Optimization and redesign of the Santo
Domingo leachate treatment plant: an
approach to environmental efficiency and
sustainable development
Optimización y rediseño de la planta de tratamiento de
lixiviados en Santo Domingo: un enfoque hacia la eficiencia
ambiental y el desarrollo sostenible
José Gerardo León Chimbolema
1
Hernán Patricio Tixi Toapanta
2
Rogel Alfredo Miguez Paredes
3
Abstract: The research stems from a growing concern about the
negative impact of leachates, which are highly contaminated and
complex liquids, on public health and the environment. Through
detailed analysis and technical data collection, including on-site
evaluation of the plant, deficiencies in the current treatment were
identified. The study included estimation of the leachate flow rate
using the volumetric method based on height differentiation. A
detailed leachate characterization was performed to determine the
efficiency of the existing treatment, focusing on the removal of
Biochemical Oxygen Demand (BOD5), Chemical Oxygen Demand
(COD) and Turbidity. In addition, a treatability test was conducted
using a specific flocculation and agitation process. The results
revealed a deficient operation of the plant, with a daily production of
26 m3 of leachate that was not adequately treated. Therefore, the
design of a vertical subsurface artificial wetland was proposed,
meticulously calculating its surface area, retention time, dimensions
and the amount of filter media required. It is concluded that there is
an imperative need to redesign and optimize all the treatment phases
of the plant.
Keywords: redesign, leachate, treatment, sustainability,
environmental efficiency.
1
D. in Chemistry, Master in Environmental
Protection.
Research Professor Escuela Superior
Politécnica de Chimborazo (ESPOCH)
gerardo.leon@espoch.edu.ec
https://orcid.org/0000-0001-9202-8542
2
D. in Chemistry, Research Professor Escuela
Superior Politécnica de Chimborazo
(ESPOCH) htixi@espoch.edu.ec
https://orcid.org/0000-0002-9462-7052
3
Computer Systems Engineer, Master in
Network Interconnectivity. Escuela Superior
Politécnica de Chimborazo (ESPOCH)
rmiguez@espoch.edu.ec
https://orcid.org/0000-0001-5063-1474
Published
Instituto Tecnológico Superior Edwards
Deming. Quito – Ecuador
Periodicity
January-March
Vol. 1, Num. 20, 2024
pp. 18-40
http://centrosuragraria.com/index.php/revista
Dates of receipt
Received: October 25, 2023
Approved: December 29, 2023
Correspondence author
gerardo.leon@espoch.edu.ec
Creative Commons License
Creative Commons License, Attribution-
NonCommercial-ShareAlike 4.0
International.https://creativecommons.org/lice
nses/by-nc-sa/4.0/deed.es
January - March vol. 2. Num. 1 - 2024
19
Resumen: La investigación parte de una preocupación creciente por
el impacto negativo de los lixiviados que son líquidos altamente
contaminados y complejos, sobre la salud pública y el medio
ambiente. Mediante un análisis detallado y la recopilación de datos
técnicos, incluyendo la evaluación in situ de la planta, se identificaron
deficiencias en el tratamiento actual. El estudio incluyó la estimación
del caudal de lixiviados utilizando el método volumétrico basado en
la diferenciación de alturas. Se realizó una caracterización detallada
de los lixiviados para determinar la eficiencia del tratamiento
existente, enfocándose en la remoción de la Demanda Bioquímica de
Oxígeno (DBO5), Demanda Química de Oxígeno (DQO) y
Turbiedad. Además, se llevó a cabo una prueba de tratabilidad
empleando un proceso de floculación y agitación específicos. Los
resultados revelaron una operación deficiente de la planta, con una
producción diaria de 26 m3 de lixiviados no tratados adecuadamente.
Por ello, se propuso el diseño de un humedal artificial vertical
subsuperficial, calculando meticulosamente su área superficial,
tiempo de retención, dimensiones y la cantidad de medio filtrante
necesario. Se concluye que es una necesidad imperante de rediseñar y
optimizar todas las fases de tratamiento de la planta.
Palabras clave: rediseño, lixiviados, tratamiento, sostenibilidad,
eficiencia ambiental.
Introduction
Canton Santo Domingo, located in the province of Santo Domingo de
los Tsáchilas, Ecuador, faces a crucial challenge in solid waste
management, exacerbated by accelerated demographic and economic
growth. With a population exceeding 450,000 inhabitants, the region is
experiencing a proportional increase in solid waste generation,
estimating a production of approximately 300 tons per day (Ministry of
Environment, 2018)This increase has direct implications on the
production of leachates, highly polluting liquid byproducts, derived
from the decomposition of garbage in landfills.
