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Steady-state analyses of activated sludge processes with plug-flow reactor
Centre for Mathematical Sciences, Lund University, P.O. Box 118, S-221 00 Lund, Sweden.
School of Business, Society and Engineering, Mälardalen University, Box 883, SE-721 23 Västerås, Sweden.ORCID iD: 0000-0002-8034-4043
Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
2017 (English)In: Journal of Environmental Chemical Engineering, ISSN 2160-6544, E-ISSN 2213-3437, Vol. 5, no 1, p. 795-809Article 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
2017. Vol. 5, no 1, p. 795-809
Keywords [en]
Activated sludge process; Burger-Diehl settler model; Plug-flow biological reactor; Secondary clarifier; Solids residence time (SRT)
National Category
Control Engineering Water Treatment
Identifiers
URN: urn:nbn:se:uu:diva-311426DOI: 10.1016/j.jece.2016.06.038ISI: 000398950800081OAI: oai:DiVA.org:uu-311426DiVA, id: diva2:1060029
Available from: 2016-07-12 Created: 2016-12-27 Last updated: 2018-09-21Bibliographically approved

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