Air Sparging Research Articles

Derivation of site-specific environmental quality guideline values for fuel-contaminated soils on sub-Antarctic Macquarie Island.

Accidental fuel spills associated with the storage, transfer, and use of diesel fuel for power generation have occurred on sub-Antarctic Macquarie Island since the establishment of the island's research station in 1948. An extensive in situ remediation program was implemented by the Australian government from 2009 to 2016 that used nutrient addition and air sparging to enhance the microbial degradation of petroleum products. During this period, a range of ecotoxicological assessments were conducted to better understand the impacts of fuel in soils on native biota and their sensitivity. This study compiles this ecotoxicological data into a species sensitivity distribution (SSD) to establish environmental quality guideline values (EQGVs) for fuels in soils on Macquarie Island. The SSD model includes 13 critical effect concentrations (CECs) selected using an expert judgment approach. These include data from functional and community-based tests as well as traditional single-species toxicity tests using microbes, plants, and invertebrates and representing the range of carbon content (~3%-48%) and fuel composition at various stages of degradation (from fresh to 18 months aged) in soils as occurs at contaminated sites on the island. A protective concentration (PC80) of 97 mg/kg TPH C9-C40 (95% CI 24-283) was derived for special Antarctic blend diesel from the SSD and is recommended as an appropriate site-specific EQGV and potential remediation target for the immediate station area in the vicinity of infrastructure. More conservative PC values are also provided for areas with higher conservation values outside the station footprint. These EQGVs are the first to be produced for fuels in the sub-Antarctic and Antarctic regions. They will be used to inform ongoing environmental management on Macquarie Island and are likely suitable and recommended for use more broadly across the sub-Antarctic. Integr Environ Assess Manag 2024;00:1-13. © 2024 Commonwealth of Australia. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Interaction between gas channels in water-saturated sands.

This work investigates the interaction between gas channels in a vertical Hele-Shaw cell when air is injected simultaneously from two points at a constant flow rate. Unlike single-injection experiments, this dual-point system induces the formation of numerous bubbles, thereby intensifying the interactions between air channels. We use an image analysis technique for tracking motion in the granular bed to define a flow density parameter throughout the cell. The vertical accumulation of this parameter (n_{z}) reveals two specific heights, one marking a finger-to-fracture transition and another indicating the average interaction height of the air channels. Conversely, its horizontal accumulation (n_{x}) assesses the extent of overlap in the fluidized zones created by each airflow. Notably, the analysis indicates that the optimum distribution of the three phases in the system is more closely related to the interaction's variability than its intensity. This finding is significant for industrial applications such as air sparging and catalytic reactors.

Mobility of Trace Elements During Remediation of Oil Polluted Groundwater: A Case Study of Al Batinah Region, Northeast Oman

A study was carried on an area polluted by oil in Oman to determine the mobility of trace elements during each step of an ex-situ treatment process. Quality of groundwater following an air flotation treatment was investigated and discussed. About 15 water samples were collected from 7 monitoring wells which are under air sparging treatment for remediation of oil contamination in Al Batinah region (Northeast of Oman). Chemical composition of groundwater during and after the treatment was compared with chemical composition of groundwater before any treatment. Water samples were also collected from different monitoring wells in the same area. The investigated elements consist in Na, Mg, Ca, K, Fe, Cr, Ni, Cu, Zn, Ag, Cd, Sr, Ba, Pb and rare earth elements (REEs). Chemical composition of trace and major elements during each step of treatment revealed that Ni, Zn, Cu and Al have been increased relative to untreated water contrary to Ag which decreased. Major elements and Cr, Pb, and Cd remain unchanged during the treatment process. The REEs were significantly depleted during the last step of treatment relative to the raw water but their distribution did not reveal any fractionation. Trace elements such as Zn, Cu, Ni show an increase and Ag and REES a decrease relative to raw water before any treatment. For treatment of groundwater, chemical investigation of different agents used during the treatment and the speciation of each key trace elements should be investigated at each step of treatment procedure.