The leachate treatment plant at the Santo Domingo Environmental
Complex has shown inadequacies in its capacity to handle these
increasing volumes and their complex composition. Leachate, which
contains dissolved organic matter, heavy metals, inorganic salts and
xenobiotics, represents a significant risk to public health and the
environment if not properly managed (Toufexi et al., 2013)..
Faced with this problem, this study advocates a redesign and
optimization of the leachate treatment plant, based on an exhaustive
review of current technologies and processes. The need for this
Optimization and redesign of the Santo Domingo leachate treatment plant: an approach to
environmental efficiency and sustainable development
20
intervention arises from the deficient operation of the plant and its non-
compliance with national environmental standards.
The proposed redesign is based on a detailed characterization of the
leachate and a critical evaluation of the deficiencies in the current
treatment stages. This proposal includes the revitalization and
optimization of the anaerobic and aeration lagoons, as well as the
implementation of more efficient physicochemical processes, such as
improved coagulation and flocculation. These improvements ensure
more effective pollutant removal throughout the different stages of the
treatment process.
In addition, the study considers the incorporation of environmentally
sustainable technologies, such as artificial wetlands, for the secondary
treatment of leachate. These systems, in addition to their efficacy in
pollutant removal, provide additional benefits in terms of landscape
conservation and biodiversity (Luna-Pabello & Aburto-Castañeda,
2014).
In the context of Santo Domingo, the redesign of the plant not only
seeks to comply with environmental regulations but also to improve the
quality of life of its inhabitants. A gradual implementation of the
improvements is recommended, accompanied by a maintenance and
continuous monitoring plan. Community awareness and environmental
education are also key to ensuring the long-term sustainability of the
project.
Leachate Treatment
Leachate treatment is essential in municipal solid waste management,
especially in landfills. Leachate, resulting from the percolation of
liquids through accumulated waste, contains a complex mixture of
contaminants such as organic and inorganic compounds and heavy
metals. This composition, which varies according to the nature of the
waste and environmental conditions, represents a significant risk to
public health and the environment due to its potential to contaminate
soils and aquifers(Chaouki et al., 2021).
Conventional methods for treating leachate include physical, chemical
and biological techniques. Physical processes, such as filtration, focus
on removing solid particles, while chemical treatments use agents such
January - March vol. 2. Num. 1 - 2024
21
as coagulants to address dissolved contaminants. Biological approaches
rely on microorganisms to break down organic matter. However,
technological evolution has introduced advanced methods such as
reverse osmosis and anaerobic digestion, which offer greater efficiency
in removing impurities and reducing environmental
impacts(Czatzkowska et al., 2023).
Effective leachate treatment goes beyond environmental compliance; it
is a vital component of sustainable waste management. By minimizing
ecological risks, biodiversity is protected, and water quality is
maintained (Abdel-Shafy et al., 2024; Lei et al., 2023).
Thus, environmental efficiency in leachate treatment is vital to mitigate
the negative impacts associated with landfills (Clemente et al., 2023;
Toufexi et al., 2013).(Clemente et al., 2023; Toufexi et al., 2013). This
approach focuses on reducing water and soil pollution, as well as
minimizing emissions of harmful gases Achieving high efficiency in
leachate treatment is crucial to preserve ecosystems and ensure the
sustainability of natural resources.
Efficient leachate treatment involves the implementation of advanced
technologies and management practices that are adapted to the dynamic
and complex nature of these wastes. This includes not only the effective
removal of contaminants, but also the optimization of energy and
resource consumption in the treatment process (Alexis et al., 2015;
Grabska et al., 2015; Tamayo Orbegozoa et al., 2012).Environmental
efficiency goes beyond mere regulatory compliance; it seeks to
continuously improve processes to reduce the ecological footprint of
waste treatment.
In the context of leachate treatment, environmental efficiency also
implies the consideration of the useful life of facilities and equipment
The adoption of durable technologies and the implementation of
adequate maintenance practices are fundamental to ensure the long-
term operability of treatment plants, thus reducing the need for frequent
replacements and reducing the waste generated by obsolete
equipment(Andrade Avalos et al., 2020).
