Thermal desorption optimization for the remediation of hydrocarbon-contaminated soils by a self-built sustainability evaluation tool

Low-temperature treatment optimization for diesel-contaminated kaolin: Mutual impacts of generated pyrolytic carbon and particle agglomeration

Efficiency improvement in low-temperature treatment for diesel-contaminated sites is urgent because changes in soil properties and the generation of new substance during the remediation process can influence the duration and energy utilization. This paper focuses on low-temperature treatment optimization based on the mutual impacts of pyrolytic carbon and kaolin aggregation. Results reveal that the peak mass loss rate occurred between 100 and 150 °C, with minimal loss beyond 200 °C. Samples thermally treated at 150-200 °C exhibited darker colors, indicating pyrolytic carbon formation, corroborated by x-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR), and three-dimensional fluorescence spectrum (3D-EEM) analyses. Additionally, diesel contamination influenced the fractal dimension of aggregates by influencing adhesion forces (<10000 mg/kg) and forming liquid bridges (≥10000 mg/kg) in untreated kaolin, resulting in an initial increase and subsequent fall in fractal dimension with increasing concentration. Decline rates of pollutant gas concentration were closely correlated with fractal dimension changes under thermal conditions due to pollutant volatilization and pyrolytic carbon formation. Based on the consistency between fractal dimension and decline rate, two critical remediation concentrations (C0) and temperatures (T0) indices were identified to optimize the low-temperature remediation.

Hydrocyclone-induced classification reduction and spin desorption of contaminated soil remediation with heavy metal and organics

The correlation between soil pollutant concentration and particle size in multi-component contaminated soil containing Cadmium (Cd) and Polychlorinated biphenyls (PCBs) has been investigated. The hydrocyclone classification process has been utilized to reduce the amount of contaminated soil, followed by the application of the hydrocyclone leaching process for the remediation of residual contamination. The results of the hydrocyclone classification process revealed that smaller soil particles have higher concentrations of Cd and PCBs, consistent with the findings from the soil sieving process. For contaminated soil with Cd and PCB concentrations exceeding national standards by 1.1 and 1.7 times, a reduction efficiency of 33.9 % was achieved using five hydrocyclones in series. The spin of soil particles caused full desorption of some surface-positioned pollutants, resulting in a removal efficiency of 32.5 % for Cd and 21.3 % for PCBs in the hydrocyclone leaching process, independent of soil size. Furthermore, the addition of preferred chemicals exhibited remarkable removal efficiencies at 59.2 % for Cd and 40.1 % for PCBs in the hydrocyclone-induced integrated unit. The remediation cost of the hydrocyclone-induced coupled process was reduced by 33.3 % at an actual electrical dismantling site compared to the conventional soil remediation process.

Macroscopic and molecular scale assessment of thermal effects on soil-water interactions of unsaturated diesel-contaminated soils

The soil-water interactions of unsaturated diesel-contaminated soil are crucial for assessing pollution transport during thermal remediation. This paper aims to improve our understanding of this issue by measuring the matric suction of unsaturated contaminated kaolin and carrying out molecular dynamics simulations under thermal conditions. Results show that the increase in pollutant concentration could reduce the water retention capacity of diesel-contaminated kaolin due to changes in electrochemical properties and pore characteristics of samples, as well as a decrease in interfacial tension. On the other hand, pollutants formed a protective film on the kaolinite surface to act as a liquid bridge and prevent water loss at higher temperatures, as confirmed by Fourier transform infrared spectroscopy. With rising temperatures (50-60 °C), kaolin matric suction generally decreased with higher pollutant concentrations, but this trend was not very evident at lower pollution concentrations (0-10,000 mg/kg). In addition, molecular dynamics simulations were used to demonstrate the validity of these findings. The presence of pollutants might strengthen the interaction energy between kaolinite and water (for example, increasing from 276.52 kcal/mol (25 °C) and 267.95 kcal/mol (40 °C) at 8000 mg/kg to 296.54 kcal/mol (25 °C) and 292.46 kcal/mol (40 °C) at 10,000 mg/kg), thereby enhancing the water retention capacity of kaolin. In short, the study revealed that the coating of pollutants on kaolinite could act as a protective film, which binds water molecules through van der Waals and electric field forces and thereby reduces the sensitivity of water retention capacity to temperature.

