FI122359B - Procedure for lake restoration, procedure for treatment of sediment mass and use of double spiral press for treatment of dredging waste - Google Patents

Description

METHOD FOR LAKE RECONSTRUCTION, METHOD FOR TREATMENT OF SEDIMENT PULP, AND USE OF DOUBLE SCREW PRESSURE FOR DIFFICULTY

FÖRFARANDE FÖR SJÖRESTAURERING, FÖRFARANDE FÖR BEHANDLING AV SEDIMENTMASS SAMT ANVÄNDNING AV DUPPELSPIRALPRESS FÖR BEHANDLING AV MUDDRINGSAVFALL

The invention relates to a method according to claim 1, mainly for the rehabilitation of a eutrophied lake or a similar water basin, wherein the aqueous bottom sediment of the lake is removed by dredging known per se to increase the water depth. A further object of the invention is to provide a method for treating an aqueous dredged sediment mass containing organic matter, as well as a specific use of a double screw press mainly for agricultural use.

As a result of organic development, there is a constant biological cycle of plants and animals in the water of lakes and water basins that have been formed after the Ice Age. so that the aquatic plants of the lake bind the sun's energy and convert the nutrients in the water into organic matter. Gradually, with the death of the plants, this material settles to the bottom of the lake basin, forming a layer of bottom sediment, mainly classified as peat, which consists primarily of the decomposition waste of aquatic plants. In bottom sediments, the decomposition of organic material continues, whereby nutrients are released into the water. In low-nutrient lakes, this cycle is usually substantially balanced, whereby the increase in bottom sediment thickness is very slow, if any.

r »o i ^ However, due to human activities, nutrients may be present in the lake so that the natural low-nutrient cycle goes out and a different kind of cycle is replaced. Typical of this cycle is that

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g nutrients are in fact present in excess of what o o the indispensable need for a crop already growing in water. In this case, the crop will continue to grow beyond the above equilibrium state, with the amount of organic material in the lake constantly increasing until a new equilibrium is reached. However, this new equilibrium, called eutrophication, deviates from the balance of the poor nutrient water in a direction unfavorable to human 2 utilization, e.g. such that the quality of the water-rich vegetation changes with respect to the species, so that the proportion of mainly floating aquatic plants increases. When this crop dies, its decomposition binds oxygen so that even the most oxygen-free conditions in the lake can occur, causing the fish to die. At the same time, abundant anaerobic decomposition of plant waste leads to, for example, odor nuisance. Such a lake is essentially worthless for recreation and other uses.

In addition to these drawbacks, anaerobic conditions alter the equilibrium of the bottom sediment so that at an accelerated rate they dissolve nutrients that remain insoluble in the bottom sediment under oxygen conditions. Thus, once started, eutrophication often accelerates spontaneously, even when no more nutritional supplements are available. The thickness of the bottom sediment increases spontaneously at this stage, thus decreasing the water depth. At the same time, the height of the crop on the bottom of the bottom sediment gets closer to the sun, whereby light and heat further accelerate the process.

All in all, eutrophication of lakes poses a problem which in some cases very quickly destroys the recreational value of water in particular. Since eutrophication is most often caused by human activity, it is also typical that this decline in recreational value is greatest where the recreational use of the lake itself would be most valuable, ie in the vicinity of population centers. Thus, in addition to stopping the addition of nutrients per se, it would be particularly valuable to reintroduce lakes and ponds in such areas to recreational use, rather than growing at an accelerated rate.

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o ^ Small eutrophied ponds have sometimes been restored to a significant extent | sediment has been removed. In most cases, this has required, for technical reasons, that the pond be temporarily dried. The removed bottom sediment is then applied to the vicinity

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g to dry, whereby the decomposition of its organic material has in most cases caused serious aesthetic and functional as well as odor nuisance in the environment. In some cases, dredging waste is again composted. In both cases, the amounts of pulp to be treated in a major refurbishment project are significant and require either a large shore treatment area or long transport. It is clear from the sheer lack of space that very large lakes cannot be restored in this way.

Another type of remediation has involved artificial aeration of the water, which has been used to artificially prevent the bottom sediment being anoxic. Such an arrangement requires constant energy consumption and does not eliminate the original problems of shallow water and excessive nutrient content. As a result, the situation today is that the Rehe Belting problem is recognized but there is no workable solution.

DE 41 10 950 discloses the production of a soil improver, whereby another substance is mixed with the sediment to produce a product having the desired properties after granulation and drying.

US 4,659,472 discloses an arrangement for treating sewage sludge in which the sludge is mainly mixed with sawdust. This is done in a mixing basin where air is introduced from below to keep the mixture fluffy. In addition to fluffiness, the air causes a composting reaction where the temperature rises rapidly. The mixture thus obtained is introduced into a belt press where a polyelectrolyte solution is added thereto, whereupon the mixture is placed in a composting container.

