Journal of Hazardous, Toxic, and Radioactive Waste

Because of its high swelling pressure and low hydraulic conductivity, compacted bentonite–sand is widely accepted as a barrier/backfill material used in deep geological repositories to safely contain highly toxic radioactive waste. The majority of research conducted in this field shows that the pore fluid salinity present in the repository’s environment reduces the swelling capacity and increases the hydraulic conductivity of backfill material. However, research has yet to determine how to improve the material properties of backfill under saline water conditions. In this study, two different percentages of nanoparticles derived from bentonite (1 and 2% with respect to dry weight of bentonite) were carefully mixed with a bentonite–sand mixture to prepare a nanoparticle-based light backfill. Next, the effect of different concentrations of NaCl and ${\mathrm{CaCl}}_2$ on the hydraulic and mechanical behavior of a $50:50$ bentonite–sand mixtures was examined, at a maximum dry density of $1.24\mathrm{Mg}/{\mathrm{m}}^3$. The results showed that ${\mathrm{CaCl}}_2$ solutions have more influence on material performance as compared to NaCl solutions. Additionally, results indicated that the presence of nanoparticles reduces the hydraulic conductivity and the rate of consolidation for saline-solution-saturated light backfill; however, no major improvement of swelling pressure was observed within the scope of this experimental approach.

Microbe-aided modification to certain geotechnical properties of soil has garnered appreciable amount of interest among the researchers in recent days. In particular, microbial influence on thermal conduction properties of soil is relevant in engineered-barrier applications as in case of a deep geological repository (DGR). In view of this, in the present investigation, a radiation resistant and extremophilic microbial species Deinococcus radiodurans has been studied for its possible influence on thermal conductivity of several geomaterial samples. Thermal conductivity measurements for varieties of geomaterials with varying moisture content and bacterial dosage are made using an indigenously fabricated thermal needle probe, efficacy of which has been established through calibration. In general, it was observed that microbial addition enhanced the thermal conductivity of soil. This observation can be attributed to any possible biogeochemical reactions in the geomaterials because of the bacterial addition. Furthermore, based on the experimental data, the following three artificial intelligence (AI) techniques are used to develop thermal conductivity prediction models for geomaterials and to quantify the influence of microbial addition on soil thermal conductivity: (1) multi-gene genetic programming (MGGP), (2) multivariate adaptive regression splines (MARS), and (3) functional networks (FN). The models proposed are found to deliver satisfactory performance in terms of statistical parameters and can be used to predict soil thermal conductivity.

In the recent years, advanced oxidation process (AOP) has shown promising hopes for the treatment of stabilized leachate. Among the various AOPs the sulfate radical based advanced oxidation process (SR-AOP) are of recent interest. The present study analyzes the effectiveness of SR-AOP to treat the stabilized leachate. The effect of certain operating parameters such as oxidant and catalyst dosages, pH, temperature, and reaction time were also studied. At optimal conditions [pH 3-4, persulfate (PS) dosage $1\mathrm{g}/\mathrm{L}$, $\mathrm{PS}:{\mathrm{Fe}}^{2+}$ molar ratio $1:1$, temperature 30°C, and time 150 min] 78% chemical oxygen demand (COD) reduction was observed. The citrate addition to improve the COD removal efficiency at neutral conditions was found to be ineffective. This study shows that sulfate radicals are very efficient to remove organic pollutants from stabilized leachate.

The hydraulic fracturing or fracking and extraction of shale gas is vital to the continued success of the human race to provide a relatively clean energy source. However, there are several environmental issues that must be solved in order to make fracking environmentally acceptable. Once these issues are resolved, it could lead to a brighter future by allowing shale gas to act as a bridge to clean energy, while providing energy independence for the United States. To achieve these goals, there is a need to find suitable solutions to the following problems: methane gas leaks while fracking and during production, trigger of earthquakes due to fracking, and the disposal of the wastewater (largely comprised of fracking fluid) after the completion of fracking. To investigate the aforementioned environmental impacts, comprehensive research was performed using data for the Marcella formation. Although it is clear that additional research must be performed to fully deal with all the issues, the following strategies have been found to solve or mitigate the problems. To prevent the impact of methane gas leaks, well workers must be properly trained and supervised. As another precaution to prevent the methane from contaminating groundwater, groundwater wells must be a minimum of 1 km away from the vertical section of fracking wells. To lessen the intensity and frequency of earthquakes caused by fracking, a regulation should be set in place that prevents disposal of wastewater by groundwater injection wells. In addition, the site should be checked for possible active and inactive faults before the approval of fracking. Finally, fracking companies must be required to withdraw most fluids from wells and to treat them according to state regulations and reuse or surface disposal as treated water. If all of these suggestions are implemented, fracking can be made much more environmentally viable and safe.

