WO2011095647A1 - Apparatus for bioremediation of soil contaminated with organic compounds - Google Patents

Abstract

This invention relates to an apparatus for the bioremediation of soil contaminated with organic compounds, preferably meant for portable use, comprising a bioreactor tank in which the soil is placed and characterized in that the gases injected during the process by means of strong, forced aeration, having a homogeneous distribution of oxygen are recirculated, such that the tainted gas is discharged to the outside after treatment inside same apparatus. The apparatus also causes the leachates generated in sufficiently high volume to periodically recirculate in order to obtain a high humidity content and a homogeneous distribution of the humidity, the nutrients and the micro-organisms. In order to counteract resistance to oxygen diffusion owing to the soil's high humidity, high-intensity injections or recirculation are used. The combination of both types of recirculation optimizes biodegradation performance and conditions with a minimal environmental impact.

Description

 EQUIPMENT FOR BIORREMEDIATE SOILS CONTAMINATED WITH ORGANIC COMPOUNDS

Object of the Invention

The invention corresponds to the technical sector of soil recovery processes contaminated by organic compounds, specifically aerobic biological degradation processes.

 Organic soil pollutants are very variable in nature (oils, oils, gasoline, phytosanitary, etc.) and their presence in the soil is due to various human activities (industry, transport, agriculture, etc.).

 Hydrocarbons are part of the most common pollutants in the soil due to the increased use of petroleum products worldwide. These pollutants are a significant risk to human health and to the environment. The development of regulations on decontamination and recovery of contaminated soils requires the development of processes that are more efficient and less expensive.

Background of the Invention

Bioremediation is one of the most common remediation processes of this type of contamination. Bioremediation techniques can be in situ or ex situ. In situ techniques include bioairration, improved biodegradation, phytoremediation, injection of compressed air and natural attenuation.

If, due to site conditions, remediation cannot be carried out on site or if you simply want to optimize the technique, you can use ex situ techniques alternatives such as composting, landfarming and biopiles. These techniques can be performed on-site, at the site where it is on the ground to be treated, or off-site, at facilities located outside it. When possible, contaminated soils are usually treated more effectively if biological treatment is performed ex-situ (Alexander, M., 1999; Biodegradation and Bioremediation; 2nd ed, Academic Press, San Diego, California), since Addition of necessary nutrients such as nitrogen and phosphorus, moisture, surfactants, bacteria, and oxygen, as well as the monitoring of the parameters that control the evolution of the process, can be performed more easily than in situ.

 One of the most studied techniques, within the biological process of soil remediation are biopiles (Von Fahnestock, FM; Wickramanayake, GB; Kratzke, RJ; Major, WR; 1997; Biopile design, operation and maintenance handbook for treating hydrocarbon-contaminated soils; United States: Battelle Press). Like the common one of bioremediation processes, the basic principle of action of biopiles is the transformation of biodegradable pollutants from the soil into harmless products, taking advantage of the action of certain microorganisms present in the soil under controlled conditions, with the particularity of that the soil is excavated, conditioned and placed in piles.

If the biopile system develops outdoors, the significant presence of volatile organic compounds and their emission into the atmosphere without prior purification, may have a negligible environmental impact. On the other hand, the development of these techniques requires a large amount of space, since the soil after being extracted must be stacked in a specific area for it. In order to optimize the applicability of this technology it is necessary to introduce some improvements to the system.

 In order to improve the biopile technique, bioreactor technology is one of the most appropriate since it allows the controlled and efficient combination of chemical, physical and biological processes, which improve and accelerate biodegradation, in the same way that allows to control emissions process contaminants (Riser-Roberts, E. (1998). Remediation of petroleum contaminated soils. Lewis Publishers). As an example of the above are the following reactors:

 The Institute for Ecology of Industrial Areas of Poland (Institute of Ecology for Industrial Areas) in its document Production-Scale Implementation of Petroleum Contaminated Soils Bioreactor (2000) designs, builds and starts up a closed reactor for the bioremediation of small volumes of contaminated soil Air is injected through the lower area of the reactor, in which the temperature, oxygen content and soil moisture are measured continuously. The experiment lasts for 97 days in which the gas outlet current is not treated. The decrease in HTP (Total Petroleum Hydrocarbons) is approximately 50% of the initial value.

