GB2422147A - Method of treating effluent comprising the provision of a plurality of bacteria supporting elements - Google Patents

Abstract

A sewage treatment apparatus comprising a treatment tank 2 containing effluent 3 in which a large number of sponge balls 4 are submerged and which are of a material such as to absorb the effluent, e.g. open cell plastic foam. A conveyor 5 such as an endless chain or belt conveyor is provided so as to convey balls from the effluent to a pair of horizontal axis compressor rollers 6 which squeeze a large proportion of the absorbed effluent from the balls which is discharged at 7 via e.g. a chute to a collecting tank. The balls are returned to the effluent after passing though the rollers. Also claimed is a device for the treatment of fluids comprising bacteria-growth supporting elements of compressible sponge or sponge-like or other synthetic foam material of a thickness and/or shape so as to enable nitrification to occur on and near the surface 9 by providing an aerobic zone and de-nitrification takes place deeper within the material in an anoxic inner zone 10. Also claimed is a method of treating effluents in an existing activated sludge system by introducing media supporting bacteria made from synthetic resilient foam balls which float or are buoyant in the effluent. The balls having a pore size sufficient to enable the inner space to be colonised by bacteria. Conditions being such that bacteria operating on the system of suspended growth continue to deveop with the aeration tank and bacteria, which operate on the fixed film principle on, and in the ball.

Description

METHOD, DEVICE AND APPARATUS FOR TREATMENT OF EFFLUENTS The present

invention relates to method, device and apparatus for treatment of sewage or waste-water or industrial or other effluents containing ammonia and/or nitrates and for de-nitrjfication It is well known that the treatment of sewage involves the use of biological systems for the removal of dissolved organic material. Aerobic bacteria utilise the contaminants as a food source and bacterial growth is proportional to the level of incoming organic load. Conversion of ammonia to nitrate, by the process of nitrifjcation is an aerobic process carried out by nitrifying bacteria. It is sometimes necessary to reduce the level of nitrate in a discharge and this is carried out by a process known as de-nitrification.

Denitrifying bacteria operate in anoxic conditions where there is no free Oxygen.

As the growth of bacteria is related to the organic strength of the influent, it is necessary to remove the excess bacteria from the treatment process. Excess sludge can be applied to land as a fertiliser, be land-filled or it can be dried and used as a secondary fuel for power generation.

In "secondary treatment" of sewage and industrial effluents the action is carried out by bacteria. In so-called fixed film applications the bacteria grow on fixed structures, such as clinker, and effluent is distributed over the clinker media by distribution arms. The oxygen for the aerobic bacteria enters into the media by natural diffusion. Excess sludge is discharged from the base of the filter for secondary settlement.

Secondary treatment can also be carried out by suspended growth systems, where the bacteria are located in a tank and air is introduced by means of rotating structures or diffused aeration. The action of the rotors or the bubbles, in addition to providing oxygen, also keep the bacteria in suspension and evenly mixed. Surplus bacteria are removed from the aerated tank and are settled during secondary treatment.

The invention concerns the inclusion of a media in an activated sludge process for colon isation by bacteria. It is effectively a combination of attached growth and suspended growth systems.

Objects of the present invention include the improvement of the performance of aerobic bacterial treatment systems, the removal of nitrate by de-nitrification and the facilitation of the removal of surplus sludge from the activated sludge process.

According to the present invention there is provided a method of treatment of effluents comprising, in an effluent treatment system including a tank or container for effluent, provision of a plurality of bacteria supporting elements of sponge or sponge-like or other synthetic foam material on which bacteria may grow, the method further comprising squeezing the elements to remove excess sludge.

Preferably, the elements for supporting bacteria which grow thereon will be removed from the effluent liquid in the container by means of a conveyor (or other mechanism or displacing means), compressed or squeezed, preferably between two rollers, to remove liquid and some bacteria or biomass as sludge, and then returned to the liquid. Preferably the sludge will be discharged to a separate collection container such as via a chute to a sludgeconditioning tank. Preferably not all the bacteria will be squeezed out of the elements so as to enable new growth. Preferably the elements will float and be removed from the upper surface.

