Disputation: Fasil Tassew

Fasil Tassew holds a trial lecture and disputation at campus Porsgrunn on January 17.

17 Jan

Practical information

  • Date: 17. January 2020
  • Time: 09.30 - 15.30
  • Location: Porsgrunn, Auditorium A-271
  • Evaluation committee

    First opponent: Professor Hinrich Uellendahl, Flensburg University of Applied Sciences.

    Second opponent: Dr.ing. Wolfram Francke, Yara Technology Centre.

    Administrator: Professor Lars Erik Øi, USN.


    Principal supervisor: Professor Rune Bakke, USN.

    Co-supervisor: Associate professor Wenche Hennie Bergland, USN. 

Fasil Tassew at the University of South-Eastern Norway, Faculty of Technology, Natural Sciences and Maritime Sciences (TNM) will be defending his thesis «Capabilities of anaerobic granular sludge bed process for the treatment of particle-rich substrates» for the degree of philosophiae doctor (PhD).


The trial lecture «Anaerobic digestion compared to other biofuels and waste management technologies – status and outlook for Europe» will be held in Auditorium A-271 at campus Porsgrunn January 17 at 09:30 am. The PhD defense will be held shortly after at 12:00 am. 

Both the trial lecture and the PhD defense are open to the public. Immediately after the defense the doctoral programme will hold a small defense reception on the first floor of Origo (upstairs from the Café), approximately from 15:00-15:30.


Biogas production from substrates that contain high concentrations of suspended solids has been a challenge mainly due to the slow disintegration and hydrolysis of solid particles. This is especially true in high-rate anaerobic reactors where solid accumulation is a common problem. As a result, a large amount of substrates such as agricultural wastes have been unable to be effectively utilized as a source of renewable energy. A better understanding of the interaction of granular sludge bed with particles is an essential step to solving this problem.

This doctoral thesis focuses on understanding the particle disintegration patterns and finding ways to increase the rate of disintegration and hydrolysis. A review of the current state of application of granular sludge beds for anaerobic digestion of particle-rich substrates was carried out in order to establish how and to what extent substrate particles influence granular sludge beds and vice versa. A new image analysis technique was developed to measure granular sludge size and settling velocity. Batch and continuous laboratory-scale experiments were conducted along with simulations of the anaerobic digestion process.

The results showed that successful high-rate digestion of particle-rich substrates with total solid contents as high as 35% was possible in some anaerobic digestion processes but in conventional high-rate reactors such as Upflow Anaerobic Sludge Blanket (UASB), the total solid limit seemed to be around 10%. Pretreatment of substrates such as hydrolytic enzyme addition has been used to improve the anaerobic digestion process. The addition of cellulase increased biomethane production rates in both high and low particle content samples enhancing yield by 54% and 40%, respectively and converting 69% and 87% of feed chemical oxygen demand (COD), respectively. Biogas production increased with temperature in both high and low particle content substrates, however, the temperature effect was found to be strongest on the high–particle substrate which was attributed to increased disintegration of larger solid particulates.