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Simulation of a UASB reactor
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.ORCID iD: 0000-0001-8241-2225
2011 (English)Article in journal (Other academic) Submitted
Abstract [en]

A model has been developed to describe the behaviour of a UASB reactor with respect to substrate degradation, microorganism growth and granule size. The model is transient and includes advection, dispersion, and reaction terms. It also considers microorganism decay and the fraction of the biomass that can be dragged by the effluent. A mass balance was established in order to obtain an expression for the rate of the reaction occurring in the granule. It takes into account the resistance due to the mass transport through the stagnant film around the granule, the intra-particle diffusion, and the degradation rate within the granule.

 The model was solved using COMSOL Multiphysics software and data from the literature were used to study the performance of the model. The agreement between the model and the experimental results was satisfactory. The majority of the substrate is degraded at the bottom of the reactor due to the high density of granules present in that region. This kind of simulation may be a very helpful tool in the development and improvement of UASB reactors by predicting the reactor performance under different operating conditions.

Place, publisher, year, edition, pages
2011.
Keyword [en]
modelling, UASB, granules, wastewater, anaerobic treatment
National Category
Other Basic Medicine
Identifiers
URN: urn:nbn:se:kth:diva-29520OAI: oai:DiVA.org:kth-29520DiVA: diva2:394735
Note
QS 20120316Available from: 2011-02-03 Created: 2011-02-03 Last updated: 2012-03-16Bibliographically approved
In thesis
1. Upflow anaerobic sludge blanket reactor: modelling
Open this publication in new window or tab >>Upflow anaerobic sludge blanket reactor: modelling
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Anaerobic treatment is widely used around the world as a biological stage in both domestic and industrial wastewater-treatment plants. The two principal advantages of anaerobic over aerobic treatment are the production of biogas, which can be used as fuel, and the lower rate of biomass production, which results in lower maintenance costs for the plant. The upflow anaerobic sludge blanket (UASB) reactor is an attractive alternative for regions in hot climates since it works better under mesophilic conditions and it does not need any supporting structure for the development of microorganisms, which grow in the form of granules.

In this thesis, a model describing the UASB reactor behaviour with respect to substrate degradation, microorganism growth and granule formation was developed. The model is transient and is based on mass balances for the substrate and microorganisms in the reactor. For the substrate, the processes included in the model are dispersion, advection and degradation of the organic matter in the substrate. The reaction rate for the microorganisms includes the growth and decay of the microorganisms. The decay takes into account the microorganism dying and the fraction of biomass that may be dragged into the effluent. The microorganism development is described by a Monod type equation including the death constant; the use of the Contois equation for describing the microorganism growth was also addressed.

 An equation considering the substrate degradation in the granule was required, since in the UASB reactor the microorganisms form granules. For this, a stationary mass balance within the granule was carried out and an expression for the reaction kinetics was then developed. The model for the granule takes into account the mass transport through the stagnant film around the granule, the intraparticle diffusion, and the specific degradation rate. The model was solved using commercial software (COMSOL Multiphysics). The model was validated using results reported in the literature from experiments carried out at pilot scale.

A simplified model was also developed considering the case in which the microorganisms are dispersed in the reactor and granules are not formed. The UASB reactor is then described as formed by many well-stirred reactors in series. The model was tested using experimental results from the literature and the sensitivity of the processes to model parameters was also addressed. The models describe satisfactorily the degradation of substrate along the height in the reactor; the major part of the substrate is degraded at the bottom of the reactor due to the high density of biomass present in that region. This type of model is a useful tool to optimize the operation of the reactor and to predict its performance.

 

Place, publisher, year, edition, pages
Stockholm: US-AB, 2011. viii, 52 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2011:4
Keyword
wastewater, anaerobic treatment, modelling, UASB reactor.
National Category
Other Basic Medicine
Identifiers
urn:nbn:se:kth:diva-29521 (URN)978917415-849-6 (ISBN)
Presentation
2011-02-15, 10:00
Opponent
Supervisors
Note
QC 20110203Available from: 2011-02-03 Created: 2011-02-03 Last updated: 2011-02-03Bibliographically approved

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Moreno, Luis

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