Challenges in Phosphorus Removal from Eutrophic Waters Using Adsorption: A Laboratory Comparison of Commercial and Moringa-Derived Adsorbents

Abstract

To reduce the concentration of phosphorus, the main nutrient responsible for eutrophication, two adsorbents were tested: a commercial activated carbon and one produced from the pods of Moringa oleifera. A concentrated phosphorus solution representative of eutrophic ecosystems was produced at 0.210 mg·L⁻¹ and used as the adsorbate. Thirty-nine laboratory samples were prepared with adsorbent dosages ranging from 0.5 g∙L⁻¹ to 2.0 g∙L⁻¹, and statistical analyses were applied to evaluate the results. An increase in the concentration of phosphorus in the solution was detected in all the tests. Desorption occurred due to the presence of nutrients in the composition of the adsorbents, in addition to the mild physical activation and the use of H₃PO₄ as a chemical activator of the natural adsorbent, which further favored desorption at equilibrium, even for activated carbon. This work, therefore, highlights the limitations of using the adsorption technique to remove phosphorus from eutrophic aquatic ecosystems. It is recommended that other activation methods for M. oleifera pods be studied for phosphorus removal from water, as well as adsorption equilibrium, kinetics, and thermodynamic studies.

1. Introduction

Eutrophication is a natural process, defined by the slow aging of a body of water, or anthropogenic when the alteration of its trophic level occurs rapidly [1,2]. Recognized as a form of environmental pollution, it is caused by the influx of nitrogen and phosphorus into aquatic ecosystems [3]. The main sources of nutrient input to aquatic systems are represented by in natura wastewater discharge and agricultural fertilizer runoff, human activities that contribute to eutrophication [4,5].

The change in the concentration of chemical elements, especially phosphorus, triggers ecological imbalance by causing an increase in primary productivity, leading to instability in this aquatic metabolism [6]. The multiple uses of aquatic environments are compromised, with the loss of biodiversity due to the reduction in dissolved oxygen, as well as the alteration of other physicochemical parameters, such as pH, turbidity, and biochemical oxygen demand [7,8]. There are other environmental impacts resulting from eutrophication, such as the increased amount of plant biomass in aquatic ecosystems, such as reservoirs, which, when decomposed anaerobically, have as a by-product the release of the greenhouse gas methane. This process leads to increased global warming and climate change [9,10]. In addition to the loss of ecosystem services, the proliferation of some species of algae and cyanobacteria in the water body, a direct result of the increase in phosphorus concentration, can release toxins into the environment, which are formed as a byproduct of their metabolism [11,12]. Exposure, whether through ingestion of contaminated water or dermal contact, causes adverse effects on aquatic and terrestrial animals, including humans [13].

Thus, the mitigation and prevention of new impacts related to anthropogenic sources of nutrients in freshwater systems contribute to the fulfillment of the Sustainable Development Goals (SDGs), especially related to goal 6 Drinking Water and Sanitation and targets 6.3 and 6.9 which deal, respectively, with improving water quality, reducing pollution, and restoring aquatic ecosystems [14]. Low-cost methods for lowering trophic levels in freshwater ecosystems have been increasingly used and researched. Mitigation tools can be indirect, such as those described by Bicudo et al. (2020) [15] and Ayele and Atlabachew (2021) [16], which interrupt nutritional input. However, they do not completely solve the pollution since there is internal fertilization through the release of nutrients already present in the sediment into the water column [17,18]. This situation makes direct nutrient removal the most effective approach to treating eutrophication [19].

Phosphorus removal is, therefore, the primary factor to be studied, since it is the determining element in this form of pollution [20]. The techniques used for this can be physical, chemical, and biological. Chemical techniques include sediment dredging, aeration, and electrodialysis, which require high financial investment. Biological mechanisms, such as biofilms and the introduction of fish species, plants, and microorganisms, take a long time to remediate, require careful maintenance and high costs, and have proven not to be effective in removing phosphorus; factors that therefore make physicochemical methods, such as coagulation and adsorption, more reliable and used [19]. Although coagulation removes more than 70% of phosphorus, it generates a large amount of sludge, which contains part of the coagulant used, such as metals [21]. Adsorption, a unitary operation that consists of retaining ions from a fluid on a solid surface [22], is proving to be as effective an alternative as coagulation. Despite its ease of operation, it also often uses metals in its composition, such as aluminum, magnesium, iron, and silver [13]. Carbonaceous materials, such as activated carbon, can be used as adsorbents of phosphate species due to their microporosity [23].

