Abstract:
A soil remediation apparatus for treating contaminated soil comprises an air deck unit and a remediation unit. The air deck unit comprises an enclosure with a contaminated soil inlet and a remediated soil outlet; at least one conveyor located inside the enclosure and operable to convey soil from the enclosure inlet to the enclosure outlet; and contaminated air extraction means having an inlet in fluid communication with the enclosure and an outlet, and operable to extract air from the air deck unit.

Description:
CROSS-REFERNCE TO RELATED APPLICATION 
       [0001]    The present application claims priority to Canadian Application No. 2,582,801 entitled “Contaminated Soil Remediation Apparatus,” filed Mar. 26, 2007, which is incorporated herein by reference. 
       FIELD 
       [0002]    The present invention relates generally to treatment of contaminated soil or material that contain organic compounds such as but not limited to hydrocarbons, and particularly to an apparatus for remediation of such soil or material. 
       BACKGROUND 
       [0003]    Impacted soils occurring from industrial applications and upstream and downstream oilfield activities are becoming an increasing concern. Due to a growing population, public pressure, and environmental awareness, oil companies and industrial firms are exploring quality and cost effective approaches for cleaning up contaminated sites having such impacted soils. 
         [0004]    Bioremediation of contaminated soils is a popular and affordable approach for treatment of most soil types and for most contaminates. For example, bio-remediation has been employed to treat hydrocarbon-impacted oilfield well sites. Bioremediation has become increasingly popular as technological advancements have made bioremediation cost-effective, and older treatment methods such as land-filling have fallen out of favor. 
         [0005]    While Bio-piles, land farms and introduction of bacterium have been popular approaches to bio-remediation, these passive operations are typically slow-acting and can take years to remediate a contaminated site. These operations also disadvantageously require a large amount of space as soil must be excavated, piled offsite, then have a passive or active aeration system installed thereon. 
         [0006]    Other known methods for treating contaminated soils include using an active mixing action that passes soil through air. Such bioremediation methods include use of an Allu™ bucket or windrow turners (large rototillers) to contact the contaminated soil. One disadvantage of using Allu™ buckets or rototillers is that when the soil is treated, the contaminant vapors are liberated and escape into the air. Rototillers have the further disadvantage of only being able to treat a relatively thin layer of soil at the surface of a contaminated site. Also, both approaches require relatively dry and unfrozen conditions in order to be effective. 
         [0007]    Another known method for treating contaminated soils is thermal desorption which actively heats the soil to a temperature which incinerates contaminated particles within the soil. Disadvantageously, this treatment tends to destroy the chemical components and structure of the soil, essentially turning the soil into ash thereby making the soil an unsuitable environment for organic growth. 
         [0008]    Recently public pressure and legislation such as the Alberta Energy Board&#39;s Directive 58 has created a need to provide an efficient and cost-effective solution for remediating and treating contaminated soil in such a way that does not cause contaminants in the soil to be released into the air. 
         [0009]    It is therefore desirable to provide an apparatus that solves at least some of the problems of the prior art. 
       SUMMARY 
       [0010]    It is an object of the invention to provide an apparatus for treating contaminated soils or other organic compound containing materials. 
         [0011]    According to one aspect, there is provided a soil remediation apparatus comprising a component for volatilizing contaminated soil (“Air deck unit”). The air deck unit comprises:
       (a) an enclosure with a contaminated soil inlet and a remediated soil outlet;   (b) at least one conveyor located inside the enclosure and operable to convey soil from the enclosure inlet to the enclosure outlet;   (c) air recirculation means having an inlet and outlet in fluid communication with the enclosure, and operable to extract and discharge air from and into the enclosure, thereby volatilizing contaminant vapours trapped therein; and   (d) contaminated air extraction means having an inlet in fluid communication with the enclosure and an outlet, and operable to extract air from the air deck unit.       
 
         [0016]    The soil remediation apparatus can further comprise a remedial device for remediating the extracted contaminated air. The remedial device can be a biofilter unit fluidly coupled to the outlet of the contaminated air extraction means and operable to bioremediate contaminated air received from the air deck unit. 
