Transformation of dissolved organic matter in membrane-concentrated landfill leachate during Cu-Fenton-biological treatment

Membrane-concentrated landfill leachate (MCLL) is a highly concentrated and recalcitrant wastewater with remarkably low biodegradability. In this study, a multi-stage Cu-Fenton oxidation coupled with biological process was proposed for MCLL treatment. Importantly, Fourier transform ion cyclotron resonance mass spectrometry was employed to unveil the molecular transformation of dissolved organic matter (DOM) in MCLL during this integrated treatment process. The multi-stage Cu-Fenton process exhibited a high capacity to remove CHON compounds, resulting in a decrease in their relative abundance from 43% to 28%. Conversely, CHOS compounds displayed an increased relative abundance. For compound classes, the relative abundance of aliphatic/protein groups increased from 11% to 20%, whereas lignin/CRAM-like structures decreased from 36% to 12%, resulting significant improvement of the effluent biodegradability. The recalcitrant species during the multi-stage Cu-Fenton process were 300-400 Da lignin/carboxylic rich alicyclic molecules and tannins with high O/C ratios, which were effectively degraded by the subsequent biological treatment, particularly for the higher molecular weight organic fractions. This work provides new insights into the transformation characteristics of DOM in MCLL at a molecular level and offers technical guidance for the treatment of this refractory organic wastewater.