Journal of Hazardous, Toxic, and Radioactive Waste

The application of biological processes to improve the behavior of soils remains a concern among the scientific, industrial, and public sectors. The amount of research in this field has increased in the last two decades. However, the complexities associated with this process for the types of soil and their heterogeneous behavior, longevity (i.e., durability), optimization of solutions and treatment methods, amount of calcite precipitation and uniformity in its distribution, upscaling in the field, and finding their effective measures require a comprehensive interdisciplinary research approach that combines geotechnical engineering, geochemistry, and microbiology. Therefore, this paper aims to encapsulate the research work from the last two decades by highlighting an overview of the mechanisms (i.e., biostimulation- and bioaugmentation-induced calcite precipitation) associated with the implications of biogeotechnology to improve the different soil types. The most commonly used biological processes [i.e., ureolysis or urea hydrolysis, denitrification, and sulfate (SO₄^2–) or iron (Fe) reduction] will be compared for their suitability, limitations, and associated bacteria and strains that are used for the biotreatment of soils. In addition, various limiting factors that control the successful application of microbial-induced carbonate precipitation (MICP) to improve the properties of soils are highlighted. The fundamental differences between the biotreatment processes from the laboratory to field scale (e.g., injection method, surface percolation method, and premixing method) will be explained categorically. This paper will discuss the current status, challenges, and future opportunities in biogeotechnology. The application of biogeotechnology to improve the behavior of clayey soil requires more attention compared with sandy or silty soils. The major limitations, biological concerns, consequences, and their possible controlling measures will be discussed to understand the complexity when adopting biological processes in geotechnical projects and practices. Finally, the paper lists out the potential areas that should be focused on for the effective, economical, sustainable, and durable application of biogeotechnology under various construction conditions.

Since the early beginning, attention has been paid to the prospective application of two-dimensional (2D) graphene (Gr) nanomaterial applications due to its exceptional conductivity, huge surface area, and high mechanical strength. Microbial fuel cells (MFCs) are one of these vital potential applications. The restricted energy production of MFCs compared with other fuel cell technologies and expensive materials are the two major hindrances in its practical application. Gr is proposed for use in the MFC assembly to overcome such challenges either as an electrode or membrane material to increase the oxygen reduction reaction (ORR) efficiently. The synthesis procedure for Gr-based electrodes and membranes is complex, expensive, and energy-inefficient and contains harmful chemicals for a scaled-up application. Therefore, there is a further need for focused research into the design and synthesis of Gr-based electrodes and membrane materials. However, regardless of these challenges, Gr-based electrodes are a favorable alternative in MFCs’ assembly to attain sustainable wastewater treatment and electricity production. Considering these facts, the objective of this critical review is to assess the latest developments in the Gr applications in MFCs, aiming at Gr background, including properties, Gr synthesis, wastewater treatment, and power generation, which will help to understand the perception of Gr in MFC operation.

The construction sector across the world involves constructing huge buildings, which usually consumes enormous energy, causing an incredibly damaging effect on the environment in terms of raw material usage, greenhouse gases (GHGs) emitted, and waste generated in huge quantities, which has drawn much attention from conservationists. Though several preventive measures have been developed to reduce the impact of construction, they are often ignored or mismanaged. Thus, things must be examined in detail with appropriate environmental tools to provide a clear view of the emission released into the environment and mitigate the problem from a broader perspective. Life cycle assessment (LCA) is one tool used for quantifying the emissions into the environment and economic impacts of the chosen product/process. As a result, this study investigates the effects of the precast structural elements for building and their carbon footprint at the different construction phases based on the LCA methodology. The construction phases include (a) the preoperational phase/building construction, (b) the operation phase, and (c) the postoperational phase/building demolition and inventory data are collected from the selected building. The results show that the precast structure’s energy (23.33 kW · h/m²) was less compared with reviewed case studies. The global warming potential (GWP) of the present study, 16.55 kg CO₂ eq/m², was the least among all the studies. The life cycle cost (LCC) analysis of buildings was performed, and the LCC of precast structures was 4.78% less than the conventional construction. The study evaluates and compares each phase’s emissions and identifies specific hotspots for emissions into the environment. Finally, the authors believe that the study provides valuable insights into the potential environmental impacts for the relevant stakeholders and experts.

