IL96974A - Submersible biological filter for the purification of waste water - Google Patents

Description

Submersible biological filter for the purifieation of waste water COFIDO Societe Cooperative P.COFI.Ol/WO ADB/wp-800101 SUBMERSIBLE BIOLOGICAL FILTER FOR THE PURIFICATION OF WASTE WATER Field of the invention The invention relates to a "biological filter" whose enclosure can be submerged in the liquid to be treated.

Biological ilters are used in particular for the treatment of waste water. These filters are in fact treatment vessels or basins comprising substrates or supports for bacteria beds involved essentially in the breakdown of the organic matter contained in the waste wate .

Technical background In biological filtration it is known to use various systems functioning aerobically or anaerobically, such as fixed or fluidised bacteria beds, biodiscs and activated sludge processes.

The document FR-A-2, 565,579 has proposed an installation for the treatment of waste water by microorganisms, in which installation the treatment microorganisms are absorbed on glass fibre assembled in the manner of a cylindrical brush; they can be desorbed therefrom by mechanical action, which regenerates the treatment members.

The use of glass fibres and their assembly in the form of a cylindrical brush makes this type of installation costly, without any guarantee of easy accessibility to the bacteria bed formed.

The document DE-A-3,110,859 describes multiple* use devices, in particular for exchanges of materials, comprising spiralled plates.

The document CH-A-621,263 describes a device for treating liquids with gases, comprising a conduit containing metal shavings or plastic materials.

All these systems offer only a small fixation surface for the bacterial film relative to the weight of the support used, or they require heavy inf astructures. Their servicing in the event of blockage is difficult, given their great volume and their lack of internal accessibility.

Aims of the invention The present invention aims to improve the surface available for the bacterial fixation and to reduce the cost of the infrastructures peripheral to the bacterial support, while at the same time providing easy accessibility for their servicing.

Principal characteristics of the invention According to the present invention, the submers-ible biological filter for the purification of waste water is characterised in that it comprises, as bacterial support, an assembly of skeins of essentially continuous bands made of plastic material in a spiral arrangement around at least two holding members.

The assembly of the skeins of bands is used by charging it with a bacteria bed according to conventional techniques and by arranging it, by virtue of the holding members, in a basin for waste water treatment, preferably in several successive vertical planes.

The holding members advantageously are in the form of a frame which can be extracted with the skeins of bands with which it is lined.

In one basin it is possible to arrange, in parallel vertical planes, 3 to 10 frames of this type per running metre.

The bands forming the skeins are essentially continuous, that is to say they have a large length so that they can be arranged easily around the holding members which in principle only need to hold the bands at their ends.

Of course, an interruption may arise as a result of tearing or when the end of a reel is reached, and in this case an intermediate fixa ion on the holding member may be required.

According to another embodiment, it is preferable to ensure the fixa ion of the bands on the holding member by clipping on a longitudinally slotted tube of a diameter greater than the holding member.

The bands can be obtained from a bar of plastic material converted into continuous bands and spiralled by turning.

The bars of plastic material used are of any plastic material capable of giving a thin band, .prefer-ably by turning, by means of a cutting tool. The width of the band is in general a few tens of millimetres and its thickness is preferably several hundredths of a millimetre. Any other dimensions can be chosen without departing from the scope of the present invention.

It has been found that the technique of obtaining bands by turning a bar of plastic material by means of a cutting tool gives a non-smooth band which is particularly suited for obtaining the desired substrate.

It is conceivable for other techniques to be used for obtaining the bands, for example by cutting-out from films.

The bands can be manufactured by extrusion of the molten plastic material. A surface treatment of one or both faces may in some cases be carried out, with a view to modifying the surface state of the band.

The plastic materials used for obtaining the bands are chosen from among polyolefins, polyamides, polyesters, ABS or other copolymers . The plastic materials used are rigid, semi-rigid or flexible.

Use will preferably be made of a plastic material such as polyethylene or polypropylene, which gives semirigid bands which are particularly well suited for obtaining the skeins.

The skeins of bands can be obtained using any manufacturing technique.

In order to obtain the skeins, the bands are wound regularly onto holding members, which consist, for example, of tubular frames or other profiles, by rotating these bands around an axis of rotation situated preferably halfway between th holding members. Any other winding techniques can be used.

According to a particularly advantageous embodiment, it is possible, simultaneously to the spiralled winding onto the holding members, to twist the band about itself.

The lining of the frames can comprise a series of successive passes on one and the same section of the frame. The fixatio of the bands on the spars of the frames is obtained by clipping, welding or any other fixation means. The frames are attached to the filter enclosure in a fixed or removable manner.

