The use of a fluorine mass balance to demonstrate the mineralization of PFAS by high frequency and high power ultrasound.

High-frequency ultrasound (sonolysis) has been shown as a practical approach for mineralizing PFAS in highly concentrated PFAS waste. However, a fluorine mass balance approach showing complete mineralization for ultrasound treatment has not been elucidated. The impact of ultrasonic power density (W/L) and the presence of co-occurring PFAS on the degradation of individual PFAS are not well understood. In this research, the performance of a 10L sonochemical reactor was assessed for treating synthetic high-concentration PFAS waste with carboxylic and sulfonic perfluoroalkyl surfactants ranging in chain length from four to eight carbons at three different initial concentrations: 6, 55, 183 µM. The mass balance for fluorine was performed using three analytical techniques: triple quadrupole liquid chromatography-mass spectrometry, a fluoride ion selective electrode, and 19F nuclear magnetic resonance. The test results showed near complete mineralization of PFAS in the waste without the formation of intermediate fluorinated by-products. The PFAS mineralization efficiency of the sonolysis treatment at two different power densities for similar initial concentrations were almost identical; the G value at 145 W/L was 9.7*10-3 g/kWh, whereas the G value at 90 W/L was 9.3*10-3 g/kWh. The results of this study highlight the implications for the scalability of the sonolytic process to treat high-concentration PFAS waste.

Microplastic Pollution Prevention: The Need for Robust Policy Interventions to Close the Loopholes in Current Waste Management Practices.

Plastic materials that are less than 5 mm in size are defined as Microplastics (MPs). MPs that are intentionally produced are called primary MPs; however, the most abundant type in the environment consists of the remainder created by the fragmentation of large plastic debris through physical, chemical, and oxidative processes, which are called secondary MPs. Due to their abundance in the environment, poor degradability, toxicological properties, and negative impact on aquatic and terrestrial organisms, including humans, MP pollution has become a global environmental issue. Combatting MP pollution requires both remediation and preventive measures. Although remediation is a must, considering where the technology stands today, it may take long time to make it happen. Prevention, on the other hand, can be and should be done now. However, the effectiveness of preventive measures depends heavily on how well MP escape routes are researched and understood. In this research, we argue that such escape routes (rather, loopholes) exist not only due to mismanaged plastic waste, but also due to cracks in the current waste management systems. One known MP loophole is facilitated by wastewater treatment plants (WWTP). The inability of existing WWTP to retain finer MPs, which are finally released to water bodies together with the treated wastewater, along with the return of captured larger MPs back to landfills and their release into the environment through land applications, are a few examples. Organic waste composting and upcycling of waste incineration ash provide other MP escape pathways. In addition, it is important to understand that the plastics that are in current circulation (active use as well as idling) are responsible for producing MPs through regular wear and tear. Closing these loopholes may be best attempted through policy interventions.

Contributions of reactor geometry and ultrasound frequency on the efficiency of sonochemical reactor.

An intermediate-scale reactor with 10L capacity and two transducers operating at 700 and 950 kHz frequencies was developed to study the scalability of the sonolytic destruction of Per and Polyfluoroalkyl substance (PFAS). The impact of frequency, height of liquid or power density, and transducer position on reactor performance was evaluated with the potassium iodide (KI) oxidation and calorimetric power. The dual frequency mode of operation has a synergistic effect based on the triiodide concentration, and calorimetric power. The triiodide concentration, and calorimetric power were higher in this mode compared to the combination of both frequencies operating individually. The sonochemical efficiency for an intermediate-scale reactor (10L) was similar that obtained from a bench-scale reactor (2L), showing the scalability of the sonolytic technology. The placement of the transducer at the bottom or side wall of the reactor had no significant impact on the sonochemical reactivity. The superposition of the ultrasonic field from the dual transducer mode (side and bottom) did not produce a synergistic effect compared to the single transducer mode (bottom or side). This can be attributed to a disturbance due to the interaction of ultrasonic fields of two frequencies from each transducer. With the encouraging results scaling up is in progress for site implementation.

A Path to a Reduction in Micro and Nanoplastics Pollution.

