Method and system for treating contaminated materials

Abstract

The present invention relates to a method for remediating hydrocarbon-contaminated soil, comprising the steps of: size-reducing the hydrocarbon-contaminated soil particles; mixing the size-reduced soil particles with water to form a slurry mixture, wherein the water is degassed prior to or during mixing within a processing vessel; subjecting the slurry mixture to ultrasonic treatment to induce acoustic cavitation and dislodge contaminants from the soil particles; separating the cleaned soil particles from the slurry mixture; and washing the cleaned soil particles with clean water to remove contaminants.

Description

[0001] METHOD AND SYSTEM FOR TREATING CONTAMINATED MATERIALS

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] This invention relates to a method and system for treating contaminated materials. In particular, this invention relates to a method and system to efficiently and effectively remediate hydrocarbon-contaminated sand and soil. The present invention addresses the significant environmental challenges associated with remediating hydrocarbon- contaminated soil, offering a comprehensive solution to restore its quality and functionality with minimal resource utilisation. The present invention can also remediate other contaminated materials like oil tank sludge, mining residues and agricultural soils.

[0004] BACKGROUND

[0005] In recent years, soil and sand remediation has become a significant focus, particularly concerning the restoration and improvement of soil quality in various environments. Traditional methods of soil remediation are however associated with several drawbacks and challenges.

[0006] The main issue with soil remediation is the inefficiency and environmental impact of known processing techniques. There have been advancements in techniques such as soil washing and scrubbing, bioremediation, electrokinetic soil remediation and thermal desorption to remove contaminants and refine the properties of remediated soil. Conventional soil remediation processes such as these however necessitate significant energy consumption and can result in depletion of water reserves. Furthermore, these processes may contribute to air and water pollution, posing risks to human health and the wider environment. In addition, the physical properties of such remediated soil, including the particle size distribution, grain shape, and mineral composition, maybe sub-optimal to the requirements.

[0007] These issues are further exacerbated in the remediation of hydrocarbon-contaminated sand and soil as a consequence of the deliberate destruction of oil wells, whether as an act of conflict, sabotage, or negligence, or through standard exploration, production and transportation phases of crude oil. Such oil leakage can have profound and far-reaching environmental consequences. When oil wells are intentionally ignited or damaged, they can release vast quantities of crude oil, leading to extensive contamination of the surrounding land, including sand and soil. Equally, leakages from oil pipelines, underground and surface fuel storage tanks can lead to significant contamination which poses significant risks to ecosystems, human health and local economies.

[0008] Oil-contaminated sand, in particular, presents a formidable challenge for environmental remediation efforts. The presence of crude oil alters the physical and chemical properties of the sand, affecting its ability to support plant life and microbial activity. Clean-up and restoration efforts require extensive resources and specialised techniques to remove the oil and restore the affected areas to a functional state. By its very nature, oil- contaminated sand is frequently found in arid and inhospitable landscapes, and sand remediation techniques are often compounded by scarce energy and water resources.

[0009] Significant challenges therefore remain in achieving sustainable and efficient soil remediation. The method and system of the present invention addresses these key issues around energy consumption, environmental impact and process quality and efficacy.

[0010] It is an object of the present invention to provide a method and system to efficiently and effectively remediate hydrocarbon-contaminated sand and soil. It is a further object of the present invention to provide a method and system which improves the quality and yield of remediated soil with minimal or no chemical or thermal processing, and which vastly improves the sustainability thereof. These efficiencies lead to both a reduced clean-up time and resource usage, such that the method and system realises significantly lower power / energy utilisation, coupled with much lower water requirements since around 80% of the process water is recycled (the contaminated soil absorbs most of the water lost). It is a further object of the present invention to provide a method and system to remediate soil to around <1% hydrocarbon residual content. The system having a modular and scalable construction and which provides around 3 to 100 tonnes / hour processing capability per unit, and multiple units can be utilised to process a higher throughput. Such a standalone, modular construction means that there is no risk of contamination from neighbouring processing units. It is a further object of the present invention to provide a method and system that can remediate other contaminated materials such as, but not limited to, any of the following: oil and gas industry byproducts (including oil tank sludge), mining and resource extraction residues, bio-mining wastes and fines from landfill sites, as well as treating agricultural and farmland pollutants and the like.

[0011] SUMMARY OF THE INVENTION

[0012] The present invention is described herein and in the claims.

[0013] According to the present invention there is provided a method for remediating hydrocarbon-contaminated soil, comprising the steps of size-reducing the hydrocarbon-contaminated soil particles; mixing the size-reduced soil particles with water to form a slurry mixture, wherein the water is degassed prior to or during mixing within a processing vessel; subjecting the slurry mixture to ultrasonic treatment to induce acoustic cavitation and dislodge contaminants from the soil particles; separating the cleaned soil particles from the slurry mixture; and washing the cleaned soil particles with clean water to remove contaminants.

[0014] An advantage of the present invention is that by employing high-frequency sound waves to disperse contaminants from within the soil particles ensures a reduced clean-up time and minimal resource utilisation.

[0015] Also according to the present invention there is provided a soil remediation system, comprising: a primary processing vessel configured to receive hydrocarbon-contaminated soil particles and water to form a slurry mixture, wherein the water is degassed prior to or during mixing within the processing vessel; one or more ultrasonic emitters being positioned around the primary processing vessel and being configured to induce acoustic cavitation within the slurry mixture; a conveyer system for transporting the slurry mixture to subsequent processing stages; and a series of processing vessels and equipment for further refining the cleaned soil particles and treating wastewater generated during the soil remediation process. In use, the water may be degassed within the processing vessel by activating ultrasonic emitters in a staged sequence from the bottom of the vessel upwards, to remove dissolved gases and / or entrained air bubbles or from a separate water degassing unit.