Berry, C. (2005), Bioremediation of Petroleum and Radiological Contaminated Soil Using an Ex Situ Bioreactor. PhD thesis Georgia Institute of Technology, developed a reactor to treat soils contaminated by hydrocarbons and radiation through a system based on bioairration. The concentration of oxygen in the soil, humidity and temperature are determining parameters for this process that lasts for 22 months. The decrease in HTP is 99% of the initial value.

 The Naval Facilities Engineering Service Center (NFESC) (1998) designs the technique called "Biocell". It is a bioremediation system in a closed container where aerobic microorganisms carry out the elimination of hydrocarbons present in the soil. In this system the volatile organic compounds generated during the process are treated with an active carbon column.

 US 5249368 is known as a transportable apparatus for carrying out the biological remediation of small amounts of contaminated soil. The objective of this apparatus is to decontaminate small amounts of soil (less than 1000 Y3 = 765 m3) in places where there is not much space; the leachates generated in said process are not recirculated inside the reactor and require treatment; Another disadvantage of this system is that the exhaust gases from the reactor are expelled into the atmosphere.

Patent document US 4962034 publishes a procedure for the biological treatment of contaminated soils in a fixed concrete reactor. The objective of the invention is to control the migration of pollution both to the atmosphere and to the ground, by using a closed concrete reactor claimed by the patent two possible systems of use. In System 1, the soil is raked by a mobile upper structure to mix and oxygenate the soil, where the air mixed with volatile organic compounds itself is not recirculated from the system to be treated, but these are returned to the soil by means of a spray system ; when the liquid is pulverized, it drags volatile contaminants that accumulate in the upper area of the reactor and reintroduces them to the ground to be treated. The leachates generated are collected to be subsequently recirculated into the reactor by spraying. In system 2, the soil is oxygenated by forced aeration, the supplied air is recirculated to be treated inside the soil. The amount of water added is the minimum to maintain the bioremediation process, so the generation of leachate is not expected, and therefore, the recirculation of these is not carried out again to the system. It is a fixed reactor whose construction must be carried out by civil works, the space requirements for its construction being considerable and its transport possibilities unthinkable. The schemes of both systems suggest that both processes are designed to work with small thicknesses of land, of the order of a few tens of centimeters, which requires greater surface requirements to treat the same volume of soil.

 A reactor for remediation of contaminated soils using a specialized inoculum is known from KR 4068638-A. This reactor recirculates the leachate generated in the process according to the needs of soil moisture.

DESCRIPTION OF THE INVENTION The present invention aims to degrade soils contaminated by organic compounds by means of ex situ-on-site technology with aerobic bioreactor that improves the reference technique (biopiles). In the In the described biopiles and in the reactors described, a limited humidity is maintained throughout the biodegradation process and less than the field capacity in order to facilitate the passage of oxygen through the pores. Specifically, when the value of this humidity decreases to values that hinder biodegradation, it is increased by adding water or recirculation of the leachates stored since the beginning of the operation or generated in rain events if the biopile is not covered.

In the present invention a large amount of water is provided at the beginning, at the initial moment of starting the biodegradation process, in order to generate a sufficient volume of leachate that is recirculated with high periodicity. The objectives are to maintain high humidity in the soil that facilitates biodegradation (the microorganisms act in the aqueous phase) and that the leachate behaves as a distribution and homogenizing agent for said microorganisms and nutrients in the soil without the need for mechanical mixing of the soil. same.

On the other hand, in the present invention the aeration is done at very high instantaneous flow rates with the intention of counteracting the resistance that the high water content opposes the transport of oxygen in the soil and thus improving its distribution. Organic compounds that could potentially be volatized as a result of these high aeration flow rates do not migrate into the atmosphere thanks to the built-in gas recirculation system that reduces or eliminates the need for secondary treatment of this gas stream. All of the above, in a transportable bioreactor and adaptable to the specific needs of each case. In order to optimize biodegradation conditions, treatment yields and at the same time decrease their costs, the following objectives have been set:

 Reduce the time required for bioremediation and achieve a homogeneous degradation in the entire soil mass.

