Ultrasonic treatment enhances the formation of oxygen vacancies and trivalent manganese on α-MnO2 surfaces: Mechanism and application.

Catalytic activity is the main obstacle limiting the application of peroxymonosulfate (PMS) activation on transition metal oxide catalysts in organic pollutant removal. Herein, ultrasonic treatment was applied to α-MnO2 to fabricate a new u-α-MnO2 catalyst for PMS activation. Dimethyl phthalate (DMP, 10 mg/L) was almost completely degraded within 90 min, and the pseudofirst-order rate constant for DMP degradation in the u-α-MnO2/PMS system was ∼7 times that in the initial α-MnO2/PMS system. The ultrasonic treatment altered the crystalline and pore structures of α-MnO2 and produced defects on the u-α-MnO2 catalyst. According to the XPS, TG, and EPR results, higher contents of trivalent Mn and oxygen vacancies (OVs) were produced on the catalyst surfaces. The OVs induced the decomposition of PMS to produce 1O2, which was identified as the main reactive oxygen species (ROS) responsible for DMP degradation. The u-α-MnO2 catalyst presented great reusability, especially by ultrasonic regeneration of OVs toward the used catalyst. This study provides new insights into regulating OVs generation and strengthening catalyst activity in the PMS activation process for its application in water purification.

Environmental impacts of antibiotics addition to algal-bacterial-based aquaponic system.

Antibiotics usage is a double-edged sword among the production promotion and environmental aggravation of aquaculture system. In this study, the effects of sulfadiazine addition on algal-bacterial-based aquaponic (AA) system were thoroughly investigated. Results showed that sulfadiazine addition increased the nitrogen (N) and carbon (C) recovery of AA system by 1.3 times and 2.9 times, respectively. Meanwhile, the global warming potential was increased by 63% due to aggravated nitrous oxide (N2O) emission. This was mainly because sulfadiazine increased the abundance of nirS genes and decreased the abundance of nosZ genes, which subsequently led to higher N2O accumulation. Furthermore, resistance gene (sul-1, sul-2, and intI-1) abundance in the treatment group was an order higher than that of the control group, which would give rise to the environmental risk for agroecological system. KEY POINTS: • Sulfadiazine addition increased NUE at expense of aggravated GHG emissions. • Sulfadiazine disrupted the balance between the abundance of nirS and nosZ genes. • Sulfadiazine addition increased the resistance gene abundance of AA system.