Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
  • B09C—RECLAMATION OF CONTAMINATED SOIL
  • B09C1/00—Reclamation of contaminated soil
  • B09C1/002—Reclamation of contaminated soil involving in-situ ground water treatment
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
  • B09C—RECLAMATION OF CONTAMINATED SOIL
  • B09C1/00—Reclamation of contaminated soil
  • B09C1/06—Reclamation of contaminated soil thermally
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
  • B09C—RECLAMATION OF CONTAMINATED SOIL
  • B09C1/00—Reclamation of contaminated soil
  • B09C1/08—Reclamation of contaminated soil chemically
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/02—Treatment of water, waste water, or sewage by heating
  • C02F1/025—Thermal hydrolysis
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/30—Treatment of water, waste water, or sewage by irradiation
  • C02F1/302—Treatment of water, waste water, or sewage by irradiation with microwaves
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
  • B09C—RECLAMATION OF CONTAMINATED SOIL
  • B09C2101/00—In situ
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2101/00—Nature of the contaminant
  • C02F2101/30—Organic compounds
  • C02F2101/32—Hydrocarbons, e.g. oil
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2101/00—Nature of the contaminant
  • C02F2101/30—Organic compounds
  • C02F2101/36—Organic compounds containing halogen
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
  • C02F2103/06—Contaminated groundwater or leachate

Definitions

• This invention relates to an in situ hydrous pyrolysis/oxidation process useful for in situ degradation of hydrocarbon contaminants in water and soil.
• the process uses heat distributed through soils and water, optionally combined with oxygen or air or catalysts, and is particularly useful for remediation of fuel or industrial contaminated sites.
• Fuel leaks contribute significantly to the contamination of groundwater by gasoline, aviation fuel, and other refined petroleum derivatives.
• Industry, such as electronic, chemical and chemical cleaning plants, are responsible for contamination of ground water with halogenated, typically chlorinated solvents.
• Many fuel hydrocarbons and chlorinated hydrocarbons among the contaminants from fuel or industrial leaks are of particular concern because they are confirmed or suspected carcinogens, even at very low concentrations.
• VOC volatile organic compounds
• DUS in situ dynamic underground stripping
• In situ bioremediation is another recently proposed method for removing aromatic hydrocarbon contaminants from the subsurface.
• Most laboratory studies described, for example, in Environ. Toxicol. Chem.. 8:75- 86 (1989); Appl. Environ. Microbiol.. 53:2129-2123 (1987); 58:786-793 (1992); 60:313-322 (1994); and in Environ. Sci. Technol.. 25:68-76 (1991), are directed at candidate microorganisms that may have potential uses in in situ aromatic hydrocarbon bioremediation. In order to simulate the normal groundwater environment, these studies have been conducted at low to moderate temperature conditions (12°C-35°C).
• In situ bioremediation can prove practical and efficient for degradation of residual contaminants remaining in the subsurface following the major decontamination efforts such as DUS, where the temperature is much higher (45°C to 75°C), when sufficient oxygen remains in the formation for the microbial metabolic destruction of the remaining fuel.
• DUS major decontamination efforts
• microbial removal of the residual amounts remaining after a thermal treatment has been demonstrated to be very efficient.
• delivery of oxygen to sediments that are water saturated is very difficult, and biodegradation processes have only been demonstrated for fuel hydrocarbons. Chlorinated hydrocarbons do not degrade under these conditions. Any method that would achieve or enhance the removal, destruction or degradation of the residual contaminants after the DUS method or complement the DUS method by degrading these compounds would be beneficial.
• a primary objective of this invention is to provide an in situ method for degradation of hydrocarbons, chlorinated hydrocarbons or other volatile contaminants using hydrous pyrolysis/oxidation following dynamic underground stripping or as a stand-alone method.
• the new method takes advantage of the already existing injection-withdrawal wells and the persistently elevated underground temperatures for hydrous pyrolysis/oxidation affecting or enhancing the removal of degradation residual contaminants.
• This invention is a process for in situ hydrous pyrolysis/oxidation of fuel hydrocarbons, polycyclic aromatic hydrocarbons, chlorinated hydrocarbons, and other volatile contaminants.
• This process is useful for in situ degradation of hydrocarbon contaminants in water and soil.
