PhD Defense by Anja Sloth Ziegler

Anja Sloth Ziegler, Department of Chemistry and Bioscience will defend her thesis on: "The microbial community in fouling membrane bioreactors: Distribution and diversity of important bacteria"


28.09.2017 kl. 10.00 - 13.00



"The microbial community in fouling membrane bioreactors: Distribution and diversity of important bacteria"


The membrane bioreactor (MBR) technology has become a promising option in wastewater treatment. However, the technology has not yet overwhelmed the market due to some serious drawbacks of which operational costs due to membrane fouling is the major contributor. A main problem seems to be the microorganisms colonizing the membrane. Therefore, a better understanding of the microbial community in MBRs and the effect of abundant microbial species on sludge characteristics and membrane fouling might lead to improved operation and widespread use of MBRs in wastewater treatment plants.

The aim of this project was to obtain better understanding of the microorganisms in the fouling layer in MBRs using state-of-the-art molecular methods and to find key parameters/factors that cause membrane fouling. Microbial community analysis by 16S ribosomal RNA (rRNA) amplicon sequencing was evaluated and optimized for activated sludge samples. A standard procedure was proposed and was subsequently used in a range of studies. The microbial community composition of bulk sludge and fouling layer from a pilot-scale MBR system connected to a full-scale conventional wastewater treatment plant was studied and compared. This difference was most pronounced in the early fouling layer and interestingly, as the fouling layer evolved, the microbial communities became more similar. Furthermore, filamentous Chloroflexi and Gordonia were enriched in the fouling layers. The changes in sludge properties and microbial community structure after start-up of a pilot-scale MBR was followed in another study. Both sludge properties and microbial community structure changed after start-up. Correlation analysis indicated that floc size and sludge compressibility were influenced by certain bacterial species, and it was possible to identify some bacteria that promoted good flocs and some that did not. Among good floc formers were the genera Dechloromonas, Ca. Accumulibacter and Nitrospira, whereas filamentous Chloroflexi caused poor flocs. In a survey of 20 Danish full-scale WWTPs Ca. Microthrix and some Chloroflexi, primarily Ca. Amarilinum were found to be correlated with bulking episodes and therefore be important for floc properties and also potentially fouling.

The overall conclusion of this project is that strong flocs are important for good plant operation, also in MBR systems, and  expanding our knowledge of good/bad floc formers in terms of ecology and physiology, the microbial community within MBR systems may be manipulated for selection of good floc forming bacteria that contribute positively to membrane fouling.


  • Professor Per Halkjær Nielsen, AAU


  • Associate Professor Lsars Haastrup Pedersen, Department of Chemistry and Bioscience, AAU, Denmark
  • Professor Britt-Marie Wilén, Department of Civil and Environmental Engineering, Chalmers University of Technology, Sweden
  • Professor Dr. ir. Ilse Smets, Chemical Engineering Department, KU Leuven Chem & Tech, Belgium





Department of Chemistry and Bioscience, AAU, Section of Biotechnology


Fredrik Bajers Vej 7H, 9220 Aalborg Ø, room number: 1.102-6