Sonochemical treatment of simulated soil contaminated with diesel

Exploring the progress and challenges of ultrasonic technology in environmental remediation

Amidst escalating environmental pollution due to accelerated industrialization and urbanization, there is an acute demand for effective and sustainable environmental remediation strategies. Ultrasonic technology, recognized for its green and efficient characteristics, has gained significant prominence in mitigating environmental pollution in aquatic, soil, and atmospheric ecosystems. The review provides a comprehensive analysis of the role of ultrasonic treatment in wastewater treatment, air quality improvement, and soil remediation. We systematically evaluate existing research to assess the effectiveness of ultrasonic technology in degrading pollutants and its potential for large-scale deployment. The review also examines the challenges associated with ultrasonic remediation, including optimizing operational parameters, enhancing energy transfer efficiency, and understanding the unique degradation mechanisms for various pollutants. Furthermore, we discuss environmental and safety considerations, along with the economic implications related to equipment costs and energy consumption. This review aims to contribute to the advancement of ultrasonic technology in environmental remediation by presenting a forward-looking perspective, aligning with the goals of environmental protection and sustainable development.

Soil washing for the remediation of dioxin-contaminated soil: A review

Dioxin-contaminated soil has attracted worldwide attention due to its potential negative impacts on human health and the ecosystem. Thus, technological development aiming at high treatment efficiency and low cost for dioxin-contaminated soil is largely needed. In this review, approximately 200 documents were involved to summarize up-to-date scientific achievements of soil washing technology for the remediation of dioxin-contaminated soil. The mechanisms, advantages, and limitations of physical separation techniques (e.g. mechanical stirring, mechanical shaking, ultrasonication, and froth flotation) and washing solutions (e.g. organic solvents, edible oils, and surfactants) used for chemical extraction were comprehensively reviewed. Froth flotation is very promising for field-scale soil washing, whereas organic solvents show high removal efficiencies (up to 99%) of dioxins from contaminated soil. Further, the combination of physical separation and chemical extraction can help enhance dioxin removal efficiency (from 1.5 to 2 times), reducing energy consumption and cost (about 2 times). Among available remediation technologies for dioxin-contaminated soil, soil washing is truly promising since it has shown high removal efficiency (66-99% different remediation scales) with reasonable cost (46 - 250 USD per metric ton). However, the washed solution and volatile organic compounds generated during the process remain a concern and should be addressed in future research.

Numerical study on the desorption processes of oil droplets inside oil-contaminated sand under cavitation micro-jets

The removal of the adsorbed oil droplet is critical to deoiling treatment of oil-bearing solid waste. Ultrasonic cavitation is regarded as an extremely useful method to assist the oil droplets desorption in the deoiling treatment. In this paper, the effects of cavitation micro-jets on the oil droplets desorption were studied. The adsorbed states of oil droplets in the oil-contaminated sand were investigated using a microscope. Three representative absorbed states of the oil droplets can be summarized as: (1) the individual oil droplet adsorbed on the particle surface (2) the clustered oil droplets adsorbed on the particle surface; (3) the oil droplet adsorbed in a gap between particles. The micro-jet generation during the bubble collapse near a rigid wall under different acoustic pressure amplitudes at an ultrasonic frequency of 20 kHz was investigated numerically. The desorption processes of the oil droplets at the three representative absorbed states under micro-jets were also simulated subsequently. The results showed that the acoustic pressure has a great influence on the velocity of micro-jet, and the initial diameter of cavitation bubbles is significant for the cross-sectional area of micro-jets. The wall jet caused by a micro-jet impacting on the solid wall is the most important factor for the removal of the absorbed oil droplets. The oil droplet is broken by the jet impinging, and then it breaks away from the solid wall due to the shear force generated by the wall jet. In addition to a higher sound pressure, the cavitation bubble at a larger initial diameter is more important for the desorption of the clustered oil droplets. Conversely, the micro-jet generated by the cavitation bubble at a smaller initial diameter (0.1 mm) is more appropriate for the desorption of the oil droplet in a narrow or sharp-angled gap.

Effects of contamination with gasoline on engineering properties of fine-grained silty soils with an emphasis on the duration of exposure

Leaking tanks may lead to severe contamination of their surrounding soil. The geotechnical behavior of the soil varies with the physicochemical processes that occur between the contaminant and the soil. In this respect, studying the geochemical properties of gasoline-contaminated soils and sediments seems to be important for engineering and especially environmental purposes. In this paper, laboratory tests were carried out to examine the effects of crude gasoline contamination on some of the geotechnical properties of a silty soil sampled from the Mashhad plain, located in the northeast of Iran. Tests consisted of basic properties, Atterberg limits, compaction, direct shear, and uniaxial compression tests, which were carried out on clean and contaminated soil samples at the same densities. The contaminated samples were prepared by mixing the soils with crude gasoline in the amounts of 3%, 6%, 9%, and 12% of dry weight and curing periods of 0, 7, 15, and 30 days. Results indicated a decrease in the friction angle and an increase in the cohesion of the soil by increasing gasoline content. Besides, a reduction in the maximum dry density and optimum moisture content was observed in the compaction test. The increase in gasoline percentage up to 6% also showed a direct effect on increasing the liquid limit and plastic limit of silty soil, which decreased thereafter. Moreover, any increase in gasoline percentage had a reverse effect on the modulus of elasticity of the soil. The increase in gasoline percentage up to 3% also had a direct impact on the uniaxial compressive strength of the soil, exceeding which it started to decline. Finally, the effects of contamination duration were examined by testing contaminated samples in periods of 7, 15, and 30 days under natural conditions. The results showed a reverse relationship with all geotechnical properties due to aging and a reduction in the gasoline content due to the evaporation of volatile compounds. Also, the numerical analysis of the laboratory results indicated an increase in settling and the percentage of shear strain beneath the foundation with increasing the contamination level, confirming the laboratory results.

