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Kinetics degradation of phenacetin by solar activated persulfate system
Separation and Purification Technology 256 (2021) 117851
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Kinetics degradation of phenacetin by solar activated persulfate system Chaoqun Tan *, Xinchi Jian , Haotian Wu , Tianyu Sheng, Kechun Sun, Haiying Gao School of Civil Engineering, Southeast University, Nanjing 210096, China
A R T I C L E I N F O
A B S T R A C T
Keywords: Kinetics Phenacetin Solar Persulfate Trihalomethanes
Kinetic degradation of phenacetin (PNT) by solar activated persulfate (PS) system was evaluated in study. The decomposition of PNT well fitted with a pseudo-first order kinetic pattern, and the exceptional removal per formance towards PNT (100%) was obtained in the presence of solar irradiation (1.14 × 10-4 E⋅ m− 2⋅ s− 1) and 0.3 mM PS at pH 7.0 in 10 min. The consume ratios of persulfate were calculated to be 2.3~16.7%. The steadystate concentrations of hydroxyl radicals ([HO*]ss) and sulfate radicals ([SO-4⋅]ss) were calculated to be (2.41~2.59) × 10-13 M and (3.75~4.06) × 10-12 M by probes of nitrobenzene (NB) and benzoic acid (BA), respectively. The contribution of HO* and SO-4⋅ accounts for 27.4% and 11.0% in degradation of PNT. The formation of typical trihalomethanes (THMs) after pre-oxidation of solar/PS was evaluated. The concentration of total THMs decreased from 16 μg⋅L-1 to 15.4 μg⋅L-1 through pre-oxidation, with cytotoxicity decreased from 1.38 × 10-5 to 1.27 × 10-5. The calculated electrical energy per order (EE/O) in solar/PS were in range of 0.069~0.106 kWh/m/order.
1. Introduction Recent years, pharmaceuticals and personal care products (PPCPs) have been detected frequently in wastewater, surface water, ground water, and drinking water in the range of ng⋅L-1 to μg⋅L-1, arousing widespread attention throughout the world [1,2]. Most pharmaceuticals are likely available in waters due to their widespread consumption including human and animal ingestion. Phenacetin (PNT), as a kind of typical PPCPs with anti-inflammatory and analgesic effects, was frequently detected in surface water. PNT had characteristics with high solubility, multiple pKa values and resistant degradation in traditional water treatment [3]. The concentration of PNT was detected to be up to 44.0 ng⋅L-1 [4] and 68.3 μg⋅L-1 [5] in drinking water purification plants and dam inlet, respectively. Therefore, it is urgent to develop high effective technologies to degrade PNT. Advanced oxidation processes (AOPs) arose great concern in water treatment, as a great number of reactive oxygen species (ROS) were generated and might be able to decompose or mineralize the recalcitrant organic contaminant [6–8]. Compared to traditional AOPs with hy droxyl radicals (HO*) as the main ROS in system, sulfate radicals (SO-4⋅) based AOPs are new technologies developed in recent years. Persulfates include peroxymonosulfate (PMS, E0 = 1.82 V [9]) and persulfate (PS, E0 = 2.01 V [10]), which are derivatives of H2O2 after one or two of hydrogen atom is replaced by SO3, respectively. Persulfates could be
activated to SO-4⋅ under the conditions of transition metal, light, and heat [11]. Organic compounds are readily degraded by SO-4⋅. Compared with heat, transition metals, and ultrasonic, UV activated PS technologies possess mild reaction conditions, highly degradation, and no secondary pollution [12]. Sulfamethazine was completely degraded in 2 min with PS concentration of 10 mM and UV of 254 nm in UV254/PS system. The sulfamethazine degradation followed pseudo-first order kinetics and SO⋅-4 was the dominant ROS identified in UV254/PS system like Eq. 1–2 [13]. Triclosan was reported to be effectively removed by SO⋅-4 in UV254/PS system [14] as well, and the kobs of tri closan degradation in UV254/PS was 4.13 times higher than that in UV254/H2O2 process, indicating that UV254 activated PS system could degrade pollutants more effectively than H2O2. S2 O28 - → 2SO⋅−4
(1)
SO⋅−4 + H2 O → SO24 - + OH⋅
(2)
hv
Although PS could be activated by UV irradiation of 254 nm to generate SO⋅-4 , UV254 based techniques are restricted in practical appli cations owing to the requirement of high energy input. Therefore, it is imperative to develop low-cost, efficient, and environmentally-friendly AOPs for environmental clean-up. Recently, sunlight for photo catalytic systems, with spectrum in ranges of 290–800 nm, have attracted increasing interest [15]. Gao et al. [16] reported that the
* Corresponding author. E-mail address: [email protected] (C. Tan). https://doi.org/10.1016/j.seppur.2020.117851 Received 13 July 2020; Received in revised form 8 September 2020; Accepted 3 October 2020 Available online 7 October 2020 1383-5866/© 2020 Elsevier B.V. All rights reserved.
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visible-light-excited Rhodamine B (RhB) could activate PS to generate SO⋅-4 . The RhB removal markedly increased from 40% in dark condition to 80% in Vis/PS system. The excited state of dye molecule could react with PS, resulting in the formation of SO⋅-4 via an electron-transfer pathway. The combination of PMS and solar radiation (λ > 300 nm) resulted in effective removal of bezafibrate by ROS generated in solar/ PMS system [17]. However, little is known about the activation of PS in the presence of solar irradiation. Accordingly, the purpose of this study is to investigate the kinetic degradation of phenacetin (PNT) in solar/PS system. The identification and contribution of reactive oxygen species (ROS) in system are assessed by probes of nitrobenzene (NB) and benzoic acid (BA). Moreover, for mation of disinfection by-products of trihalomethanes (THMs) after preoxidation of solar/PS and the electrical energy per order (EE/O) in system were evaluated as well.
v/v) at a flow rate of 0.25 mL/min. The concentrations of PNA were quantified at 315 nm with an eluent of water and methanol with a ratio of 25:75 (v/v) at a flow rate of 0.15 mL/min. The concentrations of NB and BA were measured at 270 and 227 nm with an eluent of 1% phos phoric acid and methanol with a ratio of 55:45 (v/v) at a flow rate of 0.15 mL/min. For the analysis of THMs after pre-oxidation of solar/PS, 40.0 mL of the solution after solar/PS of oxidation was collected and transferred into a brown glass bottle and 0.2 mM NaOCl were added to the sample. The bottle was kept in the dark at room temperature for 12.0 h, afterwards the sample was transferred into a headspace-free brown glass bottle and 0.5 g ascorbic acids were added for head space gas chromatography method [20]. The analyses were carried out on an HP (Agilent Technologies, Palo Alto, CA) 6890 gas chromatograph5973 N mass selective detector equipped with a 7694 headspace auto sampler and an HP-5MS fused silica capillary column (30 m × 0.25 mm × 0.25 μm film thickness) [21,22]. Persulfate concentration was measured with a rapid spectrophoto metric determination by UV–vis spectrophotometer (HACH, DR6000) using potassium iodide as the indicator at 352 nm [23]. Meanwhile, dissolved sulfate concentrations were measured with spectrophotometry using the Ba2+-based sulfaVer4 method (HACH module No.8051).
