Multivariate analysis of physicochemical water quality variables from a decantation-digester reuse system¹

Análise multivariada de variáveis físico-químicas das águas de um sistema de reuso decanto digestor

ABSTRACT

The reuse of domestic effluent in rural areas is an emerging social technology, especially in family farming systems. In this context, the adoption of these systems requires attention to the quality of the water used, since its physicochemical characteristics may influence soil and agricultural crops. Thus, this study aimed to evaluate, through multivariate analysis, the physicochemical quality of water sources from three domestic effluent reuse systems intended for irrigation in rural communities of the semi-arid region, aiming at their suitability for agricultural use and the identification of potential risks of soil salinization and sodification. Sampling was carried out in four periods throughout the year, encompassing water from the supply source, domestic effluent entering the treatment system, and effluent treated by the decanter-digester system. Physicochemical analyses focused on pH, electrical conductivity (EC), calcium, magnesium, sodium, potassium, chlorides, carbonates, and bicarbonates, assessing their suitability for agricultural use. The correlation matrix showed strong associations among electrical conductivity, sodium, chloride, and sodium adsorption ratio, indicating these parameters as the main risk factors for agricultural use. The principal components discriminated the raw effluent with high sodification potential; source waters showed low ionic load; and the treated effluent exhibited a tendency toward salinity, indicating reduction in sodicity, but without reducing the concentration of dissolved salts. The results of the factor analysis confirmed these patterns, highlighting salinity as the main limitation to the agricultural reuse of treated effluent.

Key words:
water sustainability; effluent treatment; greywater; semi-arid region

HIGHLIGHTS:

Principal component analysis (PCA) discriminated the raw effluent with high sodification potential.

Supply water samples exhibited stable composition and low ionic load, serving as reference.

PCA indicates salinity trend in treated effluent linked to EC, Ca²⁺, Mg²⁺ and hardness.

RESUMO

O reuso de efluentes domésticos em áreas rurais é uma tecnologia social emergente, especialmente nos sistemas de agricultura familiar. Nesse contexto, a adoção desses sistemas requer atenção à qualidade da água utilizada, uma vez que suas características físico-químicas podem influenciar o solo e as culturas agrí colas. Assim, o estudo teve como objetivo avaliar, por meio da análise multivariada, a qualidade físico-química das fontes hídricas de três sistemas de reutilização de efluentes domésticos destinados à irrigação em comunidades rurais da região semiárida, visando à sua adequação para o uso agrícola e à identificação dos potenciais riscos de salinização e sodificação do solo. A amostragem foi realizada em quatro períodos ao longo do ano, abrangendo a água da fonte de abastecimento, o efluente doméstico ao sistema de tratamento e o efluente tratado pelo sistema de decantação-digestor. Análises físico-químicas focaram em pH, condutividade elétrica (CE), cálcio, magnésio, sódio, potássio, cloretos, carbonatos e bicarbonatos, avaliando sua adequação para uso agrícola. A matriz de correlação evidenciou fortes associações entre condutividade elétrica, sódio, cloreto e razão de adsorção de sódio, apontando esses parâmetros como principais fatores de risco ao uso agrícola. Os componentes principais discriminaram o efluente bruto com alto potencial de sodificação; as águas da fonte apresentaram baixa carga iônica; e o efluente tratado apresentou tendência à salinidade, indicando redução da sodicidade, porém não reduziu a concentração de sais dissolvidos. Os resultados da análise fatorial confirmaram esses padrões, destacando a salinidade como principal limitação ao reuso agrícola do efluente tratado.

Palavras-chave:
sustentabilidade hídrica; tratamento de efluentes; água cinza; semiárido

INTRODUCTION

Water availability is a determining factor for the sustainability of agricultural production, especially in semi-arid regions, where the limitation of water resources imposes restrictions on the use of water for irrigation (Alotaibi et al., 2023). In this context, the search for alternative water sources becomes a strategy to mitigate the impacts of scarcity on production systems. Domestic effluents (greywater) account for 50 to 80% of the total water used in households worldwide, excluding wastewater from bathrooms (Filali et al., 2022). When properly treated, these effluents can be reused for various domestic purposes, such as toilet flushing, floor cleaning, irrigation, car washing, among other uses (Shaikh & Ahammed, 2020).

