Journal of Hazardous, Toxic, and Radioactive Waste

Antioxidant depletion from a high-density polyethylene (HDPE) geomembrane with hindered amine light stabilizers (HALS) immersed in three different high pHs solutions is examined over a 3-year period. The three solutions had the same concentration of inorganic salts but a range of pH (9.5, 11.5, and 13.5) likely to encompass those found in low-level radioactive waste leachate and other geoenvironmental applications. Increasing the pH from 9.5 to 13.5 increased the antioxidant depletion rates detected by both standard and high-pressure oxidative induction time tests (Std-OIT and HP-OIT) and also increased the residual HP-OIT values. Arrhenius modeling is used to predict the length antioxidant depletion stage for each solution.

In the context of underground storage of nuclear waste, this paper presents the characterization and laboratory tests on compacted MX80 bentonite. Various laboratory testing techniques were used for establishing the water retention behavior of the bentonite. Compacted bentonite specimens were hydrated with fluids of low and high salt concentrations both at ambient and an elevated temperature of 70°C. The swelling behavior of the bentonite was also studied by stepwise wetting compacted specimens at various suctions under isochoric condition. The influence of thermal and thermohydraulic gradients on the mechanical behavior of the bentonite was studied in a thermohydraulic column cell. The investigation showed that the development of swelling pressure in compacted bentonites upon a decrease in the applied suction is accompanied by a decrease in the magnitude suction stress, which gets manifested in the development of the interparticle repulsive pressure and a decrease in the effective stress. The influence of an elevated temperature and an increase in concentration of salt in the hydrating fluid was found to reduce the swelling pressure of the bentonite. Both thermal and thermohydraulic gradients were found to be manifested on the development of axial pressures. Applications of thermal and thermohydraulic gradients were found to cause redistributions of water content, dry density, degree of saturation, and suction within compacted bentonites.

Petroleum hydrocarbon–contaminated soil and groundwater is a worldwide environmental problem, which results in environmental hazard and human health risk problems. Because petroleum is a complex composition mixture rather than a single compound, health risk assessment for a petroleum hydrocarbon–contaminated site is a complicated process. In this study, a modified total petroleum hydrocarbons (TPH) fraction method was applied to determine the health risk level for each TPH fraction. The concentrations and toxicity data of total of 13 TPH fraction categories were evaluated and used for risk calculation. Results show that up to $\mathrm{1,772}\mathrm{mg}/\mathrm{kg}$ of TPH concentration was observed in soils collected from the studied site. Results indicate that benzene was the most concerning chemical that appeared in TPH. The calculated cancer risk for benzene was $4.48\times {10}^{-7}$, which was lower than the minimum total cancer risk level ($1\times {10}^{-6}$). The calculated hazard quotient for the noncarcinogenic compounds was slightly higher than the minimum target risk level of 1, and this was due to the $C_{12-16}$ group, which had higher concentration in groundwater. Results indicate that the major exposure pathway was through groundwater ingestion rather than vapor inhalation. The TPH fractions that needed to be analyzed would be aliphatic $C_{8-10}$, $C_{10-12}$, and $C_{12-16}$ due to their higher toxicity effect. In the exposure pathway of groundwater ingestion, the TPH fractions that needed to be analyzed included aromatic $C_{5-7}$, $C_{10-12}$, and $C_{12-16}$ due to their higher exposure potential. Light petroleum compounds (e.g., aliphatic $C_{6-10}$ and aromatic $C_{5-10}$) also need to be considered during the risk assessment process because of their higher volatility behavior. Analysis of heavy TPH ranges are unnecessary due to their low volatility and high adsorption effects. The suggested method allows a more flexible application depending on exposure routes as explained, which makes human health risk assessment more feasible and practicable. The TPH fractionation analysis could be regarded as one feasible for future health and risk assessment for the TPH-contaminated site. This study provides a streamlined process to develop a more practical and economical RBCA strategies for TPH-contaminated sites.

