Hemp hurd boosts carbon storage and environmental safety in biochar

This research paper focuses on improving biochar production from municipal sewage sludge through co-pyrolysis with agricultural residues—specifically oak bark and hemp hurd. Rather than investigating cannabis plant properties or effects, the study examines how combining different plant materials during a heating process (pyrolysis) can create more stable biochar that better stores carbon and safely traps heavy metals. The researchers found that hemp hurd, a fibrous byproduct of hemp production, performs exceptionally well when mixed with sewage sludge at a 25:75 ratio and heated to 700°C, producing biochar with superior carbon stability and environmental safety profiles.

The key innovation involves understanding how different feedstock compositions influence the final biochar properties. Hemp hurd's high cellulose content led to better pore development and carbon stability, while oak bark's higher lignin and mineral content promoted stronger heavy metal immobilization. The winning formula—MSS:HH (25:75) at 700°C—achieved the highest long-term carbon storage (0.62 t C/t biochar) and equivalent CO2 sequestration of 2.3 tonnes per tonne of biochar, while simultaneously reducing toxic zinc levels by 87% compared to sewage sludge biochar alone.

This work has significant environmental implications for waste management and carbon sequestration strategies. By finding optimal combinations of agricultural and waste feedstocks, researchers demonstrated that strategic material selection can solve dual environmental challenges—properly storing carbon to combat climate change while safely containing heavy metals that pose ecological risks. The research validates hemp hurd, an underutilized byproduct of hemp agriculture, as a valuable resource for circular economy applications beyond cannabinoid production.