REVISTA INGENIO
Analysis of the Biodegradability Index of Organic Matter in the Water of the
Machangara River in Quito City
Análisis del Indice de Biodegradabilidad de la Materia Orgánica en el Agua del Río Machángara en la
Ciudad de Quito
Suly Margoth Rodríguez Ayala | Universidad Central del Ecuador - UCE, Quito - Ecuador
Montserrat Rodríguez Ayala | Universidad de Madrid - UAM, Madrid - España
Silvia Elizabeth Garcia Gonzalez | Universidad Central del Ecuador - UCE, Quito - Ecuador
Darwin Rodolfo Caina Aysabucha | Universidad Central del Ecuador - UCE, Quito - Ecuador
https://doi.org/10.29166/ ingenio.v8i1.7376 pISSN 2588-0829
2025 Universidad Central del Ecuador eISSN 2697-3243
CC BY-NC 4.0 —Licencia Creative Commons Reconocimiento-NoComercial 4.0 Internacional ng.revista.ingenio@uce.edu.ec
, (), - , . -
La evaluación de la calidad del agua en rios es esencial para identicar el impacto de las actividades humanas
y establecer estrategias de mitigación. El objetivo de este proyecto fue analizar el índice de biodegradabilidad
de la materia orgánica en el agua del río Machángara en la ciudad de Quito en Ecuador. Este rio atraviesa
algunos lugares de Quito tales como: Las Cuadras, El Recreo, La Recoleta y Nayón. Mediante un muestreo en
los sectores mencionados, se analizaron los parámetros necesarios para el cálculo de la demanda bioquímica
(DBO5) y química (DQO) de oxígeno, junto con otros parámetros sicoquímicos como la turbidez y el color
del agua. Además, se realizó un levantamiento de información en marzo de 2023 en las zonas de estudio. Los
resultados mostraron una variabilidad signicativa en los niveles de contaminación entre los sectores analiza-
dos. Se identicó un mayor nivel de contaminación en las zonas de La Recoleta y El Recreo en comparación
con Las Cuadras y Nayón, lo cual se atribuye a descargas directas de contaminantes provenientes de tuberías
ilegales conectadas tanto a industrias como a domicilios. El índice de biodegradabilidad obtenido sugiere la
necesidad de implementar tratamientos químicos y biológicos para la remoción eciente de los contaminan-
tes orgánicos e inorgánicos presentes en el río. El análisis sicoquímico reveló que la turbidez y el color del
agua también se correlacionan con los altos niveles de contaminación observados, particularmente en los
sectores más afectados. El levantamiento de información a través de encuestas demostró que la población
local sufre de manera directa los efectos negativos de esta contaminación, manifestando síntomas como ce-
falea, náuseas, vómitos, fatiga, falta de concentración y depresión, especialmente en niños y adultos mayores.
En conclusión, los resultados de este estudio resaltan la necesidad de aplicar medidas correctivas inmediatas,
como tratamientos químicos y biológicos, para mitigar el impacto ambiental y sanitario del río Machángara y
mejorar la calidad de vida de la población afectada
e evaluation of the water quality in rivers is essential to identify the impact of human activities and establish
mitigation strategies. e aim of this project is to analyze the biodegradability index of organic matter in the wa-
ter of the Machángara river in Quito city of Ecuador. It ows through some places of Quito such as “Las Cuadras”,
“El Recreo”, “La Recoleta”, and “Nayon”. rough sampling in the aforementioned sectors, the parameters neces-
sary for the calculation of biochemical (BOD), and chemical (COD) oxygen demand were analyzed, along with
other physicochemical parameters such as turbidity and watercolor. In addition, a survey was conducted in the
study areas in March 2023. e results showed a signicant variability in the level of contamination among the
sectors analyzed. A higher level of contamination was found in the areas of La Recoleta and El Recreo compared
to Las Cuadras, and Nayon, which is attributed to direct discharges of pollutants from illegal pipes connected to
both industries and households. e biodegradability index obtained suggests the need to implement chemical,
and biological treatments for the ecient removal of organic and inorganic pollutants present in the river. e
physicochemical analysis showed that the turbidity, and color of the water also correlated with the high levels of
pollution observed, especially in the most aected sectors. e information gathered through interviews showed
that the local population suers directly from the negative eects of this contamination, manifesting symptoms
such as headaches, nausea, vomiting, fatigue, lack of concentration, and depression, especially in children, and
older adults. In conclusion, the results of this study highlight the need for immediate corrective measures, such as
chemical, and biological treatments, to mitigate the environmental, and health impacts of the Machángara River
and improve the quality of life of the aected population.
Recibido: 20/9/2024
Recibido tras revisión: 25/10/2024
Aceptado: 14/11/2024
Publicado: 03/01/2025
Biodegradability, contaminants, treat-
ment, parameters, Machángara river.
