Gauteng Smallholder December 2015-January 2016 | Page 43

From page 40

water.
holey kind themselves) which Above the tank should be
will increase the surface area
layers of fine sand, then
under the fluid to which
coarse sand (eg river sand)
anaerobic organisms (the
above it, then fine gravel,
same that are found in a
coarse gravel and finally a
septic tank) can attach
coarse, heavy covering of
themselves to do their work
something like brick grog
of digesting particles in the
(broken brick) to keep the rest
of the filter
medium in place.
Similarly, at the
bottom, you can
keep the fine sand
from sifting into
the tank by
placing down a
mat of folded 80%
or more shadecloth.
The top few
layers, eg the brick
grog and coarse
gravel will be
aerobic, ie they
will dry out
between
pumpings of the
fluid, or at least
allow air in to
their inner spaces.
Home-made domestic grey-water filter. Note
The lower layers
algae-laden green water in pond.

WATER
CRISIS
combination of phosphates

and the tank itself, however,
should be constantly moist if
not soaked, and therefore
anaerobic. In this way they
will provide a fruitful habitat
for the important anaerobic
bacteria.
(And it makes sense to, firstly,
kick-start the filter with a dose
or two of a biological septic
tank product such as
Sannitree to “seed” the
anaerobic part of the filter
with bacteria and, secondly,
to boost the bacteria periodically with additional occasional treatments).
The resultant fluid should
emerge from this process
relatively clear and odourfree. Note, however, that it is
still unsuitable as anything
other than plant irrigation
water (ie can't be used to
water livestock, and can't be
allowed legally into a
watercourse … not that you'll
have enough to do that
anyway).
The fluid will still contain a
load of dissolved chemicals,
especially soaps, which are a

41
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and nitrates, which are the
basic constituents of chemical
fertilizers, but also other less
desirable elements such as
heavy metals.
If you store the water in a
reservoir or dam at this stage
you will notice that it very
quickly goes bright green.
That's the effect of algae
Continued on page 42