Comparative life-cycle sustainability assessment of centralized and decentralized remediation strategies at the city level

Remediation of contaminated soil at industrial sites has become a challenge and an opportunity for sustainable urban land use, considering the substantial secondary impacts resulting from remediation activities. The design of soil remediation strategies for multi-site remediation from a regional perspective is of great significance for cities with a large number of brownfields. Centralized and decentralized facilities have been studied in different environmental fields, yet limited research has focused on centralized soil remediation, specifically the treatment of contaminated soil from different sites through the construction of shared soil treatment facilities. This study proposes a framework for comparing centralized and decentralized strategies for contaminated soil remediation based on the integration of life-cycle sustainability assessment and multi-objective optimization. With Zhuzhou, an industrial city in China, serving as an example, results show that after optimization, the centralized scenario can reduce total environmental impacts by 25 %-41 %. In addition, the centralized scenario can reduce economic costs by 27 %-39 %, saving up to 176 million USD. The advantages of the centralized soil remediation strategy include: (1) increased use of soil washing, (2) reduced use of off-site disposal, and (3) reduced construction and efficient utilization of soil treatment facilities. In conclusion, the centralized strategy is relatively suitable for cities or areas with a large number of medium or small-sized contaminated sites. The built framework can quantitatively evaluate multiple sites soil remediation at both the city and individual site level, allowing for a straightforward and objective comparison with the optimal remediation design.

Feasibility of soil oxidation-reduction potential in judging shear behaviour of hydrocarbon-contaminated soil

This study investigates the indicative role of oxidation-reduction potential (ORP) and pH of hydrocarbon-contaminated soils on their shear characteristics, contributing to safer and more efficient ex-situ remediation and management processes. The presence of hydrocarbons alters the soil's shear strength by affecting the hydration shell thickness, fluid's dielectric properties, and ion/electron exchange, as well as the soil's electrochemical force, which in turn affects the ORP and pH. The relationship between hydrocarbon concentrations in contaminated soils (0.1-15%) and corresponding ORP/pH values could be fitted linearly with a good correlation coefficient r (0.978), highlighting the potential of ORP/pH as an indicator for pollutant occurrence. Furthermore, the relationships between ORP/pH and shear strength, as tested in our study and obtained after processing from relevant literature sources, exhibited a strong fit (r = 0.976-0.995). The Mohr-Coulomb criterion modified using the ORP/pH parameter was established, which could improve the fitting effect of these relationships (r = 0.988-0.996), verifying the reliability of the novel criterion and application feasibility of ORP/pH. In future research, this modified criterion can be employed to conveniently assess the shear strength of contaminated soil by considering the shear behaviour of virgin soil and the ORP/pH values of the contaminated soil.

Experimental investigation on electromagnetic induction thermal desorption for remediation of petroleum hydrocarbons contaminated soil

A novel electromagnetic induction low temperature thermal desorption treatment (EMI LTTD) for petroleum hydrocarbons contaminated soil was introduced in this work. The removal rate of total petroleum hydrocarbons (TPH) under various factors, the morphology changes of soils as well as removal mechanism were investigated. Results suggested that increasing the heating temperature significantly increased the removal rate of TPH. At the beginning of 20 min, most of hydrocarbons (93.44-96.91 wt%) was removed with the temperature ranged from 200 °C to 300 °C. Besides, the initial contaminants concentration, particle size and thickness of soil slightly influenced the removal rate of TPH. Desorption kinetic study demonstrated that first-order model was well-described for desorption behavior. Response surface methodology analysis showed the temperature of 216 °C, the residence time of 21 min and the moisture content of 18% was an optimum condition recommended for potentially practical application. Under this condition, the results for the composition of hydrocarbons based on carbon number fractions indicated that the fractions of C10∼C16, C17∼C22 still existed in soil, while C23∼C28 was not detected after EMI LTTD treatment. Proposed mechanism was both hydrocarbons removed by evaporation at any temperature, while parts of heavy hydrocarbons was cracked within the soil close to induction medium, resulting in re-adsorption of light hydrocarbons. A buckwheat germination and growth test indicated that soil treated by EMI LTTD was potential in reutilization for planting.

Impact of simulating real microplastics on toluene removal from contaminated soil using thermally enhanced air injection

This paper investigated the impacts of various real microplastics (MPs), i.e., polyethylene (PE) and polyethylene terephthalate (PET) with different sizes (1000-2000 and 100-200 μm) and different dosages (0.5 and 5% on a dry weight basis), on the toluene removal during the thermally enhanced air injection treatment. First, microscopic tests were carried out to determine the MPs' microstructure and behavior. The PE was mainly a small block, and PET appeared filamentous and sheeted with a larger slenderness ratio. Second, the interactions between MPs and toluene-contaminated soils were revealed by batch adsorption equilibrium experiments and low-field magnetic resonance. The morphological differences and dosage of the MPs impacted soils' total porosity (variation range: 39.2-42.7%) and proportion of the main pores (2-200 μm). Third, the toluene removal during the air injection consisted of compaction, rapid growth, rapid reduction, and tailing stages, and the MPs were regarded as an emerging solid state to affect these removal stages. The final cumulative toluene concentrations of soil-PET mixtures were influenced by total porosity, and those of soil-PE mixtures were controlled by total porosity (influence weight: 0.67) and adsorption capacity (influence weight: 0.33); meanwhile, a self-built comprehensive coefficient of MPs can reflect the relationship between them and cumulative concentrations (correlation coefficient: 0.783).