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Multidimensional modelling to investigate interspecies
hydrogen transfer in anaerobic bioﬁlms
, C. Picioreanu
, M.C.M van Loosdrecht
AWMC, The University of Queensland, 4067 Australia
Department of Biotechnology, Delft University of Technology, Julianalaan 67, 2628 BC, Delft, The Netherlands
Received 3 March 2006
Received in revised form
6 June 2006
Accepted 14 June 2006
Available online 9 August 2006
Anaerobic digestion is a multistep process, mediated by a functionally and phylogenetically
diverse microbial population. One of the crucial steps is oxidation of organic acids, with
electron transfer via hydrogen or formate from acetogenic bacteria to methanogens. This
syntrophic microbiological process is strongly restricted by a thermodynamic limitation on
the allowable hydrogen or formate concentration. In order to study this process in more
detail, we developed an individual-based bioﬁlm model which enables to describe the
processes at a microbial resolution. The biochemical model is the ADM1, implemented in a
multidimensional domain. With this model, we evaluated three important issues for the
syntrophic relationship: (i) Is there a fundamental difference in using hydrogen or formate
as electron carrier? (ii) Does a thermodynamic-based inhibition function produced
substantially different results from an empirical function? and; (iii) Does the physical co-
location of acetogens and methanogens follow directly from a general model. Hydrogen or
formate as electron carrier had no substantial impact on model results. Standard inhibition
functions or thermodynamic inhibition function gave similar results at larger substrate
ﬁeld grid sizes (410 mm), but at smaller grid sizes, the thermodynamic-based function
reduced the number of cells with long interspecies distances (42.5 mm). Therefore, a very
ﬁne grid resolution is needed to reﬂect differences between the thermodynamic function,
and a more generic inhibition form. The co-location of syntrophic bacteria was well
predicted without a need to assume a microbiological based mechanism (e.g., through
chemotaxis) of bioﬁlm formation.
Crown Copyright & 2006 Published by Elsevier Ltd. All rights reserved.
Anaerobic degradation is conversion without an external
electron acceptor of complex organics to the most oxidised
and most reduced forms of carbon—carbon dioxide and
methane, respectively. It is a multistep process, with a
number of interdependent steps (Gujer and Zehnder, 1983).
These are, in order:
(a) Extracellular hydrolysis of complex particulates to asso-
ciated monomers (sugars and amino acids).
(b) Fermentation or acidogenesis of sugars and amino acids
to simple volatile fatty acids and alcohols.
(c) Syntrophic acetogenesis, converting alcohols and volatile
fatty acids into acetate and hydrogen or formate. This pro-
cess is obligately syntrophic with methanogens that utilise
the produced hydrogen or formate to produce methane.
(d) Aceticlastic methanogenesis, to form methane from
Phylogeny and physiology of microbes mediating
these steps is very well understood, but mechanisms of
ARTICLE IN PRESS
0043-1354/$ - see front matter Crown Copyright & 2006 Published by Elsevier Ltd. All rights reserved.
Corresponding author. Tel.: +61733469051; fax: +61733654726.
E-mail addresses: email@example.com (D.J. Batstone), C.Picioreanu@tnw.tudelft.nl (C. Picioreanu).
40 (2006) 3099– 3108