PubMed · 2026-06-19
Researchers tested whether washing 'hydrochar' — a charcoal-like soil amendment made by pressure-cooking food waste — removes the toxic compounds that leach out when it's applied to soil. They found that most toxicity washes away quickly, and that the type of food waste matters: fruit-based hydrochars are least toxic, while vegetable- and grain-based ones release more harmful compounds.
The first wash produced the most toxic leachate; toxicity dropped rapidly with each subsequent washing, suggesting most harmful compounds are water-soluble and removable.
Fruit-derived hydrochars consistently produced the least toxic wash waters, while vegetable- and grain-derived hydrochars showed higher and more variable toxicity.
Lower hydrogen-to-carbon (H:C) ratios in the feedstock were the strongest predictor of reduced toxicity, outweighing processing temperature (200–250 °C) or residence time as factors.