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Article

A Glance at a Sustainable Solution Using Vertical Constructed Wetland Based on Dewatered Drinking-Water Waste Augmented Nanoparticle Composite Substrate for Wastewater Treatment

by
Hossam A. Nabwey
1,2,* and
Maha A. Tony
2,3
1
Department of Mathematics, College of Science and Humanities in Al-Kharj, Prince Sattam bin Abdulaziz University, Al-Kharj 11942, Saudi Arabia
2
Basic Engineering Science Department, Faculty of Engineering, Menoufia University, Shebin El-Kom 32511, Egypt
3
Advanced Materials/Solar Energy and Environmental Sustainability (AMSEES) Laboratory, Faculty of Engineering, Menoufia University, Shebin El-Kom 32511, Egypt
*
Author to whom correspondence should be addressed.
Processes 2023, 11(10), 2836; https://doi.org/10.3390/pr11102836
Submission received: 26 August 2023 / Revised: 14 September 2023 / Accepted: 21 September 2023 / Published: 26 September 2023
(This article belongs to the Special Issue Solid Waste Valorization and Utilization)
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Versions Notes

Abstract

:
The current investigation introduces and demonstrates a credible, economically sound system to remove agrochemical runoff using a vertical flow constructed wetland (VFCW). DuPont 1179 carbamate insecticide was applied as a simulating greenhouse crop production controller, which resulted in runoff loaded with DuPont 1179. A novel composite of constructed wetland from an alum sludge conjugate magnetite nanoparticle substrate was applied and supported with gravel as a filtration/adsorption bed in a vertical flow constructed wetland (VFCW) system. X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM) augmented with energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR) were employed to characterize the suggested composite substrate. The experimental data showed VFCW to be significant in eliminating DuPont 1179. The isotherm time was explored at 300 min, which corresponded to complete insecticide removal (100%). The operational parameters were located at the natural pH (6.9) of the solution and room temperature (25 °C). The VFCW column was also investigated at various substrate concentrations ranging from 100% to 40% of the composite material supported by a gravel medium, and the existence of composite at a 75% concentration showed the highest yield. The experimental data verified that the adsorption followed the pseudo second-order adsorption kinetic model. Furthermore, according to the isotherm model results, the scheme followed the Langmuir isotherm model. Thus, the presented study is a promising indicator of the possibility of using alum sludge conjugate nanoparticles for the elimination of agrochemicals from wastewater.

