Aerobic granular sludge as a regenerative system for nutrient removal and metal recovery from landfill leachate

Abstract

Landfill leachate is a complex and variable wastewater rich in organic matter, ammonium, salts, and metals, with low biodegradability and highly fluctuating composition. Its management still largely relies on energy- and chemical-intensive treatment schemes, making the treatment of raw, undiluted landfill leachate particularly challenging. This study evaluates, at lab scale, the potential of aerobic granular sludge (AGS) for achieving simultaneous pollutant removal and metal recovery in a 2-L column sequencing batch reactor fed with raw, undiluted landfill leachate collected from an active municipal landfill site. The reactor was operated for 198 days without dilution or addition of co-substrates. This operation resulted in stable granulation and high removal efficiencies, 94% for chemical oxygen demand (COD) and 97% for total nitrogen. Cation analysis shows that assimilation reached 600.47 µmol g⁻¹ TS, with calcium and magnesium being the predominant cations. Quantitative analyses revealed near-equal contributions from biosorption (53%) and bioaccumulation (47%), with magnesium dominating biosorption and calcium prevailing in bioaccumulation. Then, a partial metal recovery was achieved by desorption with 0.1 M NaCl, without compromising the granule structure, as verified by FTIR and scanning electron microscopy (SEM). However, the desorption process reduced nitrification and denitrification activities by factors of 3.7 and 1.8, respectively, while heterotrophic activity increased by 2.4-fold. Metagenomic analysis revealed microbial shifts following desorption, favouring genera such as Paracoccus and Burkholderia, which are associated with heterotrophic metabolism. These results demonstrate the potential of AGS as a regenerative biosorbent for treating landfill leachate and recovering metals. This approach supports sustainable and circular strategies for managing landfill leachate and similar complex effluents.