Method and device for injecting flocculants into the bottom sediment of lakes, seas and watercourses

Abstract

In the invention is provided a method for injecting coagulants into the sediment of lakes, seas and watercourses, comprising the steps of pumping at least one coagulant from a storage position at or near the surface of a lake, sea or watercourse to a multitude of injectors positioned such that during injection, their point of discharge is in the sediment of the of lake, sea or watercourse, pumping water from the lake, sea or watercourse to the multitude of injectors. At the injectors, mixing the at least one coagulant with the pumped water, and injecting the resulting mixture into the interstitial water of the sediment, such that the mixing of the injection water and the at least one coagulant takes place in conjunction with effecting the injection. The vertical distance, from the inlet position for water to be pumped to the point of discharge of the resulting coagulant and water mixture, is 2 meters or less. Also provided is s system for use with the method of the invention.

Description

[0001] METHOD AND DEVICE FOR INJECTING FLOCCULANTS INTO THE BOTTOM SEDIMENT OF LAKES, SEAS AND

[0002] WATERCOURSES

[0003] Field of the Invention

[0004] The present invention relates to a method for injecting coagulants into the sediment of lakes, seas and watercourses, which involves mixing of injection water and coagulants. The invention relates also to a device for implementing the method according to the present invention.

[0005] Background of the Invention

[0006] High nutrient levels and excessive plant and algae growth characterize eutrophic lakes or waterways, posing several significant challenges when it comes to treatment and restoration. Some of the biggest challenges associated with treating eutrophic lakes include Nutrient Control. The primary cause of eutrophication is the influx of excessive nutrients, particularly nitrogen and phosphorus, from various sources such as agricultural run-off, sewage discharge, and industrial pollution. Controlling and reducing nutrient inputs is a complex and ongoing challenge. Climate change can exacerbate eutrophication by altering temperature and precipitation patterns, which can influence nutrient cycling and algal growth. Adapting lake management strategies to a changing climate is a challenge.

[0007] However, even if nutrient influx is reduced, there has often been accumulation of nutrients over many years (so-called "legacy nutrients") which can continue to fuel algae blooms even after external inputs are reduced. Nutrients binds to large into sediments at the lake bottom, and over time, this nutrient-rich sediment can become a source of ongoing eutrophication often referred to as "internal loading”. Addressing sediment accumulation may require dredging or other sediment management techniques. Such restoration efforts require substantial financial and human resources. Securing funding for ongoing monitoring, research, and management can be a hurdle for many lake management programs.

[0008] There are several different strategies for removing legacy nutrients from lake water. Instead of removing legacy nutrients, they can be bound into the lake sediment, thereby avoiding nutrient release with minimum effort.

[0009] US5,039,427A teaches a method for removing suspended solids and to precipitate and inactivate phosphorus in lake water by adding aluminum hydroxide sulphate. US4,877,524A teaches an apparatus for treating bodies of water for correcting chemical, biological or other imbalances. A treatment agent is dispensed within a water body, the dispensing rate being proportional to the boat speed. Both aluminum sulphate and sodium aluminate are taught as treatment materials among others.

[0010] Thus, there is still a need for cost-effective methods for lake and waterway restorations, where sediment and legacy nutrients are considered. Preferably, such methods are both energy efficient and ensure that a substantial portion of the treatment agents used are reacted with the legacy nutrients.

[0011] Summary of the Invention

[0012] Accordingly, the present invention preferably seeks to mitigate, alleviate or eliminate one or more of the above-identified deficiencies in the art and disadvantages singly or in any combination and solves at least the above mentioned problems by providing a method for injecting coagulants into the sediment of lakes, seas and watercourses, comprising the steps of: pumping at least one coagulant from a storage position at or near the surface of a lake, sea or watercourse to a multitude of injectors positioned such that during injection, their point of discharge is in the sediment of the of lake, sea or watercourse, pumping water from the lake, sea or watercourse to the multitude of injectors, at the injectors, mixing the at least one coagulant with the pumped water, and injecting the resulting mixture into the interstitial water of the bottom lower sediment, such that the mixing of the injection water and the at least one coagulant takes place in conjunction with effecting the injection, characterized in that, the vertical distance, from the inlet position for water to be pumped to the point of discharge of the resulting coagulant and water mixture, is 2 meters or less.

[0013] In one further aspect, the distance between the surface and the lower sediment of the of the lake, sea or watercourse may be at least 3 meters, such as at least 5 meters, such as between 3 to 100 meters, such as between 3 to 50 meters, such a between 5 to 30 meters. According to one further aspect, the sediment is the bottom sediment of lakes, seas and watercourses.

