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ASTUTE REUSE
Rainwater and greywater systems were installed during
the construction of the Liberty Complex. The practicalities
involved and the savings gained are discussed.
The Liberty Complex in
Umhlanga, KwaZulu-
Natal, consists of Liberty
Life’s regional headquarters,
a Southern Sun
Garden Court hotel and additional
offices which will be let.
The complex is saving water by
collecting, storing and reusing rainwater
and greywater from the hand
basins, showers and baths in the
hotel’s 200 rooms, and most of the
office component.
JFM spoke to the piped-services
consulting engineer on the project,
Benatar Consulting, to find out more
about the installation of these systems
in general and, particularly, at
the Liberty Complex and Southern
Sun Garden Court Umhlanga.
Capture of
rainwater optimised
The rainwater and greywater systems
were designed by Lawrence
Benatar of Benatar Consulting.
Rainwater is collected from the roof
and kept in a tank.
Water from the hotel’s showers,
baths and hand basins is also collected
and this greywater is purified.
It is mixed with the rainwater and
used for the cooling towers in the
air-conditioning system.
The project required three separate
systems of pipework – one for
the rainwater, one for the greywater
and another for the blackwater.
However, only the rainwater and
greywater is being recycled. The
Geberit Syphonic rainwater system
was used extensively in the design
of the rainwater system.
Benatar says that this system
allows for the capture of more rainwater,
and makes rerouting of rainwater
much easier and more efficient
than it would be with a conventional
rainwater system.
Geberit states that it uses the
gravity-induced vacuum principle to
create a siphonic action; allowing
complete drainage of a roof area with
pipes of smaller diameter than used
in a conventional gravity system.
According to the company, the
advantages of these systems include
horizontal collecting pipes, fewer
stack pipes and less groundwork
than conventional drainage systems.
In addition, they require less space
overall, reduced pipework size and
fewer fittings.
The roof outlets are linked
together directly under the roof with a
non-sloping collector pipe. Large roof
areas can thus be drained through a
single discharge stack. This simplifies
planning and reduces construction
time, Geberit notes.
Cost-intensive discharge stacks
and drains are not necessary so
more planning options are available
for the architect, the company adds.
Unconventional
cleansing commended
Chem-Free Aqua supplied the
ozone-purification and -treatment
system which cleanses the greywater
prior to its addition to the rainwater.
The system differs from conventional
water-treatment systems which use
chemicals in that it uses ozone generators
to cleanse the water.
Graham Kluk, of Chem-Free
Aqua, explains the process: “The
greywater is filtered before it goes
into the tank where it is collected to
strain it of solids. Following prefiltration,
the water in the tank is circulated
with ozone, which kills bacteria,
and filtered through a multimedia
filter.”
The multimedia filter removes
contaminants such as nitrates in
case someone has urinated in the
shower, for instance, adds Kluk. “It
ensures that the water which comes
out of the system is Class 3 which is
suitable for toilet flushing and irrigation
purposes. The water is then
pumped to the hotel for reuse.”
Ozone claims
to lower cost
The advantages of using ozone
instead of chemicals include lower
operational costs in comparison with
constant chemical use, no chemical
waste and no detrimental wear on
equipment and pipelines, according
to Kluk.
In addition, as it is manufactured
for use on site, the need for storage
is eliminated so the risks and hazards
of storing chemicals are
reduced, Kluk points out.
Benatar believes that ozone sterilises
and cleans water effectively,
and that it is a less expensive
method of achieving this. He says
that it has worked perfectly so far.
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During the construction of the Liberty Complex in Umhlanga, rainwaterand greywater systems were installed to collect, store and reuse water.
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Greywater is all wastewater except toilet waste and kitchen waste. All the water from the hand basins, showers and baths in the Southern Sun Garden Court Umhlanga’s 200 rooms is recycled and used for the adjacent office building’s air-conditioning system.
Automatic monitoring
Levels, valves, pumps, filters and backwashing
are all controlled by the PLC.
There is no need to adjust anything on
the system but the alarm monitors on the
PLC must be checked daily.
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Effective disinfection
Contamination in greywater systems
is cause for concern among facilities
managers. If treatment is not carried
out effectively, contamination could
occur, resulting in health side
effects, Benatar states.
“Effective disinfection is achieved
by subjecting the target organisms
to fixed concentrations of a disinfectant,
such as chlorine, bromine or
ozone, for a known period of time,”
Kluk states. “Compared with conventional
disinfectants, ozone
achieves superior disinfection at
lower chemical concentrations and
within shorter contact periods.”
He tells JFM that ozone is used
as an oxidizing biocide to destroy
microorganisms in water and to oxidise
many hydrocarbon chemical
compounds, as well as some inorganic
contaminates such as iron
and manganese. Kluk says that
ozone destroys organic and toxic
pollutants in water, and oxidises
inorganic elements so that they can
be filtered out and removed from the
water supply. “The type of organisms
targeted, as well as the overall
ozone demand of the water, dictate
the level of ozone residual required
for disinfections. With the correct
operating parameters and ozone
dosages, an ozone system could
achieve thorough disinfections at
lower cost.”
Why reuse greywater?
Kluk notes that all owners and operators
of facilities are attempting to
find ways to cut down on the use of
resources such as water and, in
turn, costs. Capturing and reusing
rainwater and greywater – which is
all wastewater except for toilet and
kitchen waste – saves water.
Another method is to capture
and reuse blackwater – water from
toilets – but this is not as popular as
it is easier to treat and recycle greywater
and people are more sensitive
about recycling toilet waste.
