In this study, a new ecological dam based on the microbial fuel cell principle (MFCED) was designed to remove pollutants from river sediments and water bodies. Sediment organics were better removed in the MFCED mode in comparison with the other two modes (ecological dam with open circuit (OCED) and ecological dam filled with gravel in cathode chamber (GMFCED)). The difference of nitrogen source in water had little effect on the removal of chemical oxygen demand (COD) (70–80%), while nitrate was more readily removed in the MFCED. The voltage curve and power curve were measured to understand the bioelectricity generation of MFCED. During the stable operation phase of MFCED, the voltage was stabilized between 0.09–0.15 V. The results of high-throughput sequencing indicated that the anode and cathode diversities of MFCED were more than the other systems, and the species diversity of the anode was more than that of the cathode in the MFCED. Graphical abstract

Arsenic (As) is a well-known highly toxic and carcinogenic element. A combination of electrodialytic remediation (EDR) after soil washing with flocculant addition targeting remediation of a soil polluted with As from wood preservation industry is the focus of this paper. The fine fraction (< 0.063 mm) from the washed soil after dry sieving was also considered. The EDR experiments were carried out in a 2-compartment cell applying 0.01 mA/cm² during 14, 7 and 3 days. The suspended soil slurry was placed in cathode compartment separated by anion exchange membrane (AEM) of the anolyte where the pH was kept at 10. The soil was highly polluted with As, and the EDR was able to remove between 50 and 80% corresponding to 400–478 mg As/kg of soil. The major part of the As was removed within the first 3 days (63%), and approx. 10% more of As was released doubling the time of the experiment: 72% in 7 days and 80% in 14 days. The pre-treated soil showed higher As initial concentration, but did not show a clear advantage in terms of removal rate as the original soil (not washed or sieved) showed 80% of As removal comparing with 61% and 50% for washed and fine fraction, respectively (although the absolute removed concentration was similar). The sequential extraction results confirmed that As was bound into more mobile fractions in original soil, and the higher removal was mainly due to its larger exchangeable and reducible fractions compared to the oxidizable and residual fraction in pre-treated soil.

This article identifies environmental factors that explain most of the dynamic year-to-year changes in mercury concentrations of young-of-year (YOY) yellow perch (Perca flavescens) in study reservoirs. Mercury concentrations in fish, collected each fall, were measured for 9 years in four reservoirs in northeastern Minnesota. Three to 4 years of data were also obtained for two natural lakes and one other reservoir. Average annual concentrations varied considerably from year to year with a mean change of 39% between consecutive years across all lakes. Those averages show a similar time trend for each lake over the years and suggest that important factors influencing mercury bioaccumulation change annually and are also experienced in common over the study region. Three factors satisfying that description are precipitation depth, water level, and average air temperature. This article reveals that all three have statistically significant correlations with observed mercury concentrations. Moreover, multiple regressions indicate that maximum water levels and average air temperatures explain most of the observed variations. Regressions employing precipitation depth and temperature are less significant.

The article presents the results of the study of the vapor streams from sulfide-containing tailings after gold mining by cyanidation (Ursk waste heaps, Kemerovo region, Russia). The gas survey of sulfur dioxide, dimethyl sulfide, dimethyl sulfoxide, carbon disulfide, and N-containing substances concentrations was carried out using a portable device GANK-4 on a series of profiles covering the waste heaps and the surrounding area with simultaneous measurement of temperatures in the air and soil. The concentration maps-schemes of the studied gases in the surface layer were constructed. The high positive correlation of gases between themselves is established, which indicates similar mechanisms of their formation. The electrical resistivity tomography determined the internal structure of the waste heap. Active “breathing” zones were identified in which the maximum fluctuations in the concentrations of sulfur, selenium, and nitrogen-containing compounds in the near-surface air layer were recorded. Such zones are marked with lower resistances in comparison with other areas on the geo-electric profiles. There is an inverse correlation between the resistivity of the tailings and its temperature and a direct correlation between the concentration of gas in the air and the temperature of the soil. High concentrations of CS₂, the volatile gas compound of the second hazard class, were found in the concentrations that exceed 6–8 times the daily average norm. Further investigation of the mine tailings seasonal transformation with the production of toxic gases deserves special attention due to high environmental risks and poor knowledge of this problem. The oxidation of ore cyanidation wastes in summer and methylation in winter due to seasonal temperature fluctuation lead to production of gases of great concern including toxic СS₂.

