Air Sparging
By Damien Watt
Air sparging is a low cost method of remediation that is used to remove volatile organic compounds (VOCs) and petroleum product from the ground and groundwater. Air sparging is done “in situ” or in place, meaning that uncontaminated air is injected into a subsurface VOCs or hydrocarbon saturated zone, changing the phase of the VOCs from dissolved state to a vapor phase. This method is typically used in combination with other remediation techniques such as soil vapor extraction to increase effectiveness.
There are primarily two factors that determine the effectiveness of air sparging. The two factors are weight of the compound and the permeability of the soil. Air sparging is most effective when used to remove lighter, more volatile compounds such as benzene and toluene. Heavier compounds, more stable such as diesel or kerosene do not work as well with air sparging. The permeability is a factor cause air sparging works to disrupt the equilibrium vapor and dissolved phase of the between the contaminant and the soil and/or groundwater. The passage of air through the soil is necessary for the air sparging to be effective. So knowledge of soil characteristics and the permeability is required when choosing this technique.
The design of an air sparging system requires a multiple tiered approach. It involves the installation of wells to first inject air. “Sparge” points have to be strategically placed in the affected area to get the uncontaminated air into the soil. Then wells have to be installed to monitor the plume of the contaminant to maximize removal efficiency. Lastly wells have to be installed to extract the contaminants once they have been sparged from the soil or the groundwater. All of this information is gathered by conducting what is called pilot testing. Pilot testing is conducted to design the air sparging system effective and is also used to evaluate the system performance as well.
Utilizing air sparging as a remediation technique has it advantages and disadvantages. Air sparging is low cost, easy to install, there are few groundwater consideration to be made, minimal disturbances to affected site, and the equipment in most cases readily available. The disadvantages to an air sparging system is that it can not be used with heavier or more stable compounds, if free liquids exist, can not be used to treat confined aquifers, and it does require an some knowledge of the affected area cause some of the chemical, physical, and biological interactions are not yet understood. Air sparging, if the conditions allow for the technique to be used, can be a cost effective method to remediate an affect site with minimal disturbances.
EPA. (1995, May). Air Sparging. In How to Evaluate Alternative Cleanup Technologies for Underground Storage Tank Sites: A Guide for Corrective Action Plan ReviewersHow to Evaluate Alternative Cleanup Technologies for Underground Storage Tank Sites: A Guide for Corrective Action Plan Reviewers. Retrieved
Subsurface barriers: Grout Curtains
By David J. Seidel
Grout curtains are rigid underground barriers formed by injecting grout into porous rock or soil through wells. It offers several advantages as a remediation technology:
1. With a grout curtain, soil heterogeneity has much less of an impact on wall placement than a slurry wall (Dwyer, 1994)
2. Versatile – grouting can stabilize a wide variety of soil types ranging from gravel to
heavy clays (Mutch et al., 1997)
3. Starting from a small borehole, large diameter columns or panels can be created (Dwyer, 1994)
4. Grouting can install a wall (inject) in confined places that might otherwise limit installation – for instance, cut-off walls can be constructed beneath buildings without disrupting the structure (Mutch et al., 1997)
5. Grout curtains can be installed at depths up to 150 – 200 ft (Dwyer, 1994)
6. Drilling can be done at any angle forming both vertical and horizontal water control barriers (Dwyer,1998)
7. Grout units are mobile, permitting drilling with rotation and percussion (Dwyer,1998)
8. A down-the-hole (DTH) percussion hammer coupled with the drill string results in more
reliable drilling alignments (straight and parallel), faster drilling rates, and a quieter
operation (Dwyer, 1998)
9. Innovative equipment allows injection of multiple fluids or gases (Dwyer, 1998)
a. DTH percussion hammer
b. Multi-nozzle grout injection unit increases the efficiency of injection
10. Grout curtains can be used in coordination with subsurface treatment.
References
1. Mutch, R.D., R.E. Ash, and J.R. Caputi. 1997. “Contain Contaminated Groundwater.” Chemical\Engineering, Vol. 104, No. 5, pp. 114-119.
