A Solar Desiccation Sanitation Chamber for Households Without Sewers: Computed Moisture-Removal, Pathogen Die-Off, and Safe-Storage Budgets Across Humidity and Season

SIMULATED, NOT MEASURED. A design and computation for a ventilated, solar-heated desiccation chamber serving a urine-diverting household toilet without a sewer. A seven-day batch of 8.75 kg at 75% moisture must lose 5.83 kg of water to reach 25% moisture (computed water activity 0.571); in the reference case (5.2 kWh/m2/day, 27 C, 55% relative humidity) drying takes 7.68 days at a daytime mean chamber temperature of 47.41 C, ranging from 4.44 days (hot, dry) to 18.98 days (cool winter). Computed die-off during drying is only 0.17-log for Ascaris suum eggs, so a further 141.8 days of sealed dry storage are required for a 3-log reduction (149.4 days total in the reference case; 415.5 days in a cool winter, beyond a year). A five-day overcast spell leaves the batch at 64.87% moisture and delays the safe date to 152.9 days. Parts cost US$249, or US$318 with the storage drums and backup kit the failure case requires. No chamber was built and nothing was hardware-tested; all pathogen figures are computed die-off under stated assumptions. The mechanism is desiccation plus time, not thermal pasteurisation. AI use disclosed: prepared with the assistance of Dave, an AI system, under the author's direction.