Journal of Hazardous, Toxic, and Radioactive Waste

Subsurface flow constructed wetlands (SSF CWs) are increasingly used globally for the removal of pollutants from wastewater. However, clogging of the filter bed is the main operational and maintenance risk of SSF CWs for the long-term stable treatment of wastewater. Recently, many studies have reported various strategies to combat clogging in wetland beds. To ensure the appropriate implementation of the developed strategies, a thorough understanding of the mechanism of clogging is required. Currently, there is no appropriate analytical review article that gives insight into wetland clogging and its mechanisms. Therefore, this article aims to review the major types of clogging, such as physical, chemical, and biological clogging, their mechanisms, field investigations, and clogging remedial measures. This article will provide insights into wetland clogging and will enable prospective researchers and engineers to use suitable measures against clogging for its effective alleviation.

This study presents the application of a triple-porosity nonequilibrium model (TPNE) trifurcating the liquid phase within representative elementary volume (REV) in a saturated porous medium. The model accounts for both physical and chemical nonequilibrium conditions to capture the fate of solute through a porous medium. The governing equation is numerically solved using the finite volume method and validated with semi-analytical solution of dual advection dispersion equation (DADE). Temporal moment analysis is carried out to demonstrate the model's response for a range of Peclet and Damkohler numbers. The sensitivity of number of input parameters is highlighted using global sensitivity analysis. A sensitivity-based model calibration using parameter estimation package (PEST) is employed to describe observed BTC through a heterogeneous soil column. The TPNE model captured the skewed BTC with enhanced accuracy compared with mobile immobile (MIM) model. It is concluded that TPNE model is capable of capturing the detailed signature of the various processes of a skewed breakthrough curve (BTC) having multiple inflection points.

Conventional sewage treatment techniques have shown low removal efficiency for emerging contaminants (ECs). Hence, more efficient treatment systems need to be investigated. The current study suggests that an Integrated Fixed-Film Activated Sludge Process (IFAS) could be one such alternative. The degradation of eight ECs in municipal sewage has been studied during the transition of a pilot IFAS plant to a steady state and compared with the removal of the eight ECs in a conventional sequencing batch reactor (SBR)–based sewage treatment plant at a steady state. In the six weeks before attaining a steady state, the outlet total biochemical oxygen demand, total chemical oxygen demand, and total suspended solids (TSS) decreased from 42 to 10 mg/L, 96 to 26 mg/L, and 38 to 10 mg/L, respectively. The suspended biomass concentration, hydraulic retention, and return sludge rate of the plant were 1,600 mg/L, 6.9 h, and 175% of inflow, respectively. During the transition to a steady state in the IFAS plant, the removal efficiency of Caffeine, Gemfibrozil, and Testosterone was found to increase by 41% (15%–56%), 26% (63%–89%), and 65% (19%–84%) respectively, due to enhanced biological degradation. The SBR was found to be more efficient in the removal of ECs, which could be due to the higher concentration of suspended biomass.

Leaching of zinc from sulfide minerals is a subject of considerable interest over the last few years. Ferric solutions were commonly reported to leach base metals sulfide concentrates. The current study investigates the potential of biological ferric solutions for Zn and Pb extractions from a sphalerite concentrate at 65°C. Comparative leaching experiments with ferric sulfate and ferric chloride are also performed. Actually, biological ferric ions have resulted from pyrite bio-oxidation. The aim of this work is to introduce a potential application of this metabolite as a mineral oxidizing agent to recover zinc from the sphalerite concentrate. To produce a biogenic reagent with the highest ferric, the bio-oxidation process is optimized by investigating the effects of different factors including pH, pulp density, and inoculum percent. At the optimum conditions, a metabolite with 7.87 g/L of ferric ions and a pH = 0.98 is produced. The results indicate that pyrite bio-oxidation includes three phases: chemical dissolution, lag phase, and biological dissolution. The scanning electron microscope (SEM) images showed that a layer of crystals was present on the surface of pyrite. Based on energy-dispersive X-ray spectroscopy (EDS) and Raman spectroscopy, this layer is related to the presence of potassium jarosite. The metabolite was then used for ZnS direct leaching and results were compared with sulfide and chloride leaching. The final zinc recoveries with biological ferric ions, ferric sulfate, and ferric chloride were 78.0%, 88.9%, and 85.4%, respectively.

