ES2606102A1 - Method and wastewater treatment system for flotation tanks (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Method and wastewater treatment system for flotation tanks. The present invention relates to a method and system for treating wastewater for dissolved air flotation tanks, comprising a perimeter wastewater feeder and a distributor of pressurized water with dissolved air supersaturated allowing the homogeneous distribution of floating substances by the entire surface of a flotation tank by the combined action of the homogeneous pressure exerted by the pressurized water distributor with dissolved super-saturated air and the homogeneous feed carried out by the perimeter feeder. The present invention improves the performance in the water treatment process and reduces the dimensions of the flotation tank by optimizing the space in the plant. (Machine-translation by Google Translate, not legally binding)

Description

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METHOD AND SYSTEM OF WASTEWATER TREATMENT FOR TANKS

OF FLOATING

DESCRIPTION

Technical field

The present invention relates to a method and system of sewage treatment for flotation tanks by dissolved air flotation, whose configuration and design improve the yields in the water treatment process and reduce the tank dimensions by optimizing the floor space.

Background of the invention

Water treatment tanks based on dissolved air flotation (DAF) are mainly used to eliminate buoyant substances and / or non-floatable substances contained in sewage, as well as to concentrate sludge from biological systems.

In these tanks, the wastewater to be treated is mixed, which has a high content of floating substances and / or non-floating substances (for example, solids and fatty liquids), with pressurized water containing supersaturated dissolved air. Thus, it is achieved that a part of the solids load is attached to the air bubbles allowing the floating of the floating fraction of the solid waste.

Floating substances accumulate on the surface of the flotation tank, forming a layer called sludge. Non-floating substances, with a density greater than that of water, decant towards the bottom of the flotation vessel.

Usually, the water to be treated is preconditioned with flocculants and coagulants to improve the separation and quality of the outlet water.

On the other hand, pressurized water with supersaturated dissolved air typically comes from a boiler in which air is dissolved in high pressure water. At the exit of the boiler, the pressure is reduced causing the appearance of micro bubbles (15-100 micrometers of

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diameter) or medium-sized bubbles (100-600 micrometers in diameter), distributed in the liquid evenly.

In general, flotation tanks are designed based on the content of floating substances and / or non-floating substances. The larger the quantity of these, the more surface area will be required due to the mud load limit. In turn, the surface will be limited by the flow rate. Critical parameters cannot be exceeded in these two variables since the system could cause the entrainment of contaminants that would flow out of the effluent.

In addition, both the configuration of the injection of pressurized water with supersaturated dissolved air and the distribution of wastewater along the floating surface are key to improving the performance of this type of tanks.

At present, most of the flotation tanks such as those described carry out a feed of previously conditioned residual water (flocculated and coagulated) in piston flow through the front part of the tank of the flotation tank.

US3175687 discloses a floating tank for clarification and / or concentration of solid particles in a liquid. This tank has a unique point of feeding the residual water, while the pressurized water is introduced homogeneously from the bottom of the mixing tank by means of several regularly distributed pits.

EP2796178A1 discloses a dissolved air flotation device (DAF) comprising a feeding zone, a contact zone, a separation zone, a purified water collection device in the separation zone and a discharge zone. The feed of the water to be treated is carried out by the head of the device.

MX2013013119A discloses a rapid flotation device comprising a mixing area separated from a floating area by a wall. The liquid to try to pass from the mixing area to the floating area above said wall. The bottom of the flotation area comprises a perforated base connected to a discharge zone.

WO2014182533A1 discloses a system for treating wastewater comprising an operation of depuration of a liquid mixture by floating of dissolved air, prior to a subsequent operation on the liquid mixture in a biological treatment tank.

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In these tanks the wastewater is introduced directly into the head of the tank mixing with the pressurized water at that point, therefore the mixing is done only in the initial part.

The problem with this type of feed is that, when analyzing the evolution profile of the sludge mantle along the inner part of the flotation tank, we can see that the distribution of sludge is not homogeneous along the entire surface of the tank, and it is much greater at the beginning than at the end of the tank.

This interferes with the performance in the elimination of floating substances, since the sludge mantle is much closer to the bottom of the tank in this first zone where the mixing occurs and a much larger ratio of pressurized water with supersaturated dissolved air is required in the initial part of the tank, generating more hydraulic load in the first part of the tank.

