Difference between pages "Emulsified Vegetable Oil (EVO) for Anaerobic Bioremediation" and "Landfarming"

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Emulsified Vegetable Oil (EVO) is commonly added as a slowly fermentable substrate to stimulate ''in situ'' anaerobic bioremediation.  This article summarizes information about EVO transport in the subsurface, consumption during anaerobic bioremediation, and methods for effectively distributing EVO throughout the target treatment zone.
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Landfarming is a well proven ex-situ bioremediation technology that has been successfully used since the 1980s for treating petroleum impacted soils/sediments, drill cuttings, low brine drilling fluids, oily sludges, tank bottoms and pit sludges. The material to be treated is incorporated into surface soilNaturally occurring microbes in the soil and waste material transform the organic contaminants to carbon dioxide, water and biomass (<ref name= "USEPA1993Bio">U.S. Environmental Protection Agency (USEPA), 1993. Bioremediation using the land treatment concept. US Environmental Protection Agency. Office of Research and Development, Washington, D.C. [[media:USEPA-1993._bio_using_land_treatment.pdf| Report.pdf]]</ref><ref name= "USEPA2003LF">U.S. Environmental Protection Agency (USEPA), 2003. Aerobic Biodegradation of Oily Wastes: A Field Guidance Book for Federal On-scene Coordinators, Version 1.0, October 2003. Region 6 South Central Response and Prevention Branch. [[media:USEPA-2003-Landfarming-OSC-Aerobic_Biodegradation_of_Oily_Wastes.pdf| Report.pdf]]</ref><ref>U.S. Environmental Protection Agency (USEPA), 2017. How to Evaluate Alternative Cleanup Technologies for Underground Storage Tank Sites: A Guide for Corrective Action Plan Reviewers, Chapter V: Landfarming , Land and Emergency Management 5401R, EPA 510-B-17-003. [[media:USEPA-2017._How_to_Evaluate_Alternative_Cleanup_tech_for_UST_Sites.pdf| Report.pdf]]</ref>). Maintaining optimum soil conditions for rapid biodegradation of organic contaminants can help meet cleanup goals within a reasonable timeframe.
  
 
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'''Related Article(s):'''
 
'''Related Article(s):'''
*[[Bioremediation - Anaerobic |Anaerobic Bioremediation]]
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*[[Biodegradation - Hydrocarbons]]
*[[Bioremediation - Anaerobic Design Considerations| Anaerobic Bioremediation Design Considerations]]
 
*[[Chlorinated Solvents]]
 
  
  
'''CONTRIBUTOR(S):''' [[Dr. Robert Borden, P.E.]]
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'''CONTRIBUTOR(S):''' [[Dr. Roopa Kamath]], [[Sara McMillen]], [[Rene Bernier]], and [[Deyuan Kong]]
  
  
 
'''Key Resource(s):'''
 
'''Key Resource(s):'''
 +
*[[media:USEPA-1993._bio_using_land_treatment.pdf| Bioremediation using the land treatment concept.]]<ref name= "USEPA1993Bio"/>
 +
*[[media: USEPA-2003-Landfarming-OSC-Aerobic_Biodegradation_of_Oily_Wastes.pdf| Biotreating E&P Wastes: Lessons Learned from 1992-2003]]<ref name= "USEPA2003LF"/>.
  
*[[media:2017-Borden-Post-Remediation_Evaluation_of_EVO_Treatment.pdf| Post-Remediation Evaluation of EVO Treatment – How Can We Improve Performance?]]<ref name = "Borden2017EVO">Borden, R.C., 2017. Post-Remediation Evaluation of EVO Treatment: How Can We Improve Performance. Environmental Security Technology Certification Program, Alexandria, VA. ER-201581[[media:2017-Borden-Post-Remediation_Evaluation_of_EVO_Treatment.pdf| Report.pdf]]</ref>
 
*[[media:2006-Solutions-IES-Protocol_for_Enhanced_In_Situ_Bioremediation.pdf| Protocol for Enhanced In Situ Bioremediation Using Emulsified Edible Oil (Solutions-IES, 2006)]]<ref>Solutions-IES, 2006.  Protocol for Enhanced In Situ Bioremediation Using Emulsified Edible Oil. Environmental Security Technology Certification Program, Arlington, VA, USA. ER 200221 [[media:2006-Solutions-IES-Protocol_for_Enhanced_In_Situ_Bioremediation.pdf| Report.pdf]]</ref>
 
  
 
==Introduction==
 
==Introduction==
 +
During landfarming, the waste materials are typically placed as a layer on the ground surface with variable thickness. The waste is then tilled and amended with nutrients to enhance biodegradation by naturally occurring bacteria (Figure 1). Fertilizers such as urea and triple superphosphate (TSP) are used to provide nitrogen and phosphate necessary for biodegradation. Reduction in hydrocarbon concentrations can be expected within a span of weeks to months, depending on the initial concentration and composition of hydrocarbons, and whether the soil conditions are optimized for biodegradation. Once cleanup goals have been achieved, the treated material can be i) re-used in construction activity such as berms, landfill cover, backfill, regrading, or for agricultural purposes, ii) disposed at a landfill and/or iii) left in place and revegetated, depending on local regulations or site-specific considerations.
  
Emulsified Vegetable Oil (EVO) is commonly added as a slowly fermentable substrate to stimulate the ''in situ'' [https://enviro.wiki/index.php?title=Bioremediation_-_Anaerobic anaerobic bioremediation] of chlorinated solvents, explosives, perchlorate, chromate, and other contaminants. However, effective treatment requires that EVO be distributed throughout the target treatment zone to optimize microbial growth and therefore contaminant degradation.
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Landfarming is a low-cost technology. Facilities are simple to construct and easy to operate. Standard construction and farming equipment can be used to move soils to the land treatment facility, to amend the soils with fertilizer, to apply water to the soils and to till the soils (e.g. excavator, plow, rotovator, water truck). Figures 2 through 4 show examples of equipment used at a typical landfarming facility.  
  
==EVO Properties, Transport and Retention in the Subsurface==
 
  
[[File:Borden3w2_Fig1.PNG|thumbnail| Figure 1. Photo-micrograph of EVO (0.7 µm median diameter). White scale bar 25 µm. ]]
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<div><ul>
 +
<li style="display: inline-block;"> [[File:Kamath1w2 Fig1.png|thumbnail|500 px| Figure 1. Soils Undergoing Treatment at a Landfarming Facility]]</li>
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<li style="display: inline-block;"> [[File:Kamath1w2 Fig2.png|thumbnail|500 px| Figure 2. Excavator to Move Soils]]</li>
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<li style="display: inline-block;"> [[File:Kamath1w2 Fig3.png|thumbnail|500 px| Figure 3. Water Truck to Ensure Optimal Moisture Content for Microbial Degradation in Soils]]</li>
 +
</ul></div>
  
EVO is most commonly purchased from a commercial supplier and shipped to the site as a concentrated emulsion containing 45 to 60% vegetable oil.  These factory prepared emulsions are generally stable but do have a finite shelf-life (typically several months), which can be can be significantly shortened by extremes in storage temperature.  Soybean oil is commonly used because of its availability, good handling characteristics, and relatively low cost.  The oil provides a slow release organic substrate to support long-term anaerobic activity.  The remainder of the EVO formulation consists of: (a) more readily fermentable soluble substrates (e.g. fatty acids or alcohols); (b) surfactants to reduce oil droplet interfacial tension, stabilize the emulsion and reduce oil droplet flocculation; and (c) water.  The soluble substrates are first used by bacteria to reduce other terminal electron acceptors (oxygen, ferric iron, sulfate etc) and generate rapid, initial growth of the required bacteria.  In some cases, additional nutrients are added to enhance microbial growth including nitrogen, phosphorus, yeast extract, and vitamin B<sub>12</sub>.  The median oil droplet size of factory prepared emulsions is commonly in the range of 0.5 to 2.0 µm, which provides emulsion stability during shipping and also improves transport through typical aquifer materials (Figure 1). Some product vendors provide more concentrated EVO products containing oil and surfactant that do not contain water to save on shipping costs.  These products must be emulsified in the field by adding water and mixing.  Typically, these field prepared emulsions are not as stable as factory prepared emulsions, and often have much larger oil droplets.
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[[File:Kamath1w2 Fig4.png|thumbnail|center|800 px| Figure 4. Rotovator and Plows to Till Soils]]
  
