Global trade plays an imperative role in the world economy that yields environmental degradation. Therefore, the current paper’s ambitions are to explore the trade–air pollution nexuses by introducing the value-added trade (VT) concept from a global value chain stance. The value-added trade (VT) indicator is constructed by the World Input-Output (WIOD) classifications database. Owing to scanty data accessibility, the sample set is reduced to 39 countries covering the period from 1995 to 2009. Furthermore, this paper is also contributing by including the eight different pathways of per capita air pollution in terms of ammonia (NH3), carbon monoxide (CO), carbon dioxide (CO₂), methane (CH₄), nitrogen oxides (NOₓ), nitrous oxide (N₂O), sulphur oxides (SOₓ) and non-methane volatile organic compounds (NMVOC) respectively. The valuable outcomes from empirical analysis have been found; Firstly, it explores that the preliminary stage of the development of value-added trade (VT) has a positive impact on air-bonds pollution. However, in the later stage of the economic development, trade improves the environmental quality as the square of value-added trade (VT²) has a negative impact on air pollution. Moreover, it also elaborates that the magnitude impact of trade on carbon monoxide (CO) air pollution is more than the other seven air pollutants. Thirdly, the inverted U-shape in the trade–air pollution Environmental Kuznets Curve (EKC) hypothesis, the non-linear relationship between trade and pollution is also validated in all eight air pollutants indicators. Policy proposals for green economy that underlines the global value chain stance and environmental factors in the growing economy are proposed.

Unanticipated increase in the use of silver (Ag) and copper oxide (CuO) nanoparticles (NPs) due to their antimicrobial properties is eliciting environmental health concern because of their coexistence in the aquatic environment. Therefore, we investigated the genetic and systemic toxicity of the individual NPs and their mixture (1:1) using the piscine micronucleus (MN) assay, haematological, histopathological (skin, gills and liver) and hepatic oxidative stress analyses [malondialdehyde (MDA), reduced glutathione (GSH), superoxide dismutase (SOD) and catalase (CAT)] in the African mud catfish, Clarias gariepinus. The fish were exposed to sublethal concentrations (6.25–100.00 mg/L) of each NP and their mixture for 28 days. Both NPs and their mixture induced significant (p < 0.05) increase in MN frequency and other nuclear abnormalities. There was significant decrease in haemoglobin concentration, red and white blood cell counts. Histopathological lesions observed include epidermal skin cells and gill lamellae hyperplasia and necrosis of hepatocytes. The levels of MDA, GSH and activities of SOD and CAT were impacted in C. gariepinus liver following the exposure to the NPs and their mixture. Interaction factor analysis of data indicates antagonistic genotoxicity and oxidative damage of the NPs mixture. These results suggest cytogenotoxic effects of Ag NPs, CuO NPs and their mixture via oxidative stress in Clarias gariepinus.

With the adding of tourist volume in China, carbon emissions from hotel sector increased greatly. Environmental efficiency of hotel sector considering technology heterogeneity is mainly analyzed across different regions of China from 2000 to 2013. Metafrontier global Malmquist-Luenberger (ML) is implemented to evaluate environmental efficiency of hotel sector. Furthermore, we analyze whether technology heterogeneity of different regions increased or not through technological gap ratio. The empirical analysis revealed that the east had the highest environmental efficiency under metafrontier after 2009. After 2009, technological gap ratio (TGR) in the east ranked highest among four regions in China. Environmental regulation positively impacts environmental efficiency under group frontier of hotel sector in the model of nation, east, and middle. Urbanization has U-shaped link with environmental efficiency of hotel sector for the east. It is important to strengthen environmental regulation to reduce carbon emissions. Last, it is important to enhance consciousness of energy abating and carbon emissions reduction of hotel customers.

