REMEDIATION OF PETROLEUM CONTAMINATED SOILS - SECTION 8 (END) docx

Section 8 Treatment Trains 8.1 LIMITATIONS OF SOIL TREATMENT SYSTEMS 8.1.1 PHYSICAL/CHEMICAL TREATMENT SYSTEMS Many of the chemical treatments listed in Section 2 may have limited application for organic wastes. Physical methods, such as stripping or sorption, are not as effective as biological methods for treating hazardous organic compounds (Knox, Canter, Kincannon, Stover, and Ward, 1986). Air stripping and vapor extraction are limited to volatile compounds in porous, homogeneous soil, and channeling is a problem. These are also difficult to monitor. Chemical methods may have to be used to remove heavy metals. The physical and chemical treatment systems are most useful in combination with biological methods, as dictated by the site and specific waste requirements, many serving as a pretreatment prior to biodegradation. Incineration is an effective treatment process for destroying organic contaminants in soil; however, it is considerably more expensive than biodegradation. Soil flushing is not feasible with complex wastes, and when the subsurface is not homogeneous, channeling through the soil prevents even distribution of the eluant. In addition, the use of treatment agents on the soil can change the pH or other soil properties. 8.1.2 LANDTREATMENT As with landfilling, this technology depends upon the availability of land. It is subject to weather conditions, which may interfere with application schedules. The heavy components of petroleum oils are not easily degradable and may accumulate in the soil. Volatilization of the lighter compounds can result in uncontrolled hazardous emissions. Waste constituents that are sufficiently volatile, mobile, or might bioaccumulate may be difficult to treat by this method. 8.1.3 IN SITU BIODEGRADATION In situ bioreclamation is a versatile tool for treating contaminated groundwater and soil; however, it is not the answer to all contamination problems (Brown, Loper, and McGarvey, 1986). Its applicability must be determined for each site and depends upon local site microbiology, hydrogeology, and chemistry. There are several important limitations for application of conventional biological treatment methods (Brown, Loper, and McGarvey, 1986). These include: 1. Environmental parameters must be appropriate for support of microbial growth (pH, temperature, redox state, and available nutrients); 2. Some chemicals are nonbiodegradable, according to current knowledge; 3. By-products of biodegradation may be more toxic or persistent than the original compound; 4. Substrate concentration may be too high (toxic) or too low (inadequate energy source); and 5. Complex mixtures of organics may include inhibitory compounds. It appears that microorganisms that are able to degrade chemicals in culture sometimes may not do so when introduced into natural environments because of pH, inability to survive, or preferential use of other substrates (Zaidi, Stucki, and Alexander, 1986). Some Pseudomonas strains were able to mineralize biphenyl or p -nitrophenol in lake water at the natural pH of 8.0, while another strain required the pH to be adjusted to 7.0, and yet another did not mineralize the substrate, although its population density rose. Biodegradation in the field may also be hindered by protozoa grazing (Alexander, 1994). Also, added microorganisms do not easily infiltrate the soil beyond the first 5 cm (Edmonds, 1976). A method of dispersing them uniformly throughout the contaminated site would have to be devised (Alexander, 1994). Introduction of nutrients into the environment and the residues generated by the organisms can adversely affect water quality (Lee, Wilson, and Ward, 1987). A field demonstration in a very gravelly clay loam was not very successful, due partly to the low permeability (1 × 10 –6 cm/s), which made it difficult to inject nutrients and produce water (Science Applications International Corporation, 1985). © 1998 by CRC Press LLC Other factors contributing to the poor success of this demonstration were the complexities of the site, possible mobilization of lead and antimony by the hydrogen peroxide treatment, and reductions in the permeability of the soil due to precipitation of the nutrients. Some partial degradation products might be more toxic than the parent compounds (Lee, Wilson, and Ward, 1987). Transformation of a toxic organic solute is no assurance that it has been converted to harmless or even less hazardous products (Mackay, Roberts, and Cherry, 1985). Given our limited understanding of transformation processes and the factors influencing them, hazardous contaminants must be assumed, in the absence of site-specific evidence to the contrary, to persist indefinitely. Micro- organisms can mobilize hydrocarbons by transforming them to polar compounds, such as alcohols, ketones, and phenols, or to organic acids, such as formic, acetic, proprionic, and