Landfill Response to In-situ Stabilisation

Abstract

Many landfills still pose significant emission and pollution risks because decomposition is incomplete, and contaminants persist. To mitigate these risks and reduce the duration of aftercare, in-situ stabilization techniques have been developed to accelerate waste degradation. Two methods have been tested in this context: recirculation of water to stimulate microbial activity and aeration to promote aerobic degradation. Both alter the composition of organic matter as readily degradable fractions are consumed, while more resistant components remain.

Although numerous projects worldwide have shown encouraging results, landfill stabilization remains challenged by the inherent heterogeneity of the waste body. This complexity limits uniform treatment and leaves uncertainties about the physical, chemical, and biological interactions at play. Addressing these knowledge gaps, this thesis investigates the effectiveness of aeration and water recirculation in three Dutch pilot landfills: Braambergen and Wieringermeer (aerated), and Kragge (water recirculation).

The pilots revealed that the effects of aeration are highly variable in space and time. At Braambergen, variability in aeration performance revealed the strong influence of site heterogeneity. Differences in water levels in aeration wells affected gas composition and flow, yet high water columns alone could not explain the observed contrast between compartments. Other factors, such as spatial variability in gas permeability within the waste body, also played a role. Where aeration was more effective, higher gas extraction, elevated temperatures, and greater settlement indicated enhanced microbial activity and carbon mineralization.

Beyond gas monitoring, stabilization was assessed by comparing the carbon generation of waste samples under aerobic and anaerobic conditions with model predictions and with carbon actually recovered on-site. The heterogeneity of the waste samples was reflected in the carbon potential and decay rate constants (k-values). Aerated pilots showed reduced aerobic carbon potential, reflecting advanced stabilization, while the recirculated pilot retained substantial degradable organic matter. These results highlight both the large potential of aeration to accelerate stabilization and the persistence of heterogeneity that complicates prediction and management.

A further focus was placed on building a comprehensive carbon and nitrogen balance across the solid, aqueous, and gas phases at field scale. Over seven years, aerated pilots exhibited higher organic matter degradation than the anaerobic pilot with a significant share of carbon and nitrogen released through the gas phase. In contrast, the recirculated pilot retained larger amounts of degradable carbon and poorly mobilizable nitrogen. Importantly, the analysis revealed that a substantial fraction of nitrogen remains fixed in solid or microbial pools, potentially delaying compliance with leachate emission targets.

Taken together, these findings advance understanding of how aeration and water recirculation influence landfill stabilization. They demonstrate the benefits of aeration for accelerating degradation while also underlining the challenges posed by spatial variability and persistent nitrogen pools. Such insights are crucial for improving the design and implementation of in-situ stabilization strategies and for reducing the long-term aftercare needs of landfills.