         [0017]    The air recirculation means can include at least one nozzle coupled to the outlet and directed at directed at the conveyor such that air is discharged at the soil, thereby aerating the soil and volatilizing contaminants trapped therein. The air recirculation means can further comprise a suction hood fluidly coupled to an opening in the enclosure, an air header fluidly coupled to the suction hood, at least one air duct fluidly coupled to the air header, at least one nozzle header fluidly coupled to the air duct, at least one nozzle fluidly coupled to the nozzle header, and a blower fluidly coupled to at least one of these components and operable to extract air from the enclosure via the suction hood and return the air back into the enclosure through the nozzle. The nozzle can be located in sufficient proximity to the conveyor that the nozzle will contact at least some soil conveyed along the conveyor such that the contacted soil is agitated and vapor trapped therein are volatilized. That is, when the conveyor is conveying the soil, the nozzle will plow through the soil. Multiple nozzles can be provided in the Air deck unit. The nozzles can be grouped in to one or more nozzle assemblies; each nozzle assembly can comprise a nozzle header fluidly coupled to the air recirculation means and multiple nozzles attached in transversely-spaced manner to the header. The nozzles can extend from the header at an angle towards the conveyor. Each nozzle assembly can be coupled to heating and/or dehumidifying means to supply heated and/or dehumidified air through the nozzles, respectively. 
         [0018]    The soil remediation apparatus can further comprise a heating circuit located inside the enclosure and operable to heat the soil conveyed along the conveyor such that vapors trapped in the soil are volatilized. 
         [0019]    The air deck unit can also comprise multiple conveyors arranged in a vertically spaced and stacked manner. Each conveyor is in soil communication with adjacent conveyors. The conveyors can be operated so that soil is deposited from one conveyor to another, wherein the depositing agitates the soil thereby volatilizing vapors trapped in the soil. 
         [0020]    The contaminated air extraction means can comprise a suction hood in fluid communication with an opening in the enclosure, a blower in fluid communication with the suction hood and operable to suck contaminated air through the opening and out of the outlet in the contaminated air extraction means. 
         [0021]    Alternatively, a single blower can be provided to extract air by the air extraction means, and to recirculate air by the air recirculation means. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0022]      FIG. 1  is a schematic top plan view of the soil remediation apparatus according to one embodiment. 
           [0023]      FIG. 2  is a schematic side elevation view of an Air deck unit of the soil remediation apparatus. 
           [0024]      FIG. 3  is a schematic cutaway side elevation view of the Air deck unit. 
           [0025]      FIG. 4  is a schematic cutaway rear end view of an embodiment of the Air deck unit. 
           [0026]      FIG. 5  is a schematic detailed view of the interface between an air nozzle and a conveyor of the soil remediation apparatus. 
           [0027]      FIG. 6  is a schematic perspective view of the soil remediation apparatus. 
           [0028]      FIG. 7  is a cutaway side elevation view of certain components of the Air deck unit according to an alternative embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    According to one embodiment, a soil remediation apparatus is provided for treating contaminated soils and other organic compound containing material (hereinafter collectively referred to as “contaminated soil”). The apparatus generally comprises a component for volatilizing contaminants from the contaminated soil (“Air deck unit”) and a biofilter unit or other remedial device which remediates volatilized contaminant vapors received from the Air deck unit. 
         [0030]    In the context of this description, the term “soil” includes but is not limited to sand, silt, clay, peat, organic material and blends thereof. 
         [0031]    The term “contaminants” includes but is not limited to light end hydrocarbons, and can for example also refer to hydrocarbons of all phases in the C1-C40 range. 
       Air Deck Unit 
       [0032]    Referring to in  FIGS. 1 to 4  and  6  the air deck unit of the soil remediation apparatus is referenced by numeral  10  and comprises an enclosure  11  and components therein for volatilizing contaminated soil. Contaminated soil is loaded into the air deck unit  10  through a hopper  26  located at the top front end of the enclosure  11 . The hopper  26  directs the contaminated soil onto the first of three vertically stacked and spaced conveyors  36 ( a )-( c ). As the contaminated soil moves along the three conveyors  36 ( a )-( c ), contaminant vapors trapped in the soil are volatilized. Volatilization is caused by the exposure of the soil to air while traveling on the conveyors  36 ( a )-( c ), aeration, and agitation. Alternatively, the air deck unit  10  can be provided with a different number of conveyors within the scope of the invention. Optionally, the contaminated soil can be heated inside the air deck unit  10  to promote volatilization. 
         [0033]    In the context of this application, “aerate” means to blow air at the soil, and “agitate” means to move the soil. 
