Degradation of refractory humic substances and by‐product formation in landfill leachate using ultrasonic–electrocoagulation

Abstract BACKGROUND Landfill leachate contains high levels of refractory organic matter, particularly humic acid (HA) and fulvic acid (FA), which are difficult to degrade due to their complex structures and molecular weight. This study evaluates the effectiveness of a combined ultrasonic–electrocoagulation (US‐EC) process for degrading these substances. Key treatment parameters such as total organic carbon (TOC), color, 254 nm ultraviolet light (UV₂₅₄), and UV–visible were used to assess performance. Fourier transform infrared (FTIR) and UV–visible spectroscopy were employed to analyze structural changes in organic matter, while energy‐dispersive X‐ray (EDX) analysis provided insights into elemental composition and pollutant transformation. RESULTS Optimal conditions were identified as a surface area‐to‐volume ratio of 7 m −1 , electrode spacing of 3 cm, current density of 50 mA m −2 , stirring speed of 200 rpm, and 30 min of electrolysis. The US‐EC process improved TOC removal from 41% (EC alone) to 47%, and color removal from 83.5% to 88.2%. The UV 254 absorbance of raw landfill leachate was 14.78, decreasing to 7.18 and 6.23 after EC and US‐EC, respectively. This reduction indicates lower aromaticity and molecular weight, as confirmed by spectral analysis. Additionally, by‐products contained high concentrations of oxygen, carbon, and nitrogen, according to EDX results. FTIR analysis showed significant peaks at 3450 cm −1 (OH), 1530 cm −1 and 1400 cm −1 (CC), and 570 cm −1 (CH), supporting the effective removal of organic matter by both EC and US‐EC. CONCLUSION The combined US‐EC process demonstrated improved removal of refractory organic matter in landfill leachate compared to EC alone. Despite a significant increase in energy consumption from 57.8 to 349 kWh kg −1 TOC, the process offers enhanced degradation efficiency and improved environmental performance, indicating its strong potential for advanced leachate treatment applications. © 2025 The Author(s). Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).