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This Week in Green Design, 1/23
Jamais Cascio, 23 Jan 05

Each week, Justin Thomas of Metaefficient gives us a peek into new finds in sustainable design. Metaefficient "searches out products that we believe are more effective and healthier for individuals and the world, yet are comparable in price to mainstream products." We're glad to feature the best of what Justin's found lately, here on Worldchanging:

Solar Tubes: Very Efficient Heating

Apricus makes a unique solar hot water heater which is 30-40% more efficient than flat plate solar systems. The secret to the performance is the use of cylindrical evacuated glass tubes to absorb the heat from the sun. Because the tubes are cylindrical, there is always a surface area that is perpendicular to the sun. The tubes also house a vacuum between two layers of glass. Why a vacuum? A vacuum is an excellent insulator. The insulation properties are so good that while the inside of the tube may be 304°F (150°C), the outer tube is cold to touch. This means that solar tube water heaters can perform well even in cold weather when flat plate collectors perform poorly due to heat loss. More information: Apricus

Slow Sand Filters

Slow sand filters are perhaps the most efficient means of producing clean drinking water.

Slow sand filters rely on biological processes for their action rather than physical filtration or disinfection. They require no electricity, no chemicals and no filter changes.

How is this possible? The secret is that slow sand filters work through the formation of a gelatinous layer called the hypogeal layer or "Schmutzedecke" on top of a layer of fine sand. This layer consists of bacteria, fungi, protozoa, rotifera and a range of aquatic insect larvae. As a Schmutzedecke ages more algae tend to develop and larger aquatic organisms may be present including some Endoprocta, Snails and Annelid worms.
The Schmutzedecke is the layer that provides the purification for water treatment -- the underlying sand provides the support medium for this biological layer. As water passes through the Schmutzedecke, particles of foreign matter are trapped in the mucilaginous matrix and dissolved organic material is adsorbed and absorbed and metabolised by the bacteria fungi and protozoa.

The water draining from a well managed slow sand filter can be of exceptionally good quality with no detectable bacterial content.

Blackburn and Associates produce a slow sand filters for residental use.

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