Several approaches can be used to activate persulfate anion $({\mathrm{S}}_2{\mathrm{O}}_8^{2-})$ and peroxymonosulfate anion $({\mathrm{HSO}}_5^{-})$ to generate sulfate free radical $({\mathrm{SO}}_4^{-}\bullet )$, a powerful oxidizing agent. In this study, we investigate ferrous ion (Fe²⁺) as an activator to generate ${\mathrm{SO}}_4^{-}\bullet$ for the oxidation of 2,4-dichlorophenoxyacetic acid (2,4-D), a common herbicide. Experiments were conducted using different molar ratios of 2,4-D, oxidants, and Fe²⁺. The 2,4-D concentrations used in the experiments were fixed at 0.045 mM. Results showed that 2,4-D was rapidly oxidized within minutes but plateaued to an asymptotic concentration. A possible reason for the slowdown in oxidation was the rapid conversion of Fe²⁺ to Fe³⁺, which in turn slowed the activation process. Experiments with sequential addition of Fe²⁺ at different times resulted in further 2,4-D oxidation, which indicated that Fe²⁺ was limiting in the activation process. The optimal molar ratio of persulfate:Fe²⁺ or peroxymonosulfate:Fe²⁺ for the oxidation of 2,4-D was found to be 1:1. Of the two kinetic models used, the bi-exponential first-order model gave the best fit of the experimental data with R² values greater than 0.9 as compared with the availability-adjusted first-order model. Results of the experiments showed that a low cost material such as Fe²⁺ can be used to activate persulfate or peroxymonosulfate for the removal of 2,4-D and other organic compounds in contaminated groundwater or drinking water.

Sorghum stems will be considered in this work as an alternative for the adsorption of cyanides in aqueous solution. It is an abundant material in southern Algeria, and it does not require any specific pretreatment. Therefore, it is a much cheaper adsorbent than the adsorbents usually used for cyanide adsorption, such as activated carbon. In this work, a complete study will be presented that includes the physicochemical characterization of prepared sorghum stem particles (SSPs) and the kinetic and thermodynamic adsorption studies. The pseudo-second-order kinetic model best described the experimental data with a high coefficient of determination and that the Langmuir isotherm model fitted better than the Freundlich and Temkin models. The Langmuir maximum adsorption capacity (q_m) was 76.92 mg/g at 293 K. The thermodynamic study showed that the adsorption of cyanides on SSPs was endothermic and spontaneous and that it was chemisorption. The comparison with the usual adsorbents tested by other authors showed that SSP could be an interesting candidate due to its high adsorption capacity and easy preparation.

Solid waste decision makers use waste composition studies in sustainability planning and as metrics to measure their environmental benefits (e.g., recycling rates). In many of these studies, there are varying waste components and number of samples assessed. Often, studies will rarely determine whether the number of samples sorted was actually sufficient to be statistically representative. We collected 24 US studies and assessed whether their material categories were statistically representative at a 90% confidence level and 10% precision following current standards. For each study and each material category, we calculated the number of samples required to be representative and compared it with the number of samples conducted by the study. Of the 24 studies, 17 had one to seven representative material categories, where 12 had one or two representative materials out of the average 44 original materials assessed per study. Nonrigid plastic film and food waste were most frequently statistically representative. Each study's original category list was condensed into 12 categories, and the analysis was repeated. Two studies that originally had no categories representative now had at least one. With the condensed materials, the mixed paper, mixed plastic, and food categories were most representative. The findings can be used by decision makers to gain a more comprehensive understanding of the importance of data quality analysis since most materials were not statistically representative; two approaches to being more representative are to sort more samples or condense the material list.