• the process involves thermal degradation of chlorinated or fuel hydrocarbons, petroleum distillates, polycyclic aromatic hydrocarbons, and other contaminants present in the soil and water, into non-toxic products of the degradation, such as carbon dioxide, water, chloride ion, carboxylic or hydrochloric acids, and short chain alkanes.
• the process uses heat distributed through soils and water optionally combined with oxygen or air or catalysts, and is particularly useful for remediation of fuel or industrial contaminated sites.
• This invention is a replacement for excavation and "pump and treat" technologies of environmental remediation.
• hydrous pyrolysis/oxidation is induced at a site of contamination by introducing under pressure to the site of contamination either steam, oxygen (or air), a catalyst of the hydrocarbon degradation, or any combination thereof.
• the build-in pressure may be relieved, and the hydrous pyrolysis/oxidation proceeds, resulting in degradation of the contaminants.
• the rate and degree of the hydrocarbon degradation is monitored to insure complete degredation and elimination of all contaminants.
• the pyrolysis/oxidation of contaminants may be achieved by introduction of steam to the underground water (without addition of oxygen or a catalyst) and an oxidant of the contaminant, where the oxidant is oxygen or air and/or a mineral present in the ground.
• the oxidant may include the dissolved oxygen already present in the water, or mineral oxidants such as Mn ⁇ 2 or Fe2 ⁇ 3, which are already present naturally in soils and rocks.
• the process may use already raised temperatures in the underground remaining after in situ dynamic underground stripping method, and introduce only oxygen or a hydrocarbon degradation catalyst.
• the heating of the ground may be accomplished by electrical resistance (joule) heating, RF or microwave heating, or other electrical heating means.
• This invention hydrous pyrolysis/oxidation, has been demonstrated successfully to degrade compounds such as TCE, PCE, naphthalene, pentachlorophenol (PCP), creosote compounds (e.g., as contained in pole tar), ethylbenzene, methy 1-tertbutyl ether (MTBE), and commercial machining/cutting fluids (e.g., RapidTap%o and Alumicut%o).
• PCP pentachlorophenol
• MTBE methy 1-tertbutyl ether
• commercial machining/cutting fluids e.g., RapidTap%o and Alumicut%o
• Figure 1 is a schematic of field application of in situ thermal pyrolysis.
• Figure 2 is comparison of Dynamic Underground Stripping with conventional methods for removal of gasoline.
• Figure 3 shows the boiling curve of water in constrained temperature and pressure conditions where both liquid water and steam coexist.
• Figure 4 illustrates growth of heated zones in the gasoline spill site test of Dynamic Underground Stripping.
• Figure 5 shows the oxidation of dissolved TCE with dissolved oxygen and the oxidation of TCE in the presence of rock/soil from drillcore.
• Figure 6 shows the oxidation of complex pole-tar components such as polycyclic aromatic hydrocarbons.
• Figure 7 shows oxidation of dissolved TCE by solid Mn ⁇ 2 at 100°C.
• Figure 8 is the van't Hoff plot of TCE solubility and calculated thermodynamic quantities.
• Figure 9 shows the oxygen demand for the present process for several typical contaminant chemicals.
• Figure 10 shows the range of achievable oxygen concentrations in ground water when steam injection is used to maintain an applied overpressure. Definitions:
• Hydrocarbons means hydrocarbons or halogenated, particularly chlorinated, organic solvents such as trichloroethane (TCA), trichloroethylene (TCE), perchloroethylene (PCE), dichloroethane (DCA) or dichloroe thy lene (DCE), etc.
• TCA trichloroethane
• TE trichloroethylene
• PCE perchloroethylene
• DCA dichloroethane
• DCE dichloroe thy lene
• “Fuel hydrocarbons” means those hydrocarbons commonly found in gasoline, diesel fuel, aviation fuel, etc., such as: monoaromatic substituted or unsubstituted benzenes, toluenes, ethylbenzene and xylenes (BTEX), and any and all their derivatives alone or in mixture with each other.
• Constants means all compounds falling within the term hydrocarbons and fuel hydrocarbons.
• DUS Dynamic Underground Stripping method as described in the Interim Progress Report, UCRL-ID-109906 (1991) and in UCRL-ID- 118187 (1994) DOE publications.
