A Study about Submarine Sewage Outfalls
in the Coastal Region of the State of
Paraná - Brazil (26oS 48oW)
Joseph Harari1*, Paola Galluzzi Polesi1, Tiago Cortez1 and Samuel Hora Yang
1Instituto Oceanográfico da Universidade de São Paulo, Brazil
2Instituto de Energia e Ambiente, da Universidade de São Paulo (IEE-USP), Brazil
Submission: February 04, 2019; Published: February 15, 2019
*Corresponding author: Joseph Harari, Instituto Oceanográfico da Universidade de São Paulo, Brazil
How to cite this article: Joseph H, Paola G P, Tiago C, Samuel H Y. A Study about Submarine Sewage Outfalls in the Coastal Region of the State of
Paraná - Brazil (26oS 48oW). Int J Environ Sci Nat Res. 2019; 17(1): 555960. DOI:10.19080/IJESNR.2019.17.555960
The following study aims to investigate the dispersion of pollutants in the coastal region of the State of Paraná, located on the southeastern continental shelf of Brazil, which includes two important estuarine systems, Paranaguá Estuarine Complex and Guaratuba Bay. Initially, hydrodynamic simulations were performed through the Delft3D modeling system, with the hydrodynamic module (FLOW); subsequently, the dispersion of pollutants was evaluated, using the Delft3D water quality module (WAQ). Considering that submarine sewage outfalls constitute an excellent solution for an efficient and sustainable management of effluents, the question to be addressed in the study is the possibility of evaluating this solution through numerical modeling. The results of the models are indicative of the best locations for the construction of submarine emissaries, thus constituting an important subsidy in the treatment of sewage in the coast of the State of Paraná, especially for coastal cities that suffer great environmental pressure due to activities related to tourism, fishing and maritime transport. The conclusion of the research is that the implementation and management of submarine outfalls must be done with suitable modeling of both hydrodynamics and dispersion, together with monitoring programs based on field measurements, to validate the models.
The State of Paraná is located at the southern region of Brazil, comprising two important estuarine systems, Paranaguá Estuarine Complex and Guaratuba Bay (Figure 1).
The climatology of the region and the circulation on the platform are governed by the presence of two meteorological systems: The Tropical Anticyclone (South Atlantic High) and the Polar Migratory Anticyclone. The winds from NE and E directions that occur on the continental shelf are associated with the presence of the Tropical Anticyclone, having an average intensity of 4m.s-1 , so the currents on the platform have predominant S - SW directions . The occurrence of frontal systems in the region is associated to the trajectory of the Polar Migratory Anticyclone, which propagates to N and NE directions ; during these meteorological events, winds from South may become strong and persistent enough to reverse the circulation on the platform, forcing Northeast currents . During the summer the cold fronts are less frequent, while in winter they are generally more frequent and stronger .
The dynamic of the Southeast Brazilian platform is therefore dominated by wind forcing, but tidal circulation may also be im
portant. The tidal currents are weaker and rotating in time, whereas the currents generated by the winds are persistent and stronger, parallel to the coast, predominantly to the West-Southwest, but turning to East-Northeast (and usually more intense) under the influence of frontal systems. However, within the Paranaguá Estuarine Complex and Guaratuba Bay, and adjacent coastal areas, the hydrodynamics is governed by two main forcings: fluvial discharges and tides. By continuity, the tidal currents are very intense at the entry channels of these estuaries .
The discharge of domestic sewage is one of the most common types of ocean pollution, either through diffuse pollution in watercourses or through concentrated sources, such as submarine outfalls. A submarine emissary consists of a long pipeline, implanted on the seabed, from which the effluents are released in deeper regions, thus allowing effective dilution .
In general, the amount to be disbursed in an emissary construction is much larger than in a sewage treatment plant. The latter can be built in stages, considering the populational demand, while the emissary must be built at once. However, when comparing reference values between a sewage plant and an emissary, per capita costs are lower for the second . In addition, the advantages
of a submarine outfall are numerous, including high efficiency
of sewage treatment and disposal, absence of visual pollution and
odors, low energy expenditure, low maintenance requirements
and less occupation of land .
Submarine emitters represent an extremely efficient way of
managing effluents resulting from large population centers. Both
Paranaguá Estuary and Guaratuba Bay have enormous urban
pressure due to the rapid and disorganized development of their
cities, mostly due to tourism, fishing and maritime transport activities.
An excellent option to improve the existing flaws in the
region’s basic sanitation system is the construction of sewage emissaries.
