Current status of waste problems faced by the dairy industry

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The impact of dairy processing on the environment has been summarised in the schematic in Fig. 14.3. This diagram shows the inputs and outputs for a typical dairy manufacturing plant producing market milk, butter, milk powder and cheese. Inputs include the raw milk, other ingredients, water, energy, detergents, refrigerants and packaging. Outputs include: dairy products; a range of dairy liquid effluents such as cleaning-in-place (CIP) cleaning waste, cheese whey and spills; air emissions such as combustion gases and milk powder dust; and solid wastes such as damaged stock or

Inputs Dairy processing Outputs

Inputs Dairy processing Outputs

Present Status Food Industry

Fig. 14.3 Dairy processing impact on the environment - inputs and outputs.

Source: UNEP (2000).

Fig. 14.3 Dairy processing impact on the environment - inputs and outputs.

Source: UNEP (2000).

out-of-date product. Input-output comparisons form the basis of the life cycle assessment of dairy processing conducted by a number of researchers (Cederberg & Mattsson 2000; Berlin 2002; Hogaas-Eide 2002; Nicol 2004). These studies have identified the key issues that the dairy industry needs to address to ensure the environmental sustainability of the industry based on water and energy usage, and waste disposal.

14.3.1 Water

Water is an important input in dairy production, used for irrigation of pastures for milk production and for sanitation of milking and dairy processing facilities. Its availability often determines the viability of dairy processing in different geographic areas. The highest dairy production regions are often associated with high rainfall and/or low evaporation, such as New Zealand and Northern Europe. In future, changes in rainfall patterns and global warming may adversely affect the viability of dairying regions.

In dry climates such as Australia, water availability is a key constraint. Australian studies show that dairy farming has very high water consumption compared with other agricultural production, at 5902 GL/year or 39.5% of all irrigated water (National Land & Resources Audit, 2002); correlating to 1.3-50 kL/cow/year (Rogers and Alexander 2000). Practices such as

Trade waste, 4%

Manual washing, 6%

Cooling towers, 6%

Operational processes, 12%

Trade waste, 4%

Operational processes, 12%

CIP, 28%

Fig. 14.4 Water use for market milk processing. Source: Prasad et al. (2004).

articulation of irrigation water in open channels and flood irrigation in high evaporation areas are largely responsible for these figures. More efficient irrigation practices are now encouraged.

Water usage in dairy processing is additional to farming requirements. Dairy factories use large quantities of water, mostly for cleaning and sanitation, and subsequently produce substantial volumes of liquid waste. Water usage is monitored by tracking the overall consumption of water compared with the raw milk intake. The water usage pattern for a typical market milk processor is shown in Fig. 14.4, and the water usage pattern of dairy plants surveyed by the Danish Environmental Protection Agency (EPA) is shown in Table 14.3. These figures show that the water usage varies considerably in different areas of the plant, e.g. the cheese room was reported to use between 0.06 and 20.89 L/kg product. Such variation highlights opportunities for improvements. In recent decades there have been considerable reductions in water usage, as higher charges for water and effluent disposal have now been imposed in some countries to reflect environmental costs. Recent data from Australia show average water consumption to be 1.441.64 L/L raw milk processed into market milk, cheese or powder products (see Table 14.4). Further discussion on the recovery, treatment and reuse of water is covered in Section 14.6.1.

The trend to reduce water consumption is a reflection of manufacturers realising the true cost of water. The components that make up the cost of water include: purchase price, treatment costs, heating, treatment of waste water, disposal of waste water, pumping costs, and maintenance and capital depreciation costs. An example of the estimated cost of water for dairy processing in rural regions of Australia is shown in Table 14.5.

