generate electricity and biochar with additional biomass, increase the yield of the biogas plant and produce peat substitutes
As a rule, biogas plants are poor at utilizing woody, hard-fibered and also protein-rich biomasses. NaWaRo plants in particular are therefore dependent on a basic supply of e.g. corn. Other biomasses such as grass cuttings or grasses can only be added in small quantities.
The digestate produced at the end of the biogas process is given away free of charge or at low proceeds and has a limited fertilizing effect on the cultivated area.
The biogas plant operator installs an autarkize plant next to his digester. In this plant, he can utilize additional materials such as wood residues, green waste, or grain residues. The resulting pyrolysis gas is fed directly into the fermenter of the biogas plant and converted into electricity via the biogas plant's CHP unit. The additionally generated electricity is remunerated according to the EEG for biomass plants (currently approx. 12 ct.).
The plant operator mixes the biochar produced by the autarkize plant with input substrate of the biogas plant and feeds this mixture into the digester. The exceptionally porous structure of the biochar and an increase in the carbon content of the digester result in an increase in bacterial growth and thus an increase in methane yield of up to 35%. This increased microbiology and the better C-N ratio then allow the plant operator to additionally use higher protein biomasses such as grass.
In the course of the biogas process, biochar binds nutrients such as nitrogen and phosphorus and is colonized by valuable microorganisms. At the end of the biogas process, the fermentation substrate is pressed off and the plant operator receives a mixture of fibrous fermentation residues plus charged and microbiologically activated biochar in the solid phase. This new substrate is not only an excellent fertilizer, but can also be marketed as a peat substitute. The clever combination of autarkize pyrolysis and biogas plant can thus increase yield and performance, enable new input materials and generate a high-quality peat substitute product.
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pyrolysis gas production and utilization in the fermenter
The unique autarkize process enables the production of an energy-rich pyrolysis gas from a wide variety of carbon-rich biomasses. Since the gas has a similar calorific value and properties as biogas, it can be mixed with biogas without any problems and utilized in the CHP unit of the biogas plant. The costs for an additional CHP unit are thus avoided.
The pyrolysis gas essentially consists of methane, hydrogen, carbon monoxide and carbon dioxide. When mixed with the biogas in the digester, it dilutes the ammonia regularly present there. Since too much ammonia inhibits microbiology, diluting ammonia conversely leads to better methane yield.
In total, the operator of a biogas plant receives more usable gas through the pyrolysis gas and also through a higher methane yield.
effect of biochar in the fermenter
Biochar has a very fine, porous structure. On one cubic centimeter of biochar combines 200-500 square meters of internal surfaces. On the one hand, this structure enables the binding of nutrients such as nitrogen or phosphorus and, on the other hand, it is a perfect settlement area for microorganisms.
In the fermenter, these properties lead to a binding of ammonium ions (and thus to a shift in the C-N ratio) and to a significant increase in the number of microorganisms. By settling at the biochar , these microorganisms are also more robust against disturbances balance, e.g. by too high salt concentrations.
This significantly increased and more robust microbiology as well as a better C-N ratio lead to a noticeable increase in methane yield. Studies show up to 35% higher efficiency with appropriate mixing ratios of biochar. Until now, these mixing ratios could not be achieved in practice in most biogas plants, as biochar was often too expensive to purchase. Since biogas plant operators can now produce their own biochar, even larger blending ratios are not a problem.
Biochar remains stable in the fermenter and is not degraded. It leaves the fermenter together with the fermentation residues. Advantageously, it is now immediately charged with nutrients and colonized with microorganisms and can be used directly in agriculture or horticulture.
use the produced biochar yourself or market it as a soil conditioner and fertilizer
Biochar produced in the process meets the high standards for use in agriculture, viticulture and fruit growing, as well as in horticulture and landscaping. In addition, the biochar in this process is discharged together with the digestate from the biogas plant and the digestate is pressed off. The separated solid digestate is now a mixture of hard plant fibers and activated biochar charged with microorganisms. This new substrate has excellent properties and is a peat substitute. This opens up a wide range of possibilities for biogas plant operators.
Operators of biogas plants can spread the high-quality substrate on their land as a depot fertilizer and soil conditioner to build up humus. Peat substitute substrate that is not used by the company itself can easily be resold to other farms, private individuals or larger substrate manufacturers and soil plants.
sale of CDR credits
The biochar from autarkize plants is not only a valuable soil conditioner but also a permanent carbon sink. Plants take CO2 from the atmosphere as they grow and use the carbon to build their cells and structures. Normally, this carbon sequestered in the plant is turned back into CO2 by rotting or burning. However, the autarkize process converts a larger portion of the carbon into a stable biochar . If this carbon is then introduced into soils, for example, it can hardly be decomposed and the CO2 once bound remains permanently removed from the atmosphere.
Each autarkize plant removes several thousand tons of CO2 from the atmosphere every year. For this immensely important contribution to climate protection, producers and users of autarkize biochar can obtain certificates. The so-called Carbon Dioxide Removal (CDR) credits are issued in quality-assured processes and are purchased by companies and private individuals, e.g. on international stock exchanges.
The CDR certificates not only indicate what an important contribution to climate protection farmers and biogas plant operators can make. They are also a good, additional revenue stream and offer companies and private individuals the opportunity to offset their partially unavoidable greenhouse gas emissions locally in domestic cultivation areas.
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