Journal of Hazardous, Toxic, and Radioactive Waste

Determination of thermal conductivity of buffer materials is an important aspect in the design and characterization of engineered barrier systems (EBS) in deep geological repositories (DGRs) for safe containment of high-level nuclear waste. Several factors, viz. compaction state, particle size distribution, and mineralogical characteristics of buffer materials, influence the thermal conductivity of composite buffer materials. Therefore, it is essential to give due regards to the influence of these factors while estimating thermal conductivity of buffer materials. In view of this, the present study pertains to an extensive laboratory scale determination of thermal conductivity of a wide range of sand-bentonite based buffer materials employing a thermal needle probe. Precision and accuracy of the thermal needle probe are established in relation to a contemporary and widely endorsed thermal property analyzer. Further, the efficacy of several predictive models available in the literature is evaluated to appraise the thermal conductivity of composite buffer materials in relation to the experimental data. Realizing the need of a generalized approach considering the influence of clay mineralogy and particle size fraction present in the geomaterial, the manuscript proposes generalized thermal conductivity prediction models meant for the buffer materials. The developed models are found to deliver satisfactory performance and accuracy in appraising thermal conductivity of sand-bentonite buffers used in DGRs.

The removal of uranium from aqueous solutions was studied using an organic flocculant, namely, polyacrylamide (PAM) with different molecular weights in the presence of Mg(II). The influence of major parameters, such as flocculant dosage, solution pH, initial uranium concentration, dissolved organic matter, and mixing intensity, that may influence the removal efficiency of uranium were investigated. The optimum flocculation condition was $0.1–0.5\mathrm{mg}/\mathrm{L}$ of PAM, $0.75\mathrm{g}/\mathrm{L}$ of Mg(II) (or $1.6\mathrm{g}/\mathrm{L}$ of ${\mathrm{MgCl}}_2•{6\mathrm{H}}_2\mathrm{O}$), pH of 12, rapid mixing speed of 350 revolutions per minute (rpm), and slow mixing time of 1 min. Results showed that the flocculation process was fast, achieving $>95\%$ of uranium removal within $<30\min$ at pH 12 and PAM and ${\mathrm{MgCl}}_2•{6\mathrm{H}}_2\mathrm{O}$ dosage of 0.1–0.5 ppm and $1.6\mathrm{g}/\mathrm{L}$, respectively. ${\mathrm{MgCl}}_2$ enhanced the removal of uranium from low radioactive wastewater by PAM flocculation.

Urbanization is a constant accelerating global phenomenon that demands proper understanding of the interactions between the anthropogenic activities, related emission of pollutants and the urban environment. Metals are one of such group of extensively researched contaminants ubiquitously present in the urban environment that get rapidly accumulated and reach toxic levels. Further, intensive infrastructure construction, increasing vehicular densities, and an overall change in lifestyle, especially in developing countries, have further aggravated the problem by enhancing point/diffuse sources of metal emission. Due to their prevalence, toxicity, and persistence, heavy metals are of particular concern in any environmental system. The real concern is that the accumulation of heavy metals in urban soil, sediments, road dust and water bodies should be considered as chemical time bombs waiting to be set off by vulnerable environmental triggers, and thus likely to cause heavy metal contamination to groundwater. The primary concern in heavy metal research is to understand the probable sources of heavy metal pollution in urban areas and their impact on human health and the urban environment. Ironically, human development coincides with metal pollution, and hence metals are probably the most researched environmental concern during last two decades. In this context, a concurrent review becomes more imperative when there is plenty of information available, and researchers need contemporary research directions and goals. It is therefore the aim of this paper is to provide a scenario of the heavy metal contamination in urban areas, highlighting its migration pathways and the importance of metal speciation and bioavailability. Further, several assessment tools for estimating the different compartments of metals, as well as their contamination levels along with their drawbacks, are discussed. Potential areas of future challenges in heavy metal research are also identified and discussed. A summary of the main consensus, divergences, and constraints found, as well as some recommendations, is presented as a set of conclusions, aiming to contribute to more concerted future research. This paper emphasizes that as there is a lack of efficient assessment criteria and proper quality guidelines, and that better equipped research programs with holistic approaches are needed now to set toxicological standards and improve removal techniques.

