Solar Pasteurization for Anaerobic Digestion Sludge

This thesis examines solar pasteurization as a low-cost method for sanitizing sludge from anaerobic digestion of human waste before disposal. An off-the-shelf solar water heater available in Kenya was adapted with a convection loop, heat exchanger, and thermostatic valve set to 78 °C, then field-tested in Nairobi during a low-irradiance period. Although the valve’s setpoint was not reached, sampling from the digester and main tank showed the system achieved a 99% reduction in E. coli concentrations. A Python model, calibrated on the collected temperature and irradiance data, simulated performance under varying collector area, valve setpoint, and heat exchanger efficiency across other Kenyan sites, identifying collector area and valve setpoint as the most effective control parameters. Observed tank corrosion motivated a proposed two-cycle heating design for future systems.