Insights into temporal and spatial evolutions of air saturation and its effects on nitrobenzene removal during air sparging remediation

Air saturation (Sa) can significantly influence the removal effect during air sparging (AS). However, there have been few studies focused on the temporal and spatial distribution of the Sa, which is adverse to precise remediation of AS technology. In this study, temporal and spatial evolutions of the Sa and its effects on nitrobenzene removal were investigated by the one-dimensional column experiments during AS. Experimental results demonstrated that the variation of Sa at different positions of the aquifer was significantly different with the increase of sparging time under the same air injection rate (Qinj), and the variation of middle and lower position was 0.3%-11.0%, however, the variation of Sa at the upper position was 21.0%-40.0%. When the Qinj was small, the number of airflow channels was little, and the nitrobenzene removal rates at the middle and upper position were low. With the increase of Qinj, the number of airflow channels was many, and the main region of airflow (Trapezium distribution) began to appear at the lower position, and the nitrobenzene removal rate at the upper position was low, which showed that the nitrobenzene removal rate was mainly affected by the spatial and temporal distribution of Sa in AS process. Based on the above, the mathematical model of relationship between nitrobenzene removal rate, sparging time and Sa was established, which was conducive to the accurate design of AS technology in the site application.

Impact of Heavy Metal Contamination on Soil and Crop Ecosystem with Advanced Techniques to Mitigate Them

Heavy metal pollution in soils has become widespread globally due to both natural processes and human activities. Geologic and anthropogenic activities, such as mining, industrial processes, and agricultural practices, significantly contribute to heavy metal accumulation in soil, posing threats to both plant and animal health. These metals endure in the environment and build up in organisms because they resist breakdown or metabolism. They enter the food chain via primary producers and move up as higher trophic levels consume them. This contamination adversely affects the overall human health, plant growth, performance, and yield and also impacts the soil properties. To minimize this effect of heavy metal toxicity, bioremediation emerges as a highly effective method for treating such polluted soils, often conducted in situ, making it suitable for crop establishment or reestablishment. Bioremediation encompasses various techniques like bioventing, biostimulation, air sparging, natural attenuation, phytoremediation, vermistabilization, rhizofiltration, biosorption etc. Both microorganisms and plants play crucial roles in bioremediation, with the combined approach ensuring more efficient cleanup. However, the success of this method depends significantly on the specific species involved. Traditional physical and chemical remediation methods are often costly and fail to restore soil suitability for plant growth. In contrast, bioremediation offers a more environmentally friendly and economically viable solution, leveraging natural processes to encourage plant growth on contaminated soils.

Study on the gas phase migration and distribution characteristics in horizontal well air sparging remediation

Horizontal well air sparging (AS) technology has been proven to be efficient in remediating saturated soils and groundwater contaminated with volatile organic compounds (VOCs). Nevertheless, the airflow patterns and the mechanisms governing uniformity in the horizontal well AS process remain elusive, and a quantitative characterization of the zone of influence (ZOI) has yet to be determined. In this study, we employed both model experiments and numerical simulations to investigate the distribution patterns of lateral airflow in horizontal air sparging tubes within a porous medium. The influence of parameters such as air sparging pressure, groundwater flow, the inclination angle of the air sparging tubes, and the diameter of the medium particles on the distribution patterns of gas-phase transport in horizontal well AS was analyzed. The results show that both groundwater flow and the inclination of air sparging tubes disrupt the uniformity of gas distribution. The ZOI area of AS is observed as an oblong shape in the horizontal plane and a parabolic contour along the boundaries. Additionally, a mutual influence is identified between groundwater flow and AS airflow. Furthermore, the inclination of air sparging tubes results in the formation of preferential flow near the air source end. The ZOI of horizontal AS demonstrates a positive correlation with air sparging pressure and a negative correlation with medium particle diameter. All of the results elucidated above provide valuable information for the design and theoretical modelling of AS within horizontal wells for groundwater remediation.

