Journal of Hazardous, Toxic, and Radioactive Waste

Among coal mining-related wastes, coal gangue (CG) is the heterogeneous waste generated during the mineral processing or coal washing phase of coal mining. A thorough understanding of environmental concerns associated with the current model of CG utilization and potential future application is gaining paramount importance. Though previous review articles on CG have presented the environmental concerns and current utilization of CG, an appraisal on the factors affecting its mechanical properties and feasibility of CG as a potential geotechnical material has not been taken into consideration. An attempt is made here to present the different issues associated with the disposal of CG and highlight the potential benefits of its utilization. The physical, chemical, mineralogical, geotechnical, environmental (trace metal mobilization and life-cycle assessment) characteristics of CG are comprehensively evaluated to gauge its potential in promoting sustainable development. This review article also provides insights into CG’s potential applications including its use as a subgrade and subbase material in pavements, landfill liner material, and filter material for hydraulic structures. The sustainability benefits attainable through CG utilization in geotechnical and geoenvironmental applications are also highlighted.

Vermifilter is a cost-effective and environmentally friendly technology for domestic and industrial wastewater treatment. However, filter bed clogging is an operational challenge of vermifilter. The present study was conducted to investigate the impact of different hydraulic loading rates (HLRs) on treatment performance and filter bed clogging of horizontal subsurface flow macrophyte-assisted vermifilters (HSSF-MAVF). Three laboratory-scale horizontal subsurface flow vermifilter reactors planted with Canna indica were used in this study. Each reactor was fed synthetic dairy wastewater with HLRs of 0.66, 1.5, and 2.34 m/day, respectively. Based upon the results of this study, the treatment performance and filter bed clogging of the system were observed to be closely dependent on the applied HLRs. The highest treatment performance (89 ± 2%, 94 ± 2%, 95 ± 4%, and 76 ± 5%, respectively, for COD, TSS, ammonium-N, and phosphate-P) with minimum filter bed clogging (10 ± 2% hydraulic conductivity reduction and 0.19 ± 0.05-cm head loss) was observed in the reactor fed with the lowest HLR of 0.66 m/day. Similarly, the lowest treatment performance (67 ± 3%, 61 ± 4%, 87 ± 2%, and 63 ± 4%, respectively, for COD, TSS, ammonium-N, and phosphate-P) with severe clogging of the filter bed (33 ± 2% hydraulic conductivity reduction and 2.1 ± 0.5-cm head loss) was observed in the reactor fed with the highest HLR of 2.34 m/day. The clog matter (CM) from each filter bed is composed of both organic and inorganic materials, and the quantity of CM varied from 6.46 ± 0.28 to 24.44 ± 1-mg/mL, with protein being the major organic clog matter component.

This paper presents our findings on the effect of adding biopolymers to locally available soil to form low-cost alternative landfill liner materials. Hydraulic conductivity is the key parameter for assessing the suitability of any geomaterial as a landfill liner. In view of this, the hydraulic conductivity of biopolymer-modified soil was determined at various dosages. Two biopolymers—xanthan gum and guar gum—were used in the experimental work at dosages of 0.5%, 1%, 2%, and 4% by weight of dry soil mass. The results indicated that the hydraulic conductivity values decreased with an increase in biopolymer content and consolidation pressure (σ_cp). The influence of xanthan gum content (G₁) and guar gum content (G₂) on the soil hydraulic conductivity is represented by nonlinear regression models based on experimental data obtained for σ_cps of 50, 100, 200, 400, and 800 kPa. The performance of the soils was assessed using reliability-based design optimization methodology. The optimal mixtures of cohesive soils blended with a range of G₁ and G₂ were evaluated considering the variability associated with the dosages of G₁ and G₂, and the σ_cp.

This study was conducted to check the impact of plant roots on the treatment efficiency and hydraulic behavior of a vermifilter for synthetic dairy wastewater. Two horizontal subsurface flow (HSSF) vermifilters, one with plants (MAVF) and the other without plants (VF), were used for this study. The experiment was conducted with a hydraulic loading rate of 1.5 m³/m²·day using the Eisenia fetida earthworm and Canna indica wetland plant. The average COD removal from HSSF-MAVF and HSSF-VF was 75 ± 5.7% and 64 ± 3.83%, respectively. The average total nitrogen removal for HSSF-MAVF and HSSF-VF was 44 ± 4.4% and 35.5 ± 3%, respectively, whereas the average total phosphorus removal from HSSF-MAVF and HSSF-VF was 57 ± 3.4% and 51 ± 2.8%, respectively. The activity of plant roots in HSSF-MAVF was observed to considerably delay clogging in HSSF-VF. The overall bed media porosity reduction was more in HSSF-MAVF (33%) than in HSSF-VF (28%). However, the impact of plant roots on bed media clogging was comparatively very marginal, leading to only 5%–6% additional porosity reduction over HSSF-VF. The characteristics of clog matter (CM) were composed of both organic and inorganic matter. Organic components such as protein, polysaccharides, nucleic acids, and humic acids were observed in both the reactor beds.

The use of inorganic nitrogen fertilizers in agricultural applications and oxidation of human and animal by-products, including septic discharge, has led to a considerable increase in nitrate contamination in water bodies. This excess nitrate is responsible for considerable damage to humans and biota. As a result, the removal of nitrate anions from groundwater, rivers, and lakes is critical. In most countries, the content of nitrates as an environmental quality guideline has recently been established to be less than 10 mg/L. Hence, the removal of nitrate ions from groundwater, rivers, and lakes is critical because contamination is expected to become increasingly severe in the future. Against this background, the development of an effective and sustainable treatment approach in the form of adsorption is becoming increasingly desirable. This review work specifically focuses on the effectiveness of carbonaceous materials for nitrate adsorption, with their production, modification, characterization, and morphology investigated in detail. In addition, challenges and future opportunities for applying carbonaceous materials as adsorbents for nitrate removal are also addressed. From the literature results, it has been found that there is an enhancement in the surface area through chemical activation for better nitrate adsorption. It has also been found in the literature that the maximum nitrate adsorption was on a biographene nanosheet-based wheat straw biochar at an initial nitrate concentration of 150 mg/L and a of pH of 7.17. Researchers have reported that the adsorption process with applications of carbonaceous materials is promising for the removal of the nitrate ion, but finding cost-effective, environmentally sound, and efficient adsorbents concurrently for nitrate removal from aqueous solutions remains a challenge at the industrial scale, which should be addressed in future research.

This study is an evaluation of the effects of using filter media on the performance of an integrated settler-based biofilm reactor (ISBR) for onsite treatment of domestic wastewater, as it is a known fact that filter media play an important role in the biological treatment of wastewater. The ISBR had three compartments. The first one was a settler, which was followed by two upflow anaerobic biofilm reactors, each representing a single compartment. All three compartments were accommodated within a single compact unit. The study was divided into two phases, based on the different filter media (aqwise carrier, moving bed biofilm reactor (MBBR), and brick) used in the biofilm reactors. In the first phase, aqwise carrier and MBBR media were used in the second and third compartments of the reactor, respectively; in the second phase, the MBBR medium in the third compartment was replaced with brick medium. The ISBR delivered remarkably good removal efficiency for organic pollutants. It also worked well in color removal to a considerably good extent. The average pollutant removal efficiency of the ISBR in the second phase was observed as 93.06 ± 4.5, 91.83 ± 3.2, and 90.89 ± 5.5% for total suspended solids (TSS), biochemical oxygen demand (BOD), and chemical oxygen demand (COD), respectively. As regards bacterial analysis, the total and fecal coliform removal efficiencies in the second phase were found to be 90.5 ± 3.6 and 95.36 ± 1.8%, respectively. Field scanning electron microscopy of the media showed the morphology of anaerobes as clearly visible, which was a good sign for the system. The results observed after replacement of MBBR medium with brick medium proved that the ISBR had good potential for use as an onsite sanitation system.

It is widely known that phenols and chlorophenols (CP) are two of the most toxic chemicals and a versatile treatment is imperative to tackle this evil of industrialization. Adsorption using low-cost adsorbents is advantageous and economical; however, it has not turned out to be feasible technology. Biological treatment is much more flexible, useful, and environmentally friendly and a combination of biological treatment and adsorption has yielded much better results compared with using them individually. However, very few works apply statistical methods in elucidating the importance of various options in such a combined study. This work focused on the effect of temperature, initial concentration of chemicals, and adsorbent dosage on the removal of these chemicals. Furthermore, it compares various processes, that is, biological treatment (bio), sequential biological and adsorption (seq), and simultaneous biological and adsorption (sim) methods in treating phenols and chlorophenols. A range of linear regression models was developed to predict the percentage reduction for each of the processes used (bio, sim, and seq), and each of these models was statistically significant as evident from R-square values and the ANOVA table for regression parameters. A data-mining tree-classifier for modeling the phenol and CP removal was also developed. The data mining study indicates the initial concentration of the solvent and temperature to be the primary classifying parameters.

