Waste timber pyrolysis in a medium-scale unit: Emission budgets and biochar quality

Area of Science:

• Environmental Science
• Chemical Engineering
• Soil Science

Background:

• Biochar production from organic waste offers a sustainable waste management solution.
• Emissions from medium- to large-scale pyrolysis units require thorough investigation.
• Valorization of waste timber into biochar can aid in contaminant stabilization.

Purpose of the Study:

• To assess the environmental sustainability of producing biochar from waste timber.
• To quantify gas, aerosol, heavy metal, and polycyclic aromatic hydrocarbon (PAH) emissions.
• To evaluate the quality and contaminant leaching of biochar derived from waste timber.

Main Methods:

• Pyrolysis of waste timber and clean wood/leaves in a medium-scale unit (Pyreg-500).
• Measurement of emission factors for CO, NMVOC, CH4, PM10, PIC, PAH-16, As, and NOx.
• Characterization of biochar quality, including contaminant levels and leaching.

Main Results:

• Emissions from waste timber pyrolysis were comparable to clean wood, with lower PM10, NMVOC, and PAH-16.
• Mean emission factors (g/kg biochar) for waste timber: CO=7±2, NMVOC=0.86±0.14, PM10=0.6±0.3, PAH-16=(2.0±0.2)·10⁻⁵.
• Waste timber biochar did not meet European Biochar Certificate standards due to high zinc and PAH levels, though leachable metals were <0.1%.

Conclusions:

• Pyrolysis of waste timber with after-combustion is a viable method for reducing emissions.
• Waste timber biochar requires further treatment or investigation before soil application due to contaminant levels.
• Limited use of waste timber biochar is recommended, excluding direct soil improvement or in situ remediation.