GB2106493A - Apparatus for use in the aerobic treatment of liquids - Google Patents

Abstract

Apparatus for use in the aerobic treatment of liquids includes a hollow column 14 for immersion in a tank 11, 12 of liquid to be treated, a liquid inlet 16 adjacent one end, the lower end in use, of the column 14, a liquid outlet at the opposite end 15 of the column 14, and intermediate the inlet and outlet a plurality of anchored culture retainers 24, said culture retainers 24 being spaced apart both transversely and lengthwise of the column 14 so as to be exposed in use, to a flow of liquid 13 and air bubbles along the column 14 without significantly impeding such flow. <IMAGE>

Description

SPECIFICATION Apparatus for use in the aerobic treatment of liquids This invention relates to apparatus for use in the aerobic biological treatment of liquids, primarily the treatment of aqueous sewage by means of bacteria and allied organisms.

Aerobic biological treatment of sewage is known in several forms. There is for example the well known filter bed wherein aqueous sewage is distributed by a rotating distributor, onto a filter bed composed of pebbles or the like. The liquid percolates downwardly through the bed, the pebbles providing sufficient space between them for air to enter, and also providing a large surface area upon which the purifying organisms proliferate. The various organisms colonize suitable vertically spaced zones of the filter bed.

Thus in an upper zone fungi will grow, lower down will be bacteria, then protoazoa and towards the bottom will be nitrifying and de-nitrifying organisms. Each organism colonizes a zone best suited to its own growth. For example the nitrifying organisms can not thrive in the upper zone where the liquid is rich in carbonacious compounds, but do thrive lower down where the carbonacious load is reduced by the action of the fungi and bacteria in upper zones. The natural zoning which occurs results in efficient treatment of the liquid supplied to the filter bed, suspended organic matter and dissolved nitrogenous compounds being broken-down and consumed by the bacteria and other organisms in the appropriate zones. It is however recognised that such filter beds are necessarily of a very large area, and thus are relatively expensive and wasteful of space.

It is also known to perform biological treatment by bubbling air through tanks containing the liquid to be treated. Additionally the tanks contain a sludge of bacteria and other necessary organisms which are moved in the tank by the stirring action of the air bubbles and, if necessary by mechanical agitation (Activated Sludge Process). The liquid being treated is continuously fed at a predetermined rate into the tank, and treated liquid is run-off at the same rate. The rate of flow of liquid into the tanks is limited by the rate at which the bacteria and organisms can reproduce and consume the pollutants and of course the liquid leaving the tanks must be allowed to stand to permit the spended bacteria and other organisms to settle out before the treated liquid can be discharged into waterways or the like.

Some of the settled sludge of solid matter and organisms is returned to the tank with the inflow of liquid to be treated and so provides the inflow with an initial "biomass". Thus all of the organisms are continually mixed with the liquid to be treated and the zoning effect which is so advantageous in the filter bed does not occur to the same extent. Since there is a flow from one end of the tank to the other then there will be some zoning in the flow direction as, for example, the nitrifying organisms will not be able to become active until the fungi and bacteria have reduced the carbonacious load. It is apparent therefore that if the flow rate is increased or if the pollutant loading increases then the outflow from the tank will now have been subject to treatment by all of the organisms and thus control over flow rate and oxygen content is needed.Indeed in some case it may be desirable to preactivate the returned sludge by bubbing air or oxygen through it before returning it to the tank. There have been proposed systems wherein a medium such as sand or sponge pieces is used to provide a surface area upon which the organisms can grow. However the flow of liquid through such systems has to be very accurately controlled to maintain the media in a fluidized state to that the whole surface area of each sand grain or sponge piece is accessible to the liquid. Such systems are further disadvantageous in that the natural circulation of the media prevents zoning of the organisms and repeated contact of the sand grains or sponge pieces abrades them and breaks down and abrades off the biomass adhering thereto.

Furthermore, such systems are as susceptible as the aforementioned activated sludge process, to failure in the event of sudden increases in pollutant load, since the oxygen demand of at least some of the organism types cannot be met.

It is an object of the present invention to provide apparatus for use in the aerobic biological treatment of liquids wherein the disadvantages of the aforementioned systems are minimised.

