Complementary mechanism of the Fenton and biological aerated filter in treating refractory dissolved organic matter from landfill leachate.

The Fenton and biological aerated filter (BAF) combined process have outstanding advantages in treating refractory and complex organic wastewater. However, the transformation of dissolved organic matter (DOM) in the actual wastewater treatment plant by Fenton and BAF, especially the complementary mechanism of the two processes in removing DOM at the molecular level, has rarely been reported. In this study, we evaluated the performance of a full-scale Fenton and BAF combined process for treating biochemical effluent (BE) from landfill leachate and analyzed the transformation of DOM and the complementary effects of the two processes at the molecular level using Fourier transform ion cyclotron resonance mass spectrometry. The removal efficiency of chemical oxygen demand in BE by the combined process can reach 96.78 %. The sulfur-containing refractory compounds were degraded into sulfur-free compounds by desulfonation after Fenton treatment. The Fenton can preferentially remove DOM components with high aromaticity (modified aromaticity index (AImod) = 0.257) and low O/C (intensity-weighted average value (wa) of the O/C = 0.358), producing macromolecular organic substances with low aromaticity (AImod = 0.234) and high O/C (O/Cwa = 0.524). The subsequent BAF process can complementarily remove the products of Fenton, thereby improving the overall treatment efficiency. Desulfonation (8.0 %) and oxygen addition (42.4 %) are the main paths leading to DOM transformation in the Fenton unit, while the BAF unit mainly removes Fenton products through decarboxylation (40.5 %). This study provides a more comprehensive understanding of the complementary role of the Fenton and BAF processes in effectively treating refractory organic wastewater.