In principle, the bands have a width of 1 to 5 cm and are spiralled onto the frames at a rate of 1.5 to 3.5 spirals per running metre of frame.

It appeared expedient, in one advantageous embodiment of th invention, to provide an assembly of conduits bringing air (or another gas) under pressure into the skein of band in order to clean and unbunch the skeins of band.

Other features of the invention emerge from the following detailed description of an embodiment of the invention given by way of illustration and without limitation.

Brief description of the drawings In the attached figures: - Figure 1 shows a diagrammatic view of the system for winding the bands onto the holding members; - Figure 2 shows a longitudinal cutaway view and a transverse cutaway view of the holding members; - Figure 3 shows a perspective view and a frontal cutaway view of a skein of band ready to be positioned in a biological filter module; - Figure 4 shows a cutaway view of a biological filter module.

- - Description of a or&t -rr-etA ernhnriimptyt of the invention The bands are obtained from a reel of polyethylene film of 0.03 mm in thickness and about 1,000 metres in length, which has been cut longitudinally in order to obtain bands of 20 mm in width.

Figure 1 shows a diagrammatic view of the system for winding the bands onto the holding members.

The bands (1) are wound onto two holding members (3) which are, in the present case, PVC tubes of 1 metre in length and 16 mm in diameter. These two members (3) are placed at the two ends, 1.1 m apart, of a rotating fork (5).

It is possible to wind simultaneously several bands coming from different reels (7, 9, 11) mounted on supports (13, 15, 17) integral with a common device (19) which executes a vertical displacement in order to wind the bands in a spiral around the holding members* The supports (13, 15, 17) for the reels are additionally subjected to rotation in order to twist the band about itself before being wound around the holding members .

The speed of rotation vl of the fork (5) and the speed of rotation v2 of the supports (13, 15, 17) for the various reels are regulated in order to obtain 1.5 to 2.5 spirals per running metre of band.

Figure 2 shows a longitudinal cutaway view and a transverse cutaway view of the holding members* After the desired quantity of band has been wound onto the holding members, the fixation of the band (1) on these members (3) is ensured by clipping on a PVC tube (21) slotted (22) over its entire length and of a diameter greater than that of the holding member (3)* The passage of a ring (23) of a diameter smaller than that of the tube (21) clipped on at each end conclusively secures the bands in manipulable skeins.

After the bands have been wound and fixed onto the two holding members ( 3) , the latter are detached rom the rotating fork (5 ) .

A withdrawal of about 10% of the bands when the skeins are released from the winding fork must be taken into consideration. This is due to the tensioning of the bands during the unwinding of the reels when the operation is being carried out with polyethylene.

A second effect of the release from the winding forks is that of giving the skeins greater thickness, the turns of the bands organising themselves to form a "cushion" .

Figure 3 shows a perspective view and a ' frontal cutaway of a skein of band ready to be positioned in a filter module.

The connection members are placed horizontally in the bottom and at the top of the module in such a way that the skeins are positioned in an essentially vertical manner.

By way of illustration there follows an exemplary embodiment of a skein.

A skein of 1 ma can be formed with 5 reels of band of 1,000 m in length, 2 cm in width and 0.03 mm in thickness.

This skein then consists, for each face, of 100 running m2 of support to which the bacterial flora can attach, that is to say, in total, one skein provides 200 m* of support.

If 10 skeins such as described above ar placed in a filter of 1 m3 (cubic caisson with 1 m edge), the bacterial support (bands): - weighs 30 kg - takes up 3% of the volume - offers ± 2,000 m2 of surface for attachment of the bacterial lora per m3, whereas the best results according to the prior art permit only 250 m2 of support per m3 to be obtained.

The skeins according to the present invention advantageously make it possible to obtain a very considerable support surface for the bacterial flora, while at the same time taking up only a small volume (3%).

Cutting the plastic masses into thin bands optimises the surface offered per unit of weight of material used compared to the other known systems.

In order to facilitate the cleaning and the unbundling (moving the excess bacterial flora) in the biological filter module, a device has been provided consisting of pipes (31) bringing pulsated air to the centre and/or under the skeins.

Lateral perforations (33) are provided in the pipes in order to eject the pulsated air into the. skeins.

Figure 4 shows a cutaway view of a biological filter module consisting of a cube with a one metre edge, in which there are arranged 9 skeins equipped with 3 kg of bands per skein.

The waste water is conveyed (at 101) and poured into the tank constituting the biological filter. The skeins (103) are arranged vertically.