The use of natural adsorbents for phosphorus removal is a promising alternative, made from plant biomass without the addition of metals [24]. One example is Moringa oleifera Lam, which belongs to the Moringaceae family. The Moringaceae family comprises 14 species, one of which, M. oleifera, has become known for its utilization in fertilizer, nutrition, biogas production, etc. [25,26,27]. M. oleifera is a widely abundant tree in sub-tropical and tropical regions such as Latin America, Asia, and Africa. The tree produces its seeds in pods, and is effective at adsorbing chemical elements in wastewater [28]. Its seeds and bark have been used in different states, as powder, activated carbon, and extract, and the biosorbent produced can retain metals, components of pharmaceuticals, dyes, and inorganic ions [29,30,31].

Processes using M. oleifera pods as sorbent have been reported in the literature for removing metals [32,33,34,35], diclofenac [36], atrazine [37], organic dyes [38], benzene [39], and ethyl parathion pesticide [40] from water. However, no studies were found in the literature that used M. oleifera pods as potential adsorbents for phosphorus. In addition, no studies were found evaluating the removal capacity via adsorption of phosphorus in eutrophicated aquatic ecosystems, i.e., with initial concentrations of the nutrient below 0.200 mg·L⁻¹, and this work aims to fill this knowledge gap.

In this context, this study aimed to verify the effectiveness of M. oleifera pods as a natural phosphorus adsorbent, to use them as an innovative technology to help reduce the trophic level of aquatic ecosystems. To this end, a concentration of phosphorus representative of eutrophied reservoirs was prepared. This solution was then subjected to adsorption processes using a natural adsorbent, i.e., activated carbon produced from M. oleifera pods, and a commercial adsorbent, industrialized powdered activated carbon. In addition, phosphorus concentration analyses were carried out before and after the adsorption process for the two types of adsorbents studied.

2. Materials and Methods

2.1. Preparation of the Adsorbent and Adsorbate

Moringa oleifera Lam. pods from the city of Maceió (AL, Brazil) were sent to the Hydraulics Laboratory of the Environmental Engineering Department, Institute of Science and Technology, UNESP, São José dos Campos Campus, Brazil, where the adsorbent was prepared, as described in the study by Heidarinejad et al. (2020) [41] (Figure 1). Firstly, branches and other impurities from the plant material were discarded, and their seeds and bark were reserved for later coagulation and adsorption studies, according to Batista et al. (2023) [42] and Chales et al. (2022) [43]. The pods were washed with deionized water to remove any impurities from the pods. To reduce the size of the pods, they were split with ordinary scissors and then ground in a domestic blender until a fine powder was formed.

For chemical activation, a process described by Bispo et al. (2021) [44] and Raji et al. (2023) [45], 85% phosphoric acid (H₃PO₄) from Synth was used, 0.1 M in a 1:5 m/v ratio, and this acid solution was left in contact with the crushed pods at room temperature for one hour. After this period, the material was placed in porcelain crucibles to be dried in a preheated SolidStell 42L SSDc digital oven for one hour at 105 °C. Then, for physical activation, the preheated Quimis muffle furnace was used for four hours, or until complete carbonization was observed at 300 °C [46]. Temperatures above 300 °C were not tested for activation to avoid compromising the activation yield. The material was then macerated in a mortar and pestle and washed with deionized water to remove the ash left by the carbonization and neutralize the pH, eliminating excess activating agents [47]. This process took place by adding the carbonized pods to a Whatman No. 1 filter (Whatman, Buckinghamshire, UK), which was positioned in a porcelain funnel on a kitassato connected to a SOLAB SL-61 vacuum pump (SOLAB Equipment, Piracicaba, Brazil).