The reuse of treated domestic effluents for agricultural purposes can alleviate the demand for potable water, thus reducing pressure on water resources, in addition to increasing water availability for irrigation (Nhenderere et al., 2025). Despite these benefits, the National Rural Sanitation Program (PNSR) indicates that 56.1% of rural households in Brazil dispose of their wastewater in rudimentary pits, while only 19.6% use septic tanks (BRASIL, 2019). Furthermore, approximately 85% of rural areas classified as non-clustered have inadequate or nonexistent sanitation solutions (BRASIL, 2019).

This scenario favors the adoption of informal wastewater reuse practices, especially domestic effluents, which, without treatment or adequate monitoring of their physicochemical quality, may pose environmental and agronomic risks when intended for irrigation (Saravanan et al., 2021). Thus, effluent treatment and its reuse in irrigation can help combat water scarcity and mitigate the loss of soil fertility caused by reductions in organic matter content (Choudri et al., 2020).

A previous study by Radingoana et al. (2020) demonstrated the potential use of treated domestic effluents for irrigation. The authors evaluated physicochemical parameters, including pH, electrical conductivity, major ions, and the sodium adsorption ratio, in waters intended for garden irrigation. However, the positive results reported in the study depend on controlled conditions and continuous monitoring of water quality, which does not always occur in simplified reuse systems adopted in rural areas. In such contexts, the lack of control and adequate maintenance of treatment systems may intensify environmental and agronomic risks, in addition to compromising human and animal health (Marques et al., 2021; Saravanan et al., 2021; Tusiime et al., 2022). Furthermore, the application of these effluents in irrigation may result in soil salinization and/or sodification processes (Ait-Mouheb et al., 2022), whose impacts are directly related to the physicochemical composition of the water used.

In this context, the need for studies that characterize the physicochemical quality of domestic effluents used in simplified treatment systems is evident, especially in rural areas of the Brazilian semi-arid region, where reuse occurs empirically and with limited technical support. The generation of local data is essential to evaluate the suitability of these effluents for agricultural irrigation, as well as supporting management strategies that minimize impacts on soil, crops, and environmental health.

Thus, this study aimed to evaluate, through multivariate analysis, the physicochemical quality of water sources from three domestic effluent reuse systems intended for irrigation in rural communities of the semi-arid region, aiming at their suitability for agricultural use and the identification of potential risks of soil salinization and sodification.

MATERIAL AND METHODS

The study was conducted in rural communities in the municipalities of Encanto and São Miguel, located in the state of Rio Grande do Norte, Brazil. The region has a climate characterized by precipitation concentrated between the months of February and June and an average annual temperature of approximately 28 °C.

For this study, three greywater treatment systems were selected, all installed in smallholder production areas within the semi-arid climate zone, specifically in the municipalities of Encanto and São Miguel, in the state of Rio Grande do Norte, Brazil. Both municipalities belong to the Serra de São Miguel Microregion, which is part of the Western Potiguar Mesoregion (IBGE, 1990). The municipality of Encanto covers an area of 125.749 km² and has a population of 6,016 inhabitants (IBGE, 2024a), while São Miguel spans 166.233 km² and has a population of 23,537 inhabitants (IBGE, 2024b).

Although each Family Production Unit (UPF) employs an identical treatment system, the production area and type of crops vary among them. While the primary focus is forage production, all three areas also grow fruit trees and, to a lesser extent, medicinal plants. Production area also varies: in the municipality of Encanto (Conceição community), UPF-0022 (06° 04’ 29.60” S 38° 15’ 42.11” W) has a production area of 1,660 m², and UPF-0024 (06° 04’ 55.37” S 38° 15’ 42.02” W), also in Encanto, has 609 m². Meanwhile, in the municipality of São Miguel, at Sítio Retiro, UPF-0244 has a production area of 932 m².

The implementation of these systems was made possible through the ‘Semeando Esperança no Alto Oeste Potiguar Project’, financed by the Banco do Nordeste do Brasil (BNB) via the PRODETER program, and the ‘Semeando Esperança no Semiárido Potiguar Project’, supported by MISEREOR - a Roman Catholic Church institution from Germany (SEAPAC, 2021).

The treatment systems were designed in accordance with NBR 7229 (ABNT, 2024) and consist of a grease trap (to retain most suspended solids), a single-chamber settling-digester, a filter, a treated-effluent reservoir, and an irrigation system. The effluent entering the system is collected through pipes and connections integrated into the domestic sanitation system, excluding wastewater from bathrooms (Figure 1).

