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Facile fabrication of nano zerovalent iron and granular activated carbon for enhanced nitrate removal from water

Facile fabrication of nano zerovalent iron and granular activated carbon for enhanced nitrate... GEOLOGY, ECOLOGY, AND LANDSCAPES INWASCON https://doi.org/10.1080/24749508.2023.2167626 RESEARCH ARTICLE Facile fabrication of nano zerovalent iron and granular activated carbon for enhanced nitrate removal from water a a b a c d Nafeesa Aman , Nimrah Ijaz , Irum Fatima , Muhammad Usman Farid , Haroon Rashid , Asif Ayub , e f g,h i j Dhay Ali Sabur , Israa Taha Ibrahim , Hany M. Abd El-Lateef , Iram Rafique , Yasir Mehmood k,l and Rasha M. K. Mohamed a b Department of Structures & Environmental Engineering, University of Agriculture, Faisalabad (UAF), Pakistan; Department of Chemistry, University of Wah, Wah Cantt, Rawalpindi, Pakistan; Department of Civil Engineering, The Islamia University of Bahawalpur, Bahawalpur, d e Pakistan; Institute of Chemistry, The Islamia University of Bahawalpur, Bahawalpur, Pakistan; Optics Techniques Department, Al- Mustaqbal University College, Babylon, Iraq; Department of Medical and Technologies, AL-Nisour University College, Baghdad, Iraq; g h Department of Chemistry, College of Science, King Faisal University, Al-Ahsa, Saudi Arabia; Department of Chemistry, Faculty of Science, i j Sohag University, Sohag, Egypt; Department of Zoology Postgraduate College for Women, Gojra, Pakistan; Department of Mechanical Engineering, Pakistan Institute of Engineering and Applied Science (PIEAS), Islamabad, Pakistan; Department of Chemistry, College of Science, Jouf University, Sakaka, Saudi Arabia; Department of Chemistry, Faculty of Science, Assiut University, Assiut, Egypt ABSTRACT ARTICLE HISTORY Received 21 July 2022 Nitrate contamination of groundwater has become a serious threat to the environmental Accepted 8 January 2023 health. In this study, nano zerovalent iron (nZVI) and granular activated carbon (GAC) were fabricated and characterized by some advanced analytical techniques including SEM, BET, XRD, KEYWORDS and FTIR to investigate their structural properties. Batch experiments were conducted for the Adsorption; activated adsorption of nitrate from water. The effect of various parameters including pH, adsorbent carbon; nano zerovalent iron; dose, initial nitrate concentration, and contact time was investigated. The nZVI showed max- nitrate imum adsorption capacity (q ) of 104.20 mg/g for nitrate at optimum conditions (pH 2, initial max concentration 50 ppm, adsorbent dose 3.75 g/L at room temperature), while GAC has shown q 81.07 mg/g at optimum conditions (pH 6, initial concentration 50 ppm, adsorbent dose max 3.75 g/L at room temperature). Equilibrium data of nitrate adsorption by nZVI and GAC followed the Langmuir isotherm (R = 0.999) and pseudo-second-order kinetic model. ANOVA and RCBD approaches were used to evaluate and check the significant level of various parameters. 1. Introduction have some drawbacks, that are, high cost, requires In recent decades, the contamination of groundwater intensive maintenance and they also produce second- due to nitrate is rapidly increasing and becoming ary pollution (Ayub, Srithilat, et al., 2022; Kumar et al., a serious issue for human and environmental health 2017). The adsorption-based technology has shown to (Lei et al., 2018). The reason for escalating nitrate be the best-available method andhave significant contamination in water resources is the use of syn- potential due to its adaptability, low cost, ease of use, thetic fertilizers in order to rise agricultural produc- low energy needs, and ease of operating system main- tivity, disposal of untreated municipal and industrial tenance (Aboudi Mana et al., 2017; Ayub et al., 2020). wastewater that contain high nitrate contents, escala- For the treatment of polluted water, an ideal adsorbent tion in untreated leachate from municipal solid waste has high capacity for adsorption, large surface area, the from landfill sites, and urban and rural raw sewage right volume and pore size, compatibility, and disposal without any prior treatment (Alothman et al., mechanical stability (Ayub & Raza, 2021; Srinivas & 2022; Hu et al., 2020). Due to the hazardous effect of Sundarapandian, 2019). nitrate-contaminated water on human health, the Activated carbon (AC) has been recognized as the United States Environmental Protection Agency has most reliable adsorbent to remove pollutants from set specific nitrate concentration in water at about 50 drinking water and wastewater. Furthermore, AC can mg/L (Yuan et al., 2019). be used in granular and powder form to remove per- Various wastewater techniques including reverse sistent pollutants from water (Ayub, Irfan, et al., osmosis, electrochemical removal, ion exchange, 2022). Because of its high surface area, hydrophobic nanofiltration, biological denitrification, adsorption surface, well-developed porosity, high mechanical and chemical reduction have been employed for the strength, and plenty of precursors, AC was used to removal of nitrate from water, but these techniques treat nitrate-contaminated water (Mortazavian et al., CONTACT Nafeesa Aman nafeesaaman@gmail.com Department of Structures & Environmental Engineering, University of Agriculture, Faisalabad (UAF), Pakistan © 2023 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of the International Water, Air & Soil Conservation Society(INWASCON). This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 2 N. AMAN ET AL. 2018). Nano zerovalent iron (nZVI) is a reductant that 2.3 Synthesis of GAC is used to treat organic and inorganic toxins, found in In two sets, 3 L working volume sequencing batch groundwater and soil among other environmental reactors were inoculated with 3.0 g/L activated sludge media. Numerous contaminants, such as nitroaro- as the initial inoculum and 3 g of charcoal was added matic compounds, metals and metalloids, chlorinated as augment. The charcoal was fabricated from coconut solvents, nitrate, and some dyes, have been treated by shell charcoal that was produced by pyrolyzing coco- nZVI (Azzam et al., 2016). nZVI can be used in both nut husk. To acquire the desired particle size of char- in situ and ex situ settings. It is one of the most coal, the obtained shells were grounded into the commonly used reducing agent for in situ chemical powder form. As the majority of the particles reduction of pollutants in water. Different organic remained suspended in water column during bubble contaminants have the potential to be broken down aeration, sequencing batch reactors was used to over- by nZVI. Due to its small size and large specific surface come this issue. These prepared charcoal area, nZVI can reduce contaminants even more particles having the size between 0.2to 0.5 mm were rapidly than granular ZVI. Due to its high reactivity named as granular AC. These particles were grinded and low dosage in comparison to conventional ZVI, into powder and passed through 100-mesh sieve. nZVI has been cited as an ideal adsorbent for nitrate- Before use, AC was washed by deionized water and contaminated groundwater remediation (Halpegama dried overnight in an oven to avoid any impurity et al., 2021). (Sarvajith & Nancharaiah, 2022). The main purpose of this study was to fabricate GAC and nZVI adsorbents and to compare their per- formance against nitrate removal from water. The 2.4 Batch experiments prepared material was characterized to explore their structural properties. The adoption performance of A set of batch experiments were performed to both the