Research Paper – C. Margreiter et al. 2024

Boosting Biogas with Biochar:

A 7% Increase in Methane Yield

A recent study demonstrates adding biochar to biogas plants can significantly enhance methane (CH₄) yield, with certain types of biochar increasing production by up to 7.93%. The results were published in May 2024, in a peer-reviewed paper by C.Margreiter et al. from the Department of Microbiology at the University of Innsbruck.
This finding has profound implications for the efficiency and sustainability of biogas production, a renewable energy source gaining economic traction across Europe. The increased energy production from biogas in Europe, from 6,200 GWh in 2009 to 18,012 GWh in 2019, underscores its growing importance.
Practical Implications
This boost in methane yield translates directly into more energy generated from the same amount of organic waste, which is a substantial gain for any biogas plant. It is important to note that this does not mean every biogas plant will immediately see an almost 8% increase in methane yield. The effectiveness of biochar depends on various factors, including the type of biochar used and its concentration.
Biogas plants convert organic substrates, such as wastewater and sludge, into energy through anaerobic digestion (AD). During AD, microorganisms break down biodegradable material to produce biogas, primarily composed of CH₄ and carbon dioxide (CO2).
Experiment and Findings

In wastewater treatment, gasification residues (GR) and activated carbon (AC) are often added as a fourth purification stage to help remove heavy metals and pharmaceutical residues. However, when these materials enter the AD process through the sludge, their effects are not well understood. While previous studies have shown that adding char can have positive effects on AD, systematic studies with well-characterized chars are still lacking.

This study aimed to fill that gap by characterizing different types of chars in detail, testing them in various concentrations during AD, and investigating their impact on methane production. The chars used in this study included:

  • GR from a gasification plant with floating fixed bed technology
  • Carbon made by chemical impregnation with ZnCl2 from waste wood
  • Carbon produced by thermochemical activation with CO2 from GR
  • Commercial powdered AC

To characterize these chars, researchers used thermogravimetric analysis, physisorption, pH, and conductivity analysis. They then performed mesophilic AD batch tests with different concentrations (0.025, 0.05, 0.5, 1.0, 7.0, 14.0 gL−1) of all chars using digester sludge from a wastewater treatment plant over a period of 47 days. During these tests, they monitored volatile fatty acids (VFA) as well as biogas production and methane concentrations.


The results showed that char concentrations below 1.0 gL−1 did not significantly affect CH₄ or VFA production. Higher concentrations of GR and AC did however influence both CH₄ yield and the kinetics of the process. The effects varied depending on the production process and characteristics of the chars, with both positive and negative impacts on biogas yield and methane production observed.

This study provides the first systematic evaluation of char application in AD processes, offering better predictions of how different chars can be used and their effects on methane production.

Future Prospects

The study emphasizes the importance of characterizing key parameters of char materials used in anaerobic digestion. For example, the pH of the char is crucial, with a pH of at least 7 being recommended for optimal methane production.

Gasification residues emerged as the most promising additive for biogas plants. When added in concentrations above 1.0 gL− 1 they led to an average cumulative increase in methane yield of nearly 8%. The study also notes the need for further semi-continuous anaerobic digestion experiments to better understand the long-term impacts and benefits of char addition.


The findings from this research provide a clearer picture of how biochar can be effectively used to enhance biogas production. The systematic evaluation of different types of char and their specific properties offers valuable insights for optimizing anaerobic digestion processes. While the immediate gains in methane yield are significant, the broader implications for carbon efficiency and environmental sustainability make biochar a compelling addition to the renewable energy landscape.

As research continues, we may soon be able to calculate the total carbon balance, including the energy yield increase.

Read the full paper HERE