Organic compounds with at least two fused benzene rings are known as polycyclic aromatic hydrocarbons (PAHs). These compounds are hydrophobic in nature. The toxicity exhibited by some of the PAHs has prompted many researchers to probe more in this area. The literature cites the existence of different physical, chemical, and biological techniques for the removal of PAHs. Different kinds of biological processes like algal, fungal, and bacterial remediation methods were used by different researchers for the degradation of PAHs. The literature states the presence of PAHs in the treated effluent and sludge of wastewater treatment plants (WWTPs). This study explored the feasibility of biodegradation of PAHs through extended aeration in batch reactors. This study focused on the impact of extended aeration on low-molecular-weight PAHs (naphthalene, acenapthylene, phenanthrene, and fluorene). It was found that during the aerobic degradation extending to 28 h, the degradation of selected PAHs was 81–96%. In the case of control reactors, the degradation was found to be 90–99%.

Electrical conductivity measurement of geomaterials is often used as a tool for performance appraisal of liner materials, including monitoring of solute transport, and necessarily constitutes a vital aspect in the design of barrier systems. Variations of thermal conductivity of certain geomaterials along with industrial wastes for engineered barrier applications, as in the case of a deep geological repository (DGR), have been observed to vary with addition of a radiation-resistant microbial species. As there is an interdependence between thermal and electrical conductivity of geomaterials, in the present study, experimental investigations pertaining to microbial influence on electrical conductivities of several geomaterials and industrial-waste samples meant for barrier and buffer applications are reported. Electrical conductivity measurements of the samples were carried out with the help of a fabricated electrical conductivity probe with a microcontroller unit. It is observed that Deinococcus radiodurans, the extremophilic and radiation-resistant bacterial species, has an incremental effect on the short-term electrical conductivity of the samples under consideration, which may be reasoned to any possible form of biogeochemical reaction leading to salt precipitation and subsequent alteration of salinity, or phasal augmentation in the liquid phase in the samples. Moreover, to appreciate the potential of living matter in soil to alter the engineering properties of the soil, a novel theoretical approach is also suggested to incorporate the presence of living phase in the idealized model of soil mass. Furthermore, based on the experimental data, prediction models are developed using artificial intelligence techniques and multigene genetic programming to quantify microbial influence on electrical conductivity of the samples. The models were found to be efficient in terms of statistical parameters.

Leachate data from four low-level radioactive waste and mixed waste disposal facilities operated by the U.S. DOE for environmental restoration programs are presented and analyzed. Constituents in the leachates are categorized into four groups: inorganic macrocomponents, metals and metalloids (e.g., Cu, Fe, and Zn), radionuclides, and organic compounds. The leachates are circumneutral (pH from 5.7 to 9.1) and generally oxidizing (redox potential, Eh, ranging from $-193$ to 344 mV, averaging from 72 to 144.5 mV at each of the four facilities). Ionic strength of the leachate ranges from 2.15 to 135.86 mM. Marcocomponents include ${\mathrm{Ca}}^{2+}$ (0.77–24.90 mM), ${\mathrm{Mg}}^{2+}$ (0.86–30.20 mM), ${\mathrm{Na}}^{+}$ (0.19–38.1 mM), ${\mathrm{K}}^{+}$ (0.04–1.94 mM), ${\mathrm{Cl}}^{-}$ (0.33–19.27 mM), ${\mathrm{SO}}_4^{2-}$ (0.39–29.60 mM), and ${\mathrm{NO}}_2^{-}$ or ${\mathrm{NO}}_3^{-}$ (0.00021–38.30 mM). Metals and metalloids in the leachates include Al (0.18–87 μM), As (0.033–1.89 μM), Ba (0.16–3.3 μM), Cu (0.0047–5.4 μM), Fe (0.022–43 μM), Li (0.090–139 μM), Mn (0.016–132 μM), Ni (0.010–1.86 μM), Sr (0.92–55 μM), and Zn (0.0082–2.6 μM). Uranium ($6.4–\mathrm{3,060}\mathrm{\mu g}/\mathrm{L}$), ${}^{99}\mathrm{Tc}$ ($0.15–47.9\mathrm{Bq}/\mathrm{L}$), ${}^{90}\mathrm{Sr}$ ($0.03–12.4\mathrm{Bq}/\mathrm{L}$), and ${}^3\mathrm{H}$ ($0.74–\mathrm{4,625}\mathrm{Bq}/\mathrm{L}$) are the common radionuclides.