Microalgae bio-reactive façade: Location and weather-based systematic optimization

This article explores the design of microalgae biofaçade thanks to a numerical model describing the system’s thermal and biological behavior. Design options (single vs. double glazing, radiation-selective film, culture reservoir thickness) and operation strategies (light transmission, microalgae strain, sparged air origin, boiler fumes reuse) are screened systematically. The context for this investigation was the city of Marseille over a 10-year period (2013 to 2022) for which detailed meteorological data were available (air temperature, wind velocity and orientation, cloud cover, at a 3-hour resolution). These investigations revealed a very high level of interaction between the parameters (assessed by H2 Friedman index), making the system notoriously complicated to design and optimize. Nevertheless, some conclusions can be drawn. In France, fitting double glazing equipped with a greenhouse radiation-selective film is essential to harness as much heat as possible (＋16.7 % and ＋6.5 % of operation duration over year 2018, respectively). Similarly, a thermophilic strain is not relevant because overheating events are inexistent in well-designed systems. Further refinements, such as the origin of the air blown into the culture reservoir and the reuse of combustion fumes from the boiler (＋2.1 % performance), were evaluated from a technical point of view. However, their implementation would also be subjected to other considerations, such as the financial costs and environmental benefits. Finally, the model was applied to design the most efficient possible microalgae biofaçade system in the case of a hypothetical official building renovation.

Granular activated carbon assisted biocathode for effective electrotrophic denitrification in microbial fuel cells

Granular activated carbon (GAC) has been widely used at the anode of a microbial fuel cell (MFC) to enhance anode performance due to its outstanding capacitance property. To the best of our knowledge, there haven't been any studies on GAC in the cathode for biofilm development and nitrate reduction in MFC. In this study, by adding GAC to biocathode, we investigated the impact of different GAC amounts and stirring speeds on power generation and nitrate reduction rate in MFC. The denitrification rate was found to be nearly two-times higher in MFCs with GAC (0.046 ± 0.0016 kg m−3 d−1) compared to that deprived of GAC (0.024 ± 0.0012 kg m−3 d−1). The electrotrophic denitrification has produced a maximum power density of 37.6 ± 4.8 mW m−2, which was further increased to 79.2 ± 7.4 mW m−2 with the amount of GAC in the biocathode. A comparative study performed with chemical catalyst (Pt carbon with air sparging) cathode and GAC biocathode showed that power densities produced with GAC biocathode were close to that with Pt cathode. Cyclic voltammetry analysis conducted at 10 mV s−1 between −0.9 V and +0.3 V (vs. Ag/AgCl) showed consistent reduction peaks at −0.6V (Ag/AgCl) confirming the reduction reaction in the biocathode. This demonstrates that the GAC biocathode used in this research is effective at producing power density and denitrification in MFC. Our belief that the nitrate reduction was caused by the GAC biocathode in MFC was further strengthened when SEM analysis showing bacterial aggregation and biofilm formation on the surface of GAC. The GAC biocathode system described in this research may be an excellent substitute for MFC's dual functions of current generation and nitrate reduction.

Effect of Chemical Agents on the Diffusion Behavior of Oxygen in Groundwater Under Combined Remediation Technique of Air Sparging and Soil Flushing

Effect of Chemical Agents on the Diffusion Behavior of Oxygen in Groundwater Under Combined Remediation Technique of Air Sparging and Soil Flushing

Enhanced air sparging for groundwater remediation using alginate gel-based removable hydraulic barriers

