As-built CAD and ANSYS structural–thermal validation of a locally fabricated anaerobic co-digester for institutional organic waste in Uganda

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Background Locally fabricated anaerobic digesters are commonly sized from biochemical yield assumptions without checking fabricated geometry, pressure resistance, insulation performance, or commissioning evidence. This study integrated waste assessment, as-built computer-aided design (CAD), finite-element analysis, and start-up monitoring of a stainless-steel anaerobic co-digester at Uganda Technical College Bushenyi. Methods Available food, fecal, and green-yard wastes were constrained to a C/N ratio of 25–30. The fabricated geometry was reconstructed in CAD. ANSYS Mechanical APDL evaluated shell response at 0.200 and 1.318 MPa, while an axisymmetric thermal model evaluated lateral heat loss through the double wall. Digester temperature, ambient temperature, and pH were monitored for 29 days; gas was screened once. Results Of 506.00 kg d-1 available waste, 350.32 kg d-1 met the C/N constraint. The corrected theoretical biogas potential was 33.44 m3 d-1; this was not a measured production rate. The as-built inner shell was 346 mm x 692 mm x 3 mm. At 0.200 MPa, ANSYS predicted 10.03 MPa equivalent stress and 0.0199 mm displacement. The thermal model predicted 16.68 W lateral holding loss at a 35 degrees C inner-wall boundary. The unheated prototype remained near ambient temperature, acidified before wood-ash addition, and produced non-igniting, oxygen-containing gas. Conclusions The fabricated vessel has a traceable preliminary structural and thermal basis, but commissioning did not demonstrate methane production or readiness for kitchen use. Controlled biomethane-potential testing, calibrated gas-volume and composition measurements, process-stability monitoring, and detailed pressure-vessel assessment are required before deployment.

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