GB2413292A - A receptacle used as a filter - Google Patents

Abstract

A receptacle functions as an intermittent slow sand filter if filled with sand and is stackable. Preferably the receptacle has a main compartment (10, Fig 1) partially filled with the sand or other suitable filter media. Preferably the receptacle filters water which is allowed to enter through a diffuser plate 15, travel through the filter media and exit through an outlet 13. A cavity may be formed between two components forming an inner 5 and outer wall 4 of the receptacle and wherein the inner wall is roughened to avoid water short-circuiting the filter media. The inner and outer walls 5, 4 may be held together by a clip device (15, Fig 6). Advantageously the receptacle tapers from one end to another and allows multiple receptacles to stack in a space saving manner.

Description

241 3292

IMPROVED RECEPIACLE FOR AN INTERMITTENTLY OPERATED SAND FILTER

This invention relates to intermittently operated sand filters used for improving the quality of raw water.

Sand filters are used to improve the physical and biological quality of impure water. Slow sand filters are especially effective' since they combine physical straining with biological activity.

Water is percolated through a column of sand. In the top layers of the sand, a beneficial aerobic biological layer forms. This layer is formed by numerous organisms including algae, plankton, diatoms, protozoa and bacteria. While inert particles in the raw water are removed mechanically by the sand, organic matter is entrapped, broken down and digested by the biological layer. Able to remove bacteria, parasites, Giardia cysts, Cryptosporidium oocysts and viruses, slow sand filters greatly reduce turbidity as well as pathogenic contamination. A properly functioning slow sand filter can produce water of excellent quality, often well within the quality standards set for human consumption.

Besides nutrients, the biological layer needs oxygen for survival. In ordinary slow sand filters, oxygen is supplied constantly through an incessant flow of water. Intermittent slow sand filters however, enable the biological layer to survive for a prolonged period in the absence of flowing water. This is achieved by maintaining no more than 8 cm of standing water above the top of the sand. Oxygen permeating through this shallow level of water can still reach the biological layer, maintaining it in a living condition. In contrast, traditional slow sand filters usually maintain depths of water greater than 50 cm above the sand. In the absence of a significant flow, the water turns rapidly stagnant and the biological layer starts to die.

Since no permanent flow is required, intermittent slow sand filters can be used where water is scarce or difficult to obtain or only needed in small quantities. Therefore, they are increasingly used to provide water for drinking or other purposes to people relying on contaminated water sources, especially in developing or 'third world' countries. In particular, intermittent slow sand filters are suited for what is called 'household ' or point-of-,e ' water treatment, whereby relatively small amounts of water are purified on an intermittent basis to suit the immediate needs of a user or group of users, rather than for larger communities.

In the prior art, intermittent 'household' sized filters are available as one integral piece, for instance when cast in concrete, or as one unit built up from several components joined together for instance when using plastics. The concrete 'Bio Sand Filter', for instance, is promoted by several humanitarian organizations in various Third World countries such as Medair (2003). Whilst effective in terms of filtration, concrete sand filters are difficult or expensive to transport or store because they are heavy, brittle and not stackable (voluminous). Due to the fact that one mould can make only one filter every few'days, production is limited and labour-intensive. These problems are exacerbated in rural areas of developing countries, where roads are poor. Similarly, commercially available plastic filter receptacles such as that produced by Davnor (2003) have the same problem, being built up from several components that are joined together. Already assembled, such filters are not stackable in their completed state due to the absence of a suitable taper and/or due to protruding pipes or channels or other components which prevent one complete filter unit from slotting neatly into the next. Such filters are therefore highly voluminous, which negatively impacts transporn and storage costs. The outlet of these filters is often an external pipe protruding outside from the main filter compartment. This component is vulnerable to damage during transport and use.

Alternatively' filters are available in the form of a 'kit' or 'set' and the final unit has to be assembled from several components before it can be used. The many small parts complicate a wide distribution of f Iter kits, for instance during emergencies, while the final assembly procedure presents a technical problem to the intended users. This latter problem is especially evident in many underdeveloped areas where the majority of people lack basic technical insight, are illiterate or in any other way uneducated or unexposed to such technology. As a result the number of filters successfully assembled is low (Miller, 2000). It is also possible that if a filter is assembled incorrectly, raw water 'short circuits' directly to the outlet, rather than passing through the filter medium.

An object of this invention is to provide a filter receptacle that is easy to produce, transport and install.

Accordingly. the invention is manufactured in such a way as to combine the integrity of a complete unit with a volume space-saving feature, for instance by making it stackable, collapsible or inflatable, thus reducing storage, and transport constraints while avoiding technical complications for its users.

The unit can be made from plastic, resin or similar strong and lightweight material, thus reducing the weight per unit, as well as risk of breakage when compared to using for instance concrete or ceramic. Preferably, the filter is mass-producible, resistant to ultraviolet light and having a structural integrity that is maintained within ambient temperatures of 0 50 degrees Celsius.