benzoic, when con- taminated with JP-5 (Perry, 1979; Ehrlich, Schroeder, and Martin, 1985). If it is impossible to verify “no migration” of hazardous constituents, landtreatment may be prohibited as a management alternative for RCRA wastes, as well as the use of in situ biological treatment, at Superfund sites (Scholze, Wu, Smith, Bandy, and Basilico, 1986). Also, because of the complexity of waste streams and Agency time constraints, it will be difficult for the EPA to establish a “dilute” concentration level by which biological treatment performances can be evaluated. Bacterial growth can plug the soil and reduce circulation of the groundwater (Lee, Wilson, and Ward, 1987). The plugging of well screens and the neighboring interstitial zones of an aquifer can be a direct result of biofilm generation (Cullimore, 1983). This can result in reduced flow from the wells (sometimes with complete shutdown of the system), reduced quality of the water (through the generation of turbidity, taste, odor, and color), and, eventually, the generation of serious anaerobic corrosion problems. The resulting degeneration in well productivity has, on occasion, been expensive, with an estimated annual cost between $10 and 12 million (Canadian dollars). Organisms found to be responsible for this plugging have been Gallionella , other bacteria able to deposit iron or manganese oxides or hydroxides in or around the cell (e.g., Leptothrix, Crenothrix, or Sphaerotilus ), and heterotrophic bacteria able to grow in a biofilm. The extensive growth at the aqui- fer/well interface is probably due to the increase in oxygen concentration at the site of injection. However, disinfectants and physical techniques have been reported for controlling this problem. In order to be a useful pollution abatement method, biodegradation of petroleum pollutants would have to occur rapidly (Atlas, 1977). This is generally not the case; natural biodegradation of petroleum hydrocarbons occurs relatively slowly. It is likely that the treatment will be time-consuming and expen- sive, with costs ranging from tens of thousands of dollars for simple treatment programs up to the tens of millions of dollars for complex, large sites (Lee, Wilson, and Ward, 1987). There is the possibility that potentially pathogenic noncoliform microorganisms capable of olig- otrophic life could be introduced to the subsurface during well drilling and establish resident populations, which would go undetected with the standard methods of bacterial analysis of water (Stetzenbach, Sinclair, and Kelley, 1983). Species of Pseudomonas, Flavobacterium, Acinetobacter, Aeromonas, Moraxella, Alcaligenes, and Actinomyces capable of surviving for extended periods in low nutrient concentrations have been isolated from water samples. These organisms could become established in the subsurface with a rapid and significant impact. Therefore, the identification and characterization of either autochthonous (native microorganisms) or transient noncoliform bacteria in well water is essential in understanding the overall quality of the water. Usually, oil oxidizers do not cause infections in higher organisms, although a few species of human pathogens have been induced to metabolize hydrocarbons; e.g., Mucor sp. (Texas Research Institute, Inc., 1982). There are few additional safety hazards associated with in situ bioreclamation aside from those hazards normally associated with being on a hazardous waste site or a drill site (U.S. EPA, 1985a). Since wastes are treated in the ground, the danger of exposure to contaminants is minimal during a bioreclamation operation relative to excavation and removal. The only treatment reagent that could pose a hazard, if used, is the concentrated hydrogen peroxide solution. The complexity of in situ treatment and the difficulty of obtaining data required for the permitting process, can cause delays in feasibility demonstrations. Although bioremediation may seem the method of choice, there are a variety of factors to consider before it is selected over another treatment method or disposal (Amdur and Clark-Clough, 1994). This includes evaluation of contaminants, soil type, space limitations, time of year, critical path, and local requirements. Managers must be realistic in their goals regarding treatment time and treatment levels, © 1998 by CRC Press LLC and understand the limits of the bioremediation process. These authors discuss these considerations and present a framework for selecting and contracting with a bioremediation firm. 8.1.4 ON-SITE/ EX SITU BIOLOGICAL SYSTEMS Since the organisms used in the various on-site biological treatment systems may grow slowly, population retention is important (Kobayashi and Rittmann, 1982). Microbes could be washed out (total loss of the organism from a reactor) or taken over by other microorganisms. Fixed-film processes may be the best mechanism to assure population retention, when appropriate, to avoid total loss of slow-growing com- ponents. The cell concentrations in these processes are higher than those found in suspended growth systems. Efficient removal of the organic compounds is possible only when the biomass concentration is large (Matter-Muller, Gujer, Giger, and Strumm, 1980). Sometimes it is necessary to maintain a series of microorganisms selectively in order to achieve complete degradation (Pfennig, 1978a). 