Microplastics (MP) are plastic particles less than 5 mm in size. There are two categories of MP: primary and secondary. Primary or microscopic-sized MP are intentionally produced material. Fragmentation of large plastic debris through physical, chemical, and oxidative processes creates secondary MP, the most abundant type in the environment. Microplastic pollution has become a global environmental problem due to their abundance, poor biodegradability, toxicological properties, and negative impact on aquatic and terrestrial organisms including humans. Plastic debris enters the aquatic environment via direct dumping or uncontrolled land-based sources. While plastic debris slowly degrades into MP, wastewater and stormwater outlets discharge a large amount of MP directly into water bodies. Additionally, stormwater carries MP from sources such as tire wear, artificial turf, fertilizers, and land-applied biosolids. To protect the environment and human health, the entry of MP into the environment must be reduced or eliminated. Source control is one of the best methods available. The existing and growing abundance of MP in the environment requires the use of multiple strategies to combat pollution. These strategies include reducing the usage, public outreach to eliminate littering, reevaluation and use of new wastewater treatment and sludge disposal methods, regulations on macro and MP sources, and a wide implementation of appropriate stormwater management practices such as filtration, bioretention, and wetlands.

Prediction of gas production rate from shale gas reservoirs using a micro-macro analysis.

Shale gas has become one of the important contributors to the global energy supply. The declining pattern of the gas production rate with time from an unconventional gas reservoir is due to the depletion of shale gas stored in the nanovoids of the shale formation. However, there are only limited ways to predict the variation of the gas production rate with time from an unconventional gas reservoir. This is due to the multiple transport mechanisms of gas in nano-scale pores and changes in shale gas permeability with pressures in nano-scale pores, which is impacted by the pore structure of the shale. In this study, the permeability-pressure (K-p) relationship for different shales (Eagle Ford, Haynesville, Longmaxi and Opalinus) were determined using an equivalent anisotropic pore network model (PNM). This PNM has REV-scale shale gas flow in randomly generated nanovoids and their connection in the shale matrix, and the multiphase flow of shale gas including viscous flow, slip flow and Knudsen diffusion. These predicted K-p correlations were then used in a finite element model (FEM) to predict the variation of the gas production rate with time (flux-time curves) at the macroscale. The simulation results show that the flux-time curves can be simplified to two linear segments in logarithmic coordinates, which are influenced by the fracture length and initial gas pressure. The predicted results using the PNM-FEM were validated by comparing them with the reported field test data. The method described in this study can be used to upscale the gas transport process from micro- to macroscale, which can provide a predictive tool for the gas production in shales.

A Review of PFAS Destruction Technologies.

Per- and polyfluoroalkyl substances (PFASs) are a family of highly toxic emerging contaminants that have caught the attention of both the public and private sectors due to their adverse health impacts on society. The scientific community has been laboriously working on two fronts: (1) adapting already existing and effective technologies in destroying organic contaminants for PFAS remediation and (2) developing new technologies to remediate PFAS. A common characteristic in both areas is the separation/removal of PFASs from other contaminants or media, followed by destruction. The widely adopted separation technologies can remove PFASs from being in contact with humans; however, they remain in the environment and continue to pose health risks. On the other hand, the destructive technologies discussed here can effectively destroy PFAS compounds and fully address society's urgent need to remediate this harmful family of chemical compounds. This review reports and compare widely accepted as well as emerging PFAS destruction technologies. Some of the technologies presented in this review are still under development at the lab scale, while others have already been tested in the field.

Coupled high and low-frequency ultrasound remediation of PFAS-contaminated soils.

Solids such as soils and sediments contaminated with per- and polyfluorinated alkyl substances (PFAS) from exposure to impacted media, e.g., landfill leachate or biosolids, direct contaminated discharge, and contaminant transport from atmospheric deposition, have caused significant environmental pollution. Such solids can act as secondary sources of PFAS for groundwater and surface water contamination. There are currently no proven technologies that can degrade PFAS in soil and sediments in a cost-effective, environmentally-friendly, and energy-efficient manner. This study examines the use of coupled high and low-frequency ultrasound in desorbing and degrading PFAS in soil, thereby achieving concurrent treatment and destruction of PFAS in soil. Two common PFAS, namely perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), were used to evaluate treatment performance in soils with both low and high organic matter contents. The test results showed that the ultrasound treatment could significantly reduce PFAS concentrations in artificially contaminated soil; however, no significant degradation was achieved. Ultrasound treatment did improve desorption of PFAS from solid particles, particularly from the highly absorbent organic soil; 68.8 ± 1.8% of PFOA and 45.4 ± 4.1% of PFOS were leached from the soil after ultrasound treatment compared to only 28 ± 0.2% of PFOA and 1 ± 3.1% of PFOSafter desorption in water. This work shows that sonication treatment is an effective technology for the removal of PFAS from solids, however, the presence of solids in the solid-liquid slurry can negatively impact ultrasonic cavitation, inhibiting the sonolytic degradation of desorbed PFAS.