Ultrasound-assisted soil washing processes for the remediation of heavy metals contaminated soils: The mechanism of the ultrasonic desorption

Ultrasound-assisted soil washing processes were investigated for the removal of heavy metals (Cu, Pb, and Zn) in real contaminated soils using HCl and EDTA. The ultrasound-assisted soil washing (US/Mixing) process was compared with the conventional soil washing (Mixing) process based on the mechanical mixing. High removal efficiency (44.8% for HCl and 43.2% for EDTA) for the metals was obtained for the most extreme conditions (HCl 1.0 M or EDTA 0.1 M and L:S = 10:1) in the Mixing process. With the aide of ultrasound, higher removal efficiency (57.9% for HCl and 50.0% for EDTA) was obtained in the same extreme conditions and similar or higher removal efficiency (e.g., 54.7% for HCl 0.5 M and L:S = 10:1 and 50.5% for EDTA 0.05 M and L:S = 5:1) was achieved even in less extreme conditions (lower HCl or EDTA concentration and L:S ratio). Therefore, it was revealed that the US/Mixing was advantageous over the conventional Mixing processes in terms of metal removal efficiency, consumption of chemicals, amount of generated washing leachate, and volume/size of washing reactor. In addition, the heavy metals removal was enhanced for the smaller soil particles in the US/Mixing process. It was due to more violent movement of smaller particles in slurry phase and more violent sonophysical effects. In order to understand the mechanism of ultrasonic desorption, the desorption test was conducted using the paint-coated beads with three sizes (1, 2, and 4 mm) for the free and attached conditions. It was found that no significant desorption/removal of paint from the beads was observed without the movement of beads in the water including floatation, collision, and scrubbing. Thus, it was suggested that the simultaneous application of the ultrasound and mechanical mixing could enhance the physical movement of the particles significantly and the very high removal/desorption could be attained.

Remediation of contaminated sediments containing both organic and inorganic chemicals using ultrasound and ozone nanobubbles

Most river sediments are contaminated with organic and inorganic pollutants and cause significant environmental damage and health risks. This research is evaluated an in-situ sediment remediation method using ultrasound and ozone nanobubbles to remove organic and inorganic chemicals in contaminated sediments. Contaminated sediment is prepared by mixing synthetic fine sediment with an organic (p-terphenyl) and an inorganic chemical (chromium). The prepared contaminated sediment is treated with ultrasound and ozone nanobubbles under different operating conditions. For the samples with the maximum initial concentration of 4211 mg/kg Cr and 1875 mg/kg p-terphenyl, average removal efficiencies are 71% and 60%, respectively, with 240 min of sonication with 2-min pulses, whereas 97.5% and 91.5% removal efficiencies are obtained for the same, respectively, as a single contaminant in the sediment. For the same maximum concentrations, the highest removal of p-terphenyl is 82.7% with 127.2 J/ml high energy density, and for Cr, it is 77.1% using the highest number of the treatment cycle and ozone usage with 78.75/ml energy density. The Cr highest removal efficiency of 87.2% is recorded with the reduced initial concentration of 1227 mg/kg with the highest treatment cycles. The Cr removal efficiency depends on the availability of oxidizing agents and the number of washing cycles of sediments, whereas P-terphenyl degradation is most likely influenced by the combined effects of oxidation and ultrasound-assisted pyrolysis and combustion of organics.

Recent advances in applications of power ultrasound for petroleum industry

Power ultrasound, as an emerging green technology has received increasing attention of the petroleum industry. The physical and chemical effects of the periodic oscillation and implosion of acoustic cavitation bubbles can be employed to perform a variety of functions. Herein, the mechanisms and effects of acoustic cavitation are presented. In addition, the applications of power ultrasound in the petroleum industry are discussed in detail, including enhanced oil recovery, oil sand extraction, demulsification, viscosity reduction, oily wastewater treatment and oily sludge treatment. From the perspective of industrial background, key issue and resolution mechanism, current applications and future development of power ultrasound are discussed. In addition, the effects of acoustic parameters on treatment efficiency, such as frequency, acoustic intensity and treatment time are analyzed. Finally, the challenges and outlook for industrial application of power ultrasound are discussed.

Research on mechanism and characteristics of oil recovery from oily sludge in ultrasonic fields

The acoustic parameters and operating conditions that determine efficiency of oil recovery from oily sludge are studied. Based on this, the mechanism of ultrasonic disintegration of oily sludge is analyzed. The results show that lower frequency ultrasound results in larger and more energetic cavitation bubbles that are more effective in the desorption of oil from solid particles. Moreover, acoustic intensity and treatment time that correspond to maximal oil recovery are found. Increasing the ratio of water to sludge and pH can reduce the slurry viscosity and facilitate the formation of HSiO₃^-, respectively, which improves the oil recovery efficiency. Moreover, Triton X-100 has better oil solubilizing effects than SDBS. After ultrasonic treatment, small amounts of asphaltenes are more stable on solid particles than other components. The heteroatoms such as S, N, and O in asphaltenes form hydrogen bonds with hydroxyl groups on the surface of the particles, impeding the desorption of oil. Mechanical effects such as shock waves and micro jets due to acoustic cavitation can break the hydrogen bonds between asphaltenes and solid particles, thereby facilitating oil recovery from oily sludge.

Effect of sediment particle size on polycyclic aromatic hydrocarbon bioaccessibility and degradation by ultrasound

The effect of particle size on sonochemical desorption, degradation and change in bioaccessibility of polycyclic aromatic hydrocarbons (PAHs) on contaminated sediments was investigated. Batch experiments were performed with the whole sediment (WS < 850 μm), a large size range fraction (150 μm < LSR < 850 μm), and a small size range fraction (SSR < 150 μm) of the whole sediment. PAH degradation followed pseudo first-order kinetics; PAHs on LSR sediments underwent more rapid degradation than on SSR and WS sediments (ν_PAH,LSR > ν_PAH,WS > ν_PAH,SSR). In addition, a higher sediment slurry concentration resulted in slower degradation of PAHs. Results are consistent with the more rapid particle size reduction of the LSR. More rapid particle size reduction and faster PAH degradation for the LSR fraction combined with analysis of particle velocities in both size ranges indicates that microjets as opposed to particle-particle collisions due to shockwaves are effective in rapid particle size reduction and PAH degradation. Moreover, the bioaccessible fraction (F_PAH,fast,t) of sorbed PAHs in both particle size fractions was found to increase with sonication time but was more rapid with the LSR. Likewise, the more tightly bound PAHs, those in the slow desorbing fraction (F_PAH,slow,t) of PAHs, decreased faster with sonication of LSR particles compared to SSR particles, consistent with the trend of particle size reduction. Results of this study suggest that ultrasonic treatment is more effective for larger size particle sediments, although sonication is also viable for small sediment sizes.

