Scope of the project

The aim of PyroD is to develop innovative technology to convert anaerobic digestion residue into biochar and activated carbon cost-effectively. The application of PYROD technology in biogas units will reduce the improvement additives used during the anaerobic process and contribute to the purification of biogas from H2S making the whole process more economical and environmentally friendly. Additional economic benefits will arise for the biogas units by making the products available as soil improvers.

Various problems arising from the overall management of the anaerobic digestion residue mainly concern (1) the drying required to have a reduced volume, (2) its unstable composition and quality but also (3) the management and transport of large quantities with a low percentage of solids for disposal and a long radius from the unit. Regarding the drying of the digested residue, the energy needed to reduce the moisture to a percentage lower than 10-15% is covered by the additional thermal energy produced during anaerobic digestion, making the management of digestate through pyrolysis to produce biochar and activated carbon an economically and environmentally feasible alternative. These high-added-value materials present a large specific surface area and therefore function as adsorbents from both gas and liquid phases, while additionally the biochar is used as a soil improver and can be an independent commercially exploitable product.

Research has been carried out into all the applications and uses of biochar and activated carbon that can be produced from the solid-digested residue of anaerobic digestion. Until today, no comprehensive management strategy has been proposed that combines the initial reactor feed – the composition of digested residue – an optimal product of either biochar or activated carbon – optimal product application based on cost and environmental benefits. Summarizing, the purpose of the approved project is to utilize the produced digested residue to produce high-added-value products, such as biochar and activated carbon, targeting three applications: their reuse into the anaerobic digestion unit to operate as “stabilizers” of the process, their use as filters for the capture of the produced H2S and their commercial use as soil improvers or adsorbents respectively.

A major problem for biogas plants is the management of huge amounts of digestate residue. It should be noted that per ton of dry matter entering the anaerobic digestion plants approximately 70% remains in the process residue which amounts to 0.7 tons, while the rest is transformed into biogas. The solid residue managed by a biogas plant of 1 MWe (such as the project partner BIOGAS LAGADA S.A.) after anaerobic digestion amounts to ~22 tons per 100 tons of dry biomass