Figure 1
Schematic of the simplified domestic effluent treatment system (decanter-digester model) for reuse of treated effluent in irrigation

In the study units, the reuse system was sized according to the capacity of each area. In this study, the system has a production capacity of up to 0.566 m³ per day, allowing complementary irrigation of suitable crops (Biscaro, 2014; SEAPAC, 2021). The treated effluent is intended for forage production, with predominance of prickly pear cactus (Opuntia stricta (Haw.) Haw.), cultivated in dense stands and intercropped with leucaena (Leucaena leucocephala) and Mombasa grass (Panicum maximum), and, in some cases, also associated with moringa (Moringa oleifera). Fruit trees and medicinal plants are integrated into the production system.

To evaluate the quality of water sources in each family unit, a totalof36watersampleswerecollectedfromdomesticsupplywater (source), raw effluent, andtreated effluent. Samples were collected throughout the monitoring period, during four campaigns spaced approximately four months apart. The variables selected for the evaluation of water and effluents focused on agricultural use. In quality evaluation, though desirable, no microbiological analyses were performed in the study.

The procedures for organizing the sampling campaigns, selecting materials and locations, and collecting the samples were based on the Technical Manual for Collection, Storage, Preservation, and Laboratory Analysis of Water Samples for Agricultural and Environmental Purposes by the Brazilian Agricultural Research Corporation - EMBRAPA (Prado et al., 2004).

After collection, the samples were sent to the Laboratory for Soil, Water, and Plant Analysis (LASAP) at the Federal Rural University of the Semi-Arid Region (UFERSA). The physicochemical analyses for irrigation purposes followed the laboratory’s protocol as well as guidelines from Prado et al. (2004) and BRASIL (2013). Hydrogen potential (pH) was measured using a Tecnal benchtop pH meter; electrical conductivity (EC) was measured with a LUCA-150 benchtop conductivity meter; sodium (Na⁺) and potassium (K⁺) contents were determined by flame photometry using a Weberlab flame photometer. Calcium (Ca²⁺), calcium + magnesium (Ca²⁺ + Mg²⁺), chloride (Cl⁻), carbonate (CO₃²⁻), and bicarbonate (HCO₃⁻) ions were also determined by titrimetry. Calcium was measured by EDTA titration after addition of 3 mL of 10% potassium hydroxide solution and Calcon indicator, until the color changed from pink to blue. The combined determination of calcium and magnesium was performed by EDTA titration, using pH 10 buffer solution and Eriochrome Black T indicator, until the color changed from pink to blue.

Chloride content was determined by titration with silver nitrate, using potassium chromate as indicator, until the color changed from yellow to brick orange. Carbonate was determined by acid-base titration with phenolphthalein, with its presence indicated by a pink color. Bicarbonate was determined in the same sample, after addition of methyl orange, by titration with 0.0025 M sulfuric acid until the color changed from yellow or light orange to intense orange Microbiological analysis?

Based on cation analysis, the sodium adsorption ratio (SAR) was determined according to Richards (1954), in order to assess the risk of soil sodification. SAR was calculated using Eq. 1:

(1) $$\mathrm{SAR}=\frac{{\mathrm{Na}}^{+}}{\sqrt{\frac{{\mathrm{Ca}}^{2+}+{\mathrm{Mg}}^{2+}}{2}}}$$

Where:

SAR - sodium adsorption ratio in (mmol L^-1)^0.5;

Na⁺ - sodium in water, in mmol_c L^-1;

Ca²⁺ - calcium in water, in mmol_c L^-1; and,

Mg²⁺ - magnesium in water, in mmol_c L^-1.

Interpretation of the potential use of water for irrigation, as well as the risks associated with salinity and soil infiltration problems, followed the classification of Ayers & Westcot (1985).

To interpret the results, multivariate statistics were applied using Statistica 7.0 software (Hilbe, 2007). To determine the strength and direction of relationships in the Pearson correlation matrix (ranging from 0 to 1, either positive or negative), the thresholds proposed by Cohen (1988) were used: negligible (0-0.3), weak (0.3-0.5), moderate (0.5-0.7), strong (0.7-0.9), and very strong (0.9-1). The statistical significance of correlations was evaluated using the t-test, adopting a 5% significance level (p ≤ 0.05). A positive direction indicates that an increase in one variable results in an increase in another, whereas a negative direction indicates the opposite.

Multivariate analyses were conducted based on the Pearson correlation matrix (p ≤ 0.05). The analyses considered three water sources: (i) supply water (SW), corresponding to water collected from the tap; (ii) raw effluent (RE), originating from the use of three residential family units (sinks and showers); and (iii) effluent treated by the treatment system (TTE). Based on these cases, Principal Component Analysis (PCA) and Factor Analysis were performed, considering eigenvalues greater than 1, with variable rotation using the Varimax method. Factor loadings were considered significant when ≥ 0.65, using Statistica 7.0 software (Hilbe, 2007).