Environmental-economical assessment of the use of ultrasonication for pre-treatment of the soils contaminated by phenanthrene

Removing aromatic contaminants from the soil using ultrasonic waves is a new technology with the potential for practical use in industrial scale. In this study, the ultrasonication technology was presumed as a pre-treatment for soils contaminated with phenanthrene. Since the removal of this contaminant from the soil by ultrasonication reduces the cost of treatments such as soil washing, the optimization of independent variables has been investigated in the present study. Effect of variables such as phenanthrene primary concentration (7.5-517.5 mg/kg), ultrasonic power (0-395 W), the volume of water (0-400 mL) and the overall retention time (0-1 h) on the cost-saving of treatment for 100 g soil samples has been presented. The Response Surface Methodology has been used for modeling the results of this research. Based on the results of this research, the optimal conditions have been proposed for maximization of the cost-savings by ultrasonication and minimization of the ultrasonication operating costs. The best proposed conditions to achieve the maximum pollutant removal occurred in soil pretreatments using ultrasonication in water volume of 300 mL, the ultrasonic power of 139W, and 0.5 h process duration, which led to saving of 1.42 ¢/100 g soil for the replacement of the soil washing by the ultrasonication process.

Soil Recycling Geopolymers Fabricated from High Power Ultrasound Treated Soil Slurry in the Presence of Ammonia

Soil slurry was recycled to prepare a geopolymer after treatment with high-power ultrasound (US) in the presence of NH₃, HCl, and NaOH. Under 28 kHz US, 0.1 M NH₃ additives effectively decarbonized the slurry, eliminating 72.2% of the carbon content from the original soil. The US-treated soils were used as raw materials for the geopolymer, as they contained Si and Al components in the range of 25-30 and 8-10 wt.%, respectively. The geopolymer was prepared with a Na₂SiO₄/NaOH aqueous solution at a ¼ weight ratio at 80 °C for 24 h. The resultant geopolymers from the NH₃-treated soil showed the best compressive strength of 3 MPa after 1 day of curing, with a low carbon content, when NH₃ was used as an additive as opposed to HCl and NaOH under 1200 US exposure.

Cavitational activity in heterogeneous systems containing fine particles

Ultrasound has been increasingly used in various processes containing a variety of homogeneous and heterogeneous systems. For largescale applications, a high energy efficiency of the process is required. With this view, the calorimetric energy and cavitational activity measurements were carried out in heterogeneous systems consisting of both liquid and solid phases (fine particles) in a 28-kHz double-bath sonoreactor. Ultrasonic soil washing for the remediation of clay-sized soils (∼75 µm), contaminated with metals (Cu, Pb, and Zn), was used as a case study. As the liquid height/volume in the inner vessel increased under the same input electrical power, the inner vessel calorimetric energy also increased, whereas the total calorimetric energy between the inner vessel and the outer reactor remained approximately constant. No significant differences in calorimetric energies were observed for both with and without soil conditions. The chemical activity under similar experimental conditions was evaluated using sonochemiluminescence. Different sonochemiluminescence trends were observed depending up on the presence and size of beads. The highest total sonochemiluminescence intensity with a uniform spatial distribution was obtained from fine beads (#200, 75 µm) suspended in the vessel. Ultrasound application significantly enhanced the removal efficiency of heavy metals when combined with mechanical agitation. The enhanced removal efficiency of the combined processes was attributed to a significant removal of metals from the residual (F5) fraction. It has been concluded that ultrasound has enough extraction power to be comparable to methods that employ extremely powerful acids for washing fine particles.

Progress in ultrasonic oil-contaminated sand cleaning: a fundamental review

Steady efforts in using ultrasonic energy to treat oil-contaminated sand started in the early 2000s until today, although pilot studies on the area can be traced to even earlier dates. Owing to the unique characteristics of the acoustic means, the separation of oil from sand has been showing good results in laboratories. This review provides the compilation of researches and insights into the mechanism of separation thus far. Related topics in the areas of oil-contaminated sand characterizations, fundamental ultrasonic cleaning, and cavitation effects are also addressed. Nevertheless, many of the documented works are only at laboratory or pilot-scale level, and the comprehensive interaction between ultrasonic parameters towards cleaning efficiencies may not have been fully unveiled. Gaps and opportunities are also presented at the end of this article.

A review on the application of chemical surfactant and surfactant foam for remediation of petroleum oil contaminated soil

Soil, exposed to petroleum oil contaminants (in the form of petrol, diesel, gasoline, crude oil, used motor oil), may cause potential damage to the environment, animal and human health. In this review article, mechanisms of the petroleum oil contaminant removal from soil by chemical surfactant systems such as surfactant solution, surfactant foam and nanoparticle stabilized surfactant foams are explained. Laboratory based research works, reported within the last decade on the application of similar systems towards the removal of petroleum oil contaminant from the soil, have been discussed. It is an important fact that the commercial implementation of the chemical surfactant based technology depends on the environmental properties (biodegradability and toxicity) of the surfactants. In recent times, surfactant foam and nanoparticle stabilized surfactant foam are becoming more popular and considered advantageous over the use of surfactant solution alone. However, more research works have to be conducted on nanoparticle stabilized foam. The impact of physicochemical properties of the nanoparticles on soil remediation has to be explored in depth.

Effect of ultrasound on oil recovery from crude oil containing sludge

To recover oil from crude oil containing sludge is still a research hot topic from the view of sustainability, in which ultrasonic has been proven to be an efficient and environment friendly technique. However, the effect of sludge characteristic on ultrasonic-assisted oil recovery efficiency is little known. In this study, the analysis of variance (ANOVA) was conducted based on six types of crude oily sludge with hydrophilicity and lipophilicity separately and five different ultrasonic operation factors (ultrasonic power (A), frequency (B), time (C), initial temperature (D) and pH (E)). The results showed that the oil recovery efficiency was mainly affected by the ultrasonic power and hydrophilicity of sludge (the highest 92% of oil recovery rate was achieved with the ultrasonic power of 240 W and hydrophilic sludge). Moreover, the wettability, decreased average particle size and increased specific surface area of sludge were found after ultrasonic treatment. Besides, changes in the oil component, such as the decrease of asphaltenes along with an increase of saturates, were also further observed. Therefore, the findings in this study can provide technical support for the practical application of ultrasonic technology in different kinds of oily sludge treatment.

