Feasibility of anaerobic digestion as a treatment for the aqueous pyrolysis condensate (APC) of birch bark

Biooil produced via biomass pyrolysis includes an aqueous-acidic phase and a dense and rich organic phase. The aqueous phase has a low heating value and is considered a waste stream. In this study fractional condensation was employed to separate the liquid product of birch bark pyrolysis into an aqueous pyrolysis condensate (APC) and a dense biooil fraction. The APC contained high amounts (similar to 100 g/kg) of acidic acid (AA) and was investigated for anaerobic digestion (AD). The AA in the APC could be converted to biogas, however, it contained elevated concentrations of microbial inhibitors (24 g/kg total phenolics). The inhibiting effect could be mitigated by acclimatization of the microbial population, which in turn converted some of the additional organics. The production of methane further improved with the addition of biochar to adsorb some of the inhibitors. The results imply that a waste product can be converted into a potential energy carrier.