Stormwater runoff is one of the main contributors to stream impairment in the United States and is primarily treated using best management practices (BMPs). One of the problems with BMPs (e.g., bioretention basins) is that the media used in bioretention basins are not well evaluated, including the optimal composition and physical characteristics. The objective of this research is to evaluate the use of rubber chips as a possible supplemental BMP media because of their light weight and availability. Four types of rubber-chip-mediated soil mixtures were tested, i.e., 100% rubber chips and 50% rubber chips mixed with 50% of either silty loam soil, sand, or compost. Results indicate that a $50/50$ mix of rubber chips and sand could treat contaminants in highway runoff efficiently, but lacked the best qualities for plant growth and may require addition of compost. Based on both physical and chemical properties of the media mixture, compost rubber (CR) and silty loam rubber (SLR) were found to be the best as BMP media. Tests on physical properties of BMP media can generate critical information about the media. The methodology used in this study may be used to test physical properties of other BMP media.

The present paper deals with the adsorptive removal of 4-nitrophenol (4-NP) by activated carbon prepared from waste orange peels (ACOP). A batch adsorption study has been performed to study equilibrium, kinetics, and thermodynamics of the adsorption process along with a desorption study. The ACOP characteristics, namely the Brunauer, Emmett, and Teller (BET) surface area and iodine number, were found to be $540.61{\mathrm{m}}^2/\mathrm{g}$ and $420.14\mathrm{mg}/\mathrm{g}$, respectively. The optimum adsorbent dose was found to be $5\mathrm{g}/\mathrm{L}$ with a liquid-to-solid ratio of $107:1$ ($\mathrm{v}:\mathrm{v}$). The equilibrium time was found to be 90 min with the maximum percentage removal of 94.40%. The maximum adsorption capacity of the adsorbent was found to be $73.35\mathrm{mg}/\mathrm{g}$. The equilibrium study showed Radke-Prausnitz as the best-fitted isotherm. A kinetic study revealed that the pseudo second-order kinetic model best represents the adsorption process. In the thermodynamic study, the value of $\mathrm{\Delta }G$ ($-21.10\mathrm{kJ}/\mathrm{mol}$), $\mathrm{\Delta }S$ ($0.095\mathrm{kJ}/\mathrm{mol}$), and $\mathrm{\Delta }H$ ($7.78\mathrm{kJ}/\mathrm{mol}$) at 303 K show the spontaneous, randomness, and endothermic nature of the overall adsorption process. The isosteric heat of adsorption ($\mathrm{\Delta }{H}_{st,a}$) increases with $q_e$, indicating that ACOP has energetically a nonheterogeneous surface. The batch model design shows the field applicability of the ACOP adsorbent for 4-NP sorption as per industrial need.

A reliability-based assessment of municipal solid waste (MSW) landfill slope is presented in this study, keeping in mind the large variability in MSW constituents and their mechanical properties. Typical slope geometry consisting of several layers of MSW with varying stages/degrees of decomposition is considered in consistence with evolution kinetics. A number of representative snapshots of the evolution in time are considered to capture a pseudotemporal picture of the evolution of the slope reliability. The analysis of slope employs the finite-element method in order to calculate the factor of safety, which is subsequently used in defining the limit state of failure. The limit state is then employed for the assessment of slope reliability. Repeated computation of the safety factor/limit state is avoided by adopting a response surface (RS)-based metamodeling approach. It is observed that the moving least-square-based RS provides an improved estimate of slope reliability than the conventional least-square RS. The study indicates that reliability can decline as a result of degenerating strength properties of the progressively decomposed MSW landfill. The stochastic sensitivity analysis reveals the relative importance of some variables over others in deciding the slope reliability. The effect of varying degrees of parametric uncertainty in the MSW properties is also demonstrated. Critical points are identified with respect to their safety implications that may be incorporated for reliability-based design of such systems.

