GB2247233A

GB2247233A - Root zone filtration system

Info

Publication number: GB2247233A
Application number: GB9017471A
Authority: GB
Inventors: D J Cooper
Original assignee: ARM WASTE TREATMENTS Ltd
Current assignee: ARM WASTE TREATMENTS Ltd
Priority date: 1990-08-09
Filing date: 1990-08-09
Publication date: 1992-02-26
Anticipated expiration: 2010-08-09
Also published as: GB9017471D0; GB2247233B

Abstract

A filtration system for polluted water comprises a plurality of portable, open topped tanks 10 with air inlet holes 12, 13 and 14 at different levels in its longitudinal side walls. Angle iron members 15 overlie the air inlet holes and increase the rigidity of the tank 10. The tank 10 contains filter bed layers 16 to 19 in which common reed plants 21 are grown before the tank is transported to the site of use. (Fig. 2). <IMAGE>

Description

FILTRATION This invention relates to filtration of polluted water, and is more particularly, though not exclusively, concerned with filtration with relatively small quantities of polluted water such as are produced, for example, on a farm, in a factory or in a processing plant.

US Patent 3770623 proposes a method of removing suspended and dissolved pollutants from water by first passing the water through a settling tank and then, successively, through one or more filtration beds and one or more elimination beds. The filtration beds consist of a bottom layer of coarse porous material and a top layer of a fine porous material having rooted and growing therein plants having nodes, eg the common reed (Phragamites communis).

Water from the settling tank is introduced into the filtration bed above the surface of the porous layers of the bed and the level is maintained thereabove so that the suspended matter and slime will settle on top of the bed as the water filters therethrough. The plants root and grow in the slime which is converted to top soil or humus. The water being filtered passes through the filtration bed and is removed near the bottom to be passed into the elimination bed having a layer of porous material such as sand or glass fibres therein in which plants selected for the removal of particular dissolved pollutants known to be present are growing. US Patent 3770623 indicates that, in general, the filtration and elimination beds will be in the form of trenches dug in the soil.

It is an object of the present invention to provide a filtration system for polluted water-which is convenient to install and use.

According to one aspect of the present invention, there is provided a filtration system for polluted water, comprising at least one filter bed which contains at least one layer of porous particulate material capable of supporting suitable plants such as the common reed, and an outlet at or adjacent the bottom of the filter bed, wherein the or each filter bed is provided in a portable open topped tank, and wherein the suitable plants are grown in the porous particulate material before transportation to the site of use of the filtration system.

Preferably, a plurality of air inlets are provided for introducing air into the filter bed. Means are preferably provided within the tank for preventing blinding of the air inlets by the porous particulate material. Conveniently, the air inlets are provided in at least one side wall of the tank and the means for preventing blinding of the air inlets comprise angle section struts which are secured to the tank so as to enhance the rigidity thereof and which overlie the air inlets. Additionally or alternatively, the air inlets may be provided at the lower ends of pipes which are partly embedded in the filter bed and whose upper ends are open to the atmosphere in use so as to conduct air downwards towards the bottom of the filter bed.

The advantage of the system according to the present invention is that it is very flexible and can be easily expanded as desired by purchase of one or more portable tanks. The plants can be grown under ideal conditions off site, thereby ensuring that all plants are growing before despatch. The required plumbing connections can be made quite simply and quickly and the beds can be brought into operation immediately rather than having to wait for a time operation immediately rather than having to wait for a time until the plants have become established in the bed.

The porous particulate material is preferably arranged in the filtration bed in the form of a plurality of layers of particulate material having different particle sizes, the upper layer having a smaller particle size than the underlying layer or layers. In order to reduce weight and thereby facilitate handling and transport, it is preferred for the or one of the lower layers to be formed of a particulate lightweight plastics material.

In a typical example, the layers of porous particulate material comprise a lightweight particulate plastics filler as a bottom layer, followed by a similar layer but of rather smaller particle size, followed in turn by a particulate aggregate layer such as a fly ash layer, and finally a top layer of sand or grit.

Whilst it is preferred to use the common reed because of its ease of growth and effectiveness not only in filtering but also in assisting in the breakdown of solids in organic wastes, it is within the scope of the present invention to use any other suitable type of plant, such as those which are also disclosed in US Patent 3770628. Suitable plants are generally those which have hollow stems and nodes. The hollow stems conduct considerable amounts of oxygen into the root system. This oxygen is used by aerobic organisms surrounding the roots to break down the solids in organic wastes. The nodes promote rapid root growth in material from the polluted water which is deposited on the upper surface of the filter bed in use.

Whilst it is within the scope of the present invention to arrange for the plants to provide most of the oxygen required to purify the water, it is also possible to provide an additional source of oxygen as necessary or as desired, depending upon the space available for the system, the amount and degree of pollution of the water being treated, and the nature of the pollutants.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawing, in which: Fig. 1 is a plan view of a portable tank forming part of a filtration system according to one embodiment of the present invention, and Fig. 2 is a view on the line 2-2 of Fig. 1 showing, in dotted line, the composition of a typical filter bed.

Referring now to the drawing, the filtration system is for filtration of polluted water to purify it sufficiently for re-use of the water or for discharge into a nearby drain or river. The system includes a plurality of tanks 10 (only one shown), the number being chosen to suit the particular installation. Each tank 10 is fabricated out of sheet metal suitably treated to render it corrosion resistant. The tank 10 is open topped, rectangular and has an internal volume of about 1.75 cubic metres.

Opposed longitudinal side walls are provided with three horizontal rows of air inlet holes 12, 13 and 14 therein.