RESULTS AND DISCUSSION

The Pearson correlation matrix (p ≤ 0.05) was used to evaluate the degree of association among the analyzed variables. In general, the presence of significant positive and negative, strong and very strong correlations was observed, indicating interdependence among the evaluated variables (Figure 2)

Figure 2
Pearson correlation matrix of the physicochemical water parameters in the greywater reuse system of the family production unit

According to Figure 2, very strong positive correlations were observed between calcium (Ca²⁺) and hardness (r = 0.99), magnesium (Mg²⁺) and hardness (r = 0.90), sodium (Na⁺) and SAR (r = 0.95), as well as between electrical conductivity (EC) and the set of cations (r = 0.90). Strong positive correlations were also identified between sodium (Na⁺) and cations (r = 0.85), calcium (Ca²⁺) and magnesium (Mg²⁺) (r = 0.82), chloride (Cl⁻) and anions (r = 0.81), carbonate (CO₃²⁻) and bicarbonate (HCO₃⁻) (r = 0.81), as well as between magnesium (Mg²⁺) and chloride (Cl⁻) (r = 0.81). Additionally, electrical conductivity showed positive correlations with hardness, chloride, magnesium, and calcium, with coefficients ranging from 0.73 to 0.77.

Among the variables that showed moderate positive correlations (0.50 ≤ r ≤ 0.69), the correlations of EC with Na⁺ and with anions stand out, as well as between magnesium (Mg²⁺) and anions. Correlations of chloride (Cl⁻) with cations and hardness were also observed. SAR correlated with cations. In addition, correlations also occurred between cations and anions, and between calcium (Ca²⁺) and chloride (Cl⁻) (Figure 2).

The correlation matrix made it possible to identify that the salinity of water from the water sources is strongly associated with an increase in the total concentration of dissolved ions, as evidenced by the very strong correlation between EC and cations and by the positive correlations with hardness, Cl⁻, Mg²⁺, and Ca²⁺. These results indicate electrical conductivity as an indicator of the total ionic load of water, being mainly controlled by calcium, magnesium, and chloride salts (Bernardo et al., 2019). The high correlation of hardness with calcium and magnesium indicates that these cations are primarily responsible for the hardness of the water sources. Supporting this interpretation, a study by Shrestha & Basnet (2018) indicated that both Ca²⁺ and Mg²⁺ contribute to increased electrical conductivity. However, it is important to note that, as EC reflects the overall concentration of dissolved salts, even if the water is not very hard, the presence of other ions may still increase its electrical conductivity.

The positive correlation observed between CO₃²⁻ and HCO₃⁻ indicates the existence of a carbonate system as the main pH buffering mechanism of the water sources, whereas the strong correlation between chloride ions and anions, as well as between magnesium and chloride, suggests that these ions may share both geochemical origins and anthropogenic sources, arising from the use of household products such as detergents, soap, and cleaning products commonly used in sinks, washing machines, dishwashing, and bathing (Budeli & Sibali, 2025). In addition, the very strong positive correlation between sodium and SAR (Figure 2) indicates that sodium acts as the main factor associated with increases in SAR. These results highlight the need for strict control of the water sources used in the system, particularly with regard to sodium levels, which in soil may promote particle dispersion, reduce infiltration and permeability processes, and increase the risk of sodification in agricultural systems (Mohanavelu et al., 2021).

In addition to positive correlations, the correlation matrix also revealed negative correlations among some variables. Strong negative correlations stand out between pH and Cl⁻ (-0.74), as well as between K⁺ and CO₃²⁻ (-0.75). Moderate negative correlations of pH with anions (-0.57) and with K⁺ (-0.55) were also observed. Electrical conductivity correlated negatively with CO₃²⁻ and HCO₃⁻, showing correlation coefficients of -0.74 and -0.75, respectively (Figure 2).

The negative correlations reveal electrochemical modifications in the samples as a function of increasing salts in the water sources. The negative correlation between EC and carbonated species (HCO₃⁻ and CO₃²⁻) indicates that, with the gradual increase in salinity, the carbonate system becomes less influential in controlling water chemistry, being partially consumed in neutralization and oxidation processes (He et al., 2025). This influence is directly reflected in pH, clearly observed in the negative correlations with chloride, anions, and potassium; the persistence of these ions favors pH reduction, even though the buffer system acts residually. Thus, while positive correlations define the dominant mechanisms, negative correlations explain the effects of the pressure exerted by increasing salts, of both natural and anthropogenic origin, on the chemical equilibrium of the water.