The entire Laguna Madre of Tamaulipas is a natural protected area and a Priority Marine Region of Mexico. However, its important biodiversity and high levels of endemism are threatened by the discharge of different pollutants and activities related to the ocean oil and gas industry. Therefore, the assessment of these effects on this marine ecosystem is of paramount importance. At present, the joint approach of monitoring chemical contaminant levels, alongside the use of pollution biomarkers as surrogate measures of biological impact within the environment, provides the better evaluation of the environmental hazard. Within this context, a biomonitoring study using native Chione elevata mussels sampled from four locations along the Mexican Laguna Madre coasts evaluated whether a battery of select biomarkers was suitable for identifying and quantifying pollution-induced stress in mussels. The levels of acetylcholinesterase (AChE), butyrylcholinesterase (BChE), carboxylesterase (CaE), alkaline phosphatase (ALP), glutathione s-transferase (GST), and the oxygen radical absorbance capacity (ORAC) were measured in soft tissues samples. Different metals (Cd, Pb, Cu, Zn, and Fe) as well as total heavy hydrocarbons were also determined in sediments. Higher concentrations of metals were observed in sampling localities with marine influence possibly related to the presence of marine grass. The concentration of total heavy hydrocarbons, as expected, was higher in sites with intensive fishing activity. The integrated biomarker response (IBR) and the condition index of mussels allowed discriminating between localities of continental and marine influence, revealing that the sampling stations with continental influence were subjected to a greater stress as a result of anthropogenic effects.

The immobilized algae Sargassum vulgare was used as biosorbent for Fe³⁺ removal through a batch and continuous system in order to study the biosorption capacity and to establish a new method of the valorization of this waste. The kinetic data could be described by the pseudo first-order and pseudo second-order kinetic models. The batch equilibrium was fitted by the Langmuir model with a value of correlation coefficient (R² = 0.98) higher than that of the Freundlich (R² = 0.89). The process was exothermic and spontaneous and the biomass was successfully desorbed using 0.1 M HCl. Furthermore, the Thomas model, Bohart-Adams model, and Yoon-Nelson model were successfully applied to evaluate the dynamic behavior of Fe³⁺ biosorption in a fixed-bed column. The lower flow rate of 1.04 ml/min showed the greater performance of the process. Fourier transform infrared spectroscopy revealed the presence of several active binding sites, and scanning electron microscopy micrograph confirmed the metal adsorption on the surface. The results reveal that the immobilized algae have a potential removal for Fe³⁺ in a batch and continuous system.

Environmental fate and impacts of graphene oxide (GO) nanoparticles are strongly influenced by their subsurface behaviors. The present work examined the aggregation and transport behaviors of GO in saturated sand columns under different temperature (6 and 24 °C), surfactant concentration (0.04% and 0.4%), cation valence, and electrolyte concentration conditions. In monovalent electrolyte (NaCl), although the presence of cationic surfactant (CTAB) notably increased GO stability and mobility, GO ripening happened due to their concurrent aggregation and transport in the columns. GO particles were more mobile at a lower temperature probably because the CTAB coating of GO increased with decreasing temperature, leading to stronger electrostatic repulsion. Furthermore, GO retention in the media increased with the increase of NaCl concentration due to the enhanced compression of the electric double layer. In multivalent electrolyte (CaCl₂ or AlCl₃), the presence of CTAB greatly improved GO stability and mobility and no deposition occurred in saturated porous media under all the tested conditions. This is because the CTAB coating of GO diminished the cation bridging effects in both GO-GO and GO-sand systems. Results from extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory considering steric repulsion suggest that secondary minimum aggregation and depositions were the main mechanisms of GO retention transport in monovalent electrolyte in saturated porous media.

