Handbook Biological Wastewater Treatment - Design of Activated Sludge Systems

Introduction

Activated sludge settlers are applied to effect the separation of the solid (sludge) and the liquid phase of the mixed liquor. Settlers are operated as continuous units, discharging an effluent that is substantially free of solids, while the settled solids are recycled to the aeration tank. Activated sludge settlers are also called final or secondary settlers or clarifiers to distinguish them from primary settlers that are used for settling of raw waste water. Activated sludge settlers perform two functions simultaneously:

Depending on the settling characteristics of the sludge and the operational conditions of the settler (most importantly the solids load of the incoming mixed liquor and the concentration of the outgoing return sludge), either clarification or thickening is the limiting function for the solids loading rate that may be applied. The maximum allowable solids loading rate in turn defines the minimum settler surface area and hence its minimum volume.

In this section the following subjects will be discussed:

Contents of this section

Sludge settleability Zone settling rate test and relationship between zone settling velocity and sludge concentration Alternative parameters for sludge settleability and the relationships between the different parameters Read more....	Model development Application of the solids flux model to describe the settling process in a continuous settler Determination of the limiting, critical and the minimum concentration, which define whether clarification or thickening will be the limiting process in the final settler Read more....
Final settler design Optimised settler design procedure for the situations with either clarification or thickening as the limiting process Determination of the critical sludge recirculation rate Optimisation of the system aeration tank - final settler Applicability of the design procedure Read more....	Physical design aspects Overview of physical design aspects of final settlers Layout drawings
Final settlers under variable loading conditions Static point procedure Optimisation of the operation of final settlers that have already been constructed	Sludge bulking and scum formation Filamentous organisms Causes and control of sludge bulking in aerobic systems Causes and control of sludge bulking in anoxic - aerobic systems Non-specific measures to control sludge bulking Causes and control of scum formation
We regret that the sections on "Physical design aspects of final setters", "Final settlers under variable loading conditions" and "Sludge bulking and scum problems" are not available as a free online resource. If you want to know more, please purchase the handbook. More info ?

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