Water & Wastewater Asia January/February 2023

IN THE FIELD
dimensions shrink, integrated circuits
become increasingly complex and
require additional processing steps,
including CMP, leading to increased
CMP wastewater generation.
CMP slurries generally consist of
a suspension of abrasive materials
— silica, alumina, or ceria — and
chemical additives (e.g., complexing
agents, oxidisers, corrosion
inhibitors, pH adjustors, surface
active agents, high molecular weight
polymers, and biocides) in ultrapure
water. Wastewater procured from
CMP processes contains high solids
content (often exceeding 10% by
weight) with total concentrations of
used silica reaching up to 4000mg/l.
This high solids content together
with total organic carbon (TOC)
concentrations of up to 15mg/l
makes CMP wastewater challenging
to treat.
SOLVING TREATMENT
CHALLENGES AND CAPACITY
EXPANSION IN A CONSTRAINED
FOOTPRINT
A leading Taiwanese manufacturer of
customised logic, integrated circuits,
and discrete components relied on a
tubular ceramic filtration membrane
system to treat CMP wastewater;
treated water was recycled and used
for cooling tower make-up water.
The tubular filtration system suffered
irreversible permeability loss due to
membrane fouling, which resulted
in a decrease in treatment capacity
of nearly 25% (from 168m 3 /d to
130m 3 /d). This capacity reduction
coincided with a need to expand
treatment capacity (in a constrained
footprint) due to regulation promoting
recycling and reuse of reclaimed
water. To address these issues, the
foundry piloted and subsequently
installed Nanostone ceramic UF
membranes, increasing the treatment
capacity by 200m 3 /d.
Nanostone’s compact system design
enabled this expanded capacity
within the existing constrained
footprint while simplifying operations
by eliminating the air scrub. Further,
operating predominantly in dead-end
filtration mode (rather than crossflow,
which is required by the tubular
membrane system) reduced pumping
requirements, significantly lowering
power requirements by 90%. This
approach also eliminated frequent
shutdown required to clean the feed
tank due to concentrate build-up
caused by cross-flow filtration. The
Nanostone system has proven to be
reliable, requiring minimal cleaning
and oversight, achieving 80% recovery
rate with no sign of permeability
degradation.
Nanostone’s advanced
manufacturing plant
is home to the largest
ceramic membrane
production capacity in
the world
WATER & WASTEWATER ASIA | JANUARY/FEBRUARY 2023 35