Keywords:

Coagulation

Natural coagulants

Rapid mixing

Watermelon seeds

Turbidity

Potential of Citrullus lanatus seeds as a natural coagulant in drinking water treatment

Potencial como coagulante natural de las semillas de Citrullus lanatus en el tratamiento de agua

potable

Potencial como coagulante natural de sementes de Citrullus lanatus no tratamento de água potável

Sedolfo Jose Carrasquero Ferrer

Altamira Rosa Díaz Montiel

María Carolina Pire Sierra

Rev. Fac. Agron. (LUZ). 2025, 42(2): e254224

ISSN 2477-9407

DOI: https://doi.org/10.47280/RevFacAgron(LUZ).v42.n2.VIII

Environment

Associate editor: Professor Beltrán Briceño

University of Zulia, Faculty of Agronomy

Bolivarian Republic of Venezuela

Universidad Tecnológica Empresarial de Guayaquil,

Guayaquil, Ecuador.

Facultad de Ingeniería, Universidad del Zulia, Maracaibo,

Venezuela.

Programa de Ingeniería Agroindustrial. Universidad

Centrooccidental Lisandro Alvarado. Barquisimeto,

Venezuela.

Received: 19-02-2024

Accepted: 30-04-2025

Published: 20-05-2025

Abstract

Natural coagulants have received signicant attention due to

their biodegradable nature, cost-eectiveness, and abundance of

sources. The objective of the research was to analyze the eciency

of Citrullus lanatus seeds treating synthetic waters with three levels

of initial turbidity (13, 75, and 200 NTU), applying four rapid

mixing times (1, 2, 4, and 5 min) in the purication process. The

coagulant was prepared with 5 g of the seed previously ground,

sieved, defatted, and diluted in a volume of 1 L of distilled water.

Jar tests were performed using doses of 50, 70, 90, 100, 150, 200,

250, 300, 400, and 500 mg.L

-1

using true color and turbidity as

control parameters. The coagulation was performed at a speed of

100 rpm, while occulation lasted 20 minutes at 30 rpm, and the

resting phase was 30 minutes. It was obtained that the optimal doses

of C. lanatus in the treatment process were 50, 150, and 300 mg. L

-1

for waters with 13, 75 and 200 NTU, respectively, obtaining the

highest percentages of turbidity removal (96.6 %) and true color

(94.4 %) in water with 75 NTU. Furthermore, it was concluded that

increasing the time in the rapid mixing phase caused an increase in

the levels of turbidity and true color; being the time of 2 min the

one that generated water that meet the values desired by the current

Venezuelan drinking water regulations, which contemplates 1 NTU

for turbidity and 5 UC Pt-Co for true color.

This scientic publication in digital format is a continuation of the Printed Review: Legal Deposit pp 196802ZU42, ISSN 0378-7818.

Rev. Fac. Agron. (LUZ). 2025, 42(2): e254224 April-June. ISSN 2477-9409.

2-6 |

Resumen

Los coagulantes naturales han recibido una atención signicativa

debido a su naturaleza biodegradable, rentabilidad y abundancia de

fuentes. El objetivo de la investigación fue analizar la eciencia de las

semillas Citrullus lanatus tratando aguas sintéticas con tres niveles de

turbidez inicial (13, 75 y 200 UNT) aplicando cuatro tiempos en la

fase de mezcla rápida (1, 2, 4 y 5 min) en el proceso de claricación.

El coagulante se preparó con 5 g de la semilla previamente molida,

tamizada, desengrasada, y diluida en un volumen de 1 L de agua

destilada. Se realizaron pruebas de Jarra utilizando dosis de 50, 70,

90, 100, 150, 200, 250, 300, 400 y 500 mg.L

-1

, utilizando el color

verdadero y la turbidez como parámetros de control. La coagulación

se realizó a una velocidad de 100 rpm, mientras que, la oculación

duró 20 minutos a 30 rpm y la fase de reposo fue de 30 minutos.

