WO2013025390A1

WO2013025390A1 - Process for treating lake sediment for conversion to beneficial soil products

Info

Publication number: WO2013025390A1
Application number: PCT/US2012/049752
Authority: WO
Inventors: Mohsen C. Amiran
Original assignee: Amiran Mohsen C
Priority date: 2011-08-17
Filing date: 2012-08-06
Publication date: 2013-02-21

Abstract

Methods and systems for converting sediment slurries, such as lake sediments, into nutrient enriched soil additives and potting soils are disclosed herein. The methods include processing a sediment slurry with a particle separation unit which disaggregates particles and organic materials from each other. The particle separation unit may include a device configured for inducing cavitation within the sediment slurry, such as a particle separation unit which includes high pressure jets suitable for impinging a high pressure fluid stream onto a flowing stream of the sediment slurry.

Description

PROCESS FOR TREATING LAKE SEDIMENT FOR CONVERSION

TO BENEFICIAL SOIL PRODUCTS

Cross-Reference To Related Applications

[0001] This application claims the benefit of U.S. Patent Application No. 61/524,757, filed on August 17, 2011, and U.S. Patent Application No. 61/528,006, filed on August 26, 2011, the entire contents of which are incorporated by reference herein in their entirety.

Background

[0002] Lakes in the United States and throughout the world have been significantly impacted throughout the years by water runoff containing high levels of nutrients, organics and sediment resulting in adverse water quality, regular algae blooms, and low dissolved oxygen conditions. These conditions are particularly acute in lakes that are co-located in a drainage basin with crop and livestock producing businesses that use chemical fertilizers containing phosphorus and/or that use animal manures as fertilizers.

[0003] The runoff conditions cause significant impacts to communities through reduced farm production (resulting from limitations imposed on farming and livestock production operations to reduce the discharge of organics to the watershed) and/or by reduced tourism and recreational use of lakes. In 1993, the United Nations Environment Program estimated that 54% of lakes in Asia are eutrophic; in Europe, 53%; in North America, 48%; in South America, 41%; and in Africa, 28%. The problem is world-wide and the increasing use of chemical fertilizer in order to stimulate food production from soil whose natural nutrients have been depleted only increases the problem.

[0004] Several efforts can be made to improve the ecological conditions of lakes. These include altering fertilizer usage, restricting runoff into the lake, pre-treating the runoff before it enters the lake, and intercepting the nutrients in the runoff through natural vegetative filtering systems. In combination with these techniques, removal of the accumulated mass of nutrient laden sediment from the lake through dredging has the near- term effect of restoring the health of the lake. However the disposal of the dredged sediment has been problematic because the large volumes of sediment with a high phosphorus content have been deemed a waste often requiring expensive relocation and/or disposal. Summary

[0005] The methods disclosed herein, an embodiment of which is illustrated in the attached figures, are directed to processes for converting lake sediments, particularly those containing high nutrient loading, primarily phosphorus, into high-performing, enriched, fortified commercial grade potting soil. The process may fulfill one or more of the following objectives:

• Providing a way for contaminated dredged sediments to be converted to an

economic, beneficial use product, thus facilitating overall restoration of

hypereutrophied lakes;

• Providing a way to incorporate algae blooms removed from lakes by various means to be used in a beneficial use product; and/or

• Reducing or eliminating the public economic burden associated with the disposal of contaminated sediments dredged from eutrophied lakes.

One or more additional indirect objectives may also be achieved by implementing the methods, including:

• Promoting a healthier, more balanced water resource;

• Increasing the availability and suitability of the lake for recreation and tourism;

• Creating manufacturing jobs associated with operating the decontamination and soil production facilities; and/or

• Generating a positive impact on the local economy from both increased recreational use and/or tourism as well as the production activity associated with making and selling the commercial grade potting soils or other soil products.

[0006] The present application is directed to a process for converting sediments, e.g., sediments recovered from lakes and streams, into beneficial soil products. The process includes providing a slurry of sediment, which typically has its solids content adjusted to be no more than about 35 wt.%, e.g., by adding water as needed to the recovered sediments. The sediments slurry is typically process, e.g., via screening, to remove any particles larger than about 0.5 inches in size. The sediment slurry is processed using a particle separation unit which disaggregates particles and organic materials in the sediment from each other. This is typically accomplished by impinging a fluid stream from high pressure jets on the flowing slurry material. In some instances, an oxidizing composition and/or surfactant may be added to a sediment slurry prior to it being processed in the particle separation unit. After processing in the particle separation unit, the treated slurry may be dewatered if a higher solids content is desired. Binding material (e.g., a binding material high in calcium) and bulking agent are added to the treated slurry. In many instances, additional nutrient material(s) may be added to adjust the nutrient profile of the final product.

