Electrochemical Oxidation-Membrane Distillation Hybrid Process: Utilizing Electric Resistance Heating for Distillation and Membrane Defouling through Thermal Activation of Anodically Formed Persulfate.

This study reports distillation-based salt removal by Ohmic heating in a hybrid process, in which electrochemical oxidation (EO) and direct contact membrane distillation (DCMD) are performed sequentially. In addition to anodically destructing the organics, the hybrid process also separated the sulfate-based electrolytes from treated water through distillation, without consuming external energy, owing to the temperature of the aqueous sulfate solution being elevated to 70 °C via resistive heating. The hybrid process treated organic compounds in a nonselective fashion, whereas DCMD alone did not completely reject (semi)volatile organics. Integrating EO with DCMD made the hybrid process resistant toward the wetting phenomenon; the process exhibited a steady distillate flux and salt rejection as the initial loading of amphiphilic sodium dodecyl sulfate was increased to 0.3 mM. Anodic persulfate formation from the sulfate and Ohmic heating caused an in situ yield of the sulfate radical in the feed solution; this eliminated membrane fouling, according to the observation that the water flux, which was drastically reduced upon adding alginate, was recovered immediately after an electric current was applied. The hybrid process concurrently decomposed spiked organics and removed naturally present inorganic ions in actual flue gas desulfurization wastewater, without an external supply of electrolyte and heat energy.

A multi-scale framework for modeling transport of microplastics during sand filtration: Bridging from pore to continuum.

The fate and transport of microplastics (MPs) during deep bed filtration were investigated using combined laboratory experiments and numerical modeling. A series of column experiments were conducted within the designated ranges of six operating parameters (i.e., size of the MP and collector, seepage velocity, porosity, temperature, and ionic strength). A variance-based sensitivity analysis, the Fourier amplitude sensitivity test, was conducted to determine the priority in affecting both the attachment coefficient at the pore scale, and the subsequent stabilized height of the breakthrough curve at the continuum scale, which follows non-monotonic trends with singularity in the size of MP (i.e., 1 µm). Finally, Damkohler numbers were introduced to analyze the dominant mechanisms (e.g., attachment, detachment, or straining) in the coupled hydro-chemical process. The robustness of conceptual frameworks bridges the gap between pore-scale interactions and the explicit MPs removal in the continuum scale, which could support decision-making in determining the priority of parameters to retain MPs during deep bed filtration.

Real-time morphological detection of label-free submicron-sized plastics using flow-channeled differential interference contrast microscopy.

Owing to the surge in plastic waste generated during the COVID-19 pandemic, concerns regarding microplastic pollution in aqueous environments are increasing. Since microplastics (MPs) are broken down into submicron (< 1 µm) and nanoscale plastics, their real-time morphological detection in water is necessary. However, the decrease in the scattering cross-section of MPs in aqueous media precludes morphological detection by bright-field microscopy. To address this problem, we propose and demonstrate a differential interference contrast (DIC) system that incorporates a magnification-enhancing system to detect MPs in aqueous samples. To detect MPs in both the stationary and mobile phases, a microfluidic chip was designed, taking into consideration the imaging depth of focus and flow resistance. MPs of various sizes flowing in deionized, tap, and pond water at varying speeds were observed under Static and Flow conditions. Successful real-time morphological detection and quantification of polystyrene beads down to 200 nm at a constant flow rate in water were achieved. Thus, the proposed novel method can significantly reduce analysis time and improve the size-detection limit. The proposed DIC microscopy system can be coupled with Raman or infrared spectroscopy in future studies for chemical composition analysis. ENVIRONMENTAL IMPLICATION: Microplastics (MPs), particularly submicron plastics < 1-µm, can pose a risk to human health and aquatic ecosystems. Existing methods for detecting MPs in the aqueous phase have several limitations, including the use of expensive instruments and prolonged and labor-intensive procedures. Our results clearly demonstrated that a new low-cost flow-channeled differential interference contrast microscopy enables the real-time morphological detection and quantification of MPs down to 200 nm under flowing conditions without sample labeling. Consequently, our proposed rapid method for accurate quantitative measurements can serve as a valuable reference for detecting submicron plastics in water samples.