Apparatus according to the invention comprises a hollow column for immersion in a tank of liquid to be treated, a liquid inlet adjacent one end, the lower end in use, of the column, a liquid outlet at the opposite end of the column, and intermediate the inlet and outlet a plurality of anchored culture retainers, said culture retainers being spaced apart both transversely and lengthwise of the column so as to be exposed, in use, to a flow of liquid and air bubbles along the column without significantly impeding such flow.

Desirably the culture retainer are sponge-like members supported on axially extending, transversely spaced strings or filaments, each string or filament having a plurality of sponge-like members spaced along its length.

One example of the present invention is illustrated in the accompanying drawings, wherein; Figure 1 is a side elevational view, partly in section, of apparatus for use in the aerobic biological treatment of liquid sewage, and Figure 2 is a composite view, similar to Figure 1, illustrating two alternative modifications of the arrangement illustrated in Figure 1.

Referring first to Figure 1 of the drawings, there is illustrated a treatment tank having a base 1 1 and a peripheral wall 12. Within the tank is polluted water 13, the pollutant being domestic sewage. Upstanding from the base 11 of the tank is a treatment column in the form of a hollow plastics cylinder 14 open at its upper end 15 and formed at its lower end with apertures 16 whereby the liquid 13 can, in use, flow into the lower end of the column. Supported within the lower end region of the column is a bubble generator 1 7 in the form of a dome diffuser. The dome diffuser comprises a porous dome closed at its lower end by a base plate, and supplied internally with compressed air by way of an air feed line 18.The compressed air within the dome diffuser percolates through the pores of the dome diffuser and forms a multitude of small bubbles which leave the dome diffuser and float upwardly through the column 14 towards the open end 15.

The upward flow of bubbles through the column carries liquid with it, so that there is an upward flow of liquid through the column. The bubble generator 17 is supported on a simple spider mounting arrangement 19 which does not impede the flow of liquid 13 around the generator 17.

Within the cylinder 14 and immediately above the bubble generator 17 is a rigid plastic grid 21 secured in position within the cylinder 14 by being bonded or otherwise secured to the inner surface of the cylinder 14. A similar support grid 22 is provided adjacent the open upper end 1 5 of the cylinder 14 and extending axially of the cylinder between the grids 21,22 are a plurality of nylon, or other synthetic resin cords 23. The cords 23 thus extend parallel to one another, but are spaced transversely of the cylinder. Each of the cords 23 carries a plurality of biological culture retainers 24, each of which is in the form of a piece of sponge-like material conveniently a synthetic resin foam or sponge material.The retainers 24 are spaced along the length of their respective cords 23 and thus between the grids 21 and 22 the column contains a very large number of biological culture retainers 24. However, the spacing of the cords 23 transversely of the column, and the spacing of the retainers 24 longitudinally of the column is such that the flow of bubbles vertically through the column and more particularly the flow of liquid entrained by the bubbles, is not significantly impeded.

It will be recognised therefore that while air is supplied to the generator 17 then a continuous stream of bubbles will pass upwardly through the column carrying with it the liquid to be treated.

Thus there will be a continuous flow of fine bubbles containing oxygen, and liquid to be treated, past each of the culture retainers 24. Very rapidly, by virtue of the bacteria and other organisms inherent in the liquid 13 to be treated, biological cultures will develop on and colonize the retainers 24. Thus the cultures are continuously supplied with their primary requirements, that is to say food in the form of the pollutants in the liquid 13, and oxygen from the continuous supply of air bubbles. As liquid 13 passes from one end of the column to the other it undergoes treatment by way of the biological cultures on the retainers 24, and simultaneously is aerated by the bubbles.The cultures which develop at various points along the length of the column are determined by the environment, that is to say vertical zoning of the organisms occur, as in a filter bed, in accordance with the nature and quantity of the pollutants in the liquid 13. The liquid of course continually cycles through the column, and there is a continuous flow, at an appropriate rate, of polluted liquid into the tank, treated liquid flows from the opposite end of the tank, but does not require settlement since the biological cultures are retained within the columns, and do not leave the tank with the treated liquid. It will be understood that the number of columns within a particular tank will be determined by the size of the tank, the rate at which liquid is to be treated, the nature and concentration of the pollutants.

