Biochar from Sericulture Residues: Feedstock Availability, Conversion Behaviour and Circular Utilisation Pathways in Mulberry–Silkworm Systems

Abstract

Sericulture couples a perennial woody crop with an intensive insect-rearing operation, and the resulting production system discards two chemically dissimilar residue streams at predictable times and places: lignocellulosic prunings from mulberry (Morus spp.) and nitrogen-rich excrement, litter and rearing-bed waste from the domesticated silkworm (Bombyx mori L.). Thermochemical conversion of these residues into biochar has attracted growing attention, yet the supporting literature has developed in three largely separate communities working on materials chemistry, soil remediation and sericultural agronomy, with limited cross-reference and almost no system-level integration. This critical narrative review examines what is known, what is contested and what remains unsupported across feedstock availability, conversion behaviour and utilisation pathways for sericultural biochar. Evidence was assembled through structured searching of open scholarly databases and indexes, supplemented by citation tracking and institutional sources, with all bibliographic details verified before inclusion. Three findings dominate the synthesis. Quantitative estimates of residue availability rest on a very thin empirical base, and no published study appears to have measured pruning or excrement yields across representative sericultural systems using a transparent method. Conversion behaviour is well characterised for woody mulberry material but poorly characterised for silkworm excrement, whose high protein, ash and mineral content produces charring behaviour that generic lignocellulosic models do not describe adequately. Utilisation evidence is strongly asymmetric: laboratory sorption and catalysis studies are numerous and internally consistent, whereas agronomic evidence inside the mulberry garden rests on a handful of small experiments, and no located study has tested whether sericultural biochar alters cocoon yield or silk quality. Reported successes in remediating metal-contaminated sericultural land raise an unresolved question about the fate of accumulated metal(loid)s during pyrolysis and after soil application. Priorities include transparent residue inventories, feedstock-specific conversion studies, multi-season field trials with cocoon and silk endpoints, and contaminant mass-balance work across the full conversion chain. Biochar is a plausible but not yet demonstrated route to closing nutrient and carbon loops in mulberry–silkworm systems, and its adoption should be judged against competing uses of the same residues.