[0016] Preferably, the size reduction of hydrocarbon-contaminated soil particles involves crushing and sieving to ensure uniformity in particle size before mixing with degassed water.

[0017] Further preferably, the ultrasonic treatment is performed at a frequency of around 30 to 50kHz.

[0018] In use, a surfactant is introduced into the slurry mixture to enhance the effectiveness of the ultrasonic treatment.

[0019] Preferably, the surfactant is an alkaline detergent.

[0020] Further preferably, the separation of cleaned soil particles from the slurry mixture is performed using a hydrocyclone.

[0021] In use, the cleaned soil particles may be polished using a log washer or ultrasonic energy emitted from ultrasonic emitters positioned along the polishing screw.

[0022] Preferably, the treated water is recycled for re-use in the remediation process through a desilter, clarifier and water storage system.

[0023] Further preferably, the wastewater generated during the remediation process is treated in an oil-water separator, fines separation processor, and filter press to remove oil and contaminants or passed through a dissolved air flotation (DAF) unit, desilter, clarifier and centrifuge stages.

[0024] In use, the process parameters including ultrasonic frequency, power density, process temperature and / or surfactant concentration are controlled to optimise cleaning efficiency and minimise energy consumption. Preferably, key process parameters such as water flow rate, soil particle size distribution, temperature and / or impurity levels are monitoring during the remediation process.

[0025] Further preferably, the ultrasonic treatment is performed continuously as the slurry mixture is transported between processing stages or in repeated cycles within a single processing vessel.

[0026] In use, the slurry mixture may be mechanically-agitated.

[0027] Preferably, the ultrasonic treatment is performed in a batch processing mode comprising multiple sequential ultrasonic cycles within a single vessel.

[0028] Further preferably, the surfactant disrupts hydrogen bonding between water molecules to enhance the penetration of ultrasonic waves into the slurry mixture.

[0029] In use, the surfactant may adsorb onto oil droplets, reducing their surface tension and facilitating their dispersion.

[0030] Preferably, the ultrasonic treatment is performed using ultrasonic emitters positioned around the circumference of a processing vessel at one or more vessel heights.

[0031] Further preferably, the ultrasonic treatment is enhanced by supplementary ultrasonic emitters positioned inside the processing vessel and arranged on arms disposed within the slurry.

[0032] In use, the slurry mixture may be pumped between processing vessels and subjected to ultrasonic treatment during transit using an ultrasonic tubular processor or is retained in a single vessel and subjected to multiple ultrasonic and flotation cycles.

[0033] Preferably, the cleaned soil particles are washed with clean water in a soil washing / scrubbing unit or a dewatering screen before being deposited into a cleaned soil repository. Further preferably, the remediation process is performed in a single processing vessel configured to perform multiple sequential treatment cycles.

[0034] In use, at least one of the remediation cycles may introduce compressed air and fresh water from the inlet situated towards the bottom of the processing vessel, utilising a gas flotation technique to enhance the upward movement of oil for subsequent separation.

[0035] Preferably, each remediation cycle time is around 10 minutes.

[0036] In use, the wastewater drawn from the vessel may be subsequently heated by a heating unit located downstream of the vessel before being passed to a dissolved air flotation (DAF) unit for oil removal.

[0037] Preferably, the heating unit operates at a temperature of between around 70°C to around 90°C.

[0038] Further preferably, residual tar balls and stones separated from the cleaned soil are subjected to a high-speed, heated mixing process.

[0039] In use, a flocculant can be added to the treated wastewater for the aggregation and removal of suspended solids during clarification.

[0040] Further according to the present invention there is provided an ultrasonic transducer assembly for use in soil remediation, comprising: a pair of multi-layered ultrasonic emitters mounted onto a common transducer pad, the pad having an output face that is affixed to a vessel or component of the soil remediation system for transmitting ultrasonic waves into a slurry mixture, and wherein each ultrasonic emitter comprising first and second piezoelectric elements placed in a stack and interposed between the common transducer pad and to an opposite end cap; the piezoelectric elements arranged to have their motion additive and positioned so that their positive poles contact a positive electrode that is insulated from the rest of the assembly; and being configured to generate ultrasonic vibrations in response to an applied electrical voltage between the positive terminal and the assembly. Moreover according to the present invention there is provided method for ultrasonically separating component materials disposed in an aqueous slurry, comprising the steps of: introducing the slurry into a vessel; applying ultrasonic treatment to the slurry to induce acoustic cavitation and facilitate separation of components; separating the components of the aqueous materials based on differences in density, size or other physical properties; and collecting the separated components.

[0041] Also further according to the present invention there is provided a screw conveyor apparatus, comprising: a helical screw blade configured to convey an aqueous slurry along a conveying axis; a generally cylindrical housing enclosing the screw blade and defining a conveying chamber; an inlet positioned at one end of the conveying chamber for receiving the slurry to be conveyed by the screw blade; an outlet positioned at the opposite end of the conveying chamber for discharging conveyed slurry, wherein the screw blade is configured to rotate within the conveying chamber to convey the slurry from the inlet to the outlet; and at least one ultrasonic transducer positioned adjacent to the cylindrical housing and configured to emit ultrasonic energy into the slurry as it is conveyed by the screw blade.

[0042] It is believed that a method and system for treating contaminated materials in accordance with the present invention at least addresses the problems outlined above.

[0043] It will be obvious to those skilled in the art that variations of the present invention are possible and it is intended that the present invention may be used other than as specifically described herein.

[0044] BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The present invention will now be described by way of example only, and with reference to the accompanying drawings, in which: Figure l is a partly-schematic flow diagram of the soil remediation process and system in accordance with the present invention;

[0046] Figure 2 shows isometric views of an ultrasonic transducer assembly which is utilised in the soil remediation process and system of the present invention; and

[0047] Figure 3 is a partly-schematic flow diagram of the soil remediation process and system in accordance with a second embodiment of the present invention.