The solution resulting from the vacuum filtration was measured for pH, color, and turbidity, respectively, using the Tecnopon mPA 210 pH meter (MS Tecnopon Equipment, Piracicaba, Brazil), the AquaColor PoliControl Cor (AquaColor Equipment, Diadema, Brazil), and the PoliControl AP2000 turbidimeter (AquaColor Equipment, Diadema, Brazil). The SolidStell 42L SSDc digital oven (SolidStell, Piracicaba, Brazil) was again used to dry the remaining material from the paper filters for fifteen hours at 105 °C, macerated with a mortar and pestle, and sieved through a 30-mesh sieve (600 µm) to guarantee a maximum particle size. The product was a natural powdered adsorbent produced from M. oleifera seed pods, hereafter referred to as V-MOH300.

A phosphorus solution was prepared for the adsorbate to represent eutrophied reservoirs, with a total phosphorus concentration of 0.210 mg·L⁻¹, within the range indicated by Wetzel (2001) [1]. This solution was prepared from a phosphorus standard solution with a concentration of 998 ± 4 µg·mL⁻¹ (Inorganic Ventures^®, Christiansburg, VA, USA). The phosphorus solution used in this experiment was prepared in volumetric flasks using a micropipette metal eject. The dilution water used to prepare the phosphorus solution was deionized water, and the standard phosphorus solution was diluted until reaching the desired concentration. The solution of the phosphorus was freshly prepared for every experiment.

2.2. Adsorption Tests

On an analytical balance, 0.0550 g, 0.0880 g, 0.1100 g, 0.1430 g, 0.1870 g, and 0.2200 g of V-MOH300 and industrialized Êxodo Científica powdered activated carbon (PAC) were weighed in different Erlenmeyer flasks. The choice of these masses was based on the study by Lopes et al. (2022) [30]. In each glass jar, 110 mL of phosphorus solution was added, placed in the Dubnoff Shaker (Nova Ética Products and Equipment, Vargem Grande Paulista, Brazil) and shaken at 100 rpm for 24 h at 25 °C. The tests were carried out in triplicate, with 18 treatments of each adsorbent and another 3 characterized as control, containing only the adsorbate, making a total of 39 samples. The adsorbent dosages were calculated, in g∙L⁻¹, by dividing their masses by the volume of solution added.

Additionally, to evaluate the release of phosphorus by the adsorbents, adsorption experiments containing deionized water (test medium), and 0.2200 g of each adsorbent were carried out. Each test was carried out in triplicate in addition to 3 other control samples (deionized water only), without adsorbent, making a total of 9 tests. The methodology used was the same as that for the phosphorus solution, as described above. Once the adsorption time had elapsed, the samples were removed from the shaker and filtered through a Whatman No. 1 paper filter to remove the solids and stored in polypropylene bottles. 0.5 mL of LS Chemicals 65% nitric acid (HNO₃) was added in each sample bottle for preservation. Total phosphorus concentrations were analyzed using the EPA method 200.7 [48]. The determination of phosphorus was carried out using acidified sample preparation followed by analysis by inductively coupled plasma optical emission spectrometry (Perkin-Elmer Optima, PerkerElmer Inc, Waltham, MA, USA) with an axial view mode and radio frequency (RF) generator of 1.45 kW. An analytical wavelength of 214.9 nm for phosphorus was chosen and interference check solutions was used. The limits of detection (LOD) and quantification (LOQ) for phosphorus were 0.003 mg·L⁻¹ and 0.01 mg·L⁻¹, respectively.

2.3. Data Analysis

The statistical analysis was carried out using Jamovi software version 2.2, considering a significance level of 5% (α = 0.05) and power of 80% (1 − β = 80%) in all cases. Firstly, the Shapiro-Wilk test was used to verify the normality of the data, since the experiment was carried out in triplicate, resulting in several samples (n) equal to three [49]. During the test, groups with and without normal distribution were detected. The Kruskal-Wallis non-parametric test was used in both experiments, as multiple comparative analyses were carried out between independent groups with and without normal distribution. For the groups that showed statistically significant differences, a multiple comparison analysis was carried out based on the Dwass-Steel-Critchlow-Fligner post hoc test to assess which groups showed statistically significant differences.