Se obtuvo que las dosis óptimas de C. lanatus en el proceso de

tratamiento fueron 50, 150 y 300 mg.L

-1

para aguas con 13, 75 y

200 UNT, respectivamente, obteniendo los mayores porcentajes

de remoción de turbidez (96,6 %) y color verdadero (94,4 %) en el

agua con 75 UNT. Además, se concluyó que el aumento del tiempo

en la fase de mezcla rápida ocasionó un incremento en los niveles

de turbidez y color verdadero; siendo el tiempo de 2 min, el que

generó aguas que cumplen con los valores deseados por la normativa

venezolana vigente de agua potable que contempla 1 UNT para la

turbidez y 5 UC Pt-Co para el color verdadero.

Palabras clave: coagulación, coagulantes naturales, mezcla rápida,

semillas de sandía, turbidez.

Resumo

Os coagulantes naturais têm recebido atenção signicativa

devido à sua natureza biodegradável, custo-benefício e abundância

de fontes. O objetivo da pesquisa foi analisar a eciência de sementes

de Citrullus lanatus tratando águas sintéticas com três níveis de

turbidez inicial (13, 75 e 200 NTU) aplicando quatro tempos rápidos

de mistura (1, 2, 4 e 5 min) no processo de puricação. O coagulante

foi preparado com 5 g da semente previamente moída, peneirada,

desengordurada e diluída em volume de 1 L de água destilada. Os

testes de frascos foram realizados nas doses de 50, 70, 90, 100,

150, 200, 250, 300, 400 e 500 mg.L

-1

, utilizando cor verdadeira e

turbidez como parâmetros de controle. A coagulação foi realizada a

uma velocidade de 100 rpm, enquanto a oculação durou 20 minutos

a 30 rpm e a fase de repouso foi de 30 minutos. Obteve-se que as

doses ótimas de C. lanatus no processo de tratamento foram 50, 150

e 300 mg.L

-1

para águas com 13, 75 e 200 NTU, respectivamente,

obtendo-se os maiores percentuais de remoção de turbidez (96,6 %) e

cor verdadeira (94,4 %) em água com 75 NTU. Além disso, concluiu-

se que o aumento do tempo na fase de mistura rápida provocou

aumento nos níveis de turbidez e cor verdadeira; O tempo foi de 2

min, o que gerou águas que atendem aos valores desejados pela atual

regulamentação venezuelana que contempla 1 UNT para turbidez e 5

UC Pt-Co para cor.

Palavras-chave: coagulação, coagulantes naturais, mistura rápida,

sementes de melancia, turbidez.

Introduction

The demand for drinking water is increasing globally along

with the increase in population (Dahasahastra et al., 2022). Water

pollution is becoming more frequent, which has implications for

the development of communities, both economically and socially

(United Nations Children’s Fund [UNICEF], 2014). The lack of safe

water for human use, sanitation and cleanliness represents a major

and urgent health problem; therefore, improving water resources

management could prevent approximately 10 % of all diseases that

occur (World Health Organization - United Nations Children’s Fund

[WHO-UNICEF], 2015), especially in poor and vulnerable groups,

particularly children under ve years old (Roy, 2023).

Currently, there is a lack of access to safe water in rural and semi-

urban regions, where a signicant part of the population uses turbid

raw water. In addition, it is estimated that climate change will aect

the quality of drinking water, impacting public health (Mishra, 2023).

That is why the elimination of colloidal and suspended particles from

water is advantageous since it mitigates the inconveniences caused

by turbidity. In this regard, the Ocial Gazette of the Republic of

Venezuela (GORBV) No. 36,395 dated February 13, 1998, establishes

1 NTU (nephelometric turbidity units) as the desired value and 5

NTU as the maximum permissible limit in waters intended for human

consumption.

There are several conventional treatment methods for turbidity

removal, including coagulation-occulation, chemical adsorption,

and ltration. These methods eectively remove colloidal and

suspended particles larger than 5 μm (Salinas et al., 2023). The

coagulation that involves the use of specic chemicals, such as alum,

has been employed for the removal of colloids. However, research

has highlighted the potential risks associated with residual aluminum

intake, including neurodegenerative disorders and Alzheimer’s

disease. Therefore, it is of great importance to nd an option to replace

chemical coagulants. Natural substances represent an option for use

in water clarication due to their abundant availability, low toxicity,

high biodegradability, and low rate of sewage sludge production

(Balbinoti et al. 2024).

