|
|
|
APECS focuses on the efficient use of organic residues for a sustainable production of
biogas as a valuable energy source and biochar for the improvement of soil properties.
Achieving this goal is based on an intelligent combination of bioconversion
and thermo-chemical carbonization into an innovative and productive hybrid technology.
|
|
Concept (Schematic: Svart, ATB)
|
For this purpose several innovative and patent-pending process solutions are used in
conjunction with modern chemical and microbiological analysis methods. APECS considers
the full-extent value chain – from field to field – and analyzes the climatic and
economic effects on this scale. The result is a new innovative technology which allows
producers as well as users to open up new attractive fields of application.
Biogas
APECS develops a solution for the combined production of biogas and biochar. Compared
to the overall impact of the separate processes this combined technology promises both
economic and ecological benefits. While conventional biogas reactors require high energetic
efforts to prevent the floatinon of solids, the novel upflow anaerobic solid-state UASS process
developed at the Leibniz Institute of Agricultural Engineering Bornim e.V. (ATB) uses this
phenomenon deliberately to increase productivity and energy efficiency.
Conventional biogas plants were originally designed for digestion of liquid
biomass and are therefore not optimized for treating solid raw materials. As
Solids tend to form a floating layer inside the reactor intensive stirring is
required. According to a survey of the Agency for Renewable Resources (FNR),
the energy consumption for stirring can be as high as 10% of the produced
energy. Moreover, an intensive mixing of the feedstock can have negative effects
on the digestion process as shear forces can destroy syntrophic structures.
Discharge of microbial biomass along with the digestate reduces the overall
performance. Consequently, the loading rate of completely mixed reactors digesting
solid materials is not higher than 6 kg of volatile solids (VS) per cubic meter
reactor volume and day. Higher loading rates inhibit the digestion through an
accumulation of volatile fatty acids.
|
Upstream solid-state (UASS) digester
(photo: Mumme, ATB)
|
The upflow anaerobic solid-state UASS technology allows to process fiber-rich
biomass such as straw and green waste. It can be fed continuously from the
bottom. After 1 to 2 weeks the solid digestate is removed from the top.
Stirring is not required. However, in order achieve a high reactor performance
a circulation of the liquid phase is needed. Additionally, the liquid phase can be
treated in a separate high-performance methane reactor. This helps to effectively
remove volatile fatty that formed in the UASS reactor and simultaneously supports
the accumulation of valuable microorganisms. As a result, the degradation rates
are 2-4 times higher and allow methane yields of up to 380 L / kg VS for corn
silage and 200 L for wheat straw.
The advantages of the UASS technology in detail:
| -
|
suitable for raw and waste materials with higher fiber contents
|
| -
|
high degradation rates with reduced energy requirements
|
| -
|
high methane productivity and process stability
|
| -
|
simple options for ammonia removal
|
| -
|
simple and precise process control
|
Biochar
Another goal of APECS is to develop a biochar optimized for soil improvement.
Actually both positive and negative effects are observed in the application of
biochar on soils. Therefore it is important to investigate
|
Biochar from pyrolysis
(photo: Surup, ATB)
|
| a) |
what properties of biochar on soil are responsible for certain effects |
| b) |
how these properties can be optimized specifically during production |
| c) |
which treatment of biochar makes sense |
The soil effect of biochar is investigated both in the laboratory and in field trials.
The impact on plant growth, carbon stability and greenhouse gas
emissions are the center of attention.
Simulation software is used to assess the process integration
of the biological and thermochemical conversion and identify possible synergies.
Soil
Studies of the Amazonian Dark Earths, so called “terra preta” soils in the Amazon region, have
shown that humans have been deliberately creating them for centuries and charcoal played a
crucial role in their formation.
The stable carbon particles increase the water holding capacity and help to retain nutrients. They therefore
have a positive influence on the growth of plants and microorganisms. The result is a clear contrast
between extremely fertile “terra preta” adjacent to the otherwise extremely poor soils of this region
(“Ferralsol”).
|
Green house tests with biochar
from diverse production
methods (photo: Pielert, TU Berlin)
|
This raises the question whether similar soils can be cultivated outside of tropical regions. Climate
change, an ever-increasing demand for agricultural goods and globally threatened soil fertility increase
the pressure for action. The problem is mainly the loss of organic matter in soils that is crucial
for the availability of water and nutrients to the plants.
The coal-like materials produced from biomass promise a possible solution for this pressing issue.
These so-called biochars could, as in the “terra preta”, temporarily take over the function of soil organic
matter, until stable humus is formed.
|
|
