The Building Codes
Societal Impact Matrix
Return of The Village
Habitat For Humanity
Curves of Breath & Clay
Overview of Techniques
Nature, Earth & Magic
History of Cob
Cob Q & A
Compressed Earth Blocks
German Clay Building
Earthen Plaster & Aliz
Solar Water Heater
Aerobic Pumice Wick
An aerobic pumice wick is used to filter, clean and decontaminate greywater and blackwater. To create a pumice wick, an 18" bed of pumice is laid with a 6" covering layer of soil. Grass and other plants are planted and roots grow into the pumice bed.
All household wastes drain into an "infiltrator," which captures solid waste to form a compost and allows liquid to be absorbed in the pumice wick and plant roots. This liquid is taken up by the plants, which use the nutrients and transpire the water. In the case of too much liquid, the wick acts as a filter and filtered water drains out of the exit pipe. This prevents liquid rising in the infiltrator which would keep oxygen from reaching the compost.
Pumice size is determined by fineness of passageways, not aggregate size. For example "pit run" or "mine run" pumice (2" to pan) is a mix of fine and coarse, but has the same permeability as "block mix" (1/4" to pan). If pumice or other volcanic aggregates are not available, builders' sand (1/4" down) could be used.
Topsoil should be piled separately during excavation and used as cover for the wick. Use the subsoil for the berm. There is no need to haul away excavated material: use it! If your site has no soil (e.g. bedrock conditions) then dirt can be imported and used with a retaining wall. If the soil under the wick is particularly coarse sand or gravel, then a layer of straw and manure can be laid to help anaerobic bacteria create a water-impermeable "clogging" layer.
Infiltrators and other plastic devices are commonly available. If unobtainable, a cylinder of stacked bricks or stacked tires may be used as a composting chamber to allow liquid to escape, but be sure to prevent dirt or pumice from entering the chamber.
Perennial plants are best used because of their permanent roots. Lawns, shade trees, fruit trees, berries, grape arbors etc. are all suitable as there are no disease vectors transmitted via the roots.
Success in building wicks comes with practice. This information does not guarantee success the first time. Therefore construction supervision, including site and soil analysis, should be arranged.
Tom Watson experiments with, designs and builds various sustainable projects including pumice wicks, worm toilets, night-sky refrigerators, pumice-crete buildings, site, land and water analysis, water purification and low-cost housing, and simple bridges. He is interested in exploring failures.
PO Box 8, Embudo NM 87531; ph (505) 579-4001
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