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Upflow anaerobic sludge blanket reactor: modelling
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
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 [en]
wastewater, anaerobic treatment, modelling, UASB reactor.
National Category
Other Basic Medicine
Identifiers
URN: urn:nbn:se:kth:diva-29521ISBN: 978917415-849-6 OAI: oai:DiVA.org:kth-29521DiVA: diva2:394741
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
List of papers
1. Modeling of substrate degradation and microorganism growth in an UASB reactor
Open this publication in new window or tab >>Modeling of substrate degradation and microorganism growth in an UASB reactor
2010 (English)In: CBEE 2009: Proceedings of the 2009 International Conference on Chemical, Biological and Environmental Engineering, Singapore: World Scientific Publ Co Ptd Ltd , 2010, 76-80 p.Conference paper, Published paper (Other academic)
Abstract [en]

A model for substrate degradation and microorganism growth in an UASB reactor was developed. The model is transient and takes into account advection, dispersion and degradation of the substrate. For the micro-organisms, the growth is described by a Monod type equation including a death constant. The model also assumes that a fraction of the microorganisms in the reactor may be carried out by the water flow. The UASB reactor is described as formed by many well-stirred reactors in series. Parameters for the model were taken from literature and MATLAB was used to solve the model. The sensibility of the process to the model parameters was also addressed.

Place, publisher, year, edition, pages
Singapore: World Scientific Publ Co Ptd Ltd, 2010
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-29518 (URN)000273273600016 ()
Note
QC 20110203Available from: 2011-02-03 Created: 2011-02-03 Last updated: 2011-02-03Bibliographically approved
2. Modelling of an Upflow Anaerobic Sludge Blanket reactor
Open this publication in new window or tab >>Modelling of an Upflow Anaerobic Sludge Blanket reactor
2010 (English)Collection (editor) (Other academic)
Abstract [en]

A model describing both physical and biological processes in Upflow Anaerobic Sludge Blanket (UASB) reactors was developed The main objective of the modelling was to take into account the transient growth of the microorganisms from the start-up of the reactor until a steady state is reached In addition, the model considers the degradation of the substrate and its reaction with the biomass, which is present in the form of spherical granules of different sizes For the degradation of the substrate within the granule, the mass transport through the stagnant film around the granule and the intra-particle diffusion are accounted for, together with the specific reaction rate In the model, the growth of the biomass follows the Contois kinetics The amount of biomass reaches a steady state after weeks or months Biomass is generated when substrate is degraded and a given fraction of biomass disappears per unit of time, which is determined by the decay constant The value of this constant is taken from the literature The model also considers that a fraction of the biomass may be carried out by the water flow The model was solved by using COMSOL Multiphysics Data from the literature was used in order to illustrate the processes occurring in the UASB reactor Modelling can be a useful tool for the design and optimization of UASB reactors

Keyword
UASB, COMSOL multiphysics, contois model
National Category
Chemical Sciences Dentistry
Identifiers
urn:nbn:se:kth:diva-29519 (URN)10.2495/WP100261 (DOI)000285030300026 ()2-s2.0-78149332804 (Scopus ID)
Note
QC 20110203Available from: 2011-02-03 Created: 2011-02-03 Last updated: 2011-02-03Bibliographically approved
3. Simulation of a UASB reactor
Open this publication in new window or tab >>Simulation of a UASB reactor
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.

Keyword
modelling, UASB, granules, wastewater, anaerobic treatment
National Category
Other Basic Medicine
Identifiers
urn:nbn:se:kth:diva-29520 (URN)
Note
QS 20120316Available from: 2011-02-03 Created: 2011-02-03 Last updated: 2012-03-16Bibliographically approved

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