8.2 REMEDIATION GUIDELINES The decision to remediate fuel hydrocarbon contamination can be linked to risk-based corrective actions (RBCAs) (Benson, Frishmuth, and Downey, 1995). It is too resource intensive and unjustifiable to try to remediate all fuel hydrocarbon–contaminated sites to non-site-specific cleanup goals. The RBCA approach provides a site-specific framework for defining the level of remediation necessary to protect human health and the environment. Often, natural attenuation processes (e.g., intrinsic biodegradation) and land management controls may be sufficient, without engineered remediation. Sometimes, low-cost, source reduction technologies adequately supplement the natural processes. Remedial requirements depend upon which exposure pathways may reasonably be expected to be completed at a particular site. No two contamination incidents are exactly alike (Bartha and Atlas, 1977). Consequently, control responses should be flexible and tailored to the situation. A thorough understanding of the hydrogeologic and geochemical characteristics of the area will permit full optimization of all selected remedial actions, maximum predictability of remediation effectiveness, minimum remediation costs, and more reliable cost estimates (Wilson, Leach, Henson, and Jones, 1986). The design of remediation strategies depends upon contaminant properties and distribution, infrastructure, lithology, regulatory requirements, site usage, and time restrictions. A limiting factor is delivering the contaminated subsurface material to the treatment unit, or the treatment process to the contaminated material, in the case of in situ processes (Wilson, Leach, Henson, and Jones, 1986). The total petroleum hydrocarbon (TPH) measurement is a common tool for establishing cleanup standards for underground storage tank sites and other petroleum-contaminated areas (Michelsen and Boyce, 1993). There are, however, alternative techniques for developing site-specific cleanup standards, such as chemical fingerprinting, constituent analysis, and risk assessment methods. There are advantages and disadvantages associated with all the available treatment options (Ecken- felder and Norris, 1993). However, adequate assessment of each contamination incident will allow selection of the appropriate process or combination of technologies to achieve the required remediation. Figure 8.1 presents a decision framework for remediation technologies to use at sites contaminated with petroleum hydrocarbons (Ram, Bass, Falotico, and Leahy, 1993). It provides a structured progression of decision points consisting of technology or site applicability criteria. This will help the user to select appropriate technologies for the specific remediation requirements. In decreasing order of importance, liquid-phase hydrocarbon (LPH) removal processes are considered first, then in situ vadose and saturated zone technologies, then groundwater pump-and-treat approaches. Site characterization and closure goals are necessary for assessing technology applicability and remediation criteria. Table 2.2 summarizes several technologies for their applicability in different situations. The interaction between technologies often used at sites contaminated by petroleum hydrocarbons is illustrated in Figure 8.2. 8.3 COMBINED TECHNOLOGIES 8.3.1 ON SITE/ EX SITU Contaminated waste streams are normally composed of a complex mixture of compounds of variable concentration (Wilson, Leach, Henson, and Jones, 1986; Sutton, P.M., 1987). The compounds may be © 1998 by CRC Press LLC degradable, inhibitory, or recalcitrant to various degrees. Soils may be so heavily contaminated that they have to be removed or attenuated (Brubaker and O’Neill, 1982). Excavation of contaminated soils can be costly; however, it allows a more rapid treatment of the material ex situ (Eckenfelder and Norris, 1993). There are a number of approaches whereby contaminated soil can be excavated and subjected to treatment in a reactor on- or off-site. By treating soil in a reactor, a near-perfect environment for biodegradation can be created (King, Long, and Sheldon, 1992). This controlled environment allows a combination of biological, physical, and chemical processes to be applied Figure 8.1 Decision framework for remediation technologies. (From Ram, N.M., Bass, D.H., Falotico, R., and Leahy, M. J. Soil Contam. 