<p>This study explores the resource utilization of edible mushroom dregs by synthesizing a zero-valent iron biochar composite (Fe-BC) using FeCl₃ as the iron source through an impregnation-pyrolysis method. This composite material is then used to activate peroxymonosulfate (PMS) for the degradation of malachite green (MG), investigating the feasibility of a "waste-to-waste" approach. The chemical composition and morphological characteristics of the Fe-BC composite were thoroughly analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), which confirmed the successful incorporation of zero-valent iron. The catalytic performance tests showed that the Fe/BC + PMS system exhibited minimal sensitivity to anionic interference and maintained high catalytic activity across a broad pH range (5.0 to 9.0), achieving a degradation efficiency of 98% for MG within 20 min. Quenching experiments and electron paramagnetic resonance (EPR) analysis revealed that sulfate radicals (SO₄·⁻), hydroxyl radicals (·OH), and singlet oxygen (¹O₂) were the primary reactive species responsible for the degradation process. Furthermore, the Fe-BC composite demonstrated exceptional stability and reusability, maintaining high catalytic activity after five consecutive cycles, which highlights its significant potential for sustainable environmental applications and the resource utilization of agricultural waste.</p>