Investigating the efficiency of Photo-Fenton (UV/H 2 O 2 /Fe 2+ ) in removing the indomethacin antibiotic from aqueous solutions

Abstract

Water pollution caused by antibiotics is one of the major challenges in the world today. The current research aims to investigate the effect of the Photo-Fenton process in removing indomethacin antibiotics from aqueous solutions. This experiment-based study was conducted on a laboratory scale and discontinuous manner. The influential variables affecting the removal efficiency of indomethacin include initial antibiotic concentration, pH, time, hydrogen peroxide concentration, and iron ion. The study was conducted base on standard methods (APHA, AWWA, CFWP, 2005). The Design Expert software was used to analyze the effect of independent variables on the removal efficiency of indomethacin antibiotics in the Photo-Fenton process (UV/H₂O₂/Fe²⁺) using response surface methodology (RSM) and central composite design (CCD). To ensure the repeatability of the results, each experiment was repeated three times and the reported the average. The results showed that the optimal removal conditions for indomethacin antibiotics were pH = 4, H₂O₂ oxidant concentration = 50 ppm, Fe²⁺catalyst concentration = 50 ppm, time = 75 minutes, and initial antibiotic concentration = 20 ppm, with a removal efficiency of 91.03%. The variables of initial antibiotic concentration, H₂O₂ concentration, and pH had the greatest impact on the removal efficiency of indomethacin. The results of this study indicate that under optimal conditions, more than 90% of indomethacin antibiotics can be removed from aqueous solutions using the Photo-Fenton process, which is a significant result for removing this pharmaceutical pollutant from aquatic environments.

Keywords

Pollution advanced oxidation antibiotic idomethacin water

1 Introduction

Nowadays, the presence of drugs like antibiotics in the environment is a major concern. The effects of these drugs can vary based on their type, concentration, and toxicity [1, 2]. Among various medicinal compounds, antibiotics have received special attention due to their ability to create antibiotic resistance in pathogenic bacteria [3, 4]. A significant proportion of antibiotics are not degraded after being ingested by the human body. They are excreted through urine and feces into the sewage collection network, and may ultimately be disposed of in the environment. Annually, between 3,000 and 180,000 tons of active antibiotics are released into the environment [5]. Additionally, antibiotics are high in polarity and don’t easily evaporate, so they stay in the environment [6]. The presence of these compounds in the environment causes harmful effects on aquatic organisms [7]. They may also enter drinking water which causes side effects and allergic reactions affecting human health [8, 9]. It is estimated that antibiotic consumption worldwide ranges from 100,000 to 300,000 tons [10]. Wastewater treatment operations are not enough for removing antibiotics, thus these substances enter receiving waters without sufficient treatment, leading to environmental pollution and consequently harm to public health. Moreover, they may even enter rivers, lakes and endanger aquatic life [11, 12]. The degradation of antibiotics in the environment is a significant challenge for public health and the environment [13, 14]. Depending on the chemical structure, of the antibiotics, they exhibit three types of degradation behavior: complete degradation, partial degradation, or persistence in the environment [15]. Indomethacin is one of the antibiotics that have relative stability in the environment [16]. Indomethacin belongs to a class of drugs called non-steroidal anti-inflammatory drugs. It is used to ease pain in conditions like arthritis, sprains, back pain, gout, and cramps. Indomethacin is used to control moderate to severe pain and inflammation in rheumatic diseases, acute or chronic osteoarthritis, juvenile arthritis, and non-rheumatic inflammatory conditions [17]. The half-life of indomethacin average 4.5 hours in the body. Its chemical formula is C₁₉H₁₆ClNO₄ [18]. The chemical structure of Indomethacin is presented in Fig. 1.

Fig. 1

Chemical structure of indomethacin [18].

Various methods have been proposed for removing antibiotics from aquatic environments. These methods include conventional techniques such as biological processes, filtration, coagulation, flocculation, and sedimentation, advanced oxidation processes (AOPs), adsorption, membrane processes, and combined methods [19] Multiple studies, like Cuerda et al. (2019), Wang et al. (2020), and Peng et al. (2019) have shown that advanced oxidation processes are more efficient than other methods for removing antibiotics from water [20 –22]. The photocatalysis process is a method in advanced oxidation that has received attention. This process is a combination of H₂O₂, UV radiation and Fe (II), in which iron salts act as Photo-Catalyst and H₂O₂ acts as an oxidizing agent. Electron transfer is performed in the presence of a metal ion [23]. Photo-Fenton has many advantages, including high efficiency (Polo-Lopez et al., 2013), simple technology (Giannakis, 2019), low cost (Carra et al., 2013), and low toxicity of reactants (Rodriguez et al., 2014). In the Photo-Fenton process, Ebrahiem et al (2017) found that more hydroxyl radicals are made. This helps break down organic pollutants better than other oxidation methods [24 –27].

