GB2252311A - "A sewage treatment system" - Google Patents

Abstract

A sewage treatment system is described which includes a filter bed (1). A sewage distribution means (2) distributes sewage across a top surface of the filter bed (1) and air distribution means (7, 8, 14) enables air to penetrate the filter bed (1) at positions other than the top surface where the sewage is distributed. <IMAGE>

Description

A Sewage Treatment System The invention relates to a sewage treatment system.

Conventional sewage treatment systems comprise a filter bed and distribution means to distribute sewage across the top surface of the filter bed, such as by means of a rotating arm which passes across the top surface of the filter bed, or by means of a number of pipes which run across the top surface. One of the problems with these types of systems is that as the sewage is destroyed by bacteria, a supply of oxygen for the bacteria to grow is required which is typically taken from the air. With conventional filter bed systems air penetrates the filter bed only through the top surface so there is a limited depth to which bacteria can survive within the filter bed.

In addition, efficient filter bed filtration systems all rely on mechanical moving parts, for example the rotating arms to distribute the sewage. Hence, they have a relatively complex distribution system for the sewage which may be difficult to maintain in remote locations. This is a major problem as generally locations which require their own sewage treatment system are for example remote farms or caravan sites in the country which are not connected to a sewer system. Hence, it is undesirable to have a large number of moving parts on the sewage treatment system.

One sewage treatment system which is designed for remote locations is the Biodisk which is manufactured by Klargester Environmental Engineering Limited.

However this system has a practical disadvantage as a treatment system to deal with 800 people weighs 14 tons, is 11.5 metres in length and 4.24 metres in width and requires a power supply of 30 kW hours/day.

Clearly in remote locations such a power consumption can often be impractical. In addition, there are often narrow single track roads for access to these remote locations and so the length, width and weight of the system makes it difficult to deliver to the location and in some cases may require it to be flown in, for example by helicopter.

In accordance with the present invention, a sewage treatment system comprises a filter bed and air distribution means to enable air to penetrate the filter bed at positions below the top surface of the filter bed.

Preferably, sewage distribution means is provided to distribute sewage through the filter bed, most preferably at the top surface of the filter bed.

In a first example, the air distribution means comprises means to create an air gap below the bottom surface of the filter bed and preferably, air transfer means to transfer air from the atmosphere to the air gap. This enables air to penetrate the filter bed from the bottom surface of the filter bed. Typically, the means to create the air gap comprises a support surface which is raised above the bottom of a container in which the filter bed is situated and the filter bed lies on top of the support surface, and the raised surface is such as to allow air penetration from the air gap through it and into the filter bed. Typically, the air transfer means comprises a conduit which passes from the top of the filter bed to below the bottom surface of the filter bed and through which air from the atmosphere can pass into the air gap.

In a second example, the air distribution means is formed by removing portions of the top surface of the filter bed to create a greater surface area over which air may penetrate the filter bed and so that air may penetrate the filter bed at locations which do not form part of the top surface. Typically, in this example the sewage distribution means distributes the sewage across the remaining top surface of the filter bed.

However, it could also distribute sewage across the surfaces exposed by portions of the top surface which have been removed. Preferably, all of the original top surface portions which do not have sewage distributed on them by the distribution means are removed to form the air distribution means.

Preferably, the first example of the air distribution means and the second example of the air distribution means are combined to enhance the effect of the air distribution means and the effective air penetration into the filter bed.

Typically, the filter bed comprises stone chips on which bacteria may live and the bacteria break down the sewage.

Preferably, where portions of the top surface are removed to form the air distribution means the top surface is removed to a depth of substantially half the total depth of the filter bed.

Preferably, the sewage treatment system may further comprise transfer means to transfer fluid which has passed through the filter bed to the distribution means so that the fluid passes through the filter bed at least twice.

Typically, the sewage treatment system is used in conjunction with a septic tank in which heavy sewage settles before the lighter sewage passes into the filter bed. Preferably, a filter is located between the septic tank and the filter bed to filter out any heavy material which passes through the septic tank.

Typically, the septic tank could also comprise a baffle filter to enhance the effect of the septic tank.

An example of a sewage treatment system in accordance with the invention will now be described with reference to the accompanying drawings, in which: Fig. 1 is a plan view of a sewage treatment system; Fig. 2 is a cross-sectional view along the line BB in Fig. 1; Fig. 3 is a cross-sectional view along the line CC in Fig.1; Fig. 4 is a view along the line AA in Fig. 3; and, Fig. 5 is a schematic block diagram showing a re-circulation system which may be used with the system shown in Figs. 1 to 4.

Fig. 1 shows a sewage treatment system comprising two septic tanks 10 having inlets 5 and which are connected by outlets 12 to troughs 20. The septic tanks 10 each have a baffle filter which comprises two plates 31, as shown in Fig. 2 which help prevent solid sewage 4 entering the outlet 12.

Each trough 20 is located above a filter bed 1 which comprises a number of elongated pillars 7 of stone chips on top of a bed 8 of stone chips. Five distribution channels 2 extend from each trough 20 across the length of the filter beds 1. Outlets (not shown) connect the troughs 20 to the distribution channels 2 so that sewage 3 in the troughs 20 may flow from the troughs 20 into the distribution channels 2.

The distribution channels 2 are formed from plastic guttering and have a number of holes 6 along their length so that sewage 3 in the channels 2 can exit from the channels 2, through the holes 6. Below each channel 2 extends an elongated pillar 7 of stone chips.