The aim of this study was to investigate the impact of incorporating Walnut leaves (WL) and their biochars produced at three temperatures (200, 400, and 600 °C) on fractionation, availability and maize indices in a naturally calcareous highly contaminated soil of Central Iran. A pot experiment was conducted considering soils treated with 0, 0.5, 1, and 2% (w/w) of WL and their derived biochars. After maize (Zea mays L.) planting, shoot and root dry matter and Pb and Zn concentration in shoots and roots and DTPA-extractable and fractions of Zn and Pb in soils were determined. Results showed showed that biochar amendments substantially modified the partitioning of Zn and Pb from easily available forms to less available forms. The results showed that DTPA-extractable of Zn and Pb and their bioaccumulation were reduced upon the addition of biochars produced at different temperatures and application rates in a calcareous soil. Treating soil with 2% biochar produced at 600 °C increased significantly shoot and root dry matter by 131.4% and 116.7%, respectively and reduced the bioavailability of Zn and Pb (DTPA-TEA extraction) by 49.1%, and 34.9%, respectively (P < 0.05) in comparison to the control. Therefore, biochars were able to reduce metals contamination in treatments and increase maize dry matter. Biochar decreased Zn and Pb concentration in plant tissues and promoted gradual maize growth responses through changing metals fractions. Therefore, biochar as a sorbent for contaminants can assist in maize to mitigate and phytostabilize Zn and Pb in highly contaminated soils.

A previously isolated indigenous strain of Pseudomonas sp. was used to treat effluents, a synthetic and an industrial-containing benzalkonium chloride (BAC), in continuous upflow biofilm aerobic reactors. The reactor used to treat the synthetic effluent was constructed from Plexiglas® and filled with hollow polyvinyl chloride (PVC) cylinders as support material, whereas the one used to treat the industrial effluent was constructed from PVC and had a high recirculation flow rate and lightweight expanded clay aggregate (LECA®) as support material. Biodegradation was evaluated by spectrophotometry, HPLC, and microbial growth. Detoxification was evaluated by using Vibrio fisheri, Pseudokirchneriella subcapitata, and Lactuca sativa as test organisms. Maximal BAC influent concentrations were of 383.4 and 1172.0 mg L⁻¹ respectively, which corresponds to a maximal organic load of 49.8 and 146.5 g BAC m⁻³ day⁻¹. The efficiency of the reactors was higher than 99.3% in terms of compound removal and 97.0% in terms of COD removal. Complete detoxification of the effluent was demonstrated for the synthetic effluent, whereas a toxicity removal higher than 97% was reached in the case of the industrial effluent. The promising behavior of the isolated indigenous strain to degrade BAC in continuous reactors allows us to suggest its possible use in remediation processes.

This research work is focused on the synthesis, characterization, and application of cost-effective biochar–biopolymeric hybrid adsorbents from waste agricultural biomass and sodium alginate. The adsorbents were characterized by BET (Brunauer–Emmett–Teller), FTIR (Fourier transform infrared), XRD (X-ray diffraction), FESEM (field emission scanning electron microscopy), and bulk density measurement. The performance of the synthesized hybrid adsorbents has been tested for the removal of aqueous phase Ni²⁺ and Cu²⁺ metal ions at a concentration range of 25 to 100 mg/L, adsorbent dose of 1–3 g/L, and system temperature of 298–308 K, respectively. The effect of various physicochemical process parameters such as solution pH, adsorbent dose, initial metal ion concentration, temperature, and presence of salts on metal ion adsorption has been studied here, and experimental process parameters are being optimized by response surface methodology (RSM). The model was fitted well with the experimental data. Various kinetic models, namely, pseudo-first-order, pseudo-second-order, and Weber–Morris, have been fitted with batch experimental data, and the mechanism of adsorption has been identified. The maximum Langmuir monolayer adsorption capacity for Cu²⁺ and Ni²⁺ were 112 and 156 mg/g, respectively, which are comparative to other published adsorbent’s capacity data under similar experimental conditions. Thermodynamic parameter studies showed that the system was endothermic and spontaneous in nature.

Electrochemical reduction is currently one of promising methods for nitrate removal from water, yet most treatment approaches have problems of high cost and energy consumption. In this work, a low current density was applied in electrochemical reduction of nitrate. Copper-modified titanium (Cu/Ti) electrodes with optimal electrochemical activity and fastest kinetics were firstly screened. Thirty minutes of electrodeposition time and neutral pH were found to have the greatest nitrate reduction rate of 83.14%. To further improve the removal of nitrate, activated carbon (AC) and copper-modified activated carbon (Cu/AC) particles were applied to construct three-dimensional reaction systems, with removal rates of nitrate of 88.72% and 96.05%, respectively. The average conversion rates of nitrate to ammonia nitrogen increased from 15.28% to 42.68% and 62.64% in AC- and Cu/AC-based reaction systems, respectively. Oxidation of Cu(0) on surfaces of Cu/Ti cathode and Cu/AC particles to Cu(I) was revealed by X-ray photoelectron spectroscopy (XPS) and Cu LMM spectra analysis. Besides, results of water chemistry characteristics indicated the conversion of AC to carbonate ion. It could be concluded that enhanced nitrate reduction of Cu/Ti-based reaction system was attributed by Cu particle- and AC-mediated electron transfer. This study provided a reference for low-cost electrochemical reduction of nitrate.

