WO2019221663A1

WO2019221663A1 - Continuous sand filter

Info

Publication number: WO2019221663A1
Application number: PCT/SE2019/050442
Authority: WO
Inventors: Mattias FELDTHUSEN
Original assignee: Nordic Water Products Ab
Priority date: 2018-05-18
Filing date: 2019-05-16
Publication date: 2019-11-21
Also published as: EP3793705A1; EP3793705A4

Abstract

A continuous sand filter for fluid treatment comprises a filter module (1) for holding a filter bed (2), a fluid inlet (3) and a fluid outlet provided in the filter module (1). Further, the continuous sand filter comprises a fluid distributor (4) which extend at least partially through the filter bed (2) and the fluid inlet (3) is connected to the fluid distributor (4). A diffusor (5) for creating micro or nano bubbles is provided between the fluid inlet (3) and the fluid distributor (4).

Description

CONTINUOUS SAND FILTER

Technical field

[0001 ] The present invention relates generally to a continuous sand filter according to claim 1.

Background art

[0002] In connection with municipal and many industrial water treatment systems, water/wastewater needs to be purified. For example, one such system may be a drinking water system where drinking water is produced from surface water and another system may be a municipal wastewater treatment wherein the wastewater needs to be treated so that it can be discharged or reused in industry or for irrigation and similar purposes.

[0003] In prior art it is known continuous sand filters which use one or more nozzles buried into to the filter bed in the sand filter. By means of the nozzles air bubbles are supplied into the bottom region of the filter bed. The air bubbles rise slowly from the bottom of the filter module through a filter bed up to a liquid layer above the filter bed and the air bubbles provide efficient transfer of oxygen to the fluid. The oxygen combined with the food source, sewage, allows the bacteria to produce enzymes which help break down the waste so that it can settle in the filter. A drawback with this design is that the nozzles are buried into the filter bed. Since height of the sand filter is about 11 meters, the amount of sand in the filter bed is of importance when for example the nozzle is to be replaced or need maintenance. If any of the nozzles has to be replaced or needs maintenance, the major amount of the filter medium has to be removed, which demands a great effort which is time-consuming and costly.

Summary of invention

[0004] An object of the present invention is to create a continuous sand filter for fluid treatment which is easy to maintain and which provides for good aeration. According to a first aspect of the invention, there is provided a continuous sand filter comprising a filter module for holding a filter bed, a fluid inlet and a fluid outlet provided in the filter module. Further, the sand filter comprises a fluid distributor which extend at least partially through the filter bed. Further, the fluid inlet is connected to the fluid distributor.

[0005] A diffusor is provided between the fluid inlet and the fluid distributor, wherein the diffusor is arranged to create micro or nano bubbles which are distributed into the fluid.

[0006] In a preferred embodiment, the diffusor is at least partially arranged above an upper surface of the filter bed.

[0007] In a preferred embodiment, the diffusor is arranged to create the micro or nano bubbles with diameters within the interval of 10nm - 500pm.

[0008] In a preferred embodiment, the fluid distributor is provided to supply gaseous fluid from the diffusor to a bottom area of the filter bed.

[0009] In a preferred embodiment, the fluid distributor comprises fluid distributor arms arranged in the bottom area of the filter bed. Further the fluid distributor arms are preferably arranged at a maximal distance of approximately 6.5 m from a lower part of the diffusor.

[0010] In a preferred embodiment, the gaseous fluid supplied from the diffusor is air or oxygen gas.

[001 1] In a preferred embodiment, the length of the diffusor is less than

1270 mm.

[0012] In a preferred embodiment, the continuous sand filter is an up-flow filter.

[0013] In a preferred embodiment, the continuous sand filter comprises a fluid flow capacity between approximately 10-100m³/h through the sand of the continuous sand filter.

[0014] In a preferred embodiment, the continuous sand filter comprises a decrease in pressure which is based on a water column with preferably a length in the interval of about 0.5 m to 10 m, measured between a fluid surface of the filter bed and a fluid inlet to the filter bed within the filter module.

[0015] In an additional embodiment the diffusor is a carbon ceramic diffusor.

[0016] According to a second aspect of the present invention, a method for processing fluid using the continuous sand filter is provided, comprising the steps: -supplying fluid into the fluid inlet,

-supplying micro or nano bubbles into the fluid by means of the diffusor, creating a gaseous fluid,

-distributing the gaseous fluid through the fluid distributor to the bottom area of the filter bed,

- filtering of the fluid through the filter bed.

Brief description of drawings

[0017] The invention is now described, by way of example, with reference to the accompanying drawing, in which:

[0018] Fig. 1 shows a continuous sand filter according to the invention. Description of embodiments

[0019] In the description below, various directions may be given with reference to a continuous sand filter, which is an up-flow filter, standing upright on a ground surface. Example of such directions can be up, down etc.

[0020] In this context, the term "fluid" should be construed broadly to incorporate all kinds of fluids in a continuous sand filter, such as wastewater which is to be purified or drinking water produced from surface water.