3. Results

For the natural adsorbent produced from M. oleifera pods, 204.192 g of pods were used, which resulted, after preparation, in 41.942 g of V-MOH300, with a yield of 20.5%. In this process, the main factor influencing the reduction in mass was physical activation, with a decrease of 29.2%, as well as losses during the process and the material retained on the 30-mesh sieve. The phosphorus concentration of the control samples was close to the adsorbate concentration used. As for the tests with the addition of adsorbent, all of them, except for the first replicate of PAC 0.0550 g, which indicated 0.20 mg·L⁻¹, resulted in a higher concentration of phosphorus than that present in the control sample, and there was also an increase in concentration as the dosage of adsorbent increased (Table 1).

Based on the observed increase in phosphorus concentration, the two adsorbents were evaluated again at their highest dosages to see if they were responsible for releasing the nutrient into the solution. Table 2 shows the results of the phosphorus concentrations resulting from these tests, which were carried out with deionized water as the test medium. For the control samples, the concentration of phosphorus remained at 0.01 mg·L⁻¹. However, with the presence of the adsorbents, a higher concentration of phosphorus was identified.

Table 3 shows the groups with statistically significant differences based on the Dwass-Steel-Critchlow-Fligner test. For the PAC experiments, there was no statistically significant difference in phosphorus concentrations between the control and the treatments with the three lowest dosages tested (0.5 g L⁻¹, 0.8 g L⁻¹, and 1.0 g L⁻¹) when the adsorbate was the phosphorus solution. However, at the higher dosages (1.3 g L⁻¹, 1.7 g L⁻¹, and 2.0 g L⁻¹), there was a statistically significant difference in phosphorus values compared to the concentrations of the nutrient detected in the control treatment.

In the experiments with V-MOH300 using the initial phosphorus solution, it was found that the phosphorus concentration in the control treatment was statistically different from the values resulting from all the tested dosages of the natural adsorbent (Table 3).

In addition, the difference identified is due to the increase in phosphorus concentration, similar to the behavior of PAC, which is also the case when only deionized water is used. In addition, all the tests differed statistically from each other, except when close dosages were used, i.e., there were no differences in phosphorus concentrations when comparing the following dosages of V-MOH300: 0.8 g L⁻¹ and 0.5 g L⁻¹, 1.0 g L⁻¹ and 0.5 g L⁻¹, 1.0 g L⁻¹ and 0.8 g L⁻¹, 1.3 g L⁻¹ and 1.0 g L⁻¹, 1.7 g L⁻¹ and 1.3 g L⁻¹, 2.0 g L⁻¹, and 1.7 g L⁻¹.

Based on these results, a two-by-two comparison was made between the phosphorus values measured in the PAC and V-MOH300 adsorbent dosages, for example, 0.5 g L⁻¹ of PAC and 0.5 g L⁻¹ of V-MOH300, and showed that all the groups presented statistically significant differences, with the phosphorus concentration values in the treatments with the V-MOH300 adsorbent being significantly higher than those determined in the PAC treatments. These results indicate that the natural adsorbent increases the phosphorus concentration in the solution more than the PAC, for which this also occurs, but to a lesser extent.

Based on the results presented in Table 1, adsorption isotherms were constructed and the Langmuir [50] and Freundlich [51] models were tested via nonlinear regression analysis. The maximum adsorption capacity (q_max), according to the Langmuir model, was −1.79 mg g⁻¹ and −0.06 g g⁻¹ for V-MOH300 and PAC, respectively. The value of n (dimensionless) is the Freundlich intensity parameter, which indicates the magnitude of the adsorption driving force or surface heterogeneity, and the values found in this study were −4.6 and −1.1 for V-MOH300 and PAC, respectively.

4. Discussion

Eutrophication is a process that occurs mainly due to the excess concentration of phosphorus and nitrogen in water bodies, resulting in negative consequences for freshwater quality and human health, as well as economic activities [52,53]. Phosphorus contamination is a very challenging problem for the aquatic environment, so it is important to remove this element to control eutrophication [54]. The studies on phosphorus removal using the adsorption process mainly focus on finding low-cost, high-efficiency, and easy-to-obtain adsorption materials and improving the adsorption efficiency of components through alterations [55].

The adsorption method is considered one of the most acceptable and useful for decontaminating samples of water bodies and wastewater due to its economic and environmental advantages [56]. In the scientific literature, several low-cost phosphorus adsorbent materials have been proposed [57,58,59]. Within this context, different parts of the M. oleifera tree are effective as adsorptive materials in wastewater and water treatment [60]. The use of Moringa as a sorbent is of economic and environmental interest [61,62,63].