 Improve the degree of modularity and transportability of the reactors.

 Minimize the environmental impact.

 The present invention is based on the knowledge of the processes of biological degradation, which is carried out in a closed bioreactor in which, by optimizing the operating parameters, the aerobic biodegradation processes are accelerated. For this, the design includes the characteristics explained below in comparison with the operational parameters of the biopile technology:

 In biopiles aeration is low to reduce moisture loss and volatile emission. This can facilitate the formation of preferential pathways, the heterogeneity of oxygenation with the consequent heterogeneity of degradation and the creation of anoxic / anaerobic zones both at the macropore level and at the micropore level.

Against the foregoing, the present invention is characterized by the use of forced aeration of intensity, that is, instantaneous high aeration velocities from the lower zone of the bioreactor that allow a homogeneous spatial distribution of oxygen. In this way the formation of preferential paths is minimized and homogeneity is achieved in the oxygenation (at the macropore and micropore levels due to the internal aerodynamics caused).

 This invention is distinguished by the incorporation of a closed gas recirculation system with an instantaneous aeration rate, the value of which is given depending on the type of soil. This generates a better distribution and homogenization of the air in the soil that will result in an increase in the degradation rate as a consequence of the decrease in the probability of finding anaerobic zones, that is, reducing the possibility that oxygen is a limiting factor. for bacterial growth.

 Excessive air flow favors the rapid drying of the soil in addition to desorption and entrainment of gas phase contamination. This is solved with the recirculation of the gases that is done intermittently, commanded by the concentration of oxygen in the bioreactor soil. In this way, the oxygen incorporated into the reactor is maximized.

 Thanks to this system, entrained volatile organic compounds are re-incorporated into the bioreactor to be degraded by microorganisms. During the biodegradation an oxygen consumption is produced, until at a certain moment the oxygen content of the gas that circulates through the bioreactor reaches a certain minimum value; To compensate for this, external air is dosed into the system and gas is produced from it. In this way the stoichiometry of the process is kept in balance.

The minimum necessary purge of the outgoing bioreactor gases is carried out after the treatment of said gases, either with activated carbon or other purification system, to avoid the emission of pollutants into the atmosphere.

 Within the meaning of the present invention, "external oxygen supply" means the supply of atmospheric air or pure oxygen to the reactor; "gas recirculation" the action of recirculating gases whose oxygen content is less than ambient air; and as "gas purge" the exit of gases from the reactor that is carried out during the moments of "external oxygen supply".

 The present invention achieves maximum utilization of oxygen by means of a closed aeration system, which allows to control the needs of incorporation of external oxygen. To reduce the energy consumption and the volume of gas to be treated, the external oxygen supply and gas recirculation pumps are only put into operation when the oxygen concentration in the bioreactor falls below a certain value, and they stop when it is reached. a sufficient concentration for aerobic biodegradation. Thanks to the gas recirculation system, the gases left by the bioreactor will have lower concentrations of volatile organic pollutants; therefore, its treatment can be carried out with a simple method of purification.

Unlike some types of biopiles in which the gases are emitted without control to the atmosphere, in the present invention the aeration in closed circuit is proposed by recirculation of the injected air. This causes a biological treatment of the volatile organic compounds present in the recirculated gases by passing them through the column of the soil itself to be treated, which in the degradation phase would function as a biofilter. In a conventional biopile, the application of a strong aeration can cause the drag of soil moisture with the consequent drying of the biopile and the slowdown of biodegradation. In the present invention, a closed aeration circuit is used, with a gas recirculation system and a high volume leachate recirculation system, so even if strong aerations are applied, soil moisture is maintained and, therefore, , biodegradation in optimal conditions.