Brief Description of the Drawings

[0007] Figure 1 is a schematic illustrating one embodiment of the present process for converting lake sediments into beneficial soil products.

[0008] Figure 2 is a schematic illustrating one embodiment of a particle separation unit suitable for use in the present method.

[0009] Figure 3 illustrates one suitable embodiment of an Particle Separation Unit showing the alignment and orientation of nozzles supplied with high-pressure liquid stream delivered into the flowing slurry stream from a high-pressure pump.

Detailed Description

[0010] Eutrophic lakes are those lakes that exhibit a total phosphorus concentration averaging 84 mg/m 3 with a range of 16 to 386 mg/m 3 and chlorophyll concentration averaging 14 mg/m 3 with a range of 3 to 78 mg/m 3. A subcategory of eutrophic lakes are termed hypereutrophic. Such lakes are often relatively shallow lakes with a large volume of accumulated organic sediment. Such lakes are often characterized by extensive, dense weed beds, accumulations of filamentous algae, poor water clarity, an elevated total phosphorus concentration, often in excess of 100 mg/m 3 and the chlorophyll may be over 50 mg/m 3. Thus, the hypereutrophic lake represents the extreme ranges for the eutrophic lake. The fish and other aquatic animals unfortunate enough to find themselves in these lakes are subject to extreme shifts in oxygen concentrations; sometimes very high and at other times very low, even to the point of forming oxygen depleted dead zones. These lakes are often subject to "winter kill" and even "summer kill" where the lowered oxygen concentration results in an extensive kill of fish and sometimes other organisms. Needless to say, these are not very desirable lakes for human enjoyment, but in almost every case the

hypereutrophic lakes resulted from runoff associated with by human activities.

[0011] Sediment is commonly removed from lakes by dredging, which may be achieved using, for example, a conventional mechanical clam-shell technique, by hydraulic methods or any other suitable method. Mechanical clam-shell removal is often desirable because it tends to reduce the inclusion of water in the extracted sediment. When hydraulic methods are used, their production rate must be carefully matched to the processing rate and desired slurry solids content of the decontamination/production plant. The recovered sediment may then be transported to the decontamination/production plant, e.g., via barge if clam-shelled or it may be pumped directly to shore holding tanks if hydraulic dredging is used.

[0012] After receipt at the decontamination/production plant, a slurry of the sediment may be formed by the addition of water (if needed for clam-shell dredging). Generally the slurry desirably has a solids content of no more than about 35 wt.%. The sediment slurry is commonly processed by being screened to remove all larger particles and organic material greater than, for example, 0.5 inches in size (1.3 cm) from the slurry by, for example, a conventional screening process. Depending on the nature of the oversize material that is extracted from the sediment, the removed material can then be set aside for additional processing for topical odor control and subsequent composting (preferred), used directly as fill material for construction or set aside for later disposal in a landfill.

[0013] In many instances, no additional chemicals will need to be added during the formation of the slurry unless there is excessive organic material content and/or noxious odors associated with the extracted sediment. When the sediment has a substantial organic material content, e.g., greater than about 8% by dry weight, it may be useful to add at least one surfactant material to aid in breaking down the organic structure. Any type of surfactant may be used, although natural surfactants are often quite suitable, including, for example, sulfonated vegetable oils, natural tomato surfactants, cocamidopropyl betaine (CAPB) (a surfactant derived from coconut oil and dimethylaminopropylamine), polyglucosides, and others, typically at a dosing rate of between 0.01 and 0.05% by volume of slurry. The surfactant selection and dosing percentage can be determined by bench testing various concentrations prior to bulk processing to determine the effectiveness of surfactant and dosing concentration combinations that breaks the organic structure. In those instances in which a surfactant is used, it can be mixed into the slurry at low speed in a mixing tank of conventional design for sufficient period of time (often approximately 30 minutes) to achieve a satisfactory distribution throughout the composition. In some embodiments, the method may be run as a continuous process. In such cases, it may be advantageous to conduct the mixing operation so that the slurry has a similar average residence time in the mixing tank, while slurry is continuously being introduced and removed through an appropriate outlet port.

