with ultrasonic treatment

The unique combination of the biomass recirculation filter with ultrasonic treatment enables fibres to be broken down that have not been digested and shredded yet. This further increases the gas yield.

The problem & the solution

Between 8 % and 15 % of the digestate produced are fibres that were not digested or broken down during separation. Standard separation techniques are not capable of breaking down the fibres completely.

The smart integration of a biomass recirculation filter in combination with ultrasonic treatment into the existing system of the biogas plant allows the fibres to be broken down more effectively, releasing the organic matter and thereby maximising the gas yield. This new and innovative process has already been tested successfully in practice.

The process

The biomass recirculation filter is based on our tried and tested separation technology. It was developed further so that the new technology of the Sepogant Direkt press screw separator provides both separation and liquid thickening.

The WaveBox ultrasonic treatment has a cascaded design. This cascade system with sonotrodes maximises material break-down because the ultrasonic waves cause air bubbles to form and implode in the substrate. This cavitation results in a higher proportion of organic dry matter being able to release gas due to the breaking down of fibres.

Thanks to the re-feeding method less feedstock is required. As a result, the complete gas potential of the fed substrates can be opened up.

This also makes agitators and associated stirring times in the digestate storage redundant since the material inside the tanks is homogeneous and does not separate again. Furthermore, there is reduced feedstock volume during feeding, resulting in less stress (energy and wear) on the feeding technology.

A standard biogas plant breaks down the organic matter with 75 % efficiency. This percentage increases to around 90 % after a biomass recirculation filter with ultrasonic technology has been installed. This increases the biogas yield to up to 20 % from the original feedstock fed to the biogas plant.

Design example

  • digestion approx. 40m³/d
  • mix of renewable substrates with grass/WPS content
  • residence time: 60 days
  • room load approx. 8 kg oDM/m³*dconclusion
  • WaveBox 4 sonotrodes approx. 3.5 kW
  • increase of biogas yield by approx. 14 %

Comment: The samples were taken from the Isny biogas plant (Baden-Württemberg) – May 2021.

Technological aspects of the combination

Efficiency increase of the ultrasonic system

  • by treating the thickened organic matter
  • arrangement of the sonotrodes – max immersion depth
  • optimal gas discharge
  • no deposits


Effects of ultrasonic treatment

  • increasing the efficiency of the WaveBox
  • significant reduction of the dry matter content in the overall system, resulting in lower operating costs
  • savings due to increased break-down of organic matter

Ecological aspects of the combination

  • avoiding emissions from the separation system
  • increasing the gas production potential of the feedstock
  • reduction of the residual gas potential in the digestate
  • normal biogas plant: 75 % organic matter break-down
  • biogas plant with Sepogant Direkt and WaveBox: 90 % organic matter break-down
  • up to 20 % more biogas from the original feedstock

In a nutshell

The combination of the biomass recirculation filter, the retention of fibres not completely digested and ultrasonic treatment of the biomass is currently the only functioning method to get the most out of your feedstock. No gas potential is wasted since energy-rich feedstock is not left unused – regardless of the residence times.

Feedstock volume is reduced when feeding the system which means that the feeding equipment is exposed to less stress (energy and wear).

The effective breaking down of the feedstock fibres results in gas yield increases of up to 20 %.

Need more info?

Then you can download technical information here, or just give us a call!