Efficient Removal of Analgesic and Anti-Inflammatory Drugs from Sewage Treatment Plant Effluents Using Magnetite Nanoparticles Synthesized Red Mud

Abstract

Due to the COVID-19 epidemic, the consumption of pharmaceuticals, especially paracetamol, has sharply increased on a global scale. The increasing concentration of analgesic and anti-inflammatory drugs (AAIDs) in the aquatic medium is a global problem for human and aquatic life. Therefore, simple and effective treatment options for removing AAIDs from wastewater after the COVID-19 pandemic are needed. The removal of AAIDs (acetaminophen, acetylsalicylic acid, codeine, diclofenac, ibuprofen, indomethacin, ketoprofen, mefenamic acid, naproxen, and phenylbutazone) from sewage treatment plant (STP) effluents by the prepared magnetite nanoparticles synthesized from red mud (mNPs-RM) is presented for the first time in this study. The removal efficiencies of AAIDs onto mNPs-RM were determined to be between 90% (diclofenac) and 100% (naproxen, codeine, and indomethacin). Acetaminophen (paracetamol) was used as a model compound in kinetic and isotherm model studies. The adsorption of acetaminophen was matched well with the pseudo second order kinetic model. Film diffusion governed its rate mechanism. The Freundlich isotherm model preferably fitted the adsorption data with an adsorption capacity of 370 mg/g at 120 min contact time at pH 7.0 at 25 °C. Furthermore, the regenerated mNPs-RM were used four times without affecting the adsorption capacity and the magnetic separability. mNPs-RM can be used as a simple, inexpensive and effective adsorbent for removing AAIDs from STP effluents. Also, low cost adsorbent obtained from industrial waste could be employed to replace the high cost activated carbons for the adsorption of other micro pollutants in STP effluents.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11270-023-06404-7.

Introduction

Analgesic and anti-inflammatory drugs (AAIDs) are the most commonly consumed groups of pharmaceuticals. These drugs are often used for the treatment of acute pain, inflammation and fever (Galani et al., 2021). After consumption, AAIDs are rapidly excreted by the person as the main compound or metabolites in urine (Ziylan & İnce, 2011). Therefore, the sewage system is the most important source of AAIDs reaching the aquatic medium. Many of the AAIDs can partially be removed from wastewater by conventional sewage treatment plants (STPs), as they are not specifically designed to remove these hazardous compounds. The structure, design and operation of STPs (temperature, hydraulic and sludge retention time), environmental factors and seasonal changes can affect the removal efficiency of these compounds in wastewater (Kaur et al., 2016; Oliveira et al., 2015; Rodriguez-Narvaez et al., 2017). Diclofenac was removed by activated sludge treatment at only 9% in Greece (Kosma et al., 2010), 17% in Germany (Heberer et al., 2002), 19% in China (Dai et al., 2014), 35% in Italy (Verlicchi et al., 2013), 9–60% in Finland (Lindqvist et al., 2005), 20–40% in Switzerland (Joss et al., 2005), and 50.1% in Spain (Radjenovic et al., 2007). The removal of ibuprofen was reported to be 75% in Brazil (Stumpf et al., 1999), 82.5% in Spain (Radjenovic et al., 2007), 86% in England (Jones et al., 2007), and 15–99% in Canada (Guerra et al., 2014). While high removal efficiencies for naproxen in the USA (100%) and Poland (99.8%) were obtained with a secondary STP with biological nutrient removal, naproxen was partially removed between 50–80% in Switzerland (Joss et al., 2005), 48–62% in Greece (Kosma et al., 2010), 78% in Brazil (Stumpf et al., 1999), and 74% in England (Jones et al., 2007). Additionally, low removal efficiencies for mefenamic acid (5.2%, 27%, 32.3–35.6%) and indomethacin (25%, 39%, 14.8–24.1%) were determined in China, Italy, and Türkiye, respectively (Dai et al., 2014; Verlicchi et al., 2013; Aydın et al., 2019a). While ibuprofen analgesic was completely eliminated in summer, the removal efficiency decreased to 38% in winter (Castiglioni et al., 2006). Similar results were obtained for ibuprofen (79%) and naproxen (87%) by Aydın et al. (2019a). Due to insufficient removal of AIAPs in conventional STPs, the presence of AAIDs has been detected in various water environments, such as wastewater (Radjenović et al., 2009; Nieto-Juárez et al., 2021; Aydın et al., 2019a), surface/river water (Chafi et al., 2022; Nieto-Juárez et al., 2021; Rivera-Jaimes et al., 2018; Valcárcel et al., 2011), ground water (López-Serna et al., 2013; Peng et al., 2014; Vulliet & Cren-Olivé, 2011), and even tap/drinking water (Caban et al., 2015; Valcárcel et al., 2011; Yang et al., 2014), at concentrations ranging from ng/L to µg/L in different studies in the literature. Furthermore, AAIDs were detected at higher concentrations among the investigated pharmaceuticals in studies because of sales without prescription (Cleuvers, 2004).