[0014] Further, depending on the odor characteristics of the slurry, it may be desirable to suppress noxious organic odors during subsequent processing by adding an oxidizing composition to the slurry. The oxidizing composition typically contains an oxidant, such as a percarbonate salt, hydrogen peroxide, sodium perborate, sodium hypochlorite or other peroxide material (e.g., organic peroxides, such as an organic percarboxylic acid, e.g., peracetic acid). The oxidizing composition may also contain a surfactant that is stable in the presence of the oxidant. For example, the oxidizing composition may include a fatty acyl sarcosinate salt and/or a fatty acid salt. In other embodiments, the screened slurry may be treated with ozone for odor suppression and destruction of pathogens which may be present. One example of a suitable oxidizing composition useful for the present process includes a mixture of sodium percarbonate, sodium lauroyl sarcosinate and sodium laurate. For example, the oxidizing composition may contain 30 to 60 wt% sodium percarbonate, 35 to 45 wt% sodium lauroyl sarcosinate, and 1 to 5 wt% sodium laurate. Oxidizing compositions such as those described above may be blended into the screened slurry at a weight ratio of about 1 : 1000 to 1 :4000 (oxidizing composition: screened slurry).

Variations in the composition and the desired degree of odor suppression may require other feed rates.

[0015] An example of a composition useful for this purpose includes, 30 to 60 wt% sodium percarbonate, 35-45 wt% sodium lauroyl sarcosinate, and 1-5 wt% sodium laurate blended into the screened slurry at a weight ratio of about 1 : 1000 to 1 :4000. Variations in the composition and the desired degree of odor suppression may require other feed rates. The mixer in the tank may be operated at a relatively low speed, for example, 20 to 50 rpm.

[0016] Once the material has been prepared as described above, the sediment slurry may be accelerated using a centrifugal pump, e.g., a pump having an output of about 100 to 250 gpm and in some cases as high as 350 gpm, with flow rates for the slurry of about 125 - 150 gpm at < 5 psi being quite common. For any particular situation, it is preferred that the centrifugal pump provide for a variable output flow to provide for adjustment of the conditions within the processing chamber during the course of the operation. For example, the Particle Separator may be run with a fixed pressure/flow through the impinging high-pressure jets and the efficiency of the particle disaggregation may be modified by varying the flow rate of the slurry through the unit. [0017] Following the slurry formation step (and optional surfactant/odor suppression steps) described above, the slurry may be pumped to the Particle Separator using the centrifugal pump. Figure 2 illustrates the flow through the Particle Separation Unit. The function of the Particle Separator is to disaggregate the sediment and organic particles from each other. This may be accomplished using high pressure liquid jets (also referred to herein as "high pressure jets," "high pressure liquid nozzles" and "high-pressure spray nozzles") operating at a pressure sufficient to achieve the desired modification of the slurry properties, for example, about 5,000 to 20,000 psi, commonly about 6,000 to 15,000 psi, e.g., jets operating at about 10,000 psi (680 bar). The reason for disaggregating the sediment is to prepare the sediment particles by increasing the relative surface area so that subsequent additives may more easily bind to and interface with individual solid particles.

[0018] The output of the centrifugal pump described above is typically connected to the input of the Particle Separation Unit. In a typical apparatus, the output stream is connected to the primary chamber input 140 whereby the primary liquid flow is directed along a path generally parallel to the longitudinal axis of the chamber. Two or more high-pressure spray nozzles 141 are directed at the primary input stream, converging upon the primary input stream (and in some embodiments the high pressure liquid nozzles 141 may be oriented at an angle to primary input stream as illustrated in Figure 3). The number of nozzles 141 is determined by the sediment type, solids content, form of undesired particles, and processing goals. Apparatus

configurations having as few as 2 and as many as 20 or more secondary nozzles may be employed (often 4, 6 or 8 nozzle configurations). Figure 3 illustrates one suitable embodiment of an apparatus with high-pressure spray nozzles 141 directed to impinge the primary slurry input stream. The nozzles are commonly supplied with high-pressure liquid stream (typically water) from a secondary liquid supply delivered through a high-pressure pump (e.g., providing 60 gpm at 10,000 psi) through a high pressure liquid inlet 142. The high-pressure liquid stream may suitably be generated within a range of other similar pressures. For example, the high-pressure liquid stream may be supplied to the nozzles at a pressure within the range of about 5,000 to 20,000 psi, more commonly about 8,000 to 12,000 psi. The volume of water introduced into the slurry stream from the high pressure liquid nozzles 141 may be a reasonably substantial percentage of the total inlet slurry flow, e.g., the total flow from the nozzles may be about 25 to 50 vol.% of the volume of slurry flowing into the inlet of the Particle Separation Unit. For example, where the slurry is flowing into the inlet at a rate of about 125 to 150 gpm, the total flow rate of high pressure water being introduced via the nozzles may be about 50 to 60 gpm. For incoming slurries having a solids content of about 25 to 35 wt.%, this could result in a dilution of the slurry down to a solids content of about 20 to 30 wt.%.