2(2):167–189. Lewis Pubishers, Boca Raton, FL. 1993.) © 1998 by CRC Press LLC in treatment trains tailored to the specific pollutants. It permits optimization of many of the parameters necessary for biodegradation, while controlling the release of volatile organic compounds (VOCs) and leachate produced during the process. This is one of the most cost-effective and exemplary approaches available for resolution of the problem of environmental contamination (Madsen, 1991). Bioreactors can increase the rate of polycyclic aromatic hydrocarbon (PAH) degradation in contaminated soil (Wilson and Jones, 1993). However, running costs are generally higher than in situ and other on-site treatments. Volatile organics, extractable organics, and inorganics (heavy metals) of concern in contaminated waste streams can be treated (removed) successfully by two alternative processes (Stover and Kincannon, 1983). One process consists of chemical precipitation to remove metals and steam stripping, followed by activated carbon adsorption of organics. The alternative consists of combined physical–chemical and biological treatment. The physical–chemical techniques may remove nonbiodegradable constituents and may render the contaminated material less inhibitory to microbial treatment. Metals treatment would be a safety measure against possibly higher concentrations than anticipated; it would also be required for removing high levels of iron and manganese. Chemical detoxification techniques include injection of neutralizing agents for acid or caustic leachates, addition of oxidizing agents to destroy organics or precipitate inorganic compounds, addition of agents that promote photodegradation or other natural degradation processes, extraction of contaminants, immobilization, or reaction in treatment beds (Lee and Ward, 1985, 1984; Lee, Wilson, and Ward, 1987). Physical–chemical treatment will normally be provided in conjunction with the biological step (Wilson, Leach, Henson, and Jones, 1986). Combining the unit processes of chemical precipitation, steam stripping, and biological treatment is the more feasible alternative of these two, otherwise concentrations of residual organics, measured as TOC, would still be too high (Stover and Kincannon, 1983). Various treatment trains for treating leachates to remove organic compounds are described by Enzminger, Robertson, Ahlert, and Kosson (1987). Bioreclamation with Innovative On-Site Controlled Environment Landtreatment Systems (BIOCELS) can be accomplished by integrating the information presented in this book on the variety of processes available for remediating petroleum-contaminated soils and waste streams with the methods for opti- mizing biodegradation of the contaminants. This will allow development of incident-specific bioreactors or other customized ex situ treatment trains. 8.3.2 IN SITU In most polluted hydrogeologic systems, a remediation process is so complex in terms of contaminant behavior and site characteristics that no one system or unit will usually meet all requirements (Wilson, Leach, Henson, and Jones, 1986; Sutton, P.M., 1987). It is often necessary to combine several unit Figure 8.2 System integration. (From Ram, N.M., Bass, D.H., Falotico, R., and Leahy, M. J. Soil Contam. 2(2):167–189. ©1993 Lewis Pubishers, Boca Raton, FL) © 1998 by CRC Press LLC operations, in series or in parallel, into one treatment process train to bring the contamination to an acceptable level. In situ biodegradation has sometimes been applied as a treatment for spill management after partial recovery of a contaminant by physical means, such as by excavation, free-product recovery, pumping, air sparging, air stripping, or vapor extraction (Raymond, Jamison, and Hudson, 1976; Walton and Dobbs, 1980; Brown, Mahaffey, and Norris, 1993). These auxiliary physical treatments can also be employed during bioreclamation (Brubaker and O’Neill, 1982). Biodegradation is an alternative to physical recovery processes once they become nonproductive in terms of cost and effectiveness. Integration of other removal mechanisms with the biological step should be cost-effective, if technically feasible. One case study initiated stimulation of soil organisms, after estimating that continued physical recovery methods would require 100 years of operation and maintenance to make the contaminated water potable (Raymond, Jamison, and Hudson, 1976). Biological treatment, itself, is the least-expensive method of organic destruction (U.S. EPA, 1985a). About 99% of all organic compounds can be destroyed by biological reactions. When used with other treatment technologies, essentially all the organic contaminants can be removed and destroyed. Enhanced bioremediation may not necessarily replace other control measures, but it should rather add further flexibility to integrated control programs (Bartha and Atlas, 1977). While physical and chemical procedures may help promote biodegradation, bioremediation might also render a site more amenable to treatment with nonbiological