Characteristics of Greenhouse Gas Emission Factors in Sewer Networks, Key Influencing Factors, and Responses to Network Defects
DOI:
https://doi.org/10.54097/w4pdt757Keywords:
Drainage network; Greenhouse gas; Emission factor; Methane; Nitrous oxide; Sewer defects.Abstract
Drainage networks, long treated as passive conduits, are now recognized as GHG sources, yet controls on their emission factors (EFs) remain unclear. We synthesized 138 EFs (111 CH₄, 27 N₂O) from 24 studies (1994–2024), deploying Spearman, Random-Forest-SHAP, and GAMs to pinpoint drivers and nonlinear responses, alongside defect scenarios mimicking illicit flows and rainfall intrusion. Pressurized mains exhibited the highest dissolved CH₄, whereas N₂O partitioned predominantly into the dissolved phase across systems. CH₄ EFs responded chiefly to hydraulics and organics (A/V ratio, COD, depth, temperature), while N₂O EFs shifted toward nitrogen pathways (NH₄⁺-N, NO₃⁻-N, conductivity). Simulations revealed opposing trends: defect severity suppressed CH₄ but elevated N₂O, with rainfall amplifying this divergence. These findings argue against static EFs—emission factors are context-sensitive, varying with hydraulics, chemistry, and pipe integrity. Incorporating such dynamic dependencies would sharpen urban GHG inventories and targeted abatement strategies.
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