As indicated above, the configuration of pressurized water injection with supersaturated dissolved air and the distribution of wastewater along the floating surface, as well as the sludge / air ratio contained in the water, is essential to improve performance of this type of tanks and must be proportional. The higher the sludge load, the greater the amount of air required and therefore the higher the cost (energy and economic).

A worse performance per volume of treated water / floating surface implies the need for a larger surface for water treatment, which in turn causes the dimensions of the tanks to be larger. All this translates into an increase in costs in the construction of the tank.

The object of the present description refers to a tank for the treatment of wastewater by means of dissolved air flotation, whose configuration and design improve the yields in the water treatment process and cause the tank dimensions to be reduced by optimizing the space in plant.

In the context of the present invention, wastewater refers to waters with a load of floating substances and / or non-floating substances.

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In the context of the present invention, floating substances refer to floating solids and liquids with a density lower than that of water, while non-floating substances refer to non-floating solids and liquids with a density greater than that of water.

Detailed description of the invention

In a first aspect of the invention, a sewage treatment system for flotation tanks is provided.

The wastewater treatment system comprises: a perimeter feeder for wastewater, comprising lateral channels with openings connected to a wastewater distribution grid consisting of a multiplicity of pipes separated from each other, which comprise perforations for the feed of wastewater into the flotation tank; where the perimeter wastewater feeder is disposed along the perimeter of the flotation tank; and, a pressurized water distributor with supersaturated dissolved air comprising a plurality of openings located on the sides of the flotation tank above a zone of accumulation of non-floating substances and below the perimeter feeder; so that a homogeneous distribution of wastewater is obtained over the entire surface of the flotation tank by combined action of the homogenous pressure exerted by the pressurized water distributor with supersaturated dissolved air and the homogeneous feed carried out by the perimeter feeder of such so that floating substances, non-floating substances and purified water are separated.

The perimeter wastewater feeder is disposed along the perimeter of the flotation tank in a manner suitable for distributing sewage evenly throughout the surface of the flotation tank. The perimetral feeder comprises, in turn, lateral channels and a distribution grid inside the floating tank. The lateral channels have openings every certain distance that allow the distribution of wastewater along different points of the tank. These openings are in fluid communication with the distribution grill inside the floating tank, constituted by the appropriate means for the introduction of water from the side channels into the tank. The distribution grid is arranged so that

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The wastewater can be fed perpendicular to the drain flow.

The openings of the side channels can coincide with openings in the flotation tank. In a particular embodiment, threaded bushings are welded into the openings of the flotation tank onto which tubes that make up the distribution grid are screwed. The pipes or branches of the distribution grid preferably have a disposition perpendicular to the drain flow and are separated from each other a certain distance. The tubes have perforations, suitable for the residual water to flow into the tank, preferably horizontally or vertically (depending on the water to be treated).

In a preferred embodiment of the present invention, the side channels are arranged on the outside of the flotation tank and have a corresponding secondary function to reinforce the tank to avoid buckling of it.

The distribution grid can be completely removable, facilitating the extraction of all the elements for the maintenance of them. A removable grill improves the maintenance and change of installed elements that require repositioning.

In a second aspect of the invention, a flotation tank is provided comprising the wastewater treatment system as described according to the first aspect of the invention together with any embodiment. The tank also includes:

• a system of evacuation of floating substances;

• a zone of accumulation of non-floating substances; Y

• a system for evacuating purified water.

The flotation tank of the present invention is suitable for mixing wastewater.

to be treated for the elimination of a load of floating substances and / or non-floating substances

with pressurized water with supersaturated dissolved air. The flotation tank has in its

base a zone of accumulation of non-floating substances. Depending on the way

embodiment, the flotation tank may incorporate an auger screw or an inclined bottom with

with respect to the horizontal plane for the evacuation of the same. In order to facilitate the

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When the non-floating substances are decanted, the flotation tank may have at its final end a package of slanted slats with a certain degree of inclination depending on the type of water to be treated.

