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Citation: Muguirrima, P.; Chirinza,
N.; Zerpa, F.A.L.; Perez Baez, S.O.;
Pino, C.A.M. Sizing a System for
Treating Effluents from the
Mozambique Sugar Cane Company.
Sustainability 2024,16, 8334. https://
doi.org/10.3390/su16198334
Received: 16 August 2024
Revised: 13 September 2024
Accepted: 19 September 2024
Published: 25 September 2024
Copyright: © 2024 by the authors.
Licensee MDPI, Basel, Switzerland.
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4.0/).
sustainability
Article
Sizing a System for Treating Effluents from the Mozambique
Sugar Cane Company
Paulino Muguirrima 1, Nicolau Chirinza 1, Federico A. Leon Zerpa 2, * , Sebastian Ovidio Perez Baez 2
and Carlos Alberto Mendieta Pino 2
1Faculty of Science and Technology, Zambezi University, Beira 2100, Mozambique;
paulino.muguirrima101@alu.ulpgc.es (P.M.); nicolau.chirinza101@alu.ulpgc.es (N.C.)
2Institute of Environmental Studies and Natural Resources (iUNAT), University of Las Palmas de Gran
Canaria (ULPGC), 35001 Las Palmas de Gran Canaria, Spain; sebastianovidio.perez@ulpgc.es (S.O.P.B.);
carlos.mendieta@ulpgc.es (C.A.M.P.)
*Correspondence: federico.leon@ulpgc.es
Abstract: The sugar industry must be managed in a manner that encourages innovation with regard
to the waste generated throughout the process. The organic load of sugar mill waste is high, as is
its potential to pollute water bodies at various stages of the production process, including cooling
bearings, mills, sugar cane washing, bagasse waste and cleaning products. It is therefore necessary
to identify treatment mechanisms that not only reduce this waste but also return purer water to
the environment, combining the reuse of water in various applications. The objective of this study
was to analyze the results of the physical and chemical properties of the effluents generated and the
principal treatment technologies employed for the remediation of industrial wastewater from sugar
factories. The wastewater from Mozambique’s sugar mills has high levels of dissolved or suspended
solids, organic matter, pressed mud, bagasse and atmospheric pollutants. The BOD/COD ratio is
low (<2.5), indicating the need for secondary treatment or, more specifically, biological treatment.
This can be achieved through humid systems built from stabilization ponds, with the resulting water
suitable for reuse in agricultural irrigation. In this work, an educational proposal has been developed
for engineering students where they learn to calculate and optimize, among other parameters, the
natural wastewater treatment and compare it with a conventional wastewater treatment.
Keywords: environmental management; sugar industries; wastewater; treatment systems
1. Introduction
Industrialization is a crucial factor in a country’s economic and social development.
However, the environmental impact of industrial activities represents a significant global
concern. The reduction and control of water consumption in industrialized countries is
linked to the optimization of industrial and domestic wastewater treatment processes. At
the present time, there is a global interest in avoiding or reducing the effects of pollution
on the environment. However, despite this interest, contamination continues to occur on
a large scale, particularly given that a significant proportion of the effluents generated in
industrial production processes are difficult to remedy through conventional treatments.
Furthermore, the food sector is one of the fields that consume the most water and produce
the most effluents per unit of production.
The process of transforming sugar cane is a highly complex one, resulting in the
generation of considerable quantities of wastewater. This wastewater comprises both liquid
and solid discharges, originating from the processing, handling and transformation of the
sugar cane itself.
The aforementioned discharges are the result of a number of processes, including
cooling, heating, extraction and reaction, as well as the washing of products and the control
of other rejected by-products. The quantities and qualities of these discharges are highly
Sustainability 2024,16, 8334. https://doi.org/10.3390/su16198334 https://www.mdpi.com/journal/sustainability
Sustainability 2024,16, 8334 2 of 16
variable. As the water progresses through the chambers and tanks, from the stage of
extraction to sugar crystallization, its pollutant load in terms of organic matter and a
range of pollutants increases significantly (3). However, this production route results in
the generation of considerable quantities of solid waste, including cane straw, bagasse,
molasses and pressing sludge. Bagasse is the residual material obtained after the sugar
cane stalks have been pressed (crushed) in order to extract the juice. The processing of one
ton of sugar cane results in the generation of between 0.25 and 0.30 tons of bagasse. In
39 factories in Brazil, the average yield of bagasse is 0.28 tons per ton of processed sugar
cane [
1
–
3
]. Other studies have indicated that 0.14 tons of bagasse (dry mass) and 0.14 tons
of straw (stalks) are obtained from one ton of sugar cane. Figure 1below illustrates the
flow of the sugar production process, delineating the type of effluent removed from the
process at each stage and its characterization at the subsequent point.
Sustainability 2024, 16, x FOR PEER REVIEW 2 of 16
control of other rejected by-products. The quantities and qualities of these discharges are
highly variable. As the water progresses through the chambers and tanks, from the stage
of extraction to sugar crystallization, its pollutant load in terms of organic maer and a
range of pollutants increases significantly (3). However, this production route results in
the generation of considerable quantities of solid waste, including cane straw, bagasse,
molasses and pressing sludge. Bagasse is the residual material obtained after the sugar
cane stalks have been pressed (crushed) in order to extract the juice. The processing of one
ton of sugar cane results in the generation of between 0.25 and 0.30 tons of bagasse. In 39
factories in Brazil, the average yield of bagasse is 0.28 tons per ton of processed sugar cane
[1–3]. Other studies have indicated that 0.14 tons of bagasse (dry mass) and 0.14 tons of
straw (stalks) are obtained from one ton of sugar cane. Figure 1 below illustrates the flow
of the sugar production process, delineating the type of effluent removed from the process
at each stage and its characterization at the subsequent point.
Figure 1. Sugar production flowchart, Source: Tongaat Hule, 2023.
The objective of this study was to analyze the results of the physical and chemical
properties of the effluents generated and the principal treatment technologies employed
for the remediation of industrial wastewater from sugar factories. The wastewater from
Mozambique’s sugar mills has high levels of dissolved or suspended solids, organic mat-
ter, pressed mud, bagasse and atmospheric pollutants.
Moreover, an educational proposal has been developed for engineering students
where they learn to calculate and optimize, among other parameters, the natural
wastewater treatment and compare it with a conventional wastewater treatment.
2. Materials and Methods
2.1. Description of Sugar Industry Effluents
In all areas of the food industry, food production is undertaken with considerable
energy consumption, and substantial quantities of waste are generated as a consequence
of technological processes. Consequently, the principal challenges confronting food tech-
nology are associated with the management of energy and industrial effluents. These ef-
fluents are of a solid, semi-solid and liquid nature and can be classified into two categories.
