FI59777C - FOERFARANDE FOER FOERBAETTRANDE AV DET EKOLOGISKA TILLSTAONDET FOER EN TERMISKT AVLAGRAD VATTENBASSAENG - Google Patents

Description

RS? 71 Γβ7 / ill ADVERTISEMENT R λπππ JBHa LBJ (11) utläggningsskrift 59/77 (* 5) Patent Mei .ie 1 at ^ ^ (51) Kv.lk.3 / lnt.CI.3 C 02 F 7/00 FINLAND - FINLAND (21) PK »nttlh * k * mu * - Pttmumeknlni 800990 (22) H * k * ml * pilvl - Anceknlnpdtf 28.03-80 (23) Alkupllvi —GUtlghatad ·! 28.03.80 (41) Tullut | ulklMksl - Bllvlt offentilf _ '. (44) Date of publication of the decision. - is Rl

Patent and registration authorities Aniökan utl «(d och utl. * Krift * n pubiteend J UD'οχ (32) (33) (31) Pyydetty ttuelk * u * —B * | Ird prlerltet (71) (72) Kalle Matti Lappalainen , Kirnukuja 6 BU, 70780 Kuopio 73,

Reijo Matti Oravainen, Märventie 2 D 31, 362Uo Nattari,

Ami Solin, Soinilankatu 30 D 13, 33730 Tampere 73, Finland-Finland (FI) (7 * +) Forssin & Salomaa Oy (5I *) Method for improving the ecological status of a thermally stratified water basin - Förfarande för förbättrande av det eciska till-ständet för en thermal baths with water bass

The invention relates to a method for improving the ecological status of a thermally stratified water basin, e.g. a lake with a low oxygen depth zone.

The successful use of a water basin, such as a sea area, a lake, a pond or the like, in fish production requires the maintenance of a favorable ecological status in the water body for the viability of the fish. One of the preconditions for fish production in the water is adequate plankton and benthic production in the water, ie a certain level of eutrophication, but on the other hand excessive eutrophication prevents fish from living and thus exploiting eutrophication. The level of eutrophication of a water basin can be considered appropriate when its external load, e.g. wastewater containing organic matter, and internal load, oxygen consumption due to phytoplankton decomposition, do not cause deoxygenation or harmful oxygen deficiency in the water basin or part thereof.

In addition to the habitat factor of fish and fish food animals, oxygen content also has another important link to eutrophication. Namely, if the water layers close to the bottom sediments of the lake become low in oxygen, the redox potential of the sediment decreases 2 59777 and, as a result of certain chemical reactions, iron and manganese and phosphorus previously bound to them may dissolve in the sediment. Gas bubbles and water mixing due to bubbling may also occur. As a result of these events, the lake’s lushness is rapidly increasing. There is talk of so-called rasant eutrophication.

The lack of oxygen is most evident and most harmful in the lake's underwater. The lowest oxygen concentrations are in the immediate vicinity of the bottom.

In order to remedy the above drawbacks, the lack of oxygen and the consequent consequences, attempts have been made to increase the oxygen content of the water by aeration or oxidation by supplying compressed air or oxygen from below a suitable source.

According to a known solution (U.S. Pat. No. 3,956,124, AT Pat. No. 288,273), the water in the cavity to be treated is pumped to an oxidizer above the surface of the water, where oxygen is added to the water to be treated, after which the treated water is returned to the cavity. In order to improve the operation of oxidants of this type, it is still known to separate the gases dissolved in the water to be treated before oxidation. Methods of this type are described in FI patent publications 49 703 and 52 661, in the former of which the gases are separated by decomposing the water into a mist by means of the pressure, and in the latter mechanical vibrations applied to the suction pipe of the device are used.

Although known methods of the type described above are useful per se and have obtained positive results, the disadvantages of the methods are the complexity and cost of the equipment and the high operating costs, in particular energy costs. The oxidizing power obtained by methods such as that shown is generally in the order of 1 to 3 kg O 2 / kWh. In known methods, the retention of the derived oxygen in the groundwater has also been incomplete, as much of the oxygen contained in the bubbles escapes back into the atmosphere. The transfer of oxygen in the horizontal direction has also been generally insufficient.

The object of the present invention is to avoid the disadvantages of the known methods and to provide a simple method which is inexpensive to use and set up, which can effectively affect the ecological status of a water basin, e.g. a lake, by regulating its oxygen status, eutrophication level or temperature.

In order to achieve the above and later objects, the invention is mainly characterized in that relatively oxygen-containing and lighter surface water is introduced into the low-oxygen or oxygen-free underwater via one or more flow channels to bring, mix and horizontally transfer by mixing so that the temperature stratification is maintained.