Due to the outbreak of COVID-19 in 2019, the consumption of pharmaceuticals has sharply increased on a global scale, causing an increase in the concentration of pharmaceuticals and their metabolites in hospital and urban wastewater (Wu et al., 2020; Zhang et al., 2021). The pharmaceutical load given to the aquatic environment by wastewater has increased even more. Chen et al. (2021) evaluated the post pandemic environmental impact of pharmaceuticals in surface water (lakes and STP-river-estuary system) in China (Wuhan). They reported that the levels of azithromycin and ribavirin were 217% higher than the levels of these compounds detected before the pandemic. Additionally, azithromycin and sulfamethoxazole pose potentially high risks to aquatic organisms in the environment. The occurrence, fate and ecotoxicological risk of some antiviral pharmaceuticals used for COVID-19 therapy in wastewater and environmental waters were evaluated by Kuroda et al. (2021). The removal efficiencies by conventional STPs for half of the investigated substances were determined to be less than 20%. Residues of pharmaceuticals pose a high ecotoxicological risk (risk quotient > 1) to aquatic organisms in receiving river waters. While the consumption of nonsteroidal anti-inflammatory drugs (NSAIDs) was decreased 27%, acetaminophen consumption demonstrated a 198% increase during the pandemic in 2020 in Greece (Galani et al., 2021). Acetaminophen was determined to be the most consumed pharmaceutical in central New York during the pandemic (Wang et al., 2020). Similarly, the acetaminophen concentration increased in primary sludge collected from an STP from March 19 to June 30 in 2020 in the USA (Nason et al., 2021). Due to the high consumption of antivirals, antibiotics, antiparasitics, antiprotozoals, and glucocorticoid drugs during the pandemic, the concentrations of most of the drugs used for therapy were determined in water bodies (Morales-Paredes et al., 2022).

Even low concentrations of pharmaceutical residues in aquatic environments pose acute and chronic effects on aquatic organisms in receiving media (Kümmerer et al., 2000; Halling-Sørensen, 2000; Aydın et al., 2019b; Boxall et al., 2003). Additionally, due to the coexistence of many different pharmaceutical residues in the aquatic environment, the possible synergic effects and environmental risk of detected drug residues on aquatic ecosystems are not exactly known (Patel et al., 2019). Fonseca et al. (2020) were evaluated the ecological risks posed by the 69 pharmaceutical mixtures using species sensitivity distributions built with chronic toxicity data for aquatic organisms. Acetaminophen was determined in the highest concentration among the pharmaceuticals in water. AAIDs and antibiotics were identified as compounds exerting the highest toxic pressure on aquatic ecosystems. Cleuvers (2004) reported that the ecotoxicity of a mixture of NSAIDs (acetylsalicylic acid, diclofenac, ibuprofen, and naproxen) exhibits relatively higher toxicity for Daphnia magna than the concentrations of single substances. The use of reclaimed domestic wastewater in agricultural irrigation also poses a risk in terms of AAIDs. The wheat shoot and root elongation decreased significantly with increasing acetaminophen concentration. The growth of wheat was inhibited even low concentration in chronic exposure. The chlorophyll accumulation, soluble protein synthesis of the plant and antioxidative defensive system in wheat roots were also damaged (An et al., 2009). Therefore, the presence and fate of AAIDs in the aquatic environment is a problem for human and aquatic life worldwide. Hence, it is urgent to develop simple, cheap and effective treatment options for removing AAIDs from wastewater after the COVID-19 pandemic.