In one embodiment of the flotation tank, the pressurized water with supersaturated dissolved air may come from a boiler. The boiler is suitable for dissolving air in pressurized water. This boiler is in fluid communication with the floating tank through the pressurized water distributor with supersaturated dissolved air. This pressurized water distributor with supersaturated dissolved air consists of openings or pitches located on the sides of the flotation tank at a height greater than the zone of accumulation of non-floating substances. These openings or pitches are also located in a position lower than the wastewater distribution grid. Pressurized water injection pitches with supersaturated dissolved air are positioned relative to each other at a suitable distance to generate a network of rising bubbles so that this distance allows the bubble bed to expand efficiently, creating a network that trap floating substances by mixing bubbles with sewage.

The evacuation system of floating substances is suitable for obtaining a mantle of floating substances with a concentration of up to 80 g / l or 8% in solids more or less concentrated. The evacuation system of floating substances can consist of a set of scrapers in combination with a hopper incorporated in the tank. This hopper has an inclination in its outer part for the evacuation of the floating substances. Likewise, the pouring area towards the hopper consists of a sheet of water that is variable in height. This allows to regulate the water sheet with which a blanket of more or less concentrated floating substances is obtained.

The evacuation system of purified water may consist of a partition located at the end of the floating tank, suitable for water already purified from floating substances and / or non-floating substances to ascend for removal from the tank.

In a third aspect of the present invention, there is provided a method for the treatment of wastewater for floating tanks according to the second aspect of the invention.

According to the method of the present invention, water to be treated for the elimination of a load of substances is mixed in the floating tank described above.

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floating and / or non-floating substances with pressurized water with supersaturated dissolved air. To do this, pressurized water is supplied with dissolved air supersaturated under homogenous pressure through the distributor, and waste water is also supplied homogeneously by the perimeter feeder. By combining the above steps, a homogeneous distribution of wastewater is obtained over the entire surface of the flotation tank allowing the separation and extraction of floating substances, non-floating substances and purified water, since they are distributed in layers one on top of the other as layers of sedimentation. In the context of the present invention, supplying pressurized water with supersaturated dissolved air at homogenous pressure through the distributor means that the air pressure through the openings of the distributor is the same in all openings and can also be adjustable.

In a preferred embodiment of the third aspect of the present invention, the water to be treated is conditioned with coagulants and flocculants prior to entry into the float tank, to improve the separation and quality of the outlet water.

The feed or supply of the water to be treated to the flotation tank is carried out by means of the perimetric feeder described above, which comprises lateral channels and a distribution grid inside the flotation tank. The side channels have openings every certain distance that allow the distribution of wastewater along different points of the tank. These openings are in fluid communication with the distribution grill inside the floating tank, which introduce water from the side channels into the tank. The distribution grid is arranged so that the wastewater supply is carried out perpendicular to the discharge flow. In this way a perimeter sewage feeder is obtained which provides a homogeneous distribution along the entire surface of the flotation tank. This avoids the accumulation of sludge at the head of the tank, thereby increasing the effective float surface and reducing the necessary float surface with respect to conventional floating tanks.

An advantage of the homogeneous horizontal distribution of wastewater of the present invention consists in the maximum utilization of the floating surface of the floating tank, designed according to the relationship between the hydraulic load and the load of buoyant substances and / or non-floating substances. Floating to deal with. This results in higher performance with less installed surface, which means a lower cost of the flotation tank.

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The distribution grid allows the floating substances to be deposited at a height slightly below the flotation surface, increasing the distance between the floating substances and the pressurized water injection zone. This contributes to that the supersaturated air dissolved in the injected pressurized water has an adequate height to expand, minimizing the openings or pitches of pressurized water injection with supersaturated dissolved air needed in the tank, which improves the energy efficiency up to 25% .

Pressurized water with supersaturated dissolved air may come from the boiler described above. Inside the boiler dissolves and stabilizes air in pressurized water. At the exit of the boiler, the water pressure is lowered to a sufficient pressure to generate air bubbles homogeneously distributed in the liquid. Pressurized water preferably comes from recirculating a portion of the water already treated to the boiler, typically between 50 and 80% depending on the cases.

The sewage treatment method for the flotation tank described above performs the separation of the load of buoyant substances and / or non-buoyant substances by two different forms: flotation and decantation.

On the one hand, the floating substances are removed from the flotation surface by means of a previously described system of evacuation of floating substances.