[0014] Also provided is a device for injecting coagulants into the sediment of lakes, seas and watercourses, the device comprising: a watercraft, a storage space for coagulants, a pumping device for coagulants, comprising an inlet and an outlet, a supporting member comprising a number of a number of injector pipes mounted along the supporting member, and an injection water pump comprising an inlet and an outlet, wherein the inlet of the pumping device for coagulants is connected to the storage space for coagulants and the outlet of the pumping device for coagulants is connected to the injector pipes, and the inlet of the injection water pump is in contact with the lake, sea or watercourse water, and the outlet of the injection water pump is connected to the injector pipes, such that mixing of the injection water and the at least one coagulant takes place in conjunction with effecting the injection, and wherein the vertical distance from the injection water pump inlet to point of discharge at the end of the injector pipes is less than 2 meters.

[0015] Brief Description of the Drawings

[0016] These and other aspects, features and advantages of which the invention is capable of will be apparent and elucidated from the following description of embodiments of the present invention, reference being made to the accompanying drawings.

[0017] Fig. l is a schematic illustration of part of the supporting member, here with two of the multitude of injector pipes, and an injection water pump, for the device for injecting coagulants into the (bottom) sediment of lakes, seas and watercourses.

[0018] Fig. 2 is a schematic illustration of a device for injecting coagulants into the sediment of lakes, seas and watercourses, the device comprising a watercraft, storage space for coagulants, a pumping device for coagulants, a supporting member with a number of a number of injector pipes and an injection water pump. The supporting member is currently at the bottom of the lake, sea or watercourse, such that the injectors can inject coagulant and water into the bottom sediment. Note that the injection water pump is located at the supporting member, making the vertical distance from the injection water pump inlet to point of discharge at the end of the injector pipes less than 2 meters.

[0019] Fig. 3 is a schematic illustration of an alternative embodiment of a device for injecting coagulants into the sediment of lakes, seas and watercourses, the device comprising a watercraft, storage space for coagulants, a pumping device for coagulants, a supporting member with a number of a number of injector pipes and an injection water pump. The supporting member is currently at the bottom of the lake, sea or watercourse, such that the injectors can inject coagulant and water into the sediment. Note that although the injection water pump is located at the watercraft, however, the that the injection water pump inlet is located at the supporting member, making the vertical distance from the injection water pump inlet to point of discharge at the end of the injector pipes less than 2 meters. Figure 4 is a picture showing a coagulants with a supporting member with injectors for injecting coagulants into the sediment of lakes, seas and watercourses.

[0020] Figure 5 is a picture of the injectors during operation, where the injectors during operation runs pressed down into the sediment in order to distribute the coagulant where the concentration of nutrients is the highest.

[0021] Figure 6 is a schematic illustration of the supporting member made up of shorter boom sections mounted together such that they may bend or flex slightly at the intersections, enabling the supporting member to adjust to the shape of the sediment bottom.

[0022] Description of embodiments

[0023] The following description focuses on an embodiment of the present invention applicable to a method for injecting coagulants into the sediment of lakes, seas and watercourses. The invention relates also to a device for implementing the method according to the invention.

[0024] In the invention, coagulants are mixed with water and the resulting mixture is injected into sediment. The method may be used in lakes, seas and watercourses, where watercourses includes wetlands and swamps or any other waterbodies. By injecting the coagulant / water mixture into the sediment, the coagulant can penetrate deeply into the sediment. It gives the coagulant a better chance to react with the legacy nutrients at the time of the injection, thereby binding more of the legacy nutrients in the sediment. In figure 5 it is shown how the water and coagulant can be injected into the sediment.

[0025] Thus, both water and coagulant has to be pumped to the point of injection. Since even shallow lakes or ponds may have a depth of up to more than 20 meters, this means that there will be a considerable pressure difference and pressure drop (friction) to overcome in order to inject the coagulant / water mixture into the bottom sediment. As such, a large pump is required to pump the water downwards to the lake sediment along with a smaller pump for the coagulants. If the lake or waterway is in a preservation area, for instance with sensitive birdlife, a large diesel pump may not be suitable for keeping noise levels low and environment impact at a minimum.