 In the present invention it is necessary to incorporate oxygen into the bioremediation process, which can be by air or with pure oxygen; this requires a periodic purge of gas that in turn drags moisture. For this reason, the periodic incorporation of humidity is also considered to maintain the ideal amount of water inside. This is achieved thanks to the leachate generated in the filtration of water through the soil is recirculated inside the bioreactor.

 The present invention operates with a high level of moisture that produces permeate, carrying out the recirculation of water in order to avoid that in some area of the soil column the humidity is less than optimal.

 In the face of a possible vertical stratification of the moisture in the biopile after a timely humidification, the present invention achieves a more homogeneous distribution of the humidity vertically in the soil mass, by means of the recirculation system of the leachates produced.

Faced with a possible application of water at low flow rates that would result in the surface distribution of the water, the present invention generates an application of leachates with instantaneous flow rates. high, through a recirculation system composed of a storage tank and distribution elements that guarantee a homogeneous distribution on the surface; functions commanded by level meters located in a leachate collection tank.

 Faced with the possible loss of nutrients in biopiles due to the extraction or purge of the leachate, the present invention achieves the maintenance of the nutrient content in the soil through the recirculation of the leachate.

 This recirculation system provides a uniform distribution of nutrients and microorganisms in the soil, also allowing optimum moisture for the process.

 Faced with a possible entrainment of organic compounds through the circulating water, the recirculation distributes them vertically throughout the soil and this functions as a bacterial bed for treatment and purification.

 Faced with the possible spatial heterogeneity of microbial species in a biopile, the present invention seeks continuous re-realization and redistribution through the recirculation of leachate. Advantages of the invention.

The advantages of the described reactor, mainly due to the use of a fluid recirculation system, its transportable design and its operating procedure are:

Biodegradation of the pollutant through the increase in the rate of passage of air in the pores without increasing the amount of air to be treated. Achievement of partial degradation of the exhaust gases by treating them through the soil itself.

 Greater degree of transportability and modularity. The treatment is carried out in a reactor of dimensions adapted for road transport, and so that it is easy to increase the treatment capacity simply by increasing the number of reactors.

 Alternatively you can adopt the fixed reactor configuration.

 Faster in the beginning of sanitation operations. The reactor has the basic elements to start the treatment once the excavation proceeds, so that the time that would be necessary for the on-site installation of the necessary equipment to promote biodegradation in other techniques is minimized.

 Emission Control The treatment is carried out in a closed reactor that facilitates the collection and treatment of both liquid and gaseous emissions resulting from the bioremediation process.

 In addition to reducing the amount of emissions in the process, it also decreases the contamination of these emissions thanks to their treatment.

 Reduction of the time necessary for the start of bioremediation of contaminated soil.

 Flexibility in the location of the bioremediation process by not depending on the environmental conditions of the contaminated site.

When the external conditions of the reactor are not adequate for bioremediation, it is possible to thermally isolate the reactor tank to favor the increase of temperatures in its interior and degradation rate, by means of a jacketed thermal coating, by way of example.

 Description of the figures

 To complement the description that is being made and in order to help a better understanding of the characteristics of the invention, the present descriptive report of plans is attached showing the preferred embodiment, where, for illustrative and non-limiting purposes, it has been represented the next:

 Figure 1.- Scheme of operation of the equipment.

Figure 2.- Diagram of the operation of the bioreactor with recirculation is shown.

 Figure 3.- Scheme of operation of a conventional aerated biopile.

 The following figures show the following:

 1. Waterproof tank (bioreactor)

 2. Points for sampling

 3. Oxygen probe

 4. Moisture probe

 5. Temperature probe

 6. Signal connection module

 7. Computer with software for data storage, data processing and command of pumps and valves.

 8. External oxygen / gas recirculation pump

 9. Exhaust gas purification reactor

10. Gas recirculation pipe

 11. Exhaust gas duct

 12. Oxygen inlet duct external to the system

 13. Leachate collection tank

14. Leachate recirculation pipe 15. Leachate level meters

 16. Self-priming leachate recirculation pump

17. Leachate distribution device 18. Automatic valve for external oxygen inlet

 19. Automatic valve for purging the outlet gas

 20. Automatic valve for gas recirculation 21. False Bottom

 22. Metal grid

 23. Filter material

 24. Condensate collection tank

 25. Adding water

 26. Leachate purge

 27. Expansion Deposit

 Bomb

 M valve

 Data collection line

 Air circuit

 Water circuit - leachate

 The same references represent the same elements in Figure 3 of a conventional biopile, in this case the numbers 1 ', 2', 3 ', 4', 5 '6', T, 8 'and 9' corresponding to their corresponding Figures 1 and 2.

