Journal of Hazardous, Toxic, and Radioactive Waste

Abstract

Leachate supplementation through liquid injection is applied widely in bioreactor landfills to increase moisture content within municipal solid waste (MSW) to facilitate waste decomposition and achieve early waste stabilization. This study provided a comprehensive picture of leachate supplementation systems with a critical evaluation of their advantages, applications, design aspects, and influence on the performance of bioreactor landfills. In this study, a critical review of the design characteristics of different leachate supplementation systems and their combinations was carried out, and the comparative performance of leachate supplementation systems by focusing on individual and combined systems to distribute a certain amount of injected liquid was made. In addition, this study considered the effects of MSW characteristics, the mode of leachate injection, the rate of leachate injection, the configuration of the leachate recirculation system (LRS), and the saturated and unsaturated hydraulic parameters to assess the performance of bioreactor landfills. The study identified the significant influence of LRS on moisture distribution, wetted area, pore pressures, landfill settlement, and slope stability. The majority of the literature reported that the unsaturated hydraulic properties and heterogeneous anisotropic waste (HTAW) conditions significantly resulted in an increase in lateral leachate migration and a decrease in pore pressures compared with homogeneous isotropic (HI) conditions. The field applications of these systems and their specifications in full-scale landfills were assessed. This study could help in the better planning of suitable leachate supplementation systems.

Practical Applications

The management of leachate that is generated through MSW decomposition is one of the most critical problems in landfills, because it contains a high concentration of toxic compounds and could easily contaminate the surrounding water bodies. The availability of low moisture content in conventional landfills results in a slow rate of degradation of the MSW. Based on the literature, it was proposed that the moisture content should be approximately 50% to provide optimal conditions for biodegradation. In this scenario, landfill leachate recirculation was a suitable method for leachate management, and there were several benefits associated with it, such as accelerated degradation of waste, the effective utilization of landfill space, a reduction in the volume of leachate for treatment, enhanced landfill gas generation, and minimized postclosure monitoring. This study could help with choosing and designing appropriate LRSs for uniform moisture distribution in real conditions. The observations and operational suggestions from this study could help to update the knowledge for waste management researchers on the implementation of leachate recirculation techniques to improve the performance of bioreactors.

Groups of populations, such as street vendors, spend a significant amount of time in outdoor urban hotspots, which results in varying amounts of pollutant exposure based on land use, duration, type, and emission magnitude. The present study was conducted in Bangalore, India, which has recently witnessed elevated pollutant concentrations across the city. The study focused on investigating the effect of land use (residential, industrial, and traffic intersections) on personal exposure to PM5 of street vendors in Bangalore and quantifying the contributing sources using principal component analysis (PCA). Furthermore, the study investigated the possibility of occurrence of various elemental compounds and atmospheric reactions in different land uses. Monitoring of exposure of street vendors was conducted at the three land-use subgroups for 45 days using a personal sampler. The samples were analyzed for 15 elements using inductively coupled plasma optical emission spectroscopy. The results indicated that the exposure concentrations of PM5 of street vendors at the traffic intersection, residential, and industrial areas were 548.2 ± 101.5, 190.1 ± 48.5, and 527.7 ± 131.6 µg/m³, respectively. Spearman rank coefficients among elements showed significant variation in correlation for diverse land uses, suggesting the occurrence of potentially different chemical reactions and source contributions at different locations. The PCA at the traffic intersection, residential, and industrial area indicated major contributions from road dust resuspension, construction activities, and metal industries, respectively.

