BEST* pilot project: Microbial electroactivity in biocatalytical carbonate reef sands

1-2 envisioned master theses jointly supervised by Prof. Dr. Sven Kerzenmacher (FB 4) & Prof. Dr. Christian Wild (FB 2)

Background and project justification:

Biogenic carbonate reef sands typically exhibit large grain size, high permeability, high porosity, and large specific surface. Thus, intense water-sediment coupling takes place, i.e. large volumes of water are filtered through these sands, and suspended particles are trapped between the grains so that the water is cleaned. In addition, these sands are colonised by high densities of diverse microbes that can rapidly mineralize the trapped organic matter. These two attributes transform these sands to very efficient biocatalytical filter system in aquatic environments. Carbonate sands cover large areas of shallow-water marine ecosystems, particularly coral reefs, where many different organisms (i.e. hard corals, molluscs, echinoderms) contribute to their production. Oxygen can be transported into these sands via fast (advection) or slow (diffusion) mass transfer processes, but sands are so active that oxygen usually only penetrates a few millimetres in these sands. This leads to the generation of small-scale gradients and redox cascades with alternative electron acceptors such as nitrate, Fe3+, Mn4+, and sulphate. Because of these attributes, it is very likely that microorganisms capable of extracellular electron transfer are present in carbonate reef sands. This would enable the operation of microbial fuel cells (MFCs) that generate electricity for the operation of coral reef monitoring tools. While the feasibility of this concept has already been demonstrated, there are pronounced gaps of knowledge, in particular related to the operation of MFCs in carbonate reef sands with high microbial activity. Furthermore, the potential discovery of new electroactive species in carbonate reef sands would have both ecological and technical/engineering implications.

Research questions:

1) How much energy can be harvested from a microbial fuel cell placed in carbonate reefs sands? How does this compare to other sediments or substrates? Is this energy sufficient to power long-term monitoring tools (sensors, loggers) or flow generators?
2) What are the main factors (e.g. sand mineralogy, grain size, porosity, oxygen penetration depth, organic matter addition, bioturbation) driving electricity generation by these MFCs?
3) Which microbes are electro-active in these sands? What are the conditions that they require?
4) What can we learn from carbonate sands for efficient sewage treatment?
5) How does environmental change influence microbial electroactivity in reef sands?


Small-scale microbial fuel cells will be developed and constructed by Kerzenmacher Group and then tested and used in aquarium facility of Wild Group. As soon as electroactivity measurements work, a series of replicated manipulation experiments will be conducted in order to answer the research questions. Identification of bioactive microbes will be conducted in envisioned collaboration with MPI for Marine Microbiology. The best option would be to have a tandem of two master students – one from FB 2 and one from FB 4 – working together on this project.

For further Information please contact: Christian Wild ( or Sven Kerzenmacher (
* Biology-Inspired Energy Systems