Environmental Settings for use of Granular Activated Carbon
Cherie Jourdan
31Oct09
Granular Activated Carbon (GAC) is most effective at the removal of pesticides, volatile organic compounds (VOCs), chlorine, benzene, trihalomethanes, radon and multiple other man made chemicals typically found in our tap water. If properly developed, GAC can also remove some heavy metals, Giardia and Cryptosporidium.GAC filters are not successful at removing sediment and particulates therefore they are often in conjunction with sediment filters. GAC filters would not be found in a system that is primarily looking to remove such items as sediment and particulates.GAC Technologies are often found in contaminated river beds where other remediation technologies have been deemed too complicated or too expensive. In a river bed, the GAC will have the opportunity to absorb contaminants on a continuous basis.Even more common than a contaminated river bed, GAC is often found in a filter column treating unfavorable tap water. GAC is often found in systems that can treat tap water on a slow continuous basis rather than a fast acting, immediate one.
References:
Activated Carbon Water Filters and Purification (Granular/Granulated and Carbon Block). (n.d.). Retrieved October 31, 2009, from http://www.home-water-purifiers-and-filters.com/carbon-water-filter.php
Kvech, S., & Tull, E. (n.d.). Activated Carbon. Retrieved October 31, 2009, from http://www.cee.vt.edu/ewr/environmental/teach/wtprimer/carbon/sketcarb.html
Environmental Settings for use of Subsurface Barriers: Slurry Walls
Carin Kelley
2November 2009
Subsurface barriers like slurry walls can provide a barrier to contain hazardous chemical contaminants from migrating or prevent mixing of contaminant groundwater with uncontaminated groundwater and act as a filter to lower acidic pH levels in the groundwater, or be used to change the direction of groundwater flow.Slurry walls are made up of soil, bentonite clay, and water that provide low permeability at a low cost. They can be used in all types of soil including those below the groundwater table. However, the soil bentonite cannot withstand strong acids, bases, salts and/or organic contaminants. Under those chemical conditions, other bentonite mixtures are utilized, such as; cement bentonite, attapulgite, or slurry geomembrane composite which are generally used as barriers for landfill leachates and salt water.The construction of the slurry wall depends on the chemical properties. Near the groundwater table, the slurry wall will essentially be ‘hanging’ to capture the floating contaminants with low densities such as gases, oils, or fuels. For contaminants that are soluble, such as; metals, organics, or salts, a slurry wall that is connected to bedrock is more feasible to utilize. The physical properties of a common slurry wall can be placed as deep as 100 feet, a thickness of 2 to 4 feet, with a hydraulic conductivity of 1 x 10-6 centimeters per second. Most often, for effective pollution control, the slurry wall is connected to bedrock 2 to 3 feet.
References:
FRTR Remediation Technologies Screening Matrix and Reference Guide, Version 4.0 (n.d). GW Containment Remediation Technology 4.52 Physical Barriers. Retrieved 1 November 2009, from http://www.frtr.gov/matrix2/section4/4-53.html
U.S. EPA (17 July 2009). Engineering Technical Support Center (ETSC). Retrieved 30 October 2009, from http://www.epa.gov/nrmrl/lrpcd/rr/etsc/physchem.htm
Welcome to Slurry Wall.Com (2005). Detailed Specification for Slurry Walls Including Off-Site Disposal of Excess Slurry Off-Site Materials for Slurry Wall Backfill. Retrieved 30 October 2009, from http://www.slurrywall.com/slurry-wall-specifications/default.asp
Welcome to Slurry Wall.Com (2005). Slurry Wall, Cutoff Wall, Slurry Trench Technology Overview. Retrieved 1 November 2009, from http://www.slurrywall.com/slurry-walls-technology/default.asp#WHAT-ARE-SLURRY-WALLS
Capping Systems
Arell Gray
2 November 2009
One relatively inexpensive way to control the infiltration of surface water to a contamination plume is to build a capping system. The purpose of the cap is to block infiltrating surface water and to prevent the spread of the contamination to the groundwater or to stop the emission of subsurface gasses, it also provides a stable surface to cover the contamination and improves the general looks of the site. Though capping does not actually remove any contamination from the soil, it keeps the contamination local and prevents further spreading of the plume. In many instances, excavation of the contaminated soil takes place prior to the capping to even further insure the prevention of plume migration.A variety of capping materials can be used, from natural soils to synthetic liners, and they can be designed with varying complexity from single layer caps to multilayer capping systems. The different methods used when installing capping systems vary due to several site condition variables, such as the chemistry of the contaminate, climate, type of soil, financial constraints, or future plans for the site. When these conditions are all factored in, a decision can be made about the capping material and the complexity of the system.
