Dairy Plant Wastes

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Dairy wastes are generally dilutions of milk or milk products resulting from product losses during handling and transport together with detergents and sanitizers from intensive washing operations. The following operations contribute to the major product losses [3]:

1. Sludge discharges from clean-in-place (CIP) clarifiers

2. Start-up, shutdown, and changeover in high temperature, short time (HTST) pasteurizers

3. Evaporator entrainment

4. Bottle and case washing

5. Tank, can, piping, and other equipment washing

6. Breakage and spillage in packaging equipment

7. Production changeover in filling machines

Cheese and butter making processes produce whey and buttermilk, respectively. These are high strength wastes that increase the organic waste load if discharged accidentally or intentionally.

Fluid Milk Products

Clarification

Pasteurization

Cooling

Homogenization

Packaging ^

Storage

Butter

SeDaration

Skim Milk

Cream Sold

Pasteurization

Churning

Butter

Packaging f.

Buttermilk

Whey (Recovery"/ Discharge)

Cheese

Separation

Pasteurization

Cooling

Setting (Cheese Vats)

Separation Washing Pressing

Blending

Packaging

Ice Cream and Frozen Desserts

Pasteurization

r

Homogenization

Cooling

Flavouring and Additives

Freezing

Hardening

Packaging

Condensed and Evaporated Products

Evaporation Spray Drying

Packaging

Figure 1 Flowsheet for dairy and milk processing plants. (Courtesy of Environment Canada [3].)

Table 1 Summary of Conversion Factors Relating Dairy Product to Milk Equivalents

Product Milk equivalent (lb) to 1 lb product

Butter

21.3

Whole milk cheese

9.9

Evaporated milk

2.1

Condensed milk

2.4

Whole milk powder

13.5

Cottage cheese

7.12

Non-fat dry milk

12.5

Whey

1.1

Dry whey

17.6

Whey cream butter

40.7

Dry buttermilk

249.0

Ice cream"

2.67

"One gallon of ice cream weighs 5.4 lb.

Source: Environment Canada [3].

Table 2 Water Usage in the Canadian Dairy Product Industry

Total water usage (L/kg ME)a

Commodity

Median Range

Fluid milk products

3.90 1.21-9.15

Butter products

1.30 0.82-3.21

Cheese products

2.75 0.79-5.90

Ice cream and frozen desserts

1.78 0.33-4.23

Condensed and evaporated products

1.45 0.37-2.59

"ME = milk equivalent. Source: Environment Canada [3].

"ME = milk equivalent. Source: Environment Canada [3].

Generally water use and process effluent loadings are related to the throughput in terms of milk equivalents. Table 1 provides a summary of conversion factors relating actual product to milk equivalents. Table 2 provides a summary of water use in the Canadian dairy product industry by commodity segment. The raw waste loads by commodity segment for the Canadian dairy industry are included in Table 3. The data for the American dairy industry are summarized in Table 4. Tables 3 and 4 show that waste loads in Canadian and American dairy plants are similar.

The strength and volume of the wastewater from any dairy plant will depend upon the processes employed, the volume of milk handled, the commodity produced, the condition and type of equipment, the waste reduction practices, the attitude of the management and staff, and the amount of water used in cooling and washing [5]. The chemical oxygen demand (COD) of the dairy wastewater is said to vary from less than 100 mg/L to more than 20,000 mg/L depending on the dairy product [6]; biological oxygen demand (BOD) varies from 40 mg/L to over 10,000 mg/L, and wastewater flows vary from 542 L/1000 kg milk equivalent to 900 L/1000 kg milk equivalent [7], Table 5 summarizes the characteristics of dairy wastewaters in the United States.

Milk product losses typically range from 0.5% in large advanced plants to in excess of 2.5% in small old plants [3], Many of the water-saving and waste control changes specific to the dairy industry include a number of steps [3], some of which are outlined below.

Table 3 Summary of Raw Waste Loads from Canadian Dairy Products Industry

BOD (kg/1000 kg ME)

TSS (kg/1000 kg ME)

Commodity

Median

Range

Median Range

Fluid milk products

3.8

0.75-7.43

1.4 0.59-2.42

Butter

1.4

0.53-8.78

0.5 0.19-1.45

Cheese

5.1

2.12-8.48

1.3 0.72-2.51

Ice cream and frozen desserts

6.4

0.85-21.31

2.4 0.22-11.05

Condensed and evaporated products

2.2

0.99-4.40

0.6 0.08-1.40

"ME = milk equivalent; TSS = total suspended solids.