During the long-term operation of deep geological nuclear waste repositories, the swelling properties of compacted bentonites can be affected by canister temperature and electrolyte concentration in groundwater. The present article highlights the combined effect of temperature and electrolytes on the swelling pressure of monovalent Na-bentonite (predominant Na-montmorillonite) and divalent Ca-Mg bentonite (dominated by Ca-Mg montmorillonite and palygorskite minerals). A series of isochoric swelling pressure tests were carried out on compacted bentonites at a dry density of 1.7 Mg/m³ by applying temperatures of 25°C, 55°C, and 95°C and infiltrating with 0.1 and 1.0 M NaCl and CaCl₂ electrolytes. The changes in the microstructure of bentonites were examined by using a Field Emission Scanning Electron Microscope (FESEM), X-ray diffraction (XRD), and mercury intrusion porosimetry (MIP). The experimental results indicated that the elevated temperature caused a marginal decrease and increase in the swelling pressure of monovalent and divalent bentonites, respectively. The infiltrated electrolytes caused a significant decrease in the swelling pressure of monovalent bentonite, whereas the effect was found to be negligible for divalent bentonite. At electrolyte concentrations of 0.1 and 1.0 M, the impact of CaCl₂ was noted to be higher than that of NaCl. The coupled thermochemical effect caused a significant decrease in the swelling pressure of monovalent bentonite, whereas the effect was nominal for divalent bentonite. The FESEM, XRD, and MIP results confirmed that the thermochemical effect leads to a significant change in morphology, basal position of Na-montmorillonite, and pore structure of monovalent bentonite. The performance of Ca-Mg montmorillonite and palygorskite minerals as buffer material was noted to be better than that of Na-montmorillonite subjected to coupled conditions of elevated temperature and electrolyte concentration.

The current practice of curbing the ill effects associated with the open dumping of biomedical waste (BMW) solely relies on incineration. However, the incineration of BMW and plastic-based medical gear is associated with severe health hazards due to toxic emissions. Many countries are resorting to incineration at unpermitted locations and open dumping due to the enormous surge in the generated BMW during the ongoing pandemic times. Such improper practice of incineration of BMW incineration and open dumping leads to significant environmental pollution. Therefore, an alternative and environmentally sustainable disposal facility is essential to avoid the negative effects of BMW disposal. In this study, the effectiveness of compacted clay-based barrier systems was explored, for the first time, for the encapsulation of virus-contaminated BMW. The model parameters essential for designing such exclusive BMW containment facilities, namely effective diffusion coefficient (D_e) and retardation factor (R_d) for different clay minerals, were evaluated. The evaluation was based on the limited available batch sorption test and free solution diffusion test data for various hazardous pathogens. The model parameters were utilized to understand the attenuation of viral pathogens (SARS-CoV, poliovirus, and reovirus) and bacteriophages (MS2 and φx-174) in montmorillonite and kaolinite mineral barriers. The selected pathogens were chosen such that they represented SARS-CoV-2 in terms of its surface characteristics. The results from the present study revealed that a 2- to 3- mm thick exclusive clay-based barrier system was sufficient to contain the studied pathogens and SARS-CoV-2 for 50 years.

In the present study, Pseudomonas aeruginosa MK720218 is isolated from 2,4-dinitrotolune (2,4-DNT)-contaminated soil and is investigated for its ability to produce biosurfactant and simultaneously degrade 2,4-DNT present in the soil. Pseudomonas aeruginosa MK720218 reduced both nitro groups on 2,4-DNT and generated 2,4-diaminotoluene (2,4-DAT) with one intermediate metabolite 2-amino-4-nitrotoluene (2A4NT) production. Soil bio slurry experiments demonstrated 2,4-DNT degradation in the presence and absence of rhamnolipid biosurfactants where growth of microorganism, production of nitrite, and kinetics of 2,4-DNT degradation were measured. Enhanced DNT biotransformation was observed over a period of 10 days with rhamnolipids derived from Mahua oil compared with experiments without biosurfactants. It is further shown that Pseudomonas aeruginosa MK720218 cannot utilize DNT as a sole carbon or nitrogen source and requires additional carbon source and nitrogen source for enhanced biodegradation.

