Biochar enables anaerobic digestion of aqueous phase from intermediate pyrolysis of biomass

• Aqueous fraction from pyrolysis inhibits anaerobic digestion.
• Inhibition is revealed by a volatile fatty acids accumulation and long lag phase.
• Addition of biochar in the system decreases inhibition and doubles yield.
• Semi-continuous system pre-loaded with biochar shows acceptable performances.

Intermediate pyrolysis produces a two-phase liquid whose aqueous phase is characterized by low heating value and high water content (aqueous pyrolysis liquid, APL). Anaerobic digestion can be the straightest way to produce a fuel (methane) from this material. Batch tests showed poor performance in anaerobic digestion of APL, which underlined the inhibition of biological process. Nutrient supplementation was ineffective, whereas biochar addition increased yield of methane (60 ± 15% of theoretical) with respect to pure APL (34 ± 6% of theoretical) and improved the reaction rate. On the basis of batch results, a semi-continuous biomethanation test was set up, by adding an increasingly amount of APL in a 30 ml reactor preloaded with biochar (0.8 g ml−1). With a daily input of 5 g d−1 l−1 of APL (corresponding to overall amount of 0.1 kg l−1 added before the end of the study) the yield of methane was 65 ± 5% of the theoretical.

Figure optionsDownload as PowerPoint slide