Sludge Processing Overview

Typical raw activated sludge production is in the range of 1.2-2.4 kg per person per day. Table 12 shows the production and utilization of sludge produced in EU, USA, Australia, and Japan. There may be significant changes to the indicated final disposal methods, as regulation of land spreading and ocean disposal are being implemented in many jurisdictions.

Sludge processing consists of thickening and flotation, stabilization, conditioning, dewatering, thermal drying, oxidation, or incineration, preceding ultimate solid disposal. There are a number of alternative designs, and not every sludge-processing plant incorporates all of these processes. In many plants, thermal drying and incineration are not included to reduce the capital cost,

Table 12 Global sludge production and utilization

Country

Dry metric (t yr1 x 1000)

Agricultural use (%)

Landfill (%)

Incineration (%)

Ocean (%)

Other (%)

USA

5358

33.3

34

16.1

6.3

10.3

Germany

2700

27

54

14

5

Japan

~2000

25

75

UK

1107

42

8

14

30

13

France

852

60

20

20

Italy

816

33

55

4

8

Spain

350

50

35

5

10

Netherlands

323

26

50

3

2

19

Australia

300

9

76

2

13

Denmark

170

54

20

24

2

Belgium

200

29

55

15

1

Greece

48

10

90

Ireland

37

12

45

35

8

Portugal

25

11

29

60

Luxembourg

8

12

88

Compiled from the following data sources: data on EU and USA reported by Girovich MJ (1996) Biosolids characterization, treatment and use. In: Girovich MJ (ed.) Biosolids Treatment and Management, pp. 1-46. New York: Dekker; data on Japan reported by Kasakura T, Imoto Y, and Mori T (1993) Overview and system analysis of various sewage sludge drying processes. Drying Technology 11: 871-900; which have been summarized by Chen G, Yue PL, and Mujumdar AS (2002) Sludge dewatering and drying. Drying Technology 20: 883-916 and listed in further reading, and data on Australia reported by Priestley AJ (2001) 'Report on Sewage Sludge Treatment and Disposal - Environmental Problems and Research Needs from an Australian Perspective' Clayton, VIC: CSIRO Division of Chemicals and Polymers.

Compiled from the following data sources: data on EU and USA reported by Girovich MJ (1996) Biosolids characterization, treatment and use. In: Girovich MJ (ed.) Biosolids Treatment and Management, pp. 1-46. New York: Dekker; data on Japan reported by Kasakura T, Imoto Y, and Mori T (1993) Overview and system analysis of various sewage sludge drying processes. Drying Technology 11: 871-900; which have been summarized by Chen G, Yue PL, and Mujumdar AS (2002) Sludge dewatering and drying. Drying Technology 20: 883-916 and listed in further reading, and data on Australia reported by Priestley AJ (2001) 'Report on Sewage Sludge Treatment and Disposal - Environmental Problems and Research Needs from an Australian Perspective' Clayton, VIC: CSIRO Division of Chemicals and Polymers.

energy consumption, and air pollution. A basic sludge treatment process is shown in Figure 9, in which solid concentrations achieved in various sludge handling steps are also specified. If thermal drying is adopted, the final solid concentration can reach 95%, but at the expense of higher energy consumption. Land spreading and ocean dumping have been banned in many countries due to public health and ecological considerations.

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