2. Experimental section 2.1. Chemicals and materials Chemicals were prepared with analytical standard grade chemicals and distilled water. Phenacetin (PNT, ≥98%) and p-Nitroanisole (PNA, ≥98%) were purchased from Aladdin. Pyridine (PYR, ≥99%) was pur chased from Shanghai Macklin Biochemical Technology Co., Ltd. Ben zoic acid (BA, ≥99%), nitrobenzene (NB, ≥99%), sodium dihydrogen monobasic monohydrate (≥99%), and sodium phosphate dibasic (≥99%) were obtained from Yonghua Chemical Reagent Co., Ltd., China. Persulfate (PS, ≥99%) was purchased from Nanjing Reagent. Methanol and acetonitrile of UPLC grade were purchased from SigmaAldrich. Tert-Butanol (TBA, ≥99%). The rest of chemicals (≥98%) were obtained from Energy Chemical. For actual water experiment, influent and effluent wastewater sam ples were all collected from one sewage treatment plant in Nanjing and river water samples were taken from the Dongshili Changgou, a tribu tary of the Yangtze River located in North Nanjing, and tap water were sampled from municipal pipeline. The all water quality parameters were shown in Table S1.
2.4. Data processing methods The overall rate law for the degradation of pollutants could be expressed as Eq. (3): kobs = -
dln(C/C0 ) dt
(3)
where kobs is the overall kinetic rate expression of the target species in the reaction system (min− 1), C is the concentration of target species at time t (M), and C0 is the initial concentration of target species (M). The toxicity of each disinfection by-products (DBPs) could be ob tained by Eq. (4), where c(DBPs) is the concentration of each DBPs (M), LC50 is its semi-lethal concentration (M) and M(DBPs) is its relative molecular weight. Cytotoxicity =
2.2. Experimental device and procedures
c(DBPs)/M(DBPs) LC50
(4)
3. Results and discussion
The photochemical experiments were conducted with an ultra-high voltage short-arc xenon lamp to simulate solar light (500 W, Perfect Light Co., China). The photon fluence rate of this solar module was measured by chemical actinometry of p-Nitroanisole (PNA)/pyridine (PYR) actinometer [18,19]. The quantum yield of the solar device was evaluated to be 1.14 × 10-4 E⋅ m− 2⋅ s− 1 by the method described in the Supplementary Information (SI) (Test S1, Fig. S1-S2). The light pro ceeded through the collimated tube down onto a 50.0 mL sample magnetically stirred within a cylindrical glass dish and the reaction temperature was maintained at ambient temperature (25 ± 1℃). The reaction solution contains 1.0 μМ target pollutant of PNT, 10 mM phosphate buffer agent and 0.3 mM persulfate for three pHs (5.5, 7.0, and 8.5). The lamp was warmed up at least 15 min prior to the experiments and the reaction was initiated by exposing the reactor to solar irradiation. During the sampling intervals (0, 5, 10, 20, and 30 min), 1.0 mL solution was sampled into the vials prefilled with 10.0 μL sodium thiosulfate (3.0 M) to terminate the reaction. 1.0 μM of NB and BA was added into the system and employed as probes at different pHs.
3.1. PNT degradation in solar alone and PS alone system The removal of PNT in solar and PS system was shown in Fig. S3. The decomposition of PNT were 13%, 26.3%, and 25.8% at pH 5.5, 7.0, and 8.5 in 30 min, respectively. The data of ln(C/C0) fell on a straight line with time (inner in Fig. S3a), revealing that the degradation of PNT in solar system fitted well with pseudo-first order kinetic pattern. The pseudo-first order kinetic degradation rate constants (kobs) were deter mined to be 4.2 × 10-3, 9.4 × 10-3, and 8.7 × 10-3 min− 1 at pH 5.5, 7.0, and 8.5, respectively. The results indicated that solar irradiation could lead to partial decomposition of PNT. To screen the formative ROS, probes of NB and BA were added to the solar system to evaluated for mation of ROS. As shown in Fig. S4, the degradation of NB and BA was less than 8% in 15 min, revealing that decomposition of PNT in solar system might be caused by powerful light energy and the presence of pharmaceutical weak covalent bonds [24]. In the absence of solar, the time-dependent trend of PNT degradation by PS alone in pH ranges of 5.5–8.5 was presented in Fig. S3b. The degradation of PNT by PS could be neglected (＜5%), revealing that PNT would not to be hydrolyzed under dark condition and PS will not be activated or undergo oxidative reaction with PNT.
2.3. Analytical methods Concentrations of PNT, NB, BA, and PNA were determined by an ultra-performance liquid chromatography (UPLC) system (Waters, USA) with an Acqutiy BEH-C18 column (1.7 μm, 2.1 × 100 mm) and a UV–vis detector. The concentrations of PNT were determined at 245 nm with an eluent of water, acetonitrile, and methanol with a ratio of 70:20:10 (v/ 2
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3.2. Effect of pH
kinetics (Fig. 2a), revealing that HO* was generated in system. A highest kobs of 7.3 × 10-2 min− 1 for NB degradation was observed at pH 7.0, with calculated steady concentrations of 2.59 × 10-13 M for HO* ([HO*]ss) according to Eq. (7). The concentrations of BA decreased over time followed the pseudo-first order kinetic reaction as well (Fig. 2b). The kobs of BA degradation was 3.7 × 10-1 min− 1 at pH 7.0. Assuming that BA degradation was totally resulted from HO* in system, the calculated steady concentrations of HO* ([HO*]ss) were 1.18 × 10-12 M (Eq. (8)), higher than the value of 2.66 × 10-13 M obtained by NB results. The results indicated that HO* as well as SO⋅-4 were generated in system and responsible for BA degradation. The [HO*]ss were calculated as 2.41 × 10-13, 2.59 × 10-13, and 2.50 × 10-13 M at pH 5.5, 7.0, and 8.5, respectively.
