Understanding the Software Options

This new membrane bioreactor cuts
energy costs and boosts throughput
GE Power & Water (Trevose, Penn.; ge.com) has introduced
an improved membrane bioreactor (mbr) technology
whose productivity is said to be 15% higher than that of
its predecessor for wastewater treatment plants. The new
system, called LEAPmbr, was derived from innovations to
GE’s ZeeWeed 500 mbr.
Glenn Vicevic, senior manager, Engineered Systems, says
the system has been tested on a commercial scale at three
of its customers’ plants and has demonstrated several improvements
in addition to higher productivity. These include
a 30% reduction in membrane energy costs, a 50%
reduction in membrane aeration equipment and controls,
and a 20% smaller footprint.
The system consists of rectangular cassettes of PVDF
hollow-fiber membranes, immersed in a bioreactor in which
bacteria break down pollutants. A pump draws treated
water through the membranes, while solids, bacteria and
colloidal material are retained in the tank.
An improved aeration method for cleaning the membranes
was the key element in lowering energy costs, says
Vicevic. “The conventional wisdom is that there should be a
continuous air scour of the membranes,” he says, “but over
the last decade, we experimented with bubble-size-diffuser
design and frequency of air release. From that we determined
that large bubbles delivered intermittently was the
most effective.” He adds that the improved productivity
was obtained by optimizing the manufacturing techniques,
while the smaller footprint was achieved by increasing the
surface area of the membrane.
Silicon passes a test in water-splitting
T he
use of solar energy to split water into hydrogen and
oxygen is an appealing idea, given that sunlight is abundant
in many parts of the world, but one of the challenges
to its development is to find a suitable electrode material.
Silicon, the popular photovoltaic material, seems like a
logical choice, but when it is exposed to O2 it is rapidly oxidized
and fails. Researchers at Stanford University (Stanford,
Calif.; www.stanford.edu) may have a solution.
Using atomic layer deposition, a common process in
semiconductor manufacturing, they have deposited a 2-nm
protective coating of titanium dioxide on silicon electrodes,
followed by a similar, evaporated layer of iridium. TiO2 is
transparent to sunlight and the iridium boosts the rate of
the splitting reaction, says Paul McIntyre, of Stanford’s
Materials Science and Engineering Dept. In laboratory
tests the coated electrodes have shown stable operation for
more than 24 h, without apparent corrosion or loss of efficiency,
he says, while uncoated electrodes corroded and
failed in less than 30 min.
Next, the researchers plan to scale up the process and
test other semiconductor materials. The ultimate goal, says
McIntyre, is the development of a commercial process in
which H2 and O2 would be stored and used to generate
electricity when the sun doesn’t shine. ■
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