adsorbents was investigated under various investigate the nitrate adsorption on nZVI and environmental conditions. GAC. The effect of various parameters including pH, initial concentration, adsorbent dose, and con- tact time on removal efficiency was also investi- gated. The effect of pH was studied by adjusting 2 Materials and methods the pH of nitrate solution from 2 to 11 with the 2.1 Materials help of 0.1 M NaOH or HCl. The effect of adsor- bent dose on nitrate removal efficiency was inves- For this study, the following chemicals were used and tigated by changing the adsorbent dose from 0.1 all the solutions were prepared in distilled water: g to 4 g into 50 mL of nitrate solution (50 mg/L) at potassium nitrate (KNO ), ferrous sulphate (FeSO · 3 4 optimal pH, and the effect of nitrate initial concen- 7H O), sodium borohydride (NaBH , >95% pure), 2 4 tration was evaluated by changing the nitrate con- NaOH, and HCl. All these chemicals were purchased centration from 50 to 250 mg/L at optimal pH. The from Kermel Chemical Reagent (Tianjin, China). kinetics of nitrate removal was executed by adding 0.5 g of nZVI in 50 mL of nitrate solution (50 mg/ L), and the samples were taken out of the flasks 2.2 Synthesis of nZVI after a regular time interval and analyzed. The Here, we synthesized the nZVI by the reduction nitrate-contaminated water was also treated with method as reported in literature (Ryu et al., 2011). GAC by following the same procedure described Briefly, 10 g of FeSO · 7H O was dissolved in 750 4 2 above for nZVI. Then, the results were compared mL of deionized water and after proper mixing, 250 to evaluate its efficiency with nZVI. Nitrate (NO -) mL of ethanol was added into it. The solution of concentration in the filterate was measured by NaBH (1.8 g in 50 mL of water) was prepared sepa- using atomic adsorption spectrophotometer. rately and was added dropwise into the FeSO · 7H 4 2 The adsorption capacity q (mg/g) was calculated 2+ O solution for reduction of Fe , and was stirred at using the following equation. 500 rpm. After mixing, black precipitates appeared Ci Ce that was then collected by magnet and washed sev- qe ¼ V; (1) eral times with ethanol and deionized water. The flask containing nZVI was exposed to nitrogen gas where Ci is the initial concentration of pollutant to eradicate oxygen from the flask and then it was (mg/L), Ce is equilibrium concentration (mg/L), M is sonicated for 3 min. Furthermore, nZVI was col- the mass of adsorbents (g), and V is the volume of lected with the help of magnet, washed with deio- solution (L). nized water thrice, and dried. GEOLOGY, ECOLOGY, AND LANDSCAPES 3 The adsorption rate of nitrate on both nZVI and Table 1. Brunauer–Emmett–Teller analysis for GAC and nZVI. Components Units nZVI GAC GAC was studied using pseudo-first-order and BET m /g 1407 1098 pseudo-second-order kinetic models. The pseudo- Average diameter Nm 2.4 3.1 first-order is represented in Equation (2): 3 BET constant cm /g 59 710 Total pore volume = 0.920 P/P cm /g 0.1978 0.3159 lnðqe qtÞ ¼ lnqe K t; (2) where qt represents the adsorption capacity (mg/g) at −1 microscope (SEM; FEI Quanta 400F electron micro- time t while K (min ) is the equilibrium rate scope). The SEM image of GAC showed that the constant. exterior surface of AC was very uneven and full of Pseudo-second-order is represented in Equation (3): voids of all shapes and sizes as shown in Figure 1(a). t 1 1 This might have happened as a result of the volatile ¼ þ (3) qe k qe qe substances that were created during the activation process being gasified and released (Oyarzun et al., −1 −1 where K (g mg min ) is the equilibrium rate 2018). The SEM image of nZVI particles resembled constant. globules in shape as shown in Figure 1(b). The average The values of linear coefficient regression (R ) are size of the nZVI particles was found to be 50 nm. Due used to predict the most suited isotherm and kinetic to van der Waals attraction and magnetic force, the model for the adsorption process. nZVI particles gathered in chain-like clusters in deio- Adsorption isotherms were studied by using nized (DI) water (Halpegama et al., 2021). The pre- Freundlich and Langmuir isotherm models. The linear pared adsorbents have porous, rough, and irregular form of Langmuir isotherm model is shown in surface that gives higher chances of availability of Equation (4): more adsorptive surface, which, in turn, will increase 1 1 1 1 the capabilities of metal binding. Brunauer–Emmett– ¼ : þ (4) qe k :qmax Ce qmax Teller Analysis (BET) is an analytical approach for determining the pore size and surface area of the K is Langmuir constant (L/mg), and q is adsorp- L max adsorbents. The results related to BET for GAC and tion capacity of adsorbents (mg/g). nZVI are shown in Table 1. The linear form of Freundlich isotherm model is shwon in Equation (5) 3.1.2 XRD analysis ln ðqeÞ ¼ lnðkfÞþ lnðCeÞ (5) The X-ray diffraction (XRD) patterns of the GAC and nZVI were obtained using X’PERT PRO, Kf is Freundlich constant, and 1/n is the adsorption PANanalytical diffractometer with Cu-Ka radiation intensity. source. The samples of GAC and nZVI were scanned in 2θ ranging from 10° to 70° at a scanning rate of 1°/ min. The XRD spectra of the prepared GAC and 3 Results and discussion nZVI were taken to evaluate their structural charac- teristics (Kamarehie et al., 2018). The broad peaks in 3.1 Characterization of nZVI and GAC the GAC samples at 2θ 23° and 43° were seen, which 3.1.1 SEM analysis relates to plane 100 and 101, respectively. They The morphological structures of the prepared GAC denote the GAC with largely graphitic structure and and nZVI were investigated using scanning electron match the JCPDS card number 75-2078 (Bahrami Figure 1. SEM images of (a) GAC and (b) nZVI. 4 N. AMAN ET AL. −1 absorption peak at 1610 cm was caused by the stretching vibration of the C=C bond in the aromatic −1 ring, while an absorption peak at 1115 cm was caused by the stretching vibration of the C-O bond. Additionally, the GAC’s FTIR spectrum has a modest −1 absorption peak at 873 , which is attributable to the C-H bond’s bending vibration in the high degree of aromatic ring substitution (Hu et al., 2020). In FTIR −1 spectra of nZVI, the band at 3422 and 1637 cm are attributed to the O-H stretching and bending vibra- tion band of water moiety adsorbed on the surface of nZVI. This raises the possibility that a coating of ferric oxyhydroxide (FeOOH) has formed on nZVI. The −1 bands at617 and 620 cm in the infrared spectra of nZVI corresponded to the Fe-O stretching vibration peaks of Fe O and Fe O , showing that nZVI was Figure 2. X-ray diffraction pattern of GAC and nZVI. 2 3 3 4 mildly oxidized (Mortazavian et al., 2018). 