Treatment of petroleum oil spill sludge using the combined ultrasound and Fenton oxidation process

In this paper, advanced oxidation process (AOP) combining ultrasound (US) and Fenton's process was proposed for the treatment of total petroleum hydrocarbons present in oil spill sludge. The effect of several parameters like pH, ultrasonic power, weight ratio of hydrogen peroxide to iron [H₂O₂/Fe²⁺], Fenton reagent dosage, addition of salts and contact time were analyzed for the reduction of Petroleum Hydrocarbons (PHCs) in terms of hydrocarbon fractions (nC7-C10, nC11-C20). Chemical characterization of oil spill sludge was analysed by gas chromatography- mass spectrum (GC-MS) Elemental analyser, Fourier Transform Infra Red (FT-IR) Analyser and particle size analyser. Experiments were conducted for identifying the wide range of hydrocarbons fractions (nC7-C10, nC11-C20 and nC21-C30). Results shown that maximum solubilisation and PHC removal rate of up to 84.25% could be achieved at a pH of 3.0, sludge/water ratio of 1:100, ultrasonic power of 100 W with 40-50% ultrasonic amplitude, a H₂O₂/Fe²⁺ weight ratio of 10:1, and an ultrasonic treatment time of 10 min. The lower and medium fractions (nC7-C10, nC11-C20) were amenable to degradation due to ultrasound treatment compared to the heavier carbon fraction (nC21-C30). The study concludes that the combined sono-Fenton (SF) process significantly enhanced the degradation of oil spill sludge as compared to ultrasound treatment and Fenton oxidation alone. The enhanced solubilisation achieved by US alone is highly beneficial when we couple this with biodegradation which will be greatly facilitated by the enhanced solubility.

Efficacy of Indigenously Prepared Sugarcane and Pineapple Wine Solvents for Washing Highly Dioxin-Contaminated Field Soils

Poly-chlorinated dibenzo-p-dioxins (PCDDs) and poly-chlorinated dibenzo-furans (PCDFs) negatively affect human health and are often found as unwanted by-products of chemical handling and manufacture procedures. While commercial solvents have been used to remove dioxins from contaminated soil, these solvents themselves may adversely affect soil health. In this study, we examined the effects of washing highly PCDD/F contaminated field-soil with two natural solvents (sugarcane and pineapple wine) under ambient temperature. Performing an initial three-washing-cycle experiment, we found that sugarcane wine more effectively removed the contaminants than pineapple wine (removal, 60% vs. 50%) and chose it to perform a six-washing-cycle experiment facilitated by mechanical stirring and ultrasonication. Sugarcane wine was found to have a high removal efficiency (almost 80%), largely due to its higher alcohol and acid content. We believe that both wines can be used in soil remediation tasks without further damage to soil health. This is the first study employing naturally made wines as soil washing solvents in treating highly PCDD/F contaminated field soil. After soil washing processes, the winery solvents are believed to be beneficial to (if necessary) bioremediation methods and/or monitored natural attenuation.

Study on regeneration effect and mechanism of high-frequency ultrasound on biological activated carbon

High frequency ultrasonic radiation technology was developed as a novel and efficient means of regenerating spent biological activated carbon (BAC) used in drinking water treatment plants (DWTPs). The results of this study indicated that high frequency ultrasonic treatment could recover the spent BAC, to some extent, with the following optimal conditions: a frequency of 400 kHz, sonication power of 60 W, water temperature of 30 °C, and sonication time of 6 min. Under the above conditions, the iodine value increased from 300 mg/g to 409 mg/g, the volume of total pores and micropores increased from 0.2600 cm³/g and 0.1779 cm³/g to 0.3560 cm³/g and 0.2662 cm³/g, respectively; the specific surface area of micropores and the mean pore diameter expanded from 361.15 m²/g and 2.0975 nm to 449.92 m²/g and 2.1268 nm, respectively. The biological activity increased from 0.0297 mgO₂/gC·h to 0.0521 mgO₂/gC·h, while the biomass decreased from 203 nmolP/gC to 180 nmolP/gC. The results of high throughput 16S rRNA gene amplicon sequencing showed that microorganisms such as Clostridia and Nitrospira were markedly decreased due to high frequency ultrasound. The method used in this study caused the inhibition of certain carbon-attached microbials resulting in a negative effect on the removal rate of ammonia-N during the initial stage of the long-term reuse operation. The removal of UV254 and atrazine were restored from 8.1% and 55% to 21% and 76%, respectively.

Application of an in-situ soil sampler for assessing subsurface biogeochemical dynamics in a diesel-contaminated coastal site during soil flushing operations

Subsurface biogeochemistry and contaminant dynamics during the remediation of diesel-contamination by in-situ soil flushing were investigated at a site located in a coastal region. An in-situ sampler containing diesel-contaminated soils separated into two size fractions (<0.063- and <2-mm) was utilized in two monitoring wells: DH1 (located close to the injection and extraction wells for in-situ soil flushing) and DH2 (located beyond sheet piles placed to block the transport of leaked diesel). Total petroleum hydrocarbon (TPH) concentrations and biogeochemical properties were monitored both in soil and groundwater for six months. A shift occurred in the groundwater type from Ca-HCO₃ to Na-Cl due to seawater intrusion during intense pumping, while the concentrations of Ni, Cu, Co, V, Cr, and Se increased substantially following surfactant (TWEEN 80) injection. The in-situ sampler with fine particles was more sensitive to variations in conditions during the remedial soil flushing process. In both wells, soil TPH concentrations in the <0.063-mm fraction were much higher than those in the <2-mm fraction. Increases in soil TPH in DH1 were consistent with the expected outcomes following well pumping and surfactant injection used to enhance TPH extraction. However, the number of diesel-degrading microorganisms decreased after surfactant injection. 16S-rRNA gene-based analysis also showed that the community composition and diversity depended on both particle size and diesel contamination. The multidisciplinary approach to the contaminated site assessments showed that soil flushing with surfactant enhanced diesel extraction, but negatively impacted in-situ diesel biodegradation as well as groundwater quality. The results also suggest that the in-situ sampler can be an effective monitoring tool for subsurface biogeochemistry as well as contaminant dynamics.

