A small introduction on Bioenergy and Algae

High oil prices, global warming, and emphasis in renewable technology are attracting new interest in a potentially rich source of biofuels: algae. Currently, no alternative technology seems to be able to entirely replace our vast energy demands. Yet, we need new technologies to provide us the energy we need. One of these technologies which is recieving more and more attention is bioenergy derived from algae.

Microalgae can contain up to 40% oil, they can grow in wastewater and in live places where no agriculture is possible. They are able to grow very fast and they even capture large amounts carbon dioxide while doing so. These facts look very promising for use of algae in bioenergy, but can these algae really deliver?

Currently I am researching the integration of solar energy via algae into methane and electricity. The aim of the thesis is to research and develop the potential use of microalgal biomass for conversion into bioenergy.

So, how does this work? The algae are grown in salt water ponds in our laboratories. The algae convert carbon dioxide with energy from solar radiation into biomass, a process which is called photosynthesis. After they reach a certain density, an amount of water containing algae is put into an anaerobic digestor for 20 days. In this digestor, which is basically an airtight container with an microbial inoculum, the biomass of the algae is converted into biogas (65% methane, the rest is carbon dioxide). This digestor is built in a way that no air comes in, but the biogas is being captured for analysis. Theoretically, it should generate ~0,5 l biogas per gram dry algae.

When the algal fluid is digested, it is transferred into an Microbial Fuel Cell (as seen left), which is a sort of bio battery. The main goal of the microbial fuel cell is to generate electricity while further degrading the effluent of the digestor. It contains two 165 ml compartments seperated by a membrane. One compartment contains the digested fluid and an active microbial mat which converts the organic material, the other contains water with dissolved oxygen. Organic compounds are metabolised by bacteria in the first compartment, and the electrons are transferred via the electrode to the other compartment, where they are taken up by oxygen and form water. This current can be used as electricity.

Microbial fuels should generate a potential about 100 mV or more and some current. After the fluid has passed through the microbial fuel cell, it is poured into the ponds to the algae can grow again.

Figure: scheme of a microbial fuel cell. In the left compartment, substrate is oxidized. Electrons transfer to the other compartiment and react with oxygen.

Now you know something about the general principles of this research. This work is just a tiny addition in the rapidly growing algal to bioenergy field. Converting algae to biogas and electricity is not the only possible application for algae. Other projects on algae involve the use of algae in reducing carbon dioxide emissions from energy plants (MIT – USA). Some companies use algae to produce omega-3 (SBAE – Belgium) fatty acids or pharmaceuticals. Some grow algae strains with high oil contents in order to produce biodiesel (AlgaeLink – Netherlands, Shell/Cellana – Hawaii). Many other projects worldwide are currently researching algal production for bioenergy creation.

In the coming months I’ll regularly post updates on the progress of these potentially vital researchs.