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Steady-State Analyses of Activated Sludge Processes with Plug-Flow Reactor
Lund University, Sweden. (Centre for Mathematical Sciences)
Mälardalen University, School of Business, Society and Engineering, Future Energy Center.ORCID iD: 0000-0002-8034-4043
Uppsala University, Sweden. (Division of Systems and Control, Department of Information Technology)
2017 (English)In: Journal of Environmental Chemical Engineering, ISSN 2160-6544, E-ISSN 2213-3437, Vol. 5, no 1Article in journal (Refereed) Published
Abstract [en]

Activated sludge processes (ASPs) consisting of a plug-flow reactor (PFR) and a settler are analyzed in steady-state operation using a reduced model consisting of one soluble substrate and one particulate biomass component modelling the dominating biological process. Monod biomass growth rate is assumed. Two settler models are studied. One is the commonly used ideal settler, or point settler, which is assumed to never be overloaded and to have unlimited flux capacity. The other recently published steady-state settler model includes hindered and compressive settling, and models a realistic limiting flux capacity. Generally, the steady-state concentration profiles within the PFR and the settler are governed by nonlinear ordinary differential equations. It is shown that the steady-state behaviour of the ASP can, however, be captured by equations without derivatives. New theoretical results are given, such as conditions by means of inequalities on input variables and parameters for a steady-state solution to exist. Another novel finding is that, if the incoming substrate concentration is increased from a low or moderate stationary value and the solids residence time is kept fixed, then this results in a lower effluent concentration in the new steady state. The steady-state equations are solved numerically for different operating conditions. For common parameter values, numerical solutions reveal that an ASP having a PFR, instead of a continuously stirred tank reactor, is far more efficient in reducing the effluent substrate concentration and this can be obtained for much lower recycle ratios, which reduces the pumping energy considerably.

Place, publisher, year, edition, pages
Elsevier, 2017. Vol. 5, no 1
Keyword [en]
Activated sludge process; Bürger-Diehl settler model; Plug-flow biological reactor; Secondary clarifier; Solids residence time (SRT)
National Category
Water Engineering
Research subject
Energy- and Environmental Engineering
Identifiers
URN: urn:nbn:se:mdh:diva-34550DOI: 10.1016/j.jece.2016.06.038ScopusID: 2-s2.0-85009115689OAI: oai:DiVA.org:mdh-34550DiVA: diva2:1060026
Available from: 2016-12-27 Created: 2016-12-27 Last updated: 2017-01-26Bibliographically approved

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CiteExportLink to record
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Cite
Citation style
  • apa
  • harvard1
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  • modern-language-association-8th-edition
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More styles
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  • de-DE
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