• the current invention is an in situ process for hydrous pyrolysis and/or oxidation (i.e., the degradation) of fuel hydrocarbon, chlorinated hydrocarbons or other contaminants of the soil and water following fuel or industrial spills or leaks. These materials comprise the dominant constituents of solvents, machining fluids, gasoline, etc. Hydrocarbons are degraded in situ to compounds that are non-toxic or less hazardous or have no established drinking water limits. Relatively rapid degradation is achieved by the application of heat from about 70°C-200°C, although slower degradation will occur even at lower temperatures, down to perhaps as low as 40"C, after active heating is stopped.
• the process is aided by the addition of oxygen, and/or air, and/or mineral oxidants, and/or hydrocarbon degradation catalysts, although it may also occur without added oxidants by making use of the dissolved oxygen and/or mineral oxidants naturally present in soils and rock.
• the invention is based on finding that organics are increasingly solvated by and reactive with water as temperature is increased. This occurs largely as a consequence of the precipitous drop in the dielectric constant of water as temperature increases. With increasing temperature, water becomes a progressively better solvent for organics. Under appropriate conditions when the temperature of the underground is increased, water reacts with hazardous organic contaminants to produce a relatively benign mixture of oxygenated compounds, such as carbon dioxide, chloride, alcohols, aldehydes and /or carboxylic or other acids. The rate of conversion of hazardous material and the yield of benign products resulting from the hydrothermal oxidation of hazardous organics materials is advantageously enhanced using a variety of oxidants and/or catalysts.
• the process comprises in situ acceleration of chemical hydrocarbon degradation via hydrous pyrolysis/oxidation reactions performed at increased underground temperatures.
• the process is enhanced by using degradation catalysts or oxygen or air. Both oxygen and catalysts may be added or the process may utilize the endogenously present oxygen or oxidation agents (i.e., oxide minerals) as catalysts.
• the process advantageously utilizes the conditions induced during the primary cleaning efforts of dynamic underground stripping (DUS) as well as the structures, such as wells, pumps, boilers, heaters, etc.
• DUS dynamic underground stripping
• the entire underground environment remains at elevated temperatures of 45°-80°C for an extended period of time (at least 60 days) after the heat treatment following DUS.
• the process of the invention for in situ degradation of fuel hydrocarbons, chlorinated hydrocarbons or other contaminants, in its broadest form, involves (1) increasing or utilizes increased temperature in situ at a site of contamination and (2) inducing or enhancing in situ hydrolysis or hydrous pyrolysis combined with oxidation. In this manner, the contaminants are degraded fast or slowly, depending on the process conditions.
• the degradation of contaminants is achieved by inducing or utilizing existing high temperatures above 70°C, preferably temperatures between 100°C and 125°C, or higher.
• High underground temperatures are induced, preferably by introducing steam into the contaminated zone underground.
• the ground may also be heated electrically (ohmically).
• catalysts and /or oxygen and /or air can be introduced into the contaminated underground site. In the subsurface, the steam and oxygen and/or air and/or catalysts mix together and the hydrous pyrolysis/oxidation process begins.
• the hydrocarbon degradation is achieved by hydrous pyrolysis combined with oxidation process where the steam and oxygen or air are both introduced into the contaminated underground, the underground is steam-heated to the required temperature optimal for the degradation of particular hydrocarbon contaminant, and the pressure build-up due to steam injection in the underground is optionally released.
• the steam, oxygen, and contaminated water mix together and the chemical degradation by hydrous pyrolysis and oxidation of the contaminant hydrocarbons proceeds to yield non-toxic or less harmful compounds such as carbon dioxide, chloride ion, carboxylic acids, alcohols, aldehydes, etc.
• the degree of contamination and a rate of decontamination are monitored using methods known in the art.
• the steam and the hydrous pyrolysis/oxidation catalysts such as manganese dioxide, or ferric oxide are introduced into the contaminated zone underground.
• the choice of catalysts and temperature for optimal rate of degradation depends on the particular hydrocarbon contaminant. Decontamination is monitored as described above.
• the steam is introduced alone without either the oxygen or air or catalyst.
• This mode is useful for a site where there is naturally present in the ground an oxidizing mineral, such as, for example, manganese dioxide or ferric oxide, or at a site where the dissolved oxygen naturally present in the water is sufficient to oxidize the contaminant present.