3.2 Adsorption studies 3.2.1 Effect of pH and pH PZC The solution pH affects the charge on the surface of the adsorbents as well as the nitrate removal efficiency as shown in Figure 4(a). It was observed that the removal efficiency of GAC increased from 23% to 79% with the increase in the initial pH value from 2 to 6 and then a decreasing trend was observed with an increase in pH value; on the other hand, the removal efficiency of nZVI was 83% at pH 1, but as the pH increased to 2, the removal efficiency also increased to 98% and then started decreasing with an increase in pH up to 12. The nitrate adsorption on both the Figure 3. FTIR spectra of GAC and nZVI. adsorbents is due to the electrostatic interaction et al., 2020). A strong and broad diffraction peak at between the positively charged adsorbent surface and 2θ 44.67° for the nZVI has been recorded that con- negatively charged nitrate ions (Mandal et al., 2020). firmed the existence of Fe as shown in Figure 2. The The surface of the adsorbent becomes positively lack of distinctive iron oxide peaks in the nZVI XRD charged in solution when the pH of the solution is pattern suggests that the nZVI particles were not less than the pH of the adsorbent. In this work, the PZC oxidized and had a high degree of purity. Previous pH , that is, the pH at which the net charge on the PZC research suggested that nZVI particles have a core– surfaces of the adsorbents become equal to zero, of shell structure, with the core being Fe and the shell both the synthesized adsorbent, that are, nZVI and resulting from the fast oxidation of the nascent nZVI GAC were found to be 7.2 and 6.4, respectively, as to iron oxides (Du et al., 2020). This arrangement shown in Figure 4(b). When the pH of the solution protects the iron core from oxidation that occurs wasabove the pH of the adsorbent, the surface of PZC quickly. the adsorbent becomes negatively charged and repul- sion occurred between the synthesized adsorbent sur- 3.1.3 FTIR analysis face and the negatively charged nitrate ions in water Fourier transform infrared (FTIR) spectroscopy was (S. J. Li et al., 2020). used to determine the chemical makeup and func- tional groups of nZVI and GAC. Figure 3 displays 3.2.2 Effect of adsorbent dose the FTIR spectra of nZVI and GAC. According to The effect of adsorbent dose on removal efficiency was Figure 3, the typical GAC absorption peaks emerged studied using different doses of nZVI and GAC from −1 at 3435, 2920, 2850, 1610, and 1115 cm . The 0.5 g/L to 4 g/L. The removal efficiency of GAC O-H bond stretching vibration was attributed to the increased from 23% to 79% when the amount of −1 absorption peak at 3435 cm , while the C-H bond GAC was changed from 0.5 g/L to 3.75 g/L, and no stretching vibration was responsible for those at significant change in removal efficiency was observed −1 2920 cm and 2850 cm (Mittal et al., 2020). An when the adsorbent dose was increased from 3.75 g to GEOLOGY, ECOLOGY, AND LANDSCAPES 5 (a) GAC nZVI pHf 0 1 0 1 2 3 4 5 6 7 8 9 10 Initial pH (b) GAC nZVI -1 -2 pH = 6.4 pH = 7.2 PZC PZC -3 1 2 3 4 5 6 7 8 9 10 11 pHi Figure 4. (a) Effect of initial solution pH on nitrate removal, (b) pH of GAC and nZVI. pzc 4.5 g, as shown in Figure 5(a). This higher removal 3.2.3 Effect of time on TDS and DO efficiency at higher dose was due to the availability of Figure 6 shows that TDS value initially increases to large number of binding sites for the nitrate ions a certain limit and then starts decreasing with time. (Aboudi Mana & Fatt, 2017). On the other hand, Higher value of TDS was attained at optimal a decrease in the adoption capacity from 3.5 mg/g to dosage of nZVI at pH 2 and for GAC at pH 6 at 1.0 mg/g was also seen when the amount of adsorbent contact time of 30 min. However, after the passage was increased up to 4.5 g/L. Similar trends were also of time and remedial action of adsorbent, it can be observed with the removal efficiency of nZVI when seen that the minimum values of TDS were the dose of nZVI was changed from 0.5 g/L to 4 g/L; obtained at pH 2 and 6 with retention time of 90 98% removal efficiency was recorded while a decrease min. The fluctuations of total dissolved solids after in adsorption capacity (10 mg/g to 2.3 mg/g) was also applying nZVI and GAC treatments, have been recorded at the same dose change as shown in shown in Figure 6. This shows that the level of Figure 5(b). This decrease in adsorption capacity total dissolved solids gave minimum values after may be due to the unsaturation of binding sites, as 90 min of treatment at optimum pH and dosage, the binding sites increased with increasing nZVI whereas maximum values were observed at 30 min amount, but the amount of nitrate ions remained of the experimental duration (Sen et al., 2018). constant (Kumar et al., 2017). Removal Efficiency (%) ∆ pH Final pH 6 N. AMAN ET AL. 100 4.0 (a) 3.5 3.0 2.5 Removal (%) 2.0 q (mg/g) 1.5 1.0 0.5 10 0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Adsorbent dose (g/L) 100 (b) Removal (%) q (mg/g) 20 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Adsorbent dose (g/L) Figure 5. Effect of adsorbent dose on nitrate removal efficiency and adsorption capacity of (a) GAC and (b) nZVI. 3.2.4 Adsorption isotherm adsorbents, , nZVI and GAC, followed the Langmuir The initial concentration of nitrate ions in water isotherm model. The fitting results of Langmuir iso- affects the removal efficiency of the synthesized therm are better than Freundlich model because the adsorbents (Amin et al., 2018). The effect of initial value of regression coefficient (R > 0.999) for concentration was investigated by changing the con- Langmuir is higher than that of the Freundlich centration of nitrate from 50 ppm to 250 ppm, and model (R < 0.966). This shows the monolayer a decreasing trend in the removal efficiency of both adsorption of nitrate on the surface of nZVI and nZVI and GAC for nitrate removal was observed as GAC. Maximum adsorption capacity of nZVI for shown in Figure 7(a). However, the nZVI exhibits the nitrate ions was 104.20 mg/g, while GAC showed higher removal efficiency as compared to GAC. In the less adsorption capacity of 81.07 mg/g for nitrate this study, the Langmuir and Freundlich isotherms ions as compared with the nZVI. The value R is less models were employed to the experimental adsorp- than 1, which also favors the adsorption process tion equilibrium data of nZVI and GAC to determine (Bind et al., 2018). The comparison of nitrate adsorp- the adsorption capacity and nitrate-binding mechan- tion capacity of nZVI and GAC with other different ism as shown in Figure 7(b)–(c). The results have biosorbents reported in literature has been presented been presented in Table 2 that shows that both the in Table 4. Removal efficiency (%) Removal efficiency (%) q (mg/g) q (mg/g) e GEOLOGY, ECOLOGY, AND LANDSCAPES 7 1800 14 (a) TDS DO 1400 11 1000 8 600 5 0 20 40 60 80 100 Time (min) 1800 14 (b) TDS DO 1400 11 1000 8 600 5 0 20 40 60 80 100 Time (min) Figure 6. Effect of time on TDS and DO values with (a) nZVI and (b) GAC. 3.2.6 Statistical evaluation of each parameter of used kinetic models, pseudo-first order and the experiment pseudo-second order, the process of nitrate ANOVA statistical tool was applied with significant adsorption and related mechanism were examined level fixed at 5% is shown in Table 5. According to the at room temperature as a function of contact time. results, it is clear that there is highly significant out- Figures 8(b)–(c) depict the best fitting of the come of treatments at pH 2 and pH 6. Effect of contact experimental data to the linear form of pseudo- time is non-significant for pH, whereas dosage treat- second-order kinetic model, and the result of cor- ment show high significance against it. On the other relation parameters has been presented in Table 3. hand, both dosage verses time and treatment verses The result showed that there is resemblance minutes show non-significant relation among them. between the experimental and calculated absorp- tion capacity values, which favors the pseudo- second-order kinetic model (Bahrami et al., 2020). 3.2.5 Adsorption kinetic The adsorption kinetic for nitrate on both nZVI and GAC has been shown in Figure 8(a). 