Abstract
Biochar, produced through pyrolysis of lignocellulosic biomass, is attracting increasing interest as soil amendment thanks to its potential numerous benefits to agriculture, as well as its ability to sequester carbon in soil. Solid fraction of digestate from anaerobic digestion is a well-known N-rich substrate, most often composted in large and small agro-industrial plants. Co-composting biochar and digestate has the potential to synergistically increase the agronomic value of both components: however, it needs further process and on-field research. The present research work reports on the experimental tests on producing biochar and co-composting various biochar amounts with digestate from biomass anaerobic digestion (product here named COMBI). Biochar was produced by feeding wood chips from chestnut to an innovative oxidative reactor. In order to evaluate the quality of the products obtained by composting and co-composting, correlating this with the final biochar rate in the material, the net organic matter yield, the humified organic matter, the compliance with the European Compost Network Quality Assurance Scheme (ECN-QAS) limits for inorganic pollutants, and the product stabilization and sanitization indexes were investigated. The 11.2% w/w d.b. biochar rate in the initial blend (19.8% w/w d.b final concentration in the co-composted products) offered the best performances and is recommended for further investigation. Additional benefits from co-composting were also assessed, as the reduced dust load that favors safety and health during logistics and use.
Highlights
Sustainable production of biomethane is a key option to substitute conventional natural gas and decarbonize the energy system [1]: anaerobic digestion (AD) is the leading route to generate biogas, which can be further upgraded to biomethane by CH4 separation
CB3 showed the lowest humic acid (HA) value and intermediate fulvic acid (FA) value. These results suggest that the amount of biochar in the initial windrow does not allow a linear prediction of the HA and FA content, and that the CB2 windrow apparently maximized the synergistic effects of co-composting on the microbial humification processes
The control (CD) was prepared by composting solid digestate only with straw; CB2 blend was prepared considering a field application of 3 t ha−1, while CB1 and CB3 blends were prepared with a ± 30% w/w w.b. respect to the initial biochar content in CB2
Summary
Sustainable production of biomethane is a key option to substitute conventional natural gas and decarbonize the energy system [1]: anaerobic digestion (AD) is the leading route to generate biogas, which can be further upgraded to biomethane by CH4 separation. The AD process is a well-mature process, bringing environmental and social benefits at both local and global level [2, 3]: the main co-product of biomass anaerobic digestion is a sludge (digestate), which. Biochar is the solid product from lignocellulosic biomass pyrolysis, characterized by a high content of stable C, mostly produced through slow pyrolysis. Biochars from intermediate/ fast pyrolysis and gasification are often discussed in literature, even if these show different characteristics.
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