The effect of pH on PNT degradation in solar/PS system is shown in Fig. 1. The elimination of PNT increased significantly and reached 100% within 10 min when PS was combined with solar at pH ranges of 5.5–8.5. The degradation of PNT followed a pseudo-first order kinetics, and a synergistic removal of PNT was observed for three pHs. The calculated kobs of PNT was 5.5 × 10-1, 6.4 × 10-1, and 5.2 × 10-1 min− 1 for pH 5.5, 7.0, and 8.5, respectively, which are higher than that in solar system. Neutral pH was more beneficial than acidic or alkaline conditions ac cording to the following aspects: Firstly, acidic conditions promote the transformation of PS into H2SO-8 (Eq. (5)), and H2SO-8 hardly transfer into SO⋅-4 due to more concentrations of H+ (Eq. (6)), which inhibit PNT degradation. Meanwhile, phosphate buffer had a stronger scavenging effect on HO* and SO⋅-4 as pH increased. The second-order rate constants 6 − 1 − 1 ⋅of HPO2and 1.5 × 105 4 toward SO4 and HO* were 1.2 × 10 M s − 1 − 1 M s , respectively [25], much higher than values of H2PO-4 toward SO⋅-4 (7.2 × 104 M− 1s− 1) and HO* (2.0 × 104 M− 1s− 1). The percentage of HPO24 increased as pH increase, thus lowering the amount of radicals available to PNT.
(6)
H2 SO-8 →SO⋅4- + SO24- + H+
(7)
kobs-BA = [HO*]ss⋅kOH⋅-BA
(8)
Meanwhile, reactive oxidative species (ROS) could be determined by alcohol quenching experiments (Fig. 3). tert-butyl alcohol (TBA) reacts with HO* and SO⋅-4 , with second-pseudo rate constants of 3.8–7.6 × 108 and 4.0–9.1 × 105 M− 1⋅s− 1 [29]. TBA could scavenge HO* effectively while could not scavenge easily SO⋅-4 in system. TBA with different concentrations were added in solar/PS system (Fig. 3). The removal of NB decreased from 93.1% to 11.5% rapidly with increasing dosages of TBA. Similarly, as concentrations of TBA increase from 0 μM to 100 μM, the degradation of BA was inhibited by TBA as well. This result further corroborated that HO* and SO⋅-4 were generated from persulfate active by solar in system and these ROS were almost quenched by TBA.
(5)
S2 O28- + H+ →H2 SO-8
kobs-NB = [HO*]ss⋅kOH⋅-NB
SO24
The consumption of persulfate and the formation of in solar/PS experiment system were evaluated in Fig. S5. This unveiled the based2mediated transformation of S2O28 to SO4 in the system. Persulfate was mostly consumed from 69.5 mg/L to 57.9 mg/L at pH 5.5, 71.1 mg/L to 64.7 mg/L at pH 7.0 and 70.1 mg/L to 68.2 mg/L at pH 8.5 in 30 min. The consume ratios of persulfate were calculated to be 16.7%, 8.9% and 2.3%, respectively. Persulfate was consumed rapidly in acidic condition. Meanwhile, concentrations of formed SO24 were close to the theoretical value accordingly and the summation of PS and SO24 kept approximately stable.
3.4. Contribution of active components As discussed in section 3.2, HO*, SO⋅-4 , and other active components were possibly involved in system. The contributions of HO*, SO⋅-4 , and other active components for PNT degradation were calculated according to Eq. (9). Where kPNT’ is the kobs of PNT at different pH in Solar/PS system (min− 1), kHO*- PNT’ is the contribution of HO* to PNT degradation (min− 1), k SO4⋅–PNT’ and kother-PNT’ are the contribution of SO⋅-4 and other active components to PNT degradation (min− 1). Their proportion is the contribution of each active component to the whole PNT degradation. To calculate the contribution of free reactive radicals in PNT removal, probing compounds including NB and BA were employed in solar/PS system (Fig. 4). The degradation of PNT followed a pseudo-first order kinetics, with the calculated kobs of PNT was 4.4 × 10-1, 4.2 × 10-1, and 2.9 × 10-1 min− 1 for pH 5.5, 7.0, and 8.5, respectively. Meanwhile the kobs of NB and BA were calculated for different pH values from Fig. 4 b-c. The contribution of HO* degrading PNT was determined with applying the probe of NB. The kobs of NB was 1.1 × 10-1 min− 1 at pH 7.0, with [HO*]ss of 3.88 × 10-13 M according to Eq. 8. Then kHO*- PNT’ of 1.94 × 10-3 s− 1 can be calculated by taking the [HO*]ss and the secondorder rate constants of HO* toward PNT (kOH⋅-PNT = 4.99 × 109 M− 1⋅s− 1) [30] according to Eq. (10). Meanwhile, the reaction rate constant of PNT (kobs) was 7.08 × 10-3 s− 1 at pH 7.0. Finally, the contribution ratios of HO* in removing PNT could be calculated as kOH⋅-PNT’/ kobs, which turned out to be 26.9%, 27.4%, and 17.6% for pH 5.5, 7.0, and 8.5, respectively. The contribution of SO⋅-4 was determined by probe of BA. It was calculated from Fig. 4c that [HO*]ss was 3.88 × 10-13 M and the degradation rate of BA (kobs) was 2.2 × 10-1 min− 1 at pH 7.0. According to Eq. (11) and Eq. (12) the steady-state concentration of SO⋅-4 ([SO⋅-4 ]ss) was determined to be 2.49 × 10-12, 1.38 × 10-12, and 1.04 × 10-12 M at pH 5.5, 7.0, and 8.5, respectively. Then kSO4⋅–PNT’ could be calculated by taking the [SO⋅-4 ]ss and the second-order rate constants of SO⋅-4 toward PNT (kSO4⋅–PNT = 5.64 × 108 M− 1⋅s− 1) into Eq. (13) [30]. Finally, the contribution ratios of SO⋅-4 in PNT degradation could be calculated as kSO4⋅–PNT’/kobs, which turned out to be 19.2%, 11.0%, and 12.3%
3.3. Radical identification NB reacts toward HO* with rate constants (kHO*-NB) of 4.7 × 109 M− 1s− 1, while the reaction between NB with SO⋅-4 can be ignored [26]. Whereas, BA can simultaneously react with HO* (kHO*-BA = 5.9 × 109 M− 1s− 1 [27]) and SO⋅-4 (kSO4⋅- -BA = 1.2 × 109 M− 1s− 1 [28]). Experiments were conducted with the addition of NB and BA for identification of the probable radical species formed in solar/PS system. The concentrations of NB decreased with time and the results well fits the pseudo-first-order
Fig. 1. Effect of pH on degradation of PNT by Solar/PS. Reaction condition: [PNT]0 = 1 μM, [PS] = 0.3 mM, 10 mM PBS, pH 5.5, 7.0, and 8.5, T = 25℃, Solar. 3
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Fig. 2. Degradation and determination of rate constants of (a) NB (b) BA with solar/PS under different buffer pHs. Reaction condition: [NB]0 = [BA]0 = 1 μM, [PS] = 0.3 mM, 10 mM PBS, pH 5.5, 7.0, and 8.5, T = 25℃, Solar.