Capping Materials
Natural- Natural barriers include fine grained soils like clays and clayey silts. When locally available natural capping materials can be very cheap in comparison with synthetic materials. Natural barriers also are very durable and can work effectively for many years. The process is fairly simple, just lay out the capping material and compact it using heavy machinery.Synthetic membranes- Many non-permeable synthetic materials exist and are very effective at keeping contamination from spreading. The wide variety of materials make it possible to contain a wide variety of contaminates. Once a surface is prepared over the contaminated soil, layers of synthetic membranes are placed down and sealed together. These synthetic membranes usually come in rolls of sheeting 20-140 mils, widths of 15-100 feet and lengths of 180-840 feet. The number of layers and what they are composed of is determined due to the site conditions. Extra care must be taken when installing the sheeting because any tear or puncture compromises the integrity of the cap. Another concern is the vegetation that grows on the cap, plants that have deep driving roots may also puncture the cap.
Synthetic Capping Materials include;
*HDPE (high density polyethylene)*VLDPE (very low density polyethylene)*PVC (Polyvinyl Chloride)*CSPE (chlorosulfonated polyethylene)*EIA (ethylene interpolymer alloy)*urethane*polypropylene*proprietary formulationsPavement- Asphalt or concrete, though unsightly, make an effective and easy cap for temporary capping of large areas.Multilayer systemsMany caps are composed of multiple layers. The base of which is a non-permeable or low-permeability layer either natural or synthetic. The middle layer is a permeable layer like sand or gravel and the top layer is made of vegetated native uncontaminated topsoil. The vegetation keeps the cap from eroding and provides aesthetic value, however vegetation with shallow root systems are a must to prevent punctures in the base layer. Once the surface water seeps into the middle permeable layer in flows along the non-permeable layer. The layers are graded on a slope so the water either flows off of the contaminated area or into a sump for storage.
References:
"4-26 Landfill Cap." Federal Remediation Technologies Roundtable. N.p., 7 July 2008. Web. 2 Nov. 2009. http://www.frtr.gov/matrix2/section4/4-27.html.
Pichtel, J. (2007). Fundamentals of site remediation for metal and hydrocarbon-contaminated soils. Lanham, Maryland:Government Institues.
Reible, D. (n.d.). In Situ Sediment Remediation Through Capping: Status and Research Needs. Retrieved from http://www.hsrc-ssw.org/pdf/cap-bkgd.pdf
Soil Vapor Extraction
Matthew Jacobs
2 November 2009
Soil Vapor Extraction (SVE) is a very common technology utilized globally to remove volatile constituents from contaminated sites, often from leaking underground storage tanks. SVE is also known as soil venting or vacuum extraction. Volatile compounds can be removed from the vadose zone by applying a vacuum to the soil through a series of extraction wells. Typical SVE systems consists of extraction wells, extraction piping, extraction blower, piping manifold, vapor pre-treatment, instrumentation and controls such as flow gauges, temperature sensors and vacuum gauges are typical, plus the vapor destruction unit itself (Pichtel, 2000). The removed vapors are then treated or often thermally destructed or filtered through activated carbon chambers. Highly volatile compounds such as gasoline are more easily extracted than larger less volatile compounds such as oils and diesel fuels (EPA, 2004). Therefore, the prime contaminants to be targeted by SVE systems are highly volatile, high vapor pressure petroleum hydrocarbons.