The method according to the invention causes all the derived oxygen-containing water to remain in the underwater and to mix there evenly and efficiently. This highly advantageous effect is based on the fact that the temperature and density differences and the like are smoothed out quickly by convection and that the resulting mixture initially rises until it reaches a depth at which the densities of the surrounding water and mixture are equal, thus turning horizontal. The mixture is thus always heavier than the surface water and does not rise to the surface. Improving the oxygen situation will also prevent unfavorable chemical reactions at the bottom and free up valuable bottom zones in the lake for fish production. In addition to the direct effect of the oxygen carried by the flow to the groundwater, the method of the invention reduces the water exchange between the sediment pore water and the groundwater because the lighter mixture of groundwater and surface water floats better on the heavier sediment pore water. In winter, when the derived surface water is cold, the method further cools the underwater, resulting in slower oxygen consumption and a longer spring cycle.

The economics of the method are based in part on the fact that the flow resistance of the flow channel remains very low when using a low flow rate and a large diameter channel. The flow channel only needs to withstand a small pressure due to density differences and flow resistance, so the necessary equipment can be made very lightweight. The economics of the method according to the invention are based in part on the fact that no air or gas bubbles are generated in use, which in other methods require a lot of energy in the stage of generating and conducting bubbles.

According to a particularly preferred embodiment of the invention, the surface water to be discharged into the underwater is taken from the same water basin. This equalization of the water resources of the water body is based on the fact that the surface water of the water bodies contains, with the exception of extremely polluted cases, water with sufficient oxygen content also in winter, as most of the consumption takes place in groundwater and bottom sediment. In addition, the volume of groundwater is only a fraction of the volume of surface water.

The invention will now be described in detail by way of an exemplary embodiment with reference to the accompanying drawings, in which Figure 1 shows variations in the temperature and density of water in a lake or similar basin at different depths during stratification times and Figure 5 schematically shows an embodiment of the method according to the invention.

Figure 1 shows a typical example of the stratification of water temperature and density in a lake or similar basin at different times of the year. Curves A show the situation in winter and curves B in summer. As the curves show, the water temperature varies most close to the surface in different seasons. Near the bottom, the temperature changes — little around 4 ° C, which corresponds to the maximum density of water. The equivalent is, of course, true with respect to density, so that the heaviest water is always at its deepest.

Figure 2 is a schematic cross-section of a lake stratified as described above. The zone below the water surface or in winter under the ice cover 1 is the surface water 2, where the water is relatively oxygenated. In the low-oxygen or oxygen-free underwater water, i.e. in the depth zone 3, shown shaded in the drawing below, the water is somewhat homogeneous, heavier in density than the surface water and, for these reasons, almost stationary. The volume of cover-water is generally multiples of that of underwater, as a lake or similar body of water can be compared to a cone standing at its tip as schematically illustrated in the drawing. Often the depth of the groundwater represents half of the total depth, however, even then the volume of the groundwater is only 10-20% of the total volume, depending on the morphology of the lake.

In order to improve the oxygen situation of the groundwater, oxygen-containing surface water 2 is introduced into the groundwater 3 via a large-diameter pipe 4. The upper end of the tube has intake openings 5 at a suitable depth below the surface, from which the surface water flows into the tube and further into one or more outlet openings 6 close to the bottom. Therefore, in order to optimize the structure of the pipe, the diameter of the pipe is chosen to be large and the flow rate to be small, whereby a relatively large flow is obtained with a small amount of energy. The flow is provided by a propeller 7 placed inside the pipe 4 driven by the power source 8 placed above the surface via the shaft. In addition to an electric or internal combustion engine, alternative energy sources such as wind power, wave power or the like are also well suited for powering the flow-generating propeller 7 or the like due to the low power requirement.

Since the flow channel 4 is only affected by a small pressure due to differences in density and flow resistance, the apparatus can be made very light and the flow channel 4 can consist of a light thin-walled tube or, for example, a nozzle hose. The equipment can be installed to support the raft structure 11 or directly on the ice surface in winter.

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When the device operates, the oxygen-containing water entering the pipe 4 through the inlets 5, which is typically about 0.1-0.5 ° C in winter and about 15 ° C in summer, exits close to the bottom through the lower end 6 of the pipe and mixes with underwater at a corresponding temperature. in winter 2-4 ° C and in summer e.g. 5-8 ° C. When surface water is introduced into the vessel water, the greater the differences in density and temperature of the surface water and the vessel water, or the like, are immediately generated more efficiently. The resulting mixture is always heavier than surface water and does not rise to the surface.

The inlet flow and the depths of the inlet and outlet openings are chosen so that the conducted surface water remains as well as possible in the underwater. The intake port is placed in an oxygenated water layer (usually 1-3 m below the water surface). The discharge opening is generally approx. 1-2 m above the bottom surface. If necessary, the demolition can also be applied to another layer of water. In order to improve the mixing and to prevent a rapid upward flow in the initial stage, a plate-like flow guide 10 around the pipe 4, as shown in Fig. 2, can be used, which directs the flow on the side of the pipe outwards.

