Tailings and waste rocks can be used to build covers with capillary barrier effects (CCBE) for the purposes of reclaiming acid-generating waste storage facilities while enhancing the value of the materials available on site. The efficiency of non-acid generating tailings, desulfurized tailings, and non-reactive waste rocks as cover materials was demonstrated in previous laboratory and field studies. However, acid-generating waste rocks are usually not considered for cover construction because of the risk of contamination. Nonetheless, using acid-generating waste rocks as the bottom capillary break layer in a CCBE could have economic and logistical benefits for companies, including helping to reduce the volume of waste rock piles and to valorize material that are generally considered to be problematic. In this study, laboratory column tests were performed to evaluate cover scenarios using acid-generating waste rocks from Westwood-Doyon mine (Québec, Canada). These waste rocks were placed under a moisture-retaining layer made of desulfurized tailings. A column test with non-acid-generating waste rocks was also performed for comparison purposes. Columns were submitted to eight wetting/drainage cycles. The performance of these systems was assessed by monitoring the volumetric water content in the different layers and by analyzing the water quality of the leachates. Significant reductions in contamination were observed when covers were added on the reactive waste rocks. These results suggest that it could be possible to valorize acid-generating waste rocks in cover systems.

Accurate determination of emerging contaminants in drinking water constitutes a major environmental challenge for which highly sensitive analytical methods are needed. This work details the development of a novel highly sensitive solid-phase extraction-high performance liquid chromatography-tandem mass spectrometry (SPE-HPLC-MS/MS) method for simultaneous determination of a diverse panel of widely used trace contaminants, including two pharmaceuticals (fluoxetine and gemfibrozil), three pesticides (3-hydroxycarbofuran, azinphos-methyl, and chlorpyrifos), and two hormones (testosterone and progesterone) in water. The method is highly reproducible and sensitive with detection limits at subnanogram per liter level (0.05–0.5 ng/L). It was used to monitor the occurrence of these contaminants in source and drinking water across 18 drinking water treatment facilities in Missouri, USA in 1 year including cold winter and hot summer seasons. The experiment results indicated that all of the monitored contaminant concentrations are very low, lower than or close to the method detection limits, in the selected water treatment facilities. Pesticide concentrations were slightly elevated in some source waters during hot season, whereas slightly higher pharmaceuticals were observed during cold season. The concentrations of two hormones were lower than the limits of detection in all the water samples. These contaminants were present, if any, at below detection limits in all treated drinking water samples analyzed, suggesting that treatment processes effectively removed the contaminants studied herein. Graphical Abstract

Cost-effective recycling of e-waste (from computer printed circuit boards, PCB’s) for the synthesis of metal oxide nanocomposites is demonstrated. Metals in electronic components of waste memory slots were leached out using nitric acid (HNO₃). Compositional analyses of the filtrate obtained after leaching were 66 wt.% Cu, 27.7 wt.% Zn, and 6.2 wt.% Ni. The leached out metal salt solutions were subjected to alkaline hydrothermal treatment to synthesize nanocomposites. Two nanoparticle samples were prepared, one without any stabilizing agent and another sample with PVP as a stabilizing agent. XRD, HR-XRD, HR-TEM, UV-DRS, UV-visible spectroscopy was used to characterize the as-prepared metal oxide nanoparticles. The analysis showed the formation of ZnO/CuO nanocomposites only. No nickel oxide component was precipitated under the studied hydrothermal experimental conditions. Most of the ZnO/CuO nanocomposite particles obtained by this route consisted of fine ZnO nanostructures precipitated on CuO cores. The ZnO and CuO components exhibit both direct and indirect band gaps in the visible range. The nanocomposites demonstrate good visible light photo-Fenton methyl orange (MO) degradation by pseudo-zero order kinetics.

