Method and apparatus for collecting and regionally confining blue-green algae

The invention relates to a method and apparatus for collecting and regionally confining blue-green algae.

Blue-green algae is a bacterial growth which constitutes a serious problem in lake waters worldwide. The blue-green algae problem also occurs in the Baltic Sea, which has a low salt content. Until now, there have been no means for preventing the occurrence of blue-green algae so as to lessen its ill effects, for example, on beaches.

The aim of the invention is to eliminate this lack and to provide a method and device by means of which blue-green algae can be efficiently collected and thus removed from the waters desired, or by means of which the occurrence of blue- green algae can be regionally confined.

As regards collection, this aim is achieved by the method according to the appended claim 1, and as regards confinement, by means of the method according to the appended claim 4. The characteristic features of the apparatus for collecting or confining blue-green algae are disclosed in the appended claim 6 and the characteristic features of an alternative device intended only for collection are disclosed in claim 14. Preferred embodiments of the invention are disclosed in the dependent claims.

The invention is illustrated in the following by means of an example, with reference to the accompanying drawings, in which

Figure 1 shows the device according to the invention in cross-section and in part as a perspective view diagonally from above.

Figure 2 shows a fastening device which may be used in the apparatus of Figure 1.

Figure 3 shows a method according to a preferred embodiment of the invention for collecting blue-green algae by means of the apparatus according to the invention.

Figure 4 shows a collection apparatus for blue-green algae according to a second embodiment of the invention, as seen from above.

Figure 5 shows the collection apparatus of Figure 4 as seen from the side.

The apparatus comprises a readily water-permeable felt-like fabric, such as a non- woven felt mat 1, on the top edge of which is a float 4 and on the bottom edge a weight 5. The top edge of the felt mat 1 stays on the surface of the water by means of the float 4 and the bottom edge at a depth determined by the width of the felt mat 1 by means of the weight 5. This type of a felt mat 1 can be dragged like a dragnet or trawl net in a blue-green algae collection area. During dragging, the top edge of the felt mat 1 remains on the surface of the water by means of the float 4.

The felt mat may also be used for regionally confining blue-green algae, for example, to keep a beach clean of blue-green algae. In this case the mat 1 is positioned as a boom confining the area to be protected from blue-green algae, the float 4 of the boom being on the surface of the water and anchor weights 11 being fixed, for example, in conjunction with the weight 5 on the lower hem. Blue-green algae may be collected from the area protected by the boom by means of the collection method according to the invention.

In a preferred embodiment of the invention, two floats 4 and 4a are at a distance from one another and between them is a felt-like fabric, such as a non-woven felt mat 12. The felt-like fabric or felt mat 1, 12 may of course include or be connected to a woven reinforcement. This horizontal felt mat part 12 also collects the blue- green algae thrown by waves over the float 4 on the incoming direction side of breakers. When the distance between the floats 4 and 4a is, for example, within the range from 0,3 to 1 m, typically about 0,5 m, the horizontal felt mat part 12 of the prevention boom is sufficiently long for collecting, for example, the blue-green algae carried by the breakers on the beaches of lakes. The height of the vertical part 1 of the boom may be within the range from 1,2 to 3,0 m, typically 1,4 to 2,5 m.

The felt mat 1 is preferably a geotextile used in groundwork, such as strainer cloth. This strainer cloth is typically a felt mat made of thin polypropylene or polyester

fibres and having a thickness of 0,5 to 2 mm, which is readily water-permeable, but so dense that even very small particles adhere to it. This type of non-woven felt mat can be made by needling or the fibres may be placed in layers by blowing. If necessary, reinforcement layers made by weaving may be used. Tests have shown that blue-green algae adheres to the felt mat without passing through it. The specific gravity of the felt mat 1, 12 material is somewhat lighter than that of water, and thus also the horizontal mat part 12 tends to push itself up straight. Between the floats 4 and 4a may, however, be used rigid spacers, which keep them at a distance from one another.

The blue-green algae collected can be removed from the felt mat, for example, by means of a pressure cleaner, thus making felt mat available for re-use. A typical felt mat has a smooth surface and a nap-finish surface which is used as the forward collection surface when the mat is being dragged.

In a preferred embodiment of the invention, the edges of the felt mat 1 are rolled up into channels 2 and 3 in which the float 4a and the weight 5 are located.

A uniform non-woven felt mat can be fixed around the floats 4 and 4a and the weight 5, for example, by means of the C-springs shown in Figure 2, which can be made of plastic tubing by sawing a longitudinal slit 14 in the tube and cutting it into pieces of desired length. The length of the C-springs 13 may be 30-50 mm, 0 25-30 mm, and they may be attached, for example, two per metre. Alternatively or additionally may be used straining ties, such as the cable ties used by electricians.