Preferred Embodiment of the Invention

The invention consists of a discontinuous reactor with the appropriate dimensions to allow its conventional road transport by coupling it to a tractor unit. In the reactor a treatment is carried out Biological designed for the recovery of soils contaminated by organic compounds.

 The mobility of the equipment allows its transport from one location to another; being able to adopt, alternatively, the configuration of fixed reactor.

 The bioremediation equipment consists of the following elements (although under certain conditions some of them may not be used or some other): a waterproof tank (1) resistant to corrosion constitutes the bioreactor, which contains a false bottom (21), followed of a metal grid (22), on top of which a filter material (23) is placed; a system for the recirculation of gases in the reactor equipment, cooperating in this task elements with the function of external oxygen input and other components that allow the exit of gases.

 The gas recirculation consists of a gas recirculation pipe (10) that leaves the upper part of the tank, with an automatic gas recirculation valve (20), a condensate collection tank (24) and an external oxygen supply / gas recirculation pump (8), to communicate this pipe with the bottom of the reactor at its false bottom (21).

The oxygen entering the tank (1) is carried out by means of forced aeration from the lower zone at an instantaneous high aeration rate, whose value will be determined by the type of soil. This input can be made of pure oxygen or air, and is carried out by an external oxygen supply duct (12) aided by the external oxygen / gas recirculation pump (8); this input is regulated by the automatic valve (18). The gases go outside through the duct outlet (11) after being purged in competition with the automatic valve for purging the exhaust gases (19), passing through the gas purification reactor (9) before going into the atmosphere.

 The leachate recirculation system comprises an initial supply of water that is regulated by a valve (25); the water is filtered through the soil, the liquid being named after this phase, leached; leachate distribution device (17) located in the upper area of the tank; leachate collection tank (13); self-priming leaching recirculation pump (16); condensate collection tank (24) and leachate recirculation pipe (14).

 The control of the gas recirculation system is composed of: one or several oxygen probes (3), one or several humidity probes (4), one or several temperature probes (5), a signal connection module (6 ) of the probes, and a computer with software (7) for data storage, data processing and pump control (8) and the valves that determine the recirculation of gases (18, 19, 20).

 The leachate level meters (15) are placed in the leachate collection tank (13) that control their recirculation inside the tank (1).

 The sampling points (2) are necessary in case of failure of a probe or simply to measure other parameters.

Contaminated soil, previously conditioned (addition of moisture, nutrients, sponge agents, planting of microorganisms and / or any other type of pretreatment) is introduced into the tank (1). It is placed there on the filter material (23) (it can be granular filtering material or a geotextile) which in turn is on a metal grid (22); These two elements will allow leachate drainage and optimal air distribution. As the soil is introduced, the oxygen probe (3) is placed to measure the oxygen consumption by the microorganisms, the humidity probe (4) and the temperature probe (5). The arrangement and number of probes within the reservoir (1) must be such that the information they generate is representative of the entire volume of the soil. This information, through the signal connection module (6), goes to a computer (7) that continuously records the data supplied by all probes, produces the results and operates the automatic valves (18, 19 and 20).

 Through the external oxygen / gas recirculation pump (8) air is fed to the false bottom (21); this circulates through the metal grid (22) and the filter system (23) up and through the ground, leaving the top of the tank (1) through the gas recirculation pipe (10). At this point the system can work in two ways:

Recirculating the gases: With the valves (18) and (19) closed and the valve (20) open, the gas arrives again via the pump (8) to the tank (1) through the gas recirculation pipe (10) . Gas recirculation is carried out intermittently and is controlled by the concentration of oxygen in the contaminated soil, so that when the oxygen in the ground falls below a setpoint, the gas recirculation system is activated for a sufficient time. for mixing the gas evenly in the system (soil, all of the tank and gas recirculation pipe). When after this mixing the oxygen concentration reaches critical values for degradation, that is, when new air is required to enter the system, the following work method is given.