         [0034]    The air deck unit  10  is particularly suited for treating soil contaminated with hydrocarbon contaminants. Such contaminants generally exist in an unstable bond with the soil, and during transportation along the conveyor belts  36 , clods in the soil are broken apart, thereby breaking the hydrocarbon bonds and releasing the hydrocarbons as a vapor. These volatilized contaminants are released into and mix with the air contained within the enclosure  11 . 
         [0035]    The following operations all contribute to the volatilization of the contaminated soils: (1) exposure of the soil to air while spread out and traveling along each conveyor belt, (2) movement of the soil from one conveyor belt to another (agitation), (2) physical contact with the nozzles (agitation), (3) blowing air through nozzles at the soil (aeration), and (4) heating by hot blown air or by other heating means within the enclosure  11 . 
         [0036]    The enclosure  11  comprises a frame  17 , and roof and side panels  12  covering the frame  17  such that an enclosure is formed. The frame  17  includes lateral structural supports  18  that span the width of the frame  17  and provide structural support as well as a location for mounting components within the enclosure  11 . The enclosure  11  does not have a structural floor, as the air inside the unit  10  is prevented from escaping through the bottom of the enclosure  11  by the top or upper portion of the bottom conveyor  36 ( c ) and the side skirts  48  that are mounted to the inside of the enclosure  11  and extend down to contact the third conveyor  36 ( c ). 
         [0037]    The enclosure  11  formed by the panels  12  impedes the volatilized contaminants from diffusing into the atmosphere. The volatilized contaminants are instead sucked out of the enclosure  11  by an extracted air blower  32 . The contaminated air is then bioremediated by the Biofilter unit, which is referenced as numeral  52  in these Figures. The enclosure  11  does not need to be air-tight. However, the enclosure  11  should be constructed so that when the extracted air blower  32  is operating, substantially all of the volatilized contaminant vapors is prevented from escaping into the environment. 
         [0038]    A blower skid  34  is mounted on top of the enclosure  11  and comprises a structural steel frame that is held in position on the housing  10  by vertical stops on its sides and ends of the roof panel  12 . The extracted air blower  32  is mounted to the frame, as well as a recirculation air blower  30 , and suction hoods  14 ,  16  through which air is respectively extracted by the blowers  30 ,  32 . The suction hoods  14 ,  16  are respectively mounted over openings in the roof sheathing  12  when the skid  34  is in place. The skid  34  is removable from the rest of the air deck unit  10 , which is particularly useful to reduce the height of the air deck unit  10  during transport. Removal is facilitated by lift hooks that form part of the steel frame of the skid  34 . The interface between the suction hoods  14 ,  16  and the roof  12  openings are sealed with compression neoprene gaskets (not shown) as is known to persons skilled in the art. The force necessary to seal the gaskets is supplied by the weight of the skid  34 . The skid  34  further incorporates walkways and handrails (not shown) to facilitate access to the blowers  30 ,  32  for service and repair. 
         [0039]    The skid  34  also includes a recirculation air header  38  which is coupled at an inlet end to the exhaust end of the recirculation air blower  30 . A part of the header  38  hangs over one side of the enclosure  11  and has multiple air ducts  40  which extend downwards from the header  38 . Each air duct  40  has a discharge end which mates with corresponding openings in the side of the enclosure  11 . These openings are coupled to air nozzle headers  42  which comprise nozzles  44  aimed at the top surface of the second and third conveyors  36 ( b ) and ( c ). In operation, the recirculation air blower  30  extracts air from the enclosure  11  through the suction hood  14 , and discharges the air into the recirculation air header  38 , which then directs the air back into the enclosure  11  through the air ducts  40 , the air nozzle headers  42 , and then through the air nozzles  44  and into the contaminated soil being transported on the conveyor belts  36 ( b ) and ( c ). The blown air serves to aerate the soil and volatilize the contaminants trapped therein. 
         [0040]    The recirculation air blower  30  in this embodiment utilizes an explosion-proof electric motor with a capacity of up to 25,000 ft 3 /min, with a nominal capacity of approximately 15,000 ft 3 /min. This capacity is suitable for recirculating air within the housing volume, which in this embodiment is approximately 2400 ft 3  for an empty Air deck unit  10  (this volume would be reduced by an estimated volume of the soil of 165-220 ft 3  when the unit  10  is operating). The blower capacity can of course be adjusted for different housing volumes and for different factors. Such factors to be considered when selecting the capacity of the blowers  30  include the concentration of contaminants in the soil and the moisture content of the soil. 