Biodegradabilidad, contaminantes, trata-
miento, parámetros, río Machángara
120
Analysis of the Biodegradability Index of Organic Matter in the Water of the Machangara River in Quito City
Nowadays, the Machángara river is the main destina-
tion of wastewater of Quito. It has a total length of 22.5
kilometers, where it receives 76% of the entire city’s ef-
uent [10]. e river is the result of the conuence of
various small rivers, including the “Rio Grande”, “Que-
brada Ortega”, “Quebrada Rumipamba”, and “Quebrada
El Batán” [11]. e Machángara river sanitation project
carried out by the German Cooperation Agency in 1991,
identied the main types of industries in the Quito city,
and their potential environmental impacts. e food in
-
dustry produces high pH, sultes, detergents and sedi-
ments, while the textile industry produces high pH, fats,
oils, heavy metals, sultes and sulfates. Tanneries, on the
other hand, emit high levels of pH, oats, sulde, sulte,
sulfate, dyes, and salts. e chemical industry is responsi-
ble for emissions of solvents, oating sulfates, sediments,
fats, greases, heavy metals, dyes, biocides, surfactants, ha-
logenated hydrocarbons, fats, oils, ammonium, nitrates,
and phosphates [10].
In recent years, several environmental assessment
studies have been conducted on the Machángara river.
ey have revealed environmental impacts due to the
generation of odors, and the discharge of industrial ef-
uents that exceed the limits allowed by environmental
legislation. In response to this alarming situation, the En-
vironmental Sanitation Program (PSA) of the Metropoli-
tan Public Company of Drinking Water and Sanitation of
Quito (EPMAPS-Q) implemented the “Plan for the De-
contamination of Quito’s Rivers” in 2007. It included the
collection and treatment of wastewater from parts of the
city. In 2017, the rst wastewater treatment plant was in-
augurated in “Quitumbe” sector, the rst in the city, but
no noticeable results have been seen. erefore, pollution
is still visible. A press release published in the newspaper
“El Comercio” in September 2019 showed that, despite
the inauguration of the rst wastewater treatment plant
in southern Quito, the pollution situation of the Machán-
gara river remains alarming. e treatment plant built in
the “Quitumbe” sector has the capacity to treat up to 9.5
million liters of wastewater per day. However, the plant
is not operating at 100% capacity due to technical prob-
lems. In addition, illegal discharges of wastewater into
the river have been detected from areas surrounding the
treatment plant, which has led to criticism from environ-
mental organizations, and citizens in general [12]. e
study perfomed by Campaña et al. [4], evaluated vari-
ous environmental parameters of the river, including
temperature and pH, which are in compliance with ec-
uadorian regulations. However, the values of Biochem-
ical Oxygen Demand (), Chemical Oxygen Demand (),
dissolved oxygen, and turbidity exceed the limits estab-
lished by the regulations. Furthermore, the presence of
heavy metals such as chromium (Cr), and cadmium (Cd)
exceeds acceptable levels for agricultural use [13], high-
lighting the urgent need for more eective environmental
management and pollution control measures.
1. introduction
e problem of water pollution is a contemporary chal-
lenge worldwide. is phenomenon is not only limited
to industrialized or developing countries but aects all
levels of our society [1]. e water quality in river basins
is primarily determined by natural factors such as soil
type, and geology. However, human activities, particu-
larly agriculture, livestock, and urbanization along river
sub-basins, are the predominant sources of pollution in
Ecuador [2].
In Ecuador, the situation reects a mixed response
to water treatment eorts. By 2019, 70.1% of Ecuador’s
autonomous decentralized municipal governments
(GADMs) had implemented urban wastewater treat-
ment processes. In contrast, 26.3% had no treatment at
all, opting to discharge directly into water bodies [3]. is
uneven implementation has led to signicant pollution,
especially in urban basins. e highland region hosts the
largest number of treatment plants, representing 50% of
the total in Ecuador, while 31% are located in the coast
region, 18.5% in the amazon region, and 0.5% in the in-
sular region.
e direct discharge of sewage and waste into ur-
ban drainage basins is the main source of water pollution
[4]. Rivers are aected by fecal coliforms, detergents, ni-
trates, phosphates, oils, and fats that exceed the limits set
by national environmental regulations. Rivers with com-
promised water quality oen lose their self-purication
capacity, resulting in severe ecological imbalances that
threaten biodiversity, and the sustainability of these eco-
systems [5].
To satisfy human needs, a daily consumption of three
liters of drinking water, and a total of twenty liters for
anthropogenic activities is required. Ecuador has the re-
markable advantage of having at its disposal a freshwater
supply of 22500 , a gure that exceeds the 1000 , recom-
mended by the World Health Organization (WHO) [6].
is situation reects the amount of water consumed by
the population, which increases the pollution of rivers
and seas. It aects not only the supply of drinking wa-
ter, but also the health of the organisms that depend on
it. It also causes adverse health eects such as reproduc-
tive problems, kidney damage, neurological diseases, and
cancer [7].
e Quito city exemplies the water quality challeng-
es faced by urban centers. Historically, the wastewater of
it was discharged directly into nearby streams and rivers.