Natural coagulants can be produced using as raw material the

seeds of plants with high protein content that contain carboxyl,

hydroxyl, and amino groups with a signicant anity towards

various contaminants. Organic coagulants have been made from

various parts or seeds of plants such as Moringa oleifera (Junho

et al., 2021), Cassia stula (Arias et al., 2020), Tamarindus indica

(Carrasquero et al., 2019), Cucumis melo (Abuda et al.

, 2021), and

C. lanatus (Sathish et al., 2018), which are known for their natural

coagulant properties that remove turbidity, BOD, TSS, and COD, and

also possess antimicrobial power (Ugwu et al., 2017).

The objective of the research was to analyze the eciency of C.

lanatus seeds in treating synthetic waters with three initial turbidity

levels (13, 75, and 200 NTU), applying four rapid mixing times (1, 2,

4, and 5 min) in the clarication process.

Materials and methods

Preparation of synthetic turbid water (STW)

To prepare the STW, the procedure recommended by Okuda et

al. (2001) was used. Five grams of kaolinite clay were weighed and

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Carrasquero et al. Rev. Fac. Agron. (LUZ). 2025, 42(2): e254224

3-6 |

added to 1 L of distilled water. Subsequently, the dierent turbidity

values tested (13, 75, and 200 NTU) were obtained through successive

dilutions, with the following true color levels of 9, 19, and 32 UC Pt-

Co, respectively.

Coagulant solution

C. lanatus seeds were collected from residues from producing

fruit juices and salads in Maracaibo, Zulia state, Venezuela. It should

be noted that the endosperm was used; so, the seeds were washed,

then manually peeled and dried in an oven (Hamilton Beach, Mod.

31105, USA) at a temperature of 60 ± 5 °C for 2 h, then processed in a

manual mill (Corona Nacional, Venezuela) until obtain a our, which

was sieved through a 60 sieve (0.250 mm pore diameter) and stored in

amber jars for subsequent characterization, defatting and use.

The our obtained was defatted using the Soxhlet method. Twenty-

ve grams (25 g) were weighed and placed in an extraction cartridge,

and 150 mL of hexane (Merck, Purity 98.5 %) was added to the

ask; the extraction was performed for 8 h at a temperature of 45 °C.

Once the seeds were defatted, they were dried in an oven (Hamilton

Beach, Mod. 31105, USA) for 4 h at 50 °C (Association of Ocial

Analytical Chemists [AOAC], 2005). Then, they were characterized

by the following parameters: Humidity (Venezuelan Commission of

Industrial Standards [COVENIN], 1980), ash content (COVENIN,

1981a), and extractable oils and fats (COVENIN, 1981b).

The coagulant was prepared with 5 g of the seed previously

ground, sieved, and defatted, in a volume of 1 L of distilled water.

Subsequently, the evaluated doses were obtained by dilution: 50, 70,

90, 100, 150, 200, 250, 300, 400, and 500 mg.L

-1

as recommended

by Carrasquero et al. (2019). Coagulation-occulation tests were

performed using the Jar test in variable agitation equipment (Phipps and

Brid Inc., Mod. 300, USA), treating synthetic waters of low, medium,

and high turbidity, i.e., 13, 75, and 200 NTU, simulating drought and

rainfall conditions that can cause turbidity variations in natural water

bodies (Bina et al., 2009).

Eciency of the natural coagulant in the clarication process

Five hundred (500 mL) of STW were poured into the beakers, then

the dierent quantities of coagulant were dosed, and rapid mixing was

initiated, which corresponded to coagulation, at 100 rpm for 2 min,

followed by occulation with a slow mixture at 30 rpm for 20 min,

and, nally, sedimentation was carried out for 30 min. At the end of

this time, a sample of treated water was extracted, and ltered in a

vacuum pump using Whatman paper with a pore size of 25 μm, for the

determination of the physicochemical parameters: true color (platinum-

cobalt method), turbidity (nephelometric method), total alkalinity

(volumetric method), pH (standard potentiometric method), total

dissolved solids (gravimetric method), and total solids (gravimetric

method), following the Standard Methods for the Examination of

Water and Wastewater (Lipps et al., 2022).