1. Introduction

With the rapid increase in modern lifestyles, facilities and industry, there has been an increase in the water usage per capita and the demand for fresh water [1]. The extreme application and use of toxic persistent substances has a negative effect on the biodiversity of aquatic environments. Agricultural production is associated with pests and insecticide control. Thus, insecticide use is urgent and is further increasing with changes brought about by global warming. However, although insecticides are applied to combat pests, they are known as one of the main threats to surface water [2,3]. Notably, agricultural runoff water is one of the most significant non-point sources of ecosystem contamination, due to the extensive use of insecticides and fertilizers, which flow with runoff water. It is essential to treat this runoff prior to its discharge into surface water bodies [4,5,6,7].
There is a pressing global need for the generation of clean drinking water. In this context, drinking-water treatment facilities are essential; however, they generate massive amounts of a waste by-product referred to as waterworks sludge [8,9]. Aluminum sulfate is commonly applied as the main coagulant in drinking-water treatment facilities and, as a result, aluminum ions are converted to aluminum hydroxide, and alum sludge is generated. Aluminum hydroxide absorbs insoluble water contaminants and organic compounds during water processing [10,11,12].
In order to achieve a greener environment, scientists and researchers are focusing their interest on finding a reliable option for sludge management through sustainable disposal [13]. As a result, alternative water buildup disposal techniques are being investigated, with the aim of maximizing their worth and increasing their merits, in order to convert these massive volumes of sludge from an undervalued material into a value-added product. This mechanism is a critical research topic and is explored in order to overcome constraints and limitations [14,15]. In addition, due to the chemical composition and amorphous structure of aluminum-based sludge, it is crucial to note that it is an adsorbent material [16,17,18]. Furthermore, alum sludge has a high surface area and is signified as a porous material. Thus, it is categorized as an effective adsorbent substance. Therefore, aluminum-based metals could be used in the wastewater treatment industry to eliminate a variety of impurities. Several studies conducted by separate researchers, including Yang et al. [12], Geng et al. [16] and Sharif Zein and Boccaccini [17], showed various investigations evaluating the use of alum sludge as a low-cost adsorbent material for the removal of pollutants from an aqueous medium [19,20,21]. Although Al, as well as other heavy metals in the sludge, might pose a danger to the environment [22,23], some research studies [24,25] disprove such a phenomenon and report on soil that was not affected by these heavy metals. Hence, their conclusion allows an optimistic view regarding this concern. The inclusion of aluminum in Al-based sludge increases its attractiveness for the adsorption of pollutants from polluted lines [18]—for instance, the elimination of dyes [11,15], phosphorus [21], arsenic [26] and some other heavy metals [2,21].
Recently, there has been great attention and interest in using dewatered alum sludge as a reactive substance in artificial wetlands [19]. Notably, a substrate is a crucial component of a constructed wetland; hence, an optimum substrate is selected that has several functions: (i) a supporter of biofilm formation; (ii) a plant growth medium and (iii) a pollutant adsorbent. In practice, alum sludge is a by-product of drinking-water treatment plants; thus, it is a non-toxic material in most circumstances. Furthermore, aluminum is the most abundant ingredient in alum sludge, which has a high adsorption capability for pollutants from contaminated aquatic streams [19,20,21]. Aluminum-based sludge cake has a high potential for reuse as the principal substrate in constructed wetlands to satisfy the dual advantages of reedbed vegetation and wastewater treatment [20,22]. However, some limitations still appear in wetland systems, such as the potential clogging of the bed and the release of possible elements from the alum sludge into the water [2,12,14], which are research points to further explore.
Nanoparticles are gaining global attention due to their promising results in various applications. Academia and businesses alike are showing a strong interest in the synthesis of nanoparticles [23], particularly functionalized nanoparticles for diverse tailored applications [23,24,25]. Because of their high catalytic activity, nanoparticles [26] have exhibited promising results in driving chemical processes [27]. Thus, researchers are showing a strong interest in the synthesis of numerous nanoparticles [28,29], particularly functionalized nanoparticles for diverse tailored applications [30,31]. Multiple studies [28,29,30,31] have shown that the addition of nanoparticles improved the removal of various types of pollutants from wastewater. To the best of the author’s knowledge, the application of alum sludge substrate as an enhancer in constructed wetlands has not been implemented so far. Thus, the augmentation of magnetite nanoparticles with alum sludge cake as an AlS–M composite has not been applied so far to a constructed wetland facility.
Herein, the present investigation was designed to explore the use of a VFCW system based on a gravel-dewatered aluminum-based sludge/magnetite composite (AlS–M composite) substrate. AlS–M composite was prepared via an economically reliable technique, and its effectiveness for adsorption of DuPont 1179 was studied to confirm the novel tailoring of AlS–M composite as a super-constructed wetland substrate for sustainable ecology. As a result, this redirects waste from wastewater remediation away from disposal, transforming it into a valuable resource within the economy. This approach has the potential to mitigate environmental impacts associated with waste management and improve the economic aspects of constructed wetland design. The preliminary results of the column show that it could be a significant candidate for a constructed wetland system. The composite characterization was performed through SEM, EDX, XRD, FTIR and TEM analysis. In addition, the effects of the system parameters were investigated, such as DuPont 1179 pollutant concentration, solution pH and temperature, to maximize the system yield.

2. Experimental Investigation

2.1. DuPont 1179 Aqueous Solution

DuPont 1179 insecticide (N-(methylcarbamoyl) ester) is a widely used insecticide in greenhouse farming and was selected in the current investigation as a synthetic pollutant model to simulate agricultural runoff. DuPont 1179 is highly soluble in water at normal atmospheric temperature; its solubility is 57.9 g/L. Initially, 1000 ppm was prepared as a stock aqueous solution that was then further diluted as required. The pH of the DuPont 1179 solution was adjusted, when needed, to the required values according to the test conditions by using H2SO4 or NaOH (Sigma-Aldrich, Perth, Australia). All chemicals in the current investigation were applied as received with no further purification.