The first category comprises waste from the harvesting operation, which includes cane
leaves and tips. The second category consists of waste from the cane processing flow,
which encompasses bagasse, bagasse ash from incineration, pressing sludge (sludge from
juice sedimentation and residual cake from juice filtration), and bearing lubricants in mills
[4]. Normally, crushing one ton of sugar cane yields around 280–300 kg of bagasse with
50% moisture, 30 kg of pressed mud and 41 kg of molasses. The energy from sugar cane
is distributed according to the three main components extracted from the stalks: juice
(sugar or ethanol), fibers (bagasse) and leaves (LT) have the same level of energy content,
so currently only two thirds of the total energy potential is used. The energy content of
one ton of sugar cane is 6560 MJ, distributed as follows: 140 kg of sugar for 2340 MJ; 280
kg of bagasse (50% moisture) for 2110 MJ; and 280 kg of LT (50% moisture) for 2.11 MJ [5].
Figure 1. Sugar production flowchart, Source: Tongaat Hulett, 2023.
The objective of this study was to analyze the results of the physical and chemical
properties of the effluents generated and the principal treatment technologies employed
for the remediation of industrial wastewater from sugar factories. The wastewater from
Mozambique’s sugar mills has high levels of dissolved or suspended solids, organic matter,
pressed mud, bagasse and atmospheric pollutants.
Moreover, an educational proposal has been developed for engineering students where
they learn to calculate and optimize, among other parameters, the natural wastewater
treatment and compare it with a conventional wastewater treatment.
2. Materials and Methods
2.1. Description of Sugar Industry Effluents
In all areas of the food industry, food production is undertaken with considerable
energy consumption, and substantial quantities of waste are generated as a consequence of
technological processes. Consequently, the principal challenges confronting food technol-
ogy are associated with the management of energy and industrial effluents. These effluents
are of a solid, semi-solid and liquid nature and can be classified into two categories. The
first category comprises waste from the harvesting operation, which includes cane leaves
and tips. The second category consists of waste from the cane processing flow, which
encompasses bagasse, bagasse ash from incineration, pressing sludge (sludge from juice
sedimentation and residual cake from juice filtration), and bearing lubricants in mills [
4
].
Normally, crushing one ton of sugar cane yields around 280–300 kg of bagasse with 50%
moisture, 30 kg of pressed mud and 41 kg of molasses. The energy from sugar cane is
distributed according to the three main components extracted from the stalks: juice (sugar
or ethanol), fibers (bagasse) and leaves (LT) have the same level of energy content, so
currently only two thirds of the total energy potential is used. The energy content of one
ton of sugar cane is 6560 MJ, distributed as follows: 140 kg of sugar for 2340 MJ; 280 kg of
bagasse (50% moisture) for 2110 MJ; and 280 kg of LT (50% moisture) for 2.11 MJ [5].
Sustainability 2024,16, 8334 3 of 16
2.2. Sample Collection and Analysis
The sugarcane transformation process is highly complex, generating significant quan-
tities of wastewater comprising liquid and solid discharges from the processing, handling
and transformation of sugarcane. These discharges result from cooling, heating, extraction
and reaction processes, as well as the washing of by-products and the control of other
rejected by-products [
6
]. After collecting and analyzing the effluents at the three points
of the factory, namely boilers, workshops and pumps, the analytical results for TSS show
that the workshop unit had the highest TSS of 22 mg/L, a value which is low in relation
to the values established by Mozambican legislation of 50 mg/L. As for TDS, the values
at all the collection points were as high [1137–1392] (mg/L) in relation to the value of
the legislation and in comparison with other sugar industries [
6
]. These TDS values are
due to the industry’s high crushing rate which as a result generates a greater amount of
fly ash and heavy ash. The bagasse stacking plant is also nearby, so the coarse bagasse
particles are mixing with the final effluent. In the mills, particularly in the bearings, there
is a lot of spillage of lubricants due to the long use of these vises, which have been in
use since national independence (1975 independence of Mozambique, post-colonial era)
and have several leaks which are the main contributors to TDS. BOD is the biochemical
oxygen demand (BOD); it represents the amount of oxygen consumed by bacteria and other
microorganisms while they decompose organic matter under aerobic (oxygen is present)
conditions at a specified temperature. The BOD and COD values were analyzed for each
collection point from the entrance and exit of the sector in the factory, and in the end the
average in each sector and in general in the total effluents of the factory was evaluated. All
the BOD and COD values were found to be higher than the standard values of 50 mg/L and
250 mg/L, respectively, according to Mozambican legislation [
6
]. The raw effluent values
at the outlet showed BOD and COD values of 731 mg/L and 1351 mg/L, respectively, a
COD/BOD ratio of approximately 2:1, showing that the biodegradable fraction is high
and biological treatment technology is the most suitable method. On the other hand, these
high values can be increased by the spillage of molasses and sugar leaked onto the floors
of the mills, which are swept and washed; the parameters of these effluents are tabulated
in [
6
]. Among the physical-chemical parameters of the sugar industry’s wastewater, pH
and temperature were measured immediately on site, while the other physical-chemical
parameters, such as total solids (ST), suspended solids (TSS), BOD, COD, chloride and
sulphate tests, turbidity, alkalinity, density and conductivity, were analyzed in our labo-
ratories here at Zambezi University (Table 1). To analyze these values, several items of
equipment and reactors from the Panreac company of Barcelona (Spain) were used. Also, a
spectrophotometer, conductivity meter, pH meter and turbidity meter from Hach of Bilbao
(Spain) were employed.
Table 1. Values of the physico-chemical parameters of the Mozambique sugar plantation.
Parameters Pump Boilers Workshops Decree 18/2004
Temperature (◦C) 45 50 40 ≤24
PH 6.34 8.13 6.96 6–9
Hardness (mg/L) 240.63 490.20 177.13
Alkalinity (mg/L) 187.00 215.00 138.33
Chlorides (mL/g) 105.60 172.63 81.43
TDS (mg/L) 1392.00 1174.67 1137.00
TSS (mg/L) 17.33 25.67 22.00 50
Turbidity (NTU) 9.15 11.16 15.03
BOD (m/L) 731.67 628.00 675.00 50
COD (m/L) 1048.67 991.33 1351.00 250
Sustainability 2024,16, 8334 4 of 16
Table 1. Cont.