On the other hand, non-floating substances tend to decant towards the base of the flotation tank. In order to facilitate the decantation of non-floatable substances, the tank has at the end of the flotation tank a package of inclined lamellae with a degree of inclination depending on the water to be treated. The arrangement of the lamellae is designed so that the flow of wastewater is carried out from the top down (unlike other systems, where it is usual for the flow to be carried out from the bottom up). This arrangement allows floating substances to be kept on top. The lamellae of the decanter do not occupy the entire surface of the flotation tank, leaving a water outlet zone and causing a predetermined path in the design to improve performance and avoid clogging. The injection of wastewater by means of the perimeter feeder object of the present invention is made above the lamellae of the decanter to facilitate the flotation of the fatty and solid liquids in suspension, while improving the decantation of the sedimentable matter.

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The water already treated and purified from floating substances and / or non-floating substances is removed from the tank by means of an evacuation system of purified water that can consist of a partition located at the end of the floating tank, where the water rises for withdrawal of the tank.

It has been shown that with these improvements the tank for the treatment of water by flotation can increase its capacity up to 25% for the same installed surface, compared to other existing tanks in the market, maintaining the yields as regards the reduction of substances buoyancy and / or non-buoyant substances in the water already purified from exit.

Brief description of the figures

Figure 1 shows a cross-sectional view of a flotation tank with the wastewater treatment system of the present invention.

Figure 2 shows in detail the perimeter wastewater feeder, where the side channels and the distribution grid consisting of a multiplicity of tubes are appreciated.

Figure 3 shows a detail of the joint of the openings of the side channels.

Figure 4 shows a cross-sectional view of a flotation tank with the wastewater treatment system of the present invention where the flow followed by the sewage from its entrance to the tank to its exit separated in floating substances is detailed, in non-floating substances and in purified water.

Description of a preferred embodiment of the invention

To facilitate the understanding of the figures, the list of references used is set out below:

(1) Flotation tank.

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(2) Perimeter wastewater feeder.

(3) Side channels.

(4) Pipes that make up the distribution grid.

(5) Openings or pitches for the injection of pressurized water with supersaturated dissolved air.

(6) Zone of accumulation of non-floating substances.

(7) Purified water evacuation system.

(8) Side channel openings.

(9) Threaded bushings.

(10) Package of lamellae to facilitate the decantation of non-floating substances.

(11) Water flow through the flotation tank.

(12) Floating substances evacuation system.

A particular embodiment of the present invention is described below, although the scope thereof is not limited to the details of the example in any way.

Figure 1 shows an embodiment for the flotation tank (1) with the water treatment system of the present invention.

Figure 1 shows the flotation tank (1), the perimeter feeder (2) of wastewater, a system for evacuation of purified water (7), a system for the evacuation of floating substances (12), the zone of accumulation of substances non-floating (6), the package of lamellae to facilitate the decantation of non-floating substances (10), as well as the openings or pitches for the injection of pressurized water with dissolved supersaturated air (5).

In this embodiment, a flotation tank (1) is used for the elimination of solids and fatty liquids in wastewater. The wastewater is previously treated with flocculants and coagulants before it is incorporated into the flotation tank (1). The flotation tank (1) consists of a zone of accumulation of non-floating substances (6) in its base, which in turn incorporates an auger screw for the evacuation of the same. The tank also has a package of lamellae (10) inclined 60 ° at the end of the floating tank.

The flotation tank (1) of this embodiment has openings or pitches (5) on the sides for the injection of pressurized water with supersaturated dissolved air from a boiler. This boiler is suitable for dissolving air in pressurized water. Distance

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Between the height of the bites (5) and the height of the distribution grid, the bubble network can be optimally expanded, which improves the energy efficiency of the tank. The boiler, in turn, is fed by the water previously treated in the tank that is recirculated for injection as pressurized water with dissolved air 5 supersaturated.

Figure 2 shows a realization of the perimeter feeder (2) for wastewater. The perimeter feeder (2) consists of lateral channels (3) arranged on the outside of the tank. These channels have openings (8) (see figure 3) that are connected with tubes (4) inside the flotation tank (1) forming the distribution grid.

Figure 3 shows a detail of the joint of the openings (8) of the side channels (3). Threaded bushings (9) are welded around the openings (8) onto which tubes (4) that make up the distribution grid are screwed.

Figure 4 shows an embodiment of the tank (1) with the wastewater treatment system of the present invention. Figure 4 shows the flow of water (11) through the flotation tank (1) from the perimeter feeder (2) of wastewater, to the zone of accumulation of non-floating substances (6) of the flotation tank (1), and through the package of lamellae (10) to facilitate the decantation of non-floating substances, to finally leave the tank through an evacuation system of the purified water (7).

