WO2004035480A1

WO2004035480A1 - Construction and method for batchwise separation of suspended matter from water

Info

Publication number: WO2004035480A1
Application number: PCT/SE2003/001597
Authority: WO
Inventors: Hans Ulmert
Original assignee: Flootek Wts Ab
Priority date: 2002-10-14
Filing date: 2003-10-14
Publication date: 2004-04-29
Also published as: SE523570C2; SE0203046L; SE0203046D0; AU2003269770A1

Abstract

A construction and a method for batchwise treatment of water by means of dissolved-air flotation, comprising a tank (1) with an addition, from the bottom, of a mixture of water, which is about to be purified, via a pipe (2), and a water/air dispersion, via a pipe (3). This construction and this method use a vertically adjustable inlet (4), which possibly may be used as outlet.

Description

CONSTRUCTION AND METHOD FOR BATCHWISE SEPARATION OF SUSPENDED MATTER FROM WATER

Field of the invention

The invention relates to a construction and method for batchwise separation of suspended matter from water by dissolved-air flotation and a combination of this construction and method with a Sequencing Batch Reactor (SBR) process. Prior Art

The present technique is commonly based on that a continuous flow of water, containing suspended matter, is supplied to a flotation tank. At the same time a continuous flow of an air/water-dispersion is added to the water. At this point, flocks such as suspended substances, fibres etc., oil and fat are gathered at the surface, where a layer of surface sludge is formed. The sludge is scraped off by for example a surface scraping device. The sludge may also be broaden off over the edge of the flotation tank .

The air/water dispersion is prepared in a dispersion maker, in which water is pressurised, to approximately 6 bar, and saturated with air (at 6 bar one litre water solves 100 ml air), to obtain a clear solution. When the pressure is rapidly relieved, for example over a valve, air is liberated as bubbles in the micrometer size. The bubbles attach to particles, oil, and fat and lift them to the surface . Present alternative processes: Continuous process :

The water, which is about to be purified, is streamed to the construction of flotation together with the air/water dispersion is added. The bubbles from the air/water dispersion attach to the particles and lift them to the surface. The layer of surface sludge is discarded continuously by means of scraping. Water is removed from the bottom of the flotation tank, in such way that a constant level is maintained in the flotation tank. A limiting factor is the surface load (m/h) in the flotation tank, i.e. the volume of water per unit of time, including the added amount of the air/water dispersion (volume per unit of time, m³/h) divided by the area of the tank (m²) . Common surface loads are 4-10 m/h. In this process a restriction exists in that the rising speed of the particle/air aggregates can not be lower than the load downward. If the surface load exceeds the rising speed of the particle/air aggregates, the particle/air aggregates will be withdrawn together with the outgoing water, instead of go through flotation and separation in the flotation tank.

Batchwise process , example option 1 :

The water, which is about to be purified, is added to a flotation tank. When the flotation tank is filled, dispersion is added in the bottom of the tank. The bubbles from the dispersion attach to the particles and these lift to the surface. When all of the particle/air aggregates have flotated the surface sludge is discarded by being scraped off or by letting the surface sludge be broaden off over the edge of the flotation tank. The time for the flotation process is calculated from the point of time when the addition of dispersion stops until all of the particles have flotated. The dimensioned time is the time it takes for the particle/air aggregates, which are located closest to the bottom of the flotation tank and have the lowest speed of flotation, to reach the surface. When the flotation process is terminated, and the sludge has been packed closely and removed, the tank is emptied. To be able to apply this process on a continuous flow of water, containing suspended substances, at least two flotation tanks for batchwise process has to be used, else a buffering system, for the water containing the suspended substances, has to be connected in front of the batchwise process .

Batchwise process, example option 2: The water, which is about to be purified, is added to a flotation tank together with the water/air dispersion. The addition occurs in the bottom of the flotation tank. When the flotation tank is filled the addition is stopped. The bubbles from the dispersion attach to the particles and these lift to the surface. When all of the particle/air aggregates have flotated the surface sludge is discarded by being scraped off or by letting the surface sludge be broaden off over the edge of the flotation tank. The time for the flotation process is calculated from the point of time when the addition of dispersion stops until all of the particles have flotated. The dimensioned time is the time it takes for the particle/air aggregates, which are located closest to the bottom of the flotation tank and have the lowest speed of flotation, to reach the surface. When the flotation process is terminated, and the sludge has been packed closely and removed, the tank is emptied. To be able to apply this process on a continuous flow of water, containing suspended substances, at least two flotation tanks for batchwise process has to be used, else a buffering system, for the water containing the suspended substances, has to be connected in front of the batchwise process .