Soft drinks–industry wastewater (SDIW) contains high concentrations of sugar (420–487 mg/L) and sodium (320–397 mg/L), has high pH (∼9), and contains biorefractory pollutants. Therefore, rapid and effective techniques are required for its treatment. In the present study, SDIW was subjected to microwave (MW) photocatalysis (PC) using electrodeless discharge lamps, and the outcomes were compared with other oxidative and photochemical advanced oxidation processes, including oxidation, MW oxidation (MWO), and ultraviolet–titanium dioxide PC, in terms of the removal efficiency of organics based on chemical oxygen demand (COD), total phosphate (TP), and total nitrogen (TN). The mineralization of organics was ∼3.5 times higher in the MWPC and MWO systems compared to the oxidation and PC systems. The COD removal efficiency after 60 min using the oxidation, PC, MWO, and MWPC systems was 22.7%, 25.41%, 79.36%, and 87.3%, respectively. Direct photolysis using UV (using 486 kJ/mole of energy) and photocatalytic degradation using increased hydroxyl radicals in the presence of MWs was the primary degradation mechanism in the MWPC system. The TP removal efficiency in the oxidation, PC, MWO, and MWPC systems was 15%, 40%, 50%, and 60%, respectively. The respective TN removal efficiencies for the four systems were 40%, 58%, 82%, and 85%. The main mechanism for organics, TP, and TN removal in the MWPC system involved the direct disruption of the chemical bonds of the organic molecules, photocatalytic phosphate reduction, and breaking of the primary amine bond in the organic nitrogen using the high-energy plasma and hotspots that formed in the MW-based systems. The electrical energy consumed by the systems [electrical energy per order (E_EO)] occurred in the order PC > MWO > MWPC, with respective values of 14,614, 6,919, and 4,526 Rs/kg COD removal.

Urban soils get contaminated due to the unscientific disposal of industrial effluents and solid waste, contaminating the soil with heavy metals. Contaminated soils need to be remediated to avoid the ingestion of toxic heavy metals. The immobilization of heavy metals is one of the methods to remediate contaminated soils. The primary purpose of this study was to explore the effect of grain size distribution (GSD) of soil on the efficiency of immobilization of toxic heavy metals in soil when nano zerovalent iron (nZVI) is used to immobilize the metals. Preliminary studies conducted with the 2³ factorial design method confirmed that GSD is a significant factor along with the level of contamination and nZVI dosage in the immobilization of heavy metals in soil. Experiments were conducted with cadmium (Cd) and nickel (Ni), the toxic heavy metals, and three soils with different finer particles than 75 µm. Immobilization efficiency was obtained by comparing the leachability of contaminated and treated soil samples using the toxicity characteristic leaching procedure. Reduction in available fraction and variation in the speciation of heavy metals was observed through the sequential extraction procedure. The response surface methodology was adopted for analysis with three levels of GSD, contamination, and nZVI dosage. For Cd, a reduced cubic model was the best fit with a coefficient of determination (R-square) of 0.93, and for Ni, a quadratic model was the best fit with an R-square of 0.92. Both these models were validated experimentally. The efficiency variation followed an optimum curve concerning GSD, contamination level, and the nZVI dosage. For multimetal contamination, the immobilization efficiency gradually decreased from 10% finer to 90% finer soil, both in the case of Cd and Ni. It was observed that for both single metal and multimetal contamination, the interaction between soil and the nZVI plays a vital role in immobilization along with the factors considered.

Abstract

Microbial-induced calcite precipitation (MICP) is a soil improvement technique that has shown great potential in several geotechnical applications in the previous decade. Some factors that led to the improved strength included cementation concentration. The combined influence of these factors with the cementation reagent was paramount to the calcite precipitation level within soil grain contact of a biotreated compacted fine-grained soil. In this study, the influence of the concentration of the cementation solution [(CCS) 0.25, 0.5, 0.75 and 1.00 M], curing time [(CT) 24 h, 3, 7, 14, and 28 days], and molding water content [MWC (9.8%–19.6%)] of biomediated lateritic soil or lateritic soil that was bioinfused with ureolytic microbes at different suspension densities (cells/mL) and compacted with Reduced British Standard Light (RBSL), British Standard Light (BSL), West African Standard (WAS), and British Standard Heavy (BSH) energy, respectively, were evaluated. In addition, this study focused on unconfined compressive strength (UCS). The results showed an increased UCS with the corresponding average calcite content up to peak values at 0.5 M cementation concentration for the five considered bacterial cells/mL. In addition, the results showed a linear relationship between UCS and average calcite content for the CCS that were considered. The effect of the curing period on UCS was marginal within individual cementation concentrations regardless of bacterial cells/mL. The UCS of the specimen that contained the optimal 0.5 M cementation concentration increased with higher bacterial cells/mL but decreased with the MWC. The qualitative microanalysis that used scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses that evaluated the untreated and biotreated specimens showed the formation of calcite, which increased the soil strength by blocking the soil pores through grain–grain contacts.