The cleaning and unbunching of the zones Inside the skeins is ensured by a distribution of pulsated air coming from perforated tubes (105) situated inside the skeins, while the cleaning and unbunching of the zones outside these skeins is effected by means of pulsated air coming from perforated pipes (107) placed below the said skeins.

On the pulatsed-air supply line (109) there is a branch for pulsated air intended for the cleaning devices.

The oxygen necessary for the bacterial flora also comes from the pulsated-air supply line and is conveyed towards a diffuser (111) where this oxygen diffuses towards an oxygenation column (113).

The purified water is removed (at 115) and a decanter may optionally be provided.

The materials used both for producing the support and the enclosure containing the latter make it possible to render the assembly submersible and buoyant, in view of their specific gravity close to unity.

The skeins can also serve as a lining in the basins of conventional biological filters. The service life is long, given the non-biodegradability of the materials chosen for use.

The orientation of the bands favours the removal of the activated sludge particles and makes it easy to penetrate into the lining, in the event of blockage, via conventional cleaning systems.

This biological filter system can be supplied with air and water by all conventional processes and can function aerobically or anaerobically. yrnmoT-ic l example A biological filter module of 1 m3 made- up of 9 skeins of 200 m2, i.e. 1,800 mVra8 of support surface for attachment of the bacterial flora, gives the following results s The total volume of the filter varies with the type of oxygenation chosen, for example pulsated-air system, surface emulsifier, jet pump (venturi), liquid oxygen, etc.

In this example we have used the integral pulsated-air technique (for the oxygenation, recycling and cleaning/unbunching) .

The raw water flow rate is 10 1/min or 14.4 mVday. It should be noted that 14.4 raVday corresponds to 80 or 96 population equivalents by volume, depending on whether the accepted norm is 150 or 180 1/day p.e.

The level of 02 under the bands is maintained between 1.5 and 3.2 ppm by modulating the air flow rate.

The temperature varies between 12 and 14 °C.

The results arei Mean COD at intake: 482 mg of 02 Mean COO at discharge: 68 mg 02 The efficiency is then 482 - fi8 = 85.9% 482 The successive use of modules in series makes it possible to reduce the COO to below the norms recommended in waste water treatment regulations.

Claims (1)

1. CLAIMS 96974/2. Biological filter for the purification of waste water, characterised in that it comprises, as bacterial support, an assembly of skeins of essentially continuous bands made of plastic material in a spiral arrangement around at least two holding members. Biological filter according to claim 1, characterised in that the assembly of the skeins of bands is used by charging it with a bacteria bed according to conventional techniques and by arranging it, by virtue of the holding members, in a basim for waste water treatment, preferably in several successive vertical planes. Biological filter according to any one of the preceding claims, characterised in that the holding members are in the form of a frame which can be extracted with the skeins of bands with which it is lined. Biological filter according to claim 3, characterised in that 3 to 10 frames lined with skeins of bands are positioned in parallel vertical planes per running metre. Biological filter according to any one of the preceding claims, characterised in that the bands forming the skeins are essentially continuous, that is to say they have a large length so that they can be arranged easily around the holding members. Biological filter according to any one of the preceding claims, characterised in that the fixation of the bands on the holding member is ensured by clipping on a longitudinally slotted tube of a diameter greater than the holding member. Biological filter according to any one of the preceding claims, characterised in that the bands are obtained from a bar of plastic material converted into continuous bands by turn ing . 96974/2 8. Biological filter according to any one of the preceding claims, characte ised in that the bands are obtained by cutting-out from films. 9. Biological filter according to any one of the preceding claims, characterised in that the plastic materials used for obtaining the bands are chosen from among polyolefins, polyamides, polyesters, ABS or other copolymers. 10. Biological filter according to any one of the preceding claims, characterised in that the width of the band is of the order of a few tens of millimetres and its thickness is preferably of the order of several hundredths of a millimetre. 11. Biological filter according to any one of the preceding claims, characterised in that the bands have a width of 1 to 5 cm and are spiralled onto the holding members at a rate of 1.5 to 3.5 turns per running metre of holding member. 12. Biological filter according to any one of the preceding claims, characterised in that the skeins are obtained by winding the bands regularly onto holding members by rotating these bands about an axis of rotation of a fork situated preferably halfway between the holding members. 13. Biological filter according to any one of the preceding claims, characterised in that the band is twisted about itself simultaneously to the spiralled winding onto the holding members. 14. Biological filter according to any one of the preceding claims, characterised in that it comprises an assembly of conduits bringing air or another gas under pressure into the skein of band in order to clean and/or unbunch the skeins of band. FOR THE APPLICANT: