Bioremediation of Relcalcitrant Compounds - Chapter 3 ppsx

33 chapter three Roadblocks to the implementation of biotreatment strategies Jeffrey W. Talley Contents 3.1 Introduction 34 3.2 Factors affecting biodegradation 36 3.2.1 Metals 36 3.2.2 Temperature 37 3.2.3 Water 37 3.2.4 pH 37 3.2.5 Toxic compounds 38 3.2.6 Effects of soil type 38 3.2.7 Nontechnical issues 38 3.3 Treatment zones 39 3.4 Alternative physical and chemical technologies 40 3.4.1 Incineration 40 3.4.2 Air stripping 40 3.4.3 Activated carbon adsorption 40 3.4.4 Advanced oxidation 41 3.4.5 Low thermal stripping 41 3.4.6 Pump and treat 42 3.4.7 Stabilization 42 3.4.8 Dechlorination 43 3.4.9 Compost 43 3.5 Transitioning from bench-level to full-scale design 44 3.5.1 Microscale phenomena 44 3.5.2 Mesoscale phenomena 44 L1656_C003.fm Page 33 Monday, July 18, 2005 7:42 AM © 2006 by Taylor & Francis Group, LLC 34 Bioremediation of Recalcitrant Compounds 3.5.3 Macroscale phenomena 46 3.6 Relationship between scales of observation 46 3.7 Conclusions 47 3.8 Summary 48 References 49 3.1 Introduction Biotreatment can be broken into two basic categories: in situ and ex situ . “With in-situ techniques, soil and associated groundwater are treated in place without excavation” (Blackburn and Hafter, 1993). Examples of in situ tech- niques include pump and treat, percolation (flooding), bioventing, and air sparging. In each of these systems, the contaminated media are treated without excavation. With ex situ techniques, soil and groundwater are removed from their original locations for treatment. Examples of ex situ techniques include land farming, irrigation, soil treatment units, composting, engineered biopiles, and bioreactors. Both in situ and ex situ techniques are capable of saturated and unsaturated zone remediation, although restriction exists depending on the exact system used. However, many factors can influence the effectiveness of each technique. Blackburn and Hafter (1993) (Table 3.1) evaluated the influence of these techniques for operating states of microbiological processes (i.e., bioactivity). In general, this study by Blackburn and Hafter showed that ex situ techniques allow more opportunities to control or engineer conditions for remediation; however, this is not to suggest that ex situ treatment is the preferred technique. Although some sites may be more easily controlled and maintained with ex situ configurations, others are more effective with in situ treatment. For example, many sites are located in industrial and commercial areas, and these sites normally consist of numerous structures interconnected by concrete and asphalt. These physical barriers would make excavation extremely difficult, and if the contamination is deep in the subsurface, exca- vation becomes too expensive. As a result of these physical barriers, the required excavation efforts may make ex situ biotreatment impracticable. Other factors could also have an impact on the type of treatment. At a typical site, the contamination is basically trapped below the surface. Exposing the contamination to the open environment through excavation can result in potential health and safety risks. In addition, the public’s perception of the excavation of contaminants could be negative, depending on the situation. All of these conditions clearly favor in situ biotreatment. Nonetheless, the key is to carefully consider the parameters involved with each site before evaluating which technique to use. L1656_C003.fm Page 34 Monday, July 18, 2005 7:42 AM © 2006 by Taylor & Francis Group, LLC Chapter three: Roadblocks to implementation of biotreatment strategies 35 Table 3.1 Influences of Bioremediation Techniques on Bioactivity Control In Situ Ex Situ Solid Ex Situ Slurry Bioactivity Parameter Pump and Treat Percolation Bioventing and Air Sparging Soil Treatment Units Compost Piles Biopiles Lagoon Bioreactor Air or oxygen ++ a 0+++++ +++ ++ +++ Alternative terminal electron acceptor ++ ++ + b 0 b 0 b 0 b 00 b ++ pH 0 00 00 ++ + + ++ +++ Nutrients and growth factors 0 0 0 + + + ++ ++ Inoculation bioaugmentation + 00 00 + + + ++ ++ Heterogeneity 0 00 00 + + + ++ ++ Agitation or mixing 0 00 00 + + + ++ +++ Temperature 0 00 00 0 + + 0 ++ Microbial community structure control 00 00 00 0 0 0 0 + Water activity 00 00 00 + + + 00 00 Salinity 0 0 0 + + + + + Control of inhibitors + 0 0 + + + + + Containment of effluents 0 00 00 + + + + ++ Addition of treatment chemicals 000 00 + +++ + Note : Although this table is an old source, it still provides an accurate summary . a Key: +, ease; 0, difficulty. b Ability to employ alternative terminal electron acceptor influenced by ability to limit the pr esence of air or oxygen. Source: From Blackburn, J.W. and Hafter, W.R., TIBTECH , 11 (August), 329, 1993. L1656_C003.fm Page 35 Monday, July 18, 2005 7:42 AM © 2006 by Taylor & Francis Group, LLC 36 Bioremediation of Recalcitrant Compounds 3.2 Factors affecting biodegradation The microbial population follows a growth cycle that can be divided into several distinct phases: the