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Aerobic Pumice Wick
TOM WATSON
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.
Details
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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