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 pro duction 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.

Table 10 Control schemes applied to activated sludge processes

Control scheme

Control objectives

Manipulated variables

P, PI controller PI, PID controller PI, PID controller SISO fuzzy control Single-loop PID controller Nonlinear optimal control Adaptive control Operational scheduling GMC

PI and Kalman filter LQ and DMC DMC GDPMC Aerobic Anoxic Anoxic Anaerobic Multivariable, H^-control

Sludge concentration and solid inventory COD

Effluent suspended solids Sludge age and aerator concentration Effluent Snh4, Sno3, and Snox As above

Effluent Snh4 and Sno3 DO concentration DO with adjustable set point Effluent nitrogen Regulation phosphorous

Effluent SNH|4 Interior SNO3 Outlet Sno3 Interior SPO4

Effluent Snh4, Sno3, and Spo4

Air flow rate WAS or RAS flow Additional sludge inventory RAS flow

RAS and WAS flows Cycle length of SBR External carbon source

Air flow rate Air flow rate

External carbon addition

Air flow rate Nitrogen recycle flow Nitrogen recycle flow RAS flow

RAS flow, external SA flow, and NOX recycle flow

Table 11 Model types used in model based control

Control scheme Model type Characteristics

Table 11 Model types used in model based control

Control scheme Model type Characteristics

DMC

Linear black-box models

Simple to use, but lack of physical insights

GMC

Nonlinear LPMs with ODEs

Simpler, but less accurate and flexible than GDPMC

GDPMC

Nonlinear DPMs with PDEs

General, flexible, but complex

Hœ-control

Reduced order linear models

Robust, well-developed, but requires linearity

LQ

Reduced order linear model

Mature, but requires linearity

Optimal control

Nonlinear LPMs

Fulfillment of optimality, but difficult to address uncertainty

Table 12 Global sludge production and utilization

Country

Dry metric (tyr 1 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 Glrovich MJ (1996) Blosollds characterization, treatment and use. In: Glrovich 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 Glrovich MJ (1996) Blosollds characterization, treatment and use. In: Glrovich 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.

Sludge processing consists of thickening and flota tion, 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 incorpo rates all of these processes. In many plants, thermal drying and incineration are not included to reduce the capital cost, 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.

Wastewater processing

Primary settler

Secondary settler

Flotable solid removal

Grit chamber

Secondary settler

Tertiary settler

Wastewater feed

Settled grit

(Optional)

Oxidation or

Ash

Sanitary

incineration

Tertiary settler

25% Solid

Conditioning

Dewatering

Ocean

Land

dumping

spreading

(Controversial)

(Controversial)

Figure 9 A basic sludge-processing scheme.

0 0

Post a comment