However, rapid population growth has exacerbated waste-
water production, signicantly degrading the quality of
these water bodies [8]. e high population density of cit-
ies is a factor that aggravates the pollution of their water
resources, since there is a greater emission of waste, and
liquid euents [9]. With a current population of 2.8 mil-
lion, expected to reach 4.2 million by 2040, the pressure
on Quito’s water resources is expected to intensify [4].
121
Rodríguez S., et al.
1.1 LOCATION OF STUDY
e Machángara river is one of the main ones in Quito.
It crosses the entire city, originating in the south in the
“Cutuglagua” sector [14], spanning a total length of 22
kilometers. e river receives domestic and industrial ef-
uents from the city [15]. It joins the “San Pedro” river in
“Nayon”, which, together with the “Pisque” river, forms
the “Guayllabamba” river, a tributary that reaches “Es-
meraldas”, and ows into the pacic ocean [16].
As a river located in an urban environment, the
Machángara river presents signicant problems for the
inhabitants of this sector, such as unpleasant odors, the
proliferation of harmful animals, and vectors that trans-
mit diseases [17]. Likewise, like many rivers in Quito, it is
characterized by deep riverbeds, and steep slopes, which
limit access for any type of sampling. Along the river-
banks, abandoned structures in an advanced state of de-
terioration can be observed, which has an unfavorable
impact on the aesthetics of the city [18].
2. METHODS
To assess the biodegradability index of the organic matter
in the Machángara river, wastewater sampling from dis-
charge pipes located along the riverbanks was conduct-
ed, following the methodology described by Larrea et al.
[19]. According to their study, “sampling aims to provide
accurate information for evaluating the presence of emerg-
ing pollutants”, which in this case, helped to identify the
types of contaminants present in the river and to deter-
mine the most appropriate treatment methods based on
the biodegradability index [28, 29, 30].
e sampling of wastewater from the outfall pipes
was performed during the period between 2022 and 2023,
specically in the months of October, December, Febru-
ary, April, June, August and October. Four strategic points
along the Machángara river were considered, as shown
in Figure 1.
Figure 1.
Map of sampling site locations (e map of strategic points
for water samples collection)
ese points were chosen to take dierent points
along the river. e point 1 (P1) is located in the “Las
Cuadras” park in the southern part of the city, the point
2 (P2) is located in the “El Calzado” park, the point 3 (P3)
is near to the place “La Recoleta” (located close to Quito’s
historic center), and the point 4 (P4) is in the rural com-
munity of “Nayon”, located in the northern part of the city.
Table 1 below shows the UTM coordinates obtained
from Google Maps with the sectors corresponding to the
selected sampling points along the Machángara river.
Table 1.
Coordinates of the sampling points (WGS84 UTM 17S)
Point Sector Coordinates
P1 Las Cuadras 773041.77 E 9967956.90 N
P2 El Calzado 775349.40 E 9972083.50 N
P3 La Recoleta 776456.37 E 9974102.29 N
P4 Nayon 787752.00 E 9979495.70 N
Subsequently, a reconnaissance and characterization
of each sampling point was conducted to gather primary
data. Observations were made regarding the pollutants
present in the river, and along its banks. e anthropo-
genic activities taking place, as well as an evaluation of
the existing ora and fauna at each sampling site. Surveys
were also administered to gather the perceptions of the lo-
cal population regarding river contamination.
At the rst sampling site P1, located in “Las Cuadras”
park in Quitumbe, the presence of both solid urban waste
and foam in the water was documented. As described by
Cevallos [20], “the presence of surfactants and detergents
can generate foam, while solid materials serve as sourc-
es of pollution, impeding the proper ecological function
of the river if their composition is incompatible with the
aquatic environment”. Among the waste observed were
plastic covers, cups, soda bottles, cleaning containers, wa-
ter bottles, food wrappers, and fragments of household
items and textiles. Despite this contamination, diverse
plant species, including cedar, walnut, pumamaquis, and
nettle, were recorded. Additionally, wild birds, insects,
and rodents were noted in the area.
e second sampling site P2, located in the “Parque
Lineal Machángara “ within the “El Calzado” park, fea-
tured a variety of ora such as cedar, eucalyptus, nettle,
and zambo trees. However, solid waste, including branch-
es carried by the current, was also present. is area is af-
fected by several sources of pollution, particularly plastics
and organic waste from pets, which are oen le uncol-
lected by their owners. As noted by Cevallos [20], “bio-
logical contaminants from human and animal feces pose
risks to river health by fostering the proliferation of bac-
teria, fungi, viruses, and protozoa”. In this location, a low
diversity of large shrubs, and trees was observed, with
undergrowth surrounding the discharge pipe. Regarding
122
Analysis of the Biodegradability Index of Organic Matter in the Water of the Machangara River in Quito City
fauna, terrestrial species were absent, though birds such
as pigeons and blackbirds were seen in the vicinity.
e third site P3, situated in the “Parque Río Machán-
gara”, exhibited substantial urban waste, including bottles,
plastic bags, polypropylene containers, organic matter,
and surfactants. Although this location is easily accessible,
it poses a signicant safety risk due to an old, deteriorat-
ing bridge needed to cross the river, which is in disrepair.