The use of ultrasound-assisted anaerobic compost tea washing to remove poly-chlorinated dibenzo-p-dioxins (PCDDs), dibenzo-furans (PCDFs) from highly contaminated field soils

The remediation of dioxin-contaminated soil of a specific coastal area previously employed for the manufacture of pentachlorophenol (PCP) in southern Taiwan's Tainan City has attracted much attention of researchers there. This work addresses the possibility of providing an effective and environmentally friendly option for removing PCDD/Fs from soil in that field. Soil screening/sieving was first conducted to assess particle distribution. Fine sand was observed to be the major component of the soil, accounting for more than 60% of the total mass. A combination of ultrasonification and mechanical double-blade agitation was used to facilitate the washing of the soil using the biosurfactant anaerobic compost tea. More than 85 and 95% of total removal efficiencies were achieved for moderately and highly contaminated soils after 6 and 10 washing cycles, respectively, under ambient temperature, a soil/liquid ratio 1:2.5, 700 rpm, and over a relatively short duration. These results were achieved through the collision and penetration effects of this combined treatment as well as PCDD/F partitioning between the particles and anaerobic compost tea. This study represents the first to report the use of anaerobic compost tea solvent to wash soil highly contaminated by dioxin. It was concluded that anaerobic compost tea, rich in non-toxic bio-surfactants (e.g., alcohols, humic acids), can be used to improve bioavailability and bioactivity of the soil making bio-attenuation and full remediation more efficient.

Ultrasonic and mechanical soil washing processes for the removal of heavy metals from soils

In order to determine the optimal operating conditions of full-scale soil washing processes for the removal of heavy metals, the effect of high-power ultrasound on the conventional mechanical soil washing process was investigated in a large lab-scale 28kHz sonoreactor. The soil samples were obtained from an abandoned railway station site in Seoul, Korea, which was contaminated with Cu (242.7±40.0mg/kg), Pb (441.3±49.8mg/kg), and Zn (358.0±35.7mg/kg). The treated concentrations of three heavy metal species in each process were compared with the regulation levels. It was found that higher performance, satisfying the regulation levels, was obtained in the ultrasonic/mechanical process due to the combined effects of macroscale mixing and microscale sonophysical effects. Moreover ultrasound played a more important role in less favorable conditions for the mechanical washing process (less acidic or less washing liquid conditions). Considering the application of the ultrasonic/mechanical soil washing process in real contaminated sites, the optimal conditions for the reactor with the bottom area of 15×15cm² and the input ultrasound power of 250W were determined as follows: (1) the amount of soil per an operation was a 300g; (2) the ratio of soil and liquid was 1:3; (3) the concentration of acidic washing liquid was 0.5M HCl.

A comprehensive guide of remediation technologies for oil contaminated soil - Present works and future directions

Oil spills result in negative impacts on the environment, economy and society. Due to tidal and waves actions, the oil spillage affects the shorelines by adhering to the soil, making it difficult for immediate cleaning of the soil. As shoreline clean-up is the most costly component of a response operation, there is a need for effective oil remediation technologies. This paper provides a review on the remediation technologies for soil contaminated with various types of oil, including diesel, crude oil, petroleum, lubricating oil, bitumen and bunker oil. The methods discussed include solvent extraction, bioremediation, phytoremediation, chemical oxidation, electrokinetic remediation, thermal technologies, ultrasonication, flotation and integrated remediation technologies. Each of these technologies was discussed, and associated with their advantages, disadvantages, advancements and future work in detail. Nonetheless, it is important to note that no single remediation technology is considered the best solution for the remediation of oil contaminated soil.

CAPSULE

This review provides a comprehensive literature on the various remediation technologies studied in the removal of different oil types from soil.

Remediation technologies for oil-contaminated sediments

Oil-contaminated sediments pose serious environmental hazards for both aquatic and terrestrial ecosystems. Innovative and environmentally compatible technologies are urgently required to remove oil-contaminated sediments. In this paper, various physical, chemical and biological technologies are investigated for the remediation of oil-contaminated sediments such as flotation and washing, coal agglomeration, thermal desorption, ultrasonic desorption, bioremediation, chemical oxidation and extraction using ionic liquids. The basic principles of these technologies as well as their advantages and disadvantages for practical application have been discussed. A combination of two or more technologies is expected to provide an innovative solution that is economical, eco-friendly and adaptable.

Increasing the bioaccessibility of polycyclic aromatic hydrocarbons in sediment using ultrasound

In this study, the effect of sonication on the distribution of polycyclic aromatic hydrocarbons (PAHs) in the bioaccessible and less bioaccessible fractions of three contaminated sediments (Little Scioto River, OH-LS; Gary, IN-GI; Eagle Harbor, WA-EH) was examined. After 60min sonication, the fractions of naphthalene, phenanthrene and pyrene remaining in the LS sediment were 0.76±0.18, 0.83±0.04 and 0.76±0.05, respectively, indicating ultrasonic degradation of PAHs in the sediment. In addition, there was a significant decrease in PAH concentration (i.e., up to 91.4%) in the less bioaccessible fractions for all three sediments with sonication. The bioaccessible fraction of phenanthrene and pyrene in LS and pyrene in EH increased by 12.9%, 48.3% and 27.8%, respectively, followed by a slight decrease due to degradation. The initial increase suggests that ultrasonic irradiation of sediment either transfers the PAHs from the less bioaccessible sites to the bioaccessible sites for treatment or transforms less bioaccessible sites into bioaccessible sites. A comparatively smaller reduction (i.e., 20.2%) in the less bioaccessible fraction in GI sediment is attributed to the larger fraction of black carbon in the organic carbon content of the sediment hindering the ability of ultrasound to switch the PAHs from the less to the more bioaccessible sites. Overall ultrasonic irradiation of contaminated sediments is a technique to enhance contaminant remediation by reducing the fraction of contaminants in less bioaccessible sites.