methods (Brown, Mahaffey, and Norris, 1993). The synergistic effects of the different techniques when employed in a given incident should help maximize contaminant removal. Bioremediation is currently utilized as part of an integrated system (e.g., with soil vapor extraction or air sparging) for treating highly mobile (volatile or soluble) or degradable substrates, such as gasoline or diesel fuel. It is also employed as a primary system for treating recalcitrant or nonmobile substrates, such as heavier petroleum products. Multiple technologies are being used at many sites (Brown, Mahaffey, and Norris, 1993). Since pump- and-treat methods remove only those contaminants with water solubilities greater than 10,000 mg/L, pockets of free-phase liquids and adsorbed-phase organics will remain, requiring other means of removal. A combination of in situ bioremediation, air sparging, and/or vapor extraction may be the best approach for dealing with VOCs. For example, using intermittent or low airflow rates for vapor extraction will reduce off-gas treatment and encourage biodegradation. Also, combined vapor recovery and bioremedi- ation would probably be good for unsaturated soils contaminated with biodegradable compounds with vapor pressures exceeding about 1.0 mmHg. If the soil is polluted with biodegradable contaminants that are minimally volatile, such as PAHs and heavy fuels, bioremediation may be a stand-alone technology. Treatment trains employing one or more treatment processes may be required for complex waste streams (Lee and Ward, 1986). Bioreclamation can be preceded by, or otherwise used in combination with, other on-site or in situ treatment techniques that could destroy, degrade, or by other means reduce the toxicity of contaminants (U.S. EPA, 1985a). The information presented in this book on the variety of processes available for remediating petro- leum-contaminated soils and waste streams can be combined or used in conjunction with the methods for optimizing biodegradation of the contaminants to develop site-specific, in situ treatment trains. Additional information on bioremediation of groundwater, freshwater, estuarine, and marine environ- ments contaminated with petroleum products is available to supplement the soil, leachate/wastewater, and VOC treatment processes presented in this book (Riser-Roberts, 1992). 8.3.3 PROCESSES FOR TREATMENT TRAINS Options for in situ or on-site/ ex situ treatment of soils, leachates, and emissions that have been contam- inated by petroleum products are listed in the Table of Contents and described throughout the text of this book. Depending upon the specific site and contaminant requirements, a combination or sequence of processes may be developed to achieve acceptable contaminant levels. 8.4 EXAMPLES OF THE USE OF TREATMENT TRAINS 1. A laboratory-scale treatment train was used on a Department of Energy site soil contaminated by mixed wastes, including petroleum hydrocarbons (Portier (1994). It consisted of a liquids–solids contact soil slurry reactor and an immobilized microbe bioreactor for treating aqueous wastes in the process waters from the slurry reactor. Soils were treated in a defined sequence of roughing for 3 days, biological © 1998 by CRC Press LLC treatment for 27 days, and continuous polishing involving metals chelation. The immobilized microbe bioreactor was a modified fixed-film reactor with a controlled pore surface. 2. A pilot-scale bioremediation system was integrated with pneumatic fracturing to increase subsurface permeability and establish a broader bioremediation zone with aerobic, denitrifying, and methanogenic populations (Venkatraman, Schuring, Boland, and Kosson, 1995). Phosphate and nitrogen were added to the subsurface over 50 weeks, resulting in >67% reduction in BTX. 3. Radio-frequency heating was combined with soil vapor extraction to enhance recovery of #2 fuel oil in silty soil at a depth of 20 ft (Price, Kasevich, and Marley, 1994). 4. Shallow soil mixing with bentonite, cement, or other compounds, and soil vacuum extraction were integrated and enhanced to extract VOCs from soils at a Department of Energy facility in Ohio (Carey, Day, Pinewski, and Schroder, 1995). The advantages were a relatively rapid remediation, lower cost, less exposure of waste to the surface, and elimination of off-site disposal, with this in situ approach. (See Section 2.2.1.1.) 