2.1. Raw Water Characterization
Among the examined water quality parameters, sodium had a minimum concentration of 77 mg/L, a maximum concentration of 1616 mg/L, and an average concentration of 376 mg/L. In addition, it is important to note that sodium levels might affect irrigation water by possibly causing soil aggregates to scatter and crusts to form on the soil’s surface, which could prevent water from penetrating the soil [
33]. The great solubility of sodium minerals accounts for sodium’s pervasiveness in the aquatic environment. The time of year, regional and local hydrological and geological factors, and salt consumption patterns all have a significant impact on sodium concentrations. Sodium concentrations in groundwater typically range from 6 to 130 mg/L [
34].
Contrarily, calcium concentrations varied from 43 mg/L at the lowest end to 469 mg/L at the highest, with an average of 233 mg/L. In groundwater, calcium concentrations typically vary from 10 to 100 mg/L [
35]. The principal sources of calcium are limestones and dolomites, which are carbonate rocks that have been dissolved by groundwater’s carbonic acid.
Magnesium concentrations were found to range from 21 mg/L at the lowest value to 243 mg/L at the highest, with 106 mg/L being the average. Magnesium concentrations in natural groundwater range from zero to around 50 mg/l, and rarely exceed 100 mg/L; therefore, calcium-based hardness typically predominates [
36]. It is beneficial to have an appropriate concentration of both calcium and magnesium in the water because they are both essential plant nutrients in general [
37]. Calcium and magnesium salts, however, may precipitate in the irrigation system if the water hardness is too high, damaging it or reducing its effectiveness [
38].
Additionally, potassium concentrations were measured at a low of 8 mg/L, a maximum of 79 mg/L, and an average value of 42 mg/L. Total dissolved solids were measured with a minimum concentration of 5377 mg/L and a maximum concentration of 9845.5 mg/L, with an average value of 7680 mg/L. Electrical conductivity was also measured with a minimum concentration of 3114 μS/cm, a maximum concentration of 12,328 μS/cm, and an average concentration of 6286 μS/cm. It should be noted that measuring the electrical conductivity of irrigation water is a more convenient and indirect way to find out how much salt is present in it. The concentration of salt increases with conductivity [
39]. As a result, a key measure for estimating the amount of dissolved salts in soil and water is electrical conductivity. Fresh groundwater typically has an electrical conductivity of less than 150 μS/cm. The average electrical conductivity measured in this study is 51.20 times higher than the average value for electrical conductivity in freshwater, or 5119.83% higher than the average typical value.
The findings of the data distribution analysis using the raw groundwater results are summarized in
Figure 1. The distribution of the water quality data from the investigated parameters is regarded as being “negatively skewed” since the median in the boxplots from
Figure 2a (TDS),
Figure 2b (Ca
2+), and
Figure 2c (K
+) is closer to the upper or top quartile. In the list of the analyzed samples, the data show a higher frequency of low-concentration values than high-concentration values. The median is seen to be more closely aligned with the lower quartile in
Figure 2a (EC) and
Figure 2b (Na
+), respectively, indicating that the water quality data are positively skewed, with a larger frequency of high-concentration values than low-concentration values. Additionally, the median is seen to be nearer the center in the boxplots from
Figure 1c (Mg
2+), suggesting that the distribution of the water quality data is symmetric or normal.
