Blueprint: Household Biogas Digester (from DOI 10.5281/zenodo.24109093)

Design blueprint - simulated, not measured, not built - for a household biogas digester, derived from the source paper 'Household Biogas from the Waste a Family Actually Has' (DOI: 10.5281/zenodo.24109093). The blueprint specifies a 2.48 m3 underground fixed-dome digester (1.58 m3 liquid volume, 0.90 m3 gas space, 40-day retention time) for a six-person household with three cattle, fed 18.0 kg of collectable cattle dung and 1.5 kg of kitchen waste per day with 20.0 litres of water per day (39.5 litres of feed slurry per day). It gives the construction form, materials (with quantities only where the source paper provides them, and stated gaps where it does not), a construction and assembly sequence, the operating envelope and feed regime, expected gas yield by season, tolerances, failure modes and a maintenance schedule. Calculated performance: the gas covers 53% of the household's cooking demand averaged over the year, 61% in the warmest months, 38% in a cold spell at 17 C slurry temperature, and 27% under sustained cold at 12 C. Full cooking coverage would require about 6 grazing cattle in summer and about 10 in winter. Annual production is 213 m3 of biogas; capital cost stated in the source paper is USD 520 including piping and one stove. Disclosure of AI use: this blueprint was prepared with the assistance of Dave, an AI system, which carried out the calculations, drafting and document preparation under the author's direction. Every quantity is taken from the source paper or derived in the accompanying compute.py from the source paper's stated parameters; derived items are marked in the blueprint.