In-situ full-scale aeration of a landfill with low organic content in Denmark

• Aeration increased microbial activity despite the waste being low in organic content. • The temperature in the waste body increased on average about 10 °C due to aeration. • The average settlement rate increased from 0.6 to 10 cm/year. • CH 4 concentration in the waste body reduced by ∼80 %. • Reduction of NH 4 + in the leachate and increased PFAS mobilisation were observed. Landfill aeration was investigated for accelerating the degradation of remaining organic content at AV Miljø for reducing the aftercare period. With a flow rate of 70 m 3 /h, and later 50 m 3 /h, increased aerobic microbial activity was observed after the initial displacement of existing landfill gas (LFG). On average, the temperature rose by 10 °C in the waste body, and the settlement rate went from 0.6 to 10 cm/year after 25 months of aeration. Gas emission measurements, using different methods to improve spatial and temporal resolution, including flux chambers, surface screening, eddy covariance (EC), and tracer-gas dispersion measurements, also pointed to increased biological activity, proving that aeration promoted the degradation of recalcitrant organic content at the site. In the LFG, CH 4 was reduced by about 80 %, from 43.9 %vol to 8.4 %vol, after 21 months of aeration, and CO 2 from 29.1 %vol to 17.3 %vol resulting in a change in the CH 4 -to-CO 2 ratio from 1.5 to 0.5. EC measurements of the CO 2 flux recorded a difference of ∼50 g CO 2 /(m 2 ·d) between summer emissions with and without aeration, confirming the increased activity of aerobic microbial communities. In addition, leachate quality improved during the first six months of aeration, with a reduction in NH 4 + /NH 3 -N concentration from 97.3 mg N/L to 56.1 mg N/L. However, an unusually high production of leachate volume resulted in a heightened concentration of various parameters, including PFAS, thereby masking the effect of aeration. Further research is therefore needed to elucidate the long-term effect of aeration on leachate quality.