Microwave (MW) remediation of hydrocarbon contaminated soil using spent graphite - An approach for waste as a resource

Feasibility of microwave remediation of simulative crude oil-contaminated soil assisted by bluecoke-based modifiers

Microwave (MW) remediation of organics-contaminated soil technology offers the advantages of high efficiency and minimal damage, representing a new approach of soil thermal remediation. However, soil, being a weak MW-absorbing medium, struggles to convert MW energy into thermal energy, thus failing to attain the necessary temperature for thermal remediation. This paper prepared two new bluecoke (BC)-based modifiers (KHCO3@BC and KHCO3/MnO2@BC) to address temperature problem of MW remediation, as well as enhance soil quality. Their composition, structure and electromagnetic properties were analyzed to investigate their role in assisting with the MW remediation of an artificially crude oil-contaminated soil were investigated. Additionally, the industrial feasibility of MW remediation was addressed for the first time. The results showed that the KHCO3 and MnO2 particles in the two modifiers were covered on the BC surface and exhibited local agglomeration. Their carbon crystalline grain size increased, and the electromagnetic properties were weaker than those of the BC. Following 10 min of MW remediation assisted by KBC or KMnBC, the remediation temperatures exceeded 300 °C, with the removal rates of PHs reaching 76.16% and 88.31%, respectively. The organic matter content, soil potassium and mechanical fraction of the remediated soil were improved, but soil acidification still needed to be further addressed. The industrial application analysis indicated that the technical process and techno-economics of MW remediation of crude oil-contaminated soil were feasible, suggesting significant potential for the large-scale industrial application.

Molecular and metabolic characterization of petroleum hydrocarbons degrading Bacillus cereus

Hydrocarbon constituents of petroleum are persistent, bioaccumulated, and bio-magnified in living tissues, transported to longer distances, and exert hazardous effects on human health and the ecosystem. Bioaugmentation with microorganisms like bacteria is an emerging approach that can mitigate the toxins from environmental sources. The present study was initiated to target the petroleum-contaminated soil of gasoline stations situated in Lahore. Petroleum degrading bacteria were isolated by serial dilution method followed by growth analysis, biochemical and molecular characterization, removal efficiency estimation, metabolites extraction, and GC-MS of the metabolites. Molecular analysis identified the bacterium as Bacillus cereus, which exhibited maximum growth at 72 hours and removed 75% petroleum. Biochemical characterization via the Remel RapID™ ONE panel system showed positive results for arginine dehydrolase (ADH), ornithine decarboxylase (ODC), lysine decarboxylase (LDC), o-nitrophenyl-β-D-galactosidase (ONPG), p-nitrophenyl-β-D-glucosidase (βGLU), p-nitrophenyl-N-acetyl-β-D-glucosaminidase (NAG), malonate (MAL), adonitol fermentation (ADON), and tryptophane utilization (IND). GC-MS-based metabolic profiling identified alcohols (methyl alcohol, o-, p- and m-cresols, catechol, and 3-methyl catechol), aldehydes (methanone, acetaldehyde, and m-tolualdehyde), carboxylic acid (methanoic acid, cis,cis-muconic acid, cyclohexane carboxylic acid and benzoic acid), conjugate bases of carboxylic acids (benzoate, cis,cis-muconate, 4-hydroxybenzoate, and pyruvate) and cycloalkane (cyclohexene). It suggested the presence of methane, methylcyclohexane, toluene, xylene, and benzene degradation pathways in B. cereus.

Quantifying the roles of thermal volatilization and decomposition in microwave remediation of polycyclic aromatic hydrocarbon-polluted soil and modeling remediation effectiveness

Microwave irradiation is a promising technology for the remediation of soil contaminated by organic contaminants. However, the roles of volatilization and decomposition in microwave removal of polycyclic aromatic hydrocarbons (PAHs) in soil have not yet been quantitatively determined. A model describing the removal efficiency of benz(a)anthracene (BaA) at different treatment times and varied conditions was constructed, wherein BaA removal efficiency was positively and linearly correlated with soil temperature. BaA removal in soil was attributed to thermal volatilization (97.8%) and decomposition (2.2%). Radicals such as ∙OH and ∙O 2- were found to initiate BaA decomposition, the pathway of which was elucidated through HPLC-MS analysis, revealing benz(a)anthracene-7,12-dione as the main intermediate product. The new ideas and perspectives founded in this study offer theoretical support for microwave remediation of organic compound-contaminated sites.

