Patent Application
20100222481
Sediments occurring in many of the world's aquatic environments, including Norwegian fjords, harbors and shipyard areas, are impacted by a variety of organic and/or heavy to metal contaminants. Organic contaminants can include TBT, dioxins, PCBs, PAHs and/or other petroleum products whereas heavy metals can include Pb, Cu, Cr, Cd, Hg and others. In many locations, concentrations of one or more of these sediment contaminants can pose unacceptable health risks to humans and/or ecological receptors. The most direct approach for effectively lowering these risks to acceptable levels is to remediate the offending sediment contaminants.
A variety of in place (in situ) and remote (ex situ) methods exist for remediating (managing) contaminated sediments, including removal, treatment, capping and natural recovery. The most appropriate method(s) for use at a given site will vary, depending on site and sediment conditions, remediation goals, costs and other factors.
In situ approaches for managing contaminated sediments and the risks they pose—in situ capping and in situ treatment, in particular—are rapidly gaining national and international favor. Increased positive recognition of in situ capping and treatment is likely due to the advantages of these two approaches (relatively lower cost, lower environmental impact during implementation and ability to rapidly and significantly reduce risks), in combination with the recognized drawbacks to other management approaches (e.g. high costs associated with removal and slow rates associated with natural recovery).
In situ capping involves covering contaminated sediment in place with one or more clean materials. In situ capping is typically conducted for the purpose of providing a barrier between sediment-borne contaminants and potential ecological and/or human receptors occurring in the overlying aquatic ecosystem, including benthic organisms living in bottom substrates. Materials used to cap contaminated sediments can be either inert or chemically/biologically reactive in character, and often comprise earthen materials, engineered materials or combinations thereof. Cap designs can range from relatively simple (e.g. a “monolayer” of a single material, like natural, quartz-rich sand) to relatively complex (e.g. a “composite cap” comprised of multiple materials used in various configurations). The barrier formed by the cap can intentionally be relatively permeable or impermeable in character, depending on attributes of materials included in the design. Furthermore, the contaminated sediment to be capped may comprise naturally deposited sediment, dredged sediment re-deposited in a new underwater location or combinations thereof.
In situ treatment involves physically incorporating one or more reactive materials directly into the contaminated sediment mass for the purpose of stimulating or enhancing biological and/or chemical processes that bring about an in-place reduction in contaminant mass, toxicity, solubility and/or mobility.
In situ capping and in situ treatment can both be appropriate methods for use at many impacted sites, and both have been used successfully at the field scale. Nevertheless, many more field-scale capping projects have been completed to date than have treatment projects, for various reasons. Consequently, collective knowledge and experience related to designing and placing sediment caps in a variety of aquatic settings is considerably more extensive, such that the theoretical and practical aspects of the overall “science of capping” are arguably more mature than theoretical and practical aspects of in situ treatment. Because of these recognized and significant differences in the development of capping over treatment, regulatory and related governing bodies tend to view capping as a more viable and “acceptable” method for managing sediment-related risks in place, at least at this point in time.
In situ sediment caps can generally be categorized as either “conventional” or “active” caps, depending on the relative reactivity of the capping material used.
Conventional sediment capping involves covering contaminated sediment with relatively inert (non-reactive) material like natural, quartz-rich sand (typically referred to herein as “sand”), gravel and/or geotextiles, often for the purpose of isolating sediment contaminants—including upward-migrating contaminants—from potential receptors, including benthic organisms.
Most conventional caps are relatively permeable in character, largely because of the dominant use of granular materials (sand and/or gravel) for the construction of such caps. However, some conventional caps are, by design, relatively impermeable, by virtue of inclusion of membrane liners and/or very fine-grained mineral (e.g. clay) components within the cap design. Relatively impermeable sediment caps are sometimes referred to as “hydraulic barriers” and can be considered a sub-category of conventional caps.
