NUTRIENT DELIVERY SYSTEM

Abstract: A nutrient delivery material for use in a media remediation system comprising a support material conjoined one or more nutrients, which nutrient(s) are releasable upon the flow of media thereover is described. The present invention provides nutrients to a bacterial population that in turn will breakdown contaminants. This system can be used to enhance natural attenuation processes by supplying essential nutrients in conditions where these nutrients are limiting or completely absent. The media could be water, air, etc.; generally water such as groundwater. The delivery system is maintenance free for long periods of time. It will also allow the nutrient delivered to be site-specific thereby optimising degradation. Nutrients can be released at a rate determined by growth of the microbial population. Nutrients released will immediately be utilised by the bacterial population growing on the material. This will prevent the unnecessary release of nutrients into the surrounding environment.

Description: Nutrient Delivery System This invention relates to a nutrient delivery system and material for use particularly but not exclusively in biological groundwater remediation systems. Conventionally groundwater remediation has involved ex si tu technologies such as pump-and-treat and bioventing. Pump-and-treat involves the continuous input of energy for pumping water from the extraction wells and operating the water treatment systems. Remediation costs utilising this technology therefore tend to be large. The efficiency of this method is also limited by the low solubility of many contaminants and the low rate of contaminant dissolution (Borden et al . 1997) . Emphasis has therefore switched to passive in si tu remediation technologies . Permeable Reactive Barriers (PRBs) are a passive intervention remediation technology. In PRBs, contaminated groundwater passes, under natural or induced hydraulic gradients, through an in situ reactive material, where the contaminant is either abiotically or biotically degraded or sorbed. PRB's are unique as they can be inserted to prevent contaminant movement across site boundaries prior to risk receptors, or simply to intercept a contaminant plume. They also do not suffer from the same limitations as the pump-and -treat method as only those contaminants already in solution are treated (Borden et al . 1997). Initial development of this technology took place at the University of Waterloo, Canada. Since then numerous laboratory and bench-scale investigations have been carried out. Zero valent iron (FeO) , used for the reduction of chromate and the dechlorination of chlorinated hydrocarbons such as TCE and PCE, is the most common reactive material and most full scale PRBs are of this type. However, the long -term performance of these reactors is still unpredictable. Problems also arise when products from the incomplete breakdown of contaminants accumulate within the barrier necessitating replacement of the iron. Granular Activated Carbon (GAC) is another widely investigated reactive media mostly used for the interception and sorption of hydrophobic compounds such as Polycyclic Aromatic Hydrocarbons (PAHs) . Although the applicability of this technology has been proven, periodic maintenance is required to maintain its efficiency. These systems are also strongly affected by geochemical changes and contaminant flux and the range of compounds they can act on is limited. Biological processes are ] nown to effect the cycling of numerous elements in nature. In recent years biological PRBs that utilise the attenuating capacity of the indigenous microbial population in the groundwater, have been developed. Biologically enhanced PRBs have been suggested as a method for controlling the migration of dissolved hydrocarbons and other readily biodegradable contaminants (Borden et al . 1997) such as the dissolved gasoline components benzene, toluene, ethylbenzene and toluene (BTEX) (Alvarez & Vogel 1991) . Chlorinated solvents such as tetrachloroethylene (PCE) and trichloroethylene (TCE) have also been found to be degradable in reactive barriers (Keeley et al . 1999, Kao & Lei 2000) . The rate, type of active microbial population within the barrier and the level of activity and degradation are controlled by nutrient concentration, biogeochemical and environmental conditions. In particular compounds which play a major role in the supply (electron donors e.g. toluene) , the transfer of electrons (electron acceptors e.g. N0 3 " , S0 4 2~ ) or are principal construction elements of cells (e.g. C, N and P) will strongly influence the biodegrading of contaminates. For example, BTEX degradation can occur under both anaerobic and aerobic conditions and reports of degradation of toluene and benzene under nitrate reducing (Barbaro et al . 1992), iron reducing (Lovley et al . 1989), sulphate reducing (Rabus et al . 1993) and methanogenic (Edwards & Grbic-Galic 1992) conditions, have been made. The establishment of these conditions is dependent on the supply of a terminal electron acceptor (TEA) to which reducing equivalents or electrons can be transferred, thereby producing energy (Azadpour-Keeley et al . 1999). Many organic contaminants can be used as primary substrate for microbial metabolism (Alvarez-Cohen 1993) particularly hydrocarbons in gasoline and other petroleum derivatives (Armstrong et al . 1991) . However, in cases where contaminants are degraded by secondary metabolism or co-metabolism it may be necessary to supply alternate substrates. The supply of oxygen has also been identified as a critical and limiting factor in aerobic bioremediation A number of methods have been employed to increase the availability of dissolved oxygen (DO) within contaminated groundwaters , thereby enhancing aerobic degradation. Air sparging, which involves the direct injection of air into a water-saturated soil matrix via a pervious pipe (Brown 1997), has proven to be very popular. It has been shown to aid the biodegradation of hydrocarbons and chlorinated compounds (Fiorenza et al . 