Oxygenated Leachate Recirculation for Enhanced MSW Stabilization and Landfill Space Reclamation: Lab-Scale Bioreactor Insights

This study investigates aerobic landfill stabilization using three bioreactors with different operational modes: R1 with oxygenated (~ 90% pure oxygen) leachate recirculation and waste mass aeration, R2 with conventional leachate recirculation (without oxygenation) and waste mass aeration, and R3 as an anaerobic control. The waste stabilization was assessed by reductions in COD, ammonia nitrogen, NOx (nitrate and nitrite nitrogen), and total phosphorus removal, as well as reductions in volatile solids and subsidence of waste height. Among the three reactors, R1 exhibited the best performance, with ~ 85% COD removal efficiency likely due to the high DO content during leachate recirculation. Additionally, R1 achieved ~ 99% removal efficiency of ammonia nitrogen through rapid aerobic nitrification. An exponential attenuation model was applied to describe the degradation of organic substances, with degradation rates of COD and NH₃-N increasing from 0.005 and 0.007 d⁻¹ to 0.01 and 0.021 d⁻¹, respectively, when leachate recirculation and oxygenation were applied. Reactor R1 could meet the COD emission limit of 150 mg/L, as specified by WHO surface water regulations, by day 478, while reactors R2 and R3 are expected to achieve this level by days 567 and 742, respectively. The results indicated that the aerobic conditions in R1, supplemented with pure oxygen (~ 90%) aeration, elicited rapid stabilization of the simulated landfill waste, reflected by a high waste settlement of ~ 63.5%. The findings suggest that this strategy can improve landfill stabilization in practice, optimize landfill space reuse, and enhance MSW management by reducing the load on existing leachate treatment facilities.