Essential hydrogeological parameters related to riverbank filtration, such as grain size (D50) of aquifer soils, hydraulic gradient, bed height, fine content, as well as operation and detention period, were explored in laboratory column studies to determine critical percentage total coliform removal. Increases in total coliform removal efficiency were seen for both in situ aquifer soil and altered aquifer soils as detention and operating period increased. With an increase in detention and operation period from 1 to 72 h, the percentage total coliform removal for aquifer soil increased from 42.5% to 94.3% and 10.4% to 77.11%, respectively. The removal of total coliform increased from 94.3% to 99.9% as the percentage fine content increased from 2.5% to 15%, increased from 94.3% to 98% as the hydraulic gradient decreased from 1.45 to 1.1. An increase was noticed from 73.1% to 95.9% as the mean grain size decreased from 3.2 to 0.22 mm. The importance of hydrogeological parameters impacting coliform removal was demonstrated using multiple linear regression analysis. Detention period and percentage of fine content were directly proportional to total coliform removal effectiveness among various hydrogeological parameters, but percentage total coliform removal was inversely proportional to hydraulic gradient as well as to mean grain size. The model was validated using field study data from the riverbank filtration located on the Rushikulya River, which yielded excellent results, ensuring the accuracy of the model produced. The Badamadhapur riverbank filtration facility was also shown to be effective in removing total coliform pathogens.

Lignin and its derivatives are identified as the prime pollutants in the effluents of many industries such as rice mill, paper, and pulp, which subsequently create dark coloration and toxicity to the aquatic bodies when they release without treatment. The present study focuses on the removal of lignin from aqueous solutions using an industrial by-product, dolochar as an adsorbent. The adsorbent material (before and after adsorption) was characterized with the help of SEM and EDS studies. The pseudosecond-order kinetic model with the regression coefficient (R²) of 0.99 has well defined present study of the lignin adsorption process using dolochar. For the evaluation of response surface methodology through the Box–Behnken design (BBD) technique, three input variables: adsorbent dose (4–8 g/L), contact time (60–120 min), and pH (6–10) were selected. The effect of these chosen variables was verified by conducting a total number of 15 experiments in a multivariate system for the removal of lignin through dolochar. The quadratic polynomial model has yielded the regression coefficient (R²) of 0.99 when the experimental data fitted to it, which is indicating the suitability of the model for the process. The precision and efficiency of the model were visualized using the ANOVA and lack of fit test. The process has resulted: adsorbent dose 6.21 g/L, contact time 85.15 min, and pH 7.78 as optimized parameters for the removal of lignin using the industrial by-product dolochar.

Lithium-ion batteries are widely used in consumer devices and electric vehicles due to their higher energy density, output, and extended cycle durability. Heavy metals, polymers, and toxic organic electrolytes found in used lithium batteries pose serious environmental concerns. A typical lithium-ion battery is made up of a variety of metals, including cobalt (5%–20%), nickel (5%–10%), lithium (5%–7%), and copper (6%–12%). Lithium and cobalt, in particular, face severe supply limitations, resulting in a threefold spike in lithium prices and a fourfold increase in cobalt prices between 2016 and 2018. The economic and environmental ramifications clearly show that effective and ecologically friendly lithium-ion battery recycling is no longer a choice for manufacturers but rather a must. Although various battery-recycling methods have made advances, the process’s economic feasibility and carbon footprint will be determined by the individual battery chemistry. The three most common recycling processes utilized in used batteries recycling are hydrometallurgy, pyrometallurgy, and electrometallurgy. According to the findings, the leaching process is the key to an efficient, cost-effective, and long-term closed-loop process for lithium-ion batteries. The current favored approach for leaching in the battery recovery process is acid leaching. The acid leaching method, which uses inorganic acids like H₂SO₄ and HCl as leaching solvents, produces high leaching rates and efficiency but at the cost of increased solvent prices and secondary pollution. Organic acid leaching (citric acid, formic acid, and so on) is gaining popularity due to its environmental friendliness and equivalent leaching effectiveness to inorganic leaching. Bioleaching is a new type of leaching that uses microorganisms and is currently in the early stages of development. Ammonia’s chelating properties make it an excellent leaching solvent for targeted metal ion separation, and it may also be easily removed from leached solution by simple distillation. As a result, ammoniacal leaching offers a lot of potentials for lithium-ion battery closed-loop recycling. Understanding how materials and solutions interact provides the foundation for high leaching efficiency and tailored metal selectivity. We outline the closed-loop recycling techniques for lithium-ion batteries in this study, with an emphasis on the problems and technical advancements.

