Nitrogen conservation by hardwood biochar during food waste digestate composting: pyrolytic temperature dictates microbial mechanisms

Abstract

Food waste digestate (FWD) composting is hindered by severe nitrogen loss, primarily through ammonia (NH₃) and nitrous oxide (N₂O) emissions. While biochar amendment is known to mitigate this loss, the optimal pyrolysis temperature to maximize conservation remains unclear. This study decouples the distinct influence of pyrolysis temperature (300, 400, and 800 °C) of hardwood biochar on nitrogen conservation by linking biochar properties to microbial community dynamics. A critical trade-off is revealed: 300 °C biochar maximized NH₃ reduction (39.2% vs. control, n = 2, p < 0.05) but was coincided with the enrichment of nirK/S-harboring denitrifiers (e.g., Luteimonas), posing a potential challenge from increased N₂O emissions. Conversely, 800 °C biochar achieved the greatest N₂O reduction (47.5% vs. control, n = 2, p < 0.05), an outcome consistent with suppressed microbial denitrification. Critically, biochar produced at 400 °C achieved an optimal balance, likely through enhanced NH₃ adsorption and the fostering of a microbial community correlated with lower N₂O emissions, which ultimately led to a 46.3% reduction in total nitrogen loss (vs. control, n = 2, p < 0.05), the highest performance among all treatments. This work guides the selection of biochar pyrolysis temperature toward targeted nitrogen conservation and sustainable FWD valorization.

Graphical Abstract

Keywords

Food waste digestate / Composting / Biochar / Nitrogen / Pyrolysis temperature

References

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Funding

Basic and Applied Basic Research Foundation of Guangdong Province(2024A1515110159)

Dongguan University of Technology(221110133)

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