Sludge Quantities And Characteristics

2.1 Types of sludge

2.1.1 Primary sludge

2.1.2 Secondary sludge

2.1.3 Chemical sludge

2.1.4 Other wastewater residuals

2.2 Sludge quantity

2.2.1 Primary sludge

2.2.2 Secondary sludge

2.2.3 Activated sludge

2.2.4 Attached growth system sludge

2.2.5 Chemical sludge

2.3 Sludge characteristics

2.3.1 Primary sludge

2.3.2 Activated sludge

2.3.3 Physical and biological properties

2.4 Mass balance

Municipal wastewater is generated not only from the domestic use of water, but also from commercial establishments and from industries such as chemical or petrochemical, food and beverage processing, metal processing, pulp and paper, textile, automobile, and pharmaceutical. Therefore, the characteristics of wastewater vary from one municipality to another based on the unique mix of domestic, commercial, and industrial users. When wastewater is treated using various mechanical, biological, and physiochemical methods to remove organic and inorganic pollutants to levels required by the permitting authority, the sludge produced will also vary in quantity and character-

Wastewater Sludge Processing, By Izrail S. Turovskiy and P. K. Mathai Copyright © 2006 John Wiley & Sons, Inc.

istics from one treatment plant to another. In this chapter we discuss primarily the quantities and characteristics of sludge produced by primary, biological, and chemical treatment of wastewater in order to determine the accurate design basis for selecting, sizing, and designing suitable sludge management systems, discussed later in the book.


Types of sludge and other solids, such as screenings, grit, and scum, in a wastewater treatment plant vary according to the type of plant and its method of operation. The sources and types of solids generated in a treatment plant with primary, biological, and chemical treatment facilities are illustrated in Figure 2.1.

Wastewater sludge can be classified generally as primary, secondary (also called biological), and chemical. Sludge contains settleable solids such as

Figure 2.1 Sources and types of solids generated in wastewater treatment plants.

(depending on the source) fecal material, fibers, silt, food wastes, biological flocs, organic chemical compounds, and inorganics, including heavy metals and trace minerals. The sludge is raw sludge when it is not treated biologically or chemically for volatile solids or pathogen reduction. When the sludge is treated, the resulting biosolids can be classified by the treatment, such as aerobically digested (mesophilic and thermophilic), anaerobically digested (mesophilic and thermophilic), alkaline stabilized, composted, and thermally dried. The treated sludge can be only primary, secondary, or chemical, or a mixture of any two or three of the sludges.

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