To determine the eect of coagulation time in the rapid mixing

phase, Jar tests were performed by applying the doses that generated

the lowest values of turbidity and true color obtained in the previous

section under dierent times (1, 2, 4, and 5 min).

Experimental design

The results of the physicochemical parameters measured in seed

characterization were expressed using descriptive statistics, indicating

the values of central tendency (mean) and dispersion (standard

deviation). The results of the removal of physicochemical parameters

were studied using an analysis of variance and comparison of means

through Tukey’s test, using the statistical program IBM SPSS

Statistics. Before performing the ANOVAs, both the homogeneity

of the variances (Bartlett’s test) and the normal distribution of the

residuals (Kolmogorov-Smirnov Test) were checked, complying with

these precepts without requiring mathematical transformation.

In the rst stage, the eectiveness of the coagulant solution in

removing turbidity and true color for dierent initial turbidity levels

was evaluated, using a completely randomized design with a total of 9

assays (3 turbidity levels × 3 repetitions). For this statistical analysis,

a one-way ANOVA was applied, complemented with Tukey’s mean

separation test. In the second stage, the eect of mixing time on

coagulant eectiveness was studied, applying a 3×4 factorial design

(three turbidity levels by four stirring times), with a total of 12

treatments. In this case, a two-way ANOVA was used, followed by

Tukey’s test for the comparison of means.

Results and discussion

Physicochemical characteristics of C. lanatus seed

The preliminary characterization of the seed was carried out by

determining moisture, oils and fats, and ashes, as physicochemical

parameters (table 2).

Table 2. Physicochemical characteristics of C. lanatus seed.

Parameter ( % ) Arithmetic mean value ± standard deviation

Removable oils and fats 25.40 ± 1.76

Moisture 5.43 ± 0.42

Ash content 4.07 ± 0.15

n:3. N: Number of repetitions.

The average percentage of oils and fats was 25.40 %, a value

higher than that reported for other seeds used in the clarication

process, such as Mangifera indica L. (15.00 %), and Tamarindus

indica (7.63 %) (Carrasquero et al., 2019), which conrms the need

to defat the seed before performing clarication tests because the

natural coagulant could incorporate dissolved particles, fats and oils

from the seed (Carrasquero et al., 2015). Regarding the percentage

of moisture, an average value of 5.43 % was found, which is positive,

because a higher water content would accelerate the appearance of

decomposition reactions, which would cause the deterioration of the

seed.

Eectiveness of C. lanatus seeds by applying various doses

in the treatment of synthetic waters with three levels of initial

turbidity

At the end of the treatments, a decrease in turbidity was obtained

compared to the initial values. However, the increase in coagulant dose

was associated with slight increases in measured residual turbidity,

although they always remained below the original levels, evidencing

the eectiveness of the seed in turbidity removal (gure 1).

The results obtained showed a turbidity elimination range of

46.6 to 96.8 % during the analysis of all synthetic turbid waters.

For an initial turbidity of 13 NTU, values were obtained after the

coagulation-occulation process, ranging from 0.82 to 7.43 NTU,

applying doses between 50 and 500 mg.L

-1

. The highest percentages

of turbidity reduction, 91.8 and 92.5 %, were obtained using doses

of 50 and 70 mg.L

-1

, respectively, presenting statistical dierences

(p≤0.05) with the rest of the doses applied.

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Rev. Fac. Agron. (LUZ). 2025, 42(2): e254224 April-June. ISSN 2477-9409.

4-6 |

Figure 1. Variation in the turbidity of the treated water as a function

of the dose of C. lanatus seeds. Vertical bars indicate the ari-

thmetic mean ± standard deviation for n:3. Mean followed

by dierent letters in each bar of the same color indicates

signicant dierences according to Tukey’s test (p≤0.05)

Figure 2. Variation of true color in treated water as a function of

C. lanatus seed dose. Vertical bars indicate the arithmetic

mean ± standard deviation for n:3. Mean followed by

dierent letters in each bar of the same color indicates

signicant dierences according to Tukey’s test (p≤0.05).