2.2. VFCW System

At the outset, the collection of aluminum-based sludge took place at the largest drinking-water treatment plant located in Shebin Elkowm, Menoufia Governorate, Egypt. Within the plant, aluminum sulfate is utilized as the primary coagulant, which results in an aluminum-based sludge by-product. The excess water was decanted and the air-dried sludge cake was used as the main component to produce the AlS–M composite. Thereafter, the magnetite was simply prepared by using the co-precipitation technique; the procedure is illustrated elsewhere [32,33]. The nanoparticles of the magnetite were prepared by mixing Fe2(SO4)3 and Fe(SO4) in stoichiometric ratios using distilled water, with NaOH used in a drop-wise manner to elevate the pH while heating was applied. After successive washing to reduce the pH, nanoparticles were obtained, which were dried to achieve a powder. The obtained magnetite nanoparticles were simply mixed with the aluminum-based sludge to obtain the AlS–M composite at a proportion of 1:5 by weight.
A vertical flow column that was previously designed [32] with a height of 1000 mm and a width of 150 mm was used as the adsorption column, which is described elsewhere [1]. The system was initially filled with a small-particle-size gravel support (10 mm in size) 100 mm in depth. Afterwards, the VFCW column was occupied by the dewatered aluminum sludge/magnetite-based composite, and the packed composite was up to 500 mm in depth. However, the height of the gravel and sludge composite in the column was varied and was studied as a parameter. In addition, Common reeds were supported in the column. The constructed wetland column was connected to a wastewater tank containing DuPont 1179 solution, which was supplied to the column by a peristaltic pump. The solution was supplied to the column through hydraulic loading of 0.5 m/d in a tidal flow operation. The design of the experimental VFCW system is graphically displayed in Figure 1. Afterwards, the wastewater after adsorption was subjected to analysis in three replicates for each sample.

2.3. AlS–M Composite Characterization

X-ray diffraction (XRD) analysis was conducted using a Bruker–Nonius Kappa CCD diffractometer with a CuKα radiation source of wavelength 1.5406 Å. The composite XRD was evaluated using an XR Phillips X’pert (MPD3040) diffractometer, operating at 40 kV with a scan step time of 0.6 s.
The morphologies of the samples were examined using a field-emission scanning electron microscope (FE-SEM, Quanta FEG 250) and imaged through SEM micrographs. The typical magnifications used were ×8000 and ×60,000. Additionally, energy dispersive X-ray spectroscopy (EDX) was employed.
To investigate the morphology of the sample further, a transmission electron microscope (TEM, Tecnai G20, FEI) was utilized. The particle size distribution of the composite material was determined using the IMAGEJ 1.48 V program. The Fourier transform infrared (FTIR) transmittance spectrum was obtained in the wave number range of 400–3500 cm−1 using a Jasco FT/IR-4100 spectrometer (Jasco, FT/IR-4100, type A). This spectrum was used to identify the functional groups responsible for the catalysts. BET specific surface areas were determined via nitrogen adsorption at 77 K. Five adsorption points were measured using a NOVA touch 4LX apparatus, and nine adsorption points were measured between 0.01 and 0.2 of relative pressure.

2.4. Analytical Determination

A digital pH meter was used to adjust the pH, when needed (AD1030, Adwa digital pH-meter instrument, Adwa Instrument, Hungary). After treatment, the water samples were subjected to spectrophotometric analysis to investigate the remaining DuPont 1179 (using Unico UV-2100 spectrophotometer, UNICO, USA) at a wavelength of 231 nm after the sample filtration.

3. Results and Discussion

3.1. Characterization of the AlS–M Composite

3.1.1. XRD Analysis

Figure 2 represents the X-ray diffraction pattern (XRD) of the AlS–M composite that displays the sharp diffraction peak pattern, which demonstrates the crystalline nature of the composite. Magnetite, graphite, anorthite and quartz appear in the composite. The peaks of [100], [101] and [110] indicate the occurrence of quartz, whereas the peaks of [022], [112], [202] and [114] represent the occurrence of anorthite. Furthermore, the presence of [002], [011] and [004] verifies the presence of graphite in the sample. It is noteworthy to mention that the peaks at 2θ of 30.0°, 35.3°, 43.0°, 56.9° and 62.8° correspond to [220], [311], [400], [511] and [440], respectively. The obtained XRD results of magnetite are consistent with the standard pure cubic spinel crystal structure, as referenced in [34], indicating their reliability.

