Endogenous metabolism and electricity conversion of organic clogging substances in constructed wetland microbial fuel cell

Substrate clogging in constructed wetlands (CWs) diminishes pollutant removal efficiency and exacerbates carbon emissions, while achieving simultaneous reduction of clogging substances and their potential for energy recovery remains highly challenging. This study investigates the degradation of organic clogging substances and their metabolic coupling with energy allocation in constructed wetland microbial fuel cell (CW-MFC) systems. During the 30-day clogging mitigation, porosity increased from 37.50 % to 45.45 % with substantial decreases in total solids (TS), volatile solids (VS), dissolved organic matter (DOM) especially extracellular polymeric substances (EPS), which dropped sharply from 1298.91 to 34.00 mg/L accompanied by rapid polysaccharide degradation. Van Krevelen (VK) diagrams demonstrated that CW-MFCs preferentially degraded lipids and proteins into small molecules while suppressing lignin/aromatics. Energy flow analysis showed that CW-MFC introduced electrogenic respiration (18.5 %) and enhanced aerobic and anaerobic pathways, redirecting organics from EPS synthesis toward electron transfer and respiration, thereby alleviating EPS accumulation. Community analysis of EPS-degrading bacteria (EDB) and electroactive bacteria (EAB) suggests a metabolic coupling mechanism whereby metabolites generated by EDB, including degradable intermediates according to VK diagrams, serve as substrates for EAB, and electricity production by EAB in turn stimulates EDB activity. Strong negative correlations with EPS (-1.00), VS (-0.97), and TS (-0.97) highlighted the electrochemical sensing capability of CW-MFC for in situ clogging monitoring.