Microaerobic fermentation (MF) is a process of controlled degradation of organic waste material that occurs in enclosed fermentors under micro-aerobic conditions at near-room temperature. MF processing of vegetal materials progresses to endpoints in about 2-5 weeks. During MF processing, an acidic leachate rich in organic acids and alcohols is produced. The research presented in this thesis focuses on the efficiency of MF pre-processing of feedstock containing fibrous lignocellulosic (FLC) materials; efficiency of microbial and insect larvae-based treatments of MF leachate; tolerance of the Black Soldier fly larvae (BSFL) to various biological inhibitors common in leachate; and effectiveness of using MF and BSFL solid and liquid processing products as agricultural fertilizers. Results indicate that MF is unsuitable for pre-processing of FLC materials. Enhanced MF leachate treatment may increase efficiency of FLC processing though. Leachate can be efficiently treated using BSFL which decrease overall leachate toxicity. BSFL are able to tolerate increased levels of many of the biological inhibitors within the leachate including ethanol, acetate, pH extremes and temperature. MF solid residues increased corn plant growth when amended into soil, but residues resulting from BSFL processing of solid organics stunted corn plant growth. Short-term phytotoxicity of MF leachate was eliminated by diluting it 10 - 10,000 times or through BSFL processing. It can be concluded that MF processing of organics is beneficial for producing solid soil amendments from non-FLC materials and that dilution or BSFL treatment of MF leachate leads to a beneficial liquid fertilizer.

Black Soldier Fly Larvae (BSFL) composting is a treatment procedure that generates two products: frass compost and BSFL. These products have different uses. BSFL can be used as animal feed and frass compost as soil fertiliser, and they need to be separated after the composting procedure has been finished. A separator of the vibrating sieve type, currently in use by a research group at SLU for separating BSFL from the frass compost generated by the composting process, was tested and evaluated in terms of fraction purity and separation time. It was found that the fraction purity was over 90% for the BSFL fraction, and that the separation time was approximately 1-1.5 minutes for 4 kg of material. Hotspots for improvement were identified and a new vibrating sieve was designed and built with the aim of providing flexibility for improving fraction purity, separation time and operator ergonomy for the end-customer. A CAD model of the new vibrating sieve was designed in SolidWorks with a complete set of technical drawings and purchasing components. These drawings were sent out for manufacturing at a workshop and the new vibrating sieve was built and tested. The new vibrating sieve was functioning properly, but its optimal mechanical settings need further research and testing. This separator design could be emulated by others, and also improved, and this research could be used for improving the process outcome for future BSFL separation processes.