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Challenges to Accurate Estimation of Methane Emission from Septic Tanks with Long Emptying Intervals.

Challenges to Accurate Estimation of Methane Emission from Septic Tanks with Long Emptying Intervals.

Authors :
Moonkawin J
Huynh LT
Schneider MY
Fujii S
Echigo S
Nguyen LPH
Hoang TT
Huynh HT
Harada H
Source :
Environmental science & technology [Environ Sci Technol] 2023 Oct 31; Vol. 57 (43), pp. 16575-16584. Date of Electronic Publication: 2023 Oct 19.
Publication Year :
2023

Abstract

Septic tanks in low- and middle-income countries are often not emptied for a long time, potentially resulting in poor pollutant removal efficiency and increased greenhouse gas emissions, including methane (CH <subscript>4</subscript> ). We examined the impact of long emptying intervals (4.0-23 years) on the biochemical oxygen demand (BOD) removal efficiency of 15 blackwater septic tanks and the CH <subscript>4</subscript> emission rates of 23 blackwater septic tanks in Hanoi. The average BOD removal efficiency was 37% (-2-65%), and the average CH <subscript>4</subscript> emission rate was 10.9 (2.2-26.8) g/(cap·d). The emptying intervals were strongly negatively correlated with BOD removal efficiency ( R = -0.676, p = 0.006) and positively correlated with CH <subscript>4</subscript> emission rates ( R = 0.614, p = 0.001). CH <subscript>4</subscript> emission rates were positively correlated with sludge depth ( R = 0.596, p = 0.002), but against expectation, negatively correlated with BOD removal efficiency ( R = -0.219, p = 0.451). These results suggest that shortening the emptying interval improves the BOD removal efficiency and reduces the CH <subscript>4</subscript> emission rate. Moreover, the CH <subscript>4</subscript> emission estimation of the Intergovernmental Panel on Climate Change, which is a positive conversion of BOD removal, might be inaccurate for septic tanks with long emptying intervals. Our findings suggest that emptying intervals, sludge depth, and per-capita emission factors reflecting long emptying intervals are potential parameters for accurately estimating CH <subscript>4</subscript> emissions from septic tanks.

Details

Language :
English
ISSN :
1520-5851
Volume :
57
Issue :
43
Database :
MEDLINE
Journal :
Environmental science & technology
Publication Type :
Academic Journal
Accession number :
37856469
Full Text :
https://doi.org/10.1021/acs.est.3c05724