In addition, environmental efficiency in leachate treatment must
address adaptability to changing environmental regulations and
increasing societal demands for more sustainable practices. This
includes the ability of treatment plants to integrate into broader waste
Optimization and redesign of the Santo Domingo leachate treatment plant: an approach to
environmental efficiency and sustainable development
22
management systems, contributing to the creation of cleaner and
healthier cities(De et al., 2022; Diaz et al., 2022; Karatas et al., 2022).
Therefore, in contexts such as Santo Domingo, the optimization and
redesign of leachate treatment plants are essential to achieve efficient
and sustainable waste management, contributing significantly to
environmental and social well-being.
Materials and methods
The research was oriented towards a technical approach based on an
analytical review of the literature, complemented by the collection of
technical data obtained directly on site. Qualitative and quantitative
methods were used for data collection. The detailed analysis of the plant
operation was carried out through a qualitative approach, while the
analysis of the data obtained was carried out through a quantitative
approach. In addition, the Delphi Method was used to structure and
analyze the information collected, and interviews were conducted to
obtain data on actual plant conditions.
The technical diagnosis included on-site verification of both the design
and operation of the plant. The dimensions, geometry and capacity of
each of the systems comprising the plant were examined with the help
of measurement tools and plant operations personnel. The actual
condition of the plant was also observed during field visits.
Leachate generation was estimated using the volumetric method, based
on height differentiation, recording the increase in leachate over time.
This methodology included recording the initial height of the leachate
and its proportional increase during a given period.
Regarding the treatability of the plant, a characterization of the leachate
was carried out. A single sample was taken at each treatment stage, both
at the inlet and outlet, following INEN 2169:2013. Each sample was
labeled with relevant details such as name, place, time and date of
collection, and volume. Gloves, masks, thermometer, sterile plastic
containers, among other materials, were used for sampling.
The analysis parameters included BOD5, COD, pH, conductivity and
temperature, and the analyses were performed at the Technical Analysis
Laboratory. In addition, the data obtained were compared with the
January - March vol. 2. Num. 1 - 2024
23
discharge limits stipulated in current regulations to evaluate the
efficiency of the treatments implemented at the plant.
The identification and evaluation of the environmental impact were an
essential part of the study, focusing on the impacts generated by the
plant and their relevance for their prevention and assessment.
Finally, based on the data collected and the evaluations performed, a
plant redesign proposal was issued. This proposal included treatability
tests to determine the optimum doses of coagulants and flocculants and
the design of a vertical flow sub-surface artificial wetland. Sizing was
based on recognized standards and guidelines, and corresponding
drawings were prepared using specialized software.
3. Result
Table 1 Geometry of primary treatment
Lagoon of
Sedimentation
Primary
It has an isosceles trapezoid geometry with angles of 45
0
,
whose height variation is one meter from the end of the
smaller base to the end of the larger base, with two sludge
evacuation sites of 5m wide, which are removed by a
sludge pump and the sludge generated must be evacuated
every 15 days.
Lagoon
Anaerobic
This is where the degradation process is initiated by anaerobic
bacteria. It has an isosceles trapezoid geometry with angles of
45
0
, with a height variation of one meter from the end of the
lower base to the end of the higher base.
Lagoon of
Aeration
This is where the oxidation process of organic matter is
initiated by feeding air using fine bubble diffusers from the
blowers. It has a trapezoid geometry with angles of 45
0
, with
a height variation of half a meter from the smaller base end to
the larger one.
Lagoon of
Sedimentation
Secondary
The leachate treatment plant described in Table 1 uses a sequence of
isosceles trapezoidal geometry lagoons with 45° angles, each designed
for a specific purpose in leachate treatment. The Primary Sedimentation
Lagoon focuses on the sedimentation of heavy solids, with regular
Optimization and redesign of the Santo Domingo leachate treatment plant: an approach to
environmental efficiency and sustainable development
24
sludge removal. The Anaerobic Lagoon initiates the biological
decomposition process without oxygen, while the Aeration Lagoon,
equipped with fine bubble diffusers, facilitates aerobic oxidation of
organic matter. Finally, the Secondary Sedimentation Lagoon is used
for additional sludge settling. This integrated design ensures an efficient
reduction of contaminants in the leachate, preparing it for further
treatment in the physicochemical plant, and underlines the importance
of regular maintenance to optimize the operation and efficiency of the
system.
