Energy potential of biogas generated from renewable resources still considerably untapped

Researchers at Johannes Gutenberg University Mainz, Germany are looking for microorganisms that will optimize the fermentation of biomass in biogas plants


According to scientists, it should be possible to significantly optimize the techniques used to produce biogas as a source of energy. Professor Dr Helmut König, head of the Institute of Microbiology and Wine Research at Johannes Gutenberg University Mainz (JGU), believes that the focus should be put on the microbial processes that are involved in the conversion of biomass to methane. "To date, the biogas that we have been producing from biomass is 50 to 65 volume percent methane. However, the required hydraulic retention time of the biomass of up to 70 days is still too long and can no doubt be improved considerably with optimized microorganisms," explains König. "Furthermore, overacidification frequently interferes with fermentation, sometimes bringing the whole process to a standstill. We also need to find a solution here, as methanogenic bacteria cease to proliferate in such acidic environments." In Germany, biogas is produced in biogas plants that are operated using renewable resources, mainly by means of the fermentation of corn. The resultant gas is primarily used to generate electricity and heat or, after purification, is fed directly into the gas supply network.

Because we will run short of fossil fuels such as mineral oil and natural gas within the next 40 years at the latest, far more attention will need to be paid in future to alternative sources of energy, and these will have to make a much larger contribution than before to electricity and heat generation. The European Renewable Energy Council (EREC) estimates that renewable resources will cover 50 percent of European energy requirements by 2040. Germany is currently operating some 5,800 biogas plants, which produce about 10 percent of the electricity generated from renewable resources – in addition to thermal energy. Germany is also a world leader in the sector of biogas technology.

The advantage of biogas over wind and solar energy is that it is constantly available and can thus be used to help meet basic energy needs. Furthermore, biomass and biogas can be stored and accumulated, and are thus always available to cover requirements at times of peak energy use. It is for this reason that experts believe that biogas will play an important role in making up shortfalls in the fluctuating supply of energy generated by wind and sun.

While major progress has been made in biogas plant technology in recent years, the microbiology of the underlying processes and the systematization of the microorganisms involved have received relatively scant attention so far. Ever since its foundation in the late 1960s, the Institute of Microbiology and Wine Research at Mainz University has been investigating microorganisms such as bacteria and yeasts in a wide variety of different scientific fields and is currently conducting two research projects into microbial biogas production, a further project is to be initiated soon. "We are studying the microorganisms in biogas plants, identifying them and determining their physiological capabilities. We want to find out if there are cultures of microorganisms that are more efficient than others when it comes to breaking down the plant materials and producing biogas," explains König. His work group is collaborating with the Test and Research Institute Pirmasens (Prüf- und Forschungsinstitut Pirmasens, PFI), which runs biogas plants in the federal state of Rhineland-Palatinate and is working on upgrading the process technology.

König's team sees the intestinal microflora of termites, which is capable of decomposing lignocellulose, as particularly promising in this regard. Termites mainly live in the tropics and subtropics, and they are capable of destroying large wooden constructions and even houses made of wood in next to no time. "The termites' secret is their symbiosis with intestinal bacteria, yeasts, and flagellates that require only 24 hours to break down particles of lignocellulose and are responsible for the production of an estimated 100 million tons of methane worldwide. As a species, termites originated some 150 million years ago and have used the time since then to optimize the process of microbial decomposition of lignocellulose. This is something we could utilize for our own benefit." Professor König and his Indian colleague Professor Ajit Varma have already published a book on the enteric microorganisms of the termite. The Mainz-based scientists have isolated the bacteria and yeasts involved and, together with their colleagues from the Test and Research Institute Pirmasens, are looking for solutions to comminute corn and other renewable sources of energy in such a way that would make the small particles ideally suited for microbial lignocellulose decomposition and would thus speed up the production of methane.

"Microbial techniques for the production of biogas from renewable resources are still at an early stage of their development," states König. In the near future, his team will be turning to an additional field of research: the microbial conversion of new substrates to methane. In Germany, it is currently predominantly corn that is fermented in biogas plants. However, because this promotes monoculture and means that significant areas of land can no longer be used to grow food crops, an on-going storm of criticism has resulted, not just in countries such as Mexico, but also in Germany. Alternatives such as domestic meadow grass clippings are therefore becoming more interesting. "There are currently various problems associated with the process of microbial conversion of grass to methane, but these will undoubtedly be overcome once we develop suitable techniques and use the correct microorganisms", predicts Professor Helmut König. The biogas research at the JGU Institute of Microbiology and Wine Research is being sponsored by the Rhineland-Palatinate Trust for Innovation and the Agency for Renewable Resources (Fachagentur Nachwachsende Rohstoffe, FNR), founded in 1993 by the German Federal Ministry of Food, Agriculture, and Consumer Protection.