Cadmium (Cd) is absorbed readily by rice plants and is transferred to humans when contaminated rice is consumed. Adding selenium (Se) to the plant nutrient solutions reduces the accumulation of Cd in the rice (Oryza sativa L.) seedlings. However, as the relevant underlying mechanism remains unclear, the aim of our study was to improve our understanding of the Se-mediated resistance to Cd stress in rice. We conducted hydroponic experiments to study the effects of selenite or selenate on Cd subcellular distribution and xylem transport in rice seedlings under Cd stress, and we investigated the antioxidative defense responses in the rice plants. We found that the supplementation of both Se forms decreased the Cd accumulations in the roots and shoots of the rice plants. The selenite addition significantly decreased the Cd contents in different subcellular fractions of the rice roots, increased the proportion of Cd distributed to soluble cytosol by 23.41%, and decreased the Cd distribution in the organelle by 28.74% in contrast with the treatment with Cd only. As regards the selenate addition, only the Cd distribution ratio of cytosol was increased by 13.07%. After adding selenite, a decrease of 55.86% in the Cd concentration in xylem sap was observed, whereas little change was found after treatment co-applied with selenate. The hydrogen peroxide (H₂O₂) and malondialdehyde(MDA) contents in the rice roots were elevated under Cd stress, and the addition of selenite and selenate decreased the H₂O₂ levels by 77.78% and 59.26%, respectively. Co-exposure to Cd and Se elevated the glutathione (GSH) accumulations in the rice shoots and roots, with the degree of increase being the following: co-applied with selenite > co-applied with selenate > Cd alone treatment. Exposure to Cd increased the catalase (CAT) activity in the roots significantly, whereas it decreased in the shoots. After selenite or selenate supplementation, the CAT activity in the rice roots increased compared with applying only Cd. Compared with the control, the addition of Cd or Se had no significant effect on the activities of peroxidase (POD) or ascorbate peroxidase (APX). Our results showed that Se affected the Cd accumulation in rice seedlings by altering the Cd subcellular distribution and decreasing the ROS induced by Cd stress. Such effects were more significant in the selenite than in the selenate applied treatment.

The Sub-Saharan Africa (SSA) is far lag behind the sustainable targets that set out in the United Nation’s Sustainable Development Goals (SDGs), which is highly needed to embark the priorities by their member countries to devise sustainable policies for accessing clean technologies, energy demand, finance, and food production to mitigate high-mass carbon emissions and conserve environmental agenda in the national policy agenda. The study evaluated United Nation’s SDGs for environmental conservation and emission reduction in the panel of 35 selected SSA countries, during a period of 1995–2016. The study further analyzed the variable’s relationship in inter-temporal forecasting framework for the next 10 years’ time period, i.e., 2017–2026. The parameter estimates for the two models, i.e., CO₂ model and PM₂.₅ models are analyzed by Generalized Method of Moment (GMM) estimator that handle possible endogeneity issue from the given models. The results rejected the inverted U-shaped Environmental Kuznets Curve (EKC) for CO₂ emissions, while it supported for PM₂.₅ emissions with a turning point of US$5540 GDP per capita in constant 2010 US$. The results supported the “pollution haven hypothesis” for CO₂ emissions, while this hypothesis is not verified for PM₂.₅ emissions. The major detrimental factors are technologies, FDI inflows, and food deficit that largely increase carbon emissions in a panel of SSA countries. The IPAT hypothesis is not verified in both the emissions; however, population density will largely influenced CO₂ emissions in the next 10 years’ time period. The PM₂.₅ emissions will largely be influenced by high per capita income, followed by trade openness, and technologies, over a time horizon. Thus, the United Nation’s sustainable development agenda is highly influenced by socio-economic and environmental factors that need sound action plans by their member countries to coordinate and collaborate with each other and work for Africa’s green growth agenda.

This work studies the in situ electrobioremediation of an oxyfluorfen-polluted clay soil in a two-stage method. First, a fixed-bed biofilm reactor for oxyfluorfen biodegradation in wastewater was developed; it treated wastewater with 200 mg L⁻¹ of oxyfluorfen and reached 100% of oxyfluorfen degradation in 30 h. Second, a portion of the biofilm-covered bed was included into the polluted soil and it was used as a biological permeable reactive barrier (BioPRB), whereas electrokinetics was applied to promote the contact between the pollutant and microorganisms into the soil. The electrobioremediation study was performed in a bench scale setup under 1.0 V cm⁻¹ at room temperature and under periodic polarity reversal (2 day⁻¹) in a 2-week batch experiment. Two reference tests were done: (i) a conventional in situ biological test without electrokinetics and (ii) a conventional in situ electrokinetic test without using microorganisms. The experimental conditions (temperature, pH, moisture) were correctly controlled in the soil and enabled the microbial activity during the process. A low oxyfluorfen removal efficiency was obtained after 2 weeks (11%) because of the low electrokinetic mobility of such non-polar pollutant into the soil. Despite this low efficiency value, it was considered that the combined biological-electrokinetic technology could be used as a bioaugmentation procedure to perform electrobioremediation processes because the results of both reference tests showed negligible removal efficiencies when using only biological or only electrochemical methods. According to these results, electrobioremediation could be considered a feasible technology although more retention time would be required to achieve successful remediation results.