Some advanced treatment processes, such as reverse osmosis, micro-/ultra-/nanofiltration (Radjenović et al., 2008; Sirés & Brillas, 2012), electrodialysis (Pronk & Koné, 2009), and advanced oxidation processes (Andreozzi et al., 2003; Mendez-Arriaga et al., 2010; Vogna et al., 2002), can be used for removing some AIAPs from water. High energy and chemical consumption in these treatment processes increase the treatment cost of wastewater (Monteil et al., 2018). Adsorption is a more economical process and has a high removal efficiency of over 95% for pharmaceuticals (Patel et al., 2019). The adsorption of AIAPs with different adsorbents (activated carbon, clays, biosorbents, agricultural byproducts, nanomaterials, and metal oxides) from water and wastewater has been extensively studied (Cabrita et al., 2010; Mansour et al., 2018; Patel et al., 2019; Suriyanon et al., 2015). In recent years, magnetic nanoparticles (mNPs) have been used extensively in the removal of organic materials, such as organophosphorus pesticides (Aydın, 2016), antibiotics (Aydın et al., 2019b), psychiatric drugs (Aydın et al., 2021), phenol (Al-Obaidi et al., 2021) and inorganic pollutants such as cadmium (Devi et al., 2017), nickel, chromium, lead, and cobalt (Yamini & Safari, 2018) from waters. Magnetite NPs were separated easily and effectively from aqueous solutions after adsorption by using an external magnetic field. Hence, it is low cost for wastewater treatment compared to traditional methods (Kadhim et al., 2022). Additionally, the mNPs are insoluble and can be reused after regeneration (Aydın et al., 2021). They have high adsorption capacity due to their high surface area. Red mud (RM) is a by-product of alumina production and contains a large amount of iron, aluminium, silica, calcium, titanium oxides and hydroxides. Because of this characteristic, it has been effectively used for the removal of heavy metals (Ahmaruzzaman, 2011), inorganic anions (Wang & Liu, 2020) and organic pollutants (Aydın et al., 2019b; 2021) from water. It is difficult to recover from wastewater after the adsorption process. The combination of RM with magnetic NPs makes their removal from water after adsorption easy and inexpensive. Also, the regeneration of mNPs-RM from aqueous solution allows their use. In consequence, low cost adsorbent obtained from industrial waste could be employed to replace the high cost activated carbons for the adsorption of hazardous environmental contaminants (Jabbar et al., 2022).

However up to now, adsorption removal of AAIDs from STP effluents by mNPs-RM has not been reported. Therefore, the purpose of this paper is to investigate the utilization of the mNPs-RM for the removal of ten AAIDs from urban STP effluents. For this objective, the effect of some controlling parameters, such as solution pH, contact time, adsorbent dosage and temperature, is evaluated. The adsorption isotherm models and kinetic models of mNPs-RM were determined with experimental data. Additionally, the reusability of mNPs-RM after regeneration was evaluated, and the matrix effects for urban STP effluents were also investigated.

Material and Methods

Chemicals

AAID standards, and all chemicals were of analytical grade. While codeine was purchased from Cerilliant (TX, USA), acetylsalicylic acid, mefenamic acid and phenylbutazone were obtained from Sigma (Switzerland). Acetaminophen, diclofenac, ibuprofen, indomethacin, ketoprofen, and naproxen were purchased from Fluka (Switzerland). HCl, NaOH, FeCl₂, FeCl₃, NH₃, HNO₃, HCOOH, NH₄OH, NH₄HCO₂ and C₂H₃NaO₂ were also obtained from Merck Co (Darmstadt, Germany). A nylon filter with a 0.45 μm pore diameter was obtained from Sartorius (Göttingen, Germany). Deionized water was obtained from a Millipore Milli-Q Plus water purifier (Merck, MA, USA). The nitrogen gas for high performance liquid chromatography-mass spectrometry (HPLC–MS) was acquired from a nitrogen generator (Peak Scientific, Scotland, UK).

Synthesis and Characterization of RM

RM was procured from the Seydişehir Aluminum Plant in Konya, Türkiye. The annual processing capacity of the plant is 500,000 tons of bauxite and approximately 120,000 tons/year RM. The pH value of the RM is approximately 11–12. Therefore, RM was neutralized to a pH of approximately 8.0 by deionized water. Then, the RM was dried in an oven at 40 °C (Aydın et al., 2021). The RM composition is Al₂O₃, 18.71%; Fe₂O₃, 39.70%; TiO₂, 4.90%; Na₂O, 8.82%; CaO, 4.47%; SiO₂, 14.52%; and loss on ignition, 8.15% (Ozcan et al., 2011). The mNPs-RM were synthesized following the chemical coprecipitation method described in our previous work (Aydın, 2016; Aydın et al., 2021). While its particle size was identified as 13.84 nm using the Scherer equation, its specific surface area was determined to be 83.6 m²/g using Brunauer-Emmet-Teller (BET). The saturation magnetization value of mNPs-RM was determined to be 12.1 emu/g (Aydın, 2016). The point of zero charge (pHpzc) was obtained as approximately 8.0 (Aydın et al., 2019b).