Bioreactor landfills involving leachate recirculation are emerging as the preferred option for managing municipal solid waste (MSW). Effective bioreactor landfill performance can be achieved by ensuring uniform and adequate moisture (leachate) distribution in landfilled MSW. This paper presents a numerical two-phase flow model as a tool to predict hydraulic behavior (moisture distribution and pore fluid pressures) in unsaturated MSW under leachate recirculation, mechanical response (stress-strain behavior), and coupled hydromechanical interactions of MSW in landfills. The selected mathematical model is the Fast Lagrangian Analysis of Continua (FLAC), which assumes leachate and landfill gas as two immiscible phases. The governing equations and numerical implementation are presented along with the general model implementation considerations. The model is validated by simulating the published laboratory studies, field studies, and published modeled studies. Overall, it is shown that the mathematical model is capable of providing information necessary for the design of effective bioreactor landfills by incorporating coupled hydromechanical processes.

Studies on sorption behavior of fission products like cesium (${}^{137}\mathrm{Cs}$) and strontium (${}^{90}\mathrm{Sr}$) with the soils of some Near Surface Disposal Facility sites have been undertaken along with activation products like cobalt (${}^{60}\mathrm{Co}$). Soil used in this study are silty sands and inorganic silts and clays. Sorption behaviors of these stated radioisotopes have been studied using laboratory batch experiments under varying conditions of equilibration time, pH, and liquid-to-solid ratios. The study reveals that the sorption partition coefficient is strongly affected by contact time, pH, and liquid-to-solid ratio. Initially, the sorption reaction rate increases very rapidly with increases in time and approximately after 24 h, it attains equilibrium for the radionuclide–soil system. The study reveals that chemical constituents of the soil and their amount present in the soil also control the sorption of radionuclides. The study indicates that soil that has some clay minerals (montmorillonite) has comparatively higher distribution coefficient ($K_d$) and attains dynamic equilibrium early compared to soil with lower clay content. It was also observed that $K_d$ increases with increase in liquid-to-solid ratio almost linearly but steeply.

During the postconstruction phase, the stress equilibrium conditions within the proposed underground nuclear waste repositories may alter because of various factors, such as far-field mining activity, fluctuation of the groundwater table, and seepage erosion. A reduction in the transmitted stress from the host rock may destabilize the isochoric condition, leading to swelling displacement of backfilling and buffer materials. In the current study, the swelling behavior of bentonite-based backfilling materials was studied. Laboratory tests were carried out on compacted bentonite ($\mathrm{dry}\mathrm{density}=1.26\mathrm{Mg}/{\mathrm{m}}^3$) and bentonite-sand (70% bentonite, 30% sand, $\mathrm{dry}\mathrm{density}=1.50\mathrm{Mg}/{\mathrm{m}}^3$) specimens in a strain-controlled oedometer. First, compacted specimens were hydrated with distilled water under constant volume condition. Next, predetermined displacements were introduced in a step-wise manner that caused expansion of the specimens. The swelling pressures of the specimens were measured under a constant-volume condition at each induced strain. The test results showed that induced strains caused a decrease in the swelling pressures of the saturated backfilling materials. A decrease in the swelling pressure for a maximum induced strain of approximately 1.6% was found to be approximately 19% for the bentonite specimen and approximately 30% for the bentonite-sand specimen. It was shown how the swelling index of backfilling materials can be used to assess the recoverable swelling pressure following any induced strain.

Oxidation of ammonia (${\mathrm{NH}}_3$) using electrocatalyst is highly important because of its usage in fuel cells. In this study, a Cu-ACF composite catalyst was synthesized by the liquid phase deposition (LPD) method with immobilizing copper serving as the active component onto activated carbon fiber (ACF) matrix for the electrochemical oxidation (ECO) of inorganic compounds exemplified by ${\mathrm{NH}}_3$. The electrochemical behavior and surface characteristics of the catalyst, including its redox and corrosion properties, were assessed using cyclic voltammetry (CV), fluorescence spectroscopy (FS), UV-Vis absorption spectroscopy, zeta potential measurements, environmental scanning electron microscopy (ESEM), and transmission electron microscopy–energy dispersive X-ray spectrometer (TEM-EDX). Results demonstrated that applying the CV reversible redox capability could illustrate the catalytic activity of the Cu-ACF catalysts, and the ${\mathrm{NH}}_3$ oxidation current density on the Cu-ACF catalyst increases with increasing scan rate. The wavelengths of the fluorescence peaks for the fresh catalyst varied from those of the exhausted catalyst, which reveals that FS is a valid method to the characterization of the formation of copper oxide nano-clusters in intrinsic fluorescence emission from Cu-ACF catalyst. The ESEM and TEM-EDX results demonstrate that CuO crystal nanoparticles are highly dispersed on the ACF-supported surface. These crystal structures can explain the high activity of the electrocatalyst, which is also responsible for the strong metal-support interaction.