In fact, approximately 160.00 people live on the shores of the
Paranaguá Estuarine Complex, which also comprises two major
maritime ports, of Paranaguá and Antonina, the former being the
largest port complex for solid cargo shipments in Latin America
. The region’s sewage treatment system is increasingly suffering
from high demand for quality services, especially during summer
season, due to an enormous affluence of tourists.
The detailed study of hydrodynamics in the coastal region is
necessarily the first step in the decision making of the emissary
implementation process. Without this information, the construction
may not be efficient in recycling discharged organic material,
resulting in considerable environmental damage.
Considering that submarine sewage outfalls constitute an excellent
solution for an efficient and sustainable management of
domestic effluents, the question to be addressed in present study
is on the possibility of evaluating the efficiency of submarine outfalls,
for the dispersion of sewage in the region of interest, through
numerical modeling. The hypothesis adopted is that the results of
the modeling are indicative of the best sites for the construction
of submarine emissaries. Therefore, as a result of this study, from
the analysis of circulation and dispersion, possible locations for
the installation of submarine emissaries were evaluated, seeking
to improve the local sewage treatment.
The hydrodynamics and dispersion of pollutants simulations
along the coast of the State of Paraná were carried out using the
Delft3D modeling system , considering its hydrodynamic
module (FLOW) and water quality module (WAQ). To form a full
analysis of the processes that occurs in the study area, simulations
were performed for the month of January 2016, representing
summer conditions, and for the month of July 2016, representing
winter conditions. The comparison of model results allows thus
for a complete analysis of the hydrodynamic and water quality
conditions of the region.
The hydrodynamic model implemented in this study used
an Arakawa Type C grid, built in spherical coordinates, with grid
spacing around 350m, containing 300 points both in the directions
parallel and perpendicular to the coast, as shown in Figure 1.
In this study, data of mean sea level and tidal elevation, together
with currents, temperature and salinity profiles, were used
as forcing at the open contours of the grid. In addition, the wind
shear stress and radiation fluxes were applied at the sea surface
of the whole study area. All the boundary conditions were taken
from validated global models, frequently used in the most diverse
studies, and recognized for their reliability. Both meteorological
and oceanographic boundary data were interpolated into one-
Surface wind and radiation data were extracted from the global
atmospheric model of National Centers for Environmental
Prediction (NCEP) Climate Forecast System (CFS) , being interpolated
in space and time, for grid points and for hourly intervals.
Tidal data for the open contours of the grid were obtained
through the Oregon State University TOPEX/Poseidon Global Inverse
Solution (TPXO) database , for constituents M2, S2, N2,
K2, K1, O1, P1, Q1, Mf, Mm, M4, MS4, MN4 .
Vertical profiles of temperature and salinity at the open contours
of the study area were extracted from outputs of global
models of CMEMS - Copernicus Marine Environment Monitoring
Services [14,15]. These models also provided current profiles and
mean sea level oscillations at the open boundaries, associated to
meteorological and density effects. Finally, the Riemann invariant,
which combines water level and current data, was used at the
open boundaries of the grid as flow forcing . CMEMS ocean
models have horizontal resolution of approximately 9km.
The bathymetry of the region was obtained through the digitalization
of nautical charts, available on the website of the Marine
Hydrographic Center of the Brazilian Navy, in raster format, with
maximum depth around 50 meters. Figure 2 presents the bathymetry
of the grid, ten monitoring points of model results on the
continental shelf (P1 to P10) and seven monitoring points for the
discharge points of possible submarine outfalls to be constructed
along the coast of the State of Paraná (EM1 to EM7).
The FLOW module simulates transport phenomena resulting
from tide, river discharges and meteorological effects, including
the effect of density difference due to horizontal gradients of temperature
and salinity fields. The Delft3D - FLOW may be used for
flow simulations in seas, coastal regions, estuaries, reservoirs and
rivers. This module provides the hydrodynamic conditions used
by the other modules, being the first step for any simulation to be
developed by the Delft3D program.
Fluvial discharges were considered for both Paranaguá Estuary
(eight discharge points) and Guaratuba Bay (one discharge
point), with corresponding values of temperature, salinity
and flow. For Paranaguá the total river discharges ranged from
63.23m3.s-1 in January to 26.44m3.s-1 in July, while in Guaratuba
from 126.08m3.s-1 in January to 50.88m3.s-1 in July [5,17,18].