lag phase, exponential phase, stationary phase, and death phase. In the lag phase, there is a delay in the microbial population growth until the microbes have become adjusted to the food source, which in many instances is the contaminant of interest, and surrounding conditions. The microbes cannot consume the food source until they have developed the required enzymes and metabolites necessary to break down the contam- inant. After the necessary enzymes and metabolites have been produced, the microbes enter the exponential phase of growth. The rate of exponential growth is influenced by environmental conditions (e.g., temperature) as well as by characteristics of the organism itself. However, exponential growth cannot occur indefinitely. Generally, either an essential nutrient for growth is used up or some waste product of the organism builds up to an inhibitory level and exponential growth ceases. At this point, the population has reached the stationary phase, in which there is no net increase or decrease in cell number. If conditions worsen (i.e., toxins continue to build up or the food source becomes depleted), the microbial population will enter the death phase and the viable number of microbes will decrease (Atlas, 1984; Brock et al., 1984). Given this growth cycle, almost all organic compounds are degradable provided the proper circumstances or time. However, a range of physical, chemical, and biochemical conditions or materials can interfere with biore- mediation. The biodegradability of wastes or specific waste constituents must be defined in terms of a realistic period determined by the goals of the treatment program. Biodegradability limits due to toxicity are a function of concentration. If the concentration of the toxicant can be controlled or the biomass is large enough, many highly toxic wastes or constituents can be biodegraded. By incrementally increasing contaminant concentrations, microbes can be challenged to degrade more wastes. The key is to slowly increase the contaminant concentrations, allowing the microbe population to adapt to the changing conditions and produce the required enzymes and metabolites. 3.2.1 Metals Metals can inhibit various cellular processes and their effects are often con- centration dependent. Metal toxicity for microbes will usually involve spe- cific chemical reactivity. Metals such as copper, silver, and mercury are typ- ically very toxic, particularly as ions, whereas metals such as lead, barium, and iron are usually benign to the microbes at levels typically encountered. The nutrient metals are usually found naturally in the necessary amounts for plants and microbes in fertile soils. The principal inorganic nutrients are nitrogen and phosphorus; however, trace amounts of potassium, calcium, sulfur, magnesium, iron, and manganese are also required for optimum L1656_C003.fm Page 36 Monday, July 18, 2005 7:42 AM © 2006 by Taylor & Francis Group, LLC Chapter three: Roadblocks to implementation of biotreatment strategies 37 biological growth. The availability or toxicity of these metals to the microbes is usually dependent on pH, with the metals becoming more mobile/avail- able at lower values of pH. Metals can be actively accumulated by certain microorganisms and plant species. Living cells can adsorb metals and concentrate inorganics within the cell. Although heavy metals may not be metabolically essential, they are taken up by the biomass as a side effect of the normal metabolic activity of the cell. Activated biomass removes metals from solution by a variety of mechanisms, which include ion exchange at the cell walls, complexation reactions at the cell walls, and intra- and extracellular complexation reactions (Benemann, 1991). Inactivated biomass removes metals primarily by adsorb- ing metals to the ionic groups either on the cell surface or in the polysac- charide coating found on most forms of bacteria. The metals are bound by exchange of functional groups or by sorption on polymers. 3.2.2 Temperature Most microbes prefer to grow at temperatures in a range of about 10 to 38˚C. The rate of biochemical reactions in cells increases with temperature up to a maximum, above which the rate of activity declines as enzyme denatur- ation occurs and organisms either die or become less active. Low tempera- tures seldom kill the microbes, and with warming, the microbes typically recover. Temperature also affects gas solubilities and must be taken into account when designing a remediation system. However, it is extremely difficult to control the temperature of in situ processes, and the temperature of ex situ processes can only be moderated, sometimes with great expense. Consequently, the effects of the expected temperatures should be factored into the design–basis expected degradation rate. 3.2.3 Water Microorganisms do not grow without adequate water, which is the universal solvent for their cellular biochemicals, growth substrates, oxygen, and nutri- ents. However, too much water may saturate the soil and result in anaerobic activity, which may or may not be beneficial, depending on whether aerobic or anaerobic degradation processes are preferred. If aerobic conditions are desired, a 30 to 35% saturation of the pore spaces is usually sufficient to still enable the passage of air through the subsurface. On the other hand, if anaerobic conditions are desired, a 100% saturation of the pore spaces will more than suffice. 