Table 2: On-site dimensions of the primary leachate treatment
plant
Data on in situ values of Primary Treatment dimensions
Treatment
Length
(m)
Width (m)
Height
of
lower base
end (m)
Height of
the greater
base end
(m)
Volume
(m3)
Lagoon of
Sedimentation
Primary
50
23.20
3.50
4.50
5000
Lagoon
Anaerobic
80
19.70
4
5
5000
Lagoon of
Aeration
37
16
4
4.50
1472
Lagoon of
Secondary
sedimentation
30
17.40
3
4
875
Table 3 details the on-site dimensions of the lagoons at the primary
leachate treatment plant, revealing essential characteristics for their
operation. The Primary Sedimentation Lagoon, 50 meters long, 23.20
meters wide, and with a volume of 5000 m³, is in charge of sedimenting
suspended solids. The Anaerobic Lagoon, similar in volume but 80
meters long and 19.70 meters wide, facilitates degradation by anaerobic
bacteria. The Aeration Lagoon, smaller at 37 meters long, 16 meters
wide, and 1472 m³ in volume, performs the oxidation of organic matter.
Finally, the Secondary Sedimentation Lagoon, 30 meters long and
17.40 meters wide with a volume of 875 m³, is used for sludge settling.
January - March vol. 2. Num. 1 - 2024
25
These dimensions reflect the adaptation of each lagoon to its specific
functions within the treatment process.
Table 3. Dimensions of the physical-chemical plant.
Data of the in situ values of the physical-chemical plant
dimensions
Components
Length
(m)
Width (m)
Buffer tank
4.54
2.80
Aeration tower
3
1.20
Reaction tank
1.60
1.30
Flocculation and settling tank
5.45
2.80
Tank sludge collector
Flocculator and settler
1..20
2.80
Reserve tank
2.80
2.80
Sand filter
1.86
1.10
Carbon filter
1.86
1.10
Table 3 presents the in situ dimensions of the Physical-Chemical Plant
components, highlighting the differences in size and function of each
element. The Lung Tank, measuring 4.54 meters long and 2.80 meters
wide, serves as a regulating tank. The Aeration Tower, measuring 3
meters long and 1.20 meters wide, is crucial for the oxidation of organic
matter. The Reaction Tank, more compact at 1.60 meters long and 1.30
meters wide, facilitates specific chemical reactions. The Flocculation
and Settling Tank, measuring 5.45 by 2.80 meters, and the associated
Sludge Collector, measuring 1.20 meters long by 2.80 meters wide, play
an essential role in the treatment of particulates and sludge. In addition,
a Reserve Tank of 2.80 meters in both dimensions ensures the constant
availability of treated liquids. Finally, two filters, a sand filter and a
carbon filter, both 1.86 meters long and 1.10 meters wide, provide the
final filtration in the process. These dimensions reflect the integration
and specialization of each component in the plant, underlining the
complexity and efficiency of the physical-chemical treatment.
Table 4. Dimensions of the physical-chemical plant aeration tower.
Aeration
tower
Top
length
(m)
Base
length
(m)
Width
superior
(m)
Base
width
(m)
Tray
spacing
(m)
Perforations
(mm)
Height
(m)
Optimization and redesign of the Santo Domingo leachate treatment plant: an approach to
environmental efficiency and sustainable development
26
Dish 1 and
3
1.20
0.80
0.85
0.45
0.30
6
0.30
Dish 2 and
5
1.20
0.80
0.85
0.45
0.30
Without
perforations (3 mm
tube)
0.30
Plate 4
1.20
0.80
0.85
0.45
0.30
6
0.30
Table 4 describes in detail the dimensions of the aeration tower of the
physicochemical plant, an essential component for the oxidation of
organic matter in leachate treatment. The tower consists of five trays,
each with specific dimensions and design features.
Dishes 1, 3 and 4 have identical dimensions, with an upper length of
1.20 meters and a base length of 0.80 meters. The top width is 0.85
meters, while the base width is 0.45 meters. The separation between
trays in these plates is 0.30 meters, and each one has perforations of 6
millimeters in diameter, facilitating the distribution of air in the tower.
The height of each tray is also 0.30 meters.
On the other hand, plates 2 and 5, although they share the same external
dimensions with the other plates, have a distinctive feature: they do not
have perforations, but a 3 mm tube. This suggests a different role in the
aeration process, possibly focused on a more controlled air distribution
or flow.
These detailed dimensions and specifications reflect the complexity and
precision in the design of the aeration tower, indicating the importance
of this component in the overall efficiency of the physicochemical
treatment plant.