2. Dwyer, B.P. 1998. “Treatment of Mixed Contamination in Complex Hydrogeologic
Settings.” Sandia National Laboratories.
3. Dwyer, B.P. 1994. “Feasibility of Permeation Grouting for Constructing Subsurface Barriers.” SAND94-0786
Team Delta
Organic contaminants can be found in many different soil types and textures and contain different physical and chemical compounds. Organic contaminants are usually non-volatile, insoluble in water, not readily biodegradable, some extremely toxic, and have a low molecular weight are general characteristics. The hydrophobic organic contaminants are dioxins, furans, PCBs and polyaromatic hydrocarbons are found in lower doses in soil. Organics with a low molecular weight would consist of alcohols, phenols and carboxylic acids but chlorinated dibenzodioxins would be an extreme toxic organic contaminant. Now, we have identified the characteristics and given examples of organic contaminants. the objective will to find a soil flushing co solvent or surfactant to remove the contaminants from the soil.
Common field information and gathering often includes the description of the incident, natural soil exposures, weathering that has taken place, subsurface cores, and soil sampling. This effort will identify the organic contaminant, the areas of past and present disposal through observations and information on the soil analysis. The overall objective of soil flushing is to minimize cost during the removal of organics while satisfying various requirements and specifications
The picture is a typical soil flushing system provided by FRTR remediation technologies http://www.frtr.gov/matrix2.html
Surfactant flushing involves injecting a surfactant mixture (example: water plus a miscible organic solvent such as alcohol or a special surfactant) into the contaminated area to extract organic contaminants. The aqueous mixture dissolves and mobilizes the organic. Water flooding is use to remove the residual effluent above ground and the recovered fluid can be reused in the flushing process to keep cost down. The residual solids and sludge are properly treated before disposal. Some cases air emissions of volatile contaminates from recovered flushing fluids should be collected and treated, to meet regulatory standards.
Advantages to using surfactant remediation is the use of certain surfactant can keep cost down during removal. The use of certain surfactants can enhance soil porosity and texture. The use of soil flushing can remove an organic contaminant faster out of the soil than other remediation programs. Also, eliminates the need to excavate, handle, and transport contaminated media. Surfactants mobilizes the contaminated area from spreading to other areas while being removed.
References:
Fundamentals of Site Remediation. John Pichtel. 2nd ed. pp.175 - 177.
AF Center for Engineering http://www.afcee.af.mil/resources/technologytransfer/programsand initiatives
FRTR Remediation Technologies Screening Matrix and Reference Guide, http://www.frtr.gov/matrix2/section2/2-2-1.html.
Interstate Technology Regulatory Council, http://www.itrcweb.org.
Bioreactors
By Rob Walker
Team Delta
Bioreactors are enclosed tanks that are used primarily in the biodegradation of Organic toxins. Bioreactors treatment of slurry-phase contaminated soil or sludge. The slurry is formed by the addition of water to contaminated soil in order to form a slurry density that is desired. The slurry is mixed to maintain suspended soils and to increase contact between microorganism and contaminated materials. Bioreactors can be aerobic or anaerobic. Biodegradation in Bioreactor is affected by pH, temperature, nutrients, concentration of contaminants, microorganism, dissolved Oxygen and aeration in aerobic systems. Bioreactors are commonly used due to the low cost to operate, using minimal man power and minimal sludge. Bioreactors are very efficient at degradation of recalcitrant compounds and very efficient at removal of toxic substances. Disadvantages are; long optimization time, extensive design time, requires large area of land, poor understanding of microbial biokinetics, and lack of VOC control.
In conclusion Bioreactors are an efficient way to remove anthropogenic organic compounds from soil. Bioreactors provide a low cost remediation technique. Bioreactors require a large amount of area, VOC emissions must be taken into account when considering using Bioreactors.