Ideally, the filter lacks protruding pipes or other components that can easily be damaged during transport and use. It is also preferred that the walls of the iMer compartment are roughened, to avoid raw water from 'short-circuiting' via the walls to the bottom of the sand column. In plan view, the receptacle can be of any shape, including round, oval, square or triangular, without interfering with its volume space saving feature.

A preferred embodiment of the invention will now be described with reference to the accompanying, drawings. One alternative arrangement is shown only by Figure 3, while all other figures refer to one embodiment.

Figure I shows a front elevation of a complete filter receptacle showing the sand level.

Figure 2 shows a cross section, in which an internal cavity between two walls forms a channel.

Figure 3 illustrates a cross section of an alternative type of filter receptacle using a vertical partition as a channel.

Figure 4 shows an optional diffuser plate.

Figure 5 illustrates how the two components that form the receptacle in Figure] fit together to Intake an integral unit whilst throning a channel between the two walls.

i:igures 6 and 7 illustrate how the two components are securely joined to make one integral unit.

Figures 8' 9, 10 and 11 illustrate the stackability oftwo identical filter receptacles.

Figure 12 shows the outlet and spout section of the filter.

As shown in 1; igure I, the receptacle is an integral unit that contains a water inlet I and outlet 2 and is partially filled with sand or other suitable filter material in the main compartment 10. In Figure 2, the channel consists of a cavity 3 formed between the two eomponenix that make up th< rc.pincle an outer wall 4 and inner wall 5. The inner compartment has holes hi the botl'm so Ihat wretch can pass into the channel cavity 3. the inner wall of the main filter compartment 5 can be roughened to avoid water shortcircuiting via the walls.

In Figure 3, an alternative type of channel 7 is formed by a vertical partition protruding slightly from the wall of the receptacle ').

In the application shown in Figure 2, a channel 3 is formed between the main filter compartment 10 and the outlet 2. Figure 5 illustrates how the channel is formed when the two parts of the receptacle body are assembled. The top of the channel 14 is positioned in relation to the column of sand within the filter so as to ensure simultaneously a sufficient depth of sand to ensure proper filtration and a minimum level of water above the top of the sand 11, even when no more water is added to the filter. This water level is usually maintained between I and 8 cm above the filter medium. 'I'he biological layer, which forms at the top of the filter medium, therefore remains submerged to such a depth so that it does not dry out and sufficient oxygen continues to permeates into the water to prevent the organisms from dying, yet deep cuough so that it is not significantly disturbed by water pouring into the filter. When the filter is in operation, water, having passed through the sand. is forced through this channel 3 before emerging from the outlet 2.

Figures 6 and 7 show an example of a joining mechanism of the two compartments using a clip device IS that locks into place.

As shown in Figures 5 and 12, the outlet is protected from contamination by a cover 12. which is part of the inner compartment. The outlet can be enhanced by means of a specially formed spout 13 to reduce uncontrolled water dribbling from the opening, facilitating easier collection in for instance a Jerry can.

As shown in Figure 4, a diffuser plate 15 can be fitted to break the force of water poured into the filter. This can also be made as an integral part ofthe filter compartment.

As shown in Figures 8, 9, to and l l, to ensure stackability, the receptacle is tapered towards the bottom' so that each filter f Is into the next up to the level of the outlet 2. The channel 3 (Figure 2) and (I; 'igure 3) can be shaped in several ways, but always so that it does not interfere with slackability.

Claims (9)

1. receptacle, capable of functioning as an intermittent slow sand filter if filled with suitable sand or other filter media to the correct level, produced as one integral unit, being stackable, collapsible or inflatable, thus saving space when grouped with other identical receptacles.

2. A receptacle as claimed in Claim 1, whereby an internal channel is formed between the inner and outer wall of the receptacle compartments.

3. A receptacle as claimed in Claim], whereby a channel is formed by a vertical partition protruding slightly from the wall of the receptacle, or by any other means that allows filtered water to reach the outlet without contamination

4. A receptacle as claimed in Claim 2 or Claim 3, whereby volume space saving is achieved by tapering the receptacle downwards.

5. A receptacle as clahned in Claim 2 or ('[aim 3, whereby volume space saving is achieved by using an inflatable or collapsible receptacle.

6. A receptacle as claimed in Claim 4 or Claim 5, whereby the outlet and spout is embedded in the body of the receptacle, so as to prevent areas for accidental hooking or leverage that might result in damage.

7. A receptacle as claimed in Claim 4 or Claim 5, whereby the spout is given a particular shape to ensure that water emerging from the outlet runs freely and does not dribble.

X. A rcccptacic as in any of the previous Claims. whereby the inner wall of the main compartment is roughened.

9. A receptacle as claimed in any of the above Claims, whereby a diffuser plate is either an integral part of the unit or a separate piece.