Practical Applications

Microbial-induced calcite precipitation (MICP) techniques have been carried out successfully in numerous studies under laboratory conditions for civil engineering infrastructures. However, data on its application in engineered municipal solid waste (MSW) containment that uses lateritic soil remains limited. Upscaled MICPs have been used in geotechnical applications. In addition, the increased attention, expectations or both of other application areas has established how the previous laboratory scale studies corroborated the field expectations and applications. This study showed the applicability of a ureolytic MICP process (i.e., through ex situ biostimulation). This was used to improve the shear strength performance of lateritic soil under several selective coupled factors when the overburden stress in a barrier waste containment application was contained. The requirements of materials for use in satisfactory waste containment include a number of factors; however, this study was limited to shear strength performance. This is one of the significant criteria that are used when delineating a suitable acceptable zone or limit when materials for engineered barrier systems are selected. This laboratory scale study could provide practical applications for biotreated lateritic soils, which satisfy the strength requirement (i.e., ≥200 kN/m²) for MSW containment applications.

N-doped carbon (CP) was synthesized through carbonization of a polyaniline (PANI) prepared using interfacial polymerization. Different forms of PANI, such as emeraldine salt (ES), emeraldine base (EB), and aniline oligomers, were carbonized at different temperatures (700°C–1,000°C) in the presence of the N₂ atmosphere to form CPs (CP7–CP10). CP prepared under different conditions was applied as adsorbent for antibiotics. It was observed that ES-PANI carbonized at 1,000°C formed graphitic N-doped carbon (CP10) and showed better adsorption of metronidazole (MET) compared with other CPs. The adsorption results showed that CP10 derived from the ES-form of PANI (PA1) achieved ∼97% MET removal within 5 min following pseudo-second-order kinetics (k = 0.347 g mg⁻¹ min⁻¹). CP10 has a high specific surface area (S_a) of 800.65 m² g⁻¹ and high graphitic nitrogen content (52.26% of total N) responsible for the rapid adsorption of the antibiotics through π-π electron acceptor-donor interaction, hydrogen bonding, and electrostatic attraction. In addition, CP10 has an adsorption capacity of 200.8 mg g⁻¹ for MET. The highest activity of CP10 was due to high graphitic nitrogen content and high S_a. However, CPs formed from EB-PANI and aniline oligomers did not perform efficiently due to low S_a and graphitic nitrogen content. Similarly, CP10 applied for the adsorption of the ciprofloxacin (CIP) and tetracycline (TET) achieved maximum adsorption capacity of 344.8 and 263.2 mg g⁻¹, respectively. Therefore, CP10 is a promising adsorbent for removing emerging pollutants from an aqueous solution.

Landfill leachate is of environmental concern due to its high levels of organic and inorganic pollutants. Leachate treatment using natural materials such as cover soil of sandy loam texture, laterites, and compost was performed through soil column experiment. This study aims to analyze the natural attenuation of physiochemical parameters such as pH, turbidity, electrical conductivity, biological oxygen demand, chemical oxygen demand (COD), ammonia, phosphate, heavy metals (Fe, Ni, and Pb) of leachate in the cover soil of the Sisdole landfill site (SLS) and enhanced cover soil, that is, a mixture of SLS soil, compost, and laterite (SCL). In addition, this study analyzes the response of the cover soil after infiltration of leachate in terms of physiochemical parameters. Two columns of specific heights and diameters were taken and leachate was fed manually into the soil columns to evaluate the attenuation of the physiochemical parameters of leachate by standard methods after passing through SLS and SCL soil. From the results, it was observed that the removal efficiency was the highest for the first three days (>70%), after which the capacity of the soil to attenuate leachate parameters decreased. Consistent and greater removal efficiency was seen for heavy metals and phosphate for the SLS soil column. Amendments such as laterite and compost were added to cover soil to enhance the performance of SLS soil. The results showed a consistent and greater removal percentage for COD and ammonia in SCL than in SLS soil column. It was observed that that studied soil (sandy loam) is capable of removing pollutants from leachate to a satisfactory level and adding materials with higher sorption capacity such as laterite and compost to sandy loam soil can improve removal ability for certain selected parameters.