Once injected, the oil droplets are transported through the aquifer pore spaces by flowing groundwater. Experimental and mathematical modeling studies by Soo and Radke<ref>Soo, H. and Radke, C.J., 1984. Flow mechanism of dilute, stable emulsions in porous media. Industrial & engineering chemistry fundamentals, 23(3), pp.342-347. [https://doi.org/10.1021/i100015a014 doi: 10.1021/i100015a014]</ref><ref >Soo, H. and Radke, C.J., 1986. A filtration model for the flow of dilute, stable emulsions in porous media-I. Theory. Chemical Engineering Science, 41(2), pp.263-272. [https://doi.org/10.1016/0009-2509(86)87007-5 doi: 10.1016/0009-2509(86)87007-5]</ref><ref>Soo, H., Williams, M.C. and Radke, C.J., 1986. A filtration model for the flow of dilute, stable emulsions in porous media-II. Parameter evaluation and estimation. Chemical Engineering Science, 41(2), pp.273-281. [https://doi.org/10.1021/es304641b doi: 10.1016/0009-2509(86)87008-7]</ref> have shown that oil droplets larger than the sediment pores are rapidly removed by straining with a large, permanent permeability loss.  The median pore size of sand aquifers is typically over 100 µm<ref>Coulibaly, K.M. and Borden, R.C., 2004. Impact of edible oil injection on the permeability of aquifer sands. Journal of Contaminant Hydrology, 71(1-4), pp.219-237. [https://doi.org/10.1016/j.jconhyd.2003.10.002 doi: 10.1016/j.jconhyd.2003.10.002]</ref> which is orders of magnitude greater than the oil droplet diameter (< 2 µm) of factory prepared emulsions, so physical straining is not a significant retention mechanism in sands. However, field prepared emulsions often have larger oil droplets, so physical straining of the large droplets can be significant.
+
Some of the disadvantages of the technology are:
 +
*It requires a large land area for treatment.
 +
*There may be regulatory limitations on wastes that can be treated by landfarming. For example, U.S. regulations prevent landfarming soil impacted with hazardous wastes such as motor oil, hydraulic oil, and solvents.
 +
*It may not be effective for highly impacted soils or soils impacted with severely degraded hydrocarbons (e.g. if soils contain >8% w/w petroleum hydrocarbons after spreading).  
 +
*Although landfarming is effective for reducing hydrocarbon concentrations, it is not effective for reducing concentrations of other oil field waste components, such as elevated concentrations of metals, salt or wastes containing naturally occurring radioactive materials (NORM).
 +
*Concentration reductions >95% or final concentrations <0.1% may not be successfully obtained based on the extent impacted and nature of the hydrocarbons.
 +
*Dust and vapor emissions may pose air quality concerns.
  
Common factory prepared emulsions are retained by aquifer material when the small oil droplets collide with sediment surfaces and stick (referred to as interception).  Retention of small oil droplets (diameter < 2 µm) by aquifer material can be described by deep-bed filtration theory<ref name= "Ryan1996">Ryan, J.N. and Elimelech, M., 1996. Colloid mobilization and transport in groundwater. Colloids and surfaces A: Physicochemical and engineering aspects, 107, pp.1-56. [https://doi.org/10.1016/0927-7757(95)03384-X doi: 10.1016/0927-7757(95)03384-X]</ref><ref name= "Logan1999">Logan, B.E., 1999.  Environmental transport processes.  John Wiley & Sons, New York</ref><ref name= "Coulibaly2006">Coulibaly, K.M., Long, C.M. and Borden, R.C., 2006. Transport of edible oil emulsions in clayey sands: One-dimensional column results and model development. Journal of Hydrologic Engineering, 11(3), pp.230-237. [https://doi.org/10.1061/(asce)1084-0699(2006)11:3(230) doi: 10.1061/(ASCE)1084-0699(2006)11:3(230)]</ref> where droplet capture by the sediment surfaces is a function of: (1) the frequency that droplets collide with sediment surfaces; and (2) the collision efficiency, which is the fraction of droplets colliding with the sediment surfaces that are actually retained<ref>Westall, J.C. and Gschwend, P.M., 1993. Mobilizing and depositing colloids. Manipulation of groundwater colloids for environmental restoration. ISBN 9780873718288]</ref><ref name= "Ryan1996"/><ref name= "Logan1999"/>.
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==Suitability of Wastes for Landfarming==
 +
Landfarming has been successfully used to reduce hydrocarbon concentrations in soils impacted with kerosene, diesel, jet fuel, and crude oil. It has also been successfully used to treat oil-based drilling wastes (drill cutting, low brine drilling), oily sludge, tank bottoms and pit sludges.  
  
[[File:EOS in the subsurface.gif|thumbnail|right|600 px| Figure 2. Animation illustrating oil droplet transport and retention in porous media<ref name = "Borden2007b"/>.]]
+
Wastes may not be suitable for landfarming for a number of reasons:
  
Collision frequency between oil droplets and sediment surfaces depends on groundwater flow velocity (advection), Brownian motion (diffusion), and gravitational settling or floatation.  Very small droplets vibrate rapidly due to Brownian motion, resulting in frequent collisions with particle surfaces and rapid removal. Large droplets float, colliding with the roof of the sediment pores, increasing removal. For vegetable oil emulsions at typical groundwater velocities, the lowest collision frequency occurs at a particle size of 0.5 to 2 µm<ref name = "Borden2007b">Borden, R.C., 2007. Engineering Delivery of Insoluble Amendments. Partners in Environmental Technology Symposium & Workshop, SERDP, Washington, DC</ref>.  
+
*There may be regulatory or permit limitations. For instance, in the United States, wastes that are not exempted under RCRA <ref>U.S. Environmental Protection Agency (USEPA), 2002. Exemption of Oil and Gas Exploration and Production Wastes from Federal Hazardous Waste Regulations. Office of Solid Waste, EPA530-K-01-004. [[Media:USEPA-2002._Exemption_of_Oil_and_Gas_exploration_and_Production_Wastes....pdf| Report.pdf]]</ref> such as motor oil, hydraulic oil, and solvents cannot be treated by landfarming by law.  
 +
*Wastes unsuitable by their composition such as solid, non-spreadable paraffins from pig trap scrapings from the maintenance of pipelines, or highly weathered wastes, or asphaltic wastes
 +
*Wastes containing contaminants that do not biodegrade: e.g., NORM, metals or salt.  
  