3.1.2. SEM Images and EDX

SEM images were utilized to examine the morphology and size of the prepared AlS–M composite material, and the corresponding data are presented in Figure 3. The SEM micrograph illustrates a semi-hexagonal sheet of alum sludge containing an increased semi-spherical amount of magnetite. In addition, magnetite spheres augmented on AlS sludge are displayed in the SEM images. Hence, AlS sludge was agglomerated in various shapes with the magnetite particles.
Furthermore, the elemental chemical analysis of the AlS–M composite material was performed to investigate the main elements on the surface of the substance. The elemental analysis is displayed in Figure 4 and the weight percent data are tabulated in the inset of Figure 4. AlS–M composite bands are mainly C and O, as well as Si and Al, with the existence of trace amounts of Ca, Na and Fe. The existence of such impurities is associated with the use of aluminum sulfate as a primary coagulant in the waterworks plant, used in its dried form as the substrate of VFCW. In addition, these results confirm the presence of magnetite with AlS.

3.1.3. FTIR

The Fourier transform infrared (FTIR) spectroscopy analysis of the prepared composite is depicted in Figure 5. In Figure 5, the observed bands at approximately 1427, 1631 and 3427 cm−1 can be attributed to the stretching vibrations of C-O, C=C and O-H, respectively. Notably, the intense band at 1088 cm−1 corresponds to the asymmetric stretching of Si-O-Si bonds in SiO2, indicating the motion of oxygen in the Si-O-Si anisometric stretch [33]. Additionally, the band at 695 cm−1 is related to the Al-O-Si bond [35]. There is also a band at 800 cm−1, which is assigned to the weak deformation bond of Al-Mg-OH [33]. The presence of Si-O-Fe is indicated by the intensities in the range of 554–557 cm−1. Other peaks are assigned to the presence of quartz (Si-O) and other oxides (Si-O-Fe, Al-O-Si) in close proximity to the bands across the spectra from 1088 to 444 cm−1. Furthermore, the distinctive peak associated with Al-O-Si bonding, located in the wavenumber range of 1000–1100 cm−1, is difficult to define precisely due to the overlap with the Si-O-Si peak [34].

3.1.4. BET Surface Area

The Brunauer–Emmett–Teller (BET) specific surface area of the AlS–M composite was established to evaluate the adsorption tenancy. According to previously reported data in the literature, the alum sludge surface area ranges from 61 to 67 m2/g [36]. Figure 6 displays the BET surface area of the composite sludge, and the data revealed 78 m2/g as the BET specific surface area of the AlS–M composite. These data confirm the role of magnetite in increasing the pore volume and therefore the surface area of the composite. The high Brunauer–Emmett–Teller (BET) specific surface area suggests the reduction in the particle aggregation on the composite’s surface. Thus, these results reflect the importance of magnetite in enhancing the adsorption tendency of the substrate [37].

3.1.5. TEM Images

Figure 7 presents the TEM images of the AlS–M composite substrate captured at various magnifications. The images reveal that AlS is represented by mixed hexagonal sheet particles. These sludge sheets are adorned with uniformly shaped spherical particles, with some small edges attached to specific nanoparticles. This decoration of particles confirms the presence of magnetite on the sludge particles, which is also supported by the SEM images. Additionally, it is worth noting that the magnetite particles in the sample tend to aggregate. Consequently, the AlS–M composite particles consist of a mixture of hexagonal particles derived from alum sludge, adorned with spherical magnetite particles. Furthermore, based on the data presented in the inset of Figure 7, the AlS–M composite exhibits an average particle size ranging from 5 to 20 nm.

3.2. DuPont 1179 Adsorption on AlS–M Composite Substrate

3.2.1. Effect of Composite Height

The influence of the quantity of AlS–M composite on the bed height breakthrough for DuPont 1179 adsorption was obtained. The content of the AlS–M composite in the adsorption column varied between 100%, 75%, 50% and 40%, and the data are displayed in Figure 8. The AlS–M composite assists in the DuPont 1179 removal, as it serves as a dual filter medium and adsorption surface in all the designed column trials. However, the effectiveness is substantially reduced when the AlS–M composite is less than 50% and maximal adsorption is attained in the 75% AlS–M composite column, which reached 100% complete insecticide removal. This might be associated with the high hydraulic loading through the adsorption column. Remarkably, in the non-gravel-containing system, the adsorption and the DuPont 1179 removal were reduced to only 64% compared to that in the joint gravel/AlS–M composite substrate. These data are supported by the phenomenon of increasing DuPont 1179–substrate contact, enhancing the removal rates [38]. Thus, the 75% AlS–M composite/gravel substrate column was used in the further investigations throughout this study.