Fig. 3. Effect of TBA concentrations on degradation of probes: (a) NB (b) BA. Reaction condition: [NB]0 = [BA]0 = 1 μM, [PS] = 0.3 mM, pH = 7.0 with phosphate buffer, T = 25℃, Solar, [TBA]0 = 0, 0.5 ,1 ,20 ,100 μM.
respectively at pH 5.5, 7.0, 8.5, respectively. The contribution ratio of solar in PNT degradation were 2.1%, 1.0%, and 3.0% at pH 5.5, 7.0, 8.5, respectively (Section 3.1). Therefore, the contributions of the remaining active components could be obtained by subtracting that of the other three species, according to Eq. (11). The remaining contributions of the remaining active species in PNT degra dation were 51.8%, 60.7%, and 67.1% at pH 5.5, 7.0, and 8.5 respec tively. The contributions of four reactive species were summarized in Fig. 5, expressed as the absolute values of overall observed rate con stants. With pH increasing, the overall observed rate constants by solar, HO*, and SO⋅-4 remained around 9.4 × 10-2 min− 1, whereas the remaining active components contributed the highest value of 2.6 × 10-1 min− 1 for PNT degradation at pH 7.0, which would mostly be caused by superoxide radical (⋅O–2) or singlet oxygen (1O2). kPNT’=kHO*-PNT’+kSO4⋅–PNT’+kSolar-PNT’+krest-PNT’
3.5. Dbps formation during solar/PS pre-oxidation with post chlorine In the drinking water treatment plant, residual PPCPs during peroxidation will react with disinfectants such as chlorine in disinfection process, producing a large number of genotoxic, cytotoxic and carci nogenic disinfection byproducts (DBPs), such as trihalomethanes (THMs) and haloacetic acids (HAA) [31–33]. The (THMs formation during chlorination with or without solar/PS pre-oxidation systems were evaluated (Table.1). In the absence of solar/PS pre-oxidation, the concentration of THMs was determined to be 16.0 μg⋅L-1 at pH 7.0. Among the four monitored THMs, the proportion of trichloromethane (TCM) accounts for the highest of 15.4 μg⋅L-1, followed by bromodi chloromethane (BDCM) of 0.6 μg⋅L-1. For solar/PS pre-oxidation system, the concentration of THMs decreased to 14.7 μg⋅L-1. Among the four THMs, TCM was more prevalent in solar/PS pre-oxidation system, with concentration of 14.1 μg⋅L-1, followed by BDCM of 0.6 μg⋅L-1. The decrease of THMs with solar/PS irradiation at pH 7.0 was due to the decrease of DBPs precursors, such as low-molecule organics, after HO* or SO⋅-4 attack. In addition, the mineralization rate of the system was tested in the study. The mineralization ratios of PNT for solar/PS system
(9)
kHO*-PNT’=kHO*-PNT⋅[HO*]ss
(10)
kobs-SO4⋅-’=kobs-BA’-kobs-HO*’
(11)
kobs-SO4⋅-’=kSO4⋅–BA⋅[SO⋅-4 ]ss
(12)
kSO4⋅–PNT’=kSO4⋅–PNT⋅[SO⋅-4 ]ss
(13) 4
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Fig. 4. Degradation and determination of first-order rate constants of PNT (a), NB (b) and BA (c) with solar/PS under different buffer pHs. Reaction condition: [PNT]0 = [NB]0 = [BA]0 = 1 μM, [PS] = 0.3 mM, 10 mM PBS, pH 5.5, 7.0, and 8.5, T = 25℃, Solar. Table 1 Concentration and toxicity of the THMs detected in this study. Condition
Compound
Concentration (μg/L)
LC50 value (M)
Toxicity
Chlorine
Trichloromethan
15.3
Bromodichloromethane
0.6
Chlorodibromomethane
NA
1.34 × 10-5 4.37 × 10-7 NA
Tribromomethane
NA
Trichloromethan
14.1
Bromodichloromethane
0.6
Chlorodibromomethane
NA
Tribromomethane
NA
9.62 × 10-3 1.15 × 10-2 5.36 × 10-3 3.96 × 10-3 9.62 × 10-3 1.15 × 10-2 5.36 × 10-3 3.96 × 10-3
Solar/PS as preoxidation with post chlorine
Fig. 5. Contribution rates of active components in the degradation of PNT. Reaction condition: [PNT]0 = [NB]0 = [BA]0 = 1 μM, [PS] = 0.3 mM, 10 mM PBS, pH 5.5, 7.0, and 8.5, T = 25℃, Solar.
NA 1.23 × 10-5 4.37 × 10-7 NA NA
DBPs. Fig. S7 showed the effect about frontier electro densities (FED) of the highest occupied molecular orbital (HOMO) on the atoms of PNT. Du et al. [34] proposed that the possible sites of chlorine attack on the ar omatic rings could be predicted by calculating the sum of Hammett
at different pHs were in range of 14.3%-35.6% (Fig. S6) at reaction time of 10 min. Therefore, it was confirmed that intermediates are formed in the reaction, which was consistent with the experimental results of 5
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∑
constant values ( σ) for the substituents present. It was reported that ∑ the site with minimum σ was the most frequently attacked by chlorine [35]. Observing the unsubstituted ortho and meta positions to the phenolic function (sites 1 and 2) of PNT (Fig. S7), the most probable sites of chlorine attack on PNT were the meta to the benzamide (6C–7C) [36]. TCM would probably be formed from the attack of benzene ring [37]. The changes of DBPs cytotoxicity for THMs with or without solar/PS were calculated (Table. 1) according to LC50 and 50% tail DNA values of THMs in this research [38,39]. The calculated cytotoxicity decreased from 1.38 × 10-5 to 1.27 × 10-5 after solar/PS pre-oxidation, as the decreased concentrations of TCM.
Table 2 economic calculation in the Solar system. kobs, min−
pH = 5.5
0.439 ± 0.03 0.425 ± 0.03 0.286 ± 0.02
pH = 7.0 pH = 8.5
1
T, h
V, m3
P, kW
EE/O, kWh/m3/ order
0.087
2.5 × 10-5 2.5 × 10-5 2.5 × 10-5
1.19 × 10-3 1.19 × 10-3 1.19 × 10-3
0.069
0.090 0.134
0.072 0.106
screened, and the mechanism of degradation on PNT with ROS should be figured out in future.
3.6. Economic calculation The efficiency of the solar/PS process in the degradation of PNT was evaluated by electrical energy per order (EE/O), a parameter recom mended by Photochemistry Commission of International Union of Pure and Applied Chemistry (IUPAC). EE/O is defined as the kilowatt-hour (kWh) of electricity required to degrade pollutant of one order of magnitude [40,41]. EE/O = Pt/(60V)
Solar/PS system
CRediT authorship contribution statement Chaoqun Tan: Writing - review & editing, Supervision. Xinchi Jian: Data curation. Haotian Wu: Writing - original draft. Tianyu Sheng: . Kechun Sun: . Haiying Gao: Writing - review & editing.