The application of conventional physicochemical and microbiological techniques for the removal of organic pollutants has limitations for its utilization on wastewaters as landfill leachates because of their high concentration of not easily biodegradable organic compounds. The use of ozone-based technologies is an alternative and complementary treatment for this type of wastewaters. This paper reports the study of the degradation of landfill leachates from different stages of a treatment plant using ozone and ozone + UV. The experimental work included the determination of the temporal evolution of COD, TOC, UV254, and color. Along the experimental runs, the instantaneous off-gas ozone concentration was measured. The reaction kinetics follows a global second order expression with respect to COD and ozone concentrations. A kinetic model which takes into account the gas liquid mass transfer coupled with the chemical reaction was developed, and the corresponding parameters of the reacting system were determined. The mathematical model is able to appropriately simulate COD and ozone concentrations but exhibiting limitations when varying the leachate type. The potential application of ozone was verified, although the estimated efficiencies for COD removal and ozone consumption as well as the effect of UV radiation show variations on their trends. In this sense, it is interesting to note that the relative ozone yield has significant oscillations as the reaction proceeds. Finally, the set of experimental results demonstrates the crucial importance of the selection of process conditions to improve ozone efficiencies. This approach should consider variations in the ozone supply in order to minimize losses as well as the design of exhaustion methods as multiple stage reactors using chemical engineering design tools.

A waste–struvite/diatomite compound (MAP@Dia) recovered from nutrient-rich wastewater treated by MgO-modified diatomite (MgO@Dia) was provided to immobilize lead in aqueous solution and contaminated soil. The mechanism and effectiveness of lead immobilization was investigated, and the pHₛₜₐₜ leaching test and fixed-bed column experiments were carried out to assess the risk of MAP@Dia reuse for lead immobilization. The results showed that MAP@Dia were effective in immobilizing lead in aqueous solution with adsorption capacity of 832.47–946.50 mg/g. The main mechanism of Pb immobilization by MAP@Dia could be contributed by surface complexation and dissolution of struvite followed by precipitation of hydroxypyromorphite Pb₁₀(PO₄)₆(OH)₂. Lead(II) concentration reduced from 269.61 to 78.26 mg/kg, and residual lead(II) increased to 53.14% in contaminated soil when the MAP@Dia application rate was 5%. The increased neutralization capacity (ANC) and lower lead extraction yields in pHₛₜₐₜ leaching test in amended soil suggested 5 times of buffering capacity against potential acidic stresses and delayed triggering of “chemical time bombs.” The results of column studies demonstrated that amendment with MAP@Dia could reduce the risk of lead and phosphorus (P) leaching. This study revealed that MAP@Dia could provide an effective solution for both P recycling and lead immobilization in contaminated soil.

The aim of this work was to study the adsorption kinetic, isotherm, and thermodynamic of 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide in raw and boiling-treated sterile bracts of Araucaria angustifolia as novel alternative natural adsorbents. The sterile bracts were characterized by scanning electron microscopy and Fourier-transform infrared spectroscopy. The adsorption and removal of 2,4-D from aqueous solutions were conducted at different contact times, bract granulometries, solution pH, bract masses, initial 2,4-D concentrations, and temperatures. The adsorption kinetic, mechanism, and thermodynamic were evaluated using pseudo-first- and pseudo-second-order kinetic models, non-linear Langmuir, Freundlich, Redlich-Peterson and Sips isotherm models, and Gibbs free energy, enthalpy, and entropy. The maximum removal efficiency of 2,4-D was found with 720 min of contact, 5.0 g of bract containing 31 micron particle sizes, pH = 2.0, and room temperature. The best kinetic and isotherm fits were found with the non-linear pseudo-second-order kinetic model and non-linear Freundlich isotherm model, respectively. Therefore, the adsorption mechanism in the bract structure takes place with multi-layer formation and multi-site interactions due to chemisorption reactions. The adsorption process is thermodynamically favorable, spontaneous, and exothermic. Overall, sterile bract of Araucaria angustifolia could be useful as alternative natural adsorbent for the treatment of water and wastewater contaminated with 2,4-D, mitigating the environmental pollution caused by agricultural crops. Graphical Abstract