Adsorption is one of the most commonly used water/wastewater treatment processes. Clays and biomasses have been studied widely as adsorbents for different classes of contaminants. However, these materials possess some drawbacks that prevent their application on a large scale. To overcome their drawbacks, attempts have been made in recent years to synergistically combine these two classes of low-cost adsorbents to form a new class of materials called clay–biomass composites. This paper reviews the studies reported in the recent past on the use of these composites synthesized from clay and biomass, and subsequently modified, for removal of different classes of pollutants. Synthesis of composites by different methods, and the characterization of resulting composites are presented. Further, detailed discussion on the use of these composites for removal of different classes of pollutants such as heavy metals, dyes, nutrients, dyes, organic micropollutants and microbial pathogens is included. Various factors affecting the adsorption process along with mechanisms of removal of different pollutants by these composites are presented. Reported studies on regeneration and reuse of spent adsorbents are also given. It is evident from the literature review that the clay–biomass composites show significant enhancement of adsorption capacity for different classes of pollutants. Directions for further research for utilizing these composites in industrial applications are discussed. Overall, the paper indicates the potential of these composites for use in removal of different classes of pollutants.

Oil–water emulsion discharge or reuse is a major problem for the environment and ecological systems. This discharge cannot mix with fresh water, owing to the high oil content, total dissolved solids, and chemical oxygen demand (COD). Membrane separation is a unique process to reprocess oily wastewater. The membrane has additional advantages compared with other commercial processes, such as adsorption, distillation, and centrifugation, for example, less energy requirement, no addition of chemicals, and a reduction of the COD to within permissible limits. Transient flux decline and foulant deposition during the operating time are the main drawbacks of the membrane separation process. Transient flux decline could be minimized by using a cross-flow setup. In a cross-flow filtration unit, the cell consists of a flat sheet comprising a polyamide membrane with pore diameters under the microfiltration range. During experiments, the membrane was first fouled, and the fouled membrane was cleaned using a cleaning agent. The membrane fouling experiment was conducted at a 138-kPa transmembrane pressure (TMP) difference in the laminar flow zone. The membrane cleaning operation was essential to recover the initial hydraulic membrane permeability. Deionized water, the anionic surfactant [i.e., sodium dodecyl sulfate (SDS)], and the chelating agent [i.e., ethylenediaminetetraacetic acid (EDTA)], were used to recover the original flux value. A thorough study was conducted into how the membrane performance was improved with variation of chemical agent doses.

This study concerned the field of radioactive waste conditioning by cementation, involving the optimization of cemented radioactive spent resin form quality by the development of new formulations based on mixtures of Class 45 portland cement, sand, and water, with metakaolin (MK) as a mineral additive. Here, the MK contribution to the cemented-waste form quality was evaluated. In this context, four new formulations were prepared containing 2%, 4%, 6%, and 8% MK relative to a mixture of cementing materials without MK. The mechanical quality of each of the cemented-resin forms was determined, after 28 days of curing, by measuring the compressive strength and analyzing the porosity. Characterizations of the prepared cemented-resin forms were completed using X-ray fluorescence, X-ray diffraction spectrometry, and scanning electron microscopy. It was found that, for each formulation, the phases of early and secondary pozzolanic hydration were marked by accelerations in the hydrate formation reactions. These phases, characterized by an increase in mechanical resistance following the silicate and aluminate dissolution phase, justify the inclusion of the MK and prove its participation in the early formation of hydrates. Among the four developed formulations, the one with 6% MK produced a cementitious mixture that allowed the containment of 14.38% of the spent ion-exchange resins, with a mechanical resistance to compression equivalent of to 15.92 MPa and a low-porosity equivalent to 34.98%. This formulation allowed the identification of the course of pozzolanic reactions favored by the addition of MK.

This paper reports on laboratory-based treatability and field quality assurance (QA) testing completed on interbedded sands and silts at an industrial site heavily impacted by a chlorobenzene (CB)-rich nonaqueous phase liquid (NAPL) to depths of approximately 30 ft (9.1 m) below the ground surface (bgs). Total CB concentrations were measured up to 4,200 and 11,000 mg/kg in untreated sandy and silty soil samples, respectively. EPA 1316M testing indicated that the effective solubility of CB was on the order of 90–210 mg/L in two of the most impacted sand samples, the highest of which (from hotspot location 4370) was selected as the principal threat waste condition. A full depth [25 ft (7.6 m)] soil core from this location was homogenized to form a soil surrogate containing approximately 1,500 mg/kg CB. Three stabilization/solidification (S/S) mix designs using Type I/II portland cement (PC) doses ranging from 5 to 10 wt% were then prepared using the soil surrogate. The unconfined compressive strength (UCS) and hydraulic conductivity (K) values after 28 days of curing were, respectively, on the order of 190–265 lb/in.² (1.31–1.83 MPa) and 1.0 × 10⁻⁹ cm/s, easily meeting the performance criteria. All mix designs showed essentially the same EPA 1315M leaching response, with percent leaching reductions (%LRs) greater than 99% for CB and benzene (B) compared with the untreated sand. This was well above the minimum of 90% LR established for successful mix designs. During remedial construction, bucket and auger S/S-mixing techniques using 7.5 wt% PC were used to treat approximately 9,335 CY of impacted soils to depths up to 30 ft (9.1 m) bgs (12 bucket-mixed cells and 527 auger columns) in approximately 6 months. The UCS and K criteria were both satisfied. The relative vertical positioning of the EPA 1315M cumulative mass release curves for CB from the field QA samples appeared to be more strongly influenced by the total CB content than by K, because all S/S-treated samples were characterized by K < 1 × 10⁻⁶ cm/s (i.e., were diffusion-controlled). EPA 1315M testing of the field-mixed sample from hotspot location 4370 again indicated %LRs greater than 99% for both CB and B. Samples from a second location in the western portion of the ISS treatment area demonstrated similar results.