Parameters Pump Boilers Workshops Decree 18/2004
Conductivity (S/cm) 2.49 1.96 7.83
Phosphate (mg/L) 11.91 16.22 16.23 2
Nitrogen (mg/L) 14.11 10.58 11.39 10
2.3. Effluent Treatment Techniques
In environmental engineering and more specifically in effluent treatment technologies,
the concentration of organic matter in the effluent is measured using two main analytical
parameters, biochemical oxygen demand (BOD) and chemical oxygen demand (COD). BOD
shows the amount of oxygen required to stabilize carbonaceous organic matter through
biochemical processes, indirectly indicating the amount of biodegradable organic carbon,
while COD measures the consumption of oxygen due to the chemical oxidation of organic
matter, indirectly measuring the content of organic matter present [
7
]. The choice of
treatment technologies for any effluent depends on the COD/BOD ratio, according to
a previous study [
8
]. The author of that study suggests the following: Low COD/BOD
ratio (<2.5): the biodegradable fraction is high, and the use of biological treatment is
recommended. Intermediate COD/BOD ratio (from 2.5 to 4.0): the biodegradable fraction
is not high, and it is recommended to carry out treatability tests to validate the use of
biological treatment. Biological treatment refers to secondary level treatment [
9
,
10
]. High
COD/BOD ratio (>4.0): the inert (non-biodegradable) fraction present in the effluent is
high, it is not recommended to use a biological system, and the potential for using a
chemical treatment system should be assessed [
11
]. The processes used to treat industrial
effluents can be categorized as physical, chemical and biological. Physical treatment
includes processes in which there is no chemical or biological alteration of the substances.
It is a primary treatment that aims to use physical phenomena to remove particles such as
suspended solids and separate immiscible liquids. Examples of physical processes include
filtration, flocculation and sedimentation [
9
]. Chemical treatment involves carrying out
chemical reactions to improve the quality of the wastewater. In this type of treatment,
neutralization is commonly used to adjust the pH of the effluent. Operations such as
electrochemical processes and advanced oxidative processes are also classified as chemical
treatment [
12
]. Most effluent treatment plants use biological processes to remove organic
compounds from wastewater. Biological treatment aims to break down polluting substances
into stable products through the biochemical reactions of microorganisms, mostly bacteria.
The main biological processes used in this type of wastewater treatment are the following:
aerobic, anaerobic, facultative, and a combination of the three types. In aerobic biological
treatment, oxygen is present and used by microorganisms to degrade organic compounds
into carbon dioxide and water. An example of an aerobic reactor widely used for effluent
treatment is the conventional activated sludge reactor [10].
2.3.1. Activated Sludge
The purpose of wastewater treatment using the activated sludge process is to biochemi-
cally oxidize dissolved organic matter in colloidal suspension by microorganisms, clustered
in flakes, which are kept in suspension, forming suspended biomass within a reactor. This
can be inserted into the treatment line as a secondary treatment (when the objective is
limited to reducing BOD, COD and TSS) and/or as a tertiary treatment (when the aim is to
remove nutrients), and it is possible to combine secondary and tertiary treatments in a sin-
gle reactor. The biomass (live and dead microorganisms) and non-biodegradable SS present
in the biological reactor effluent must be separated from the liquid phase, generally in a
decanter downstream of the biological reactor, because their concentration of organic matter
and TSS presents values incompatible with discharge into a receiving environment [
13
]. It
can even be said that this separation operation is an integral part of biological treatment.
Sustainability 2024,16, 8334 5 of 16
The biodegradation process can be significantly intensified by increasing the concentra-
tion of biomass in the reactor. This increase is achieved by recirculating sedimented sludge
from the decanter to the reactor, since the TSS content of the sludge is largely composed of
biological flocs. The part of the sludge that is not recirculated to the biological reactor is
called excess sludge and must be periodically removed by sludge purging.
The efficiency of the Activated Sludge process is affected by the electrical energy of the
aeration system, which is essential to supply oxygen to the microorganisms that degrade
organic matter and offers a very efficient treatment, but at a higher electrical cost due to
the demand for continuous aeration. The COD/BOD ratio is an important indicator of
the biodegradability of the effluents and the effectiveness of the treatment processes. Each
range of this ratio suggests a specific type of treatment that may be more appropriate. Each
type of treatment must be considered in the specific context of the effluent in question and
the regulatory requirements for disposal.
2.3.2. UASB Reactor
The UASB anaerobic reactor is an upflow treatment unit that uses the anaerobic process
to degrade matter in the form of sludge using colonies of anaerobic microorganisms, such as
sewage. For our project, this technology would not be ideal because to maintain the upflow
within the reactor we need electric pumps, which means consuming electrical energy.
Considering the cost of energy, which has been increasing, the most ideal solution would
be to build an economically viable and environmentally acceptable system which would
have a higher efficiency in terms of removing the effluent load. It would be necessary to
build a gas turbine to compensate for the production and consumption of electrical energy
from the grid. If we look at the issue of HRT in these systems, it is greater than 60 days
in relation to the operational lagoons, there is the possibility of generating bad odors and
corrosion of the structure, and Sofala being in the coastal area, this phenomenon would
occur more quickly; or, if we look at materials that are more efficient in terms of corrosion,
their acquisition value would be higher.
2.3.3. Wetlands
Macrophyte beds (known in the literature as constructed wetlands) are nature-based
systems that imitate and enhance the action of marshy areas in purifying the water that
flows into them. The word “macrophytes” refers to tall plants, while “microphytes” are
small plants commonly referred to as algae. These beds constitute secondary treatment
units that must include a primary treatment stage upstream (septic tank or anaerobic
lagoon) to retain solids that would otherwise end up clogging the bed and making treat-
ment unfeasible. The purification mechanisms in a macrophyte bed include the following:
(1) Physical mechanisms: sedimentation, filtration, adsorption. (2) Chemical mechanisms:
precipitation (nitrogen and phosphorus), oxidation and reduction (heavy metals). (3) Bi-
ological mechanisms: bacterial metabolism (BOD, nitrogen), phytological metabolism
(pathogenic microorganisms), phytological adsorption (nitrogen, phosphorus, heavy met-
als). (4) Natural decay: pathogenic microorganisms. The wetlands play an important role
in the development of ecosystems. They are home to a wide variety of invertebrate and
vertebrate animals whose activities significantly affect ecological processes, such as the
disintegration and consumption of organic material by insects, insect larvae and earth-
worms. The development of the invertebrate community naturally stimulates the spread of
predators, which include resident amphibians and birds that pass through the area.