Micelles have unique solubilizing properties. Here has been exploited the solid supported micellar bilayer (called admicelle) to extract Cu(II) ion from aqueous medium via adsorption, or more appropriately called adsolubilization. The adsorbent used in the present study is alumina modified with anionic surfactant. The material has been designated as surfactant-modified alumina (SMA). Batch adsorption results show efficient Cu(II) extraction (94.45%) by SMA at equilibrium conditions. The batch adsorption of Cu(II) obeyed Freundlich isotherm and pseudo second order kinetic model. Thermodynamic parameters ($\mathrm{\Delta }G$, $\mathrm{\Delta }H$, and $\mathrm{\Delta }S$) indicate that the adsorption process is spontaneous, endothermic, and favorable. Desorption of copper from Cu(II)-adsorbed SMA is possible by 0.2 M ${\mathrm{Na}}_2\text{-}\mathrm{EDTA}$. The applicability of SMA for the removal of Cu(II) from Cu(II)-spiked real wastewater has been examined. The results show that SMA is capable of treating wastewater containing Cu(II) having an initial concentration of $20\mathrm{mg}{\mathrm{L}}^{-1}$ with approximately 92% removal efficiency. The same amount (up to $\sim 92\%$) has been recovered again by ${\mathrm{Na}}_2\text{-}\mathrm{EDTA}$ treatment. A continuous fixed-bed column study has been performed for the design of adsorption columns.

This study explores the influence of ultrasonic pretreatment on the performance of a hybrid bioreactor treating synthetic textile wastewater. The study primarily focuses on assessing the decolorization and chemical oxygen demand (COD) reduction efficiency of a hybrid bioreactor. The hybrid bioreactor provided anaerobic-aerobic sequential treatment to the ultrasonically pretreated textile wastewater containing two new generation diazo dyes namely, reactive black 5 (RB5) and reactive red (RR120), along with other chemical constituents. Ultrasonic pretreatment produced approximately 52% color and 48% COD reduction efficiency at an optimized power of 200 W and 180 min sonication time. For the hybrid reactor treating ultrasonically pretreated textile wastewater, a maximum of 98% COD and 92% color removal efficiencies were obtained at an HRT of 32 h [organic loading rate $(\mathrm{OLR})=0.74\mathrm{kg}\mathrm{COD}{\mathrm{m}}^{-3}{\mathrm{d}}^{-1}$] and 24 h ($\mathrm{OLR}=1.0\mathrm{kg}\mathrm{COD}{\mathrm{m}}^{-3}{\mathrm{d}}^{-1}$), respectively. Significant levels of aromatic amines formation were observed in the anaerobic phase. However, those were effectively eliminated in the subsequent aerobic phase inside the hybrid bioreactor. Volatile fatty acids to bicarbonate alkalinity (VFA/B-alk.) ratios, one of the health indicators of the bioreactor operation, were found in the range of 0.23–0.32 at different hydraulic retention times (HRTs), thus indicating the adequate buffering capacity for stability of the bioreactor. The study demonstrates the importance of ultrasonic pretreatment for mineralizing organic and inorganic impurities present in textile wastewater, which significantly improves the performance of subsequent hybrid bioreactor.