• the temperature is increased, by steam introduction and/or by ohmic heating, to a temperature optimal for degradation of the contaminant hydrocarbon in the presence of the naturally occurring oxidizing agent. Decontamination is monitored as described above.
• the last mode of practicing the invention is by introducing oxygen and /or an appropriate catalyst into the contaminated zone following the dynamic underground stripping or other thermal remediation processes where the underground is already sufficiently warmed by the dynamic underground stripping.
• the temperatures between 45°C and 80°C remain in the underground for about two to three months or longer following dynamic underground stripping.
• the remaining high temperatures are utilized for in situ hydrous pyrolysis/oxidation of the invention.
• the temperatures are further raised to higher temperatures by introducing steam with oxygen and/or air and/or catalysts.
• no oxygen or air or catalysts are added, but the temperature is further raised by steam additions.
• the last mode of the invention complements the primary dynamic underground remediation stripping. Decontamination is monitored as described above.
• This invention has been demonstrated to be applicable to a wide variety of hydrocarbon and chlorinated hydrocarbon contaminants. Based on the range of classes of organic compounds already demonstrated to be amenable to hydrous pyrolysis/oxidation, this process is broadly applicable to any and all organic compounds, including substituted aliphatics, branched aliphatics, substituted aromatics, polyaromatics, oxygenated forms of all the preceding classes. ⁇ . Theoretical Basis for Hydrous Pyrolysis /Oxidation
• thermodynamic properties of hydrolysis and oxidation reactions involving degradation of compounds like chlorinated hydrocarbons such as: TCE, TCA, DCE, DCA, PCE or chloroform, according to the invention, can be estimated and their thermodynamic driving force calculated.
• Figure 1 shows the aquifer 20 containing site 30 contaminated with hydrocarbons or chlorinated hydrocarbons.
• Figure 1 illustrates a system for the hydrocarbon degradation where only one well 40 is used. In system variations, two or more wells may be utilized. Generally, the number of wells will depend on the size of the spill area.
• two pipes 42 and 44 preferably made of stainless steel, are introduced into the underground water reservoir 20, preferably to the site of contamination 30.
• the well is placed approximately in the middle of the contaminated site 30.
• Oxygen is supplied through pipe 42 from the gas tanker 50 or from any other gas storage place.
• the oxygen pipe is straight or preferably it branches into ducts 48 so that oxygen is distributed to various depths of the contaminated site and there it is mixed with steam having predetermined temperature optimal for degradation of the particular contaminant.
• Air may be substituted for oxygen when the presence of nitrogen in the air will not be deleterious. In general air will suffice for all but the most highly contaminated sites, where the build-up of nitrogen gas bubbles in the subsurface may impede injection of steam through permeability reduction.
• Steam temperature is such that it suffices to warm the underground to temperatures typically above 75°C, preferably between 100°C to about 125°C.
• the degree to which the underground is warmed depends on the contaminant as well as on the degree of contamination. Generally, the higher the degree of contamination, the higher the temperature. The higher temperatures lead to higher rates of degradation. Similarly, more refractory compounds such as TCE require higher temperatures to oxidize than less refractory compounds such as TCA and therefore higher temperature are used for their degradation.
• Steam is introduced to the site of contamination through the pipe 44 under pressure from a pump, compressor or a boiler 60.
• the pipe 44 may be straight or branched as seen for oxygen pipe.
• the higher pressure forces the steam/oxygen mixture into the gravel, sand and rock cracks, crevices and spaces, and thus promotes greater degradation of contaminants.
• certain amount of water may be optionally pumped out to relieve the pressure, using the reverse pumping or vacuum. In such an instance, the removed water is submitted to ex situ decontamination. However, it is only a small portion of the contaminated water, if at all, which needs to be removed and therefore the ex situ clean-up is not extensive.
• Steam is introduced via tube 44, which typically has a higher diameter and is also preferably made of steel as both steam and oxygen are corrosive agents.
• Oxygen and steam are introduced to the site of contamination separately. In the mixture, these agents are very corrosive. Steam is introduced preferably in successive steam pulses. These steam pulses expand the heated zone through the contaminated site. Ground water returns between steam pulses and flows through the hot, oxygenated region destroying contaminants and washing away or diluting the decontamination products (typical carbon dioxide gas and chloride ion).