Active sediment capping involves covering contaminated sediment with chemically and/or biologically reactive material for the purpose of treating sediment-borne contaminants. Like in situ treatment, contaminant treatment within the context of active capping generally involves bringing about a reduction in contaminant mass, toxicity, solubility and/or mobility. However, unlike in situ treatment, the “zone of treatment” for active capping occurs within the capping layer itself rather than within the underlying sediment mass. That is, in order for active capping layers to be effective, sediment-borne contaminants must first migrate up into the active capping layer, in one or more forms (i.e. dissolved phases and/or particle-bound phases). Little to no “passive” contaminant treatment is typically expected to occur within the sediment mass beneath active caps.
The specific process or processes by which contaminant treatment occurs through active capping (e.g. biodegradation, decreased solubility due to increased contaminant sorption or exchange to reactive organic or mineral solid phases, etc.) depends on the type of reactive material included as well as the mobilized contaminant(s) targeted for treatment. A non-exhaustive but fairly representative listing of recognized reactive materials that are more-or-less proven for use within the context of in situ active capping and/or in situ treatment is provided in Table 1. Use of additional or different reactive materials for treating other contaminants (e.g. phosphorous) is also described in Table 2.
Calcium nitrate (Golder, 2003)
Various nutrients, electron
acceptors (Mitchell et al.,
Aqueous O2, nutrients (Hyun
Activated carbon (Werner et
Gypsum (Rothermich et al.,
Activated carbon
Aqueous sulfate, nitrate
Activated carbon (Ghosh et
Calcium nitrate (Golder, 2003)
Various nutrients, electron
acceptors (Mitchell et al.,
ZVI (Mikszewski, 2004)
Activated carbon (Werner et
ZVI (Lowry & Johnson, 2004)
ZVI (Gardner et al., 2004)
Activated carbon
Activated carbon (Ghosh et
“Sludge cake” as OC source (Kao
Activated carbon and other
organic sorbents (no
“Haloprimer” (Haagblom, 2002)
organic shales (Gullick &
Activated carbon (Messing
Zeolite for Pb (Jacobs &
Zeolite for Fe, Mn (Jacobs
Apatite (Crannell et al,
Activated carbon for Hg
Me-S precip. (no specific
ZVI (ITRC, 2005)
Virtually all active sediment caps are, by design, at least somewhat permeable. In concept, active sediment caps are generally analogous to “permeable reactive barriers”, or PRBs, which are commonly used for in-situ treatment of contaminants contained within flowing ground waters.
Both conventional and active capping can be appropriate techniques for effectively managing contaminated sediments in place. The choice of which technique to use at a given site will depend on a variety of factors, including the contaminants present, sediment and site conditions, project goals and objectives, costs and other factors.
To date, many more conventional capping projects have been completed on a field scale than active capping projects, for various reasons. Thus, similar to the immaturity of in situ treatment relative to in situ capping (in general), active capping significantly lags behind conventional capping in terms of experience and theoretical/practical development. Regardless, interest in active capping continues to grow, both in Norway and abroad, because active caps are believed to offer several advantages over conventional caps:
Perhaps the most high-profile example of active sediment capping on a field scale is a demonstration project conducted on the Anacostia River, Washington D.C., U.S.A. This project, occurring from 2002-07, involved evaluating the placement and long-term performance of selected products or materials designed to treat or otherwise control contaminant migration through various processes. For reference, significant technical information is available on this project and can be found on the web at: http://www.hsrc-ssw.org/ana-index.html
The invention relates to a product that, in its initial form (prior to placement into water), occurs as relatively small (typically 0.5 to 4 cm equivalent diameter), relatively dry and irregularly shaped (sub-angular to plate-like) solid particles. Each dry particle is composed of three different materials which are more-or-less evenly distributed spatially throughout the mass of each particle. The three materials, which can comprise variable percentages of the dry particles by mass and/or volume, consist of the following: an inert material; a reactive material; and a binding material. Furthermore, the three materials are different from one another, both in composition and function.
The inert material collectively comprises one or more relatively non-reactive (inert) minerals. The inert material is typically fine-grained in character, but can be coarser grained as needed. The primary function of the inert material is to serve as the dominant particle matrix, providing mass, volume and density to the dry particles.
The reactive material collectively comprises one or more minerals, naturally occurring materials and/or processed materials that are each, in their own way, chemically and/or biologically reactive. The reactive material can occur in either solid or liquid form, with solid minerals or materials occurring in a range of size fractions and/or particle densities. The primary function of the reactive material is to render the product, once placed, “active” and thus appropriate for use as an active capping material, as generally described in Section 1b.