(14)
Declaration of Competing Interest
Where P is the total electrical power of the system, t is the operating time and V is the volume of the solution. The quantum yield of the solar system was 1.14 × 10-4 E⋅m− 2⋅s− 1 with calculated electrical power of 1.19 × 10-3 kW. The calculated EE/O were 0.069. 0.072, and 0.106 kWh/m/order at pH 5.5, 7.0 and 8.5, respectively (Table. 2). The elec trical energy per order in the solar/PS system were in range of 0.069 ~ 0.106 kWh/m/order, which were close to the lower range of 0.017 ~ 2.26 kWh/m/order in Guo et al. experiment in the UV254 system [42]. The EE/O results suggest that solar/PS system are more economical in degrading pollutants. Table. 2 To evaluate the degradation performance of PNT in actual water, experiments were conducted in the wastewater influent, effluent, river and tap water samples. Fig.S8 showed the degradation of PNT in different actual water. PNT degradation was totally inhabited in wastewater influent which could be attributed to the existence of various competitive substances [43]. Decomposition of PNT was less than 3% and the kobs of PNT was 4.1 × 10-3 min− 1. Although decom position of PNT in effluent and river was restrained comparing the tap water, PNT were degrade to 80% and 90 within 10 min, respectively. The kobs of PNT was calculated to 1.3 × 10-1 ~ 6.8 × 10-1 min− 1. It indicated that the Solar/PS system had broad application prospects in actual water treatment process. Meanwhile, the EE/O values in matrix from different actual water were measured in range of 0.045 ~ 7.417 kWh/m/order (Table S3), which is close to the results reported by Zhou et al. [44].
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgement This work was financially supported by the National Natural Science Foundation of China (No.52070041, 51608109), China; Natural Science Foundation of Jiangsu Province (No. BK20160675), China; the Priority Academic Program Development of Jiangsu Higher Education In stitutions, the Fundamental Research Funds for the Central Universities, the Research Fund of Key Laboratory of Yangze River Water Environ ment, Ministry of Education (Tongji University), China. In addition, Chaoqun Tan wishes to thank Zhishan Youth Scholar Program Of SEU. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.seppur.2020.117851. References [1] Y. Wang, et al., Competitive adsorption of ppcp and humic substances by carbon nanotube membranes: Effects of coagulation and ppcp properties, Sci. Total Environ. 619 (2018) 352–359. [2] I. Tamura, et al., Contribution of pharmaceuticals and personal care products (ppcps) to whole toxicity of water samples collected in effluent-dominated urban streams, Ecotoxicol. Environ. Saf. 144 (2017) 338–350. [3] A.J. Ebele, M. Abou-Elwafa Abdallah, S. Harrad, Pharmaceuticals and personal care products (ppcps) in the freshwater aquatic environment, Emerging Contaminants 3 (1) (2017) 1–16. [4] D. Simazaki, et al., Occurrence of selected pharmaceuticals at drinking water purification plants in japan and implications for human health, Water Res. 76 (2015) 187–200. [5] B.P. Gumbi, et al., Detection and quantification of acidic drug residues in south african surface water using gas chromatography-mass spectrometry, Chemosphere 168 (2017) 1042–1050. [6] F. Qi, W. Chu, B. Xu, Comparison of phenacetin degradation in aqueous solutions by catalytic ozonation with cufe2o4 and its precursor: Surface properties, intermediates and reaction mechanisms, Chem. Eng. J. 284 (2016) 28–36. [7] A. Borgeat, et al., The effect of nonsteroidal anti-inflammatory drugs on bone healing in humans: A qualitative, systematic review, J. Clin. Anesth. 49 (2018) 92–100. [8] M. Cheng, et al., Hydroxyl radicals based advanced oxidation processes (aops) for remediation of soils contaminated with organic compounds: A review, Chem. Eng. J. 284 (2016) 582–598. [9] E.A. Betterton, M.R. Hoffmann, Kinetics and mechanism of the oxidation of aqueous hydrogen-sulfide by peroxymonosulfate, Environ. Sci. Technol. 24 (12) (1990) 1819–1824.
4. Conclusion The work demonstrated that the degradation of PNT was enhanced by PS in solar irradiation system. The removal of PNT reached 100% within 10 min in pH range of 5.5–8.5. Neutral pH was more beneficial than acidic or alkaline conditions and the kobs of PNT was calculated to 6.4 × 10-1 min− 1 for pH 7.0 because of effect with H+ and HPO24 . The consume ratios of PS were 3%-17% for PNT degradation in Solar/PS system. HO*, SO⋅-4 , and related ROS were produced and responsible for PNT degradation in the system. The contribution of HO*, SO⋅-4 , and related ROS to degrading PNT were 27.4%, 11.0%, and 60.7%, respec tively. The concentration and toxicity of THMs decreased and the mineralization rate of PNT were in range of 14.3%-35.6% with solar/PS pre-oxidation. Moreover, the EE/O values of solar/PS system were in range of 0.069 ~ 0.106 kWh/m/order in pH range of 5.5–8.5. Solar/PS system had broad application prospects in actual water treatment pro cess. Based on the results obtained herein, related ROS should be 6
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7
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Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur
Kinetics degradation of phenacetin by solar activated persulfate system Chaoqun Tan *, Xinchi Jian , Haotian Wu , Tianyu Sheng, Kechun Sun, Haiying Gao School of Civil Engineering, Southeast University, Nanjing 210096, China
A R T I C L E I N F O
A B S T R A C T
Keywords: Kinetics Phenacetin Solar Persulfate Trihalomethanes
Kinetic degradation of phenacetin (PNT) by solar activated persulfate (PS) system was evaluated in study. The decomposition of PNT well fitted with a pseudo-first order kinetic pattern, and the exceptional removal per formance towards PNT (100%) was obtained in the presence of solar irradiation (1.14 × 10-4 E⋅ m− 2⋅ s− 1) and 0.3 mM PS at pH 7.0 in 10 min. The consume ratios of persulfate were calculated to be 2.3~16.7%. The steadystate concentrations of hydroxyl radicals ([HO*]ss) and sulfate radicals ([SO-4⋅]ss) were calculated to be (2.41~2.59) × 10-13 M and (3.75~4.06) × 10-12 M by probes of nitrobenzene (NB) and benzoic acid (BA), respectively. The contribution of HO* and SO-4⋅ accounts for 27.4% and 11.0% in degradation of PNT. The formation of typical trihalomethanes (THMs) after pre-oxidation of solar/PS was evaluated. The concentration of total THMs decreased from 16 μg⋅L-1 to 15.4 μg⋅L-1 through pre-oxidation, with cytotoxicity decreased from 1.38 × 10-5 to 1.27 × 10-5. The calculated electrical energy per order (EE/O) in solar/PS were in range of 0.069~0.106 kWh/m/order.