Also, according to the present invention there is provided a device for treatment of fluids comprising a bacteria growth supporting element of compressible Sponge or sponge-like or other synthetic foam material of a thickness and/or shape such as to enable nitrification to occur on and near the surface and to enable de-nitrification to take place deeper within the material - especially as bacteria growth develops.

Preferably the bacteria growth supporting elements will be compressible and Preferably of resilient sponge or foam material and preferably of synthetic foam material. The elements can be of any suitable shape although will Preferably be ball-shaped and each normally of foam material to its core and Preferably being substantially the size of a tennis ball although other shapes such as cubes, rings or doughnutlj shapes or any regular solid or irregular solid shape. Preferably the elements will be buoyant so as to float in the effluent.

Preferably the bacteria growth supporting element will be of such a size and/or shape as to provide a thickness of material which will enable aerobic bacterial activity such as nitrification to occur on the surface and in regions adjacent thereto, and also to provide anoxjc Conditions further inwardly and away from the surface regions the more the material becomes Colonised so as to enable de-nitrification to also take place where there is lithe or no oxygen available.

The elements may all be the same size and shape although such may be of mixed size, e.g. large and smaller elements may be used in the same tank.

In a preferred embodiment, into an existing activated sludge system there is introduced a media or elements for Supporting bacteria and made from a plurality of synthetic resilient foam balls which float or are buoyant in the effluent. The pore size of the foam is sufficient to enable the inner space to become colonised by bacteria. Bacteria operating on the principle of suspended growth will continue to develop within the aeration tank. Bacteria, which operate on the fixed film principle will develop on, and in, the sponge ball.

A sponge ball that is fully colonised supports a wide range of bacteria.

The conditions for the bacteria, however, will depend on the relative position of the bacteria in the sponge ball itself. Those bacteria on the outside and just beneath the surface of the ball will be in aerobic conditions with a dissolved oxygen (DO) concentration of 2 -4 mg/I. Bacteria which colonise the sponge ball towards the centre will experience conditions where the DO level is reduced. At some distance from the edge of the sponge ball the DO level will reduce to zero and the condition is referred to as anoxic. Under anoxic conditions bacteria will use the oxygen from nitrate as an oxygen source and de-nitrify the effluent. Nitrifjcation and de-nitrification will be carried out, therefore, simultaneously and in the same tank without the need for additional tanks and processes.

The removal of excess sludge is carried out by means of a conveyor, which removes the sponge balls and transfers them to two rollers. The rollers squeeze the sponge balls and the liquid, including some of the bacteria as sludge, and it is discharged via a chute to a sludge-conditioning tank. Sponge balls that have been de-sludged are returned to the aeration tank for re-use using a conveyor.

The advantages of the invention are as follows:- (i) It can be used in and to modify an existing activated sludge system.

(ii) It provides a fixed film growth environment for bacteria in a suspended growth tank, thereby increasing the biodiversity of the treatment System.

(iii) It enables simultaneous de-nitrification in an aerobic tank.

(iv) It enables removal of surplus bacteria.

(v) The support media/elements may be compressed and held compressed for transportation purposes to minimize freight costs prior to installation The invention will be described further, by way of example, with reference to the accompanying drawings, in which:- Fig. 1 is a schematic cross-section through a secondary treatment tank in a fixed film system and including a conveyor, squeezing rollers, a sludge discharge chute and an effluent return conveyor; and Fig. 2 is a cross- section through a sponge media in the form of an open cell plastics material Sponge ball.

In Fig. I sewage effluent treatment apparatus i is illustrated comprising a treatment tank 2 operating by known effluent treatment processes and containing effluent 3 in which a large number of sponge baIls 4 are submerged and which are of a material such as to absorb the effluent, e.g. , open cell plastics material foam. A conveyor 5 such as an endless chain or belt conveyor is provided which extends with one end in the effluent and inclinedly upwardly so as to convey balls 4 from the effluent to a pair of horizontal axis compressor rollers 6 which squeeze a large proportion of absorbed effluent from the sponge balls and which effluent is discharged at 7 e.g., via a chute (not shown) to a collecting tank. Means 8 are provided, such as a further conveyor to return the balls 4 to the effluent after passing through the rollers 6.