The binding material collectively comprises one or more variably sized processed materials that are organic and/or inorganic in character. The binding material can occur in either solid or liquid form, with solid material occurring in a range of size fractions. The primary function of the binding material is to assist in establishing and maintaining the overall integrity (physical form and strength) of the individual dry particles, above and beyond that integrity imparted to each dry particle by virtue of characteristics (e.g. cohesive properties) inherent to the co-occurring materials.
Additional details related to preferred embodiments of the dry product are provided in Section 3a.
The general procedure for manufacturing the dry particles is described below, in step-wise fashion (Steps 1 through 7). A generalized, graphical depiction of this procedure is also provided in
A typical method for use of the above-described dry particles for the purpose of creating an active sediment cap is described below, in chronological order. A graphical depiction for typical product use is also provided in
According to the invention:
According to the invention, the inert material in the product preferably comprises, but may not be limited to:
Some inert materials may, depending on the conditions, also be reactive. One such material is olivine.
According to the invention, the reactive material in the product preferably comprises one or more reactive materials occurring in solid and/or liquid form.
According to the invention, the binding material in the product preferably comprises one or more organic and/or inorganic binding materials.
In one example of the invention, the active capping product is designed to manage TBT-contaminated sediment occurring within a relatively low-energy, inner-harbor environment (average water depth approximately 6 m). In this example, the TBT contamination is managed (treated) by creating an active capping layer containing activated carbon. The specific treatment process involves sorption of migrating, dissolved-phase TBT to activated carbon surfaces contained within the active capping layer, which immobilizes the TBT. The active capping layer is also relatively low-permeability in character (˜10−7 cm/s), an attribute that, in addition to carbon sorption, assists in minimizing long-term TBT migration through the cap.
In addition to containing activated carbon (the reactive material), the product also contains a 50/50 blend of dolomite+bentonite (the inert materials) as well as polyvinyl acetate (the binding material).
Dry particles of the product range in size from 0.5 to 2.0 cm and have an average particle density of approximately 2.5 g/cm3. Larger and denser (and more rapidly settling) particles than this are not required because this is a relatively low-energy environment, and particles with these physical characteristics can be placed through the water column and across the seabottom in an adequate manner.
In another example of the invention, the active capping product is designed to manage petroleum-contaminated sediment occurring within a relatively high-energy, outer-harbor environment (average water depth approximately 20 m). In this example, petroleum contamination is managed (treated) by creating an active capping layer containing gypsum as well as N+P fertilizer. The specific treatment process involves enhancing the activity of indigenous populations of sulfate-reducing bacteria occurring within the active capping layer by adding abundant sulfate (i.e. provided by slow dissolution of gypsum into cap pore waters) in combination with major nutrients (soluble N+P) into the cap. As microbial activity within the cap increases as a result of adding these bioreactive materials, so does the biodegradation of migrating, dissolved-phase petroleum constituents (namely, aliphatic hydrocarbons and low-ring polycyclic aromatic hydrocarbons) within the active capping layer. The active capping layer displays moderate permeability (104 to 10−5 cm/s).
In addition to containing gypsum and fertilizer (the reactive materials), the product also contains a 50/50 blend of barite+quartz-rich sand (the inert materials). Polyvinyl acetate is also included in the product (as a binding material). However, only a small amount of this organic binder is included because the treatment process is biotic in nature, and thus sensitive to influences that inclusion of abundant biodegradable organic binder may have on redox conditions within the active capping layer. The gypsum component, included mainly as a reactive material, also provides some particle-binding attributes.
Dry particles of the product range in size from 1.5 to 3.0 cm and have an average particle density of over 3 g/cm3. Such relatively large and dense (and rapidly settling) particles are required in order to create, with an appropriate level of control, an active capping layer across the seabottom in this high-energy environment.