1. Introduction Recent years, pharmaceuticals and personal care products (PPCPs) have been detected frequently in wastewater, surface water, ground water, and drinking water in the range of ng⋅L-1 to μg⋅L-1, arousing widespread attention throughout the world [1,2]. Most pharmaceuticals are likely available in waters due to their widespread consumption including human and animal ingestion. Phenacetin (PNT), as a kind of typical PPCPs with anti-inflammatory and analgesic effects, was frequently detected in surface water. PNT had characteristics with high solubility, multiple pKa values and resistant degradation in traditional water treatment [3]. The concentration of PNT was detected to be up to 44.0 ng⋅L-1 [4] and 68.3 μg⋅L-1 [5] in drinking water purification plants and dam inlet, respectively. Therefore, it is urgent to develop high effective technologies to degrade PNT. Advanced oxidation processes (AOPs) arose great concern in water treatment, as a great number of reactive oxygen species (ROS) were generated and might be able to decompose or mineralize the recalcitrant organic contaminant [6–8]. Compared to traditional AOPs with hy droxyl radicals (HO*) as the main ROS in system, sulfate radicals (SO-4⋅) based AOPs are new technologies developed in recent years. Persulfates include peroxymonosulfate (PMS, E0 = 1.82 V [9]) and persulfate (PS, E0 = 2.01 V [10]), which are derivatives of H2O2 after one or two of hydrogen atom is replaced by SO3, respectively. Persulfates could be
activated to SO-4⋅ under the conditions of transition metal, light, and heat [11]. Organic compounds are readily degraded by SO-4⋅. Compared with heat, transition metals, and ultrasonic, UV activated PS technologies possess mild reaction conditions, highly degradation, and no secondary pollution [12]. Sulfamethazine was completely degraded in 2 min with PS concentration of 10 mM and UV of 254 nm in UV254/PS system. The sulfamethazine degradation followed pseudo-first order kinetics and SO⋅-4 was the dominant ROS identified in UV254/PS system like Eq. 1–2 [13]. Triclosan was reported to be effectively removed by SO⋅-4 in UV254/PS system [14] as well, and the kobs of tri closan degradation in UV254/PS was 4.13 times higher than that in UV254/H2O2 process, indicating that UV254 activated PS system could degrade pollutants more effectively than H2O2. S2 O28 - → 2SO⋅−4
(1)
SO⋅−4 + H2 O → SO24 - + OH⋅
(2)
hv
Although PS could be activated by UV irradiation of 254 nm to generate SO⋅-4 , UV254 based techniques are restricted in practical appli cations owing to the requirement of high energy input. Therefore, it is imperative to develop low-cost, efficient, and environmentally-friendly AOPs for environmental clean-up. Recently, sunlight for photo catalytic systems, with spectrum in ranges of 290–800 nm, have attracted increasing interest [15]. Gao et al. [16] reported that the
* Corresponding author. E-mail address: [email protected] (C. Tan). https://doi.org/10.1016/j.seppur.2020.117851 Received 13 July 2020; Received in revised form 8 September 2020; Accepted 3 October 2020 Available online 7 October 2020 1383-5866/© 2020 Elsevier B.V. All rights reserved.
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visible-light-excited Rhodamine B (RhB) could activate PS to generate SO⋅-4 . The RhB removal markedly increased from 40% in dark condition to 80% in Vis/PS system. The excited state of dye molecule could react with PS, resulting in the formation of SO⋅-4 via an electron-transfer pathway. The combination of PMS and solar radiation (λ > 300 nm) resulted in effective removal of bezafibrate by ROS generated in solar/ PMS system [17]. However, little is known about the activation of PS in the presence of solar irradiation. Accordingly, the purpose of this study is to investigate the kinetic degradation of phenacetin (PNT) in solar/PS system. The identification and contribution of reactive oxygen species (ROS) in system are assessed by probes of nitrobenzene (NB) and benzoic acid (BA). Moreover, for mation of disinfection by-products of trihalomethanes (THMs) after preoxidation of solar/PS and the electrical energy per order (EE/O) in system were evaluated as well.
v/v) at a flow rate of 0.25 mL/min. The concentrations of PNA were quantified at 315 nm with an eluent of water and methanol with a ratio of 25:75 (v/v) at a flow rate of 0.15 mL/min. The concentrations of NB and BA were measured at 270 and 227 nm with an eluent of 1% phos phoric acid and methanol with a ratio of 55:45 (v/v) at a flow rate of 0.15 mL/min. For the analysis of THMs after pre-oxidation of solar/PS, 40.0 mL of the solution after solar/PS of oxidation was collected and transferred into a brown glass bottle and 0.2 mM NaOCl were added to the sample. The bottle was kept in the dark at room temperature for 12.0 h, afterwards the sample was transferred into a headspace-free brown glass bottle and 0.5 g ascorbic acids were added for head space gas chromatography method [20]. The analyses were carried out on an HP (Agilent Technologies, Palo Alto, CA) 6890 gas chromatograph5973 N mass selective detector equipped with a 7694 headspace auto sampler and an HP-5MS fused silica capillary column (30 m × 0.25 mm × 0.25 μm film thickness) [21,22]. Persulfate concentration was measured with a rapid spectrophoto metric determination by UV–vis spectrophotometer (HACH, DR6000) using potassium iodide as the indicator at 352 nm [23]. Meanwhile, dissolved sulfate concentrations were measured with spectrophotometry using the Ba2+-based sulfaVer4 method (HACH module No.8051).
2. Experimental section 2.1. Chemicals and materials Chemicals were prepared with analytical standard grade chemicals and distilled water. Phenacetin (PNT, ≥98%) and p-Nitroanisole (PNA, ≥98%) were purchased from Aladdin. Pyridine (PYR, ≥99%) was pur chased from Shanghai Macklin Biochemical Technology Co., Ltd. Ben zoic acid (BA, ≥99%), nitrobenzene (NB, ≥99%), sodium dihydrogen monobasic monohydrate (≥99%), and sodium phosphate dibasic (≥99%) were obtained from Yonghua Chemical Reagent Co., Ltd., China. Persulfate (PS, ≥99%) was purchased from Nanjing Reagent. Methanol and acetonitrile of UPLC grade were purchased from SigmaAldrich. Tert-Butanol (TBA, ≥99%). The rest of chemicals (≥98%) were obtained from Energy Chemical. For actual water experiment, influent and effluent wastewater sam ples were all collected from one sewage treatment plant in Nanjing and river water samples were taken from the Dongshili Changgou, a tribu tary of the Yangtze River located in North Nanjing, and tap water were sampled from municipal pipeline. The all water quality parameters were shown in Table S1.