Sewage Treatment Plant Effluent Samples

Twenty-four-hour composite effluents were obtained from the Konya urban STP in Türkiye. STP includes primary treatment, biological treatment with activated sludge and disinfection processes. The STP flow diagrams are given in Fig. S1. Some physicochemical properties of effluent samples taken at two different times were determined by the Konya water and sewage administration STP laboratory. The pH of effluent samples 1 and 2 is 7.86 and 8.06, respectively, the electrical conductivity of effluent samples 1 and 2 is 1537 and 1990 µS/cm, respectively, and the total suspended solids of effluent samples 1 and 2 are 11 mg/L and 47 mg/L, the chemical oxygen demand of effluent samples 1 and 2 was 32 mg/L and 86 mg/L, respectively.

Adsorption Experiments

The adsorption of AAIDs on mNPs-RM was carried out with batch experiments. One hundred milliliters of deionized water including 1 mg/L AAIDs in a flask at pH 7.0 was prepared. Then, 5 g/L mNPs-RM was added to the flask. The solution was shaken for 1 h using a thermostat shaker at 221 rpm at 25 °C (Shin Saeng, Korea). After adsorption, the solution was extracted from the flask, while an external magnet precipitated mNPs-RM at the bottom of the flask. The remaining concentration of AAIDs in solution was determined by using an Agilent high-performance liquid chromatograph (HPLC) coupled to a mass spectrometer (MS). The removal efficiency of AAIDs from water after the adsorption process was calculated with Eq. (1). Herein, C_o and Ce are the initial and equilibrium concentrations of AAIDs in mg/L, respectively.

$$Removalefficiency(\%)=\frac{C_o-C_e}{C_o}x100$$ 1

The adsorption capacity of AAIDs onto the mNPs-RM was investigated as a function of pH from 1.5 to 11, contact time from 5 to 240 min, dosage of the mNPs-RM from 0.01 to 2 g/L, and temperature from 15 to 35 °C. The effect of the amount of RM used in synthesis was also investigated. Aqueous 0.1 N HCl/NaOH was used to adjust the solution pH. Acetaminophen, also called paracetamol, was used as a model compound. Acetaminophen is the most widely consumed analgesic (Aydın et al., 2019a; Igwegbe et al., 2021). There is 58–68% of acetaminophen excreted by humans as an active compound (Natarajan et al., 2022). Because it is widely used to treat COVID-19 symptoms, the concentration of acetaminophen in aquatic environments has increased (Galani et al., 2021). The adsorbed amount of acetaminophen was estimated with Eq. (2). Herein, C_o and C_e are the initial and equilibrium concentrations of acetaminophen in mg/L, respectively. q_e is the adsorption capacity of mNPs-RM at equilibrium (mg/g). m is the weight of mNPs-RM (g), and V is the solution volume (L).

$$q_e=\frac{C_o-C_e}{m}xV$$ 2

Analytical Procedures

The determination of AAIDs was performed on an Agilent 1260 series HPLC–MS (Agilent, USA) equipped with a 100 × 3.0 mm Poroshell 120 EC-C18 column with a particle size of 2.7 µm (Agilent, USA). The temperature was 35 °C. The injection volume was 2 μL. Chromatographic separation was performed using water (eluent A) and methanol (eluent B) as the mobile phase, and the flow rate was 0.5 mL/min. While water containing 10 mM ammonium acetate for the negative ion mode (electrospray ionization (ESI)-) was used for ibuprofen and acetylsalicylic acid, water containing 0.5% formic acid and 2 mM ammonium formate for the positive ion mode (ESI +) was used for other AAIDs. Monitored precursor and product ions (m/z), limits of detection (LODs) (ng/L), limits of quantification (LOQs), linearity range (ng/L), linearity (R²), and repeatability (%) are given in the Supplementary Material (Table S1). The chromatogram of 1 ng/µL AIAP standards is given in Fig. S1.

Results and Discussions

Adsorption of AAIDs onto mNPs-RM

The removal efficiencies of AAIDs by mNPs-RM are presented in Fig. 1. The removal of AAIDs by mNPs-RM was between 90% (diclofenac) and 100% (naproxen, codeine, and indomethacin). Satisfactory removal efficiencies were obtained for the studied AAIDs with 5 g/L mNPs-RM prepared with 1.0 g RM at pH 7 after 60 min of contact time. RM, an aluminum refinery waste, is an inexpensive adsorbent. However, time and cost consuming processes, such as filtration and centrifugation, are required for the removal of RM from water after adsorption. The mNPs-RM from water after the adsorption process are easily separated using an external magnetic field, providing the advantage of economical and fast treatment. Despite being a waste, RM can be used safely in the treatment of effluents due to its quite stable properties (Yue et al., 2010). Therefore, the effects of various operating parameters in further adsorption experiments were investigated using acetaminophen as a model AAID.