The process has become more attractive because these radicals combine with oxidation compounds and metal catalysts in the presence of UV light [28, 29]. Considering the advantages of this method and the harmful effects of antibiotics in the environment, in this research, the removal of indomethacin antibiotics from aquatic environments using Photo-Fenton was studied.

2 Materials and methods

The present study is an experimental intervention conducted on a laboratory scale and discontinuous manner.

The dependent variables (final concentration relative to antibiotics) and independent variables including the main components of antibiotics, pH, retention time, hydrogen peroxide, and iron ion were analyzed and assessed. The study was done in a lab reactor. The tests were performed using standard methods for analyzing water and wastewater.

2.1 Chemicals and reagents

2.1.1 Indomethacin antibiotic

The antibiotic indomethacin, with chemical formula C₁₉H₁₆ClNO₄ was came from Elixir pharmaceutical factory in Tehran (Table 1). To adjust the alkaline pH, A solution called sodium hydroxide (NaOH-1/.molar hydroxide) was used Nitric acid HNO₃ (0.1 M nitric acid) to adjust acidic pH. Also Double-distilled distilled water was used to prepare synthetic wastewater.

Table 1
The chemical characteristics of indomethacin antibiotic

Indometacin

Chemical formula C₁₉H₁₆ClNO₄

Molar mass 357.787 g.mol^–1

Density 1.32 g/cm³

Solubility in water 734μg/ml

half life Adults: 4.5 hours

Melting Point 155–162°C

Flash Point 255.8°C

Solubility DMS 100 mg/mL

Indometacin
Chemical formula	C₁₉H₁₆ClNO₄
Molar mass	357.787 g.mol^–1
Density	1.32 g/cm³
Solubility in water	734μg/ml
half life	Adults: 4.5 hours
Melting Point	155–162°C
Flash Point	255.8°C
Solubility DMS	100 mg/mL

2.2 Equipment

In this study, we used specific equipment to carry out the Photo-Fenton process. This included a 30-watt low-pressure mercury lamp from MMGS company for UV light, a pH-meter from AZ Instrument in Taiwan, a digital balance model TE313S from Sartoriuy Company for accurate measurements, a spectrophotometer model DR/5000 from HACH company, and a data logger model 147H for temperature control.

2.3 Preparation of indomethacin antibiotic stock solution

To make a 1000 ppm stock solution of indomethacin antibiotic, weigh 1 gram accurately using a scale to 0.001 precision. Weighed it and transferred it into a 1000 ml volumetric flask and made it up to volume with high purity double distilled water, then we prepared solutions with concentrations of 20–40–60 ppm from the stock solution. $\begin{matrix} N_{1} V_{1} = N_{2} V_{2} \\ (Indomethacin) 1000 ppm \times 20 ppm = 20 ppm \times 1000 ml \\ V_{1} = \frac{20 \times 1000}{1000} = 20 ml \end{matrix}$ (1)

Then, we took 20 ml of the stock solution with a concentration of 1000 ppm. We transferred it into a 1000 ml volumetric flask and added double distilled water until it reached 1000 ml. The concentration of the above solution is 20 ppm. We followed the same process as described in Equation 1 to get indomethacin at 20 mg/liter. We used this process to also obtain indomethacin at concentrations of 40 and 60 mg/liter.

2.4 The calibration curve

To draw the calibration curve, it was prepared a solutions of indomethacin with concentrations of 5–15–25–50–100 ppm. Then, we read at a wavelength of 242 nm to draw the calibration curve. Based on the obtained linear equation, the amount of drug removed from the solution was presented in Fig. 2.

Fig. 2

Calibration curve of indomethacin removal from water.

The experiments were conducted based on the experimental design table and specified concentrations. For example, to 100 ml of 60 ppm antibiotic solution, we added H₂O₂ with a concentration of 20 ppm and then added 2 ml of Fe iron solution with a concentration of 20 ppm we put the contents on the hot player with a speed of 300 per minute and under the UV lamp with a power of 30 watts and a duration of 30 minutes.

The solutions were transferred to the quartz cell of the spectrophotometer. Then we placed the vessel inside the device. The absorbance number was recorded and read from the device.