Experiments were conducted under lead (Pb), cadmium (Cd), and copper (Cu) exposure to observe germination and seedling growth of wheat (Triticum aestivum L), pea (Pisum sativum), and tomato (Solanum lycopersicum L.). Metals were applied in five concentrations (20, 65, 110, 175, and 220 ppm) and Hoagland solution was used to feed the seedlings. Irrespective of the tested crop seeds, copper revealed maximum effect (51.2%) on germination followed by lead (47.5%) and cadmium (35.3%). Tomato seeds were most sensitive in germination stage followed by pea and wheat. In seedling stage, tomato also showed highest sensitivity to both Cd and Cu. However, pea seedlings showed higher tolerance to Pb and wheat seedlings had the highest tolerance to both Cu and Cd. Toxicity and tolerance of metals was found to vary with crops and growth stages. Higher transfer of metals (Pb, Cd, and Cu) in wheat seedling indicates higher risk of food chain contamination when grown in polluted soil. Higher mobility and uptake of Cd in tomato and wheat seedlings even under lower concentration of exposure needs further study.

The purpose of this study is to experimentally investigate the effect of unsaturation of the biodiesels obtained from grapeseed oil, wheat germ oil and coconut oil (reference fuel) for compression ignition (CI) engine application. Fatty acid profile analysis and physio-chemical properties were determined by standard test procedures. Engine testing was carried out in a 5.2-kW single-cylinder CI engine and the combustion, performance and emission characteristics were analysed. The effect of fuel property variation and the combustion reaction kinetics due to unsaturation difference have been discussed. The maximum brake thermal efficiency at full load for diesel was found to be 32.3% followed by 31.3%, 30.2% and 27.4 %, respectively, for coconut biodiesel (CBD), grapeseed biodiesel (GSBD) and wheat germ biodiesel (WGBD). Maximum heat release rate as observed for diesel, CBD, GSBD and WGBD are 63.2 J/°CA 60.7 J/°CA and 59 J/°CA and 43.4 J/°CA respectively. The brake-specific NO emission at full load is higher for CBD followed by GSBD, WGBD and diesel having values of 9.23 g/kWh, 8.91 g/kWh, 8.21 g/kWh and 7.6 g/kWh respectively. Conversely, the smoke emission is lower for CBD compared to the other tested fuels.

A bibliometric analysis was performed to assess historical and recent research trends regarding e-waste studies from 1998 to 2018. Documents related to e-waste were identified from the Clarivate Analytics Web of Science© (WoS) database, and a total of 3311 academic articles was retrieved. The analysis was performed from four main aspects: (1) publication activity by year, by WoS category, and by geographic distribution; (2) journals; (3) most-cited papers; and (4) top 10 countries and author keyword analysis. The number of publications concerning e-waste issues has increased substantially over the last 20 years, especially in the environmental science category, and more than a third of the publications were produced in China (1181 records). Waste Management and Environmental Science & Technology were the most sought-after journals for disseminating the results. Studies related to “e-waste flow analysis,” “recycling,” “recovery of precious metals,” and “risk assessment of recycling areas” have been the most common for several years. The analysis of keywords suggested that there are many topics on electronic waste and that each country has presented a different focus of research. Overall, the bibliometric analysis proved to be an efficient tool with which to monitor historical and current research trends and to evaluate the sheer volume of currently existing scientific literature on e-waste topics.

Washing of contaminated soils or sediments using humic substances (HS) extracted either from source-rich materials or compost has been tested effective to remove various heavy metals. Nevertheless, the remaining chemical fractionation of metals and post-washing biological responses were not discussed in previous research. In this study, we used a HS extracted from green waste compost to wash off Cd, As, and Ni from a contaminated sediment, and evaluated the washing effect on sediment microbes by measuring a series of indexes with regard to microbial biomass and enzyme activities. Results showed that HS washing was more effective in removing the cationic metals Cd and Ni than the anionic metal As. The highest HS dose of 2000 mg L⁻¹ resulted in 24.5-, 33.1-, and 12-fold increases of removal for Cd, Ni, and As, respectively. The remaining Cd and As were found to migrate to less stable fractions, whereas the remaining Ni was dominantly found in the residual fraction. Increases of metal removal efficiency, microbial biomass, and dehydrogenase activity were found to correlate with the increase of HS concentrations. Increasing doses of HS slightly altered sediment pH to the lower range but did not cause any significant effect on microbial activities. The study proves that HS washing is indeed a more environmental-friendly strategy than many existing washing agents which have exerted various side effects on soil properties.