Fig. 1.

Adsorption capabilities of AAIDs by mNPs-RM (concentration of each AIAP: 1 mg/L; pH of the solution: 7.0; amount of mNPs-RM: 5 g/L; contact time: 60 min; shaking speed: 220 rpm; temperature, 25 °C)

Effect of pH on Acetaminophen Adsorption

In this study, the effect of pH values ranging from 1.5 to 11 on acetaminophen adsorption from water was studied. The determined results are presented in Fig. 2. The removal efficiency of acetaminophen was increased from 39 to 63% by increasing the pH of the solution from 1.5 to 5.0. The removal efficiency was consistent between pH 5.0 and 7.0, and it was determined to be approximately 66%. The removal of acetaminophen decreased to 23% when the pH rose from 7 to 11. The highest removal was determined to be 66% at the natural pH of the solution. The pH of the solution, pKa (9.38) of acetaminophen (Igwegbe et al., 2021) and pHpzc (8.3) of mNPs-RM (Aydın et al., 2019b) are important factors affecting the adsorption process. Since acetaminophen molecules are mostly in neutral or nonionic form between solution pH values of 3 and 9, the adsorption efficiency of acetaminophen did not change in this pH range. The removal efficiency was decreased at the solution pH over the pKa values of acetaminophen. Because acetaminophen is in an anionic form, the solution pH is above this value. Additionally, the surface of mNPs-RM is negatively charged at a solution pH above the pHpzc value. This situation caused electrostatic repulsion between acetaminophen and mNPs-RM. Therefore, the acetaminophen removal efficiency decreases at this pH value. The removal efficiency of acetaminophen at a solution pH under 3.0 was decreased. An electrostatic repulsion force occurred between the positively charged mNPs-RM and cationic acetaminophen molecules.

Fig. 2.

Effect of pH on the adsorption of acetaminophen by mNPs-RM (concentration of acetaminophen: 4 mg/L; pH of the solution: 1.5–11; amount of mNPs-RM: 1 g/L; contact time: 60 min; shaking speed: 220 rpm; temperature, 25 °C)

Natarajan et al. (2022) used Rh-cMNPs (chitosan-encapsulated magnetic nanoparticles coated with rhamnolipids) for the adsorption of acetaminophen. The maximum removal is observed as 96.7% at pH 5. The removal efficiency of acetaminophen was consistent between pH 3 and 8. Moussavi et al. (2016) also reported that the maximum adsorption of acetaminophen onto double-oxidized graphene oxide was obtained as approximately 83% below pH 8. Due to the neutral form of acetaminophen molecules between solutions at pH 2 and 8, the adsorption efficiency did not change in this pH range. Here, the main mechanisms of acetaminophen removal might be hydrophobic interactions. Quesada et al. (2019) stated that the adsorption of acetaminophen onto modified Moringa oleifera Lam. Seed husks were not affected between pH 3 and 9. The adsorption mechanism was explained by hydrogen bonds and π-stacking. Similar results have been published by Akpotu & Moodley, 2018; Bernal et al., 2017; Villaescusa et al., 2011; Yanyan et al., 2018; Wong et al., 2018. As a result, the adsorption of acetaminophen was independent of pH variations between pH values of 2 and 9. The adsorption mechanisms of acetaminophen on adsorbents, such as modified activated carbon, encapsulated with reduced graphene oxide, grape stalk, Yohimbe bark, and modified multiwalled carbon tubes, were mainly π-π interactions, hydrogen bonds, and hydrophobic effects. The study results have a trend similar to the results presented in the literature. As a consequence, the removal of acetaminophen using mNPs-RM occurs by π–π and hydrophobic interactions and hydrogen bonds.

Effect of Contact Time and Adsorption Kinetics

Figure 3 presents the effect of contact time on the adsorption of acetaminophen by mNPs-RM. Acetaminophen (4 mg/L) using 1 g/L mNPs-RM at pH 7 was removed at 41% after 5 min of contact time. The removal of acetaminophen increased with increasing contact time and reached 85% removal efficiency at the end of 120 min. After this point, the removal efficiency did not change with increasing time. Therefore, 120 min of contact time was selected for the adsorption kinetic studies. Similar results have been reported for the adsorption of acetaminophen onto double-oxidized graphene oxide (Moussavi et al., 2016), chitosan-encapsulated magnetic nanoparticles coated with rhamnolipids (Natarajan et al., 2022), NaX nanosheets (Rad et al., 2015), and activated carbon synthesized from spent tea leaves (Wong et al., 2018).