 External oxygen inlet: With the valves (18) and (19) open and the valve (20) closed, there is a discharge of stale gas into the atmosphere through the outlet gas duct (11), previously passing through the reactor gas purification (9) consisting of a reservoir in which an adsorbent material of organic molecules is introduced, for example activated carbon, through which the gas stream is passed, the remaining organic compounds present in the gas being adsorbed , purging previously in the valve (19) for this purpose; and the external oxygen is introduced to the system through the external oxygen inlet duct (12) through the pump (8). In this way, the concentration of oxygen in the contaminated soil reaches an adequate value for biodegradation and the gas recirculation cycles begin.

 The moisture found in the gas recirculation pipe (10) condenses and goes to the condensate collection tank (24).

 The gas recirculation pipe (10) contains an expansion tank (27) in order to keep the system in depression or over pressure.

In the initial starting condition, the soil contains a humidity equal to the field capacity together with a sufficient volume of water in circulating excess to perform the recirculation of said water in the form of leachate. The application of leachate is carried out with very high instantaneous flows, which ensure the surface distribution of the same with low pooling height.

 The recirculation of the leachate generated produces the soil humidification, and is performed intermittently in a pumping of instantaneous flow, depending on the maximum volume stored in the collection tank (13), the recirculation being commanded by a timer or by the values collected by level meters (15) or by humidity probes, or by the combination of the variables and components mentioned. The leachate recirculation (14) is carried out by means of the pump (16) and its dispersion inside the bioreactor tank (1) is done from top to bottom, by means of the distribution device (17) located in the upper area of the bioreactor. The organic compounds contained in the leachate are percolating along the soil, functioning as a bacterial bed for treatment and purification.

 The leachate falls to the false bottom (21) that will present a punctual or permanent inclination that will allow its collection in the leachate collection tank (13). Said inclination can be designed on the false bottom (21) of the tank on a permanent basis, or, as in the case of the planes shown, achieve the slope only at specific times when this leachate exit function is required, by the slight elevation of the trailer where it is transported or, in the case of a fixed reactor, with a chock element that causes this position.

In case of unfavorable external climatic conditions, the bioreactor can have a heating system that can be, by gas heating system, leachate or the tank itself. Execution Example

Next, the operation of a pilot plant of the described process is described (Figure 2), comparing it with the operation of the biopile technique process, (Figure 3), with the following particularities:

 Two pilot scale models have been made up of methacrylate columns that act as deposits; column A, (Figure 2), and B, (Figure 3). Both have the same conditions of contamination, organic matter, nutrients, external temperature, etc., and only differ from each other in the aeration process and the initial humidity. Column A corresponds to a Bioreactor with Recirculation, object of the invention and column B is a Conventional Aerated Biopile. In both cases the air flow is ascending. The measurements of the columns are: diameter 200 mm and height 800 mm.

 Contaminated soil is introduced into the reactor tank (1, 1 '), columns A and B, respectively. Holes are provided on the surface of each column that are used for sampling the probes (2, 2 ').

The process control elements are introduced at the top of each column: oxygen probe (3, 3 ') _/ humidity probe (4, 4') and temperature probe (5, 5 ') ) _/ that are located inside the contaminated soil as the columns are filled. The information generated by the probes, through the signal connection module (6, 6 '), goes to a computer (7, 7') that continuously records the data supplied by all the probes, elaborates the results and triggers the various automatic valves. In column A the external oxygen / gas recirculation pump (8) introduces air through the floor through the bottom of the tank (1); This air leaves the tank at the top through the gas recirculation pipe (10). At this point the system can operate in two ways, with recirculation of gases or with the input of external oxygen, according to the parameters and operation described above.