Bentonite addition enhances the biodegradation of petroleum pollutants and bacterial community succession during the aerobic co-composting of waste heavy oil with agricultural wastes

Soil contamination with petroleum significantly threatens the ecological equilibrium and human health. In this context, aerobic co-composting of waste heavy oil with agricultural wastes was performed in the present study to remediate petroleum pollutants through four treatments: CK (control), T1 (petroleum pollutant), T2 (petroleum pollutant with bentonite), and T3 (petroleum pollutant with humic acid-modified bentonite). Comprehensive analyses were conducted to determine the physicochemical parameters, enzymatic activities, removal of petroleum pollutants, microbial community structure, and water-extractable organic matter in different composting systems. Structural equation modeling was employed to identify the key factors influencing the removal of petroleum pollutants. According to the results, petroleum pollutant removal percentages of 44.94%, 79.09%, and 79.67% could be achieved with T1, T2, and T3, respectively. In addition, the activities of polyphenol oxidase (51.21 U/g) and catalase (367.91 U/g), which are the enzymes related to petroleum hydrocarbon degradation, were the highest in T3. Moreover, bentonite addition to the treatment increased the nitrate nitrogen storage in the compost from 10.95 mg/kg in T1 to 18.63 and 17.41 mg/kg in T2 and T3, respectively. Humic acid-modified bentonite could enhance the degree of compost humification, thereby leading to a higher-quality compost product. Collectively, these findings established bentonite addition as an efficient approach to enhance the compost remediation of petroleum pollutants.

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.

Synthesis of zero-valent iron supported with graphite and plastic based carbon from recycling spent lithium ion batteries and its reaction mechanism with 4-chlorophenol in water

Graphite and plastic recycled from spent lithium ion batteries were used to synthesize zero-valent iron/graphite (ZVI/G), zero-valent iron/plastic-based carbon (ZVI/P), and zero-valent iron/graphite and plastic-based carbon (ZVI/GP) with iron oxide through carbothermic reduction. The aim of preparing these catalysts is to improve the performance of ZVI in the removal of 4-chlorophenol (4-CP) in water through heterogeneous Fenton reactions. The structural and textural properties of materials were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N₂ adsorption/desorption, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The synthesis procedure successfully disperses ZVI particles on the synthesized materials. The combination of graphite and plastic-based carbon in ZVI/GP resulted in the best 4-CP removal performance. The degradation data fitted pseudo-first-order kinetic well. The Increase in the ZVI/GP dosage and the hydrogen peroxide concentration enhanced the 4-CP removal due to the increase in the amount of Fe²⁺ ions and reactive sites. Acidic pH increased the 4-CP removal percentage due to the high H⁺ concentration. The increase in the temperature favored the •OH formation and facilitated the 4-CP removal. The reaction energy of ZVI/GP reaches 53.54 kJ mol^-1, which is competitive among the iron catalysts reported in literatures, and showing the 4-CP removal is reaction-controlled process. This study shows a promising way of recycling graphite and plastic in spent LIBs to prepare ZVI materials for wastewater treatment with the advantages of improved conductivity by graphite and added functional groups by plastic based carbon.

Microwave-induced steam distillation (MISD) remediation in petroleum hydrocarbon-contaminated sites: From process improvement to pilot application

