4 April  2005 

Dung Water Filter

An Australian scientist has developed a new water filtration system, an invention that potentially will benefit millions of people in developing countries and would enable anyone in the world to drink water safely.

Contact: Mr. Tony Flynn Department of Engineering, Faculty of Engineering & Information Technology, The Australian National University, Canberra ACT 0200 International Telephone: +61 2 6125 0078 FAX: +61 2 6125 0506 Email: tony.Flynn@anu.edu.au Website: http://info.anu.edu.au/mac/Media/_pdf/ClayPotFilter_final_web.pdf

TRANSCRIPT:

BLANCH : The system uses a filter made of clay and other simple organic materials such as rice husks, tea leaves and coffee grounds and does not require any kiln, furnace or western technology. Material scientist at The Australian National University, Tony Flynn, developed the invention.

Now Tony, the key to this innovative new technology is its simplicity and its effectiveness and you’ve deliberately not patented this technology in the hope that it will be used widely around the world, so what do you need to make your filter?

FLYNN : Clay, that you can dig up where you live, waste tea leaves, coffee grounds, rice hulls, a compliant cow and a match – it’s that simple and a means of measuring the two materials in equal volumes. We specified in the first publication of this that the unit of volume was a handful but it can equally be a coconut shell or a jam tin or a bucket, but as long as the volumes of the clay and either the tea leaves or the coffee grounds or the rice hulls are measured equally with the same coconut shell or whatever, it works.

BLANCH : So how do you make a filter, what’s required in the process?

FLYNN : I anticipate that local clay can be used anywhere where terracotta clay is found and terracotta is the typically red to yellow coloured clay that’s found certainly in Australia, maybe six to eight inches underneath the surface of the ground. You’ll see it, typically, in roadside cuttings. If that’s dug, dried in the sun, then crushed up, put it through a piece of old flyscreen sieve so that large stones and large unbreakable particles are removed, then if you’re using coffee grounds or tea leaves, they too should be dried in the sun and then added to a bucket where your first measurement of clay has been put so that you have dry powered clay and, say, an equal volume of coffee grounds, into it.

Mix it so that the coffee grounds are distributed through the dry clay as evenly as can be, then all you need to do is add enough water so that the mix that you get is a very stiff biscuity sort of mixture which, when you begin to form it into a container shape for the filter, it doesn’t move or slump or slide, it should remain fairly stiff. Now it can be formed inside another container, it can be formed inside say a coconut shell as I’ve done or inside a form that could be made by woven straw or coconut fronds as I’ve seen done in other parts of Asia and the developing world.

When the clay is ready to go it’s formed into a hollow container that can be any shape as long as it’s capable of holding water. The thickness should be about as thick as an average adult finger, say about a centimetre, maybe a little more. Put it out into the sun to dry. Depending upon the climate of course that can take anywhere from a few hours to a couple of days, but then when it’s dry the next step is to fire it or sinter it.

BLANCH : And a potter’s kiln is not required, so how do you fire the terracotta water filter?

FLYNN : Simply by using cow manure. I found that by putting down a layer of lumps of cow manure exactly as they were found in the field, they don’t have to be broken up, processed or treated in anyway. One layer of cow manure on the ground, a handful of straw or leaves – the filters then go onto that light straw base. Another couple of layers of cow manure over the top so that it’s completely enclosed in a mound of cow manure that’s probably about 400-500 millimetres in diameter at the base and maybe 300-400 high, then light the straw. If your cow manure is dry and it should be bone dry, in about half an hour you’ll see through the holes between the lumps of cow manure a colour of the fire that is approximately orange. It should be an orange to red colour and at that point--we’ve measured the temperature in the centre of the fire around the filter forms as being about 700 degrees – that’s 30 minutes after lighting. Another half an hour will see the temperature increase from 700 to about 950 centigrade and it will remain at that temperature as long as you keep adding fuel to the fire. You shouldn’t let the fuel burn down so that the filters become exposed. Now after about an hour at that temperature--that’s an hour after you light it, the filter should be ready for removal and it’s just a matter of removing it from the fire and putting it aside to cool.

