Other treatment options
New pollution problems have created
additional burdens on wastewater
treatment systems, such as heavy
metals, chemical compounds, and
toxic substances, all of which are
more difficult to remove from water.
Rising demands on the water supply
only exacerbates the problem. The
increasing demand to reuse water calls
for better wastewater treatment. These
challenges are being met through
better methods of removing pollutants
at treatment plants, or through
prevention of pollution at the source.
Pre-treatment of industrial waste,
for example, removes many pollutants
at the start, not the end, of the
pipeline. To return more usable water
to receiving lakes and streams, new
methods for removing pollutants are
being researched and developed.
Some of these advanced waste
treatment techniques, either in use
or under development, range from
biological treatment capable of
removing nitrogen and phosphorus,
to physical-chemical separation
techniques such filtration, carbon
adsorption, distillation, and reverse
osmosis. These wastewater
treatment processes, alone or in
combination, can attain almost any
degree of pollution control sought.
Waste effluents purified by such
treatment can be used for industrial,
agricultural, or recreational purposes,
or even drinking water supplies.
28
Bio case study
SewTreat designs, manufactures and installs state-of-the-art and eco-friendly
onsite wastewater treatment systems throughout Africa. It has a proprietary
bacterial strain developed for use in easy-to-install modular units. The plants
successfully transform wastewater into clean, clear, odourless treated water.
In fact, so successful is its biological
wastewater and sewage treatment
technology, that it is helping to
ensure the longevity of the pristine
waters of the Okovango Delta.
In a joint venture with the
Botswana government and a
private Italian firm, the company
has supplied a water filtration and
sewage treatment plant for project
that aims to recycle 2 000 litres of
Okovango River water per day. The
joint venture was entered into for
the purposes of constructing the
1.2km-long Mohembo bridge across
the Okavango River near Mohembo
Village in Northern Botswana.
The construction camp that was
set up to house the team developing
the bridge required the provision of
a wide spectrum of solutions. One
of these requirements was water
fi l tra ti o n and w as t e t r eat m ent
infrastructure for the camp. The
solution had to have the capacity
to clean and filter 2 000 litres of
Okavango River water per day to a
drinkable standard and treat 50kl of
sewage onsite, per day, with minimal
environmental impact.
nutrients (sewage). As these nutrients
require oxygen, this is introduced
into the treatment tank (bioreactor) at
the correct levels to encourage and
promote bacteria growth. In so doing,
the chemical oxygen demand (COD)
levels are reduced, nitrification and
de-nitrification occurs, and nitrates
and ammonia levels are controlled,
resulting in water that is safe for
recycling. Once the bacteria mature
and die, the system washes them off
the media.
This effluent then passes into the
clarifier where the heavier sludge
settles at the bottom and the clear
water separates at the top. The clear
water can then be treated by means
of an ozone or UV technology. Once
sterilisation is completed, the treated
effluent is ready for discharge, either
by means of irrigation, or to return into
dams or rivers, while the accumulated
sludge at the bottom of the clarifier
is recycled back into the septic tank
where it is further digested.
Further treatment will be required to
make the water suitable for drinking.
The containerised plants are designed for
ease of transport, security and modularity.
Water Sewage & Effluent November/December 2017
S e w Tr e a t w a s c o n t r a c t e d
to manufacture the required
infrastructure; both the water filtration
plant and the sewage waste treatment
plant. As a sewage treatment solution,
the company supplied a containerised
wastewater treatment plant capable of
treating 50kl per day, based on a ‘plug-
and-play’ design, while their water
filtration system has a capacity of 2kl
per hour.
The containerised plants are
designed for ease of transport,
security and modularity, taking into
consideration that the plant may be
moved to various locations and the
complete WWTP is built into ISO high
cube containers.
Both the water filtration and
sewage treatment plant have
been completed and are now
operational onsite in Mohembo. The
bio technology is ensuring that the
Okavango Delta, a UNESCO World
Heritage Site, is kept pristine and
unpolluted, at a rate of 18 million
litres per year. This is equivalent to
12 Olympic swimming pools of water
being treated and discharged into the
Okavango Delta.
Capable of treating 50kl per day of
wastewater, and based on a ‘plug-and-
play’ design, the water filtration system
has a capacity of 2kl per hour.