Portable Filter System | waterengineering2030

What is the need for a Portable Filter System?

Water supplies can be damaged in the event of a natural disaster, resulting in many people becoming ill from contaminated water. For example, in 2005 after the earthquake in Pakistan, waterborne diseases (like hepatitis E and A and diarrhoeal diseases) were common in the areas with poor access to safe water. These illnesses can be very serious and can spread quickly in unsanitary areas. Therefore, it is important that when a water supply has been contaminated, there is a easy way of distributing filter systems to the areas as soon as possible in order to clean the water and prevent epidemics. A temporary filter system that can be transported compactly (so that many can be fitted into one container) would be useful as it could be distributed to many people in a short space of time, before they drink/use contaminated water. Another benefit of having a filter system that can be folded down is that the whole system can be moved readily. Evacuees may have to move several times and having a large filter system that can be folded small for transporting makes this easier and means that the filters are less likely to be damaged during transit. The design is for temporary use, to clean the available water until the supply can be fixed. However, the filters can be changed with ease so that the system can last longer if need be.

The Design

The most important points to consider when designing a filtration system are:

How reliable the device is
How easy is it to understand how to use
How long the device will last before needing to be replaced
How to distribute the device easily
How cost effective the system is to mass produce (we have tried to keep the price feasible, however, our main focus is the design of the system and not the price)

With these points in mind our design was a foldable system that consists of 2 cube shaped buckets, a set of filters in a box and a lid. The upper bucket (with the lid) is connected to the set of filters and the set of filters is then connected to the lower bucket. Both the upper and lower buckets have been designed so that they can fold flat. This means that the system could be easily transported in a compact way and then, with a simple twisting motion, the system can be reassembled ready to use. Each section is able to be taken apart for cleaning.

DISCLAIMER- this project is only a theoretical design by students for an engineering competition and has not undergone any official testing.

The benefits of this design are that the filter is easy to transport, simple to open and it is easy to understand how to use it. This means that the filters could be distributed to anywhere that has need for them, all around the world .

The design requires a plastic that can be tough (able to be bent several times without breaking) for the buckets and strong for the filter box. However, the plastic must also be easy to source and the design must be watertight.

Although we have not done extensive investigations into the best type of plastic to be used, we would suggest polyethene because this plastic can be formed both as a flexible film layer thick enough for the buckets and as a strong solid material that is needed for the middle. Another benefit for using polyethene that it is thermosoftening, this means it melts when heated. Therefore, once the filter system has been used, the filters can be removed and the rest recycled into something else (another huge issue in today's world is the amount of waste we produce so recycling as much as possible is a good idea). In addition, polyethene burns cleanly and so in those areas where recycling is not an option the plastic could be burnt as a fuel instead. The chemical equation for the burning of Polyethene is C₂H₄ + 3O₂ ---> 2CO₂ + 2H₂O, showing that burning polyethene does not produce any toxins. We have done calculations for the mass of the system for a 30cm by 30cm base and for a 20cm by 20 cm base which are on a separate document for those involved in the competition to view.

For our prototype we could not source both high-density and low-denity polyethene so instead our prototype is made from laminate plastic (mainly polyethene) and foam boards.

The Ins and Outs

The Filter Box

The Filter box is made from high-density polyethene so that it is sturdy enough to contain and protect the filters. The box opens from the side to access the filters and to change them if need be, Then the filters can be slid into the correct places. To ensure the filters are replaced in the correct order, each filter slot is colour coordinated, numbered and is a slightly different size from the others so that only the correct filter will fit the slot.

The order of the filters is important and in order to ensure the filters work to the highest capacity, the larger objects must be removed first, then the smaller objects, then the fine filters can clean the water to make sure it is fit for consumption.

The Buckets

The buckets are cubes made from low-density polyethene so that they are flexible and are folded diagonally from the bottom left to the top right, on the four side faces. This folding pattern means that when the top is twisted to the right the box will flattern. Once open, the boxes are reinforced to ensure they do not collapse unintentionally, using supports down the centre of the faces.

These supports consist of a tube (or straw) attached to the side of the face that can fold along with the bucket, and a dowel made of high-density polyethene that can be slid down the tube to prevent the side from folding. When folded, the dowel would be stored on the ridge between the bucket and the filter box, the dowel can then be unclipped and slid down the tube once the system is erected.

The Filters

This project did not focus on the best types of filters that could be used; instead it focused on a system that uses the filters. However, we have done some research into the filters that could be used.

There are many types of water contamination:

bacteria
parasites & protozoa
viruses
chemical pollutants
turbidity (cloudiness of water: mud, sediments and organic matter)

Types of filtration:

ceramic filters use tiny pores in the solid filter material to reduce sediment and exclude many bacteria and protozoa, they cannot exclude chemicals on their own and are not reliably effective against viruses
active carbon filters: reduce chemicals and organic compounds in the water
reverse osmosis filters: pores that exclude particles larger than 0.1 nanometre, thus making very pure water, however these are not efficient and need energy and pressure in order to work.
multistage setups use a mixture of many different types of filter.

Our suggested setup for the filters would be a multi stage set up similar to this:

a mesh/sieve like filter to remove large particulates
a coarse ceramic filter to remove turbidity
micro filters to remove bacteria and parasites
activated carbon filters to remove chemical pollutants.
a filter that is able to release some sterilizing chemicals (e.g chlorine) over a period of time.
more micro filters and carbon filters if possible to fully cleanse the water.

Another addition to the filters could be an indicator that changes colour if exposed to certain pollutants, this could act at a warning for when the filters need to be replaced.

How it fits together

The boxes can easily be taken apart because there are no bonding parts between the sections, instead the sections are linked like lids (as shown in the image on the right). Because water flows down, the top bucket has a rim on the bottom face that slots tightly to the inside of the filter box. The water will not escape up the side as gravity would be pulling it down and the design would require the water to go back up again in order to escape. The same link is replicated between the filter box and the bottom bucket.

When the system is folded, it is held together by straps attached to the base of the system and fastened to the lid with clips (or buttons).

Click the buttion to read about the prototype for the design.

Design Prototype