In the two modifications illustrated in Figure 2 it can be seen that on the left-hand side of Figure 2, the bubble generator 17 has been replaced by a hollow, porous, ceramic, cylinder 27 set in the wall of the synthetic resin cylinder 14. An externally disposed air chamber 28 overlies the outer surface of the cylinder 27 and is supplied with air under pressure through an air line 18. The operation is similar to that of the generator 1 7 of Figure 1 in that the air under pressure percolates through the pores of the cylinder 27 and enters the liquid within the column as a multitude of tiny bubbles. Thereafter the operation of the column is identical to that described with reference to Figure 1, in that the bubbles passing up the column entrain with them a flow of liquid to be treated.

The modification illustrated on the right-hand side of Figure 2 is similar in principle to the use of the cylinder 27, but in place of the cylinder 27 the wall of the synthetic resin cylinder 1 3 is formed with a multitude of small holes 31, covered on the exterior of the cylinder 14 by an external air chamber 28. The air chamber 28 is similarly supplied with compressed air by way of an air supply line 1 8 and the air from the chamber 28 passes through the multitude of small holes 31 in the wall of the cylinder 14 to form small bubbles within the liquid in the cylinder 14. Again the principle of operation is identical in that the bubbles entrain with them the liquid 13 within the cylinder 14 and thus generate a flow of liquid 13 from the inlets 16, vertically through the treatment column and out of the open end 1 5.

The foregoing examples of apparatus for use in the aerobic biological treatment of liquid are described with reference to the treatment of aqueous sewage on a continuous basis. However, the apparatus is not restricted in its usage to the continuous treatment of a continuous supply of domestic sewage, and can find useful application in other areas. For example, in the field of fish farming trout, and other fish being farmed, are grown in holding tanks. The holding tanks contain the water in which the fish live, and the water needs to be oxygenated. Since the fish are fed, and live in the tanks, it becomes necessary periodically to change the water since it become polluted by uneated food, but more particularly by the waste products of the fish.One way to do this is to change the water on a continuous basis, having an inflow of water and an equal outflow the whole time. Such an arrangement is, however, wasteful of water, and where the fish are being reared in water at a temperature above the ambient temperature then clearly there is a considerable energy wastage in permitting warmed water to flow from the tank.

Installation, in the fish rearing tank, of a treatment column as described with reference to Figure 1 and 2 of reduces the need for replacement of water of the tank, and at the same time oxygenates the water. Thus the flow of bubbles through the column serves to oxygenate the water and the culture retainers 24 become colonized by biological cultures which consume the waste products of the fish. Thus simultaneously the water is oxygenated and purified, and the need to replace the water is much reduced, or indeed in some instances completely obviated. Clearly where the fish are being reared at an elevated temperature there is a saving not only in the cost of the water, but more particularly in the cost of energy to heat the water since the heated water is not being allowed to run to waste.

It will be recognised that in many instances it will not be necessary to supply the bubble generator as an integral part of the apparatus.

Bubble generators of the dome diffuser type 1 7 (Figure 1) are widely used both in the treatment of domestic sewage, and in the oxygenation of fish rearing tanks and pools. It will be recognised therefore that where such bubble generators, or similar bubble generators, are in use then the apparatus which needs to be supplied is just the cylinder 14 containing the culture retainers 24.

The cylinder is then lowered over the existing bubble generator and if necessary is anchored in position by the application of weights. It will be understood that the oxygen supplied to the column will be in excess of the needs of the organisms within the column and thus the system will be less susceptible than certain previously proposed systems to sudden increases in pollutant loading in the liquid being treated. This is of course of more interest in sewage treatment plants than in fish rearing tanks.

Claims (5)

1. Apparatus for use in the aerobic treatment of liquids comprising a hollow column for immersion in a tank of liquid to be treated, a liquid inlet adjacent one end, the lower end in use, of the column, a liquid outlet at the opposite end of the column, and intermediate the inlet and outlet a plurality of anchored culture retainers, said culture retainers being spaced apart both transversely and lengthwise of the column so as to be exposed, in use, to a flow of liquid and air bubble along the column without significantly impeding such flow.

2. Apparatus as claimed in claim 1 wherein said culture retainers are sponge-like members supported on axially extending, transversely spaced strings or filaments, each string or filament having a plurality of sponge-like members spaced along its length.

3. Apparatus as claimed in claim 1 or claim 2 wherein the apparatus further includes a bubble generator disposed adjacent the inlet end of the column.

4. Apparatus for use in the aerobic treatment of liquid substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

5. Apparatus for use in the aerobic treatment of liquids substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.