by William Lidwell
August 08, 2005
I love this submission. Great analysis, approach, design, and presentation. The addition of the water hyacinth virtually eliminates the need for activated charcoal, which makes this approach robust. Two quibbles: layering of the sand filter should be fine-to-course versus course-to-fine, and the time required to make the activated charcoal plus other elements would, I think, extend beyond the two-day limit. All in all, though, a great submission. Congratulations, Mark!
This filtration system makes use of parallel filters for sediment, organic materials, and chemicals, and in the final stage, uses heat to kill remaining pathogens. The most effective alternative to several-stage filtration is distillation. However, the immense energy expenditure necessary to convert all the drinking water to gas and then to liquid again make this method unreasonable. The procedure below makes the assumptions that the engineer of the system has a way to communicate with the villagers (reasonable since traveling in the region, one would either know the language or have a translator) and that the villagers can provide strong rope, cloth, vessels for the water, and fire. These are also reasonable assumptions given any civilization of people in almost any stage of development across the world.
Begin by enlisting the help of several villagers. You will need them to help you collect the materials and install the filtration tubes.
Gather eight of the bamboo tubes with the widest diameter. They should be about four feet long. You will fill half the tube with filtering materials, described below. The top half will remain empty and will hold water that is to be filtered. This will increase the pressure in the system, aiding the gravity-driven filtration as well as holding a greater volume of water in each tube.
Tightly lash cloth, folded four times, to the bottom of each of the tubes. The sari cloth that the villagers use for clothing is perfect. This will be used to keep the contents of the tubes in the tubes and is also a filtration device in itself: according to the US National Science Foundation, old cloth folded this way removed plankton from water as well as nylon filters. This is especially important because cholera lives in a symbiotic relationship with the plankton: by removing the plankton from the water, observed cholera deaths were cut in half.
Have some villagers gather sand, gravel, and medium-sized rocks to put into four of the tubes. Fill roughly the bottom foot with sand, the next six inches with gravel, and the next six inches with the larger rocks. Leave about two feet at the top of the tube empty. This system will filter out much of the sewage, and also many of the larger particles and the parasites living in the water.
Meanwhile, have another group of villagers collect a large quantity of the water hyacinth plants native to the area. Water hyacinth is a weed found in almost every water system on every continent, and is especially prevalent in East Asia. It has been found that its dried and powdered root is an excellent absorbing agent for arsenic in water. According to a report published by the Royal Society of Chemistry, filtering water using the weed reduces the arsenic content of water to below World Health Organization standards. Have the villagers dry and crush the roots.
Now, get one more small group of villagers to collect as many coconuts as they can find. They must then separate the meat and milk of the coconut from the shells. Save the shells–you’ll need them soon. Have the villagers save the milk and meat to eat later.
The final ingredient in the second stage of the water purification will be activated carbon. You must construct an apparatus to make the carbon and instruct the villagers on its use (Note: Method for charcoal production adapted from this).
Make the first large barrel and make five 2-inch holes in the bottom using the drill. Make one 2-inch hole in the side of the barrel near the top large enough to snugly fit a bamboo tube of medium diameter. Take the top off the barrel and save it. This barrel will be used to make the activated carbon.
Nail a heavy piece of bark, three to four inches square, by one corner above the hole. This will be used to cover the hole when necessary. Bend the nail over inside the barrel so it doesn’t come out. (If, for some reason, you brought a hammer but no nails, you could just tie the bark around the top of the barrel and slide it down over the hole when necessary.)
Set the barrel up on a few rocks so the bottom is level and high enough off the ground to allow air to enter the holes in the bottom.
Drill an identical hole into the side of the second barrel to allow the bamboo tube to connect the two. Set this barrel over a small pit where a fire can be made and sustained. This barrel will be used for two purposes: it will heat the filtered water and kill remaining bacteria, and the steam produced will be piped into the first barrel to activate the carbon inside.
For now, take the bamboo tube out of the first barrel.
Put kindling in the bottom of the barrel and light it. If, for some reason, you do not have access to fire, you could use the car battery to start a fire by *carefully* placing a strand of steel wool between the two terminals to create a spark.
Once you have a good fire going, add the coconut shells to the barrel. Do not pack them tightly: there must be air space between them.
Once the fire is strong, heap up dirt around the base to restrict the air access. Leave about a 4-inch gap. Put the lid on the barrel, leaving the hole in the side open for smoke to exit.
A dense white smoke will come out of the barrel for a time. Bang on the side of the barrel as necessary to ensure the shells move and all burn evenly.
When the smoke turns from white to a thin bluish tint, most of the water has been driven off and the charcoal is now burning. Plug the gap in the bottom with soil and plug the hole in the side with the bark covering, filling all gaps with soil to make an airtight seal. The remaining burn will take about four hours.
Let the sealed barrel sit for half a day. Then, stick the bamboo tube in the holes on the sides of the two barrels so they are connected. Put the bottled water into the second barrel, and tightly close the lid. (In the future, the villagers will use their filtered water. You will need to place large rocks on the lids of both the barrels so the pressure from the steam doesn’t push the tops off. In addition, remove the dirt from around the bottom of the first barrel to allow for steam exhaust once it has passed through the charcoal. This will help to ensure that the steam displaces the air in the charcoal barrel.
Light a fire under the second barrel (the one with the water in it). This will heat the water and create steam and pressure. The steam and pressure help to activate the charcoal inside the other barrel.
Let this go for at least one hour.
Carbon is a very absorptive substance, with millions of pores that can capture many kinds of particles. It can be obtained from any organic substance. Coconut shell is used in modern activated carbon filters because of its exceptional qualities of absorption. By adding steam and pressure, more pores are opened and the charcoal becomes more effective. In addition, this treatment will give the carbon a slight positive charge, which makes it even more effective at attracting compounds in the water. The carbon will remove bad tastes, odors, chlorine, benzene, volatile organic compounds, radon, herbicides, and most other man-made contaminants that may have found their way into the water.
Let the barrel cool for 24 hours. Then, dump the contents out and crush the carbon. Put this granulated carbon into the bottom of the remaining four large bamboo tubes, evening out the amount in each tube. There must be at least one foot of the granulated carbon in each tube, so it may only be possible to fill one or two for now. That’s alright–the villagers can easily make more carbon on their own to increase the volume of water that can be processed at a time.
Put the powdered water hyacinth root one foot deep on top of the granulated carbon.
Affix the large filled bamboo tubes to coconut trees as shown. Put the four rough filters on one tree and the four fine/chemical filters on another. Have a villager clearly mark which is which. Hang the bamboo tubes using rope or, if the rope isn’t strong enough, the brake and shifting cables of the bicycle. Make sure they are high enough for a pot to fit underneath each one.
Now, the system is complete. To filter water for drinking, the villagers first collect water and pour it into the top of the rough filter bamboo tubes. They will collect the water in four new pots at the bottom of these tubes. Then, they will pour the water from here into the second set of filters, and collect the water in new pots to avoid contamination by unfiltered water. Finally, this twice-filtered water will be poured into the second barrel and boiled. The water lost as steam will be used to activate further supplies of carbon to replace the spent carbon in the filters. The whole system can be fully changed and maintained by the villagers.