In the last few decades, vermifiltration has become a well-known alternative to conventional wastewater remediation methods owing to its economic viability and environmental sustainability. In the present study, we examined the effect of the organic strength [i.e., chemical oxygen demand (COD)] of an influent (i.e., synthetic dairy wastewater) and the depth of the vermibed on the performance of a macrophyte-assisted vermifilter (MAVF), in terms of organic-carbon and nitrogen removal. The to-date inadequately explored possible N-removal pathways in the designed MAVF system were also investigated. The designed MAVF, with its vertical subsurface flow, achieved maximum COD removal up to 96.5 ± 1.5% when the influent COD and vermibed depth were at 1,400 ± 89 mg/L and 20 cm, respectively. Similarly, the MAVF produced a significant reduction in the ammonium–nitrogen ( ${\mathrm{NH}}_4^{+}$–N) and total nitrogen (TN) concentrations, whereas the effluent nitrate ( ${\mathrm{NO}}_3^{-}$)–N concentration was markedly enhanced compared to the influent concentration. The experimental run, using an influent COD of 1,400 ± 89 mg/L and a vermibed depth of 50 cm, yielded the maximum ${\mathrm{NH}}_4^{+}$–N conversion efficiency, at 96.4 ± 1.2%. In the same experimental run, the greatest increase in the ${\mathrm{NO}}_3^{-}$–N concentration (21.5 ± 3 times its influent concentration) was recorded. The TN removal reached a maximum of 71.4 ± 0.7% in the experimental run, with an influent COD of 2,900 ± 94 mg/L and a vermibed depth of 50 cm.

The accumulated water in the drainage layer of the municipal solid waste landfill veneer cover system becomes the principal cause of the failure of landfill cover. In this study, seismic stability evaluation is carried out using the pseudostatic approach considering direct sliding and uplifted floating failures. The factors of safety against direct sliding failure (FS_ds) and uplifted floating failure (FS_uf) are estimated considering hydrostatic and hydrodynamic pressures. Hydrodynamic pressures acting along the failure planes are computed using Westergaard’s theory. The different cases based on the height of accumulated seepage levels in the drainage layer (h_w) are considered in the analysis. The angle of the sliding plane (ψ) for direct sliding failure and the failure ratio (Ω) for the uplifted floating failure are evaluated to determine the critical values of FS_ds and FS_uf. It is observed that the immersion ratio (I_r) is the most important parameter that significantly affects the factor of safety against both failure modes (FS_ds and FS_uf) under seismic loading. The results of the present study under static loading are compared with the available results in the literature. The effects of the slope angle (θ), the ratio of the thickness of the cover soil layer to the height of the landfill (h/H), the stability number (c/γ_satH), the horizontal seismic acceleration coefficient (k_h), and the ratio of vertical to horizontal seismic acceleration coefficients (k_v/k_h) on FS_ds and FS_uf are presented for different values of immersion ratios (I_r). The magnitude and the direction of seismic inertia forces also govern the factor of safety values against both direct sliding and uplifted floating failure modes. The design charts are established to estimate the allowable thickness of the cover soil layer (h) for different values of immersion ratios by targeting the factors of safety, FS_ds and FS_uf ≥ 1.15. This condition ensures the safety of the landfill veneer cover system against direct sliding and uplifted floating failures simultaneously.

