Anaerobic Digestion – Microbial Ecology, Improved Operational Design and Process Monitoring

Marika Murto

Research output: ThesisDoctoral Thesis (compilation)


The implementation of anaerobic digestion is important in the concept of sustainable development, especially regarding the environmental benefits. Biogas is produced when organic matter is degraded by microorganisms under oxygen-free (anaerobic) conditions. Biogas production occurs in nature where oxygen is absent; in rice fields, landfills, sediments, the intestinal tract of animals, etc. The advantage of degrading organic matter and at the same time producing renewable energy in the form of energy-rich methane, as well as other environmental benefits, has made anaerobic digestion interesting in industrial applications. Anaerobic digestion has been exploited as an effective biotechnological method for organic waste and wastewater treatment. Current national environmental regulations and other policies governing land use and waste disposal have increased interest in anaerobic digestion.

However, the anaerobic degradation of organic matter is a complex process involving microorganisms in an advanced interaction. Our knowledge about the anaerobic digestion process is increasing, but to increase the efficiency of the process and to make it more economically beneficial there is a need for improvements in the technology in many areas.

Studying the microbial ecology is important for in-depth understanding of the anaerobic degradation process. Fluorescence in situ hybridisation (FISH) was employed to identify microorganisms in the anaerobic process with the focus on methanogens. Probes commonly used in FISH for detecting methanogens were re-evaluated and redesigned, giving better coverage of the methanogens, and the experimental conditions were optimised for use of the probes in FISH. Using FISH, changes in microbial composition could be detected when changing feed composition in anaerobic reactors, which could be correlated to changes in process conditions.

A new application for partitioning in aqueous two-phase systems was developed. The mixed culture from an anaerobic digestion process was multi-step partitioned in an aqueous two-phase system in order to obtain a “fingerprint” of the culture. Differences in operational conditions could be reflected in the distribution profiles obtained.

Process control and monitoring are of great importance in improving the efficiency of the anaerobic degradation process. Traditional and new methods were evaluated for the monitoring of anaerobic digestion processes. Since the anaerobic process is so complex, one parameter is seldom sufficient to monitor the conditions in a reactor, and a combination of parameters should be used for reliable process monitoring and control. With a good monitoring and control strategy it is possible to run the digesters closer to their maximum capacity thereby improving the treatment capacity and the process economy.

The development of process designs and configurations has improved treatment rates making the process more cost-efficient. The successful co-digestion of agricultural waste with sewage sludge and pig manure was reported. Mixing of waste must be done with care as unsuitable mixtures can lead to unstable process conditions resulting in failure of the anaerobic digestion process.

The development of new high-rate reactor designs has increased the efficiency and stability of the biogas process compared with the conventional reactor configuration. Three different high-rate reactor designs were evaluated and successfully applied to the treatment of solid agricultural waste.
Original languageEnglish
Awarding Institution
  • Biotechnology
  • [unknown], [unknown], Supervisor, External person
Award date2003 Dec 12
Print ISBNs91-89627-18-0
Publication statusPublished - 2003

Bibliographical note

Defence details

Date: 2003-12-12
Time: 13:15
Place: Lecture hall A, Center for Chemistry and Chemical Engineering, Sölvegatan 39, Lund Institute of Technology.

External reviewer(s)

Name: Angelidaki, Irini
Title: Professor
Affiliation: Environment & Resources DTU, Technical University of Denmark, Lyngby, Denmark.


Article: 1. Crocetti, G., Murto, M. and Björnsson, L. Updating and optimisation of molecular probes for fluorescence in situ hybridisation (FISH) of methanogenic Archaea. Submitted for publication

Article: 2. Murto, M., Crocetti, G. and Mattiasson, B. The influence of the substrate composition on the methanogenic populations in anaerobic digesters. Manuscript

Article: 3. Murto, M., Dissing, U. and Mattiasson, B. (2002) Characterisation of anaerobic mixed cultures by partition in an aqueous two-phase system. Biotechnology Letters 24: 335-341.

Article: 4. Björnsson, L., Murto, M. and Mattiasson, B. (2000) Evaluation of parameters for monitoring an anaerobic co-digestion process. Applied Microbiology and Biotechnology 54: 844-849.

Article: 5. Björnsson, L., Murto, M., Jantsch, T. G. and Mattiasson, B. (2001) Evaluation of new methods for the monitoring of alkalinity, dissolved hydrogen and the microbial community in anaerobic digestion. Water Research 35: 2833-2840.

Article: 6. Murto, M., Björnsson, L. and Mattiasson, B. Impact of food industrial waste on anaerobic co-digestion of sewage sludge and pig manure. Accepted for publication in Journal of Environmental Management

Article: 7. Parawira, W., Murto, M., Zvauya, R. and Mattiasson, B. Comparison of the performance of a UASB reactor and an anaerobic packed-bed reactor when treating potato waste leachate. Submitted for publication

Article: 8. Mshandete, A., Murto, M., Kivaisi, A., Rubindamayugi, M. and Mattiasson, B. Influence of recirculation flow rate on the performance of anaerobic packed bed reactors treating potato waste leachate. Submitted for publication

Subject classification (UKÄ)

  • Industrial Biotechnology


  • monitoring
  • UASB
  • Biotechnology
  • Bioteknik
  • methanogens
  • fluorescence in situ hybridisation
  • FISH
  • co-digestion
  • biogas
  • biofilm
  • aqueous two phase system
  • anaerobic digestion
  • 16S rDNA
  • alkalinity


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