Before an SVE is installed, there are many steps to take in the evaluation process to determine if the right technology is being chosen. First of all, an initial screening is usually completed to test the potential success rate of a full system. This can be done as a pilot test on just one extraction well. If deemed successful, a full system can be designed and installed at the site. A full system usually consists of several extraction wells up to several dozen wells. The number of wells is determined by the area needing treatment. During installation, extraction wells are strategically placed to draw the greatest area of influence of each well. The soil types and contaminants of concern are thoroughly evaluated prior to well placement. Sandy and gravel soils are much better candidates for SVE systems than clay and silty areas. Sites with shallow groundwater are more prone to problems due to upwelling and low vacuum flow. If groundwater is a concern, another remediation technology should be selected. One of the most important factors to determine is the vapor pressure of the targeted contaminants. If the contaminants will easily evaporate, then the vacuum will be able to pull the compounds from the vadose zone successfully. If the contaminants have lower vapor pressures, the SVE will not be as effective. Compounds such as Methyl t-butyl ether, benzene, toluene, and ethylbenzene have higher vapor pressures and are better candidates for SVE systems (EPA, 2004). Therefore, the best environmental settings to utilize SVE systems have deeper groundwater, highly volatile, easily evaporative organic compounds, and sandy or gravel soil.
Each extraction well is then tied into the vapor destruction unit by piping, often pvc piping placed a few feet below grade. Once up and running, the system can be modified to best reach maximum extraction. As the contaminants are removed, the concentration will decrease. Flow rates may need to be increased as the contaminant concentrations drop. SVE systems can also be complemented by other technologies such as air sparging and dual phase extraction systems for vadose and groundwater treatment.
References:
EPA. 2004. How to Evaluate Alternative Cleanup Technologies for Underground Storage Tank Sites. EPA 510-R-04-002. http://www.epa.gov/swerust1/pubs/tum_ch2.pdf
Lambert, Steve and Mohamad Kotob. 2000. Soil Vapor Extraction. UCSD, Chemical Engineering. http://chemelab.ucsd.edu/sve/ProjSum.htm
Pichtel, John. 2000. Fundamentals of Site Remediation. pp. 193-208.
Wetland Construction: Environmental Settings, Contaminants, and Technologies
James Jackson
2 November 2009
The construction of wetlands for environmental remediation can be used in a variety of settings including agricultural, industrial, residential and municipal operations. However, the use of a constructed wetland for remediation in these environmental settings is dependent on the available flow rate of water into the wetland and the availability of sizable land for the construction (Huddleston, et al. 2003). If the flow rate and available land requirement is satisfied it is possible to establish a wetland to remediate contaminated water as disposal occurs. For example, many municipalities have established wetlands as a means of wastewater disposal from treatment plants. Constructed wetlands are capable of remediating metals, solid wastes and organic compounds found in contaminated water (Huddleston, et al. 2003; House, et al. 1998). The technology used for the wetland construction can be considered simple, inexpensive and readily available. Based on physical and computer modeling and testing a wetland is constructed for a specific set of contaminates (Huddleston, et al. 2003). The modeling and testing determines the vegetation type, soil characteristics and the hydraulic properties that will be used for the constructed wetland (Huddleston, et al. 2003).
References:
Huddleston, George and Rodgers, John. “A Design Approach for Constructed Wetlands for Storm Water and Point-Source Wastewater Treatment” 2003. Proceedings of the 2003 Georgia Water Resource Conference. Retrieved from the World Wide Web November 1, 2009 at http://cms.ce.gatech.edu/gwri/uploads/proceedings/2003/Huddleston%20and%20Rodgers.PDF
House, C.H., Bergmann, B.A., Stomp, A.M. and Frederick, D.J. “Combining constructed wetlands and aquatic and soil filters for reclamation and reuse of water” 1998. Retrieved from the World Wide Web November 1, 2009 at http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VFB-3VF1HP2-4&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1074979782&_rerunOrigin=sch
Flushing organics from soil using surfactants
Arti Jain
2 November 2009
A surfactant is briefly defined as a material that can greatly reduce the surface tension of water when used in very low concentrations.
A particular type of molecular structure performs as a surfactant. This molecule is made up of a water soluble (hydrophilic) and a water insoluble (hydrophobic) component.