 Leachate collection is carried out in the leachate collection tank (13). The leachate recirculation (14) is commanded by the soil probes, by means of a timer, by the level meters (15) or by a combination of the above elements, in competition with the recirculation pump (16).

 The recirculation of leachate (14) is carried out by means of the pump (16) and its distribution within the bioreactor tank (1) is done from above by means of the distribution device (17).

 In the case of column B, the aeration is performed in open circuit; an aeration pump (8 ') introduces external oxygen to the system through the lower area of the reactor tank (1') · Aeration is commanded by the concentration of oxygen in the contaminated soil; when the set oxygen minimum is reached, the external oxygen supply pump (8 ') is activated, and when it reaches the set maximum it stops. The outlet gas is treated in the gas purification reactor (9 ') before being discharged into the atmosphere. No recirculation, either of gases or leachate is carried out in this reactor.

The pumps used for the supply of external oxygen / gas recirculation (8, 8 ') in both columns They are vacuum pumps. The leachate recirculation pump (16) of column A is a peristaltic pump.

 Both columns were introduced in a room with controlled temperature and in darkness.

 The main operational data are indicated below. A soil whose dry composition was 96.4% sand and 3.6% humus was used for experimentation and was mixed with commercial diesel (initial contamination value 10000 mg / kg dry weight). The empirical formula obtained for diesel was C16H34 and its aliphatic / aromatic ratio 84/16. Before introducing it into the columns, the soil was kept in contact with the diesel in closed tanks for four months, after which an average H.T.P value of 7000 mg / kg was measured. An instantaneous aeration rate of 12.7 m / h was applied in column A and 0.44 m / h in column B. The nutrients added to the soil for both columns were nitrogen and phosphorus in a Carbon, Nitrogen, Phosphorus (C: N: P) 100: 10: 2; and the initial humidities were 15% w / w in column A and 8% w / w for column B. The daily recirculation of leachates generated in the pilot plant of the process object of invention (column A) was 75 % of total volume generated. The external working temperature for both columns remained close to 30 ° C throughout the experimentation.

 The results are shown in the Table shown below, indicating the cumulative oxygen consumption in both columns over 11 weeks of experimentation.

Curve 1 represents the cumulative oxygen consumption for column A, and curve 2 the cumulative oxygen consumption for column B. The horizontal axis represents the time in weeks and the consumption of oxygen is expressed in grams. Taking into account the stoichiometry of the reactions involved in the process, it is theoretically possible to study the evolution of degradation through the measurement of oxygen consumption (respirometric methods). Each gram of HTP (Total Petroleum Hydrocarbons) consumes 3.47 grams of oxygen in its aerobic degradation.

 Accumulated Oxygen Consumption

 5 6 7 10 12

Weeks

 ♦ Column B A Column A

Both curves (1 and 2) experience a marked increase in oxygen consumed in week 1, possibly due to the degradation of easily biodegradable organic matter (humus) through soil microorganisms. In column A, as can be seen in curve 1, oxygen consumption experiences an acceleration during weeks 2, 3, 4, 5, and 6. From there, oxygen consumption slows down and tends to stabilize at over weeks 7, 8, 9, 10 and 11 of experimentation. In the case of column B, (curve 2) the speed of consumption during weeks 2 to 6 is lower than in the previous case (column A) and remains almost constant during practically the whole period of experimentation.

 Comparing the above with the values of H.T.P. measured throughout the experiment it is observed that in week 6 the percentage of decrease in H.T.P. in column A it was 61% of the initial value, which represented approximately 90% of the decrease in TPH in the whole period of experimentation. After six weeks of experimentation, the soil in column A shows a decrease in the degradation rate, so an option to reduce treatment costs would be to remove it from the bioreactor and proceed to its treatment under less demanding control conditions. The results obtained indicate that the design and construction of the Bioreactor with Recirculation (Column A) together with the process monitoring system should provide a useful tool for the remediation of soil contaminated by organic compounds, in this case, hydrocarbons.

