Hot stuff:
making the
most of
sewer heat
Technology now allows heat from
sewage to be extracted and utilised.
But what is the true potential of the
innovation? Martin Osborne explores the
issues at stake
www.wwtonline.co.uk | WWT | MAY 2018 | 25
BY MARTIN OSBORNE,
TECHNICAL DIRECTOR,
WSP
The Knowledge
Heat from sewage
E
xtracting heat from sew-
age is a current "hot"
topic. Every week a
new technology or a potential
scheme is announced. But
what is the real opportunity?
At WSP we have a lot of
experience in both sewerage
and heat management, so we
have put the two together to
consider three issues for man-
aging heat using sewage: how
much, where and how?
How much?
Renewable heat sources
are becoming increasingly
popular, partly driven by the
Renewable Heat Incentive
scheme. They are now oƒen
used for public buildings and
office blocks, and even some-
times for domestic properties.
The most common source of
heat is the ground. To avoid
causing long term changes in
the ground temperature, there
is a need to balance the heat
extracted from the ground
for heating in winter with the
heat returned to the ground
for cooling in summer. Using
sewage as the source has
the advantage that there is a
constant flow bringing in and
taking away energy, so that
balance is less important.
Sewage is normally above
ambient temperature, as much
of the water that we use is
heated; schemes currently
being planned in the UK are
focussed on extracting that
energy for heating. Future
schemes are already consider-
ing both heating and cooling.
However, one drawback
is that the temperature of the
sewage is important for the
effectiveness of wastewater
treatment. At lower tempera-
tures, plants are less able to
treat ammonia; some plants
already struggle to do this
in winter. Even a one degree
reduction could be significant.
So extracting heat from sew-
age might mean that we need