[0019] After passage through the Particle Separation Unit, the point the slurry is usually ready to be modified with additives in order to produce the desired type of soil product. Optionally, however, analysis and bench testing of different blends of additives may be particularly useful in those instances in which: a. One or more of the characteristics of the incoming sediment have changed or may have been changed since the last production run by, for example, relocating the dredging operation, extracting different strata from the lake bed and/or heavy rains in the relevant watershed; and/or b. The specification of the output soil product(s) has been changed and require, for example, a different package of additives, soil conditioners, N-P-K adjusters, in order to achieve the desired output.

[0020] The output from particle separator , including any optional nutrient additive steps is typically pumped to a thickening tank where excess water, if any, may be removed by any common means such as settling or centrifuging. The objective is generally to produce a slurry with a solids-moisture ratio of approximately 1 : 1 ± 10% (i.e., a solids-moisture ratio on a weight basis of about 0.9: 1.0 to 1.1 : 1.0). Laboratory analysis and/or field tests may be used to monitor the process performance and adjust the relative ratios of the slurry components as necessary to maintain the target composition range.

[0021] Following the dewatering operation, a binding material high in calcium may be added in order to stabilize the availability of nutrients that will be included in the final product. A suitable binding material is gypsum, which may be added to the slurry at a rate of approximately 2 to 10 %, commonly 3 to 5%, e.g., about 5% by weight. However, if the sulfur content of the incoming material is high (for example, 1,000 mg/kg dry weight or above), lime (which contains no sulfur) may be used in place of gypsum, also typically at a rate of about 2 to 10 %, more commonly about 3 to 5%, and often about 5% by weight.

[0022] After adding the binding material, additional additives may be mixed with the slurry in the same mixing tank or alternatively the now bound mixture can be transferred by conventional means to a separate mixing tank. This tank may also be operated at 20 - 50 rpm. In this next step, liquid or solid nutrients, either humus or non-humus based, and one or more bulking agents may be added. Suitable bulking agents may be selected from a group consisting of finely shredded yard waste, perlite, vermiculite, sphagnum peat moss and combinations thereof. Selection of the additives and the proportions used depend upon the characteristics of the desired output products as measured by soil moisture holding capacity, cation exchange capacity, and N-P-K content. The pH of the final product should be between 6 and 8 (7 preferred). The target soil moisture holding capacity will typically be between 0.7 to 2.2 inches/foot with a preferred value of 1.5 inches/foot. The target cation exchange capacity will typically be between 10 and 60 meq/100 g, depending on the soil product being manufactured. The product may be mixed for about 20 to 60 minutes (typically about 30 minutes). At the completion of mixing the product is ready for final testing to verify composition, and then sent to packaging and distribution.

[0023] Agricultural and residential use of fertilizers, and other human activity, has moved many lakes from a desirable eutrophic level wherein nature and human activity is balanced to a state where hypereutrification exists that directly impacts human health, the

environment, and economic activity. Human activity can, however, be mitigated through sustainable environmental stewardship and beneficial use of contaminated materials formerly thought of as wastes. The process disclosed in this application, when combined with pollutant source reduction, can be a powerful agent for restoration of eutrophic lakes.

[0024] The disclosed process may provide one or more of the following advantages:

• Existing phosphorous loading in lake sediments is mitigated;

• Cyanobacteria blooms related to phosphorus loading are mitigated;

• Odor generated by cyanobacteria is mitigated;

• Water is clarified by reductions in phosphorus loading and cyanobacteria;

• Chemical control additions to lakes are reduced or eliminated;

• Contaminated sediment is treated as a resource, thus supporting local, national, and global sustainability goals;

• Proven technology converts contaminated sediments into high quality soil

products;

• Increased recreational activity lake usage, jobs, and economic development; and The economic burden on governments associated with efforts to mitigate contamination and/or improve water quality is greatly reduced by the reuse and recovery of economic value by converting contaminated sediments into high-quality soil products.