2.5 Design experiment of the pilot in the research

Five ranges (2, 4, 6, 8, and 10) were selected to determine the pH effect. Antibiotic removal test was performed with the Photo-Fenton process in five initial concentrations of 20, 30, 40, 50, and 60 mg/liter of indomethacin antibiotic. We determined the ratio of antibiotic concentration to contact time. The values were obtained from pH and constant voltage of the UV lamp. The contact time was 30, 45, 60, 75, and 90 minutes. The ratio was determined using one-to-one concentration (H₂O₂/Fe²⁺). Experiments related to the advanced oxidation process were carried out in a 1000 cc Pyrex container equipped with a UV lamp, wavelength 252 nm, placed in the reactor. A solution with 1000 mg/L indomethacin antibiotic was prepared. Then, different concentration solutions were made from the stock solution.

Glass containers with specific volume were used for the experiments. The Maximum wavelength was obtained using a spectrophotometer by placing some of the raw pollutants in the spectrophotometer with wavelengths ranging from 200 to 900 nm and then obtaining the Maximum wavelength from the graph displayed by the device.

The experiments were done in a lab at a temperature of 28.3°C and humidity of 28.8%. The lab had a data logger to measure the conditions. It was used the Design Expert software (response surface methodology-RSM and central composite design-CCD) to investigate the effect of independent variables including indomethacin antibiotic concentration, oxidant (H₂O₂) concentration, catalyst (Fe²⁺) concentration, contact time, pH at three levels of minimum (–1), average (0), and maximum (+1) with alpha equal to 1 on the efficiency of indomethacin antibiotic removal in the UV/H₂O₂/Fe²⁺ Photo-Fenton process.

To ensure the repeatability of the results, each experiment was repeated three times and the mean of the numbers was reported. The removal efficiency of the indomethacin antibiotic was calculated from equation (2). $R = \frac{C_{0} - C_{r}}{C_{0}} \times 100$ (2) where R is the removal efficiency (percent), “C0” is the initial concentration (mg/L) C_r is the residual concentration (mg/L). Using the analysis of variance (ANOVA) at a significance level of 0.05, the determination of the experimental model of removing the antibiotic indomethacin, and the optimal management conditions, as well as drawing diagrams using CCD were done.

2.6 Antibiotic analysis

1 cc of 0.01 M potassium permanganate solution and 1 cc of 0.1 M potassium carbonate solution were added to the sample volume of 10 cc, then mixed well and reached the volume using distilled water Subsequently, the adsorption level was measured using a spectrophotometer at a wavelength of 242 nanometers.

Wavelength Detection Method: The highest adsorption was obtained using the spectrophotometric method (Fig. 3). The test schematic is displayed in Fig. 4.

Fig. 3

Max wavelength of indomethacin in antibiotic.

Fig. 4

Schematic of the pilot and tests.

3 Results and Discussion

In the present study, sampling was done based on experiments designed by Design Expert software, response surface method (RSM) and tested. After testing the samples, the obtained results were analyzed. To analyze data from Design Expert software was used. In this study, using the response surface method and central composition design (CCD) to investigate the effect of independent variables of indomethacin concentrations, contact time and pH at three levels of minimum (–1), medium (0) and maximum (1+) on efficiency. The removal of indomethacin antibiotics was studied in the Photofenton process. The response was evaluated as the removal efficiency of indomethacin antibiotics. ANOVA analysis was conducted at a significance level of 0.05, determination of the experimental model of indomethacin antibiotics removal and optimal conditions were conducted, and graphs were also drawn using CCD.

The results of indomethacin removal percentage in different experimental phases are presented in Table 2.

Table 2
The results of indomethacin removal percentage under various experimental conditions

Factor 1 Factor 2 Factor 3 Factor 4 Factor 5 Response 1 RP

Std Run A: B: Indomethacin C: time D: Fe E: H2o2 Concentration Removal

pH (ppm) (min) (ppm) (ppm) percentage (%)