Fig. 3.

Effect of contact time on the adsorption of acetaminophen by mNPs-RM (concentration of acetaminophen: 4 mg/L; pH of the solution: 7.0; amount of mNPs-RM: 1 g/L; contact time: 5–240 min; shaking speed: 220 rpm; temperature, 25 °C)

The kinetic information obtained from pseudo first order, pseudo second order and intraparticle diffusion models with the experimental results was used to evaluate the adsorption mechanism. Kinetics and adsorption mechanism plots achieved by using the model equations presented in Table 1 are given in Fig. 4. The kinetic parameters and intraparticle diffusion model parameters are presented in Table 1. The R² value obtained for the pseudo second order was higher than the correlation coefficient obtained for the pseudo first order. Additionally, the model adsorption capacity (q_e = 340 mg/g) value achieved for the second order model more closely matches the experimental q_e (333 mg/g) value. As a result, the pseudo second order kinetic model represents the adsorption of acetaminophen by mNPs-RM. Accordingly, the uptake mechanism of acetaminophen onto mNPs-RM can be explained with chemisorption (Ho & McKay, 1999; Natarajan et al., 2022; Wong et al., 2018). Other researchers have also reported that the pseudo second order model was the best fitted model for the adsorption of acetaminophen onto double-oxidized graphene oxide (Moussavi et al., 2016), rhamnolipid-based chitosan magnetic nanosorbents (Natarajan et al., 2022), and activated carbon synthesized from spent tea leaves (Wong et al., 2018). As seen in the diffusion model plot presented in Fig. 4c, the fitting curves do not pass the origin. For this reason, the adsorption rate of acetaminophen on mNPs-RM was managed mainly by a film diffusion mechanism (Aydın et al., 2021; Natarajan et al., 2022; Wong et al., 2018). Additionally, Fig. 4c shows that there are two distinct regions in the diffusion model plot. The film diffusion mechanism is the rate-limiting step of acetaminophen onto mNPs-RM in the first stage in the first 10 min. After this time, intraparticle diffusion occurred with a 42 mg/g adsorption capacity.

Table 1.

The adsorption kinetic parameters calculated for pseudo-first order, pseudo-second order, and intra-particle diffusion kinetic models for adsorption of acetaminophen by mNPs-RM

Models	Parameter	Value	Model equations	References
Pseudo- first order	model qe (mg/g) k1 (1/min) R2	214 0.0095 0.965	$\log \left(q_e,-,q_t\right)=log{q}_e-{}^{k_1.t}\left./,{}_{2.303}\right)$	Lagergren, 1898
Pseudo-second order	experimental qe (mg/g) model qe (mg/g) k2 (1/min) R2	333 340 0.00023 0.998	${}^t\left./,{}_{q_t}\right)={}^1\left./,{}_{k_2.q_e^2}\right)+{}^t\left./,{}_{q_e}\right)$	Ho & McKay, 1999
Intra-particle diffusion	y (mg/g) k3 (1/min) R2	42 0.0136 0.965	$q_t=k_3.t^{1/2}+y$	Zhu et al., 2007

t contact time (min), k₁ rate constant of pseudo-first order adsorption (1/min), k₂ rate constant of pseudo-second order adsorption (1/min), k₃ rate constant of intra-particular diffusion (1/min), y intercept, q_e equilibrium capacity at equilibrium (mg/g), q_t adsorption capacity at time (mg/g)

Fig. 4.

a Pseudo first order, b pseudo second order, and c intraparticle diffusion model plots for adsorption of acetaminophen

Effect of Initial Adsorbent Dosage and Adsorption Isotherm Models

The effect of the mNPs-RM dosage on the removal of acetaminophen is presented in Fig. 5. The removal of acetaminophen was 15% at the 0.1 g/L initial adsorbent dosage. The removal of acetaminophen increased to 95% with the increase of the adsorbent dosage to 3.0 g/L. When the mNPs-RM dosage was increased from 3.0 g/L to 20 g/L, the removal increased by 5%. Similar results have been reported in many studies. The removal efficiency of acetaminophen increases by increasing the initial adsorbent dosage to an optimum point and becomes stable above this point (Aydın et al., 2021; Moussavi et al., 2016; Wong et al., 2018). The adsorption capacity of acetaminophen was decreased from 600 mg/g to 20 mg/g when the initial mNPs-RM dosage was increased from 0.1 g/L to 20 g/L. In further experiments, the optimal mNPs-RM dosage for the removal of acetaminophen was taken as 3 g/L.