Collision efficiency varies due to a variety of factors including pH, droplet and matrix grain surface coatings, ionic strength, surface roughness, sediment surface charge heterogeneity, and blocking of the sediment surface with previously retained droplets<ref>Bolster, C.H., Mills, A.L., Hornberger, G.M. and Herman, J.S., 2001. Effect of surface coatings, grain size, and ionic strength on the maximum attainable coverage of bacteria on sand surfaces. Journal of Contaminant Hydrology, 50(3-4), pp.287-305. [https://doi.org/10.1016/S0169-7722(01)00106-1 doi: 10.1016/S0169-7722(01)00106-1]</ref><ref>Johnson, P.R. and Elimelech, M., 1995. Dynamics of colloid deposition in porous media: Blocking based on random sequential adsorption. Langmuir, 11(3), pp.801-812. [https://doi.org/10.1021/la00003a023 doi: 10.1021/la00003a023]</ref><ref>Rijnaarts, H.H., Norde, W., Bouwer, E.J., Lyklema, J. and Zehnder, A.J., 1996. Bacterial deposition in porous media related to the clean bed collision efficiency and to substratum blocking by attached cells. Environmental Science & Technology, 30(10), pp.2869-2876. [https://doi.org/10.1021/es960597b doi: 10.1021/es960597b]</ref><ref>Rijnaarts, H.H., Norde, W., Bouwer, E.J., Lyklema, J. and Zehnder, A.J., 1996. Bacterial deposition in porous media: effects of cell-coating, substratum hydrophobicity, and electrolyte concentration. Environmental Science & Technology, 30(10), pp.2877-2883. [https://doi.org/10.1021/es9605984 doi: 10.1021/es9605984]</ref>.  Oil droplets and sediment particles typically take on an electrical charge and are surrounded by a [https://en.wikipedia.org/wiki/Double_layer_(surface_science) double layer] of charged ions.  When both the oil droplets and sediment surfaces have a negative charge, the oil droplets tend to be repelled by the sediments, reducing oil retention by the sediments.  When the oil droplets are negatively charged and the sediments are positive or neutral, the oil droplets are more likely to stick and be retained by the sediment. 
+
==Biodegradation Potential==
 +
The initial concentration and composition of hydrocarbons strongly influences the biodegradation potential of a waste. [[File:Kamath1w2 Fig5.png|thumbnail|right| Figure 5. Correlation between API gravity (specific weight of the crude) and the predicted extent of biodegradation as measured by oil and grease (O&G)<ref name= "McMillen2004"/>.]]
  
As a dilute emulsion containing millions of negatively charged oil droplets migrates through the aquifer pore spaces, it encounters some positively charged locations.  If the oil droplet ‘bumps into the sediment’ at that location, the droplet will likely stick and fill up that site (Figure 2). Additional oil droplets will be repelled by the attached droplet and migrate further through the aquifer, gradually filling up the available attachment sites.  In this way, the emulsion gradually saturates the available attachment sites and continues to migrate with the flowing groundwater.  The maximum amount of oil that can be retained by an aquifer is a function of the oil droplet properties (diameter, surface charge), chemical characteristics of the sediment surface (e.g., presence of organic or iron oxide coatings), and surface area available for droplet attachment.  Sediments with a high clay content are expected to have a higher maximum oil retention because of the greater surface area and number of sites available for oil droplet attachment.  Fine grain sediments will also have smaller pores, so physical straining of oil droplets becomes more important.
+
*Wastes with >5% (w/w) of hydrocarbons may have physical and chemical characteristics that hinder biodegradation. For example, oily wastes tend to repel water, and can be poorly aerated. This can hinder or inhibit biodegradation.  
  
A common measure of suspension or emulsion stability is [https://en.wikipedia.org/wiki/Zeta_potential zeta potential] which is the potential difference between the bulk fluid and the stationary fluid layer attached to the particle surface. Particles that have a highly negative (or highly positive) zeta potential will not flocculate. However, when zeta potential is close to zero, attractive forces may exceed the electrostatic repulsion and the emulsion may break and flocculate. Typical rules of thumb for negatively charged emulsions (zeta potential < 0) are:
+
*The molecular structure and molecular weight of hydrocarbons in the waste may make them either more or less susceptible to attack by microorganisms. Typically, aliphatic hydrocarbons are more readily biodegraded than aromatic hydrocarbons.  Structurally more complex molecules such as isoprenoids and steranes are relatively recalcitrant to biodegradation. For crude oils, the API gravity is a reliable indicator of the composition of a crude oil and by extension, a good predictor of the biodegradation potential of a crude oil (see Figure 5)<ref name= "McMillen2004">McMillen, S.J., Smart, R., Bernier, R. and Hoffmann, R.E., 2004, January. Biotreating E&P wastes: lessons learned from 1992-2003. In SPE International Conference on Health, Safety, and Environment in Oil and Gas Exploration and Production. Society of Petroleum Engineers. [https://doi.org/10.2118/86794-ms  doi: 10.2118/86794-ms]</ref>. For example, a crude oil with API gravity of 40 (by virtue of its composition) may degrade by 75% within 4 weeks. A crude oil with API gravity of 25 may only degrade by 55%, and a crude oil with API gravity of 10 may not degrade more than 10% within that same timeframe.  
  
{|
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This same correlation can be used to determine the maximum initial hydrocarbon concentration that can be treated using conventional landfarming within 4 weeks and/or the maximum endpoint achievable for a given waste material.
|-
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|align=left|- rapid flocculation||&nbsp;&nbsp;&nbsp;&nbsp; 0 mV||&nbsp;&nbsp;&nbsp;&nbsp; < ||&nbsp;&nbsp;&nbsp;&nbsp; zeta potential ||&nbsp;&nbsp;&nbsp;&nbsp; <||&nbsp;&nbsp;&nbsp;&nbsp; -5 mV
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Using analytical methods such as gas chromatography to determine the quantity and composition of organic contaminants in a waste may be useful in determining biodegradation potential. Lighter ends (lower boiling point components that elute earlier in the chromatogram) will typically degrade faster than heavier end components.
|-
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|align=left|- incipient instability||&nbsp;&nbsp;&nbsp;&nbsp;-10 mV ||&nbsp;&nbsp;&nbsp;&nbsp; < ||&nbsp;&nbsp;&nbsp;&nbsp; zeta potential ||&nbsp;&nbsp;&nbsp;&nbsp; <||&nbsp;&nbsp;&nbsp;&nbsp; -30 mV
+
*The extent of weathering (volatilization and biodegradation) may influence the rate and extent of biodegradation. Fresh crude oils with API gravity >30 are generally readily biodegradable; however, after extensive weathering as might be encountered at an old spill site, the oil may not be very biodegradable as most of the more volatile and biodegradable fractions of hydrocarbon have already disappeared.  It is recommended that feasibility evaluations include hydrocarbon analysis of wastes using gas chromatography (GC) to assess the extent of weathering.  (Figures 6a and 6b)
|-
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|align=left|- moderate stability||&nbsp;&nbsp;&nbsp;&nbsp; -30 mV||&nbsp;&nbsp;&nbsp;&nbsp; < ||&nbsp;&nbsp;&nbsp;&nbsp; zeta potential ||&nbsp;&nbsp;&nbsp;&nbsp; <||&nbsp;&nbsp;&nbsp;&nbsp; -40 mV
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<div><ul>
|-
+
<li style="display: inline-block;"> [[File:Kamath1w2 Fig6a.png|thumbnail| none| 600 px| Figure 6a. Chromatogram of Fresh Crude Oil]]</li>
|align=left|- good stability ||&nbsp;&nbsp;&nbsp;&nbsp; -40 mV||&nbsp;&nbsp;&nbsp;&nbsp; < ||&nbsp;&nbsp;&nbsp;&nbsp; zeta potential ||&nbsp;&nbsp;&nbsp;&nbsp; <||&nbsp;&nbsp;&nbsp;&nbsp; -61 mV
+
 
|-
+
<li style="display: inline-block;"> [[File:Kamath1w2 Fig6b.png|thumbnail| none| 600 px| Figure 6b. Chromatogram of Weathered Crude Oil]]</li>
|align=left|- excellent stability||&nbsp;&nbsp;&nbsp;&nbsp; ||&nbsp;&nbsp;&nbsp;&nbsp;  ||&nbsp;&nbsp;&nbsp;&nbsp; zeta potential ||&nbsp;&nbsp;&nbsp;&nbsp; <||&nbsp;&nbsp;&nbsp;&nbsp; -61 mV
+
</ul></div>
|}
+
 
 +
*Light refined products, such as diesel and jet fuels, are highly biodegradable, similar to crude oils with API gravity >40. Heavy refined products like Bunker C or heavy fuel oils will biodegrade at rates similar to low API-gravity crude oils.
 +
 
 +
 
 +
==Facility Design and Operation==
 +
Landfarming facilities are designed to prevent impacts to groundwater and surface water. The facilities typically include an impermeable or low permeability liner for the treatment pad to prevent leaching of chemical constituents from the treatment waste to the groundwater, and berms/dikes to prevent storm water runoff. (See Figure 7.)
  