US 5,129,167 discloses a water separation arrangement for a sand suction device in which -r-separated turbid water is returned to the suction head such that turbid water substantially "circulates" in the system and does not cloud the rest of the water mass.

It is an object of the present invention to provide a process for: | large amounts of bottom sediment can be removed efficiently, economically and ecologically from lakes and similar waters.

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It is a further object of the invention to provide an arrangement that can also be utilized near human dwellings.

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A further object of the invention is to provide an arrangement whereby nutrients which are valuable in themselves and in fact close to the end users are utilized in the form of a plant medium. Alternatively, according to another embodiment of the invention, the sediment containing the dredged organic material is made available for energy recovery.

According to the invention, the foregoing objects are achieved as set forth in the appended claims and according to the features defined therein. Thus, the restoration method of the invention is known for mixing dredged material and separate impregnating material during dredging, and subjecting the mixture to a mixing and compression step such that at least a substantial portion of the dredging mass is compressed into the tissue of the impregnating material. Thus, the dredging mass is subjected to mixing and pressing with the impregnating material to be mixed with it, in particular with peat, whereby the water of the dredging mass is pressed into the impregnating material.

Correspondingly, the dredged sediment treatment method of the invention is known for contacting dredging material with absorbent cellular structure having absorbent cellular structure, for mixing dredged material and absorbent material, and for further subjecting the mixture to mechanical compression. Preferably the sediment mass is mixed with the peat and the mixture is mechanically pressed so that the water is pressed into the peat.

The use according to the invention comprises dredging waste from the bottom sediment of a natural water body such as a lake using a double screw press for impregnation material such as peat, mainly for agricultural use.

| Other advantageous features of the invention and their features are apparent from the appended independent claims.

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The invention will now be described in more detail with reference to a preferred embodiment and the accompanying drawing, which, in general view, is a side view of a water basin with bottom sediments.

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According to the figure, basin 1, such as a lake, pond or the like, contains water whose surface is designated by reference 2. Lake bottom sediment 3 contains organic material from a lake biotope such as plants, fish, and microorganisms with varying degrees of degradation such that the deepest layers 3a somewhat mineralized, while the upper layers 3b and 3c contain fresher organic material. Particularly in a heavily eutrophied lake, the upper layers 3c of the bottom sediment 3 are strongly aqueous, sometimes even so that the boundary 4 between the free water and the bottom sediment is somewhat difficult to recognize as the solids concentration increases towards the bottom 5 as shown in the figure.

The figure shows that, in particular, the larger floating-leaf aquatic plants 6, such as algae and the like, grow such that their leaves 7 are somewhat near surface 2, while the root system 8 is at a height suitable for the plant. Similarly, smaller aquatic plants 6a, whose roots may sometimes form the surface layer of hard sediment 3, are also shown. It is often considered that a depth of about two meters is critical to the lake in the sense that deeper aquatic vegetation 6 is generally unable to rise to the surface and thus to the most effective solar radiation. Instead, in shallower water, growing conditions, both in terms of light and temperature, support the strong growth of aquatic plants, which in turn results in an increase in biomass if nutrients are available. In the figure, a depression line 9 of the bottom sediment 3 is shown with a diagonal line which would require removal of the entire lake for successful restoration. With this layer 9 being w, for example, a 1 meter thick restoration produces 10,000 m3 of sediment material per hectare of water. For such an amount, a site should be found where the degradation of organic material does not adversely affect the environment. Here is the Note that although the decomposition waste of the aquatic plants 6, 6a, i.e. the sediment material which is essentially comparable to peat, is highly aqueous in itself, the water C 1 g contained therein is highly nutritious. Removing the sediment layer 9 so that nutrient-rich water cannot flow back into the basin 1 would thus be quite important.

According to the invention, it is expedient that the removable layer 9 is dredged, for example by a suction dredger, so that the sediment 3c is removed as such. Fig. 6 is only a schematic representation of a dredging arrangement known per se, which may comprise, for example, a suitably sheared suction head 11 on a pontoon 10, from which the removed dredging mass 13 is removed from the basin 1 by known arrangements, e.g.

The treatment of the dredging masses according to the invention consists in making the dredging masses 13 as such substantially mixed with the porous impregnation material 14, in particular peat, so that the water and fine solids and nutrients in the dredging masses 13 are compressed into the cellular structure of the impregnation material 14. This step is preferably carried out in a screw press known per se, generally disclosed at 15. The screw press 15 has a suitably cooperating twin screw arrangement 16 which, in connection with the mixing of the materials 13, 14, also makes the materials subject to mutual compression. With compression, a substantial part of the dredging mass 13 is transferred to the cellular structure of the impregnating material 14.