5. In a study of a site polluted by hydrocarbons, chlorinated hydrocarbons, and organochloride pesticides, it was found that no single technology could remove or destroy all of the contaminants (Rickabaugh, Clement, Martin, and Sunderhaus, 1986). However, when microbial degradation, surfactant scrubbing, photolysis, and reverse osmosis were combined, nearly total destruction of these compounds could be attained on-site. 6. A combined technology approach was also employed at a site where 130,000 gal of several organics had been spilled (Lee and Ward, 1985). Treatment of the site was by clarification, adsorption onto granular activated carbon, air stripping, then reinjection. After levels of the contaminants had fallen below 1000 mg/L, a biodegradation program employing facultative hydrocarbon-degrading bacteria, nutrients, and oxygen was begun. Biodegradation by both the indigenous microbes and the added organisms reduced the levels of the contaminants in soil cores from 25,000 to 2000 mg/L within 2 months. The monitoring wells showed no levels above 1 mg/L at the end of the program. 7. Another example involving the use of multiple treatment processes was a bench-scale study on a site in Muskegon, MI, contaminated by several priority pollutants and at least 70 other organics at levels in the hundreds of ppm (Lee and Ward, 1985). Acclimation of an activated sludge culture to the contaminated groundwater was unsuccessful, and a commercial microbial culture was ineffective at degrading the contaminants. However, coupling an activated sludge process to granular activated carbon treatment proved beneficial, as the organisms were able to degrade the organics that passed through the carbon system. This treatment train was able to remove up to 95% of the total organic carbon in the wastewater, as long as the activated carbon continued to function properly. 8. The release of phenol and chlorinated derivates in the soil in the Midwest was corrected by installing a recovery system and using activated carbon filters on the groundwater (Walton and Dobbs, 1980). Surface waters were contained in a pond. Mutant bacteria were injected into the pond and into the contaminated soil. After an incubation and adaptation period, the phenol was completely degraded in 40 days, while the o -chlorophenol was reduced from 120 to 30 ppm. 9. The Thermatrix flameless oxidation process combined with other contaminant separation and removal technologies can result in effective integrated systems. Thermal desorption can be combined with the Thermatrix flameless oxidation process for near zero emissions when treating contaminated soil in situ (see Section 2.2.1.2). 10. Combined biological–carbon systems can be used for leachate treatment (see Section 2.1.1.2.1). 11. Vapor phase biofilters can be used to decompose VOCs, in combination with SVE and air-based biodegradation (see Section 6.3.4.5). This will help lower costs of treating off-gases. For instance, activated carbon treatment of leachate can be used with biological pretreatment of effluent in a sequenc- ing-batch reactor. 12. Wet air oxidation can be used for hazardous waste leachate treatment for treating concentrated organic streams generated by other processes, e.g., steam stripping, ultrafiltration, reverse osmosis, still bottoms, biological treatment process waste sludges, and regeneration of powdered activated carbon (see Section 2.1.1.2.4). © 1998 by CRC Press LLC 13. Chemical oxidation removes most organics poorly from wastewaters but could facilitate treatment by other processes. Chemical oxidants can be used as a pretreatment to oxidize partially refractory, toxic, or inhibitory organic compounds, e.g., ozonation alone or in combination with ultraviolet irradiation as a pretreatment for biological treatment (see Section 2.1.1.2.6). 14. Ozonation and granular activated carbon combination depends upon the composition of the wastewater (see Section 2.1.1.2.6). 15. Hydrogen peroxide or ozone plus ultraviolet light degrade or destroy VOCs in water (see Section 2.1.1.2.6). 16. Sedimentation must be used with another technique, such as chemical precipitation, or as a pretreatment prior to another process, such as carbon or resin adsorption (see Section 2.1.1.2.10.1). 17. Flocculation must be used with a solid/liquid separation process, e.g., sedimentation, as a pretreat- ment for carbon adsorption. It is often preceded by precipitation (see Section 2.1.1.2.11). 18. Air stripping is a useful pretreatment for adsorption, and steam stripping is a good pretreatment to reduce VOC levels for following treatments (see Section 2.1.1.2.13). 19. Filtration can be used as a polishing step subsequent to precipitation and sedimentation or as a dewatering process for sludges generated by other processes (see Section 2.1.1.2.15). 20. Ion exchange could serve as a polishing step to remove ionic constituents that could not be reduced by other methods (see Section 2.1.1.2.18). 21. A chemical coagulation/flocculation process removed up to 100% of suspended solids and 98% of BOD 5 (see Section 2.1.2.2.1.2). 22. Biological activated carbon and wet air oxidation are not feasible alone, but in combination can treat dilute contaminated groundwater (see Section 2.1.2.2.1.2). 