In the comprehensive standard work on bioenergy "Energy from biomass: basics, techniques and processes" (Kaltschmitt, Hartmann, Hofbauer) will be presented as proven fermenter materials stainless steel and concrete. For special solutions, however, this book already refers to plastic and wood as rare building materials for biogas fermenters. So far, however, I have only seen the classic fermenters made of stainless steel and concrete in practical use. On the first Biogas World I am now on a wooden fermenter of that Plant manufacturer Biogas-Ost became aware of the Thuringian housing and would like to briefly introduce this climate-friendly and economically interesting alternative.
Steel, concrete and wood - sustainability through fermentation materials
"Whoever has the choice is spoiled for choice", the saying goes. In fact, it can be very difficult to choose the right fermenter material for a biogas plant.
I find this freedom particularly interesting when it comes to sustainability. The term “sustainability” is often used with a strong focus on ecological sustainability, but should also take into account the economic and social sustainability aspects of a project and product. This triad of sustainability can also play an important role when choosing a biogas fermenter.
The diversity of the existing fermenter materials influences the sustainability in the construction and operation of a biogas plant. The following parameters vary more or less obviously between the different types of fermenters:
- Material requirements for the fermenter
- Energy requirements for manufacturing the fermenter and building the biogas plant (CO2 emissions)
- Machine use in manufacturing and construction
- “Money requirement” (costs) of the fermenter
The advantages of concrete and steel in direct comparison with a wood fermenter cannot be found in these 4 points. In return, these robust materials underline the longevity of the fermenter and only make their stability possible the construction of larger biogas plants! Therefore, planners of biogas plants are happy to use these reliable fermenter types made of concrete and steel.
An advantage of wood fermenters can therefore be seen in the positive climate balance and the comparatively low need for building materials and energy with the same biogas output.
Lower installation costs thanks to wood fermenters
A fermenter made of wood not only looks good and supports climate protection, it also brings with it other advantages that are most interesting for biogas plant operators.
After all, what does it mean when the energy requirement for processing wood is lower (compared to concrete and stainless steel) and the use of machines is less energy? Less manpower and less use of machines and energy also mean lower manufacturing and product costs. Thus the construction costs are lower and the construction time is also shorter compared to concrete.
The disadvantage of wood fermenters is of course the comparatively little operating experience with this promising material. The purchase decision for a wood fermenter therefore also requires a certain portion of pioneering spirit and a willingness to take risks. For this, the plant operator may be one of the first to take advantage of a previously unused market opportunity.
How much you can save with a specific biogas plant and up to what size a wood fermenter can also meet the necessary stability criteria, ask one of the providers of wood fermenters - for example, at Biogas East. Only a direct comparison of two otherwise equivalent offers can provide information as to whether the decision for the wood fermenter is worthwhile.
As a special treat and at the same time the reason why the wood fermenter celebrated its first success elsewhere on the planet, there is also the earthquake protection of a wood fermenter. Admittedly, earthquakes are not the main concern of European biogas plant operators.
Advantages of wood fermenters for mini biogas plants
Most biogas actors are familiar with the current debate about the Mini biogas plants according to EEG 2012.
- "The systems are not economical"
- "Mini biogas plants based on pure liquid manure are most likely to have a chance"
- "The almost identical administrative effort for mini biogas plants is problematic."
Ultimately, the criticism is rarely about the technological, but mostly about the economic feasibility of the mini-biogas plants. A mini biogas plant with 75 kW can quickly cost up to 500.000 euros before commissioning. Getting this investment back in an acceptable period of time is not that easy for the small biogas plants with somewhat lower efficiency.
Especially for these small mini-biogas plants, the use of wood as a fermentation material can be an interesting alternative to achieve the profitability of the plant more quickly. I am convinced that the EEG amendment 2012, with the special support for mini-biogas plants, is also a special opportunity for wood fermenters!
The biogas plant in the Waimakariri District in New Zealand shown at the beginning of the article is a classic mini biogas plant with an electrical output of 50 kW. Even if the information provided by the operator there spoke in favor of the optics and earthquake protection for the selection of the wood fermenter, as a future operator of a mini-biogas plant I would also have an offer for a wood fermenter made. A non-binding conversation certainly doesn't hurt.
What do you think about the wood variant among the fermenters and the potential for mini-biogas plants?