Dissolved organic matter (DOM) irradiated by sunlight generates photo-oxidants that can accelerate organic contaminant degradation in surface waters. However, the significance of this process to contaminant removal during engineered UV water treatment has not been demonstrated, partly due to a lack of suitable methods in the deep UV range. This work expands methods previously established to detect (1)O2, HO•, H2O2, and DOM triplet states ((3)DOM*) at solar wavelengths to irradiation at 254 nm, typical of UV water treatment. For transient intermediates, the methods include a photostable probe combined with selective scavengers. Quantum yields for (1)O2, (3)DOM* and H2O2 were in the same range as for solar-driven reactions but were an order of magnitude higher for HO•, which other experiments indicate is due to H2O2 reduction. With the quantum yields, the degradation of metoxuron was successfully predicted in a DOM solution irradiated at 254 nm. Further modeling showed that the contribution of DOM sensitization to organic contaminant removal during UV treatment should be significant only at high UV fluence, characteristic of advanced oxidation processes. Of the reactive species studied, (3)DOM* is predicted to have the greatest general influence on UV degradation of contaminants.
Hydraulic fracturing of unconventional gas wells utilizes large volumes of water-based fluid to increase formation permeability and, as a result, generates large amounts of wastewater as flowback. This water requires suitable treatment before being reused or discharged into the environment. A principal ingredient of flowback water is guar gum (a gelling agent), which may adversely affect advanced flowback water treatment such as membrane separation. This study demonstrates the potential of an activated sludge mixed liquor to degrade guar under typical flowback conditions [i.e., high concentrations of total dissolved solids (TDS)]. Guar was efficiently degraded at a TDS concentration of 1500 mg/L, with more than 90% of the dissolved chemical oxygen demand (COD d ) having been removed after 10 h. Increasing the TDS concentration to 45000 mg/L inhibited COD d degradation to 60% removal after 31 h. A high TDS concentration additionally resulted in an increased effluent level of total suspended solids and turbidity; however, these were efficiently reduced using ferric chloride coagulation followed by sedimentation and filtration. Biological reduction of the guar concentration increased the flux of a bench-scale ultrafiltration membrane, demonstrating the potential of the process to treat flowback water prior to membrane separation.
The efficiency of wastewater treatment systems in removing pharmaceuticals is often assessed on the basis of the decrease in the concentration of the parent compound. However, what is perceived as "removal" during treatment may not necessarily mean mineralization of the pharmaceutical compound but simply conversion into different transformation products (TPs). Using liquid chromatography coupled to a quadrupole time-of-flight mass spectrometer (LC-QToF-MS), we demonstrated conversion of iopromide in wastewater to at least 14 TPs after an advanced oxidation process (AOP) using UV (fluence = 1500 mJ/cm(2)) and H2O2 (10 mg/L). Due to the complexity of the wastewater matrix, the initial experiments were performed using a high concentration (10 mg/L) of iopromide in order to facilitate the identification of TPs. Despite the high concentration of iopromide used, cursory inspection of UV and mass spectra only revealed four TPs in the chromatograms of the post-AOP samples. However, the use of METLIN database and statistics-based profiling tools commonly used in metabolomics proved effective in discriminating between background signals and TPs derived from iopromide. High-resolution mass data allowed one to predict molecular formulas of putative TPs with errors below 5 ppm relative to the observed m/z. Tandem mass spectrometry (MS/MS) data and isotope pattern comparisons provided necessary information that allowed one to elucidate the structure of iopromide TPs. The presence of the proposed iopromide TPs was determined in unspiked wastewater from a municipal wastewater treatment plant, but no iopromide and TPs were detected. Using analogous structural modifications and oxidation that results from the AOP treatment of iopromide, the potential TPs of iopamidol (a structurally similar compound to iopromide) were predicted. The same mass fragmentation pattern observed in iopromide TPs was applied to the predicted iopamidol TPs. LC-QToF-MS revealed the presence of two iopamidol TPs in unspiked AOP-treated wastewater.
The COVID-19 pandemic has severely impacted public health worldwide. Evidence of SARS-CoV-2 transmission via aerosols and surfaces has highlighted the need for efficient indoor disinfection methods. For instance, the use of ozone gas as a safe and potent disinfectant against SARS-CoV-2 virus is of particular interest. Here we tested the use of pseudoviruses as a model for evaluating ozone disinfection of the coronavirus at ozone concentrations of 30, 100, and 1000 ppmv. Results show that ozone disinfection rate of pseudoviruses was similar to that of coronavirus 229E (HuCoV-229E) at short contact times, below 30 min. Viral infection decreased by 95% following ozone exposure for 20 min at 1000 ppmv, 30 min at 100 ppmv and about 40 min at 30 ppmv. This findings mean that ozone is a powerful disinfectant toward the enveloped pseudovirus even at low ozone exposure. We also showed that viral disinfection occurs on various contaminated surfaces, with a positive association between disinfection and surface hydrophilicity. Infected surfaces made of aluminum alloy, for example, were better disinfected with ozone as compared to brass, copper, and nickel surfaces. Lastly, we demonstrate the advantage of ozone over liquid disinfectants by showing similar viral disinfection on top, side, bottom, and interior surfaces. Overall, our study demonstrates the potential use of ozone gas disinfection to combat the COVID-19 outbreak.
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