2.2. Relationship between the Investigated Water Quality Parameters
In this part of the study, the correlation matrix was computed from sodium, calcium, magnesium, total dissolved solids, and pH. The selection of the investigated parameters is based on the fact that they have a relatively high potential of affecting irrigation systems. Major basic cations, also known as macronutrients, such as sodium, potassium, calcium, and magnesium, are geogenic solutes that primarily result from the weathering of rocks. Additionally, being close to the sea can raise the concentrations of these ions in the groundwater [
40]. The correlation matrix aids in forecasting how the relationships between the variables will change over time. The correlation matrix gives a broad overview of the more or less significant relationship between various variables. It is an effective tool for compiling a sizable dataset and for locating and displaying data patterns. From
Table 1, it can be seen that the highest correlation coefficient (0.966) was achieved from sodium and electrical conductivity. The phenomenon can be related to the fact that the conductivity rises with an increase in ion concentration because the ions in the solution carry the electrical current. As a result, conductivity rises when substances combine with water and split into ions. In that regard, more electrical conductivity is equivalent to more free ions [
41,
42]. To be more specific, due to their ability to move, ions in solutions can conduct electricity, which explains the strong correlation between sodium and electrical conductivity. When sodium (Na
+) and chlorine (Cl
−) combine to form sodium chloride in seawater, more electricity is conveyed, increasing the conductivity of the solution. In water, conductivity is caused by the transfer of electricity between ions. In plainer terms, conductivity rises in proportion to salinity [
43]. In the study conducted by Yupeng et al. [
44], on the total tissue sodium content at 3T/4T and quantitative conductivity mapping, a relatively high positive correlation was also observed between tissue conductivity and total sodium concentration with a
p-value < 0.005.
TDS and sodium resulted in a correlation coefficient of 0.946, which also falls under the “very high” correlation group. Water’s total dissolved solids content is one of the main contributors to the particles and sediments that give it its color, flavor, and odor, as well as a general indicator of water quality. Therefore, the high correlation between total dissolved solids and sodium can be linked to the fact that total dissolved solids are the inorganic salts that are dissolved in water, mostly calcium, magnesium, potassium, sodium, bicarbonates, chlorides, and sulfates [
45]. Therefore, an increase in sodium content in the water definitely increases the concentration of total dissolved solids.
Moreover, a high correlation coefficient (0.945) can also be observed between total dissolved solids and electrical conductivity. Conductivity, a metric of water’s capacity to carry an electric current, is directly related to the total amount of dissolved salts in the solution. This is due to the fact that as salts dissolve, positive and negative ions that can conduct an electrical current in proportion to their concentration. It should also be noted that water quality measures such as conductivity (EC) and total dissolved solids (TDS) are used to describe salinity levels. In the literature, the two parameters have been observed to be linearly correlating and can be expressed using Equation (1) [
46].
where k is the proportionality constant.
More steps are involved in determining TDS from a water sample than in determining EC. TDS analysis is crucial since it can show groundwater quality, and because it allows us to understand the impact of seawater intrusion better than EC analysis. These factors make it interesting to conduct a study on the determination of TDS/EC ratios. From the EC result, the ratio value can be used to calculate the TDS concentration.
From
Table 1, it can also be observed that pH correlated favorably with some of the parameters that were examined as determined by the correlation coefficients. In other words, the concentration of the parameters under investigation somewhat rose when pH was high.
On the other hand, most of the analyzed water quality parameters were found to be significantly correlated with one another, which is a phenomenon that can also be strongly related to their point of origin [
47].
2.4. Removal Efficiency
The results of the removal efficiency after the raw groundwater samples were subjected to the 0.5 m column depth are shown in
Figure 3.
Figure 3 shows that calcium had the highest recorded removal efficiency at 98.9% and sodium (Na
+) had the lowest removal efficiency at 40.2%. On the other hand, the highest recorded Na
+ removal efficiency from 0.5 m filter depth was 93.51%. It is important to note that ion exchange, adsorption, and salt storage are the major mechanisms controlling the process by which zeolites remove salt [
48]. The ion exchange procedure is influenced by a number of variables, including the geochemical characteristics of zeolite, pH, co-existing anions, concentration, valency, surface charge, and experimental circumstances. The behavior of the Na
+ ion adsorption isotherm on zeolites is composition-dependent and is generally claimed to follow either the Langmuir or Freundlich isotherm [
49]. Most of the time, Na+ adsorption kinetics on zeolites are of an exothermic pseudo-second-order kind. To make the most of low-quality saline/sodic wastewater’s beneficial uses, sodium removal using zeolites seems to be an efficient water treatment technology.
