Enhancing the performance of bioreactor landfills by recirculating alkalinized leachate: Continuous operation and feasibility analyses

Recirculation of near-neutral pH-buffered leachate has been shown to improve the performance of bioreactor landfills (BLs). Prior studies have focused on pH adjustment without specifically targeting higher pH levels above 8. Motivated by the successful application of alkaline pretreatment in anaerobic digestion systems, it was hypothesized that raising the pH of the recirculated leachate in BLs could also enhance organic bioconversion and prevent acid accumulation. This study explored the effect of pretreating the recirculated leachate by alkalinization on the performance of BLs. Batch experimental optimization was carried out using biochemical methane potential assays in duplicates to determine the optimal operating conditions for alkaline addition. Increasing the leachate pH to 10 led to the optimal methane production at 397 mL CH₄ per g of volatile solids (35 % enhancement compared to the control). Afterward, continuous pilot-scale experiments were performed in duplicates with 25-L bioreactors over 28 weeks, and their findings confirmed that alkaline augmentation improved biogas production and methane content by 11 % and 30 %, respectively, while maintaining the pH of the leachate output within the favorable conditions for methanogenic activity. Economic analysis demonstrated that leachate alkalinization was 15 % more cost-effective compared to the control reactor. Energy analyses revealed that the alkalinized bioreactor achieved a 43 % net energy efficiency; 63 % higher than the control, leading to a 15 % increase in cost-effectiveness. This study presents an applicable upgrading strategy to existing and new BLs toward more sustainable waste management.