A novel magnetic hydrogel coupling with a wastewater treatment prototype is proposed in this study for the removal of various types of anionic pollutants from wastewater. Within 5 min of kinetic studies, 97.5, 99.9, 100.0, 81.7, and 98.9% of Cr(VI), amaranth, methyl orange, nitrate, and phosphate were removed from wastewater, whereas these adsorbed anions were desorbed to varying extents using NaCl for 15 min. The maximum adsorption capacities of Cr(VI), amaranth, methyl orange, nitrate, and phosphate were $205\mathrm{mg}/\mathrm{g}$, $830\mathrm{mg}/\mathrm{g}$, $\mathrm{1,390}\mathrm{mg}/\mathrm{g}$, $188\mathrm{mg}/\mathrm{g}$, and $227\mathrm{mg}/\mathrm{g}$, respectively. An industrial wastewater treatment prototype was developed featuring a magnetic separation unit for the recovery of spent magnetic hydrogel. A separation efficiency over 98% can be maintained throughout 60 adsorption-desorption cycles of Cr(VI) wastewater treatment. The estimated wastewater treatment cost in consideration of chemical usage only is USD $0.58/{\mathrm{m}}^3$. The chemical cost of the treatment is comparatively less expensive than chemical reduction and precipitation methods.

The synthetic dye solution of Acid Red 131 monoazo dye was ozonated in a semibatch reactor. The effect of ozone dose, initial dye concentration in the solution, and solution pH on the rate of decolorization was studied and the results were analyzed in terms of color-removal efficiency (CRE), which was found to increase with an increase in the ozone dose. Alkaline pH of the synthetic solution was found suitable for ozonation and 100% CRE was obtained after 23 min of ozone treatment at pH 11. The CRE was found to decrease with an increase in initial dye concentration of the synthetic dye solution, but the quantity of the dye removal was greater at higher concentrations. The results of decolorization kinetic research showed that ozonation of the reactive dye were a pseudo-first-order reaction with respect to the dye concentration in the solution. Experiments were performed to remove dye from the textile industry effluent by oxidation with ozone and 100% CRE was obtained. The quantities of ozone and power consumption were determined.

Assessing the accurate performance of incinerators is imperative for policymakers to chalk out appropriate solid waste management plans. Being a treatment facility, with high capacity to destroy hazardous waste, incinerators also have the disadvantage of producing toxic ash and polluted air during the incineration process. It is, therefore, required to develop a model, which considers not only desirable inputs and outputs (I/O) but also the undesirable I/O to assess the relative performance of incinerators. This study illustrates the use of data envelopment analysis (DEA) to assess the performance of 14 common biomedical waste (BMW) treatment plants, i.e., incinerators (government- and private-owned facilities) in the state of Uttar Pradesh (UP), India, using the 2013 data obtained from the state’s pollution control agency. These 14 plants receive waste from 5,301 healthcare facilities (HCFs) and hospitals, with a total of 84,751 beds. A Charnes-Cooper-Rhodes (CCR) DEA model with two inputs and four outputs is proposed to assess the relative efficiency. The inputs are treatment cost of waste and incinerator capacity; whereas the outputs are quantity of waste treated, particulate matter, NOx, and HCl. The model involves desirable and undesirable outputs. Results reveal that only one plant, located in Agra, is fully efficient and the other 13 plants need to be improved. In fact, four out of the top five efficient plants are privately owned. To improve the performance of inefficient plants, benchmarking was done using the reference set analysis and strategies suggested.