The other macrophyte systems, submerged aquatic plants and subsurface flow, feature
plants of different species, namely reed (Phragmites australis), bulrushes (Schoenoplectus
lacustris,Typha latifolia) and rush (Juncus effusus), which can be planted in soil or in a gravel
layer. The dimensions of a macrophyte bed for wastewater treatment are determined
by the hydraulic retention time and simultaneously by the organic load, both quantified
empirically, taking into account the natural factors mentioned above (temperature, wind
speed and soil porosity). The level of pollutant removal is higher for a high retention time
Sustainability 2024,16, 8334 6 of 16
(6 to 8 days) and low flow velocities (EU Guide, 2001). Subsurface flow beds can also be
dimensioned for a certain reduction in influent BOD [7,11,14,15].
A=Q∗Ln(BODaBOe)/(KT ∗E∗n)(1)
where Ais the surface area of the macrophyte [m
2
], Qis the average influent flow rate
[m
2
/d], BOD
a
and BOD
e
are BOD concentrations in the influent and effluent, respectively
[mg/L], KT is the BOD reduction rate [d
(−1)
], at the design temperature, T[
◦
C] determined
by the following relationship:
KT =K20 ×1.06T−20 (2)
where K20 is the BOD reduction rate [d
(−1)
] at 20
◦
C, Eis the water height in the wetland [m]
and n is the porosity of the support medium. Looking at these two systems and evaluating
the effluents provided in Table 1, wetlands are more effective for removing effluents in
which the focus would be phosphate and nitrogen but at temperatures above
≤
24
◦
C, which
can be a problem for wetlands because high temperatures can affect the effectiveness of
plants and microorganisms for their treatment. In relation to lagoon systems, macrophyte
beds require a larger installation area than a facultative pond, as well as more construction
material. However, they can be used in combination with facultative ponds [
16
–
18
]. Below
is a representation of a combination of facultative ponds and wetlands in Figure 2.
Sustainability 2024, 16, x FOR PEER REVIEW 6 of 16
𝐴
=𝑄∗𝐿𝑛(𝐵𝑂𝐷
𝐵𝑂)/(𝐾𝑇 ∗ 𝐸 ∗ 𝑛) (1)
where A is the surface area of the macrophyte [m2], Q is the average influent flow rate
[m2/d], BODa and BODe are BOD concentrations in the influent and effluent, respectively
[mg/L], KT is the BOD reduction rate [d(−1)], at the design temperature, T [°C] determined
by the following relationship:
𝐾𝑇 = 𝐾20 × 1.06 (2)
where K20 is the BOD reduction rate [d(−1)] at 20 °C, E is the water height in the wetland
[m] and n is the porosity of the support medium. Looking at these two systems and eval-
uating the effluents provided in Table 1, wetlands are more effective for removing efflu-
ents in which the focus would be phosphate and nitrogen but at temperatures above ≤24
°C, which can be a problem for wetlands because high temperatures can affect the effec-
tiveness of plants and microorganisms for their treatment. In relation to lagoon systems,
macrophyte beds require a larger installation area than a facultative pond, as well as more
construction material. However, they can be used in combination with facultative ponds
[16–18]. Below is a representation of a combination of facultative ponds and wetlands in
Figure 2.
Figure 2. A combination system of facultative pond and wetlands.
Considering the data presented in reference [6], we have elected to utilize a combi-
nation of stabilization ponds as the optimal solution for this particular undertaking. Sta-
bilization ponds are biological treatment systems that employ bacteriological oxidation
(either aerobic or anaerobic fermentation) and/or photosynthetic reduction by algae to
stabilize organic maer. The diagram below illustrates the sequence of treatment pro-
cesses for these effluents, which will be conducted in the following order: physical, chem-
ical, and finally biological. The laer will focus on the stabilization ponds and their sizing
(Figure 3).
Figure 3. A combination system of anaerobic pond and wetlands.
3. Results
Firstly, preliminary treatment is carried out, where solid parts of the effluent are re-
moved, such as silt and residual bagasse from extraction that may be in the effluent. This
usually consists of the following stages: grating, desander and Parshall flume. The main
purpose of this treatment is to remove coarse solids and sand through physical removal
mechanisms, to protect the sewage transport equipment (pumps and pipes), to protect the
subsequent treatment units, and to protect the body receiving the treated effluent. In
Figure 2. A combination system of facultative pond and wetlands.
Considering the data presented in reference [
6
], we have elected to utilize a com-
bination of stabilization ponds as the optimal solution for this particular undertaking.
Stabilization ponds are biological treatment systems that employ bacteriological oxidation
(either aerobic or anaerobic fermentation) and/or photosynthetic reduction by algae to
stabilize organic matter. The diagram below illustrates the sequence of treatment processes
for these effluents, which will be conducted in the following order: physical, chemical, and
finally biological. The latter will focus on the stabilization ponds and their sizing (Figure 3).
Sustainability 2024, 16, x FOR PEER REVIEW 6 of 16
𝐴
=𝑄∗𝐿𝑛(𝐵𝑂𝐷
𝐵𝑂)/(𝐾𝑇 ∗ 𝐸 ∗ 𝑛) (1)
where A is the surface area of the macrophyte [m2], Q is the average influent flow rate
[m2/d], BODa and BODe are BOD concentrations in the influent and effluent, respectively
[mg/L], KT is the BOD reduction rate [d(−1)], at the design temperature, T [°C] determined
by the following relationship:
𝐾𝑇 = 𝐾20 × 1.06 (2)
where K20 is the BOD reduction rate [d(−1)] at 20 °C, E is the water height in the wetland
[m] and n is the porosity of the support medium. Looking at these two systems and eval-
uating the effluents provided in Table 1, wetlands are more effective for removing efflu-
ents in which the focus would be phosphate and nitrogen but at temperatures above ≤24
°C, which can be a problem for wetlands because high temperatures can affect the effec-
tiveness of plants and microorganisms for their treatment. In relation to lagoon systems,
macrophyte beds require a larger installation area than a facultative pond, as well as more
construction material. However, they can be used in combination with facultative ponds
[16–18]. Below is a representation of a combination of facultative ponds and wetlands in
Figure 2.
Figure 2. A combination system of facultative pond and wetlands.
Considering the data presented in reference [6], we have elected to utilize a combi-
nation of stabilization ponds as the optimal solution for this particular undertaking. Sta-
bilization ponds are biological treatment systems that employ bacteriological oxidation
(either aerobic or anaerobic fermentation) and/or photosynthetic reduction by algae to
stabilize organic maer. The diagram below illustrates the sequence of treatment pro-
cesses for these effluents, which will be conducted in the following order: physical, chem-
ical, and finally biological. The laer will focus on the stabilization ponds and their sizing
(Figure 3).
Figure 3. A combination system of anaerobic pond and wetlands.