3.2.7 Variation in pH Maximum adsorption of nitrate was observed in Figure 9 shows the fluctuation in pH values of the initial 10 min and finally equilibrium estab- samples during treatments with nZVI. It shows lished in 1 h. This fast binding of nitrate is due that the maximum pH level of 7 was achieved at to the availability of maximum binding sites on two points when the adsorption was performed at both nZVI and GAC surface. Using two widely pH 2, contact time 90 min and pH 6, contact time TDS (mg/L) TDS (mg/L) DO (mg/L) DO (mg/L) 8 N. AMAN ET AL. (b) (a) 0.6 GAC nZVI nZVI GAC 0.5 0.4 0.3 0.2 0.1 0.0 0.0 0.1 0.2 0.3 0.4 0 50 100 150 200 250 300 1/C Initial Concentration (mg/L) e nZVI (c) 2.0 GAC 1.6 1.2 0.8 0.4 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Log C Figure 7. (a) Effect of initial concentration on nitrate removal by nZVI and GAC, (b) Langmuir’s isotherm plots for the adsorption of nitrate on nZVI and GAC, and (c) Freundlich’s isotherm plots for the adsorption of nitrate on nZVI and GAC . Table 2. Isotherm parameters for the removal of nitrate from Figure 10 illustrated the variations in pH levels after groundwater by nZVI and GAC. applying treatment of adsorbent GAC. It showed that Type of isotherm Parameters nZVI GAC the ideal pH value was obtained at dosage of 0.625 g Langmuir q (mg/g) 104.20 81.07 max with contact time of 30 minutes both at pH 2 and pH 6. K (L/mg) 0.0213 0.003 R 0.4833 0.8687 GAC has negative zeta potential at above pH 7.2; on the R 0.999 0.999 other hand, point for zero charge for GAC was at 6.2 Freundlich K 4.069 1.09 where the adsorbent net surface charge was equal to 1/n 0.5905 0.5343 R 0.966 0.987 zero. TDS level for the GAC adsorbent first increased, then started to decrease and the dissolved oxygen con- centration gradually decreased (Sun et al., 2022). 60 min. pH is the most significant characteristic to determine the adsorbate equilibrium and surface 4 Regeneration charge. The pH of the groundwater was affected by the zeta potential of nZVI, degree of ionization, An important parameter to determine the sustain- and various aqueous pollutants. The pH of every ability of the adsorbent is based on its reusability. sample was measured via using digital pH meter In this study, the prepared adsorbents were reused (Amin et al., 2018). Results shown in Figure 9 for five times to remove nitrate from water. Using depict that there was a fluctuation in pH value of alkaline solution (0.1 M NaOH), the weakly bonded samples during treatments with adsorbent nZVI. At nitrate on nZVI and GAC surface was desorbed pH 2, nitrate removal was about 98%, DO was 55%, and the adsorbents were washed with DI water and TDS was removed approximately 43%. several times (Du et al., 2020). The dried material Removal Efficiency (%) Log q 1/q e GEOLOGY, ECOLOGY, AND LANDSCAPES 9 (a) nZVI (b) GAC GAC nZVI 0 10 20 30 40 50 60 70 80 90 100 0 20 40 60 80 100 Time (min) Time (min) nZVI (c) GAC -1 -2 -3 -4 0 20 40 60 80 100 Time (min) Figure 8. (a) Effect of contact time on the nitrate removal by nZVI and GAC, (b) pseudo-second-order kinetic plots for the adsorption of nitrate on nZVI and GAC, and (c) pseudo-first-order plots for the adsorption of nitrate on nZVI and GAC. Table 3. Kinetic parameters for the removal nitrate from groundwater by nZVI and GAC. Parameters nZVI GAC Order of reaction q (mg/g) 22.15 9.12 e, exp Pseudo-first order q (mg/g) 0.780 1.442 e, cal −1 −4 −4 k (min ) −3.8 × 10 −4.9 × 10 R 0.745 0.812 Pseudo-second order q (mg/g) 23.62 9.36 e, cal −1 −1 k (g mg min ) 0.141 0.076 R 0.999 0.999 Table 4. Comparison of adoption capacity of prepared biosorbents with the literature. Adsorbents q (mg/g) References max Activated carbon 28 (El-Sayed et al., 2014) Pit-toilet leachate 32 (Mittal et al., 2020) GAC/NZVI 55 (Hu et al., 2020) Magnetic cationic hydrogel 95.88 (J. Li et al., 2020) PAM/AC 48.9 (Kamarehie et al., 2018) GAC 81.07 Present study nZVI 104.20 Present study Removal Efficiency (%) ln (q - q ) e t t/q t 10 N. AMAN ET AL. Table 5. Analysis of variance of pH values of samples for eight treatments of nZVI adsorbent. Source DF Adj. SS Adj. MS F P Unit 1 94.75 94.75 Factors 1 132.017 132.07 86.96 0.0000** Treatments 4 16.896 4.224 2.87 0.0406** ns Minutes 2 0.067 0.034 0.02 0.9775 Factors*Treatments 4 58.047 14.512 9.86 0.0000** ns Factors*Minutes 2 0.082 0.082 0.03 0.9724 ns Treatments* vs. Minutes* 8 2.113 0.264 0.18 0.9920 ns Factors*Treatment*Minutes* 8 1.954 0.244 0.17 0.9938 Error 29 42.687 1.472 Total 59 348.616 ns Note: *Significant; ** Highly Significant; Non-significant. nZVI 0.625g t1 nZVI 1.25g t2 nZVI 2.5g t3 nZVI 3.75g t4 pH2, 30min pH2, 60min pH2, 90min pH6, 30min pH6, 60min pH6, 90min Figure 9. Change in pH value of nitrate containing groundwater samples after treatment of nZVI at 25 ±5°C at different pH and adsorbents dose. GAC, 0.625g t1 GAC, 1.25g t2 GAC, 2.5g t3 GAC, 3.75g t4 pH2, 30min pH2, 60min pH2, 90min pH6, 30min pH6, 60min pH6, 90min Figure 10. Change in pH value of nitrate-containing groundwater samples after treatment of GAC at 25 ±5°C at different pH and adsorbents dose. were reused for nitrate adsorption for the next proceeded for the fifth regeneration cycle, nitrate cycle. In the first and second regeneration cycle, removal efficiency was 91% and 70% for nZVI and the removal efficiency of nZVI for nitrate was GAC, respectively. This little change in the removal almost same, that was, 98%, whereas in case of efficiency of both the adsorbents is due the reduc- GAC, efficiency rate slightly decreased from 79% tion in the amount of surface area available for the to 77% as shown in Figure 11. Moreover, as we reaction. pH values pH level GEOLOGY, ECOLOGY, AND LANDSCAPES 11 nZVI Funding GAC The work was supported by the Deanship of Scientific 90 Research [GRANT2093]. ORCID Nafeesa Aman http://orcid.org/0000-0003-3631-6069 Asif Ayub http://orcid.org/0000-0003-0590-3906 References 1st 2nd 3rd 4th 5th Aboudi Mana, S. C., & Fatt, N. T. (2017). Arsenic speciation Regeneration cycles using ultra high-performance liquid chromatography and inductively coupled plasma optical emission spectrome- Figure 11. Regeneration of nZVI and GAC. try in water and sediments samples. Geology, Ecology, and Landscapes, 1(2), 121–132. https://doi.org/10.1080/ 24749508.2017.1332855 Conclusion Aboudi Mana, S. C., Hanafiah, M. M., & Chowdhury, A. J. K. (2017). Environmental characteris- The adsorption of nitrate by nZVI and GAC under tics of clay and clay-based minerals. Geology, Ecology, and Landscapes, 1(3), 155–161. https://doi.org/10.1080/ various pH levels with different initial concentration 24749508.2017.1361128 of adsorbent was investigated. However, nZVI showed Alothman, A. A., Ayub, A., Hachim, S. K., high affinity for the nitrate with 98% removal efficiency Mohammed, B. M., Hussain, F., Altaf, M., at 2 pH with 3.75 g/L of dose; therefore, it is considered Kadhim, Z. J., Lafta, H. A., Alnassar, Y. S., as an effective adsorbent. On the other hand, GAC at 6 Shams, M. A., Almuhous, N. A., Ouladsmane, M., & Sillanpaa, M. (2022). Facile synthesis and comparative pH was found to be better to remove nitrate contam- study of the enhanced photocatalytic degradation of two ination with 79% from groundwater. pH had significant selected dyes by TiO2-g-C3N4 composite. Environmental effects on the adsorption capacity and contamination Science and Pollution Research, 1–12. https://doi.org/10. removal; acidic pH was more likely to be favorable for 1007/S11356-022-24839-Z nitrate removal. Nitrate adsorption by nZVI and GAC Amin, H., Arain, B. A., Jahangir, T. M., Abbasi, M. S., & Amin, F. (2018). Accumulation and distribution of lead was more consistent with Langmuir isotherm model as (Pb) in plant tissues of guar (Cyamopsis tetragonoloba L.) compared to Freundlich model. Finally, the nZVI and and sesame (Sesamum indicum L.): Profitable phytore- GAC were tested for its reusability and the adsorption mediation with biofuel crops. Geology, Ecology, and efficiency was still remarkable after five cycles. Landscapes, 2(1), 51–60. https://doi.org/10.1080/ 24749508.2018.1452464 Ayub, A., Irfan, A., Raza, Z. A., Abbas, M., Muhammad, A., Ahmad, K., & Munwar, A. (2022). Development of poly Interest statement (1-vinylimidazole)-chitosan composite sorbent under microwave irradiation for enhanced uptake of Cd(II) On behalf of all the authors, the corresponding author ions from aqueous media. Polymer Bulletin, 79(2), states that there is no conflict of interest. 