Wastes are used increasingly as construction materials to make the building industry more sustainable. In this regard, the European standards indicate the characteristics to be met by fly ashes used as cement replacement for the concrete manufacturing; such requirements dictate that the fly ash must not contain dangerous substances or to emit radiation. However, the tests to be performed are not indicated, nor are the maximum limits that cannot be exceeded. In this study, two different fly ashes are analyzed, one of which is obtained from the traditional coal combustion and the other from the cofiring of 70% by weight of petroleum coke and 30% of coal. Several mortar mixes with different compositions were manufactured, and chemical, physical, mechanical, leaching, and radiological tests were carried out on them. Both ashes satisfy the normative requirements about their chemical properties, volume stability, and setting time. The compressive strength of the cocombustion ash mortars was lower than those made with coal ash, although they showed a high strength activity comparable to that obtained for portland cement, in compositions up to 20%. Cements with cocombustion ashes as additive have not presented leaching nor radiological problems with regard to standards and recommendations.

The energy crisis has become a major problem in this energy-driven world, so there is a need to explore new ways to meet the energy demands. Production of biodiesel from algae is one such method. Algae production using present technologies is quite challenging. Because algae are known to grow in wastewater, a possible solution is to integrate algal production with treatment of nutrient-rich wastewater and utilization of ${\mathrm{CO}}_2$ from power plant flue gas. The present study focuses on simulation of algae production by photosynthesis in an airlift photobioreactor (PBR) in a batch process. The simulation studies are carried out using computational fluid dynamics (CFD) software, considering mass transfer of ${\mathrm{CO}}_2$ from gas phase to liquid phase and ${\mathrm{O}}_2$ from liquid phase to gas phase. The effect of geometry of PBR on hydrodynamic properties such as gas holdup and liquid circulation velocities are investigated. The results of the work are compared with past studies which did not consider the actual photosynthesis reaction. The results show (1) that algae production is not uniform throughout the PBR and (2) higher gas holdup due to the presence of algae produced in photosynthesis reaction.

The current study reports the utilization of Acacia nilotica (babool) sawdust activated carbon (AAC) for indigo carmine (IC) dye adsorption from aqueous medium. The surface area and surface chemistry of AAC were studied using SEM and FTIR analyses. Batch studies were performed to determine the influence of different adsorption factors, viz, AAC dose, solution pH, time of contact, IC concentration, and absolute temperature on the adsorption of IC dye. Five adsorption isotherm equations were used to analyze experiment data. To optimize and find the most suitable isotherm, HYBRID, MPSD, and ARE functions were applied. The mechanism of adsorption has been analyzed by considering pseudo first and second-order kinetic equations. The adsorption study revealed that, the maximum removal of IC was found to be about 99.45 and 75.82% at the concentrations of 50 and $500\mathrm{mg}/\mathrm{L}$ with adsorption uptake of 4.792 and $37.908\mathrm{mg}/\mathrm{g}$, respectively, for $10\mathrm{g}/\mathrm{L}$ of AAC dosage, 2 h contact time and 303 K temperature. The equilibrium study revealed that, adsorption data follows all isotherm equations for IC adsorption on AAC. The kinetic study revealed that, adsorption of IC onto AAC followed the second-order model of kinetics. Thermodynamic study illustrated endothermic nature of adsorption. From the study, it is found that the AAC can be utilized for the adsorption of dyes and similar other adsorbates materials from wastewaters.