Magnetite (Fe₃O₄) is the most important iron oxide species that has received considerable attention by many researchers because of its strong magnetic susceptibility, lack of a remanent field, coercivity, and absence of a hysteresis loop. In this study, Fe₃O₄ was prepared by three different techniques: coprecipitation, hydrothermal, and sonochemical. The samples prepared by coprecipitation, sonochemical, and hydrothermal methods possessed magnetic saturation values of 60, 52, and 27 emu/g (A·m²/kg), respectively. Therefore, the coprecipitated sample was functionalized by mono- and diamino silane coupling agents (ASCs). The loading of ASCs onto the Fe₃O₄ surface was carried out in different solvents, such as toluene, ethanol, and water. The functionalized surfaces were characterized by using different techniques, namely, X-ray powder diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, vibrating-sample magnetometry, thermogravimetric analysis, scanning electron microscopy, energy-dispersive X-ray analysis, transmission electron microscopy, and Brunauer–Emmett–Teller analysis. The adsorption of eosin-Y (EY) dye onto the Fe₃O₄-APTS surface was affirmed by fitting in the Langmuir isotherm model. Besides, the q_max value (38.32 mg/g) obtained from the Langmuir isotherm model was matched with the theoretical q_ecal value calculated from the pseudosecond-order (PSO) model. Furthermore, the adsorption mechanism of EY onto the functionalized Fe₃O₄ surface was by physisorption, according to the lower free energy values (ΔG°) obtained. In addition, the adsorption process is endothermic in nature. However, adsorption kinetics was best described by the PSO model.

This study compares and analyzes removal of Pb (II), Cu (II), Mn (II), and Zn (II) from aqueous solution as individual ions (monometal system) or as mixed ions (quadruple system) by commercial laboratory-grade calcium carbonate (C–CaCO₃) and as-synthesized CaCO₃ (S–CaCO₃) as adsorbents. This was performed to determine whether heavy metal ion adsorption can be influenced by the polymorphic phases of CaCO₃. C–CaCO₃ and S–CaCO₃ were equally efficient in the removal of Pb (II) and Cu (II) from a monometal system. However, S–CaCO₃ exhibited only 49.3% ± 0.14 heavy metal removal when compared with 96.7% ± 0.08 by C–CaCO₃ in a quadruple system. FTIR and HR-SEM analysis revealed C–CaCO₃ consisted of a mixture of calcite and aragonite polymorphs, whereas S–CaCO₃ was pure calcite polymorph. These results indicated the importance of identification of the polymorphic phase and phase transformation in any experiment while utilizing CaCO₃ as adsorbent.

Industrial complexes with contaminated zones are polluted by organic biodegradable contaminants such as phenol. For such contamination, bioremediation using microbial cultures is economic and suitable. The bioremediation process involves the injection of microorganisms to enhance the degeneration of the contaminant to bring it within permissible limits. Due to the nonlinear, nonanalytical nature of groundwater, numerical methods are used for better clarity. Mesh-free methods, which do not need a grid or mesh, only nodes, can be very effective for such complex problems. In this study, a numerical model (PCM-MICROBE) was developed using the mesh-free point collocation method with radial basis function. A physical aquifer model (PAM) was also developed to understand phenol transportation and the phenomenon of in situ bioremediation. A tank, 1.5 × 0.5 m, was fabricated with sand as a porous medium. The results of the mesh-free PCM-MICROBE model were compared with observations in PAM. The comparative results were found to be within the error band of −9.54% to 17.19%

This study will focus on the preparation of activated carbon (AC) from biowaste [walnut shells (WS)] and its further chemical activation with potassium hydroxide (AC-KOH) and orthophosphoric acid (AC-H₃PO₄) for the treatment of Congo red (CR). Maximum removal of 99.54% was observed with H₃PO₄ modified carbon (C) at 298 K, pH 7, and 0.2 g adsorbent dose, and an initial dye concentration (C₀) of 10 mg/L. The Langmuir adsorption model fitted well with a maximum adsorptive capacity of 122 mg/g for AC-H₃PO₄; however, the kinetics followed the pseudo second-order model. In addition, the degradation of CR will be studied using hydrogen peroxide (H₂O₂) and several species from the degradation are analyzed using electrospray ionization mass spectrometry (ESIMS). In addition, after degradation, the adsorption characteristics resulted in 99% efficiency. The adsorbents performance based on economic aspects reported that the expenditure of INR 21.0, 41.5, and 53.5 were evaluated to synthesize 1 kg of AC, AC-KOH, and AC-H₃PO₄, respectively.

