Methane leakage can erase the climate benefits of wastewater biogas recovery

Wastewater utilities use anaerobic digestion and biogas utilization to reduce energy costs and emissions, but methane leakage can undermine both the climate benefits and project economics of these systems, especially as power grids decarbonize. Safeguarding climate integrity will require performance-based methane policies that pair robust monitoring with enforceable leakage thresholds and targeted leak detection and repair.

Recommendations for policy

• Advance facility-wide methane measurement, reporting and verification with whole-system accounting and transparent disclosure, so performance reflects real, measured leakage

• Shift incentives and project approval requirements towards verified outcomes by linking credit value and eligibility to measured leakage, with thresholds that tighten as grids decarbonize

• Standardize leak detection and repair for wastewater biogas systems, including inspection frequency, leak thresholds and repair timelines, aligned with proven oil and gas frameworks

• Strengthen low-leak infrastructure and operational capacity for RNG through upgrades, workforce training and residual-emissions controls to preserve climate benefits

BASED ON X. Li, J.-J. Zhu, Y. Yan, T. Le & Z. J. Ren Nature Sustainability https://doi.org/10.1038/s41893-026-01818-7 (2026).

The policy problem

Water resource recovery facilities are critical public infrastructure and among the most energy-intensive municipal services. Anaerobic digestion with biogas recovery is widely promoted as a core decarbonization strategy for wastewater systems, yet its net climate benefit depends on controlling fugitive methane across production, storage, upgrading and use. As a potent short-lived climate pollutant, methane can rapidly negate emissions reductions from renewable energy generation. While policy frameworks and life-cycle analyses typically assume low leakage (1–5%), field data show highly variable real-world losses ranging from 0.4% to 65%. Emissions occur throughout the biogas chain, including digesters, gas handling, pipelines, engines and flaring systems. They are rarely directly measured or consistently reported. Often excluded from project-level climate and economic evaluations, these losses risk turning nominal climate solutions into liabilities, particularly as grid decarbonization reduces the value of displaced electricity.

The findings

This study presents a national-scale assessment of methane leakage thresholds that determine whether wastewater biogas systems provide net climate benefits. Thresholds generally range from 2% to 10%, depending on heat recovery, grid emissions intensity and biogas use pathway (Fig. 1). As grids decarbonize, upgrading biogas to renewable natural gas (RNG) becomes more climate-viable than combined heat and power (CHP), as the benefit of displacing grid electricity declines while upgrading electricity becomes cleaner. Using measured data from more than 50 full-scale facilities and an extensive literature review, we find leakage rates spanning nearly two orders of magnitude, from <1% to >60% of produced biogas. Many observed losses exceed these thresholds, indicating that numerous systems risk reduced or reversed climate benefits. These methane losses also undermine project economics, as leaked gas represents lost fuel that reduces electricity or RNG output, lowers revenues and increases operational and safety risks.

Fig. 1: National-scale methane leakage thresholds for achieving net-zero emissions from biogas utilization at US water resource recovery facilities.

a–d, Net greenhouse gas emissions from CHP systems (a,c) and from RNG systems (b,d) shown as a function of methane leakage rate, overlaid with the compiled leakage observations. Shaded regions indicate the upper and lower bounds of simulation results. Horizontal red lines and shaded regions mark methane leakage thresholds for achieving net-zero emissions; exceeding these thresholds results in net-positive emissions and adverse climate impacts. Vertical dashed lines indicate net-zero emission point. Dots represent observed leakage rates, independent of the model. ADR, anaerobic digestion-only heat recovery, where recovered heat is used only to meet on-site digester heating demand; BAU, business-as-usual electricity scenario (2022 grid emissions); CET, clean electricity transition scenario aligned with the US’s carbon neutrality goals under 2050 grid projections; FHR, full heat recovery, where all CHP-generated heat is fully utilized. MtCO₂e, million tonnes CO₂ equivalent. Figure adapted from X. Li et al. Nat. Sustain. https://doi.org/10.1038/s41893-026-01818-7 (2026) under a Creative Commons license CC BY-NC-ND 4.0.

The study

We developed an integrated greenhouse gas framework that combines Scope 1 methane leakage with Scope 2 offsets from recovered energy to compare CHP and RNG pathways across regional grids and future decarbonization scenarios. The framework quantifies methane leakage thresholds beyond which wastewater biogas systems no longer deliver net climate benefits. We also benchmark these thresholds against measured leakage from full-scale facilities and assess how leakage control affects emissions, energy recovery and project economics by translating methane losses into foregone energy and revenue. Results show that methane leakage is a structural yet controllable driver of biogas sustainability, linking climate performance directly to financial viability and offering policymakers a clear, performance-based lens to turn high-risk systems into durable decarbonization assets under evolving grid conditions.