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August 5, 2016
How to make a wooden mold for biosand water filters
contributor: Rob Goodier
Household biosand water filters are proven effective and long lasting. Traditionally, the filters are built from concrete poured into a steel mold. Now, a non-profit called OHorizons has developed a new wooden mold that can be built for one-tenth of the cost using common household tools.
What is a biosand filter?
These filters deploy mechanical and microbiological attacks against microbes in water. At their core, biosand filters are long columns of sand and gravel. Microbes and most of the grit and scum that make water look dirty get caught in the sand grains. At the top of the column, a thin layer of living organisms eats the pathogens in water as it passes through. This layer builds up naturally and lends the filter the “bio” prefix in its name.
Studies have shown that these filters strip away up to 90 percent of viruses, more than 99.9 percent of protozoa and helminthes, up to 98.5 percent of Escherichia coli, and up to 85 percent of turbidity. They are also sturdy. Some that were built in Haiti have been going strong for 12 years. For more please see OHorizons’ page on how biosand filters work. And visit the Centre for Affordable Water and Sanitation Technology’s site for information, technical consultation and a construction guide to a traditional steel mold.
The wooden mold advantage
Here, we show how to build a biosand filter mold in photos and videos.
The wooden mold can be made just about anywhere in the world using locally available materials and basic tools, says Dylan Lunney at OHorizons. And with their construction manual, no woodworking experience or even the ability to read are necessary. With this technology, OHorizons plans to provide safe drinking water for 1 million people worldwide within six years, Lunney says.
Skeptics have pointed out that wooden molds fall apart after producing 10-15 filters. But OHorizons’ design appears to be long lasting. Lab and field tests have shown that each mold can make at least 50 filters without breaking down, and more with high-quality plywood, Lunney says.
“Our design is significantly more durable due to the use of our patented collapsible inner core and 2” x 2” supports that hold the outer walls of the Mold together with bolts rather than screws that strip the wood every time it is de-molded,” Lunney says.
Let’s get started.
How to build the wooden mold
The basic steps:
- Construct and assemble the wooden mold
- Mix and pour concrete into the mold, let it sit overnight
- De-mold the bioSand filter and prepare filter media
- Install the filter media and operate the biosand filter