Design, Implementation, and Validation of a Continuous Anaerobic Digestion Pasteurization Plant for Decentralized Sanitation in Malawi

This thesis addresses the challenge of ensuring pathogen-safe effluent from decentralized anaerobic digestion sanitation systems in low-income settings. It investigates the transition from custom-built pasteurization prototypes to a robust treatment plant built from adapted, mass-produced components. At a research site in Mzuzu, Malawi, a modular gas-driven pasteurization unit combining a modified domestic water boiler, a plate heat exchanger, and a thermal residence tank was designed, built, and evaluated to reach a 75 °C pathogen-inactivation target. Field measurements showed the collected waste supplied only up to 6% of the thermal energy needed for self-powered operation, and a salt-based tracer study revealed hydraulic short-circuiting that let untreated effluent bypass adequate heating, with surviving bacteria confirmed biologically. The study concludes that forced-path reactor designs are required to guarantee disinfection in decentralized systems.