THE ACTIVATED SLUDGE PROCESS

THE ACTIVATED SLUDGE PROCESS

Rebecca Dohse and Amy Heywood

Introduction

Definition of the process: In general, the activated sludge process is a continuous or semicontinuous(fill and draw) aerobic method for biological wastewater treatment, including carbonaceous oxidation and nitrification. This process is based on the aeration of wastewater with flocculating biological growth, followed by separation of treated wastewater from this growth. Part of this growth is then wasted, and the remainder is returned to the system. Usually, the separation of the growth from the treated wastewater is performed by settling (gravity separation) but it may also be done by flotation and other methods.

History and Development of the Activated Sludge Process

The activated sludge process presently represents the most widespread technology for wastewater purification. Activated sludge plants can be found in different climate conditions - from the tropics to the polar regions, from sea level(wastewater treatment plants in ships) to extreme elevations(mountainous hotels). The scale of activated sludge plants ranges from package plants for one family to huge plants serving big metropolises. Wastewater treatment plants equipped with the activated sludge process are able to fulfill the most stringent effluent criteria.

The invention of the activated sludge process is connected with the efforts of British and American engineers at the end of the last century to intensify biological purification in fixed-film systems. The experiments with wastewater aeration did not provide the expected results until May, 1914 when Ardern and Lockett introduced a recycle of suspension formed during the aeration period. The suspension, known as activated sludge was in fact an active biomass responsible for the improvement of treatment efficiency and process intensity.

Structure and Features

Types of Activated Sludge Processes

Advantages versus Disadvantages

Microorganisms in the Activated Sludge Process

References

Ground Water Pollution Table of Contents

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