Towards an off-grid fecal sludge treatment unit: demonstrating energy positive thermal treatment

Abstract

Background: There is an unmet demand for community-scale fecal sludge treatment units (FSTUs) that serve communities of between 1,000 and 50,000 people and are able to operate in non-sewered and off-grid environments. An emerging industry standard for FSTUs includes as a key criteria energy independence in steady-state. Theoretically, there is sufficient thermal energy available in fecal sludge to provide the electrical power needed to run the FSTU. However, such a system had never been implemented. Methods: Biomass Controls has previously demonstrated the thermal treatment of fecal sludge using the Biogenic Refinery, a thermal FSTU deployed in three sites in India. In this article we describe testing where a Biogenic Refinery was paired with a thermal fluid heat exchanger and organic Rankine cycle generator to generate electrical power. Results: This Biogenic Refinery combined heat and power system generated sufficient electrical power to offset electrical parasitic loads in steady-state operation and produce a surplus of 1.2 kWe. Conclusions: The results of the study demonstrate that there is an excess of energy available and reliable mechanisms to generate electrical energy using an FSTU. Additional steps are necessary to transition to a true off-grid FSTU.

Financial Viability and Environmental Sustainability of Fecal Sludge Treatment with Pyrolysis Omni Processors

“…According to the manufacturer, the Biogenic Refinery can process feedstock at a rate of 18 kg·h –1 (moisture content of 35%). We used empirical models for the Biogenic Refinery based on information from the design team, their pilot systems, and a laboratory study of the system . These included assumptions that the pyrolysis process liberates embedded energy from fecal sludge for drying and generation of electrical energy.…”

“…We used empirical models for the Biogenic Refinery based on information from the design team, their pilot systems, and a laboratory study of the system. 41 These included assumptions that the pyrolysis process liberates embedded energy from fecal sludge for drying and generation of electrical energy. The dryer is assumed to provide the necessary heat to reduce the moisture content from feedstock from 85 to 35%.…”

“…22,25,26,37−40 For example, a laboratory study of the Biogenic Refinery (a pyrolysis-OP from Biomass Controls PBC) showed that this system could support its steady state electrical and heating needs when paired with a combined heat and power system (i.e., it does not require any energy inputs). 41 The development of OPs as part of a portfolio of technologies to address global sanitation needs presents a timely opportunity to investigate their relative sustainability.…”

“…However, this early-stage study highlighted biological processes (e.g., anaerobic digestion) as a core treatment strategy and argued that thermal conversion (e.g., pyrolysis) was too complex with no systems available for fecal sludge management at the time . Although biological treatment is common for community-scale treatment, greenhouse gas emissions (i.e., CH 4 and N 2 O) can be substantial, as deviation from optimal operation conditions commonly occurs. , Significant innovation has made thermal treatment of excreta feasible, with several of the OPs having gone through multi-year pilot studies, and limited publicly available information suggests promising technical viability. ,,,− For example, a laboratory study of the Biogenic Refinery (a pyrolysis-OP from Biomass Controls PBC) showed that this system could support its steady state electrical and heating needs when paired with a combined heat and power system (i.e., it does not require any energy inputs) . The development of OPs as part of a portfolio of technologies to address global sanitation needs presents a timely opportunity to investigate their relative sustainability.…”