Chemical Engineering February 2021 - 9

Bacteria for wastewater treatment
esearchers from the National University of Singapore
(www.nus.edu.sg), led by associate professor He Jianzhong,
have found a new strain of bacterium called
Thauera sp. strain SND5, which is capable of simultaneous
nitrification and denitrification and phosphate removal
from wastewater. The discovery has the potential to significantly
reduce the operational costs and emission of greenhouse gases
associated with traditional wastewater treatment methods.
Sewage contains nitrogen in ammonia and phosphorus in
phosphates. Too much of either can pollute the environment
and they must therefore be removed before the treated water
can be released.
R
Most existing sewage treatment systems use separate reactors
to remove nitrogen and phosphorus, which is a bulky and
expensive process. Some existing systems use a single reactor,
but they are inefficient because different bacteria in the same
reactor will compete with one another, lowering the system's
overall efficiency.
Also, some existing systems release nitrous oxide, a greenhouse
gas. The NUS team's new bacterium converts the ammonia
into harmless nitrogen gas instead. Compared with
conventional nitrogen removal processes of nitrification and denitrification,
the NUS team's use of the new bacterium can save
about 62% of electricity due to its lower oxygen demand.
The researchers are now planning to test their process at a
larger scale, and formulate a " soup " of several bacteria to boost
SND5's performance even further.
n
a highly efficient supercapacitor based on a sustainable
graphene-hybrid material.
The TUM researchers developed a graphene hybrid material
that serves as the positive electrode in supercapacitors, and
combined this with a proven negative electrode based on titanium
and carbon. The new energy storage device not only
attains an energy density of up to 73 Wh/kg, which is roughly
equivalent to the energy density of a nickel-metal-hydride battery.
It also performs much better than most other supercapacitors
at a power density of 16 kW/kg, according to TUM.
The researchers combined the novel positive electrode of
the storage unit (with chemically modified graphene) with a
nano-structured metal organic framework (MOF). This graphene
hybrid has a large specific surface (up to 900 m2/g)
and controllable pore sizes, as well as a high electrical conductivity.
When used in a cell, the TUM material retained
around 90% capacity after 10,000 cycles. For comparison,
the useful life of a " classic " lithium accumulator is around
5,000 cycles, says TUM.
The research - performed in collaboration with scientists
from India, Australia, Spain, the Czech Republic and the U.S.
- was published in a recent issue Advanced Materials.
FLAT SILICON COMPOUNDS
Researchers at the University of Bonn (Germany; www.unibonn.de),
led by professor Alexander C. Filippou of the Institute
for Inorganic Chemistry, have constructed silicon-containing
molecules in which the four ligands do not form a tetrahedron,
but a distorted square - a trapezoid. They lie in one plane
together with the silicon. The influence of the unusual structure
on the properties of Si -an important element for the electronics
industry - is completely unclear at the moment.
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Chemical Engineering February 2021

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