Pun Pun Farm: 3. Making Charcoal for Water Filtration

Nate Reents gives a presentation on water purification.

Everyone is familiar with using charcoal for water filtration. Charcoal is used in large-scale filtration systems in most of the developed world. You might be more familiar with home water filtration systems like Brita, as an example. Charcoal is extremely porous. It attracts particles, metals, and pathogens - all sorts of matter, and is used to finish the filtration process to produce pure, clean drinkable water.

One problem with poor rural areas in developing countries is access to clean drinking water. To buy a fancy activated charcoal filter system and continually purchase filters is not a practical solution. Many communities just buy water at the expense of other necessary community needs, such as education. Many rural children, then, do not go to school at all. If money spent on basic living needs, like water, could be reduced and allocated to, say, education, that would go a long way to help a community.

Pun Pun farm built their own water filtration system as an example of how relatively cheap and easy it is to do. The system was suggested by Josh Kearns, currently a Ph.D. candidate at the University of North Carolina, Raleigh. He and Nate Reents thought about how folks in poor rural areas could have access to pure drinking water for little cost to build and maintain. They formed an organization called Aqueous Solutions, which provides practical examples about their research on water management.

At Pun Pun, Josh and Nate came up with an experimental water filtration system that works. The entire farm community drinks the water from their system.

Here is a photo of Pun Pun Farm's Water filtration system:

Pun Pun Farm's Water Filtration System

Starting from the left, the first tank contains large pebbles. Water is fed from the top of the tank, but is piped down to the bottom. With the force of gravity from the water falling down the pipe, the water is pushed up through the pebbles, capturing large impurities before flowing into the second tank. The second tank contains sand. Water is fed from above the sand level and flows downward through the sand, removing microorganisms and smaller matter. Sand filtration is a good method to remove quite a bit more impurities and many pathogens, but is a little slower. A thin layer of microorganisms grows at the top surface of the sand, helping to capture them. Then the water is piped up to the third tank and falls through the charcoal filter. The charcoal removes the remaining chemical and pathogen residues, rendering the water drinkable. But where did they get the charcoal? Recall: to purchase commercial charcoal can be expensive, so where did they get it?

They made it.

Josh and Nate came up with a simple design using cheap, used materials to burn wood to make very high quality charcoal. Essentially, an old oil barrel with holes drilled in the bottom and the lid cut off is the wood burner. An additional piece is made to form a chimney. When the wood is filled in the barrel, a fire is lit at the top and the chimney is placed on the barrel. Oxygen is pulled up through the barrel through the holes in the bottom, feeding the fire and creating high temperatures, reaching around 900 degrees Centigrade. They found the high temperature creates a very high quality charcoal, rivalling commercially-produced charcoal. They call this device a gasifier.

After about 50 minutes to an hour and a half (depending on the type of wood burned) the barrel is sealed with mud to prevent oxygen from entering the barrel and killing the fire. Once it cools down you are left with charcoal. The charcoal is broken down into small (1 cm) chunks and is ready for use.

Simple, huh?

Below are photos showing how it's made.