What is biogas technology

Bioeconomy BW

In addition to solar, water and wind energy, biogas is a regenerative energy source that helps save fossil fuels. The approximately 7,100 biogas plants in Germany, of which 796 (as of 2011) are in Baden-Württemberg, accounted for 11 percent of electricity from renewable energies in 2010. The high-energy methane, the main component of biogas, is created during the anaerobic breakdown of organic substances by bacteria and drives systems that generate electricity and heat. However, optimal generation methods have not yet been achieved. Current research deals, among other things, with prokaryotes who metabolize their metabolism with amounts of energy at the lower limit of viability.

Biogas results from the natural breakdown of organic substances by bacteria. It can be obtained by recycling waste or from plants. Possible starting products are, for example, organic waste, meat waste, sewage sludge, liquid manure, manure and energy crops. The main components of biogas are methane with an average of 60 percent, carbon dioxide with an average of 35 percent and up to 10 percent water vapor. However, only methane can be used to generate energy. However, the values ​​are subject to large fluctuations depending on the source material. The high proportion of methane makes biogas a very energy-rich fuel.

In recent years, Germany, the world market leader in biogas technology, has created 25 bioenergy regions, two of which are in Baden-Württemberg. They have set themselves the goal of generating as much electricity and heat as possible from renewable energies and are home to several bioenergy villages. The 32 in Baden-Württemberg, that is more than a third of all bioenergy villages in Germany, get the majority of their energy from environmentally friendly systems such as bioreactors. Solar and wind energy are also part of the repertoire, but unlike biogas, they are subject to weather-related fluctuations. Biogas, on the other hand, is always available, can be stored and thus compensate for bottlenecks. In addition, biomass plants can be flexibly regulated and adapted to the relationship between energy demand and the availability of solar and wind energy. After the fermentation of the biomass, the remaining digestate can be applied to fields for fertilization.

Bacteria as little helpers

The microbial production of biogas has a lot of potential that has not yet been exhausted. The fermentation process still carries the risk of being brought to a standstill due to over-acidification. The aim of today's research and development is to increase production efficiency. Important helpers in the production of biogas are bacteria, which break down organic substances into their components in oxygen-free containers. They produce acids and gases such as acetic acid, hydrogen, carbon dioxide and finally methane in several steps. The absence of oxygen in the biogas reactors is of considerable importance because this is the only way for microorganisms to release the high-energy methane. In an oxygen-containing atmosphere, the more effective aerobic metabolism would use up most of the energy instead of letting it escape unused in methane form.

In order to optimize methane gas production, bacteria are therefore in the foreground of current research. For example, a research project at the University of Konstanz deals with the viability of prokaryotes in deep sediment layers. In the oxygen-free environment, they have to get by with amounts of energy at the lower limit of viability, which are not even sufficient to form the universal biological energy carrier adenosine triphosphate (ATP). Because the microorganisms need this in order to be able to operate their metabolism, they form cooperations and share the energy.

Other research at Johannes Gutenberg University in Mainz focuses on lignocellulose-degrading intestinal microbiota of termites. They are responsible for around 17 percent of global methane production, which makes up 100 million tons. The research thus addresses the problem of the decomposition of cellulose in the biogas reactor. Although the diverse communities of microorganisms can break down almost all substances, there are still difficulties here in particular. Due to the ability to use harvest waste and grasses, biomass plants have become much more attractive in the last two years.

Coupling of power and heat energy

Since the simultaneous generation of electricity and heat is most productive, biogas-powered combined heat and power plants are the most common in Germany. In these, the waste heat generated - in contrast to conventional power plants - does not remain unused, but instead heats swimming pools as well as residential and greenhouses, for example. The heat remaining after the generation of electricity is usually bound in water, which feeds heating systems. The electricity itself is generated by a generator driven by an internal combustion engine.

Resource-saving processing in focus

Biogas can not only drive specially built power plants, it can also be fed into existing natural gas networks, which is particularly attractive when there is a surplus. In order to guarantee natural gas quality, the biogas must be processed, but this step could be omitted in the future thanks to more efficient production methods. Researchers at the University of Hohenheim are currently developing a new process for producing biogas with 40 percent cost savings. To do this, they use the pressure resistance of the bacteria to prevent laborious reprocessing. The high pressure keeps the biogas pure during production, which means that it can be fed directly into natural gas networks.

At the moment, however, the use of biogas still requires complex processing. Not only to operate motor vehicles or to feed it into natural gas networks, but also for the conventional operation of combined heat and power plants. To protect against corrosion, the water vapor and hydrogen sulfide are first removed from the biogas. For further processing to natural gas quality, the separation of the carbon dioxide is also necessary. In this way, a methane content of almost 100 percent can be achieved. As a result of the different quality requirements of the German natural gas networks, additional substances such as air or liquid gas must be added to the biogas, depending on the requirements.

Corn deserts instead of biodiversity - new law aims to limit damage

In addition to the many advantages of biogas, government subsidies have created false incentives and promoted monocultures. The demand for land for growing energy crops, mainly maize, rose sharply. As a result, the lease costs for agricultural land skyrocketed. Furthermore, the increased cultivation of energy crops instead of food crops is questionable. The food prices have already risen due to the reduced supply. In addition, the increasing import of organic goods from abroad attracts higher CO due to transport2Emissions after themselves. Apart from that, the monocultures affect biodiversity.

In order to counteract the large-scale cultivation and the associated problems, the federal government recently decided to revise the Renewable Energy Sources Act (EEG), which also stipulates the promotion of biomass. The new regulation, which has been in force since the beginning of 2012, limits the use of grain to 60 percent, favors previously largely unused manure and strengthens smaller plants. Although the approaches are going in the right direction, according to widespread expert opinion, implementation has so far failed. Too many blunders in the rapid revision of the law in order to drive the energy transition forward, experts say, the attractiveness of biogas is dwindling. For example, the specification of 60 percent heat use for small systems is problematic, whereas coal-fired power plants do not require heat use. The Biogasrat e.V. association is also pushing for reasonable remuneration before customers return to more attractively funded fossil fuels.