ppm min ppm ppm ppm %

34 32 2 40 60 40 40 8.15 79.62

33 36 2 40 60 40 40 8.15 79.62

21 4 4 30 75 30 50 4.62 84.60

29 6 4 30 75 50 50 2.69 91.03

17 9 4 30 45 30 50 5.89 80.36

13 40 4 30 75 50 30 3.88 87.06

9 43 4 30 45 50 30 4.51 84.96

1 48 4 30 45 30 30 6.63 77.90

25 56 4 30 45 50 50 3.09 89.70

5 57 4 30 75 30 30 6.11 79.63

11 16 4 50 45 50 30 10.22 79.56

31 17 4 50 75 50 50 5.57 88.86

19 26 4 50 45 30 50 11.32 77.36

7 28 4 50 75 30 30 13.13 73.74

23 44 4 50 75 30 50 9.96 80.08

15 46 4 50 75 50 30 8.06 83.88

27 54 4 50 45 50 50 6.99 86.02

3 58 4 50 45 30 30 13.59 72.82

37 15 6 20 60 40 40 3.31 83.45

38 20 6 20 60 40 40 3.31 83.45

57 1 6 40 60 40 40 7.98 80.05

47 3 6 40 60 60 40 7.90 80.25

55 5 6 40 60 40 40 7.99 80.02

51 11 6 40 60 40 60 7.44 81.40

50 21 6 40 60 40 20 8.92 77.70

46 22 6 40 60 20 40 8.51 78.72

48 23 6 40 60 60 40 7.88 80.30

52 24 6 40 60 40 60 7.44 81.40

41 25 6 40 30 40 40 8.93 77.67

45 27 6 40 60 20 40 8.43 78.92

49 34 6 40 60 40 20 8.92 77.70

43 37 6 40 90 40 40 7.09 82.27

60 38 6 40 60 40 40 7.99 80.02

44 39 6 40 90 40 40 7.06 82.35

56 42 6 40 60 40 40 7.91 80.22

53 45 6 40 60 40 40 7.98 80.05

58 50 6 40 60 40 40 7.91 80.22

59 52 6 40 60 40 40 7.98 80.05

54 53 6 40 60 40 40 7.98 80.05

42 60 6 40 30 40 40 8.93 77.67

40 7 6 60 60 40 40 13.87 76.88

39 35 6 60 60 40 40 13.80 77.00

6 8 8 30 75 30 30 10.15 66.16

14 12 8 30 75 50 30 9.61 67.96

2 13 8 30 45 30 30 11.15 62.16

22 14 8 30 75 30 50 9.22 69.26

26 31 8 30 45 50 50 9.49 68.36

18 33 8 30 45 30 50 10.85 63.83

30 49 8 30 75 50 50 8.94 70.20

10 55 8 30 45 50 30 10.79 64.03

8 2 8 50 75 30 30 18.91 62.18

20 10 8 50 45 30 50 20.11 59.78

4 18 8 50 45 30 30 21.65 56.70

16 19 8 50 75 50 30 18.08 63.84

32 30 8 50 75 50 50 16.37 67.26

24 47 8 50 75 30 50 17.46 65.08

12 51 8 50 45 50 30 19.97 60.06

28 59 8 50 45 50 50 18.00 64.00

36 29 10 40 60 40 40 23.32 41.70

35 41 10 40 60 40 40 23.12 42.20

		Factor 1	Factor 2	Factor 3	Factor 4	Factor 5	Response 1	RP
Std	Run	A:	B: Indomethacin	C: time	D: Fe	E: H2o2	Concentration	Removal
		pH	(ppm)	(min)	(ppm)	(ppm)		percentage (%)
			ppm	min	ppm	ppm	ppm	%
34	32	2	40	60	40	40	8.15	79.62
33	36	2	40	60	40	40	8.15	79.62
21	4	4	30	75	30	50	4.62	84.60
29	6	4	30	75	50	50	2.69	91.03
17	9	4	30	45	30	50	5.89	80.36
13	40	4	30	75	50	30	3.88	87.06
9	43	4	30	45	50	30	4.51	84.96
1	48	4	30	45	30	30	6.63	77.90
25	56	4	30	45	50	50	3.09	89.70
5	57	4	30	75	30	30	6.11	79.63
11	16	4	50	45	50	30	10.22	79.56
31	17	4	50	75	50	50	5.57	88.86
19	26	4	50	45	30	50	11.32	77.36
7	28	4	50	75	30	30	13.13	73.74
23	44	4	50	75	30	50	9.96	80.08
15	46	4	50	75	50	30	8.06	83.88
27	54	4	50	45	50	50	6.99	86.02
3	58	4	50	45	30	30	13.59	72.82
37	15	6	20	60	40	40	3.31	83.45
38	20	6	20	60	40	40	3.31	83.45
57	1	6	40	60	40	40	7.98	80.05
47	3	6	40	60	60	40	7.90	80.25
55	5	6	40	60	40	40	7.99	80.02
51	11	6	40	60	40	60	7.44	81.40
50	21	6	40	60	40	20	8.92	77.70
46	22	6	40	60	20	40	8.51	78.72