Source: Environment Canada [3],

Table 4 Summary of American Dairy and Milk Processing Plant Effluent Characteristics

Waste vol.

coefficient"

I

BOD coefficientb

No. of

Product

plants

Range

Avg

Range Avg

Milk

6

0.1-5.4

3.25

0.2-7.8 4.2

Cheese

3

1.63-5.7

3.14

1.0-3.5 2.04

Ice cream

6

0.8-5.6

2.8

1.9-20.4 5.76

Cond, milk

2

1.0-3.3

2.1

0.2-13.3 7.6

Butter

1

0.8

— 0.85

Powder

2

1.5-5.9

3.7

0.02-4.6 2.27

Cottage cheese

3

0.8-12.4

6.0

1.3—71.2C 34.0

Cottage cheese and milk

19

0.05-7.2

1.84

0.7-8.6C 3.47

Cottage cheese, ice cream, and milk

9

1.4-3.9

2.52

2.3-12.9 6.37

Mixed products

5

0.8-4.6

2.34

0.9-6.95 3.09

Overall

56

0.1-12.4

2.43

0.2-71.2 5.85

"Volume: kg wastewaler/kg milk (or milk equivalent) processed.

bBOD: kg BOD/IOOO kg milk (or milk equivalent) processed.

'Whey included; whey excluded from all other operations manufacturing cottage cheese.

Source: Harper and Blaisdell [4],

"Volume: kg wastewaler/kg milk (or milk equivalent) processed.

bBOD: kg BOD/IOOO kg milk (or milk equivalent) processed.

'Whey included; whey excluded from all other operations manufacturing cottage cheese.

Source: Harper and Blaisdell [4],

1. Complete drainage of all tanks and pipes before rinsing

2. Recovery of low-volume, concentrated initial rinses of tanks, cans, and equipment

3. Automatic shutoff valves on all hoses

4. Recovery of solid material such as fruit and cheese curd prior to discharge to a sewer system

5. Removal of defective containers from bottling lines

6. Installation of control systems on all equipment where overflow might occur

7. Use of drip savers for milk car unloading in small plants

8. Routine inspection of all lines, valves, and pumps to eliminate leakage, especially in CIP lines

9. Adequate temperature control in coolers and heaters to prevent freeze-on or burn-on leading to excessive product loss and water consumption during cleaning

10. Drip shields to prevent spilled products from entering the sewer system

11. Adequate entrainment control equipment on evaporators equipped with barometric condensers

Table 5 Characteristics of Wastewaters from Dairy Plants in United States

Value"

Table 5 Characteristics of Wastewaters from Dairy Plants in United States

Value"

Characteristic

Range

Mean

BOD

40-48,000

2300

COD

80-95,000

4500

SS

24-4500

820

Total solids

135-8500

2500

Nitrogen

1-180

64

Phosphorus

9-210

48

Carbohydrate

250-930

520

PH

4.4-9.4

7.2

Temperature (°C)

18-55

35

aAll values except pH and temperature are in mg/L. Source'. U.S. EPA [8,9], aAll values except pH and temperature are in mg/L. Source'. U.S. EPA [8,9],

12. Use of postcleaning rinses as make-up water for sanitizing and/or cleaning

13. Control or collection of leakage from damaged product containers

14. Collection and recovery of valuable by-products, especially whey

An extensive account of good management practices in waste control in the dairy industry is included in a publication issued by U.S. EPA [8]. Milk rinsings and whey contribute to the dairy waste loads and can be recovered. Whey is a by-product of cheese-making and can be used as a supplement in livestock or poultry feed.

Harper et al. [10] discuss the results of a study undertaken to reduce water and waste discharges at the Kroger Dairy Company, a complex multiproduct dairy plant in Indianapolis, Indiana, through management control and modification of equipment and processes. Before control procedures were introduced, the plant discharged 400,000-800,000 gal of wastewater per processing day, with a total BOD load of 10,000-15,000 lb. As long as direct supervision was maintained on a regular basis, water use in the plant was reduced by one-third and the organic waste load was reduced by one-half. Process and equipment changes were made in the plant that reduced waste discharges by 100,000 gal/day and reduced waste strength about 20% at an economic savings projected at $200,000 per year.

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