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The functioning of a WWTP
Wastewater treatment plants collect water
from the sanitation network and returns it to
the riverbed with the suitable contamination
parameters. These waters, when dischar-
ged, are not always totally clean, that is, the
water is sometimes discharged into the river
with certain parameters that are calculated
so that the contamination is eliminated in a
natural fashion. This is called natural was-
tewater treatment which is constantly pro-
duced in all rivers, brooks or lakes.
In the case of the Ávila WWTP the process
is as follows:
●
Before arriving at the plant, water is
subjected to an external preliminary
treatment which involves the filtering
through a screen with 7cm holes to
remove the largest pieces of waste
(tree branches, stones, wood, cork,
plastic materials…). This phase is
essential to ensure the appropriate
functioning of subsequent processes
and to protect all of the plant’s elec-
tro-mechanical equipment.
●
The water flows by gravity into the
WWTP. From there, it is pumped to a
height of 10 meters so that it can flow
on its own weight through the remai-
ning parts of the treatment.
●
Water first goes through a preliminary
treatment where it is broken down,
filtered, and the sand and floating
particles are removed. Larger than
3 mm waste particles (stones, sand,
food, paper, plastic, cotton swabs for
cleaning ears…) are sent to the local
landfill site.
●
Water then goes through the primary
treatment where it flows into primary
cone-shaped decanters where solids
which are dissolved or in suspension
are removed at the bottom and na-
rrow part of the cone.
●
It then passes through a rotating
drum screen (1mm perforated mesh)
for its filtering and then goes to the
biological reactor, the heart of a was-
tewater treatment plant. Several mi-
croorganisms – an actual ecosystem
– lives in this reactor. They feed on
the organic material dissolved in was-
tewater. Processes for eliminating nu-
trients (nitrogen and phosphorus) are
also implemented.
●
For peak flows, separating tanks are
used to store water which is subse-
quently treated when the flow is redu-
ced.
●
After passing through the biological
reactor, a blower is used to inject air
As Jaime Lobato explained, with the refur-
bishment completed in 2014, a gasometre
(reservoir) was created to store surplus bio-
gas, most of which is methane gas, which is
used to generate part of the electricity used
at the plant (specifically, in the control and
monitoring) after burning it in a generator en-
gine. Over the course of 2015, another part
of the station will start operations and it is ex-
pected that the sludge will be heated more
efficiently, producing more biogas and there-
by generating more electricity for the plant.
The sludge is also used. Each day, six ten-
tonne trucks come to the plant to collect this
material, converted into fertilizer, and distri- bute among farmers who use it to grow ce-
reals. Three-hundred tonnes of this material
are produced every week. It is used in the
land that is also irrigated by the same water
from the nearby reservoirs which collect the
treated water.
This is how the cycle ends, where nature,
technological innovation, and men work to-
gether to ensure that this good can be reu-
sed with an optimal quality and, after subse-
quent processes, can be consumed by the
residents of Ávila.
Jaime Lobato, manager of the Ávila plant.