Laboratory snow melting experiments were conducted with actual late-winter snow samples, collected just before the final snowmelt, in two similar northern Swedish cities, Luleå and Umeå, to investigate releases of the selected heavy metals (HM) (Cu, Pb, Zn, and Cd) and 16 USEPA PAHs from melting snow. Metal concentrations were determined in three fractions: total, dissolved, and truly dissolved (defined as the fraction passing through a 3-kMWCO ultrafilter). Total HM concentrations in snowmelt were rather high at both sites and reflected the accumulation of pollutants in the roadside snowbanks over a period of about 5 months: Cd = 0.43, Cu = 303, Pb = 41.9, Zn = 817 (μg/l), and TSS = 2000 (mg/l) in Luleå samples and Cd = 1.87, Cu = 905, Pb = 165, Zn = 3150 (μg/l), and TSS = 4800 (mg/l) in Umeå samples. The difference between metal and TSS concentrations at the two sites of similar characteristics was attributed to a smaller volume snowbank in Umeå. The dissolved HM concentrations represented relatively small fractions of the total concentrations (0.3–6.9% in Luleå and 0.01–3.1% in Umeå). The truly dissolved fraction represented 71–90% of the dissolved fraction in Luleå and 74–98% in Umeå. At both sites, the dissolved fractions exhibited preferential elution from the laboratory snow piles. The PAHs studied (16 US EPA PAHs) were mostly particulate bound, with only 5–12% of the total burden contributed by the meltwater, and most dissolved concentrations below the reporting limits. PAH concentrations in the Luleå samples were about one-third to one-fourth of those in Umeå. In general, the releases of PAHs from the snowbank were delayed, compared with releases of meltwater, and showed similar release patterns as TSS.

With increasing concern related to sustainable chemistry, we investigated the biosorption of Pb²⁺ ions from aqueous medium using an environmental friendly and economic biosorbent Bougainvillea spectabilis (BS). The BS was modified effectively using citric acid by hydrothermal method. The biosorbent(s) was characterized by scanning electron microscope (SEM), energy dispersion X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), and point of zero charge (pHₚzc). Various process parameters including biosorbent dosage, time of contact, temperature, solution pH, and initial Pb²⁺ ions concentration were studied in batch mode. Kinetic modeling was performed to evaluate the kinetic data and results showed that the studied process followed the pseudo second order (PSO) kinetics. Equilibrium modeling was done using famous equilibrium models, i.e., Langmuir, Freundlich, Dubinin-Kaganer-Radushkevish, and Temkin in non-linear fashion to evaluate equilibrium data by varying initial Pb²⁺ ions concentration from 20 to 180 mg/L. Based on RMSE values, Langmuir model fits best. This paper also discusses thermodynamic parameters (i.e., enthalpy, entropy, and free energy) showing that the process was spontaneous and endothermic in nature. In comparison with BS (B. spectabilis), an appreciable increase in uptake capacity of CABS (citric acid modified B. spectabilis) was observed in sequestration of Pb²⁺ ions from aqueous medium showing advantage of citric acid modification making it industrially favorable and socially acceptable biosorbent for efficient removal of lead from water.

This article presents a review of the main physical, chemical, electrochemical, and biological technologies used for treating heavy metals in the wastewater of industrial processes and in synthetic aqueous solutions which could be applied to leachate from landfills. This paper outlines the generalities, operating principles, and modifications made to the technologies described. It discusses and assesses which of these have better removal rates and higher levels of efficiency in minimizing the heavy metal concentrations contained in leachates, such as mercury, chromium, lead, nickel, and copper among others. The first part of the document presents the so-called conventional technologies, such as chemical, physical, and electrochemical treatment. These have been used to treat different wastewater, especially industrial waste, operating adequately from the technical topic, but with high costs and the secondary products’ production. The second part exposes biological treatments tend to be most widely used due to their versatility, effectiveness, and low cost, when compared with traditional technologies. It is important to note that there is no single treatment and that each of the technologies reviewed has different heavy metal decontamination rates. All technologies search to reduce concentrations of heavy metals to values that are safe for the natural resources where they are discharged or disposed, thereby complying with the regulatory limits regulated in each of the regions.