Hatching a solution
While desalination must form part of the future water-source mix in a
large coastal city like Cape Town, it must be carried out responsibly
from an environmental and financial perspective.
Case study by Hatch
W
hile the City of Cape Town
is investigating large-scale
desalination for the city,
it is constructing several smaller-
scale desalination plants, which are
expected to deliver two million litres
of an expected seven million a day.
However, the impact of higher water
tariffs to fund water augmentation
schemes will be long-lasting,
and may be a future burden for
ratepayers, especially when the
drought has passed, cautions Hatch’s
Pieter de Kock.
The city of Stellenbosch is taking delivery of eight containerised borehole water treatment
plants, supplied by Hatch.
8
Water Sewage & Effluent May/June 2018
Desalination is carried out by means
of reverse osmosis (RO), whereby
saltwater is passed through a very
fine membrane to strip the water
molecule of salts and other minerals,
leaving demineralised water that
is further treated before it is fit for
human consumption. De Kock notes
that the cost of conducting RO on a
large scale is hugely expensive as it
is energy hungry, owing to the high
pressures required for the process.
In addition, transporting millions of
litres of treated water from the coast
to the main reservoirs to distribute
via the existing distribution network,
poses significant challenges,
and requires new large-diameter
pipelines and pump stations. This
could escalate the relative unit cost
per kilolitre of water produced up
to three times more than surface
water, depending on the location and
cost of connecting infrastructure. So
too, the impact of brine discharge
on the environment and coastal
areas must also be considered, and
detailed coastal modelling studies
are essential.
Hatch is managing a R60-million
emergency water augmentation
project for the Stellenbosch Local
Municipality in the Western Cape,
which includes the implementation
of 15–20 new boreholes, and at least
eight new containerised borehole
water treatment plants to assist
in mitigating the effects of the
drought. This will make Stellenbosch
Municipality largely independent
from the City o