Geosynthetics June/July 2021 - 34

Dewatering of sludge from a sewage treatment plant with geotextile tubes
FIGURE 2 Aerial view of the sewage treatment
plant in Boituva, São Paulo, Brazil
The waste generated then needs proper
transportation and final disposal, but
the transporting and disposing of these
untreated wastes can be impracticable,
resulting in the transport of large wet
volumes, being charged (disposal cost)
for this volume, and allowing the formation
of larger amounts of slurry in
the landfill, which represent a risk for
the environment in case of leakage.
Therefore, techniques and processes
that collaborate with the dewatering of
these sludges are fundamental, allowing
the transport of a smaller volume, with
lower tariffs and implying more safety
for disposal in landfills.
In view of the problems caused by
The project consists of
the dewatering of the
material contained in
three sedimentation
lagoons of the STP
Campos de Boituva in
São Paulo. Using the
existing drying beds in
the STP for the correct
positioning of geotextile
tubes, the STP sought
lower intervention
costs and increased
dewatering capacity in
relation to existing beds.
the generation of wet waste, this article
examines the use of the dewatering technique
in geotextile tubes (Figure 1 on
pages 32-33), providing the elevation
of the solid content of the dewatered
material, decreasing its volume, and
facilitating its handling as solid or semisolid
(Müller 2019; Vertematti 2015).
The geotextile tube dewatering technique
is a mixed dewatering solution
consisting of a geosynthetic tube that
receives hydraulically filling cycles with
sludge (Castro 2005; Koerner 2005;
Müller 2019; Pilarczyk 2000; Tominaga
2010; Vertematti 2015). In the filling
step, corresponding to the mechanical
dewatering, hydraulic pressure causes
liquid to be expelled through the geosynthetic
(forced filtration), while the
solids are retained by it. After the filling
and relieving of pressure, the sludge is
naturally dewatered, where the evaporation
process becomes increasingly relevant
as unsaturated zones begin to form.
For the correct use of this dewatering
technique, the geotextile tubes must be
positioned over a draining cradle; the cradle
is responsible for collecting percolated
water from the tubes, allowing their recirculation
in the treatment system or their
correct return to the relevant water body.
34
Geosynthetics | June July 2021
In this article, then, a dewatering
project is presented and discussed. The
project consists of the dewatering of the
material contained in three sedimentation
lagoons of the STP Campos de Boituva
in São Paulo. Using the existing drying
beds in the STP for the correct positioning
of geotextile tubes, the STP sought
lower intervention costs and increased
dewatering capacity in relation to existing
beds.
Boituva STP
STP Campos de Boituva is operated by
Companhia de Saneamento Básico do
Estado de São Paulo S.A. (SABESP) (Basic
Sanitation Co. of the State of São Paulo)
and serves a large portion of the city.
The treatment plant has three aeration
ponds for its processes, three decantation
ponds and 20 covered drying beds, each
807 square feet (75 m²) in size. Layout of
the station can be seen in Figure 2.
Necessity
The three settling ponds of the Campos
de Boituva STP were heavily loaded with
solid organic material in their interiors,
compromising the receipt of more effluent
and impairing its operating processes.
Thus, cleaning of the three ponds
was necessary.
Through tests performed by the treatment
plant, 423,776 cubic feet (12,000
m³) of densified material with 5% solid
content per mass was identified. This
material was predominantly composed
of organic matter.
Solution
Given the need to clean the three settling
ponds, solutions were evaluated.
Initially, it was considered to pump the
dense material with hydrovacuum tank
trucks, but soon it was realized that the
wet volume to be transported was too
great, making this option unfeasible.
Geosynthetics June/July 2021

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