Biochar-enhanced iron cycling in Fenton systems for the degradation and transformation of dissolved organic matter in hydrothermal liquid.

Abstract

The hydrothermal liquid from co-processing incineration fly ash and sewage sludge contains high levels of salts and organics, posing treatment challenges and environmental risks. This study developed a stepwise heterogeneous Fenton advanced oxidation process (S-HG-Fenton-AOPs) using bagasse-derived biochar (BSBC) to enhance organic matter removal. This approach capitalizes on the rapid reaction kinetics of the Fenton reaction while overcoming challenges related to slow Fe2+ regeneration. The investigation first analyzed BSBC's catalytic effect on reducing Fe3+ to Fe2+. Results revealed the key factors influencing this catalytic reduction include the abundant carbon defects and high specific surface area of the biochar. The system achieved a TOC removal efficiency of 49.22 % by enhancing iron cycling with biochar and supplementing •OH, representing a 7.84 % improvement over the conventional Fenton process. Furthermore, the total treatment time was significantly reduced, from 4 h to 1.5 h. The results of Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS) confirmed that the primary dissolved organic matter (DOM) components in the hydrothermal liquid were lignin/carboxylic-rich alicyclic molecules (45.81 %) and protein/peptides (37.79 %). The transformation pattern of DOM under the combined action of •OH and BSBC was clarified: Compounds such as lipids, protein/peptides and amino sugars in DOM undergo mineralization, while a fraction of phenolic DOM polymerizes to regenerate tannins and condensed aromatics. This study demonstrates that renewable biochar effectively accelerates Fe2+ regeneration, advancing the development of S-HG-Fenton-AOPs system, and providing both a theoretical basis and technical support for the industrial treatment of organic wastewater.

Abstract as supplied by the indexing source. © the authors / publisher.