1999). More recently a patented formulation called Oxygen Release Compound (ORC) has been developed. This consists of magnesium peroxide that slowly releases oxygen when hydrated. It has proven effective in the bioremediation of BTEX (Bianchi-Mosquera 1994) as well as methyl tert butyl ether (MTBE) , pentachlorophenol (PCP) and vinyl chloride (VC) . The typical lifetime of ORC is approximately 6 months and it does not require continuous maintenance. It is currently being used in groundwater and soil remediation on over 2800 sites in the USA and in several other countries with an estimated treatment cost of $47-83 per 1000 gallons. However, its performance is limited by the presence of elevated concentrations of metals, particularly iron, in target waters. More recently the use of oxygen releasing concrete briquettes has been investigated for the remediation of a BTEX plume (Borden et al . 1997). The supply of inorganic and organic nutrients also poses a problem and may be a limiting factor to the use and efficiency of biological PRBs. In the past organic carbon sources such as lactic acid have been added in regular high concentration pulses to stimulate natural attenuation (Johnson et al . 1999). However, this tends to be expensive and in many situations results in fouling of injection wells. Hydrogen Release Compound (HRC) , which was developed by Regenesis, San Jan Capistrano, California, is a lactic acid ester which, when on delivery to the subsurface, releases lactic acid. The lactic acid serves as an electron donor for the enhancement of natural biodegradation processes. It can be used to deliver nutrients passively and has been shown to be effective in the remediation of chlorinated volatile organic compounds (cVOC's) with a lifetime of 12 months being predicted (Johnson et al . 1997) . Although the above nutrient delivery systems have proven to be effective, their limited life span and large replacement cost have made them prohibitively expensive in the United Kingdom and led to limited use in Europe. It is therefore of vital importance that a nutrient delivery system be developed for the sustained release of nutrients into the surrounding environment . According to one aspect of the present invention, there is provided a nutrient delivery material for a media remediation system comprising a support material having immobilised therewith one or more nutrients, which nutrient (s) are releasable upon the flow of media thereover. The nutrient delivery material that has been developed will facilitate the delivery of a range of nutrients, both organic and inorganic, possibly to a subsurface, over an extended period of time i.e. a number of years. The nutrient immobilised within the material will be dependent on the specific site requirements but will normally be an inorganic or organic nutrient that is deficient in the media that is to be treated. The media could be water, air, etc.; generally water such as groundwater. The release of the nutrient from the material, either by active mechanisms or passive diffusion, will stimulate the growth of a population of bacteria. This population of bacteria will break down the contaminant in question, thereby remediating the groundwater . This delivery material provides a system will have numerous advantages over other systems in that it will be maintenance free for long periods of time i.e. it will only need to be replaced once the nutrient has run out. It will also allow the nutrient delivered to be site-specific thereby optimising degradation. Nutrients can be released at a rate determined by the growth of the microbial population. Nutrients released will immediately be utilised by the bacterial population growing on the material. This will prevent the unnecessary release of nutrients into the surrounding environment. The material of the nutrient system could be made and provided in a number of different ways and forms. It could be manufactured in pellets and granules of different size and shape. It could be used as a matrix or solid surface on which bacteria can attach and grow. The material could also be sprayed onto suitable surfaces. The material could also be used as a pH control mechanism for the treatment of acidic media. In this the incoming acidic media will flow over the material and due to the release of hydroxides and carbonates, the pH of the water will be elevated. The material could also be injected into media (e.g. sub-surface) where it will dry. forming a barrier. This material can be used in ex-si tu treatment processes i.e. processes above ground. The material could also be used as a material in biological trickling filters and bioscrubbers . The material could serve as a matrix for the growth of bacteria while also compensating for any pH changes that may occur in the incoming air or water stream. The support material for the nutrient system generally has the following composition: Any fine aggregate, e.g. sand. Any cement, e.g. Portlandite cement Water The sand: cement :water is preferably in an approximate ratio of 3:2:1 by volume. However these ratios can be different depending on the strength of the product that is to be obtained and the nutrients to be added to this mixture. More than one nutrient can be added. Preferably the support material includes an aluminium, and the aluminium: silica and/or cement: aluminium: silica ratio also varies the strength of the support material as desired or necessary. Optionally, the support material also includes an admixture. An admixture is a material other than water, aggregate, cement and fibre support, which can be used as an ingredient