Preparation of composite coagulant for the removal of microplastics in water.

In this work, a composite flocculant (polyferric titanium sulfate-polydimethyldiallylammonium chloride [PFTS-PDMDAAC]) with a rich spatial network structure was prepared for the treatment of simulated wastewater containing polystyrene (PS) micro-nanoparticles. Characterization results showed that the surface of the PFTS-PDMDAAC was a three-dimensional network polymer of chain molecules that exhibited good thermal stability and formed an amorphous polymer containing multiply hydroxyl-bridged titanium and iron. When n(OH- ) : n(Fe) = 1:2, n(PO4 3- ) : n(Fe) = 0.35, n(Ti) : n(Fe) = 1:8, n(DMDAAC) : n(Fe) = 5:100, and the polymerization temperature is 60°C, the prepared composite flocculant has the best effect. The effects of dosage, pH, and agitation intensity on the flocculation properties of PFTS-PDMDAAC were also studied. The optimal removal rates of PS-µm and haze by PFTS-PDMDAAC were 85.60% and 90.10%, respectively, at a stirring intensity of 200 rpm, a pH of 9.0, and a PFTS-PDMDAAC dosage of 20 mg/L. The flocs produced by the PFTS-PDMDAAC flocculation were large and compact in structure, and the flocculation mechanism was mainly based on adsorption bridging. Kaolin played a promoting role in the process of PS-µm removal by PFTS-PDMDAAC floc and accelerated the formation of large and dense flocs. This study provided a reference for the coagulation method to remove micro-nanopollutants in the actual water treatment process. PRACTITIONER POINTS: A composite flocculant with rich spatial network structure (PFTS-PDMDAAC) was prepared. PFTS-PDMDAAC can effectively remove micro-nano polystyrene (PS) in wastewater. The floc produced by PFTS-PDMDAAC is large and compact in structure. The flocculation mechanism of PFTS-PDMDAAC is mainly adsorption bridging.

One-step hydrothermal generation of oxygen-deficient N-doped blue TiO2-Ti3C2 for degradation of pollutants and antibacterial properties.

In this study, TiO2 was generated in situ on the surface of Ti3C2 by a hydrothermal process, and urea was added to form N-doped TiO2-Ti3C2. The surface morphology and functional group properties of the prepared materials were analyzed by SEM, TEM, XRD, XPS, etc. The results showed that anatase TiO2 formed on the surface of the Ti3C2 monolayer. Nitrogen-doped nanomaterials show good phenol degradation and good recyclability under visible light. At a urea content of 0.5 g, the photocatalytic degradation of phenol under visible light is best, reaching 88.9% in 3 h, with ·OH and ·O2- holes playing the leading role. However, at lower pH and higher ion concentration, the degradability of N-TiO2-Ti3C2 for phenol is reduced. Furthermore, the material prepared in this work is a two-dimensional layered material, and the adsorption of phenol best fits the Langmuir adsorption isotherm model and the pseudo-second-order kinetic equation. In terms of the antibacterial performance of the material, the N-doped TiO2-Ti3C2 nanomaterial made with 0.2 g of urea has an Escherichia coli scavenging efficiency of about 97.86%, which is an excellent antibacterial material. This study shows that the N-TiO2-Ti3C2 produced in this experiment can be used for environmental applications.

Toxic effects of aging mask microplastics on E. coli and dynamic changes in extracellular polymeric matter.

Contamination of disposable medical masks has become a growing problem globally in the wake of Covid-19 due to their widespread use and improper disposal. Three different mask layers, namely the outer layer, the meltblown (MB) filler layer and the inner layers release three different types of microplastics, whose physical and chemical properties change after prolonged environmental weathering. In this study, physical and chemical changes of mask microplastics before and after aging were characterized by different characterization techniques. The toxic effect and mechanism of aged mask microplastics on Escherichia coli (E. coli) were studied by measuring the growth inhibition of mask microplastics, the change in ATPase activity, the change in malondialdehyde content and reactive oxygen species production, and the release of the chemical composition of exopolymeric substances (EPS). The microplastics of the aged MB filter layer had the most significant inhibitory effect on E. coli growth, reaching 19.2 % after 36 h. Also, under the influence of mask microplastics, ATPase activity of E. coli was inhibited and a large amount of EPS was released. The chemical composition of EPS has also changed. This study proposed the possible toxicity mechanism of mask microplastics and the self-protection mechanism of E. coli, and provided a reference for future research on the toxic effects of mask microplastics on environmental organisms.

Different weathering conditions affect the release of microplastics by masks.