3.2.4 pH Extreme values of pH (i.e., pH values of <3 and >9 or 10), as well as sudden changes in the pH of the waste-treatment system matrix, can inhibit microbial growth by interfering with the following: (1) microbial metabolism, (2) gas L1656_C003.fm Page 37 Monday, July 18, 2005 7:42 AM © 2006 by Taylor & Francis Group, LLC 38 Bioremediation of Recalcitrant Compounds solubility in soil water, (3) nutrient availability in soil water, and (4) heavy metal solubilities. Most natural environments (i.e., soils) have pH values between 5.0 and 9.0. Consequently, this range is optimal for microbial-enhanced biodegra- dation of waste contamination. This pH range is maintained by a natural buff- ering capacity that exists in most fertile native soils due to the presence of carbonates and other minerals. However, this buffering capacity can be depleted over time as a result of acidic by-products of degradation. Although microbes can adapt to a broader range of pH values, there typically is an accompanying decrease in growth/metabolic rates. Likewise, there is a reduc- tion in the variety of microbial strains, with the microbes themselves becoming more specialized for living under certain environmental conditions. 3.2.5 Toxic compounds Just as contaminant concentrations that are too low can complicate bioreme- diation, high aqueous phase concentrations of some contaminants can create problems. At high concentrations, some chemicals are toxic to microbes, even if the same chemical is readily degraded at lower concentrations. Toxicity prevents or slows metabolic reactions and often prevents the growth of new biomass needed to stimulate rapid contaminant removal. The degree and mechanisms of toxicity vary with specific toxicants, their concentration, and the exposed microorganisms. Microbial cells cease to function when at least one of the essential steps in their numerous physiological processes is blocked. The blockage may result from gross physical disruption of the cell structure or competitive binding of a single enzyme essential for metaboliz- ing the toxicant (National Research Council, 1993). By design, some organic compounds are toxic to targeted life forms such as insects and plants and may also be toxic to microbes. These compounds include herbicides, pesticides, rodenticides, fungicides, and insecticides. In addition, some classes of inorganic compounds such as cyanides and azides are toxic to many microbes; however, these compounds may be degraded following a period of microbial adaption. 3.2.6 Effects of soil type The soil type affects the rate of mass transport of nutrients, contaminants, water, air (i.e., oxygen), and pH adjusters. This effect on mass transport in return affects the operation of the degradation process and the potential for migration of the wastes and amendments. In addition, highly organic soils can be sorptive and act as a barrier to organic migration. 3.2.7 Nontechnical issues As already established, the technical parameters for biotreatment can be complex and numerous; however, nontechnical issues are also of vital impor- tance for an effective design. Some considerations may include the following: L1656_C003.fm Page 38 Monday, July 18, 2005 7:42 AM © 2006 by Taylor & Francis Group, LLC Chapter three: Roadblocks to implementation of biotreatment strategies 39 • Ability to achieve cleanup levels • Cost with respect to other treatment options • Risk assessment of site before, during, and after treatment • Regulatory acceptance and familiarity • Public perception •Time constraints • Space limitations Although there are many other criteria that can influence the design, the most basic objective for biotreatment is to design a system that will optimize microbial conditions. If the fundamental parameters exist for microbial growth (i.e., adequate supply of nutrients) and favorable conditions are maintained (i.e., optimal temperature and pH), biotreatment has the poten- tial to be exceptionally effective. 