[0048] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] The present invention has adopted the approach of utilising a method and system to efficiently and effectively remediate hydrocarbon-contaminated sand and soil. Advantageously, the present invention provides a method and system which improves the quality and yield of remediated soil with minimal or no chemical or thermal processing, and which vastly improves the sustainability thereof. Further advantageously, these efficiencies lead to both a reduced clean-up time and resource usage, such that the method and system realises significantly lower power / energy utilisation, coupled with much lower water requirements since around 80% of the process water is recycled (the contaminated soil absorbs most of the water lost). Further advantageously, the present invention also provides a method and system to remediate soil to around <1% hydrocarbon residual content. The system having a modular and scalable construction and which provides around 3 to 100 tonnes / hour processing capability per unit, and multiple units can be utilised to process a higher throughput. Such a standalone, modular construction means that there is no risk of contamination from neighbouring processing units. Further advantageously, the present invention also provides a method and system that can remediate other contaminated materials such as, but not limited to, any of the following: oil and gas industry by-products (including oil tank sludge), mining and resource extraction residues, bio-mining wastes and fines from landfill sites, as well as treating agricultural and farmland pollutants and the like.

[0050] Referring now to the drawings, a partly-schematic flow diagram of the soil remediation process and system 10 in accordance with the present invention is shown in Figure 1. For the sake of clarity, not all components or elements of the soil remediation system 10 are depicted in the drawings. For example, the skilled person will understand that additional control elements such as sensors, transducers, valves, etc., which regulate the process, are present but are not depicted.

[0051] When used in this specification and claims, the terms “soil” and “sand” are used interchangeably and “soil” refers to the loose layer of earth that covers the surface of the planet. The skilled person will understand that “sand” is therefore a variant of soil and it refers to a loose material that predominately consists of rocks or mineral grains that have been broken down over time. Accordingly, the present invention is applicable to both soil and sand remediation.

[0052] The system 10 that implements the soil remediation process of the present invention begins with a mechanical handling and size reduction phase involving loading oil- contaminated soil from a contaminated soil laydown area 12 into a hopper 14 above a crusher 16.

[0053] The contaminated soil laydown area 12 serves as the designated deposit site for oil- contaminated soil awaiting processing. This area is designed to facilitate the systematic handling and processing of contaminated soil materials, ensuring efficient remediation processes.

[0054] The contaminated soil undergoes the first stage of size reduction, breaking it down into smaller uniform particles which facilitates efficient processing. The crusher 16 being one that is known in the art for breaking aggregate materials down into smaller, more manageable sizes.

[0055] After passing through the crusher 16, the size-reduced soil particles are conveyed along a conveyer 18 to a mechanical sieve 20 which plays a crucial role in ensuring uniformity in particle size. This sieving step involves using a mesh screen to separate particles based on size, thereby ensuring consistent processing throughout the soil remediation system 10. A conveyor belt system 22 is then utilised to transport the sieved soil to the next stage of in the remediation process. As shown in Figure 1, the sieved soil is deposited into the top 24 of a primary remediation processing vessel 26.

[0056] In a preferred embodiment, the shape of the primary remediation processing vessel 26 is cylindro-conical. This is in no way intended to be limiting as in use any number of geometric configurations can be utilised. What is evident from Figure 1 is that the primary remediation processing vessel 26 serves as an enclosed volume into which sieved soil 12 and process water can be combined by mixing to form a contaminated slurry. This mixing process ensures that the soil particles are evenly suspended in the water, creating a homogeneous mixture.

[0057] A surfactant can also be introduced into the processing vessel 26 from a dedicated surfactant vessel 28 which enhances the effectiveness of the cleaning process, as described in further detail below.

[0058] As described above, water is added to the primary remediation processing vessel 26 through an inlet 30 situated towards the bottom 32 of the vessel 26. The process water is being pumped 34 from a dedicated recycled water supply tank 36 through a degassing water unit 38 into the inlet 30.

[0059] The degassing water unit 38 is required to further enhance the efficiency and effectiveness of the ultrasonic processing. The degassing water unit 38 removes dissolved gases and air bubbles from the water before it enters the processing vessel 26. Dissolved gases and air bubbles would otherwise interfere with the cavitation process induced by the ultrasonic waves, potentially reducing the effectiveness of oil and contaminant removal. Removal of these gases from the water will result in maximum ultrasonic cleaning performance, and, in a preferred embodiment of the invention, this is achieved using ultrasonic emitters 40.

[0060] Ultrasonically degassing is an efficient method of removing dissolved gasses and / or entrained gas bubbles from a variety of liquids, including water. Whilst Figure 1 illustrates the use of ultrasonic degassing 40, this is in no way intended to be limiting or exhaustive, as the degassing water unit 38 can instead utilise degasification methods including vacuum degassing, thermal degassing, membrane degassing, chemical degassing, absorption-based degassing, steam stripping degasification and the like, as would be known in the art.

[0061] At its core, the primary remediation processing vessel 26 enables the contaminated slurry to be homogenously mixed and ultrasonically remediated.

[0062] The primary processing vessel 26 is where the first stage of the ultrasonic soil remediation process takes place. Within the processing vessel 26, the sieved soil is mixed with clean degassed water using series of agitator blades 44, creating a homogeneous slurry mixture. Ultrasonic emitters (schematically shown as numerals 42a-42f) are positioned around the circumference of the vessel 26 at various heights, and which aid in optimising dispersion and agitation, thereby enhancing the effectiveness of subsequent cleaning stages. The ultrasonic emitters 42a-42f are part of an ultrasonic transducer assembly 108 (as described in further detail in relation to Figure 2) which operates at a frequency of around 30kHz to 50kHz ± 2kHz, emitting powerful ultrasonic waves that permeate the slurry mixture.