of concrete and added to the batch immediately before or during mixing. The addition of these admixtures serves to enhance the properties of the support material . Chemical admixtures that can be used in the present invention include: water reducers, superplasticisers, polymers, retards, accelerators and air entrainers . Mineral admixtures that can be added include microsilica, pulverized fuel ash, ground granulated blastfurnace slag, rice husk ash, high reactivity metakaoline, zeolite or fuel ash. Any inorganic nutrient can be added to the material of the nutrient delivery system, either in the form of a powder or salt that will dissolve in water, or in the form of a concentrated liquid solution. The nutrient can also be added in the form of a nutrient sorbed onto a porous aggregate that is used. Organic nutrients can be added in the same form. The support material can be formed as a clay-like material, but is more usually a concrete-like material. The material is generally allowed to dry and then ground into the required size. According to a second aspect of the present invention, there is provided a process for the preparation of a nutrient delivery material comprising the steps of; (a) admixing a fine aggregate, cement, water, and optionally aluminum and/or an admixture as hereinbefore defined, to form a support material, and one or more nutrients either simultaneously or thereafter; (b) drying the so-formed material; and (c) grinding the dried material; wherein the ratio of ingredients in step (a) and/or degree of grinding in step (c) determines the rate of release of the or each nutrient from the support material. According to a third aspect of the present invention, there is provided a process for delivering one or more nutrients for a media, generally water, remediation system, comprising locating a nutrient delivery material as hereinbefore defined in the path of the media. According to a fourth aspect of the present invention, there is provided a support material for a media remediation nutrient delivery system, which material is adapted to immobilise one or more nutrients which are releasable upon a flow of media thereover . In general, the present invention provides a material that can be used in a PRB or other reactive zone for enhanced natural attenuation. The material can be formed as a porous structure, e.g. if the nutrient (s) are within a suitable aggregate, or in a more solid- formed material like concrete, which can be subsequently crushed to form the desired shaped and/or sized material suitable for nutrient release over time. The nutrient (s) are well known in the art, and comprise any substance adapted to sustain bacteria known for their media-remediation. Embodiments of the present invention will now be described by way of example only and with reference to the accompanying figures and Tables. A general Biological Nutrient Delivery System (hereafter "BiNDs") material was prepared comprising sand, Portlandite cement and water in a ratio of 3:2:1 respectively. The BiNDs material was characterised by Powder X-ray diffraction and Infra-red spectroscopy. These techniques serve to give a fingerprint of the main components in the material and indicate how the structure of the material changes during nutrient release. To the BiNDs material was added either a "nitrate" in the form of potassium nitrate, an "ammonium" in the form of ammonium phosphate, or a "phosphate" in the form of potassium phosphate. Figures 1-14 and Tables 1-7 hereinafter show X-ray powder diffraction or Infra-Red patterns, peaks and scans for samples of the BiNDs materials either before leaching or at times after leaching. Figure 15 hereinafter is an electron microscope photograph of the BiNDS material at the initial stages of biofilm development. The leaching data was provided by passing deionised water over time through a column of the relevant BiNDs material. In-si tu implementation of the material in a groundwater remediation system could, for example, be carried by the digging of a trench as conventionally done when constructing permeable reactive barriers. The material can then be added to the trench either in pockets separated by an appropriate metal or chemically inert material or in a continuous trench. Pockets will facilitate the removal of sections of the barrier for replacement and investigation. The groundwater will flow through the material. Bacteria present in the groundwater will attach to the material to gain access to the immobilised nutrients either by active mechanisms or by passive diffusion from the material. An active biofilm will form on the material. This microbial biofilm will breakdown contaminants in the groundwater passing through the material Ex-si tu implementation of the material could involve, for example, the packing of the material into a reactor of appropriate design e.g. biological trickling filter, air scrubber. The reactor will be seeded with a population of micro-organisms that are able to degrade the contaminant of interest. When used as a method for elevating the pH of acidic effluents, the material will be placed into a bed over which the effluent will flow. The flow rate will be determined by the pH and composition of the effluent. The present invention provides a nutrient delivery system which can supply nutrients to a bacterial population that in turn will breakdown contaminants. This system can be used to enhance natural attenuation processes by supplying essential nutrients in conditions where these nutrients are limiting or completely absent. This nutrient delivery system can be used in sub- surface environments e.g. as a packing material in Permeable Reactive Barriers (PRBs) , or in reactors treating contaminated wastewater and gaseous streams. This nutrient delivery system will passively supply nutrients for extended periods of time.