How successful is the soil flushing is dependent upon the polarity / solubility of the contaminant. Highly soluble ones can be easily removed by just flushing with water. But organic compounds which are hydrophobic need a surfactant for remediation process. The contaminants for which surfactant may be required include aromatic compounds in petroleum and fuel residue, chlorinated compounds in commercial solvents like trichloroethene and chemicals no longer produced in the United States, for example DDT(chlorinated pesticides).
Several factors can influence the efficiency of soil flushing with surfactants. Groundwater that is too hard can lower the effectiveness of a surfactant. Surfactants can adsorb onto clay fractions, reducing their availability. Removal of the surfactant from the recovered water from flushing can be difficult and lead to high consumption rates. pH, ionic strength, particle size, density of soil are also critical factors. The hydraulic conductivity of soil, recovery of applied surfactant, how efficiently the soil can be flooded with the flushing solution is a critical factor. Too quick biodegradation can inactivate the surfactant although some degradability is required to avoid accumulation.
The main factors that should be considered when selecting surfactants include effectiveness, cost, public and regulatory perception, biodegradability and degradation products, toxicity to humans, animals and plants and ability to recycle. Though, the first consideration is that the surfactants are efficient in removing the contaminant.
References:
American Academy of Environmental Engineers ( AAEE), 1993. In: Anderson, W.C. (Ed.), Soil washing/soil flushing, Innovative Site Remediation, vol. 3, WASTEC.
Pichtel, John. Fundamentals of Site Remediation. Maryland: Government Institutes, 2007. Print.
Schafer, Andrea. Natural Organics Removal Using Membranes: Principles, Performance, and Cost. Boca Raton: CRC, 2001. Print.
"Surfactant - Wikipedia, the free encyclopedia." Wikipedia, the free encyclopedia. N.p., n.d. Web. 1 Nov. 2009.
Dwarakanath, V., Kostarelos, K., Shotts, D., Pope, G., & Wade, W. (1999). Anionic surfactant remediation of soil columns contaminated by nonaqueous phase liquids . Journal of Contaminant Hydrology, 38(4), 465-488.
Treatment of Contaminated Groundwater by Air Stripping – Considerations of Environmental Settings and Contaminants in Application of the Technology
Curtis Kempton
2 November 2009
Air stripping is a groundwater treatment technology applied in situations where volatile organic compounds (VOCs) or some semivolatiles have been released into soil and have contaminated the groundwater. Because air stripping is a mass transfer technology, transferring the contaminants from water to air without destroying them, its application is extremely dependent on the properties of the contaminant. There are also factors associated with general environmental settings that must be considered.
Air stripping has been utilized to remove contaminants such as BTEX, Chloroethane, TCE, DCE, and PCE. The Henry’s law constant is used to determine if air stripping is a good candidate treatment technology for the contaminant in question. Henry’s Law constant is a temperature dependent property of the contaminant that is a measure of how well the contaminant will separate from the water into the air. A higher Henry’s Law constant means easier separation into the air from the contaminated water. In general, air stripping is only effective for VOC or semivolatile contaminants with a Henry’s Law constant greater than 0.01 m3-atm/mol. (FRTR, 2007).
Because Henry’s Law constant is temperature dependent, the ambient temperature is an environmental factor that must be considered. Heating of either the water (CPEO, 2002) or the air (Pichtel, 2007) in the air stripping process may be done to increase the effectiveness of the process. This practice, however, is very energy intensive and costly.
References:
Center for Public Environmental Oversight. (2002). Technology tree: Air stripping. Retrieved October 31, 2009, from http://www.cpeo.org/techtree/ttdescript/airstr.htm
Federal Remediation Technologies Roundtable. (2007). Remediation technologies screening matrix and reference guide, version 4.0: Section 4.45 air stripping. Retrieved October 31, 2009, from http://www.frtr.gov/matrix2/section4/4-46.html
Pichtel, J. (2007). Fundamentals of site remediation (2nd ed. ed.). U.S.A.: Government Institutes.
