Efficient degradation of polystyrene microplastic pollutants in soil by dielectric barrier discharge plasma

In this study, the atmospheric dielectric barrier discharge (DBD) plasma was proposed for the degradation of polystyrene microplastics (PS-MPs) for the first time, due to its ability to generate reactive oxygen species (ROS). The local temperature in plasma was found to play a crucial role, as it enhanced the degradation reaction induced by ROS when it exceeded the melting temperature of PS-MPs. Factors including applied voltage, air flow rate, and PS-MPs concentration were investigated, and the degradation products were analyzed. High plasma energy and adequate supply of ROS were pivotal in promoting degradation. At 20.1 kV, the degradation efficiency of PS-MPs reached 98.7% after 60 min treatment, with gases (mainly COx, accounting for 96.4%) as the main degradation products. At a concentration of 1 wt%, the PS-MPs exhibited a remarkable conversion rate of 90.6% to COx, showcasing the degradation performance and oxidation degree of this technology. Finally, the degradation mechanism of PS-MPs combined with the detection results of ROS was suggested. This work demonstrates that DBD plasma is a promising strategy for PS-MPs degradation, with high energy efficiency (8.80 mg/kJ) and degradation performance (98.7% within 1 h), providing direct evidence for the rapid and comprehensive treatment of MP pollutants.

Mass concentration and distribution characteristics of microplastics in landfill mineralized refuse using efficient quantitative detection based on Py-GC/MS

Landfilling is the most traditional disposal method of domestic waste. Plastic waste in landfill sites could degrade to microplastics (MPs) and diffuse to the surrounding environment with leachate. However, MPs pollution in landfill mineralized refuse has not been well recognized. In the present research, a detection method for mixed MPs of polyethylene (PE), polypropylene (PP), and polystyrene (PS) based on Py-GC/MS was established and verified. The method is suitable for the rapid quantitative detection of large-batch of complex solid matrix samples, with an average deviation of less than 10%. Based on the method, samples from a landfill site in South China were studied, where PE was found to be the main component. The total concentration of MPs in mineralized refuse was 7.62 kg/t in the old area and 5.49 kg/t in the young area. Further analysis showed that the content of MPs was correlated with that of plastic waste and the landfill age, indicating that a considerable proportion was secondary MPs. The reserves of MPs in landfill sites may have reached an alarming number. In the absence of adequate safeguards, quantities of MPs may spread from the landfill sites, resulting in serious pollution of the surrounding soil and groundwater.

Dechlorination of waste polyvinyl chloride (PVC) through non-thermal plasma

Dechlorination is essential for the chemical recycling of waste polyvinyl chloride (PVC) plastics. This study investigated the use of non-thermal plasma (NTP) for chlorine removal, with a focus on the effects of treatment time and discharge power on dechlorination efficiency. The results showed that longer treatment times and higher discharge powers led to better dechlorination performance. The maximum efficiency (98.25%) and HCl recovery yield (55.72%) were achieved at 180 W power after 40 min of treatment where 96.44% of Cl existed in the form of HCl gas, 1.44% in the liquid product, and 2.12% in the solid residue product. NTP at a discharge power of 150 W showed better dechlorination performance compared to traditional thermal pyrolysis treatment in temperatures ranging from 200 to 400 °C. The activation energy analysis of the chlorine removal showed that compared to pyrolysis-based dechlorination (137.09 kJ/mol), NTP-based dechlorination (23.62 kJ/mol) was more easily achievable. This work presents a practical method for the dechlorination of waste PVC plastic using a novel technology without requiring additional thermal and pressure input.

Dechlorination and fuel gas generation in chemical looping conversion of waste PVC over inherently Na/Ca/K-containing bauxite residue-based oxygen carriers

The inert atmosphere in chemical looping (CL) technology can considerably inhibit the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans during the thermal treatment of polyvinyl chloride plastic (PVC) waste. In this study, PVC was innovatively converted to dechlorinated fuel gas via CL gasification under a high reaction temperature (RT) and the inert atmosphere by applying an unmodified bauxite residue (BR) as both a dechlorination agent and oxygen carrier. The dechlorination efficiency reached 49.98% at an oxygen ratio of only 0.1. Furthermore, a moderate RT (750 °C in this study) and an increased oxygen ratio enhanced the dechlorination effect. The highest dechlorination efficiency (92.12%) was achieved at an oxygen ratio of 0.6. Iron oxides in BR improved the generation of syngas from CL reactions. The yields of the effective gases (CH4, H2, and CO) increased by 57.13% to 0.121 Nm3/kg with an increase in oxygen ratio from 0 to 0.6. A high RT improved the production of the effective gases (an 809.39% increase to 0.344 Nm3/kg from 600 to 900 °C). Energy-dispersive spectroscopy and X-ray diffraction were used to study the mechanism, and formation of NaCl and Fe3O4 was observed on the reacted BR, indicating the successful adsorption of Cl and its capability as an oxygen carrier. Therefore, BR eliminated Cl in situ and enhanced the generation of value-added syngas, thereby achieving efficient PVC conversion.

