Effluent Gas Flux Characterization during Pyrolysis of Chicken Manure

Pyrolysis is a viable option for the production of renewable energy and agricultural resources from diverted organic waste streams. This high temperature thermochemical process yields material with beneficial reuses, including bio-oil and biochar. Gaseous forms of carbon (C) and nitrogen (N) are also emitted during pyrolysis. The effluent mass emission rates from pyrolysis are not well characterized, thus limiting proper evaluation of the environmental benefits or costs of pyrolysis products. We present the first comprehensive suite of C and N mass emission rate measurements of a biomass pyrolysis process that uses chicken manure as the feedstock to produce biochar and bio-oil. Two chicken manure fast pyrolysis experiments were conducted at controlled temperature ranges of 450-485 °C and 550-585 °C. Mass emission rates of nitrous oxide (N₂O), nitric oxide (NO), carbon monoxide (CO), carbon dioxide (CO₂), methane (CH₄), and ammonia (NH₃) were measured using trace gas analyzers. Based on the system mass balance, 23-25% of the total mass of the manure feedstock was emitted as gas, while 52-55% and 23% were converted to bio-oil and biochar, respectively. CO₂ and NH₃ were the dominant gaseous species by mass, accounting for 58-65% of total C mass emitted and 99% of total reactive N mass emitted, respectively. Temperature variations within the two set of temperature ranges had a perfunctory effect on bio-oil production and gaseous emissions, but the higher temperature range process produced more bio-oil and slightly less emissions. However, a larger effect on the relative amounts of CO and CO₂ produced were observed between the different temperature regimes. These results have important implications for greenhouse gas and reactive N life cycle assessments of biochar and bio-oil.