The feasibility of using phytoremediation to remediate an alkaline-slag-filled wet meadow site contaminated with polycyclic aromatic hydrocarbons (PAHs) and heavy metals has been studied. The objective of the present work is to investigate the ability of nine native grasses and trees to survive and remediate PAHs such as benzo(a)pyrene (BaP) and heavy metals such as arsenic (As), chromium (Cr), lead (Pb), and manganese (Mn) existing at the site during the three complete growing seasons. Replicate test plots were prepared by tilling and homogenizing the fill material to approximate depth of approximately 0.3 m. Soil samples from each plot were collected before and after preparing the test plots and analyzed for physicochemical properties and contaminant concentrations. The survival and growth of the plant species were monitored for two growing seasons. Only one plant species out of the total nine initially planted, specifically False Indigo Bush (Amorpha fruticosa) (FIB), survived the three growing seasons. Soil, plant root, and plant shoot samples were collected at the end of the second and third growing seasons at the plot where FIB was planted. PAHs and heavy metals were analyzed in the soil and plant samples. In addition, a sequential extraction procedure was followed to determine the fractionation of the heavy metals in soils before and after planting. The results showed no significant decrease in BaP, As, Cr, and Pb concentrations in the soil. In addition, there were no significant changes in heavy-metals fractions. However, Mn uptake in roots and shoots was observed, with a corresponding decrease in soil, at the end of the third growing season. The adaptability and survival of FIB and its high tolerance to harsh site conditions (high pH, fluctuating moisture, and contaminant toxicity) demonstrated the potential of this species for its use in the remediation of the study area.

High concentrations of arsenic in groundwater, affecting the districts lying on either side of the Ganga River in India, are reported as a serious environmental issue. Groundwater that is dominated by the presence of arsenic is not suitable for domestic consumption. Recharge of abstraction wells using river water may dilute the arsenic concentration in groundwater. Experiments were conducted to monitor arsenic concentration in the river and an abstraction well for a period of more than six months at a study site located near Patna, Bihar, India. A model to explain the variation of arsenic concentration in the abstracted water is developed. The model assumes that no arsenic is picked up from the porous media as river water travels through the porous media to reach the abstraction well. The contribution of groundwater or river water to the abstraction water is found to be related to the depth of water in the river. Such an approximate relationship is utilized in simulating the arsenic concentration. The simulated values appear to be in good match with observed values.

The longer time required for complete mineralization in the electro-Fenton (EF) process can be rectified by combining the EF process with a biological method. This paper analyzes textile wastewater treatment by integrating EF and biological processes. The removal of color, chemical oxygen demand (COD), and total organic carbon (TOC) by the EF process was 63, 48, and 29% respectively. Further treatment of this wastewater by a biological process resulted in removal of 85% of color, 86% of COD, and 56% of TOC. In addition, better mineralization of dyes requires integration of aerobic and microaerophilic conditions. The phytotoxicity and microbial toxicity analysis of the treated wastewater shows that there is a significant reduction of toxicity compared with the raw wastewater. Therefore it is recommended that the combined EF and biological degradation processes be applied in the treatment of textile wastewater for removing color, COD, and TOC effectively.

