Green cascade - high load fermentation

The anaerobic microorganisms, which degrade the substrates in biogas plants, multiply comparatively slowly compared to the aerobic microorganisms due to their metabolism. The retention of organisms is therefore particularly important for the rapid and efficient degradation of biomass. During the operation of continuous stirred tank reactors in conventional biogas plants, bacteria are continuously removed from the system with the fermentation residue. How long the substrate remains in the plant is therefore determined by the rate at which the bacteria multiply. If the residence time is too short, the organisms are washed out and biogas production ends.

With more bacteria to better results

The use of a reactor that keeps the microorganisms in the system can increase the bacterial density in the reactor and thus the rate of degradation. The retention of the organisms can, for example, take place through the formation of granulates and the retention of the granulates, as in the upflow anaerobic sludge blanket (UASB) in industrial wastewater technology. In the past, the anaerobic treatment of textile waste water has already been investigated at Münster University of Applied Sciences. These experiments showed how waste water can be successfully degraded after a residence time of five instead of 40 days.

The development of an equivalent process for the degradation of agricultural residues with a high water content can make the energy recovery of these substances immensely more efficient. Technically, the process in biogas technology would represent a new stage in the development of biogas plants.

A new high-performance reactor for biogas plants is under construction

In this research project, a novel biogas reactor for the fermentation of manure and other liquid residues, such as press waters, is being developed and investigated. This is a high-performance reactor with a reactor design that clearly sets itself apart from agricultural biogas plants. These reactors achieve considerably higher loads and thus shorter residence times, smaller reactor volumes and lower investment and operating costs. In this way, gas yields can also be increased in agriculture and a more intensive, faster degradation of organic matter can be achieved.

However, these high-load reactors can only be fed with substrates that are largely liquid and low in solids. They are therefore particularly suitable for low-viscosity farm manure, press water and filtrates from the separation of farm manure. These in particular accumulate in large quantities and can thus be used to generate energy cost-effectively with an efficient reactor concept. In addition, the decomposition of the organic matter contained after energetic use enables a more effective use of important, non-degraded nutrients, such as nitrogen.

Sustainable, ecological and at the same time economical

We are currently carrying out basic experiments in a semi-industrial test reactor, for example with a so-called fixed-bed reactor with ceramic packed bodies. Here, the framework conditions for the use of liquid substrates in a high-load system and comparative reaction concepts are developed and optimization potentials are identified. First results point to a significant increase in efficiency through the novel reactor model.

The experiences and results from the planned test series prepare a subsequent use in a large-scale biogas plant. The focus of the project is on the use of biogenic residual material flows in order to guarantee a sustainable, ecological and at the same time economical operation of the new high-load biogas plant concept.