Zeta potential and maximum oil retention were measured in sediments from two sites (SA17 Zone B and OU2) using either deionized water (DI water) or a solution of 200 mg/L CaCl<sub>2</sub><ref name = "Borden2017EVO"/>. In DI water, the zeta potential of the EVO (EOS 598B42) was -43 mV indicating good stability, while the zeta potential of the soil varied from -20 to -30 mV indicating incipient instability (Table 1).  However, in the CaCl<sub>2</sub> solution, zeta potential of the soils and emulsion were much closer to zero indicating rapid flocculation.  The much weaker repulsion of the oil droplets by the sediment particles in the CaCl<sub>2</sub> solution resulted in a large increase in maximum oil retention (Table 2). These results are consistent with the common practice of adding multivalent cations to water treatment systems to reduce zeta potential and enhance flocculation of suspended particles.  In general, trivalent cations (Fe<sup>+3</sup>, Al<sup>+3</sup>) are more effective flocculants than divalent cations (Ca<sup>+2</sup>, Mg<sup>+2</sup>, Fe<sup>+2</sup>, Mn<sup>+2</sup>), which are more effective than mono-valent cations (Na<sup>+</sup>, K<sup>+</sup>).
+
[[File:Kamath1w2 Fig7.PNG|thumbnail| right| 500 px| Figure 7. Typical Landfarming Operation]]
  
These results demonstrate that dissolved cation concentration (Na<sup>+</sup>, K<sup>+</sup>, Ca<sup>+2</sup>, Mg<sup>+2</sup>, Mn<sup>+2</sup>, Fe<sup>+2</sup>) can have a major impact on zeta potential and oil retention.  High concentations of dissolved cations will occur naturally in aquifers with high total dissolved solids (Na<sup>+</sup>, K<sup>+</sup>) or with carbonate minerals (Ca<sup>+2</sup>, Mg<sup>+2</sup>).  In situ bioremediation can increase cation concentration by release of dissolved Mn<sup>+2</sup> or Fe<sup>+2</sup> and by addition of alkaline materials (NaHCO<sub>3</sub>, Mg(OH) <sub>2</sub>), if needed to raise pH.
+
Successful landfarm operation requires maintaining optimum conditions in the soil/waste materials (moisture, oxygen, pH and nutrient levels) to enhance biodegradation of petroleum hydrocarbons (see Table 1). Before beginning landfarm operations, the waste and the soil at the landfarm site should be characterized to establish the soil baseline characteristics and the need for soil additives such as agricultural lime for pH correction.
  
{| class="wikitable" style="margin-left: auto; margin-right: auto; border: none; text-align: center;"
+
{| class="wikitable" style="text-align: left;"
|+ colspan="3" | Table 1.  Effect of Solution Composition on Zeta Potential
+
|+ colspan="2" | Table 1.  Optimum Conditions for Landfarming
|-
 
! rowspan="2" | Colloid
 
! colspan="2" | Average Zeta Potential (mV) (standard deviation)
 
|-
 
! DI Water
 
! 200 mg/L CaCl<sub>2</sub>
 
|-
 
| SA17 Soil 15-23’ || -29.4 (0.8) || -8.5 (0.5)
 
 
|-
 
|-
| SA17 Soil 30-40’|| -22.3 (0.9) || -7.5 (0.9)
+
! Parameter
 +
! Optimum Condition
 
|-
 
|-
| OU2 Soil 37-40’ || -19.9 (0.5) || -12.2 (0.9)
+
| Initial&nbsp;HC&nbsp;Concentration || 1% - 5% by weight in dry soil
 
|-
 
|-
| EOS 598B42|| -43.0 (0.7) || -10.3 (0.4)
+
| pH || 6 – 8.5. Agricultural lime can be added to increase soil pH.
|}
 
 
 
 
 
{| class="wikitable" style="margin-left: auto; margin-right: auto; border: none; text-align: center;"
 
|+ colspan="3" | Table 2. Oil Retention in Laboratory Columns Flushed with EOS598B42 and either DI Water or 200 mg/L CaCl<sub>2</sub>
 
 
|-
 
|-
! rowspan="2" | Aquifer Material
+
| Aeration/Tilling || Initially and every 2 – 4 weeks.
! colspan="2" | Average Oil Retention (g oil/g sediment) (standard deviation)
 
 
|-
 
|-
! DI Water
+
| Moisture Content || 60% – 80% of water holding capacity (field capacity).
! 200 mg/L CaCl<sub>2</sub>
 
 
|-
 
|-
| SA17 Zone B || 0.0027 (0.0027)|| 0.0133 (0.0060)
+
| Salt Content || Electrical conductance of leachate <30 mS/cm (mhos/cm). Preferably <4 mS/cm for maximum reuse potential after cleanup. Ocean water has an electrical conductance of ~50 mS/cm.
 
|-
 
|-
| OU2 || 0.0144 (0.0018)|| 0.0381 (0.0114)
+
| Nutrients ||  
 +
* Total Nitrogen: 250 – 500 ppm. Action Level: 50 ppm. Nitrogen source should be added if nutrient concentration falls below action level (e.g. urea).  
 +
* Available phosphate: 125 – 250 ppm. Action Level: 25 ppm. Phosphate source should be added if nutrient concentration falls below action level (e.g. triple superphosphate).
 