Wastewater at this site is discharged directly into the river
via a concrete channel. e steep slopes in this area lead
to the accumulation of debris on the embankments, fur-
ther exacerbating pollution. e dominant plant species
observed was Kikuyo grass, described by Gonzalez [21],
as “drought-resistant and acting as a natural herbicide”.
Although, it is considered an invasive species and com-
monly used to feed livestock in nearby areas. Additional-
ly, the accumulation of garbage has attracted rodents and
insects, which have signicant environmental and public
health implications.
e fourth sampling point P4 in “Nayon”, known as
“Quebrada de Tanda or Quebrada Urahuaycu”, near the
Nayon hydroelectric plant. e presence of solid waste,
mainly plastic, and polypropylene, has been detected on
the banks of the river, as well as a large number of sur-
factants oating on the surface of the water. Despite this,
the site is easily accessible and has adequate infrastructure
to carry out the activity without physical risks. Regard-
ing the pollution in the sector, there is an accumulation
of garbage on the river banks, including plastic bags, food
leovers, and glasses. In addition, to the presence of a hy-
droelectric plant, and numerous nearby housing develop-
ments. In terms of ora, native shrubs, and plants such as
ferns, chilcas, and kikuyo were observed. As for the fau-
na, a wide variety of species were recorded, such as wild
birds and chickens, as well as cows, rats, and some insects
near the discharge point.
In addition, in this investigation, information was col-
lected in March 2023, obtaining a high margin of contam-
ination observed by the population in the surrounding
areas. Since more than 70% of those surveyed consider
them to have a high level of contamination. More than
half of those surveyed at all four sampling points report-
ed noticeable foul odors emanating from the Macháng-
ara river. e highest percentage of this perception was
reported at point 3, which is the “La Recoleta” sector, with
99%. e presence of foul odors can be a sign of water
contamination, and although it does not always directly
indicate the presence of toxic substances, it is important
to consider this perception of the respondents as a warn-
ing sign about the quality of the river water [22]. e pres-
ence of these odors has been related to various symptoms,
including headaches, nausea, vomiting, diarrhea, fatigue,
diculty concentrating, and depression. According to the
respondents, children are the most aected population
by the contamination of the Machángara river, with the
highest percentage on point 2 “Parque el calzado” (63%),
and the lowest in point 4 “Nayon” (44%). erefore, it
can be armed that all respondents in the dierent sec-
tors agree that the child population is the most aected
by this contamination. Furthermore, 97% of all surveyed
agreed on the necessity of mass environmental education
campaigns to promote social responsibility and increase
awareness about environmental protection.
e process of determining the biodegradability of or-
ganic matter was carried out by sampling in the areas of
interest. Considering their representativeness in the study,
four sampling points were selected as there was evidence
of the presence of pipes with direct discharges to the ef-
uent. Several parameters such as pH, total dissolved
solids (TDS), conductivity, temperature, alkalinity, tur-
bidity, total suspended solids (TSS) and residual chlorine
were measured in situ. While for the Biochemical Oxy-
gen Demand () and the Chemical Oxygen Demand () of
the water resource was analyzed directly in the laboratory.
Subsequently, the biodegradability index was quantied
according to the following ratio formula [23]. Equation 1
shows the formula for the biodegradability index.
Depending on the value obtained, the nature of the ef-
uent is indicated, and interpreted. If the euent contains
organic matter, degradation is relatively easy. Although,
there are exceptions such as fats, and oils, as well as inor-
ganic matter [24]. e range that classies the two types
of euents is shown in Table 2.
Table 2.
Organic and inorganic waste by biodegradability value [24]
Type of discharge
Inorganic <0.2
Organic >0.6
e intermediate ranges in the COD ratio, between
0.2 and 0.5, could indicate the combined presence of or-
ganic and inorganic euents.
e ability to degrade organic compounds provides
another variation for the result, which is reected in Ta-
ble 3, where the biodegradability capacity of the euent
is shown according to the ratio.
Table 2.
Relationship between the ratio and biodegradability in water [26]
Biodegradability
Highly biodegradable water >0.6
Fairly biodegradable water 0,4-0,6
Poorly biodegradable water 0,2-0,4
Non-biodegradable water <0.2
123
Rodríguez S., et al.
e results will also serve to establish an optimal pu-
rication mechanism for the organic matter present in the
Machángara river, as shown below:
Table 3.