The bed 8 of stone chips is supported by an arrangement of paving slabs 9, which are raised above the bottom 11 a container or hole in which the filter bed 1 is located by a number of concrete pillars 13, as shown in Figs 2 and 3, to create an air gap 16.

In this particular example the pillars 7 extend for a height of about 2 feet above the bed 8, the bed 8 has a depth of about 2 feet and the paving slabs 9 are raised about 1 foot above the bottom 11 of the filter bed 1.

As shown in Fig. 3 two conduits 14 extend from above the bed 8 to below the paving slabs 9 and these conduits 14 enable air to circulate from the atmosphere to the air gap 16 created between the bottom 11 and the paving slabs 9.

Fig. 4 shows a view of the arrangement of the paving slabs 9. Each paving slab 9 is supported at its-centre by a concrete pillar 13 and at each of its four corners by a concrete pillar 13. Each pillar 13 supporting the corner of one slab 9, also supports the adjacent corners of three other slabs 9. There are gaps 15 between each slab 9 which enable air to penetrate through the slabs 9 from the air gap 16 into the bed 8.

The pillars 7 of stone chips are held in the position shown by wire mesh which is moulded to form the outline of the pillars 7 and which retains the stone chips.

In use, sewage passes through the inlet 5 into the septic tanks 10 where the heavy, solid sewage 4 settles in the bottom of the tanks 10. The lighter, fluid sewage 3 flows out of the septic tanks 10 via an outlet 12 and into the troughs 20 in the filter beds 1. The sewage 3 then passes from the troughs 20 into the distribution channels 2 where it then passes through the holes 6 in the channels 2 and falls on to the top of the pillars 7. The sewage then passes down through the stone chips in the pillars 7 and through the bed 8.

As the fluid passes through the stone chips which form the pillars 7 and bed 8 the sewage is broken down by bacteria living on the stone chips. In order for the bacteria to survive they require a plentiful supply of oxygen and a damp habitat. The dampness is provided by the fluid sewage 3 and the oxygen penetration into the stone chips is provided by the large surface area of the pillars 7 and by enabling air penetration into the bottom of the bed 8 by means of the conduits 14 and the air gap 16 below the bed 8.

These two features when combined provide for efficient air penetration and hence, oxygen penetration into the stone chips and enables bacteria to survive throughout practically the entire bed 8 and pillars 7. Hence, because there is a large proportion of bacteria throughout the filter bed 1 it is possible to obtain high water purities from the filter bed 1.

In addition the purity of the final water can be enhanced further by recirculating the water through the filter bed a number of times. Fig. 5 shows how this may be done. Typically, after the fluid has passed through the filter bed 1 it is transferred into a reservoir 17 by a transfer pipe 18. A pump 19 then transfers water from the reservoir 17 via a pipe 21 into the inlet 12 of the filter beds 1. Hence, the water in the reservoir 17 can be circulated a number of times through the filter beds 1 to increase still further the purity of the water. This also has the advantage of keeping the bacteria damp even when there is not enough sewage 3 in the septic tanks 10 to pass into the filter beds 1. A filter 32 may also be incorporated into the outlet 12 to filter sewage 3 before it passes into the filter bed and before it mixes with water from the reservoir which is being recirculated.

When the reservoir 17 is full it can be emptied by a pump 22, via a pipe 23, into an external water passageway, such as a river.

For a system to deal with about 800 people, or 250 caravan units, there are two septic tanks 10, each with a width of 1.8m, a length of 4.8m and a depth of 1.3m.

These are connected by the outlets 12 to two filter beds 1 having a width of 2.72m, a length of 6.5m and the depths given above for the pillars 7, bed 8 and air gap 16. In addition, a pump 19 having a capacity of 2500 gallons per hour is used.

Such a system in tests, has been found to give water purities as high as 4/6, where 4 represents the biochemical oxygen demand of the water at 200C and 6 represents the amount of suspended solid in mg/litre.

these figures are extremely low for a sewage treatment system with no moving parts and compares favourably with water purity levels obtained by local authority sewage treatment systems.

In addition, this sewage system requires no moving parts to distribute the sewage and the only power required is for the two pumps 19, 22. Hence, very little maintenance is required and the power consumption is low.

Modifications and improvements may be incorporated without departing from the scope of the invention.

Claims (10)

1. A sewage treatment system comprising a filter bed, and air distribution means to enable air to penetrate the filter bed at positions other than the top surface of the filter bed.

2. A sewage treatment system according to Claim 1, wherein the air distribution means comprises means to create an air gap below the bottom surface of the filter bed.

3. A sewage treatment system according to Claim 2, wherein the air distribution means includes an air transfer means to transfer air between the atmosphere and the air gap.

4. A sewage treatment system according to Claim 3, wherein the air transfer means comprises a conduit.

5. A sewage treatment system according to any of claims 2 to 4, wherein the means to create the air gap comprises a support surface which is raised above the bottom of a container in which the filter bed is situated, and the filter bed is on top of the support surface.

6. A sewage treatment system according to Claim 1, wherein the air distribution system is formed by removing portions of the top surface of the filter bed to increase the surface area over which air may penetrate the filter bed.

7. A sewage treatment system according to any one of the preceding claims, including sewage distribution means to distribute sewage across a top surface of the filter bed.

8. A sewage treatment system according to Claim 1, wherein the system includes the air distribution means as defined in any of claims 2 to 5 and the air distribution means as defined in Claim 6.

9. A sewage treatment system according to any of the preceding claims, wherein the system further includes re-circulating means to circulate sewage through the filter bed repeatedly.

10. A sewage treatment system as hereinbefore described with reference to the accompanying drawings.