According to the invention:
In one example of the invention, which is directly related to Example 1 under Section 3a, appropriate quantities of granular activated carbon, powdered dolomite and powdered bentonite are mixed together in a cement mixer. In a separate mixing tank, appropriate quantities of polyvinyl acetate plus seawater are mixed together. The solid (dry) and liquid materials are then both added into a second cement mixer and the materials are mixed together into a flowable paste. In preparing this product mix, the quantity of polyvinyl acetate used is not critical since the treatment process is abiotic in nature (that is, anaerobic conditions potentially encouraged by including significant quantities of biodegradable organic binder should not adversely affect this abiotic treatment [sorption] process).
Multiple mixer loads of the paste are prepared and poured onto a flat concrete floor for air drying. After approximately one week, the large, plate-like masses of now air-dried and cracked material is scooped up with a front-end loader and placed into a hopper that feeds a rock crusher, and the material is then crushed. Size fractions of less than 0.5 cm are retrieved and re-used in paste preparation. Size fractions of greater than 2.0 cm are re-crushed and re-sieved.
The 0.5 to 2.0 cm size fraction of sub-angular to plate-like solid material is then isolated and placed onto a large conveyor belt that passes continuously and slowly through an industrial-sized oven with the temperature set at 110° C. (total oven drying time approximately one hour). The now oven-dried particles are completed active capping product. The particles are off-loaded from the conveyor belt and stockpiled on a warehouse floor until the stockpiles can be transported, in covered dump trucks to the TBT-impacted sediment site and used in active capping.
In another example of the invention, which is directly related to Example 2 under Section 3a, appropriate quantities of powdered gypsum, powdered barite and quartz-rich sand are mixed together in a cement mixer. In a separate mixing tank, appropriate quantities of liquid N+P fertilizer, polyvinyl acetate and seawater are mixed together. The solid (dry) and liquid materials are then both added into a second cement mixer and the materials are mixed together into a flowable paste. Enough gypsum is incorporated into the product formulation to help maintain particle integrity during above-water handling and during water-column descent, but not so much that it precludes the particles, once placed across the seabottom, from disaggregating and transforming into a compositionally homogeneous active capping layer.
Multiple mixer loads of the flowable paste are prepared and placed directly onto a large conveyor belt that passes intermittently through an industrial-sized oven set at a temperature of 110° C. (total oven drying time approximately 24 hours). The large, plate-like masses of now oven-dried and cracked material are then offloaded directly into a hopper that feeds a rock crusher, and the material is then crushed. Size fractions of less than 1.5 cm are retrieved and re-used in paste preparation. Size fractions of greater than 3.0 cm are re-crushed and re-sieved.
The 1.5 to 3.0 cm size fraction of sub-angular to plate-like solid material, which is completed active capping product, is then isolated and packaged into multiple, water-resistant bags. The bags are then placed onto pallets and stacked in a warehouse until they are transported, via flatbed trailers, to the petroleum-impacted sediment site and used in active capping.
According to the invention:
In one example of the invention, which is directly related to Example 1 under Sections 3a and 3b, a composite (multi-layer) active sediment cap is designed and constructed for in situ management of the TBT-contaminated sediments. The composite cap design comprises a target 15 cm-thick basal layer of active capping product (containing activated carbon as the reactive material) covered by a target 15 cm-thick surficial layer of sand. The surficial sand layer is included to provide clean “replacement” habitat for benthic organisms. Given the relatively low-energy nature of this inner-harbor environment (low current), a surficial armoring layer overtop the sand layer is not necessary.
By virtue of its larger particle size (and despite similar material densities), the active capping product settles more rapidly through the water column than does the sand material. Thus, the procedure for cap construction first involves using an excavator to dry-mix appropriate bulk quantities of the active capping product together with bulk quantities of sand at a shore-based staging area. Masses of the mixed capping material are then transferred onto a material barge and transported to the equipment barge. Discrete quantities of the mixed capping material are then placed at the water surface using a clamshell bucket plus crane (parked on the equipment barge). Because of its faster settling character, the active capping product deposits first across the seabottom, followed by deposition of the relatively slower-settling sand material—thus forming two more-or-less separate layers of material.
Within approximately 24 hours following placement of the basal layer of particles of the reactive capping product, each particle saturates with seawater+extruded sediment pore waters and each particle disaggregates in-place. This results in an in-filling of macroscopic pore spaces with crumbling particle material and, ultimately, the formation of a compositionally homogeneous active capping layer (with a permeability of approximately 10−7 cm/s).