3. Results
Firstly, preliminary treatment is carried out, where solid parts of the effluent are re-
moved, such as silt and residual bagasse from extraction that may be in the effluent. This
usually consists of the following stages: grating, desander and Parshall flume. The main
purpose of this treatment is to remove coarse solids and sand through physical removal
mechanisms, to protect the sewage transport equipment (pumps and pipes), to protect the
subsequent treatment units, and to protect the body receiving the treated effluent. In
Figure 3. A combination system of anaerobic pond and wetlands.
3. Results
Firstly, preliminary treatment is carried out, where solid parts of the effluent are
removed, such as silt and residual bagasse from extraction that may be in the effluent. This
usually consists of the following stages: grating, desander and Parshall flume. The main
purpose of this treatment is to remove coarse solids and sand through physical removal
mechanisms, to protect the sewage transport equipment (pumps and pipes), to protect
the subsequent treatment units, and to protect the body receiving the treated effluent. In
Sustainability 2024,16, 8334 7 of 16
addition to the physical removal mechanisms, this system has a flow measurement unit
(e.g., Parshall flume) [
13
,
19
]. The grating is made of iron or steel grids, depending on the
corrosive action of the effluent, and the spacing between the bars varies between 0.5 and
2 cm, which can be simple grids or mechanized grids depending on the volume of solids to
be removed and to facilitate cleaning. The desander removes the coarse solids that may be
present in the effluent, such as sand and earth, especially during rainy periods, which need
to be separated. This is to prevent these particles from damaging the structures and causing
blockages in the pipes and negative interference in biological processes. The Parshall flume
is used to take flow measurements which, by means of throttling and bouncing, establish,
for a given vertical section upstream, a relationship between the flow rate and the water
table in that area. They have a low pressure drop and are very accurate at reading flow
rates [19]. Figure 4below shows the flume model and the flow calculation ratios.
Sustainability 2024, 16, x FOR PEER REVIEW 7 of 16
addition to the physical removal mechanisms, this system has a flow measurement unit
(e.g., Parshall flume) [13,19]. The grating is made of iron or steel grids, depending on the
corrosive action of the effluent, and the spacing between the bars varies between 0.5 and
2 cm, which can be simple grids or mechanized grids depending on the volume of solids
to be removed and to facilitate cleaning. The desander removes the coarse solids that may
be present in the effluent, such as sand and earth, especially during rainy periods, which
need to be separated. This is to prevent these particles from damaging the structures and
causing blockages in the pipes and negative interference in biological processes. The Par-
shall flume is used to take flow measurements which, by means of throling and bounc-
ing, establish, for a given vertical section upstream, a relationship between the flow rate
and the water table in that area. They have a low pressure drop and are very accurate at
reading flow rates [19]. Figure 4 below shows the flume model and the flow calculation
ratios.
Figure 4. Parshall flume model for flow measures [19].
To calculate the flow rate, we use the following relationship:
𝑄=𝑘×ℎ
(3)
where
Q—flow in m3/s
k and n—coefficients as a function of throat width
h—water blade.
Typical values for calculating effluent flow in Parshall flumes are shown below in
Table 2.
Table 2. Values of the constants k and n [13,19,20].
Throat (W) W (m) n k
3″ 0.076 1546 0.176
6″ 0.152 1580 0.381
9″ 0.229 1530 0.535
1″ 0.305 1522 0.690
2″ 0.610 1550 1.426
3″ 0.915 1566 2.182
4″ 1.220 1578 2.935
6″ 1.830 1595 4.515
8″ 2.440 1606 6.101
After passing through the previous stages, in particular the Parshall flume, the efflu-
ent goes to a stabilization tank, where it is completely homogenized. This is where some
preliminary treatment processes take place, such as minimizing shocks caused by over-
loading the system, diluting substances in the effluent and stabilizing the pH, in order to
improve the final quality of the treated effluent. In this way, the effluent becomes suitable
for biological treatment. A detention time of between 3 and 6 days is used to calibrate the
Figure 4. Parshall flume model for flow measures [19].
To calculate the flow rate, we use the following relationship:
Q=k×hn(3)
where
Q—flow in m3/s
kand n—coefficients as a function of throat width
h—water blade.
Typical values for calculating effluent flow in Parshall flumes are shown below in
Table 2.
Table 2. Values of the constants k and n [13,19,20].
Throat (W) W (m) n k
3′′ 0.076 1546 0.176
6′′ 0.152 1580 0.381
9′′ 0.229 1530 0.535
1′′ 0.305 1522 0.690
2′′ 0.610 1550 1.426
3′′ 0.915 1566 2.182
4′′ 1.220 1578 2.935
6′′ 1.830 1595 4.515
8′′ 2.440 1606 6.101
After passing through the previous stages, in particular the Parshall flume, the ef-
fluent goes to a stabilization tank, where it is completely homogenized. This is where
some preliminary treatment processes take place, such as minimizing shocks caused by
overloading the system, diluting substances in the effluent and stabilizing the pH, in order
to improve the final quality of the treated effluent. In this way, the effluent becomes suitable
Sustainability 2024,16, 8334 8 of 16
for biological treatment. A detention time of between 3 and 6 days is used to calibrate the
equalizer tank [
21
]. The established detention time is the most suitable for stabilization
and the first biological treatment. A time of less than 3 days could cause the methanogenic
bacteria in the effluent in the lagoon to exceed their own reproduction rate, which may be
slow, depending on the temperature and the time of year. Times longer than 6 days can
promote the emergence of an aerobic zone in the lagoon. Such a condition would be fatal
to anaerobic bacteria. The detention times recommended in industry standards are shown
in Table 3below [20].
Table 3. Recommended retention times.
Average Temperature of the
Lagoon in the Coldest Month (◦C) Detention Time (d)
Start of Plan End of Plan
≤20 ≥4≤6
>20 ≥3≤5
When the effluent leaves the factory, its temperature plays an important role in the
degradation process in the lagoon. If it coincides with a time when the ambient temperature
is warm, then there will be greater degradation of the effluent in terms of BOD removal;
but if it is cold, the degradation time will be longer [
8
]. This means that the temperature of
the effluent at the outlet may not require a longer detention time for anaerobic processes.