Table 5. Estimated Leachate Flow Rate produced at the
Environmental Complex
Date
Time range
(5h)
Leachate height (m)
Height of rise
(m)
Saturday,
June 9, 2018
6:00 am
2.52
-
11:00 am
2.53
0.01
16:00 pm
2.54
0.01
21:00 pm
2.549
0.009
Length (m)
Width (m)
Depth (m)
January - March vol. 2. Num. 1 - 2024
27
Dimensions
of the cube
65.42
38.33
5.4
Table 5 provides a detailed estimate of the leachate flow rate produced
at the Environmental Complex for June 9, 2018. The data show that,
throughout the day, the leachate height gradually increased, starting
from 2.52 meters at 6:00 am and reaching 2,549 meters at 21:00 pm.
These increases, although small, were constant and significant for
evaluating leachate generation. Considering the dimensions of the
basin, with a length of 65.42 meters, a width of 38.33 meters and a depth
of 5.4 meters, a daily flow of 116 m³ was calculated. This value is within
the design capacity of the leachate treatment plant, which is 120 m³/day,
indicating that the plant is adequately sized to handle the volume of
leachate generated in the complex. The flow generated in the
environmental complex is 116 m3/day; the leachate treatment plant is
designed to treat 120 m3/day, which means that the design is suitable
to treat the volume of leachate generated.
Table 6. Analysis of leachate from the primary sedimentation pond.
Type of
treatment
Parameters
Unit
Sampling
Entrance
Output
Average
output
Average
input
Primary
sedimentation
lagoon
BOD
5
mg/L
Week 1
2610.0
2590.0
2577
2603
Week 2
2599.0
2570.0
Week 3
2600.0
2571.0
COD
mg/L
Week 1
4600.0
5440.0
4914
4625,667
Week 2
4678.0
4602.0
Week 3
4599.0
4700.0
Conductivity
uS/cm
Week 1
8.40
7.81
7,947
8,150
Week 2
8.00
8.00
Week 3
8.05
8.03
pH
-
Week 1
7.40
8.30
8,123
7,217
Week 2
7.10
8.00
Week 3
7.15
8.07
Table 6 shows the results of the leachate analysis of the Primary
Sedimentation Lagoon, revealing consistency in the Biochemical
Oxygen Demand (BOD5) and Chemical Oxygen Demand (COD)
values, although with a slight decrease in the output. Conductivity
values decrease slightly, indicating a small reduction of ions in the
Optimization and redesign of the Santo Domingo leachate treatment plant: an approach to
environmental efficiency and sustainable development
28
water. The pH increases at the outlet, suggesting a slight increase in
alkalinity. These results, especially the slight change in BOD5 and
COD values, suggest that the sedimentation process in the lagoon is
having a minimal impact on reducing the organic load and the overall
quality of the leachate, which may be insufficient to meet the required
environmental standards.
Analysis of leachate from the anaerobic lagoon.
Type of
treatment
Parameters
Unit
Sampling
Entrance
Output
Average
output
Average
input
Lagoon
Anaerobic
BOD
5
mg/L
Week 1
2590.0
2210.0
2577
2213
Week 2
2570.0
2223.0
Week 3
2571.0
2206.0
COD
mg/L
Week 1
5440.0
3500.0
4914
3400,667
Week 2
4602.0
3260.0
Week 3
4700.0
3442.0
Conductivity
uS/cm
Week 1
7.81
3.45
7,947
3,530
Week 2
8.00
4.00
Week 3
8.03
3.14
pH
-
Week 1
8.30
8.85
8,123
8,757
The analysis of the Anaerobic Lagoon, according to Table 7-3, shows
an effective reduction of the organic load, evidenced by the significant
decrease in BOD5 and COD values at the outlet compared to the inlet.
The reduction in conductivity at the outlet suggests an effective removal
of soluble ions. In addition, an increase in pH at the outlet is observed,
which could indicate the generation of alkaline products during the
anaerobic process.
However, the lagoon operation is deviating from the original design.
The 10 HP pump is pumping leachate at a flow rate of 50 m³/hour, but
it is being operated for 5 hours per day, resulting in a daily total of 250
m³, which exceeds the design flow rate of 120 m³/day. This
overoperation could be causing a lower efficiency in the treatment
January - March vol. 2. Num. 1 - 2024
29
process, since the hydraulic retention time is reduced, not allowing the
anaerobic processes to occur optimally.
Table 8. Analysis of leachate from the Aerobic
Lagoon.
