Qualitative Assessment of Hazardous Gas Emissions from Sewage Sludge-Derived Biochar

Approximately 10 million megagrams of sewage sludge is produced each year in the European Union alone. To date, options to utilize sewage sludge are limited. Local regulations and sludge characteristics strictly determine waste management options. Thermal disposal methods are recommended for highly contaminated sludge. Pyrolyzed sewage sludge generates biochar that can be used as a value-added agricultural product or as an alternative fuel. The biochar production itself carries the risk of emitting harmful compounds. Unfortunately, these important safety considerations are rarely addressed in the literature. This research investigates the mechanistic effects of the storage headspace-to-biochar volume ratio and stored biochar headspace ventilation on hazardous gas emissions. Five hazardous organic compounds were emitted by biochar. However, based on this initial proof-of-the-concept research, we could not derive conclusive trends for the effects of the headspace-to-biochar volume ratio or air exchanges in the biochar headspace. Further research, which is broader in scope (feedstock type, pyrolysis conditions), should be carried out. Nevertheless, caution should be exercised when designing biochar storage, aiming to lower the risk of occupational exposure to hazardous gas emissions. Monitoring air pollutants, tracking the highest permissible concentrations and workers’ exposure, and using personal protective equipment are recommended.