Project

Anaerobic Methane Oxidation for Biological Sulfate & Sulfur Reduction

Anaerobic oxidation of methane (AOM) was first discovered in anoxic marinesediments. It was shown that methane from deeper sediment disappeared in the same zone as sulfate, before any contact with oxygen occurred. In such anoxic zones, sulfate is the only electron acceptor that can account for methane oxidation. AOM is catalyzed by methanotrophic archaea (ANME) that form aggregates with sulfate reducing bacteria (SRB).

In our previous research, biomass from the Eckernförde bay in the Baltic Sea was incubated in a membrane bioreactor (MBR) with methane and sulfate as sole energy sources. After 884 days, a conversion rate of 0.6 mmol sulfate/liter/day was achieved. The AOM activity was 286 μmol/g dry weight/day, which is the highest AOM rate ever reported. The microbial community consisted of the anaerobic methanotrophic archaea subgroup type ANME-2a and bacteria belonging to the Deltaproteobacteria and Bacteriodetes. There was no observed direct association of ANME-2a with a bacterial partner in the reactor (figure 1).

Figure 1: FISH image with a probe for the ANME-2a ( red), probe for the DSS subgroup of the SRB (green), and non-specific stain for DNA (DAPI, blue). Insert is a bright field microscopy image of a typical loose aggregate found in the bioreactor enrichment (Jagersma et al, 2009)

The high AOM rate offers opportunities for industrial application in waste-water treatment of inorganic waste streams which contain sulfur compounds and/or metals.

This research aims to further increase the conversion rate in the MBR. To reach this aim microbiological studies and bioreactor studies will be done. Investigation of the molecular biology, physiology and biochemistry of the involved microorganisms yields information on the mechanism of methane conversion, optimal growth conditions, and versatility of the microorganisms with respect to growth substrates and electron acceptors. The knowledge gained from microbiological studies is used for optimization of the process in laboratory bioreactors with respect to design, start-up and operation. In addition, the effect of conditions relevant for technological applications is investigated in the bioreactors.

If you have any more questions or if you are interested in working on this project (thesis / internship subject) which is in close collaboration with the sub-department of Environmental Technology (ETE-WUR), please contact me.

Methods: FISH, RT-qPCR, DGGE, RFLP, clone libraries, sequencing, batch
experiments, 13C labeling, membrane bioreactor systems.