48	23	6	40	60	60	40	7.88	80.30
52	24	6	40	60	40	60	7.44	81.40
41	25	6	40	30	40	40	8.93	77.67
45	27	6	40	60	20	40	8.43	78.92
49	34	6	40	60	40	20	8.92	77.70
43	37	6	40	90	40	40	7.09	82.27
60	38	6	40	60	40	40	7.99	80.02
44	39	6	40	90	40	40	7.06	82.35
56	42	6	40	60	40	40	7.91	80.22
53	45	6	40	60	40	40	7.98	80.05
58	50	6	40	60	40	40	7.91	80.22
59	52	6	40	60	40	40	7.98	80.05
54	53	6	40	60	40	40	7.98	80.05
42	60	6	40	30	40	40	8.93	77.67
40	7	6	60	60	40	40	13.87	76.88
39	35	6	60	60	40	40	13.80	77.00
6	8	8	30	75	30	30	10.15	66.16
14	12	8	30	75	50	30	9.61	67.96
2	13	8	30	45	30	30	11.15	62.16
22	14	8	30	75	30	50	9.22	69.26
26	31	8	30	45	50	50	9.49	68.36
18	33	8	30	45	30	50	10.85	63.83
30	49	8	30	75	50	50	8.94	70.20
10	55	8	30	45	50	30	10.79	64.03
8	2	8	50	75	30	30	18.91	62.18
20	10	8	50	45	30	50	20.11	59.78
4	18	8	50	45	30	30	21.65	56.70
16	19	8	50	75	50	30	18.08	63.84
32	30	8	50	75	50	50	16.37	67.26
24	47	8	50	75	30	50	17.46	65.08
12	51	8	50	45	50	30	19.97	60.06
28	59	8	50	45	50	50	18.00	64.00
36	29	10	40	60	40	40	23.32	41.70
35	41	10	40	60	40	40	23.12	42.20

The results of the indomethacin antibiotic test design with a wavelength of 242 nm in Table 3 show that the model had a favorable match with the experimental data. The p.Value for all test components is 0.0433. This value is less than 0.05, so the model is efficient. Table 4’s statistics reveal that the R² index is 0.8762, indicating a strong match.

Table 3

The results of the indomethacin antibiotic test design with a wavelength of 242 nm

Source	Sum of squares	df	Mean square	F-value	p-value
Model	1474.72	20	73.74	107.17	<0.0001	significant
A-pH	636.34	1	636.34	924.89	<0.0001
B-Indomethacin	493.25	1	493.25	716.91	<0.0001
C-time	17.41	1	17.41	25.31	<0.0001
D-Fe	28.23	1	28.23	41.03	<0.0001
E-H2o2	21.05	1	21.05	30.60	<0.0001
AB	26.15	1	26.15	38.01	<0.0001
AC	0.7970	1	0.7970	1.16	0.2884
AD	10.11	1	10.11	14.70	0.0004
AE	1.17	1	1.17	1.71	0.1991
BC	1.59	1	1.59	2.31	0.1367
BD	3.96	1	3.96	5.75	0.0214
BE	3.00	1	3.00	4.35	0.0435
CD	0.0979	1	0.0979	0.1423	0.7081
CE	0.0034	1	0.0034	0.0049	0.9443
DE	0.1365	1	0.1365	0.1984	0.6585
A²	227.66	1	227.66	330.89	<0.0001
B²	4.42	1	4.42	6.43	0.0154
C²	1.13	1	1.13	1.64	0.2079
D²	1.92	1	1.92	2.79	0.1027
E²	1.92	1	1.92	2.79	0.1027
Residual	26.12	22	1.15
Lack of fit	26.12	6	5.02
Pure error	0.0000	15	0.0000
Cor total	2501.55	42

Table 4

Adjustment statistics

Std. Dev.	5.76	R²	0.8762
Mean	16.85	Adjusted R²	0.7855
C.V. %	34.17

Table 3, on the other hand, is the analysis table that simultaneously examines the combined effect of two factors and is analyzed by software to determine how impactful the combination of two factors will be. As indicated in the table below, Factor A corresponds to the PH variable, Factor B relates to the initial concentration of the antibiotic, Factor C is associated with time, Factor D pertains to the concentration of iron (Fe), and Factor E is linked to the hydrogen peroxide (H₂O₂) variable.