Fig. 2 is a cross-section through a baIl 4 schematically illustrating the decreasing oxygen level as occurs in the Sponge material in use. The outer region 9 provides an aerobic zone (where NH3 is converted to NO3) and an inner zone 10 which is an anoxic zone (where NO3 is converted to N2 in use over time).

Claims (21)

1. A method of treatment of effluents comprising, in an effluent treatment system including a tank or container for effluent, provision of a plurality of bacteria-supporting-elements of sponge or sponge-like or other synthetic foam material on which bacteria may grow, the method further comprising squeezing the elements to remove excess sludge.

2. A method as claimed in claim 1, in which the elements for supporting bacteria which grow thereon are removed from the effluent liquid in the container by means of a conveyor (or other mechanism or displacing means), compressed or squeezed, (preferably between two rollers), to remove liquid and some bacteria or biomass as sludge, and then returned to the liquid.

3. A method as claimed in claim I or 2 in which the sludge is discharged to a separate collection container, such as via a chute, to a sludgeconditioning tank.

4. A method as claimed in any of claims I to 3, in which not all the bacteria are squeezed out of the elements so as to enable new growth.

5. A method as claimed in any of claims t to 4, in which the elements float and are removed from the upper surface.

6. A device for treatment of fluids comprising a bacteria-growthsupporting element or elements of compressible sponge or sponge-like or other synthetic foam material of a thickness and/or shape such as to enable nitrification to occur on and near the surface and to enable denitrification to take place deeper within the material - especially as bacteria growth develops.

7. A device as claimed in claim 6, in which the bacteria growth supporting elements are compressible

8. A device as claimed in claim 7, in which the elements are of resilient sponge or foam material.

9. A device as claimed in claims 7 or 8 in which the elements are of synthetic foam material.

10. A device as claimed in any of claims I to 9, in which the elements are ball-shaped or shaped as cubes, rings or doughnut-like shapes or any regular solid or irregular solid shape.

II. A device as claimed in any of claims 6 to 10, in which the elements are each normally of foam or foam material to the core or centre.

12. A device as claimed in any of claims 6 to 11, in which the elements are each substantially the size of tennis balls.

13. A device as claimed in any of claims 6 to 12, in which the elements are buoyant so as to float in the effluent.

14. A device as claimed in any of claims 6 to 13, in which each bacteriagrowth-supporting element is of such a size and/or shape as to provide a thickness of material which will enable aerobic bacterial activity such as nitrification to occur on the surface and in regions adjacent thereto, and also to provide anoxic conditions further inwardly and away from the surface regions the more the material becomes colonised so as to enable de- nitrification to also take place where there is little or no oxygen available.

15, A device as claimed in any of claims 6 to 14, in which a plurality of elements are provided and the element are all the same size and shape or of mixed size, e.g. large and smaller elements are used in the same tank.

16. A method of treatment of effluents in an existing activated sludge into which system there is introduced a media or elements for supporting bacteria and made from a plurality of synthetic resilient foam balls which float or are buoyant in the effluent and of which the pore size of the foam is sufficient to enable the inner space to become colonised by bacteria and conditions being such that bacteria operating on the principle of suspended growth continue to develop within the aeration tan and bacteria, which operate on the fixed film principle develop on, and in, the sponge ball.

17. In an activated sludge effluent treatment system, including a conveyor and wherein the removal of excess sludge is carried out by means of the conveyor, which removes the sponge balls and transfers them to two rollers which act to squeeze the sponge balls and the liquid, including some of the bacteria as sludge which is discharged via a chute to a sludgeconditioning tank, and a further conveyor is provided to return the sponge balls that have been de-sludged to the aeration tank for re-use.

18. A device for treatment of fluid substantially as herein described with reference to the accompanying drawings.

19. An effluent treatment system substantially as herein described with reference to the accompanying drawings.

20. A method of treating effluent substantially as herein described.

21. Effluent whenever treated by the method of claim 1.