Chemical Engineering June 2021 - 7

An electrotrophic system that treats
swine sewage in one step
R
esearchers from the Biological
Systems Unit at
the Okinawa Institute of
Science and Technology
Graduate University (OIST; Japan;
www.oist.jp) have developed a bioelectrochemical
system that uses
bacterial communities to break
down organic material from raw
wastewater, and removes both nitrates
and phosphates from aerated
wastewater. A proof-of-concept
have been demonstrated in
both the laboratory and on a local
swine farm in Okinawa, Japan.
Across Okinawa, large amounts
of wastewater are produced by
pig farms. The traditional aeration
system currently utilized by farmers mainly
treats organic matter in the wastewater
and also converts the ammonium present
to nitrate, but it does not treat the nitrate
further. In Japan, the nitrate discharge limit
for the livestock industry will soon be lowered
to one fifth of the current 500-mg/L
level - more than 35% of farms in Okinawa
are likely to exceed this impending
change, according to OIST.
" Our new system uses two different
chambers, " explains Anna Prokhorova,
lead author of an article recently published
in Bioresource Technology. " In one
chamber, full strength swine wastewater is
treated for the removal of odor, pathogens
and organic matter, whereas in the other
chamber, excess nitrate and phosphate is
R
CO2
Organic
material
Anode chamber
Potentiostat
OIST
Reference
electrode
Nitrate
Bacterial
Nitrogen
gas
Cathode chamber
communities
Raw wastewater Aerated wastewater
removed from wastewater that has already
been treated through the traditional aeration
system. To the best of our knowledge,
this is the first system to successfully treat
two different types of wastewater at the
same time, " she says.
In the anode chamber, bacteria react
with the organic molecules present, releasing
electrons in the process (diagram).
These electrons are then transferred to
the cathode chamber via the electrodes.
The cathode chamber contains wastewater
that has already gone through the
aeration process and thus has high levels
of nitrate. Bacteria on the surface of the
cathode chamber accept these electrons
and use them to power the conversion of
nitrates to nitrogen gas.
Reducing the cost of redox flow batteries
edox flow batteries (RFBs) are a promising alternative
to lithium-ion batteries for storing large
quantities of renewable energy (see Chem. Eng.,
September 2016, pp. 14-20), but they have always
been too expensive for the mass market. Now, researchers
at the Fraunhofer Institute for Environmental,
Safety and Energy Technology (Umsicht; Oberhausen,
Germany; www.umsicht.fraunhofer.de) have completely
redesigned the heart of a RFB - the stack - resulting in
a " massive " reduction in material usage and costs.
" The stack that has been developed is 40% more
cost-effective in terms of material costs, " says professor
Christian Doetsch. " Production costs have also been significantly
reduced. The stack weighs 80% less than a conventional
stack and is only about half the size, " he adds.
Stacks usually comprise 160 stacked components
that are held together by a large number of screws
and solid metal plates and sealed with numerous gaskets.
Some of these components are injection molded,
meaning they are brittle. To avoid this problem, the team
of researchers used similar base materials - graphite
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
and carbon black - but approached the process differently:
plastic pellets are cooled to temperatures as low
as -80°C, then ground into powder and mixed with 80
wt.% graphite. The powder is sent through a system of
several rollers moving at different speeds and heated to
different temperatures. As a result, the powder is briefly
melted between the rollers at moderate temperatures
and low pressures, and then kneaded and rolled up. The
process makes it possible to manufacture bipolar plates
of up to several square meters in size. This powder-toroll
process is the key to reducing production costs, because
very thin (0.1-0.4 mm) plates can be produced.
Because less material is used, the costs, weight and
footprint of the device are reduced.
The stack is being marketed by the spin-off Volterion
GmbH (Dortmund, Germany; www.volterion.de). The
company has already built and sold more than a thousand
stacks. Christian Doetsch and Lukas Kopietz from
Fraunhofer Umsicht and Thorsten Seipp from Volterion
have been awarded the Joseph von Fraunhofer Prize for
this development.
JUNE 2021
7
Engineering at Tohoku University
(Japan; www.tohoku.
ac.jp) has developed an
ion-selective, smart porous
membrane that can respond
to external stimuli for controlling
permeation. The technology
has potential applications
in molecular separation and
sensing applications.
Nanostructure properties,
such as pore size, thickness
and film density, affect molecular
selectivity and molecular
permeability. Surface
properties also have a significant
impact on molecular
selectivity. Therefore, it is important
to be able to control
both the 3-D nanostructures
and surface properties of ultrathin
porous films.
" In our study, we succeeded
in developing responsive porous
SiO2 thin films with an
extremely thin film thickness
of 8 nm with a uniformly covered
surface in a pH-responsive
silane coupling agent, "
says Yuya Ishizaki, a co-author
of the study published in
Langmuir. " The responsive
porous thin film can adjust
the surface charge depending
on the pH change in the
solution, resulting in selective
ion permeation. "
To prepare the porous films
with a controlled structure to
nanometer-scale accuracy,
the research group focused on
(Continues on p. 8)
Electrode
Anion exchange membrane
Electrode
http://www.tohoku http://www.ac.jp http://www.oist.jp http://www.umsicht.fraunhofer.de http://www.volterion.de http://WWW.CHEMENGONLINE.COM
Chemical Engineering June 2021

Table of Contents for the Digital Edition of Chemical Engineering June 2021