A generation of microplastics caused by improper disposal of disposable masks has become a non-negligible environmental concern. In order to investigate the degradation mechanisms of masks and the release of microplastics under different environmental conditions, the masks are placed in 4 common environments. After 30 days of weathering, the total amount and release kinetics of microplastics released from different layers of the mask were studied. The chemical and mechanical properties of the mask were also discussed. The results showed that the mask released 25141±3543 particles/mask into the soil, which is much more than the sea and river water. The release kinetics of microplastics fit the Elovich model better. All samples correspond to the release rate of microplastics from fast to slow. Experiments show that the middle layer of the mask is released more than the other layers, and the amount of release was highest in the soil. And the tensile capacity of the mask is negatively correlated with its ability to release microplastics in the following order, which are soil > seawater > river > air > new masks. In addition, during the weathering process, the C-C/C-H bond of the mask was broken.

Exploring the toxicity of the aged styrene-butadiene rubber microplastics to petroleum hydrocarbon-degrading bacteria under compound pollution system.

As a new pollutant, microplastics have increasingly drawn public attention to its toxic behavior in the environment. The aim was to investigate the effect of styrene-butadiene-rubber microplastics (mSBR) with different degrees of aging on petroleum hydrocarbon (PHC) degrading bacteria in an environment with simultaneously existing pollutants. A series of experiments were carried out to investigate the changes in the physical and chemical properties of mSBR with aging and to examine the influence of these changes on the inhibition of PHC-degrading bacteria by mSBR in the vicinity of coexisting pollutants. The results showed that in the early stage of ultraviolet aging (10d), the particle surface shows wrinkles, but the structure is intact. After reaching the late stage of aging (20d), nano-scale fragments were generated on the surface of mSBR, the average particle size decreased from 3.074 µm to 2.297 µm, and the zeta potential increased from - 25.1 mV to - 33.1 mV. The inhibitory effect of bacteria is greater. At the same time, these changes in the physicochemical properties increase the adsorption effect of Cd by 20%, and also improve the stability of mSBR in solution, whereby bacterial growth is inhibited by inhibiting the LPO activity and protein concentration of PHC degrading bacteria.

Red soil amelioration and heavy metal immobilization by a multi-element mineral amendment: Performance and mechanisms.

This field study aims to identify the performance and mechanisms of red soil amelioration and heavy metal immobilization by a multi-element mineral amendment (MMA) mainly containing a mixture of zeolites (laumontite and gismondine), montmorillonite, gehlenite, grossular and calcium silicate powder. The results indicated that the acidity of red soil was neutralized, and the soil EC, CEC, and content of montmorillonite and illite were increased after application of MMA, improving the soil fertility as well as the ability of heavy metals immobilization. The high amounts and reactivity of dissolved and colloidal Fe provided by the ferralsol (red soil) combined with the abundant available Si, Ca, Mg, Na and K supplied by MMA, readily destabilizes kaolinite and facilitates the formation of 2:1 type clay minerals. Meanwhile, the application of MMA was effective in reducing the bioavailability of soil heavy metals due to the activated mineralogical compositions of MMA as well as the increase of pH and 2:1 type clay minerals in the soil, which significantly decreased the up-taking and accumulation of Cd, Pb, Cr and Hg in lettuce tissues (p < 0.05). Compared with the untreated soil, the plant height, the total yield and content of vitamin C in the edible parts of lettuce in MMA-treated soil was increased by 7.6%, 23.6%, and 12.8%, respectively. These results showed that MMA could be a promising amendment for red soil amelioration and heavy metal immobilization.

Novel chitosan-based flocculants for chromium and nickle removal in wastewater via integrated chelation and flocculation.

Carboxylated chitosan (CPCTS) is used as substrates in the design and synthesis of CPCTS-based flocculants through UV-initiated polymerization techniques. The synthesized flocculants are applied to remove Cr and Ni ions from chromic acid lotion and electroplating wastewater through two-stage flocculation. This study investigates the effect of flocculant dosage, pH, reaction time, and stirring speed on the removal efficiency of Cr and Ni ions. Results indicated that the total Cr removal ratios by CPCTS-graft-polyacrylamide-co-sodium xanthate (CAC) and CPCTS-graft-poly [acrylamide-2-Acrylamido-2-methylpropane sulfonic acid] (CPCTS-g-P(AM-AMPS)) are 94.7% and 94.6%, respectively. The total Ni removal efficiencies by CAC and CPCTS-g-P(AM-AMPS) are 99.3% and 99.4%, respectively. The two-stage flocculation with CPCTS-based flocculants could reduce the total concentrations of Cr and Ni to 1.0 mg/L and 0.5 mg/L, respectively. The relationship of removal capacity and structural properties between the flocculants with different functional groups is established through Fourier transform infrared spectroscopy, nuclear magnetic resonance, scanning electron microscopy, and X-ray diffraction. The micro-interfacial behavior between the colloidal particles and the solution during the integrated chelation-flocculation are elucidated. Thus, CPCTS-based flocculants could be a potential material for the removal of high amounts of Cr and Ni ions in industrial wastewater.