The calculated performance for the tank described in this preferred embodiment of the invention provides an improvement of up to 25% compared to a piston flow feed tank on the front of a flotation tank of similar dimensions.

Claims (12)

5 10 fifteen twenty 25 30 35 1. Wastewater treatment system for flotation tanks (1), characterized in that it comprises: • a perimeter wastewater feeder (2), comprising lateral channels (3) with openings (8) connected to a wastewater distribution grid consisting of a multiplicity of pipes (4) separated from each other, which comprise perforations for the supply of wastewater into the flotation tank (1); and where the perimeter feeder (2) of wastewater is disposed along the perimeter of the flotation tank (1); • a pressurized water distributor with supersaturated dissolved air comprising a plurality of openings (5) located on the sides of the flotation tank (1) above a zone of accumulation of non-floating substances (6) and below the perimeter feeder (2); so that a homogeneous distribution of wastewater is obtained over the entire surface of the flotation tank (1) by combined action of the homogenous pressure exerted by the pressurized water distributor with supersaturated dissolved air and the homogeneous feed carried out by the feeder perimeter (2) in such a way that floating substances, non-floating substances and purified water are separated. 2. Wastewater treatment system for floating tanks (1) according to revindication 1, characterized in that the openings (8) of the side channels coincide with openings in the floating tank so that the distribution grid is connected to the same by means of threaded bushings (9). 3. Wastewater treatment system for floating tanks (1) according to any one of claims 1 to 2, characterized in that the lateral channels (3) are arranged outside the floating tank (1). 4. Wastewater treatment system for flotation tanks (1) according to any one of claims 1 to 3, characterized in that the distribution grid is removable. 5. Flotation tank (1) for sewage treatment, characterized in that it comprises the sewage treatment system for flotation tanks 5 10 fifteen twenty 25 30 defined in any one of claims 1 to 4, and additionally comprising: • an evacuation system for floating substances (12); • a zone of accumulation of non-floating substances (6); Y • a system for evacuating purified water (7). 6. Flotation tank (1) for wastewater treatment according to the Claim 5, characterized in that it comprises a boiler for supplying pressurized water with supersaturated dissolved air. 7. Flotation tank (1) for wastewater treatment according to the Claim 5, characterized in that the system for evacuating floating substances (12) is a scraper system in combination with a hopper. 8. Flotation tank (1) for the treatment of wastewater according to any one of claims 5 to 7, characterized in that the flotation tank (1) comprises inclined lamellae (10) at the end end of the tank with such an arrangement that the flow of purified water be from top to bottom. 9. Wastewater treatment method for flotation tanks, characterized in that it comprises the following steps: • supply pressurized water with supersaturated dissolved air under homogeneous pressure through a distributor; Y, • Supply wastewater homogeneously using a perimeter feeder (2); • combine the previous steps getting as! a homogeneous distribution of wastewater over the entire surface of the flotation tank (1); • separate and extract floating substances, non-floating substances and purified water. 10. Wastewater treatment method for flotation tanks according to claim 9, characterized in that the supply of pressurized water with supersaturated dissolved air is carried out by means of a boiler. 11. Wastewater treatment method for flotation tanks according to any one of claims 9 or 10, characterized in that the wastewater is subjected to a coagulation and flocculation process prior to entering the tank. 5 12. Wastewater treatment method for flotation tanks according to a any of claims 9 to 11, characterized in that the floating substances are extracted from the tank through scrapers that lead them to at least one evacuation system. 10 13. Wastewater treatment method for floating tanks according to a any of claims 9 to 12, characterized in that the non-floating substances are extracted from a zone of accumulation of non-floating substances at the base of the floating tank by means of a screw with respect to the horizontal plane, located in the zone of accumulation of substances non-floating (6) of the floating tank (1). fifteen 14. Wastewater treatment method for flotation tanks according to any one of claims 9 to 12, characterized in that the non-buoyant substances are removed from a zone of accumulation of non-buoyant substances at the base of the float tank by means of an inclined bottom with respect to the horizontal plane, located in the 20 zone of accumulation of non-floating substances (6) of the flotation tank (1).