Comparison of the eectiveness of C. lanatus coagulant for

dierent turbidity levels using optimal doses

Table 3 shows the selected optimal doses with the residual values

of pH, total solids, total dissolved solids, and total alkalinity. For

waters with a turbidity of 13 NTU, the dose of 50 mg.L

-1

was selected,

which allowed obtaining a nal true color value of 1.5 UC Pt-Co

and a turbidity of 0.82 NTU, while for waters with 75 NTU and 200

NTU, the doses of 150 and 300 mg.L

-1,

were chosen, which generated

residual values after treatment of 2.60 NTU and 2.2 UC Pt-Co, and

13.80 NTU and 6 UC Pt-Co, respectively.

According to the statistical analysis carried out, in waters of

13 NTU, it is possible to identify ve groups of doses that present

residual levels of turbidity with signicant dierences: 50-70, 90

-150, 200, 250-300, 400, and 500 mg.L

-1

. It is inferred that low doses

are eective in signicantly reducing the initial low turbidity. For all

the doses evaluated in this type of water, removal percentages greater

than 90 % were obtained.

From a dose of 90 mg.L

-1

, a partial saturation eect could be

observed, where the removal eciency begins to decrease. Partial

saturation is a phenomenon that occurs in coagulation processes when

an excessive amount of coagulant is added (such as C. lanatus seeds

in this case), exceeding the point at which the removal of suspended

particles is maximized, without yet reaching complete supersaturation

(Arciniega et al., 2024).

For waters with a turbidity of 75 NTU, the maximum removal of

95.7 % was achieved with a dose of 150 mg.L

-1

, obtaining a residual

value of 3.2 NTU. Concerning the waters of 200 NTU, even though

turbidity removals greater than 86.5 % were obtained, the nal values

of this parameter did not comply with the maximum value allowed in

the Venezuelan drinking water regulations (GORBV No.36.395, 1998).

The oscillating trend of the removal percentages obtained for the

natural coagulant and the increase in turbidity produced with doses

greater than 300 mg.L

-1

conrms that seed removal occurs because

the seed provides high molecular weight polymers (cationic proteins)

that can chemically adsorb the colloidal particle at xed adsorption

sites. As this phenomenon occurs between dierent colloids, the

particles agglomerate in groups. According to Mandizvo et al. (2022),

C. lanatus seeds are a rich source of protein, with protein fractions

including globulins (63.7 %), albumins (18.6 %), and glutelins (14.0

%).

A true color reduction was obtained for waters of 75 NTU, ranging

from 92.7 to 97.3 % with doses between 50 and 150 mg.L

-1

, obtaining

residual values between 2.0 and 5.5 UC, presenting signicant

dierences (p≤0.05) with the rest of the doses applied (gure 2). For

waters with 200 NTU, the dose range with the lowest residual values

was obtained when 50 and 200 mg.L

-1

was used with residual color

values ranging from 10 to 15 UC.

The increase in color may be because the seeds of C. lanatus

caused the dispersal of colloids that generated color in the water;

therefore, the seeds were ineective when doses greater than 300

mg.L

-1

were used, achieving the highest residual value (6.7 UC Pt-

Co) and the lowest percentage of color removal (33.3 %) for a dose of

500 mg.L

-1

in waters of 13 NTU.

It was shown that the natural coagulant did not produce signicant

changes in the residual pH of the treated water, maintaining this

parameter between 6.76 and 6.93 units. Awad et al. (2013) also

found that natural coagulants did not aect the pH of the water after

treatment.

Regarding alkalinity, values between 70 and 143 mg CaCO

-1

were obtained, being in the typical range for drinking water, which

ranges between 50 and 200 mg.L

-1

CaCO

(Pérez, 2016). When waters

have lower alkalinities, they are prone to contamination, because they

do not have the capacity to resist modications that generate pH

decreases.

Eect of rapid mixing time variation on the eectiveness of C.

lanatus seeds

Increasing the rapid mixing time from 1 to 5 minutes raised the

residual turbidity levels for the three types of water analyzed, when

comparing the results obtained for each time of the coagulation phase

(gure 3). This may be because the precipitated particles that formed

the oc have been resuspended (Adugna and Gebresilasie, 2018). For

an initial turbidity of 13 NTU, the lowest turbidity values after treatment

(0.84 and 0.92 NTU) were achieved with rapid mixing times of 1 and

2 min, with no signicant dierences (p>0.05) between these times.

