Evaluation of Sorbed Organics On Biochars and Potential Impacts.

A potential abatement strategy to increasing atmospheric levels of carbon dioxide (CO₂) is to sequester atmospheric CO₂ into a more stable form through the use of pyrolysis. Biomass materials are used to generate a more stable carbon form (biochar) that is returned to the soil sequestering atmospheric carbon into a slower cycling pool, resulting in alterations in plant growth/yield and microbial soil processes.  However, the mechanisms behind the “biochar effect” have not been fully elucidated.  In the present work, we have determined the sorbed volatile organic fingerprints for various parent materials and pyrolysis conditions, using headspace thermal desorption and solvent extraction techniques.  In general, higher pyrolysis temperatures lead to lower amounts of lighter molecular weight organic components being sorbed to the biochar.  However, this is not a universal conclusion and the sorbed organic compounds are highly variable across different pyrolysis units, despite similarity in production temperature, feedstock and residency times.  The total amount of sorbed organics is typically within the ppm range.  Higher pyrolysis temperatures typically favor higher molecular weight semi- and non-volatile organics (e.g. polyaromtic hydrocarbons) retention on the biochar.  These heavier organics could pose a concern for human health implications.  These sorbed volatiles could provide additional insight into the soil and plant system responses observed from biochar additions, particularly due to the lack of universal responses to biochar amendments.