The removal of metronidazole (MNZ), a pharmaceutical antibiotic, from a synthetic wastewater matrix will be investigated in this study using biomass immobilized with powdered activated carbon (PAC) in an alginate matrix (Al–AC–Bio). First, the Al–AC–Bio beads will be synthesized using 2% sodium alginate (SA 2%), 0.1% PAC, and 12.5 g/L mixed biomass. For comparison, beads without PAC will be prepared with SA and biomass (Al–Bio) under similar conditions. The MNZ removal experiments will be conducted under the following conditions: MNZ of approximately 1 mg/L; bead loading of approximately 5%, 10%, and 20%; and wastewater organic carbon (OC) of approximately 300 mg/L (low carbon) and 1000 mg/L (high carbon). The MNZ removal was mainly abiotic and followed second-order kinetics under all conditions. A maximum MNZ removal efficiency of 87.7% and specific MNZ removal (SMR) capacity of 0.34 mg/g were observed using Al–AC–Bio after 24 h. The increase in bead concentration and organic content showed an insignificant improvement in MNZ removal efficiency. However, total organic carbon (TOC) and ammonia (NH₃) removal were 67.4% and 90.2%, respectively, under optimized conditions. The addition of PAC showed a significant improvement in MNZ removal and insignificant improvements were observed for TOC and NH₃ removal. The PAC–biomass beads with lower bead loading could be efficient for the removal of MNZ and NH₃ from wastewater.

A study was conducted to introduce an efficient alternative such as bioelectrochemical degradation of pharmaceuticals. Six earthen pot MFCs were operated in batch mode, in which the pharmaceuticals were added in two different concentrations, and their effect on the performance on a microbial fuel cell (MFC) was compared with a control MFC. While the MFC dosed with paracetamol (4.2 W/m³) generated more electricity than the control MFC (3.7 W/m³), the rest of the MFCs dosed with the pharmaceuticals caffeine (3.4 W/m³), salicylic acid (3.1 W/m³), trimethoprim (2.7 W/m³), and sulfamethoxazole (2.8 W/m³) generated less electricity than the control, indicating the negative effects of the pharmaceuticals on the electricity generation by MFCs. A marginal difference in the COD removal efficiency was noted. Sulfamethoxazole and trimethoprim rapidly degraded (more than 90% in 24 h). Paracetamol and caffeine took nearly 48 h to get completely degraded and salicylic acid got 100% degraded in 90 h.

Reverse osmosis (RO) has been an extensively implemented membrane technology for both domestic and industrial use. This wide implementation has been possible due to the availability of potable drinking water with high quality, but the RO concentrate volume associated with this technology has a significant limitation. As an alternative, a desalting technique, called capacitive deionization (CDI), was explored for purifying/treating salt contaminated water. In the present article, biomass-derived active material was coated on nickel foam, which resulted in efficient electrodes for ion sorption. The developed electrode was characterized with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), which revealed a specific capacitance of 49.72 F/g and a resistance of 2.15 Ω. Moreover, its implications were explored for deionizing a concentrated stream of 500–1,500 ppm total dissolved solids (TDSs) in batch mode via the potential application of 1.2 V. An electrosorption capacity of 22.98 mg/g was obtained with salt adsorption rates of 0.51 mg · g⁻¹ · min⁻¹. The application of fabricated biochar-coated nickel foam electrodes was explored by treating the collected samples from domestic and commercial RO units located in Malviya Nagar, Jaipur, India, and it was found that treated water characteristics were well within the prescribed standards.

Uncertainties associated in tracer transport arising through various geological formations are often sorted by laboratory experiments on representative elementary volume (REV). To understand the effect of grain size and packing on plume behavior, tracer transport experiments were performed in fully saturated condition for four different geological materials (glass beads, sand, and coarse and fine natural soil). A mini-aquifer setup having inner dimensions of 150 × 10 × 50 cm was used with sodium chloride (NaCl) as a tracer. The materials were selected to gradually increase the heterogeneity from relatively homogeneous (glass beads) to heterogeneous (natural Himalayan foothill field soil). The aim of the experimental investigation was to study contaminant transport and to examine applicability of various porosity models for particles for a range of geological materials. Simulation of observed breakthrough curves (BTCs) were carried out using a mobile–immobile model (MIM) and continuous time random walk (CTRW) model. Observed experimental breakthrough curves demonstrated relatively symmetrical spreading in glass beads, while natural soil exhibited the presence of preferential flow (physical nonequilibrium). The estimation of porosity from empirical relations deviated significantly from in situ measured porosity. Comparing CTRW and MIM with various porosity model, it is concluded that MIM provided a better representation of observed BTCs.

