Innovative Bioreactors for the Degradation of Polycyclic Aromatic Hydrocarbons

Research output: ThesisDoctoral Thesis (compilation)

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 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.

Details

Authors
  • Benoit Guieysse
Organisations
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Industrial Biotechnology

Keywords

  • Environmental technology, Bioteknik, Biotechnology, PAH, degradation, aromatic, contaminant, pollutant, bioreactor, organic pollutant, kontroll av utsläpp, Miljöteknik, pollution control
Original languageEnglish
QualificationDoctor
Awarding Institution
Supervisors/Assistant supervisor
  • [unknown], [unknown], Supervisor, External person
Award date2001 Nov 1
Publisher
  • Department of Biotechnology, Lund University
Print ISBNs91-89627-02-4
Publication statusPublished - 2001
Publication categoryResearch

Bibliographic note

Defence details Date: 2001-11-01 Time: 14:00 Place: Kårhuset Hörsalen (John Ericssons väg 3, Lund) External reviewer(s) Name: Margesin, Rosa Title: Assistent Professor Affiliation: Inst. of Microbiology, University of Innsbruck, Austria ---