits are based many factors such as location, type of treatment available at POTW, type of discharge (river, municipality, land application, etc.).

TABLE 1: Compiled profile of wastewater from fluid milk plant.

TSS – Total Suspended Solids
FOG – Fat, Oil and Grease
BOD5 – A five day Biochemical Oxygen Demand
COD – Chemical Oxygen Demand
TKN – Total Kjeldahl Nitrogen

Other Resources

• Typical Dairy Process Diagram

Sustainability Resources for Dairy

• General
• Air
• Water/Wastewater
• Energy