In this study, the extraction of phenol from an aqueous solution with the help of an emulsion liquid membrane (ELM) has been carried out. This membrane has the edge over the conventional separation processes in selectivity, efficiency, and feasibility. Certain factors such as surfactant, carrier, and diluent play an essential role in membrane synthesis. In our case, Span 80 (sorbitan monooleate) was taken as a surfactant, kerosene as a diluent, and Aliquat 336 and Isodecanol as carriers. Under different optimum operating conditions, it was found that external-to-membrane phase ratio, surfactant concentration, carrier concentration, agitation speed, time of extraction, membrane-to-internal phase ratio, and solute concentration were the significant parameters. At optimum conditions, 89.52% phenol removal has been recorded. The percentage removal changes with time, and it was seen that it tends to remain constant after a while. The experiment was also carried out in two stages, taking into account the higher concentration of phenol from around 1,000 ppm to a lower concentration of around 100 ppm. It was observed that the final concentration of phenol after the two-stage process had been reduced to around 7–10 ppm.

In the current study, dustfall during 2019 was collected at 10 sites in Cairo, Egypt, to analyze the metal contents and assess the rate of metal deposition as well as the risks of exposure to metals by analyzing the results using techniques of contamination assessment methods to determine the Geoaccumulation Index of metal pollution (I_geo), hazard index (HI), and hazard quotient (HQ). The results of the current study show that the annual rate of dustfall during 2019 in Greater Cairo was 32.8 g/m² per month. The highest deposition rate was recorded during the autumn, while the lowest deposition rate was recorded during the summer. According to Muller’s classification, it appears that the examined sites in Greater Cairo were virtually uncontaminated with Cr, Cu, Ba, Mn, Fe, and As; low nickel and zinc contamination; moderately contaminated with Pb, Cd, and Sb; and highly contaminated with Ag, Se, and B. Cancer risk values (R) indicate an increased risk of cancer developing between 1/1,000,000 persons to 1/10,000 persons. In the case of children, the R values for Ni, Cr, As, and Cd were above 1.0 × 10⁻⁴. This indicates an increased risk of cancer. The R values for Pb were less than 1.0 × 10⁻⁶ – 1.0 × 10⁻⁴ for Greater Cairo, indicating no significant cancer risk for this metal.

One of the major concerns of developing countries, regarding public health, the economy, and the environment, is municipal solid waste (MSW) management; waste management is one of the costliest services provided by the municipality in developing countries. Because waste management imposes huge costs in developing countries, one of the most important strategies in these countries is to minimize waste production and thus to simplify the process of waste collection and transportation for disposal. The main problems of waste management in Iranian cities include low technical quality, low investment, and low attention to cost in the stages of collection, transportation, and disposal. In this study, the factors affecting costs and their impact percentages were identified by univariate analysis. The correlation between factors was determined by Pearson’s correlation coefficient, and their prediction and determination were performed by factor analysis with an exploratory method. According to the results, transportation (43%) had the greatest impact on the management costs of regional waste organization, followed by: wiping and cleaning of sidewalks, sweeping, and dredging of rivers (26%); other costs (12%); burial of waste (10%); washing of urban elements (4%); wiping and mechanized cleaning of passages and refuges (3%); and collection and transportation of construction debris (2%). Determining the share of each factor is a useful and practical way of comparing different factors and planning to improve organizations activities. Moreover, the results of exploratory analysis show that two factors had the most effect on the costs of waste organization.

To reduce carbon dioxide (CO₂) emissions from the use of cement and lime in civil engineering applications, microbially induced calcite precipitation (MICP) is one of the sustainable technologies being explored. MICP utilizes the metabolic activities of bacterial species to produce chemical environments that are conducive for calcite formation, which either plugs the pore spaces and/or bonds the soil particles together to reduce permeability and increase the strength and stiffness of soils. This study examined the reduction in use of chemical stabilizers by employing microbially induced carbonate cementation (MICC) along with magnesium oxide (MgO) stabilization. A soft soil [unconfined compressive strength (UCS) = 20 kPa] was prepared in the laboratory by mixing equal-weight proportions of kaolinite (50%) and sand (50%) at a high (21%) water content. Simultaneous pozzolanic and microbial activity was induced in the soft soil by the addition of MgO and cattle manure (CM). Degradation of the CM by native microbes produced CO₂, which dissolved in the water to form bicarbonate ions $({\mathrm{HCO}}_3^{-})$. The alkaline pH generated by the addition of MgO transformed the ${\mathrm{HCO}}_3^{-}$ ions to carbonate ions, and these precipitated as calcium and magnesium carbonates. The alkaline pH (11.73 to 8.89) facilitated by the addition of MgO also induced pozzolanic reactions. The deposition of carbonate precipitates and pozzolanic reaction products at aggregate contacts transformed the soft soil into a hard (UCS > 400 kPa) soil. For every tonne of chemical required in the field for ground improvement, augmenting pozzolanic stabilization using the proposed MICC method has the potential to reduce CO₂ emissions by 0.78 t.