Figure 3. Variation of residual turbidity and true color as a

function of rapid mixing time and dose of the solution

of watermelon seed (C. lanatus) for waters of dierent

turbidity levels. Vertical bars indicate the arithmetic

mean ± standard deviation for n:3. MPV: Maximum

permissible value. DV: Desirable value.

This scientic publication in digital format is a continuation of the Printed Review: Legal Deposit pp 196802ZU42, ISSN 0378-7818.

Carrasquero et al. Rev. Fac. Agron. (LUZ). 2025, 42(2): e254224

5-6 |

Regarding true color values, a behavior similar to that reported for

turbidity was obtained; that is, an increase in the residual color values

was observed. The lowest residual color values, 1.1 and 1.3 UC Pt-

Co, were obtained with mixing times of 1 and 2 min in low turbidity

waters (13 NTU). These values are lower than the maximum limit

established by Venezuelan regulations (15 UC Pt-Co).

The highest percentages of turbidity (91.6 – 93.9 %) and true

color (80.7 – 88.2 %) reduction were recorded when the times in the

1- and 2-min rapid mixing phase were used (gure 4).

Figure 4. Variation in the percentage of turbidity and true color

removal as a function of the rapid mixing phase in

the treatment process with C. lanatus for waters with

dierent levels of turbidity. Vertical bars indicate the

arithmetic mean ± standard deviation for n=3. Mean followed

by dierent letters in each bar of the same color indicates

signicant dierences according to Tukey’s test (p≤0.05).

Conclusions

The characterization of the watermelon seeds showed low

moisture content (5.43 %), ash content of 4.07 %, and a concentration

of oils and fats of 25.40 %, which indicates that the seed, once the

lipids have been extracted, can be used as a coagulant in the treatment

of drinking water.

The optimal doses of C. lanatus seed for the removal of turbidity

and true color in the coagulation-occulation process were 50, 150,

and 300 mg.L

-1

for waters of 13, 75, and 200 NTU. The highest

percentages of turbidity (96.6 %) and color (94.4 %) removal for

water with 75 NTU for a dose of 150 mg.L

-1

When analyzing the quality of the water treated with C. lanatus

seeds as a coagulant, it was possible to reduce turbidity values to levels

lower than the maximum limits established by the sanitary standards

of drinking water quality of 13 and 75 NTU. While for waters of

200 NTU, none of the doses used managed to obtain residual values

below this limit.

Increasing the rapid mixing time caused a rise in the residual

values of turbidity and color during the treatment of the waters of 13,

75 and 200 NTU; being the times of 1 and 2 minutes, which presented

signicant dierences compared to the others tested and resulted

in treated waters that meet the maximum values established in the

Venezuelan regulations for drinking water.

Acknowledgment

The authors express their gratitude for the support provided

by the Water Resources Sanitation Network using Innovative and

Sustainable Technologies (RED-AMARU) of the Ibero-American

Program of Science and Technology for Development (CYTED).

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Table 3. Comparison of watermelon seed coagulant (C. lanatus) for dierent turbidity levels using optimal doses

IT (NTU)

Dose

(mg.L

-1

)

% Removal

of turbidity

Removal

of true color

Total solids

(mg. L

-1)

Total Dissolved

Solids

(mg.L

-1

)

Total Alkalinity

(mg CaCO

-1

)

13 50 93.7 ± 1.7

86.6 ± 2.5

6.76

± 0.15 200 ± 17 103 ± 5 70 ± 17

75 150 96.5 ± 1.1

88.4 ± 2.1

6.93

± 0.61 240 ± 35 95 ± 4 140 ± 36

200 300 93.2 ± 1.8

81.3 ± 5.0

6.91

± 0.33 402 ± 67 99 ± 6 143 ± 12

IT: Initial turbidity. N:3. Mean followed by dierent letters in each row indicates signicant dierences according to Tukey’s test (p≤0.05)

This scientic publication in digital format is a continuation of the Printed Review: Legal Deposit pp 196802ZU42, ISSN 0378-7818.

Rev. Fac. Agron. (LUZ). 2025, 42(2): e254224 April-June. ISSN 2477-9409.

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