Fig. 5.

The removal and adsorption capacity of acetaminophen by mNPs-RM (concentration of acetaminophen: 4 mg/L; pH of the solution: 7.0; amount of mNPs-RM: 0.1–20 g/L; contact time: 120 min; shaking speed: 220 rpm; temperature, 25 °C)

The adsorption isotherm information was obtained from the Langmuir and Freundlich equations given in Table 2. The plots of the Langmuir isotherm (a) and Freundlich isotherm are given in Fig. 6. The adsorption isotherm parameters of the Langmuir (q_max and K_L) and Freundlich isotherm (K_F and n) models for acetaminophen onto the mNPs-RM are given in Table 2. The R² (0.950) value obtained for the Freundlich isotherm model was found to be higher than the value (0.798) obtained for the Langmuir model. The Freundlich isotherm model best fits the chemisorption of acetaminophen onto mNPs-RM and achieves the highest multilayer uptake of 370 mg/g on the heterogeneous surface of the NPs. The n value is also determined to be 2.04 (between 1 and 10). These results also show that there is a strong interaction between mNPs-RM and acetaminophen (Sivaraj et al., 2001).

Table 2.

Langmuir and Freundlich isotherm parameters calculated for adsorption of acetaminophen by mNPs-RM

Models	Parameter	Value	Model equations	References
Langmuir isotherm	qmax (mg/g) KL R2	588 1.31 0.798	$\frac{C_e}{q_e}=\frac{1}{q_{\mathit{max}}.K_L}+\frac{C_e}{q_{\mathit{max}}}$	Langmuir, 1916
Freundlich isotherm	KF (mg/g) n R2	370 2.04 0.950	$loq{q}_e=log{K}_F+\left(\frac{1}{n}\right)log{C}_e$	Freundlich, 1906

C_e carbamazepine concentration at equilibrium (mg/L), Q_max monolayer capacity of the mNPs-RM, K_L Langmuir adsorption constant, K_F sorption capacity (mg/g), n Freundlich adsorption constant

Fig. 6.

a Langmuir isotherm, b Freundlich isotherm for adsorption of acetaminophen

The adsorption capacity of acetaminophen by different adsorbents is presented in Table 3. The adsorption capacity of some adsorbents, such as double-oxidized graphene oxide, mobilized catalytic material-41-graphene, ordered mesoporous carbons, biomass-based carbon materials modified with ZnCl₂, and activated carbons derived from Brazil nutshells, was higher than that of mNPs-RM. In addition, it exhibited a higher adsorption capacity than some adsorbents, such as commercial activated carbon, carbon nanotubes, and modified activated carbon obtained from natural materials. The most important advantages of magnetic NPs obtained with RM compared to the other adsorbents can be listed as follows. RM, which is a waste material, is cheap and easy to remove from water magnetically after adsorption. The adsorbent can be reused after regeneration. These advantages reduce the overall treatment cost.

Table 3.

Adsorption of acetaminophen by different adsorbent

Adsorbent	Adsorption capacity (mg/g)	Kinetics	Isotherm	References
DGO	704	PSO	Langmuir	Moussavi et al., 2016
MCM-41-G MCM-41-GO	555.6 322.6	PSO	Freundlich	Akpotu & Moodley, 2018
OMC	501.91	PSO	Langmuir–Freundlich	Jedynak et al., 2019
BBPM-ZnCl2	411.1	PSO	Langmuir	dos Reis et al., 2022
AC-BN	411.1	PFO	Freundlich	Lima et al., 2019
mNPs-RM	370	PSO	Freundlich	This study
AC	300	PSO	Redlich–Peterson	Gómez-Avilés et al., 2021
CBM	270.3	PSO	Langmuir	Galhetas et al., 2014
CAC	260	PSO	Langmuir–Freundlich	Nguyen et al., 2020
MWCNTs	250	PSO	Freundlich	Yanyan et al., 2018
Al-AHC	165.94	PSO	Langmuir	de Araújo et al., 2022
Rh-cMNP	96.3	PSO	Langmuir	Natarajan et al., 2022
STL-AC	59.2	PSO	Langmuir	Wong et al., 2018
AC-MB	30.8	PSO	Langmuir	Nadolny et al., 2020
MOL-SH	17.48	PSO	Freundlich	Quesada et al., 2019
AC-CSH	16.18	PSO	Freundlich	Sajid et al., 2022