Air Sparging
Jaime Hernandez
3 November 2009
Air sparging is a system which injects atmospheric air into the subsurface, allowing for hydrocarbons to return to a vapor phase. This type of application is also called “in situ air stripping” and “in situ volatilization” (OUST, 2009). The soil vapors are extracted and processed through different remedial technologies, such as thermal oxidation or carbon adsorption. Air sparging is commonly used in “lighter gasoline constituents“ remediation projects, because of the increased ability to transfer from dissolved phase to gaseous phase (OUST, 2009). “The effectiveness of air sparging depends primarily on two factors:1. Vapor/dissolved phase partitioning of the constituents determines the equilibrium distribution of a constituent between the dissolved phase and the vapor phase. Vapor/dissolved phase partitioning is, therefore, a significant factor in determining the rate at which dissolved constituents can be transferred to the vapor phase. 2. Permeability of the soil determines the rate at which air can be injected into the saturated zone. It is the other significant factor in determining the mass transfer rate of the constituents from the dissolved phase to the vapor phase.” (OUST, 2009)Air sparging may also aid in aerobic biodegradation processes. As decomposition progresses, subsurface oxygen concentration may be depleted. “Air, oxygen, or other oxygen source (e.g., hydrogen peroxide, ozone) may need to be added to the infiltration water.” (Pitchel, 2007, p. 284) Atmospheric air may be injected by sparging mechanisms and therefore replenish oxygen for biodegradation to continue. The sparger abatement system has also been designed for geothermal non-condensable gas (NCG) applications. In this case, the contaminated air is sparged through the treatment liquid. A sparger system is currently installed to abate H2S using a chemical oxidant in a pH controlled cooling water at geothermal facilities in Imperial County (CalEnergy, 2005). The sparging pipes run the length of the cooling tower basin. Non-condensable gas is cooled to approximately 160 F via a heat exchanger prior to entering the sparging system. The NCG stream bubbled in the cooling water is oxidized to sulfuric acid by oxidizing agents (CalEnergy 2005). Abatement efficiency for this type of sparger system is calculated to be 80%.
References:
Air Sparging Office of Underground Storage Tanks (OUST) US EPA. (n.d.). U.S. Environmental Protection Agency. Retrieved November 3, 2009, from http://www.epa.gov/oust/cat/airsparg
Imperial County. Air Pollution Control District. (2005, April) CalEnergy Leathers Permit 1927F Review. El Centro, CA: Cesar Flores.
Pichtel, J. (2007). Fundamentals of Site Remediation for Metal- and Hydrocarbon-contaminated Soils (null ed.). Rockville: Government Institutes.
Bioreactors
Makasha Hibbeler
4 November 2009
Once you’ve had a spill, leak, breach of containment or release of any kind of hazardous or toxic substance, you must protect the groundwater.[1] When deciding on what type of pump and treatment method you need, you must first take into consideration site characteristics and the contaminant type.[3] The first step should be to fully contain the release. To know if the containment method you have chosen is effective and holding the released materials in place, groundwater monitoring needs to be done. Once you have established the plume where the groundwater/soil is contaminated and have outlined the areas that are non-contaminated, then you can decide on what type of treatment is most effective and efficient to the desired level of treatment.[3]Bioreactors can be used in groundwater, wastewater and soil remediation. It is an Ex Situ process yet the bioreactor can be located both on and off the site. In Situ processes of the bioreactor maybe used though. The types of reactors can be either anaerobic (Oxygen is not needed or present, an example of this process would be used for a landfill) or aerobic (Oxygen is required, an example of this process would be removing Mercury from wastewater) processes but the reactors are primarily aerobic. The bioreactors are extremely diversified when it comes to their uses. They can be used on both organic and inorganic material ranging from human domestic waste to toxic organic waste and heavy metal contamination. [2]
References:
1 Khan, “An Overview and Analysis of site remediation technologies”, Journal of Environmental Management yr:2004 vol:71 iss:2 pg:952
2 Nyer, “Groundwater Treatment Technology”, [0-471-28414-9], 19923
3 Pichtel, J. (2007). Fundamentals of site remediation for metal and hydrocarbon-contaminated soils. Lanham, Maryland: Government Institues
No comments:
Post a Comment