The objective of this study was to investigate the effect of a removable physical barrier on the air sparging performance using a lab-scale aquifer model was investigated. The barrier was installed in water-saturated porous media, prior to the air sparging, by injecting calcium chloride aqueous solution into the aquifer with pre-applied alginate solution. Changes in the air flow direction and air flux at the media surface during air sparging were evaluated. With a hydrogel barrier set at the center of the media, the airflow detoured the barrier resulting in a bimodal air flux distribution at the media surface. While employing two gel-formed barriers positioned away from the media's center, the airflow concentrated specifically on the gap between the barriers. The hydrogel was successfully removed using a sodium bicarbonate solution (1.0 mol/L). Using the hydrogel barrier, the performance of air sparging was significantly enhanced for removing contaminants [tetrachloroethene (PCE) and n-hexane mixture] due to increased air flux; 9.8% of PCE applied (7.8 g) was removed during 120 min air sprging for the gel barrier system whereas no PCE was removed for the control. Alginate gel did not show significant sorption capacity for PCE. It was stable in the contaminant up to 68 days with reasonable loss of its mass. Findings of this study present a promising option for air sparging process specifically targeting the contaminant source zone in the aquifer.

Air sparging remediation of VOCs contaminated low-permeability soil based on pressure gradient control

Air sparging (AS) is deemed unacceptable for remediating VOCs contaminated soil with low-permeability. To improve air flow and contaminant removal in sparging process, an original approach, termed as pressure gradient-enhanced air sparging (PGEAS) approach, is proposed by controlling pressure gradient in soil. Then the remediation efficiency, mass transfer characteristics, and remediation mechanism are investigated. Results showed that, the PGEAS approach accelerates gaseous contaminant exhaust, reduces residue contamination in soil, and promotes total contaminant removal, finally results in an improved remediation efficiency compared to the conventional approach. Controlled by sparging pressure and flow distance, the pressure gradient is created in soil, and a critical value needs to be exceeded to enhance the VOCs removal and mass transfer characteristics. The measured results of pore pressure and liquid saturation confirm a notable pressure gradient and drainage behavior in soil, which indicate the massive air subchannel formation during air sparging. At a two-dimensional scale, discrete distributions of contaminant concentrations in exhaust air and soil are presented, the removal extent and area are both enhanced using the PGEAS approach with a pressure gradient higher than the critical value. The reached conclusions are of great importance to contaminant removal in heterogeneous stratigraphy at sites.

Insights into air flowrate distribution and benzene removal in the heterogeneous aquifer during surfactant-enhanced air sparging

Surfactant-enhanced air sparging (SEAS) is an effective method of remediating volatile organic compounds in groundwater. In this study, the airflow migration mechanism and benzene removal in a heterogeneous aquifer during air sparging (AS) and SEAS remediation were studied using a light transmission visualisation technology. The blocking effect of the heterogeneous geological interface on airflow clearly decreased owing to the surfactant injection. At a surfactant concentration of 800 mg/L, the ΔPe value (i.e., the air entry pressure difference of the media above and below the interface) decreased from 0.3 kPa to 0.1 kPa. After surfactant injection, there was obvious downward migration owing to gravity. Compared with AS, the lateral migration of airflow at the interface and the fingered distribution of air flowrate above the interface improved considerably during SEAS, which increased the total benzene removal rates from 0.624 to 0.979. Moreover, the spatial distribution of the surfactant changed due to prolonged AS, which decreased the zone of influence area and airflow distribution range. However, the surfactant redistribution further enhanced the rectangular distribution of air flowrate, which was beneficial for continuous benzene removal in the low-permeability zone above the interface. These findings are useful for further understanding remediation mechanisms and optimising the technological parameters of SEAS technology in layered heterogeneous aquifer.