In a literature review on the application of M. oleifera as a biosorbent for water treatment, Benettayeb et al., 2022 [64], highlighted that further research is needed on the advantages and disadvantages of different parts of this tree as biosorbent, as well as the conditions favorable to this biosorption must be investigated. The current research focused on the removal of phosphorus from aqueous solutions using M. oleifera seed pod as a biosorbent, which is the unexploited part of M. oleifera seeds. This study demonstrated that the adsorption process with M. oleifera pods increases the phosphorus concentration in the solution. Processes for removing phosphorus from aqueous solutions using biosorption by M. oleifera seeds have been described in the literature. The capacity of Ficus carica seed in the adsorption of phosphate in solution was found to be more effective than M. oleifera [65]. Sané et al. (2024) [66], studying the pollutants removal in a domestic wastewater treatment prototype treated with seeds of M. oleifera, verified that phosphorus removal was ineffective. No other studies on the applicability of M. oleifera pods in the adsorption of phosphorus concentrations representative of eutrophicated aquatic environments were found in the scientific literature.

In the present study, the observed phenomena of increased phosphorus concentration in test solutions in the laboratory tests can be explained by the concept of chemical equilibrium, i.e., the equality of the speeds at which the ions available in the solution are adsorbed/desorbed [67]. This is the case for the three lowest PAC dosages tested, as no effects are observed on the concentration of phosphorus in the medium, indicating a state of equilibrium. For the other PAC dosages and all the V-MOH300 dosages, equilibrium was likely reached in the opposite direction to adsorption, desorbing phosphorus ions from the solution. This conclusion is consistent with the negative Freundlich intensity parameter (n) and the negative Langmuir maximum adsorption capacity (q_max) observed in this study. These values indicate that the adsorption process is not suitable for the given system. A negative n value suggests that the adsorption capacity decreases as the adsorbate concentration increases, which contradicts typical adsorption behavior. Likewise, a negative q_max implies that the Langmuir model is inappropriate for this system and may indicate that desorption is occurring instead of adsorption.

The adsorbent dosages used in this study are similar to those used by Xu et al. (2009) [68], who studied modified wheat residue as a phosphorus adsorbent, and Mor et al. (2016) [67], who evaluated the use of activated rice husk for the same purpose. Both studies showed that there was an increase in adsorption capacity as the dosage of the adsorbent was increased, but from 2 g∙L⁻¹ there was no improvement in efficiency. The range of adsorbent concentrations used by the authors, from 0.5 g∙L⁻¹ to 2 g∙L⁻¹, proved to be adequate. However, the phosphorus concentrations used by Xu et al. (2009) [68] and Mor et al. (2016) [69], 50 mg·L⁻¹ phosphorus and 10 mg·L⁻¹ phosphorus, respectively, were higher than those used in the present study (0.210 mg·L⁻¹).

In this study, the concentration of phosphorus tested (0.210 mg·L⁻¹) simulated the average amount of nutrients in eutrophied freshwater environments. Scientific research investigating the feasibility of natural adsorbents for phosphorus removal simulates high concentrations of the nutrient (10–1000 mg·L⁻¹), being characteristic of wastewater and effluents [70,71]. The low initial concentration of phosphorus used in this study may have contributed to the chemical equilibrium tendency towards desorption for both adsorbents tested. Low initial concentrations of the nutrient have a direct effect on decreasing adsorption, as observed by Xu et al. (2009) [68], who found that the adsorption capacity of phosphorus by wheat waste (adsorbent) decreased from 22 mg∙g⁻¹ to 5 mg∙g⁻¹ as the initial concentration of phosphorus also decreased from 50 mg·L⁻¹ to 10 mg·L⁻¹. Hendrasarie and Maria (2021) [29] tested M. oleifera pod seeds as an adsorbent at an initial phosphorus concentration of 993 µg∙L⁻¹ and observed 87.31% removal of the nutrient. In addition, the authors used HCl as a chemical activator and physically activated the adsorbent at 600 °C, different activation methods from those used in this study.