Naphthalene is a common polycyclic aromatic hydrocarbon that is widely present in aquatic environments and has colossal negative health effects on living beings. Thus, the removal of naphthalene from wastewater using sustainable, low-cost geomaterials and novel technologies is of prime importance. In this study, the efficacy of a locally available silty–sandy soil in attenuating aqueous naphthalene was assessed using a laboratory-scale constructed wetland. The hydraulic conductivity of the soil was found to be 1.66 × 10⁻⁵ cm/s. Batch adsorption data showed that the Langmuir and pseudo-second-order models were the best fitting isotherm and kinetics models, with coefficient of determination values of 0.98 and 0.99, respectively. A one-dimensional vertical-column study using the tested soil on naphthalene showed that the exhaustion time of a 40-mm-deep soil bed was about 1.6 days. A laboratory-scale rectangular-tank test conducted using that soil, with the same test numerically modeled using HYDRUS solute-transport software, revealed that 90% of the initial concentration of naphthalene would reach the outlet in 102 days. The wetland constructed using the selected soil indicated a reduction in the naphthalene concentration of up to 92.8%, which corroborated the results from the CW2D HYDRUS module.

Riverbank filtration (RBF) is one of the most productive and low-cost technologies for obtaining purified water throughout the year. The inevitable problem associated with RBF is clogging, a complex phenomenon that obstructs the flow. The present study conducted laboratory experiments on two different filter materials (uniformly graded) collected from the Ganges River bed from an RBF site in Haridwar. The primary focus is to study the factors influencing the clogging mechanism that affects the hydraulic conductivity, K of the filter material. The variation in the piezometric head, porosity, specific infiltration resistance, and the progressive clogging of the filter material is studied considering the experimental results. It is observed that the retention and intrusion of suspended particles depend on the grain size of filter material and fine sediments. The clogging of pores is more at the initial depths (2–7.5 cm), demonstrating the phenomenon of physical clogging. For every experimental run performed, as time progressed, with increased resistance and head difference, K and porosity of the filter materials decreased (Filter material-1, 47.17% and 48%; Filter material-2, 93.43% and 81%). With an increase in initial discharge, q₀, K is partially recovered, presenting the initial desiltation process. Further, as time elapsed and with an increase in the turbidity, C, from 500 to 1,000 ppm, the clogging advanced resulting in decreased K of the filter materials. Therefore, taken as a whole, the ratio of mean size of filter material to suspended particles, q₀, C, and time are considered as the dominant factors influencing the clogging process. Mathematical regression models for both the filter materials are formulated and found to estimate K reliably. The correlation coefficients calculated for both the models at a 95% confidence level are 0.814 and 0.965, respectively, and are statistically significant, presenting the functional dependency of K on the ascertained parameters as acceptable.

Emerging contaminants (ECs), especially pharmaceuticals and personal care products (PPCPs), that are present in aquatic and soil matrixes, have become a major concern for the competent authorities, because they are persistent and pose potential threats to human health, aquatic life, and the soil ecosystem. As an environmentally sustainable and economical EC remediation technology, constructed wetlands (CWs) and vermifiltration (VF) have become popular for treating wastewater and vermicomposting (VC) has gained the attention of the researchers as a sewage sludge or solid waste treatment technology. Although extensive literature is available on the potential of CWs for the remediation of ECs, a review of earthworm-based EC removal technologies has not been performed, to the best of the authors’ knowledge. Therefore, this paper aims to review the potential of all the aforementioned natural EC remediation technologies. CWs and VF could emerge as suitable alternatives to conventional wastewater remediation methods to eradicate ECs, and VC has the potential to substantially eliminate ECs from organic solid wastes. In addition, risk assessments suggest that these technologies are more efficient in expurgating the level of toxicity imposed by ECs on the ecosystems that receive them than the conventional treatment methods.

The present research investigated the impact of heavy metals such as lead (Pb²⁺), copper (Cu²⁺), and zinc (Zn²⁺) on different bentonite’s characterization. Two types of bentonites, possessing a difference in physiognomies, were adopted for this objective. Interesting observations were extracted from the study; first, a decrement in the values of liquid limit (LL), swelling pressure (SPr), and swelling potential (SPo) was observed in both the bentonites. Also, a higher variability in the LL (36.3, 39.2, and 38.1% decrease), free swell (FS) (73.8%, 77.2%, and 80.0% decrease), and SPr (48.4%, 50.4%, and 54.4% decrease) was observed in presence of Pb, Cu and Zn for the bentonite with a higher LL, swelling capacity, specific surface area (SSA), cation exchange capacity (CEC), and montmorillonite content. Likewise, the time–swelling test confirmed a decline in the time consumed for primary swelling with a rise in heavy metal concentration. The void ratio–pressure study revealed lower void ratio values for samples with heavy metals than deionised (DI) water under any assigned pressure. On the other hand, this shrinkage in the void ratio was predominantly evident for Zn²⁺ and Cu²⁺ solutions, compared to Pb²⁺ solution. Furthermore, the compression index and time required for 90% of consolidation were found to vary inversely, whereas the coefficient of consolidation varied directly with the heavy metal concentrations. Finally, the unconfined compressive strength study at multiple concentration ranges (from 0 to 2,000 mg L⁻¹) revealed a value higher than 200 kN/m², the mandatory criteria for a liner material for application in landfills. The results obtained will aid in understanding the dynamics of heavy metals on the bentonites’ characterization.