Sequencing Batch Reactor (SBR) :

SBR is a batchwise reactor supplied with active sludge. Just as for other processes with active sludge, a (kultur) of microorganisms develop in the SBR, which (kultur) is effective in decomposing contaminants and nutrients, which are commonly present in wastewater.

The water, which is about to be purified, is added to a SBR tank. When the tank is filled the addition is stopped, and air is allowed to bubble through the SBR tank. The percolating air moves the active sludge around in the SBR tank, and oxygen is dissolved in water, which brings about a biological degradation. When the aeration is completed the sludge is allowed to settle. When the sludge has settled the aqueous phase is decanted with a swivel. After the process one may possibly draw off excess sludge (This is done when you start to get to much sludge, since new sludge is continually formed) . To be able to apply this process on continuous flow of water, which needs to be purified, at least two SBR tanks has to be used, else a buffering system for the water, which needs to be purified, has to be connected in front of the SBR tank. SBR may be used at the following process needs: removing organic compounds (BOD; Biologically Oxygen Demanding compounds, and COD; Chemically Oxygen Demanding compounds), nitrification (reducing of ammonia), denitrification (reducing of nitrogen) , and biological phosphorus reducing.

It is a purpose with the present invention to supply a batchwise construction and method, which accomplish a flotation faster and more efficient than the prior art. Another purpose with the present invention is to supply a construction and method, which considerably reduce costs and industrial space, when the present invention is applied in combination with a SBR process. Summary of the Invention These purposes may be accomplished by the present invention when a mixture of water, which is about to be purified, and water/air dispersion is lead in to, and possibly lead out from, a tank by means of a vertically adjustable inlet, and possibly outlet, where the vertically adjustable inlet, and possibly outlet, always is held on a constant and/or controllable distance from the water surface in the tank.

The addition of water is made in the bottom of the tank by a vertically adjustable means. Flocks (suspended matter), oil, and fat are lifted to the surface, where a surface sludge is formed, which thereafter may be discarded from the water mixture. When the water level in the tank rises, during the filling of the tank, the vertically adjustable means is elongated in such way that the addition of water always is carried out with a constant and/or controllable distance from the mouth of the vertically adjustable means to the surface.

The water may possibly be led out from the tank with the vertically adjustable means of the tank. As the water level in the tank is decreased, when the water is led out from the tank, the vertically adjustable means is lowered, in such way that the water always may be led out from the tank with a constant and/or controllable distance from the mouth of the vertically adjustable means to the surface. Otherwise the water is led out via a valve in the bottom of the tank.

The mouth of the vertically adjustable means is provided with a rim, with is parallel with the mouth, which leads the water radially from the mouth of the vertically adjustable means to the surface layer of the tank. When the water is led out over the rim, parallel with the surface of the water, the flowrate velocity of the added water will decrease .

The surface load in the tank is, as in all other batchwise processes, zero. Separation has not been accomplished until the particle/air aggregates have reached the surface. As the water inlet always is positioned close to the surface, the distance from the particle/air aggregates to the surface is lower in the present invention than in conventional batchwise construction. The shorter distance signify that the separation is completed faster in the present invention than in a conventional construction and thus the size of the tank may be reduced, which lowers investment cost and need of space for the construction. The rim, around the mouth of the vertically adjustable means, leads the incoming water parallel with the surface of the water, which lowers the turbulence at the mouth of the vertically adjustable means and lowers the risk of mixing incoming water with the water in the tank, in which particles already have been separated. By the fact that the water is introduced parallel and with a limited distance from the surface, at the same time as the flow is directed from the centre of the tank towards the circumference of the tank, at which the velocity of the water flow decreases, the distance that the particle/air aggregates have to rise to be separated at the surface is limited. This means that the separation is obtained faster and the size of the tank may thereby be reduced, which reduce the investment cost and need of space for the construction.

Another effect is that the difference in density between the incoming water and the water in the tank (the incoming water has dissolved air, which decreases density) , which directs the flow along the surface, when the water/air dispersion is introduced into the tank, and the separation is thereby improved. Since the vertically adjustable means follows the surface in the tank, the effect of a compact accumulation of dispersion is accomplished, which results in that the flotation is completed much faster than in the batchwise processes in the prior art .