References:
Alok Bhandari, A. B., Rao Y Surampalli, R. Y. S., Passcale Champagne, P. C., Say Kee Ong, S. K. T., R D Tyagi, R. D. T., & Irene M C Lo,
Juana B. Eweis, J. B. E., Sarina J. Ergas, S. J. E., Daniel P Y Chang, D. P. Y. C., & Edward D Schroeder, E. D. S. (1998). Bioremediation Principles.
The Advantages and Benefits of
Team Delta – Dan South
A chelating agent is a molecule that has several localized negative groups that can bond strongly with a metal cation, thereby making the cation unavailable for other bonding and essentially inactive (Williams, James, and Roberts, 2000). There are many benefits to using chelating agents in a fluid to flush metals out of soil.
The first benefit is that by locking up the binding sites, the agent prevents or at least reduces the ability of the metal cation to form insoluble complexes or to adsorb onto soil particles. This makes the metal more vulnerable to remediation. By adding properly chosen chelating agents that make the target metal more soluble, a person can extract more of the compound by methods such as extraction wells (Peters, 1999). In one study, researchers were able to remove 85% of the copper in a test column from all soil fractions, even the clay fraction where the metal bonds the strongest (Tsang, Zhang, Lo, 2007). Other experiments showed that by using different chelating agents or changing the techniques in administering the chelating agent, a person can remove almost 100% of lead or 73% of copper in a contaminated soil, much better than can be achieved using just water alone (Peters, 1999). A third benefit is that soil flushing with chelating agents can be more economical and safer than soil removal or soil washing because there is no excavation required (Tsang, Zhang, Lo, 2007). This would reduce impact on an active area such as a operating industrial facility. There is no soil that needs to be moved, hauled, or disposed of. The safety effect is also important as construction projects can be extremely dangerous having had nearly 1,000 fatal injuries in 2008 (U.S. Dept. of Labor, 2009).
In summary, using chelating agents to flush metals from soil can have several beneficial effects. It isolates the metals from other molecules by locking up the binding sites. It also makes the metals more soluble and therefore easier to extract. Because of that, using chelating agents with soil flushing fluids increases the amount of metals that can be extracted from contaminated soil. By being an in-situ technique, soil flushing can be less expensive in terms of money and human safety.
References
Peters, R. W. (1999). Chelant extraction of heavy metals from contaminated soils. Journal of Hazardous Materials, 66(1-2), 151-210.
Tsang, D. C. W., Zhang, W., & Lo,
Williams, P. L., James, R. C., & Roberts, S. M. (Eds.). (2000). Principles of toxicology (Second ed.).
Granular Activated Carbon Filtration
Team Delta
By Mary Steffen-Deaton
Granular Activated Carbon (GAC) Filtration is a treatment method that can be used to remove contaminates from water and air. “A GAC filter system is used to remove semi-volatile and volatile organic compounds (SVOCs and VOCs), such as constituents of gasoline, heating oil, and chlorinated solvents, from polluted drinking water.”(DEP, 2006). Granular Activated Carbon Filtration uses filters made of natural materials from coal, wood, lignite, peat, coconut shells, and coke and then an adsorption process occurs to remove contaminates from liquids and gases. Each of the types of materials in the filter has its own adsorption properties so to remove specific contaminates. The contaminated water is directed through the GAC columns or canisters and a heat source like steam is used to expand the surface area of the carbon to help remove the dissolved organics then the pollutants are removed releasing water free of contaminates or at lower levels. This can be an effective method in removing chlorine, and volatile organic compounds that are carbon based. “Adsorption by activated carbon has a long history of use in treating municipal, industrial, and hazardous wastes.” (Pitchel, 2007).
Advantages:
1. Not too costly as far as treatment cost go.
2. The average well owner can have this method installed to help remove man-made and naturally occurring organics. So whole homes can have systems to prevent ingestion of contaminates.
