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| Final
Dispersal Option: Bottomless Sand Filter |
Wastewater is applied under
low pressure to the top of a 2foot deep bed of sand media through
a PVC-pipe distribution system. The distribution network is
embedded in peastone to protect it. Wastewater percolates down
through the sand media and into the understory soil. Media
filters with an open bottom are specifically intended to disperse
wastewater into the soil immediately under and adjacent to
their footprint. Unlike single-pass sand filters, the bottomless
version is not buried, in order to allow for sufficient gas
exchange between the filter and the atmosphere. The filter
can either be installed at-grade, with 6 to 10 inches of the
filter above the ground surface, or above grade, with 2 to
3 feet of filter above grade. |
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| A treatment train
containing a bottomless sand filter |
Wastewater
leaves the home through the building sewer (A) flowing
by gravity to the processing tank (B), where
solids, fats, oils and greases are trapped and
stored. Wastewater is pumped to the textile media filter
(C), where the textile
media and bacteria reduce the strength of the wastewater
before it is recirculated back to the inlet-end of the
processing tank,
where nitrogen removal occurs. Recirculation continues
until the effluent level in the processing tank is high;
at this
point the effluent is routed to a drainfield
pump chamber (D) and pumped to the final dispersal technology:
a bottomless
sand filter (E). The effluent is dispersed onto
and filters through specific sand media in the bottomless
sand filter before
it reaches the shallow surface soils where further
nutrient removal and pathogen reduction may occur. Shallow
narrow drainfields
may also be used as a final dispersal option with this technology. |
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| Treatment
performance observed for bottomless sand filters in RI |
| System |
BOD5 |
TSS |
TN |
% TN Reduction |
Fecal Coliform |
| Coming
Soon! |
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| For
more information on bottomless sand filters: |
| Web
Links: This drainfield option has been studied
in great detail, with the above-referenced results summarizing
some of the data obtained. The construction of a BSF must adhere
to Rhode Island DEM regulations as per the BSF Guidance Document,
which can be found on the RI
DEM ISDS site. |
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