Flotation with the vertically adjustable means may also be combined with a SBR process. The SBR tank is then provided with a vertically adjustable means as inlet and/or outlet. In the prior art you had to have separate tanks for flotation and biological degradation, in addition to the system of dispersion, in a combined flotation/SBR process.

With combination of flotation, by the vertically adjustable means according to the present invention, and SBR, the flotation and the biological degradation may be performed in the same tank. This results in saved industrial space and saved money.

This invention refers to all embodiments that may give a vertically adjustable inlet, and possibly outlet, of a mixture of water, which is about to be purified, and water/air dispersion in a flotation tank or a SBR tank, such as a telescopic tube, telescopic pipe, telescopic wall, telescopic bellow, hose etc.. Brief Description of the Drawings

Fig. 1 shows a construction of a batchwise process according to the present invention.

Fig. la shows a horizontal cross-section of the mouth of a vertically adjustable means. Fig. 2 shows a combination of flotation, by means of a vertically adjustable means, according to the present invention, and SBR.

Detailed Description of Preferred Embodiments

In connection with preferred embodiments a vertically adjustable means is used as inlet, and possibly as outlet, of a mixture, consisting of water, which is about to be purified, and water/air dispersion (a water/air dispersion is prepared by pressurising water and saturating it with air, whereby a clear solution is obtained) , in a flotation tank or a SBR tank, but the invention concerns all embodiments that may present a vertically adjustable inlet, and possibly outlet, of a mixture consisting of water, which is about to be purified, and water/air dispersion, in a flotation tank or SBR tank, such as a telescopic tube, telescopic pipe, telescopic wall, telescopic bellow, hose etc ..

Embodiment 1 (Fig. 1) :

Water, which is about to be purified, is added to a tank 1, via a pipe 2, together with the water/air dispersion, via a pipe 3. The addition of the mixture is made from the bottom by a vertically adjustable means 4. As the water level in the tank rises during the addition, the vertically adjustable means 4 is elongated in such way that addition of water through the means 4 always is made with a constant and/or controllable distance from the mouth of the vertically adjustable means to the surface. The regulation of the distance between the surface and the mouth of the vertically adjustable means 4 may, for example, be performed by continually measuring the water level in the tank with a depth recorder above surface or with a pressure sensor in the bottom of the tank, which control the position of the vertically adjustable means. The amount of added water may also be measured, and the position of the vertically adjustable means may, for example, be adjusted by a wire, which is driven by a motor 6, which motor 6 is controlled by the position of the surface.

When the tank is filled the addition is stopped. The mouth of the vertically adjustable means is supplied with a rim 7, which is parallel with the mouth, which rim leads the water radially from the mouth of the vertically adjustable means into the surface layer of the tank. When the water is led out over the rim 7, parallel with the surface, the flow rate of the added water will decrease.

Fig. la shows how a mixture flow 8 flows out over the rim 7, which is parallel with the mouth of the vertically adjustable means 4. When the water is added parallel to and with a limited distance from the surface, at the same time as the flow is directed from the centre of the tank towards the periphery of the tank, the rate 9 of the water flow will decrease, and the distance 10, which the particle/air aggregates 11 will have to rise to be separated to the sludge layer 12, at the surface 13, will be limited. This implies that the separation is accomplished faster and the size of the tank may thereby be reduced, which lowers the investment cost and the need of space of the construction.

When the maximum water level in the tank has been achieved the surface sludge layer is scraped off or broaden off to a sludge channel 14 into a pipe 15 (Fig. 1) .

Thereafter the purified water is tapped off from the tank, either through a separate valve, which leads the purified water into a pipe 16, or through the vertically adjustable means 4, at the same time as the vertically adjustable means 4 is lowered to its original position. When the water level has reached a point at which the vertically adjustable means 4 can not be lowered any further, if a constant distance is to be held between the surface and the mouth of the vertically adjustable means 4, the outlet of water from the tank is stopped, and a refill of the tank may be performed.

Several batchwise constructions may be operated in parallel, in such way that some are in filling position and some are in emptying position. By this operation it will be possible to treat a constant flow. Optionally, water may be buffered in front of the construction, when the sludge is removed and the tank is emptied.

