2.1 Objective and Comparative Strategy

This study was designed to evaluate and compare the efficiency of pitaya cladode, moringa, and aluminum sulfate as coagulants for drinking water treatment. In addition to verifying the ideal acidic and natural pH conditions for the pitaya cladode, this investigation aims to assess the viability and sustainability of this plant coagulant for direct use (without an extraction step) and its application in areas with limited access to chemical coagulants.

2.1.1 Description of the Study Area

Itapeva Lagoon was selected as the study area due to its economic, cultural, environmental, and political relevance for the region. This lagoon, belonging to the Tramandaí River Basin, supplies the city of Torres, in Rio Grande do Sul, through the distribution system of the Rio Grande do Sul Sanitation Company (CORSAN) (Castro, 2019). Water samples were collected directly at CORSAN’s Water Treatment Plant (WTP), located on the north bank of Itapeva Lagoon, before any treatment. The collection followed the guidelines of the Brazilian National Guide for Collection and Preservation of Samples of the Brazilian National Water and Basic Sanitation Agency (Ana, 2023), ensuring adequate preservation for analysis.

2.1.2 Preparation of Coagulants

2.1.2.1 Pitaya Cladode (Selenicereus undatus (Haw.) D.R. Hunt)

The cladodes were collected in the garden of the Federal Institute of Santa Catarina (IFC), Santa Rosa do Sul/SC campus. After removing the spines, they were washed and cut transversely into slices 0.5 to 1 cm thick (Idris et al., 2013). The slices were dried in an oven at 65 °C until constant weight (Malavolta et al., 1997), crushed in a knife mill, and sieved to use the particle size fractions smaller than 600 µm.

2.1.2.2 Moringa Seeds (Moringa oleifera Lam.)

The seeds were macerated in a mortar and dried in an oven at 40 °C until constant weight (Hendrawati et al., 2016), without additional sieving due to oiliness.

2.1.2.2 Aluminum Sulfate

A concentrated solution of 5000 mg/L-1 of aluminum sulfate P.A was prepared for use in the tests.

2.1.2.3 Coagulation Assays

The coagulation tests were conducted at the IFC Soil Laboratory using JarTest equipment with a capacity of 1 L. The operating conditions were rapid stirring at 120 rpm for 1 minute, followed by slow stirring at 30 rpm for 20 minutes, and resting for 1 hour for sedimentation (Idris et al., 2013).

2.1.3 Tests Performed

Two triplicate tests were performed to identify the best conditions for coagulants to act in water treatment:

2.1.3.1 Test I - Influence of pH on the Water Clarification Process

The pH of the water was varied between 2 and 11, with a fixed rapid stirring time of 1 minute, to identify the pH with the best performance for each coagulant.

2.1.3.2 Test II - Influence of Rapid Agitation Time on the Water Clarification Process

The pH identified in Test I was used for each coagulant (pH 3 for pitaya cladode, pH 6 for aluminum sulfate, and natural pH for moringa), varying the rapid agitation time by 1, 4, 8, and 12 minutes, according to previous experiments and literature (Yu et al., 2011; Di Bernardo et al., 2005; Kan et al., 2002). Table 1 summarizes the varied and fixed parameters for each test.

Table 1 – Varied and fixed parameters in Tests I and II

Source: Authors (2025)

The concentration of aluminum sulfate was defined based on the levels generally used by the local sanitation utility, while the concentrations for the vegetable coagulants were based on previous studies (Hendrawati et al., 2016; Idris et al., 2013). In Test II, the performance of pitaya cladode at pH 3 and natural pH was compared to aluminum sulfate and moringa to evaluate the effect of rapid agitation time on the removal of turbidity and apparent color.

2.1.4 Monitored Potability Parameters

The efficiency of the coagulants was evaluated based on the parameters of turbidity, pH, and apparent color (wavelength of 460 nm) (Apha, 2023) according to the potability criteria defined by Ordinance GM/MS 888/21.

2.1.4.1 Statistical Analysis

Statistical analysis was conducted using the SISVAR software developed by the Department of Statistics of the Federal University of Lavras (UFLA). In a completely randomized design, the Tukey test was applied to compare means with a significance level of 5%.

The raw water used in this study was characterized to measure essential potability parameters. The mean initial values are presented in Table 2 and were measured before each test, aiming to evaluate the efficiency of the proposed coagulation and flocculation process.

Table 2 shows that water’s turbidity and apparent color values in Itapeva Lagoon exceed the limits established by Ordinance GM/MS 888/2021, highlighting the need for treatment before distribution for human consumption. Additional monitoring data (such as turbidity, BOD, and iron) provided by the Sanitation Company throughout 2021 indicate that the water exceeds the limits for Class 2 of CONAMA Resolution 357/2005, falling into Class 3 for some specific parameters. This classification reinforces the need for advanced treatment to guarantee the potability and safety of public supply (Brasil, 2005).

Table 2 – Initial physical-chemical parameters of the water from Itapeva Lagoon

aMPV - Maximum Permitted Value. Source: Authors (2025)

3.1 Test I – Influence of pH on the Water Clarification Process

The pH is a critical parameter in coagulation and flocculation as it directly affects the performance of natural and chemical coagulants (Som et al., 2021). Table 3 presents the results for turbidity removal at different pH, while Table 4 presents the apparent color values, indicating how performance varies according to pH for each coagulant.

