WASTEWATER SOLUTION
Davyhulme is one of the biggest
wastewater treatment works in the
UK, draining the entire western side of
Manchester. Thermal hydrolysis plant reaction vessels.
“This is done by capturing the bugs in
a nal settlement tank and returning
these to the start of the activated sludge
process, thereby matching the food
and bugs to the correct ratio: quite an
ingenious process that considerably
reduces the footprint of a wastewater
treatment process, while having the ability
to treat variable loads,” he says.
Before the modernisation project,
Davyhulme WwTW had two activated
sludge plants running in parallel (ASP1
and ASP2, each dealing with half of the
ows). ASP1 has now been replaced
with a new 10-lane plant (ASP3), which
handles 60% of the ows.
MODERNISATION IN ACTION
The activated sludge process used
in the modernisation process is still
the same basic one devised by Arden
and Lockett, but the way in which
it is controlled has been massively
enhanced, resulting in a much
better controlled and energy-ef cient
treatment of the sewage. The dissolved
oxygen is now introduced from the
bottom of the basin, instead of at the
surface, ensuring it is uniformly ef cient
throughout the entire process. The bugs
receive the right amount of food and air
at all times.
The modernisation project also included
replacing the old inlet works and building a
new odour-controlled inlet consisting of a
two-stage screening facility, all controlled
automatically via a distributed control
system. “For the rst time on site, we
have a facility to capture the fats, oils and
grease that enter the works, and we now
store this and send it to a green energy
recovery company, which converts it into
a biodiesel,” adds Frain. There are other
key differences between the old treatment
works and the new one, in terms of
operation and what could be achieved
before and now.
“The new activated sludge process
treats both ammonia and BOD
(Biochemical Oxygen Demand). The
original Arden and Lockett design utilised
a carbonaceous treatment for the removal
of BOD only. However, we now have a
nitrifying activated sludge process that
also removes ammonia, which is achieved
in the same way as before, but far more
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