3. The GAC systems do not restrict flow nor do they produce any wastewater.
References:
Pichtel, John. Fundamentals of Site Remediation. 2nd ed. 2007,
Department of Environmental Protection. 2006, Bureau of Water Protection and
Samco Technologies, Inc. From: http://www.samcotech.com/qw_granular_activated_carbon_filters.php
Air Stripping
By Doug Sposito
Air Stripping is a treatment system that removes volatile organic compounds (VOCs) from contaminated ground water or surface water by forcing an air stream through the water and causing the compounds to evaporate.
Engineers use the Henry’s law constant to determine if air stripping will be a good treatment method. Henry’s law states that at a constant temperature, the amount of a given gas dissolved in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid. Constants in the range of 10-5 to 10-3 m3/mol are required. Volatile organics with a constant less than 10-5 evaporate too slowly. Benzene toluene and chlorinated are typical molecules suitable for air stripping.
Another consideration is the air to water flow ratio. Ratios ranging from 5-200 are considered good. Too much air flow will prevent the water from moving and create a condition known as “flooding”.
Air strippers are advantageous due to the relatively low installation and operational costs and ease of operation. Air strippers are now considered a proven technology. Air strippers only need intermittent checking by a technician so are useful in remote locations also reducing the financial costs for those responsible for maintaining the system. The disadvantages are the limited use to only volatile organic compounds. Air stripping unfortunately is also a mass transfer technology; transferring the contamination from one environment, the ground water to another, the air.
If the water contains other contaminants it may need to be pretreated. Iron and hardness also need to be removed prior to treatment.
In a typical air stripper the water is also oxygenated as it is moved opposite of the air current. This oxygenation precipitates the iron out of solution; a necessary step prior to treatment. If the water tests hard, calcium and magnesium would also need to be precipitated and removed prior to treatment to help avoid clogging of the system.
Controlling environmental pollution: an introduction to the technologies ...
By P. Aarne Vesilind, Thomas D. DiStefano
Control of emissions from an air stripper treating contaminated groundwater
W. D. Byers
Industrial Processes and Hazardous Waste, CH2M HILL,
Development of an Air-Stripping and UV/H2O2 Oxidation Integrated Process To Treat a Chloro-Hydrocarbon-Contaminated Ground Water
Li, Ku-Yen
Institution:
Wikpedia
Benefits of Constructed Wetlands
Constructed wetlands are just as the name implies- they are replicas of natural wetlands made by man. Wetlands are a natural filtration system trapping contaminants and sediments that are received by runoff, precipitation and environmental “incidents” such as spills. These contaminates are then biodegraded through various processes. One such process is the uptake of said contaminants through plant roots and then releasing them to the air. Another process is by trapping them in the plant root matrix where they can be collected and disposed of.
So why fabricate a constructed wetland? Because you get all the benefits of a natural wetland at basically any location you desire. Establishing a constructed wetland is a relatively simple process including excavating, inserting a liner (if needed), laying a dike of desired size and water control devices (if applicable). Once this has been completed, the vegetation is planted. Care must be taken in choosing the type of vegetation as certain plants are needed for maximum uptake. Growth of natural vegetation can also occur. Another benefit of constructed wetlands is that they are cheaper to build than a water treatment plant and maintenance and operation costs are low in comparison.
Constructed wetlands are frequently used to treat water from treatment plants and have been shown to be highly effective in removing metals from other sources of contamination. But this is not the only location where they are useful. In addition to pollution control and low costs, constructed wetlands also provide habitats for various flora and fauna and, depending on location, serve as public attractions.
Picture from Federal Remediation Technologies Roundtable
Http://www.frtr.gov/matrix2/selection1/list-of-figures
References
Constructed Wetlands- Natural processes t treat water, Build Habitats
http://ag.arizona.edu/azwater/arroyo/094wet.html
Constructed Wetlands
http://en.wikipedia.org/wiki/constructed_wetland
Innovative Onsite Sewage Treatment Systems: Constructed Wetlands
http://www.extension.umn.edu/distribution/naturalresources/DD7671.html
EPA-Constructed Treatment Wetlands
http://www.epa.gov/owow/wetlands/watersheds/cwetlands.html
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