Activation of peroxymonosulfate using biochar for the removal of trimethoprim: Effect of ball milling on catalytic efficiency, degradation pathway, and the contribution of the radical and non-radical processes

Chandola, Dinesh and Veres, Bence and Varga, Gábor and Szamosvölgyi, Ákos and Páli, Tibor László and Sebők-Nagy, Krisztina and Kozma, Gábor and László, Zsuzsanna and Kónya, Zoltán and Alapi, Tünde (2026) Activation of peroxymonosulfate using biochar for the removal of trimethoprim: Effect of ball milling on catalytic efficiency, degradation pathway, and the contribution of the radical and non-radical processes. JOURNAL OF WATER PROCESS ENGINEERING, 81. no.-109371. ISSN 2214-7144

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Abstract

The combination of biochar (BC) and peroxymonosulfate (PMS) is a cost-effective strategy for removing pollutants; however, optimization of BC synthesis and reaction parameters is essential. In this work, one-step pyrolysis was used for biochar production, and trimethoprim (TRIM) antibiotic degradation was investigated in the presence of PMS-containing biochar suspension. For the production of an effective biochar catalyst, grass pellets as the raw material, a pyrolysis temperature of 700 degrees C, and a ball-milling time of 15 min proved optimal for TRIM degradation. The effect of pyrolysis temperature highlighted that the appropriate degree of graphitization is a key factor in catalytic efficiency, while persistent free radicals (PFRs) on the surface play only a moderate role. Ball milling significantly reduced the amount of biochar (3.0 gdm-3-* 0.5 gdm-3) and PMS (2.0 mM-* 0.2 mM) required for TRIM degradation. In addition to the increased surface area, the enhanced density of structural defects serves as active sites, and changes in surface oxidation state also contribute to the enhanced efficiency of ball-milled biochar. The effect of radical scavengers clearly confirmed that, without ball milling, the main reactive species is 1O2, and the non-radical pathway leads to the conversion of TRIM. In the case of ball-milled biochar, radical (HO center dot and SO4 center dot-) formation is favored, and the radical-based pathway dominates in the TRIM conversion. Although treated wastewater reduced the degradation efficiency, this effect was mitigated by higher BC and PMS doses. Furthermore, the results regarding the reusability of BC and its successful regeneration by UV/PDS underscore the potential of this process.

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