[0063] In an alternative embodiment of the invention, supplementary ultrasonic emitters may be positioned inside vessel 26, and arranged on arms within the slurry itself.

[0064] The surfactant is introduced from the dedicated surfactant vessel 28 into primary remediation processing vessel 26 and which enhances the effectiveness of the cleaning process. Again, there are a number of sensors, pumps, valves, etc., that are omitted from the drawing for the reasons of clarity, but the skilled person will understand that the control of the remediation process, and introduction of the surfactant, is a closed-loop control process, the actual implementation of which is embedded in a controller (not shown).

[0065] In use, the surfactant is selected for its surface-active properties, and serves a dual purpose in enhancing the effectiveness of the cleaning process. Firstly, the surfactant molecules adsorb onto the oil droplets, reducing their surface tension and facilitating their dispersion within the aqueous phase. Secondly, the surfactant molecules disrupt the hydrogen bonding between water molecules, further reducing surface tension and enhancing the penetration of ultrasonic waves into the slurry mixture.

[0066] In a preferred embodiment of the invention, the surfactant is an alkaline detergent which may be in liquid or powder form.

[0067] The emitted ultrasonic waves induce a phenomenon known as acoustic cavitation within the slurry mixture. Cavitation involves the rapid formation and collapse of microbubbles, generating localised shockwaves and turbulence. This cavitation process exerts mechanical forces on the soil particles, dislodging oil and contaminants adhering to their surfaces.

[0068] The combined action of ultrasonic cavitation by emitters 42a-42f and surfactant- mediated surface tension reduction synergistically enhances the cleaning efficacy within the primary processing vessel 26. As ultrasonic waves penetrate deeper into the slurry mixture, aided by the surfactant, they exert greater mechanical forces on oil droplets and contaminants enabling their detachment from the soil particles. This synergistic effect ensures thorough and efficient separation of oil and contaminants from the soil matrix, resulting in significantly cleaner soil particles.

[0069] The skilled person will equally understand that the soil remediation process of the present invention can also operate without the addition of any surfactant, but the efficiency will inevitably be reduced and the clean-up time prolonged.

[0070] The primary processing vessel 26 is engineered to maintain precise control over ultrasonic frequency, power density, and surfactant concentration. These parameters are optimised to maximise cleaning efficiency while minimising energy consumption and process time. The primary processing vessel 26 achieves exceptional cleaning results, ensuring the production of high-quality, remediated soil suitable for re-use.

[0071] Figure 1 also shows that within the vessel are a series of agitator blades 44 located on a common shaft and driven by a motor 46 which is positioned towards the top 24 of the vessel 26. The agitation blades 44 ensures continuous slurry movement, allowing the application of sound waves to proficiently separate oil and contaminants. A scum scraper 48 is also positioned within the vessel 26 at what would be the height of a batch of slurry. The vessel 26 also comprises the number of oil outflows which are positioned generally at the height of the soil level 50 and generally at the height of the water level 52, respectively. These outflows 50, 52 can be used selectively to draw-off already liberated oil formations which will rise to the surface of the soil and the water. This oil and oil-water mix drawn-off from the vessel 26 is then treated at the oil-water separator 86, as described in further detail below.

[0072] The internal structure of the pressure vessel 26 may also include various internal fins or ribs (not shown in Figure 1) which also aid with the mixing effect.

[0073] After a period of batch processing, any freely-liberated oil and oily water is then drawn- off through outflows 50, 52, but the bulk of the slurry mixtures exits the vessel 26 at outflow 54 which is positioned at the at very bottom of the cylindro-conical vessel 26 for further remediation.

[0074] The soil-water slurry mixture is then pumped 56 from one processing vessel 26 to a secondary stage vessel 26' for further processing. As it does so it undergoes a continuous and intense ultrasonic treatment. Although not shown fully in Figure 1, the soil-water slurry mixture is subject to a consistent and intense blast of ultrasonic energy during its transit between the processing vessels 26, 26' by virtue of ultrasonic tubular processor 58.

[0075] The ultrasonic tubular processor 58 functions as a conduit for the transmission of ultrasonic waves, amplifying the energy and intensity of the ultrasonic treatment. This amplification mechanism ensures thorough and efficient cleaning of the soil particles, maximising the removal of oil and contaminants with each processing step. The ultrasonic tubular processor 58 comprises a tube or conduit around which a series of ultrasonic emitters (not shown in Figure 1) are positioned.

[0076] Within the ultrasonic tubular processor 58, the high-frequency ultrasonic waves induce acoustic cavitation phenomena, creating microscopic bubbles that implode upon contact with the soil-water mixture. These implosions generate intense localised energy, effectively dislodging and disintegrating oil and contaminants adhering to the soil particles.

[0077] The seamless integration of the ultrasonic tubular processor 58 into the remediation system 10 ensures a continuous and uninterrupted treatment cycle. As the soil-water mixture progresses from one processing vessel 26 to the next 26', it undergoes multiple cycles of ultrasonic treatment, enhancing thorough cleaning of the soil particles.

[0078] By subjecting the soil-water mixture to multiple intense blasts of ultrasonic energy, the remediation system achieves unparalleled cleaning efficiency. The ultrasonic tubular processor 58 augments the effectiveness of ultrasonic technology and delivers enhanced results in oil and contaminant removal.

[0079] After the slurry has transited the ultrasonic tubular processor 58 it then enters the secondary vessel 26' via a slurry hydrocyclone 60. The hydrocyclone is a high- throughput gravity separation device used for separating slurry particles based on particle weight. Particles of different specific gravity (such as oil or oily water) can then drawn- off through overflow 62. The slurry then passes into the secondary vessel 26'.