The Model F-value of 107.17 implies the model is significant. There is only a 0.01% chance that an F-value this large could occur due to noise. P-values less than 0.0500 indicate model terms are significant. In this case A, B, C, D, E, AB, AD, BD, BE, A², B² are significant model terms. Values greater than 0.1000 indicate the model terms are not significant. If there are many insignificant model terms (not counting those required to support hierarchy), model reduction may improve your model. The impact of various parameters on the pollutant removal process by the adsorbent follows the sequence: PH > Initial antibiotic concentration > Fe>H₂O₂ > Process time

3.1 Predicted actual curve

The Predicted Actual chart is a key tool in test design. It shows the difference between model predictions and lab test results. In the figure below, the X-axis (Actual) is the actual value and the Y-axis (Predicted) is the predicted value. The closer these points are to each other, the more accurate the selected model is the figure below clearly shows that many of the results match or are close to the software’s prediction points.

3.2 Optimum PH selection

The indomethacin antibiotic’s removal efficiency decreased when the pH increased, as seen in Fig. 6. The average removal percentage at pH 4 was 91.03%, which was achieved in the 29th treatment. The drug combination in the tested solution achieves better absorption on the catalyst surface with the help of the oxidizing agent H₂O₂ at a lower pH. Hydroxyl radicals generally form in acidic environments. Therefore, the Photo-Fenton process is more effective in acidic environments. The results showed that at pH = 2, the removal percentage decreased to 79.62%. At pH levels less than 2, the Photo-Fenton process becomes slow due to the formation of iron complexes and oxidants. In alkaline pH, the production of hydroxyl radicals is slower due to the formation of iron-hydroxide complexes. Ahmed et al. (2020) found that the Photo-Fenton process reduced antibiotic resistance [30]. This happened when the process was done at neutral pH and under visible LED light. Fiorentino et al (2019) showed that the Photo-Fenton process experienced a 10% reduction in the efficiency of removing antibiotics from municipal wastewater when exposed to a neutral pH, but it also reduced bacterial resistance [31].

Fig. 5

Predicted Actual diagram resulting from the design of the experiment in this research.

Fig. 6

The effect of pH on indomethacin removal efficiency.

3.3 Optimum H₂O₂ selection

In accordance with Fig. 7, an increase in the oxidizing agent concentration has resulted in an elevated drug removal percentage from the solution, reaching its peak efficiency of 91.03% at the 50 ppm concentration of the oxidizing agent H₂O₂. One of the primary reasons for this increased efficiency lies in the generation of OH radicals, acknowledged as the most potent oxidizing species among pollutants, serving as the cornerstone for the decomposition of organic substances.

Fig. 7

The effect of H₂O₂ on the removal efficiency of indomethacin.

The results obtained from the analysis of experimental samples, as depicted in Fig. 5, indicate a significant surge in the removal percentage, reaching 91.03% at a concentration of 50 ppm. However, at a concentration of 60 ppm, this efficiency experiences a reduction to 81.04%. The optimal removal of indomethacin from the aqueous solution is achieved at the 29th treatment level with an efficiency of 91.03%. The heightened production of hydroxyl radicals resulting from increased hydrogen peroxide concentration leads to an enhanced efficiency of the photophenton process. Hydrogen peroxide photolysis contributes to increased production of hydroxyl radicals, ultimately resulting in a more extensive degradation of antibiotics. In the Photo-Fenton process, Zhang et al (2022) found that using 50 ppm persulfate and waiting for 60 minutes worked best to remove tetracycline antibiotics [32]. Tian et al. (2022) stated that the use of peroxy-mono-sulfate and peroxidisulfate can be used as oxidants in the Photo-Fenton process for emoving antibiotics from aquatic environments [33].

3.4 Optimum iron (Fe²⁺) selection

Figure 8 shows the results of the study on the effect of iron ions on the removal of indomethacin antibiotics “The removal percentage increased to 91.03% at a concentration of 50 ppm but dropped to 80.25% at 60 ppm”. When there is a lot of iron, it combines with hydroxyl radicals and makes the process less efficient. Iron ions are the most used catalysts for oxidizing pollutants. Mixing hydrogen peroxide and iron ions at low pH causes the kinetic decomposition of hydrogen peroxide by iron ions into hydroxyl radicals. Another result of the study was the determination of the optimal iron ion level (60 ppm) for removing indomethacin, which is consistent with the results of Huang et al. [34]. In their study, the optimal iron level for removing tetracycline was 60 ppm, which led to the removal of more than 90% of the antibiotic. Iron plays a role as an initiator and catalyst in the Photo-Fenton process. Thus determining the optimal concentration of iron will have a significant role in the removal efficiency of antibiotics.