In the present study, the decolorization of a solution containing four dyes––acid violet 17 (AV 17), malachite green (MG), methylene blue (MB), and Congo red (CR)––was performed using electrocoagulation (EC) with the help of aluminum electrodes. A Box–Behnken design with three factors––current, electrode spacing, and pH––was used to optimize the factors for greater dye removal efficiency. A reasonably good fit was obtained for acid (AV17 and CR) and basic (MG and MB) dye removal under optimized conditions (pH 5, electrode spacing 1 cm, and current 0.03 A/cm²). High coefficient-of-determination values was obtained for the acid and basic dyes (R² = 0.979 and 0.977, respectively), implying a good fit for both regression models. Maxima of 76.6% and 73.8% dye removal were obtained under optimized conditions, confirming that the EC process is a viable option for dye removal.

Contaminants of emerging concerns (CECs) persist in the environment and are present in the air, water, and soil. They include various industrial, chemical, pharmaceutical, and personal care products (PCPs) and metallic elements, pesticides, and endocrine disruptors. CECs can cause adverse ecological and health impacts by passing into plants and human foods via different routes. Recently, different treatment processes have been investigated for the remediation of CECs that are present in wastewater, and a current review emphasized different biological treatments for the removal of a wide range of CECs. Based on these studies, endocrine disrupting compounds (EDCs) can be removed by a membrane bioreactor (MBR) and pharmaceuticals and pesticides can be effectively removed by biological activated carbon (BAC). Microalgae-based treatment can remove some types of CECs, to some extent, and the activated sludge process (ASP) and trickling filters (TFs) can remove an average amount of CECs from wastewater. Due to the deficiencies of these treatment processes when removing CECs in wastewater, various hybrid treatment systems have been explored. This study will focus on the different conventional and novel biological treatment processes for the removal of different CECs.

Geosynthetic clay liners (GCLs) are widely used as hydraulic barriers in landfills and mine tailings facilities due to their low hydraulic conductivity. The average grain size of the granular bentonites (GBs) used in GCLs varies depending on the manufacturer and also between batches from the same manufacturer. The influence of GB grain size and plasticity on the sealing ability and volume-change characteristics under extreme chemical loads is important for long-term stability. Furthermore, GCLs are subjected to mechanical loading from landfill waste. The influence of different grain-size distributions in GB samples was assessed in terms of their self-sealing ability, hydraulic infiltration, and volume-change behavior under extreme chemical loadings and a 50-kPa mechanical load. The performance of fine-grained GBs was found to be satisfactory, in terms of hydraulic infiltration and volume change, under the test conditions. The plasticity of the GB also influenced its sealing and swelling ability under chemomechanical loading. The mechanism underpinning the influence of plasticity and grain size on the self-sealing behavior and hydraulic conductivity equilibrium is explained. We recommend fine-grained GBs for use in GCLs for containment applications.

There is a strong need for a sustainable and ecofriendly approach from the construction industry toward mitigating climate change, as it is one of the critical sectors accountable for exploiting natural reserves and generating greenhouse gases. In order to resolve this issue, various supplementary cementitious materials (SCMs) and artificial aggregates are now in use. The use of recycled aggregate (RA) also seems to be a possible alternative to natural aggregate. However, the practical utilization of RA is rare. The amount of porous attached mortar and the source of the RA determines the quality of RA concrete (RAC). In this study, efforts were made to improve the quality of high-strength RAC, made with 100% RA, by incorporating metakaolin (MK) and silica fume (SF) using the well-known two-stage mixing approach (TSMA). In addition, DIN standards were followed to obtain the maximum particle packing of the aggregate. In total, 10 types of RAC were mixed––two comprising RACs at water-to-binder (w:b) ratios of 0.25 and 0.35, and eight mixes for obtaining a high-strength RAC. Both MK and SF were incorporated into those eight mixes at 10% and 15% replacement levels and w:b ratios of 0.25 and 0.35. The synergistic effects on fresh and hardened RACs, and their durability performance, considering DIN standards, the TSMA, and SCMs, were addressed. In this context, a comparative analysis showed positive results for using SF and MK in RAC, bearing in mind its mechanical and durability performance.