The float 4, 4a is, for example, a cellular plastic tube or bar and the weight 5 may be a metal chain. As weights may also be used separate anchor weights 11 positioned at a distance from one another.

The floats 4 and 4a may also be made solely of strainer cloth which is rolled up. The strainer cloth itself thus acts as the float which is lighter than water and a good drag-line due to its strength. The roll rolled up of strainer cloth 1,12 may be clamped by means of a C-spring according to Figure 2.

The prevention boom formed by the felt mat 1, 12, which is L-shaped in cross- section, may consist of elements of desired length, for example, 10-20 m, which are joined at their ends as extensions of each other. For the purpose of this joining, the ends of the felt mat may be made to overlap and the channels 2 and 3 may be joined, for example, with cable ties which are led through holes made in the felts 1, 12. Other joining means, such as binding means at the ends of the elements, may also be used.

For joining may be used, for example, ropes 6 placed inside hollow floats 4, at the ends of which are loops that can be utilized in extension joints. The rope 6 receives the tensile stress when the boom is tightened between the various anchor means or when the boom 1, 12 is dragged in order to collect blue-green algae.

Figure 3 shows a collection vessel, such as a pontoon raft 7, on top of which is a relatively large perforated container 10 lined with strainer cloth, which is preferably similar to that described above in connection with the prevention boom 1, 12. The long collection boom 1, 12 fixed at one end to the vessel 7 is dragged by a towboat or boat 8 so that the boom forms a loop diminishing in size in the vicinity of the vessel 7. The blue-green algae sludge concentrating inside the loop is pumped by means of a floating sludge pump 9 inside the container 10, from which water discharges through the strainer cloth and the holes while the blue-green algae remains in the container 10.

The felt mat used for blue-green algae prevention does not need to reach very deep because the blue-green algae problem occurs during warm periods when the blue- green algae rises close to the surface. When dragging long felt mats, it may be advantageous to use a net resembling a dragnet as a support structure. The support net may be located behind the felt mat.

The invention is not limited to the preferred embodiment presented above. For example, the shape of the boom may also be an I-shape if sufficient floating capacity is ensured for the float 4 so that the blue-green algae layer on the surface of the water will not drift over it even in slightly rough seas.

Figures 4 and 5 show an apparatus according to a second embodiment of the invention for collecting blue-green algae. This apparatus is a type of tubular dragnet comprising a tube 15 closed at one end 15b, which is made of a readily water- permeable felt-like material, such as non-woven felt mat. On both sides of the tube 15, at least in the vicinity of the open end 15a of the tube, are floats 16. To the floats 16 are attached guide wings 17, which form a throat tapering towards the open end 15a of the tube 15.

In the case shown, the floats 16 form a catamaran-type vessel equipped with an outboard motor 18 for pushing the collection vessel in the advancing direction with the guide wings 17 at the front. In this case, the blue-green algae will collect in the long bag formed by the tube 15, the length of which is preferably more than five times greater than the diameter of the tube 15. The flow resistance formed by the tube or bag 15 will thus not become excessive and it will be able to receive a large amount of blue-green algae. The mouth 15a of the tube 15 is kept open by means of a rigid rim fixed to the guide wings 17. One or more bridges or covers 16a connecting the floats or pontoons 16 will maintain the structure intact. The guide wings 17 may be plastic sheets.

The long pontoons 16 shown in Figure 4 and 5 may be completely left out and replaced by shorter floats fixed to the guide wings 17. Since the material of the tube or bag 15 is somewhat lighter than water, it will float on the surface and expand to open at the mouth 15a by the effect of the flow funnelling inside the tube or bag. In this case, the tube or bag 15 may be very long and will not need to be supported in any way. An outboard motor 18 is not required, but the apparatus may instead be pulled along behind a vessel, for example, with a tow rope.

The end 15b of the tube 15 can be closed simply by means of a straining tie wound around the tube. At the point of closure may additionally be fixed a rope which comes out of the open end 15a of the tube 15. Using this rope (not shown), the tube or bag 15 may be pulled inside out, that is, the bottom 15b may be pulled out through the opening 15a, whereupon the tube or bag 15 can be emptied of the blue-green algae collected therein. The tube or bag may be emptied, for example, into a tank on a towboat. Cleaning may be carried out using, for example, a pressure cleaner.

b

Several of the collection apparatuses according to Figures 4 and 5 may be connected in parallel to widen the cleaning area.

The collection apparatus according to Figures 4 and 5 resembles the use of the collection apparatus according to Figures 1 and 3 as a dragnet-type loop. The only difference is that in the embodiment of Figures 4 and 5, the loop is made up into a bag and floats or pontoons and required to carry and support the guide wings, in which case they at the same time hold the bag or tube at the correct height with respect to the surface of the water.