Financial Viability and Environmental Sustainability of Fecal Sludge Treatment with Pyrolysis Omni Processors.
ACS ENVIRONMENTAL AU 2022;
2:455-466. [PMID:
36164351 PMCID:
PMC9502014 DOI:
10.1021/acsenvironau.2c00022]
[Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/10/2022] [Revised: 07/11/2022] [Accepted: 07/11/2022] [Indexed: 11/30/2022]
Abstract
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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.
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