|}
 
|}
  
Detailed laboratory column, sandbox, and field studies have shown that EVO can be transported substantial distances through fine silty or clayey sand and fractured rock<ref name= "Coulibaly2006"/> <ref>Jung, Y., Coulibaly, K.M. and Borden, R.C., 2006. Transport of edible oil emulsions in clayey sands: 3D sandbox results and model validation. Journal of Hydrologic Engineering, 11(3), pp.238-244. [https://doi.org/10.1061/(asce)1084-0699(2006)11:3(238)  doi: 10.1061/(asce)1084-0699(2006)11:3(238)]</ref><ref name= "Borden2007a">Borden, R.C., 2007. Effective distribution of emulsified edible oil for enhanced anaerobic bioremediation. Journal of Contaminant Hydrology, 94(1-2), pp.1-12. [https://doi.org/10.1016/j.jconhyd.2007.06.001 doi: 10.1016/j.jconhyd.2007.06.001]</ref><ref>Borden, R.C., Beckwith, W.J., Lieberman, M.T., Akladiss, N. and Hill, S.R., 2007. Enhanced anaerobic bioremediation of a TCE source at the Tarheel Army Missile Plant using EOS. Remediation Journal: The Journal of Environmental Cleanup Costs, Technologies & Techniques, 17(3), pp.5-19. [https://doi.org/10.1002/rem.20130 doi: 10.1002/rem.20130]</ref><ref>Riha, B.D., Looney, B.B., Noonkester, J.V., Hyde, K. and Solutions, S.R.N., 2009. Treatability Study for Edible Oil Deployment for Enhanced cVOC Attenuation for T-Area, Savannah River Site: Interim Report–Year One. Technical Report SRNL-RP-2009-00539. Savannah River National Laboratory, Aiken, SC. [[media:2009-Riha-Treatability_Study_for_Edible_deployment..._SRNL-RP-2009-00539-F.pdf| Report.pdf]]</ref> <ref>Kovacich, M.S., Beck, D., Rabideau, T., Pettypiece, K.S., Noel, M., Zack, M.J. and Cannaert, M.T., 2007, May. Full-scale bioaugmentation to create a passive biobarrier to remediate a TCE groundwater plume. In Proceedings: Ninth International In Situ and On-Site Bioremediation Symposium, Baltimore, Maryland, USA. [[media:2007-Kovacich-Full-Scale_Bioaugmentation_to_Create_a_Passive_Biobarrier....pdf| Report.pdf]]</ref><ref name = "Watson2013">Watson, D.B., Wu, W.M., Mehlhorn, T., Tang, G., Earles, J., Lowe, K., Gihring, T.M., Zhang, G., Phillips, J., Boyanov, M.I. and Spalding, B.P., 2013. In situ bioremediation of uranium with emulsified vegetable oil as the electron donor. Environmental science & technology, 47(12), pp.6440-6448. [https://doi.org/10.1021/es3033555 doi: 10.1021/es3033555]</ref>.  However, once oil droplets attach to soil surfaces, they are strongly retained and do not migrate further.  Much effort has focused on developing EVO formulations with low retention to reduce the amount of oil required to treat a given volume of aquifer. However, in some cases, higher oil retention is required to treat very high permeability gravels or fractured rock.  In these cases, EVO with large oil droplets can be used.  The large droplets increase oil retention by straining and by oil droplet buoyancy which causes the large droplets to collide with the roof of the sediment pores.
+
Maintaining optimum conditions for biodegradation is the key to achieving target cleanup goals within a reasonable timeframe. Figure 8 is an illustration of the effect of tilling and adding fertilizer on the rate of degradation of petroleum hydrocarbons.  
 
 
==EVO Consumption==
 
Shortly after injection, most oil droplets are immobilized on sediment surfaces.  The soluble substrates are rapidly consumed during reduction of background electron acceptors (oxygen, nitrate, manganese, iron and sulfate).  The oil (triglyceride) is fermented to hydrogen and acetic acid through a two-step process where the ester linkages between the glycerol (an alcohol) and the long-chain fatty acids (LCFAs) are hydrolyzed releasing free fatty acids and glycerol to solution.  Glycerol is very soluble and relatively easy to biodegrade, so this material is quickly consumed releasing 1,3-propanediol and then H<sub>2</sub> and acetate.  The LCFAs undergo further breakdown by ''beta''-oxidation releasing hydrogen (H<sub>2</sub>), one molecule of acetic acid (C<sub>2</sub>H<sub>4</sub>O<sub>2</sub>), and a new acid derivative with two fewer carbon atoms<ref name= "Sawyer1994">Sawyer, C.N., P.L. McCarty, and G.F. Parkin. 1994. Chemistry for Environmental Engineering. McGraw-Hill Inc. ISBN 10: 0070549788 / ISBN 13: 9780070549784</ref>. 
 
 
 
<div class="center"><big>C<sub>n</sub>H<sub>2n</sub>O<sub>2</sub> + 2 H<sub>2</sub>O &rArr; 2 H<sub>2</sub> + C<sub>2</sub>H<sub>4</sub>O<sub>2</sub> + C<sub>n-2</sub>H<sub>2n-4</sub>O<sub>2</sub>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</big> ''Reaction 1''</div>
 
 
 
By successive oxidation at the ''beta'' carbon atom, long-chain fatty acids (LCFAs) are whittled into short chain fatty acids (SCFAs) and acetic acid.  Four hydrogen atoms are released from saturated fatty acids for each acetic acid unit produced<ref name= "Sawyer1994"/>.  Unsaturated fatty acids undergo the same general process, but release two atoms of hydrogen for each acetic acid unit.
 
  
Microcosm, modeling, and field studies by Tang et al.<ref>Tang, G., Wu, W.M., Watson, D.B., Parker, J.C., Schadt, C.W., Shi, X. and Brooks, S.C., 2013. U (VI) bioreduction with emulsified vegetable oil as the electron donor–microcosm tests and model development. Environmental science & technology, 47(7), pp.3209-3217. [https://doi.org/10.1021/es304641b doi: 10.1021/es304641b]</ref><ref>Tang, G., Watson, D.B., Wu, W.M., Schadt, C.W., Parker, J.C. and Brooks, S.C., 2013. U (VI) bioreduction with emulsified vegetable oil as the electron donor–model application to a field test. Environmental science & technology, 47(7), pp.3218-3225. [https://doi.org/10.1021/es304643h doi: 10.1021/es304643h]</ref>, and Watson et al <ref name = "Watson2013"/> indicate that the LCFA consumption rate, and associated H<sub>2</sub> and acetate production rate, is controlled by LCFA solubility.  LCFAs have a relatively low aqueous solubility and will precipitate in the presence of divalent cations (Ca<sup>+2</sup>, Mg<sup>+2</sup>, Mn<sup>+2</sup>, Fe<sup>+2</sup>) or sorb to clay<ref>Angelidaki, I., Petersen, S.P. and Ahring, B.K., 1990. Effects of lipids on thermophilic anaerobic digestion and reduction of lipid inhibition upon addition of bentonite. Applied Microbiology and Biotechnology, 33(4), pp.469-472. [https://doi.org/10.1007/BF00176668 doi: 10.1007/BF00176668]</ref>, reducing their bioavailability and fermentation rate.  Since LCFA precipitation/sorption is an equilibrium process, a portion of LCFA will be in the aqueous phase and available for fermentation.  The short chain fatty acids are much more soluble and sorption/precipitation of these materials is not a significant factor.
+
[[File:Kamath1w2 Fig8.png|thumbnail|left|400 px| Figure 8. Typical Results for Total Petroleum Hydrocarbon (TPH) Reduction without Tilling/Fertilizer Addition (Natural Attenuation, shown in blue), with Tilling Only (Orange), or with Periodic Tilling and Fertilizer Addition (Grey)]]
  
