Efficient removal of nitrogen and organic matter strategy from landfill leachate under high seasonal substrate variations

Landfill leachate is commonly used as a co-substrate in aerobic granular sludge (AGS) systems due to its high nitrogen concentration and variable organic matter content, which have a substantial impact on the removal efficiency. Typically, the nutrient content and biodegradability of leachate are categorized based on landfill age, often overlooking important factors such as seasonal variations. To address this limitation, a two-step process consisting of an anaerobic digestion (AD) reactor followed by an AGS reactor was evaluated over 431 days. Landfill leachate from the winter and spring seasons was chosen for its favorable biodegradability characteristics. Raw landfill leachate assays revealed a biodegradability range of 25%–92% within a single year, with higher values observed during winter compared to summer. To effectively handle the nutritional variations of landfill leachate, the hydraulic retention time (HRT) emerged as a crucial parameter influencing the performance of the reactors. When the AD reactor was operated in a hydrolytic configuration with an OLR of 68.4 g COD L−1 d−1, the proposed system showed 76.9% and 78.3% of organic matter and nitrogen removals, respectively. Best performance was obtained with COD/N 6.30 in the influent, ensuring required conditions for anoxic reactions (denitrification) at the center of the AGS. The proposed system offers valuable design tools for effectively removing nitrogen and organic matter from landfill leachates, despite significant seasonal nutrient variations. This approach can also be applied to wastewater with organic and nitrogen variations to face organic matter fluctuations in the AD and nitrogen fluctuations in the AGS. [Display omitted] •Climatic season have a large effect on landfill leachate biodegradability.•A two-step robust process treated variable landfill leachate over 431 days.•In spite of high seasonal variations carbon and nitrogen removal is over 77%.•The C/N ratio directly controls the removal of nitrogen in the AGS reactor.•High granular sedimentation improves the AGS denitrification process.