807–827. https://doi.org/10.1007/s00289-020-03523-7 Ayub, A., & Raza, Z. A. (2021). Arsenic removal approaches: A focus on chitosan biosorption to conserve the water sources. International Journal of Biological Acknowledgments Macromolecules, 192, 1196–1216. https://doi.org/10. The authors acknowledge the Deanship of Scientific Research, 1016/j.ijbiomac.2021.10.050 Vice Presidency for Graduate Studies and Scientific Research Ayub, A., Raza, Z. A., Majeed, M. I., Tariq, M. R., & Irfan, A. at King Faisal University, Saudi Arabia, for the financial (2020). Development of sustainable magnetic chitosan biosor- support under the annual funding track [GRANT2093]. bent beads for kinetic remediation of arsenic contaminated The authors would also like to thank Environmental water. International Journal of Biological Macromolecules, 163, Services Pakistan (ESPAK) and Environmental Engineering 603–617. https://doi.org/10.1016/j.ijbiomac.2020.06.287 Labs (UAF) for the laboratory support. Ayub, A., Srithilat, K., Fatima, I., Panduro Tenazoa, N. M., Ahmed, I., Akhtar, M. U., Shabbir, W., Ahmad, K., & Muhammad, A. (2022). Arsenic in drinking water: Overview of removal strategies and role of chitosan bio- Disclosure statement sorbent for its remediation. 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Facile fabrication of nano zerovalent iron and granular activated carbon for enhanced nitrate removal from water

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GEOLOGY, ECOLOGY, AND LANDSCAPES INWASCON https://doi.org/10.1080/24749508.2023.2167626 RESEARCH ARTICLE Facile fabrication of nano zerovalent iron and granular activated carbon for enhanced nitrate removal from water a a b a c d Nafeesa Aman , Nimrah Ijaz , Irum Fatima , Muhammad Usman Farid , Haroon Rashid , Asif Ayub , e f g,h i j Dhay Ali Sabur , Israa Taha Ibrahim , Hany M. Abd El-Lateef , Iram Rafique , Yasir Mehmood k,l and Rasha M. K. Mohamed a b Department of Structures & Environmental Engineering, University of Agriculture, Faisalabad (UAF), Pakistan; Department of Chemistry, University of Wah, Wah Cantt, Rawalpindi, Pakistan; Department of Civil Engineering, The Islamia University of Bahawalpur, Bahawalpur, d e Pakistan; Institute of Chemistry, The Islamia University of Bahawalpur, Bahawalpur, Pakistan; Optics Techniques Department, Al- Mustaqbal University College, Babylon, Iraq; Department of Medical and Technologies, AL-Nisour University College, Baghdad, Iraq; g h Department of Chemistry, College of Science, King Faisal University, Al-Ahsa, Saudi Arabia; Department of Chemistry, Faculty of Science, i j Sohag University, Sohag, Egypt; Department of Zoology Postgraduate College for Women, Gojra, Pakistan; Department of Mechanical Engineering, Pakistan Institute of Engineering and Applied Science (PIEAS), Islamabad, Pakistan; Department of Chemistry, College of Science, Jouf University, Sakaka, Saudi Arabia; Department of Chemistry, Faculty of Science, Assiut University, Assiut, Egypt ABSTRACT ARTICLE HISTORY Received 21 July 2022 Nitrate contamination of groundwater has become a serious threat to the environmental Accepted 8 January 2023 health. In this study, nano zerovalent iron (nZVI) and granular activated carbon (GAC) were fabricated and characterized by some advanced analytical techniques including SEM, BET, XRD, KEYWORDS and FTIR to investigate their structural properties. Batch experiments were conducted for the Adsorption; activated adsorption of nitrate from water. The effect of various parameters including pH, adsorbent carbon; nano zerovalent iron; dose, initial nitrate concentration, and contact time was investigated. The nZVI showed max- nitrate imum adsorption capacity (q ) of 104.20 mg/g for nitrate at optimum conditions (pH 2, initial max concentration 50 ppm, adsorbent dose 3.75 g/L at room temperature), while GAC has shown q 81.07 mg/g at optimum conditions (pH 6, initial concentration 50 ppm, adsorbent dose max 3.75 g/L at room temperature). Equilibrium data of nitrate adsorption by nZVI and GAC followed the Langmuir isotherm (R = 0.999) and pseudo-second-order kinetic model. ANOVA and RCBD approaches were used to evaluate and check the significant level of various parameters. 1. Introduction have some drawbacks, that are, high cost, requires In recent decades, the contamination of groundwater intensive maintenance and they also produce second- due to nitrate is rapidly increasing and becoming ary pollution (Ayub, Srithilat, et al., 2022; Kumar et al., a serious issue for human and environmental health 2017). The adsorption-based technology has shown to (Lei et al., 2018). The reason for escalating nitrate be the best-available method andhave significant contamination in water resources is the use of syn- potential due to its adaptability, low cost, ease of use, thetic fertilizers in order to rise agricultural produc- low energy needs, and ease of operating system main- tivity, disposal of untreated municipal and industrial tenance (Aboudi Mana et al., 2017; Ayub et al., 2020). wastewater that contain high nitrate contents, escala- For the treatment of polluted water, an ideal adsorbent tion in untreated leachate from municipal solid waste has high capacity for adsorption, large surface area, the from landfill sites, and urban and rural raw sewage right volume and pore size, compatibility, and disposal without any prior treatment (Alothman et al., mechanical stability (Ayub & Raza, 2021; Srinivas & 2022; Hu et al., 2020). Due to the hazardous effect of Sundarapandian, 2019). nitrate-contaminated water on human health, the Activated carbon (AC) has been recognized as the United States Environmental Protection Agency has most reliable adsorbent to remove pollutants from set specific nitrate concentration in water at about 50 drinking water and wastewater. Furthermore, AC can mg/L (Yuan et al., 2019). be used in granular and powder form to remove per- Various wastewater techniques including reverse sistent pollutants from water (Ayub, Irfan, et al., osmosis, electrochemical removal, ion exchange, 2022). Because of its high surface area, hydrophobic nanofiltration, biological denitrification, adsorption surface, well-developed porosity, high mechanical and chemical reduction have been employed for the strength, and plenty of precursors, AC was used to removal of nitrate from water, but these techniques treat nitrate-contaminated water (Mortazavian et al., CONTACT Nafeesa Aman nafeesaaman@gmail.com Department of Structures & Environmental Engineering, University of Agriculture, Faisalabad (UAF), Pakistan © 2023 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of the International Water, Air & Soil Conservation Society(INWASCON). This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 2 N. AMAN ET AL. 2018). Nano zerovalent iron (nZVI) is a reductant that 2.3 Synthesis of GAC is used to treat organic and inorganic toxins, found in In two sets, 3 L working volume sequencing batch groundwater and soil among other environmental reactors were inoculated with 3.0 g/L activated sludge media. Numerous contaminants, such as nitroaro- as the