Importance of scale and hydrodynamics for modeling anaerobic digester performance

•A simplified anaerobic digestion model was developed.•The performance of the reactor at lab-scale and pilot-scale was predicted.•The influence of mixing was investigated.•Unmixed conditions resulted at pilot-scale in reduced biogas production and VFA accumulation. In this study it is demonstrated t...

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Bibliographic Details
Published in:Chemical engineering journal (Lausanne, Switzerland : 1996) Switzerland : 1996), 2014-11, Vol.255, p.71-77
Main Authors: Van Hulle, Stijn W.H., Vesvikar, Mehul, Poutiainen, Hannu, Nopens, Ingmar
Format: Article
Language:English
Subjects:
Anaerobic digestion
Biogas
Biogas production
Chemical engineering
Digesters
Fatty acids
Mathematical models
Methane
Mixing behavior
Modeling
Reactors
Scale (ratio)
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Summary:•A simplified anaerobic digestion model was developed.•The performance of the reactor at lab-scale and pilot-scale was predicted.•The influence of mixing was investigated.•Unmixed conditions resulted at pilot-scale in reduced biogas production and VFA accumulation. In this study it is demonstrated that a correct description of the mixing behavior of an anaerobic digester is necessary to accurately model and predict the reactor performance, especially at a larger scale operation. A lab-scale (3.78l) and a pilot-scale (120l) anaerobic digester were operated at both mixing and non-mixing conditions. At lab-scale no significant difference in performance was found between these conditions. In each case about 0.25lCH4/lreactor/d of biogas was produced. The model predictions were in close agreement with measured values. At pilot-scale, however, the influence of mixing became important. A reduction of about 10% of methane production occurred during unmixed conditions. Furthermore also a build-up of volatile fatty acids (up to 3gCOD/l) prevailed. This behavior could not be predicted by using a CSTR approach. In contrast, it was accurately predicted with the proposed model, which includes a more rigorous mixing next to common reaction kinetics. Prediction of the daily biogas production assuming a perfectly mixed reactor revealed an overestimation of the biogas production by 10%. It is therefore recommended to use more accurate mixing models in order to predict biogas production from anaerobic digesters.
ISSN:1385-8947
1873-3212
DOI:10.1016/j.cej.2014.06.041