As a note, during field execution of the capping project, there is some spatial overlap between separate clamshell loads of material placed and, thus, a “perfectly discrete” layering of the two materials is not achieved. Regardless, it is determined that the final constructed cap is adequate for meeting project performance goals and thus provides for cost-effective in-situ management of the TBT-contaminated sediments.
In another example of the invention, which is directly related to Example 2 under Sections 3a and 3b, a composite (multi-layer) active sediment cap is designed and constructed for in situ management of petroleum-contaminated sediments. The composite cap design comprises—from bottom to top—a target 15 cm-thick basal layer of active capping product (containing gypsum and N+P fertilizer as the reactive materials), a target 15 cm-thick layer of sand (as a filter layer) and a target 15 cm-thick surficial layer of approximately 3 cm-diameter armoring stone (to provide for erosion protection within this relatively high-energy, outer-harbor environment).
Similar to Example 1, the active capping product settles much faster than the sand material, by virtue of its much larger particle size and higher particle density. Such differential settling attributes could potentially allow for constructing two relatively discrete capping layers by placing mixed material at the water surface (also similar to Example 1). However, a different construction approach for placing the bottom two layers is used in this example for two reasons: (a) current flow within this higher-energy environment is expected to significantly and selectively disperse the much smaller/lighter sand material during its descent through the water column, thus making controlled placement of the sand component (when added at the water surface) a significant challenge; and (b) as opposed to Example 1, performance objectives for this project call for tighter control (i.e. lower tolerance) with respect to constructing discrete layers of the cap according to specifications.
For the above reasons, the following approach to cap construction is considered to be the most practical and cost-effective: First, the basal layer of active capping product is placed at the water surface and across the entire seabottom area using a continuous-feed conveyor (parked on the equipment barge and supplied with product from the material barge). Second, the overlying layer of sand is constructed by creating a sand-seawater slurry and conveying the material across the entire seabottom area by tremie piping the slurried material down through the water column, to within a couple meters of the seabottom (at which time the sand only descends within the open water a short distance, which greatly improves placement precision and accuracy). And third, the final/surficial armor layer is placed over the sand layer using the same equipment and method used to place the basal layer of active product.
As a note, the process for formation of the basal active capping layer in Example 2 occurs in the same manner as the process described in Example 1 (i.e. particle dissaggregation, in-filling of macroscopic pores and ultimately, formation of a compositionally homogenous active capping layer). However, in the case of Example 2, several days (rather than 24 hours) are required for the gypsum-rich active capping particles to disaggregate and in-fill macropore spaces. Also, once the active capping layer for Example 2 is formed, its permeability is two to three orders of magnitude higher than that for the active capping layer in Example 1 as a result of the relatively higher permeability inherently associated with barite (when compared to bentonite-bearing material) coupled with the significant sand content of the active capping layer in Example 2.
A number of products or materials have already been specifically developed for, or additionally used for, creating active sediment caps 1. A non-exhaustive but fairly representative summary listing of these existing products or materials and methods is provided in Table 2. 1 For the purposes of this document, active capping “products” can typically be defined as manufactured or engineered products typically comprised of two or more naturally occurring and/or synthetic materials that are physically connected in some fashion. In contrast, active capping “materials” can typically be defined as naturally occurring or processed materials (e.g. residual by products) of a non-manufactured and non-engineered nature. Active capping materials would include simple physical combinations, or blends, of masses of inert material (e.g. sand) with masses of reactive material (e.g. granular activated carbon, GAC).
Generally speaking, most of the products or materials listed in Table 2 are intended for use in forming only the chemical isolation layer portion of a typical active sediment cap design: other, inert materials (e.g. sands, stones, geotextiles, etc.) are often also included in the overall cap design to serve additional functions (e.g. erosion control, habitat enhancement, etc.). Furthermore, the listed products or materials vary widely with respect to the extent to which each has been used on a field scale.
Although not developed specifically for use as active capping products, other products have been developed that are similar, in some respects, to the invention.
