Metronidazole (MTZ), an extensively used antibiotic and antiparasitic drug for treating infections, has been reported as a hazardous micropollutant that has detrimental ecotoxic effects on aquatic species and the environment. Therefore, effective treatment to remove hazardous MTZ from water is needed. Sulfate radical anion–based advanced oxidation processes (S-AOPs) are promising water treatment techniques for the degradation of organic pollutants. Hence, we aimed to study the ability of heat-activated persulfate (HA/PS)–based S-AOP for the degradation and detoxification of MTZ. The pseudo-first-order rate constant value for the degradation of MTZ by HA/PS was calculated to be 0.059 min−1 in reverse osmosis (RO) water, achieving 99.2% of MTZ within 80 min under optimum conditions. As the initial concentration of MTZ was increased (60–2000 µg/L), the degradation efficiency decreased, whereas with an increase in initial PS (0.1 to 0.8 mM) concentration, the degradation efficiency increased. The thermal activation energy was determined to be 134.47 kJ·mol−1. The HA/PS system was effective in the wide pH range (2.5 to 10.5). The <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11356_2025_36984_Article_IEq1.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="40" /> </InlineMediaObject> <EquationSource Format="TEX">$\mathrm{SO}_4^{\bullet-}$</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mi mathvariant="normal">SO</mi> <mn>4</mn> <mrow> <mo>∙</mo> <mo>-</mo> </mrow> </msubsup> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11356_2025_36984_Article_IEq2.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="33" /> </InlineMediaObject> <EquationSource Format="TEX">$\mathrm{HO}^\bullet$</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <mi mathvariant="normal">HO</mi> </mrow> <mo>∙</mo> </msup> </math></EquationSource> </InlineEquation> were attributed to the degradation of MTZ with <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="11356_2025_36984_Article_IEq1.gif" Format="GIF" Height="20" Rendition="HTML" Resolution="72" Type="Linedraw" Width="40" /> </InlineMediaObject> <EquationSource Format="TEX">$\mathrm{SO}_4^{\bullet-}$</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mi mathvariant="normal">SO</mi> <mn>4</mn> <mrow> <mo>∙</mo> <mo>-</mo> </mrow> </msubsup> </math></EquationSource> </InlineEquation> as a prominent reactive species. Chloride and humic acid water constituents reduced the degradation efficiency by 48.66% and 28.75%, respectively, as compared to RO water. Further, density functional theory (DFT) identified the susceptible sites of MTZ for the radical attack. Degradation byproducts were analyzed by liquid chromatography mass spectrometry (LC–MS), and degradation pathways were presented. Importantly, more than 95% mineralization was observed in 240 min of treatment. ECOSAR analysis predicted MTZ as toxic, whereas the degradation byproducts were non-toxic. Electrical energy per order (EEO) and cost for the degradation of MTZ were determined to be 19.394 kWh/m3/order and $1.520/m3, respectively. Degradation of MTZ occurred in various water matrices, namely, tap water (TW) and wastewater (WW), revealing that the HA/PS system effectively removed MTZ micropollutant. Therefore, the HA/PS system is efficient, energy-saving, and cost-effective, and the study provides insight to augment the HA/PS system as an effective S-AOP for degradation and detoxification of hazardous organic micropollutants. Graphical abstract Degradation of metronidazole by heat-activated persulfate system.

Degradation of metronidazole by heat-activated persulfate: mechanism, water matrix, ecotoxicity removal, and energy-efficiency analysis

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发表日期：

2025年9月26日

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Himani Arora,
Atul Patel,
Jemi Gandhi,
Athul Krishna Makkoottathil,
Halan Prakash

摘要

Metronidazole (MTZ), an extensively used antibiotic and antiparasitic drug for treating infections, has been reported as a hazardous micropollutant that has detrimental ecotoxic effects on aquatic species and the environment. Therefore, effective treatment to remove hazardous MTZ from water is needed. Sulfate radical anion–based advanced oxidation processes (S-AOPs) are promising water treatment techniques for the degradation of organic pollutants. Hence, we aimed to study the ability of heat-activated persulfate (HA/PS)–based S-AOP for the degradation and detoxification of MTZ. The pseudo-first-order rate constant value for the degradation of MTZ by HA/PS was calculated to be 0.059 min⁻¹ in reverse osmosis (RO) water, achieving 99.2% of MTZ within 80 min under optimum conditions. As the initial concentration of MTZ was increased (60–2000 µg/L), the degradation efficiency decreased, whereas with an increase in initial PS (0.1 to 0.8 mM) concentration, the degradation efficiency increased. The thermal activation energy was determined to be 134.47 kJ·mol⁻¹. The HA/PS system was effective in the wide pH range (2.5 to 10.5). The $\mathrm{SO}_4^{\bullet-}$ ${SO}_{4}^{∙ -}$ and $\mathrm{HO}^\bullet$ ${HO}^{∙}$ were attributed to the degradation of MTZ with $\mathrm{SO}_4^{\bullet-}$ ${SO}_{4}^{∙ -}$ as a prominent reactive species. Chloride and humic acid water constituents reduced the degradation efficiency by 48.66% and 28.75%, respectively, as compared to RO water. Further, density functional theory (DFT) identified the susceptible sites of MTZ for the radical attack. Degradation byproducts were analyzed by liquid chromatography mass spectrometry (LC–MS), and degradation pathways were presented. Importantly, more than 95% mineralization was observed in 240 min of treatment. ECOSAR analysis predicted MTZ as toxic, whereas the degradation byproducts were non-toxic. Electrical energy per order (EEO) and cost for the degradation of MTZ were determined to be 19.394 kWh/m³/order and $1.520/m³, respectively. Degradation of MTZ occurred in various water matrices, namely, tap water (TW) and wastewater (WW), revealing that the HA/PS system effectively removed MTZ micropollutant. Therefore, the HA/PS system is efficient, energy-saving, and cost-effective, and the study provides insight to augment the HA/PS system as an effective S-AOP for degradation and detoxification of hazardous organic micropollutants.

Graphical abstract

Degradation of metronidazole by heat-activated persulfate system.