Fig. 8

The effect of Fe²⁺on indomethacin removal performance.

3.5 Optimum time selection

Figure 9 shows the effect of time on the removal percentage of indomethacin antibiotics.

Fig. 9

The effect of time on indomethacin removal efficiency.

The appropriate reaction time is one of the effective factors in performing advanced oxidation processes. The removal efficiency increased to 77.67% after 30 minutes. It reached its highest efficiency, averaging 91.03%, at 75 minutes. During the Photo-Fenton reaction, a lot of hydroxyl radicals are created in the beginning. Over time, more intermediate products form as hydrogen peroxide breaks down. This creates turbulence, increasing the chance of iron ions and intermediate products coming into contact. As a result, more hydroxyl radicals are produced, making the process more efficient. The required time for oxidation in the Photo-Fenton process relies on the concentration of the catalyst, oxidant, and pollutant. The results of Pesqueira et al. (2021) also showed that time have a direct effect on increasing the removal efficiency of pollutants in the Photo-Fenton process [35].

3.6 Optimal selection of initial antibiotic

Figure 10 shows that as the concentration of indomethacin in the aqueous solution increased, the removal efficiency dropped. (Fig. 8). The best results were obtained when the initial concentration was 20 ppm, with a removal rate of 83.45% The antibiotic was most effectively removed at an initial concentration of 20 ppm. which means that lower pollutant concentrations lead to better removal. Lower concentrations of antibiotics in water pollution have led to an increase in removal efficiency in the antibiotic process. The results of Dias et al. (2014) showed that the removal of trimethoprim and sulfamethoxazole antibiotics from aqueous solutions was higher at lower concentrations [36].

Fig. 10

The effect of initial antibiotic concentration on indomethacin removal efficiency.

3.7 Investigating the simultaneous effect of effective parameters in the process of removing indomethacin

To analyze the simultaneous effect of the effective components on the removal of indomethacin in the photo-Fenton process, multi-dimensional diagrams and surface response were used, the results of which are shown in Fig. 11.

Fig. 11

Results of multivariate analysis of indomethacin removal from water by photo-Fenton process.

Figures 11A and 11B: In photo-Fenton reactions, organic compounds break down into hydroxyl free radicals [37]. If the hydrogen peroxide be added to increase the amount of hydroxyl radicals, the reaction rate will go up. Hydrogen peroxide, in the presence of a catalyst like iron, produces hydroxyl radicals. These radicals react with organic molecules, leading to their degradation. To achieve the highest efficiency in removing indomethacin from wastewater, an increase in the concentration of hydrogen peroxide and iron solution simultaneously is necessary. Multivariate analysis results showed that the highest percentage of pollutant removal was observed at a concentration of 50 ppm hydrogen peroxide and iron solution. The removal percentage decreased with less of each compound.

Figures 11C and 11D: The initial pH is one of the influential parameters in the photo-Fenton reaction [38]. The results showed that the highest efficiency in removing indomethacin from wastewater was at pH = 4 and an initial concentration of 30 ppm. If the indomethacin concentration increases, the percentage of drug removal from wastewater decreases. It is worth mentioning that pH plays a crucial role removing drugs from wastewater.

Figures 11E and 11F: The study found that the best way to remove indomethacin from wastewater was at pH 4 and with 50 ppm of hydrogen peroxide.

Also, an increase in pH value leads to a decrease in the percentage of indomethacin removal.

Figures 11G and 11H: The results indicate that the highest efficiency in removing indomethacin is achieved at pH 4 and an iron solution concentration of 50 ppm. When the pH value goes up and the iron solution concentration goes down, the removal percentage decreases.

3.8 Optimum conditions for removal of indomethacin in Photo-Fenton

Table 5 shows the impact of the Photo-Fenton process on removing the indomethacin antibiotic. The optimal values were pH = 4, H₂O₂ oxidant concentration = 50 ppm, Fe²⁺catalyst concentration = 50 ppm, the reaction time of 75 minutes, and an initial antibiotic concentration of 20 ppm, resulting in a removal efficiency of 91.03%. The parameters of initial antibiotic concentration, H₂O₂ concentration, and pH had the greatest impact on the experiment.