Mathematical models for electrochemical conversion of CO₂ to CO in a solid oxide electrolysis cell (SOEC) are formulated. Model simulation has been carried out on a button cell having Ni-yttria stabilized zirconia (YSZ) composite as cathode, YSZ as electrolyte, and lanthanum strontium manganite (LSM) as anode material. The simulation results were used to estimate the overpotentials associated with the electrochemical reduction reactions of CO₂ to CO and hence predict the overall performance of a SOEC under varying operating conditions. Overpotential includes the contribution from activation, concentration, and ohmic losses corresponding to cathode, anode, and electrolyte components of the SOEC. Fick’s model, the Butler–Volmer equation, and Ohm’s law are used to estimate the values of concentration, activation, and ohmic overpotential losses, respectively. Of the three, ohmic overpotential dominates over other losses throughout the operating voltages. The calculated value of ohmic overpotential loss is 0.19 V at an operating voltage of 1.2 V and current density of 0.8 A/cm². The model is simulated for varying fuel gas compositions (CO₂/CO = 99/01, 70/30, 50/50, and 30/70) at a temperature of 1,073 K, and corresponding current–voltage characteristics of the SOEC are predicted. As the CO₂ content in fuel gas increases from 30% to 99%, the estimated current density is raised from −0.28 to −0.76 A/cm² at an applied potential of 1.1 V, indicating the presence of CO₂ in fuel and leading to improved performance of the SOEC. Similarly, at higher temperatures, part of the thermal energy contributes to activation of CO₂ molecules; hence, the calculated current density at a particular applied voltage (1 V) is enhanced from −0.2 to −0.6 A/cm² with a rise in temperature from 1,073 to 1,123 K of the SOEC system.

In this study, a sequential fed-batch anaerobic–anoxic–aerobic (A²/O) moving bed biofilm reactor (MBBR) (A²/O MBBR) system will be employed for the simultaneous treatment of highly concentrated phenol, ammonia (NH₄), and oxyanions [e.g., nitrate (NO₃) and sulfate (SO₄^2-)] from wastewater. The A²/O system efficiently removed phenol (99%) and NH₄–nitrogen [NH₄–N (95%)] with a 99% reduction in the chemical oxygen demand (COD) of the effluent for 3,000 and 200 mg/L of the maximum initial feed concentration, respectively with a 10-day hydraulic retention time (HRT). However, high removal of SO₄^2- was achieved under anaerobic conditions (96%) for 100 mg/L of the initial feed concentration. The increasing feed phenol concentration (1,500–3,000 mg/L) inhibited NO₃ reduction by releasing significant levels of NO₃ in the anoxic reactor effluent and increased the SO₄^2- accumulation in the anoxic and oxic reactors. Heterotrophic denitrification was reduced in the anoxic reactor by 15%–17% and increased the phenol concentration from 2,000 to 3,000 mg/L due to the highly toxic effect on the denitrifying microbes. NH₄ removal by the anaerobic (R1) and anoxic (R2) reactors reduced from 87% to 65% and 66% to 46%, respectively, and increased the phenol concentration from 1,500 to 3,000 mg/L but the oxic reactor showed stable performance. Scanning electron micrographs (SEM) of the carrier media showed the better adherence of well-grown round and rod-shaped mixed microbes in different environments. Bacillus licheniformis was identified as the dominant species in the anoxic and oxic reactors by the VITEK 2 COMPACT system. Similarly, Kocuria kristinae was the predominant microbe identified in the anaerobic reactor. The outcome of this study revealed that an A²/O MBBR system that had an established indigenous mixed microbial culture could be a feasible technique to treat highly concentrated phenol combined with NH₄ and oxyanions that are present in wastewater.

Samples of fine tailings from shallow depths of a waste depository (i.e., tailings pond) from uranium (U) ore processing in Jaduguda, India, were investigated to determine the speciation of the U and its association with certain physicochemical parameters. The aim was to understand the phenomena that can lead to the migration of U from the tailings pile to the adjoining environment. Natural processes were found to impact the physicochemical features of the tailings, as reflected in samples collected from a non-operational (first stage) and an operational (third stage) tailings pond. The average concentrations of U were 63.73 ± 5.34 mg/kg and 91.98 ± 9.33 mg/kg in the first- and third-stage ponds, respectively. A sequential extraction of tailings samples showed that the major fraction of U was bound to the residual phase, followed by an iron/manganese (Fe/Mn) oxide phase. The average fractions of U bound to these two phases were 38.7% and 35.8% as residual and 30.7% and 25.1% as Fe/Mn oxide in the first- and third-stage ponds, respectively. The findings demonstrate that, on average, 5% and 2.5% of the total U in the samples from the nonoperational and operational tailings ponds were active/mobile. This low mobility substantially minimizes the impact on the adjoining environment. In addition, the state-of-the-art technology used for waste immobilization, along with the site condition, are favorable for the long-term storage of the fine tailings from the ore-processing unit.

