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Innovative Bioreactors for the Degradation of Polycyclic Aromatic Hydrocarbons

Guieysse, Benoit LU (2001)
Abstract
The development of biological reactors for the treatment of toxic and recalcitrant organic pollutants is a complex task. Firstly, microbial inoculation, acclimation and selection must be optimized to provide the best microflora possible. Secondly, innovative technologies must be developed to overcome the intrinsic low degradation rates of hardly-degradable pollutants in order to allow short treatment times. Finally, since the pollutants involved are often toxic, it is also important to use well-managed treatment system that limit potential process hazards.



Efficient inoculum was provided by using a mixture of indigenous soil microflora, most likely containing contaminant-degrading species, and activated sludge sample to... (More)
The development of biological reactors for the treatment of toxic and recalcitrant organic pollutants is a complex task. Firstly, microbial inoculation, acclimation and selection must be optimized to provide the best microflora possible. Secondly, innovative technologies must be developed to overcome the intrinsic low degradation rates of hardly-degradable pollutants in order to allow short treatment times. Finally, since the pollutants involved are often toxic, it is also important to use well-managed treatment system that limit potential process hazards.



Efficient inoculum was provided by using a mixture of indigenous soil microflora, most likely containing contaminant-degrading species, and activated sludge sample to provide microbial diversity as a protection against metabolite accumulation and substrate inhibition effects. Both fed-batch and continuous cultivations were suitable for microbial selection. Since the selection of degrading species depends on the origin of the inoculum and the procedure and system used, inoculation, acclimation and selection should be performed each time the treatment of a new effluent or the performance of a new process is studied.



Both Suspended-Carrier and Packed-Bed reactors allowed the fast treatment of diluted contaminated effluent. The packed-bed reactor was preferred since it favored the development of very diverse microflora and was based on the use of a cheaper carrier. Special care should be taken in controlling pollutant adsorption to the carriers. Biphasic reactors were found to be suitable for the treatment of concentrated mixtures of contaminants such as soil extracts. Besides reducing the aqueous toxicity of the contaminants, the use of an organic phase in biphasic reactor advantageously permitted to avoid pollutant volatilization and adsorption. However, their large-scale application remains dependent on several improvements. The potential of algae photosynthesis to produce oxygen in-situ in the reactor, which limits the risk for pollutant volatilization, was clearly demonstrated. Emphasis should be given on optimizing photosynthesis efficiency, which depends on the light intensity and the algal population size, rather that the degradation of the pollutants.



Since recording pollutant disappearance does not inform about the mechanism of removal and the pollutants involved are toxic, it is very important to monitor microbial activity during the entire process. The rate of disappearance of the electron acceptor used by the microflora could often be well correlated with the microbial activity and the pollutant biodegradation rate. This could lead to the development of biosensors and monitoring strategies suitable for the biological treatment of toxic and recalcitrant pollutants. Finally, although it was often difficult to avoid abiotic removal mechanisms and to monitor microbial degradation, it was still possible to evaluate and control these phenomena in most of the systems described in this thesis work. This clearly demonstrates a very important advantage of ex-situ remediation processes compared to in-situ processes. (Less)
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author
opponent
  • Assistent Professor Margesin, Rosa, Inst. of Microbiology, University of Innsbruck, Austria
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Environmental technology, Bioteknik, Biotechnology, PAH, degradation, aromatic, contaminant, pollutant, bioreactor, organic pollutant, kontroll av utsläpp, Miljöteknik, pollution control
pages
158 pages
publisher
Department of Biotechnology, Lund University
defense location
Kårhuset Hörsalen (John Ericssons väg 3, Lund)
defense date
2001-11-01 14:00
external identifiers
  • other:ISRN: LUTKDH/TKBT- - 01/1053- -SE
ISBN
91-89627-02-4
language
English
LU publication?
yes
id
ba60533f-41f6-46c1-aed2-77fbec041160 (old id 42019)
date added to LUP
2007-06-21 10:49:27
date last changed
2016-09-19 08:45:07
@phdthesis{ba60533f-41f6-46c1-aed2-77fbec041160,
  abstract     = {The development of biological reactors for the treatment of toxic and recalcitrant organic pollutants is a complex task. Firstly, microbial inoculation, acclimation and selection must be optimized to provide the best microflora possible. Secondly, innovative technologies must be developed to overcome the intrinsic low degradation rates of hardly-degradable pollutants in order to allow short treatment times. Finally, since the pollutants involved are often toxic, it is also important to use well-managed treatment system that limit potential process hazards.<br/><br>
<br/><br>
Efficient inoculum was provided by using a mixture of indigenous soil microflora, most likely containing contaminant-degrading species, and activated sludge sample to provide microbial diversity as a protection against metabolite accumulation and substrate inhibition effects. Both fed-batch and continuous cultivations were suitable for microbial selection. Since the selection of degrading species depends on the origin of the inoculum and the procedure and system used, inoculation, acclimation and selection should be performed each time the treatment of a new effluent or the performance of a new process is studied.<br/><br>
<br/><br>
Both Suspended-Carrier and Packed-Bed reactors allowed the fast treatment of diluted contaminated effluent. The packed-bed reactor was preferred since it favored the development of very diverse microflora and was based on the use of a cheaper carrier. Special care should be taken in controlling pollutant adsorption to the carriers. Biphasic reactors were found to be suitable for the treatment of concentrated mixtures of contaminants such as soil extracts. Besides reducing the aqueous toxicity of the contaminants, the use of an organic phase in biphasic reactor advantageously permitted to avoid pollutant volatilization and adsorption. However, their large-scale application remains dependent on several improvements. The potential of algae photosynthesis to produce oxygen in-situ in the reactor, which limits the risk for pollutant volatilization, was clearly demonstrated. Emphasis should be given on optimizing photosynthesis efficiency, which depends on the light intensity and the algal population size, rather that the degradation of the pollutants.<br/><br>
<br/><br>
Since recording pollutant disappearance does not inform about the mechanism of removal and the pollutants involved are toxic, it is very important to monitor microbial activity during the entire process. The rate of disappearance of the electron acceptor used by the microflora could often be well correlated with the microbial activity and the pollutant biodegradation rate. This could lead to the development of biosensors and monitoring strategies suitable for the biological treatment of toxic and recalcitrant pollutants. Finally, although it was often difficult to avoid abiotic removal mechanisms and to monitor microbial degradation, it was still possible to evaluate and control these phenomena in most of the systems described in this thesis work. This clearly demonstrates a very important advantage of ex-situ remediation processes compared to in-situ processes.},
  author       = {Guieysse, Benoit},
  isbn         = {91-89627-02-4},
  keyword      = {Environmental technology,Bioteknik,Biotechnology,PAH,degradation,aromatic,contaminant,pollutant,bioreactor,organic pollutant,kontroll av utsläpp,Miljöteknik,pollution control},
  language     = {eng},
  pages        = {158},
  publisher    = {Department of Biotechnology, Lund University},
  school       = {Lund University},
  title        = {Innovative Bioreactors for the Degradation of Polycyclic Aromatic Hydrocarbons},
  year         = {2001},
}