It is also important to consider that different activation parameters might influence the material’s adsorption behavior. These parameters include chemical agents (e.g., KOH, NaOH, or HCl) and pyrolysis temperatures (300–800 °C) could have yielded better-performing sorbents. According to Abdullah et al. (2017) [72], the type of chemical activating agent and activation temperature were important specifications affecting the production of biosorbent from M. oleifera seed pod. The physical activation used in this research, 300 °C for 3 h, was mild compared to the studies by Hendrasarie and Maria (2021) [29]. The authors used 800 °C and, even with different chemical activators (H₂SO₄ and NaOH), recorded the effectiveness of M. oleifera pods as an adsorbent. The low temperature used in this investigation may have led to the presence of organic matter in the pod, which did not volatilize, with the intrinsic phosphorus of the M. oleifera pods prevailing in the desorption of the chemical balance. Chemical activation with H₃PO₄ may also have contributed to this desorption, since even if the adsorbent is washed before use, the acid is impregnated on its surface, according to studies by Tolentino Brandão et al. (2020) [73]. These authors observed a lower capacity of activated carbon produced from pequi bark (Caryocar brasiliense) to attract oppositely charged ions, such as phosphate ions in aqueous solution, when activation was carried out with phosphoric acid, which was due to the addition of carboxylic acid groups on the surface of the carbon.

The chemical composition of the adsorbents is also a favorable factor for phosphorus desorption. In a study on the removal efficiency of phosphate in a solution using rice husk ash as adsorbent, Barajas et al. (2016) [74] verified that rice husk ash contained large amounts of soluble phosphate that contributed to an increase in phosphate concentration in the solution. The presence of this element in M. oleifera pods has already been demonstrated in studies by Ahmad et al. (2017) [75], by Brilhante et al. (2017) [76], and by Yadav et al. (2022) [77] for which up to 120 mg of phosphorus is found per 100 g of pod. According to Melesse et al. (2012) [78], the M. oleifera species generally has higher levels of P, Fe, Mn, Zn, and Cu than the M. stenopetala species, with a phosphorus concentration of 5.45 g Kg⁻¹. Research on nutritional values of different parts of M. oleifera has shown high levels of potassium and phosphorus in ponds [79,80]. Since the element phosphorus is found in the composition of the M. oleifera pod, this is in line with what was observed in this study, indicating that the resulting phosphorus values are higher for V-MOH300 than PAC.

Table 4 provides a comparative analysis against various adsorbents used for phosphorus removal from water, considering key parameters discussed, such as maximum adsorption capacity (q_max) and initial phosphorus concentration. In this study, a negative q_max value indicates that the adsorption capacity decreases as the adsorbate concentrations increase, suggesting that desorption is occurring instead of adsorption.

5. Conclusions

The results found in the present study make important contributions to the advancement of studies on phosphorus removal in aquatic environments since the use of adsorbents in specific conditions of activation can increase the concentration of phosphorus in cases of low initial concentration of this nutrient. The two adsorbents tested in the present research demonstrated desorption of phosphorus in the medium. V-MOH300 released a greater amount of phosphorus than PAC, for which this effect was also observed, but at lower concentrations. However, different activation parameters might influence the material’s adsorption behavior, and it is recommended that other activation methods for Moringa oleifera pods be studied for phosphorus removal from water. Additionally, adsorption isotherms, kinetics, and equilibrium constants should be determined in future studies. This study, therefore, warns of the risk of phosphorus desorption in the aqueous environment and the possibility of organic adsorbents causing this effect. In terms of limnology and environmental sciences, this research has provided information for the appropriate selection of natural adsorbents and activation methods to be used in the treatment of eutrophicated aquatic environments.

Author Contributions

Conceptualization, S.R. and A.G.d.R.; methodology, D.R.D., S.R. and A.G.d.R.; formal analysis, D.R.D., S.R., A.G.d.R. and J.K.S.F.; writing—original draft preparation, D.R.D., S.R., A.G.d.R. and J.K.S.F.; writing—review and editing, D.R.D., S.R., A.G.d.R. and J.K.S.F. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are available upon request.

Acknowledgments

Our appreciation goes to the researchers and laboratory technicians who contributed to laboratory work.

Conflicts of Interest

The authors declare no conflicts of interest.

Footnotes

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Figure and Tables

[Image omiited. Please see PDF.] Table 1

Real masses of the adsorbents and phosphorus concentrations measured.