Claims

What is Claimed is:

1. A method for converting sediment into a beneficial soil treatment product comprising:

processing a sediment slurry with a particle separation unit which disaggregates particles and organic materials from each other, thereby providing a processed sediment slurry.

2. The method of claim 1 , wherein the particle separation unit is a device configured for inducing cavitation within the sediment slurry.

3. The method of claim 1, wherein the particle separation unit comprises high pressure liquid nozzles suitable for impinging a fluid stream onto a flowing stream of the sediment slurry.

4. The method of claim 3, wherein the particle separation unit has an inlet port; and the total liquid flow from the high pressure liquid nozzles is about 25 to 50 vol.% of the volume of the sediment slurry flowing into the inlet port of the particle separation unit.

5. The method of claim 1, further comprising adding an oxidizing composition to the sediment slurry prior to processing the sediment slurry in the particle separation unit.

6. The method of claim 5, wherein the oxidizing composition comprises an oxidant selected from percarbonate salts, hydrogen peroxide, sodium perborate, sodium hypochlorite, organic percarboxyhc acids and combinations thereof.

7. The method of claim 5, wherein the oxidizing composition comprises an oxidant-stable surfactant selected from fatty acyl sarcosinate salts, fatty acid salts and combinations thereof.

8. The method of claim 5, wherein the oxidizing composition comprises about 30 to 60 wt.% sodium percarbonate, about 35-45 wt.% sodium lauroyl sarcosinate, and about 1-5 wt.%> sodium laurate.

9. The method of claim 1 , further comprising adding surfactant material to the sediment slurry prior to processing the sediment slurry in the particle separation unit.

10. The method of claim 9, wherein the surfactant material comprises a surfactant selected from sulfonated vegetable oils, natural tomato surfactants, cocamidopropyl betaine, polyglucosides, fatty acyl sarcosinate salts, fatty acid salts and combinations thereof.

11. The method of claim 9, wherein about 0.01 and 0.05 vol.% (based on the volume of the sediment slurry) of the surfactant material is added to the sediment slurry.

12. The method of claim 1, wherein the processing step comprises processing a sediment slurry having a solids content of no more than about 35 wt.%.

13. The method of claim 1, further comprising removing particles larger than about 0.5 inches in size from the sediment slurry prior to the processing operation.

14. The method of claim 1, further comprising dewatering the processed sediment slurry to provide a dewatered sediment slurry.

15. The method of claim 14, further comprising adding binding material to the dewatered sediment slurry.

16. The method of claim 14, further comprising adding nutrient material to the dewatered sediment slurry.

17. The method of claim 1, further comprising adding one or more of binding material, bulking agent and nutrient material to the processed sediment slurry.

18. The method of claim 1, further comprising:

removing particles larger than about 0.5 inches in size from the sediment slurry prior to the processing operation;

adding an oxidizing composition to the sediment slurry prior to processing the sediment slurry in the particle separation unit;

adding surfactant material to the sediment slurry prior to processing the sediment slurry in the particle separation unit;

dewatering the processed sediment slurry to provide a dewatered sediment slurry;

and

adding one or more of binding material, bulking agent and nutrient material to the dewatered sediment slurry.

19. A treated sediment slurry produced according to the method of any of claims 1 to 18.

20. A system for treating a sediment slurry comprising:

the particle separation unit which includes a device configured for inducing cavitation within the sediment slurry, such that particles and organic materials in the sediment slurry are disaggregated from each other.

21. The system of claim 20, wherein the particle separation unit comprises high pressure nozzles suitable for impinging a high pressure fluid stream onto a flowing stream of the sediment slurry.

22. The system of claim 21 , wherein the high pressure nozzles impinge the high pressure fluid stream at an angle in a countercurrent direction onto the flowing stream of the sediment slurry primary.

23. The system of claim 21, wherein the high pressure nozzles are capable of impinging the fluid stream at a pressure of about 5,000 to 20,000 psi onto the flowing stream of the sediment slurry.

24. The system of claim 20, wherein particle separation unit further comprises inlet and outlet ports; and the system further comprises:

(a) a dewatering unit in fluid communication with the outlet port;

(b) a screening device, which is capable of removing particles larger than about 0.5 inches in size from the sediment slurry, in fluid communication with an inlet of a low pressure centrifugal pump; wherein an outlet of the low pressure centrifugal pump is in fluid communication with the inlet port of the particle separation unit.