• the heating methods according to the invention are extremely robust. Since the contaminant is destroyed in place and does not have to be transported back out of the formation and treated ex situ, the overall process is even more efficient and economical than dynamic underground stripping as implemented at the gasoline spill areas.
• the system and the process of the invention can, however, be supplementary to a primary decontamination effort, such as dynamic underground stripping.
• a primary decontamination effort such as dynamic underground stripping.
• stripping provides a method for fast removal of large amounts of contaminants using hot underground temperatures.
• Underground stripping does not necessarily completely remove all residual contaminants.
• the current invention takes over and degrades, via hydrous pyrolysis/oxidation, these residual contaminants.
• the dynamic underground stripping combined with in situ pyrolysis provide the best available decontamination process for hydrocarbon contamination.
• Figure 2 illustrates results of gasoline removal during the dynamic underground stripping as compared to gasoline removal by conventional methods at the same site. This comparative study shows that large-scale heating and monitoring can be conducted safely and effectively and that large, stable steam zones can be constructed and maintained below the water table. As seen in Figure 2, vapor recovery was extremely efficient from these zones, and where the conventional vacuum recovery pump and treat was able to remove 2.5 gallons of vapor per day, dynamic underground stripping method removed about 64 gallons of vapor per day.
• Figure 3 shows the boiling curve of water under constrained temperature and pressure where both liquid water and steam coexist.
• the effect of reducing the applied pressure on a heated zone is to generate vapor (steam).
• the effect of cooling a heated region is to create a vacuum as water condenses.
• Figure 4 illustrates growth of heated zones in the gasoline spill site test of Dynamic Underground Stripping.
• Figure 4 shows temperature logs from one well located near the center of the pattern. During injection, temperatures exceed 100°C as the zone pressurizes. Adjacent silty layers heat by conduction and water is expelled from these zone by boiling. Oxygen-rich steam is able to occupy these areas, and condense to oxygenated water when steam pressure is released.
• Figure 4 further shows lower steam zone collapse and reformation over five months of operation and the distribution of steam throughout various depth zones of wells and its dependence on the underground temperature.
• the applied pressure on the formation is atmospheric and the applied pressure on the steam zone represents the boiling point of water at the temperature achieved, then when steam injection is halted the formation behaves like the cylinder in a steam engine. As heat is lost to the formation from the steam zone, steam condenses and a vacuum occurs, drawing water in from the surrounding formation just as the condensation in a steam engine draws in the piston.
• Fluid displacement of water in the permeable parts of the aquifer allows removal of a certain percentage of the contaminant. Due to dispersion, however, most of the contaminant appears to be in the peripheral zones which are still somewhat permeable but which have more surface area.
• the current process can be advantageously coupled to the other treatment methods as already described above.
• the process is particularly cost effective when it is used as a follow-up on the primary cleaning using dynamic underground stripping. Additionally, the process can be combined with a biofilter built-in downstream.
• the hydrous pyrolysis/oxidation process provides an active drive mechanism forcing water through the biofilter as described in Example 1.
• the process can be also advantageously combined with a pump and treat process. Warming the water will reduce sorption, increase diffusion, reduce viscosity, and in general increase the effectiveness of pump and treat operations.
• Pump and treat screens can be very effective at controlling the flow of contaminant downstream from a thermal remediation operation. If there are other contaminants that are not destroyed in situ, pump and treat (water or vacuum extraction) can be used to extract the contaminant in huff- and puff mode. The efficiency of such a combination would be very high. Extracted hot water could be airstripped before cooling, which is both an effective cleaning and cooling method.
• the current process can also be modified for use in small spills or leaks, such as for treatment of cleaning stored waste water or for small industrial leaks.
• in situ temperature can be advantageously raised by other thermal means such as electric heating. Slow electrical heating of the soil or water, over a period of several years, will allow destruction of fuel or chlorinated hydrocarbon in place, if enough oxygen is present.
• This application may be most advantageous in soils with very low permeability, or in cases where additional radioactive contamination such as tritium is present. It is generally advantageous in these cases to permit no movement of contaminated fluid, so as to not re-distribute the radioactive contaminants.
• laboratory static autoclave experiments were used to determine the optimum chemical conditions for remediating contaminants via hydrous pyrolysis/oxidation.
• the initial phase of this experimental work was used as a vehicle for designing an in situ thermal remediation technique applicable to fuel hydrocarbons, halogenated hydrocarbons, and other contaminants.
