Nationwide evaluation of microplastic properties in municipal wastewater treatment plants in South Korea.

Wastewater treatment plants (WWTPs) are considered a significant microplastic discharge source. To evaluate the amount and characteristics of microplastics discharged from WWTPs in South Korea, we selected 22 municipal WWTPs nationally and investigated microplastics at each treatment stage. The mean microplastic removal efficiency by WWTPs was >99%, and most of the microplastics were removed by sedimentation with the second clarifier during wastewater treatment. Consequently, the microplastic removal efficiency of WWTPs did not significantly differ from that of the adopted wastewater treatment technology because a second clarifier was applied in most WWTPs. However, for WWTPs operating a tertiary treatment process, the removal efficiency was enhanced compared with that of WWTPs discharging after a second clarifier. Although the microplastic removal efficiency was high by WWTP, the discharge contribution to the water environment could not be ignored because of the amount of treated wastewater, resulting in an increase of 5.8-270.9 items/m3 of microplastics in the receiving water. The characteristics of microplastics in WWTPs, including their components, shape, and size, were also evaluated. The most detected components included polytetrafluoroethylene and polyester. Most microplastics detected were categorized as fragments and fibers, while other types were hardly detected. The size of more than 70% of the microplastics detected in WWTPs was under 300 µm, implying that the size of microplastics required to control in WWTPs was much smaller than the defined size of microplastics. An evaluation of the correlation between other pollution factors and microplastic abundance did not reveal positive correlations, and microplastic occurrence was not affected by changing seasons, which may need to be evaluated with further studies. Research should also be performed on the effect of influent sources on the level of microplastic abundance and fate of ultrafine plastics in WWTPs.

Preparations and Thermal Properties of PDMS-AlN-Al2O3 Composites through the Incorporation of Poly(Catechol-Amine)-Modified Boron Nitride Nanotubes.

As one of the emerging nanomaterials, boron nitride nanotubes (BNNTs) provide promising opportunities for diverse applications due to their unique properties, such as high thermal conductivity, immense inertness, and high-temperature durability, while the instability of BNNTs due to their high surface induces agglomerates susceptible to the loss of their advantages. Therefore, the proper functionalization of BNNTs is crucial to highlight their fundamental characteristics. Herein, a simplistic low-cost approach of BNNT surface modification through catechol-polyamine (CAPA) interfacial polymerization is postulated to improve its dispersibility on the polymeric matrix. The modified BNNT was assimilated as a filler additive with AlN/Al2O3 filling materials in a PDMS polymeric matrix to prepare a thermal interface material (TIM). The resulting composite exhibits a heightened isotropic thermal conductivity of 8.10 W/mK, which is a ~47.27% increase compared to pristine composite 5.50 W/mK, and this can be ascribed to the improved BNNT dispersion forming interconnected phonon pathways and the thermal interface resistance reduction due to its augmented compatibility with the polymeric matrix. Moreover, the fabricated composite manifests a fire resistance improvement of ~10% in LOI relative to the neat composite sample, which can be correlated to the thermal stability shift in the TGA and DTA data. An enhancement in thermal permanence is stipulated due to a melting point (Tm) shift of ∼38.5 °C upon the integration of BNNT-CAPA. This improvement can be associated with the good distribution and adhesion of BNNT-CAPA in the polymeric matrix, integrated with its inherent thermal stability, good charring capability, and free radical scavenging effect due to the presence of CAPA on its surface. This study offers new insights into BNNT utilization and its corresponding incorporation into the polymeric matrix, which provides a prospective direction in the preparation of multifunctional materials for electric devices.

Enhancement of Isotropic Heat Dissipation of Polymer Composites by Using Ternary Filler Systems Consisting of Boron Nitride Nanotubes, h-BN, and Al2O3.