Integrating gravity-driven ceramic membrane filtration with hydroponic system for nutrient recovery from primary municipal wastewater

In this study, a gravity-driven membrane (GDM) filtration system and hydroponic system (cultivating basil and lettuce) were combined for nutrient recovery from primary municipal wastewater. The GDM system was optimized by increasing the periodic air sparging flow rate from 1 to 2 L/min (∼15 hr per 3–4 days), resulting in a ∼52% reduction of irreversible fouling. However, the total fouling was not alleviated, and the water productivity remained comparable. The GDM-filtrated water was then delivered to hydroponic systems, and the effects of hydroponic operation conditions on plant growth and heavy metal uptake were evaluated, with fertilizer- and tap water-based hydroponic systems and soil cultivation system (with tap water) for comparison. It was found that (i) the hydroponic system under batch mode facilitated to promote vegetable growth with higher nutrient uptake rates compared to that under flow-through feed mode; (ii) a shift in nutrient levels in the hydroponic system could impact plant growth (such as plant height and leaf length), especially in the early stages. Nevertheless, the plants cultivated with the GDM-treated water had comparable growth profiles to those with commercial fertilizer or in soils. Furthermore, the targeted hazard quotient levels of all heavy metals for the plants in the hydroponic system with the treated water were greatly lower than those with the commercial fertilizer. Especially, compared to the lettuce, the basil had a lower heavy metal uptake capability and displayed a negligible impact on long-term human health risk, when the treated water was employed for the hydroponic system.

Zone of flow: A new finding on the characteristics of airflow within the zone of influence during air sparging in aquifers

Air sparging (AS) is a popular technology for the in-situ remediation of groundwater contaminated by volatile organic compounds. The scope of the zone within which injected air exists, i.e., zone of influence (ZOI) and the airflow characteristics within ZOI are of great interest. However, few studies have shed light on the scope of the zone within which air flows, namely, the zone of flow (ZOF) and its relation with the scope of ZOI. This study focuses on the ZOF characteristics and its relation with ZOI based on quantitative observations of ZOF and ZOI using a quasi-2D transparent flow chamber. The relative transmission intensity obtained by the light transmission method presents a rapid and continuous increasing near the ZOI boundary, providing a criterion for the quantitative determination of ZOI. An integral airflow flux approach is proposed to determine the scope of ZOF based on the airflow flux distributions through aquifers. The ZOF radius decreases with the growth of particle sizes of aquifers; while it increases first and then keeps constant with the increase of sparging pressure. The ZOF radius is around 0.55– 0.82 times of the ZOI radius, which depends on air flow patterns related to particle diameters dp, that is, 0.55– 0.62 for channel flow (dp < 1– 2 mm), while 0.75– 0.82 for bubble flow (dp > 2– 3 mm). The experimental results show that the sparged air is entrapped with little flowing inside ZOI regions that are outside the ZOF, which should be considered carefully in the design of AS.

Selective Recovery of Ethyl Acetate by Air-Sparged Membrane Distillation Using Carbon Nanotube-Immobilized Membranes and Process Optimization via a Response Surface Approach

Ethyl acetate (EA) is an extensively used industrial solvent, and typically, aqueous mixtures containing EA are discarded as hazardous waste. The recovery of EA from wastewater streams would have significant environmental benefits and be a circular economy approach to solvent recycling. However, with a relatively high water solubility (8.3% w/v at room temperature), it remains a challenge. In this paper, we report the recovery of EA from water using air-sparged sweep gas membrane distillation (AS-SGMD) with carbon nanotube-immobilized membranes. A central composite rotatable design was used to study the effect of process parameters on flux and selectivity via conventional SGMD and AS-SGMD. The experiments were run at different operating conditions of temperature, concentration, and flow rate. The flux reached as high as 1.41 kg/m2 h–1, and selectivity as high as 10.8 was obtained. The introduction of air sparging improved the flux by as much as 12% and the selectivity by 17%. The response surfaces of flux and selectivity as a function of operating variables were studied, and regression models were developed. For both regular SGMD and AS-SGMD, the selectivity of EA recovery followed a quadratic model, while the flux showed a linear response. The predicted and experimental responses were in agreement with a R2 value of 0.94. The optimization efforts showed that relatively low temperatures, higher concentrations, and high flow rates favored higher selectivity.