The heavy metal Cd(II) in wastewater is highly toxic to organisms and must be removed. In this work, an efficient Cd(II) adsorbent consisting of ground calcium carbonate (GCC) and nano-TiO₂ (GCC/TiO₂) was harvested through a facile two-step strategy. Firstly, GCC was immersed in titanium sol which prepared from titanium butoxide to form the precursor. Secondly, GCC/TiO₂ was obtained via hydrothermal reaction and the optimal hydrothermal condition was determined to be pH of 3, temperature of 200 °C and reaction time of 12 h. The removal of Cd(II) from aqueous solution by adsorbents under different hydrothermal conditions and adsorption experiments was studied by means of SEM, FT-IR, XPS, and ICP. The maximum Cd(II) removal capacity was approximately 124.07 mg/g at 25 °C and the adsorption equilibrium was attained in only 8 min (at 100 mg/g initial Cd(II) concentration, 0.8 g/L adsorbent dosage, and an initial Cd(II) solution pH of 5). Furthermore, the Cd(II) removal capacity of GCC/TiO₂ was significantly higher than that of isolated GCC and TiO₂ and exhibited an excellent self-settlement property, which is beneficial for adsorbent separation in practical applications. The Cd(II) removal mechanisms include ion-exchange reaction between Cd(II) and the Ca²⁺ ions on the GCC/TiO₂ surface and electrostatic attraction. Moreover, the GCC/TiO₂ adsorbent could be regenerated by ethylenediaminetetraacetic acid disodium salt and exhibited a high reusability. The adsorption data could be well fitted by the Langmuir model, and the adsorption kinetic follows the pseudo-second-order model indicating that the removal processes are controlled by the chemisorption mechanism.

Noise is the most frequently encountered type of environmental pollution in everyday life and has a direct negative effect on humans. Individuals who are constantly exposed to noise tend to have a high incidence of cardiovascular disease and hypertension. Noise sources range from construction sites to political rallies and assemblies, but traffic is one of the most long-lasting and chronic sources of noise. Previously, researchers have conducted valuations of road traffic noise reduction, but they did not consider residents’ annoyance levels in response to traffic noise. However, individuals’ annoyance levels affect the economic value of noise reduction policies and thus must be considered to obtain an accurate estimate. Therefore, this study investigated residents’ willingness to pay for traffic noise reduction depending on their annoyance level. We used the contingent valuation method and a survey to analyze how much 1022 respondents in Korea were willing to pay for noise reduction. We found that people who were annoyed and extremely annoyed by noise had a willingness to pay KRW 8422 (US $7.55) and KRW 9848 (US $8.83) annually per household, respectively, to reduce their annoyance level to zero. In addition, we determined the economic benefits of noise reduction policies using the respondents’ willingness to pay to reduce noise by 1 dB(A), which totaled KRW 3.28 billion (US $2.91 million) per year. The results of this study provide estimates of the annual benefits of traffic noise reduction considering residents’ annoyance level.

Crops are the main source of toxic cadmium for humans due to uptake from naturally or anthropogenically polluted soils. Chronic Cd ingestion causes kidney, liver, and skeletal damage along with an increased risk of cancer. Cacao is known to accumulate Cd and may therefore be potentially harmful to human health. Consequently, cocoa production on intensely polluted soils should be avoided. Cocoa products from South America in particular often exceed the limits for Cd, but the factors that drive Cd uptake are as yet poorly studied. In this study, we measured Cd concentrations in defatted cocoa powder from unfermented seeds of 40 different trees on 20 farms in the Huánuco Region, Peru, and associated the Cd levels with the farms’ soil, field management, and nearby vegetation diversity. The mean Cd concentration found in cocoa of the study region was 2.46 mg kg⁻¹ with a range of 0.2–12.56 mg kg⁻¹. The maximum content measured was an order of magnitude higher than the allowed limit of 1.5 mg kg⁻¹ and was the highest reported so far in the literature. Soil Cd content was the most relevant driver of Cd concentration in cacao. In addition, fertilizer use caused significantly higher Cd concentration in cocoa. Higher biodiversity of herbs was positively correlated with Cd contents in cocoa. The study shows that, apart from the known correlation of soil conditions with Cd accumulation in cacao seeds, changes in fertilization and plant composition may be promising measures to counteract Cd contamination in regions with high soil Cd content.

This article studies the price competition and cooperation in a duopoly that is subjected to carbon emissions cap. The study assumes that in a departure from the classical Bertrand game, there is still a market for both firms’ goods regardless of the product price, even though production capacity is limited by carbon emissions regulation. Through the decentralized decision making of both firms under perfect information, the results are unstable. The firm with the lower maximum production capacity under carbon emissions regulation and the firm with the higher maximum production capacity both seek market price cooperation. By designing an internal carbon credits trading mechanism, we can ensure that the production capacity of the firm with the higher maximum production capacity under carbon emissions regulation reaches price equilibrium. Also, the negotiation power of the duopoly would affect the price equilibrium.