Landfill liner materials are required to provide reliable hydraulic performance for very long times after construction, and at least for the design lifespan of the facility. To meet this objective, liner systems must retain their low hydraulic conductivity over their service lives. In this paper, we report on the durability aspects of iron-ore tailings (IOT)–bentonite mixtures in extended hydraulic conductivity experiments. The hydraulic conductivity tests were conducted on mixtures containing 20%, 25%, 30%, 35%, and 40% bentonite, compacted at 2% wet of optimum by the British standard light (BSL) effort, and permeated with municipal solid waste (MSW) landfill leachate (electrical conductivity = 25.60 mS/m, pH = 7.94) with or without prehydration for a duration of 120 days. Under these influences, permeation with leachate showed no detrimental effect on mixtures with 25% and 30% bentonite, but was rather beneficial in reducing the hydraulic conductivity (k) values of the two mixtures at the end of testing by two orders of magnitude to 4.19 × 10⁻⁸ and 9.25 × 10⁻⁹ cm/s for the prehydrated specimens and 2.4 × 10⁻⁸ and 9.9 × 10⁻⁹ cm/s for the nonprehydrated specimens. For mixtures containing 20%, 35%, and 40% bentonite, k values representing a 1.6 times decrease from the average were recorded for both the prehydrated and nonprehydrated conditions at the end of testing. Further analysis showed that prehydration had a slightly substantial effect on those specimens containing 20%, 35%, and 40% bentonite, whereas it had a minor effect, if any, on mixtures with 25% and 30% bentonite. In terms of durability, only mixtures containing 25% and 30% bentonite that consistently maintained low k values up to the end of testing are projected to be effective as liner materials in the construction of geological repositories for MSW. Regarding the hydraulic conductivity characteristics of the mixtures upon exposure to the combined effects of leachate and the elevated temperatures expected in landfill conditions, all mixtures maintained relatively good hydraulic performance, exhibiting a decrease in hydraulic conductivity with time.

The main purpose of treatability testing is to tailor a proposed remedial approach and related testing to site-specific conditions to ensure the maximum possible applicability of the bench-scale results at the full scale, and thus the success of the approach. One such adaption involves the use of modified (“M”) EPA 1315 tests to assess the leaching of volatile organic compounds (VOCs) under simulated brackish-water conditions to provide insights into the mass transfer rates that result from the in situ stabilization/solidification (ISS) of sediments at coastal sites heavily impacted by nonaqueous-phase liquids (NAPLs). As shown in this study, the use of saltwater (SW) baths during EPA 1315M testing can result in the formation of surface crusts on ISS samples and mass-transfer reductions in naphthalene, this effect being very pronounced in Gowanus Canal sediments. At the same time, the pH of the SW bath can drop from greater than 11 for a corresponding deionized water (DIW) bath to approximately 8, thus enabling biological activity. The newly formed ISS sample crusts (primarily aragonite and brucite) were similar in many respects to crusts that form on concrete under marine exposure conditions, based on mineralogical and x-ray-based analyses. However, surprisingly, while some SW baths were shown to be biologically active based on gene-probing analyses, petroleum hydrocarbon degraders, when present, did not necessarily reduce the observed leaching rates. The authors concluded that, while the surface crusts do appear to be associated with mass-transfer reductions, to varying degrees, remedial design should conservatively proceed on the basis of EPA 1315M tests utilizing DIW baths only, and any crusts potentially occurring under field conditions constitute an inherent benefit.

Over the years, the level of healthcare services has evolved worldwide. Simultaneously, more pharmaceutical ingredients are being detected in water bodies. Pharmaceutical compounds have been detected in water resources in Jordan at levels similar to European and US waters. Although environmental protection regulatory frameworks have generally reached an influential level, pharmaceutical waste management is still facing several challenges, rendering its regulatory framework weak. This study evaluates the current regulatory framework and its application in guiding pharmaceutical waste management in Jordan. The regulatory framework evaluation study consisted of reviewing the regulations according to the level of coverage, integration, overlap, and presence of conflicts. The compliance with the regulatory framework was evaluated using a semistructured interview with pharmaceutical waste generators and conducting a Strengths, Weaknesses, Opportunities, and Threats (SWOT) analysis. The study showed that the regulatory system does not contain specific regulations for pharmaceutical waste management. Nevertheless, the regulations consider industrial and medical pharmaceutical waste types of hazardous waste. The study shows that pharmaceutical wastes are regulated by two main authorities: The Ministry of Environment and the Ministry of Health. These authorities supervise pharmaceutical waste at manufacturing and health service facilities. The study revealed that the regulations of these authorities overlap and lack multirule integration. Site visits and interviews revealed that the lack of documentation and record keeping are the main challenges facing pharmaceutical waste tracking at the source. Site visits showed that the current disposal methods do not eradicate pharmaceutical waste threats to the environment properly. The current pharmaceutical waste management practices do not provide a reliable and infallible system. The study indicated a dire need for devising a waste management auditing system, applying complete waste destruction methods, a compliance incentive system, and introducing a reliable municipal pharmaceutical waste recovery system when applicable.