Boron in the forms of boric acid or borate salts are found widely in the environment, either in natural or anthropogenic sources. A variety of technologies can be used to remove boron from drinking water, but not all of them are cost-effective. An analysis and comparison were made of two different industrial solid wastes—red mud (RM) and fly ash (FA)—that are used to remove boron from the aqueous solution. Sorption equilibrium and kinetic studies were carried out using batch mode. The effect of pH (2–11), sorbent dosage (4–75 g/L), shaking period (10–210 min), shaking speed (80–180 rpm), and sorbate concentration (10–200 mg/L) on the sorption for both the sorbents were studied in experiments conducted in batch mode. At a pH value of 8 for RM and 10 for FA, a sorbate dose of 30 g/L and shaking speed of 150 min, the percentage boron removal was maximum for both the sorbents. Out of various sorption isotherm models, the Langmuir isotherm appeared to be the best fit (R² > 0.99). It was found that the sorption kinetics were in agreement with the pseudo second-order model for boron on RM and FA, as it gave the highest R² value as compared with the pseudo first-order and intraparticle diffusion models. According to the findings, these industrial wastes could be used to remove boron at a much lower cost than commercial sorbents.

The study focuses on the potential use of municipal solid waste (MSW) fine fractions, that is, fraction below 4.75 mm size for geotechnical applications (backfill/embankment material). In addition, the utilization of these MSW fine fractions in seismic-prone regions demand the dynamic characterization of the material under dynamic loading conditions before its application in the field. Hence, to check the influence of different parameters, that is, relative compaction, effective confining pressure, loading frequency, and strain amplitude on dynamic shear modulus (G) and damping ratio (D) of MSW fines, a set of 44 consolidated undrained cyclic triaxial tests (CTT) were performed. The investigation verifies that some parameters, such as relative compaction, effective confinement, and strain amplitude, have a more significant influence on the dynamic properties of the considered MSW fine fractions than do others, such as loading frequency. The results of this dynamic study can be successfully implemented using the considered MSW fine fractions as soil replacement.

The present study aims to evaluate simultaneously, for the first time in the Doukkala region (Morocco), the degree of physicochemical and metallic contamination as well as the concentration of ²²²Rn radionuclides in freshwaters from the sources to the households. From March to June 2019, 23 water samples were collected from the Oum Er-Rbia River, wells located in the town of Ouled Ghanem, Sidi Abed, and El Oualidia, water treatment stations (before and after treatment), water towers, the irrigation canal of Sidi Bennour, and dwellings. Physicochemical parameters [temperature, conductivity, turbidity, pH, chlorides, alkalinity (TAC), total hardness (TH), oxidizability, nitrites, nitrates, ammoniums, and sulfates], heavy metal parameters [copper (Cu), zinc (Zn), and cadmium (Cd)], and radioactive measurements (²²²Rn) were determined for each sample. The results of the physicochemical analyzes of the water collected from the Oum Er-Rbia River showed that most of the values of the physicochemical parameters, namely conductivity (44,800 μS/cm), turbidity (17.41 NTU), sulfates (2,506.5 mg/L), and chlorides (18,105 mg/L), exceed the Moroccan and World Health Organization (WHO) standards. For the water collected from treatment stations and wells, the analyses showed that some parameters exceed the acceptable limits of drinking water in the towns of Ouled Ghanem, Sidi Abed, and Sidi Daoui station. In dwellings, almost all the water sampled is drinkable except a few ones in the towns of Ouled Ghanem and Sidi Abed. As for heavy metals, the concentrations of Cu, Zn, and Cd varied, respectively, from (0.002 to 0.061 mg/L), (0.02 to 7.5 mg/L), and (0.002 to 0.086 mg/L). These concentrations were within the national permissible limits for drinking water except for the water of Oum Er-Rbia River for Zn and the water in a dwelling of Sidi Abed for Cd. The mean volume activities of radon in the water samples ranged from 29.64 to 130.72 Bq/m³ and do not show any significant difference except for the water in the Ouled Ghanem dwellings. All the radon volume activities were within the admissible limit which is about 11.1 Bq/L set by WHO.