Electrochemical degradation of oxytetracycline by Ti-Sn-Sb/γ-Al2O3 three-dimensional electrodes.

In this work, Ti-Sn-Sb/γ-Al2O3 particle electrodes were prepared and employed for the degradation of oxytetracycline (OTC) by three-dimensional electrocatalytic technology. Factors associated with the preparation of Ti-Sn-Sb/γ-Al2O3 particle electrodes were investigated. The effects of initial concentration, conductivity, pH value, aeration intensity, current density, plate spacing, and particle electrode dosage on OTC removal were studied. The removal rate of OTC and total organic carbon were achieved approximately 92.0% and 41.0% under the optimal operating condition, respectively. In addition, Ti-Sn-Sb/γ-Al2O3 particle electrode was analyzed by Fourier Transform Infrared spectroscopy (FT-IR), scanning electron microscope (SEM), energy dispersive spectrum analysis (EDX), X-Ray Fluorescence Spectrometer (XRF), and X Ray Diffraction analysis (XRD), which indicated that a significant amount of TiO2, SnO2, and Sb2O3 were formed on the surface of Ti-Sn-Sb/γ-Al2O3 particle electrode. It was also observed that the primary function of Ti-Sn-Sb/γ-Al2O3 particle electrode in the three-dimensional electrode electrolysis process is the strong oxidizing function of ·OH for degrading OTC. Consequently, the analysis of degradation products of oxytetracycline (OTC) demonstrates. In addition, the results and conclusions of this study provide a methodological basis and engineering practice basis for removing the low concentration of antibiotics in water.

Degradation of chloramphenicol using Ti-Sb/attapulgite ceramsite particle electrodes.

Ti-Sb/attapulgite ceramsite particle electrodes were prepared for the efficient degradation of chloramphenicol (CAP) in wastewater. To observe the surface morphology and structural characteristics of the Ti-Sb/attapulgite ceramsite particle electrodes, Fourier transform infrared spectroscopy, X-ray fluorescence, scanning electron microscopy, and X-ray diffraction were used for characterization. Parameters affecting the degradation efficiency and the energy consumption of the Ti-Sb/attapulgite ceramsite particle electrodes, such as current density, electrode distance, initial pH, conductivity, air flow, and packing ratio, were examined. Results showed that the optimal conditions were 20 mA/cm2 current intensity, 3 cm electrode distance, 5,000 µS/cm conductivity, 2.0 L/min air flow, 50.0% packing ratio, and initial pH 1. The removal efficiency of chloramphenicol was 73.7% under the optimal conditions, and the energy consumption was 191.3 (kW h)/kg CAP. PRACTITIONER POINTS: Attapulgite ceramsite with good physical performance was prepared. The removal efficiencies for CAP in water by Ti-Sb/attapulgite ceramsite particle electrodes were studied. CAP was effectively removed by 3-D electrode system. CAP removal was significantly influenced by operational parameters. Three-dimensional electrode system shows good degradation ability.

Characterization and flocculation evaluation of a novel carboxylated chitosan modified flocculant by UV initiated polymerization.

In this work, carboxylated chitosan modified flocculant (CC-g-PCD) was prepared by graft copolymerization technique to enhance the charge-attracting and adhesion of bridges and net-sweeping capacity of flocculants. The dimethyldiallylammonium chloride (DMDAAC), carboxylated chitosan (CMCS), and 3-chloro-2-chloropropyltrimethylammonium chloride (CTA) were utilized for synthesis of CC-g-PCD via photopolymerization techniques. The synthesized CC-g-PCD was characterized by 1H NMR, SEM, XRD, and FTIR, and the characteristic groups on the main chain and surface morphological structure of CC-g-PCD were investigated. The obtained results indicated that CTA and DMDAAC were successfully grafted into the CPCTS. In ordered to evaluate the flocculation performance of CC-g-PCD at various dosages, stirring intensity (G value), and pH value by detecting Chl a, COD, and turbidity, the actual lake water that contains algae was used for flocculation assessment tests. The experimental results of the water sample with flocculation showed that the maximum flocculation efficiency of turbidity (91.1%), Chl a (97.2%), and COD (97.0%) can be achieved by CC-g-PCD at pH 7, G value 200 s-1, and 4.0 mg/L. The comparison results demonstrated that CC-g-PCD had better flocculation efficiency than commercial flocculants. Finally, based on the analysis of algae removal in combination with Zeta potential measurements, the flocculation mechanisms in actual lake water at various dosages and pH values were adsorption bridging and electrical neutralization.