Relationship between the ratio and the type of water [26]
Type of water
Highly biodegradable water >0.6
Can be treated biologically
Not biologically treatable
0,3-0,6
<0.3
2.1 BIOCHEMICAL OXYGEN DEMAND BOD5 AND
CHEMICAL OXYGEN DEMAND ANALYSIS
2.1.1 Determination of BOD by the APHA 5210 – B method.
e Biochemical Oxygen Demand (BOD) test is used as
an indirect measure of the amount of organic matter in
a sample. is analysis involves measuring the change
in dissolved oxygen (DO) concentration, caused by mi-
crobial activity that degrades organic matter in a sam-
ple. at is kept in a closed bottle and incubated under
specied temperature and dark conditions for 5 days.
DO measurements are taken before and aer incuba-
tion, and BOD is calculated from the dierence between
these measurements. e rst DO measurement is taken
shortly aer sample dilution, and any additional oxygen
consumption that occurs aer this measurement is add-
ed to the BOD [25].
2.1.2 Determination of Chemical Oxygen Demand (COD)
by the APHA 5220 – D method.
In Chemical Oxygen Demand (COD) analysis, the di-
chromate ion is used to oxidize the constituents present
in the sample. is process induces a change in the state
of chromium from hexavalent (VI) to trivalent (III), with
both coloring properties and absorption in the visible re-
gion of the spectrum. e dichromate ion shows high
absorption in the 400 nm region, while the absorption of
the chromic ion is signicantly lower in this region. On
the other hand, the chromic ion shows strong absorp-
tion in the 600 nm region, where dichromate has hardly
any absorption. In 9M sulfuric acid solution, the molar
extinction coecients for these forms of chromium are
approximately as follows: is 50 L/mol cm at 604 nm, is
380 L/mol cm at 444 nm, and is 25 L/mol cm at 426
nm. erefore, the point of maximum absorbance is at
420 nm. For COD concentrations between 100 and 900
mg/L, there is an increase in concentration in the 600
nm region. It is possible to dilute the sample to obtain
higher values. For COD concentrations equal to or less
than 90 mg/L, the reduction of the dichromate ion is de-
termined at 420 nm. Although, the corresponding for-
mation of causes a slight increase in absorbance at 420
nm, this eect is accounted for in the calibration proce-
dure [25].
3. results
e following are the results of the analysis of the 5-day
Biochemical Oxygen Demand (BOD5) and Chemical
Oxygen Demand (COD) at four sampling points during
a period of one year.
In terms of BOD5, sampling point 2 (El Recreo) had
the highest mean value with 199.71 ± DE 66.67 mg/L, fol-
lowed by point 3 (La Recoleta) with 205.43 ± DE 58.00
mg/L, point 1 (Las Cuadras) with 106.14 ± DE 75.50
mg/L, and nally point 4 (Nayon) with the lowest mean
value of 19.29 ± DE 21.55 mg/L (Table 5). e mini-
mum BOD5 value was recorded in P4 with 5 mg/L and
the maximum in P1 with 285 mg/L. ese results indi-
cate that P2 and P3 have signicantly higher and variable
BOD5 values throughout the year, with notable peaks in
February, June and August. In contrast, P4 showed low
variability with a peak in October 2022.
For COD, the sampling points followed a similar pat-
tern as for BOD5. e point P2 had the highest mean val-
ue with 395.86 ± DE 104.68 mg/L, followed by the point
P3 with 395.86 ± DE 104.68 mg/L, P1 with 221.86 ± DE
117.17 mg/L and the point P4 with the lowest mean value
of 31.00 ± DE 28.77 mg/L. e minimum COD value was
observed in point P4 with 9 mg/L and the maximum in
point P2 with 531 mg/L, indicating signicant variations.
As with BOD5, point P2 and point P3 showed signicant-
ly high and variable COD values, with peaks in February,
April, and August, while in point P4 showed less vari-
ability and a peak in October 2022. When comparing the
four sampling points, it is observed that in point P2 and
P3 have higher and more variable organic pollution levels,
both in BOD5 and COD, especially in certain periods of
the year such as February and August. is could indicate
environmental inuences or specic activities that aect
water quality at these points. In point P1, although it also
shows variability, it shows moderate levels of contamina-
tion compared to the two previous points. On the other
hand, point P4 stands out for its consistently low levels
of organic contamination, with little variability through-
out the year.
124
Analysis of the Biodegradability Index of Organic Matter in the Water of the Machangara River in Quito City
Since the biodegradability index values are moderate
to high (minimum 0.32, maximum 0.78) in the dierent
measurements over a year (Table 6). It could be concluded
that water contains a signicant amount of biodegradable
organic matter. In addition, there are seasonal variations
that should be taken into account in the implementation of
wastewater treatment. At the sampling point P1, April 2023
and August 2023 stand out as the periods with the great-
est inuence on the biodegradability index, with values of
0.71 and 0.64, respectively (Table 6 and Figure 2). At the
sampling point P2, the months of February 2023 and April
2023 show a higher biodegradability with indexes of 0.60,
while June and August 2023 show lower indexes around
0.41. On the other hand, the sampling point P3 shows sig-
nicant variations with a maximum in June 2023 with a
biodegradability index of 0.61 and a minimum in Febru-
ary 2023 of 0.44. At the sampling point P4, December 2022
stands out with an index of 0.78, showing high biodegrad-
ability compared to June 2023, which shows an index of
0.43. ese dierences highlight the importance of taking
into account seasonal variations when evaluating the ca-
pacity of wastewater to biodegrade organic matter, which
is crucial for eective water resource management and en-
vironmental protection.
