For domestic energy – fuel sources biomass such as wood, animal dung and agricultural waste that are normally burned in traditional stove is used by the developing world. Diverse biomass resource is found in Ethiopia which can be used for energy through pyrolysis cook stove co-producing biochar. Specifically, coffee husks are the major solid residues from the handling and processing of coffee in the study area. The purpose of this study is to evaluate these Biochar producing pyrolysis cooking stove with respect to energy and emission. The selection of the stove design was made from both allothermal and autothermal type of pyrolysis cook stove. Both with and without biomass insertion was the experiment done for the allothermal stove design to understand the effect of the pyrolysis gas. The Water boiling test was used for the selected indirect and direct type stove design using wood and Corn cob respectively as fuel for testing stove efficiency. Both coffee husk and corncob as a biomass resource was used for generating pyrolysis gas and biochar using the selected indirect stove design. HOBO Carbon Monoxide Data logger and University of California Berkeley Particle Monitor device was used for measuring Carbon Monoxide and Particle Matter. The results from the water boiling test suggest that the indirect type stoves, without biomass insertion, average thermal efficiency was found between 15.86 to 18.6% during high power test and 20.02% average thermal efficiency was found for clay made stove during low power test. With biomass insertion corn cob and coffee husk the maximum average thermal efficiency is obtained during low power test using clay made stove 23.78% and 24.19% respectively. For direct type stoves the maximum and minimum thermal efficiency was found 34.11% for clay made stove and 20.4% for ELSA stove respectively during high power hot start phase.

The escalating global waste crisis necessitates sustainable valorization strategies, with biochar production emerging as a promising solution for converting organic residues into a carbon-rich material. This study evaluated biochar derived from corncob and khat waste pyrolyzed using allo-thermal and auto-thermal multi-purpose stoves. Biochar was fractionated into four particle sizes (>2 mm, 1–2 mm, 0.6–1 mm, and <0.6 mm) and characterized for ash content, pH, and electrical conductivity (EC). Results demonstrated that the auto-thermal stove, operating at higher temperatures (up to 800 °C), consistently produced biochar with greater ash content (khat: 12–19%; corncob: 11–14%), alkaline pH (9.2–10.0), and significantly higher EC compared to the allo-thermal stove (maximum 350 °C). EC values ranged from 0.38 mS/cm (coarse allo-thermal corncob) to 6.6 mS/cm (fine auto-thermal khat), with auto-thermal biochar exhibiting EC values 5–10 times higher than their allo-thermal counterparts. khat waste consistently yielded biochar with higher ash content, pH, and EC than corncob, reflecting its richer mineral composition. Particle size fractionation revealed that pH and EC increased progressively with decreasing particle size across all treatments, with the finest fraction (2 mm) to 6.6 mS/cm (<0.6 mm). This study demonstrates that decentralized biochar production using multi-purpose stoves can yield materials with tunable properties, and that khat waste—an underutilized regional resource—shows particular promise for producing high-ash, high-EC biochar suitable for acidic soil amendment.