GB1579623A

GB1579623A - Filtration medium for the biological treatment of waste water

Info

Publication number: GB1579623A
Application number: GB23602/76A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1976-06-08
Filing date: 1976-06-08
Publication date: 1980-11-19
Also published as: DE2725510A1; BE855426A

Description

(54) FILTRATION MEDIUM FOR THE BIOLOGICAL TREATMENT OF WASTE WATER (71) I, GEORGE FRANCIS GILBERT CLOUGH of Allmeadows Farm, Wincle, Macclesfield, Cheshire, SK11 OQJ, a British subject do hereby declare the invention, for which I pray that a patent may be granted to me and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a process and plant for the treatment of liquid effluent and sewage hereinafter referred to as waste water.

Waste waters are treated by passing them through a biological filtration medium which carries on its contacting surfaces a growth of aerobic micro-organisms. The growth of micro-organisms establishes itself on the available surfaces within the filtration medium as the waste water passes through the filtration medium and effects a reduction in the biological oxygen demand (B.O.D.) of the waste water thereby converting it to a state which meets the standards laid down by the appropriate authorities.

The filtration medium, which may be of the random or ordered type, is retained within suitable walls which are mounted over air-inlet and drainage channels. The air necessary for the oxidation process passes up from the air inlet channels through the spaces in the filtration medium and the treated waste water passes down through the drainage channels.

In the past filtration medium have been used consisting of randomly disposed pieces of coke, clinker, gravel, slag or rock. Recently, randomly or orderly arranged pieces of a plastics material such as polyvinyl chloride, polystyrene or polypropylene have been used as the filtration medium. A suitable random filtration medium consists of small extruded corrugated tubular pieces of polyvinyl chloride which are sold by Imperial Chemical Industries Limited under the Registered Trade Mark "Flucor". Other random filtration media which are being used are injection moulded rings of polypropylene of various shapes and sizes.

A suitable ordered filtration media is marketed by Imperial Chemical Industries Limited under the Registered Trade Mark "Flocor" and consists of alternating plain sheets and corrugated sheets of polyvinyl chloride which are adhered together to form a self supporting unit. Such units are capable of bearing heavy loads and in use are stacked one above the other in a tower.

Generally speaking, with both random and ordered plastics filtration media, the major parameter governing the suitability or otherwise of the media is the available surface area per unit volume of the media. However, whilst the above described plastics media have quite a high surface area per unit volume, the methods used in the manufacture of these media inevitably impose limitations on the surface area which can be achieved.

We have now found that the effective surface area on, and so the performance of, a filtration media can be increased significantly merely by providing a layer of a granular material on at least some of the surfaces on the filtration media.

According to the present invention, therefore, a filtration medium for biologically treating waste water in an aerated filter comprises pieces of an inert material on at least some of, and preferably all of, the available surfaces of which is adhered a coating of a granular material.

The filtration medium may be of the random or ordered type. It also may be of a plastics material or a ceramic material.

The granular material is preferably activated carbon. However, other granular materials including inorganic materials such as sand, coke, clay, pulverised fly ash, glass, vermiculite and foam slag and organic materials such as nylon chips, granules of polyvinyl chloride, polypropylene or polyethylene may be used.

The granular material may, for example, be adhered directly on to the surface of the medium when such surfaces are in a suitable plastic condition, for example, immediately after the plastics medium has been manufactured. Alternatively, the granules may be adhered on the surfaces of the medium by means of a suitable adhesive. The adhesive is applied as a thin coating on the surfaces of the medium and then, while it is still tacky, the granules are sprinkled or otherwise applied on the adhesive coated surfaces in such a manner as to protrude from the adhesive coating.

The presence of the layer of granular material on the surfaces within the filtration medium serves to increase the effective surface area up to many thousand fold and so improve the performance of the filtration medium. In particular, if an otherwise smooth surface is provided with a continuous coating of granular material such as activated carbon having an average particle size of approximately 0.8 mm, the surface area is increased by a factor of up to something like 30,000.

Also, the provision of a rough surface on the filtration medium allows a growth of micro-organisms to readily establish itself on the filtration medium so that the filtration medium can quickly achieve optimum performance.

Furthermore, when granules of activated carbon are used they provide an adsorbent surface on the filtration media which is effective in reducing any chemical contamination, such as organic chemicals which are normally regarded as difficult to biologically degrade, present in the waste water. The activated carbon retains the chemicals until such time as they are biologically degraded by extra cellular enzymes produced by the micro-organisms present on the surface of the medium. If, however, the granules of activated carbon, after long useage, become saturated by non bio-degradable chemical contamination so reducing its effectiveness, reactivation of the activated carbon using chemical methods can be achieved.

The invention will now be described by way of the following Examples. The mesh members referred to are according to the British Standard scale as set out on page 907 of Vol Il of "Chemical Engineering", by J.M. Coulson and J.F. Richardson London: Pergamon Press, 1955).