[0080] Subsequently, the slurry undergoes further refinement within the secondary processing vessel 26', and the cleaned solids are transferred to the secondary processing vessel 26' where fresh water is added through inlet 30'. Again utilising ultrasonic technology, this vessel 26' ensures comprehensive cleaning, maximising the removal of residual impurities and contaminants from the soil particles. Similar to the primary processing vessel 26, surfactant can also be introduced from surfactant vessel 28.

[0081] Again, after a period of batch remediation processing in the secondary processing vessel 26', the next stage in the remediation process involves the treated slurry passing to separation and polishing stages.

[0082] The secondary vessel outflow 54' supplies the slurry to a liquid-solid separator 64. In this crucial stage, the slurry undergoes separation to efficiently remove solid particles and oil from the water. The system 10 includes a liquid-solid separator 64 which is utilised to achieve precise separation, maximising the purity of the resulting water at outflows 66. Within the separator 64, ultrasonic technology, shown as emitters 68a, 68b is seamlessly integrated to again augment separation efficiency. The liquid-solid separator 64 is engineered to ensure optimal performance and reliability. Precision-designed components, including inlet and outlet 66 configurations, ensure uniform flow distribution and maximise particle retention efficiency.

[0083] Again ultrasonic emitters 68a, 68b are strategically positioned within the liquid-solid separator 64 which emit high-frequency ultrasonic waves. These waves induce controlled cavitation within the slurry mixture, generating microbubbles that disrupt the adhesion between solid particles, oil droplets, and water molecules. This acoustic cavitation process enhances particle agglomeration and facilitates their separation from the water phase, thereby contributing to the overall effectiveness of the separation process.

[0084] The purified soil then passes to a polishing screw 70. This stage of the process involves a screw system 70 which lifts and polishes the soil, again augmented by acoustic energy from ultrasonic emitters 72.

[0085] The polishing screw 70 further refines the soil quality, ensuring the elimination of any remaining contaminants and impurities. Ultrasonic emitters 72 strategically positioned along the screw enhance the polishing process by providing additional energy input. The ultrasonic emitters 72 integrated along the polishing screw 70 emit high-intensity ultrasonic waves into the water stream.

[0086] The polishing screw 70 is tubular and elongate having an inlet 74 at one end and an outlet 76 at the other, opposite end thereof. Rotational motion of an internal lead screw (not shown) pushes the purified soil to the outlet 76. The polishing screw 70 is manufactured from corrosion-resistant materials, ensuring durability and longevity in harsh operating environments. Advanced surface coatings and treatments may be applied to minimise fouling and deposition, thereby prolonging operational life and reducing maintenance requirements when in use.

[0087] The purified soil is then supplied into a soil wash unit 78. In use, the purified soil enters a soil washing / scrubbing unit 78, in which the soil is rinsed with clean washing water 80. The wash water 82 is then drained from the washed soil. After washing, the heavier cleaned soil is allowed to settle and is removed. The result is that oil-free soil is deposited into a designated cleaned soil repository 84.

[0088] The clean water is stored within dedicated tanks 80. These tanks ensure the availability of a continuous and reliable water supply to i) facilitate the first fill of the system 10, and ii) provide top-up water to the system 10 which is used for the final soil wash with clean water.

[0089] The final stage of the soil wash processing reduces the contained water from typically 20% down to around 5%. This enables the optimum amount of water to be recirculated and enables to the final soil to be discharged to the designated cleaned soil repository 84.

[0090] The water flow rate, pressure, and temperature are also precisely regulated to achieve maximum washing efficacy while minimising water consumption and environmental impact.

[0091] The soil wash unit 78 is equipped with advanced monitoring and control systems to ensure consistent washing performance. Real-time sensors and instrumentation are employed to monitor key parameters such as water flow rate, soil particle size distribution, and impurity levels. This data is continuously analysed and used to adjust operating parameters, optimising washing efficiency and maintaining product quality standards.

[0092] Following successful remediation, the reconditioned soil is deposited within designated laydown areas 84. These areas are strategically located within the facility and are equipped with appropriate containment measures to ensure the proper storage and containment of cleaned soil materials, ready for subsequent re-use.

[0093] After completion of the primary remediation process of the system 10, the next pivotal stage involves wastewater treatment. This phase is dedicated to the removal of oil contaminants from the wastewater, thereby transforming it into an effluent suitable for recycling within the process loop. While distinct from the primary remediation process, wastewater treatment is indispensable for ensuring comprehensive recovery of both wastewater and contaminants, thereby promoting environmental sustainability and process efficiency.

[0094] The wastewater returning from outlets 50, 50', 52, 52', 62, 66, 82 is returned to a wastewater treatment process. The first stage of the wastewater treatment involves passing the wastewater and oily water to an oil-water separator 86 which is a gravitybased separator. The oil-water separator relies on the gravity difference between water and the specific gravities of oils and solids to initially remove as much waste oil as possible. The waste oil separated during the remediation process is then stored within storage tanks 88. These tanks ensure the proper containment of waste oil, mitigating the risk of environmental contamination. When the waste oil storage tanks 88 approach capacity, the waste oil is taken away by dedicated loading 90 for further treatment or recycling. This practice adheres to responsible waste management principles, ensuring the efficient handling and recycling of waste oil.

[0095] The water obtained from the oil-water separator 86 is held in a sump 92 before being pumped 94 to a fines separation processor 96. The fines separation processor 96 is an important stage in the wastewater treatment process which focusing on the removal of fine particles suspended within the water. By employing various separation techniques, including hydrocyclones and centrifuges, this stage ensures the separation of solids from the residual oily water.

[0096] Particles around 65 pm and above are recovered as additional processed soil 98.

[0097] Fines below around 65 m are sent to a filter press 100.