However, the values measured at the plant ranged from 40
◦
C to 50
◦
C, and taking into
account that the area where the plant is located has high ambient temperatures ranging
from 29
◦
C to 38
◦
C [
22
], this could lead to a shorter detention time and greater efficiency
in removing the load from the effluent. Stabilization pond systems comprise units specially
designed and built for the purpose of treating effluents, and are the simplest form of
wastewater treatment [
23
], due to their low operating cost, but also due to the good
efficiencies in removing organic matter, which can exceed 90% BOD removal [
24
] and
pathogenic microorganisms, with 99.9% removal of fecal coliforms in the case of maturation
ponds [
19
] that can be achieved in these systems. Among stabilization pond systems, the
facultative pond process is the simplest, depending solely on natural phenomena, according
to [
20
]. To calculate the volume of stabilization ponds, we need the hydraulic retention
time (HRT), which is the time required for the effluent to remain in the pond for proper
treatment. The typical HRT for stabilization ponds varies from 20 to 50 days, depending
on the organic load and the temperature of the environment [
13
]. According to our data,
the temperatures of the effluent leaving the factory ranged from 400
◦
C to 50
◦
C, so we can
consider the lowest HRT to be between 15 and 20 days, depending on whether the season
is cold or hot, which is why we found the highest value to be 20 days [25–29].
Veql =Qind ∗TRH (4)
where
Veql—volume of effluent in m3/day
Qind—effluent flow rate
Tdetention—Hydraulic Retention Time (HRT) in days
As the plant pumps 900 to 1000 m
3
/h, this must be converted to m
3
/day: Q= 900
×
24 h a1000
×
24 h for the flow range, which gives 21,600 m
3
/day to 24,000 m
3
/day. With this
flow data, we can estimate the volume of effluent in the lagoon and estimate its occupied area;
bearing in mind that according to [
30
] the typical depth of anaerobic lagoons varies from 3
to 5 m, for our work we consider a depth of 4 m. From here, we calculate the volume of the
lagoon considering a HRT of 20 days (an average value):
V=21600 m3/day ×20 days or 24000 m3/day ×20 days
V=432000 m3or V =480000 m3(5)
Sustainability 2024,16, 8334 9 of 16
With this volume of effluent and adopting a minimum depth of 4 m [
19
], we can find
the area of our stabilization pond.
Area =V
Dee p =432000 m3
4 m or 480000 m3
4 m (6)
Area =108000 m2a120000 m2
When the temperature of the effluent is higher, the microbial activity in the anaerobic
and facultative treatment process tends to be even more efficient, potentially allowing the
hydraulic retention time (HRT) to be reduced [
31
–
35
]. By analyzing the data in the table,
we can analyze the load of the effluent contaminated using the following equation:
CDBO =S0×Qma x
1000 (7)
In which
CBOD—BOD load in kg BOD/day
S0—BOD concentration (S0= 731.67 mg/L)
Qmax—maximum effluent flow (Qmax = 24,000 m3/day)
With this data we can estimate the load, as follows:
CDBO =S0xQmax
1000 =731.67 mg/L 1 kg
1000000 ×24000 m3/dia
1000 =17.560 kg/day (8)
Next, we need to determine the surface application rate (LS). According to [
19
],
there are several empirical equations available internationally that correlate the surface
application rate (LS) and the local temperature. This work will use the equation proposed
by [14], which is stated to be applicable worldwide.
Ls=350 ×h1.107 −0.002 ×T0
min iT0
min −25 (9)
In which
Ls—surface application rate, in kgBOD/ha·day
T0
min —average air temperature in the coldest month of the year (T◦min = 20 ◦C).
Ls=350 ×[1.107 −(0.002 ×20)]20−25 =338.83 kgBOD/ha·day (10)
Next, we calculate the area required (A
lagf
) for the implementation of the lagoons.
According to [
20
], the area required for the implementation of the facultative lagoon is
calculated based on the following equation:
Ala g f =CBOD
Ls
=17.560 ka/day
338.83 kgBOD/ha·day =0.0518 ha (11)
Therefore, 0.0518 hectares, or 51.8 m
2
, will be needed to set up the ponds. Comparing
the values in (4) and (9) leads us to make series connections for each type of stabilization
pond, i.e., anaerobic, aerobic and facultative ponds, and further on we will show how
many of each type will be needed. Facultative ponds are made up of three treatment
zones: aerobic, anaerobic and facultative (Figure 5). Formed by algae and aerobic bacteria,
the aerobic zone is responsible for decomposing organic matter by means of oxidative
processes on the surface of the pond. In contrast, the anaerobic zone is characterized by
the absence of oxygen and anaerobic bacterial activity, which is found at the bottom of the
lagoon. The facultative zone is found in the middle of the two aforementioned zones and is
formed by the combination of the two types of microorganisms (aerobic and anaerobic),
which eliminate the organic material still present in the liquid medium [36–38].
Sustainability 2024,16, 8334 10 of 16
Sustainability 2024, 16, x FOR PEER REVIEW 10 of 16
Figure 5. Drawing of a facultative lagoon representing the different zones of microbiological activ-
ity, aerobic, facultative and anaerobic, and the exchange of gases with the atmosphere [36].
Given that in anaerobic lagoons the degradation efficiency of BOD removal is around
50% (for temperatures less than or equal to 20 °C) to 60%, this alone is not enough to make
the effluent suitable. This is why it is not implemented as the only treatment, and is more
commonly followed by a facultative lagoon for an organic maer removal efficiency of
82% on average [20]. However, a disadvantage of the anaerobic process is the generation
of bad odors due to the production of methane and the reduction of sulfur which produces
hydrogen sulfide gas:
𝐵𝑂𝐷 = 731.67 mg/L × (1 − 0.60) = 292.67 mg/L (12)
To determine the removal of the BOD/COD effluent load, this is determined as a
function of the average temperature. The higher the temperature, the higher the rate ap-
plied, reducing the total volume of the pond to be dimensioned. Next, we will analyze the
concentration of BOD and COD and their removal expectations according to the type of
stabilization pond [17,39–42].
Determine the total contaminant load in terms of BOD and COD.
Maximum flow: 24,000 m3/day
Maximum BOD concentration: 731.67 mg/L
Maximum COD concentration: 1351 mg/L
𝐷𝐵𝑂 = 𝑄 × 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝐷𝐵𝑂
𝐶ℎ𝑎𝑟𝑔𝑒 𝐵𝑂𝐷 = 24000 m
da
y
× 731.67 mg
l× 1 kg
1000000 mg = 17.560 kg/da
y
(13)
𝐶𝑎𝑟𝑔𝑎 𝑑𝑒 𝐷𝑄𝑂 = 𝑄 × 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑐𝑎𝑜 𝐷𝑄𝑂
𝐶ℎ𝑎𝑟𝑔𝑒 𝐶𝑂𝐷 = 24000 m/da
y
× 1351 mg/L × 1 kg
1000000 mg = 32.424 kg/da
y
(14)
Figure 5. Drawing of a facultative lagoon representing the different zones of microbiological activity,
aerobic, facultative and anaerobic, and the exchange of gases with the atmosphere [36].