The water quality module (WAQ) is a three-dimensional model
used for representing water quality in natural and artificial environments. This module solves the advection-diffusion-reaction
equations for a predefined computational grid and several different
substances, using the finite element method . In present
case, the dispersion of fecal coliforms was simulated, discharged
in hypothetical positions for the construction of submarine outfalls,
in order to support their construction, based on the premise
of minimum influence of contaminants at the coast and adjacent
When the effluent is discharged in the marine environment
through a submarine outfall, a mixing process takes place. This
process presents three distinct zones: near-field, intermediate
field and far-field [20-22]. Near-field models are used to simulate
the blending processes in the region of the initial discharge. For
this, they rely on specific information about the effluent discharge,
such as number of emitter holes, their dimensions and flows, and
environmental characteristics of the receiving body. Far-field
models are important for simulations of dispersion of pollutants
regardless of how they are released into the marine environment.
Therefore, they are commonly used for coastal or estuarine regions
or in situations aiming to simulate the dispersion of effluents
from previous results of the near field models. In this study,
only far-field simulations were performed.
Coliform bacteria have been commonly used in the evaluation
of the microbiological quality of the environment [23,24]. In
addition to meeting the requirements of a good indicator of fecal
contamination, Escherichia coli, one of the species of the coliform
group, presents thermotolerant characteristics and habitat
restricted exclusively to the intestinal tract of humans and
warm-blooded animals. Thus, as they do not occur naturally in the
environment, this species constitutes an excellent indicator for the
presence of fecal contamination in the environment . According
to the Brazilian Council CONAMA, Resolution No. 274/2000,
concerning “freshwater, brackish and saline waters intended for
bathing (primary contact recreation)”, waters considered proper
for human use can be subdivided according to Table 1 .
In this study, values referring to a nearby outfall, the Praia
Grande Submarine Emissary - Subsystem 1 in Sao Paulo State,
were used as base for the initial discharge’s concentration in Parana
State. Information on the concentrations of pollutants discharged
by Praia Grande emissary, during summer and winter
seasons, was obtained from SABESP  and Yang & Harari .
Thus, in the simulations of the far field model, the following values
of E. coli were used for hourly discharges, 3.17x105MPN/100mL
and 1.36x105MPN/100mL, for summer and winter respectively, in
five levels equally spaced along the vertical, for the seven emissaries
proposed in this study. Standard values were used for other
Delft3D-WAQ parameters . In order to identify the pollution
of the marine environment exclusively from the proposed submarine
emissaries, zero concentration of fecal coliform was defined
as the initial condition for all the grid points.
In this study, time series from the Copernicus Marine Environment
Monitoring Service (CMEMS) database were used for validation
of the Delft3D model, by comparing mean sea level elevation,
and surface values of temperature, East-West component (EW)
and North-South component (NS) of currents. The validation used
data from the observational points on both the continental shelf
and emissary points (Figure 2).
For a complete analysis of the data, some statistical parameters
were used: the means of the differences between the results
of the two models (M_D), the standard deviation of these differences
(DP_D), the correlation coefficient between Delft3D and
CMEMS time series (CC), the significance of the correlation coefficient
(SIGN_CC), the mean absolute error (MAE), the absolute
error in relation to the amplitude (RMAE), the percent absolute
error in relation to the amplitude (RMAE%), and the Willmott
 index of agreement (IOA).
To analyze the model results for the months of January and
July 2016, the model was processed starting from rest in the
months of December 2015 and June 2016, respectively. This procedure
corresponds to the “heating” of the model, allowing the
January and July 2016 analyses to be performed without the influence
of a resting state initial condition.
For the comparison between the results from the Delft3D
model and the values obtained through the CMEMS database, statistical
calculations and graphs of the respective time series were
performed, for points P1 to P10 and EM1 to EM7. As an example,
the comparison between the time series of sea level elevation for
the P5 position, located on the continental shelf, are shown on Figure
3. Table 2 presents the mean statistical parameters for all the
analyzed positions (P01 to P10 and EM1 to EM7).
Examples of surface current distributions computed by FLOW
module are given on Figure 5, referent to times of maximum current
intensity for EM4, with corresponding values of 0.62 and
0.61m.s-1, which occurred on January 25th at 23:00, and on July
21st at 11:00.
Using Delft3D-WAQ module, E. coli concentration time series
were obtained for all emissary points, for several depth levels. The
results for point EM4, at the surface, in January and July 2016, are
shown on Figure 6. These results are relative to OBS1, the precise
location of the emissary, and at OBS5, at a distance of 1400 m
from EM4 towards the coastline, including the levels of satisfactory,
very good and excellent water quality, following the limits of
CONAMA Resolution No. 274/2000 (Table 1).
