HEALTH AND SANITATION
39
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manner. In addition to the general rules for harvesting
greywater, the following applies to the use of GDDs:
• Use diverted, untreated greywater for subsurface
irrigation only (at least 10cm below the surface of
soil or mulch).
• Ensure the greywater diversion device is switched
back after irrigation periods so that greywater is
diverted to sewer.
• Make use of a filter to screen solids when using a
diversion device.
• Ensure that regular maintenance is undertaken,
including cleaning out the GDD filter weekly and
maintaining the subsurface irrigation system.
Regularly clean the whole irrigation system, as
greywater causes bio-slimes to build up in the
filter and pipes, leading to blockages. Take care
to use gloves and avoid splashing as there may
be considerable numbers of disease-causing
organisms that have built up in the bio-slimes over
time.
• Mark/label all pipes and use signs to indicate
greywater reuse.
When using a GDD to harvest greywater, do not leave
the device on continuously. Treat it like a garden tap and
only reuse greywater when the garden needs watering.
Greywater is for reuse, not disposal. It is also particularly
important — as a GDD offers no form of treatment — to
recognise that GDDs should have a device that allows the
greywater to be diverted to the formal sewerage system.
This should be done under the following circumstances:
when nappies or pets are being washed; when someone
in the household is ill; during wet weather or when the
water is likely to pool and run-off; and when any harmful
chemicals have been used that would otherwise drain
directly to the garden. Once installed, it is necessary
to maintain the GDD regularly. General maintenance
guidelines are provided in Table 2.3.
GREYWATER TREATMENT SYSTEMS (GTS)
A greywater treatment system (GTS) collects and treats
greywater — the range of treatment processes vary
according to the level of sophistication of the system and
the intended use of the greywater. Currently in South
Africa, the level of treatment in these systems is limited
to fine sieving or filtration and chlorination. Where the
treated greywater is not disinfected, it should only be
reused via subsurface irrigation — as with GDDs. Where
the treated greywater from a GTS is (i) disinfected (for
example by UV/chlorination), and (ii) meets required
standards, additional uses such as: surface irrigation,
toilet flushing, and cold-water laundry washing machine
use may be considered.
Throughout the world, there are numerous systems
(some patented) which aim to treat greywater to
www.plumbingafrica.co.za
Table 2.3: GDD maintenance requirements
acceptable standards for reuse. The cost implications,
maintenance requirements, and social acceptability of
such systems would however have to be considered
before deciding which treatment technology to adopt.
It is particularly important, as with GDDs, to ensure
that GTSs have a device that allows greywater to be
diverted to the formal municipal sewer, should the
GTS fail or be overwhelmed. Similarly, if the GTS is
supplying greywater for toilet flushing, there needs
to be a back-up in the form of municipal supply into
the cistern for situations when the greywater system
fails. This is particularly relevant in South Africa,
where the threat of electricity outages may interfere
with the proper functioning of a GTS. Furthermore,
care should be taken to ensure the GTS provides
adequate treatment.
When uncertain, greywater should not be harvested
in the following circumstances: when nappies or pets
are being washed; when someone in the household
is ill; during wet weather or when the water is likely
to pool and run-off; and when any harmful chemicals
have been used that would otherwise drain directly
to the garden. Once a GTS is installed, it needs
to be maintained. This is the responsibility of the
property owner / occupier, who should arrange for an
appropriately trained service company or person to
maintain their system. At a minimum, a GTS should be
inspected annually. Regular maintenance (as for GDDs)
may be required and can be undertaken by the property
owner / occupier. PA
February 2019 Volume 24 I Number 12