23. The ability of microorganisms to biosorb organic compounds can be combined with the use of reactors for both readily degradable or more refractory contaminants. The degradable are removed by biodegradation in the reactors, and the refractory, by microbial absorption. The reactors can be aerobic, anaerobic, chemotrophic, phototrophic, or a series of several types, depending upon the nature of the contaminants (see Section 2.1.2.2.1.4). 24. A reactor combining an upflow anaerobic sludge blanket with a fixed film gives better performance than a sludge blanket alone (see Sections 2.1.2.2.2.2 and 6.3.3.3.5). 25. An air/water separator, trickling filter, and biofilter in series can be used to treat VOCs generated during in situ bioventing and air sparging (see Section 6.3.4.5). 26. Combined oxidation, i.e., combined use of ozone and other chemical or physical treatment, can improve destruction of biodegradation-resistant organic compounds (see Section 2.2.1.2). 27. Soil containing organics and inorganics can be pretreated with land application to remove or reduce metals by precipitation followed by land application of the elutriate (see Soil Flushing, Section 2.2.1.7.) 28. The pump-and-treat method can be combined with bioventing, if the groundwater has become contaminated (see Section 2.2.1.7). 29. Soil vapor extraction removes VOCs adsorbed to unsaturated soils, but fluctuations in groundwater level affect the rate of removal. When combined with air sparging, VOCs are removed from saturated soils and groundwater, as well (see Section 2.2.1.11). 30. A soil vapor extraction system can be used in situ with a combined thermal-catalytic oxidizer vapor treatment system on petroleum-contaminated soils with low permeability (see Section 2.2.1.11). 31. Cyclic steam injection can be combined with vacuum extraction to lower residual hydrocarbon content of JP-5 jet fuel–contaminated soil. Additional cycles should remove even more (see Section 2.2.1.14.2). 32. Wet or dry steam can strip and vaporize contaminants from fuel-contaminated soil, while a vacuum extracts and condenses the vapors. This can employ portable steam systems and a packed-bed thermal oxidizer for the vapors. Extracted liquids can go to an oil/water separator to collect fuel for recycling. © 1998 by CRC Press LLC Contaminated groundwater and condensate are treated with filters and carbon adsorption (see Section 2.2.1.14.2). 33. Radio-frequency heating was combined with soil vapor extraction to improve recovery of #2 fuel oil in silty soil at a depth of 20 ft. Radio-frequency heating vaporizes pollutants or decomposes or pyrolyzes them to more-volatile compounds, which are removed by soil vapor extraction. The method is appropriate for higher-boiling-point soil contaminants (see Section 2.2.1.14.3). 34. Active warming of contaminated soil in cold climates can be combined with bioventing to improve biodegradation (see Section 2.2.2.2). 35. An alternative bioventing approach includes low rates of pulsed air injection, a period of high-rate soil venting extraction, and off-gas treatment followed by long-term air injection (see Section 2.2.2.2). 36. Regenerative resin for ex situ vapor treatment can be combined with in situ bioventing to reduce bioremediation costs (see Section 2.2.2.2). 37. Bioslurping combines vacuum-enhanced recovery of free product with in situ bioventing to aerate the vadose zone for improved biodegradation of low-volatility hydrocarbons, while promoting vapor extraction of the more volatile fractions (see Section 2.2.2.3). 38. Hydraulic/pneumatic soil fracturing might be combined with other processes to enhance bioreme- diation (see Section 2.2.2.5). For instance, it can be used to facilitate transport of materials in the subsurface. 39. Aerobic and anaerobic biotreatment may be used in sequence (see Sections 3.2.2.1, 5.1.4.5, 5.1.4.6, 5.1.4.7, and 5.1.4.8). 40. Aerobic and anaerobic treatment can be employed in a single step, if the microorganisms are immobilized in matrices where anaerobiosis can occur (see Section 3.2.2.1). 41. Fungi, yeasts, and bacteria can be combined for more complete biodegradation. Bacteria should be present to break down mutagens produced by the fungi. Mixed microbial populations are more effective (see Sections 3.4, 5.2.1, 5.2.1.4, and 5.2.2.3). 42. Microorganisms can be combined with chemical analogs of organic compounds to promote co- oxidation of the latter (see Sections 3.4 and 5.2.3). 43. When chemical and biological treatments are combined, the soil pH and redox boundaries should be carefully monitored (see Section 5.1). 44. Soil moisture can be controlled through irrigation, drainage, soil additives, or combinations of these. Moisture optimization may be enhanced when used with other techniques to increase biological activity (see Section 5.1.1). 45. Combined air–water flushing disperses oxygen through soil and detaches solubilized hydrocarbons, while providing moisture for biodegradation. Contaminants are removed in the airstreams and water streams (see Sections 2.2.2.7 and 5.1.4.5). 