Biochar in anaerobic digestion: investigation of biogas production potential enhancement with the addition of biochar

Anaerobic digestion is a valuable source of renewable energy in the combat against climate change. However, the anaerobic digestion process can be challenging to operate at optimal performance, due to disturbances that can occur. Biochar is considered to be a possible additive in the anaerobic digestion process, since earlier studies have shown that biochar can enhance the methane production. However, the results are non-conclusive, sometimes even showing a negative impact on the anaerobic digestion process. This thesis examines the effect of adding biochar to the anaerobic digestion process in a laboratory test setting. Two tests with biochar were tested with the AMPTS II methane potential testing system, and the methane production as well as BMP was examined. In the first test, two types of biochar were tested, one made from wastewater sludge mixed with wood residue obtained from a waste treatment facility in Helsinki region. The other was a commercially available biochar. The feedstock was a mixture of household organic waste and inoculum, obtained from a waste handling facility in Ostrobothnia. The amount of biochar added to the first test samples amounted to 5 gram fresh weight biochar per litre of feedstock. In the second test, wastewater sludge biochar mixed with wood was tested, with a variation in dosages ranging from 1.25 to 25 gram dry weight per litre (g/L). The first test with the AMPTS II did not show any statistically significant change in biogas production, while in the second test, a dosage of 6.25 g/L biochar increased the methane production by 4.3%. This is a good basis for further testing