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Project: Harvest Rainwater with Sand Filters
Posted By admin On October 10, 2012 @ 9:00 am In Green Building | Comments Disabled
Here’s a great tip from Stephen and Rebekah Hren from their book The Carbon-Free Home: 36 Remodeling Projects to Help Kick the Fossil-Fuel Habit. Harvested rainwater needs filtration before it is potable. Pollution, particles from the air, debris from the collection system (your gutters) are not things you want to find in your tall glass of ice water. Instead of investing in a garage-sized Brita pitcher, Stephen and Rebekah have another idea: sand.
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From The Carbon-Free Home:
Sand filters (also called biofilters) are a biological way of purifying drinking water. Low turbidity (suspended sediment in the water) is a requirement for sand filters to function effectively. Fortunately, a well-functioning rainwater-catchment system should meet this requirement. Sand filters can purify only small amounts of water at a time, as they are unpressurized and work using gravity, so purifying is limited to drinking water. Essentially a sand filter is a large drum filled with sand. Water enters the top and slowly percolates through. A thin, biologically active layer (called the hypogeal layer) quickly forms on top, feeding on the bits of organic residue and other impurities in the water. By the time the water has made it through the several feet of sand, it is potable and remarkably clean. Eventually, the hypogeal layer becomes too thick and needs to be either scraped off or destroyed by drying and backflushing (the water from the flush being disposed of into a nearby thirsty plant). A new one quickly forms and water filtration can continue.
Drawing courtesy of Dennis “Mad Man” Pacheco
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