initial inoculum and 3 g of charcoal was added matic compounds, metals and metalloids, chlorinated as augment. The charcoal was fabricated from coconut solvents, nitrate, and some dyes, have been treated by shell charcoal that was produced by pyrolyzing coco- nZVI (Azzam et al., 2016). nZVI can be used in both nut husk. To acquire the desired particle size of char- in situ and ex situ settings. It is one of the most coal, the obtained shells were grounded into the commonly used reducing agent for in situ chemical powder form. As the majority of the particles reduction of pollutants in water. Different organic remained suspended in water column during bubble contaminants have the potential to be broken down aeration, sequencing batch reactors was used to over- by nZVI. Due to its small size and large specific surface come this issue. These prepared charcoal area, nZVI can reduce contaminants even more particles having the size between 0.2to 0.5 mm were rapidly than granular ZVI. Due to its high reactivity named as granular AC. These particles were grinded and low dosage in comparison to conventional ZVI, into powder and passed through 100-mesh sieve. nZVI has been cited as an ideal adsorbent for nitrate- Before use, AC was washed by deionized water and contaminated groundwater remediation (Halpegama dried overnight in an oven to avoid any impurity et al., 2021). (Sarvajith & Nancharaiah, 2022). The main purpose of this study was to fabricate GAC and nZVI adsorbents and to compare their per- formance against nitrate removal from water. The 2.4 Batch experiments prepared material was characterized to explore their structural properties. The adoption performance of A set of batch experiments were performed to both the adsorbents was investigated under various investigate the nitrate adsorption on nZVI and environmental conditions. GAC. The effect of various parameters including pH, initial concentration, adsorbent dose, and con- tact time on removal efficiency was also investi- gated. The effect of pH was studied by adjusting 2 Materials and methods the pH of nitrate solution from 2 to 11 with the 2.1 Materials help of 0.1 M NaOH or HCl. The effect of adsor- bent dose on nitrate removal efficiency was inves- For this study, the following chemicals were used and tigated by changing the adsorbent dose from 0.1 all the solutions were prepared in distilled water: g to 4 g into 50 mL of nitrate solution (50 mg/L) at potassium nitrate (KNO ), ferrous sulphate (FeSO · 3 4 optimal pH, and the effect of nitrate initial concen- 7H O), sodium borohydride (NaBH , >95% pure), 2 4 tration was evaluated by changing the nitrate con- NaOH, and HCl. All these chemicals were purchased centration from 50 to 250 mg/L at optimal pH. The from Kermel Chemical Reagent (Tianjin, China). kinetics of nitrate removal was executed by adding 0.5 g of nZVI in 50 mL of nitrate solution (50 mg/ L), and the samples were taken out of the flasks 2.2 Synthesis of nZVI after a regular time interval and analyzed. The Here, we synthesized the nZVI by the reduction nitrate-contaminated water was also treated with method as reported in literature (Ryu et al., 2011). GAC by following the same procedure described Briefly, 10 g of FeSO · 7H O was dissolved in 750 4 2 above for nZVI. Then, the results were compared mL of deionized water and after proper mixing, 250 to evaluate its efficiency with nZVI. Nitrate (NO -) mL of ethanol was added into it. The solution of concentration in the filterate was measured by NaBH (1.8 g in 50 mL of water) was prepared sepa- using atomic adsorption spectrophotometer. rately and was added dropwise into the FeSO · 7H 4 2 The adsorption capacity q (mg/g) was calculated 2+ O solution for reduction of Fe , and was stirred at using the following equation. 500 rpm. After mixing, black precipitates appeared Ci Ce that was then collected by magnet and washed sev- qe ¼ V; (1) eral times with ethanol and deionized water. The flask containing nZVI was exposed to nitrogen gas where Ci is the initial concentration of pollutant to eradicate oxygen from the flask and then it was (mg/L), Ce is equilibrium concentration (mg/L), M is sonicated for 3 min. Furthermore, nZVI was col- the mass of adsorbents (g), and V is the volume of lected with the help of magnet, washed with deio- solution (L). nized water thrice, and dried. GEOLOGY, ECOLOGY, AND LANDSCAPES 3 The adsorption rate of nitrate on both nZVI and Table 1. Brunauer–Emmett–Teller analysis for GAC and nZVI. Components Units nZVI GAC GAC was studied using pseudo-first-order and BET m /g 1407 1098 pseudo-second-order kinetic models. The pseudo- Average diameter Nm 2.4 3.1 first-order is represented in Equation (2): 3 BET constant cm /g 59 710 Total pore volume = 0.920 P/P cm /g 0.1978 0.3159 lnðqe qtÞ ¼ lnqe K t; (2) where qt represents the adsorption capacity (mg/g) at −1 microscope (SEM; FEI Quanta 400F electron micro- time t while K (min ) is the equilibrium rate scope). The SEM image of GAC showed that the constant. exterior surface of AC was very uneven and full of Pseudo-second-order is represented in Equation (3): voids of all shapes and sizes as shown in Figure 1(a). t 1 1 This might have happened as a result of the volatile ¼ þ (3) qe k qe qe substances that were created during the activation process being gasified and released (Oyarzun et al., −1 −1 where K (g mg min ) is the equilibrium rate 2018). The SEM image of nZVI particles resembled constant. globules in shape as shown in Figure 1(b). The average The values of linear coefficient regression (R ) are size of the nZVI particles was found to be 50 nm. Due used to predict the most suited isotherm and kinetic to van der Waals attraction and magnetic force, the model for the adsorption process. nZVI particles gathered in chain-like clusters in deio- Adsorption isotherms were studied by using nized (DI) water (Halpegama et al., 2021). The pre- Freundlich and Langmuir isotherm models. The linear pared adsorbents have porous, rough, and irregular form of Langmuir isotherm model is shown in surface that gives higher chances of availability of Equation (4): more adsorptive surface, which, in turn, will increase 1 1 1 1 the capabilities of metal binding. Brunauer–Emmett– ¼ : þ (4) qe k :qmax Ce qmax Teller Analysis (BET) is an analytical approach for determining the pore size and surface area of the K is Langmuir constant (L/mg), and q is adsorp- L max adsorbents. The results related to BET for GAC and tion capacity of adsorbents (mg/g). nZVI are shown in Table 1. The linear form of Freundlich isotherm model is shwon in Equation (5) 3.1.2 XRD analysis ln ðqeÞ ¼ lnðkfÞþ lnðCeÞ (5) The X-ray diffraction (XRD) patterns of the GAC and nZVI were obtained using X’PERT PRO, Kf is Freundlich constant, and 1/n is the adsorption PANanalytical diffractometer with Cu-Ka radiation intensity. source. The samples of GAC and nZVI were scanned in 2θ ranging from 10° to 70° at a scanning rate of 1°/ min. The XRD spectra of the prepared GAC and 3 Results and discussion nZVI were taken to evaluate their structural charac- teristics (Kamarehie et al., 2018). The broad peaks in 3.1 Characterization of nZVI and GAC the GAC samples at 2θ 23° and 43° were seen, which 3.1.1 SEM analysis relates to plane 100 and 101, respectively. They The morphological structures of the prepared GAC denote the GAC with largely graphitic structure and and nZVI were investigated using scanning electron match the JCPDS card number 75-2078 (Bahrami Figure 1. SEM images of (a) GAC and (b) nZVI. 4 N. AMAN ET AL. −1 absorption peak at 1610 cm was caused by the stretching vibration of the C=C bond in the aromatic −1 ring, while an absorption peak at 1115 cm was caused by the stretching vibration of the C-O bond. Additionally, the GAC’s FTIR spectrum has a modest −1 absorption peak at 873 , which is attributable to the C-H bond’s bending vibration in the high degree of aromatic ring substitution (Hu et al., 2020). In FTIR −1 spectra of nZVI, the band at 3422 and 1637 cm are attributed to the O-H stretching and bending vibra- tion band of water moiety adsorbed on the surface of nZVI. This raises the possibility that a coating of ferric oxyhydroxide (FeOOH) has formed on nZVI. The −1 bands at617 and 620 cm in the infrared spectra of nZVI corresponded to the Fe-O stretching vibration peaks of Fe O and Fe O , showing that nZVI was Figure 2. X-ray diffraction pattern of GAC and nZVI. 2 3 3 4 mildly oxidized (Mortazavian et al., 2018). 