The effects of liquid height/volume, initial concentration of reactant and acoustic power on sonochemical oxidation

Even though much knowledge on acoustic cavitation and its application has been accumulated over the past decades, further research is still required to develop industrial uses of acoustic cavitation. It is because the available information is mainly based on small-scale sonoreactors and the design and optimization of sonoreactors for large-scale applications have not been widely studied. In this study, the effects of liquid height/volume, initial concentration of the reactant and input acoustic power on sonochemical oxidation reactions including iodide ion oxidation, As(III) oxidation, and hydrogen peroxide generation were investigated using a 291kHz sonoreactor with various liquid height/volumes (50, 100, 200, 300, 500, and 1000mL) and input powers (23, 40, and 82W). As the liquid height/volume and the input power changed, the power density varied from 23 to 1640W/L and the maximum cavitation yields of triiodide ion for 23, 40, and 82W were observed at 0.05, 0.1, and 0.2/0.3L, respectively. It was found that low power was more effective for the small volume and the large volume required high power level and the moderate power density, approximately 400W/L, was suggested for the sonochemical oxidation of iodide ion in the 291kHz sonoreactor in this study. Similar results were observed in the generation of hydrogen peroxide and the sonochemical oxidation of As(III) to As(V). It was also revealed that KI dosimetry could be applicable for the estimation of the sonochemical reactions of non-volatile compounds such as As(III).

Ultrasonic oil recovery and salt removal from refinery tank bottom sludge

The oil recovery and salt removal effects of ultrasonic irradiation on oil refinery tank bottom sludge were investigated, together with those of direct heating. Ultrasonic power, treatment duration, sludge-to-water ratio, and initial sludge-water slurry temperature were examined for their impacts on sludge treatment. It was found that the increased initial slurry temperature could enhance the ultrasonic irradiation performance, especially at lower ultrasonic power level (i.e., 21 W), but the application of higher-power ultrasound could rapidly increase the bulk temperature of slurry. Ultrasonic irradiation had a better oil recovery and salt removal performance than direct heating treatment. More than 60% of PHCs in the sludge was recovered at an ultrasonic power of 75 W, a treatment duration of 6 min, an initial slurry temperature of 25°C, and a sludge-to-water ratio of 1:4, while salt content in the recovered oil was reduced to <5 mg L(-1), thereby satisfying the salt requirement in refinery feedstock oil. In general, ultrasonic irradiation could be an effective method in terms of oil recovery and salt removal from refinery oily sludge, but the separated wastewater still contains relatively high concentrations of PHCs and salt which requires proper treatment.

Recent development in the treatment of oily sludge from petroleum industry: a review

Oily sludge is one of the most significant solid wastes generated in the petroleum industry. It is a complex emulsion of various petroleum hydrocarbons (PHCs), water, heavy metals, and solid particles. Due to its hazardous nature and increased generation quantities around the world, the effective treatment of oily sludge has attracted widespread attention. In this review, the origin, characteristics, and environmental impacts of oily sludge were introduced. Many methods have been investigated for dealing with PHCs in oily sludge either through oil recovery or sludge disposal, but little attention has been paid to handle its various heavy metals. These methods were discussed by dividing them into oil recovery and sludge disposal approaches. It was recognized that no single specific process can be considered as a panacea since each method is associated with different advantages and limitations. Future efforts should focus on the improvement of current technologies and the combination of oil recovery with sludge disposal in order to comply with both resource reuse recommendations and environmental regulations. The comprehensive examination of oily sludge treatment methods will help researchers and practitioners to have a good understanding of both recent developments and future research directions.

Ultrasonic desorption of petroleum hydrocarbons from crude oil contaminated soils

Ultrasonic irradiation was applied to improve the desorption of petroleum hydrocarbons (PHC) in crude oil from three types of soil. Soil A was an Ottawa sand, while soil B and soil C were fine soils that contained 27.6% and 55.3% of silt and clay contents, respectively. It was found that the ultrasonic desorption was highly related to soil types, with the highest and the lowest desorption occurring in coarse soil (i.e., soil A) and finer soil (i.e., soil C), respectively. Under the experimental conditions, the maximum ultrasonic desorption enhancement of the total petroleum hydrocarbons (TPH) reached 22% for soil A, 61% for soil B, and 49% for soil C, respectively. The maximum enhancement on the F2 (n-C10 to n-C16), F3 (n-C16 to n-C34), and F4 (n-C34 to n-C50) fractions of PHC reached 91, 44, and 51% for soil B, and 90, 38, and 31% for soil C, respectively. The desorption enhancement also illustrated an increasing trend with initial soil TPH concentration.

Comparison of energy consumptions between ultrasonic, mechanical, and combined soil washing processes

Vigorous physical effects including micro-jet and micro-streaming can be induced in heterogeneous systems by acoustic cavitation. This can be useful for the removal of pollutants from contaminated soil particles. In this study, the diesel removal efficiencies in ultrasonic, mechanical, and combined soil washing processes have been compared considering the electrical energy consumptions for these processes. The combined process showed synergistic effects for both removal efficiency and effective volume also has the advantage of a short operation time compared to the sequential processes. Thus the ultrasonic soil washing process with mechanical mixing is considered a promising technology for industrial use.

Oil recovery from refinery oily sludge via ultrasound and freeze/thaw

The effective disposal of oily sludge generated from the petroleum industry has received increasing concerns, and oil recovery from such waste was considered as one feasible option. In this study, three different approaches for oil recovery were investigated, including ultrasonic treatment alone, freeze/thaw alone and combined ultrasonic and freeze/thaw treatment. The results revealed that the combined process could achieve satisfactory performance by considering the oil recovery rate and the total petroleum hydrocarbon (TPH) concentrations in the recovered oil and wastewater. The individual impacts of five different factors on the combined process were further examined, including ultrasonic power, ultrasonic treatment duration, sludge/water ratio in the slurry, as well as bio-surfactant (rhamnolipids) and salt (NaCl) concentrations. An oil recovery rate of up to 80.0% was observed with an ultrasonic power of 66 W and an ultrasonic treatment duration of 10 min when the sludge/water ratio was 1:2 without the addition of bio-surfactant and salt. The examination of individual factors revealed that the addition of low concentration of rhamnolipids (<100mg/L) and salt (<1%) to the sludge could help improve the oil recovery from the combined treatment process. The experimental results also indicated that ultrasound and freeze/thaw could promote the efficiency of each other, and the main mechanism of oil recovery enhancement using ultrasound was through enhanced desorption of petroleum hydrocarbons (PHCs) from solid particles.

