Phosphorus-assisted biomass thermal conversion: reducing carbon loss and improving biochar stability

Area of Science:

• Biomass conversion
• Soil science
• Environmental chemistry

Background:

• Biochar production often results in over 50% carbon loss, questioning its efficacy for carbon sequestration.
• Biochar stability in soil is crucial for long-term carbon storage but can be compromised by various reactions.

Purpose of the Study:

• To investigate the use of phosphorus-bearing materials as additives to wheat straw for biochar production.
• To alleviate carbon loss during pyrolysis and enhance biochar-C stabilization.

Main Methods:

• Wheat straw was pyrolyzed at 500°C with three phosphorus additives: phosphoric acid (H3PO4), phosphate rock tailing (PRT), and triple superphosphate (TSP).
• Biochar yield, carbon loss, thermal stability, oxidative stability, and microbial mineralization were analyzed.

Main Results:

• Additives increased biochar yield from 31.7% to 46.9%-56.9% and reduced carbon loss from 51.7% to 35.5%-47.7%.
• Modified biochars showed enhanced oxidative stability and significantly reduced microbial mineralization (up to 67.8% less CO2 emission with TSP-BC).
• Additives did not affect thermal stability but likely enhanced stability through meta-phosphate or C-O-PO3 formation.

Conclusions:

• Pre-treating biomass with phosphorus-bearing materials is an effective strategy to reduce carbon loss during pyrolysis.
• This method enhances biochar stabilization, improving its potential as a carbon sequestration strategy.
• Phosphorus modification offers a novel approach to designing biochar for increased carbon sequestration capacity.