Title: Optimal design of multi-stage bioreactors performing wastewater treatment using the MATLAB optimisation function (fmincon)

Authors: Ibrahim M. Abu-Reesh; Raafat Alnaizy

Addresses: Department of Chemical Engineering, Qatar University, P.O. Box 2713, Doha – Qatar ' American University of Sharjah, P.O. Box 26666, Sharjah, UAE

Abstract: Optimum design of continuous stirred tank reactors (CSTRs) in series to biodegrade organics in wastewater was carried out. It was assumed that cell growth kinetics follows Contois model with endogenous decay. The optimal design was based on the minimum overall reactors volume required for a certain degree of substrate removal. The effect of operating parameters such as substrate inlet feed concentration to the first reactor, substrate removal efficiency, and number of CSTRs in series on the optimum design were investigated. The non-linear constrained optimisation problem was solved using the MATLAB function fmincon. For equal CSTRs, the system of non-linear equations was solved by 'fsolve' MATLAB function. Results indicate that the optimum multi-stage bioreactors are beneficial only at high substrate conversion. The substrate concentration in the feed to the first reactor has little effect on the total reactors volume. Recycle of biomass to the first reactor reduces the required total reactors volume. In general, at high percentage of substrate removal the optimum reactors design requires smaller volume compared to equal-size reactors.

Keywords: multi-stage bioreactors; bioreactor design; MATLAB; wastewater treatment; Contois kinetic modelling; equal-size reactor series; minimum volume design; nonlinear constrained optimisation; biomass recycling; optimal design; continuous stirred tank reactors; CSTRs; endogenous decay; substrate removal.

DOI: 10.1504/IJEE.2014.067009

International Journal of Environmental Engineering, 2014 Vol.6 No.4, pp.403 - 414

Received: 20 Feb 2012
Accepted: 29 Dec 2012
Published online: 31 Jan 2015 *

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