Immediately adjoining the precipitated LCFAs, H<sub>2</sub> and acetate will be produced, and aquifer redox conditions will become sulfate-reducing to methanogenic with H<sub>2</sub> varying between 1 and 10 nM<ref>Chapelle, F.H., Haack, S.K., Adriaens, P., Henry, M.A. and Bradley, P.M., 1996. Comparison of E h and H<sub>2</sub> Measurements for Delineating Redox Processes in a Contaminated Aquifer. Environmental Science & Technology, 30(12), pp.3565-3569. [https://doi.org/10.1021/es960249 doi: 10.1021/es960249]</ref> and acetate varying between 10<sup>5</sup> to 10<sup>7</sup> nM (6 to 600 mg/L). H<sub>2</sub> concentrations are maintained at low levels by rapid consumption of background electron acceptors or chlorinated solventsIf the chlorinated solvents and other electron acceptors are depleted in the area immediately adjoining the LCFAs, H<sub>2</sub> will be fermented to CH<sub>4</sub> and will no longer be available for enhanced reductive dechlorination (ERD)In contrast, acetate turnover is much slower, and dissolved acetate can migrate with flowing groundwater, eventually reaching contaminated portions of the aquifer, stimulating the reduction of PCE, TCE and other more highly chlorinated compounds. However, ''c''DCE and VC are only efficiently degraded by <u>Dehalococcoides spp.</u> which require H<sub>2</sub> as an electron donor.  Since elevated H<sub>2</sub> levels only occur near where LCFAs are being fermented, ''c''DCE and VC will only be reduced to ethene in close proximity to the precipitated LCFAs.
+
*Fertilizer: Fertilizers can be added either manually or with mechanical spreaders. During landfarming, the nutrient conditions should be monitored, and additional fertilizer should be added if the concentration falls below action levels. Care should be taken not to add excess nutrients as it can result in fertilizer runoff and/or inhibit biodegradation.
 +
*Moisture: Moisture should be maintained in the landfarm between 60 and 80% of the water holding capacity (field capacity) of the soil (roughly 15%-24% moisture by weight for most soils). For soils with less than 20% water holding capacity, some form of irrigation will likely be requiredFor water saturated soils, no tilling should be performed while the water content is high since this can impair soil texture. Irrigation water should be freshLow quality water may result in concentration of salt and subsequent inhibition of biotreatment.
 +
*Aeration: Locally available agricultural equipment is most often used for tilling soils to break up clumps of clay and uniformly mix in amendments such as fertilizers, soil conditioners and water. 
 +
*Monitoring Needs: Commonly monitored parameters include hydrocarbon concentration, moisture content, nutrients, and pH. Parameters are monitored on a biweekly or monthly basis as needed to confirm that the biodegradation process is progressing smoothly.
  
Given that the contaminant distribution in the aquifer is almost never known, the best approach is to distribute EVO as uniformly as possible throughout the target treatment zone.
+
==Cleanup levels that can be attained==
 +
Landfarming has been successful in meeting cleanup goals for a variety of hydrocarbon impacted wastes within a reasonable timeframe (see Figure 9). It is important to note that reductions in concentrations of total petroleum hydrocarbons (TPH) that are greater than 95% of the original concentrations are difficult to achieve.  It is also difficult to achieve a final concentration of TPH that is <0.1% of the dry weight of the soil. Cleanup goals for soils impacted with refined products such as gasoline may be lower than cleanup goals for crude oil based on risk to receptors and mobility of those products in the environment.
  
[[File:Borden3w2 Fig3.png|thumbnail| Figure 3. EVO mixed in field during early pilot test]]
 
  
==Injection System Design==
+
[[File:Kamath1w2 Fig9.png|thumbnail|center|500 px| Figure 9. Chromatogram Change Illustrating a Crude Oil Degradation with Initial API Gravity > 30 (Week 0, 3, 7, and 15)]]
There are a variety of different approaches that can be used to [https://enviro.wiki/index.php?title=Injection_Techniques_for_Liquid_Amendments inject emulsions] in the subsurface including: (a) injection only using grids of temporary or permanent wells; (b) recirculation using systems of injection and pumping wells; and (c) barriers.  Each of these approaches has advantages and disadvantages with the ‘best’ approach dependent on site-specific conditions.  For each approach, cost and effectiveness are a function of the well layout and injection sequence.
 
 
 
Projects involving injection of oil emulsions typically, but not always, involve the following steps: (1) installation of injection wells and associated equipment; (2) preparation or purchase of a concentrated emulsion; and (3) dilution of the concentrated emulsion with water and (4) injection.  Emulsions can be injected through the end of [https://enviro.wiki/index.php?title=Direct_Push_(DP)_Technology direct push] tools, through temporary direct-push wells, or through permanent conventionally-drilled wells.  The selection of the most appropriate method for installing injection points depends on site-specific conditions including drilling costs, flow rate per well, and volume of fluid that must be injected. 
 
 
 
Using properly prepared emulsions, it is possible to move injected emulsions 10, 20, or in some cases even 50 ft away from the injection point.  However, achieving effective distribution of the emulsified oil often requires injecting large volumes of water.  Depending on the injection well layout and formation permeability, emulsion injection can require an hour to several days per well.  For greater efficiency, several wells may be injected at one time using a simple injection system manifold.
 
 
 
Modeling studies by Clayton and Borden (2009)<ref>Clayton, M.H. and Borden, R.C., 2009. Numerical modeling of emulsified oil distribution in heterogeneous aquifers. Groundwater, 47(2), pp.246-258. [https://doi.org/10.1111/j.1745-6584.2008.00531.x doi: 10.1111/j.1745-6584.2008.00531.x]</ref> showed that EVO distribution throughout a target treatment zone is controlled by: (1) injection point spacing; (2) mass of oil injected relative to the maximum oil retention capacity of the treatment zone (Mass Scaling Factor, SF<sub>M</sub>); (3) volume of dilute emulsion and/or chase water injected to distribute the emulsion relative to the total treatment zone pore volume (Volume Scaling Factor, SF<sub>V</sub>); and (4) timing of injection into different wells.  If too little oil is injected or too little fluid is injected, the oil will be retained by the sediment close to the injection wells and large portions of the aquifer will remain untreated.  Figure 4 shows the effect of SF<sub>M</sub> and SF<sub>V</sub> on volume contact efficiency (the fraction of treatment zone contacted) for a moderately heterogeneous aquifer treated with a uniform grid of injection wells.  For SF<sub>M</sub>> 0.4 and SF<sub>V</sub>>0.4, contact efficiencies greater than 50% can be achieved.  However, contact efficiencies greater than 70% are very difficult to achieve due to the spatial variations in permeability common to most aquifers. 
 
 
 
[[File:Borden3w2 Fig4.png|thumbnail|Figure 4. Effect of volume scaling factor (SFV) and mass scaling factor (SFM) on volume contact efficiency for a moderately heterogeneous aquifer with well spacing approximately equal to row spacing<ref name = "Borden2008">Borden, R.C., Clayton, M., Weispfenning, A.M., Simpkin, T. and Lieberman, M.T., 2008. Development of a design tool for planning aqueous amendment injection systems. Environmental Security Technology Certification Program, Arlington, Virginia. ESTCP Project ER-0626. [[media:2008-Borden-Development_of_a_design_tool_for_injections.pdf| Report.pdf]]</ref>. ]]
 
 
 
Designing an effective and efficient injection system is challenging due to the trade-offs between cost and performance.  In general, closer well spacing with more oil and more distribution water will improve contact efficiency, but also increase costs.  There are also trade-offs between costs for injection point installation and labor for fluid injection.  Increasing the separation between injection wells will reduce the number of wells, reducing drilling costs.  However, a larger well spacing can also increase the time required for injection, increasing labor costs.  An Excel spreadsheet-based <u>design tool</u> is available to assist in developing efficient and effective injection systems<ref name= "Borden2008"/><ref>Weispfenning, A.M. and Borden, R.C., 2008. A design tool for planning emulsified oil‐injection systems. Remediation Journal: The Journal of Environmental Cleanup Costs, Technologies & Techniques, 18(4), pp.33-47. [https://doi.org/10.1002/rem.20180 doi: 10.1002/rem.20180]</ref>.
 
 
 
Once the well spacing and injection volumes are selected, there are two basic approaches to injecting emulsions: (1) injection of a small volume of more concentrated emulsion (typically 10 to 20% oil by volume) followed by additional chase water to distribute the emulsion throughout the formation; or (2) continuous injection of a more dilute emulsion (typically 0.5 to 2% oil by volume).  Numerical modeling results indicate that the two approaches are both effective in distributing emulsion<ref name= "Borden2007a"/> and the choice should be based on personal preferences and site logistics.  In all cases, the concentrated emulsion should be diluted with enough water to reduce the viscosity to near that of water, reducing injection pressures.  After emulsion injection is complete, clean water should be injected at the end to push mobile oil out away from the injection point to reduce well fouling with bacteria and oil. 
 
