A walnut shell biochar-nano zero-valent iron composite membrane for the degradation of carbamazepine via persulfate activation

Abstract

In this study, novel walnut shell biochar-nano zero-valent iron nanocomposites (WSBC-nZVI) were synthesized using a combined pyrolysis/reduction process. WSBC-nZVI displayed a high removal efficiency (86 %) for carbamazepine (CBZ) compared with walnut shell biochar (70 %) and nano zero-valent iron (76 %) in the presence of persulfate (PS) (0.5 g/L catalyst, 10 mg/L CBZ, 1 mM persulfate). Subsequently, WSBC-nZVI was applied for the fabrication of the membrane using a phase inversion method. The membrane demonstrated an excellent removal efficiency of 91 % for CBZ in a dead-end system (2 mg/L CBZ, 1 mM persulfate). In addition, the effect of various operating conditions on the degradation efficiency in the membrane/persulfate system was investigated. The optimum pH was close to neutral, and an increase in CBZ concentration from 1 mg/L to 10 mg/L led to a drop in removal efficiency from 100 % to 24 %. The degradation mechanisms indicated that oxidative species, including ¹O₂, OH, SO₄^-, and O₂^-, all contribute to the degradation of CBZ, while the role of ¹O₂ is highlighted. The CBZ degradation products were also investigated, and the possible pathways and the predicted toxicity of intermediates were proposed. Furthermore, the practical use of the membrane was validated by the treatment of real wastewater.

Keywords: Catalytic membrane; Mechanisms; Nano zero-valent iron; Persulfate; Walnut shell biochar.