         [0041]    The extracted air blower  32  typically comprises a motorized explosion proof blower as is known in the art. A suitable such blower is a 10 HP blower manufactured by Twin City Fan. For this embodiment of the invention, an air exchange rate of between 1800 ft 3 /min and 3000 ft 3 /min has been found to be suitable. Of course, the capacity of the extracted air blower  32  can be adjusted for different housing volumes and different factors. The extracted air blower  32  can be further equipped with a variable frequency drive that controls blower speed and, consequently, rate of output. The output of the extracted air blower  32  can be controlled to vary with the mass quantity of the Biofilter unit  52  and the desired retention time of the volatilized contaminants within the Biofilter  52 . In other words, the blower output can be controlled to provide suitable retention time of the contaminated air within the Biofilter unit  52 ; the blower output can also be adjusted to operate with different remedial devices. 
         [0042]    The recirculation air header  38  is mounted to the exterior of the enclosure  11 . Alternatively, it can be supported by structural members (not shown) attached to the blower skid  34 . The air header  38  is sized such that the backpressure in the air header  38  is minimized. 
         [0043]    Referring particularly to  FIG. 2 , air ducts  40  are directly connected to the air header  38  and extend downwards on the outside of the enclosure  11 . The nozzle headers  42  extend transversely across the inside of the enclosure  11  and penetrate the side panel of the enclosure  11  to meet with the discharge ends of the air ducts  40 . The air ducts  40  channel recirculated air from the air header  38  to the air nozzle headers  42 . Optionally, the air ducts  40  further comprise valves  43 . The valves  43  are typically ¼ turn butterfly valves, are sized to minimize backpressure, are placed in each individual air duct  40  and allow the volume of air that reaches each air nozzle header  42  to be regulated. 
         [0044]    The air nozzle headers  42  connect the air ducts  40  to air nozzles  44  and serve a number of purposes. First, the air nozzle headers  42  channel recirculated air from the air ducts  40  to the air nozzles  44 . Additionally, the air nozzle headers  42  can be used to support optional heating pipes  24  (shown in  FIG. 8 ). Also, the headers  42  span the entire width of the interior of the enclosure  11  and are attached to the frame extending along the inside of side panels  12  thereby providing additional structural support for the enclosure  11 . 
         [0045]    Referring now to  FIGS. 3 to 5 , multiple air nozzles  44  are made of metal pipe and are attached to each air header  42  in a spaced array to form a nozzle assembly. In this embodiment, there are provided six nozzle assemblies each having an air header  42  with three laterally spaced nozzles  44 . The nozzles assemblies are spaced along the bottom two conveyors  36 ( b ), ( c ). However, a different number of header assemblies and a different number of nozzles  44  per header  42  can be selected at the preference of the designer and depending on the properties of the soil to be treated. For example, when treating sand, a first header  42  can contain five spaced nozzles  44 , the next downstream header  42  can contain six spaced nozzles  44 , and the next downstream header  42  can contain five spaced nozzles. The nozzles  44  can be staggered to move the sand and expose as much sand as possible to the recirculated air. 
         [0046]    The air nozzles  44  blow air into the soil to aerate the soil, which helps to volatilize the contaminants trapped therein. The nozzles  44  also are positioned to plow the soil as it travels along the conveyors  36 ( b ), ( c ), thereby agitating the soil to help volatilize the contaminants trapped therein. 
         [0047]    As shown in  FIG. 5 , air nozzles  44  are connected to the nozzle headers  42  by means of a flanged joint  41  so as to facilitate quick replacement when necessary. The nozzles  44  extend from the header  42  at an angle towards the conveyor  36 ( b ), ( c ). This angle, the shape and sizing of the nozzles  44 , the spacing between the distal end of the nozzles  44  and the conveyor  36 ( b ), ( c ), and the lateral spacing between nozzles  44  are selected to ensure that the nozzles  44  contact enough soil to cause sufficient aeration but not cause the soil to build up and clog up at each header. In this embodiment, the nozzles  44  have equal lateral spacing; however other spacing patterns, nozzle end treatments, nozzle angle and other nozzle parameters can be varied within the scope of the invention. Also in this embodiment, each nozzle  44  is a metal pipe with a 2″ diameter opening (2⅜″ outside diameter) mounted at 45 degrees to the horizontal. The end of each nozzle  44  terminates at an angle slightly greater than 45 degrees such that the leading edge of the pipe is slightly closer to the conveyor surface than the trailing edge. In this embodiment, there is a ½″ clearance between the nozzle leading edge and the conveyor surface, and ¾ to 1″ clearance between the nozzle trailing edge and the conveyor surface. This configuration reduces the tendency of soil from entering into the nozzle opening and clogging the nozzle. 