Dielectric barrier discharge plasma for the remediation of microplastic-contaminated soil from landfill

The huge amount of plastic waste accumulated in landfills has caused serious microplastic (MP) pollution to the soil environment, which has become an urgent issue in recent years. It is challenging to deal with the non-biodegradable MP pollutants in actual soil from landfills. In this study, a coaxial dielectric barrier discharge (DBD) system was proposed to remediate actual MP-contaminated landfill soil due to its strong oxidation capacity. The influence of carrier gas type, applied voltage, and air flow rate was investigated, and the possible degradation pathways of MP pollutants were suggested. Results showed the landfill soil samples contained four common MP pollutants, including polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC) with sizes ranging from 50 to 1500 μm. The MP pollutants in the soil were rapidly removed under the action of reactive oxygen species (ROS) generated by DBD plasma. Under the air flow rate of 1500 mL min^-1, the maximum remediation efficiency represented by mass loss reached 96.5% after 30 min treatment. Compared with nitrogen, when air was used as the carrier gas, the remediation efficiency increased from 41.4% to 81.6%. The increased applied voltage from 17.5 to 24.1 kV could also promote the removal of MP contaminants. Sufficient air supply was conducive to thorough removal. However, when the air flow rate reached 1500 mL min^-1 and continued to rise, the final remediation efficiency would be reduced due to the shortened residence time of ROS. The DBD plasma treatment proposed in this study showed high energy efficiency (19.03 mg kJ^-1) and remediation performance (96.5%). The results are instructive for solving MP pollution in the soil environment.

BTEX recovery from waste rubbers by catalytic pyrolysis over Zn loaded tire derived char

Recovering valuable chemicals (BTEX: Benzene, toluene, ethylbenzene, and xylene) via catalytic pyrolysis of waste tires is a promising and sustainable approach. Zinc loaded tire derived char (TDC) was used as cheap catalyst for recovering valuable BTEX products from waste tire through pyrolysis in this study. The catalytic capability of TDC on BTEX production were experimentally investigated with respect to Zn content, catalytic temperature, and catalyst-to-tire ratio. Due to the abundant acid sites on the surface, the TDC showed notable catalytic capability for improving BTEX yield which was 2.4 times higher than that from uncatalyzed case. The loading of additional Zn increased the acid sites on the TDC and the catalytic performance was further improved. The increase of catalytic temperature and catalyst-to-tire ratio favored the formation of BTEX, but it also brought undesirable consequences, such as the mass loss of tire pyrolysis oil (TPO) and the formation of polycyclic aromatic hydrocarbons. The optimal TPO products were obtained at 600 °C with catalyst-to-tire ratio of 20. At this condition, the relative content of BTEX reached 54.70% and the cumulative BTEX yield was 10.13 wt%, increasing by 5.95 times compared to that of non-catalytic condition. This work provided a novel strategy of replacing traditional expensive catalysts with low-cost and effective carbon-based materials in the field of catalytic pyrolysis of waste tires.

Perceptions on caring for adult survivors of childhood cancer in the primary care setting

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Background: Encouraging cure rates for childhood cancers have resulted in a population of adult childhood cancer survivors (CCS) that are at risk for late effects of cancer-directed therapy. Late effects often occur when CCS are older and receive routine medical care from internists and family practitioners. Our study identifies facilitators and barriers to providing optimal late effects screening as well as evaluating information sources primary care providers (PCPs) perceive as useful, including cancer treatment summaries, survivorship care plans, and Children's Oncology Group (COG) guidelines. Methods: We sampled 1,500 randomly selected general internal medicine and family practice physicians from the American Medical Association Physician Masterfile for a nationwide mail survey. We received 351 surveys with data. Using chi-squared tests or t-tests to compare responders and non-responders we found a higher response rate for family practice (30.2%) compared to general internal medicine (16.5%) (p<.0001). Results were tabulated for descriptive purposes and linear regression and logistic regression were used for the multivariable modeling. Results: Most (84–86%) PCPs stated that they had never received a cancer treatment summary or survivorship care plan; despite this, greater than 90% thought these documents would be useful. Most PCPs (93%) had never used COG guidelines, but 86% agreed that they would follow their recommendations. A minority of PCPs perceived that their medical training was adequate to recognize late effects of chemotherapy (27.6%), cancer surgery (36.6%), and radiation therapy (38.1%). Conclusions: PCPs have a low level of awareness about the medical problems of CCS; receive inadequate training to recognize late effects; and infrequently utilize, cancer treatment summaries, survivorship care plans, and COG guidelines. By evaluating the perceptions of PCPs, we have identified problematic areas for future investigation and have begun to lay the groundwork for incorporating follow-up care for CCS into routine general medical practice.