BLANCH : So what are the basic principles that allow the filtration process to work so effectively?

FLYNN : Well, in the case of the addition of coffee grounds to the local clay, it does a couple of things. First of all it greatly increases the total volume of the tiny holes or pores within the filter structure and when it’s fired as I’ve just described in the manure mound, the heat burns the coffee out, leaving the holes but which also contain small fractions of silica that aren’t combustible and are a result of the combustion of the combustible fraction of the coffee grounds. Now these small voids or holes in conjunction with their silica content and the network of tiny holes that are joined in three dimensions within the clay particle mass, act as the filter structure and they are small enough to allow the simultaneous passage of water through them, while equally being small enough to remove bacteria that we tested for – in this case E-coli.

BLANCH : I was about to ask you how effective is the device and what have your tests demonstrated that the filter can remove?

FLYNN : Well again, in the case of coffee additions which produce the best results – the trials that we did using commercially supplied and estimated volumes of E-coli in water showed a filtration removal rate of between 94.6 and 99.8 per cent.

BLANCH : So how much water can be processed and how long does the filtering process take?

FLYNN : Again it depends upon the choice of the organic material that’s added. Coffee produces the best removal rates, but it also produces the slowest filtration rates. Rice hulls produce a much faster rate, but equally produce a somewhat lower rate of removal of the bacteria. Coffee would require about an hour to produce a litre. Rice hulls will produce a litre in about eight minutes, so it’s a trade-off. But you don’t have to use one filter. The results that I’ve mentioned to you produce a range of results between 94.6 and 99.8 and so, given that this is capable of removing pathogens and that there is this range, I think the possibility also exists for multiple filtration of water so that you could use a filter that used rice hulls with a higher volume, but a lower rate of removal to initially filter the water and then, use a filter that used coffee grounds to clean up the result if you wish, so that the result would be maximised through the use of two filters in succession rather than just relying on one.

And, the first firing will be improbable. Anyone who’s doing this will have to do a number of firings and observe the results – see what happens. It’s not a golden bullet solution, but it is a bullet and it will help in those communities around the world who for whatever combination of reasons, don’t have access to clean water. And the other thing with this is, if the water that is being filtered is being filtered principally for the removal of pathogens, the filter of course will eventually block. But if it’s only pathogens that have been removed the filter can then be put back into another manure fire and re-fired for the same time and the pathogens, being organic material, will burn out and my thinking is that if that is the case then the filter can be again used, but, if the water’s dirty and contaminated with clay or large volumes of vegetable material, then it too will block it. Vegetable material will burn out, but clay particles that have blocked the holes in the filter won’t and, in the firing process they will become an integral part of the structure. So it may be that once one’s blocked, this filter will have to be discarded and another one made, but it’s so easy and it’s so cheap that I think that’s a viable option.

BLANCH : You mentioned tea leaves, coffee grounds and rice hulls, are the materials that would not be suited or are these the ones we need to work with?

FLYNN : I chose them simply because they’re a renewable resource and they’re waste materials. They grow quickly and they are in widespread use around the developing world.

BLANCH : So what is the next step for the water filter now?

FLYNN : I’d like to be able to access multiple samples of clays from around the world and subject them to the usual rigorous processes of material science and see exactly what happens to them when organic material is added and when they are fired by the same process that we have used here, but that means collection of the material and getting it through AQIS (Australian Quarantine & Inspection Service) and having them eradiate it with gamma radiation and it takes time and it’s expensive. To date the work has been done for nothing – it’s something that we did in our spare time and when I say ‘our’, I was very ably assisted by one of the department’s Fourth Year honour students , David Goggin, and he and I did this literally in our spare time before and after our other work and at weekends.

BLANCH : So how do you get this to the people who need it most?

FLYNN : Hopefully by talking to you!

BLANCH : I hope it works in that way too.

FLYNN : People will hear it, their curiosity I hope will be pricked through the improbable fuel and the means that it’s used and they’ll be curious.

BLANCH : Tony Flynn from The Australian National University in Canberra with a simple and cheap water filter to make clean water accessible to people in economically undeveloped countries.