3.2 Adsorption studies 3.2.1 Effect of pH and pH PZC The solution pH affects the charge on the surface of the adsorbents as well as the nitrate removal efficiency as shown in Figure 4(a). It was observed that the removal efficiency of GAC increased from 23% to 79% with the increase in the initial pH value from 2 to 6 and then a decreasing trend was observed with an increase in pH value; on the other hand, the removal efficiency of nZVI was 83% at pH 1, but as the pH increased to 2, the removal efficiency also increased to 98% and then started decreasing with an increase in pH up to 12. The nitrate adsorption on both the Figure 3. FTIR spectra of GAC and nZVI. adsorbents is due to the electrostatic interaction et al., 2020). A strong and broad diffraction peak at between the positively charged adsorbent surface and 2θ 44.67° for the nZVI has been recorded that con- negatively charged nitrate ions (Mandal et al., 2020). firmed the existence of Fe as shown in Figure 2. The The surface of the adsorbent becomes positively lack of distinctive iron oxide peaks in the nZVI XRD charged in solution when the pH of the solution is pattern suggests that the nZVI particles were not less than the pH of the adsorbent. In this work, the PZC oxidized and had a high degree of purity. Previous pH , that is, the pH at which the net charge on the PZC research suggested that nZVI particles have a core– surfaces of the adsorbents become equal to zero, of shell structure, with the core being Fe and the shell both the synthesized adsorbent, that are, nZVI and resulting from the fast oxidation of the nascent nZVI GAC were found to be 7.2 and 6.4, respectively, as to iron oxides (Du et al., 2020). This arrangement shown in Figure 4(b). When the pH of the solution protects the iron core from oxidation that occurs wasabove the pH of the adsorbent, the surface of PZC quickly. the adsorbent becomes negatively charged and repul- sion occurred between the synthesized adsorbent sur- 3.1.3 FTIR analysis face and the negatively charged nitrate ions in water Fourier transform infrared (FTIR) spectroscopy was (S. J. Li et al., 2020). used to determine the chemical makeup and func- tional groups of nZVI and GAC. Figure 3 displays 3.2.2 Effect of adsorbent dose the FTIR spectra of nZVI and GAC. According to The effect of adsorbent dose on removal efficiency was Figure 3, the typical GAC absorption peaks emerged studied using different doses of nZVI and GAC from −1 at 3435, 2920, 2850, 1610, and 1115 cm . The 0.5 g/L to 4 g/L. The removal efficiency of GAC O-H bond stretching vibration was attributed to the increased from 23% to 79% when the amount of −1 absorption peak at 3435 cm , while the C-H bond GAC was changed from 0.5 g/L to 3.75 g/L, and no stretching vibration was responsible for those at significant change in removal efficiency was observed −1 2920 cm and 2850 cm (Mittal et al., 2020). An when the adsorbent dose was increased from 3.75 g to GEOLOGY, ECOLOGY, AND LANDSCAPES 5 (a) GAC nZVI pHf 0 1 0 1 2 3 4 5 6 7 8 9 10 Initial pH (b) GAC nZVI -1 -2 pH = 6.4 pH = 7.2 PZC PZC -3 1 2 3 4 5 6 7 8 9 10 11 pHi Figure 4. (a) Effect of initial solution pH on nitrate removal, (b) pH of GAC and nZVI. pzc 4.5 g, as shown in Figure 5(a). This higher removal 3.2.3 Effect of time on TDS and DO efficiency at higher dose was due to the availability of Figure 6 shows that TDS value initially increases to large number of binding sites for the nitrate ions a certain limit and then starts decreasing with time. (Aboudi Mana & Fatt, 2017). On the other hand, Higher value of TDS was attained at optimal a decrease in the adoption capacity from 3.5 mg/g to dosage of nZVI at pH 2 and for GAC at pH 6 at 1.0 mg/g was also seen when the amount of adsorbent contact time of 30 min. However, after the passage was increased up to 4.5 g/L. Similar trends were also of time and remedial action of adsorbent, it can be observed with the removal efficiency of nZVI when seen that the minimum values of TDS were the dose of nZVI was changed from 0.5 g/L to 4 g/L; obtained at pH 2 and 6 with retention time of 90 98% removal efficiency was recorded while a decrease min. The fluctuations of total dissolved solids after in adsorption capacity (10 mg/g to 2.3 mg/g) was also applying nZVI and GAC treatments, have been recorded at the same dose change as shown in shown in Figure 6. This shows that the level of Figure 5(b). This decrease in adsorption capacity total dissolved solids gave minimum values after may be due to the unsaturation of binding sites, as 90 min of treatment at optimum pH and dosage, the binding sites increased with increasing nZVI whereas maximum values were observed at 30 min amount, but the amount of nitrate ions remained of the experimental duration (Sen et al., 2018). constant (Kumar et al., 2017). Removal Efficiency (%) ∆ pH Final pH 6 N. AMAN ET AL. 100 4.0 (a) 3.5 3.0 2.5 Removal (%) 2.0 q (mg/g) 1.5 1.0 0.5 10 0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Adsorbent dose (g/L) 100 (b) Removal (%) q (mg/g) 20 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Adsorbent dose (g/L) Figure 5. Effect of adsorbent dose on nitrate removal efficiency and adsorption capacity of (a) GAC and (b) nZVI. 3.2.4 Adsorption isotherm adsorbents, , nZVI and GAC, followed the Langmuir The initial concentration of nitrate ions in water isotherm model. The fitting results of Langmuir iso- affects the removal efficiency of the synthesized therm are better than Freundlich model because the adsorbents (Amin et al., 2018). The effect of initial value of regression coefficient (R > 0.999) for concentration was investigated by changing the con- Langmuir is higher than that of the Freundlich centration of nitrate from 50 ppm to 250 ppm, and model (R < 0.966). This shows the monolayer a decreasing trend in the removal efficiency of both adsorption of nitrate on the surface of nZVI and nZVI and GAC for nitrate removal was observed as GAC. Maximum adsorption capacity of nZVI for shown in Figure 7(a). However, the nZVI exhibits the nitrate ions was 104.20 mg/g, while GAC showed higher removal efficiency as compared to GAC. In the less adsorption capacity of 81.07 mg/g for nitrate this study, the Langmuir and Freundlich isotherms ions as compared with the nZVI. The value R is less models were employed to the experimental adsorp- than 1, which also favors the adsorption process tion equilibrium data of nZVI and GAC to determine (Bind et al., 2018). The comparison of nitrate adsorp- the adsorption capacity and nitrate-binding mechan- tion capacity of nZVI and GAC with other different ism as shown in Figure 7(b)–(c). The results have biosorbents reported in literature has been presented been presented in Table 2 that shows that both the in Table 4. Removal efficiency (%) Removal efficiency (%) q (mg/g) q (mg/g) e GEOLOGY, ECOLOGY, AND LANDSCAPES 7 1800 14 (a) TDS DO 1400 11 1000 8 600 5 0 20 40 60 80 100 Time (min) 1800 14 (b) TDS DO 1400 11 1000 8 600 5 0 20 40 60 80 100 Time (min) Figure 6. Effect of time on TDS and DO values with (a) nZVI and (b) GAC. 3.2.6 Statistical evaluation of each parameter of used kinetic models, pseudo-first order and the experiment pseudo-second order, the process of nitrate ANOVA statistical tool was applied with significant adsorption and related mechanism were examined level fixed at 5% is shown in Table 5. According to the at room temperature as a function of contact time. results, it is clear that there is highly significant out- Figures 8(b)–(c) depict the best fitting of the come of treatments at pH 2 and pH 6. Effect of contact experimental data to the linear form of pseudo- time is non-significant for pH, whereas dosage treat- second-order kinetic model, and the result of cor- ment show high significance against it. On the other relation parameters has been presented in Table 3. hand, both dosage verses time and treatment verses The result showed that there is resemblance minutes show non-significant relation among them. between the experimental and calculated absorp- tion capacity values, which favors the pseudo- second-order kinetic model (Bahrami et al., 2020). 3.2.5 Adsorption kinetic The adsorption kinetic for nitrate on both nZVI and GAC has been shown in Figure 8(a). 3.2.7 Variation in pH Maximum adsorption of nitrate was observed in Figure 9 shows the fluctuation in pH values of the initial 10 min and finally equilibrium estab- samples during treatments with nZVI. It shows lished in 1 h. This fast binding of nitrate is due that the maximum pH level of 7 was achieved at to the availability of maximum binding sites on two points when the adsorption was performed at both nZVI and GAC surface. Using two widely pH 2, contact time 90 min and pH 6, contact time TDS (mg/L) TDS (mg/L) DO (mg/L) DO (mg/L) 8 N. AMAN ET AL. (b) (a) 0.6 GAC nZVI nZVI GAC 0.5 0.4 0.3 0.2 0.1 0.0 0.0 0.1 0.2 0.3 0.4 0 50 100 150 200 250 300 1/C Initial Concentration (mg/L) e nZVI (c) 2.0 GAC 1.6 1.2 0.8 0.4 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Log C Figure 7. (a) Effect of initial concentration on nitrate removal by nZVI and GAC, (b) Langmuir’s isotherm plots for the adsorption of nitrate on nZVI and GAC, and (c) Freundlich’s isotherm plots for the adsorption of nitrate on nZVI and GAC . Table 2. Isotherm parameters for the removal of nitrate from Figure 10 illustrated the variations in pH levels after groundwater by nZVI and GAC. applying treatment of adsorbent GAC. It showed that Type of isotherm Parameters nZVI GAC the ideal pH value was obtained at dosage of 0.625 g Langmuir q (mg/g) 104.20 81.07 max with contact time of 30 minutes both at pH 2 and pH 6. K (L/mg) 0.0213 0.003 R 0.4833 0.8687 GAC has negative zeta potential at above pH 7.2; on the R 0.999 0.999 other hand, point for zero charge for GAC was at 6.2 Freundlich K 4.069 1.09 where the adsorbent net surface charge was equal to 1/n 0.5905 0.5343 R 0.966 0.987 zero. TDS level for the GAC adsorbent first increased, then started to decrease and the dissolved oxygen con- centration gradually decreased (Sun et al., 2022). 60 min. pH is the most significant characteristic to determine the adsorbate equilibrium and surface 4 Regeneration charge. The pH of the groundwater was affected by the zeta potential of nZVI, degree of ionization, An important parameter to determine the sustain- and various aqueous pollutants. The pH of every ability of the adsorbent is based on its reusability. sample was measured via using digital pH meter In this study, the prepared adsorbents were reused (Amin et al., 2018). Results shown in Figure 9 for five times to remove nitrate from water. Using depict that there was a fluctuation in pH value of alkaline solution (0.1 M NaOH), the weakly bonded samples during treatments with adsorbent nZVI. At nitrate on nZVI and GAC surface was desorbed pH 2, nitrate removal was about 98%, DO was 55%, and the adsorbents were washed with DI water and TDS was removed approximately 43%. several times (Du et al., 2020). The dried material Removal Efficiency (%) Log q 1/q e GEOLOGY, ECOLOGY, AND LANDSCAPES 9 (a) nZVI (b) GAC GAC nZVI 0 10 20 30 40 50 60 70 80 90 100 0 20 40 60 80 100 Time (min) Time (min) nZVI (c) GAC -1 -2 -3 -4 0 20 40 60 80 100 Time (min) Figure 8. (a) Effect of contact time on the nitrate removal by nZVI and GAC, (b) pseudo-second-order kinetic plots for the adsorption of nitrate on nZVI and GAC, and (c) pseudo-first-order plots for the adsorption of nitrate on nZVI and GAC. Table 3. Kinetic parameters for the removal nitrate from groundwater by nZVI and GAC. Parameters nZVI GAC Order of reaction q (mg/g) 22.15 9.12 e, exp Pseudo-first order q (mg/g) 0.780 1.442 e, cal −1 −4 −4 k (min ) −3.8 × 10 −4.9 × 10 R 0.745 0.812 Pseudo-second order q (mg/g) 23.62 9.36 e, cal −1 −1 k (g mg min ) 0.141 0.076 R 0.999 0.999 Table 4. Comparison of adoption capacity of prepared biosorbents with the literature. Adsorbents q (mg/g) References max Activated carbon 28 (El-Sayed et al., 2014) Pit-toilet leachate 32 (Mittal et al., 2020) GAC/NZVI 55 (Hu et al., 2020) Magnetic cationic hydrogel 95.88 (J. Li et al., 2020) PAM/AC 48.9 (Kamarehie et al., 2018) GAC 81.07 Present study nZVI 104.20 Present study Removal Efficiency (%) ln (q - q ) e t t/q t 10 N. AMAN ET AL. Table 5. Analysis of variance of pH values of samples for eight treatments of nZVI adsorbent. Source DF Adj. SS Adj. MS F P Unit 1 94.75 94.75 Factors 1 132.017 132.07 86.96 0.0000** Treatments 4 16.896 4.224 2.87 0.0406** ns Minutes 2 0.067 0.034 0.02 0.9775 Factors*Treatments 4 58.047 14.512 9.86 0.0000** ns Factors*Minutes 2 0.082 0.082 0.03 0.9724 ns Treatments* vs. Minutes* 8 2.113 0.264 0.18 0.9920 ns Factors*Treatment*Minutes* 8 1.954 0.244 0.17 0.9938 Error 29 42.687 1.472 Total 59 348.616 ns Note: *Significant; ** Highly Significant; Non-significant. nZVI 0.625g t1 nZVI 1.25g t2 nZVI 2.5g t3 nZVI 3.75g t4 pH2, 30min pH2, 60min pH2, 90min pH6, 30min pH6, 60min pH6, 90min Figure 9. Change in pH value of nitrate containing groundwater samples after treatment of nZVI at 25 ±5°C at different pH and adsorbents dose. GAC, 0.625g t1 GAC, 1.25g t2 GAC, 2.5g t3 GAC, 3.75g t4 pH2, 30min pH2, 60min pH2, 90min pH6, 30min pH6, 60min pH6, 90min Figure 10. Change in pH value of nitrate-containing groundwater samples after treatment of GAC at 25 ±5°C at different pH and adsorbents dose. were reused for nitrate adsorption for the next proceeded for the fifth regeneration cycle, nitrate cycle. In the first and second regeneration cycle, removal efficiency was 91% and 70% for nZVI and the removal efficiency of nZVI for nitrate was GAC, respectively. This little change in the removal almost same, that was, 98%, whereas in case of efficiency of both the adsorbents is due the reduc- GAC, efficiency rate slightly decreased from 79% tion in the amount of surface area available for the to 77% as shown in Figure 11. Moreover, as we reaction. pH values pH level GEOLOGY, ECOLOGY, AND LANDSCAPES 11 nZVI Funding GAC The work was supported by the Deanship of Scientific 90 Research [GRANT2093]. ORCID Nafeesa Aman http://orcid.org/0000-0003-3631-6069 Asif Ayub http://orcid.org/0000-0003-0590-3906 References 1st 2nd 3rd 4th 5th Aboudi Mana, S. 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Journal

Geology Ecology and Landscapes – Taylor & Francis

Published: Jan 23, 2023

Keywords: Adsorption; activated carbon; nano zerovalent iron; nitrate

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