Electrocatalytic oxidation of tetracycline by Bi-Sn-Sb/γ-Al2O3 three-dimensional particle electrode.

In this work, highly efficient Bi-Sn-Sb/γ-Al2O3 particle electrodes were prepared for effectively degrading tetracycline. The effects of a mass ratio (Sn: Sb), the mass ration of Bi:(Sn + Sb), impregnation times, calcination temperature, and calcination time on the electrocatalytic oxidation capacity of Bi-Sn-Sb/γ-Al2O3 particle electrode was investigated. Conditions in which mass ratio of (Sn: Sb) = 10:1, the mass ratio of Bi:(Sn/Sb) = 1:1, impregnation times 2 h, calcination temperature 500 °C., and calcination time 3 h were considered as optimal preparation conditions for Bi-Sn-Sb/γ-Al2O3 particle electrode. It was cherecterized by infrared spectroscopy (IR), scanning electron microscope (SEM), energy dispersive X-ray detector (EDX), X-Ray Diffraction (XRD), and X-ray fluorescence (XRF) techniques to conforming that the triclinic Bi2O3 formed in the preparation conditions has superior electrocatalytic activity. The electrocatalytic oxidation mechanism of tetracycline by Bi-Sn-Sb/γ-Al2O3 particle electrode is proposed by determining degradation intermediates through LC-MS detection. Electrocatalytic oxidation experiments by adding tert-butyl alcohol indicate that the formation of OH is the primary responsibility for degradating tetracycline. Electrocatalytic degradation of tetracycline at different initial concentration shows that the degradation of tetracycline meets the pseudo first-order kinetics. Results suggest that the three-dimensional electrochemical reactor with Bi-Sn-Sb/γ-Al2O3 particle electrodes could be an alternative for the pretreatment of antibiotic wastewater before biological treatment.

Mechanism of organic pollutants sorption from aqueous solution by cationic tunable organoclays.

A variety of quaternary ammonium salts with different carbon chain lengths were used to modify and convert montmorillonite clay to organoclays. The surface modification attributing to the wettability was investigated using various techniques. The zeta-potential values of all clays showed pH dependency. The prepared organoclays were utilized for phenol (protic) and nitrobenzene (aprotic) adsorption in a batch system, with pH and contact time as variables. The optimized removal for phenol and nitrobenzene within 30 min of equilibrium observed at pH 9.0 and 5.0, respectively. Observed equilibrium data followed the Langmuir monolayer adsorption kinetics with two adsorption sites (outer-layer and interlayer) for purified clay, and third additional sites for organoclays. Kinetic studies revealed that the adsorption of phenol was in the order of mono- > tetra- > di- > benzyl-substituted organoclays, which is similar to the hydrophilicity order. However, the exact opposite trend of adsorption was observed for nitrobenzene. From the performed quantitative study, it is inferred that -OH functional phenol and -NO2 functional nitrobenzene have an affinity towards the hydrophilic clay surface and hydrophobic surfaces of quaternary ammonium salts as its first preference, respectively. This study brings promising observations and implications to the vital structural-property relationship for selective adsorption of pollutants from aqueous solutions.

Advances and challenges in sustainable tourism toward a green economy.

This paper provides an overview of the interrelationships between tourism and sustainability from a cross-disciplinary perspective. The current challenges and barriers in the tourism sustainability, such as high energy use, extensive water consumption and habitat destruction, are first reviewed. Then the key cross-disciplinary elements in sustainable tourism, including green energy, green transportation, green buildings, green infrastructure, green agriculture and smart technologies, are discussed. To overcome the challenges and barriers, a few implementation strategies on achieving sustainable tourism from the aspects of policy/regulation, institution, finance, technology and culture are proposed, along with the framework and details of a key performance indicator system. Finally, prospects of the potential for tourism to contribute to the transformative changes, e.g., a green economy system, are illustrated. This paper shine a light on issues of importance within sustainable tourism and encourage researchers from different disciplines in investigating the inter-relationships among community/culture, environment/ecology, and energy/water/food more broadly.

Rate Control versus Rhythm Control for Atrial Fibrillation after Cardiac Surgery.