PFO Pseudo First Order, PSO Pseudo Second Order

DGO double-oxidized graphane oxide; MCM-41-G mobil catalytic material-41-graphene; MCM-41-GO mobil catalytic material-41-graphene oxide; OMC ordered mesoporous carbons; BBPM biomass-based carbon materials; AC-BN activated carbons derived from Brazil nutshells; AC activated carbons from microwave-assisted FeCl₃-activation of lignin; CBM carbon-based materials prepared from pine gasification; CAC commercial activated carbon; MWCNTs multi-walled carbon nanotubes (ozone treated); Al-AHC alginate-activated hydrochar; Rh-cMNP Rhamnolipid based chitosan magnetic nanosorbents; STL-AC Spent tea leaves-activated carbon; AC-MG Activated carbon produced from malt bagasse; MOL-SH Moringa oleifera Lam. Seed husks; AC-CSH Activated carbon-cannabiz sativum hemp

Effect of Temperature

The effect of varying the temperature on acetaminophen adsorption by the mNPs-RM was also investigated. For that study, 3 g adsorbent was added to 100 mL of water containing acetaminophen at a concentration of 4 mg/L acetaminophen at pH 7. Then, adsorption was performed for 120 min at 15, 25 and 35 °C. The removal of acetaminophen at 15, 25, and 35 °C was 88 ± 4%, 95 ± 5, and 90 ± 6%, respectively. According to the results, temperature has no significant effect on the adsorption efficiency of acetaminophen.

Recycling and Reusability of the mNPs-RM

The recycling and reuse of the spent adsorbent ultimately reduces operating costs and contributes to the protection of the environment. Therefore, after the mNPs-RM were sequentially treated three times with a 5 mL 0.01 M HNO₃ and 5 mL deionized water. Then, their reusability was evaluated in four adsorption–desorption cycles. The removal of acetaminophen by mNPs-RM after regeneration was between 87 and 95%. The adsorption capacity of the adsorbent after four cycles was stable and exhibited good reusability.

Applicability to Sewage Treatment Plant Effluents

Whether the adsorption of mNPs-RM was affected by the matrix in STP effluents was also investigated. First, acetaminophen was determined in the STP effluents. The analysis of STP effluents was carried out using the analytical method previously reported by Aydın et al. (2019a). Briefly, effluent samples were extracted and cleaned up by solid phase extraction. The quantification of acetaminophen was determined using HPLC-tandem mass spectrometry (MS/MS). The concentration of acetaminophen was determined to be 1.13 ng/L in STP effluent 1 and 1.28 ng/L in STP effluent 2. Later, the applicability of the mNPs-RM for the removal of acetaminophen from STP effluents was evaluated in the study. For that part of the study, 3 g adsorbent was added to 100 mL effluents spiked with 4 mg/L with acetaminophen. Then, the solution was shaken for 120 min at 25 °C, and the remaining concentration of acetaminophen was determined. The removal efficiency of acetaminophen in STP effluent sample 1 and effluent sample 2 was determined to be 88 ± 7% and 90 ± 5%, respectively. These results indicated that the mNPs-RM can be used effectively to eliminate acetaminophen from STP effluents.

Conclusions

mNPs-RM synthesized to remove AAIDs from STP effluents was used successfully as an alternative adsorbent. With 5 g/L mNPs-RM at pH 7 after 60 min of contact time, over 90% removal efficiency was obtained for target AAIDs (acetaminophen, acetylsalicylic acid, codeine, diclofenac, ibuprofen, indomethacine, ketoprofen, mefenamic acid, naproxen, and phenylbutazone). According to the experimental data, the adsorption kinetics fit the pseudo second order kinetic model. The adsorption process was controlled mainly by the film diffusion mechanism. The Freundlich adsorption isotherm model better describes the kinetics than the Langmuir adsorption isotherm model. The adsorption capacity of recycled mNPs-RM was not affected up to four regenerations. mNPs-RM can be used as a simple, inexpensive and effective adsorbent for removing AAIDs from STP effluents.

Supplementary Information

Below is the link to the electronic supplementary material.

Author Contribution

All authors have participated in methodology, sampling and analyzing, writing- reviewing.

Data Availability

All data generated or analyzed during this study are included in the published article and its supplementary information files.

Declarations

Competing Interests

The authors have no competing interests to declare that are relevant to the content of this article.