Photocatalytic applications of paper-like poly(vinylidene fluoride)-titanium dioxide hybrids fabricated using a combination of electrospinning and electrospraying.

A paper-like photocatalyst was fabricated by electrospraying an N,N'-dimethylformamide (DMF) dispersion of titanium dioxide (TiO2) nanoparticles (NPs) on a poly(vinylidene fluoride) nanofiber (PVDF NF) mat prepared by electrospinning. Morphological studies revealed that the TiO2 NPs uniformly deposited as clusters on the surface of the PVDF NF mat. The immobilized amount of TiO2 was found to be 2.08, 2.44, 3.80, and 4.73 mg per 45 cm(2) of PVDF-TiO2 hybrids for the electrospraying of 10, 20, 40, and 60 ml of TiO2-DMF, respectively. The hybrid photocatalysts were effective in degrading bisphenol A (BPA), 4-chlorophenol (4-CP), and cimetidine (CMT), which dissolved in both deionized water and secondary wastewater effluents, with activity being proportional to the quantity of TiO2 NPs immobilized. For the highest loading amount of TiO2, BPA, 4-CP, and CMT degraded completely within 100, 100, and 40 min of UV irradiation, respectively. Stable photo-oxidation of CMT was maintained through 10 repeated cycles. During these cycles, it was confirmed that there was no loss of TiO2 NPs by inductively coupled plasma optical emission spectrometry. Our results suggest that effective and stable PVDF-TiO2 hybrid photocatalysts can be fabricated on a large scale by combining electrospinning and electrospraying techniques.

Titanium dioxide nanofibers integrated stainless steel filter for photocatalytic degradation of pharmaceutical compounds.

A photocatalytically active stainless steel filter (P-SSF) was prepared by integrating electrospun TiO2 nanofibers on SSF surface through a hot-press process where a poly(vinylidene fluoride) (PVDF) nanofibers interlayer acted as a binder. By quantifying the photocatalytic oxidation of cimetidine under ultraviolet radiation and assessing the stability of TiO2 nanofibers integrated on the P-SSF against sonication, the optimum thickness of the TiO2 and PVDF layer was found to be 29 and 42 µm, respectively. At 10L/m(2)h flux, 40-90% of cimetidine was oxidized when the thickness of TiO2 layer increased from 10 to 29 µm; however, no further increase of cimetidine oxidation was observed as its thickness increased to 84 µm, maybe due to limited light penetration. At flux conditions of 10, 20, and 50 L/m(2) h, the oxidation efficiencies for cimetidine were found to be 89, 64, and 47%, respectively. This was attributed to reduced contact time of cimetidine within the TiO2 layer. Further, the degradation efficacy of cimetidine was stably maintained for 72 h at a flux of 10 L/m(2) h and a trans-filter pressure of 0.1-0.2 kPa. Overall, our results showed that it can potentially be employed in the treatment of effluents containing organic micropollutants.

Mechanism of C60 photoreactivity in water: fate of triplet state and radical anion and production of reactive oxygen species.

The mechanism involved with (1) energy and electron transfer by C60 in the aqueous phase during UV irradiation and (2) subsequent production of reactive oxygen species (ROS) such as singlet oxygen and superoxide radical anion was investigated. Electron paramagnetic resonance (EPR) study showed that C60 embedded in micelles of nonionic surfactant (Triton X 100) or anionic surfactant (sodium dodecylbenzenesulfonate) produced ROS, but aggregated C60 did not, consistent with our earlier findings made using indicator chemicals. Nanosecond and femtosecond laser flash photolysis showed that the aggregation of C60 significantly accelerates the decay of excited triplet state C60, which is a key intermediate for energy and electron transfer, thus blocking the pathway for ROS production. This finding suggests that C60 clusters will not contribute to oxidative damage or redox reactions in natural environment and biological systems in the same way molecular C60 in organic phase reportedly does. In contrast, C60 embedded in surfactant micelles produces ROS and the evidence is presented for the formation of C60 radical anion as an intermediate.