The occurrence of natural estrogens including estrone (E1), 17β-estradiol (E2), and synthetic 17α-ethinylestradiol (EE2), which can be excreted by both humans and animals, and can enter the aqueous environment along with the discharge of domestic sewage, is a major concern since this may represent a serious health risk to humans even at extremely trace levels (ng·L⁻¹). Simultaneous degradation of three coexisting steroid estrogens (SEs) in aqueous solutions by coupled ultrasound and KMnO₄ systems (KMnO₄/ultrasound) were investigated to find out whether there is a competitive degradation of multiple contaminants or not. Results indicate that the degradation ratios of target SEs were all more than 50% after 120 min reaction contact, greatly enhanced when compared with the single KMnO₄ (2 mg·L⁻¹) oxidation of E2 (37.0%), EE2 (34.4%), and E1 (34.0%), and the single sonochemical oxidation of E2 (37.1%), EE2 (31.1%), and E1 (29.7%). In the adopted processes, the degradations of SEs fit the first-order kinetic reaction, with different reaction rates. Kinetic parameters revealed there was little difference between coexisting SEs, which means there was almost no competitive degradation. The removal efficiency and degradation rate of SEs in natural water was higher than those in pure water, which suggested that the coupled KMnO₄/ultrasound technology had prospective applications in the removal of complex contaminants in actual drinking water treatment.

The overall objective of this study is to conduct pilot-scale experiments to examine the effects of the direct continuous recycling of combined residual streams (CRS) of clarifier sludge (CS) and filter backwash water (FBWW) on effluent quality in summer and winter. Specifically, the parameters of sedimentation and filtration effluent quality such as turbidity, color, organic matter [e.g., dissolved organic carbon (DOC) and total organic carbon (TOC)], ultraviolet absorbance at 254 nm (${\mathrm{UV}}_{254}$ ), Trihalomethane formation potentials (THMFPs), and metallic elements (e.g., Fe, Al, and Mn) were measured. The experimental results indicate that the continuous direct recycling of the CRS is a feasible method for not only reducing the required coagulant dosage but also improving the contaminant removal efficiency. The coagulant usage was reduced by up to 33.33% at 20°C and 25.00% at 4°C compared to control trials. Over the entire operation period, there was no significant accumulation of contaminants. The temperature exerted a significant impact on the required coagulant dosage and treatment efficiency. Additionally, this study proposes that the continuous operation periods are at the range of 10 to 12 days.

Iron-rich sludge, generated during flocculation/sedimentation processes by using Fe-based coagulant in drinking water treatment plants, could be used as a precursor to prepare an effective peroxymonosulfate (PMS) activator (Fe₃O₄@SiO₂) for the ciprofloxacin (CIP) degradation via facile hydrothermal treatment. The catalytic performances of raw iron-rich sludge and Fe₃O₄@SiO₂ were evaluated. The removal rate of CIP in Fe₃O₄@SiO₂/PMS system increased from 44.7% to 82.8% within 60 min compared with the raw iron-rich sludge. The effects of PMS, catalyst loadings, temperature, and initial pH on the CIP degradation were examined, demonstrating that acidic conditions and higher temperatures were beneficial for CIP degradation. Both sulfate radicals (SO₄^•−) and hydroxyl radicals (^•OH) contributed to the CIP degradation, and SO₄^•− was predominated in the Fe₃O₄@SiO₂/PMS system, which was confirmed by the result of electron paramagnetic resonance (EPR) analysis and radical quenching tests. The mechanisms of the PMS activation process by Fe₃O₄@SiO₂ were elucidated, and the influencing factors were among which the role of the iron mineral phase was emphatically explored. This study provides a facile method to convert the recycled waste iron-rich sludge to magnetic heterogeneous catalysts for CIP degradation with PMS activation.