Fouling behaviours and mitigation in pressure-retarded osmosis processes with geothermal water/brine-based draw solutions

In this study, we examined pressure-retarded osmosis (PRO) performance using naturally high temperature NaHCO3-enriched geothermal water (i.e., capturing CO2 waste gas) and geothermal brine. The results showed that increasing draw solution temperature from 20 °C to 60 °C, NaHCO3-enriched geothermal water facilitated improving water flux (Jw) without compromising reverse salt flux (Js), leading to lower Js/Jw ratios compared to NaCl-based solution. With NaHCO3-enriched geothermal water (60 °C) as draw solution, periodically physical cleaning (clean water flushing with/without air sparging, osmotic backwashing) displayed ∼17 % lower permeability recovery ratio (p < 0.05), dissimilar foulant morphology and inorganic compositions compared to chemical cleaning (acid, base, NaClO); while the average permeability levels under both cleaning conditions were comparable (p > 0.05). However, the recovery ratio decreased with extending cleaning cycle, resulting in an almost comparable permeability to that without cleaning after 60-h operation. In addition, the presence of Ca2+ at 5 mM in the NaHCO3-enriched geothermal water (60 °C) led to more significant water flux drop and less reverse flux decrease compared to those with Ca2+ at 0 and 30 mM, possibly due to its dense fouling layer formed by smaller-sized CaCO3 precipitates. When geothermal brine (low or high salinity, pH = 3 or 9.7, 60 °C) was used as draw solution, it was noticed that (1) with low salinity brine, basic pH levels led to higher water fluxes; (2) with high salinity brine, the water flux was impacted by the ionic compositions of draw solutions, instead of pH levels.

Direct Membrane Filtration of Municipal Wastewater: Studying the Most Suitable Conditions for Minimizing Fouling Rate in Commercial Porous Membranes at Demonstration Scale.

This study aimed to evaluate the feasibility of applying a commercial porous membrane to direct filtration of municipal wastewater. The effects of membrane pore size (MF and UF), treated influent (raw wastewater and the primary settler effluent of a municipal wastewater treatment plant) and operating solids concentration (about 1 and 2.6 g L-1) were evaluated on a demonstration plant. Filtration periods of 2-8 h were achieved when using the MF membrane, while these increased to 34-69 days with the UF membrane. This wide difference was due to severe fouling when operating the MF membrane, which was dramatically reduced by the UF membrane. Use of raw wastewater and higher solids concentration showed a significant benefit in the filtration performance when using the UF module. The physical fouling control strategies tested (air sparging and backwashing) proved to be ineffective in controlling UF membrane fouling, although these strategies had a significant impact on MF membrane fouling, extending the operating period from some hours to 5-6 days. The fouling evaluation showed that a cake layer seemed to be the predominant reversible fouling mechanism during each independent filtration cycle. However, as continuous filtration advanced, a large accumulation of irreversible fouling appeared, which could have been related to intermediate/complete pore blocking in the case of the MF membrane, while it could have been produced by standard pore blocking in the case of the UF membrane. Organic matter represented more than 70% of this irreversible fouling in all the experimental conditions evaluated.

Fouling management in oceanic carbon capture via in-situ electrochemical bipolar membrane electrodialysis

To assist reaching net-zero emissions, the dissolved carbon in the ocean can be extracted to enable an indirect air capture. An electrochemical bipolar membrane electrodialysis (BPMED) is a sustainable method for such capture. The BPMED enables a pH-swing that manipulates the oceanic carbonate-equilibrium using electricity. However, at alkaline-pH, an in-situ process suffers from inorganic fouling within the stack, increasing the cost of capture. In the current work, we investigate fouling management strategies including fouling control (i.e., membrane- configuration and current-flow rate optimization) and fouling removal methods. Fouling removal methods including air and CO2(g) sparging, dissolved CO2 (aq) cleaning, back-pressure, flow rate increase, and acid-wash are investigated under accelerated fouling conditions. The stack configuration containing the BPM-AEM pairs shows 4 × lower fouling than the BPM-CEM stack, while the carbonate-extraction and faradaic efficiency are similar for both configurations. From the scaling removal methods, only the acid wash combined with the back-pressure removed all the inorganic fouling, recovering both the cell voltage and pressure drop to their initial values. Upon the air sparging, the total cell voltage and pressure drop increased even more due to the trapped gas inside the netted spacers. Cleaning via dissolved and gaseous CO2 decreases the cell pH, dissolving hydroxide/carbonate-based fouling, but decreases the carbonate-removal significantly which is not preferred. Applying the back-pressure and higher flow rates decelerated the scaling buildup but was not enough to remove the fouling. Using BPM-AEM stacks in combination with periodic acid cleaning has potential as resilient oceanic carbon removal via BPMED.