In this embodiment, there are eighteen holes in the lower row of holes 12, six holes in the intermediate row of holes 13 and five holes in the upper row of holes 14 in each of longitudinal side walls of the tank. Each angle iron member 15 is orientated so that its apex is upwardly directed and is disposed directly above a respective one of the holes 12, 13 and 14 in each longitudonal side wall so that the lower longitudinal side edges of the angle iron member 15 terminate in the horizontal plane in which the respective row of holes is disposed.

As shown in dotted line in Fig. 2, each tank 11 is partly filled with a filter bed comprising layers 16, 17, 18 and 19. The lowermost layer 16 is formed of relatively coarse particles of a low density material (eg plastics) and of a size such that they rest on the angle iron members 15 overlying the lowermost row of holes 12. The next layer 17 of the filter bed is constituted by particles of a similar material but of a rather smaller particle size. The interface between the layers 16 and 17 occurs just below the row of holes 13. The layer 18 rests on the layer 17 and is formed of a fly ash-type aggregate. The interface between the layers 17 and 18 is just below the row of holes 15. The uppermost layer 19 rests on the layer 18 and is formed of grit.

The tank 11 has a water outlet 20 situated just below the bottom row of air inlet holes 12 but spaced a short distance above the base of the tank 11 so as to define a waterretaining sump which ensures that the filter bed remains moist at all times.

Before use, common reed seedlings or plants 21 (only three shown) are planted in the layer 19 in the works and cultivated under optimum conditions to ensure proper growth.

Any plants 21 which fail to grow are removed and replaced by fresh plants so that growth of plants 21 over the whole of the area of the tank 10 is ensured.

The required number of the above-described tanks 10 containing the filter bed layers 16 to 19 and established plants 21 are delivered to a site at which the filtration system is to be provided by container lorry, the shape and size of the tanks being such that they can conveniently be fitted into a standard-sized container and can be handled by crane or fork lift. Once the tanks 10 have been installed into the desired position, the necessary plumbing connections are made so as to connect the outlet 20, to a suitable filtered water run-off system. Additionally, a suitable polluted water distribution system (not shown) is provided for feeding polluted water to be filtered into the open top of each tank 10.

In use, polluted water to be filtered is fed via the inlet distribution system into each tank 10 so as to form a layer on top of the uppermost layer 19 of the filter bed. If desired or necessary, the polluted water may be subjected to primary settling. The polluted water introduced into each tank 10 percolates through the layers of the filter bed and the majority of the water leaves via the outlet 20. During passage through the filter bed, filtration of suspended solids takes place and also some of the pollutants in the water act as nutrients for the common reed plants 21 and are thereby removed from the water. Furthermore, supply of oxygen through the stems of the plants 21 can be used at least partially to satisfy the chemical and/or biological oxygen demand of the polluted water.However, in his embodiment, the air inlet holes 12, 13 and 14 ensure a good supply of air to at least the bottom three layers 16, 17 and 18 of the filter bed. If necessary, further oxygen or air can be supplied to the tank by one or more bubblers (not shown) or by vertical tubes which are open to the atmosphere at their top ends and which are perforated in the region of the layers 16 and 17 so that air is conducted downwards.

It will be appreciated that the above-described filtration system is very versatile in that further tanks can be added as desired to cope with increases in the quantity of polluted water to be treated. The angle iron members 15 not only strengthen the tank but also assist in preventing the holes 12, 13 and 14 from becoming blinded by material from the filter bed and help to promote supply of air to the centre of the filter bed. When the plants 20 have outgrown the tank 10, they can be cut back or cropped. If, however, the filter bed becomes contaminated with chemicals which are harmful to the plants, either the tank 10 can. be replanted with fresh plants after cleaning or replacing the filter bed, or the whole tank can be removed and replaced by a fresh tank, the used tank being returned to the works for cleaning and replanting.

Claims

1. A filtration system for polluted water, comprising at least one filter bed which contains at least one layer of porous particulate material capable of supporting suitable plants such as the common reed, and an outlet at or adjacent the bottom of the filter bed, wherein the or each filter bed is provided in a portable open topped tank, and wherein the suitable plants are grown in the porous particulate material before transportation to the site of use of the filtration system.

2. A system as claimed in claiml, wherein a plurality of air inlets are provided for introducing air into the filter bed.

3. A system as claimed in claim 2, wherein means are provided within the tank for preventing blinding of the air inlets by the porous particulate material.

4. A system as claimed in claim 3, wherein the air inlets are provided in at least one side wall of the tank and the means for preventing blinding of the air inlets comprise angle section struts which are secured to the tank so as to enhance the rigidity thereof and which overlie the air inlets.

5. A system as claimed in claim 2, 3 or 4, wherein air inlets are provided at the lower ends of pipes which are partly embedded in the filter bed and whose upper ends are open to the atmosphere in use so as to conduct air downwards towards the bottom of the filter bed.

6. A system as claimed in any preceding claim, wherein the porous particulate material is arranged in the filtration bed in the form of a plurality of layers of particulate material having different particle sizes, the upper layer having a smaller particle size than the underlying layer or layers.

7. A system as claimed in claim 6, wherein the or one of the lower layers is formed of a particulate lightweight plastics material.

8. A system as claimed in claim 7, wherein the layers of porous particulate material comprise a lightweight particulate plastics filler as a bottom layer, followed by a similar layer but of rather smaller particle size, followed in turn by a particulate aggregate layer such as a fly ash layer, and finally a top layer of sand or grit.

9. A system as claimed in claim 1, substantially as hereinbefore described with reference to the accompanying drawing.