Environmental water pollution currently deserves growing attention due to water contamination, because water is an essential element on earth. The presence of heavy metals released from wastewater effluents from different industrial plants has become a great concern to treat water. Developing a novel material with enhanced adsorption efficiency has become a difficult task; therefore, in the present study, nanocomposite (Mn-SCL BC) was synthesized using biochar derived from plant biomass Saccarum ravvanne and decorated with manganese dioxide used to remove toxic heavy metals from water. The effects of pH, adsorbent dose, contact time, and concentration on the adsorption were studied to know the interaction of heavy metal ions and adsorbent. The kinetics studies confirm pseudosecond-order kinetics for the adsorption of copper (II) and zinc (II). Two nonlinear isotherm models, Langmuir and Freundlich, were used. The highest R² value reveals the Langmuir adsorption isotherm. The maximum monolayer adsorption efficiency is found to be 1,124 and 995 mg/g for copper (II) and zinc (II), which is relatively higher than other materials found in the literature. The findings investigated here suggest that MnO₂-functionalized nanocomposite (Mn-SCL BC) has an eco-friendly, economical, and alternative adsorbent with potential applicability for the adsorption of heavy metal ions from aqueous media.

Biomediated soil improvement has been established as a promising solution for improving soil engineering properties in the last decade. The primary factor determining the efficacy of biocementation is the material properties of the precipitated crystals, which are highly impacted by the concentration of cementation reagents. In the present study, the biocementation potential of specific microbes liable for the augmentation and stimulation approaches are investigated at different concentrations of cementation media (CM) ranging from 250 to 2,000 mM. An indigenous soil microbe (BS3) and a consortium (C), both obtained from a natural riverbank environment, are analyzed for their potential to improve the soil strength in comparison with the standard biocementing microbe Sporosarcina pasteurii (SP). The soil strength improvement is investigated by conducting the needle penetration test on the biocemented soil samples. Maximum needle penetration resistance was observed at 500 mM concentration of CM for all the microbes. The isolated soil microbe (BS3) exhibited 30% more penetration resistance than SP at the optimal concentration (500 mM) of CM. The needle penetration resistance decreased at the higher concentrations of CM. The biochemical properties of the microbes were evaluated via a laboratory shake-flask batch test to determine the potential reasons behind the variation in the penetration resistance. Their biochemical properties, including the urease activity, urea hydrolysis rate, calcium depletion rate, and carbonate precipitation potential are compared at different concentrations of CM. The findings revealed that the microbes respond distinctively to different concentrations of CM. A detailed microstructure analysis on the precipitated CaCO₃ crystals suggested that the morphology, texture, and quantity are possibly the major strength influencing parameters. The present study unravels the potential reasons for the distinct responses of the augmentation and stimulation-inducing microbes at the different concentrations of CM.

The increased scarcity of natural quarry material has resulted in increases in the cost and burden on the environment. Pavement materials comprising asphalt coated aggregates that can be reused are called reclaimed asphalt pavement (RAP). RAP is crushed and screened, and then blended with one or more stabilization agents to produce a stabilized base or subbase aggregate. In the present study, the influences of fly ash dosage, lime dosage, and curing period on the strength, stiffness, and durability characteristics of RAP fly ash–lime (RFL) mixes were studied for utilization as a base layer material in flexible pavements. The dry density and moisture content relationship were determined by conducting a modified proctor test on all RFL mixes. Unconfined compression tests were conducted on specimens with different dry weight percentages of fly ash (10%–25%) and lime (5%–10%) content for different curing periods (0, 7, and 28 days). The optimum mix obtained as RFL2 had the proportions 70% RAP:22.5% fly ash:7.5% lime. A resilient modulus of 540 MPa at 28 days was observed for RFL2. The durability of RFL2 tested using the resistance index and a wet–dry cycle (weight loss) was observed to be 0.88% and 7.3%, respectively. Pavement analyses were performed for a pavement system with three layers using the KENLAYER program. The RFL2 mix as the base layer material was found to be superior to conventional wet mix macadam, hence the service life of an RFL2 pavement would be higher. Trial sections of the stabilized base and conventional pavement were constructed on a major district road. The falling weight deflectometer showed a better modulus (286 MPa) in RFL2. An RFL mix could therefore be used in a stabilized base layer to replace a conventional base layer.