[0026] Thus, the method of the invention comprising the steps of pumping at least one coagulant from a storage position at or near the surface of a lake, sea or watercourse to a multitude of injectors positioned such that during injection, their point of discharge is in the sediment of the of lake, sea or watercourse, pumping water from the lake, sea or watercourse to the multitude of injectors, at the injectors, mixing the at least one coagulant with the pumped water, and injecting the resulting mixture into the interstitial water of the sediment, such that the mixing of the injection water and the at least one coagulant takes place in conjunction with effecting the injection. The method is characterized in that the inlet position for water to be pumped is closer to the water surface than the point of discharge and that the vertical distance, from the inlet position for water to be pumped to the point of discharge of the resulting coagulant and water mixture, is 2 meters or less.

[0027] The distance between the surface and the sediment of the of the lake, sea or watercourse may be at least 3 meters, such as at least 5 meters, such as between 3 to 100 meters, such as between 3 to 50 meters, such a between 5 to 30 meters.

[0028] The sediment may be the bottom sediment of lakes, seas and watercourses. This also includes any accumulated lower sediments, such as sediment accumulated on top of a hard rocky bottom of a lake, sea or watercourse.

[0029] That is, although the sediment may be on a depth of for instance 25 meters, the pump will only need to pump maximum two meters downwards (against the increasing water pressure) in order to inject the water and coagulant mixture into the lake sediment.

[0030] The pressure will increase roughly 10 kPa per meter of water (this roughly follows the formula for pressure in a fluid: Pressure (P) = Density (p) x Gravitational Acceleration (g) x Depth (h); If we average the density (p) as approximately 1000 kg / m3and the gravitational acceleration (g) is approximately 9.81 m / s2, then the pressure at 1 meter is: P_lm = 1000 kg / m3x 9.81 m / s2x 1 m = 9,810 pascals (Pa)). As such, the pressure difference between the surface and at 25 meters depth is almost 250 kPa, while the pressure difference between 23 meters and 25 meters is only about 20 kPa.

[0031] Also, a very high pressure difference (such as 250 kPa or more) means that a pump will require very high power consumption during operation. In addition, it requires a high torque in order to start at all. Thus, the pump can be equipped with a much smaller (i.e. less powerful) motor. This makes a cheaper, less power consuming and less heavy pump arrangement for injecting the water and coagulant using the method of the invention.

[0032] The position at or near the surface of a lake, sea or watercourse may be from between 0 to 2 meter below the surface, such as between 0.2 to 1.5 meter, such as 0.5 to 1 meters below the surface of the lake, sea or watercourse.

[0033] In the invention, coagulant compounds are used to bind legacy nutrients in the bottom sediment. Phosphorus is considered one of the most important legacy nutrients in lake bottoms due to its significant impact on the water quality and ecological health of lakes. Phosphorus is often the limiting nutrient in freshwater ecosystems. This means that its availability can control the growth of aquatic plants and algae. Even a small increase in phosphorus levels can lead to excessive plant and algae growth, causing disruptions to the lake's ecosystem. Phosphorus has the characteristic of being relatively persistent in sediments at the bottom of lakes. Over time, it can accumulate in lake sediments as a legacy nutrient, even if external inputs of phosphorus are reduced. Phosphorus cycles through the lake ecosystem at a slower rate compared to other nutrients like nitrogen. It can be trapped in sediments for extended periods and then be released under certain conditions, such as when sediments are disturbed or when anoxic (low-oxygen) conditions prevail in the lake bottom. This release can further exacerbate water quality problems. Thus, legacy phosphorus in lake sediments can contribute to ongoing water quality issues, even if external phosphorus inputs are reduced. This makes phosphorus management in lakes particularly challenging. Due to its persistence and long-term impact, managing legacy phosphorus in lake bottoms is a critical aspect of lake restoration and water quality improvement efforts.

[0034] Thus, the coagulants may be phosphorus-binding coagulants.

[0035] Examples of such coagulant compounds used for this purpose are Aluminum- Based Coagulants, Iron-Based Coagulants, or Calcium-Based Coagulants.

[0036] Aluminum sulfate (or aluminum salts such as “alum”) and polyaluminum chloride (PAC) are commonly used aluminum-based coagulants. They work by forming aluminum hydroxide flocs, which can adsorb and chemically bind with phosphorus, resulting is aluminum phosphate compounds that are less soluble and thus will stay in the sediment. The low solubility of the formed compounds provide a very stable long term binding of legacy phosphorus. Aluminum-based coagulants, such as aluminum sulfate (“alum”) and polyaluminum chloride (PAC) can be used at a slightly acidic pH. Aluminum sulfate (alum) and polyaluminum chloride (PAC) are most effective at binding phosphorus in the pH range of approximately 5.5 to 7.5.