In this study, a novel Fe–Mn–Ce oxide-modified biochar composite (FMCBC) was synthesized via pyrolysis to enhance the adsorption capacity of biochar (BC). Scanning electron microscopy-energy-dispersive X-ray spectroscopy confirmed that Fe, Mn, and Ce were successfully loaded onto the surface of the BC. A series of adsorption experiments showed that the FMCBC exhibited improved adsorption of As(III) in an aqueous environment. The adsorption process was well expressed by the pseudo-second-order kinetic model. The adsorption capacity of FMCBC reached 8.74 mg L⁻¹, which was 3.27 times greater than that of BC. The pH of the solution significantly influenced the adsorption of As(III), where the amount of As(III) adsorbed by FMCBC was maximized at pH 3. A high phosphate concentration inhibited adsorption, whereas nitrate and sulfate ions promoted As(III) adsorption and increased the FMCBC adsorption capacity. Similarly, with increasing humic acid concentration, the adsorption capacity of FMCBC for As(III) decreased; however, a low concentration of humic acid promoted adsorption. X-ray photoelectron spectroscopy analysis revealed that the adsorption of As(III) by FMCBC occurred through redox and surface complexation reactions. Therefore, FMCBC has excellent potential for purifying arsenic-contaminated water.

This work comprises results of the laboratory tests on formation and potential release of contaminants from underground gasification of lignites. Four large scale and multi-day trials were carried out using ex-situ gasification facilities. Two different kinds of lignite were tested, i.e. Velenje lignite (Slovenia) and Oltenia lignite (Romania). Gasification tests were conducted in the artificial coal seams under two distinct pressure regimes—atmospheric and high pressure regime (35 bar and 10 bar for the Velenje and Oltenia samples respectively). The UCG wastewater samples were periodically collected from the gas purification module to measure the rate of the wastewater and contaminants production at each phase of the experiment and to assess the effect of gasification pressure and lignite physicochemical properties. The group of target contaminants included: phenols, aromatic hydrocarbons, and some non-specific water parameters. The effect of gasification pressure was confirmed, especially for BTEX and phenols and significant drops in the contents of these compounds were observed at elevated pressures. The effect of pressure was more pronounced for the geologically older coal (Velenje), i.e. drop in the average concentrations from 1994 μg/l (atmospheric) to 804 μg/l (35 bar) and from 733 mg/l (atmospheric) to 17 mg/l (35 bar) for BTEX and total phenols, respectively. The differences in the macromolecular structure and ash content of the both coals were found to be the main reason behind the differences in the contents of organic and inorganic species respectively. The study also shown that composition of UCG wastewaters significantly varied over the time of the particular experiments, which reflected changes in the gasification thermodynamic conditions and development of oxidation and pyrolysis zones. During the atmospheric gasification experiments, the values of BTEX for the Velenje lignite dropped from 3434 μg/l to 1364 μg/l and for the Oltenia lignite from 1833 μg/l to 978 μg/l. A similar downward trend in the concentrations of BTEX was observed for the pressurized experiments. For the Velenje trial a drop from 1111.6 μg/l to 211.2 μg/l and for the Oltenia - from 1695 μg/l to 688 μg/l was observed. Concentrations of phenolic compounds during the atmospheric gasification experiments varied significantly during both atmospheric trials and no significant trends were noticed.

Hydrothermal synthesis followed by a calcination step was used to prepare porous Zn₂SnO₄ powders using carbon black as a pore-forming agent. The porous Zn₂SnO₄ was used as a photocatalyst to degrade the Rhodamine B dye from aqueous solution under UV artificial light. X-ray diffraction, N₂ adsorption-desorption isotherms, and UV-Vis diffuse reflectance were used to characterize the material. The addition of pore-forming agent (carbon black) did not change the crystalline structure of Zn₂SnO₄ phase. In addition, increasing the surface area and porosity as well as decreasing the band-gap energy was observed. The combination of these characteristics favored the photodegradation of Rhodamine B, reaching 96% of dye degradation at 15 min of reaction time. In addition, the photocatalyst was active after six cycles of reuse. Therefore, the produced material in this work showed to be a potential photocatalyst to remove Rhodamine B dye from aqueous solution.