Aerobic Digestion

4.1 Introduction

4.1.1 Process theory

4.2 Conventional aerobic digestion 4.2.1 Process design considerations

Feed sludge characteristics

Temperature

Volatile solids reduction

Oxygen requirements

Mixing

4.2.1 System design considerations Method of operation Tank volume and detention time Tank design

Aeration and mixing equipment 4.2.3 Operational considerations pH reduction Foaming problems Supernatant quality Dewatering

4.3 Process variations

4.3.1 High-purity oxygen digestion

4.3.2 Low-temperature aerobic digestion

4.3.3 Dual digestion

4.3.4 Mesophilic aerobic digestion

4.3.5 Autothermal thermophilic aerobic digestion Process theory

Process design Odor control

Performance and operation

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

4.3.6 Technological improvements Thickening Detention time Disinfection Technological schemes

Stabilization of wastewater sludge is processing the sludge for the purpose of eliminating the potential for putrefaction, inhibiting or reducing odor, and reducing pathogens, and thus converting it to a stable product for use or disposal. Although it is not practiced by all wastewater treatment plants, an overwhelming majority of plants, ranging in size from small to very large, use one of the following principal methods for stabilizing sludge:

1. Aerobic digestion

2. Autothermal thermophilic aerobic digestion

3. Anaerobic digestion

4. Alkaline stabilization

5. Composting

6. Thermal drying

In addition to the health and aesthetic reasons cited above, stabilization, except in the case of alkaline stabilization, reduces the volume of sludge solids to be used or disposed of. The stabilization processes listed above are described in this and subsequent chapters.

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