The process improvement, a pilot remediation test and the decontamination mechanism of microwave-induced steam distillation (MISD) for petroleum hydrocarbons (PHs) removal were conducted. Processes of multistage steam distillation and carbon reinforcement were compared to determine the best remediation process. Pilot project was then carried out to explore the applicability of MISD in site-scale remediation. The remediation efficiency, procedures and influencing factors of site-scale MISD project were studied by monitoring variations of soil moisture, temperature and PHs concentrations. Furthermore, the decontamination mechanisms of PHs were clarified based on kinetic analysis. The results showed that the multistage steam distillation could improve 10%∼15% remediation efficiency, and the carbon reinforcement could shorten remediation duration of each steam distillation stage by 50%. Pilot MISD project adopted multistage steam distillation process and went through four (initial, rapid heating-up, gentle heating-up and quasi-equilibrium) remediation stages (overall temperature ≤100 °C). The final PHs removal rate was about 60%, which would get better with greater proportion of low boiling points components and stronger vapor extraction. Kinetic studies showed that PHs was removed by steam stripping and limited by intraparticle diffusion in the "steam distillation zone", while local high temperature (＞100 °C) greatly improved PHs volatilization and provided activation energy for PHs desorbed and degraded in the "selective heating zone".

Polycyclic aromatic hydrocarbons (PAHs) in mangrove ecosystems: A review

Polycyclic aromatic hydrocarbons (PAHs) are organic pollutants of increasing concern in the different fields of the environment and human health. There are 16 of them that are recognized as priority pollutants by the US environmental protection agency due to their mutagenic and carcinogenic potentials. Due to their hydrophobicity and stability, they are persistent in the environment and can be transported over long distances. Their toxicological effects on multiple species, including humans, as well as their bioaccumulation in the food web became major topics in organic pollutants research this last decade. In the environment, multiple studies have been conducted on their accumulation in the soil and their degradation processes resulting in numerous review papers. However, the dynamics of PAHs in mangrove ecosystems is not yet completely understood. In this review paper, an exhaustive presentation of what is known about PAHs and their transfer, accumulation, and degradation in mangrove ecosystems is offered. This article brings to light the knowledge already acquired on the subject and the perspective research necessary to fully comprehend PAHs dynamics in mangrove ecosystems.

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

Current thermal desorption practices of hydrocarbon-contaminated soils focus on remediation efficiency and cost, with little systematic assessment of the reuse value of treated soils. This study evaluated various integrated indices of treatment cost and reuse of treated soils at three desorption temperatures. Various typical engineering and ecological characteristics closely related to soil reusability were selected to analyze the changes in various treated soils, including shear strength, Atterberg limits, particle size distribution, permeability, soil carbon, and soil biomass. A sustainability evaluation tool was developed for the greener disposal of hazardous soils considering both the treatment cost and reuse indices. Such an evaluation led to the conclusion that the contaminated soils treated at 350 °C generated the highest soil reusability with an excellent remediation efficiency. The sensitivity analysis confirmed that the tool had better stability in a common situation where the weight of the remediation cost was heavier than the soil reusability. Meanwhile, published data were input into the tool to validate its applicability under different scenarios. The results were consistent with the qualitative assessment of the literature. The tool can quantitatively select a more sustainable desorption method for the disposal and reuse of hazardous soils.

Insights into removal efficiency and mechanism of microwave remediation of soils contaminated with polyaromatic hydrocarbons of low molecular weight assisted by bluecoke-based conditioner

Microwave remediation of polyaromatic hydrocarbons-contaminated soils has garnered extensive attention owing to its cost effectiveness, time saving, homogeneous heating, and low energy consumption. The prepared bluecoke-based conditioner (KHCO₃@BC) was used in this study to enhance microwave remediation and improve the naphthalene (NA) removal efficiency and soil properties. We investigated the optimal conditions, including the heating time, microwave power, bluecoke-based conditioner, initial concentration of NA, and moisture content of the soils. We evaluated the removal efficiency of NA and compared the remediation products after the addition of bluecoke, KHCO₃, and KHCO₃@BC conditioners. The results showed that the removal efficiency of NA reached 96.46% under the following optimized conditions: heating time of 20 min, microwave power of 700 W, 2 g of KHCO₃@BC conditioner, initial NA concentration of 1 wt%, and soil moisture content of 4 wt%. The KHCO₃@BC conditioner improved the contents of total K and fast-acting K during microwave remediation, and the mechanical components of the remediation soils were also optimized significantly. We proposed a feasible mechanism and evaluated the main reasons for the removal of NA from the soils based on the mechanical components of remediation soil and the remediation products, namely, gas stripping, boiling vaporization of NA, and breakage of soil grains by thermal stress.