Over the one-year period, the total biodegradability
indexes (BOD5/COD) were 0.48, 0.50, 0.52, and 0.57 for
P1, P2, P3, and P4 sampling points, respectively (Table
7). e sampling point P1 has the lowest index with 0.48,
which indicates that approximately 48% of the COD load
at this point is biodegradable. is suggests a signicant
presence of non-biodegradable organic matter or complex
chemical compounds that require more specic treatment
methods for their eective removal. On the other hand,
the sampling point P2 has an index of 0.50, which indi-
cates a similar proportion of biodegradable organic mat-
ter compared to P1, but with a slight improvement in
biodegradability. As for P3, a biodegradability index of
0.52 was recorded, indicating a moderately high level of
biodegradable organic matter in relation to the total COD
load. is could be due to the environmental conditions
and the composition of the pollutants, which favor great
-
er degradation by the microorganisms present in the wa-
ter. Finally, the sampling point P4 has the highest index
at 0.57, indicating that approximately 57% of the COD
load at this sampling point is biodegradable. is could
indicate a simpler pollutant composition or a lower to-
tal organic load, which is favorable from a water quali-
ty perspective.
Figure 2.
Temporal variation of the biodegradability index (DBO5/
DQO) at the sampling points over a one-year period
Table 5.
BOD5 and COD parameters of the sampling points in the period of one year (2022-2023)
Sampling points Parameters
Study period
October December February April June August October
2022 2022 2023 2023 2023 2023 2023
Las Cuadras (P1)
BOD5 65 38 102 77 93 285 83
COD 158 120 307 108 276 448 136
El Recreo (P2)
BOD5 120 146 316 232 193 161 230
COD 248 269 531 387 470 397 469
La Recoleta (P3)
BOD5 159 163 205 266 277 252 116
COD 320 341 468 469 451 508 214
Nayon (P4)
BOD5 66 18 7 9 6 5 24
COD 91 23 13 20 14 9 47
125
Rodríguez S., et al.
e results obtained for the biodegradability index
(BOD5/DQO) for the different wastewater sampling
points classify the water as fairly biodegradable, with val-
ues ranging from 0.48 to 0.57 (Table 7). is biodegrad-
ability is related to the presence of mixed discharges with
a signicant proportion of biodegradable organic matter.
At sampling points such as P2, P3, and P4 could be con-
sidered that there is a tendency towards organic matter.
In relation to the recommended treatment, the analyses
indicate that the evaluated wastewater requires mainly a
biological treatment approach to eectively reduce the
organic load. Eective treatment of this water resource is
likely to include aerobic biological processes, such as bi-
ological oxidation, to break down biodegradable organic
matter to reduce COD levels. In addition, initial physico-
chemical treatment may be required to adjust pH, remove
suspended solids, and other contaminants that could in-
terfere with biological processes.
In addition, during the development of this research,
color and turbidity were measured in situ at the four sam-
pling points and analysis of variance (ANOVA) was ap-
plied as described below:
Figure 3.
Sampling location-related relationship between color and turbidity.
From the information obtained in Figure 3, it was de-
termined that there are signicant dierences in the col-
or and turbidity measurements taken in the water of the
Machángara river with respect to the sampling locations.
erefore, there is a greater variation in water quality for
points P2, and P3 with respect to the rest of the sampling
points in the river.
Finally, this study also aims to be a contribution to the
study of the biodegradability index in the rivers of Ecua-
dor. In this regard, there are already some contributions
in this regard, as can be seen in a study carried out by
Molina [27], on the quality of water in a sector of the city
of Manta. e results obtained by calculating the biode-
gradability index indicate that the levels of contamination
are high, falling within the range of high biodegradabili-
ty of organic matter, as indicated by other similar studies.
4. CONCLUSIONS
rough the physicochemical analysis of the water of
the Machángara river, data on biochemical, and chemi-
cal oxygen demand were obtained from October 2022 to
October 2023. e biodegradability index was determi-
ned with these values, to establish, as a recommendation
in this research, the application of a biological treatment
to reduce the organic load, which can be accompanied
by a chemical treatment to avoid interference from sus-
pended solids and other impurities present in the water.