2.4. Data processing methods The overall rate law for the degradation of pollutants could be expressed as Eq. (3): kobs = -
dln(C/C0 ) dt
(3)
where kobs is the overall kinetic rate expression of the target species in the reaction system (min− 1), C is the concentration of target species at time t (M), and C0 is the initial concentration of target species (M). The toxicity of each disinfection by-products (DBPs) could be ob tained by Eq. (4), where c(DBPs) is the concentration of each DBPs (M), LC50 is its semi-lethal concentration (M) and M(DBPs) is its relative molecular weight. Cytotoxicity =
2.2. Experimental device and procedures
c(DBPs)/M(DBPs) LC50
(4)
3. Results and discussion
The photochemical experiments were conducted with an ultra-high voltage short-arc xenon lamp to simulate solar light (500 W, Perfect Light Co., China). The photon fluence rate of this solar module was measured by chemical actinometry of p-Nitroanisole (PNA)/pyridine (PYR) actinometer [18,19]. The quantum yield of the solar device was evaluated to be 1.14 × 10-4 E⋅ m− 2⋅ s− 1 by the method described in the Supplementary Information (SI) (Test S1, Fig. S1-S2). The light pro ceeded through the collimated tube down onto a 50.0 mL sample magnetically stirred within a cylindrical glass dish and the reaction temperature was maintained at ambient temperature (25 ± 1℃). The reaction solution contains 1.0 μМ target pollutant of PNT, 10 mM phosphate buffer agent and 0.3 mM persulfate for three pHs (5.5, 7.0, and 8.5). The lamp was warmed up at least 15 min prior to the experiments and the reaction was initiated by exposing the reactor to solar irradiation. During the sampling intervals (0, 5, 10, 20, and 30 min), 1.0 mL solution was sampled into the vials prefilled with 10.0 μL sodium thiosulfate (3.0 M) to terminate the reaction. 1.0 μM of NB and BA was added into the system and employed as probes at different pHs.
3.1. PNT degradation in solar alone and PS alone system The removal of PNT in solar and PS system was shown in Fig. S3. The decomposition of PNT were 13%, 26.3%, and 25.8% at pH 5.5, 7.0, and 8.5 in 30 min, respectively. The data of ln(C/C0) fell on a straight line with time (inner in Fig. S3a), revealing that the degradation of PNT in solar system fitted well with pseudo-first order kinetic pattern. The pseudo-first order kinetic degradation rate constants (kobs) were deter mined to be 4.2 × 10-3, 9.4 × 10-3, and 8.7 × 10-3 min− 1 at pH 5.5, 7.0, and 8.5, respectively. The results indicated that solar irradiation could lead to partial decomposition of PNT. To screen the formative ROS, probes of NB and BA were added to the solar system to evaluated for mation of ROS. As shown in Fig. S4, the degradation of NB and BA was less than 8% in 15 min, revealing that decomposition of PNT in solar system might be caused by powerful light energy and the presence of pharmaceutical weak covalent bonds [24]. In the absence of solar, the time-dependent trend of PNT degradation by PS alone in pH ranges of 5.5–8.5 was presented in Fig. S3b. The degradation of PNT by PS could be neglected (＜5%), revealing that PNT would not to be hydrolyzed under dark condition and PS will not be activated or undergo oxidative reaction with PNT.
2.3. Analytical methods Concentrations of PNT, NB, BA, and PNA were determined by an ultra-performance liquid chromatography (UPLC) system (Waters, USA) with an Acqutiy BEH-C18 column (1.7 μm, 2.1 × 100 mm) and a UV–vis detector. The concentrations of PNT were determined at 245 nm with an eluent of water, acetonitrile, and methanol with a ratio of 70:20:10 (v/ 2
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3.2. Effect of pH
kinetics (Fig. 2a), revealing that HO* was generated in system. A highest kobs of 7.3 × 10-2 min− 1 for NB degradation was observed at pH 7.0, with calculated steady concentrations of 2.59 × 10-13 M for HO* ([HO*]ss) according to Eq. (7). The concentrations of BA decreased over time followed the pseudo-first order kinetic reaction as well (Fig. 2b). The kobs of BA degradation was 3.7 × 10-1 min− 1 at pH 7.0. Assuming that BA degradation was totally resulted from HO* in system, the calculated steady concentrations of HO* ([HO*]ss) were 1.18 × 10-12 M (Eq. (8)), higher than the value of 2.66 × 10-13 M obtained by NB results. The results indicated that HO* as well as SO⋅-4 were generated in system and responsible for BA degradation. The [HO*]ss were calculated as 2.41 × 10-13, 2.59 × 10-13, and 2.50 × 10-13 M at pH 5.5, 7.0, and 8.5, respectively.
The effect of pH on PNT degradation in solar/PS system is shown in Fig. 1. The elimination of PNT increased significantly and reached 100% within 10 min when PS was combined with solar at pH ranges of 5.5–8.5. The degradation of PNT followed a pseudo-first order kinetics, and a synergistic removal of PNT was observed for three pHs. The calculated kobs of PNT was 5.5 × 10-1, 6.4 × 10-1, and 5.2 × 10-1 min− 1 for pH 5.5, 7.0, and 8.5, respectively, which are higher than that in solar system. Neutral pH was more beneficial than acidic or alkaline conditions ac cording to the following aspects: Firstly, acidic conditions promote the transformation of PS into H2SO-8 (Eq. (5)), and H2SO-8 hardly transfer into SO⋅-4 due to more concentrations of H+ (Eq. (6)), which inhibit PNT degradation. Meanwhile, phosphate buffer had a stronger scavenging effect on HO* and SO⋅-4 as pH increased. The second-order rate constants 6 − 1 − 1 ⋅of HPO2and 1.5 × 105 4 toward SO4 and HO* were 1.2 × 10 M s − 1 − 1 M s , respectively [25], much higher than values of H2PO-4 toward SO⋅-4 (7.2 × 104 M− 1s− 1) and HO* (2.0 × 104 M− 1s− 1). The percentage of HPO24 increased as pH increase, thus lowering the amount of radicals available to PNT.