Claims: Claims 1. . A nutrient delivery material for use in a media remediation system comprising a support material conjoined with one or more nutrients, which nutrient (s) are releasable upon the flow of media thereover. 2. A material as claimed in Claim 1 wherein the or each nutrient is an inorganic or organic nutrient that is deficient in the media that is to be treated. 3. A material as claimed in Claim 1 or Claim 2 wherein the media is water. 4. A material as claimed in Claim 3 wherein the media is groundwater. 5. A material as claimed in any one of the preceding Claims wherein the release of the or each nutrient is adapted to stimulate the growth of a population of bacteria. 6. A material as claimed in Claim 5 wherein the or each nutrient is adapted to be released at a rate determined by the growth of the microbial population. 7. A material as claimed in any one of the preceding Claims wherein the material is used as a matrix or solid surface. 8. A material as claimed in any one of the preceding Claims wherein the remediation system provides a pH control mechanism. 9. A material as claimed in any one of the preceding Claims wherein the material is provided in a biological trickling filter or a bioscrubber. 10. A material as claimed in any one of the preceding Claims wherein the support material comprises one or more fine aggregates, one or more cements, and water. 11. A material as claimed in Claim 10 wherein the fine aggregate is sand. 12. A material as claimed in Claim 10 or Claim 11 wherein the cement is Portlandite cement. 13. A material as claimed in Claim 10, 11 or 12 wherein the aggregate : cement :water has an approximate ratio of 3:2:1 by volume. 14. A material as claimed in any one of Claims 10 to 13 wherein the support material further includes an aluminium. 15. A material as claimed in Claim 14 wherein the aluminium: silica ratio or cement : aluminium: silica ratio varies the strength of the support material. 16. A material as claimed in any one of the preceding Claims wherein the material includes an admixture. 17. A material as claimed in Claim 16 wherein the admixture is one or more of the group comprising.-water reducers, superplasticisers, polymers, retards, accelerators, air entrainers, microsilica, pulverized fuel ash, ground granulated blastfurnace slag, rice husk ash, high reactivity metakaoline, zeolite and fuel ash. 18. A material as claimed in any one of the preceding Claims wherein the or each nutrient is added to the support material in the form of a powder or a salt. 19. A material as claimed in any one of the preceding Claims wherein the conjoined support material and nutrient are ground to size. 20. A material as claimed in any one of the preceding Claims wherein the delivery material is provided in pellet or granule form. 21. A process for the preparation of a nutrient delivery material comprising the steps of; (a) admixing a fine aggregate, cement, water, and optionally aluminum and/or an admixture as defined in Claim 17, to form a support material, and one or more nutrients either simultaneously or thereafter,- (b) drying the so-formed material; and (c) grinding the dried material ,- wherein the ratio of ingredients in step (a) and/or degree of grinding in step (c) determines the rate of release of the or each nutrient from the support material . 22. A process for delivering one or more nutrients for a media remediation system comprising locating a nutrient delivery material as defined in any one of Claims 1 to 20 in the path of the media. 23. A support material for a media remediation nutrient delivery material, which support material is adapted to immobilise one or more nutrients which are releasable upon a flow of media thereover.

Inventors: BOSHOFF GENEVIEVE ANN, KALIN ROBERT M, WALSH KAYLEEN, BOSHOFF, GENEVIEVE, ANN, KALIN, ROBERT, M., WALSH, KAYLEEN
Applicants: BOSHOFF GENEVIEVE ANN, KALIN ROBERT M, UNIV BELFAST, WALSH KAYLEEN, BOSHOFF, GENEVIEVE, ANN, KALIN, ROBERT, M., THE QUEEN'S UNIVERSITY OF BELFAST, WALSH, KAYLEEN
Application year: 2001
Main classification: C02F3
IPC codes: B09C1, C12N1