BACKGROUND: Atrial fibrillation after cardiac surgery is associated with increased rates of death, complications, and hospitalizations. In patients with postoperative atrial fibrillation who are in stable condition, the best initial treatment strategy--heart-rate control or rhythm control--remains controversial. METHODS: Patients with new-onset postoperative atrial fibrillation were randomly assigned to undergo either rate control or rhythm control. The primary end point was the total number of days of hospitalization within 60 days after randomization, as assessed by the Wilcoxon rank-sum test. RESULTS: Postoperative atrial fibrillation occurred in 695 of the 2109 patients (33.0%) who were enrolled preoperatively; of these patients, 523 underwent randomization. The total numbers of hospital days in the rate-control group and the rhythm-control group were similar (median, 5.1 days and 5.0 days, respectively; P=0.76). There were no significant between-group differences in the rates of death (P=0.64) or overall serious adverse events (24.8 per 100 patient-months in the rate-control group and 26.4 per 100 patient-months in the rhythm-control group, P=0.61), including thromboembolic and bleeding events. About 25% of the patients in each group deviated from the assigned therapy, mainly because of drug ineffectiveness (in the rate-control group) or amiodarone side effects or adverse drug reactions (in the rhythm-control group). At 60 days, 93.8% of the patients in the rate-control group and 97.9% of those in the rhythm-control group had had a stable heart rhythm without atrial fibrillation for the previous 30 days (P=0.02), and 84.2% and 86.9%, respectively, had been free from atrial fibrillation from discharge to 60 days (P=0.41). CONCLUSIONS: Strategies for rate control and rhythm control to treat postoperative atrial fibrillation were associated with equal numbers of days of hospitalization, similar complication rates, and similarly low rates of persistent atrial fibrillation 60 days after onset. Neither treatment strategy showed a net clinical advantage over the other. (Funded by the National Institutes of Health and the Canadian Institutes of Health Research; ClinicalTrials.gov number, NCT02132767.).

Selective Gas Capture Ability of Gas-Adsorbent-Incorporated Cellulose Nanofiber Films.

The 2,2,6,6-tetramethylpiperidine-1-oxyl radical-oxidized cellulose nanofibers (TOCNF) were hybridized with cation and anion-exchange organoclays, where poly(amido amine) dendrimers were loaded to enhance the functionality of gas adsorption, since dendrimers have the high adsorbability and the enough selectivity on the gas adsorption. The thin films were prepared from the organoclay-TOCNF hybrids and supplied to the gas adsorption. The adsorption of CO2 and NH3 gases increased with an increasing amount of organoclays in TOCNF films, but the behavior of the increase depended on gases, clays, and dendrimers. The hydrotalcite organoclay-TOCNF films displayed the highest adsorption of both gases, but the desorption of CO2 gas from hydrotalcite organoclay-TOCNF films was drastically high in comparison with the other systems. While the CO2 gas is adsorbed and remained on cationic dendrimer sites in cation-exchange organoclay-TOCNF films, the CO2 gas is adsorbed on cationic clay sites in anion exchange organoclay-TOCNF films, and it is easily desorbed from the films. The NH3 adsorption is inversive to the CO2 adsorption. Then the CO2 molecules adsorbed on the cationic dendrimers and the NH3 molecules adsorbed on the anionic dendrimers are preferably captured in these adsorbents. The present research incorporated dendrimers will be contributing to the development of gas-specialized adsorbents, which are selectively storable only in particular gases.

Controlling wettability and hydrophobicity of organoclays modified with quaternary ammonium surfactants.

The montmorillonite clays were modified with quaternary ammonium salts (QASs) having different alkyl chain lengths and a benzyl substitute group. The modified organoclays were characterized by different analytical techniques. The wettability and hydrophilicity/hydrophobicity of the modified clays was evaluated using water or oil penetration (adsorption) and contact angle measurements. The loading of QASs was in the range of 0.60-0.75 mmol/g per clay, irrespective of the type of QAS used for the modification of the clay. From the analytical investigations, it was elucidated that the modification of clay with QAS affected the structural, textural, and surface properties. Moreover, it should be noted that the modification with QAS having benzyl substitute group resulted in water-non-wettable and superhydrophobic surface, whereas clays modified with QAS without benzyl substitute group became more water-wettable and hydrophilic than the pristine clay. The presence of benzyl groups on the clay prevents water from penetration into the inter-clay or interlayer spacing, which yields the hydrophobic surface. These behaviors can arise from molecular arrangement of QAS on clay but not be attributable to the amount of QASs, and the surface area, size, and zeta potential of particles.