<p>Peroxymonosulfate (PMS) alkaline activation has gained considerable interest in advanced oxidation processes for wastewater treatment due to its reduced secondary pollution, high economic efficiency, and strong degradation capability. This study hypothesized that a gradual increase in pH would improve and maintain the alkaline activation of PMS more than rapid pH shift. Magnesium peroxide (MgO₂)-based PMS system was proposed to control the alkaline activation of PMS. Under equal molar dosage, the MgO₂/PMS system removed 60.7% of acetaminophen (ACT), while NaOH/PMS and CaO₂/PMS systems oxidized 43.3% and 18.2% of ACT, respectively. Although the initial reaction rate in CaO₂/PMS system was faster than that in the MgO₂/PMS system, the MgO₂/PMS system ultimately demonstrated greater overall ACT removal, even with higher PMS consumption. These results indicate that MgO₂-based gradual activation enhances pollutant removal and prolongs the persistence of reaction. Furthermore, the MgO₂-PMS system showed less interference by co-existing anions, including Cl⁻, SO₄²⁻, NO₃⁻, HCO₃⁻, and HPO₄²⁻. In the system, singlet oxygen (¹O₂) and superoxide radical (O₂˙) were the dominant reactive species responsible for degradation of ACT. In conclusion, the MgO₂/PMS system proposed in this study is a promising alternative for wastewater treatment due to its simple process, efficient PMS utilization, high adaptability, and significantly enhanced pollutant removal via gradual alkaline activation.</p>