[0098] The final stage of water treatment involves the utilisation of a sophisticated filter press 100. The filter press 100 employs precision filtration mechanisms to remove any residual impurities present in the water. Through the application of pressure, the filter press 100 effectively separates solid particles from the water. Once the filtration process is complete, the filter press 100 is opened, and the solid cake 104 is discharged from the chambers of the press 100. The filtrate, which is the clean water 106 that has passed through the filter media 100, and / or the aqueous output of the fines separator 96 is then passed on to a water clarifier 102 for further cleaning. Within the water clarifier 102, the treated water undergoes a precision clarification process aimed at enhancing water quality. This process involves the removal of suspended solids through the application of settling agents and other clarification aids as would be known to a person skilled in the art. The clarifier 102 removes residual contamination enabling the processed water to be recycled for re-use in the recycled water supply tank 36, or it can be discharged into the environment.

[0099] Post-treatment, the recycled water is stored in a dedicated tank 36 for future use. This practice minimises water wastage and promotes environmental sustainability by facilitating the reuse of treated water in subsequent processing operations.

[0100] Various other components and facilities are not shown in Figure 1 primarily for reasons of clarity.

[0101] These include an air compressor (not shown) which is utilised to generate compressed air required for various operational functions, including powering pneumatic equipment and facilitating air-driven processes essential for the efficient operation of the remediation system 10.

[0102] Power generation within the facility relies on the availability of stored fuel oil and dedicated generator sets (not shown). These components ensure a reliable and uninterrupted power supply essential for sustaining continuous processing operations throughout the remediation process.

[0103] A control room (not shown) oversees all operational aspects of the remediation system 10 and which facilitates efficient power distribution and monitoring of system parameters, ensuring smooth and coordinated system operation.

[0104] Figure 2 shows isometric views of an ultrasonic transducer assembly 108 which is utilised in the soil remediation process and system 10 of the present invention. In a preferred embodiment, a pair of multi-layered ultrasonic emitters 42 can be mounted onto a single common transducer bar or pad 110 and which provides an enhanced acoustic cavitation for dislodging oil and contaminants from the slurry mixture.

[0105] Each ultrasonic emitter 42 is configured as a multi-layered piezoelectric transducer having piezoelectric elements which are interposed between two metallic faces.

[0106] The outer metallic face 112 provides structural support, and forms the outermost layer of the assembly 108.

[0107] A first piezoelectric element 114 is sandwiched between the outer metallic face 112 and a positive electrode 116. The electrode 116 serves to connect the positive pole of both piezoelectric elements 114, 118 to an electrical circuit (not shown). When subjected to an electric field, piezoelectric elements 114, 118 undergo deformation, generating mechanical vibrations.

[0108] The second piezoelectric element 118 is sandwiched between the positive electrode 116 and a negative electrode 120. The remaining parts of the assembly 108 including the two masses 108, 112 are at negative or ground potential and complete the circuit for the negative poles of the piezoelectric elements 114, 118.

[0109] The two piezoelectric elements 114, 118 are arranged in such a way that their motion is additive. As shown in Figure 2, the two piezoelectric elements 114, 118 are positioned so that their positive faces contact the centre positive electrode 116 which is insulated from the rest of the assembly 108.

[0110] Finally, the single transducer bar or pad 110 forms the innermost part of the transducer assembly 108. This bar 110 comes into contact with the cleaning vessels 26, 26' or the environment (38, 58, 70) in which the assembly 108 operates, facilitating the transmission of ultrasonic waves into the slurry.

[0111] The assembly 108 is resonant at the desired operating frequency.

[0112] The entire assembly 108 is cylindrical in shape, and is clamped together by a bolt 122 running through the centre thereof. This bolt 122 applies compression to the piezoelectric elements 114, 118, ensuring proper contact and alignment between the components. This compression is crucial for proper operation and resonance at the desired frequency.

[0113] In use, the transducer bar or pad 110 is affixed to the various vessels 26, 26' or components 38, 58, 70 through an opening 124.

[0114] This configuration is tailored to optimise energy transfer and cavitation efficiency for ultrasonic cleaning applications. By carefully controlling the shape, thickness, and material properties of the various components, it is possible to maximise the cleaning effectiveness and efficiency of the ultrasonic system.

[0115] Figure 3 shows a second embodiment of the soil remediation process and system 10. The construction of the second embodiment is very similar to that of the first embodiment and corresponding features have been given the same reference numerals. The second embodiment differs from the first embodiment in a number of ways, but fundamentally instead of passing the soil-water slurry mixture through two processing vessels 26, 26' in series, the soil remediation process and system 10 of the second embodiment utilises only a single remediation processing vessel 26 configured to execute two or more processing cycles. In addition, the remediation process and system 10 of the second embodiment involves heating, as described in further detail below.

[0116] In the second embodiment of the present invention, acoustic cavitation of the slurry mixture is performed in the processing vessel 26 very much like in the first embodiment. However, the subsequent refining process has been modified after this initial separation of the different waste streams, resulting in a higher yield of remediated materials and improved processing efficiency.

[0117] The process and system 10 is specifically designed for the remediation of oil- contaminated soil with a hydrocarbon residual content, sometimes referred to as a total petroleum content (TPC), of around 3% to around 15%. At its core, the process and system 10 again utilises ultrasonic technology, gas flotation, mechanical separation and multi-stage treatments to achieve efficient oil removal and soil recovery. The process and system 10 is fully scalable by adding additional processing vessels to meet higher throughput requirements. Very much like that described in the first embodiment, the contaminated soil 12 is first crushed 14 and sieved 16 to remove oversized debris, ensuring uniform particle size distribution. The sieved sand is then stored in a hopper 20 before being conveyed 22 into the ultrasonic processing vessel 26. Water is then added to the primary remediation processing vessel 26 through an inlet 30 situated towards the bottom 32 of the vessel 26. As the vessel 26 fills, ultrasonic transducers 42a-42f are activated in activated in a staged sequence from the bottom of the vessel 26 upward, to degas the water, removing dissolved gases and entrained air bubbles. In one embodiment, the agitator 44 operates at around 17 rpm to aid mixing and improve cavitation efficiency.

