Biochar as a soil amendment in street tree pits can be used to increase the soil’s ability to retain contaminants found in urban runoff. The increased retention can potentially decrease peak concentrations of soluble trace metals and de-icing salts in the soil solution, thereby decreasing the amounts taken up by tree roots or percolated out of the tree pits into the ground water. A leaching test measured the retention of trace metals (Cd, Zn, Cu, and Pb) and deicing salts (Na) by different kinds of biochar. The biochar was produced from hardwood (North American ash tree, Fraxinus americana) under different pyrolysis conditions, with three temperatures (350, 465 and 550 °C) and two residence times (10 and 30 min). Biochar pyrolyzed at 550 °C for 30 min significantly reduced the soluble concentrations of Zn, Cu, and Pb in the column leachate, most likely due to the its higher pH, surface area, and ash content. The pH of each treatment group was measured while the increase in ash content and surface area was inferred according to relevant literature. This biochar was then combined with soil and compost at rates ranging from 0 to 7.5% by dry weight to determine the proportion that optimally sorbed the contaminants. An application rate of 7.5% biochar by dry weight increased the soil mixture’s sorption capacity for Cd and Na while maintaining similar sorption of Cu, Zn, and Pb. The role of organic matter, such as that in compost, was especially important for the sorption of Zn and Cu. Hardwood biochar can thus improve the health of street trees and groundwater quality by sequestering trace metals and de-icing salts. Biochar can also be a useful tool to remediate contaminated soil, especially in urban environments.

We investigated the Fe-regeneration-based cathodic electro-Fenton process using commercial electrodes, to achieve reducing the initial Fe dose and consequent sludge accumulation. The obtained results provided insights into the cathodic electro-Fenton process using two-electrode electrochemical system. The grade 2 Ti mesh electrode could effectively regenerate Fe(II) at 1.2 V, whose potential was lower than those of the two other electrode systems reported in the literatures. In the actual wastewater treatment, compared with general-Fenton process, the reduction in the initial Fe injection was 33% and the sludge reduction was 38%. Furthermore, the removal efficiency using electro-Fenton was at least 5% higher than that of the general-Fenton process at the same initial dose. The low cell voltage (1.2 V) led to lower energy consumption (3.5 J mg⁻¹) relative to those of other electro-Fenton systems, i.e., anodic electro-Fenton and peroxide generation. With its competitive degradation performances, low energy consumption, and reduced initial Fe injection, the present cathodic electro-Fenton process was shown to be a promising route of waste treatment.

Polychlorinated biphenyls (PCBs) are ubiquitous and persistent organic pollutants generated exclusively from human sources and found in the environment as several congeners (e.g. Apirolio, produced in Italy and used for electrical transformers). To evaluate the ability of the natural microbial community of historically PCB-contaminated soil to transform or degrade PCBs after fresh contamination through the addition of Apirolio, a microcosm experiment was conducted in a greenhouse for approximately 8 months. Compost and Medicago sativa (alfalfa) were additionally used in the microcosms to stimulate microbial PCB degradation. Chemical analyses were performed to evaluate PCB concentrations in the soil and plant tissue. Changes in the microbial community under the different experimental conditions were evaluated in terms of total abundance, viability, diversity, and activity. Interestingly, the addition of Apirolio did not negatively affect the microbial community but did stimulate the degradation of the freshly added PCBs. The plant and compost co-presence did not substantially increase PCB degradation, but it increased the microbial abundance and activity and the occurrence of α-Proteobacteria and fungi.

