Anaerobic mono-digestion of wheat straw in a three-stage semi-continuous system inspired by a beetle larva gut

Based on the efficient digestive system of the larva of sun beetle (Pachnoda marginata) in utilizing lignocellulose-rich biomass, a reactor system was designed to mimic processes that occur in the larval gut. We aimed developing a process with this system for anaerobic mono-digestion of wheat straw to produce volatile fatty acids (VFAs) and biogas. Three stirred tank reactors connected in series were customized with polyurethane foam and operated at mesophilic condition. The first two reactors were designed to mimic the midgut of the larva with enhanced VFA production and the third one to resemble the hindgut and optimized for methanogenesis. The system was fed in a semi-continuous regime with ground wheat straw in an alkaline medium. Enrichment cultures from midgut and hindgut of the larva were used as inocula and three conditions with increasing organic loading rate were tested. The microbial community structures were investigated by amplicon sequencing of the 16S rRNA and mcrA genes. The designed process was stable and capable to convert wheat straw into methane and carboxylates. Further adaptations are suggested to improve the anaerobic digestion and decrease assembly and operating costs.