 
 
==Summary==
 
Emulsified Vegetable Oil (EVO) is commonly added as a slowly fermentable substrate to stimulate ''in situ'' anaerobic bioremediation.  Commercially available EVO typically contains a mixture of 45 to 60% vegetable oil present in small (0.5 to 2.0 µm) droplets, more readily fermentable soluble substrates (e.g. fatty acids or alcohols), surfactants, nutrients and water.  Oil droplets are retained by aquifer material when they collide with sediment surfaces and stick (referred to as interception).  The tendency of oil droplets to stick to aquifer material varies due to a number of factors including pH, droplet and matrix grain surface coatings, ionic strength, surface roughness, sediment surface charge heterogeneity, and blocking of the sediment surface with previously retained droplets.  Following injection, the vegetable oil is hydrolyzed to glycerol and long-chain fatty acids (LCFAs), which are subsequently fermented to hydrogen (H<sub>2</sub>) and acetate.  The rate of LCFA fermentation and resulting H<sub>2</sub> production is limited by sorption to sediment surfaces and/or precipitation with divalent cations (Ca<sup>+2</sup>, Mg<sup>+2</sup>, Mn<sup>+2</sup>, Fe<sup>+2</sup>).  Since H<sub>2</sub> is rapidly consumed near where it is produced, the oil droplets should be distributed as uniformly as possible throughout the target treatment zone.  This involves injecting sufficient EVO and sufficient water to distribute the EVO throughout the treatment zone.
 
  
 
==References==
 
==References==
 
+
<references />
<references/>
 
  
 
==See Also==
 
==See Also==
*[https://www.serdp-estcp.org/Program-Areas/Environmental-Restoration/Contaminated-Groundwater/ER-1205/ER-1205 Development of Permeable Reactive Barriers Using Edible Oils]
+
*[https://doi.org/10.2118/126982-MS Hoffmann, R., Bernier, R., Smith, S. and McMillen, S., 2010, January. A Four-Step Biotreatability Protocol for Crude Oil Impacted Soil. In SPE International Conference on Health, Safety and Environment in Oil and Gas Exploration and Production. Society of Petroleum Engineers.]
*[https://www.serdp-estcp.org/Program-Areas/Environmental-Restoration/Contaminated-Groundwater/ER-200221/ER-200221 Edible Oil Barriers for Treatment of Chlorinated Solvent- and Perchlorate-Contaminated Groundwater]
+
*[https://doi.org/10.1080/15320389409383471 Huesemann, M.H., 1994. Guidelines for land‐treating petroleum hydrocarbon‐contaminated soils. Soil and Sediment Contamination, 3(3), pp.299-318.]
*[https://www.serdp-estcp.org/Tools-and-Training/Environmental-Restoration/Groundwater-Plume-Treatment/Protocol-for-Enhanced-In-Situ-Bioremediation-Using-Emulsified-Edible-Oil Protocol for Enhanced In Situ Bioremediation Using Emulsified Edible Oil]
+
*[https://doi.org/10.1080/21622515.2017.1310310 Lukić, B., Panico, A., Huguenot, D., Fabbricino, M., van Hullebusch, E.D. and Esposito, G., 2017. A review on the efficiency of landfarming integrated with composting as a soil remediation treatment. Environmental Technology Reviews, 6(1), pp.94-116.]
*[https://www.serdp-estcp.org/Tools-and-Training/Environmental-Restoration/Groundwater-Plume-Treatment/Emulsion-Design-Tool-Kit Emulsion Design Tool Kit]
+
*[https://link.springer.com/journal/11157 Maila, M.P. and Cloete, T.E., 2004. Bioremediation of petroleum hydrocarbons through landfarming: Are simplicity and cost-effectiveness the only advantages?. Reviews in Environmental science and bio/Technology, 3(4), pp.349-360.]

Revision as of 14:22, 26 November 2018

Landfarming is a well proven ex-situ bioremediation technology that has been successfully used since the 1980s for treating petroleum impacted soils/sediments, drill cuttings, low brine drilling fluids, oily sludges, tank bottoms and pit sludges. The material to be treated is incorporated into surface soil. Naturally occurring microbes in the soil and waste material transform the organic contaminants to carbon dioxide, water and biomass ([1][2][3]). Maintaining optimum soil conditions for rapid biodegradation of organic contaminants can help meet cleanup goals within a reasonable timeframe.


Related Article(s):


CONTRIBUTOR(S): Dr. Roopa Kamath, Sara McMillen, Rene Bernier, and Deyuan Kong


Key Resource(s):


Introduction

During landfarming, the waste materials are typically placed as a layer on the ground surface with variable thickness. The waste is then tilled and amended with nutrients to enhance biodegradation by naturally occurring bacteria (Figure 1). Fertilizers such as urea and triple superphosphate (TSP) are used to provide nitrogen and phosphate necessary for biodegradation. Reduction in hydrocarbon concentrations can be expected within a span of weeks to months, depending on the initial concentration and composition of hydrocarbons, and whether the soil conditions are optimized for biodegradation. Once cleanup goals have been achieved, the treated material can be i) re-used in construction activity such as berms, landfill cover, backfill, regrading, or for agricultural purposes, ii) disposed at a landfill and/or iii) left in place and revegetated, depending on local regulations or site-specific considerations.

Landfarming is a low-cost technology. Facilities are simple to construct and easy to operate. Standard construction and farming equipment can be used to move soils to the land treatment facility, to amend the soils with fertilizer, to apply water to the soils and to till the soils (e.g. excavator, plow, rotovator, water truck). Figures 2 through 4 show examples of equipment used at a typical landfarming facility.


  • Figure 1. Soils Undergoing Treatment at a Landfarming Facility
  • Figure 2. Excavator to Move Soils
  • Figure 3. Water Truck to Ensure Optimal Moisture Content for Microbial Degradation in Soils
Figure 4. Rotovator and Plows to Till Soils

Some of the disadvantages of the technology are:

  • It requires a large land area for treatment.
  • There may be regulatory limitations on wastes that can be treated by landfarming. For example, U.S. regulations prevent landfarming soil impacted with hazardous wastes such as motor oil, hydraulic oil, and solvents.
  • It may not be effective for highly impacted soils or soils impacted with severely degraded hydrocarbons (e.g. if soils contain >8% w/w petroleum hydrocarbons after spreading).
  • Although landfarming is effective for reducing hydrocarbon concentrations, it is not effective for reducing concentrations of other oil field waste components, such as elevated concentrations of metals, salt or wastes containing naturally occurring radioactive materials (NORM).
  • Concentration reductions >95% or final concentrations <0.1% may not be successfully obtained based on the extent impacted and nature of the hydrocarbons.
  • Dust and vapor emissions may pose air quality concerns.

Suitability of Wastes for Landfarming

Landfarming has been successfully used to reduce hydrocarbon concentrations in soils impacted with kerosene, diesel, jet fuel, and crude oil. It has also been successfully used to treat oil-based drilling wastes (drill cutting, low brine drilling), oily sludge, tank bottoms and pit sludges.

Wastes may not be suitable for landfarming for a number of reasons:

  • There may be regulatory or permit limitations. For instance, in the United States, wastes that are not exempted under RCRA [4] such as motor oil, hydraulic oil, and solvents cannot be treated by landfarming by law.
  • Wastes unsuitable by their composition such as solid, non-spreadable paraffins from pig trap scrapings from the maintenance of pipelines, or highly weathered wastes, or asphaltic wastes
  • Wastes containing contaminants that do not biodegrade: e.g., NORM, metals or salt.

Biodegradation Potential

The initial concentration and composition of hydrocarbons strongly influences the biodegradation potential of a waste.

