Novel high rate system for biogas production from energy crops

Up-flow leach-bed process: a two-phase two-stage continuous process

In order to eliminate the disadvantages of conventional systems for the fermentation of energy crops, a novel continuous up-flow leach-bed (ULB) process was developed at the Leibniz Institute for Agricultural Engineering Potsdam-Bornim.

Key component of the new two-stage two-phase ULB process is a continuously operated anaerobic ULB reactor. Plant raw material is continuously fed to the reactor bottom and, after fermentation, removed from the top as solid residue (Figure).

Two-stage process: Up-flow anaerobic leach-bed reactor (right) with leachate circulation and high rate anaerobic reactor (left)

Gas bubbles generated by bacteria adhere to plant particles and thus, naturally induce flotation like in common digesters. Due to missing agitation inside the leach bed a liquid phase is formed. This leachate circulates upwards through the leach-bed reactor and downwards through a high rate anaerobic digester with immobilised bacteria. Volatile fatty acids are leached from the solids and efficiently converted to biogas in the high rate reactor. Excess bacteria are transferred to the ULB reactor enhancing degradation of the solids as well. As a result, this reactor combination allows higher productivity and stability as well as a simplified and precise process control.
The risk of overloading is practically eliminated.
 

The system