One such known product is the SediMite technology recently developed in the USA by Charles Menzie and associates. Following is a brief summary of various aspects of the product, as reported in Menzie et al., 2007:
AquaBlok® products have also been described in EP A2 1,710,025 and US 2007/0113756. CN 1927747 describes a product that appears to be a direct imitation of AquaBlok. All of these products are described as having a “core” coated with another layer and hence describe a compositionally non-homogenous material. The present invention involves neither a core nor material layering, and hence each particle of the present invention is more-or-less compositionally uniform in terms of spatial distribution of materials contained therein (please see “particle” in detail of
KR 100574025B also describes a presumably granular and/or pelletized product, similar to AquaBlok, This product involves manufacturing steps of “shaping” or “molding”. The present invention involves neither manufacturing step.
US 2007/0025820 describes a product comprising “fibrous organic matter” and “multivalent metal”. The present invention includes neither material component.
In summary, all of the above-noted products are clearly different from the present invention in terms of compositional homogeneity; steps involved in manufacture; and/or composition.
Various aspects of the invention can be compared with (and amongst) the listed products or materials and methods for creating active capping layers. A summary of such aspect-specific comparisons, including an identification of apparent similarities as well as apparent differences, is provided below.
The other listed products and materials are also designed or intended to treat mobilized, sediment-borne contaminants within the context of the concept of active capping, as the concept is defined and described herein.
Although not explicitly stated for all products, particles of most products—including the invention—likely undergo some type of significant “phase change” upon particle contact with water: that is, relatively rapid, partial to complete destruction of the initial particle structure or form likely occurs through the processes of hydration, swelling, disaggregation and/or crumbling. Two exceptions to this would be products 2 and 9, which would remain in-tact, over the long-term, upon contact with water. NOTE: Except for product 1, no other product explicitly states that such a phase change occurs as product particles are wetted, or that such a phase change is, in fact, integral to effective functioning and use of the product (i.e. ultimate formation of a homogeneous active capping layer).
Only one other product (product 1) explicitly states that the permeability of the sediment cap or barrier formed using the product can be controlled or modified as a function of the materials included therein.
Only one other product (product 1) explicitly states that it can be selectively formulated for and applied into fresh, brackish or full-strength seawater environments. The option of selective formulation and use of other products in such different aquatic environments is unclear.
With the exception of product 2 (reactive core mats), all listed products and materials are, like the invention, comprised of particles, which are placed in bulk to form an active capping layer across the sediment surface.
Although not explicitly stated for all products, most product particles—including those of the invention—are likely of a relatively dry and solid nature in their pre-placed form.
Most products and materials are or can be, like the invention, of a relatively high specific gravity, i.e. ˜2 g/cm3 or higher. In contrast, the “apparent density” of activated carbon products is typically well below 1 g/cm3, and the specific gravity of organic components of organic-rich soil or sediment is typically well below 2 g/cm3. Also, note that the specific gravity of many clay based products or materials (e.g. products 3, 4, and 5; material 6) will vary not only as a function of the specific gravity of the key clay mineral or oxide component(s) present, but also as a function of other factors (moisture content, porosity, degree of mineral packing into the particle, etc.).
Excluding product 2, only the invention and product 1 seem to include the reactive material as one of several material components, whereby the product particles are essentially acting to deliver the reactive material to the sediment surface, and whereby the additional components present are typically serving only to facilitate this delivery process. In contrast, all other product particles appear to be solely comprised of the reactive material itself (e.g. products 3, 4, 5 and 9).
The shape/form of particles of the invention are irregularly shaped, sub-angular to plate-like, solid particles. In contrast, the shape/form of other products' particles (excluding product 2) is highly variable, and includes semi-round, pelletized, granular and/or powdered particles.
Only a couple other products (product 1 and perhaps also product 6) can selectively comprise particles of substantially different sizes and size gradations (i.e. ranging from mm- to cm-scale). For other products, the level of control over the size and size gradation of the particles (pellets, granules, briquettes, tablets, etc.) is less clear, and may be limited by respective procedures for manufacture. In contrast to these other products, significant control over such attributes is, in fact, probably possible for many of the listed materials, particularly the mineral- or ore-based materials (materials 3, 4 and 5).