Table 5
The control parameters and their different levels are set for experimentation

Row Parameters Unit Levels of parameters

α– 1– 0 1+ α+

1 pH – 2 4 6 8 10

2 Fe ppm 20 30 40 50 60

3 H₂O₂ ppm 20 30 40 50 60

4 Antibiotic concentration ppm 20 30 40 50 60

5 Time min 30 45 60 75 90

Row	Parameters	Unit	Levels of parameters
1	pH	–	2	4	6	8	10
2	Fe	ppm	20	30	40	50	60
3	H₂O₂	ppm	20	30	40	50	60
4	Antibiotic concentration	ppm	20	30	40	50	60
5	Time	min	30	45	60	75	90

Hospital effluents Wastewater from one of the hospital departments, where the antibiotic indomethacin is extensively used, has been sampled. Following the collection of the wastewater sample from this hospital department, known for its high consumption of the antibiotic indomethacin, it was transferred to the laboratory environment. Various parameters such as turbidity, total organic carbon, pH, TSS (Total Suspended Solids), COD (Chemical Oxygen Demand), and BOD (Biochemical Oxygen Demand) were measured to assess the characteristics of the wastewater (Table 6).

Table 6

The results of the effect of the Photo-Fenton process on the removal of indomethacin antibiotic in optimal conditions

After removal by the Photo-Fenton	Hospital	Parameter
process in optimal conditions	effluents
72	206	Turbidity (NTU)
4	5.5	pH
124	195	TSS (ppm)
75.6	451	COD (ppm)
19.2	164	TOC (ppm)
34.1	273	BOD⁵ (ppm)
8.4	49.6	Concentration of Indomethacin(ppb)

In this study, 7 out of 10 identified antibiotics were removed between 60 and 100% in the Photo-Fenton process. Rozas also found an optimal level of around 90% removal of ampicillin. The optimal removal rate of indomethacin in the present study was 91.03% [39].

4 Conclusion

In recent years, advanced technologies have been evaluated to remove pollutants such as heavy metals from soil. The Photo-Fenton process has been successfully used to purify many resistant pollutants to biodegradation or as a treatment method.The present research found that in ideal conditions, over 90% of the antibiotic indomethacin can be eliminated from water using the Photo-Fenton process. This is a significant finding for removing this medicine pollutant from water.

Ethics approval and consent to participate:

Data Availability

All data generated or analyzed during this study are included in this published article.

Declaration of competing interest

There are no conflicts to declare.

Funding

No funding was obtained for this study.

Author contributions

Conceptualization: Mostafa Azizpour, Hamed Ghaedi, Reza Jalilzadeh Yengejeh. Data curation and analysis: Mostafa Azizpour. Investigation and methodology: Mostafa Azizpour. Supervision: Hamed Ghaedi, Reza Jalilzadeh Yengejeh, Masoud Saberi, Writing-original draft, Writing-review and editing: Mostafa Azizpour, Reza Jalilzadeh Yengejeh and Masoud Saberi.

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Investigating the efficiency of Photo-Fenton (UV/H 2 O 2 /Fe 2+ ) in removing the indomethacin antibiotic from aqueous solutions

Abstract

Keywords

1 Introduction

2.1 Chemicals and reagents

2.1.1 Indomethacin antibiotic

Table 1 The chemical characteristics of indomethacin antibiotic Indometacin Chemical formula C19H16ClNO4 Molar mass 357.787 g.mol–1 Density 1.32 g/cm3 Solubility in water 734μg/ml half life Adults: 4.5 hours Melting Point 155–162°C Flash Point 255.8°C Solubility DMS 100 mg/mL

2.3 Preparation of indomethacin antibiotic stock solution

3.2 Optimum PH selection

Table 5 The control parameters and their different levels are set for experimentation Row Parameters Unit Levels of parameters α– 1– 0 1+ α+ 1 pH – 2 4 6 8 10 2 Fe ppm 20 30 40 50 60 3 H2O2 ppm 20 30 40 50 60 4 Antibiotic concentration ppm 20 30 40 50 60 5 Time min 30 45 60 75 90

Ethics approval and consent to participate:

Data Availability

Declaration of competing interest

Funding

Author contributions

References

Table 5
The control parameters and their different levels are set for experimentation

Row Parameters Unit Levels of parameters

α– 1– 0 1+ α+

1 pH – 2 4 6 8 10

2 Fe ppm 20 30 40 50 60

3 H₂O₂ ppm 20 30 40 50 60

4 Antibiotic concentration ppm 20 30 40 50 60

5 Time min 30 45 60 75 90