Ceramic Filtration
The LifeStraw
Clay Pot Filtration
Clay pot filtration is a type of ceramic filtration that uses the pores within fired clay as a physical barrier to separate water from its microbial contaminants. The unfired clay pots are lined with organic material such as coffee grounds, rice, or wheat and are then fired in an open cow dung kiln. The firing process combusts the organic material leaving small pores in the bottom of the pot. Clay pot filtration is able to remove upto 99.8% of pathogens like E. coli, but researchers are still unsure about whether it has an affect on virial concentrations.1 The filters were developed by Australian scientist Tony Flynn, pictured on the right demonstrating one of his filters.
See: A Step-by-step guide on how to make these filters
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Advantages
•Low-cost and Sustainable - The filter uses all natural products that can be obtained locally, even the fuel for the firing, cow dung, can be aquired for free
•Simple but effective. The filters are able to remove around 95% of pathogens from water (including 94.6-99.8% of E. coli)
Disadvantages
•Only physical separation - The filters can’t get rid of any organisms that are small enough to get through the pores, they contain no chemicals or energy to inactivate pathogens
•Slow filtration - One of these filter can only produce 0.5L water per hour
See:
Transcript of ABC TV Interview with Tony Flynn
Filtron: Ceramic Water Filter
In 1998 the organization Potters for Peace began to develop silver-treated ceramic water filters in order to bring clean water to rural communities. Since then the technology has been developed to the point were these filters are able to remove 98 to 99.88% of parasites and harmful bacteria from drinking water. Furthermore, the technology is relatively low cost and portable making it a viable solution to the water scarcity issue. These filters are used all over the world by organizations like the International Red Cross and Doctors Without Borders. The filter system is made up of a silver treated porous clay filter placed inside a 5 gallon lidded water container with a spigot.2
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The Filter Element
The filter element is shaped like a conical flowerpot and has a diameter of 31 cm and a height of 24 cm. Flow through the clay can be enhanced by the addition of materials like cornhusk, wheat, saw dust, etc. and the firing of the pot in order to create larger whole and increase the porosity of the clay.2
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The Colloidal Silver
Colloidal silver is a liquid suspension of submicroscopic particles of silver. It is created by suspending bars of pure silver in water, then running a positive electric current through the bars in order to create positively charged silver colloid particles with diameters of 0.005 - 0.15 µm.2
The positively charged silver colloid particles are germicides because:
•They are able to suffocate bacteria by reacting with the thiol groups on peptide chains4, disabling the enzyme that the bacteria use for oxygen metabolism
•Their charge causes the collapse of the internal protoplast of pathogens
•They can sterilize the pathogens
•They can kill the pathogen eggs
Only a small amount of colloidal silver is used in the filter element, through a one time saturation of the filter element in a 32% silver solution in about 200g of water2, therefore the silver isn’t enough to be toxic to humans. The picture on the right is of the silver saturation process. As you can see the silver is just brushed onto the inside of the filter like paint.
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The Container
The container can be made out of any material, as long as the rim is thin enough to allow the filter to hang from it. Potters for Peace normally use to types of materials, clay or plastic. Clay containers are able to naturally cool the water because the pores allow evaporative cooling, and plastic containers are very durabble and easy to clean out. However, clay containers are usually very fragile and are hard to transport, and plastic containers are not environmentally friendly.
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Advantages
•Very effective in inactaving microbes. The Filtron is able to kill 98 - 99.8 % of all pathogens in contaminated water.2
•Can be constructed from local materials
Disadvantages
•Can be very fragile, especially if it uses a clay container
•Slow flow rate. The Filtron can only filter 1-1.75 L of water per hour.
•Moderately expensive. Costs about $3.50, which is probably too expensive for the people that need it the most.3
For more information, please see:
•Potters for Peace.
•Investigation of PFP Colloidal Silver Impregnated Ceramic Filter
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LifeStraw
The LifeStraw is a personal water purification device that filters out particulates and disinfects water as yyou drink. It was the winner of the 2005 INDEX International Desgin Award, and although it is currently only in the prototype stage, the developers, Swiss company Vestergaard Frandsen, are currently manufacturing and selling these prototypes in a limited amount.
The LifeStraw is a combination of a filtration device and a disinfectant. It is made up of a 25 cm long high impact polystyrene tube5, that contains two polyester pre-filters, followed by three reaction chambers. The first pre-filter has openings that are 100 microns in size, while the second filter has openings that are 15 microns in size. The job of the two filters is to remove large particulate matter and bacterial clusters before the water enters the disinfection chambers.7
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After being pre-filtered, the water enters the first chamber which is packed with beads that have been impregnated with iodine. The iodine dissolves into the water and kills various bacteria, viruses, and other pathogens. The next reaction chamber is empty, allowing for an extended contact time for iodine disinfection. The last chamber that the water enters is the activated charcoal chamber which contains activated charcoal granules that remove the iodine odor and improve the smell and taste of the water. The charcoal also removes any residual contaminants that were not picked up by the pre-filters or inactivated by the iodine.7
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Advantages
•The iodine is very effective, can kill 99.99% of bacteria.6 (see: Test Results)
•Filters particles from 6 to 125 microns
•The LifeStraw has no moving parts, so it does not need electricity
•It disinfects as you drink, therefore you get instant clean water.
•One LifeStraw can filter up to 700L of water (an entire years worth) before it needs to be replaced.6
Disadvantages
• The filtered water has high levels of Iodine.
•The LifeStraw is not effective against Giardia, which is 5 microns in size, and resistant to Iodine.
•Too expensive for the people that need it to most (costs ~$3.50/yr)6
•Lacks sustainability, people will have to go out and buy a new one every year
For more informationn, please see: LifeStraw
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