The photocatalytic degradation of dyes (Allura Red AC and Brilliant Blue FCF) in water using ultraviolet light-emitting diodes (UV-LED) and an immobilized titanium dioxide (TiO₂) as a photocatalyst was investigated using a novel bench-top Teflon® reactor. This reactor has been uniquely designed to contain low-powered UV-LEDs combined with TiO₂ immobilized substrates. A sol-gel method was used to anneal TiO₂ to three different substrates: standard microscope quartz slides, quartz cylinders, and borosilicate beads. Scanning electron microscopy (SEM), Raman spectroscopy, and mass comparisons techniques were performed for TiO₂ characterization. High-resolution images confirmed the presence and morphology of TiO₂ on the substrates. These analyses demonstrated the TiO₂ coating was uniform and predominantly had the anatase crystalline phase structure. The slide had the largest individual TiO₂ surface area of 0.187 mg cm⁻². Results indicated the size, shape, packing, and stirring properties were factors that determine overall photocatalytic properties and degradation inside the reactor. The adjusted rate constants for an ideal completely mixed batch reactor (CMBR) were 1.69 * 10⁻³, 5.39 * 10⁻³, and 4.46 * 10⁻³ min⁻¹ for the slides, beads, and cylinders, respectively. Beads were the best-performing substrate as determined by the greatest degradation rate for the model organic compound, Allura Red AC. The beads and cylinders showed 58 and 51% degradation of Allura Red AC, respectively. Actinometry experiments revealed cylinders had the largest fluence rate of 0.0782 J·L⁻¹ s⁻¹. Optimization of the sol-gel application method and reactor operating parameters was performed to maximize the degradation rate and the overall degradation of Allura Red AC. Electric energy per order (EEO) was calculated and optimized at 9.20, 10.5, and 12.7 kWh·m⁻³ order⁻¹ for the glass beads, cylinders, and slides, respectively. Graphical abstract ᅟ

Liquid elemental mercury occurrence in the subsurface as dense non-aqueous phase liquid (DNAPL) is reported worldwide in proximity of several industrial facilities, such as chlor-alkali plants. Insight into Hg⁰ DNAPL infiltration behavior is lacking and, to date, there are no experimental observations of its infiltration and distribution in water-saturated porous media, except for capillary pressure-saturation column experiments. To better understand the processes governing elemental mercury DNAPL flow behavior, a series of flow container experiments were performed using mercury DNAPL (in sands and glass beads) and tetrachloroethylene (PCE) (in sands). While liquid Hg⁰ was not able to infiltrate in the sand-filled container due to an overall lower permeability of the sample and a defect of the setup, in the glass beads experiment mercury DNAPL infiltration occurred. Dual gamma ray measurements showed that, in glass beads, liquid Hg⁰ preferentially migrated towards higher porosity zones. As for PCE, infiltration and distribution of Hg⁰ DNAPL are strongly affected by the heterogeneities within the porous formation. However, compared to other DNAPLs, liquid Hg⁰ shows a strong attenuation potential of gamma rays. Finally, numerical simulations of the glass beads experiment showed an overall good agreement with the experimental results, highlighting that, among the factors influencing the prediction of liquid Hg⁰ migration in water-saturated porous media, the most critical are (i) the knowledge of the inflow rate, (ii) the reliable estimation of the porous formation permeability, and (iii) the accurate representation of the correlation between retention properties and intrinsic permeability.

Arsenic (As) accumulation in agricultural soils is prone to crop uptake, posing risk to human health. Passivation shows potential to inactivate soil labile As and lower crop As uptake but often contributes little to improving the microbiota in As-contaminated soils. Here, the combined addition of ferrihydrite and Trichoderma asperellum SM-12F1 as a potential future application for remediation of As-contaminated soil was studied via pot experiments. The results indicated that, compared with the control treatment, the combined addition of ferrihydrite and T. asperellum SM-12F1 significantly increased water spinach shoot and root biomass by 134 and 138%, respectively, and lowered As content in shoot and root by 37 and 34%, respectively. Soil available As decreased by 40% after the combined addition. The variances in soil pH and As fractionation and speciation were responsible for the changes in soil As availability. Importantly, the combined addition greatly increased the total phospholipid fatty acids (PLFAs) and gram-positive (G+), gram-negative (G−), actinobacterial, bacterial, fungal PLFAs by 114, 68, 276, 292, 133, and 626%, respectively, compared with the control treatment. Correspondingly, the soil enzyme activities closely associated with carbon, nitrogen, and phosphorus mineralization and antioxidant activity were improved. The combination of ferrihydrite and T. asperellum SM-12F1 in soils did not reduce their independent effects.

