<p>Green-synthesized magnetite nanoparticles were used as catalysts in the electro-Fenton process for treating real pulp and paper industry wastewater. To synthesize nanoparticles Mangifera indica leaf extract was used. The synthesized nanoparticles were characterized using Field-Emission Scanning Electron Microscopy, Fourier Transform Infrared Spectroscopy, Energy-dispersive X-ray spectroscopy, and X-ray diffraction. The Electro-Fenton reactor with graphite electrodes achieved 84.03 ± 1.84% chemical oxygen demand removal in 30&#xa0;min under optimized conditions (voltage 7&#xa0;V, pH 3, catalyst 200 mg L^− 1, and electrode spacing 3&#xa0;cm). Radical scavenging experiments indicated the significant involvement of hydroxyl radicals in the oxidation process. High-resolution mass spectrometry illustrated the breakdown of high-molecular-weight lignin oligomers into lower-molecular-weight oxygenated intermediates. Comparative homogeneous and heterogeneous electro-Fenton experiments indicated that the surface-mediated catalysis was the predominant oxidation pathway. The increase in the ratio of biochemical oxygen demand to chemical oxygen demand from 0.254 to 0.450 denoted that the treated effluent was more biodegradable. The efficiency of the catalyst remained at 71.89% after three cycles. Thus, the electro-Fenton technique, which uses green-synthesized nanoparticles, is an efficient treatment approach for pulp and paper industry wastewater.</p> Graphical Abstract <p></p>