Combined humic acid adsorption and enhanced Fenton processes for the treatment of naphthalene dye intermediate wastewater

► A combined HA adsorption and enhanced Fenton oxidation was applied. ► A two-staged Fenton with inner circulation was introduced as enhanced Fenton. ► 1,2,4-Acid can be effectively removed in this combined process. ► The increased COD removal and reduced H2O2 consumption was achieved. ► Main intermediates were detected using UPLC-(ESI)-TOF-HRMS technique.