3.2.2. Effect of Isotherm Time

Primarily, to investigate the adsorption matrix, it is vital to initially investigate the isotherm time of the DuPont 1179 removal on the AlS–M composite. Thus, the time profile of a DuPont 1179 insecticide was assessed on a column with 75% AlS–M composite/gravel substrate. However, the DuPont 1179 concentration was kept at 300 ppm and the substrate was pumped at room temperature. The results displayed in Figure 9 exhibit the inflow and outflow DuPont 1179 concentration into and from the column, respectively. The major DuPont 1179 removal occurred within an initial 100 min time period (reaching 63%), and complete removal was attained after 300 min. This result confirms the ability of the AlS–M composite in eliminating DuPont 1179 due to the existence of aluminate, silica and graphite in the composite, as well as the magnetite nanoparticles. In addition, the porous structure of the AlS–M composite, which is mentioned above and verified by means of the X-ray diffraction and the scanning electron microscope images, is responsible for the adsorption matrix. Furthermore, the graphite particles in the composite have a role and help in the adsorption uptake capacity, as they induce hydrophobic interactions [39].
The results of this test verify the significance of the AlS–M composite role as a substrate in the adsorption wetland column. Similar results were previously reported in the literature [32,40]. However, the current study takes a leading role in decorating the substrate with magnetite nanoparticles. Thus, the performance of the augmented aluminum-based sludge with magnetite nanoparticles as a dual adsorption material is pronounced, showing the novelty of this study.

3.2.3. Effect of DuPont 1179 Loading in Influent Stream

The influence of the DuPont 1179 concentration on the adsorption process through the removal rate column was investigated, and the data are displayed in Figure 10. The experiments were conducted at DuPont 1179 loaded concentrations of 300, 500, 800 and 1000 ppm, while the other operational parameters, i.e., operating time (300 min), room temperature (25 °C) and the natural solution pH (6.9), remained constant for all experiments. Remarkably, a great enhancement in the DuPont 1179 removal was noticed with the reduction in the loaded concentrations that flowed into the column. The removal rate reached 100, 95, 85 and 59% removal for 300, 500, 800 and 1000 ppm loading, respectively. This performance may be illustrated by low concentrations of the initial DuPont 1179; the insecticide molecules surround the sorbent sites and thereby enhance the mass transfer rate between the adsorbent material and the adsorbed solute, resulting in a high removal rate [23]. However, excess DuPont 1179 insecticide crowds the adsorption media, and the sorption active sites are occupied by the insecticide molecules [1,2].
Such results are as expected, as the active sites of the AlS–M composite substrate are loaded with the DuPont 1179 particles [30]. The trend of the association of the adsorption uptake with the loadings of the aqueous effluent is in agreement with previous records in the literature [2,30,38] that confirmed that the rate of mass transfer for the solid–aqueous interface is reduced and linked to the wastewater concentration.

3.2.4. Effect of Aqueous Stream pH

The adsorption process is affected by the solution pH value due to its effect on the sorption between the adsorbate and the substrate adsorbent material. In this regard, the initial pH values of the DuPont 1179 solution ranged from 3.0 to 8, whereas the natural solution pH was 6.9. Figure 11 clearly displays the influence of the pH on the column performance during 300 min of adsorption time. Decreasing the pH value of the solution results in a decline in the adsorption uptake. However, increasing the pH to reach the natural solution pH showed a pronounced removal. However, a further increase in the pH to the alkaline range (pH 8.0) results in another decline in the removal rate.
This observation is most likely due to the maximal active sites available at the natural pH of the solution. At high pH values, unfavorable adsorption uptake is achieved due to the zeta potential of the adsorbent material. This might be associated with the different chemical structures of both the DuPont 1179 insecticide and the alum sludge, making them undesirable intermediates. In addition, the organometallic complex might be released at acidic or alkaline pH, which competes with the DuPont 1179 to occupy the available active sites on both the magnetite and alum sludge surfaces. Thus, such an investigation leads to the production of repletion forces between the adsorbent AlS–M composite substance surface and the DuPont 1179 molecules. Furthermore, increasing the pH value to alkaline (pH 8.0) delays the interaction between the DuPont 1179 molecules and the AlS–M composite substance. Previous studies have reached similar conclusions in textile effluents [41,42].