46. The low-volume airflow of bioventing is combined with a closed-loop concept to regulate soil moisture, nutrients, and oxygen with Biopurge SM , when the vapor is injected above groundwater, and with Biosparge SM , when the vapor is injected below groundwater level. The vapors are extracted in wells and treated on-site (see Sections 2.2.2.4 and 5.1.4.6). 47. Seeding of microorganisms should be combined with soil moisture management, aeration, and fertilization (see Section 5.2.2). 48. Surfactants can be used in conjunction with other treatments to solubilize contaminants (see Sections 5.3.1.1 and 5.3.1.2). 49. Solvent extraction can be used with steam stripping to remove contaminants from waste streams. Solvents are chosen with low aqueous solubility and strong affinity for the VOCs in the waste. The solvent is removed by steam stripping and regenerated by distillation (see Section 6.3.3.1.3). 50. A biofilter can be used to clean gasoline-contaminated air from a stripping tower (see Section 6.3.4.5). © 1998 by CRC Press LLC 51. Biofilters can be backed up with GAC filters for more efficient VOC removal. Such units are much less expensive than conventional GAC filters and catalytic/thermal oxidation (see Section 6.3.4.5). 52. Bioventing can be combined with bioslurping to recover LNAPLs while bioventing the vadose zone (see Sections 2.2.1.11, 2.2.2.2, 3.2.1.6, and 5.1.4.5). 53. Bioventing can also be applied to excavated soil, such as with the Ebiox vacuum heap bioreme- diation system (see Sections 2.1.2.1.5 and 5.1.4.5). 54. Bioventing can be used to introduce gaseous ammonia as a form of nutrients to the subsurface (see Section 5.1.5). 55. A vacuum-inducing airflow can supply oxygen through the soil, then nutrients percolated through the soil with the vent-system piping. VOCs are removed by the venting (see Section 5.1.5). 56. Photochemical reactions combined with soil mixing can be effective for treating relatively immobile contaminants (see Sections 2.1.1.2.6, 2.1.2.1.7, 5.3.2, and 6.3.4.6). 57. Figure 8.3 shows how biological and carbon sorption processes can be combined in a treatment train (Shuckrow, Pajak, and Touhill, 1982b). Figure 8.4 illustrates a process train that could be used for a leachate that contains metals. In Figure 8.5, the processes of air stripping, carbon adsorption, and ion exchange are combined in a treatment train (Bove, Lambert, Lin, Sullivan, and Marks, 1984). Figures 8.6 and 8.7 show the in situ use of a Detoxifier™ system in a treatment train on a site contaminated by hydrocarbons (Ghassemi, 1988) (see also Sections 2.2.1.13 and 6.3.3.3.6). The system is composed of • The process tower, including the drill bit assemblies, tower shroud, and the rotary and hydraulic motors that control the up-and-down and rotating motions of the drill assemblies; • The control room containing the on-line monitoring equipment; • The crawler tractor, which moves the drilling rig, the control room, and a diesel engine power generator; • Gas treatment and power feed systems, mounted on two trailers, and consisting of Suction blowers Cooling coil Figure 8.3 Schematic of biological/carbon sorption process train. (From Shuckrow, A. J. et al. Hazardous Waste Leachate Management Manual. Noyes Data Corp., Park Ridge, NJ, 1982. With permission.) © 1998 by CRC Press LLC [...]... 19 98 by CRC Press LLC Figure 8. 5 Air stripping, carbon adsorption, and ion exchange process flow diagram (typical) (From Bove, L.J et al Report to U.S Army Toxic and Hazardous Materials Agency, Aberdeen Proving Ground, MD, on Contract No DAAK1 1 -8 2-C-0017, 1 984 AD-A162 5 28/ 4.) © 19 98 by CRC Press LLC Figure 8. 6 Process diagram for the Detoxifier™ II Treatment Train (From Ghassemi, M J Haz Mat 17: 189 –206,... (From Ghassemi, M J Haz Mat 17: 189 –206, Elsevier Science Publishers, Academic Division 1 988 With permission.) © 19 98 by CRC Press LLC Figure 8. 7 Treatment train used at a southern California site (From Ghassemi, M J Haz Mat 17: 189 –206, Elsevier Science Publishers, Academic Division 1 988 With permission.) © 19 98 by CRC Press LLC ...Figure 8. 4 Process train for leachate containing metals (From Shuckrow, A J et al Hazardous Waste Leachate Management Manual Noyes Data Corp., Park Ridge, NJ, 1 982 With permission.) Demisters Refrigeration and heating coils Activated carbon adsorption unit Powder storage bins and feeding . No. DAAK1 1 -8 2-C-0017, 1 984 . AD-A162 5 28/ 4.) © 19 98 by CRC Press LLC Figure 8. 6 Process diagram for the Detoxifier™ II Treatment Train. (From Ghassemi, M. J. Haz. Mat. 17: 189 –206, Elsevier. Sullivan, and Marks, 1 984 ). Figures 8. 6 and 8. 7 show the in situ use of a Detoxifier™ system in a treatment train on a site contaminated by hydrocarbons (Ghassemi, 1 988 ) (see also Sections 2.2.1.13. processes available for remediating petroleum- contaminated soils and waste streams with the methods for opti- mizing biodegradation of the contaminants. This will allow development of incident-specific bioreactors or