The Liberty complex as a whole
is measuring the savings gained
through meter readings but the
results were not vailable at the time
of writing. Benatar states that it is
economical to capture greywater in
a hotel because it can easily be
rerouted as services are on top of
each other.
The payback period for a greywater
system can be as early as two
years, according to Benatar. “The
cost of many litres of water from
200 showers, baths and basins,
which are used every day, sometimes
more than once, amounts to a
large sum of money saved as it is
not bought from the city council,”
Kluk comments.
There is also the added benefit
that recycling greywater is a “green”
solution, Kluk adds. This improves
the public’s perception of the facility,
and the owner and tenant foster a
good reputation among those who
place value on environmentfriendliness,
Benatar says.
Installing these systems is “doing
what is right for the country” as
there is a national shortage of water,
he adds.
Benatar says that the Liberty complex
satisfies the requirements for a
green building. He claims that, if it
was audited, it would achieve close
to maximum points. He says this is
an important selling point should
future owners or tenants want a
Green Star-rated building.
Mitigating factors to consider
If the installation of a greywater system
is being considered, a few factors
need to be taken into account. Firstly,
Benatar states that the feasibility and
practicality of installing a greywater
system in a facility must be investigated.
Secondly, what is technically
possible must be calculated in terms
of what can be captured and reused.
“The owners or operators of the
facility must determine whether or not
the manner in which the water will be
reused is feasible for a particular project.
Aspects such as cost and ease
of maintenance, and practicalities
such as space for the large storage
tanks, a structure that can hold the
weight of the tanks and the distance
of the tanks from the point of use all
need to be kept in mind.”
Regarding operating costs, it
needs to be understood that,
although there is a saving in water
costs, energy costs will increase,
Benatar says. This is due to the
energy required to pump the water.
“A lot of people believe that they
save 100 000 l and then convert that
into a cost saving. However, they are
not considering the additional energy
cost which is incurred in order to
pump that water.” |
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Determining use
The next step is determining the
use of the greywater. It can be
used for irrigation, flushing of toilets
and supplying an airconditioning
system. “For the
Liberty complex, it wasn’t feasible
to do more than supply the airconditioning
system because it is
the biggest user of water in the
entire project. None of the water
can be used for irrigation or flushing
toilets because it is all being
used for the air-conditioning,”
Benatar imparts.
He says that, if greywater is
used for irrigation, one has to look
at hygiene as the water, which is
not suitable for drinking, will be
circulating in the garden and the
garden taps. It is vital that the taps
and pipework are identified properly
as conveyors of non-potable
water to avoid health risks.
Using greywater for flushing toilets
presents a perception problem
as the water in the toilet does not
look clean and is, therefore, not
perceived as clean. This is why
some owners and operators steer
clear of this option, Benatar notes.
He warns that, if the system is
not designed properly and does
not allow for proper evacuation of
water, the building could flood,
especially when the tanks are
inside the building. In addition, if
the filters do not function properly,
an offensive odour could emanate
from a greywater system, Benatar
notes. Lack of maintenance will
present problems, he adds. |
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Easy to maintain
The rainwater system
does not need
maintenance and the
greywater system was
built to be selfbackwashing
so its
maintenance is minimal. |
Minimal maintenance
Regarding maintenance, the rainwater
system does not need to be
cleaned but the greywater system
should be cleaned at least every five
years – it should be drained and
washed down with suitable cleaning
products and solids should be
removed, Benatar informs JFM.
The greywater system was built to
be self-backwashing so its maintenance
is minimal, Kluk says.
However, the facility’s maintenance
team has to change the pre-filters
once a week which, according to
Kluk, should only take half an hour
and does not require a specialist.
“The pre-filters are reusable so a
spare set is loaded into the containers
and the dirty pre-filters are taken
out and washed during the week so
that they can be used again the following
week. This keeps costs low.”
Practical challenges conquered
It was a challenge to find a suitable
location for the greywater tank at
Southern Sun Garden Court
Umhlanga, Benatar says. “It was difficult
to find a position for the tank
because of its size. We put it in a
parking garage at the bottom righthand
corner of the site. This created
another challenge in routing all the
greywater from the top left-hand corner
to the bottom right-hand corner
by gravity.”
According to Benatar, a parking
garage is a prime position for greywater
tanks as they are normally situated
below ground to enable the use
of gravity, the corner spaces are usually
available as it is not possible to
park there and these unsightly tanks
can be hidden behind concrete walls
and remain completely out of sight.
For drainage, fortunately, there
was sufficient space to route the
services to the opposite corner of the
site, Benatar notes. Another challenge
he mentions was not clashing
with other services which were being
installed, such as the air-conditioning
and electrical systems. This required
careful course-plotting.
Becoming more
and more common
It is generally possible to retrofit a
greywater system in a facility but a
survey on a facility’s existing system
would have to be undertaken to
determine whether or not it would
be possible, Benatar imparts. It also
depends on the intended use of the
greywater. Benatar Consulting is
investigating fitting a system into a
20-year-old, 30-storey high-rise
building at the moment.
The size of the system could also
be altered to cater for large and
small facilities – even a single
household. Kluk mentions that a
greywater scheme was completed
for a single household in
Bloubergstrand where the water
was used for the garden and toilets.
Other installations mentioned by
Kluk include the BP building on the
Foreshore in Cape Town, the
Woolworths and Checkers distribution
centres in Midrand, the City of
Cape Town’s Shared Services building
in Athlone and Nedbank’s
Ridgeside in Umhlanga.
With many complete installations
and many more to come, it seems
that greywater systems are becoming
popular solutions for reducing
water costs. |
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