3.2.5. Effect of Temperature

Temperatures ranging from room temperature to 60 °C were inspected to study their influence on the constructed wetland column, as the waste loaded with the insecticide might be discharged at various temperatures. All other operational parameters were kept constant. The data displayed in Figure 12 show that the temperature elevation results in the removal rate increasing within the studied temperature range. Hence, complete removal was reached in 150 min with temperature elevation, a shorter adsorption time compared to the complete removal at room temperature being achieved in 300 min. Thus, DuPont 1179 in such a sorption system is endothermic in nature, as the temperature elevation increases the collision rate of the insecticide molecules in the aqueous media, increasing the adsorption uptake. Thus, a shorter adsorption time is attained with a temperature increase. Furthermore, the temperature increase improves the available active sites of the alum sludge surface, allowing for extra insecticide molecules to be adsorbed on the composite surface [33].
Such a conclusion is in agreement with that previously stated in research articles [43,44] examining dye removal. However, other studies [45] have commented that temperature elevation hinders the adsorption uptake. This may be related to the type of substrate and the pollutant nature affecting the sorption capacity.

3.2.6. Kinetic Investigation

To further understand DuPont 1179 adsorption from the aqueous solution, the kinetics of the adsorption should be studied. Based on this concept, the kinetics of DuPont 1179 adsorption into the AlS–M composite substrate was studied using a series of experiments with contact periods ranging from 100% to 40% for the AlS–M composite substrate amount in the substrate column. The experiments were concerned with varying the DuPont 1179 loading through the various adsorption columns. The adsorption of DuPont 1179 insecticide through the AlS–M composite substrate was then analyzed using the first- and second-order rates of adsorption according to Equations (1) and (2):
log q e − q t = K 1 2.303 t + l o g   ( q e )
t q e = 1 K 2 q e 2 + 1 q e t
After plotting Equations (1) and (2) for the acquired data, the most acceptable adsorption kinetics were evaluated, and the regression coefficients (R2) were verified, where higher values represent a more appropriate model; the data are displayed in Table 1. According to the R2 values that refer to the best model fit, the most acceptable adsorption kinetics were recorded. Fitting to the R2 values, the best correlated adsorption is associated with a pseudo second-order adsorption. K2 is significantly affected by the adsorption as it decreased from 53.3 × 10−5 to 22.5 × 10−5 L/mg min with the change in the AlS–M composite substrate according to the data displayed in Table 1.
Pseudo second-order adsorption fitting signifies that the rate-limiting step of the adsorption is chemisorption, and the adsorption is dependent on the DuPont 1179 adsorption uptake rather than the loading of the DuPont 1179 insecticide. Such data are in accordance with the previously reported literature [46] on treating contaminated water with phosphorus.

3.2.7. Isotherm Models

The adsorption capacity at different DuPont 1179 equilibrium concentrations can be elucidated by the adsorption isotherm. The following two isotherm models in Equations (3) and (4) were used to describe DuPont 1179 on the adsorption column. The linearized forms of the Langmuir (Equation (3)) and Freundlich (Equation (4)) models [33] were applied to analyze the isotherm results, where KL and KF are the Langmuir and Freundlich constants, respectively. Meanwhile, qe is the equilibrium adsorption capacity, aL is the constant related to the Langmuir model, and 1/n signifies the heterogeneity constant of the Freundlich model.
C e q e = 1 K L + a L K L C e
l n ( q e ) = l n ( K F ) + 1 n C e
As shown in Table 2 and Figure 13, the isotherms of the adsorption were calculated for the various column substrates. According to the correlation coefficient results (R2) tabulated in Table 2, the data were best fitted to the Langmuir isotherm model for the four substrate systems. This verifies that the maximum adsorption capacity is associated with monolayer adsorption on a homogeneous surface. In addition, it is verified from the data in Table 2 that the value of n is 1 < n < 10, indicating that the adsorption process is favorable.