[0037] Ferric chloride and ferric sulfate are examples of iron-based coagulants. They can react with phosphorus in water to form iron phosphate compounds, which are less soluble and thus will stay in the sediment. Iron-based coagulants are effective at binding phosphorus in a slightly acidic to neutral pH range. The optimal pH range for the removal of phosphorus using iron-based coagulants is typically between 6.0 and 7.5.

[0038] Calcium -Based Coagulants: Calcium-based compounds like calcium chloride and calcium hydroxide can also be used in some cases to remove phosphorus. They work by forming calcium phosphate compounds that can precipitate into the sediment. The precipitation of calcium phosphate primarily occurs in the pH range of 8.0 to 10.0. It is common to adjust the pH of the water to be within the optimal range to facilitate the precipitation of calcium phosphate compounds by adding chemicals such as lime (calcium hydroxide).

[0039] Thus, it is important to note that the effectiveness of coagulants in removing phosphorus depends on various factors, including the pH of the water, the concentration of other ions and substances in the water, and the specific forms of phosphorus present (e.g., orthophosphate, polyphosphate, or organic phosphorus). Additionally, the selection of the appropriate coagulant and the optimization of the treatment process depend on the water quality characteristics and treatment goals of a particular system.

[0040] In the invention, the the at least one phosphorus-binding coagulant is selected from a list consisting of Aluminum -Based Coagulants, Iron-Based Coagulants, and Calcium-Based Coagulants, or a mix of these coagulants.

[0041] Preferably, the coagulant, or mix of coagulants, is suitable to the pH and chemical makeup of the water and sediment makeup is used.

[0042] Keeping the coagulant in dissolved form to enable pumping, most coagulants need to be dissolved in water. As such, the concentration of the coagulant in generally less than 100 %, such as between 2 to 50% (by weight), such as between 5 to 40% (by weight).

[0043] Further, in order to penetrate the sediment effectively, and to get an opportunity to react with the legacy sediments upon injection, water in added to the coagulant before injection. The ratio of coagulants to injector water is from 1 :5 to 1 :100, preferably between 1 :10 to 1 :50, such as 1 : 10 to 1 :20.

[0044] Using the method of the invention, a system for injecting coagulants into the sediment of lakes, seas and watercourses can have many advantages. The pump can be placed close to the injector pipes, enabling use of a smaller pump.

[0045] Furthermore, high capacity water hoses for transporting the injection water down to the injector pipes can be avoided, resulting in less drag, requiring less energy to move the water craft. In fact, it was found that the decrease in drag enabled the unit for injection (supporting member with a number of a number of injector pipes) to hang more vertical under the watercraft, whereby the coagulat hoses can be shorter, leading to even less resistance through less pumping friction.

[0046] Also, the water pumps may be electric (and also the smaller coagulant pumps) making it possible to have a quiet and fully electric system for injecting coagulants into the bottom sediment, which may be especially desirable in fragile environments. Such a device can be seen depicted in Figs. 1 and 2.

[0047] The device for system for injecting coagulants into the sediment of lakes, seas and watercourses comprises a watercraft 1, storage space 2 for coagulants, a pumping device for coagulants 3 comprising an inlet 4 and an outlet 5, a supporting member 6 with a number of a number of injector pipes 7, and an injection water pump 8 comprising an inlet 9 and an outlet 10. The inlet 4 of the pumping device for coagulants 3 is connected to the storage space 2 for coagulants and the outlet 5 of the pumping device for coagulants 3 is connected to the injector pipes 7. Furthermore, the outlet 10 of the injection water pump 8 is connected to the injector pipes 7, such that the mixing of the injection water and the at least one coagulant takes place in conjunction with effecting the injection. The vertical distance from the injection water pump 8 inlet 10 to point of discharge at the end of the injector pipes 7 is less than 2 meters.

[0048] During use, the injector pipe will be almost perpendicular to the sediment bottom.

[0049] The sediment may be the bottom sediment of lakes, seas and watercourses.

[0050] In figure 1 is shown how the injection water pump 8 can be mounted directly on the supporting member, thus making the pumping distance from the injection water pump inlet 10 to point of discharge at the end of the injector pipes 7 is less than 2 meters. This way, water hoses for transporting the injection water down to the injector pipes can be avoided.

[0051] The support member 6 may be a spreader boom, where the injector pipes 7 are mounted along length of the boom. In figure 4 it is shown a watercraft 1 with a support boom with injector pipes.