Figure 5. Correlation between API gravity (specific weight of the crude) and the predicted extent of biodegradation as measured by oil and grease (O&G)[5].
  • Wastes with >5% (w/w) of hydrocarbons may have physical and chemical characteristics that hinder biodegradation. For example, oily wastes tend to repel water, and can be poorly aerated. This can hinder or inhibit biodegradation.
  • The molecular structure and molecular weight of hydrocarbons in the waste may make them either more or less susceptible to attack by microorganisms. Typically, aliphatic hydrocarbons are more readily biodegraded than aromatic hydrocarbons. Structurally more complex molecules such as isoprenoids and steranes are relatively recalcitrant to biodegradation. For crude oils, the API gravity is a reliable indicator of the composition of a crude oil and by extension, a good predictor of the biodegradation potential of a crude oil (see Figure 5)[5]. For example, a crude oil with API gravity of 40 (by virtue of its composition) may degrade by 75% within 4 weeks. A crude oil with API gravity of 25 may only degrade by 55%, and a crude oil with API gravity of 10 may not degrade more than 10% within that same timeframe.

This same correlation can be used to determine the maximum initial hydrocarbon concentration that can be treated using conventional landfarming within 4 weeks and/or the maximum endpoint achievable for a given waste material.

Using analytical methods such as gas chromatography to determine the quantity and composition of organic contaminants in a waste may be useful in determining biodegradation potential. Lighter ends (lower boiling point components that elute earlier in the chromatogram) will typically degrade faster than heavier end components.

  • The extent of weathering (volatilization and biodegradation) may influence the rate and extent of biodegradation. Fresh crude oils with API gravity >30 are generally readily biodegradable; however, after extensive weathering as might be encountered at an old spill site, the oil may not be very biodegradable as most of the more volatile and biodegradable fractions of hydrocarbon have already disappeared. It is recommended that feasibility evaluations include hydrocarbon analysis of wastes using gas chromatography (GC) to assess the extent of weathering. (Figures 6a and 6b)
  • Figure 6a. Chromatogram of Fresh Crude Oil
  • Figure 6b. Chromatogram of Weathered Crude Oil
  • Light refined products, such as diesel and jet fuels, are highly biodegradable, similar to crude oils with API gravity >40. Heavy refined products like Bunker C or heavy fuel oils will biodegrade at rates similar to low API-gravity crude oils.


Facility Design and Operation

Landfarming facilities are designed to prevent impacts to groundwater and surface water. The facilities typically include an impermeable or low permeability liner for the treatment pad to prevent leaching of chemical constituents from the treatment waste to the groundwater, and berms/dikes to prevent storm water runoff. (See Figure 7.)

Figure 7. Typical Landfarming Operation

Successful landfarm operation requires maintaining optimum conditions in the soil/waste materials (moisture, oxygen, pH and nutrient levels) to enhance biodegradation of petroleum hydrocarbons (see Table 1). Before beginning landfarm operations, the waste and the soil at the landfarm site should be characterized to establish the soil baseline characteristics and the need for soil additives such as agricultural lime for pH correction.

Table 1. Optimum Conditions for Landfarming
Parameter Optimum Condition
Initial HC Concentration 1% - 5% by weight in dry soil
pH 6 – 8.5. Agricultural lime can be added to increase soil pH.
Aeration/Tilling Initially and every 2 – 4 weeks.
Moisture Content 60% – 80% of water holding capacity (field capacity).
Salt Content Electrical conductance of leachate <30 mS/cm (mhos/cm). Preferably <4 mS/cm for maximum reuse potential after cleanup. Ocean water has an electrical conductance of ~50 mS/cm.
Nutrients
  • Total Nitrogen: 250 – 500 ppm. Action Level: 50 ppm. Nitrogen source should be added if nutrient concentration falls below action level (e.g. urea).
  • Available phosphate: 125 – 250 ppm. Action Level: 25 ppm. Phosphate source should be added if nutrient concentration falls below action level (e.g. triple superphosphate).

Maintaining optimum conditions for biodegradation is the key to achieving target cleanup goals within a reasonable timeframe. Figure 8 is an illustration of the effect of tilling and adding fertilizer on the rate of degradation of petroleum hydrocarbons.

Figure 8. Typical Results for Total Petroleum Hydrocarbon (TPH) Reduction without Tilling/Fertilizer Addition (Natural Attenuation, shown in blue), with Tilling Only (Orange), or with Periodic Tilling and Fertilizer Addition (Grey)
  • Fertilizer: Fertilizers can be added either manually or with mechanical spreaders. During landfarming, the nutrient conditions should be monitored, and additional fertilizer should be added if the concentration falls below action levels. Care should be taken not to add excess nutrients as it can result in fertilizer runoff and/or inhibit biodegradation.
  • Moisture: Moisture should be maintained in the landfarm between 60 and 80% of the water holding capacity (field capacity) of the soil (roughly 15%-24% moisture by weight for most soils). For soils with less than 20% water holding capacity, some form of irrigation will likely be required. For water saturated soils, no tilling should be performed while the water content is high since this can impair soil texture. Irrigation water should be fresh. Low quality water may result in concentration of salt and subsequent inhibition of biotreatment.
  • Aeration: Locally available agricultural equipment is most often used for tilling soils to break up clumps of clay and uniformly mix in amendments such as fertilizers, soil conditioners and water.
  • Monitoring Needs: Commonly monitored parameters include hydrocarbon concentration, moisture content, nutrients, and pH. Parameters are monitored on a biweekly or monthly basis as needed to confirm that the biodegradation process is progressing smoothly.

Cleanup levels that can be attained

Landfarming has been successful in meeting cleanup goals for a variety of hydrocarbon impacted wastes within a reasonable timeframe (see Figure 9). It is important to note that reductions in concentrations of total petroleum hydrocarbons (TPH) that are greater than 95% of the original concentrations are difficult to achieve. It is also difficult to achieve a final concentration of TPH that is <0.1% of the dry weight of the soil. Cleanup goals for soils impacted with refined products such as gasoline may be lower than cleanup goals for crude oil based on risk to receptors and mobility of those products in the environment.


Figure 9. Chromatogram Change Illustrating a Crude Oil Degradation with Initial API Gravity > 30 (Week 0, 3, 7, and 15)

References

  1. ^ 1.0 1.1 U.S. Environmental Protection Agency (USEPA), 1993. Bioremediation using the land treatment concept. US Environmental Protection Agency. Office of Research and Development, Washington, D.C. Report.pdf
  2. ^ 2.0 2.1 U.S. Environmental Protection Agency (USEPA), 2003. Aerobic Biodegradation of Oily Wastes: A Field Guidance Book for Federal On-scene Coordinators, Version 1.0, October 2003. Region 6 South Central Response and Prevention Branch. Report.pdf
  3. ^ U.S. Environmental Protection Agency (USEPA), 2017. How to Evaluate Alternative Cleanup Technologies for Underground Storage Tank Sites: A Guide for Corrective Action Plan Reviewers, Chapter V: Landfarming , Land and Emergency Management 5401R, EPA 510-B-17-003. Report.pdf
  4. ^ U.S. Environmental Protection Agency (USEPA), 2002. Exemption of Oil and Gas Exploration and Production Wastes from Federal Hazardous Waste Regulations. Office of Solid Waste, EPA530-K-01-004. Report.pdf
  5. ^ 5.0 5.1 McMillen, S.J., Smart, R., Bernier, R. and Hoffmann, R.E., 2004, January. Biotreating E&P wastes: lessons learned from 1992-2003. In SPE International Conference on Health, Safety, and Environment in Oil and Gas Exploration and Production. Society of Petroleum Engineers. doi: 10.2118/86794-ms

See Also