Prior publications in this series presented information on the nonaqueous phase liquid (NAPL) impacts, pore fluid saturation (PFS) relationships, stabilization/solidification (S/S) treatability work, and an in-canal in situ S/S (or ISS) pilot test at the Gowanus Canal Superfund Site in Brooklyn, New York, which was impacted by three historic manufactured gas plants (MGPs). This paper reports on the decision-making strategy applied for selecting the planned areas to implement ISS to a depth of 5 ft (1.5 m) into the native sediments after dredging of the overlying soft sediments in remedial target areas (RTA-1 and -2). ISS target areas were developed primarily from in-canal Tar-specific Green Optical Screening Tool (TarGOST) analysis of sediments at a 2-in. (5 cm) layer resolution and the development of an empirical correlation relating the TarGOST percent reference emitter (%RE) response to the NAPL PFS in the cores, and the measured NAPL PFS threshold above which NAPL was considered potentially mobile. A volume accommodation model (VAM) evaluated the ability of various individual NAPL PFS exceedances and their associated layer thicknesses in the sediment to trigger a PFS exceedance above the threshold value of the entire overlying horizon, resulting in NAPL breakthrough from as deep as 10 ft (3 m) into the native sediment. The output from the VAM was integrated with ArcGIS spatial mapping and visualization tools to generate Thiessen polygons that indicated the areas having overall NAPL exceedances. In this way, and coupled with engineering judgment, mobile NAPL areas were effectively targeted for ISS, totaling 82,798 and 227,297 ft² (7,692 and 21,117 m²) in RTA-1 and -2, respectively, or 15,227 and 49,843 cu yd (11,642 and 38,128 m³) based on the aforementioned ISS mass thickness.

This paper presents research that proposes a new standard fire curve to simulate exterior wildfire due to burning trees and bushes. An extensive inquiry was performed in the existing scientific literature, in the search of measured temperature versus time wildfire curves by other authors, in trees and bushes using in situ thermocouples. The gathered wildfire curves for both trees and bushes are plotted together, and envelope upper-bond wildfire design curves are proposed. The objective of these new proposed fire curves is for them to be used in the design of the protection of dwellings located in the urban wildland interface against the action of a natural wildfire. To access the efficiency of these proposed fire curves, a thermal numerical analysis is performed using the commercial finite-element software Abaqus, in which a wood specimen is subjected to real wildfire and compared with the proposed wildfire design temperature versus time curves.

In this study, a novel biogeochemical cover system comprising biochar-amended soil and basic oxygen furnace (BOF) steel slag was explored as a sustainable alternative cover system to mitigate methane (CH₄), carbon dioxide (CO₂), and hydrogen sulfide (H₂S) simultaneously from landfill gas (LFG). Long-term column studies of a simulated biogeochemical cover (BGCC) profile investigated CH₄, CO₂, and H₂S removal potential. The performance of the BGCC system was compared with a conventional soil cover (SC) profile. The CH₄ oxidation rates of biochar-amended soil were significantly higher, ranging from 185 to 407 µg CH₄/g-day in comparison with the barrier soil in the SC system (6–7.5 µg CH₄/g-day), based on the batch incubation of column-exhumed samples. In addition, the biochar-amended soil showed higher relative abundance of methanotrophic bacterial communities (20%–51%) in comparison with soil cover (10%–27%). In both columns, complete attenuation of H₂S occurred near the inlet (75 cm bgs) and sulfur oxidizing bacteria (e.g., Thiobacillus) and methanotrophs were both detected. The sulfur content was elevated (0.68%) at the base of both columns and H₂S may have imparted an inhibitory effect on CH₄ oxidation rate in the SC system. The BOF slag showed a CO₂ removal potential of 67 g CO₂/kg BOF slag. Overall, the BGCC system outperformed the SC system, effectively mitigating CH₄, CO₂, and H₂S simultaneously.