[0118] The primary or first ultrasonic cleaning cycle then commences. Once the vessel 26 is filed, the ultrasonic transducers 42a-42f operate for around 10 minutes, generating cavitation forces that detach oil from the soil particles. After ultrasonic treatment, the oily water, containing dislodged oil and fine particles can be drawn-off through outflows 50, 52. This wastewater is passed to a dissolved air flotation (DAF) unit 128 for initial oil separation. The soil remains in the vessel 26 for one or more further secondary remediation cycles.

[0119] A secondary remediation cycle then commences with compressed air and fresh water being reintroduced from the inlet 30 situated towards the bottom 32 of the vessel 26. Such a gas flotation technique encourages the upward movement of residual oil through the vessel 26, supporting additional separation through outflows 50, 52. Once the vessel 26 is filled, the ultrasonic transducers 42a-42f are activated for an additional cycle of around 10 minutes. This maximises the further breakdown of oil residues.

[0120] This second batch of contaminated water is drained through outflows 50, 52 and passed to the dissolved air flotation (DAF) unit 128 to ensuring removal of suspended oil and fines before moving to the final soil processing stage.

[0121] The cleaned or purified soil then exits the vessel 26 through outflow 54 and is drawn, using a screw conveyer 130, to an oversized screen 132 over a material screw washer 134 for further machinal scrubbing, as will be described below. The soil is screened on the oversized screen 132 to separate tar balls and stones before being transferred to a log or screw washer 134, which is additionally fitted with ultrasonic transducers 136 to further remove any remaining oil from the soil.

[0122] A dewatering screen 138 then ensures the remediated soil achieves the required moisture content standards, after which the cleaned soil (around +500 microns) is conveyed 140 and collected as the final treated product 142.

[0123] The oversized screen 132 separates tar balls and stones from the cleaned soil. While the tar balls are removed, the recovered stones are directed to a return sump mixing unit 144. From there, they are pumped 148 through a heating unit 126 and subjected to a highspeed, heated mixing process 146 at around 70°C to 90°C to break down any residual tar. The heated mixture is then processed through an oversized screen 150, followed by a final dewatering screen 152, to ensure complete separation. The result is fully remediated soil 154.

[0124] As described above, the separated oily water from the primary and secondary cleaning cycles is heated by heating unit 126 before being passed to a dissolved air flotation (DAF) unit 128 for initial oil separation. At the DAF unit 128, the oil and solids are separated, with the recovered oil being sent to the oil storage tank 88.

[0125] The treated water is transferred to a desilter 156 for fine particulate removal 158. Water from the desilter 156 is sent to a clarifier 160 where flocculants 162 aid in final separation. The oil skimmed from the clarifier 160 is sent to an oil-water storage tank 164. The fines that settle are sent, via a buffer tank 166, to a decanter centrifuge 168 where a filter cake 104 is produced. The clean water is then stored in a process water tank 170 for re-use.

[0126] A second desilter 172 is also used for fine particulate removal 174. This being fed from the treated water from the dewatering screen 138.

[0127] Recovered oil from the flotation 128 and clarification 160 units is collected in the oil storage tank 88. The oil can be further refined or disposed of 90 in an environmentally compliant manner. To further enhance the efficiency of oil separation, a thermal oil heater 176 is incorporated into the system. This heater warms the oily water circulating around the log or screw washer 134 and the dissolved air flotation (DAF) unit 128, maintaining the process wastewater at an elevated temperature, typically between 70°C and 90°C. The increased temperature lowers the viscosity of the oil, thereby improving its separation from the soil and water phases during both mechanical scrubbing and flotation. This thermal conditioning step ensures that the oil removal processes within the washer 134 and DAF unit 128 operate at optimal performance, contributing significantly to the overall remediation effectiveness.

[0128] Therefore, a method and system 10 is provided to efficiently and effectively remediate contaminated soil.

[0129] When used in this specification and claims, the terms “comprises” and “comprising” and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components. The singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes” and / or “including” when used herein, specify the presence of stated features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0130] The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, separately, or in any combination of such features, can be utilised for realising the invention in diverse forms thereof.

[0131] The invention is not intended to be limited to the details of the embodiments described herein, which are described by way of example only. It will be understood that features described in relation to any particular embodiment can be featured in combination with other embodiments. It is contemplated by the inventor that various substitutions, alterations and modifications may be made to the invention without departing from the spirit and scope of the invention as defined by the claims.

Claims

CLAIMS1. A method for remediating hydrocarbon-contaminated soil, comprising the steps of: size-reducing the hydrocarbon-contaminated soil particles; mixing the size-reduced soil particles with water to form a slurry mixture, wherein the water is degassed prior to or during mixing within a processing vessel; subjecting the slurry mixture to ultrasonic treatment to induce acoustic cavitation and dislodge contaminants from the soil particles; separating the cleaned soil particles from the slurry mixture; and washing the cleaned soil particles with clean water to remove contaminants.

2. A soil remediation system, comprising: a primary processing vessel configured to receive hydrocarbon-contaminated soil particles and water to form a slurry mixture, wherein the water is degassed prior to or during mixing within the processing vessel; one or more ultrasonic emitters being positioned around the primary processing vessel and being configured to induce acoustic cavitation within the slurry mixture; a conveyer system for transporting the slurry mixture to subsequent processing stages; and a series of processing vessels and equipment for further refining the cleaned soil particles and treating wastewater generated during the soil remediation process.

3. The method or system of claims 1 or 2, wherein the water is degassed within the processing vessel by activating ultrasonic emitters in a staged sequence from the bottom of the vessel upwards, to remove dissolved gases and / or entrained air bubbles or from a separate water degassing unit.