In this research article, a poly(dimethylsiloxane) (PDMS)-based composite was postulated adapting an interactive ternary filler system consisting of Al2O3, hexagonal boron nitride (h-BN), and boron nitride nanotubes (BNNT) to construct a continuous three-dimensional (3D) structure for thermal attenuation. Al2O3 was imposed as a main filler, while h-BN and BNNT were assimilated to form interconnected heat conduction pathways for effective thermal dissipation. The structured framework articulates a profound improvement in isotropic thermal conductivity considering both axial and radial heat dissipation. The presence of h-BN entails uniform heat distribution in a planar mode, eliminating the occurrence of hotspots, while BNNT constructed a connecting phonon pathway in various directions, which insinuates effective overall thermal transport. The generated ternary filler composites attained an isotropic ratio of 1.35 and a thermal conductivity of 7.50 W/mK, which is a 36-fold (∼3650%) increase compared to neat PDMS resin and almost 3-fold (∼297%) that of the Al2O3 unary filler composite and ∼53% that of its binary counterpart, partaking interfacial thermal gaps of ∼36.15 and ∼62.24% on practical heating performance relative to its counterparts. Moreover, the incorporation of BNNT on a traditional spherical and planar filler offers an advantage not only in thermal conductivity but also in thermal and structural stability. Improvement in thermal stability is stipulated due to a melting point (Tm) shift of ∼11 °C upon the assimilation of BNNT. Mechanical permeance reinforcement was also observed with the presence of BNNT, showcasing a 31.5% increase in tensile strength and a 53% increase in Young's modulus relative to the singular filler composite. This exploration administers a new insight into heat dissipation phenomena in polymeric composites and proposes a simple approach to their design and assembly.

Detection of microplastic traces in four different types of municipal wastewater treatment plants through FT-IR and TED-GC-MS.

Large amounts of microplastics are discharged into wastewater treatment plants (WWTPs), from where some of them are released into natural waterbodies on account of their not being fully eliminated by WWTPs. To investigate the behavior and emission of microplastics from WWTPs, we selected four WWTPs with different treatment technologies, including anaerobic-anoxic-aerobic (A2O), sequence batch reactor (SBR), media, and membrane bioreactor (MBR). The number of microplastics detected using Fourier transform infrared (FT-IR) spectroscopy ranged from 520 to 1820 particles/L in influent and from 0.56 to 2.34 particles/L in effluent. The microplastic removal efficiencies of four WWTPs were over 99%, indicating that the type of treatment technologies did not significantly affect the removal rate of microplastics. In the unit process for each WWTP, the major stages relating to microplastic removal were the secondary clarifier and tertiary treatment processes. Most microplastics detected were categorized as fragments and fibers, while other types were hardly detected. The size of more than 80% of microplastic particles detected in WWTPs ranged between 20 and 300 µm, indicating that they were significantly smaller than the size threshold defined for microplastics. Therefore, we used thermal extraction-desorption coupled with gas chromatography-mass spectroscopy (TED-GC-MS) to evaluate the microplastic mass content in all four WWTPs, and the results were compared with those of the FT-IR analysis. In this method, only four components, namely polyethylene, polypropylene, polystyrene, and polyethylene terephthalate, were analyzed because of the analysis limitation, and the total microplastic concentration represented the sum of four components concentrations. The influent and effluent microplastic concentrations estimated by TED-GC-MS ranged from not detectable to 160 µg/L and 0.04-1.07 µg/L, respectively, indicating a correlation coefficient of 0.861 (p < 0.05) between the TED-GC-MS and FT-IR results, when compared to the combined abundance of the four microplastic components by FT-IR analysis.

Noble Metal Nanoparticles Decorated Boron Nitride Nanotubes for Efficient and Selective Low-Temperature Catalytic Reduction of Nitric Oxide with Carbon Monoxide.

Parallel to CO2 emission, NOx emission has become one of the menacing problems that seek a simple, durable, and high-efficiency deNOx catalyst. Herein, we demonstrated simple syntheses of platinum group metal nanoparticle-decorated f-BNNT (PGM = Pd, Pt, and Rh, and f-BNNT stands for -OH-functionalized boron nitride nanotubes) as a catalyst for efficient and selective reduction of NO by CO at low-temperature conditions. PGM/f-BNNT with a low amount of noble metal nanoparticles (0.7-0.8 wt %) presents very efficient catalytic activity for NO reduction as well as CO oxidation during their removal process. The removal efficiencies of NO and CO with Pd/f-BNNT, Pt/f-BNNT, and Rh/f-BNNT catalysts were investigated under various temperatures, flow rates, and reaction times, respectively. For most cases, NO catalytic reduction with CO reaction was >99% at a temperature as low as ∼200 °C. The catalyst robustness and efficiency were also verified by presenting almost 100% conversion of NO using a Rh/f-BNNT catalyst, which was aged under humid air at 600 and 700 °C for 24 h, respectively. The synergic effect of the catalytic efficacy of the well-dispersed noble metal nanoparticles and the excellent surface properties of BNNT are reasons for the high selectivity and catalytic property at a low temperature. On the basis of this investigation, we demonstrated that the noble metal nanoparticle-decorated f-BNNT catalysts are possible to save expensive PGM catalysts, such as Pt, Pd, and Rd, as much as 100 times while presenting similar or better catalytic performance for simultaneous NO and CO removals.