Impact of de-ionized water on changes in porosity and permeability of shales mineralogy due to clay-swelling.

Hydraulic fracturing is widely applied for economical gas production from shale reservoirs. Still, the swelling of the clay micro/nano pores due to retained fluid from hydraulic fracturing causes a gradual reduction of gas production. Four different gas-bearing shale samples with different mineralogical characteristics were investigated to study the expected shale swelling and reduction in gas permeability due to hydraulic fracturing. To simulate shale softening, these shale samples were immersed in deionized (DI) water heated to 100 °C temperature and subjected to 8 MPa pressure in a laboratory reactor for 72 hours to simulate shale softening. The low-temperature nitrogen adsorption and density measurements were performed on the original and treated shale to determine the changes in micro and nano pore structure. The micro and nano pore structures changed, and the porosity decreased after shale treatment. The porosity decreased by 4% for clayey shale, while for well-cemented shale the porosity only decreased by 0.52%. The findings showed that the initial mineralogical composition of shale plays a significant role in the change of micro and nano pores and the pore structure alteration due to retained fluid from hydraulic fracturing. A pore network model is used to simulate the permeability of shale used in this study. To define pore structure properties, specific factors such as porosity, pore size, pore throat distribution, and coordination number were used. Furthermore, the anisotropy characteristics of shale were integrated into the model via a coordination number ratio. Finally, the change in permeability due to shale softening was determined and compared with untreated with the progress of shale softening. The simulation showed that the permeability of Longmaxi shale could decrease from 3.82E-16 m2 to 4.71E-17 m2 after treatment.

An anisotropic pore-network model to estimate the shale gas permeability.

The permeability of shale is a significant and important design parameter for shale gas extraction. The shale gas permeability is usually obtained based on Darcy flow using standard laboratory permeability tests done on core samples, that do not account for different transport mechanisms at high pressures and anisotropic effects in shales due to nano-scale pore structure. In this study, the permeability of shale is predicted using a pore network model. The characteristics of pore structure can be described by specific parameters, including porosity, pore body and pore throat sizes and distributions and coordination numbers. The anisotropy was incorporated into the model using a coordination number ratio, and an algorithm that was developed for connections of pores in the shale formation. By predicting hydraulic connectivity and comparing it with several high-pressure permeability tests, the proposed three-dimensional pore network model was verified. Results show that the prediction from the anisotropic pore network model is closer to the test results than that based on the isotropic pore network model. The predicted permeability values from numerical simulation using anisotropic pore network model for four shales from Qaidam Basin, China are quite similar to those measured from laboratory tests. This study confirmed that the developed anisotropic three-dimensional pore network model could reasonably represent the natural gas flow in the actual shale formation so that it can be used as a prediction tool.

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

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

A Review of the Applications, Environmental Release, and Remediation Technologies of Per- and Polyfluoroalkyl Substances.

Per- and polyfluoroalkyl substances (PFAS) are pollutants that have demonstrated a high level of environmental persistence and are very difficult to remediate. As the body of literature on their environmental effects has increased, so has regulatory and research scrutiny. The widespread usage of PFAS in industrial applications and consumer products, complicated by their environmental release, mobility, fate, and transport, have resulted in multiple exposure routes for humans. Furthermore, low screening levels and stringent regulatory standards that vary by state introduce considerable uncertainty and potential costs in the environmental management of PFAS. The recalcitrant nature of PFAS render their removal difficult, but existing and emerging technologies can be leveraged to destroy or sequester PFAS in a variety of environmental matrices. Additionally, new research on PFAS remediation technologies has emerged to address the efficiency, costs, and other shortcomings of existing remediation methods. Further research on the impact of field parameters such as secondary water quality effects, the presence of co-contaminants and emerging PFAS, reaction mechanisms, defluorination yields, and the decomposition products of treatment technologies is needed to fully evaluate these emerging technologies, and industry attention should focus on treatment train approaches to improve efficiency and reduce the cost of treatment.