Example 1 In this Example, the filtration media used was an ordered media marketed by Imperial Chemical Industries Limited under the Registered Trade Mark "Flocor". An individual self-supporting unit of the media consisted of alternating plain and corrugated sheets of polyvinyl chloride which are adhered together. The individual units had a specific surface area of 90m2/m3 and had the dimensions 0.6 x 0.6 x 3.0 m.

The surfaces of the self-supporting units were coated with a layer of granular activated carbon having a size in the range 12 - 30 mesh. The granular activated carbon was attached to the surfaces of the 'Flocor' units by immersing the units in a bath of polyurethane coating composition, allowing the units to drain and then immersing the units in dry granulated activated carbon. The total weight of coating applied was equivalent to 0.38 Kg/m2 of specific surface.

A number of coated units were stacked one above the other in the usual way to form a biological filter. A comparison filter was formed by stacking the same number of uncoated units one above the other.

Both filters were irrigated at a load of 1.5m3/m2 hour with trade waste mixed with settled sewage which represented a hydraulic load of 12.96 m3/m3 day a biological load of 3.3 Kg.

BOD/m3 day. The waste/settled sewage flowed over the surfaces in the units and bacteria and other micro-organisms grew as a slimy film on the wetted surfaces in the units by fecding on the organic impurity absorbed from the effluent. In time a balanced community of organims developed on the wetted surfaces within the units.

When these conditions prevailed the filter formed from the coated units removed 52% of B.O.D. and 36% of C.O.D. in comparison with the filter formed from uncoated units which removed 44% of B.O.D. and 32C/c of C.O.D. so demonstrating that the coated units were more effective in reducing both B.O.D. and C.O.D.

It was also observed that the filter formed from the coated units voided less solids than the filter formed from the uncoated units. This may be due to a form of indigenous respiration which may be promoted by the rougher surface of the coated units causing a larger retention of biological solids in the filter.

Exanlple 2 In this Example the two filters used in Example 1 were both irrigated at a load of 1.5m31m hour with a trade waste mixed with settled sewage which represented a hydraulic load of 12.96m3/m3 day and a biological load of 2.8 Kg BOD/m3 day. Under identical conditions as in Example 1, the filter formed from the coated units removed 62% of B.O.D.

and 45% of C.O.D. in comparison with the filter formed from uncoated units which removed 58% of B.O.D. and 41% of C.O.D., again demonstrating that the coated units were more effective in reducing both B.O.D. and C.O.D.

Example 3 Coated units were prepared in an identical manner to Example 1, with the exception that the surfaces were coated with a layer of industrial sand instead of the granular activated carbon. The sand used had the following sieve analysis: Mesh Retention 16 0 22 12-30 30 35-50 44 15-25 60 12-18 The total weight of coating applied was 0.51 Kg/m2 of specific surface.

The filter was loaded, identically in all respects with the filters operated in Example 2 above. The sand coated filter removed 61% of B.O.D. and 45% of the C.O.D. applied.

WHAT I CLAIM IS: 1. A filtration medium for biologically treating waste water in an aerated filter comprises pieces of an inert material on at least some of the available surfaces of which is adhered a coating of a granular material.

2. A filtration medium as claimed in Claim 1 in which the coating of granular material is adhered to all of the available surfaces of the pieces of inert material.

3. A filtration medium as claimed in Claim 1 or Claim 2 in which the granular material is either activated carbon or sand.

4. A filtration medium as claimed in any one of Claims 1 to 3 in which the granular material has been adhered to the surfaces of the inert material by means of an adhesive.

5. A filtration medium as claimed in Claim 1 and substantially as described with reference to the Examples provided.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

load of 12.96m3/m3 day and a biological load of 2.8 Kg BOD/m3 day. Under identical conditions as in Example 1, the filter formed from the coated units removed 62% of B.O.D.

and 45% of C.O.D. in comparison with the filter formed from uncoated units which removed 58% of B.O.D. and 41% of C.O.D., again demonstrating that the coated units were more effective in reducing both B.O.D. and C.O.D.

Example 3 Coated units were prepared in an identical manner to Example 1, with the exception that the surfaces were coated with a layer of industrial sand instead of the granular activated carbon. The sand used had the following sieve analysis: Mesh Retention 16 0

22 12-30

30 35-50

44 15-25

60 12-18 The total weight of coating applied was 0.51 Kg/m2 of specific surface.

The filter was loaded, identically in all respects with the filters operated in Example 2 above. The sand coated filter removed 61% of B.O.D. and 45% of the C.O.D. applied.

WHAT I CLAIM IS: 1. A filtration medium for biologically treating waste water in an aerated filter comprises pieces of an inert material on at least some of the available surfaces of which is adhered a coating of a granular material.
2. A filtration medium as claimed in Claim 1 in which the coating of granular material is adhered to all of the available surfaces of the pieces of inert material.
3. A filtration medium as claimed in Claim 1 or Claim 2 in which the granular material is either activated carbon or sand.
4. A filtration medium as claimed in any one of Claims 1 to 3 in which the granular material has been adhered to the surfaces of the inert material by means of an adhesive.
5. A filtration medium as claimed in Claim 1 and substantially as described with reference to the Examples provided.