Patent Publication Number: US-2018043404-A1

Title: Site Remediation System and A Method of Remediating A Site

Description:
PRIORITY CLAIM 
     This PCT application claims priority to Australian provisional application number 2015900954 entitled “A site remediation system and a method of remediating a site” which was filed on Mar. 17, 2015, the entirety of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     This disclosure relates, generally, to the remediation of contaminated sites and, more particularly, to a site remediation system and to a method of remediating a site. 
     BACKGROUND 
     Many remediation technologies, for example, those adopted by the retail petroleum sector to remediate a filling station site, utilize extraction and treatment equipment to effect “aggressive” remediation strategies in order to remediate the site. These strategies result in high energy consumption since a key driver is a need to complete remediation work in an accelerated timeframe while often needing to comply with regulator-enforced clean-up requirements. This reactionary and high energy usage approach tends to ignore the energy impact and greenhouse gas emission associated with remediation. 
     In addition, at many sites where the bulk of the primary and secondary contaminant sources have been removed, longer timeframes may be required for close out due to the need to treat lower level contamination that may be diffuse or is less amenable to common remediation approaches. The cost and greenhouse gas impact of continuing to operate conventional approaches, such as, for example, pump-and-treat and air-sparging, at these sites can mean that any net improvement to the environment is often outweighed by the environmental impact due to energy usage of the remediation equipment. 
     Soil and groundwater remediation, although designed to remedy contamination and reduce risks to human health and/or the environment, also has the potential to cause environmental, economic and social impacts. If poorly selected, designed and implemented, remediation technologies and activities may cause greater impact than the contamination that they seek to address. The best solution, therefore, is remediation that minimizes unacceptable risks in a safe and timely manner while maximizing the overall environmental, social and economic benefits of the remediation work. 
     SUMMARY 
     In a first aspect, there is provided a site remediation system which includes 
     a liquid recirculation mechanism powered by a low energy power source, the liquid recirculation mechanism comprising
         a liquid extraction component for extracting liquid to be remediated from a substrate at the site; and   a heater component for heating the extracted liquid, in turn, to increase a subsurface temperature of the substrate upon re-injection of the heated liquid into the substrate; and       

     a bioremediation mechanism arranged downstream of the heater component of the liquid recirculation mechanism, the bioremediation mechanism comprising a liquid treatment unit for treating the heated liquid prior to re-injection of the liquid into the substrate to effect enhanced substrate bioremediation. 
     In this specification the term “low energy power source” is to be understood, unless the context clearly indicates otherwise, as a source which results in minimal greenhouse gas emissions. A non-exhaustive list of low energy power sources includes a battery powered energy source, a solar powered energy source, a wind powered energy source, or the like. Further, the term “enhanced bioremediation” is to be understood, unless the context clearly indicates otherwise, as a term used to describe the process of increasing the activity of indigenous contaminant utilising microbes to reduce contaminant mass. 
     Thus, the basis of the site remediation system comprises an active component, the liquid recirculation mechanism, and a passive component, the enhanced substrate bioremediation. 
     The liquid recirculation mechanism may be configured to extract contaminated liquid from, or downgradient of a fringe of a plume, and to re-inject the heated, treated liquid into, or upgradient of, a source zone of the plume. 
     The liquid extraction component may comprise at least one extraction pump. The at least one extraction pump may be a solar powered pump. 
     The heater component may comprise at least one solar collector. In an embodiment, the heater component may comprise an array of solar collectors. 
     The heater component may be configured to heat the liquid to a temperature in a range of about 20° C.-50° C. More particularly, the heater component may be configured to heat the liquid to a temperature of between about 5° C.-15° C. greater than the subsurface temperature of the substrate. 
     The bioremediation mechanism may comprise at least one entrainment device for at least one of oxygenating the liquid, by entraining air in the liquid, and entraining nutrients in the liquid prior to re-injection of the liquid into the substrate. The at least one entrainment device may comprise a venturi (also referred to as an eductor). In an embodiment, the system may comprise a plurality of venturis arranged in parallel. The number of venturis employed will be dependent on the capacity of the system. 