Application of the Diffused Double Layer Theory to Nanobubbles.

Nanobubbles have electrically charged interfaces; hence, the diffused double layer theory can be applied to explain the behavior of nanobubbles in different electrolytic solutions. In this research, oxygen nanobubbles were generated in NaCl solutions of different concentrations, and bubble size and ζ potentials were measured just after the generation and after 1 week. The measured data and diffused double layer theory were used to compute the surface charge density, the potential due to the surface charge, and the interaction energy between bubbles. With the increased NaCl concentration, bubble size, surface charge density, and the number of negative charges increased, while the magnitude of ζ potential/surface potential, double layer thickness, internal pressure, and the electrostatic repulsion force decreased. The same trend was observed after 1 week. The net total energy calculation for the 0.001 M NaCl solution showed that the bubble repulsion for an intermediate separation distance had a 6.99 × 10-20 J energy barrier, which prevented bubble coalescence. Hence, the 0.001 M NaCl solution produced stable nanobubbles. The calculation of internal pressure inside nanobubbles showed a reduction in the interfacial pressure difference with the increased NaCl concentration. The test results, as well as diffuse double layer and net total energy calculations, showed that the most stable bubbles were obtained with 0.001 M NaCl concentration and the least stability was recorded with the highest amount (0.1 M) of NaCl concentration.

Crop Residue Burning in India: Policy Challenges and Potential Solutions.

India, the second largest agro-based economy with year-round crop cultivation, generates a large amount of agricultural waste, including crop residues. In the absence of adequate sustainable management practices, approximately 92 seems a very small number of metric tons of crop waste is burned every year in India, causing excessive particulate matter emissions and air pollution. Crop residue burning has become a major environmental problem causing health issues as well as contributing to global warming. Composting, biochar production and mechanization are a few effective sustainable techniques that can help to curtail the issue while retaining the nutrients present in the crop residue in the soil. The government of India has attempted to curtail this problem, through numerous measures and campaigns designed to promote sustainable management methods such as converting crop residue into energy. However, the alarming rise of air pollution levels caused by crop residue burning in the city of Delhi and other northern areas in India observed in recent years, especially in and after the year of 2015, suggest that the issues is not yet under control. The solution to crop residue burning lies in the effective implementation of sustainable management practices with Government interventions and policies. This manuscript addresses the underlying technical as well as policy issues that has prevented India from achieving a long-lasting solution and also potential solutions that have been overlooked. However, effective implementation of these techniques also requires us to look at other socioeconomic aspects that had not been considered. This manuscript also discusses some of the policy considerations and functionality based on the analyses and current practices. The agricultural waste sector can benefit immensely from some of the examples from other waste sectors such as the municipal solid waste (MSW) and wastewater management where collection, segregation, recycling and disposal are institutionalized to secure an operational system. Active stakeholder involvement including education and empowerment of farmers along with technical solutions and product manufacturing can also assist tremendously. Even though the issue of crop residue burning touches many sectors, such as environment, agriculture, economy, social aspects, education, and energy, the past governmental efforts mainly revolved around agriculture and energy. This sectorial thinking is another barrier that needs to be broken. The government of India as well as governments of other developing countries can benefit from the emerging concept of nexus thinking in managing environmental resources. Nexus thinking promotes a higher-level integration and higher level of stakeholder involvement that goes beyond the disciplinary boundaries, providing a supporting platform to solve issues such as crop residue burning.

Organic Waste Buyback as a Viable Method to Enhance Sustainable Municipal Solid Waste Management in Developing Countries.