A number of the products include or can selectively include, like the invention, as a key component montmorillonite clay or some mineralogic/geologic “relative” thereof, i.e. smectite clay, bentonite (products 1, 3, 4 and 5).
A couple other products (products 1 and 2) may include, like the invention, multiple reactive materials, e.g. AC plus Fe oxides plus nutrients, for simultaneous cap-based treatment of multiple contaminants. In contrast, still other products (e.g. products 4, 5, 6 and 7) can only, or are designed to only, treat a single contaminant, e.g. phosphorous.
A couple other products (products 1 and 2) can alternatively include, like the invention, different reactive materials, e.g. AC or coke or organoclay or ZVI, to accomplish cap-based treatment of selected contaminants. In contrast, still other products can only, or are designed to only, treat a limited number/group of contaminants by virtue of limitations in the variety of reactive materials that can be incorporated into the product, e.g. as limited by the extent to which smectite clay can be chemically modified (products 3, 4, 5).
Only the invention explicitly and optionally allows for inclusion of relatively dense minerals (specific gravity of well over 3 g/cm3) such as barite, ilmenite, olivine and/or hypersthene as part of its compositional make-up. In this way, only particles of the invention can be significantly modified in terms of their specific gravity. As discussed below, this has direct implications with respect to the rate of particle settling and thus the overall success in product placement through the water column.
As described in Sections 2b and 3b, key steps in the manufacture of particles of the invention involve drying of a relatively flat mass of flowable paste (thus forming the “raw” and relatively large, solid material mass), followed by crushing the solid mass into smaller-sized (and more manageable) solid masses (which may then be optionally sieved into selected particle size fractions).
The method for manufacture of particles of the invention is clearly and significantly different from methods for respective manufacturing of products 1, 2 and 9.
Manufacture of products 3, 4, 5, 6 and 7 appear to include, as initial key steps, some type of chemical modification, which is not part of the process for manufacture of particles of the invention. Furthermore, subsequent, final to near-final, steps for manufacture of all of these products (plus product 8) appear to involve some type of material extrusion, molding and/or pulverizing step, as evidenced by the words “pellets”, “briquettes”, “tablets” or “powdered”. Such steps are not part of the procedure for manufacture of particles of the invention.
It may be concluded from the information provided that the procedure for manufacturing particles of the invention, which exclusively involves the following sequence of steps: material mixing to form a flowable paste→paste drying→crushing (but not pulverizing)→sieving (optional), with or without an additional optional drying step (post-crushing and/or post-sieving) is a unique procedure for manufacturing such particles.
The process for manufacturing particles of the invention also appears unique when compared to any of the processes generally described for manufacturing SediMite pellets, as described at the beginning of Section 4a.
Whether or not explicitly stated, all other products and materials can, like the invention, be placed in such environments using a variety of equipment and techniques.
All “loose”, or particle-based, capping products and materials can—in theory—be placed in bulk into water, like the invention, with the intention that the mass of particles descends through the water column and ultimately distributes (deposits) across the target sediment surface. However, the level of success2 with which active capping products or materials can, in fact, be placed in a controlled and uniform manner will be highly dependent upon a variety of factors, including: 2 “Success” in placing active capping products or materials through the water column in a controlled and uniform manner may be defined in various ways, including: layer thickness constructed as intended, with minimal “±” vertical variability; placement across intended footprint, with minimal lateral inaccuracies; minimal “stripping” losses of material or product to the water column during descent; vertically uniform distribution of reactive material throughout the placed layer; overall efficiency of the process; etc.
Additional issues related to the overall success of cap construction—which are not addressed above—include the short- and long-term responses of the capped sediment (e.g. re-suspension and mixing; consolidation; geotechnical stability; etc.) during and after the masses of capping product or material have been deposited.
The “art” of successfully placing conventional and active capping products and materials through the water column and across submerged sediment surfaces, towards the end-goal of constructing cap designs as intended (and in an environmentally protective manner), is a subject of great interest and study amongst sediment-management practitioners worldwide (e.g. McDonough et al, 2006; Palermo, 2004; SFT, 2006; Thompson et al., 2004; US ACE, 2005; Verduin, 2004). In fact, within the context of overall project success, many practitioners consider successful placement of active capping products and materials to be just as important as the demonstrated treatment effectiveness of the reactive material(s) included within the cap (e.g. as confirmed through controlled laboratory treatability testing).