In the present work, cenospheres were modified to synthesize zeolite in order to improve their adsorption capacity. The synthesized zeolite was characterized by attenuated total reflectance-Fourier transform infrared (ATR-FTIR), scanning electron microscope (SEM), energy dispersive X-ray (EDX), laser particle size analyzer (CILAS), and Brunauer-Emmett-Teller (BET) method to confirm the desired modifications in cenospheres. Batch adsorption study was conducted to optimize physical parameters such as pH, adsorbent dosage, dye concentration, agitation speed, and contact time at 25, 35, and 45°C for the removal of Disperse Orange 25 (DO) and Disperse Blue $79:1$ (DB) dyes from wastewater. Maximum 93 and 89% removal has been achieved in 100 and 120 min contact time having 0.6 and $0.8\mathrm{g}/\mathrm{L}$ adsorbent dosage in case of DO and DB dyes, respectively, at optimized pH 6, dye concentration $40\mathrm{mg}/\mathrm{L}$, and agitation speed 140 rpm at 45°C. Monolayer adsorption capacity was found to be $125.0\mathrm{mg}/\mathrm{g}$ for DO and $109.8\mathrm{mg}/\mathrm{g}$ for DB. Adsorption of dyes on zeolite followed Langmuir isotherm and pseudo-second order kinetic. Thermodynamics data suggest conclusively exothermic and spontaneous adsorption of dyes. Synthesized zeolite was regenerated after dye recovery in organic media. Moreover, zeolite has been applied for treatment of textile mill effluent and analyzed through ultraperformance liquid chromatography (UPLC) to confirm the removal of dye.

The objective of this study is to analyze the time processes of hazardous waste management (HWM) in Turkey. There should be a holistic evaluation of a country’s hazardous waste management program in terms of theoretical qualifications, best practice applications, and, of course, problems and their solutions. This paper offers a similar approach to evaluate HWM in compliance with the European Union under the laws of environmental applications. In 2010, 786,418 tons of hazardous waste (HW) were produced in Turkey. Of this, around 18% is sent to municipal garbage dumps, 0.6% is burned, and the remaining 81.4% is disposed of by other methods (such as controlled landfill or haphazard throwaways).

This paper directs its aim to present a new approach to convert fly ash from becoming a hazardous waste for the environment into an artificial resource as effective construction material. The fly ash slopes analyzed were made at a 60° inclination from horizontal, having wrapped facia made of steel grid–jute geotextile composite reinforcement. Postconsumer plastic water bottles, another unwanted waste material usually disposed to the geoenvironment in bulk quantity, were used to form the cellular mattress reinforcements in slope backfill. The three-dimensional reinforcement layers were positioned keeping an even vertical spacing of $0.2H$, while reinforcements were in strip forms with coverage ratios of 0.5 and 0.6 and in continuous form, i.e., coverage ratio ($C_r$) of 1. The influence of the height, length, coverage ratio, and varying edge distances ($1.0B$, $1.5B$, and $2.0B$, where $B$ = footing width) of cellular reinforcement on the bearing capacity of the slopes subjected to strain-controlled static strip loading over the top slope surface through a rigid steel plate as footing was studied systematically. Test results indicated that improved footing capacity for a continuous mattress is 1.93 times greater and for a coverage ratio of 0.6 improved footing capacity is 1.58 times greater at 10-mm settlement for $L=0.6H$ (where $L$ = length of cellular reinforcement and $H$ = height of slope) when $D_e/B=1.5$ ($D_e$ = edge distance) and $\mathrm{CR}{50}_{20}$ ($\mathrm{CR}{50}_{20}$ = cellular reinforcement of diameter 50 mm and geocell height 20 mm) over reinforced fly ash slopes as compared with that over unreinforced slopes for both mattress and strips. Substantial improvement was observed on the settlement of the backfill with the alteration in edge distances and length of the cellular reinforcement.

Discharge of textile effluents creates serious environmental problems. This paper investigates the ability of various natural and modified soils to remove heavy metals present in the textile wastewater. Natural soils such as kaolinite, bentonite, and laterite, along with modified soils such as organoclay and biopolymer-amended laterite are considered as the potential adsorbents. Iron and chromium present in the textile wastewater are considered as model pollutants. Batch adsorption studies are carried out to determine the heavy metals sorption capacity of soils. The heavy metals removal efficiency of soils follows the order bentonite > biopolymer amended laterite soil > laterite soil > kaolinite > organoclay. Almost complete removal of heavy metals is observed with bentonite and biopolymer-amended laterite. Therefore soil is determined to be a cost-effective and efficient adsorbent for the removal of heavy metals from textile wastes.