         [0048]    The conveyors  36 ( a )-( c ) are installed on sliding support structures such that they can be easily removed from the apparatus  10  for cleaning and repair. The conveyors  36 ( a )-( c ) are powered by hydraulic, variable speed motors (not shown). Typically, the motors used are low speed/high torque variable speed motors, as are well known in the art. Each conveyor  36 ( b )-( c ) has a belt with a width that spans substantially the width of the enclosure  11 ; the belt width can be varied at the preference of the designer. Optionally, the conveyor units  36  are corrugated to enhance retention of soil during conveyor motion. 
         [0049]    Conveyor skirts  48  are installed along the longitudinal edges of the conveyor units  36 ( a )-( c ). The conveyor skirts  48  are made of strips of rubber and metal as is well known in the art. The conveyor skirts  48  serve to help prevent soil from falling off the edges of the conveyor units  36 ( a )-( c ). Also, the conveyor skirts  48  prevent recirculated air from escaping through the gap between the conveyor units  36  and the side of the enclosure  11 . This increases the contact between the recirculated air and the contaminated soil, and consequently increases contaminant volatilization. The skirts  48  also help to seal each conveyor to the enclosure  11 , thus forcing the recirculated air to travel the full length of the conveyor back to the suction hood  14 . Without the skirts  48 , some of the recirculated air could travel vertically along the enclosure  11  body back to the suction hood  14 , thus degrading the aeration process. 
       Air Deck Unit Operation 
       [0050]    In operation, the soil remediation apparatus is located near a site where contaminated soil is to be treated. As the soil is treated ex-situ by the apparatus, a loader (not shown) is used to excavate the contaminated soil and deliver it to the Air deck unit  10 . The loader drops the soil into the hopper  26 , which directs the soil on to the topmost conveyor unit  36 ( a ) (the first conveyor unit”). The hopper  26  spans the full internal width of the enclosure  11  and adds to the soil storage capacity of the apparatus  10 . This allows the loader to continuously feed contaminated soil into the apparatus  10 . The first conveyor unit  36 ( a ) transports the contaminated soil longitudinally through the enclosure  11 . When the soil is deposited onto the first conveyor unit  36 ( a ), the soil spreads out onto the conveyor&#39;s surface, thereby exposing more soil to air while inside the enclosure  11 ; such exposure increases the air-soil interface thereby increasing the rate of volatilization while the soil travels on the conveyor  36 ( a ). A hydraulically controlled feed gate  28  is positioned above the first conveyor unit  36 ( a ) near the hopper  26  and controls the depth of contaminated soil that is allowed to travel along the conveyor units  36 . The hopper  26  is suitable for fine grained solids that do not contain large aggregates and/or sandy materials and/or silty materials. Processing of materials containing any large aggregates would be accomplished by pre-screening with a deck type screener that&#39;s common in the aggregate processing industry or by fitting either a “tipping grizzly” or “grizzly bars” to the top of the hopper to prevent large aggregates from entering the Air-Deck. Such pre-screen equipment is commonly used equipment that is commercially available from numerous suppliers. 
         [0051]    While the contaminated soil travels along the conveyor units  36 ( a )-( c ), it comes into contact with recirculated air, which helps to dry out the contaminated soil and volatilize the soil&#39;s contaminants. Drying the soil makes it easier for the air nozzles  44  to break the soil apart. The soil falls off the end of the first conveyor unit  36  and lands on the middle conveyor unit  36 ( b ) (the “second conveyor unit”). The second conveyor unit  36 ( b ) runs in the opposite direction as the first conveyor unit  36 ( a ) and is positioned such that it catches soil that falls off the end of the first conveyor unit  36 ( a ). While being transported by the second conveyor unit  36 ( b ), the soil comes into contact with the first set of nozzle assemblies. As described above, the air nozzles  44  plow through the soil thereby agitating the soil and helping to volatize contaminants trapped therein and to break apart lumps of soil. Also, the air blown through the nozzles aerate the soil and also help in the volatilization process. Optionally, the air can be heated and dried to further enhance the volatilization process. Optionally but not shown, the air can be heated and/or dehumidified by heater(s) and dehumidifier(s). 