Real Masses of the Adsorbents (g)		Adsorbent Dosage (g L−1)	Phosphorus Concentration (mg·L−1)
PAC	V-MOH300		PAC	V-MOH300
0.0000 (Control)		0.0	0.23
0.0000 (Control)			0.23
0.0000 (Control)			0.24
0.0549	0.0551	0.5	0.20	2.42
0.0555	0.0554		0.33	2.29
0.0550	0.0550		0.34	2.31
0.0881	0.0888	0.8	0.30	3.63
0.0886	0.0884		0.38	3.28
0.0880	0.0882		0.37	3.61
0.1101	0.1107	1.0	0.33	4.18
0.1103	0.1104		0.37	3.96
0.1098	0.1100		0.40	4.44
0.1431	0.1433	1.3	0.37	5.33
0.1431	0.1429		0.96	5.22
0.1429	0.1431		0.42	5.88
0.1871	0.1871	1.7	0.66	6.73
0.1871	0.1876		0.45	6.63
0.1873	0.1873		0.46	7.59
0.2208	0.2200	2.0	0.45	8.03
0.2205	0.2206		0.47	7.80
0.2198	0.2201		0.47	9.30

Table 2

Real masses of the adsorbents and phosphorus concentration measured using deionized water.

Real Masses of the Adsorbents (g)		Adsorbent Dosage (g L−1)	Phosphorus Concentration (mg·L−1)
PAC	V-MOH300	0.0	PAC	V-MOH300
0.0000 (Control)			0.01
0.0000 (Control)			0.01
0.0000 (Control)			0.01
0.2200	0.2209	2.0	0.24	10.82
0.2204	0.2210		0.26	7.81
0.2201	0.2206		0.26	8.09

Table 3

Dwass-Steel-Critchlow-Fligner p-value results for all phosphorus concentrations in the tests performed.

Adsorbate	Adsorbent Dosage(g L−1)	p-Value
		Adsorbate
		Phosphorus Solution (0.210 mg·L−1)						Deionized Water
	PAC	0.5	0.8	1.0	1.3	1.7	2.0	0.0	2.0
Phosphorus solution (0.210 mg·L−1)	0.0	0.966	0.405	0.254	0.009	0.001	0.007	0.009	1.000
	0.5	─	0.954	0.845	0.082	0.006	0.064	0.001	0.998
	0.8		─	1.000	0.516	0.064	0.441	0.001	0.633
	1.0			─	0.709	0.117	0.633	0.001	0.441
	1.3				─	0.919	1.000	0.001	0.020
	1.7					─	0.954	0.001	0.001
	2.0						─	0.001	0.002
Deionized water	0.0							─	0.004
	2.0								─
	V-MOH300	0.5	0.8	1.0	1.3	1.7	2.0	0.0	2.0
Phosphorus solution (0.210 mg·L−1)	0.0	0.022	0.001	0.001	0.001	0.001	0.001	0.009	0.001
	0.5	─	0.465	0.057	0.001	0.001	0.001	0.010	0.001
	0.8		─	0.927	0.037	0.001	0.001	0.001	0.001
	1.0			─	0.349	0.002	0.001	0.001	0.001
	1.3				─	0.184	0.001	0.001	0.001
	1.7					─	0.258	0.001	0.044
	2.0						─	0.001	0.983
Deionized water	0.0							─	0.001
	2.0								─

Table 4

Comparison of the maximum adsorption capacity of adsorbents from different sources for phosphorus.

Absorbents	Initial Phosphorus Concentration (mg·L−1)	qmax(mg g−1)	Reference
Ce-Zr-Al composite	0.5–100	73.51	Wang et al. (2023 [55]
Ball-milled magnetic sphere	10–20	16.47	Zhang et al. (2020) [57]
Granulated silica pellets -Fe	3–130	278	Gómez-Carnota et al. (2023) [59]
Rice husk ash	10	0.736	Mor et al. (2016) [69]
Filopaludina bengalensis shell	100–1200	62.50	Paul et al. (2022) [71]
Phila globosa shell	100–1200	66.66	Paul et al. (2022) [71]
PAC	0.210	−0.06	This study
Moringa oleifera pods	0.210	−1.79	This study

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