3.2.8. Comparative Study

It is essential to compare this investigation with the data previously reported in the literature to explore the significance of the current study. Table 3 displays the numerous studies linked to using alum sludge to treat various types of wastewater polluted with different materials. According to the data tabulated in Table 3, the application of alum sludge as a low-cost adsorbent material is promising for treating various effluents, including dyes, phenols and heavy metals such as arsenic, phosphorus, copper and zinc. However, several authors have dealt with heavy metal elimination, and limited studies have dealt with dye effluents [47] and other pollutants such as insecticides. The presence of amorphous aluminum in the alum sludge maximizes the sludge’s affinity to adsorb anions from polluted effluents [19,20]. However, the sorption tendency is associated with the properties of alum sludge, such as its surface area and the charge density. In addition, the sorption is related to operating variables such as the solution pH. Further, the time of sorption differs according to the type of pollutant and potentially the type of sludge. Thus, such a level of attained treatments validates the great potential of using aluminum-based sludge waste in treating various pollutants, including wastewater contaminated with insecticide effluents.
The utilization of sludge cake as an economical material for the removal of various contaminants from water and wastewater offers several advantageous features. These include cost reduction in waste disposal and contributing to environmental preservation. It is worth noting that the present study demonstrated a nearly complete removal of insecticides, surpassing the findings of previous studies. It is also important to highlight that previous studies have focused on single adsorption systems, whereas the current study implemented a constructed wetland adsorption column combining two ecological advancements. Hence, the process is more economic. However, further research is essential to verify the successive system reuse to check the feasibility of such a composite for a regeneration and reuse facility prior to final disposal. However, it is important to mention that the final sludge after treatment is still one of the concerns regarding real applications. However, it is notable that the final sludge could be incinerated to convert it into a fuel instead of a waste [56,57], but this is a research topic for future studies.

4. Conclusions

The current study integrated agricultural runoff treatment using a vertical flow constructed wetland system and its recreation function through using nanoparticles embedded in alum sludge as a composite. The results show that the system could enhance the function of a wetland. The system showed a pronounced effect on agricultural wastewater treatment loaded with DuPont 1179 insecticide, with removal at the isotherm time of 300 min. The system revealed complete DuPont 1179 removal under the optimal conditions at room temperature (25 °C) and the natural solution pH (6.9). The kinetic data validated the system following the second-order adsorption kinetic model as guided by the correlation coefficient factor. In addition, the Langmuir isotherm scheme is well fitted to the experimental results. A pilot-scale study demonstrated a promising suggestion for decorating the alum sludge cake with magnetite nanoparticles to enhance the constructed wetland system. Complete pollutant removal was achieved when a 75% composite substrate was supported by a gravel medium in the adsorption column. The data from the present study area provide a valuable indicator for introducing alum sludge waste as a constructed wetland system for eliminating pollutants from aqueous streams. However, extra study is essential in the future to estimate successive composite use and estimate its potential for incineration to generate energy instead of final disposal.

Author Contributions

Conceptualization, M.A.T.; Methodology, H.A.N. and M.A.T.; Writing—original draft, M.A.T.; Writing—review and editing, H.A.N. and M.A.T.; Visualization, H.A.N.; Project administration, H.A.N. All authors have read and agreed to the published version of the manuscript.

Funding

Prince Sattam bin Abdulaziz University funded this research work (PSAU/2023/01/2194222).

Data Availability Statement

Data are available upon request.