Numerous authors prepared Fe₃O₄ magnetite for different applications, but still Fe₃O₄ magnetite encourages investigators for new ideas due to its superior physical and chemical properties, which have excellent implications in various fields. In the past several decades, Fe₃O₄ magnetite has played an important role in wastewater treatment. There are growing appeals for surface-modified Fe₃O₄ magnetite due to high affinity of modified nanoparticles (NPs) toward contaminants. In this study, a chemical coprecipitation method was applied to synthesize the Fe₃O₄ NPs. The scanning electron microscopy (SEM) images of the Fe₃O₄ NPs (uncoated or free) revealed the agglomeration of the magnetite (Fe₃O₄) particles. But the horseradish peroxidase enzyme (HRP) and activated carbon-coated (ACC) Fe₃O₄ oxide exhibited homogeneous distribution of particles with relatively less agglomerate of the particles. In this work, the adsorption potential of free-Fe₃O₄, HRP-Fe₃O₄, and ACC-Fe₃O₄ were explored for removal of acid violet 17 (AV 17), rhodamine B (RhB), Congo red (CR), and methylene blue (MB) from aqueous solutions. The present work highlights the synthesis techniques, modification, and characterization of prepared NPs using SEM, x-ray defractometry (XRD), and Fourier transform infrared (FTIR). In addition, this study covers adsorption equilibrium isotherms, kinetics, thermodynamics, and future applications. At optimum operating conditions, 60% AV 17, 78% RhB, 85% CR, and 90.62% MB removed using free-Fe₃O₄. Similarly, in the case of HRP-Fe₃O₄, 90% AV 17, 92% RhB, 98% MB, and 99% CR removed successfully. While in the case of ACC-Fe₃O₄, 93% AV 17 and >98% RhB, MB, and CR dyes were removed. The Langmuir adsorption capacity obtained in the present study is 19.6, 35.2, and 37 mg/L for AV 17; 31, 42, and 47 mg/g for RhB; 45.4, 50, and 52 mg/g for CR; and 35.4, 47.1, and 49.2 for MB, obtained using free-Fe₃O₄, HRP-Fe₃O₄, and ACC-Fe₃O₄ nanoparticles, respectively. The obtained results suggest that the data are in fit with the Langmuir model for all the dyes. Kinetic and thermodynamic studies signifying that the present adsorption process is feasible with spontaneous as well as endothermic. The prepared green magnetite nanoparticles could be use in different application due to their magnetic property.

Controlling methane emissions from landfills has been a significant concern over the last decades. Researchers have identified the use of landfill cover with oxidative capacity (biocover) as a promising solution to mitigate these methane emissions. However, the geotechnical conditions in a biocover can affect the methane fluxes and the pressure buildup inside landfills. In this paper, the effect of the porosity, degree of saturation, and absolute permeability of the biocovers on the atmospheric methane flux and pressure buildup inside landfills is studied. Numerical modeling with TOUGH3 EOS7CA was carried out to assess the methane migration (one dimensional) and methane oxidation in biocovers. Simulations revealed the role of geotechnical properties in controlling the dynamic outflow of methane and inflow of oxygen in the biocover. The relations between methane migration and pressure development are also established, and the effect of geotechnical properties in these aspects is quantified. The importance of coupling these factors for improving the efficiency of a biocover is highlighted. An absolute permeability in the order of 10⁻¹³ m² and a degree of saturation less than 0.5 is suggested for achieving optimal performance. The role of atmospheric pressure and temperature on the atmospheric methane emissions is also described.