ENGINEERING WATER DISTRIBUTION

Design Decisions of our Water Filter

 

When designing our water filter, we first looked into the three branches of effective water filtration systems: physical, biological, chemical. Not all of stages in each branch are needed to treat water but in most water filters, there are at least two. For inspiration, we looked into the UK's water treatment processs and into current water filters which are set up in third world countries. It was interesting to see the innovative design of some relief water filters as well, such as LifeSack and LifeStraw, and it encouraged us to think outside the box when choosing the materials for our filter.

 

In-depth look at the three branches of water filtration

 

1) Physical: Screening; flitration; boiling; distillation

 

Boiling and distillation are two ways of physical filtering – these are not included

in our water filter as they require a lot of energy. This energy could come from

either the combustion of fossil fuels or from solar energy (supplied by the solar

panel), however if more solar energy would be needed then more solar panels

would be required. This would increase the costs and thus reduce the number of

water filters which could be distributed to different villages as there would only be

a certain amount of money to pay for these water filters and their distribution.

 

 

2) Biological: storage to allow for bacterial breakdown; biofilms (layer of microorganisms and bacteria which eat the organic waste, bacteria and viruses); carbon filters

 

Our filter does not include storage space as it takes up unnecessary space and we wanted our filter to be as compact as possible. Our filter also doesn’t include any biofilms as these would need replacing and and would need regular maintenance – hence taking away from the idea of an ‘automatic’ water filter. Therefore, the only biological filtering we have included is the use of carbon filters (activated carbon) through the use of coconut shells. The micro pores in the shells match the size of the contaminant molecules (e.g. pesticides, herbicides and VOC’s) in the dirty water. Many contaminant molecules are hydrophobic so therefore bind irreversibly to the non-polar surface of the coconut shells. Coconut shells also have a tight structure due to these micro pores, thereby making them very resistive to erosion due to friction.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3) Chemical: flocculation; chlorination; UV-radiation

 

Usually the storage stage in water filtration allows for the particles to clump together and end up at the bottom of the container due to the force of gravity. However, as our filter does not include this, we have compensated by using flocculation. Chlorination is one of the most common ways of treating water, however it requires specific chemicals which may not always be readily available to those in developing countries. Due to its efficiency, chlorination was initially included in our filter. However, after revision of this, we have decided to just rely on the next stage, UV radiation to do the job. The UV-radiation stage is explained later on under the ‘Materials’ subtitle.

 

Research of other filters

 

Our research into long term water treatment processes/filters is explained below. We looked predominantly at the Thames Water's water treatment process and WSP's ceramic water filters as they are both very effective at cleaning water whilst use very different techniques from one another.

 

Thames Water’s water treatment process

 

The Thames Water's water treatment proworks as follows:

 

1. Rain collection - rainwater flows into rivers and streams and is then collected and put through the water treatment process

2. Storage - the water is stored in reservoirs. This is due to two reasons: 1) to make sure that there is always a reserve of water incase the UK goes through a season of drought, and 2) storing water in a reservoir allows for the heavier particles to fall to the bottom, thereby starting up a natural cleaning process without the use of chemicals. Our filter does not include stage so as to speed up the water filtration process and to minimise the size of our filter 

3. Screening - the water is passed through a screen to get rid of any branches or leaves

4. Removal of particles through flocculation and filtering - there are two types of filter which Thames Water use: rapid gravity filters and slow sand filters. Rapid gravity filters use a layer of course sand to trap particles as the water passes through, whereas slow sand filters sieve out the smaller remaining particles by passing the water through a layer of fine sand. In our filter, we have just used the slow sand filter as the rapid gravity filters are not essential and would just take up more room

5. Ozone/carbon/ion exchange - this step is not used at all the Thames Water sites. It is used to remove invisible or dissolved particles from the water through use of specific chemical reactions. Au lieu of this, our filter includes UV-radiation as a form of eradicating any remaining organisms and bacteria. UV light also makes our filter more automatic as no manual labour would be required to add the 'ingredients' for the exchange

6. Chlorination - less than one milligram per litre of chlorine is added

7. Storage - after storage, the water is pumped to homes as drinking water

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

WSP's Ceramic Filters

 

UNICEF funded for the Water and Sanitation Prgram (WSP) to distribute their ceramic permanent water filters to different villages around Cambodia. The filters' porous fired clay uses microfiltration to filter out almost all protozoa and bacteria that may be present in the contaminated water. The size of the pores can be reduced to 0.2μm. These ceramic filters are very simple by design and so can be produced locally, thus providing an income for townsfolk.

 

Other advantages include:

• lightweight

• chemical-free

• portable

• fairly inexpensive

• low maintenance

 

 The main disadvantages of ceramic filters are that they:

• are not automatic - the flow rate is between one and three hours

• require regular cleaning and good maintenance

 

The regular cleaning of the filters eventually wears away the ceramic filtering surface which means that another filter must then be bought. WSP have predicted that a new filter must be bought about once a year due to this erosion. Our main aim for our filter – aside from providing clean water – was to allow people in developing countries to have a similar water experience to how we in the developed countries have it; we are able to simply to turn on the tap and have clean water run out. We believe that having access to clean water should be seen as an expetation, not a luxury.

 

Materials

 

Our research into a few current relief water filters really opened our eyes to some different clever materials which are used in order to remove bacteria from water. Our personal favourite was LifeSack.

 

The LifeSack product, made of PET (Polyethylene Terephthalate) plastic, is sent to villages in developing countries, initially filled with grains. Once all the grains have been consumed, the bag acts as a water filter using the SODIS technique. SODIS (Solar Water Disinfection) uses thermal treatment and UV-A radiation from the sun to inactivate microbes and bacteria in the water.  We particuarly liked this method as it doesn't require any chemicals and is low maintence. However, it does require manual work to pour water into the bag and thus does not make it automatic. Therefore, we decided to use LifeSack's unique use of the SODIS technique as inspiration for our filter: instead of using UV lamps to supply the UV-A radiation, the outside of the container for this stage in our filter would be made out of a PET bag with a hole at the top and bottom for the transfer of water to and from the different stages within the filter. As the PET bag would be blocked from sunlight from other stages above it in the filter, we decided to put mirrors around the outside at 45 degree angles to the container to concentrate the sunlight.