Principal Component Analysis (PCA) allowed synthesizing the variability of the evaluated physicochemical parameters into a few representative components, explaining 64.1% of the total variance through the first two principal components (Figure 3).

Figure 3
Correlation of physicochemical variables and distribution of samples in the F1 × F2 factorial plane, showing groupings by type and origin across water sources

The patterns observed in the correlation matrix, which indicated consistent positive associations between electrical conductivity and the main dissolved ions, are confirmed by the results of principal component analysis. In Figure 3, it can be observed that most physicochemical variables of the water sources are predominantly distributed along the horizontal axis, corresponding to the first principal component (PC1), which accounts for 44.4% of the total variability. Along this axis, EC, cations, Cl⁻, Ca²⁺, Mg²⁺, hardness, and anions stand out. This component describes the transition between source water and raw and treated effluents, reflecting the accumulation of dissolved salts throughout domestic use and the treatment process. In the opposite direction of PC1, the variables pH, HCO₃⁻, and CO₃²⁻ are observed, which are located closer to the center of the plot, indicating a lower relative contribution to the variability explained by this component. Despite this, pH stability throughout the system suggests the action of the carbonate-bicarbonate buffer system, which regulates the acid-base balance of the water, attenuating variations resulting from domestic use and treatment processes. Thus, unlike ions associated with salinization and sodicity, carbonated species play a regulatory role, contributing to pH maintenance but not to sample differentiation.

Variations in pH in domestic effluents are directly related to their sources of origin. Waters from sinks show greater pH variability due to the presence of fats, food residues, and detergents, whereas bathroom and laundry waters tend to show values close to neutrality to slightly alkaline (5.98-8.40). This pH range is due to the use of personal hygiene products such as shampoo, soap, toothpaste, chemical compounds present in detergents, oils, solvents, bleaches, and paints (Shaikh & Ahammed, 2020).

The low contribution of pH, bicarbonate, and carbonate to sample variability in this study indicates that water composition is likely dominated by bathroom wastewater, which would explain the high concentrations of dissolved salts that increase ionic load without promoting expressive changes in pH.

The second axis (PC2) explains 19.7% of the total data variance, reflecting a secondary gradient of variation among samples. Na⁺, K⁺, SAR, and cations contribute secondarily to the overall salinization gradient, being more strongly associated with a sodicity gradient (Figure 3). This result highlights the need to monitor Na⁺ levels in irrigation water, especially because it is a factor that contributes to soil particle dispersion, as well as to increased soil salinization and sodification (Zhang et al., 2024). In addition, another important aspect to consider is the potential risk of clogging in drip irrigation systems (Paiva et al., 2024).

Regarding sample distribution in the PCA across sampling campaigns, source waters (SW) are clustered near the origin, on the negative side of the first principal component (PC1), indicating low salinity and sodicity. It is also observed that samples from the different campaigns (SW_I, SW_II, SW_ III, and SW_IV) remain grouped within this same region, evidencing maintenance of water quality throughout the evaluated period (Figure 3). Proximity to pH and HCO₃⁻ reinforces the characterization of these waters as having lower salinity and greater chemical stability, with good hydrochemical quality and low risk of soil salinization and sodification, making them suitable for agricultural use.

On the other hand, the raw effluent (RE) shows greater spatial dispersion in the PCA, concentrating in the region influenced by Na⁺, K⁺, and SAR, which is even more evident in samples RE_III and RE_IV, indicating a high risk of sodification of the samples in these campaigns. The treated effluent (TE) exhibited an intermediate position, being mainly associated with variables related to mineralization and hardness, with better performance in samples TE_I and TE_II, whereas TE_III and TE_IV show greater proximity to salinity vectors. Considering the use of both raw and treated effluents for agricultural purposes, the results indicate that the raw effluent presents significant restrictions in all campaigns, especially in samples III and IV, while the treated effluent may be used for agricultural reuse with restrictions, provided that appropriate management practices are adopted.

The factor analysis reaffirms the patterns observed in the correlation matrix and in the PCA. The results indicate five factors (F1, F2, F3, F4, and F5), which together accounted for 90.58% of the total cumulative variance. Factor 1 explained 44.36% of the total variance and included the most relevant variables: EC, Ca²⁺, Mg²⁺, Cl⁻, hardness, cations, and anions, indicating that water quality is predominantly controlled by salinity and ionic mineralization (Table 1).