No significant financial relationships to disclose.

Plasminogen kringle 5 reduces vascular leakage in the retina in rat models of oxygen-induced retinopathy and diabetes

AIMS/HYPOTHESIS

Retinal vascular leakage is an early pathological feature in diabetic retinopathy and can lead to macular oedema and loss of vision. Previously we have shown that plasminogen kringle 5 (K5), an angiogenic inhibitor, inhibits retinal neovascularisation in the rat model of oxygen-induced retinopathy (OIR). The purpose of this study was to examine the effect of K5 on vascular leakage in the retina.

METHODS

Neonatal rats were exposed to hyperoxia to induce OIR. Diabetes was induced in adult rats by injecting streptozotocin. Vascular permeability was measured by Evans blue method. Expression of vascular endothelial growth factor (VEGF) was evaluated using immunohistochemistry and western blot analysis.

RESULTS

Rats with OIR and diabetes showed abnormal vascular hyperpermeability in the retina and iris. Intravitreal injection of K5, reduced vascular permeability in both animal models, but did not affect permeability in normal rats. K5 reduced vascular permeability at doses substantially lower than that required for inhibition of retinal neovascularisation. The K5-induced reduction in vascular permeability correlated with its down-regulation of VEGF expression in the retina. Moreover, K5 inhibited IGF-1-induced hyperpermeability, which is known to arise through up-regulation of endogenous VEGF expression. However, K5 had no effect on the hyperpermeability induced by injection of exogenous VEGF.

CONCLUSIONS/INTERPRETATION

Very low doses of K5 reduce pathological vascular leakage in the retina. K5 thus has therapeutic potential in the treatment of diabetic macular oedema. This effect can be ascribed, at least in part, to the down-regulation of endogenous VEGF expression.

On the computational complexity of binary and analog symmetric hopfield nets

We investigate the computational properties of finite binary- and analog-state discrete-time symmetric Hopfield nets. For binary networks, we obtain a simulation of convergent asymmetric networks by symmetric networks with only a linear increase in network size and computation time. Then we analyze the convergence time of Hopfield nets in terms of the length of their bit representations. Here we construct an analog symmetric network whose convergence time exceeds the convergence time of any binary Hopfield net with the same representation length. Further, we prove that the MIN ENERGY problem for analog Hopfield nets is NP-hard and provide a polynomial time approximation algorithm for this problem in the case of binary nets. Finally, we show that symmetric analog nets with an external clock are computationally Turing universal.

[Result of orthokeratology for treatment of young people with myopia]

PURPOSE

To evaluate the effectiveness of orthokeratology (Ortho-K) for treatment of myopia in youngths.

METHODS

110 eyes of 56 young peoples with myopia received Ortho-K were studied. The patients were divided into 3 groups according to preoperative diopters. No. I: -1.00(-)-3.00 D, No. II: -3.25(-)-6.00 D, NO. III: -6.25(-)-7.50 D. The uncorrected visual acuities, residual diopters and corneal refractive powers at various time of three months after the operation were statistically analyzed and compared with that of preoperation. Correlation analysis and linear regression analysis were performed between the corneal refractive reduction (X) and clinical refractive reduction (Y) after 3 months of the operation.

RESULTS

In 110 eyes, the uncorrected visual acuities in the first day, first week, first month, second month and third month after operation were significantly improved than that of the preoperation (P < 0.01). The mean residual diopters were significantly reduced than that of preoperation (P < 0.01). The mean refractive powers of cornea were significantly decreased than that of the preoperative (P < 0.01). There was significant correlation between the corneal refractive reduction and clinical refractive reduction. (r = 0.3181, P < 0.001).

CONCLUSION

Orthokeratology is a safe and effective therapeutic method for treatment of myopia in youngths. The long term effect of Orthokeratology need further observation.