Thermoelectric energy harvesting for a solid waste processing toilet

Abstract

Over 2.5 billion people do not have access to safe and effective sanitation. Without a sanitary sewer infrastructure, selfcontained modular systems can provide solutions for these people in the developing world and remote areas. Our team is building a better toilet that processes human waste into burnable fuel and disinfects the liquid waste. The toilet employs energy harvesting to produce electricity and does not require external electrical power or consumable materials.RTI has partnered with Colorado State University, Duke University, and Roca Sanitario under a Bill & Melinda Gates Foundation Reinvent the Toilet Challenge (RTTC) grant to develop an advanced stand-alone, self-sufficient toilet to effectively process solid and liquid waste. The system operates through the following steps: 1) Solid-liquid separation, 2) Solid waste drying and sizing, 3) Solid waste combustion, and 4) Liquid waste disinfection. Thermoelectric energy harvesting is a key component to the system and provides the electric power for autonomous operation. A portion of the exhaust heat is captured through finned heat-sinks and converted to electricity by thermoelectric (TE) devices to provide power for the electrochemical treatment of the liquid waste, pumps, blowers, combustion ignition, and controls.

Remediation of suspended solids and turbidity by improved settling tank design in a small‐scale, free‐standing toilet system using recycled blackwater

“…We are developing a free‐standing toilet system that is designed to separate liquid and solid waste, drying the solids for use as a combustible fuel to drive thermoelectric devices and disinfecting the liquid with an electrochemical process enabling safe onsite reuse (Stokes et al, ; Rogers et al, ; Sellgren et al, ). The ultimate goal is an integrated system that requires no addition of external water or power; however, the energy required to achieve effective and reliable disinfection of blackwater using the electrochemical process currently exceeds what can be generated onsite.…”

Development of an Electrochemical Process for Blackwater Disinfection in a Freestanding, Additive-Free Toilet

“…The electrochemical process explored in this manuscript is intended to be used in a self-contained toilet apparatus where solid waste (feces) will also need to be disinfected. Burning the solid waste could mitigate this problem, and the exhaust stream from the combustion unit could be used to heat the liquid disinfection process in addition to driving the electrochemical process through conversion to electrical energy (Stokes et al, 2014). On the basis of our assumptions for toilet usage, we estimate we will have enough heat energy to heat the liquid being treated to approximately 50°C (this modeling is a part of a different study and not shown here).…”

“…This study is intended to support the continued development of an electrochemical blackwater disinfection system, which will ultimately be integrated into a modular toilet system designed and developed by RTI International researchers for use in low-income countries and rural areas ( Figure 1). Development and testing of the other components of this system (solids processing and energy recovery) are described elsewhere (Stokes, Baldasaro, Bulman, & Stoner, 2014).…”