Water & Wastewater Asia May/Jun 2021

IN THE FIELD WATER & WASTEWATER ASIA | MAY/JUNE 2021
further reverse osmosis stages (see
Fig. 3) were implemented to ensure
reflects that water retention by the
reverse osmosis membranes is
In a nutshell, the upgrade of the
wastewater treatment plant into a
Process chain of the
ZLD plant from start
to finish
the production of an optimal clean
better than expected and feed is
ZLD-system plant for the cosmetics
permeate, making it as concentrated
saltier than assumed. Reversely,
manufacturer client was a complete
as possible before feeding it into the
this indicates that the salts in the
success, both in terms of the
evaporator to be thickened.
membrane were greatly enriched,
achieved quality of recycled water
increasing the osmotic pressure in
and how it has minimised the quantity
After both the construction and the
the system. This rise in pressure
of residue disposal: approximately
commissioning phases, the plant
was counter-acted by reducing
95.5% of the wastewater is reused
operation was supervised for a
the second and third stages of
during the first stage of the reverse
further six months, where it became
reverse osmosis, i.e. RO II and RO
osmosis procedure, flotation
clear that the process is a success.
III, a measure which optimised the
makes up 4.25% and a mere 0.25%
Only the hydraulic mode required
operation without deteriorating the
is disposed as an evaporator
special attention as the plant was
overall permeate yield.
concentrate.
fed with merely 4-6m 3 /h during the
supervision period despite being
designed for a significantly higher
membrane reactor throughput of
14.6 m 3 /h and 8m 3 /h at the reverse
Fig. 4: From left:
Ultrafiltrated,
RO I, RO II, RO III
and evaporated
concentrate
osmosis stage. Consequentially,
parts of the plant had to be
regularly halted and resumed at
different intervals. From a processengineering
point of view, this is
feasible but not advantageous, since
it leads to higher mechanical fatigue
of its components.
OPTIMISATION OF THE
REVERSE OSMOSIS STAGES
If the results show recycled water
was less salty than required, this
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