Given that in anaerobic lagoons the degradation efficiency of BOD removal is around
50% (for temperatures less than or equal to 20
◦
C) to 60%, this alone is not enough to make
the effluent suitable. This is why it is not implemented as the only treatment, and is more
commonly followed by a facultative lagoon for an organic matter removal efficiency of 82%
on average [
20
]. However, a disadvantage of the anaerobic process is the generation of
bad odors due to the production of methane and the reduction of sulfur which produces
hydrogen sulfide gas:
BODRemai ning =731.67 mg/L ×(1−0.60)=292.67 mg/L (12)
To determine the removal of the BOD/COD effluent load, this is determined as a
function of the average temperature. The higher the temperature, the higher the rate
applied, reducing the total volume of the pond to be dimensioned. Next, we will analyze
the concentration of BOD and COD and their removal expectations according to the type of
stabilization pond [17,39–42].
Determine the total contaminant load in terms of BOD and COD.
Maximum flow: 24,000 m3/day
Maximum BOD concentration: 731.67 mg/L
Maximum COD concentration: 1351 mg/L
DBO =Qmaxim ×C oncentration o f DBO
Charge BOD =24000 m3
day ×731.67 mg
l×1 kg
1000000 mg =17.560 kg/day (13)
Carga de DQO =Qmaxim ×Concentracao DQO
Charge COD =24000 m3/day ×1351 mg/L ×1 kg
1000000 mg =32.424 kg/day (14)
Sustainability 2024,16, 8334 11 of 16
3.1. Removal Efficiency by Lagoon Type
In the anaerobic lagoon: 50–70% BOD and COD removal.
Charge BOD remaining : 17.560 kg/day ×(1−0.6)=7.024 kg/day (15)
Charge COD remaining : 32.424 kg/day ×(1−0.6)=12.970 kg/day (16)
In the facultative lagoon: 60–80% BOD and COD removal (after the anaerobic lagoon).
Charge BOD remaining : 7.024 kg/day ×(1−0.7)=2.107 kg/day (17)
Charge DQO remanescence : 12.970 kg/day ×(1−0.7)=3.891 kg/day (18)
In the aerobic lagoon: 80–90% BOD and COD removal (after the facultative lagoon).
Charge BOD remaining : 2.107 kg/day ×(1−0.85)=0.3160 kg/day (19)
Charge COD remaining : 3.891 kg/day ×(1−0.85)=0.584 kg/day (20)
The rate of application of the parameters for sizing anaerobic lagoons depends on the
temperature, where warmer locations allow for a higher rate and consequently a smaller
volume. In Table 4, there is an estimate of BOD removal in an anaerobic lagoon with
a minimum depth of 4 m depending on the temperatures in the coldest months of the
year [43–47].
Table 4. Estimated BOD removal in anaerobic lagoon [24].
Average Temperature in Lagoon in a Cold
Month (◦C) BOD Removal Efficiency %
≤20 ≤50
>20 ≤60
3.2. Lagoon Numbers Calculation
To determine the number of ponds, we must consider the load removal capacity of
each pond. Sizing based on load:
In anaerobic lagoons: Average BOD removal efficiency of 60%, with removal capacity
per typical lagoon: Let us assume 5.000 kg of BOD/day.
Number o f An aerobic Lago ons =Charge o f BOD removal
Ca pacit y o f Remo tion per la goon =17.560 kg/day×0.6
5.000 kg/days
Number o f An aerobic Lago ons =2.11 (21)
Rounding the value up will give us 3 anaerobic ponds.
Facultative ponds with a BOD removal efficiency of 70% after anaerobic ponds, which
have a typical removal capacity of 2000 kg of BOD/da
Number o f Facul tative lago ons =Charge o f BOD removal
Ca pacit y o f Remot ion per lag oon =7.024 kg/dia×0.7
2.000 kg/dia
Number o f Facul tative lago ons =2.46 (22)
Rounding the value up will give us three facultative ponds.
For aerobic lagoons, the average removal efficiency is 85% of BOD after the facultative
lagoons. The removal capacity per typical lagoon: approximately 1.000 kg of BOD/day.
Number o f Aerobic l agoons =Charge o f BOD removal
Ca pacit y o f Remo tion per la goon =2.107 kg/day×0.85
1.000 kg/day
Number o f Aerobic l agoons =1.79 (23)
Sustainability 2024,16, 8334 12 of 16
Rounding the value up will give us two aerobic ponds. In summary, Table 5shows
the calculations, and below there is a more detailed explanation of the results in the context
of the study objective.
Table 5. Lagoon number results.
Lagoon Number Calculations
Number of Anaerobic lagoons 2.11
Number of Facultative lagoons 2.46
Number of Aerobic lagoons 1.79
A quantitative analysis of the calculations for the system in question reveals that the
number of lagoons required based on the contaminant load will consist of the following:
the system will require three anaerobic lagoons, three facultative lagoons, and two aerobic
lagoons, for a total of eight lagoons. It is important to note that the pumping system must
be designed in a way that allows for gravity-fed flow, as this will help to minimize energy
consumption. It is essential that the connections between the lagoons be designed in a
manner that allows for the continuous flow of effluent, with the preference being for this
to occur by gravity. However, the use of pumps is an acceptable alternative in instances
where gravity is not feasible. It is essential to install flow control to guarantee sufficient
flow at each stage and to maintain load balance. It is crucial to monitor the contaminant
load in each lagoon and to make any necessary adjustments to the process [48–50].
Maintenance and access must be monitored for each lagoon, and it must be ensured
that all environmental and safety regulations are complied with in the construction and
operation of the lagoons. Expected efficiency in our system of anaerobic lagoons: 50–70%
BOD/COD removal; facultative lagoons: 60–80% additional removal after anaerobic; aero-
bic lagoons: 80–90% additional removal after facultative. After the preliminary treatment,
where most of the processes are physical, we move on to the biological treatment phase,
which takes place in the stabilization ponds for primary treatment [
51
–
53
]. We have already
analyzed the detention time, depth and BOD removal rate of the incoming effluent, and we
will now focus on primary treatment, which involves anaerobic reactions carried out by
microorganisms in the presence of sunlight, which take place in the ponds over a period of
3 to 6 days.
These results align with the objective of this study, which was to analyze the results of
the physical and chemical properties of the effluents generated and the principal treatment
technologies employed for the remediation of industrial wastewater from sugar factories.
This can be achieved through humid systems built from stabilization ponds, with the
resulting water suitable for reuse in agricultural irrigation.