Figures 7 & 8 show the distribution of E. coli plumes at the
times of maximum concentration and maximum dispersion from
emissary EM4, in January and July 2016. At the times of maximum
concentration, the limit for satisfactory water quality was exceeded,
respectively on January 3rd 09:00 and July 27th 08:00 (see Figure
6); the times of maximum dispersion were January 25th 23:00
and July 21st 11:00
The results for both the FLOW (hydrodynamic) and the WAQ
(water quality) modeling, at the different points selected along
the coast and on the adjacent continental shelf, allowed a complete
analysis of the hydrodynamic conditions and dispersion of
pollutants in the coastal region of the State of Paraná, especially
in relation to the proposed sites for the construction of submarine
emissaries (Figure 2). The results obtained in the research and
analyses are discussed below, especially for emissary EM4, located
near the Paranaguá Estuarine Complex, with biggest population
involved and most important economic region of the study
The comparison between the results from the Delft3D coastal
model (with horizontal resolution of 350m) and the values obtained
through the CMEMS global database (with horizontal resolution
of about 9km) suggest that the coastal model can be considered
as fully validated. In terms of dispersion analysis, the most
important hydrodynamic parameter is the horizontal current,
which presented Index of Agreement IOA above 0.73 and percent
absolute error in relation to the amplitude below 20% (Table 2).
Results from the hydrodynamic simulation reproduced well
known characteristics of the shelf circulation, especially the influence
of the meteorological conditions. The general features do
not differ from summer to winter, as the angular histograms of
January and July are very similar (Figure 4). On the other hand,
frontal systems significantly change the current patterns at the
continental shelf, as presented on Figure 5, which represents the
standard circulation and the circulation under the effect of a cold
front, although within Paranaguá Estuary and Guaratuba Bay, and
adjacent areas, the tides act as primary effect. It is worth noting
that cold fronts occur both on summer and winter months, and although
being in general stronger and more frequent in winter, for
the simulated months of 2016, the cold system at the beginning of
January had stronger effect than that at the end of July.
For the analysis of the dispersion of pollutant’s plumes, the
focus is on the pollutants concentration between the discharge points and the coastline, by comparing the model results to the
CONAMA limits of water quality.
When dealing with submarine emissaries, the “Legal Mixture
Zone” is defined as a region where the parameters of the contaminants
are above the limits established by legislation. In practice,
this region is admittedly a zone of sacrifice. The better the emissary,
the smaller the mixture zone will be .
The E. coli concentration time series for EM4 and nearby
point (1440m towards the coastline), for January and July,
present several periods with very high values at the discharge
point, exceeding the limit established for the satisfactory quality
(800NMP/100mL); however, more than 1 km away from the
discharge point, the concentrations are negligible (Figure 6) .
Figures 7 & 8, corresponding to the E. coli plumes in the vicinity
of EM4, at the times of maximum concentration and maximum
dispersion, in January and July respectively, show that for the position
of the proposed emitter, high concentrations are limited to
regions close to the points of effluent discharge, without reaching
deeper areas or the coastline.
The characteristics of the pollutants dispersion here presented
and analyzed for EM4 were also observed for the remaining
The hydrodynamic results obtained are consistent with previous
studies carried out in the region. The analysis of the dispersion
associated to all seven emissaries proposed along the coast
of the State of Paraná, through the representation of the E. coli
distributions, indicates that high concentrations are limited to
the regions very close to the effluent discharge points, proving
that the local current systems do not cause the return of pollution
towards the coast. It is important to remember that the use of submarine emissaries is associated with a Legal Mixing Zone,
where concentrations of pollutants are still high, and constitute
an area of environmental sacrifice.
The use of submarine outfalls for the efficient treatment of
sewage has become increasingly common around the world. Effluent
disposal in the ocean is an efficient, rapid and sustainable
way to manage effluents. When considering the alternatives to
improve the sewage treatment system in Paraná State, submarine
outfalls are an excellent choice, due to their high efficiency, low
cost and limited environmental impact. But the implementation
and management of submarine outfalls must be done with suitable
modeling of both hydrodynamics and dispersion, together
with monitoring programs based on field measurements, to validate
To Institute of Oceanography (IO-USP) and Institute of Energy
and Environment (IEE-USP) of the University of Sao Paulo, for their
support to authors. To Conselho Nacional de Desenvolvimento
Científico e Tecnológico (CNPq), for providing a scholarship to
Paola Galluzzi Polesi.