3.3 Treatment zones When considering bioremediation, two zones for treatment must be consid- ered: unsaturated and saturated. The unsaturated zone (vadose zone) is “a composite or materials coexisting in the solid, liquid, and gaseous phases” (Tursman and Cork, 1992). The unsaturated zone contains solid particles of variable sizes interconnected with water and air. The amount of water and air contained within these pore spaces depends on the lithology, recharge characteristics, and discharge characteristics of the site (Tursman and Cork, 1992). The water contained in these pore spaces slowly percolates downward under the influence of gravity until it reaches the saturated zone. The unsat- urated zone is normally the easiest to treat because its characteristics favor chemical, biological, and physical interactions. The saturated zone is that region where 100% of the pore volume con- tains liquid water (Tursman and Cork, 1992). This region is where water-bearing formations will yield groundwater. If groundwater is in suf- ficient quantity, it is referred to as an aquifer. Unlike the unsaturated zone, chemical, biological, and physical interactions can be limited. This charac- teristic makes the saturated zone the most difficult region for biotreatment. The water table divides the saturated and unsaturated zones. Typical pat- terns of contamination occur in both zones. Frequently, the contamination drains through the unsaturated zone, leaving a portion that is trapped by capillary forces. If the contaminant is volatile, a plume of vapors fills the soil air in the vadose zone. Some contaminants drain or pass further into the water table and then spread laterally. Groundwater moving through the aquifer comes into contact with the contaminants and transports the water-soluble components. Therefore, it is not uncommon to deal with three distinct regions of contamination: •A plume of vapors in the soil air •A groundwater solute plume • The region that contains the source of contamination L1656_C003.fm Page 39 Monday, July 18, 2005 7:42 AM © 2006 by Taylor & Francis Group, LLC 40 Bioremediation of Recalcitrant Compounds 3.4 Alternative physical and chemical technologies Several alternative remediation technologies, excluding biological processes, are described below. This section will give background on technologies that are currently available for site remediation. The advantages and disadvan- tages of these technologies can be compared with bioremediation to show that in many cases bioremediation will be the treatment technology of choice. However, each site has unique characteristics that may favor one treatment technology over another. The appropriateness of each technology must be evaluated prior to choosing one and implementing a remediation strategy. 3.4.1 Incineration Incineration is a technology that results in the complete destruction of organic compounds using high temperatures. Typical operating tempera- tures are in excess of 1500˚F. For most site remediation applications, incin- erators are used for the treatment of contaminated soils and free products. Although the incineration of liquid is possible, it is typically not used to remediate groundwater and surface water from contaminated sites. The fact that incineration is a destructive technology that results in the complete destruction of organic contaminants is a major advantage. Disadvantages of this technology involve the high cost of operation, poor public acceptance, and regulatory constraints. 3.4.2 Air stripping Air stripping is a physical treatment process that relies on contaminant phase change. This process removes contaminants through volatilization from the aqueous phase into the gas phase; consequently, it is not a destructive tech- nology. The higher the contaminant’s Henry’s law constant, the easier it is to desorb or “strip” the compound from the aqueous phase to the air phase. For air stripping to be cost effective, the contaminant must be significantly more volatile than water. Air stripping is commonly used to remove volatile organic compounds from contaminated groundwater. Dissolved cations such as iron can present problems with stripper operation by oxidizing and precipitating out in the column, thereby clogging the column. Many states are now requiring treatment of off-gases from air stripping units, which can significantly increase the cost of treatment because of disposal problems associated with spent activated carbon. Also, recent emphasis on destructive technologies is limiting the acceptance and use of this technology by the regulatory community (Zappi et al., 1993). 3.4.3 Activated carbon adsorption Activated carbon adsorption is a treatment process generally used for the removal of dissolved organics, color, and taste- and odor-causing L1656_C003.fm Page 40 Monday, July 18, 2005 7:42 AM © 2006 by Taylor & Francis Group, LLC Chapter three: Roadblocks to implementation of biotreatment strategies 41 compounds in water through adsorption of the contaminant onto the surface of the carbon. The most frequently used form of activated carbon is granular activated carbon (GAC). The activated carbon process is not a destructive technology because it involves a phase change of the contaminants from the aqueous phase into the solid phase. The phase transfer of GAC treatment results in a concentrating effect of the contaminants onto the GAC surface. However, because the contaminant is not destroyed, the spent carbon must be either disposed of, usually as hazardous waste, or regenerated, which can be very costly. Logistic and economic disadvantages arise from the need to transport and decontaminate spent carbon and, therefore, waste streams with high contaminant concentration levels are typically pretreated. 