Ultrasound enhanced gradient elution of super heavy oil from weathered soils using TX100/SBDS mixed salt micellar solutions

An ultrasound-enhanced five-stage gradient elution system employing mixed solutions of Triton X-100 (TX100), sodium dodecyl benzenesulfonate (SBDS), and salt (abbr. MSTS) was used to elute super heavy oil from weathered soils. The use of ultrasound increased the elution of super heavy oil by 13-14% and improved first-stage dissolution and dispersion by 62%. However, the amount of super heavy oil dissolved or dispersed in the second through fifth elution stages was unchanged by the application of ultrasound. Saturated hydrocarbons were more quickly eluted in the first two stages. During the final three stages the order of elution for the four identified super heavy oil fractions was: asphaltenes>saturated hydrocarbons>aromatics>resins. A large number of elution stages aided in eluting markers containing a large number of C atoms in the absence of ultrasound. The elution at each stage was higher when ultrasound was employed, and ultrasound-enhanced elution is a potentially useful method for removing super heavy oil from weathered soils.

Impact of ultrasonication time on elution of super heavy oil and its biomarkers from aging soils using a Triton X-100 micellar solution

An ultrasound-enhanced elution system with Triton X-100 solution was used to remediate aging soils contaminated with super heavy oil. We used GC/MS, SEM, and X-ray diffraction (XRD) to analyze the effect of ultrasonic time (0-1800 s) on the elution of super heavy oil and its three characteristic biomarkers (C(26-34) 17alpha 25-norhopanes, C(26-28) triaromatic steroid [TAS], and C(27-29) methyl triaromatic steroid [MTAS]). The oil and biomarkers remaining in the treated soils followed similar second-order functions with increasing ultrasonication times. Biomarker elution was closely related to carbon numbers in the marker. For C(26-34) 17alpha 25-norhopanes, the smaller molecules were more readily eluted during 0-360 s ultrasound. This trend was reversed upon application of ultrasound during 1080-1800 s, with improved elution of larger molecules and elution followed a similar second-order function. For C(26-28) TAS, smaller molecules were more readily eluted but the elution of larger molecules followed a similar second-order function. For C(27-29) MTAS, elution of larger molecules was close to that of C(26-34) 17alpha 25-norhopanes. Results of SEM and XRD indicated that the mineral and chemical compositions of soils eluted at ultrasonication times of 1080-1800 s closely resembled clean soils.

Impact of ultrasonic time on hot water elution of severely biodegraded heavy oil from weathered soils

An ultrasound-enhanced elution system employing water at a temperature of 70 degrees C was used to remedy weathered soils contaminated with severely biodegraded heavy oil (SBHO). The effect of varying the ultrasonic irradiation time from 0 to 1800 s on the elution of SBHO and three characteristic biomarkers (C(26-34) 17alpha 25-norhopanes, C(26-28) TAS, and C(27-29) MTAS) was analyzed using GC/MS, scanning electron microscopy (SEM), and X-ray diffraction (XRD). Elution of the three biomarkers was closely related to the carbon number of the marker. C(26-34) 17alpha 25-norhopanes and C(26-28) TAS species with higher carbon numbers and C(27-29) MTAS species with lower carbon numbers were more readily eluted using sonication times of 1080-1800 s, while smaller TAS homologs were more readily eluted after sonication times of 0-360 s. SEM images of samples treated for longer periods revealed larger "bare patches" on the soil surface. The results of XRD and energy spectroscopy experiments indicated that ultrasound irradiation for 1080 s negatively affected the deposition of CaCO(3), but overall improved the mineral and chemical compositions of treated soils and removal of SBHO.

Impact of ultrasonic power density on hot water elution of severely biodegraded heavy oil from weathered soils

An ultrasound-enhanced elution system using water at a temperature of 70 degrees C was employed to remove severely biodegraded heavy oil (SBHO) from weathered soil. The effect of varying the ultrasonic power density from 0 to 100 W L(-1) on the elution of SBHO and three characteristic biomarkers (C(26-34) 17alpha 25-norhopanes, C(26-28) triaromatic steroids (TAS), and C(27-29) methyl triaromatic steroids (MTAS) was analyzed using GC/MS, scanning electron microscopy (SEM), and X-ray diffraction (XRD). The amount of SBHO and biomarkers present in the treated soils and eluent had significant negative correlation with increasing ultrasonic power density. Elution of the three biomarkers was closely related to the number of C atoms in the marker: C(26-34) 17alpha 25-norhopanes with more carbon numbers and MTAS homologs with less carbon numbers were more readily eluted at higher power densities. The smaller TAS species were more readily eluted at a power density of less than 60 W L(-1), while larger TAS species displayed improved elution at power densities greater than 60 W L(-1). SEM images of samples treated at higher power densities revealed a more compact SBHO accumulation layer at the water-soil interface. The results of XRD and energy spectroscopy experiments indicated that ultrasound at a power density of 20 W L(-1) was helpful for the formation and sedimentation of calcite, although this effect disappeared at higher power of greater than 60 W L(-1).

Bench-scale tests on ultrasound-assisted acid washing and thermal desorption of mercury from dredging sludge and other solid matrices

A series of ultrasonic assisted acid washing and thermal desorption tests were performed on sludge and other solid matrices with the aim to assay these removal technologies and to determine if the application of low frequency ultrasound was effective to enhance mercury removal. Unpolluted dredging sludge, 820 K calcinated dredging sludge, silica and alumina were characterized, polluted with a known concentration of mercury and treated both by acid washing and thermal desorption with and without low frequency ultrasound application. The acid washing was carried out by a 4% HNO(3) acid solution and the thermal desorption was performed in a 370-620K range. X-ray semi-quantitative analysis of dredging sludge before and after acid washing and granulometric curves of the matrices after the ultrasonic treatment were considered in order to evidence chemical or physical changes during these treatments. Total residual mercury measurements were carried out before and after sonication. Results showed not measurable acid washing extraction from polluted dredging sludge, a little (3%) extraction from 820K heat-treated sludge and a significant (10-20%) extraction from alumina and silica within 120 min of treatment. The ultrasound application gave generally poor improvement of the mercury removal. On the contrary thermal desorption of mercury was somewhat effective for alumina, silica and heat-treated dredging sludge samples in which mercury removal was 30-40% at 370 K and 90-99% at 570 K. Likewise ultrasound application did not improve desorption. Instead, the thermal treatment of dredging sludge had a negligible amount of mercury desorption at 370 K but it reached 95% at 570 K. The application of ultrasound improved the thermal extraction of 25% in the 470-520 K range of temperature.