This study tested for the first time ¹⁴⁷Sm/¹⁴⁴Nd and ¹⁴³Nd/¹⁴⁴Nd ratios as tracers of rare earth element (REE) sources in semi-terrestrial organisms from a subtropical estuary affected by fertilizer industry activities. The isotopic composition of claw muscles and shells of male crabs (Ucides cordatus) were obtained by thermal ionization mass spectrometry, and provided contrasting signatures incorporated from the physical components by the biota. Our findings showed that crab shells had isotopic compositions similar to seawater, while the claw muscles incorporated the isotopic signature of sediments contaminated by fertilizer. The isotopic ratios (¹⁴⁷Sm/¹⁴⁴Nd and ¹⁴³Nd/¹⁴⁴Nd) proved that the anthropogenic source is transferring contaminants to the crabs, emerging as a reliable tool to diagnose REE pathway and source to the biota in impacted environments.

This study reports on the feasibility of remediation of catechol- and resorcinol-contaminated water using low-cost sunflower seed hull activated carbon (SSHAC). Sunflower seed hull (SSH), an abundant agricultural waste in Malawi, was used as precursor to prepare highly porous activated carbon by physicochemical activation, with zinc chloride (ZnCl₂) as an activating agent. The activated carbon was characterized by FTIR, SEM-EDS, XRD and BET analyses. In this work, pertinent parameters that affect the adsorption efficiency—pH, initial adsorbate concentration, contact time, adsorbent dosage, and solution temperature—were investigated in batch mode. At the same experimental conditions, more catechol was adsorbed than resorcinol may be due to the compound’s affinity towards water and the position of the hydroxyl group on the benzene ring. A maximum equilibrium adsorption of 271 and 250 mg/g was obtained at pH 9.0 and pH 8.0 for catechol and resorcinol, respectively. The adsorption behaviour of both adsorbates (catechol and resorcinol) on SSHAC can be well described by Langmuir isotherm model and pseudo-second-order kinetic model. The value ∆G, ∆S and ∆H indicated spontaneous and endothermic adsorption process. The adsorption process was readily reversible allowing reusability of the adsorbate. This study’s outcome is value addition to this category of wastes for environmental protection.

The lower Seine River is severely affected by the release of the treated wastewater from the 12 million inhabitants of the Paris agglomeration. Whereas urban effluents were the major source of phosphorus pollution in the late 1980s, the ban on polyphosphates from detergents in 1991 considerably reduced the phosphorus (P) loading to the Seine River and was followed in 2000 by the implementation of phosphorus treatment in the largest wastewater treatment plant of Paris conurbation (Seine Aval). Phosphorus discharged to the rivers from domestic wastewater was reduced by 80 %, significantly decreasing phytoplankton biomass in the large branches of the Seine River. Considering that phosphorus treatment (the use of ferric salts in the P treatment line) might change the adsorption of ortho-phosphates on suspended matter, we experimentally studied again their sorption processes in these new conditions. We found parameters of the Langmuir equation (Pac = 0.003 mgP mgSS⁻¹; Kps = 0.04 mgP L⁻¹) that significantly differed from the values previously considered for modeling of the whole Seine, especially for Kps (Pac = 0.0055 mgP mgSS⁻¹; Kps = 0.7 mgP L⁻¹). Using the Seneque-Rivertrahler modeling approach, we showed a better agreement between P observations and simulations with the new P sorption parameters, with slight effect on the simulation of the development of phytoplankton in the water column.

In this work, the effects of various operating parameters (pressure, pH, BPA concentration, and filtration time) toward bisphenol A (BPA) removal via ultrafiltration (UF) membrane system were investigated using response surface methodology (RSM). Historical data design of RSM was used to obtain the interaction between variables and response as well as optimizing the process. The analysis of variance (ANOVA) showed that the third-order polynomial model was significant in which pH and filtration time were identified as significant terms that influence BPA removal. The 3D response surface plots revealed the two-factor interaction between independent and dependent variables. The optimization process of the model predicted optimum conditions of 99.61% BPA removal at 1 bar, pH 6.7, 10 μg/L BPA concentration, and 10-min filtration time. The predicted optimum conditions for BPA removal were consistent with the obtained experimental values, indicating reliable application of historical data design RSM for modeling BPA removal in UF membrane system.