Dewetting of Thin Polymer Films on Wrinkled Graphene Oxide Monolayers.

We investigated the effect of the morphological structure of a graphene oxide (GO) monolayer on the dewetting dynamics of the upper polymer thin films. The Langmuir-Schaefer (LS) technique was used to prepare a wrinkled GO ( wrGO) structure with a root mean square (rms) roughness of 22.7 Å. The dewetting behavior of poly(methyl methacrylate) (PMMA) thin films on the wrGO monolayers was perfectly prevented, whereas the PMMA thin films on a flat GO monolayer were dewetted at 203 °C. This wrinkle effect of the GO can be also obtained when the GOs monolayers are intercalated to the PMMA/polystyrene (PS) interface. In this multilayer, the flat GO monolayer at the interface between the PS and PMMA layers was spontaneously roughened with rms roughness of 46.9 Å after annealing and also prohibited the dewetting behavior. From the results, we found that to improve the compatibility of polymer blends by adding the two-dimensional nanosheets, it is important to control the morphological structure of the sheets at the interface, along with manipulation of the GO-polymer interactions.

Free-Standing Janus Graphene Oxide with Anisotropic Properties for 2D Materials as Surfactant.

We present a simple and facile approach to creating asymmetrically modified graphene oxide sheets by grafting polymers with different polarities. Single-layered Janus graphene derivatives were prepared by grafting polymers with different polarities at the liquid-gas interface through one step functionalization. This approach allows obtaining free-standing monolayers of Janus graphene oxide sheets for large area, and also controlling the morphology (i.e., wrinkled Janus graphene oxide sheets) by a compression monolayer. A neutron reflectivity technique is used to check the functionalization on each side of the monolayer, and the results are compared with contact angles to determine its amphiphilic nature. The free-standing Janus monolayers become robust after UV-irradiation, and are able to withstand various solvents. Because these robust Janus graphene films can maintain their anisotropic functionalities over time, this technique provides a new strategy for fabricating functional materials that require amphiphilic properties (i.e., oil-water separation membranes and chemical compatibilizers functioning as a 2D surfactant) and different electrical functionalities (i.e., flexible lightweight p-n junction semiconductors and stimuli-driven actuators).

Perpendicular Orientation of Diblock Copolymers Induced by Confinement between Graphene Oxide Sheets.

We have studied an orientation structure of self-assembled block copolymers (dPS-b-PMMA) of deuterated polystyrene (dPS) and poly(methyl methacrylate) (PMMA) confined between graphene oxide (GO) surfaces. The results of combination techniques, such as neutron reflectivity, time-of-flight secondary-ion mass spectrometry, grazing-incidence small-angle X-ray scattering, and scanning electron microscopy, show that self-assembled domains of the block copolymers in thin films near the GO sheets are oriented perpendicular to the surface of the GO monolayers, in contrast to the horizontal lamellar structure of the copolymer thin film in the absence of the GO monolayers. This is due to the amphiphilic nature of the GO, which leads to a nonpreferential interaction of both dPS and PMMA blocks. Double-sided confinement with the GO monolayers further extends the ordering behavior of the dPS-b-PMMA thin films. Continuous vertical orientation of the block copolymer thin films is also obtained in the presence of alternating GO layers within thick copolymer films.

Long-Term Cyclability of Electrochromic Poly(3-hexyl thiophene) Films Modified by Surfactant-Assisted Graphene Oxide Layers.

