Geosynthetics June/July 2021 - 35

Then, dewatering techniques were considered,
aiming to separate the liquid part
from the solid part, providing a smaller
volume to be treated.
At the top of the list of the various
dewatering techniques available in Brazil,
the mechanical options were soon discarded,
representing high acquisition
and maintenance costs. Therefore, as the
existing drying bed dewatering technique
was not able to deal with the required
volume in pertinent time, the geotextile
tube dewatering technique was chosen.
Implemented dewatering
solution
The selected dewatering technique corresponds
with the use of containers made
of geosynthetics, assuming a linear tubular
shape upon filling, which is designed
in a variety of perimeters and lengths to
result in a geotextile tube (Müller 2019).
Geotextile tubes have, then, the function
of filtering the sludge, retaining the
solid particulate inside and allowing the
water to percolate (Castro 2005; Koerner
2005; Moo-young et al. 2002; Müller
2019; Pilarczyk 2000; Tominaga 2010;
Vertematti 2015).
Through filtration and retention of
solid particulate, this dewatering technique
increases the solid content of the
sludge. The operation reduces the moisture
content so the generated waste can
be handled as a semisolid/solid, thus providing
much easier and more efficient
handling and transportation than would
happen with the previous wet material
(Castro 2005; Koerner 2005; Müller
2019; Pilarczyk 2000; Tominaga 2010;
Vertematti 2015).
As mentioned previously, for the
correct operation of the technique, the
geotextile tubes must be arranged over
a draining cradle, ensuring the collection
and concentration of the percolate,
gauging its quality and then promoting
FIGURE 3 Geotextile tubes specially designed for the drying beds of the treatment plant
its correct destination (Müller 2019;
Vertematti 2015). In the application
scenario, the drying beds were used as
drainage cradles for the geotextile tubes,
the percolate being redirected to the
settling ponds. This avoided the need to
build a cradle, saving costs and speeding
up the beginning of the necessary
dewatering process.
The geotextile tubes were then
designed and quantified, taking into
account the length and width constraints
of the existing drying beds, which were
16-feet (5-m) wide and 49-feet (15m)
long. The software GepCoPS 3.0
(Leshchinsky and Leshchinsky 1996) was
used and, by geometric and stress analysis,
14 geotextile tubes were defined for
cleaning the lagoons. Figure 3 shows the
geotextile tubes designed, with a perfect
fit in the existing drying beds.
Through cone testing (Vertematti
2015), high-strength polypropylene woven
geotextile was defined as the best option
for the sludge filtration. This geotextile
was then used to make the geotextile tubes
for the pond-cleaning service. The geotextile
had the following characteristics:
Filtration aperture (NBR 12.956 2013) of
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