Method and device for blowing off gaseous contaminants from crude water in the production of drinking water

Abstract

The invention relates to a method for blowing off gaseous contaminants from crude water in the production of drinking water, comprising the step of introducing the water to be treated to the top of a shielded aerator and letting it pass through stacks of tubular elements interspersed with perforated sheets, while subjected to counter current suction. In a second aspect a device is provided for blowing off gaseous contaminants from crude water according to said method.

Claims

1. A method for blowing off a gaseous contaminant from crude water in the production of drinking water, said method comprising the step of introducing the water containing the gaseous contaminant into the top of a shielded aerator, said aerator comprising means for forming drops at the initiation of the treatment process, and division means for causing division of said drops by contact therewith, said division means being arranged below the means for forming drops, wherein the division means for causing division of the drops comprise a plurality of tubular elements in the form of pipes having reticulate pipe walls, said tubular elements being placed in horizontal layers of plural parallel tubular elements stacked in such a way that the longitudinal axes of the tubular elements in one layer are angularly displaced in relation to the longitudinal axes of the tubular elements in the one or more adjacent layers; letting the water pass through said aerator to the bottom thereof by the force of gravity; and wherein air is introduced to the bottom of the aerator and is drawn to the top of the aerator and discharged together with blown-off contaminant by a pump at the top of the aerator, and wherein bubble formation and horizontal redistribution of the water is brought about as the water passes through one or more perforated sheets, which are intercalated between a number of said horizontal layers of tubular elements.

2. The method according to claim 1, wherein the gaseous contaminant is hydrogen sulphide, aggressive carbon dioxide, a volatile pesticide or methane.

3. The method according to claim 2, wherein the gaseous contaminant is methane.

4. The method according to claim 1, wherein treated water is led from the bottom of the aerator to a sand filter for removal of residual contaminants.

5. A device for blowing off a gaseous contaminant from crude water in the production of drinking water, said device comprising a shielded aerator, said aerator comprising means at a top thereof for forming drops at the initiation of the treatment process, and division means for causing division of said drops by contact therewith, said division means being arranged below the means for forming drops, wherein the division means for causing division of the drops comprise a plurality of tubular elements in the form of pipes having reticulate pipe walls, said tubular elements being placed in horizontal layers of several parallel tubular elements stacked in such a way that the longitudinal axes of the tubular elements in one layer are angularly displaced in relation to the longitudinal axes of the tubular elements in the one or more adjacent layers; said elements allowing divided drops to pass through said aerator to the bottom thereof by the force of gravity, the device further comprising a suction pump at the top exterior part of the aerator and an air inlet at the bottom of the aerator, as well as one or more perforated sheets being intercalated between a number of the horizontal layers of tubular elements.

6. The device according to claim 5, wherein said shielded aerator is of a modular constitution and comprises a top module holding the means for forming drops at the initiation of the treatment process; one, two, three or more processing modules each holding several horizontal layers of said tubular elements and at least one of said perforated sheets; and a bottom module; wherein all of the modules or their respective contents are independently exchangeable and amenable to servicing.

7. The device according to claim 5, wherein said shielded aerator is contained within a volume presenting external dimensions of 80 cm 120 cm 300 cm.

Description

(1) In the following, a preferred embodiment of the invention will be illustrated by reference to the non-limiting figures.

(2) FIG. 1 illustrates an embodiment of the device according to the second aspect of the invention, said device being for carrying out the method according to the first aspect of the invention. The device is depicted in perspective from an elevated, diagonal viewpoint. In the figure, a part of the exterior surface of said device is made invisible in order to enable inspection of its interior parts.

(3) FIG. 2 illustrates a similar embodiment of said device from a slightly different viewpoint. The external surface of the closed device is shown, so that the modular constitution of the embodiment may be observed.

(4) Referring to FIG. 1, the main features of the illustrated plant are referenced by numbers as follows: 1 is an inlet for receiving water to be treated in the device; 2 is a pipe provided with slots (not shown) for forming drops by flow of the water through the slots at the initiation of the treatment process; 3 is one of many tubular elements for causing division of drops, in the form of pipes having reticulate pipe walls; 4 is a perforated sheet, 5 is a suction pump with an air outlet 6; 7 is an air filter, which is shown in a disassembled state for the sake of visibility.

(5) On FIG. 2, the main additional features of the illustrated closed device are referenced by numbers as follows: 8 is a top module holding means for forming drops at the initiation of the treatment process (not shown); 9a, 9b, and 9c are processing modules holding tubular elements and perforated sheets (not shown) and each provided with wickets for service; 10 is a bottom module, from which treated water leaves through the water outlet 11.

(6) An overall description of a preferred embodiment of the method according to the invention will now be given.

(7) An amount of crude water loaded with gaseous contaminants is led through the inlet 1 to the pipe 2, which is provided with a number of slots, so that the water arrives as drops into the aerator. During the course of their fall through the aerator, the drops impinge on a multitude of alternating layers of reticulate tubular elements 3, mutually displaced by 90, so that the drops are divided into droplets. The formation of droplets results in a substantially larger drop surface area relative to drop volume, so that enhanced enrichment with oxygen can take place. In the current embodiment, the reticulate tubular elements are made of plastic and present an external diameter of 70 mm. The tubular elements are fixed with strips and contained in three processing modules 9a, 9b, and 9c, each of which is packed with six layers of said elements. Within and between layers, the tubular elements abut each other.

(8) At the bottom of each of said processing modules, the water arrives at a sheet 4 made of stainless steel of a thickness of a few millimeters and provided with numerous slots, each being a few millimeters broad and somewhat longer. Oblong openings are preferred over round holes, because they are not so easily obstructed by ferric and calcareous deposits. The sheets are hold in guides, from which they may be drawn out for cleaning like baking sheets in an oven. In order to accommodate variations in the amount of supplied water, sheets with a differing number of openings may be replaced one another.

(9) The sheets serve the double purpose of spreading evenly the water, which might otherwise have concentrated in certain areas of the aerator during its passage across the tubular elements, and, notably, being the hotbed of bubble formation, thus playing an important role in oxygen enrichment and expulsion of gaseous contaminants.

(10) The generation of bubbles at the perforated sheets is significantly furthered by the suction pump 5 that produces a countercurrent air stream from the inlet of the air filter 7 to the outlet 6 of the suction pump, which assists in blowing off contaminants and further aerating the water. Moreover, a vacuum is effected by the suction within the aerator, which makes it easier to keep it tight and protected against intrusion of contaminant particles or organisms. The suction pump is set to an air flow of approximately 4000 m.sup.3 atmospheric air per hour through the aerator, which in the current embodiment presents a horizontal cross section area of about 0.8 m.sup.2. The vacuum might have been adjusted also by varying the diameter of the inlet of the air filter 7.

(11) Finally, the water reaches the bottom module 10, from where it passes through the outlet 11 to a sand filter with a view to scavenging of residual gaseous contaminants.

EXAMPLE

(12) A device according to the invention was installed and received crude water containing a high level of methane in two test runs. The device was equipped with intercalated sheets of stainless steel showing a thickness of 1.5 mm and having 42% of their surface area punched as oblong perforations. Each perforation presented a width of 2 mm and a maximum length of 20 mm.

(13) In one test, the methane concentration was reduced from 20 mg/L to 0.6 mg/L at a water flow rate of 13 m.sup.3/h.

(14) In the other test, the methane concentration was brought down from 8 mg/L to 0.13 g/L, while maintaining a water flow of 35 m.sup.3/h.

(15) In both tests, a profuse production of bubbles was observed at the perforations.