At extreme pH values (pH 2), the water showed good clarification even without using coagulants (blank analysis). This phenomenon may be related to the variable load of inorganic and organic materials that cause turbidity and color, a characteristic influenced by the soil composition in the region (Stumm & Morgan, 1981 apud Fontes et al., 2001). In this sense, the Zero Charge Point (ZPC) of the colloidal particles present minimized the electrostatic repulsion and favored their spontaneous flocculation, resulting in water clarification (Fontes et al., 2001). The ZPC varies according to the mineral composition of the soil, ranging between pH 2 and 4 for some Si and Mn oxides and between pH 8 and 10 for certain Fe and Al oxides, which reinforces this observation (Fontes et al., 2001).

Table 3 – Influence of pH (T2) on turbidity removal by different coagulants (T1)

Where: lowercase letters indicate statistically significant differences between rows; uppercase letters indicate statistically significant differences between columns. CV - Coefficient of variation of repetitions; Pr>Fc - Significance of the F value for the T2 evaluations at each T1 level and of T1 at each T2 level (Tukey test). Source: Authors (2025)

The chemical coagulant aluminum sulfate showed its highest efficiency in removing turbidity in the pH range between 3 and 6 (Table 3), confirming its effectiveness within the range commonly used in WTPs. The pitaya cladode, in turn, demonstrated maximum efficiency at pH 3, with 91.55% turbidity removal, and a second performance at pH 10, reaching 40.51% removal. This behavior is consistent with Idris et al., (2013), who observed equivalent results with pitaya cladode in industrial effluents from rubber processing.

Previous studies have demonstrated the potential of pitaya cladode as a natural coagulant under different pH and concentration conditions. Shafad et al., (2013) reported that powdered pitaya cladode showed considerable efficiency in removing turbidity in neutral pH water, especially at low concentrations, reaching up to 85% removal at initial turbidity of 400 NTU with less than 20 mg/L-1. Rayudu et al., (2022) complemented this finding by reporting turbidity removals close to 84% in waters with an initial turbidity of 55 NTU, using a concentration of 250 mg/L-1. In the present study, however, the maximum efficiency of pitaya cladode was obtained at acidic pH (pH 3), achieving 91.55% turbidity removal at a moderate concentration (100 mg/L-1), a performance comparable to that of aluminum sulfate at the ideal conditions of pH 3 to 6.

Furthermore, it is noteworthy that this study uses pitaya cladode powder directly, without the coagulant extraction step, differing from the methodologies used in previous studies. This approach simplifies the process, making it more accessible for applications in locations with limited infrastructure. The results, therefore, reinforce the potential of pitaya cladode as a sustainable and easily applicable alternative for water treatment, especially in rural communities or regions with restricted access to conventional coagulants.

According to Freitas et al., (2015), the adsorption of cations in natural adsorbents is favored at pH above the charge neutrality point (Zeta Potential), while the adsorption of anions occurs at pH below this point. In studies by Idris et al., (2013) with the pitaya cladode (H. undatus), the charge neutrality point in distilled water remained stable between pH 4 and 8, a range corresponding to the lowest turbidity removals observed in this study. The higher removal of turbidity (Table 3) and apparent color (Table 4) at pH 3 indicates the predominance of negatively charged particles in the raw water of Itapeva Lagoon, a characteristic confirmed by Libânio (2010), who reports that the colloidal particles in the water are mainly negative.

Moringa seed demonstrated consistent performance across the pH range, achieving turbidity removals higher than 87% at all pH values assessed and showing similar efficacy to aluminum sulfate at pHs 7, 8, and 11. Studies such as those by Ndabigengesere and Narasiah (1998) also confirm this versatility of moringa in varying pH conditions. It is worth noting that the use of moringa (Moringa oleifera) in water treatment is already widely accepted, with consistent evidence of its efficiency in removing turbidity at different pHs values (Franco et al., 2017; Hendrawati et al., 2016), and it was used in this study for comparative purposes.

Table 4 – Influence of pH (T2) on removing the apparent color by different coagulants (T1)

Where: lowercase letters indicate statistically significant differences between rows; uppercase letters indicate statistically significant differences between columns. CV - Coefficient of variation of repetitions; Pr>Fc - Significance of the F value for the T2 evaluations at each T1 level and of T1 at each T2 level (Tukey test) Source: Authors (2025)

For the apparent color parameter (Table 4), aluminum sulfate performed better at pH 6, in line with the recommendations of Viessman and Hammer (2004), who identify the range between pH 5.5 and 8 as ideal for using this coagulant. On the other hand, the pitaya cladode had its maximum effectiveness at pH 3, a behavior also reported in other cacti, such as the prickly pear (Antilon et al., 2012).

Moringa showed better performance for the apparent color parameter at pH 8 and 11, remaining comparable to aluminum sulfate at the other pH values. However, none of the coagulants assessed managed to reach the 15 uH limit established by Ordinance GM/MS 888/21 for apparent color.

