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How is Biochar made? 

Biochar is made from renewable raw materials such as wood or vegetable residues (e.g. trimmings, leaves, or green waste). To produce Biochar, the biomass is burned within a modern pyrolysis plant with very little oxygen. This pyrolysis method allows all gases and vapours to be filtered out completely, making it 100% pollutant-free. This production process is often referred to as the carbonation of biomass. 

Biochar used for AD Plants 

In recent years, Biochar has built a strong reputation in the biogas sector, as it is known to significantly improve the biogas yield. 


An interesting fact: Biochar has a surface area of up to 300m2 per gram, which allows it to act like a sponge that can absorb up to five times its own weight! 

Biochar's porous structure and large surface area allow it to stabilise the biogas process by binding impurities. It also has an adsorption capacity for hydrophobic substances, which means that microorganisms can settle, and water and nutrients can be stored. Besides that, Biochar enables a more efficient breakdown of the substrates in the fermenter, and successfully reduces nutrient losses when added to the fermentation residue. 

Biochar sample

How Biochar can help reduce your Carbon Footprint 

When Biochar is employed in the anaerobic digestion process, a number of advantages arise for climate protection. When added to the fermentation residue, nutrient losses are prevented, and climate-damaging methane gas emissions are minimised. If the digestate is carbonated, it can be used to produce high-quality Biochar. The carbon contained in the digestate on the other hand will be bound long-term. This not only protects the environment but also significantly improves the efficiency of the gas production process.  

Biochar in Practice  

 Several international studies have, in recent years, measured a significant gas increase for anaerobic digestion plants utilising Biochar. It is said that the accumulation of methanogens and the increased growth area of the microbial functionality are supported, thus resulting in an increased yield. 

Recent results have found that the large surface area of the Biochar binds it to any inhibiting and interrupting substances, thereby stabilising the anaerobic digestion process. Additionally, the large proportion of mineral components in the Biochar ensures that microorganisms are supplied with micronutrients in the digester. Furthermore, the porous structure of the Biochar leads to faster degradation of the substances and metabolites as the microorganisms are better protected in the Biochar matrix. This results in better substrate utilisation in the main digester as well as noticeably higher exploitation of the fermentation residue potential. 

The published results for the methane increase for different users vary between 9-16% in the main digester and up to 24% in the storage tank. 

Biochar not only helped to increase the gas yield but also benefitted users with very high digester load or systems with very low space capacities. By building a greater surface area for the bacteria, Biochar improved the methane results and stabilised the entire biological process for these plants. 

Our Experience with Biochar

4CleanTech operates a 600kWel biogas plant in Somerset.

Much of our knowledge and experience comes from the mature biogas sector in Germany; Germany has in the region of 9,000 biogas sites compared to the UK with nearly 1,000. 

In 2018, we noticed a widespread and growing take-up of Biochar in the biogas process across the German sector, and after further research decided to trial Biochar in our plant. Throughout the year, the results were excellent. We recorded an overall methane increase of 10.5%.

In practical terms, we spent £13,640 on Biochar and the increased gas production meant that we could reduce our feedstock for the year by 1,100 tonnes. Given an average feedstock price of £32.50 per tonne, we achieved a gross saving of £35,750 and a net saving of £22,110. A return on capital employed (ROCE) of 162%. 

Whilst we continue to include Biochar day-to-day in our plant, our positive experiences have encouraged us to make certified Biochar, produced in Germany, available to other UK operators. Please contact us to discuss how Biochar might be incorporated into your plant and to get a price quote. 

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