Free nitrous acid (FNA)-based applications have been broadly adopted in the development of novel wastewater management technologies, but a basic understanding of the effect of the chemical properties of FNA on the elimination of micropollutants is still lacking. This study aims to comprehensively evaluate FNA-based elimination of sulfamethoxazole (SMX), which is a typical species of sulphonamide antibiotics. Batch experiments were conducted under different influencing factors to investigate the antibiotics elimination processes. We found that FNA showed specific efficacy on sulphonamides characterized by sulfonamide and aniline functional groups, such as SMX. SMX degradation was affected by the initial SMX concentration, FNA concentration and solution pH and described by $d\left[SMX\right]/\text{dt}=-0.29e^{-1.69pH}{\left[SMX\right]}^{0.945}{\left[FNA\right]}^{1.35}$. The cationic forms of SMX were more reactive towards FNA-based active components. Sulfonamide bond (S-N or C-S bonds) cleavage, nitrosubstitution, deamination and radical oxidation were proposed to be the relevant transformation pathways. The FNA-based technique was not effective for diminishing toxicity, but this process could strongly control antibacterial activity.

基于游离亚硝酸（FNA）的应用已广泛用于新型废水管理技术的开发中，但仍缺乏对FNA的化学性质对消除微量污染物的影响的基本了解。这项研究旨在全面评估基于FNA的磺胺类抗生素的典型消灭作用-磺胺甲恶唑（SMX）。在不同的影响因素下进行了批量实验，以研究抗生素消除过程。我们发现FNA对以磺酰胺和苯胺官能团（例如SMX）为特征的磺酰胺显示出特定功效。SMX降解受初始SMX浓度，FNA浓度和溶液pH值的影响，并通过$d\left[\mathrm{小号}\mathrm{中号}X\right]/\text{dt}=-0.29{Ë}^{-1.69pH}{\left[\mathrm{小号}\mathrm{中号}X\right]}^{0.945}{\left[Fñ\mathrm{一种}\right]}^{1.35}$。SMX的阳离子形式对基于FNA的活性成分更具反应性。磺酰胺键（SN或CS键）的裂解，硝基取代，脱氨基和自由基氧化被认为是相关的转化途径。基于FNA的技术无法有效降低毒性，但是此过程可以强烈控制抗菌活性。