Type of
treatment
Parameters
Unit
Sampling
Entrance
Output
Average
output
Average
input
Lagoon
Aerobia
BOD
5
mg/L
Week 1
2210.0
1621.0
1625,667
2213
Week 2
2223.0
1630.0
Week 3
2206.0
1626.0
COD
mg/L
Week 1
3500.0
3000.0
2986,333
3400,667
Week 2
3260.0
2960.0
Week 3
3442.0
2999.0
Conductivity
uS/cm
Week 1
3.45
3.81
3,770
3,530
Week 2
4.00
3.50
Week 3
3.14
4.00
pH
-
Week 1
8.85
8.88
8,753
8,757
Week 2
8.62
8.68
Week 3
8.80
8.70
The analysis of the Aerobic Lagoon, according to the Aerobic Lagoon
Leachate Analysis Table, shows a considerable performance in the
reduction of the organic load, as reflected in the decrease of BOD5 and
COD values from the inlet to the outlet. This decrease suggests that the
aerobic process is working effectively in the degradation of organic
matter.
Conductivity, an indicator of the presence of dissolved ions in the water,
shows a slight increase at the outlet, which could indicate a
concentration of ions as a result of the treatment process. This may
require additional attention, depending on discharge standards and
specific treatment objectives.
As for the pH, it remains relatively stable between the inlet and outlet,
indicating that the aerobic process is not causing significant fluctuations
Optimization and redesign of the Santo Domingo leachate treatment plant: an approach to
environmental efficiency and sustainable development
30
of acidity or alkalinity in the leachate. This is favorable for maintaining
the balance of the biological process in the lagoon.
Table 9. Analysis of leachate from secondary
sedimentation.
Type of
treatment
Parameters
Unit
Sampling
Entrance
Output
Average
output
Average
input
Lagoon of
Sedimentation
Secondary
BOD
5
mg/L
Week 1
1621.0
1504.0
1625,667
1471
Week 2
1630.0
1400.0
Week 3
1626.0
1509.0
COD
mg/L
Week 1
3000.0
2910.0
2986,333
2843
Week 2
2960.0
2820.0
Week 3
2999.0
2799.0
Conductivity
uS/cm
Week 1
3.81
5.39
3,770
5,223
Week 2
3.50
5.00
Week 3
4.00
5.28
pH
-
Week 1
8.88
8.65
8,753
8,603
Week 2
8.68
8.56
Week 3
8.70
8.60
Table 9 reflects an analysis of the leachate from the Secondary
Sedimentation Lagoon, showing a slight decrease in BOD5 and COD
levels, indicating a partial removal of organic matter. However, the
change is not significant, suggesting limited efficiency in the removal
of organic contaminants. In addition, an increase in conductivity is
observed, implying an increase in soluble salt concentrations, an aspect
that may require additional attention. The pH remains relatively stable,
which is positive, but the overall efficiency in reducing the pollutant
load appears to be moderate. This analysis suggests that, although there
is some treatment effectiveness, improvements or additional steps may
be necessary to achieve the desired discharge standards.
January - March vol. 2. Num. 1 - 2024
31
Table 10. Effluent leachate analysis
Sampling
Parameters
Unit
Affluent
Limit
Maximum
Permissible
07-01-2018
Chlorides
mg/L
1110
1000
Color Real
Color
units
44.9
Inappreciable
in 1/20
dilution:
Ammonia nitrogen
mg/L
745
30.0
Suspended Solids
Totals
mg/L
696
130
Oils and fats
mg/L
1.0
30
Total Phosphorus
mg/L
25
10
Total Nitrogen
Kjedahl
mg/L
250
50
Total solids
mg/L
4344
1600
Fecal Coliforms
MPN/100
ml
150
2000
Cadmium
mg/L
<0.0010
0.02
BOD5
mg/L
2700
100
COD
mg/L
4780
200
pH
-
7.97
6-9
Table 10 on the characterization of the influent leachate revealed
several parameters that exceed the maximum allowable limits,
indicating significant environmental concerns. The levels of chlorides,
ammonia nitrogen, total suspended solids, total phosphorus, total
Kjedahl nitrogen, and total solids greatly exceed the established
standards. Specifically, ammonia nitrogen and total solids levels are
alarmingly high compared to permitted limits. Although cadmium and
oil and grease levels remain within limits, the Biochemical Oxygen
Demand (BOD5) and Chemical Oxygen Demand (COD) are extremely
high, indicating a high concentration of organic matter and a
Optimization and redesign of the Santo Domingo leachate treatment plant: an approach to
environmental efficiency and sustainable development
32
considerable contaminant load in the leachate. The pH of the leachate
is within the acceptable range, but the overall data suggest an urgent
need for more effective treatment and management to reduce these
contaminant levels and protect the environment.