Likewise, this tributary was characterized as fair-
ly biodegradable with the presence of mixed discharg-
es containing organic and inorganic pollutants coming
mainly from the anthropogenic activities developed in
the study area. e presence of illegal pipes coming from
homes and industries that discharge directly into the riv-
er. In addition, by measuring in situ parameters such as
color and turbidity in the water coming from the Machán-
gara river. It was concluded that in the point P2 and P3,
there are high levels of contamination that signicantly af-
fect water quality, while in the point P1 and P4, there are
moderate levels. Urgent interventions, alongside stron-
ger public awareness eorts, are essential to restore water
quality and mitigate the river’s environmental and pub-
lic health impacts.
On the other hand, we must point out that there are
various types of biological treatments that can be carried
out in these cases, taking into consideration many aspects,
among which may be, depending on the type of contam-
inant and the medium to be treated. Among the most
common are aerobic biological treatment and anaerobic
biological treatment. Aerobic biological treatment, this
process is mainly used for the treatment of urban and in-
dustrial wastewater, where microorganisms decompose
organic matter in the presence of oxygen. While anaerobic
biological treatment is used in the treatment of wastewa-
ter from the food and agricultural industry, where mi-
croorganisms decompose organic matter in the absence
of oxygen, generating biogas as a byproduct.
REFERENCES
[1] R. Guadarrama Tejas, J. Kido Miranda, G. Roldan Antu-
nez, y M. Salas Salgado, «Contaminación del agua, Cien-
cias Ambientales y Recursos Naturales», pp. 1-10, 2016.
[2] G. Pauta, M. Velazco, D. Gutierrez, G. Vázquez, S. Rivera,
O. Morales, A. Abril, «Evaluación de la calidad de agua
126
Analysis of the Biodegradability Index of Organic Matter in the Water of the Machangara River in Quito City
de los ríos de la ciudad de Cuenca, Ecuador», Maska-
na, pp. 76-88, 2019.
[3] K. Mero, «Evaluación de las características sicoquímicas
y toxicológicas en aguas residuales de industrias farma-
ceúticas para la vericación de la calidad del agua en la
parroquia Tarqui y Pascuales, provincia del Guayas»,
Universidad Estatal de Milagro, 2023.
[4] A. Campaña, E. Gualoto, y V. Chiluisa, «Evaluación físi-
co-química y microbiológica de la calidad del agua de
los ríos Machángara y Monjas de la red hídrica del Dis-
trito Metropolitano de Quito», Bionatura, vol. 2, 2, pp.
305-310, 2017.
[5] J. Morocho, «Evaluación de la remoción de nitratos y fos-
fatos con microalga, especie “Chorella Vulgaris” en
agua residual procedente del río Machángara del sector
Chimbacalle, cantón Quito, provincia Pichincha 2022-
2023», Universidad Politécnica Salesiana, 2023.
[6] C. Soto, E. Reina, «Análisis de la calidad del agua en
la subcuenca del río Coca. Estudio técnico: DN-
CA-DHN-12-01. Coca, Ecuador», Secretaría Nacional
del Agua, 2012.
[7] Organización Mundial de la Salud, «Guías para la calidad
del agua de consumo humano», 2018.
[8] L. Gómez, M. Torres, A. Landázuri, L. Mayorga, «Progra-
ma para la Descontaminación de los Ríos de Quito»,
PDRQ, 2014.
[9] B. Villacis, «La crisis del oro azul: un análisis de la susten-
tabilidad del agua en la ciudad de Quito», Facultad La-
tinoamericana de Ciencias Sociales, 2005.
[10] I. Chisaguano, «Evaluación Ambiental del Río Machánga-
ra», Escuela Politécnica Nacional, 2015.
[11] A. Aguilar, «Modelación hidrológica de crecidas en la
Cuenca del río Machángara en la ciudad de Quito», Es-
cuela Politécnica Nacional, 2010.
[12] El Comercio, «Planta de Tratamiento de Aguas Residua-
les de Quitumbe procesa 80 litros de desechos por se-
gundo», 2019. Available at: https://www.elcomercio.
com/videos/agua-residual-quitumbe-tratamiento-de-
sechos.html
[13] E. Hidalgo, E. Osorio, «Evaluación y determinación de la
capacidad secuestrante de los metales pesados cromo
(Cr) y cadmio (Cd) por taxas de mohos aisladas de los
alrededores de los ríos Cutuchi y Machángara», Univer
-
sidad Politécnica Salesiana, Quito, 2013.
[14] El Telégrafo, «El río Machángara es un foco de contami-
nación», 2017. Available at: https://www.eltelegrafo.
com.ec/noticias/quito/1/el-rio-machangara-es-un-fo-
co-de-contaminacion
[15] J. Martínez, «El Machangara y el incansable intento por
descontaminarlo», 2019. Available at: https://www.ex-
preso.ec/actualidad/machangara-incansable-desconta-
minarlo-19742.html
[16] MAATE, «Ministerio del Ambiente, Agua y Transi-
ción Ecológica», 2019. Available at: https://www.
ambiente.gob.ec/sedimentos-que-llegan-hacia-man-
duriacu-son-arrastrados-por-el-guayllabamba-des-
de-el-inicio-de-su-formacion/
[17] J. Guerrero, «Tratamiento de aguas residuales utilizando
un consorcio de microorganismos encapsulados obte
-
nido del río Machangara, Quito: s.n», 2016.