• the field treatment process in the laboratory was simulated to measure the impact of treatment on soil transport properties and fluid chemistry, and to identify the organic /aqueous fluid-solid reactions that occur.
• the static autoclave experiments were run in Dickson-type, gold-bag rocking autoclaves.
• the autoclave reaction vessel uses a flexible gold bag sealed with a high purity titanium head and is contained within a large steel pressure vessel.
• the autoclave design allows periodic sampling of the reaction cell under in situ conditions throughout the course of an experiment without disturbing the temperature and pressure of the run. During the experiment the solution contacts only gold and carefully passivated titanium so that unwanted surface catalytic effects are eliminated.
• Various combinations of solid, liquid or gaseous catalysts or oxidants were introduced into the reactor in order to study their effects on reaction mechanisms and rates.
• the sampled fluids and gases were analyzed using a variety of analytical techniques including ICP-ES, IC, gas chromatography (using purge and trap), gas MS, GC/MS, and high pressure liquid chromatography.
• TCE trichloroethane
• PCE trichloroethane
• naphthalene e.g., as contained in pole tar
• creosote compounds e.g., as contained in pole tar
• ethylbenzene e.g., MTBE
• machining/cutting fluids e.g., RapidTapXo and Alumicut%o
• a Dickson-type autoclave as described above, equipped with a precision high pressure liquid chromatography pump to control pressure / 0
• TCE Dissolved oxygen was found to rapidly and completely degrade TCE to benign products, predominantly to carbon dioxide and chloride anion at temperatures easily achieved in in situ conditions of thermal remediation techniques. At temperatures above 90°C, the TCE was completely degraded to minimal detection limits in from one to a few days to several weeks, depending on the temperature. The TCE concentration in the initial runs with high starting concentrations decreased as much as 10,000-fold, eventually reaching the drinking water MCL (5 ppb). The TCE degradation products were hydrogen ions, free chloride anions and C ⁇ 2 as expected for complete oxidation (mineralization) of the chlorinated hydrocarbon.
• the “Partially Reacted Water” is the result of reacting the free-product/ water mix at up to 120°C until all oxygen was consumed, stopping the reaction.
• the “Completely Reacted” test used the decanted, equilibrated water (no free product) with an excess of oxygen. The results of this test are shown as a function of time and temperature in Figure 6.
• the completely reacted water (14 days at 100 * C followed by 6 days at 120°C) shows no detectable trace of polycyclic aromatic hydrocarbon contaminants; at the detection limits of this measurement, that corresponds to at least 92% destruction. All compounds were destroyed, even notably difficult compounds to bio-degrade such as benzo(a) pyrene.
• the "partially reacted” experiment which consumed all the oxygen, stopping the process in mid-reaction, no deleterious intermediate products were detected. Only hydroxylated forms of the original compounds were seen as intermediates. These disappear when the water is completely reacted.
• Oxidation of TCE via coupled Mn ⁇ 2 reduction was also investigated at 100°C and 150"C, as shown in Figure 7. These runs were designed using very high TCE concentrations, again with the intent of maximizing the ability to detect deleterious reaction products and to demonstrate useful degradation even under conditions of extreme contamination.
• the oxidation of TCE by mineral phases common in soils, such as manganese dioxide or ferric oxide, can occur in the absence of dissolved oxygen.
• d-Mn ⁇ 2 very well-crystallized mineral with very low specific surface area was used.
• d-Mn ⁇ 2 very well-crystallized mineral with very low specific surface area was used.
• the soil mineral Mn ⁇ 2 can oxidize TCE, and produced benign products (C ⁇ 2, Cl- anion and Mn+2 cation).
• the heterogeneous reaction is limited by the surface area of oxide mineral present and by the rates of the various surface chemical processes involved in the coupled oxidation-reduction reaction, therefor, the overall rate of TCE oxidation can be slower than that achieved in homogeneous aqueous phase reaction involving dissolved oxygen in solution.
• thermodynamic data are, however, required for designing strategies for the thermal remediation of these compounds.
• the experimental and analytical approach that was used and the manner in which thermodynamic quantities are calculated from liquid- liquid solubility measurements, are described in Geochim. Cosmochim. Acta.. 59:2443-2448 (1995). By making mutual solubility measurements values for the Henry's Law constant as a function of temperature and pressure can also be calculated.