Many developing countries have inadequate Municipal Solid Waste (MSW) management systems due to lack of not only the awareness, technologies, finances, but also a proper governance that is able to enforce and monitor the regulations. Not all the solutions practiced by and in developed countries fit to the developing country contexts. The local conditions and limitations must always be taken into account when proposing waste management options for developing countries. The excessively high organic waste fraction in MSW and relatively inexpensive labor markets available in developing countries are two of the strengths that have not yet been utilized fully. This manuscript is an attempt to point out the benefits we receive from the above two strengths if we establish organic waste buyback programs. This can only become successful if we find solutions to: (1) collect source-separated organic waste, and then (2) find stable markets for the products made from organic waste. Compost or biogas could be the best bet developing countries can consider as products. However, there must be some policy interventions to support buyback programs at the waste collection stage as well as at the product marketing stage. Implementation of such organic waste buyback centers that can offer some incentives can indirectly motivate residents to do source separation. This will in turn also help promote more recycling, as any waste bin that has no organics in it is much easier for anyone (e.g., waste pickers) to look for other recyclables. Developing country settings such as the Green Container composting program in Cajicá, Colombia, and buyback centers in South Africa that are presented later in the manuscript are thought to be the places where the concept can be implemented with little effort. The environment, economy, and society are considered to be the three dimensions (or pillars) of sustainability. Interestingly, the organic waste buyback centers solution has positive implications on all three aspects of sustainability. Thus, it also supports the 2030 Agenda of the United Nations (UN), by making specific contributions to the Sustainable Development Goals (SDGs) such as zero hunger (SDG 2), affordable and clean energy (SDG 7), climate action (SDG 13), clean water and sanitation (SDG 6), and sustainable cities and communities (SDG 11).

A Review of the Processes, Parameters, and Optimization of Anaerobic Digestion.

Anaerobic digestion is a technology that has been used by humans for centuries. Anaerobic digestion is considered to be a useful tool that can generate renewable energy and significant research interest has arisen recently. The underlying theory of anaerobic digestion has been established for decades; however, a great deal of current research is directed towards the optimization of anaerobic digestion under diverse digestion conditions. This review provides a summary of the processes underlying anaerobic digestion, commonly-utilized measurements of anaerobic sludge, operating parameters of anaerobic digesters, and methods of acceleration and optimization used to improve process efficiency. Recent developments in addition to older research are considered to provide a general but comprehensive summary of accumulated knowledge in the theory of anaerobic digestion, as well as considerations in the efficient operation of digesters. We have determined that the numerous factors pertinent to the design and operation of batch-based anaerobic digesters must each be considered to ensure the maximum efficiency and cost-effectiveness of a digester provided its respective operating conditions.

Pore-Scale Simulation and Sensitivity Analysis of Apparent Gas Permeability in Shale Matrix.

Extremely low permeability due to nano-scale pores is a distinctive feature of gas transport in a shale matrix. The permeability of shale depends on pore pressure, porosity, pore throat size and gas type. The pore network model is a practical way to explain the macro flow behavior of porous media from a microscopic point of view. In this research, gas flow in a shale matrix is simulated using a previously developed three-dimensional pore network model that includes typical bimodal pore size distribution, anisotropy and low connectivity of the pore structure in shale. The apparent gas permeability of shale matrix was calculated under different reservoir pressures corresponding to different gas exploitation stages. Results indicate that gas permeability is strongly related to reservoir gas pressure, and hence the apparent permeability is not a unique value during the shale gas exploitation, and simulations suggested that a constant permeability for continuum-scale simulation is not accurate. Hence, the reservoir pressures of different shale gas exploitations should be considered. In addition, a sensitivity analysis was also performed to determine the contributions to apparent permeability of a shale matrix from petro-physical properties of shale such as pore throat size and porosity. Finally, the impact of connectivity of nano-scale pores on shale gas flux was analyzed. These results would provide an insight into understanding nano/micro scale flows of shale gas in the shale matrix.

Micro/Nano-pore Network Analysis of Gas Flow in Shale Matrix.

The gas flow in shale matrix is of great research interests for optimized shale gas extraction. The gas flow in the nano-scale pore may fall in flow regimes such as viscous flow, slip flow and Knudsen diffusion. A 3-dimensional nano-scale pore network model was developed to simulate dynamic gas flow, and to describe the transient properties of flow regimes. The proposed pore network model accounts for the various size distributions and low connectivity of shale pores. The pore size, pore throat size and coordination number obey normal distribution, and the average values can be obtained from shale reservoir data. The gas flow regimes were simulated using an extracted pore network backbone. The numerical results show that apparent permeability is strongly dependent on pore pressure in the reservoir and pore throat size, which is overestimated by low-pressure laboratory tests. With the decrease of reservoir pressure, viscous flow is weakening, then slip flow and Knudsen diffusion are gradually becoming dominant flow regimes. The fingering phenomenon can be predicted by micro/nano-pore network for gas flow, which provides an effective way to capture heterogeneity of shale gas reservoir.