[18] I. Reinoso, «Evaluación del Río Machángara, Escuela Po-
litécnica Nacional», 2015.
[19] J. Larrea, B. Romeu, D. Lugo, M. Rojas, «Aspectos funda-
mentales del monitoreo de calidad de las aguas: el río
almendares como caso de estudio», CENIC, 2(53), pp.
148-159, 2022.
[20] D. Cevallos, «Los derechos del río Machángara», Ponti-
cia Universidad Católica del Ecuador, 2020.
[21] K. Gonzalez, «Ficha Técnica del Pasto Kikuyo (Pennisetum
clandestinum) », 2020. Available at: https://infopastosy-
forrajes.com/pasto-de-pastoreo-de-clima-frio/pasto-ki-
kuyo-pennisetum-clandestinum
[22] H. Yamberla, «Sistema electrónico para medir los niveles
de contaminación del aire provocado por la desembo-
cadura de aguas servidas en el Río El Tejar en el sector
el Batán del cantón de Otavalo provincia de Imbabura»,
Universidad Técnica del Norte, 2023.
[23] J. Arteaga, D. Chingal, «Diagnóstico ambiental del “Bos-
que Protector Proyecto Ecológico Chiriboga” hacia la
inclusión al Sistema Nacional de Áreas Protegidas del
Ecuador (SNAP) y propuesta de estrategias de conser-
vación», Escuela Politécnica Nacional, 2017.
[24] P. Osorio, D. Peña, «Determinación de la relación DQO/
DBO5 en aguas residuales de comunas con población
menor a 25.000 habitantes en la VIII región», 2002.
Available at: https://www.studocu.com/bo/document/
universidad-cristiana-de-bolivia/algebra-lineal/trab-12-
apuntes/10467385
[25] E. Rice, L. Bridgewater, A.P.H. Association, «Standard me-
thods for the examination of water and wastewater»,
10(23), 2012.
[26] R. Miranda, M. Oliet, T. Pérez-Corona, V. Alonso, Y. Ma-
drid, J.C. Domínguez, P. García, «Tratamiento de Aguas
Residuales: Ejercicios Resueltos y Prácticas de Labora-
torio», Dextra Editorial S.L., 2019.
[27] L. Molina, «Análisis de calidad del agua en el sector
urbano del Malecón de Manta, provincia de Manabí»,
Universidad de Especialidades Espíritu Santo UEES,
2015. Available at: http://repositorio.uees.edu.ec/hand-
le/123456789/2178
[28] R. Saravanathamizhan, V.T. Perarasu, «Chapter 6 - Im-
provement of Biodegradability Index of Industrial Was-
tewater Using Different Pretreatment Techniques»,
Wastewater Treatment, Elsevier, pp. 103-136, 2021. ht-
tps://doi.org/10.1016/B978-0-12-821881-5.00006-4.
[29] F. Liu, D. Wang, «Dissolved organic carbon concentra-
tion and biodegradability across the global rivers: A
meta-analysis», Science of e Total Environment, Vol.
818, pp. 151828, 2022. https://doi.org/10.1016/j.scito-
tenv.2021.151828.
127
Analysis of the Biodegradability Index of Organic Matter in the Water of the Machangara River in Quito City
[30] N.T. Anh, L.D. Can, N.T. Nhan, B. Schmalz, T.L. Luu, «In-
uences of key factors on river water quality in urban
and rural areas: A review», Case Studies in Chemical
and Environmental Engineering, Vol. 8, pp. 100424,
2023. https://doi.org/10.1016/j.cscee.2023.100424.
annexes
Table 6.
Biodegradability index calculated for each sampling point over a one-year period (2022-2023).
Biodegradability index (BOD5/ COD)
Study period
Oct. Dec. Feb. Apr. Jun. Aug. Oct.
2022 2022 2023 2023 2023 2023 2023
Las Cuadras 0,41 0,32 0,33 0,71 0,34 0,64 0,61
El Recreo 0,48 0,54 0,60 0,60 0,41 0,41 0,49
La Recoleta 0,50 0,48 0,44 0,57 0,61 0,50 0,54
Nayon 0,73 0,78 0,54 0,45 0,43 0,56 0,51
Table 7.
Type of discharge, biodegradability of the water and recommended treatment according to the ratio.
Biodegradability index
(BOD5/COD)
Type of discharge Water biodegradability Recommended treatment
Las Cuadras 0.48 Mixed Fairly biodegradable
water
Biological
El Recreo 0.50 Mixed Fairly biodegradable
water
Biological
La Recoleta 0.52 Mixed Fairly biodegradable
water
Biological
Nayon 0.57 Mixed Fairly biodegradable
water
Biological