         [0052]    At the end of the second conveyor unit  36 ( b ), the soil again drops to the bottommost conveyor unit  36 ( c ) (the “third conveyor unit”), which operates in the same direction as first conveyor unit  36 ( a ) and is positioned to catch all the soil that falls off the end of the second conveyor unit  36 ( b ). As on second conveyor unit  36 ( b ), the soil is exposed to recirculated air and is aerated and agitated by the air nozzles  44  in each nozzles assembly. After the soil falls off the end of the third conveyor unit  36 ( c ), one pass through the apparatus  10  is complete. The remediated soil is discharged from the air deck unit  10  through an remediated soil outlet  70  at the rear of the enclosure  11 , and is deposited in a pile at the end of the third conveyor unit  36 ( c ). If necessary, the discharged soil can be returned to the apparatus  10  for further treatment if further remediation is required. 
         [0053]    Referring to  FIG. 7 , a heating circuit  24  can be optionally placed within the enclosure  11  to supply heat for volatilizing the contaminated soil. In this embodiment, the heating circuit comprises heating fluid pipes  24  supported by the structural supports  18  and which extend longitudinally within the enclosure  11 . Alternatively or additional, the heating fluid pipes  24  can extend transversely between the sides of the enclosure  11  (not shown). Heating fluid can be hot water or steam or another heating fluid as known in the art, and is supplied to the pipes  24  by a heating fluid source such a boiler (not shown). Optionally, the temperature within the enclosure  11  may be controlled by thermostat control system (not shown). 
         [0054]    Heat improves the functionality of the apparatus  10  in a number of ways. First, heat enhances volatilization of soil contaminants. Liquids have a tendency to evaporate to a gaseous form, and all gases have a tendency to condensate back to a liquid; the addition of heat trends to assist in the evaporation of a liquid and cooling tends to assist with condensation of a gas. Second, the heating circuit  24  enables the apparatus  10  to be used in cold climates or during cold seasons. Third, the heating tubes  24  warm the contaminated air that is extracted from the enclosure  11 , which aids in bioremediating the contaminated air. 
         [0055]    Referring now to  FIGS. 2 to 4 , the apparatus  10  may also comprise stabilizing jacks  46 , support legs  20 , wheels  21 , and an axle support frame  22 . The stabilizing jacks  46  are hydraulically operated and raise the apparatus  10  for loading if the apparatus  10  is not equipped with axles  22  for transport. The support legs  20  are mounted to the exterior of the frame of the enclosure  11  and are designed to support the increased weight of the apparatus  10  when it is filled with contaminated soil. The wheels  21  may be used to increase the mobility of the apparatus  10  in transporting it from various locations on the same remediation site or from site-to-site. The axle support frame  22  can be fabricated to accommodate either a conventional tandem or a Tridem axle setup. 
         [0056]    The apparatus  10  may include a nitrogen flood system (not shown), which automatically releases nitrogen gas into the enclosure  11  if the concentration of volatilized contaminants increases beyond a specified Lower Explosive Level. The nitrogen gas is inert and safely dilutes the volatilized contaminants such that their concentration declines below the Lower Explosive Level and, consequently, makes it so that the contaminants are no longer at risk for explosion. A large quantity of nitrogen gas is stored in a nitrogen storage header under pressure. Connected to this supply of nitrogen gas are injection tubes that extend to various locations within the enclosure  11 . 
       Biofilter Unit 
       [0057]    Contaminated air is extracted by the extracted air blower  32  and exits the enclosure  11  through the suction hood  16 . The contaminated air travels through a conduit  45  to the biofilter unit  52  for bioremediation. The biofilter unit  52  contains biomass selected to bioremediate the volatilized contaminants that are fed into the biofilter  52  by the extracted air blower  32 . The biomass includes a blend of silage, compost, wood chips and fertilizer material. A suitable biofilter container structure and biomass composition are commercially available, and thus are not described in detail here. 
         [0058]    While  FIG. 1  shows a single biofilter unit  52 , additional biofilter units (not shown) can be provided depending on the bioremediation capacity required. When multiple biofilter containers are required, the conduit downstream of the extracted air blower  32  can be branched to each of the biofilter units. 
         [0059]    While a particular embodiment of the present invention has been described in the foregoing, it is to be understood that other embodiments are possible within the scope of the invention and are intended to be included herein. It will be clear to any person skilled in the art that modifications of and adjustments to this invention, not shown, are possible without departing from the spirit of the invention as demonstrated through the exemplary embodiment. The invention is therefore to be considered limited solely by the scope of the appended claims.