[0052] If the lake, sea or waterway bottom is particularly uneven, the boom may comprise shorter boom sections mounted together such that they may bend or flex slightly at the intersections, enabling the supporting boom to adjust to the shape of the sediment bottom.

[0053] An example of such a boom with flexible intersections is illustrated in figure 6.

[0054] The shorter boom sections may be mounted together with a hinge mounted in the same plane as the lake bottom, such that it allows the supporting member (6) to bend only in the plane perpendicular to the lake bottom, allowing the support member to adjust its shape to conform to the curvature of the lake bottom, while keeping the support member straight in other planes. Preferably, the injection water pump 8 or pumps are electric, only requiring a thin electric cable between the water craft 1 and the supporting member 6 for running the pump. Similarly, only a hose from the pumping device for coagulants 3 is required. Using wires between the water craft 1 and the supporting member 6 to control the supporting member 6 when used at the sea or lake bottom, only a minimal drag is created.

[0055] Thus, the pumping device for coagulants 3 and / or storage space 2 for coagulants may be located at the watercraft 1.

[0056] The injection water pump 8 and its water inlet 9 may be located at the supporting member 6.

[0057] Figure 3 shows an alternative embodiment, where the injection water pump 8 is located at the water craft 1, however, the injection water pump inlet 9 for lake water is located within less than 2 meters of the point of discharge at the end of the injector pipes 7. This can be achieved by for instance attaching the injection water pump inlet 9 to the supporting member 6. Although this will require larger water hoses for the injection water between the watercraft 1 and the supporting member 6, the pressure difference between the water inlet and outlet will still be less than 2 meters of water, thus from a pressure standpoint only requiring energy for pumping the water less than 2 meters down (cf. siphon effect). However, such a solution will have more drag (due to hoses between the watercraft 1 and the pump inlet 9 and outlet 10 and friction in the longer hoses). However, in certain applications, such a solution might have benefits.

[0058] Thus, the injection water pump 8 may be located at the watercraft 1, or at a similar height as the watercraft 1, while its water inlet 9 is positioned less than 2 meters vertical distance from the point of discharge at the end of the injector pipes 7.

[0059] This can be achieved by having the water inlet 9 positioned on or at the supporting member 6.

[0060] The device according to the present invention may comprise hoisting means 12 comprising lines 13 and line wheels, connecting the supporting member 6 to hoisting means. The hoisting means comprise motive power sources (not depicted) for rotating the line wheels 12 so that the supporting member 6 can be caused to move upwards and downwards in the water. This can be seen in figures 2 to 4.

[0061] When the device is in the water region which is to be treated, the supporting member 6 is immersed so that the free ends of the injector pipes 7 are below the upper surface of the bottom sediment, which can be seen in figure 5. The fact that the coagulantswill normally be in motion during the setting of the supporting member 6 means that the injector pipes 9 will trail after the watercraft 1, resulting in the injector pipes 9 assuming the oblique position depicted in Fig. 5.

[0062] When the supporting member 6 / injector pipes 7 are correctly set, coagulants are supplied to the bottom sediment by pumping both injection water and coagulant to the injector pipes 7. The result is mixing of coagulants and injection water at the free ends of the injector pipes 9. In this context it should be noted that it is extremely advantageous that the mixing of coagulants takes place at the free ends of the injector pipes 9, since flocculation of the respective mixture is instantly initiated.

[0063] Example 1

[0064] The water craft depicted in figure 4 was used for test runs using the method and device of the invention. The water flow during experimental runs were 120 m3 / h requiring hoses for injection water having a 9 cm diameter. The chemical flow was 8.3 m3 / h. Injecting at 1.6 knots, this resulted in 25 grams of Aluminum -Based Coagulants per square meter of bottom sediment.

[0065] Example 2

[0066] The watercraft 1 depicted in figure 4 was used for test runs using the method and device of the invention.

[0067] Having the injection water pump mounted at the supporting member 6 meant that the pump could have over 35% lower energy consumption than a pump mounted in the watercraft 1.

[0068] Furthermore, the 9 cm diameter water hoses could be omitted, resulting in lower drag during experimental runs. In practice, the less drag meant that the supporting member 6 with injector pipes 7 would hang more vertically under the watercraft 1.

[0069] The setup used electric pumps and a generator supplying electricity, resulting in a lower volume during operation. However, a battery could be used to run all pumps (and also the support craft while injecting coagulants), making the operation very quiet.