Identification of virus sources is one of the most important activities to control the spread of epidemics. Virus sources can be identified using an inverse optimization model. The inverse optimization model minimizes the error between simulated and observed concentrations at observation locations of the aquifer. The observed concentration can be obtained from field observation of contaminants. The simulated concentration can be obtained through the flow and virus transport simulation models. As such, the flow and transport simulation models need to be incorporated into the optimization model. As a result, the complexity of the problem is related to the dimension of the simulation models. For reducing the computational burden, generally, one- or two-dimensional simulation model is considered in finding the virus sources. However, to mimic the real world situation, one has to use the three-dimensional (3D) virus transport processes. Furthermore, in earlier studies, the number and the source locations are considered to be known. Thus, this study deals with the identification of a virus source in an unconfined 3D groundwater aquifer considering source location and number as variables. The methodology proposed allows running the models in an external environment to generate the simulated concentrations with arbitrary sources. The optimization model is solved using the pattern search algorithm. Two hypothetical problems have been considered to show the potential of the algorithm. The promising results show that virus sources in an aquifer can be identified even when the location and number of sources are not known.

Electronic waste (e-waste) in concrete is the new revolutionary concept of sustainable concrete because it reduces the environmental pollution and solid waste problem. In this paper the extracted outer casing insulation of electrical wire was made into fibers. These fibers were added to the concrete at 0.6, 0.8, and 1% with respect to the weight of cement. Fibers were added to the concrete with the aspect ratio of 35 to make fiber reinforced concrete. The fresh and hardened properties like slump, fresh density, dry density, compressive strength, flexural strength, split tensile strength, and Young’s modulus of fiber-reinforced concrete and normal concrete was compared at the respective age of curing. In order to reduce the cement content and to enhance the properties of concrete, silica powder was added to the fiber-reinforced concrete with 10% replacement of cement with respect to volume of cement and the properties were compared with normal concrete and fiber-reinforced concrete. The experimental results reveal that the optimal percentage addition of e-waste fibers to the concrete was found to be 0.8% with respect to the weight of cement for both fiber-reinforced concrete and silica fiber-reinforced concrete. Thus, fiber-reinforced concrete and silica fiber-reinforced concrete using e-waste fibers was an alternative to normal concrete because it gives increased trend in properties and also reduces the amount of dumping e-wastes into nature.

Phenol is a harmful substance found in the wastewaters from certain chemical industries. In the present study phenol present in synthetic wastewater has been biodegraded in a bubble column bioreactor using Pseudomonas putida (NCIM-2650). Experiments have been carried out to determine gas holdup at various feed flow rates of synthetic wastewater, feed concentration, and air flow rate. Two dimensionless correlations, one in terms of bubble diameter and the other in terms of column diameter, have been developed for gas holdup.

Contamination of water and sediment in water bodies is caused by the runoff from agriculture fields, and release of untreated/partially treated domestic and industrial wastewaters. Polluted water can affect the health of humans and aquatic organisms, and nutrient discharge can lead to algal blooms. A sustainable solution is required to treat these pollutants to protect future populations from environmental hazards. Sediment microbial fuel cells (SMFCs) is a new technology that has the potential to remediate sediment and water from sluggish water bodies and ponds, and generate some electricity as a byproduct. This critical review discusses types of SMFCs, factors affecting performance of the SMFCs, its capability to offer in situ treatment of sediment and wastewater, and challenges to overcome to make this technology efficient for remediating water quality and harvesting electricity.

In the present investigation, a defluoridation study was carried out using the bacteria Shewanella putrefaciens in the bulk phase as well as immobilized phase in a batch reactor. Growth of the bacterial cells and their acclimatization in a fluoride media as well as under substrate stress has been investigated. Optimization of process parameters for the removal of fluoride in the bulk phase is investigated and the performance under optimum conditions is compared with the simultaneous adsorption and bioaccumulation (SABA) process using Citrus limetta (mosambi peels) and Ficus religiosa (peepal) leaves as an adsorbent along with the bacteria. Optimum pH, nutrient broth (N.B.). media concentration, time and initial concentration were found 7, $2.5\mathrm{g}/\mathrm{L}$, 24 h, and $20\mathrm{mg}/\mathrm{L}$, respectively. The simultaneous adsorption and bioaccumulation (SABA) process shows maximum fluoride removal capacity followed by bioaccumulation in bulk phase and adsorption. Both bioaccumulation and SABA are able to reduce the initial concentration of fluoride from 20 to below $1.5\mathrm{mg}/\mathrm{L}$.