A kinetic model describing Fenton and photo-Fenton degradation of paracetamol (PCT) and consumption of hydrogen peroxide (H₂O₂) was proposed. A set of Fenton and photo-Fenton experiments (18 runs in total) was performed by fixing the initial concentration of PCT to 40 mg L⁻¹ and varying the initial concentrations of H₂O₂ and ferrous ion, Fe²⁺. The experimental set-up was a well-stirred annular photoreactor equipped with an actinic BL TL-DK 36 W/10 1SL lamp. Experimental results highlighted that PCT is no more detected by HPLC analysis within a minimum reaction time of 2.5 and a maximum reaction time of 15.0 min. Besides, a maximum conversion of total organic carbon (TOC) of 68.5% was observed after 75 min of reaction in case of using UV radiation and the highest concentrations of the Fenton reagents. The experimental data were used to fit the kinetic model. The radiation field inside the reactor was taken into account through the local volumetric rate of photon absorption, evaluated by assuming a line source model with spherical and isotropic emission. The kinetic parameters were estimated by using a non-linear least-squares regression procedure and root mean square errors (RMSE) were calculated in order to validate the feasibility of the proposed model. A good agreement between experimental and predicted data was observed and the lowest values of RMSE resulted in 5.84 and 9.59% for PCT and H₂O₂ normalized concentrations, respectively.

The presence of pathogens in drinking water can seriously affect human health. Therefore, water disinfection is needed, but conventional processes, such as chlorination, result in the production of dangerous disinfection by-products. In this regard, an alternative solution to tackle the problem of bacterial pollution may be the application of advanced oxidation processes. In this work, the inactivation of total coliforms, naturally present in a Colombian surface water by means of UV/H₂O₂, UV/US, and the UV/US/H₂O₂ advanced oxidation processes, was investigated. Under the investigated conditions, complete bacterial inactivation (detection limit equal to 1 CFU 100 mL⁻¹) was found within 5 min of treatment by UV/H₂O₂ and UV/US/H₂O₂ systems. UV/US oxidation process also resulted in total bacterial load elimination, but after 15 min of treatment. Bacterial reactivation after 24 h and 48 h in the dark was measured and no subsequent regrowth was observed. This phenomenon could be attributed to the high oxidation capacity of the evaluated oxidation systems. However, the process resulting in the highest oxidation potential at the lowest operating cost, in terms of energy consumption, was UV/H₂O₂ system. Therefore, UV/H₂O₂ advanced oxidation system can be used for disinfection purposes, enabling drinking water production meeting the requirements of regulated parameters in terms of water quality, without incurring extremely high energy costs. Nonetheless, further researches are required for minimizing the associated electric costs.

In order to improve the catalytic properties of Fe₃O₄ nanoparticles in wastewater treatment, the Cu-doped Fe₃O₄/graphene oxide (Fe₃₋ₓCuₓO₄/GO) nanocomposites were prepared by a modified co-precipitation method and used as heterogeneous catalyst for p-Nitrophenol (p-NP) degradation. The effect of the GO and Cu contents in the nanocomposites was investigated. Compared with the unsupported Fe₃O₄ nanoparticles, the Fe₃O₄/GO nanocomposites have obviously improved catalytic performance, especially for the nanocomposite with 6.25 wt.% of the GO content. Furthermore, the catalytic efficiency is greatly improved by doping Cu in the nanocomposite. The Fe₃₋ₓCuₓO₄/GO nanocomposite achieves the best catalytic property in our catalyst system when the x value is about 0.075. Under the optimal reaction condition (0.8 g L⁻¹ of catalyst dosage, 15 mmol L⁻¹ of initial H₂O₂ concentration, 3.0 of pH value, and 30 °C of temperature), the p-NP conversion and chemical oxygen demand removal efficiencies in 120 min for the Fe₂.₉₂₅Cu₀.₀₇₅O₄/GO nanocomposite are about 98.4% and 74.7%, respectively. And the p-NP conversion efficiency is still as high as 96.2% after four recycles under the optimum condition. The results clearly show that the Fe₂.₉₂₅Cu₀.₀₇₅O₄/GO nanocomposite has outstanding catalytic properties for the p-NP degradation.