Claims

1.- Equipment for bioremediation of soils contaminated with organic compounds, through aerobic biodegradation, of which they work with a leachate recirculation system, this recirculation being carried out intermittently, by means of an instantaneous flow pump dispersed by means of a distribution device ( 17) located in the upper area of the bioreactor tank (1), which comprises:  a sealed tank (1),  a gas recirculation system,  external oxygen supply duct (12),  gas outlet components, the lower part of the tank (1) containing a false bottom (21), and the gas recirculation system of a gas recirculation pipe (10) coming out of the upper part of the tank (1); presenting a recirculation valve (20), a condensate collection tank (24) and an external oxygen supply pump (8); said pipe communicating with the lower part of the tank in the false bottom (21) and oxygen entering the tank by means of forced aeration from the lower area of the tank (1) at an instantaneous high aeration rate; and because the generation of the leachates is achieved with the presence in the soil of a humidity equal to the field capacity together with a volume of circulating water in excess sufficient to perform the recirculation of said water in the form of leachates; performing the application of leachate to the ground with very high instantaneous flow rates, which ensure the Leachate distribution over the entire soil surface, generating a low pooling height.  2. - Equipment for bioremediation of contaminated soils, according to claim 1, characterized in that, on top of the false bottom (21) a metal grid (22) is arranged, placing a filter material (23) on top of the grid.  3. - Equipment for bioremediation of contaminated soils, according to the preceding claims, characterized in that the gas recirculation pipe (10) has an expansion tank (27), in order to keep the system in depression or overpressure.  4. - Equipment for bioremediation of contaminated soils, according to claim 1, characterized in that both pure oxygen and air can be introduced through the oxygen supply duct to the system, cooperating a contribution pump at this inlet (8) , regulating this contribution by means of an automatic valve (18).  5. - Equipment for bioremediation of contaminated soils, according to claim 1, characterized in that the gas outlet consists of a conduit (11) that has an automatic valve (19) that purges these exhaust gases, passing afterwards by a purification reactor of these gases (9) consisting of a reservoir in which an adsorbent material of organic molecules is introduced. 6. - Equipment for bioremediation of contaminated soils, according to the preceding claims, characterized by treating the volatile organic compounds present in the gases recirculated to the system, by passing them through the soil column, which in the degradation phase operates Like a biofilter 7. - Equipment for bioremediation of contaminated soils, according to claim 1, characterized in that oxygen measuring probes (3), humidity (4) are disposed within the soil mass that is placed inside the tank (1). and temperature (5).  8. - Equipment for bioremediation of contaminated soils, according to claim 1, characterized in that the gas recirculation system is made intermittently and is commanded by the concentration of oxygen measured in the soil; when this concentration falls below a setpoint, the gas recirculation is activated for a sufficient time for mixing the gas throughout the system (soil, tank and gas recirculation pipe).  9. Equipment for bioremediation of contaminated soils, according to the preceding claim, characterized in that when, after mixing caused by the recirculation of gases, the concentration of oxygen falls below a certain level, external oxygen enters the system ( 12) by means of the input pump (8), in turn the output of a volume of gas through the outlet duct (11).  10. Equipment for bioremediation of contaminated soils, according to the preceding claims, characterized in that the data provided by the probes introduced into the soil (3, 4 and 5) are processed in a computer (7) for the operation of the pumps and valves of the gas recirculation system. 11. - Equipment for bioremediation of contaminated soils, according to claim 1, characterized in that it has an external leachate collection tank (13) to store leachates generated in the process.  12. - Equipment for bioremediation of contaminated soils, according to claim 1, characterized in that the frequency and volume of leachate recirculation is commanded by a timer or by the values collected by the level meters (15), or by the values marked by the probes, or, in a combination of the above parameters, which coordinate the operation of a pump (16).  13. - Equipment for bioremediation of contaminated soils, according to claim 1, characterized in that it can be a transportable modular reactor or be fixed in a location.  14. - Equipment for bioremediation of contaminated soils, according to claim 1, characterized by having a heating system produced by heating the gas, the leachate or the tank itself.  15. - Equipment for bioremediation of contaminated soils, according to claim 1, characterized in that the tank can be thermally insulated.