[0070] Although the present invention has been described above with reference to (a) specific embodiment(s), it is not intended to be limited to the specific form set forth herein. Rather, the invention is limited only by the accompanying claims and, other embodiments than the specific above are equally possible within the scope of these appended claims, e.g. different than those described above. In the claims, the term “comprises / comprising” does not exclude the presence of other elements or steps. Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by e.g. a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly advantageously be combined, and the inclusion in different claims does not imply that a combination of features is not feasible and / or advantageous. In addition, singular references do not exclude a plurality. The terms “a”, “an”, “first”, “second” etc. do not preclude a plurality. Reference signs in the claims are provided merely as a clarifying example and shall not be construed as limiting the scope of the claims in any way.

Claims

CLAIMS1. A method for injecting coagulants into the sediment of lakes, seas and watercourses, comprising the steps of: pumping at least one coagulant from a storage position at or near the surface of a lake, sea or watercourse to a multitude of injectors positioned, such that during injection, their point of discharge is in the sediment of the of lake, sea or watercourse, pumping water from the lake, sea or watercourse to the multitude of injectors, at the injectors, mixing the at least one coagulant with the pumped water, and injecting the resulting mixture into the interstitial water of the sediment, such that the mixing of the injection water and the at least one coagulant takes place in conjunction with effecting the injection, characterized in that, the vertical distance, from the inlet position for water to be pumped to the point of discharge of the resulting coagulant and water mixture, is 2 meters or less.

2. The method according to claim 1, wherein the distance between the water surface and the sediment of the of the lake, sea or watercourse is at least 3 meters, such as at least 5 meters, such as between 3 to 100 meters, such as between 3 to 50 meters, such a between 5 to 30 meters.

3. The method according to claim 1 or 2, wherein the at least one coagulant is a phosphorus-binding coagulant or a mix of different phosphorus-binding coagulants.

4. The method according to claim 3, wherein the at least one phosphorus- binding coagulant is selected from a list consisting of Aluminum-Based Coagulants, Iron-Based Coagulants, and Calcium-Based Coagulants, or a mix of these coagulants.

5. The method according to any one of claims 1 to 4, wherein the ratio of coagulants to injector water is from 1 :5 to 1 : 100, preferably 1 : 10 to 1 :50.

6. The method according to any one of claims 1 to 5, wherein the sediment is the bottom sediment of lakes, seas and watercourses.

7. A device for injecting coagulants into the sediment of lakes, seas and watercourses, the device comprising: a watercraft (1), a storage space (2) for coagulants, a pumping device for coagulants (3), comprising an inlet (4) and an outlet (5), a supporting member (6) comprising a number of a number of injector pipes(7) mounted along the supporting member (6), and an injection water pump (8) comprising an inlet (9) and an outlet (10), wherein the inlet (4) of the pumping device for coagulants (3) is connected to the storage space (2) for coagulants and the outlet (5) of the pumping device for coagulants (3) is connected to the injector pipes (7), and the inlet (9) of the injection water pump (8) is in contact with the lake, sea or watercourse water, and the outlet (10) of the injection water pump (8) is connected to the injector pipes (7), such that mixing of the injection water and the at least one coagulant takes place in conjunction with effecting the injection, and wherein the vertical distance from the injection water pump (8) inlet (10) to point of discharge at the end of the injector pipes (7) is less than 2 meters.

8. The device according to claim 7, wherein the pumping device for coagulants (3) and / or storage space (2) for coagulants is located at the watercraft (1).

9. The device according to claim 7 or 8, wherein the injection water pump inlet (9) is located at the supporting member (6).

10. The device according to claim 7 or 8, wherein the injection water pump (8) is located at the supporting member (6).

11. The device according to anyone of claims 7 to 9, wherein the injection water pump (8) is located at the watercraft (1) and its water inlet (9) is located less than 2 meters vertical distance from the point of discharge at the end of the injector pipes (7).

12. The device according to any one of claims 7 to 11, wherein the water injector pump (8) is electric.

13. The device according to any one of claims 7 to 12, wherein the supporting member (6) is a spreader boom.

14. The device according to any one of claims 7 to 13, wherein the supporting member (6) comprises shorter boom sections mounted together such that they may bend or flex slightly at the intersections, enabling the supporting member (6) to adjust to the shape of the sediment bottom.

15. The device according to any one of claim 14, wherein the shorter boom sections are mounted together with a hinge mounted in the same plane as the lake bottom, such that it allows the supporting member (6) to bend only in the plane perpendicular to the lake bottom, allowing the support member to adjust its shape to conform to the curvature of the lake bottom, while keeping the support member straight in other planes.

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