4. The method or system of claims 1 or 2, wherein the size reduction of hydrocarbon-contaminated soil particles involves crushing and sieving to ensure uniformity in particle size before mixing with degassed water.

5. The method or system of claims 1 or 2, wherein the ultrasonic treatment is performed at a frequency of around 30 to 50kHz.

6. The method or system of claims 1 or 2, further comprising introducing a surfactant into the slurry mixture to enhance the effectiveness of oil removal.

7. The method or system of claim 6, wherein the surfactant is an alkaline detergent.

8. The method or system of claims 1 or 2, wherein the separation of cleaned soil particles from the slurry mixture is performed using a hydrocyclone.

9. The method or system of claims 1 or 2, wherein the cleaned soil particles are polished using a log washer or ultrasonic energy emitted from ultrasonic emitters positioned along a polishing screw.

10. The method or system of claims 1 or 2, further comprising recycling the treated water for re-use in the remediation process through a desilter, clarifier and water storage system.

11. The method or system of claims 1 or 2, wherein the wastewater generated during the remediation process is treated in an oil-water separator, fines separation processor, and filter press to remove oil and contaminants or passed through a dissolved air flotation (DAF) unit, desilter, clarifier and centrifuge stages.

12. The method or system of claims 1 or 2, wherein the process parameters including ultrasonic frequency, power density, process temperature and / or surfactant concentration are controlled to optimise cleaning efficiency and minimise energy consumption.

13. The method or system of claims 1 or 2, further comprising monitoring key process parameters such as water flow rate, soil particle size distribution, temperature and / or impurity levels during the remediation process.

14. The method or system of claims 1 or 2, wherein the ultrasonic treatment is performed continuously as the slurry mixture is transported between processing stages or in repeated cycles within a single processing vessel.

15. The method or system of claims 1 or 2, wherein the slurry mixture is mechanically-agitated.

16. The method or system of claims 1 or 2, wherein the ultrasonic treatment is performed in a batch processing mode comprising multiple sequential ultrasonic cycles within a single vessel.

17. The method or system of claims 6 or 7, wherein the surfactant disrupts hydrogen bonding between water molecules to enhance the penetration of ultrasonic waves into the slurry mixture.

18. The method or system of claims 6 or 7, wherein the surfactant adsorbs onto oil droplets, reducing their surface tension and facilitating their dispersion.

19. The method or system of claims 1 or 2, wherein the ultrasonic treatment is performed using ultrasonic emitters positioned around the circumference of a processing vessel at one or more vessel heights.

20. The method or system of claims 1 or 2, wherein the ultrasonic treatment is enhanced by supplementary ultrasonic emitters positioned inside the processing vessel and arranged on arms disposed within the slurry.

21. The method or system of claims 1 or 2, wherein the slurry mixture is pumped between processing vessels and subjected to ultrasonic treatment during transit using an ultrasonic tubular processor or is retained in a single vessel and subjected to multiple ultrasonic and flotation cycles.

22. The method or system of claims 1 or 2, wherein the cleaned soil particles are washed with clean water in a soil washing / scrubbing unit or a dewatering screen before being deposited into a cleaned soil repository.

23. The method or system of claims 1 or 2, wherein the remediation process is performed in a single processing vessel configured to perform multiple sequential treatment cycles.

24. The method or system of claims 1 or 2, wherein at least one of the remediation cycles introduces compressed air and fresh water from the inlet situated towards the bottom of the processing vessel, utilising a gas flotation technique to enhance the upward movement of oil for subsequent separation.

25. The method or system of claims 1 or 2, wherein each remediation cycle time is around 10 minutes.

26. The method or system of claims 1 or 2, wherein the wastewater drawn from the vessel is subsequently heated by a heating unit located downstream of the vessel before being passed to a dissolved air flotation (DAF) unit for oil removal.

27. The method or system of claim 26, wherein the heating unit operates at a temperature of between around 70°C to around 90°C.

28. The method or system of claims 1 or 2, wherein residual tar balls and stones separated from the cleaned soil are subjected to a high-speed, heated mixing process.

29. The method or system of claims 1 or 2, further comprising the addition of a flocculant to the treated wastewater for the aggregation and removal of suspended solids during clarification.

30. An ultrasonic transducer assembly for use in soil remediation, comprising: a pair of multi-layered ultrasonic emitters mounted onto a common transducer pad, the pad having an output face that is affixed to a vessel or component of the soil remediation system for transmitting ultrasonic waves into a slurry mixture, and wherein each ultrasonic emitter comprising first and second piezoelectric elements placed in a stack and interposed between the common transducer pad and to an opposite end cap; the piezoelectric elements arranged to have their motion additive and positioned sothat their positive poles contact a positive electrode that is insulated from the rest of the assembly; and being configured to generate ultrasonic vibrations in response to an applied electrical voltage between the positive terminal and the assembly.

31. A method for ultrasonically separating component materials disposed in an aqueous slurry, comprising the steps of: introducing the slurry into a vessel; applying ultrasonic treatment to the slurry to induce acoustic cavitation and facilitate separation of components; separating the components of the aqueous materials based on differences in density, size or other physical properties; and collecting the separated components.

32. A screw conveyor apparatus, comprising: a helical screw blade configured to convey an aqueous slurry along a conveying axis; a generally cylindrical housing enclosing the screw blade and defining a conveying chamber; an inlet positioned at one end of the conveying chamber for receiving the slurry to be conveyed by the screw blade; an outlet positioned at the opposite end of the conveying chamber for discharging conveyed slurry, wherein the screw blade is configured to rotate within the conveying chamber to convey the slurry from the inlet to the outlet; and at least one ultrasonic transducer positioned adjacent to the cylindrical housing and configured to emit ultrasonic energy into the slurry as it is conveyed by the screw blade.

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