Remediation Technologies for Polluted Sites: Review

A polluted site can have serious consequences for human health, water supplies, ecosystems, and even building structures, which is why various safeguards have been put in place to address contamination issues. This systematic review will conduct a literature search on remediation technologies for polluted sites. Sources of information and search, eligibility and exclusion criteria, and a systematic searching strategy are used to retrieve articles related to remediation technologies for polluted sites. Heavy metal pollution in the soil is a worldwide problem that humanity is attempting to address. Heavy metal pollution can be found in varying degrees in the soils of all countries worldwide. Heavy metal-contaminated soil is cleaned using chemical, physical, and biological remediation technologies. Many methods have been developed over the last thirty years to remediate oil-contaminated soil. Biological techniques such as phytoremediation and land farming are used to remediate oil-contaminated soil. Groundwater poisoning by heavy metals, which can come from natural soil sources or man-made sources, is a major public health concern. Because contaminated groundwater serves as a source of drinking water for billions of people worldwide, remediation is a top priority. The best remediation technologies for containing groundwater water are pump and treatment, excavation method, permeable reactive barrier, air sparging, electrokinetic remediation, chemical oxidation, and bioremediation. The selection of remediation methods necessitates a thorough examination of technological effectiveness and economic environmental safety. Personal and trial examinations of remediation advancements continue. As a result, in future research, investigating the zero-valent iron powder restoration method in conjunction with other restoration methods to treat soil heavy metal pollution is critical to soil restoration and ecological restoration, revealing the main influencing factors of the restoration process as well as the promotion and implementation of this method. Keywords: - Remediation, Polluted site, Technology DOI: 10.7176/JEES/12-12-02 Publication date: December 31 st 2022

Mass transfer enhancement of air sparging on VOCs contaminated low-permeability soil by establishing pressure gradient

As one of the most effective methods for remediating VOCs contaminated site, air sparging technology is not suitable to low-permeability soil due to the poor remediation efficiency. To solve this problem, an improved approach aiming for mass transfer enhancement by establishing pressure gradient in soil is proposed in this study, and the remediation efficiency, removal mechanism, as well as the mass transfer characteristic are comprehensively investigated. Test results showed that, using the proposed approach significantly reduced the time for exhaust air contaminants reaching concentration equilibrium, and improved the contaminant removal zone and extent in soil, which were especially strengthened at sparging pressures higher than 40 kPa. The total contaminant removal rate was improved by introducing the proposed approach, with a maximum improved removal rate of 23.7% at 100 kPa sparging pressure. In mechanism analysis, the recorded changes in total pore pressure and average liquid saturation illustrated the pressure drop and discrete drainage phenomena, confirming the pressure gradient and air sub-channels formed in low-permeability soil. Finally, contaminant mass transfer characteristic was quantitatively analyzed using the lumped parameter model, in which the mass transfer coefficient and the air channel influencing fraction were enhanced almost fourfold and fivefold respectively by introducing the proposed approach. Compared to the conventional approach, the improved remediation efficiency using the proposed approach tackled the in-situ remediation challenge on low-permeability soil, and further expanded the application scope of air sparging technology on VOC contaminated site.