Extraction of bitumen, crude oil and its products from tar sand and contaminated sandy soil under effect of ultrasound

In the present paper, the kinetics of the water extraction of bitumen from tar sand and crude oil or residual fuel oil from model contaminated soils under the effect of ultrasound is studied. The influence of process temperature, ultrasound power, the nature, and properties of the components of heterogeneous mixtures being separated, and the concentration of added alkaline reagents on the rate and degree of oil recovery is investigated. A functional form of the dependencies of separation efficiency on the mean size of solid particles and the temperature of a working medium is found. Optimum concentrations of reagents in the process solution are determined. It is shown that the spent solution of sodium silicate can be multiply used for separation, its reuse even speeding up the yield of oil in the initial period. Taking into account obtained results, a multipurpose pilot plant with a flow-type reactor for ultrasonic extraction of petroleum and its products from contaminated soils was manufactured and tested. During tests, the purification of sandy soil contaminated with residual fuel oil was carried out which verified the results of laboratory studies.

Soil remediation by an advanced oxidative method assisted with ultrasonic energy

A new process for the remediation of soil contaminated with hydrocarbons is proposed. The innovation consists on coupling an advanced oxidative method, using a Fenton-type catalyst, with the application of ultrasonic energy. The use of ultrasonic energy not only assists the desorption of the contaminants from the soil, but also promotes the formation of OH radicals, which are the oxidant agents involved in the oxidation process. Different Fenton-like catalysts were employed in the present study; however, the highest removal of toluene and xylenes were obtained with iron sulfate and copper sulfate, respectively. Also, hydrogen peroxide was tested at different concentrations, and it was found that increasing its concentration enhanced the removal of all the contaminants. Finally, it was demonstrated that applying ultrasonic energy to the reacting system process noticeably enhanced the global efficiency of the process due to a synergistic effect in conjunction with the hydrogen peroxide concentration and type of catalyst.

Regeneration of granular activated carbon using ultrasound

To evaluate the feasibility of ultrasonic regeneration of granular activated carbon (GAC), desorption of trichloroethylene (TCE) from GAC by ultrasound was investigated at 20 kHz. About 64% of TCE was desorbed from 5 g of GAC loaded with 6.5 mg TCE for 1 h in ultrasonic field and TCE desorbed to liquid phase were rapidly degraded by ultrasound. 34-43% of stoichiometrically calculated chloride, final degradation product of TCE, was observed in liquid phase during ultrasonic treatment. However, there was desorption limitation at 20 kHz ultrasound. Despite of prolonged ultrasonic irradiation, desorption efficiency of TCE did not exceed critical value. And also, the higher percentage of TCE was desorbed when a sample of 2 mg TCE/4 g GAC was treated ultrasonically than that of 2 mg TCE/g GAC under the same experimental conditions. These results indicate that desorption of TCE by 20 kHz ultrasound occurred mainly at a nearby surface of GAC. In conclusion, the ultrasonic regeneration showed a possibility as an alternative to chemical and thermal regenerations of GAC.

Sonolytic desorption of mercury from aluminum oxide

As discrete particles and/or as coatings on other mineral surfaces in natural systems, aluminum (hydr)oxides are efficient sinks for Hg(II). Ultrasound at 20 kHz was applied to enhance the desorption of Hg(II) from aluminum oxide particles (5.0 micromol of Hg g(-1)). Results showed that at short times ultrasound enhanced Hg(II) release at pH 4.0 compared to both that from hydrodynamic mixing and that expected on the basis of the Hg(II) sorption isotherm. The higher the input power of sonication, the higher the desorption of Hg(II). However, with longer times, much less desorption occurred by ultrasound than by hydrodynamic mixing, with mass balance measurements demonstrating that the desorbed Hg(II) was resorbed back to the particles. The particles were characterized to explore the mechanism for resorption of Hg(II) by prolonged sonication. No surface area change was observed even though ultrasound dramatically reduced the particle size and changed the surface morphology. Although a decrease in the point of zero charge (PZC) due to sonication was observed, it was excluded as the primary mechanism for Hg(II) resorption. Hg(II) occlusion by aluminum hydroxide precipitation was supported by X-ray photoelectron spectroscopy results and the formation of solutions supersaturated with AI. Experiments on presonicated particles verified the occlusion theory by ruling out the effects of the surface area and PZC.

Leaching behavior of lead from ultrasonically treated MSWI fly ash

This study was conducted to evaluate the effect of ultrasound widely used for extraction of contaminants and for synthesis of complexes, on extraction and stabilization of heavy metals in MSWI fly ash. Ten grams of fly ash was treated at 10 of liquid--solid (L/S) ratio with and without ultrasonic irradiation of 20 kHz. The extractability of Pb from fly ash was enhanced by ultrasound at the acidic condition. At neutral and alkaline conditions, however, ultrasound did not affect the enhancement of extractability. The results of the maximum availability leaching test (MALT) of the residues treated under various pH conditions with or without ultrasound indicated that the stability of Pb in the fly ash residues was enhanced after ultrasonic irradiation irrespective of treated pH conditions. However, there was a critical point on the enhancement of lead stability in the residues even though the extraction efficiency of Pb decreased gradually with increasing ultrasonic intensity during fly ash treatment. Ultrasonic irradiation was effective for phosphate stabilization of Pb in fly ash. Irrespective of leaching tests, less amount of Pb was leached out from the phosphate stabilized residues treated with ultrasound than without ultrasound. The extraction efficiency of Pb from fly ash decreased with increasing treatment time but the fractions available for leaching at MALT increased with increasing treatment time. Conclusively, although the effect of ultrasound on the extraction of Pb from fly ash highly depends on the pH condition of solvent, the stability of lead in the fly ash residues can be enhanced with ultrasonic irradiation.