A minimum removal efficiency from Ca
2+ of 76.04% was observed, and a maximum removal efficiency of 99.38% was observed. It is crucial to emphasize that calcium is among the parameters leading to water hardness [
50]. Calcium hardness is a measurement of the number of calcium ions in the water. Calcium and magnesium carbonates, bicarbonates, chlorides, and sulfates make up the majority of these minerals. In the study conducted by Hailu et al. [
51], natural zeolite was used in the ion exchange process for groundwater to remove calcium, magnesium, and overall hardness; up to 80.2% removal efficiency was achieved for calcium.
From Mg
2+, the minimum recorded removal efficiency was 50.97%, while the maximum removal efficiency was 97.37%. Natural zeolite has also been found to be quite effective at removing magnesium from water in the literature. For instance, a magnesium removal efficiency of up to 81.73% was attained in the work by Shahmirzadi et al. [
52], who improved the removal and recovery of magnesium from aqueous solutions by employing modified zeolite.
Moreover, a minimum removal efficiency of 59.34% was recorded from K
+, with 97.20% being the maximum recorded removal efficiency. Nevertheless, the removal efficiencies of TDS and EC ranged between 53.38% and 92.29%. Generally, the treatment system showed a relatively high removal performance for all the investigated parameters. In the literature, natural zeolite has also been observed to be highly effective in the removal of other contaminants apart from the ones investigated in this study. For instance, in the study conducted by Magalhães et al. [
53], natural zeolite was reported to remove up to 96% of heavy metals and 90% of phosphoric compounds and was 96% effective for dyes, 80% effective for nitrogen compounds, and 89% effective for organics. It is also important to note that despite the fact that Cl
− removal was not a focus of the study, it remains one of the major challenges in treating water with natural zeolites. For example, in the study conducted by Takaaki Wajima et al. [
54], it was reported that the natural zeolite performance for the removal of Cl
− was only 20% removal efficiency. High chloride levels in irrigation water or soil are hazardous to plants and may have an impact on how well they perform and how productive they are [
55]. Therefore, it would be more appropriate to integrate the natural zeolite treatment system with other treatment approaches.
The more pores there are in the treatment media, the better the filtering effectiveness might be when it comes to filters. Because zeolite media have numerous pores, they not only catch particles between grains but also absorb them into their pores where they are then captured. The ability of the zeolite mineral to engage in cation exchange, whereby it absorbs positive ions from the water (such as dissolved metals, sodium, and ammonia) and exchanges them with other ions, contributes to this. Zeolite has a high pore density and a very effective surface area, allowing it to collect large quantities of pollutants without the need for backwashing. The adsorption process can be used by the media to catch and remove particles. Instead of passively becoming stuck between grains, particles cling to the surface of the media during this process, which is an active effect. According to conducted by Magalhães et al. [
53], the authors reported that the removal efficiency of contaminants by zeolite varies depending on the substance to be removed and can reach up to 96% for the removal of contaminants in water.
The filter depth plays a significant role in the removal of physicochemical contaminants in water. Surface and depth filtration are the two methods used by mechanical filtering to remove particles. Surface filtration, a sieving technique that captures large particles on the top or leading surface of the filter, is used to eliminate many particles. Smaller particles are eliminated using depth filtering after passing through the surface layer. With depth filtration, smaller particles get caught as they pass through a filter’s progressively smaller pores. Finally, a process known as adsorption is used to remove the tiniest particles and dissolved molecules. During this process, particles are drawn to the surface of the filter medium and held there by weak electrical forces. For instance, in the study conducted by Yong et al. [
56], that examined the performance of sand filtration system for polishing wastewater treatment with different sand bed depths (30 cm, 60 cm, and 90 cm), the highest total suspended solids and turbidity removal efficiencies of about 91.0% and 77.3%, respectively, were achieved from the sand depth of 90 cm.
Up to around 99.7% removal efficiency from the 1 m column depth treatment system was attained for potassium (K
+), with magnesium (Mg
2+) having the lowest removal efficiency of approximately 61.2%.