• thermodynamic properties ⁇ Gsoln free energy of solution
• ⁇ Hsoln enthalpy of solution
• ⁇ S S oln entropy of solution
• the amount of contaminant that can be destroyed by this process is determined by the oxygen demand for that compound, and the oxygen solubility in water at the reaction conditions.
• Figure 9 shows the relative oxygen demand for several typical contaminants. Chlorinated compounds such as PCE require very little oxygen to be converted entirely to mineral components H2O, C ⁇ 2/ and Cl" ion. Only 0.19 grams of oxygen per gram of PCE are required. Alternatively for typical gasoline (represented by n- heptane) over 3.5 grams of oxygen are required per gram of contaminant. A typical, well-oxygenated ground water contains 4 parts per million of oxygen.
• Figure 10 shows the amount of oxygen that can be achieved in water which is heated, and is thus in equilibrium with steam.
• Air-saturated water contains about 1/5 as much oxygen as that saturated with pure oxygen gas.
• the solubility of oxygen decreases slightly to a minimum at 100 C of 25 ppm. Above that point, much more oxygen can be held in the water, because of the applied pressure from steam.
• Figure 10 shows the limits of how much oxygen can be obtained through addition of air or oxygen gas with steam. In cases where even this amount is insufficient, such as large amounts of free organic liquids, multiple injections of oxygen-saturated steam may be made, sequentially destroying portions of the contaminant, similar to the experimental process described in Table 1.
• the utility of this invention stems from the finding that in situ hydrous pyrolysis/oxidation can convert harmful and toxic hydrocarbon contaminants, such as chlorinated hydrocarbons and fuel hydrocarbons, into benign products.
• the method is particularly useful as a follow-up to and complements other primary remediation techniques.
• the in situ hydrous pyrolysis/oxidation process of the invention provides several advantages over any other method previously employed. First, it is compatible with the temperatures produced during steam stripping or Joule heating and therefore offers a technology that is useful and can be applied to any site where steam or electrical heating is utilized or with other primary remediation techniques. Second, the invention does not require any special equipment other than the one used for DUS as long as the high temperatures is present and oxygen can be introduced. Third, the lifetime of the hydrous pyrolysis/oxidation process is extended over the period of time over which the soils and sediments remain at elevated temperatures. Fourth, optimal conditions for degradation of hydrocarbon contaminants can be easily induced or improved by introducing steam or using electrical heating to fine tune subsurface temperature regimes.
• the overall rate of contaminant degradation may be set and controlled by addition of oxygen or air or degradation catalysts.
• the invention is practical, inexpensive, versatile and useful for a large-scale field remediation or for small industrial leaks or spills.
• more than half of the cost removal of the currently existing remediation techniques is for surface treatment facilities, while in the current invention, surface treatment is a minimal aspect of even the largest scale cleanups.
• This example describes a field treatment using the process of the invention for degradation of residual tri chloroethy lene in combination with the primary treatment methods: dynamic underground stripping and biofilter.
• a huff-and-puff treatment is utilized as the prime treatment method for degradation of TCE according to Figure 1.
• the primary treatment is followed by hydrous pyrolysis/oxidation. In this system, only one well is used. Oxygen is mixed into the steam. As the steam front proceeds into the formation, at temperature approximately 140°C, all TCE encountered is oxidized and converted to carbon dioxide and chloride. After a small steam zone is established, steam pressure is stopped, and the ground water returns to the well bore through the new-heated-and oxygenated steam zone. TCE in this water is also oxidized. Steam is then turned on once more and a slightly larger steam zone is formed and then allowed to collapse. The cyclic steaming ensures that any water displaced by the steam injection only moves a few meters before being pulled back through the hot zone and cleaned.
• a biofilter can be installed. The water is allowed to move away from the injection site, forcing untreated water ahead of it.
• Process monitoring can be used to measure the extent of the steam zone, and the oxygen and TCE contents of the ground water.
• the process is optimized to allow the maximum rate of steam injection while obtaining full TCE destruction.
• Down-hole sensors can be used for this type of process control. Addition of oxygen can be minimized to keep down costs and to avoid any air-stripping of contaminant into the vadose zone. These process control measures can be sufficient to allow automation or semi-automation of the system.

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