For Test II, the best-performing pHs for each coagulant were selected: natural pH (~7) for moringa, pH 6 for aluminum sulfate, and pH 3 for pitaya cladode, with the inclusion of the natural pH for the latter, allowing a more robust comparative analysis.

3.2 Test II – Influence of Rapid Agitation Time on the Water Clarification Process

The rapid agitation step allows uniform mixing between the coagulant and the sample, facilitating the formation of flocs (Libânio, 2010). The speed gradients favor encounters between particles, enabling the formation of larger and denser flakes (Di Bernardo et al., 2017). In Test II, the rapid agitation time was varied between 1, 4, 8, and 12 minutes to evaluate the performance of the coagulants.

For the turbidity (Table 5A) and apparent color (Table 5B) parameters, aluminum sulfate and pitaya cladode at pH 3 did not present statistically significant differences over the tested times, reaching removals above 90% at all times. However, for the pitaya cladode at pH 3, agitation times of 8 and 12 minutes provided slightly higher removals, reaching 97.40% and 98.2% turbidity, respectively. These values indicate that the pitaya cladode may exhibit even higher efficiency with prolonged contact time, suggesting a potential need for adjustment in agitation time to optimize its performance.

The pitaya cladode and moringa at natural pH demonstrated variation in efficiency according to the rapid agitation time. Moringa showed good performance in short times (1 and 4 minutes), with turbidity removal of 87.76% in 1 minute, which is close to enough to meet the turbidity limit of 5 uT established by Ordinance GM/MS 888/2021, although still lower than the performance of aluminum sulfate. This performance reflects the effectiveness of moringa at reduced contact times, a result also observed by Cardoso et al., (2008) at neutral pH. The pitaya cladode at natural pH required longer agitation (8 and 12 minutes) to reach an effective removal level, with removal percentages of 74.62% and 88.27%, respectively.

Table 5 – Effect of rapid agitation time (T2) on the removal of turbidity (5A) and apparent color (5B) after use of coagulants (T1)

Where: lowercase letters indicate statistically significant differences between rows; uppercase letters indicate statistically significant differences between columns. CV - Coefficient of variation of repetitions; Pr>Fc - Significance of the F value for the T2 evaluations at each T1 level and of T1 at each T2 level (Tukey test). Source: Authors (2025)

In comparison, aluminum sulfate at pH 6 achieved a removal percentage of 97.50% in 1 minute and maintained values of 97.50% or higher at all times assessed, meeting the turbidity limit under all conditions. Regarding the apparent color parameter, aluminum sulfate met the limit of 15 uH in agitation times starting from 4 minutes, while the pitaya cladode at pH 3 met this limit only with 12 minutes of rapid agitation. These results highlight the need to adjust the agitation time for each coagulant and reinforce the consistency of moringa as an efficient alternative for turbidity removal, especially at shorter contact times.

Statistical analysis of the results, applying the Tukey test, revealed that, in the removal of turbidity, the pitaya cladode at pH 3 presented statistically equivalent performance to aluminum sulfate at agitation times of 8 and 12 minutes, with removal values higher than 97%. However, for the apparent color parameter, pitaya cladode met the regulated limit only after 12 minutes of rapid agitation, differing significantly from moringa and aluminum sulfate (p < 0,05). Moringa was effective in shorter times, while aluminum sulfate was efficient throughout the range of times studied. These data suggest that agitation time is a critical variable for optimizing pitaya cladode performance, especially under decentralized treatment conditions.

The results reinforce the potential of pitaya cladode as a promising biocoagulant, especially at acidic pH, presenting performance comparable to aluminum sulfate. These findings support the continuation of the research, which will evaluate how different concentrations influence additional parameters, such as DOC, in search of practical and sustainable solutions for water treatment.

This article presents significant contributions by highlighting the potential of pitaya cladode as a plant coagulant in the treatment of water for human consumption, meeting, under different conditions, the potability parameters of Ordinance GM/MS 888/2021. The use of agricultural waste as raw material promotes the economic development of rural producers and represents an advance in the replacement of chemical coagulants, reducing environmental impacts related to waste in treated water and in the sludge generated.

At pH 3, pitaya cladode demonstrated statistically equivalent performance to aluminum sulfate in turbidity removal, proving its effectiveness in acidic conditions. However, with just 12 minutes of rapid agitation, it was possible to meet the potability limit for apparent color established by legislation, suggesting that its use may be more suitable for effluents or naturally acidic waters, where pH adjustments are already part of the process.

Under natural pH conditions, pitaya and moringa cladodes showed efficiency in turbidity removal. However, both presented limitations in meeting the apparent color parameter, as required by Brazilian legislation. Adapting operational variables, such as extended agitation times, demonstrated the potential to optimize pitaya cladode performance, especially in decentralized applications.

Unlike most studies that explore the use of the fruit, this study stands out for its innovation in investigating the pitaya cladode applied directly in powder form without prior extraction of the coagulant. This approach simplifies the process, reduces costs, and increases the viability of application in areas with limited infrastructure. The absence of publications documenting this application for drinking water reinforces this research’s originality and practical relevance.

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