[0021 ] In the following, a detailed description of a continuous sand filter according to the invention is given with reference to Fig. 1. The continuous sand filter is a device for continuous cleaning of a filter bed material. This in turn means a liquid treatment process for liquid purification of e.g. sewerage. Further, the continuous sand filter is an up-flow filter, which means that suspended solids within the fluid are filtered out as the fluid flows up through the continuous sand filter.

[0022] The continuous sand filter comprises a filter module 1 which is provided with a filter bed 2 comprising sand, a fluid inlet 3 and a fluid outlet (not shown).

The fluid inlet 3 is in fluid connection to a fluid distributor 4 which extend at least partially through the filter bed 2. Further, a diffusor 5 is provided between the fluid inlet 3 and the fluid distributor 4. The diffusor 5 is at least partially arranged above an upper surface 6 of the filter bed 2, so that it is easily accessible. The position of the diffusor 5 facilitates maintenance or replacement in case of malfunction.

[0023]The diffusor 5 is arranged to create bubbles which is distributed into the fluid by means of the fluid distributor 4. The bubbles are preferably micro or nano bubbles. The size of the bubbles is of importance since if the sizes are too large the bubbles tend to merge with one another too quickly and the oxygen feed into the filter bed will not be sufficient. If the size of the bubbles is too small organic nitrogen may dissolve into the fluid which is not desirable, since gives rise to nitrogen fixation. The diffusor 5 is arranged to create micro or nano bubbles into the fluid with diameters preferably within the interval of 10nm - 500pm.

[0024] In one embodiment the diffusor 5 may be a diffusor using carbon ceramic technology. The carbon ceramic diffusor is provided with a compressor which is arranged to deliver gas under pressure, which gas is arranged to deliver micro or nano bubbles into the liquid. The carbon ceramic diffusor comprises a bubble generation medium which is porous and having several pores. The bubble generation medium may be a compound of a carbon-based material which is porous. The gas delivered under pressure by the compressor passes through the pores of the bubble generation medium and further into liquid of the continuous sand filter as micro or nano bubbles. Thus, the micro or nano bubbles are created by the carbon ceramic diffusor when the gas from the compressor is squeezed through the pores of the bubble generation medium.

[0025] The fluid distributor 4 is provided to supply gaseous fluid from the diffusor 5 to a bottom area 7 of the filter bed 2. The diffuser 5 produces very small bubbles which are introduced through the fluid distributor 4 to the bottom area 7 of the filter bed 2. The small bubbles rise slowly through the filter bed 2 from the bottom of the filter module 1 to a liquid layer 11 above the filter bed 2 and provide efficient transfer of oxygen to the fluid. The oxygen combined with the food source, sewage, allows the bacteria to produce enzymes which help break down the waste so that it can settle in the filter. The fluid distributor 4 comprises fluid distributor arms 8 arranged in the bottom area 7 of the filter bed 2. A stream of bubbles ascend up from the fluid distributor arms 8 to the liquid layer 1 1 above the filter bed 2.

[0026] A filter medium distributor pipe 10, for conveying polluted filter medium, in this case sand, extends through the central portions of the filter bed 2, from its lowest level to a washing apparatus 12. Air is used for transporting the sand to the washing apparatus 12, whereby the air is taken down centrally in an air distributor pipe 9 disposed concentrically around the filter medium pipe 10. The washed sand is returned to the top of the filter bed 2 and moves downwards in the filter bed 2 as the sand at the bottom is taken away for washing. The fluid distributor 4 is arranged concentrically around the air distributor pipe 9. The fluid, preferably wastewater, that is to be treated in the filter bed 2 is taken via the fluid distributor 4 down into the bottom portion of the filter bed 2, e.g. by means of a plurality of fluid distributor arms 8 departing from the fluid distributor 4. A cone 13 is arranged below the fluid distributor arms 8. The cone 13 guides the downward movement of the sand for achieving its uniform cross-sectional distribution. The treated liquid is taken out (not shown) somewhere above the filter bed 2. The wastewater is oxygenated during this counterflow process between water and sand. Oxygenation suitably takes place using air that is introduced into the filter bed 2 by means of the fluid distributor arms 8. The distributor arms 8 are preferably provided with apertures, through which the gaseous liquid is allowed to escape into the filter bed material.

[0027] Further the fluid distributor arms 8 are arranged at a maximal distance A of approximately 6.5 m from a lower part of the diffusor. The maximal distance A is determined by constructional design of the filter module and the limited space available within the filter module 1. The gas supplied to the gaseous fluid by means of the diffusor 5 is air or oxygen gas.

[0028] In this context the diffusor 5 relates to an oxygenation device in the shape of a tube. The diffusor 5 is used to transfer oxygenated air or oxygen gas into the filter module 1. Oxygen is required by microorganisms/bacteria in the fluid or on the grains in the filter bed 2 to break down pollutants such as inorganic substances. Diffusers in this context produce fine bubbles which are used to oxygenate the inlet fluid for treatment. The length B of the diffusor 5 is less than approximately 1.5 m. The length B is determined by constructional design of the filter module and the limited space available within the filter module 1.