3.3. Biological Treatment in Stabilisation Ponds
In stabilization ponds, bacteria such as Achromobacter, Proteus, Alcaligenes, Pseu-
domonas, Thiospirillum and Rhodothecae predominate, and are responsible for degrading
organic matter by oxidation [
10
]. The predominance of sunlight and the CO
2
synthesized
by bacteria further facilitates the process of algae growth and thus increases photosynthesis
in lakes, subsequently increasing the oxygen concentration. The most common algae are
Chlorella, Euglena, Scenedermus and Microcistis [
9
]. As more and more algae grow inside
the lake, the oxygen produced by the algae with the help of sunlight and the photosynthetic
process increases, allowing the bacteria to break down more waste and achieve a reduction
in the organic level [12]. The most common redox reactions are the following:
Oxidation:
Organic matter +O2+bacteria →CO2+N H3+NO3(24)
Sustainability 2024,16, 8334 13 of 16
Reduction:
Algae +Solar Energy +CO2+N H3+NO3→O2+H2O(25)
During the night, the upwelling process is weak and the organic solids and sludge
settle to the bottom of the WSP and in the absence of oxygen, the anaerobic bacteria convert
the insoluble inorganic waste into soluble organics such as ethanol and others which are
broken down by anaerobic bacteria to form H
2
S,NH
3
,CH
4
,CO
2
. The sludge deposited
at the bottom of the tank can be removed by dredging [
12
]. Below, Figure 6shows the
biological cycle that takes place in the stabilization ponds mentioned above, which is the
final process for removing the contaminant load from the effluent in its entirety.
Sustainability 2024, 16, x FOR PEER REVIEW 13 of 16
Algae + Solar Energy+ 𝐶𝑂 + 𝑁𝐻+𝑁𝑂 → 𝑂+ 𝐻𝑂 (25)
During the night, the upwelling process is weak and the organic solids and sludge
sele to the boom of the WSP and in the absence of oxygen, the anaerobic bacteria con-
vert the insoluble inorganic waste into soluble organics such as ethanol and others which
are broken down by anaerobic bacteria to form 𝐻2𝑆, 𝑁𝐻3, 𝐶𝐻4, 𝐶𝑂2. The sludge deposited
at the boom of the tank can be removed by dredging [12]. Below, Figure 6 shows the
biological cycle that takes place in the stabilization ponds mentioned above, which is the
final process for removing the contaminant load from the effluent in its entirety.
Figure 6. Load removal cycle by biological processes.
3.4. Alternative Technologies Evaluated
Other alternative technologies were evaluated but no in-depth studies were carried
out because we have a low COD/BOD ratio (<2.5); the biodegradable fraction is high, and
the use of biological treatment is recommended. Other technologies, such as anaerobic
reactors (UASB), activated sludge systems and aerobic biofilm reactors, require longer pe-
riods such as 120 days to start the degradation process and are not economically viable.
3.5. Advantages and Disadvantages
Advantages of Using Stabilization Pond Systems
The use of different types of lagoons has a number of advantages: high BOD and
coliform removal efficiency; reduced operating and maintenance costs; and simple oper-
ation.
3.6. Disadvantages of Using This Type of Stabilization Pond System
The main disadvantages are that large areas are required to implement these systems;
biological activity is affected by temperature; if they are in cold regions the process is slow;
and they generate bad odors.
4. Conclusions
The treatment of industrial effluents is of immeasurable importance and the conse-
quences of improper disposal can be seen in various spheres of society. In environmental
Figure 6. Load removal cycle by biological processes.
3.4. Alternative Technologies Evaluated
Other alternative technologies were evaluated but no in-depth studies were carried
out because we have a low COD/BOD ratio (<2.5); the biodegradable fraction is high, and
the use of biological treatment is recommended. Other technologies, such as anaerobic
reactors (UASB), activated sludge systems and aerobic biofilm reactors, require longer
periods such as 120 days to start the degradation process and are not economically viable.
3.5. Advantages and Disadvantages
3.5.1. Advantages of Using Stabilization Pond Systems
The use of different types of lagoons has a number of advantages: high BOD and col-
iform removal efficiency; reduced operating and maintenance costs; and simple operation.
3.5.2. Disadvantages of Using This Type of Stabilization Pond System
The main disadvantages are that large areas are required to implement these systems;
biological activity is affected by temperature; if they are in cold regions the process is slow;
and they generate bad odors.
4. Conclusions
The treatment of industrial effluents is of immeasurable importance and the conse-
quences of improper disposal can be seen in various spheres of society. In environmental
Sustainability 2024,16, 8334 14 of 16
terms, the improper disposal of wastewater causes eutrophication of water bodies, death of
aquatic life, contamination of soil and groundwater, since these systems use huge quantities
of water for their production activities. For the first time, based on the parameters obtained
from the effluents from this factory, we were able to design a system for treating these
effluents using anaerobic, aerobic and facultative ponds. The lagoon system represents a
reliable and dependable solution for basic sanitation, and is widely implemented in several
countries. In Mozambique, due mainly to its tropical climate, lagoons represent a reliable
and dependable solution for basic sanitation. In general, lagoons are easy to operate, have
relatively low maintenance and construction costs and consume little energy. In terms of
BOD removal efficiency, the typical range is between 75 and 85 per cent. With regard to
coliform removal, up to 99.9 per cent efficiency can be achieved. This serial scheme, with
three anaerobic, three facultative and two aerobic lagoons, maximizes contaminant removal
efficiency and ensures that the treated effluent meets regulatory parameters before being
released into the environment. We now need approval for the proposal from the sugar
factory and support from the government of Mozambique to introduce our solution all
across the country.
Author Contributions: Conceptualization, P.M. and S.O.P.B.; methodology, P.M.; software, N.C.;
validation, P.M., F.A.L.Z. and C.A.M.P.; formal analysis, N.C.; investigation, P.M.; resources, F.A.L.Z.;
data curation, C.A.M.P.; writing—original draft preparation, P.M.; writing—review and editing,
F.A.L.Z.; visualization, C.A.M.P.; supervision, S.O.P.B.; project administration, F.A.L.Z.; funding
acquisition, C.A.M.P. All authors have read and agreed to the published version of the manuscript.
Funding: This research was co-funded by Project PIE 2023-60 CONVOCATORIA DE PROYECTOS
DE INNOVACIÓN EDUCATIVA 2023 de la Universidad de Las Palmas de Gran Canaria. This
research was also co-funded by the INTERREG V-A Cooperation, Spain–Portugal MAC (Madeira-
Azores-Canaries) 2014–2020 program, MITIMAC project (MAC2/1.1a/263).
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.
Data Availability Statement: The data presented in this study are available on request from the
corresponding author.
Conflicts of Interest: The authors declare no conflict of interest.
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