Water, Sewage & Effluent September October 2018 | Page 41

In the ensuing drama, a misguided
message
was
repeated
that
desalination is too costly. Too costly
compared to what? A failed economy,
massive unemployment, capital flight,
and growing social unrest?
The reality is that we are only water
constrained if we continue to manage
water as a stock. That means it is
finite and scarce, so the only solution
is to build more dams to trap water
that no longer exists. The end game is
a failed economy.
The good news is that water is a
flux that moves in time and space. If
we choose to manage it this way, then
it is an infinitely renewable resource.
In this model — the Paradigm of
Abundance — we can attract both
capital and technology back into the
water sector.
Central to the New Paradigm of
Abundance, is recycling of water
from waste, so sewage becomes a
resource rather than a problem. An
example is the Potsdam Waste Water
Treatment Works (WWTW) in the
Western Cape. For some reason, this
is a secret, along with the Durban
South WWTW, which pioneered the
recovery of industrial process water
from sewage. In both cases, water is
already being recovered from waste,
but nobody is excited about this.
A new technology is available for this
purpose. It is called a Membrane Bio
The hollow fibres are placed under
negative pressure (within a vacuum),
drawing the clean water through the
membrane, leaving the nasties adhering
to the outside walls of each tube.
Water Sewage & Effluent September/October 2018
39
Membrane filtration diagram.
innovations
Reactor (MBR) and it works the same
as the normal activated sludge process
— with one exception. A module is
lowered into the wastewater at an
appropriate point in the process chain.
That module consists of long hollow
fibres, the thickness of spaghetti.
These fibres are woven from a single
strand and designed in such a way
that a uniform mesh size is created.
Depending on the membrane selected,
this is between 0.05μm and 0.4μm,
capable of removing most troublesome
solids, including bacteria.
These hollow fibres are placed
under negative pressure (within a
vacuum), thereby drawing the clean
water through the membrane, leaving
the nasties adhering to the outside
walls of each tube. Through clever
engineering design, the waste product
clinging to the outside of the tubes
is then purged, using air bubbles.
The flexibility of the tubes in each
rack enables them to vibrate in the
turbulence, thereby shedding their
load, which is then removed as sludge
and dealt with in the normal way. The
treated water is of a high quality, but
the big benefit is that the footprint of
the plant does not need to increase.
Now, it gets more interesting,
because there are over 800 WWTWs in
South Africa, collectively processing
over five billion litres of sewage daily.
Many of these are dysfunctional, and
T
he Day Zero crisis in Cape Town
brought this ugly truth out of
the closet, by exposing the risk
associated with water. The response
to Day Zero was to drastically
manage demand, but the unintended
consequences were many. Loss of
investor confidence ensued, but an
even bigger risk was laid bare for all
to see. Reduced demand also meant
that revenues to the city crashed,
necessitating a drought levy to plug the
gap. This meant that good behaviour
was being penalised simply because
of the illogical way that we price water.