Research got the microorganisms going
Today ever greater amounts of biogas are being produced from each unit of raw material. One of the secrets is keeping the methane-producing microorganisms happy by giving them the right amount of food. Researchers at Linköping University know all about this.
In Linköping and the surrounding region there are currently 150 buses and a number of refuse collection trucks, taxis and private vehicles that run on biogas. The biogas initiative is run as a joint project between the municipality, Tekniska Verken (an energy company owned by the municipality) and several different research teams at Linköping University (LiU). A strong research environment is one of the cornerstones of the Biogas Research Centre@LiU, now nearing completion.
The researchers at WES (LiU’s centre for Water and Environmental Studies) were the first to get involved in the process, and they were quick to get the microorganisms going.
In the early 1990s the head of development at Tekniska Verken contacted Jörgen Ejlertsson, a researcher who is currently acting professor at WES and involved with Scandinavian Biogas Fuels.
“Jörgen Ejlertsson doubled the gas yield with just a few simple measures. And then he doubled it again,” recalls Bo Svensson, professor at WES.
“We knew from previous studies that the methane-producing microorganisms need access to metals such as nickel and cobalt in order to thrive, but Jörgen Ejlertsson showed us how it worked in practice as well,” he continues.
At WES, this research has continued along several different tacks, one of them being specifically about how different trace elements – metals such as nickel, cobalt or molybdenum – affect the process.
In a recently published doctoral thesis, for example, Jenny Gustavsson shows that nickel is taken up by the microorganisms despite being strongly bonded to sulphides in the reactor. When biogas is produced from ethanol production waste, known as draff, this contains sulphate. Sulphate-reducing bacteria in the reactor transform the sulphate into foul-smelling hydrogen sulphide. By adding iron this undesired sulphide is bound, but unfortunately some of the crucial trace elements are also bound.
“Jenny Gustavsson’s thesis is among the leading research in the area at the moment, and provides new knowledge about how to dose trace metals in order to maximise biogas production,” Svensson says.
A large research effort is also underway to examine the organic material that exists in the wet streams of paper and pulp mills. If that material can be used for biogas production, and there is much that indicates it can, then it will provide a considerable addition to biogas substrates – raw materials for biogas production.
The potential is equal to the entire amount of biogas currently being produced at Swedish wastewater treatment plants. If biogas processing is set up near the mills, there will also be a reduction in power consumption for aeration of the wastewater treatment tanks, a savings equivalent to the electricity production of half a nuclear power station.
“Another advantage is that many of the mills are in the northern part of the country, where there is less access to other types of substrates,” Svensson points out.
If you’re driving north in biogas-fuelled car or bus, you don’t want to risk getting stranded in Gävle because it’s too far between the filling stations. And biogas will obviously be a more interesting proposition to station owners if there is access to gas nearby.
Another line of research is about the viscosity in the reactor, or the viscosity of the material. Among other challenges, a change in viscosity brings problems concerning the dimensions of pumps and mixers. A number of reactors have broken down when the propeller in the mixer has come loose because the material’s viscosity grew too high.
“Previously, only the dry substance was studied when dimensioning mixing, but Annika Björn, a researcher here at WES, has shown that there is no reliable rule of thumb for that,” Svensson explains.
In the spring of 2010, for example, the large biogas facility in Uppsala ran into even greater problems, and in the end the reactor had to be shut down completely during the summer and into the autumn. This breakdown was due precisely to problems with the mixer and changed viscosity in the reactor.
“It turned out that there were two metres of solid material at the bottom of the reactor. There have been similar problems in biogas reactors in the southern part of the country as well,” he continues.
This year Annika Björn and her colleagues are going to continue investigating the role of microorganisms in changes to viscosity. It is a known fact, for instance, that a lack of trace elements can lead to the secretion of organic substances that thicken the fluid in the digestion chamber, making its flow more sluggish.
Several other divisions and departments at LiU are involved in biogas research:
• Division for Energy Systems
• Division for Environmental Technology and Management
• The interdisciplinary unit for Technology and Social Change
• The groups for Biochemistry, Biology and for Surface Physics and Chemistry
A thesis about gasification of biofuels, generally referred to as second generation biofuels, was published last spring and received a considerable amount of attention. Its author, Elisabeth Wetterlund from the Division of Energy Systems, shows that gasification of forest products is not optimal from a European perspective if the goal is to reduce carbon dioxide emissions. The forest products can be put to better use elsewhere. However, she does see a potential for the gasification of the ‘grot’, the branches and tops left over after logging, in Sweden – particularly if production is integrated with the rest of the energy system so that surplus heat can be utilised.
A considerable number of articles have also been published in scientific journals, in which experiences of the introduction of biogas as vehicle fuel in Sweden are studied from several different perspectives.
Looking at the past few years only, biogas research at LiU has led to a couple of doctoral theses, a handful of reports, a large number of scientific articles and almost 40 degree projects.
“One of our greatest contributions is to have trained a large number of people who now have specialist knowledge in this area,” Svensson concludes.
Monica Westman Svenselius, 14 June, 2012
Photo of biogas filling station by Göran Billeson, other photos by LiU
LiU’s centre for Water and Environmental Studies
Jenny Gustavsson’s doctoral thesis
Division of Energy Systems
Tekniska Verken http://www.tekniskaverken.se/om-oss/in-english/
Biogas Research Center@LiU
Linköping to get biogas research centre
Last updated: Fri Jul 06 10:38:00 CEST 2012