Particularly close to the surface, dredging masses 13 from a typical slightly eutrophic lake contain <2 ... 20%, typically approx.

6 ... 10%. The dry matter consists mainly of decayed plant waste, a material that can be defined as peat, which in itself is comparable to fully composted peat. The chemical composition of sediment 3, 3c initially includes, in addition to organic carbon compounds, conventional substances which are mainly classified as fertilizers and trace elements, such as phosphorus, nitrogen, potassium, sodium, calcium, magnesium, boron, copper, iron, etc. useful substances which in turn contribute to the fact that the arrangement according to one embodiment of the invention, as a final product, produces very well the plant | or as a raw material for such material, which is in short supply in population centers. However, in addition to the useful substances mentioned, the mass may

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g also contains heavy metals and other harmful substances, mainly due to external effects. Often, the presence of such substances is quite local, as shown in Ref. 17, and it is therefore appropriate, by sediment analysis, to delineate the areas and depths from which dredging 13 to be removed or mix 18 resulting from impregnation molding is suitably treated.

The deeper the dredging is performed, the higher the dry matter content of the dredged organic material, and thus, according to a preferred embodiment of the invention, the compression process is controlled by at least partially adjusting the suction depth 11 of the dredging means. The water portion (e.g., about 80 ...> 98% of the total volume) of the cedar layer 3 contains a significant amount of nutrients that should be removed from the lake 1. Thus, it is expedient that a substantial portion of this water be impregnated into the absorbent material 14. in this case peat has proved to be particularly useful because its hollow tissue is capable of receiving water and finely divided solids almost equal to the output volume of peat.

A double screw press 15, known per se for agricultural manure treatment, which mixes material placed on top of the screws, i.e. dredging spreader 13 and impregnation peat 14, is suitable for mixing and pressing operations. by blowing, or by other means known per se, on the absorbent peat layer 20. In this context, according to one embodiment of the invention, it is appropriate that the peat 14 is slightly moistened to reduce dust. Likewise, in some embodiments, the arrangement is such that an additive which enhances one of the desired properties of the end product 18 is added at the same time to the peat 14 and / or dredging 13. Such are e.g.

9 bacteria for further composting of the final product 18, possible σ> nutrient balance supplement for the final product, surface tension reducing agent, buffering agent

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£ such as lime or the like and / or any other appropriate additive 21.

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With the rotation of the screws 16, the absorbing peat 14, 20, the dredging mass 13 0 added thereto, and any additives 21 are mixed together, and at the same time the highly aqueous dredging mass 13 and any additive 21 are compressed into the cellular material of peat 14. The mixing ratio depends on the properties of the dredging mass 13, but a typical mixture ratio is about 1 part dredging mass to 1-1.5 parts peat. The mixing ratio and compression pressure are conveniently maintained within the limits such that substantially all of the dredging mass 13, including the water contained therein, binds to the peat 14, whereby nutrient-rich water does not flow back into the pool and remains useful in the peat. Suitably, these parameters are controlled by adjusting dredging power, rotation speed of screws 16 and / or peat addition rate. Correspondingly, the elevation of the water surface 2 of the basin 1 during dredging, at least with respect to the water exiting the system via dredging masses 13, is controlled e.g. by damming, as shown in reference 22. Also, dam 22 often prevents the downstream nutrient rich water.

Particularly due to the properties of the impregnation peat 14, the amount of end product 18 is significantly smaller than the total amount of materials 13, 14 to be mixed together, since under pressure, the hollow tissue of peat 14 binds water in dredging waste 13 very efficiently. Typically, 1 part of dredging waste 13 added to 1.5 parts of peat 14 after mixing and compression still gives only 1.5 parts of the final product 18. Unlike the original plant substrate, which is somewhat inert, 14, the product 18 produced by the process of the invention now contains substantially all of the nutrients required. Thus, if the dark peat, already composted, is used as the impregnation peat 14, the end product 18 is thus even available as a growing medium immediately. If, on the other hand, light, somewhat crude, absorbent peat is used, which in itself has a higher absorption capacity, the final product 18 will again be particularly useful for energy production. In either case, the impregnation peat 14 prevents the odors otherwise caused by rotting dredging waste 13 and makes it hygienic, solid and easy to handle and transport.

