Analysis of an activated sludge model in which dead biomass is recycled into slowly biodegradable particulate substrate

A significant drawback of the activated sludge process is the production of excess ‘sludge’; the disposal of which can account for 50–60% of the running costs of a wastewater treatment plant. We investigate a model for the activated sludge process in which the influent contains a mixture of soluble...

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Bibliographic Details
Published in:Asia-Pacific journal of chemical engineering 2015-07, Vol.10 (4), p.580-597
Main Authors: Alharbi, Asma O. M., Nelson, Mark Ian, Worthy, Annette L., Sidhu, Harvinder S.
Format: Article
Language:English
Subjects:
activated sludge
Activated sludge process
Biodegradability
Biomass
Mathematical models
modelling
Oxygen demand
recycling
Reproduction
Settling
settling unit
Sludge
wastewater
water treatment
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Summary:A significant drawback of the activated sludge process is the production of excess ‘sludge’; the disposal of which can account for 50–60% of the running costs of a wastewater treatment plant. We investigate a model for the activated sludge process in which the influent contains a mixture of soluble and slowly biodegradable particulate substrate. Within the bioreactor, the particulate substrate is hydrolyzed to form soluble substrate. In turn, these are used for growth by the biomass. Biomass decay produces slowly biodegradable substrate and non‐biodegradable particulates. Steady‐state analysis is used to investigate how the amount of sludge formed depends upon the residence time and the use of a settling unit. We show that when the steady‐state sludge content is plotted as a function of the residence time that there are three generic response diagrams. The value of the effective recycle parameter determines which type of response diagram is observed. If this parameter is greater than a critical value, then the sludge content is guaranteed to be greater than a target value. The dependence of this critical value upon the chemical oxygen demand in the feed and how the chemical oxygen demand is partitioned between its constitutive components is investigated. Copyright © 2015 Curtin University of Technology and John Wiley & Sons, Ltd.
ISSN:1932-2135
1932-2143
DOI:10.1002/apj.1906