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

Lewis Stetson Rowles; Victoria L Morgan; Yalin Li; Xinyi Zhang; Shion Watabe; Tyler Stephen; Hannah A C Lohman; Derek DeSouza; Jeff Hallowell; Roland D Cusick; Jeremy S Guest

doi:10.1021/acsenvironau.2c00022

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

ACS Environ Au. 2022 Sep 21;2(5):455-466. doi: 10.1021/acsenvironau.2c00022. Epub 2022 Jul 29.

Authors

Affiliations

¹ Institute for Sustainability, Energy, and Environment, University of Illinois Urbana-Champaign, Urbana, Illinois 61801, United States.
² Department of Civil & Environmental Engineering, University of Illinois Urbana-Champaign, Urbana, Illinois 61801, United States.
³ Biomass Controls PBC, Woodstock, Connecticut 06281, United States.

Abstract

Omni Processors (OPs) are community-scale systems for non-sewered fecal sludge treatment. These systems have demonstrated their capacity to treat excreta from tens of thousands of people using thermal treatment processes (e.g., pyrolysis), but their relative sustainability is unclear. In this study, QSDsan (an open-source Python package) was used to characterize the financial viability and environmental implications of fecal sludge treatment via pyrolysis-based OP technology treating mixed and source-separated human excreta and to elucidate the key drivers of system sustainability. Overall, the daily per capita cost for the treatment of mixed excreta (pit latrines) via the OP was estimated to be 0.05 [0.03-0.08] USD·cap^-1·d^-1, while the treatment of source-separated excreta (from urine-diverting dry toilets) was estimated to have a per capita cost of 0.09 [0.08-0.14] USD·cap^-1·d^-1. Operation and maintenance of the OP is a critical driver of total per capita cost, whereas the contribution from capital cost of the OP is much lower because it is distributed over a relatively large number of users (i.e., 12,000 people) for the system lifetime (i.e., 20 yr). The total emissions from the source-separated scenario were estimated to be 11 [8.3-23] kg CO₂ eq·cap^-1·yr^-1, compared to 49 [28-77] kg CO₂ eq·cap^-1·yr^-1 for mixed excreta. Both scenarios fall below the estimates of greenhouse gas (GHG) emissions for anaerobic treatment of fecal sludge collected from pit latrines. Source-separation also creates opportunities for resource recovery to offset costs through nutrient recovery and carbon sequestration with biochar production. For example, when carbon is valued at 150 USD·Mg^-1 of CO₂, the per capita cost of sanitation can be further reduced by 44 and 40% for the source-separated and mixed excreta scenarios, respectively. Overall, our results demonstrate that pyrolysis-based OP technology can provide low-cost, low-GHG fecal sludge treatment while reducing global sanitation gaps.