Table 11. Analysis of leachate discharged vs. Agreement 097-
A Table 9: "Discharge limits in a freshwater body".
Sampling
Parameters
Unit
Effluent
Limit
Maximum
Permissible
Compliance
of the
discharge
regulation
07-01-2018
Chlorides
mg/L
6.7
1000
COMPLIANCE
Color Real
Color
units
Inappreciable
in dilution
1/20:
Inappreciable
in 1/20
dilution:
COMPLIANCE
Ammonia nitrogen
mg/L
28
30.0
COMPLIANCE
Suspended Solids
Totals
mg/L
9
130
COMPLIANCE
Oils and fats
mg/L
<0.3
30
COMPLIANCE
Total Phosphorus
mg/L
0.28
10
COMPLIANCE
Total Nitrogen
Kjedahl
mg/L
46
50
COMPLIANCE
Total solids
mg/L
157
1600
COMPLIANCE
Fecal Coliforms
MPN/100
ml
90
2000
COMPLIANCE
Cadmium
mg/L
<0.0001
0.02
COMPLIANCE
BOD5
mg/L
52
100
COMPLIANCE
COD
mg/L
109
200
COMPLIANCE
Conductivity
uS/cm
385
-
-
pH
-
9
6-9
COMPLIANCE
The analysis of the leachate discharged, according to Table 11, shows
that all parameters analyzed comply with the maximum permissible
limits according to Agreement 097-A for discharge into freshwater
bodies. The levels of chlorides, ammonia nitrogen, total suspended
January - March vol. 2. Num. 1 - 2024
33
solids, oils and fats, total phosphorus, total Kjedahl nitrogen, total
solids, fecal coliforms and cadmium are considerably below the
allowable limits. Likewise, Biochemical Oxygen Demand (BOD5) and
Chemical Oxygen Demand (COD) are well within acceptable limits,
which is indicative of effective treatment of the leachate prior to
discharge. The pH is also in the acceptable range. This set of results
demonstrates effective compliance with environmental regulations for
leachate discharge, reflecting proper management and treatment of
these wastes prior to release into the aquatic environment.
The analysis of the results of the Landfill operation reveals an efficient
management in terms of modules and capacity. Currently in its third
module, the design of this phase is aligned with the previous ones,
ensuring uniformity in storage capacity until the end of its estimated
useful life in 2025. The leachate treatment plant is designed to handle a
flow rate of 120 m³/day, which is perfectly in line with the current flow
rate of 116 m³/day, indicating that the plant has the necessary capacity
to efficiently treat the leachate generated.
However, during on-site verification, minor variations in the
dimensions of the primary treatment lagoons were detected compared
to the original plans. These variations include a reduction in the width
of the primary sedimentation lagoon and anaerobic lagoon, and an
increase in the dimensions of the aeration lagoon and secondary
sedimentation lagoon. These discrepancies, although small, can have
implications for treatment efficiency.
In addition, it was observed that the primary sedimentation lagoon
receives a flow of 250 m³/day, significantly exceeding the design flow
of 120 m³/day. This excess flow reduces the hydraulic retention time,
altering the sedimentation process and negatively affecting the
efficiency of the plant. This overloading can lead to inefficient leachate
treatment, which could have environmental and operational
consequences. Therefore, it is crucial to address these challenges to
ensure leachate treatment efficiency and the long-term sustainability of
the Landfill.
Redesign proposal for optimization
Several key activities were carried out to develop the leachate treatment
plant redesign project at the Environmental Complex for Solid Waste
Disposal in Canton Santo Domingo. These included the
characterization of the leachate generated, a complete evaluation of the
structure, functionality and effectiveness of the existing treatments, and
the precise measurement of the volume of leachate produced. A detailed
Optimization and redesign of the Santo Domingo leachate treatment plant: an approach to
environmental efficiency and sustainable development
34
study of the site was also carried out and the financial resources
available from the Autonomous Decentralized Municipal Government
of Santo Domingo were analyzed. All these elements were considered
essential to formulate an effective proposal for the redesign of the plant
(Figure 1).
Figure 1: Redesign of the leachate treatment plant of the
environmental complex.
The proposal focuses on optimizing the leachate treatment plant,
including several stages as shown in Table 12:
January - March vol. 2. Num. 1 - 2024
35
Table 12 Stages to optimize the leachate treatment plant
Stage
Shares
Objectives
Primary
Treatment
Lagoon management to treat 120 m3/day.
