Energy-effective elimination of harmful microcystins by a non-thermal plasma process

Enhanced oxidation of parabens in an aqueous solution by air-assisted cold plasma

Various contaminants of emerging concern (CECs) including pharmaceuticals and personal care products (PPCPs) have been known to threaten the aquatic ecosystem and human health even at low levels in surface water. Among them, the wide variety use of parabens as preservatives may pose potential threat to human because parabens may present estrogenic activity. Various advanced oxidation processes have been attempted to reduce parabens, but challenges using cold plasma (CP) are very rare. CP is worth paying attention to in reducing parabens because it has the advantage of generating radical ions, including reactive oxygen/nitrogen species and various ions. Accordingly, this study demonstrates how CP can be utilized and how CP competes with other advanced oxidation processes in energy requirements. Quantified ethyl-, propyl-, and butyl-paraben indicate that CP can effectively degrade them up to 99.1% within 3 h. Regression reveals that the kinetic coefficients of degradation can be increased to as high as 0.0328 min-1, comparable to other advanced oxidation processes. Many by-products generated from the oxidation of parabens provide evidence of the potential degradation pathway through CP treatment. In addition, we found that the electrical energy consumption per order of CP (39-95 kWh/m3/order) is superior to other advanced oxidation processes (69∼31,716 kWh/m3/order). Overall, these results suggest that CP may be a viable option to prevent adverse health-related consequences associated with parabens in receiving water.

Cooperative and Bifunctional Adsorbent-Catalyst Materials for In-situ VOCs Capture-Conversion

Volatile organic compounds (VOCs) are gases that are emitted into the air from products or processes and are major components of air pollution that significantly deteriorate air quality and seriously affect human health. Different types of metals, metal oxides, mixed-metal oxides, polymers, activated carbons, zeolites, metal-organic frameworks (MOFs) and mixed-matrixed materials have been developed and used as adsorbent or catalyst for diversified VOCs detection, removal, and destruction. In this comprehensive review, we first discuss the general classification of VOCs removal materials and processes and outline the historical development of bifunctional and cooperative adsorbent-catalyst materials for the removal of VOCs from air. Subsequently, particular attention is devoted to design of strategies for cooperative adsorbent-catalyst materials, along with detailed discussions on the latest advances on these bifunctional materials, reaction mechanisms, long-term stability, and regeneration for VOCs removal processes. Finally, challenges and future opportunities for the environmental implementation of these bifunctional materials are identified and outlined with the intent of providing insightful guidance on the design and fabrication of more efficient materials and systems for VOCs removal in the future.

Near dissolved organic matter microfiltration (NDOM MF) coupled with UVC LED disinfection to maximize the efficiency of water treatment for the removal of Giardia and Cryptosporidium

Microfiltration (MF) membranes with a mean pore size same as or smaller than 0.45 µm have been typically used to separate pathogenic protozoa in water since materials larger than 0.45 µm are considered particulates. However, 0.45 µm is too small to separate protozoa which are 4-6 µm (Cryptosporidium oocyst) or 8-15 µm (Giardia cyst) in size. In this study, we optimized the mean pore size of MF membranes to maximize the producibility and guarantee a high removal rate simultaneously and proposed the membrane filtration using an MF membrane with an optimum mean pore size larger than but close to dissolved organic matter (DOM), which is called near DOM MF (NDOM MF). According to the MF test using polystyrene surrogate beads with diameters of 3 and 8 µm, an MF membrane with a 0.8 µm mean pore size was the best in that it showed 52% to 146% higher water fluxes than a 0.45 µm MF membrane while maintaining the removal rate at 3-4 log. It was also the case for a low-temperature MF test, revealing the NDOM MF is highly effective regardless of temperature changes. Lastly, we tried to find the possibility of combining the NDOM MF with disinfection by an ultraviolet light emitting diode (UVC LED) to further guarantee the high quality of treated water while providing high process efficiency.

Cold plasma-assisted regeneration of biochar for dye adsorption

Environmental remedies, including adsorption-based water purification, are now being asked to meet the requirement for a low-carbon circular economy requiring low energy and low material consumption. In this regard, we tested the possibility of regenerating adsorbents via cold plasma (CP) treatment for less use of adsorbents and no washing solution. In the adsorption of methylene blue (MB) using carbonized rice husk (CRH) and five successive regeneration cycles by CP treatment, the removal efficiencies were maintained at a moderate level (∼70% of the initial performance), unlike five consecutive adsorption without CP treatment (∼9-13% of the initial performance). The regeneration of CRH by CP treatment was also double-checked by the FESEM, EDS, BET, FTIR, XPS, and surface zeta potential measurements. The successfully recovered adsorption capability is related to the remediation of adsorption sites. It is also worth noting that the required power consumption for recycling by CP treatment was about 6.4 times lower than carbonizing new rice husks. This work provides insights into recovering adsorbents using CP without rigorous, costly, and energy-intensive processes.

Effect of temperature control conditions on DPF regeneration by nonthermal plasma

A regeneration test of a diesel particulate filter (DPF) was conducted under different temperature conditions with air as the gas source and a nonthermal plasma (NTP) injection system. We investigated the influence of the ambient temperature on the DPF regeneration performance and the oxidative decomposition amount of particulate matter (PM) and analyzed the changes in the PM oxidation characteristics by thermogravimetric analysis (TGA). The higher the temperature, the lower the decomposition amount of PM was under constant temperature conditions. The decomposition amount of PM was the highest at 80 °C (3.74 g), and the PM at interface P2 was not completely removed. The volume concentrations of the DPF regeneration products (CO and CO₂) were higher under variable than constant temperature conditions. In addition, the peak temperature of interface P1 occurred 10-30 min earlier, complete regeneration occurred at interface P2, and DPF regeneration occurred faster than under temperature conditions. The initial temperature of the control device was 110 °C, and the maximum mass of PM oxidation decomposition was 4.26 g after regeneration for 15 min cooling to 80 °C. The main form of elemental carbon (EC) transformed into the low ignition point component and the oxidation activity was improved after NTP injection.

Zero Discharge of Dyes and Regeneration of a Washing Solution in Membrane-Based Dye Removal by Cold Plasma Treatment

Although dye removal from wastewater streams has been investigated via several approaches using adsorbents, resins, or membranes, it is still hard to avoid the fact that dyes are persistently left in the adsorption materials or washing solutions used to regenerate the used adsorbents. In particular, given that cleaning agents are composed of acid/base, organic solvents, or electrolytes, dye adsorption and adsorbent regeneration processes leave behind more hard-to-manage wastewater containing dyes. In this study, we demonstrated that cold plasma (CP) treatment, which is one of the advanced oxidation processes (AOPs), can be used for zero discharge of dyes and regeneration of a washing solution in a membrane-based dye removal process. Specifically, CP treatment was found to successfully remove dyes released from a washing process to regenerate a used membrane, thereby effectively recycling a cleaning solution. As a result, the regenerated washing solution was more favorable for the adsorbed dyes’ elution, leading to the successful regeneration of a used membrane without a significant loss of dye removal efficiency. This fact was evidenced by a comparative study on the effect of CP treatment on the reusability of membranes and washing solutions and the kinetic analysis of the AOP of the desorbed dyes. We hope that this study contributes to opening a new door for environmentally friendly and sustainable dye removal.