Acknowledgments

The authors extend their appreciation to Prince Sattam bin Abdulaziz University for funding this research work.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Overview of the experimental arrangement of the filter bed-constructed wetlands.
Figure 1. Overview of the experimental arrangement of the filter bed-constructed wetlands.
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Figure 2. XRD pattern of the AlS–M composite material.
Figure 2. XRD pattern of the AlS–M composite material.
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Figure 3. SEM image with magnification of the AlS–M composite material.
Figure 3. SEM image with magnification of the AlS–M composite material.
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Figure 4. EDX chemical composition of the AlS–M composite.
Figure 4. EDX chemical composition of the AlS–M composite.
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Figure 5. FTIR spectra of AlS–M composite substrate.
Figure 5. FTIR spectra of AlS–M composite substrate.
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Figure 6. BET surface area of the AlS–M composite substrate.
Figure 6. BET surface area of the AlS–M composite substrate.
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Figure 7. TEM images of the AlS–M composite substance at different magnifications and the inset graph shows the particle size distribution.
Figure 7. TEM images of the AlS–M composite substance at different magnifications and the inset graph shows the particle size distribution.
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Figure 8. Configuration data of the AlS–M composite column.
Figure 8. Configuration data of the AlS–M composite column.
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Figure 9. Time profile plot for the AlS–M composite column concerning DuPont 1179 removal.
Figure 9. Time profile plot for the AlS–M composite column concerning DuPont 1179 removal.
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Figure 10. DuPont 1179 removal dependent on the insecticide loading.
Figure 10. DuPont 1179 removal dependent on the insecticide loading.
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Figure 11. Effect of DuPont 1179 solution pH on the column performance.
Figure 11. Effect of DuPont 1179 solution pH on the column performance.
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Figure 12. Effect of temperature elevation on DuPont 1179 solution removal in the adsorption column.
Figure 12. Effect of temperature elevation on DuPont 1179 solution removal in the adsorption column.
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Figure 13. Comparison of isotherm models for the linear form of the (i) Langmuir and (ii) Freundlich models for DuPont 1179 removal.
Figure 13. Comparison of isotherm models for the linear form of the (i) Langmuir and (ii) Freundlich models for DuPont 1179 removal.
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Table 1. Comparing Lagergren’s first-order and pseudo second-order models for the DuPont 1179 sorption system.
Table 1. Comparing Lagergren’s first-order and pseudo second-order models for the DuPont 1179 sorption system.
Kinetic ModelKinetics Parameters100% Composite VFCW75% Composite VFCW50% Composite VFCW40% Composite VFCW
Lagergren’s first-orderqe, mg/g0.270.090.290.28
k1, min−14.674.294.774.82
R20.670.970.630.62
Pseudo second-orderqe, mg/g25,00033,33320002000
k2 × 10−5, g·mg/min53.322.541.625.0
R20.990.990.970.95
Table 2. Isotherm parameters for DuPont 1179 sorption system adsorption on different VFCW systems.
Table 2. Isotherm parameters for DuPont 1179 sorption system adsorption on different VFCW systems.
Isotherm ModelIsotherm Parameters100% Composite VFCW75% Composite VFCW50% Composite VFCW40% Composite VFCW
LangmuiraL (L/mg)0.00990.00410.00880.01668
KL0.76740.89070.45871.2004
Qo (mg/g)76.92217.3952.0871.94
R20.960.960.980.99
FreundlichKF14.87971.915111.82247.5007
n3.225802.12762.98412.7778
R20.890.920.840.95
NA—not available.
Table 3. Summarized list of studies using alum sludge in wastewater treatment compared with the current study.
Table 3. Summarized list of studies using alum sludge in wastewater treatment compared with the current study.
Alum Sludge DosePollutant in WastewaterOperating pHTreatment TimeRemovalsRef.
Adsorption columnDuPont 1179 Insecticide6.95 hComplete removalCurrent study
4 g/LPhosphorus6.212 d0.89 mg/g[46]
8 mg/kgMercury6.57 d79 mg/g[48]
250 mg/LArsenic8.120 h0.001–0.003 mg/g[46]
Adsorption columnLead5–8NA0.21–0.22 mmol/g[49]
0.1 gZinc and copper4.524 h0.040 mmol/g[50]
Adsorption columnCobalt6.048 h17.31 mg/g[51]
19.71 g/LHumic acid5.56NA0.47 mg/g[52]
0.5 g/LPhosphorus7.024 h;0.90 mg/g[18]
Adsorption columnPhenolNA1 h275 mg/g[53]
300 g/LAmmoniumNA60 min11.3 mg/g[54]
2 g/LTextile dye7.01 h6.5 mg/g[47]
Adsorption columnPhosphorus4.3NA22.4 mg/g[55]
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Nabwey, H.A.; Tony, M.A. A Glance at a Sustainable Solution Using Vertical Constructed Wetland Based on Dewatered Drinking-Water Waste Augmented Nanoparticle Composite Substrate for Wastewater Treatment. Processes 2023, 11, 2836. https://doi.org/10.3390/pr11102836

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Nabwey HA, Tony MA. A Glance at a Sustainable Solution Using Vertical Constructed Wetland Based on Dewatered Drinking-Water Waste Augmented Nanoparticle Composite Substrate for Wastewater Treatment. Processes. 2023; 11(10):2836. https://doi.org/10.3390/pr11102836

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Nabwey, Hossam A., and Maha A. Tony. 2023. "A Glance at a Sustainable Solution Using Vertical Constructed Wetland Based on Dewatered Drinking-Water Waste Augmented Nanoparticle Composite Substrate for Wastewater Treatment" Processes 11, no. 10: 2836. https://doi.org/10.3390/pr11102836

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