Table 14.3 Areas of water consumption for a dairy processing plant, from a Danish EPA 1991 study. Source: UNEP (2000)

Area of use

Water consumption (L/kg product)

Percentage of total (%)

Locker room

0.01-1.45

2

Staff use

0.02-0.44

2

Boiler

0.03-0.78

2

Cold storage

0.03-0.78

2

Receipt area

0.11-0.92

3

Filling room

0.11-0.41

3

Crate washer

0.18-0.75

4

Cooling tower

0.20-1.80

5

Cleaning

0.32-1.76

8

Cheese room

0.06-20.89

13

Utilities

0.56-4.39

16

Incorporated into products

1.52-9.44

40

Total

2.21-9.44

100

Table 14.4 Water usage ratios for the production of different dairy products Source: Prasad et al. (2004)

Product

Water consumption (L/L milk) Minimum Maximum Average

White and flavoured milk

1.05

2.21

1.44

Cheese and whey products

0.64

2.90

1.64

Powdered products

0.07

2.70

1.52

Table 14.5 Costing for ambient and hot water for

a dairy processor in Australia.

Source: Prasad et al. (2004)

Cost component

Cost (AUS$/kL)

Water purchase

$0.54

Wastewater treatment

$0.75

Wastewater pumping

$0.05

Wastewater discharge (volume

charge)

$1.09

Heating to 80 °C

$2.80

Cost of ambient water

$2.43

Cost of hot water (80 °C)

$5.23

Waste management and co-product recovery in dairy processing 341 14.3.2 Energy

Large dairy processing plants consume significant amounts of energy in the processing, packaging and transport of dairy products. Electricity is used for the operation of machinery, refrigeration, ventilation, lighting and the production of compressed air. As with water consumption, the use of energy for cooling and refrigeration is important for ensuring good keeping quality of dairy products. Storage temperatures are often specified by regulation. Thermal energy, in the form of steam, is used for heating and cleaning. As well as depleting fossil fuel resources, the consumption of energy causes air pollution and greenhouse gas emissions, which have been linked to global warming (UNEP 2000). Life cycle assessment, one of the tools within the ISO 14000 series, has enabled tracking of energy consumption throughout the life of a product by systematic analysis of all the inputs and outputs. Life cycle assessments of market milk in Sweden and Australia are compared in Table 14.6 using data from Nicol (2004) and Svenskmjolk (2004). The Swedish study shows that half the energy was used on the farm; this was due to fuel used by tractors, energy used in fertiliser production and electricity used for milk harvesting and cooling. Australia requires relatively less energy on the farm, as the dairy farming there is mainly pasture based. However, much more energy is required for transport and distribution in Australia, due to the greater distances between farm and processor, and the consumer. Table 14.6 also reviews the energy required for long-life milk, showing larger energy requirements for the more sophisticated processing, packaging and distribution. The shelf-stable nature of long-life milk enables the milk to be transported considerably greater distances (Nicol 2004).

Table 14.6 Life cycle energy consumption for market milk and long-life milk in Australia (Nicol 2004) and Sweden (Svenskmjolk 2004)

Australian

Swedish

Australian

Activity

market milk

market milk

long-life milk

(GJ/tonne)

(GJ/tonne)

(GJ/tonne)

Farm

1.79

2.99

1.77

Raw milk transport

0.51

0.10

0.50

Manufacturing

1.19

0.42

2.35

Packaging

1.19

1.51

2.55

Warehouse

0.17

0.54

Transport to market

0.26

0.24

2.47

Supermarket/consumer

1.19

0.73*

0.58

Consumer transport

1.79

1.94

Home refrigeration

0.43

0.50

* Swedish market and consumer energy consumption added together.

* Swedish market and consumer energy consumption added together.

Energy consumption also depends on the type of product. Processes that involve the concentration and drying of milk, whey or buttermilk are very energy intensive. In comparison, the production of market milk involves only some heat treatment and packaging, and therefore requires considerably less energy, see Table 14.7.

Plants producing powdered dairy products employ a wide range of energy efficiencies, depending on the type of evaporation and drying processes used. Energy consumption depends on the number of evaporation effects (the number of evaporation units that are used in series) and the efficiency of the powder dryer (UNEP 2000). Energy consumption also depends on the age and scale of a plant as well as the level of automation. Table 14.8 shows examples of different evaporation and drying systems. Fuel consumption per unit of product decreases as the processing plants become larger and more energy efficient. However, the dairy industry needs to become more responsive by employing renewable sources of energy to ensure long-term sustainability of the industry.

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