The surface load in the tank is, as in all batchwise operations, zero. Separation has not been accomplished until the particle/air aggregates have reached the surface. As the inlet of water always occurs close to the surface the distance, for the particle/air aggregates to the surface in the present invention, is shorter than in a conventional batchwise construction. The shorter distance imply that the separation occurs faster than in a conventional construction, and the size of the tank may thereby be reduced, which lowers the investment cost and the need of space for the construction.

Another effect is that the density difference, when adding the water/air dispersion, localises the flow more along the surface, and a better separation is thereby accomplished. Since the vertically adjustable means 4 follows the surface in the tank an effect of dense accumulation of water/air dispersion in a thin layer is obtained, which results in that the flotation is accomplished considerably faster than during the batchwise processes in the prior art. Embodiment 2 : Combination of flotation, by a vertically adjustable means, and SBR (Fig. 2) :

In this example two SBR tanks are used to treat a continual flow of watewater, which is about to be purified. The SBR tanks in this example are filled by turns. When the first SBR tank is filled the other one is emptied, and vice versa, to be able to treat a continual flow. This may obviously be performed with more than two SBR tanks, if the construction demands this, which is within the scope of the invention .

To easier explain this embodiment of the invention only the operation of one tank (part A) will be explained. The wastewater, which is about to be purified, is led, via a pipe 17, and is mixed with a water/air dispersion from pipe 18, which origins from a dispersion system (part B) , the operation of which is known for the person skilled in the art. The mixture is led into a SBR tank 19, by a vertically adjustable means 20 according to the invention. The SBR tank 19 has an active sludge located in the bottom of the tank, according to the description of the SBR process above. When the tank is filled the addition of the mixture is stopped. The flotation sludge, which flotate according to the technique described above, is allowed to broaden off to a sludge channel 21. A pipe 22 leads off the sludge, which is collected in the sludge channel 21. Air, via a pipe 23, is now allowed to bubble through the SBR tank 19, comprising the vertically adjustable means 20. The air perculation makes the active sludge move around in the SBR tank 19 and oxygen is thereby dissolved in the water, which results in a biological degradation. When the aeration is completed the active sludge is allowed to settle .

When the active sludge has settled the water phase is decanted off by the vertically adjustable means 20 into a pipe 24, which recirculates the water phase to the dispersion system (part B) .

Since the culture of microorganisms grows all the time, occasionally you may have to tap off a portion of the culture of microorganisms, via a pipe 25, not to fill the SBR tank with culture of microorganisms. To be able to apply this process on a continual flow of water, which is about to be purified, at least two SBR tanks with vertically adjustable means have to be used, as described before, or a buffering system for the water, which is about to be purified, has to be connected in front of the SBR tank.

In the prior art you had to have separate tanks for flotation and for biological degradation, in addition to the dispersion system.

With the combination of flotation, by a vertically adjustable means, and SBR, the flotation and the biological degradation may be performed in one tank.

Flotation in combination with SBR is performed in total accordance with the present invention.

Claims

1. Construction for batchwise purification of water by means of dissolved-air flotation, comprising a tank

(1;19) having an inlet for a mixture of water, which is about to be purified, and a water/air dispersion, c h a r a c t e r i z e d by a vertically adjustable inlet (4;20), which possibly may be used as outlet, of said mixture.

2. Construction according to claim 1, wherein the vertically adjustable inlet (4;20), which possibly may be used as outlet, includes adjustment means, such as telescopic tube, telescopic pipe, telescopic wall, telescopic bellow, and hose.

3. Construction according to claim 1, wherein the vertically adjustable inlet (4;20), which possibly may be used as outlet, is provided with a rim (7) at its mouth, said rim (7) being totally or partially parallel with the surface in the tank.

4. Construction according to claim 1, which is combined with SBR (SBR = Sequencing Batch Reactor) .

5. Method for batchwise purification of water by means of dissolved-air flotation in a tank (1;19), where the water, which is about to be purified, and a water/air dispersion are mixed to a mixture before being added to said tank, c h a r a c t e r i z e d by introducing said mixture to, and possibly drawing off from, said tank (1;19) by a vertically adjustable inlet (4;20), which possibly may be used as outlet, where the mouth of said vertically adjustable inlet (4;20), which possibly may be used as outlet, always is kept at a constant and/or controllable distance from the surface in said tank (1;19) .