     The entrainment device may be configured to entrain both air to oxygenate the liquid and nutrients for enhancing bioremediation effected by subsurface microbes in the substrate. 
     The system may include a passive media filtration device (granular activated carbon) arranged upstream of the bioremediation mechanism, the filtration device removing contaminants from the heated liquid prior to treating the liquid in the bioremediation mechanism. In certain applications, for example, in sandy substrates, the substrate itself may serve as an infiltration gallery for effecting distribution of the heated, treated liquid upon re-injection into the substrate. In other applications, for example, in more rocky substrates, the system may include an infiltration gallery located within the source zone of the plume for distributing the re-injected treated liquid in the substrate. 
     The system may be mounted on a displacement mechanism for ease of placement at the site. In an embodiment, the displacement mechanism may comprise skids. In another embodiment, the system may, in use, be mounted in an elevated position, for example, a roof, to reduce space requirements. 
     In a second aspect, there is provided a method of remediating a site, the method including 
     extracting liquid to be remediated from a substrate at the site using a low energy power source; 
     heating the extracted liquid prior to re-injecting the liquid into the substrate to increase a subsurface temperature of the substrate upon re-injection of the heated liquid into the substrate; and 
     treating the heated liquid prior to re-injection of the liquid into the substrate to effect enhanced substrate bioremediation. 
     The method may include extracting liquid from, or downgradient of a fringe of, a plume and re-injecting the heated, treated liquid into, or upgradient of, a source zone of the plume. 
     The method may include extracting the liquid using at least one extraction pump, the, or each, extraction pump being a solar powered pump. 
     The method may include heating the liquid using at least one solar collector. In an embodiment, the method may include heating the liquid using an array of solar collectors. 
     The method may include heating the liquid to a temperature in a range of about 20° C.-50° C. More particularly, the method may include heating the liquid to a temperature of between about 5° C.-10° C. greater than the subsurface temperature of the substrate. 
     The method may include treating the liquid prior to re-injection into the substrate by at least one of oxygenating the liquid, by entraining air in the liquid, and entraining nutrients in the liquid prior to re-injection of the liquid into the substrate. 
     The method may include entraining material in the liquid using at least one venturi. The method may include entraining both air to oxygenate the liquid and nutrients for enhancing bioremediation effected by subsurface microbes in the substrate. 
     The method may include filtering the heated liquid prior to treating the liquid to remove contaminants. 
     The method may include distributing the re-injected, treated liquid in the substrate using an infiltration gallery or infiltration wells at, or upgradient of, the source zone of the plume. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Embodiments of the disclosure are now described by way of example with reference to the accompanying drawings in which: 
         FIG. 1  shows a schematic representation of a prototype of an embodiment of a site remediation system; 
         FIG. 2  shows a schematic representation of another embodiment of the site remediation system; and 
         FIG. 3  shows a schematic representation of a further embodiment of the site remediation system. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     In the drawings, reference numeral  10  generally designates an embodiment of a site remediation system. The system  10  includes a liquid recirculation mechanism  12  powered by a low energy power source which, in the illustrated embodiment, is in the form of one or more solar panels  14 . 
     It will be appreciated that, in other embodiments, the low energy power source could, instead, be any other power source having minimal greenhouse gas emissions such as, for example, a wind powered energy source, a battery powered energy source, or the like. 
     The liquid recirculation mechanism  12  further comprises a liquid extraction component in the form of at least one solar powered pump  16 . The liquid extraction component is mounted within a pumping well  18  formed in a substrate  20  at a site  22  to be remediated. More particularly, the pumping well  18  is arranged at a downgradient fringe of a plume of the site  22 . 
     The liquid recirculation mechanism  12  further includes a heater component  24  for heating the extracted liquid, in turn, to increase a sub-surface temperature of the substrate  20  upon re-injection of the heated liquid into the substrate. As illustrated more clearly in  FIGS. 2 and 3  of the drawings, the heater component  24  comprises a plurality of solar collectors  26 , one of which is shown, schematically, in  FIG. 1  of the drawings. 
     The system  10  includes a bioremediation mechanism  28  arranged downstream of the heater component  24  of the liquid recirculation mechanism  12 . The bioremediation mechanism  28  includes a liquid treatment unit  31  for treating the heated liquid prior to re-injection of the heated liquid into the substrate  20  to effect enhanced substrate bioremediation. 
     The heated liquid is re-injected into the substrate at, or upgradient of, a source zone  30  of the plume in the substrate  20  of the site  22 . 
     In an embodiment, the system  10  includes a system controller  34  which monitors and controls operation of the liquid recirculation mechanism  12  and the bioremediation mechanism  28 . The system controller has a thermometer  36  connected to it, the thermometer  36  monitoring ambient temperature. In addition, a second thermometer  38  is arranged in a recharge trench  40  at, or upgradient of, the source zone  30  of the plume for monitoring the temperature of the re-injected liquid. 
     Level control switches  42  and  44  are mounted in the pumping well  18  and recharge trench  40 , respectively, for controlling the level of liquid in each of the pumping well  18  and the recharge trench  40 . The level control switches  42  and  44  are connected to the system controller  34 . 
     A solar pump controller  46  is interposed between the solar panels  14  and the pumps  16  for controlling operation of the pumps  16  under control of the system controller  34 . 
     The system  10  further includes a thermostatic mixer, or mixing valve,  48  arranged downstream of the heater component  24 . The thermostatic mixer  48  is configured to mix heated and unheated liquid, in appropriate circumstances, to obtain the desired temperature of the liquid to be re-injected into the substrate  20 . 
     If necessary, where ambient temperatures can drop to freezing levels, the system  10  includes a drain venting valve  50 . The drain venting valve  50  is connected to the system controller  34  and is opened under control of the system controller  34  to drain the system  10  of liquid when the ambient temperature drops below a predetermined threshold, e.g. freezing. It will be appreciated that in regions not susceptible to very low temperatures, the drain venting valve  50  can be omitted. 
     The system  10  also includes an optional filtration device  52  arranged intermediate the heater component  24  and the bioremediation mechanism  28 . The filtration device  52  is, preferably, a passive media filtration device, such as a granular activated carbon filter, for removing contaminants from the heated liquid prior to treating the liquid in the bioremediation mechanism  28 . 
     The solar pumps 16 are selected to pump at a rate of between about 2000 L and 40,000 L per day, for example, about 5000 L per day. It will be appreciated that the actual pumping rate will be dependent on the capacity of the system  10  and the desired remediation rate, factors which are, in turn, influenced by the size of a contaminant plume and the hydraulic properties of the substrate. A suitable pump for use with the system  10  is a Grundfos pump available from Solarpumps.com.au, a division of Irrigation Warehouse Group of Glen Innes, New South Wales Australia. 
     The Grundfos pump range includes pumps which can pump at a rate of up to 14,500 L per day at a head of 10 m. The system  10  employs at least two such pumps  16  with the associated number of solar panels  14  for the pumps  16 . Depending on the capacity of the pumps  16 , each pump  16  has at least two or three solar panels  14  associated with it. 
     The system  10  is configured to heat the water to a temperature in the range of about 20° C. to 60° C., preferably, about 30° C. Other suitable ranges include 20° C. to 30° C., 30° C. to 40° C., 40° C. to 50° C. and 50° C. to 60° C. In general, it is desired to increase the temperature of the substrate to a more optimal range for bioremediation, in particular, where biodegradation can occur. This optimal range is typically between about 25° C. and about 35° C. 
     To achieve the desired temperature range, the heater component makes use of a plurality of solar collectors  26 . In an embodiment of the system  10 , the applicant has found that the use of ten solar collectors  26  for heating the liquid provides the necessary heating capacity to achieve the desired range of sub-surface temperatures in the substrate  20 . For example, where ambient temperatures are in the low 20s, using ten solar collectors  26  as the heater component  24  of the system  10  results in an increase in temperature of the liquid of more than 7° C. 
     As indicated above, the increase in sub-surface temperature of the substrate  20  enhances bio-degradation effected by microbes present in the substrate  20 , which reduce contaminant mass more efficiently as a result of the increase in sub-surface temperatures. 
     The liquid treatment unit  31  is in the form of at least one entrainment device, or venturi,  54 . In an embodiment, the liquid treatment unit  31  employs a plurality of venturis  54  arranged in parallel as shown in  FIG. 2  of the drawings. The venturis  54  effect oxygenation of the heated liquid by entraining air in the liquid. This enhances aerobic bio-degradation by the microbes in the substrate  20 . In addition, other nutrients for the microbes are also entrained in the liquid by the venturis  54 . 
     The contamination of the site  22  is, typically, due to hydrocarbons. To effect bioremediation of such a site, air is entrained in the liquid by the venturis  54  in a ratio sufficient to cause saturation of the liquid. Typically, air is entrained in a ratio of about 3 to 4 parts oxygen to one part hydrocarbon. Further, the nutrients used depend on the hydrocarbons to be treated. Nutrients are entrained by the liquid treatment unit  31  in a ratio of approximately 100 parts hydrocarbon to 10 parts nitrogen to 1 to 2 parts phosphorus. 
     In some areas, the substrate  20  may comprise sandy materials which can act as an infiltration gallery for effecting distribution of the heated, treated liquid upon re-injection into the substrate  20 . In other applications, the substrate  20  may consist of materials less amenable to functioning as the infiltration gallery. For example, the substrate  20  may be of a rocky material. In such a case, the system  10  includes an infiltration gallery  56  surrounding the recharge trench  40  or an array of infiltration wells. 
       FIGS. 2 and 3  show further embodiments of the system  10 . With reference to  FIG. 1  of the drawings, like reference numerals refer to like parts unless otherwise specified. 
     In  FIG. 2  of the drawings, each pump  16  has a pressure gauge  60  associated with it mounted in a conduit  62  leading from the pump. A non-return valve  64  is mounted in each conduit  62 . Downstream of the valves  64 , the conduits  62  are connected together in a feed conduit  66  via which the extracted liquid is fed into the heater component  24 . A thermometer  68  is mounted in the feed conduit  66  together with a temperature transducer  70  for feeding data back to the system controller  34  (not shown in this embodiment), a pressure gauge  72  and a filter  74 . 
     The liquid to be heated is pumped via the non-return valves  64  into the solar collectors  26  of the heater component  24  through valves  76 . Each solar collector  26  has a pressure gauge  78  associated with it. It is to be noted that the solar collectors  24  are arranged in two banks of parallel connected solar collectors. In this embodiment, the liquid to be heated is pumped into the solar collectors  26  of each bank in parallel. 
     Heated liquid output from the heater component  24  is fed via a conduit  80  to the bioremediation mechanism  28  which, in this embodiment, comprises three venturis  54  arranged in parallel to provide the required dosing to the liquid. A thermometer  82  is mounted in the conduit  80  together with a temperature transducer  84 , a flow rate transducer  86  and a flow meter  88 . 
     A tap-off valve  90  is arranged downstream of the bioremediation mechanism  28  to provide a flow test sampling point. 
     Treated liquid output from the bioremediation mechanism  28  is injected into, or upgradient of, the source zone  30  via a plurality of parallel conduits  92  to distribute the treated liquid in the substrate  20 . 
     A pressure gauge  94  and a control valve  96  are mounted in each conduit  92 . 
       FIG. 3  shows a further embodiment of the system  10 . In this embodiment, as in the case of the embodiment shown in  FIG. 1  of the drawings, part of the extracted liquid remains unheated and is tapped off, upstream of the heater component  24 , by the conduit  58 . In this embodiment, an entrainment unit  31  is arranged in the conduit  58  for treating the liquid by dosing it with air and nutrients. It is therefore to be noted that the thermostatic mixer  48  is omitted. 
     Further, the system  10  includes a flow meter  98  for measuring the flow rate of the extracted liquid and a flow transducer  100  for feeding data back to the system controller  34  (not shown in this embodiment) arranged upstream of the heater component. 
     Unlike the embodiment of  FIG. 2 , where the extracted liquid is fed separately into each solar collector, in the embodiment of  FIG. 3 , the extracted liquid is split to be fed into the upstream solar collectors of each bank of solar collectors  24 . The liquid then flows serially through the solar collectors of each bank before being re-combined in an outlet conduit  102 . 
     In addition, a portion of the extracted liquid is, as described above, fed via the conduit  58  and a further venturi  54  of the bioremediation mechanism  28 , where the unheated liquid undergoes dosing, back into the source zone  30  via conduits  104 . 
     Due to the serial heating of the extracted liquid as it passes through the banks of solar collectors  24 , greater heating of the liquid occurs. Thus, this embodiment is intended for use where a higher temperature gain than that obtainable with the embodiment of  FIG. 2  is required but at a lower flow rate. 
     To improve the versatility of the system  10 , the system  10  may be mounted on a displacement mechanism (not shown), such as skids, for ease of placement at the site  22 . Instead, the system  10  could be mounted in an elevated position, for example, a roof, to reduce space requirements. 
     In use, the system  10  is intended for use at sites  22  where the bulk of primary and secondary contaminant sources has already been removed with the system  10  being used for further reducing residual contamination in a cost-effective, environmentally friendly manner. 
     Thus, liquid in the form of groundwater to be treated is extracted from the substrate  20  via the solar pumps  16  located in the pumping well  18 . The pumps  16  receive power from the solar panels  14  via the solar pump controller  46  under the control of the system controller  34 . 
     The extracted groundwater is pumped into the solar collectors  26  of the heater component  24 . The solar collectors  26  heat the extracted groundwater to a temperature which, after re-injection into the substrate  20 , will raise the sub-surface temperature of the substrate to approximately 25° C. to 35° C. If necessary, to ensure that the groundwater is at the required temperature, a part of the extracted groundwater is fed directly via the conduit  58  back into the source zone  30  or via the thermostatic mixer  48  where it is mixed with heated groundwater discharged from the solar collectors  26  of the heater component  24  before being treated and re-injected into the source zone  30 . 
     The heated groundwater water from the solar collectors  26  is then fed to the venturis  54  where air is entrained in the heated groundwater together with additional nutrients, if applicable. The heated, treated groundwater water is re-injected into the substrate  20  via the recharge trench at, or upgradient of, the source zone of the plume in the substrate  20 . 
     The heated, treated groundwater, firstly, raises the sub-surface temperature of the substrate to a range of approximately 25° C. to 35° C. which is the optimal range where aerobic bio-degradation occurs. The oxygenated and nutrient-carrying groundwater further stimulates the microbes in the substrate to effect bio-degradation of the contaminants thereby enhancing bioremediation of the site  22 . 
     At present, in the retail petroleum industry legacy sites are typically left to bioremediate themselves. A “legacy site” is a property which has elevated levels of contamination that will cost more than the worth of the property to remediate to an “as of right uses” under land zoning. As a result of these legacy sites being left to bioremediate themselves, many are left in a derelict state for long periods creating an eyesore and public nuisance. This may result in the issuance of regulatory clean-up notices requiring remediation on a regulator-enforced timeline with the resultant significant expense. 
     In addition, many operational service station sites are also allowed to remain in a contaminated state as long as any existing contamination is appropriately managed and there is no danger of imminent environmental harm occurring. While such an approach can be cost-effective while the site is being operated it can lead to unnecessary expenditure during periodic re-tanking works or at times when existing contamination impacts on the site. 
     It is therefore an advantage of the disclosure that a system  10  is provided which significantly reduces these and related problems. The system  10  provides a low cost, low-maintenance method for enhancing the natural bioremediation processes of petroleum hydrocarbons resulting in significantly decreased periods over which contaminated sites, both legacy sites and operational petroleum sites, are able to be remediated. 
     The use of low-energy power sources, in particular solar energy power sources, means that the rate of contaminant bioremediation is able to be significantly increased whilst occurring in a substantially carbon neutral manner. In addition, the system  10  obviates the need for high energy consumption extraction and treatment equipment whilst operating in an environmentally friendly manner. 
     It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.