Maintenance and periodic cleaning.
Implementation of bacteria.
Increase treatment efficiency.
Maintain operational capacity.
Physical-
Chemical Plant
Acquisition of a dosing pump. Addition of
coagulants and flocculants. Use of sand and
carbon filters.
Improve treatment of 90 m3/day of
leachate. Optimize the separation and
purification process.
VSEP Plant
Improvement of primary and physical-
chemical treatment. Reduction of maintenance
and extension of membrane life.
Reduce operating costs. Improve
treatment efficiency.
Design of New
Stages
Modification of the reservoir tank. Design of
an artificial wetland.
Adapt infrastructure to new needs.
Implement sustainable and efficient
solutions.
Redesign
Calculations
Installation of flow pump. Calculation of
reaction constant, area, and wetland
dimensions.
Ensure effective design of the
artificial wetland. Optimize the
performance of the new system.
It also provides a detailed breakdown of the strategies adopted for the
optimization and redesign of a leachate treatment plant, highlighting a
holistic and proactive approach. In the Primary Treatment stage, actions
focus on efficiently managing the lagoons to treat 120 m3/day,
complemented by regular maintenance and the introduction of
specialized bacteria. This approach not only seeks to improve treatment
efficiency but also to maintain the system's operational capacity, which
is essential for effective leachate management.
At the Physical-Chemical Plant, the acquisition of a dosing pump and
the implementation of coagulants, flocculants, and sand and carbon
filters show an effort to optimize the treatment of 90 m3/day of leachate.
These actions are vital to improve the separation and purification
processes, which are crucial in the elimination of a wide range of
contaminants.
On the other hand, improvements at the VSEP Plant, such as the
optimization of primary and physicochemical treatments and the
reduction of maintenance work, are aimed at reducing operating costs
and increasing treatment efficiency. This reflects a strategy of resource
optimization and technological improvements for a more efficient and
economical management of leachate treatment.
The inclusion of the New Stage Design, such as the modification of the
holding tank and the design of an artificial wetland, indicates an effort
to adapt the infrastructure to current and future needs, integrating
sustainable and efficient solutions. The implementation of an artificial
wetland is particularly noteworthy, as it represents an innovative and
environmentally friendly approach to leachate treatment.
Optimization and redesign of the Santo Domingo leachate treatment plant: an approach to
environmental efficiency and sustainable development
36
Finally, the Redesign Calculations, which include the installation of a
flow pump and detailed planning of the constructed wetland,
underscore the importance of effective design and optimization of
system performance. This level of planning detail is crucial to ensure
the long-term efficiency and sustainability of the treatment plant.
Taken together, these steps demonstrate a commitment to continuous
improvement and adaptation to changing needs in leachate treatment,
combining advanced technology, efficient management and
environmental sustainability.
4. Conclusions
After performing a detailed characterization of the leachate treatment
plant, significant deficiencies were identified in the primary treatment.
The sedimentation ponds showed a removal efficiency well below
expected standards, with minimal percentages of BOD5 and COD
removal. This inefficiency is attributed to poor operation, lack of
maintenance and inadequate staff training.
The efficiency of the Physical-Chemical Treatment Plant could not be
evaluated since it is not in operation. On the other hand, the VSEP
Treatment Plant proved to be efficient, with high BOD5 and COD
removal rates, although its operation entails high operating and
maintenance costs, reducing the useful life of the membranes.
As for the structural evaluation, minor variations were observed in the
dimensions of the lagoons compared to the design drawings. However,
all lagoons were found to be full of sludge and the treatment was
operating beyond its designed capacity, requiring urgent maintenance.
The physicochemical plant showed no significant structural differences,
but was found to be inactive and without adequate dosing of coagulants
and flocculants. The VSEP plant, although efficient, faces challenges
due to the treatment of raw leachate, which increases operating costs.
It was determined that the leachate flow generated is manageable by the
primary treatment, but a dosing pump is required in the physical-
chemical plant. In addition, a treatability test was carried out in this
plant, concluding that aluminum polychloride is effective in reducing
turbidity to the required levels.
Finally, an artificial wetland was proposed as a viable and efficient
solution to treat the excess flow, designing a system that meets
environmental and economic needs, and improves the landscape, while
managing flow fluctuations and effectively removing pollutants.
January - March vol. 2. Num. 1 - 2024
37
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