Other factors being equal (i.e. factors 1, 2 and 4 above), optimal settling characteristics of active capping particles should typically be achieved when: (a) the particles are of a relatively high specific gravity (well above 2 g/cm3), which promotes relatively rapid settling (b) the particles are of a relatively coarse-grained nature (sand-sized or much larger) which also promotes relatively rapid settling; and (c) the particles remain in-tact during descent and deposition. The invention fits these criteria and thus should be able to be successfully placed through the water column.
Two of the products or materials listed in Table 2 that also clearly fit all of the criteria for optimal settling, and for which field-scale placement has already been successfully demonstrated, is the AquaBlok® technology (product 1) and apatite (material 3). Based on the same criteria for optimal settling, a number of other active capping products or materials also have the potential for successful placement through water columns, although the number of field-scale projects demonstrating effective placement of these other products or materials appears to be quite limited.
Conversely, active capping particles that do not fit all of the criteria for optimal settling should typically be more difficult to place successfully through the water column. Activated carbon and organic-rich soil or sediment would tend to fall into this category, because of their relatively low specific gravity and often fine-grained character. Challenges in effectively placing these reactive products or materials, either on their own or when blended with sand, have, in fact, been previously noted by other practitioners (e.g. McDonough et al., 2006; Reible, 2002; BBL, 2006).
In summary: the invention as well as all of the products and materials listed in Table 2 are designed or intended to accomplish essentially the same remedial goal: treatment of mobilized, sediment-borne contaminants within the context of the concept of active capping. In this fundamental way, then, the invention is not unique. The invention is also not unique from many of the products and materials in terms of: its particle-based nature; the manner in which bulk masses of particles can be placed across exposed or submerged sediment surfaces; the contaminants targeted for cap-based treatment; the reactive materials included or involved; or the processes/mechanisms by which cap-based treatment occurs.
The invention is, however, unique from nearly all—if not all—other active capping products or materials in a number of important ways, as summarized below.
Invention Uniqueness with Respect to Intended Function and Use
The occurrence of a significant phase change upon contact of dry particles of the invention with water (i.e. transformation from solid to disaggregated material) is explicitly stated as integral to effective functioning and use of the invention, i.e. the ultimate formation of a compositionally homogenous active capping layer.
The permeability of a sediment cap or barrier formed using the invention can be controlled or modified as a function of the materials included in the product.
Particles of the invention can be selectively formulated for and applied into fresh, brackish or full-seawater environments.
Invention Uniqueness with Respect to Composition and Physical Character
Particles of the invention include reactive material as one of several material components, rather than being solely comprised of such reactive material.
The shape/form of particles of the invention are irregularly shaped, sub-angular to plate-like particles.
The invention can selectively comprise particles of substantially different sizes and size gradations (as a function of the manufacture procedure) as well as particles of different specific gravity (as a function of optionally including relatively dense minerals).
The invention can optionally include multiple reactive materials for simultaneous cap-based treatment of multiple contaminants.
Invention Uniqueness with Respect to the Method of Product Manufacture
The process for manufacturing particles of the invention exclusively involves the following sequence of steps: material mixing to form a flowable paste→paste drying→crushing (but not pulverizing)→sieving (optional), with or without an additional optional drying step (post-crushing and/or post-sieving).
Invention Uniqueness with Respect to Material Placement
By virtue of flexibility in their composition and method for manufacture, particles of the invention can possess characteristics that are optimal for product settling through the water column (relatively high specific gravity, relatively large particle size and relatively high integrity). Thus, the potential for successful placement of masses of the particles across submerged sediment surfaces is also optimized.
Various unique aspects of the invention are summarized above. As also described above, many of these unique aspects represent significant improvements over existing products or materials and methods for creating active sediment caps (i.e. active capping layers).
In brief, the invention is a unique and versatile product that should be at least as successful as existing (and competing) products and materials in terms of providing for cost-effective as well as technically effective active capping of contaminated sediments.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20074750 | Sep 2007 | NO | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/NO08/00338 | 9/18/2008 | WO | 00 | 5/7/2010 |
