Long-term emission behavior of biowindows replacing gas extraction wells

Older municipal solid waste (MSW) landfills that received organic waste over past decades struggle in aftercare with declining gas production and fluctuating gas quality, making gas extraction systems inefficient. Methane (CH₄) oxidation systems, such as biowindows, provide a sustainable, cost-effective passive alternative for mitigating residual emissions. This study presents long-term monitoring of three pilot biowindows at an Austrian MSW landfill to replace gas extraction wells and reduce CH₄ emissions. Over a 10-year period, CH₄ emissions and their relationship with environmental factors were analyzed through periodic field campaigns during two monitoring phases (2014-2016 and 2021-2024). Monitoring included gas and temperature profiles, surface screenings, and chamber flux assessments. Statistical analyses, including Pearson correlation and decision tree modeling, identified key factors influencing CH₄ emissions, which were driven by a combination of temporal trends, gas composition dynamics, and environmental factors like ambient pressure and temperature. Results revealed a 60 % reduction in median hotspot CH₄ emission rates (from 162 to 70 g/m² d) at one biowindow between the two monitoring phases, while another biowindow demonstrated high performance over the period. In contrast, the third biowindow, installed at a newer landfill section, exhibited hotspots and increased emissions (median 80-265 g/m² d across campaigns), likely linked to formerly installed and still remaining leachate and gas collection infrastructure, highlighting the need for site-specific interventions to address localized issues and optimize performance. The study confirms that biowindows require minimal maintenance during their first decade of operation and can achieve considerable CH₄ reductions under appropriate conditions and well-designed construction.