Table 1
Factor loadings, eigenvalues, and explained variance (%) of the first five principal components for physicochemical water variables in the domestic wastewater reuse system of three household units in the municipalities of Encanto and São Miguel, RN, Brazil

Variable	F1	F2	F3	F4	F5
pH	-0.27	0.16	0.47	0.22	0.79
EC	0.88	-0.31	0.01	-0.75	0.06
K+	0.59	0.58	-0.12	0.28	0.13
Na+	0.54	0.80	0.11	-0.19	-0.08
Ca2+	0.65	-0.42	0.24	-0.56	0.09
Mg2+	0.86	-0.18	-0.04	0.35	0.14
Cl-	0.88	-0.2	-0.09	0.38	-0.1
CO32--	-0.16	-0.01	0.75	0.16	-0.28
HCO3-	-0.33	-0.03	0.69	0.05	-0.21
SAR	0.34	0.91	0.06	-0.08	-0.09
Hardness	0.83	-0.4	0.17	-0.3	0.13
Cations	0.85	0.41	0.16	-0.28	0.01
Anions	0.82	-0.22	0.18	0.43	-0.2
Eigenvalues	5.77	2.56	1.45	1.13	0.88
Total variance (%)	44.36	19.68	11.14	8.67	6.73
Cumulative Total Variance (%)	44.36	64.04	75.18	83.85	90.58

Factor 2 represented 19.68% of the variance and was strongly influenced by Na⁺ and SAR, characterizing the sodicity of the water sources and the potential risk of soil sodification. Factor 3 contributed 11.14% and reflected the equilibrium of the system with CO₃²⁻ and HCO₃⁻, related to alkalinity and pH. Factors 4 and 5 had a lower contribution to the total variance, explaining 8.67 and 6.73%, and were associated with secondary variations and operational adjustments of the system, not representing dominant processes in water quality control.

The results obtained in this study reflect the efficiency of the treatment system adopted in the household units, especially with regard to the removal of organic matter and the overall improvement of treated effluent quality. However, the literature points out that the quality of treated effluent in decentralized systems is strongly influenced by factors such as household habits, number of residents, type of products used in the household, and climatic variability (Awasthi et al., 2024). In this context, although the system proves to be efficient in the removal of impurities, a limitation is observed regarding the reduction of dissolved salt concentration, since these compounds tend to be conservative throughout the treatment, and may become concentrated in the treated effluent. Despite this limitation, the reuse of treated effluent is feasible for different non-potable purposes, such as cleaning of external areas, floor washing, and use in sanitary flushes, as well as for agricultural irrigation, provided that appropriate water and soil management practices are adopted, aiming to minimize risks of salinization and sodification over time (Shaikh & Ahammed, 2020). Thus, the results confirm that the treatment system contributes significantly to the improvement of treated effluent quality, although the control of dissolved salts remains a challenge and should be considered carefully in reuse strategies.

CONCLUSIONS

• 1. The correlation matrix showed that the quality of the evaluated waters is strongly controlled by variables associated with salinity and sodicity, with emphasis on the correlations among electrical conductivity, sodium, chloride, total anions, and the sodium adsorption ratio, indicating that these parameters represent the main risk factors for agricultural use.

• 2. Principal component analysis (PCA) discriminated the raw effluent as having a high sodification potential, whereas the source waters showed a stable hydrochemical composition and low ionic load throughout the evaluated period. The treated effluent occupied an intermediate position, showing a tendency toward salinity, mainly associated with the variables electrical conductivity, calcium, magnesium, and hardness, indicating that the treatment system reduces sodicity but does not limit the concentration of dissolved salts.

• 3. Factor analysis confirmed the patterns observed in the PCA, reinforcing the separation between factors associated with sodicity and salinity as the main limiting component for the agricultural reuse of the treated effluent.

• 1
  Research developed at Universidade Federal Rural do Semi-Árido, Mossoró, RN, Brazil
• Ref. 300719
• Financing statement:
  There was no funding for this research.

Data Availability Statement:

There is no data underlying the article texts.

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Edited by

• Editors:
  Toshik Iarley da Silva & Hans Raj Gheyi

Publication Dates

• Publication in this collection
  21 Aug 2026
• Date of issue
  2026

History

• Received
  11 Sept 2025
• Accepted
  26 Apr 2026
• Published
  31 July 2026