3.4.4 Advanced oxidation Advanced oxidation processes (AOPs) are destructive technologies. These processes typically rely on the synergistic effect of both ultraviolet (UV) light or other catalysts and chemical oxidizers for the destruction of organic com- pounds. Hydrogen peroxide and ozone are examples of commonly used chemical oxidizers. Four different ultraviolet oxidation processes have been evaluated by the U.S. Army Environmental Center (USAEC) at both the bench and pilot scales. The demonstration site for this evaluation was the Savannah Army Depot Activity in Illinois. The evaluation showed that ultra- violet oxidation technology is effective and cost competitive (when com- pared with the current technology of utilizing granular-activated carbon) in treating groundwater contaminated with explosives. Problems typically associated with AOPs include fouling of the UV quartz due to solubilized cations and the formation of chemical intermedi- ates caused by incomplete oxidation of the parent compounds. A way to minimize the effects of fouling is to treat the water prior to its treatment by an AOP. Typical pretreatment processes include flocculation, filtration, pH adjustment, oxidant addition, and additive addition. Another drawback of AOPs is the relatively high operational cost caused by the electrical require- ments of these systems. 3.4.5 Low thermal stripping Low thermal stripping uses elevated temperatures to desorb organic con- taminants from contaminated soils. It is a physical separation process and is not designed to destroy organics; however, this process can be a destructive one if the vapors produced in the desorption device are destroyed in a secondary destruction unit. The target contaminant groups for this technol- ogy are nonhalogenated volatile organic compounds and fuels, although it can be used to treat semivolatile organic compounds at reduced effective- ness. A drawback of the technology is that it can be expensive to operate, depending on the fate of the gases. Also, the presence of heavy metals in the feed stream may produce a treated solid residue requiring stabilization. L1656_C003.fm Page 41 Monday, July 18, 2005 7:42 AM © 2006 by Taylor & Francis Group, LLC 42 Bioremediation of Recalcitrant Compounds Likewise, dewatering of saturated solids is necessary because all of the moisture has to be driven off before contaminants can be efficiently desorbed. 3.4.6 Pump and treat Pump-and-treat methods pump any contaminated water from the ground and treat it either at an on-site plant or off-site. The advantage of this system is that the contaminant is actually removed entirely from this system. This is one of the most traditional methods of remediation, but it is not the most effective method for all contaminants. For contaminants that bind very closely to the soil, such as polycyclic aromatic hydrocarbon (PAHs), desorp- tion of the contaminant from the soil to the groundwater is very slow. When the groundwater is pumped out of the system, the contaminant present in the aqueous phase is also removed, but a significant portion of the contam- inant still remains present in the ground and will leach out in the future. In order for pump and treat to be effective, it must be done over a long period, in order to give the contaminant sufficient time to desorb from the soil. However, this option becomes much more cost efficient and timely with the addition of surfactants, such as amphiphilic polyurethane nanoparticles, extracellular polymers, and cyclodetrins, that will loosen the bond of the contaminant to the soil particles and increase the apparent solubility of the contaminant (Tungittiplakorn et al., 2004). The addition of surfactants will greatly increase the mass recovery rate for this method. 3.4.7 Stabilization In stabilization, the contaminant is trapped within the soil matrix and is effectively removed from being a future threat. It is a nondestructive method and relies on the strength of the bond between the contaminant and the soil particles or additive for its immobilization. The contaminated soil is then often removed and placed in a landfill. Unfortunately, this method can cause the volume of the soil to increase by as much as 20%, which increases disposal costs. Stabilization can occur in two ways — through either covalent bonding or pore trapping. Binding occurs when the contaminant actually becomes part of the binder (such as cement or fly ash). Entrapment occurs when the contaminant becomes trapped in the pores of an additive, but that contaminant may be released if that additive is ever crushed (Magar, 2003). Stabilization requires leaching monitoring in order to confirm that the con- taminant stays locked in the matrix. Because the contaminant is not destroyed, there is a possibility that it could be removed in the future. One form of stabilization that has been examined recently is the use of plants to trap the contaminant and also increase microbial growth so that the contaminant can be destroyed. Phytoremediation, as this is called, con- tains two components: phytodecontamination, which removes the contam- inant from the soil by taking it up into the plant, and phytostabilization, in which the plant helps to lock the contaminant in place. The latter is often L1656_C003.fm Page 42 Monday, July 18, 2005 7:42 AM © 2006 by Taylor & Francis Group, LLC [...]