Industrial symbiosis of anaerobic digestion and pyrolysis: Performances and agricultural interest of coupling biochar and liquid digestate

The sustainability of the anaerobic digestion industry is closely related to proper digestate disposal. In this study, an innovative cascading biorefinery concept coupling anaerobic digestion and subsequent pyrolysis of the digestate was investigated with the aim of enhancing the energy recovery and improving the fertilizers from organic wastes. Continuous anaerobic co-digestion of quinoa residues with wastewater sludge (45/55% VS) exhibited good stability and a methane production of 219 NL CH4/kg VS. Subsequent pyrolysis of the solid digestate was carried out (at 500 degrees C, 1 h, and 10 degrees C/min), resulting in a products distribution of 40 wt% biochar, 36 wt% bio-oil, and 24 wt% syngas. The organic phase (OP) of bio-oil and syngas exhibited higher and lower heating values of 34 MJ/kg and 11.8 MJ/Nm(3), respectively. The potential synergy of coupling biochar with liquid digestate (LD) for agronomic purposes was investigated. Interestingly, coupling LD (at 170 kg N/ha) with biochar (at 25 tons/ha) improved the growth of tomato plants up to 25% compared to LD application alone. In parallel, co-application of biochar with LD significantly increased the ammonia volatilization (by 64%) compared to LD application alone, although their simultaneous use did not impact the C and N mineralization rates. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study explored an innovative cascading biorefinery concept that combines anaerobic digestion with pyrolysis of digestate to improve energy recovery and fertilizer quality from organic waste. Anaerobic co-digestion of quinoa residues with wastewater sludge demonstrated stability and high methane production. Pyrolysis of solid digestate yielded biochar, bio-oil, and syngas, with potential applications in agronomy. Coupling biochar with liquid digestate enhanced tomato plant growth but also increased ammonia volatilization.