[0029] There is provided a blower (not shown), e.g. an air lift pump which is adapted to transport contaminated filter material from the bottom area 7 of the filter module 1 , preferably a bottom cone 14 of the filter module 1.

[0030] The air-lift pump extends down close to the bottom of the filter module 1 for removal of contaminated filter material. Thus, the filter module 1 is defined as a filter unit having a system for the removal of contaminated filter material. The filter employs a backwash rinse that is performed continually while the tank is

processing the fluid. The air lift pump, located a in a center region of the bottom area of the filter bed draws the liquid from a bottom area 7 of the filter bed 2 up to a washing apparatus 12, e.g. a wash box. As the liquid is released into the washing apparatus 12, it falls into a sand washer where the filtered solids are separated from the sand. The filtered liquid, i.e. filtrate carries the solids out as waste so called“backwash”. The washed sand falls down onto the filter bed 2 for continued use.

[0031 ] The fluid flow capacity is between approximately 10-100m³/h through each filter module of the continuous sand filter. Thus, the continuous sand filter may be built up by one or multiple filter modules. A decrease in pressure is based on a water column with preferably a length in the interval of about 0.5 m to 10 m. The water column is measured between the fluid surface of the filter bed 2 and the fluid inlet 3 to the filter bed 2 within the filter module 1. [0032] The operation of the continuous filter will now be explained with reference to Fig. 1. Fluid is supplied through the fluid inlet 3 into filter module 2 which is indicated by the arrow“IN”. Simultaneously, air or oxygen gas is supplied by means of the diffusor 5 through the fluid distributor 4 and out through the distributor arms 8 into the filter bed 2. Fluid contained in the filter material will be oxygenated by means of the distributor arms 8 by means of the aerated air or oxygen gas therefrom. During filtering of the fluid through the filter bed 2 undesirable substances are removed from the fluid, which substances are filtered out as the liquid flows up through the filter bed 2. As the fluid reaches an upper region of the filter module 1 , it passes out through the fluid outlet and is

discharged.

[0033] The sand filter has been described up to now as continuously operating. This does not mean that each operational phase is continuous. For example, the upward conveyance of polluted filtering medium (in this case sand) can be arranged to be stopped while building up a bacterium strain in the bed.

Claims

1. A continuous sand filter for fluid treatment comprising

a filter module (1 ) for holding a filter bed (2),

a fluid inlet (3) and a fluid outlet provided in the filter module (1 ),

a fluid distributor (4) which extend at least partially through the filter bed (2) further the fluid inlet (3) is connected to the fluid distributor (4)

c h a racte r i zed i n t h at

a diffusor (5) is provided between the fluid inlet (3) and the fluid distributor (4), wherein the diffusor (5) is arranged to create micro or nano bubbles which are distributed into the fluid.

2. The continuous sand filter according to claim 1 , wherein the diffusor (5) is at least partially arranged above an upper surface (6) of the filter bed (2).

3. The continuous sand filter according to claim 1 , wherein the diffusor (5) is a carbon ceramic diffusor.

4. The continuous sand filter according to any one of claims 1 -3, wherein the diffusor (5) is arranged to create the micro or nano bubbles with diameters within the interval of 10nm - 500pm.

5. The continuous sand filter according to any one of claims 1 -4, wherein the fluid distributor (4) is provided to supply gaseous fluid from the diffusor (5) to a bottom area (7) of the filter bed (2).

6. The continuous sand filter according to any one of claims 1 -5, wherein the fluid distributor (4) comprises fluid distributor arms (8) arranged in the bottom area (7) of the filter bed (2), further the fluid distributor arms (8) are preferably arranged at a maximal distance (A) of 6.5 m from a lower part of the diffusor.

7. The continuous sand filter according to any one of the claims 1 -6, wherein gaseous fluid supplied from the diffusor (5) is air or oxygen gas.

8. The continuous sand filter according to any one of the claims 1 -7, wherein the length (B) of the diffusor (5) is less than 1 5m.

9. The continuous sand filter according to any one of the claims 1 -8, wherein the continuous sand filter is an up-flow filter.

10. The continuous sand filter according to any one of claims 1 -9, wherein a fluid flow capacity is between 10-100m³/h through the sand of the continuous sand filter.

11. The continuous sand filter according to any one of claims 1 -10, wherein a decrease in pressure is based on a water column with preferably a length in the interval of about 0.5 m to 10 m, measured between a fluid surface of the filter bed (2) and the fluid inlet (3) to the filter bed (2) within the filter module (1 ).

12. Method for processing fluid using the continuous sand filter according to any of claims 1 -1 1 , comprising the steps:

-supplying fluid into the fluid inlet (3),

-supplying micro or nano bubbles into the fluid by means of the diffusor (5), creating a gaseous fluid,

-distributing the gaseous fluid through the fluid distributor (4) to the bottom area (7) of the filter bed (2),

-filtering of the fluid through the filter bed (2).