Organic electrochromic (EC) materials are generally known to be electrochemically unstable during the ion intercalation/deintercalation process. One effective method to stabilize them is incorporating graphene derivatives in the polymer matrix, thereby creating strong interaction between graphene derivatives and polymer. However, previous studies are limited to specific polymers and bulk-blended systems, such as mixing the polymer with graphene derivatives. In this study, we developed a polymer-graphene derivative complex with the chemical assistance of a surfactant (octadecylamine, ODA). Graphene oxide (GO) was introduced as a protective layer on the electrochromic poly(3-hexyl thiophene) (P3HT) films by the Langmuir-Schaefer method. The deposition of the GO-ODA protective layer with high coverage was confirmed by atomic force microscopy and high-resolution X-ray reflectivity. The strong interactions between GO-ODA and P3HT were examined with UV-vis spectrophotometry and X-ray photoelectron spectroscopy. Electrochemical and electrochromic investigations revealed that the GO-ODA layer greatly improved the long-term cyclability of the P3HT film. These findings imply that the GO-ODA complex can significantly stabilize the EC cycling, due to its strong interaction with the P3HT film.

Graphene Oxide Monolayer as a Compatibilizer at the Polymer-Polymer Interface for Stabilizing Polymer Bilayer Films against Dewetting.

We investigate the effect of adding graphene oxide (GO) sheets at the polymer-polymer interface on the dewetting dynamics and compatibility of immiscible polymer bilayer films. GO monolayers are deposited at the poly(methyl methacrylate) (PMMA)-polystyrene (PS) interface by the Langmuir-Schaefer technique. GO monolayers are found to significantly inhibit the dewetting behavior of both PMMA films (on PS substrates) and PS films (on PMMA substrates). This can be interpreted in terms of an interfacial interaction between the GO sheets and these polymers, which is evidenced by the reduced contact angle of the dewet droplets. The favorable interaction of GO with both PS and PMMA facilitates compatibilization of the immiscible polymer bilayer films, thereby stabilizing their bilayer films against dewetting. This compatibilization effect is verified by neutron reflectivity measurements, which reveal that the addition of GO monolayers broadens the interface between PS and the deuterated PMMA films by 2.2 times over that of the bilayer in the absence of GO.

Leaching of brominated flame retardants from TV housing plastics in the presence of dissolved humic matter.

In this study, we investigated the contents of several brominated compounds in TV molding plastics, as well as their leaching characteristics in the presence of DHM. The PBDE content was about 3% of the sample weight, and deca-BDE was the most abundant homologue, accounting for over 80% of the total amount. TBBPA, PBPs and PBBs content was 8100, 4700 and 250 ng/g, respectively. Despite no detection of most of the lower brominated DEs in distilled water, most homologues could be detected in DHM solution, and their solubility increased according to the contact time; those of highly brominated compounds increased to 10 times their maximum solubility in distilled water. Especially, contrary to the relatively faster equilibrium in distilled water, BFR solubility in DHM solution was maintained even after 20 days. In addition, a modified first-order model adequately reflected rapid desorption for each compound in the initial period, but slow desorption afterwards. From an overall perspective, it is clear that hydrophobic BFRs can leach out to a great extent in the presence of DHM, which is a matter of great concern in E&E waste as the potential contaminant source of BFRs, especially in landfills and open dump sites that provide the perfect conditions for exposure of BFRs to abundant DHM.

Fundamental characteristics of input waste of small MSW incinerators in Korea.

Waste incineration in a small incinerator is a simple and convenient way of treating waste discharged from small areas or from large facilities and buildings such as business centers, marketplaces, factories, and military units. Despite their ostensible advantages, however, many small incinerators frequently suffer from serious problems, e.g., unsystematic waste feeding, unstable combustion, deficient air pollution control devices, and consequently, environmental pollution. To obtain a better understanding of the characterization of wastes in small incinerators, we investigated a series of fundamental characteristics, i.e., physical composition, bulk density, proximate and ultimate analysis, potential energy content, and so on. The main waste components in small incinerators were identified as paper and plastic; the proportion of food waste was less than that in large incinerators. Especially, a low ratio of food waste had a strong influence on other waste characteristics, e.g., lower moisture content and bulk density, and higher potential energy. On the other hand, in contrast with that of HCl, there was no distinguishable linear relationship between Cl content in waste and PCDD/DF concentration in combustion gas.

Evaluation of environmental burdens caused by changes of food waste management systems in Seoul, Korea.