... implementation of biotreatment strategies Acc.V Spot Magn Det WD 15.0 kV 3. 0 15000x SE 20.7 Upal L1656_C0 03. fm Page 45 Monday, July 18, 2005 7:42 AM Chapter three: 50 L1656_C0 03. fm Page 46 Monday, July 18, 2005 7:42 AM 46 Bioremediation of Recalcitrant Compounds Figure 3. 2 Mesoscale: Mesocosm study displaying laboratory work at the bench level at the Hazardous Waste Research Center, ERDC 3. 5 .3 Macroscale... implementation of biotreatment strategies 47 Figure 3. 3 Macroscale: Hazardous waste site showing spatial heterogeneity of contamination bioremediation at a site Table 3. 2 lists the phenomena influencing bioremediation at each level of observation It is important to note that observations made at one scale may not apply to another scale For example, field-measured half-lives tend to be longer than laboratory-measured... Literature Review on the Use of Bioaccumulation for Heavy Metal Removal and Recovery, WSRC-TR-175-Vol 2 (February) Westinghouse Savannah River Co., Aiken, SC Blackburn, J.W and Hafter, W.R 19 93 The input of biochemistry, bioavailability, and bioactivity on the selection of bioremediation techniques TIBTECH 11 (August): 32 9 Brock, T.D., Smith, D.W., and Madioan, M.T 1984 Biology of Microorganisms, 4th ed... bench-scale compost conditions Environ Sci Technol 33 : 1717–1725 Sturman, P.J., Stewart, P.S., Cunningham, A.B., Bouwer, E.J., and Wolfram, J.H 1995 Engineering scale-up of in-site bioremediation processes: a review J Contaminant Hydrol 19: 171–2 03 Talley, J.W., Ghosh, V., Luthy, R.G., Gillette, S., Zane, R.N., Furey, J.S., Felt, D.R., and Tucker, S 2001 Assessment and prediction of biostabilization of. .. & Francis Group, LLC L1656_C0 03. fm Page 50 Monday, July 18, 2005 7:42 AM 50 Bioremediation of Recalcitrant Compounds Kamath, R., Schnoor, J.L., and Alvarez, P.J.J 2004 Effect of root derived substrates on the expression of nah-lux genes in Pseudomonas flourescens HK44: implications for PAH biodegradation in the rhizosphere Environ Sci Technol 38 : 1740–1745 Magar, V.S 20 03 PCB treatment alternatives and... contaminants, such as five- and six-ring compounds (Potter et al., 1999) Currently, it is also a very inexact method for remediation 3. 5 Transitioning from bench-level to full-scale design Systems at the bench level are relatively simple by design, whereas systems naturally occurring in the field can be complex The bench level focuses on specific aspects of a process (i.e., ascertaining rates of degradation) Individual... impact of any or all of the limiting factors at each level of observation on the overall system For example, the microscale may be limited by a low concentration of degrading microorganisms, whereas at the mesoscale, a low-porosity soil (such as a tight clay) may limit the ability of the microorganisms to reach the contaminant Furthermore, the heterogeneity of the site (e.g., multiple types of contaminant...L1656_C0 03. fm Page 43 Monday, July 18, 2005 7:42 AM Chapter three: Roadblocks to implementation of biotreatment strategies 43 done due to the increase of organic material in the soil, which increases the ability of contaminants such as PAHs to adsorb to the soil particles (Tugun et al., 20 03) Furthermore, this organic material contains many molecules... dimension of this scale is 10–2 to 102 m or larger and incorporates the entire field site (Figure 3. 3) When assessing the limiting factors at this scale, the underlying question is: Are the conditions optimal for the bugs to work? Other associated issues that pertain to the scale include the following: the impact of spatial heterogeneity on bioremediation of the site, the effects of advective-dispersive... rate of biodegradation at the site, and the ability of an engineered system to effectively influence the limiting phenomena 3. 6 Relationship between scales of observation The three scales of observation have been developed in order to organize and identify limiting phenomena that may apply to implementation of © 2006 by Taylor & Francis Group, LLC L1656_C0 03. fm Page 47 Monday, July 18, 2005 7:42 AM Chapter . 36 3. 2.1 Metals 36 3. 2.2 Temperature 37 3. 2 .3 Water 37 3. 2.4 pH 37 3. 2.5 Toxic compounds 38 3. 2.6 Effects of soil type 38 3. 2.7 Nontechnical issues 38 3. 3 Treatment zones 39 3. 4 Alternative physical. Dechlorination 43 3.4.9 Compost 43 3.5 Transitioning from bench-level to full-scale design 44 3. 5.1 Microscale phenomena 44 3. 5.2 Mesoscale phenomena 44 L1656_C0 03. fm Page 33 Monday, July 18,. Group, LLC 34 Bioremediation of Recalcitrant Compounds 3. 5 .3 Macroscale phenomena 46 3. 6 Relationship between scales of observation 46 3. 7 Conclusions 47 3. 8 Summary 48 References 49 3. 1 Introduction