Getting microorganisms to thrive
Methane-forming microorganisms do much of the heavy work in a biogas reactor. Prof Bo Svensson and Dr Annika Björn are managing a BRC project that will identify the conditions in which microorganisms function best.
The lab at Water and Environmental Studies (WES) contains several small biogas reactors, four of which are part of the BRC project aimed at discovering the role of various trace elements in efficient, stable biogas production. In the room it is dark and 37 degrees – to ensure that the methane-forming microorganisms thrive.
Once a day, seven days a week, the reactors are fed with new substate in order to keep the production going. The process has been underway for six months, using a blend of primary sludge and bio sludge from Henriksdal sewage treatment plant in Stockholm.
The trials aimed at increasing the production of biogas began in late May. The researchers added household waste to one of the small reactors, and fat to another. The volume of organic material has also been increased over time. In the third reactor, sodium sulphide was added, to adjust the proportion between sulphur and iron. The fourth reactor was left as it was.
“We run them the same way as a biogas facility, just on a smaller scale,” says Sepehr Shakeri Yekta, PhD student at WES.
The fat is added because it is an energy-rich substrate that is found in grease traps in the food industry, restaurants and commercial kitchens. However there can be problems as the fat rots, because even if it has started to melt, it often forms droplets in the 37-degree heat. It is important to ensure the fat does not clump.
“It’s important to find a stable process that works well, to extract as much of the energy content as possible,” says Dr Björn.
The four reactors at Linköping University are run in a collaboration between WES and Scandinavian Biogas. At Tekniska verken, a Linköping utility, a number of trials have been conducted, in order to study and compare the effects of additives of cobalt sulphide and cobalt chloride. Six reactors were recently started at NSR in Helsingborg, where the effects of nitrogen-rich substrate will be studied. Kemira in Helsinki is also participating, and tests from the reactors are sent there for specific analysis.
“This is one of BRC’s development projects, that will identify important research questions ahead of the next stage, questions related to optimisation of the biogas processes,” says Bo Svensson, professor at WES, and project manager together with Dr Björn.
“Of course we could have done all our tests separately and combined the results, but we decided to set up the project together, and it has been a stimulating, creative collaboration, with rewarding exchanges between academia and the business sector. The tests in all reactors are now everybody’s responsibility,” explains Prof Svensson.
Dr Björn: “We have also developed a joint analysis package. We hope it will provide valuable information on the importance of various trace elements as well as of rheology, that is, the viscosity of the substrate and the flow characteristics it gets.”
Rheology is Annika Björn’s specialty, while Sepehr Shakeri Yekta studies trace elements such as nickel and cobalt. Trace elements are added where required, to ensure the growth of the microorganisms in the reactor. But in the reactor sulphides are also formed, which can bind with trace elements, making them less available to microorganisms.
“The sewage treatment plants have a surplus of iron, but we don’t know exactly how this affects the process. Lots of iron and small amounts of sulphides should make the trace elements more available but we don’t know for sure,” says Prof Svensson.
There are five graduation projects linked to the four reactors at WES. The students, mainly technical biologists, analyse samples from the reactors.
Slowly but surely we are learning more about the miniature world inside the reactors. In the long term, in the next stage and with the results from several of the projects, the researchers hope to develop recipes for which trace elements should be added, in which volumes, and how much stirring is required, for various types of substrates. The aim is to develop stable processes that yield as much gas as possible, for a particular blend of substrate.
Development project DP6: Increased methane production and process stability in biogas reactors
Participants: Project leaders Assistant Professor Annika Björn and Professor Bo Svensson, PhD student Sepehr Shakeri Yekta, and research assistant Pascal Ojong, from the division Water and Environmental Studies, Department of Thematic Studies. Researchers from the division Environmental Technology and Management, Department of Management and Engineering, IEI, and the division Molecular Biotechnology, Department of Physics, Chemistry and Biology, IFM. Participants from Kemira OYJ, NSR AB, Scandinavian Biogas Fuels AB, and Tekniska Verken i Linköping AB.
Last updated: 2014-01-29