A multi-aspect application of microwave radiation on rehabilitating and improving the geotechnical properties of polluted-sand-clay mixture

Crude oil products are among the most common pollutants of soils which can drastically affect the engineering properties of soils. In the current study, a series of laboratory tests were conducted to investigate the interaction between crude oil and sandy soil with clay and the effect of crude oil, crude oil residence time, absorbent additives type and content, microwave power, specimen weight, maximum grain size and fine grain fraction on the removal efficiency of pollution through microwave radiation to extract optimum values for potential and high efficiency in hydrocarbon removal. The present study also investigated geotechnical properties, including cohesion, internal friction angle, shear strength in three conditions before and during pollution and after cleanup utilizing direct shear and static triaxial tests. The results showed that the presence of clay particles, oil content and saturation effect in the soil could significantly control the engineering soil behavior. In the presence of 4% crude oil in direct shear tests, the whole oil content is accumulated on clay particles due to the high specific area of clay particles, reducing the cohesion and the internal friction angle. By contrast, beyond the 4% of crude oil, sand particle in the soil was the controlling factor of the whole behavior of the mixture. In triaxial tests, the trend of soil parameters is almost similar to direct shear tests by increasing crude oil, except that, with an increase of 4% of oil, the friction angle of the soil increases due to the presence of a large number of flocculated clay particles.

Cost reduction strategies in the remediation of petroleum hydrocarbon contaminated soil

Petroleum hydrocarbon spill on land pollutes soil and reduces its ecosystem. Hydrocarbon transport in the soil is aided by several biological, physical, and chemical processes. However, pore characteristics play a major role in the distribution within the soil matrix. Restoring land use after spills necessitates remediation using cost-effective technologies. Several remediation technologies have been demonstrated at different scales, and research is ongoing to improve their performances towards the reduction of treatment costs. The process of removing the contaminants in the soil is through one or a combination of containment, separation, and degradation methods under the influence of biological, physical, chemical, and electrically-dominated processes. Generally, performance improvement is achieved through the introduction of products/materials and/or energy. Nevertheless, the technologies can be categorized based on effectiveness period as short, medium, and long term. The treatment cost of short, medium, and long-term technologies are usually in the range of $39 - 331/t (/tonne), $22 - 131/t, and $8 - 131/t, respectively. However, the total cost depends on other factors such as site location, capital cost, and permitting. This review compiles cost-saving strategies reported for different techniques used in remediating petroleum hydrocarbon polluted soil. We discuss the principles of contaminant removal, performance enhancing methods, and the cost-effectiveness analysis of selected technologies.

Performance and mechanisms of microwave-assisted zerovalent iron/pyrite for advance remediation of strongly alkaline high Cr(VI) contaminated soil

Strongly alkaline high Cr(VI) contaminated (SAHCR) soil poses a high risk to the environment and public health, yet lacks rapid and efficient remediation technology. In this study, a novel approach combining microwave irradiation with zerovalent iron/pyrite (FeS₂/ZVI) was developed for the remediation of SAHCR soil. The results indicated that fast and efficient remediation of the SAHCR soil was achieved by microwave irradiation-assisted FeS₂/ZVI, with 99.9% of removal rate of Cr(VI) within 10 min, and Cr(VI) concentration from 3900.8 plummeted to 2.38 mg kg^-1. The data of Cr(VI) reduction kinetics at different temperatures indicated that the activation energies (E_a) for microwave-FeS₂/ZVI system was 27.4 kJ mol^-1, 28.5% lower than that without microwave irradiation, suggesting that in addition to the heating effect of microwave, the accelerated Cr(VI) reduction also comes from the catalytic effect of "hot spots" on FeS₂/ZVI under microwave irradiation. Furthermore, it was demonstrated that microwave irradiation promoted the transformation of reduced Cr(III) into the stable FeCr₂O₄ mineral and the excellent long-term stability of the remediated SAHCR soil. These findings can provide a perspective for advanced remediation of the difficult-to-treat SAHCR soil by the synergism of microwave irradiation with the iron-sulfur based reducing materials.