In winter, the temperature distribution of the bottom sediment is such that the temperature of the surface parts follows the water temperatures and at deeper the temperature is usually 5-7 ° C. If the water temperature is e.g. 3 ° C, it tends to penetrate the sediment heavier than e.g. 6 ° C water and displace the pore water of the sediment, as a result of which the oxygen consumption of the bottom is transferred to the water. In the method of the invention, when the temperature of the groundwater decreases in winter, the water becomes lighter and floats on the pore water of the heavier sediment. In this case, the majority of the convection takes place inside the sediment and less pore water enters the water than before. In summer, heating the groundwater appropriately causes the groundwater to float better on top of the sediment, as the sediment is colder than the groundwater.

EXAMPLE

The method according to the invention was tested in a lake suffering from oxygen depletion of groundwater during stratification periods, with an area of 76 ha and a total depth of about 14 m. The equipment according to the application example presented above was installed in winter about a month after the lake froze.

The propeller was rotated by a 0.55 electric motor at 127.5 rpm. Water was taken into the pipe from a depth of 1.5 m under the ice (temperature 0.6 ° C) and passed to the bottom in a 0.32 m diameter plastic pipe. The lower end of the pipe was about one meter above the sediment surface (total depth 13.3 m). The amount of water flowing in the pipe was estimated to be 20-30 1 / s.

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The results obtained are shown in the table below, which shows the temperature and oxygen content of the lake water at different depths at the time of start-up of the device and one month after start-up, and the corresponding values for the two reference years.

SCORE

Temperature ° C Reference years

Depth m start 1 month year 1 year 2 at start time 11.01.80 11.02.80 22.02.71 01.02.72 I 0.5 0.6 1.2 0.7 3 1.2 1.6 3.2 2.1 5 1.9 2.6 4.1 3.2 7 2.2 2.8 4.3 3.5 9 2.6 2.8 4.7 10 2.7 2.8 - 3.9 11 2.9 2.8 12 3.0 2.8 - 4.0 13 3.2 3.0 14 3.4 3.0 4.9 4.3

Oxygen content mg O2 / I Reference years

Depth m start 1 month year 1 year 2 at start time 11.01.80 11.02.80 22.02.71 01.02.72 1 11.5 10.4 9.4 9.5 3 10.9 9.3 7.0 8.7 5 9.4 5.8 3.1 5.6 7 8.0 3.4 1.8 3.0 9 6.3 - - 10 5.2 3.6 0.6 0.5 II 4.0 - 12 1.6 3.3 - 0 13 0 2.6 0.2 14 0 2.5 - 0 b 7 Ί Ί Ί 7

As can be seen from the table, the effects are very clear from the values measured one month after start-up. The groundwater had become almost constant in temperature and the normally observed continuous rise in groundwater temperature had stopped. Oxygen-free water was no longer found in the deep groove area. During the corresponding period in the comparison years, the groundwater was practically oxygen-free below the depth level of 10 m, when the oxygen concentration in this water layer was 2.5-3.5 mg O2 / I a month after the device was started. · The oxygen situation in the surface water was not worse than in comparison years. The underwater temperature had also clearly decreased and was 2.8-3.0 ° C after the experiment. In the comparison years, the groundwater temperature exceeded 4.0 ° C. In such a low temperature range, the change is significant in terms of the intensity of the decomposition activity for the benefit of the test equipment.

Based on the test results, the device could be found to work as expected.

Although the invention has been described above in connection with a particular embodiment, it is clear that the invention can be modified in many different ways within the scope of the claims set out below. Thus, for example, lighter oxygen-containing water from another suitable source may also be introduced into the vessel water of the water basin to be treated. In some cases, water derived from a suitable higher water body or other source by the flap method may be used for this purpose, in which case external energy is only required to initiate the flow. In connection with the invention, chemicals known per se can also be added to the flow into the underwater to mix them with the underwater.

Claims (6)

59777 8 A method for improving the ecological status of a thermally stratified water basin, e.g. a lake with a low-oxygen depth zone, characterized in that relatively oxygen-rich and lighter surface water (2) is introduced into the low-oxygen or oxygen-free underwater (3) via one or more flow channels (4) ) for introducing, mixing and horizontally transferring this oxygen content to the underwater by mixing under the action of convection to compensate for temperature and density differences so that the temperature stratification is maintained. Method according to Claim 1, characterized in that the surface water is introduced into the underwater within the limits required by the state of the remediation site and the intensity of the mixing events, e.g. between 10 ... 2000 1 / s. Method according to one of Claims 1 to 2, characterized in that the surface water (2) to be introduced into the underwater water (3) is taken from the same water basin. Method according to one of Claims 1 to 3, characterized in that the surface water (2) to be introduced into the underwater is taken from a different water basin. Method according to Claim 4, characterized in that the flow to the vessel water (3) is taken from a second water basin located above on a flap basis. Method according to one of Claims 1 to 5, characterized in that the reduction in the phytonutrient content of the groundwater or other desired change in the status of the groundwater is enhanced by the addition of chemicals known per se or corresponding active ingredients.