During the last decade, there have been remarkable changes in food waste management in Korea following a ban on direct landfilling. To evaluate the environmental impacts of food waste management systems, we examined individual treatment systems with the LCA approach -- landfill, incineration, composting, and feed manufacturing -- and estimated the change from 1997 to 2005. The efficient system was different in each impact category, but it was evaluated that landfill is the main contributor to human toxicity and global warming (based on fossil CO(2)). In contrast, due to the increase of food waste recycling, acidification, eutrophication, and fresh water aquatic ecotoxicity impact was increased. Especially, the high energy consumption and generated residue in recycling systems caused the large burdens in toxicity categories.

The prediction of PCDD/DF levels in wet scrubbers associated with waste incinerators.

Wet scrubber is one of the most conventional types of air pollutant control devices (APCDs), which is specially designed to treat dust and acidic gases in the flue gas simultaneously. In spite of its outstanding ability to control them, however, wet scrubbers have been considered as potential contaminant sources that may increase PCDD/DF concentrations in the flue gas. In this study, we investigated the change of PCDD/DF concentrations at the inlets and outlets of seven wet scrubbers, and compared them with other published data. With a multi-regression analysis of dust concentrations and temperature at the inlets and outlets of given wet scrubbers, we developed an empirical model to understand factors dominating the change of PCDD/DF concentrations. As a result, we confirmed that the changes of PCDD/DF concentrations in wet scrubbers are closely related to their concentrations at the inlets, which would usually be determined by the type of APCDs installed upstream of the wet scrubber.

PCDD/DF concentrations at the inlets and outlets of wet scrubbers in Korean waste incinerators.

To further understand the effects of wet scrubbers on PCDD/DF levels, it was measured the concentrations of PCDD/DF, dust, and other gaseous pollutants at both the inlets and the outlets of seven wet scrubbers. As a result, the concentrations of PCDD/DF at the inlets and outlets of the wet scrubbers ranged from 0.2 to 37.4, and 0.8 to 6.0 ng TEQ N m-3, respectively. With the exceptions of wet scrubbers F and G, the PCDD/DF levels decreased by and large in most wet scrubbers. It was thought that their relatively high removal efficiencies were more increased with heavier loads of dust and particle-bound PCDD/DF. On the other hand, it was also surveyed the increase of gaseous PCDD/DF in wet scrubber, where the total level of PCDD/DF was decreased. However, it was not sure whether it had been resulted from the thermal adsorption/desorption phenomenon between packing materials and emission gases or not. At the very least, however, although there still remains an unexplained aspect for the increase of gaseous PCDD/DF, it is clear that wet scrubbers can be sufficiently applied to remove PCDD/DF to a certain extent, if only removal efficiencies for the particle loads are high, and if a significant part of the PCDD/DF at the inlets is particle associated.

PCDD/DF in leachates from Korean MSW landfills.

We analyzed levels of PCDD/DF in leachate liquid and solid from five Korean municipal solid waste landfills to investigate the relationship between PCDD/DF and dissolved organic carbon and suspended solids in raw leachate. The concentrations of PCDD/DF ranged from 173.2 to 1329.4 pg/l and 4.1 to 46.22 pg-TEQ/l. The range of PCDD/DF was 123.2-1161.3 pg/l in leachate solid and 50.0-383.3 pg/l in leachate liquid. Our results indicated that PCDD/DF in solid play a major role in determining their concentration levels, and the distribution of isomers in solid was almost the same as in liquid leachate. In addition, highly chlorinated PCDD/DF, such as HpCDD/DF and OCDD/DF, accounted for more than 70% of all isomers. Levels of PCDD/DF in liquid were strongly correlated with dissolved organic carbon concentrations, which increase the leachability (R2 = 0.92 in Korean leachate) of PCDD/DF from contaminant sources. Despite this high linearity between dissolved organic carbon and dissolved PCDD/DF, we observed no strong relationship between dissolved organic carbon and solid phase PCDD/DF (R2 = 0.001). Dissolved organic carbon scarcely affects dissolved PCDD/DF to be combined with solids. As a result, it is not appropriate for incinerated ash to be dumped with municipal solid wastes, as they have a large potential to result in high levels of organic matter, and therefore PCDD/DF, in leachate.