Figure 4 reveals further that despite the relatively high removal efficiency of the treatment system, the removal of sodium was generally low compared to the other investigated water quality parameters. According to Karmen et al. [
57], natural zeolite–clinoptilolite can achieve up to 100% removal efficiency for groundwater.
2.6. Tukey’s Honest Significance Test
When further examining the significance level of differences in terms of concentrations in the water samples using Tukey’s honest significance test, calcium and total dissolved solids were chosen as case studies.
Table 3 shows that when the list of data from calcium in the effluent treated by the 0.5 m column depth was compared against the list of data from the raw groundwater, the difference produced a
p-value of 0.001005, which is less than 0.01, making it statistically significant. Moreover, a
p-value of less than 0.01 was retrieved when the list of data from raw groundwater was compared against the list of data from the treated effluent with 1 m column depth. However, when the list of data from 0.5 m column depth was compared against the list of data from 1 m column depth, a
p-value of 0.899995 was retrieved, which is higher than 0.01, making the difference statistically insignificant. Similarly, the results of Tukey’s honest significance test continue to justify that the applied treatment systems are effective because of the disparities between the concentration values of treated effluents and raw groundwater; especially between the raw groundwater and the treated effluent using the 1 m column depth.
Similar to what was observed for calcium,
Table 4 demonstrates that the difference between the data lists from total dissolved solids in the effluent treated by the 0.5 m column depth and the data lists from the raw groundwater yielded a
p-value of 0.001005, which is less than 0.01, making it statistically significant. However, a
p-value of 0.136821 was found when the list of data from the 0.5 m column depth was contrasted with the list of data from the 1 m column depth, making the difference statistically insignificant.
2.7. Salinity Hazard Potential Analysis
The investigation of the salinity hazard potential in the raw groundwater was one of the study’s most significant components. Salinity hazard potential analysis was then performed on the purified samples from the two treatment systems, as defined by the column depths, to assess whether they were suitable for irrigation. Wilcox diagrams were then used to condense the salinity hazard potential analysis data. The two most important variables used in the salinity hazard potential study were the sodium adsorption ratio and electrical conductivity. The salinity hazard potential analysis of the unprocessed groundwater is summarized in
Figure 5a.
Figure 5a shows that the majority of the samples from the untreated groundwater were within the C4S4 range. Based on the electrical conductivity, it means most of the samples fell within C4, which is a “very high salinity” class, and based on the quality it means the water cannot be directly applied for irrigation purposes. Such water has to be purified before being used for irrigation for most of the plant species in the world. Additionally, based on the SAR, most of the samples fell within S4, which is a “very high sodium hazard” class, and based on the quality it means the water is generally unsatisfactory for irrigation purposes. Normally, when the total amount of salts in the irrigation water is such that the salts build in the root zone to the point that crop yields are negatively affected, then there is a salinity problem related to water quality [
58].
The salinity hazard potential analysis from the wastewater treated at the 0.5 m column depth is summarized in
Figure 5b.
Figure 5b shows that the majority of the samples from the raw groundwater fell within the C3S4 range. According to electrical conductivity, the majority of the samples fell into the “high salinity” C3 class, and according to water quality, the water can be used for irrigation with appropriate management techniques. Additionally, according to the SAR, the majority of the samples were classified as S4, or “extremely high sodium hazard,” which indicates that the water is typically unsuitable for irrigation. Still, such water has to be purified before being used for irrigation for most of the plant species in the world. The salinity hazard potential analysis from the wastewater treated at a 1 m column depth is summarized in
Figure 5c.
Figure 5c demonstrates that the majority of the samples from the untreated groundwater fell within the C1S3 range. Electrical conductivity indicates that the majority of the samples fell into the “low salinity” C1 classification, and water quality indicates that the water can be used right away for irrigation. SAR presents a small obstacle, with most samples falling in the S3 range and some in the S2 range. According to the classifications, the treated water can be utilized for irrigation in combination with some appropriate management measures.