O) | The invention brings with it a number of significant advantages which make it possible to restore even large lakes. First of all, the need for dredging areas gj is eliminated because, even after years of decomposition, odorous dredging waste does not have to be placed anywhere. Rather than being a hazardous waste, dredging waste becomes, according to the invention, a useful material that is even in short supply, especially in the vicinity of eutrophied lakes. At the same time the odor nuisance caused by dredging waste is eliminated and a commercially available product is replaced. The end product 9 itself is easily handled, transported and possibly further processed according to its end use. As such, the method according to the invention is field-based, easy to implement and reliable, and recover as much of the nutrients as possible. Thus, for example, nutrient-containing water also remains in the product and does not return to the water system. The technique used in the method is known per se, tested and readily available.

A further advantage is that even the very problematic dredging waste 13 formed from the problem areas 17 is easily manageable in such a way that it is possible to remove the harmful substances from the water and to prevent their spreading to the environment. Thanks to the method of the invention, a severely eutrophied lake can often be restored to its natural state, and in any case its water depth can be safely and without causing environmental problems increased by increasing the depth of the lake as the depth increases and vegetation disappears.

Some advantageous embodiments of the invention have been described above, but it will be apparent to one skilled in the art that the invention may be utilized in many other ways within the scope of the appended claims. It is clear, for example, that in some cases it is expedient to supplement the rehabilitation arrangement according to the invention with other measures. Thus, aeration and / or chemical treatment of water may be required to increase the oxygen content and, for example, to precipitate any nutrients and solids that may be mixed during dredging after dredging c3. It is also clear that, where reference is made above to the use of peat as a leaching material, this attribute must be considered to be very broad in scope 2 so that the term peat itself covers all such organic matter, mainly vegetation degradation. materials classified as products having an absorbent cellular structure.

r- It is also clear that other cm impregnation material having substantially the same properties may be appropriate in some cases.

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It is also clear that the aforesaid additive 21 may comprise a binder such that the final product 18, after compression, is suitably shaped and thereafter preferably solidified as such for use in, for example, garden and terrestrial construction, preferably such that binder and / or product 18 decomposes and / or as such provides a substrate. It will also be appreciated that the binder 21 may be such that the article 18 in a shaped and more cured form will be usable for other purposes such as a substantially hard building material or the like.

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Claims (11)

11 Patent Claims A method for reclamation of a eutrophic lake (1) or a natural water basin having a sedimentation layer which is removed in a manner known per se to dredge the aqueous bottom sediment (3, 3a, 3b, 3c) of the lake (1) to increase the water depth. (13) and the separate impregnating material (14, 20) are subjected to mixing and the mixture is subjected to a mixing and pressing step such that at least a substantial portion of the dredging mass (13) is compressed into the tissue of the impregnating material (14, 20). Method according to claim 1, characterized in that at least the coarse root (8) and / or any other coarse bodies of the aquatic plants (6, 6a) are removed from the dredged sediment layer (3c, 9) before dredging. Method according to Claim 1 or 2, characterized in that the dredging masses (13) to be impregnated contain both solids and at least a substantial part of the water in the dredging layer (9), wherein the level of the surface (2) of the basin (1) such that the volume to be absorbed is replaced by water sinking into the basin (1). Method according to one of Claims 1 to 3, characterized in that an agricultural waste treatment device (15) is known for the mixing and pressing step, preferably a double screw press (16) known per se. o (M h- · Method according to one of Claims 1 to 4, characterized in that the final product (18) obtained from the compression of σ> is subjected to post-composting to form a product of growth X £ to form a suitable product. h- · sj- {M Method according to one of Claims 1 to 5, characterized in that, after dredging at 0 °, the lake (1) undergoes a chemical treatment known per se to clarify the water and / or aerate the water to increase the oxygen content. 12 Method according to one of Claims 1 to 6, characterized in that the solids content of the dredging material (13) entering the mixing and pressing process is adjusted by adjusting the suction depth of the suction head (11). A process for treating and removing organic dredged organic sediment mass (13) in and from a natural water body, characterized in that the dredging material (13) is brought into contact with an absorbent cellular structure absorbent material (14, 20), and the dredging material (13) 14, 20) is subjected to mutual mixing, and that the mixture is further subjected to mechanical compression (16). Method according to Claim 8, characterized in that the method is carried out in a single suitably continuous working step with a double screw press (15, 16). Method according to claim 8 or 9, characterized in that dark, already at least partially composted, peat peat is used as the impregnation material (14, 20), or alternatively light crude peat, which is mainly suitable for energy production, thus , that a suitable additive is added to the mixable materials (13, 14, 20) prior to mixing, in particular the properties and / or further processing agents (21) of the final product (18). δ (M 9 11. Use of double screw press (15, 16) mainly for agricultural use, consisting of bottom sediment (3, 3c, 9) of natural water such as lake (1) | for compressing dredging waste (13) into a cell of impregnating material (14, 20), such as peat. ^ r CM CM O O O CM 13