A review of centrifugal testing of gasoline contamination and remediation.

Leaking underground storage tanks (USTs) containing gasoline represent a significant public health hazard. Virtually undetectable to the UST owner, gasoline leaks can contaminate groundwater supplies. In order to develop remediation plans one must know the extent of gasoline contamination. Centrifugal simulations showed that in silty and sandy soils gasoline moved due to the physical process of advection and was retained as a pool of free products above the water table. However, in clayey soils there was a limited leak with lateral spreading and without pooling of free products above the water table. Amount leaked depends on both the type of soil underneath the USTs and the amount of corrosion. The soil vapor extraction (SVE) technology seems to be an effective method to remove contaminants from above the water table in contaminated sites. In-situ air sparging (IAS) is a groundwater remediation technology for contamination below the water table, which involves the injection of air under pressure into a well installed into the saturated zone. However, current state of the art is not adequate to develop a design guide for site implementation. New information is being currently generated by both centrifugal tests as well as theoretical models to develop a design guide for IAS. The petroleum contaminated soils excavated from leaking UST sites can be used for construction of highway pavements, specifically as sub-base material or blended and used as hot or cold mix asphalt concrete. Cost analysis shows that 5% petroleum contaminated soils is included in hot or cold mix asphalt concrete can save US$5.00 production cost per ton of asphalt produced.

Centrifugal study of zone of influence during air-sparging.

Air sparging (AS) is one of the groundwater remediation techniques for remediating volatile organic compounds (VOCs) in saturated soil. However, in spite of the success of air sparging as a remediation technique for the cleanup of contaminated soils, to date, the fundamental mechanisms or the physics of air flow through porous media is not well understood. In this study, centrifugal modeling tests were performed to investigate air flow rates and the evolution of the zone of influence during the air sparging under various g-levels. The test results show that with the increase in sparging pressure the mass flow rate of the air sparging volume increases. The air mass flow rate increases linearly with the effective sparging pressure ratio, which is the difference between sparging pressure and hydrostatic pressure normalized with respect to the effective overburden pressure at the sparging point. Also the slope of mass flow rate with effective sparging pressure ratio increases with higher g-levels. This variation of the slope of mass flow rate of air sparging volume versus effective sparging pressure ratio, M, is linear with g-level confirming that the air flow through soil for a given effective sparging pressure ratio only depends on the g-level. The test results also show that with increasing sparging pressure, the zone of influence (ZOI), which consists of the width at the tip of the cone or lateral intrusion and the cone angle, will lead to an increase in both lateral intrusion and the cone angle. With a further increase in air injection pressure, the cone angle reaches a constant value while the lateral intrusion becomes the main contributor to the enlargement of the ZOI. However, beyond a certain value of effective sparging pressure ratio, there is no further enlargement of the ZOI.

Physical modeling of air flow during air sparging remediation.

Air sparging (AS) is one of the most efficient techniques for remediating saturated soils and groundwater contaminated with volatile organic compounds. A series of physical modeling tests for different sizes of porous media under varied injection pressure were conducted to investigate the effect of particle size and air injection pressure on size and shape of the zone of influence (ZOI). The test results show that ZOI can be expressed by two components: the horizontal expansion due to pneumatic fracture or preferential intrusion around the injection point and the angle of ZOI which is the angle between the vertical line and the boundary of ZOI. There exists a limited angle of ZOI for each type of porous media. The measured minimum and maximum air injection pressures in 1g tests are compared with corresponding theoretical values, and it is found that the measured minimum injection pressure is slightly lower than the theoretical value, while the measured maximum injection pressure is much higher than the theoretical maximum injection pressure. Centrifugal test results confirmed nonapplicability of theoretical maximum injection pressure to air sparging design. All of the above provide valuable information for design and theoretical modeling of air sparging for groundwater remediation.