Removal of Total Petroleum Hydrocarbons from Contaminated Soil through Microwave Irradiation

In this study, we investigated the removal mechanism of total petroleum hydrocarbons (TPH) from soil by microwave heating. TPH contaminated soil was investigated to determine the desorption behavior of five carbon number-based fractions of TPH. The applied operating microwave power density influenced the final temperature that was reached during heating. For low operating power density applications, microwave effectiveness was limited due to the soil’s dielectric properties, which exhibited a direct relationship with temperature variation. Soil particle distribution could be attributed to permeability, which significantly influenced the evaporation of contaminated soil during the microwave treatment. The results indicate that the activation energy was correlated with the influence of particle size. The removal efficiency of the coarse soil reached 91.1% at 15 min, whereas that of fine soil was low. A total of 30 min had passed, and a removal efficiency of 71.2% was found for the fine soil. Residual TPH concentration was decreased when irradiation time was increased with a removal rate dependent on soil temperature variation. The surface functional groups of the contaminated soil were influenced by microwave irradiation, and changes in the hydrocarbon fraction affected contaminant removal.

Comparison of the behavior of ZVI/carbon composites from both commercial origin and from spent Li-ion batteries and mill scale for the removal of ibuprofen in water

Zero valent iron/carbon composites were successfully synthesized from commercial iron oxide and graphite (ZVI/C) and also by using graphite obtained from spent Li-ion batteries and iron oxide from mill scale (ZVI/C-X) as a new approach for the valorization of these waste. The composites were synthesized through carbothermic reactions and tested as catalysts for the degradation of ibuprofen from water by Fenton reaction. The optimal conditions for synthesizing ZVI/C composites were a temperature of 1000 °C maintained for 2 h. The structural, and textural features of ZVI/C with different ZVI mass ratios were characterized by different techniques. ZVI/C composites with higher ZVI mass ratios showed higher degradation rates for the removal of ibuprofen both in presence and absence of H₂O₂. Moreover, ZVI/C-X composite, obtained from industrial waste, showed activity even after four consecutive cycles of use with very low concentration of iron ions in solution after reaction (4.8 mg L^-1 after 4 h), which supports the high stability and low Fe-lixiviation of ZVI/C-X composite. The results of this study prove the possibility of synthesizing composites using graphite from spent Li-ion batteries and iron oxide from mill scale, and their potential for the degradation of ibuprofen in water, with comparable activities to those obtained from commercial feedstocks.

Preparation of 3D network CNTs-modified nickel foam with enhanced microwave absorptivity and application potential in wastewater treatment

Multi-walled carbon nanotubes (MWCNTs) modified nickel foams (MWCNTs-NF) were developed with an electrophoretic deposition methodology for microwave (MW) assisted catalysis and processing enhancement. A nickel foam (NF) was selected to serve the dual purpose both as the MW absorbing catalytic materials and the matrix for MWCNTs loading in order to maximize the recyclability of the catalysts. The effects of electrophoretic voltage and concentration of electrophoretic fluid on the morphology and deposition characteristics of MWCNTs on the NF matrix were investigated. It was found that the MWCNTs-NF composite material resulted in strong enhancement of MW absorptivity with synergistic heat-generating effects that were not observed when MWCNTs or NF was exposed to MW alone. The combination of NF and MWCNTs brought a catalytic total organic carbon removal efficiency of 97% in wastewater treatment, while that using bare MWCNTs and NF were only 65.2% and 79.3%, respectively. The coupling of NF with MWCNTs led to the formation of additional MW-absorbing channels and focal sites with strong MW absorptivity, which in turn gave rise to the synergistic MW heating effects. This research highlights the great prospect of the MW-assisted reaction enhancement using the MWCNTs-NF composite material as the catalyst in wastewater treatment and other similar engineering applications.

Editorial: Technically-based use of by-products as a tool to control pollution

This Virtual Special Issue of Journal of Environmental Management dealt with the recycling of waste and by-products, focusing on their use in controlling environmental pollution. The field of research was previously considered as promising, in view of its relevance and the increasing number of papers published in last years. And this Special Issue allows going a step ahead in the matter, with 90 submissions and a number of 48 high quality papers finally accepted and published. We think that it will be useful at a global level, especially for researchers, social partners, and social actors involved in environmental and public health issues related to environmental pollution.