Deep geological repositories are the sole option for safeguarding the atmosphere from hazardous radiation from high-level radioactive waste. Hyperalkaline pore fluids are produced when fluids from host rocks penetrate through the concrete/cement layers of such repositories, the layers created as bulkheads in vaults or to facilitate gallery access between buffers and the host rock. Such fluids also disperse through the compacted bentonite layers placed around the steel canisters that contain the waste in the repositories. The corrosion of steel canisters inside such repositories can be observed over a certain time. Chemical corrosion can lead to harmful leachates that can seep through the compacted bentonite layers that surround the steel canisters, altering the bentonite properties. In addition, these compacted bentonite layers are subjected to thermal histories due to the canisters emitting continuous heat (150°C to 200°C). These compacted bentonite layers have to hold up under these three conditions in repositories, all of which can affect the swelling properties of the bentonite. Two bentonite samples (B₁ and B₂) from Rajasthan’s Barmer area were mixed with corrosion products and compacted to dry densities of 1.5, 1.75, and 2.0 Mg/m³ for this investigation. Thermal histories were induced at 110°C and 200°C for 3 h to prepare samples that were then saturated with hyperalkaline cement water. The presence of corrosion products resulted in a decrease in swelling pressure values when compared with samples without adding corrosion products. This decrease was more significant with an increase in the temperature of the induced thermal history.

In 2016, the Thai government established a new Act, the Nuclear Energy for Peace Act. As a result, various regulations, requirements, and guidelines regarding radioactive waste (RW) management were established under the Act. The waste management activities conducted by the waste operator were carefully reviewed and demonstrated regulatory compliance. The operator can deal with the waste that currently exists. However, to maintain continuity for the safe and sustainable management of the waste, it is necessary to overcome various challenges, such as the decommissioning of the disused facilities that will be released from regulatory control. The contaminated metals require special attention, because they are increasing rapidly. The use of melting treatment technology and the monitoring of the radioactive contamination in materials might be a solution to reduce the quantities of these metals. The presence of cesium-137 (Cs-137) contaminated dust from steel production factories is a concern due to the large volume. No decision on the management of the dust has been made. However, researchers are now carrying out experiments to determine methods to deal with it. In addition, the operator should consider important issues, such as the development of an additional storage facility to support the decommissioning of waste and the dust waste, and the reuse and recycling of disused sealed radioactive sources (DSRS). This paper will discuss the aspects of waste disposal, the strategic plans that deal with the challenges, and naturally occurring radioactive materials (NORMs).

This study presents a framework for water-quality-based ranking of river stretches by employing a modified multicriteria decision-making method, Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS), that coupled water-quality indicators with their prescribed standards. The methodology was applied to rank a total of 468 river stretches located across 19 states in India based on eight water-quality indicators. These indicators were dissolved oxygen (DO), temperature, conductivity, pH, biochemical oxygen demand (BOD), nitrate (NO³⁻), fecal coliform (FC), and total coliform (TC). The surface water classification based on “designated best use criteria,” which classify water bodies into five classes, namely A, B, C, D, and E was used to develop the standard matrix for use in TOPSIS. The results revealed that out of the top 10 best river stretches for water quality, the first four were located on the Beas River in the state of Punjab. These best stretches were located at Harike, Gowindwal, d/s Pathankot, Talwara, and G.T. Road near Kapurthala. The next best five in ranking were located on tributaries of the Indus river, passing through the northern states of Punjab and Himachal Pradesh. The bottom/worst 10 river stretches were all located in urban areas with high levels of population and industrialization. These were the Yamuna at Okhla, downstream of Shahdara Drain in Delhi; Vasishta at Salem in Tamilnadu; Arkavathi d/s of Kanakapura in Karnataka; the Yamuna at Nizamuddin in Delhi; and Ghatprabha at the town of Gokak in Karnataka state. It was observed that the best stretches were those with high DO, low BOD, and low FC and TC, whereas the worst polluted stretches were those with very high levels of BOD, FC, and TC. To the best of the authors’ knowledge, this is the first attempt wherein a modified TOPSIS involving the coupling of water-quality indicators and their prescribed standards has been used to rank river stretches. The findings of this study will have implications for the pollution control authorities and researchers in applying the proposed approach in the development of effective and robust river water-quality management plans.