(6)
H2 SO-8 →SO⋅4- + SO24- + H+
(7)
kobs-BA = [HO*]ss⋅kOH⋅-BA
(8)
Meanwhile, reactive oxidative species (ROS) could be determined by alcohol quenching experiments (Fig. 3). tert-butyl alcohol (TBA) reacts with HO* and SO⋅-4 , with second-pseudo rate constants of 3.8–7.6 × 108 and 4.0–9.1 × 105 M− 1⋅s− 1 [29]. TBA could scavenge HO* effectively while could not scavenge easily SO⋅-4 in system. TBA with different concentrations were added in solar/PS system (Fig. 3). The removal of NB decreased from 93.1% to 11.5% rapidly with increasing dosages of TBA. Similarly, as concentrations of TBA increase from 0 μM to 100 μM, the degradation of BA was inhibited by TBA as well. This result further corroborated that HO* and SO⋅-4 were generated from persulfate active by solar in system and these ROS were almost quenched by TBA.
(5)
S2 O28- + H+ →H2 SO-8
kobs-NB = [HO*]ss⋅kOH⋅-NB
SO24
The consumption of persulfate and the formation of in solar/PS experiment system were evaluated in Fig. S5. This unveiled the based2mediated transformation of S2O28 to SO4 in the system. Persulfate was mostly consumed from 69.5 mg/L to 57.9 mg/L at pH 5.5, 71.1 mg/L to 64.7 mg/L at pH 7.0 and 70.1 mg/L to 68.2 mg/L at pH 8.5 in 30 min. The consume ratios of persulfate were calculated to be 16.7%, 8.9% and 2.3%, respectively. Persulfate was consumed rapidly in acidic condition. Meanwhile, concentrations of formed SO24 were close to the theoretical value accordingly and the summation of PS and SO24 kept approximately stable.
3.4. Contribution of active components As discussed in section 3.2, HO*, SO⋅-4 , and other active components were possibly involved in system. The contributions of HO*, SO⋅-4 , and other active components for PNT degradation were calculated according to Eq. (9). Where kPNT’ is the kobs of PNT at different pH in Solar/PS system (min− 1), kHO*- PNT’ is the contribution of HO* to PNT degradation (min− 1), k SO4⋅–PNT’ and kother-PNT’ are the contribution of SO⋅-4 and other active components to PNT degradation (min− 1). Their proportion is the contribution of each active component to the whole PNT degradation. To calculate the contribution of free reactive radicals in PNT removal, probing compounds including NB and BA were employed in solar/PS system (Fig. 4). The degradation of PNT followed a pseudo-first order kinetics, with the calculated kobs of PNT was 4.4 × 10-1, 4.2 × 10-1, and 2.9 × 10-1 min− 1 for pH 5.5, 7.0, and 8.5, respectively. Meanwhile the kobs of NB and BA were calculated for different pH values from Fig. 4 b-c. The contribution of HO* degrading PNT was determined with applying the probe of NB. The kobs of NB was 1.1 × 10-1 min− 1 at pH 7.0, with [HO*]ss of 3.88 × 10-13 M according to Eq. 8. Then kHO*- PNT’ of 1.94 × 10-3 s− 1 can be calculated by taking the [HO*]ss and the secondorder rate constants of HO* toward PNT (kOH⋅-PNT = 4.99 × 109 M− 1⋅s− 1) [30] according to Eq. (10). Meanwhile, the reaction rate constant of PNT (kobs) was 7.08 × 10-3 s− 1 at pH 7.0. Finally, the contribution ratios of HO* in removing PNT could be calculated as kOH⋅-PNT’/ kobs, which turned out to be 26.9%, 27.4%, and 17.6% for pH 5.5, 7.0, and 8.5, respectively. The contribution of SO⋅-4 was determined by probe of BA. It was calculated from Fig. 4c that [HO*]ss was 3.88 × 10-13 M and the degradation rate of BA (kobs) was 2.2 × 10-1 min− 1 at pH 7.0. According to Eq. (11) and Eq. (12) the steady-state concentration of SO⋅-4 ([SO⋅-4 ]ss) was determined to be 2.49 × 10-12, 1.38 × 10-12, and 1.04 × 10-12 M at pH 5.5, 7.0, and 8.5, respectively. Then kSO4⋅–PNT’ could be calculated by taking the [SO⋅-4 ]ss and the second-order rate constants of SO⋅-4 toward PNT (kSO4⋅–PNT = 5.64 × 108 M− 1⋅s− 1) into Eq. (13) [30]. Finally, the contribution ratios of SO⋅-4 in PNT degradation could be calculated as kSO4⋅–PNT’/kobs, which turned out to be 19.2%, 11.0%, and 12.3%
3.3. Radical identification NB reacts toward HO* with rate constants (kHO*-NB) of 4.7 × 109 M− 1s− 1, while the reaction between NB with SO⋅-4 can be ignored [26]. Whereas, BA can simultaneously react with HO* (kHO*-BA = 5.9 × 109 M− 1s− 1 [27]) and SO⋅-4 (kSO4⋅- -BA = 1.2 × 109 M− 1s− 1 [28]). Experiments were conducted with the addition of NB and BA for identification of the probable radical species formed in solar/PS system. The concentrations of NB decreased with time and the results well fits the pseudo-first-order
Fig. 1. Effect of pH on degradation of PNT by Solar/PS. Reaction condition: [PNT]0 = 1 μM, [PS] = 0.3 mM, 10 mM PBS, pH 5.5, 7.0, and 8.5, T = 25℃, Solar. 3
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Separation and Purification Technology 256 (2021) 117851
Fig. 2. Degradation and determination of rate constants of (a) NB (b) BA with solar/PS under different buffer pHs. Reaction condition: [NB]0 = [BA]0 = 1 μM, [PS] = 0.3 mM, 10 mM PBS, pH 5.5, 7.0, and 8.5, T = 25℃, Solar.
Fig. 3. Effect of TBA concentrations on degradation of probes: (a) NB (b) BA. Reaction condition: [NB]0 = [BA]0 = 1 μM, [PS] = 0.3 mM, pH = 7.0 with phosphate buffer, T = 25℃, Solar, [TBA]0 = 0, 0.5 ,1 ,20 ,100 μM.
respectively at pH 5.5, 7.0, 8.5, respectively. The contribution ratio of solar in PNT degradation were 2.1%, 1.0%, and 3.0% at pH 5.5, 7.0, 8.5, respectively (Section 3.1). Therefore, the contributions of the remaining active components could be obtained by subtracting that of the other three species, according to Eq. (11). The remaining contributions of the remaining active species in PNT degra dation were 51.8%, 60.7%, and 67.1% at pH 5.5, 7.0, and 8.5 respec tively. The contributions of four reactive species were summarized in Fig. 5, expressed as the absolute values of overall observed rate con stants. With pH increasing, the overall observed rate constants by solar, HO*, and SO⋅-4 remained around 9.4 × 10-2 min− 1, whereas the remaining active components contributed the highest value of 2.6 × 10-1 min− 1 for PNT degradation at pH 7.0, which would mostly be caused by superoxide radical (⋅O–2) or singlet oxygen (1O2). kPNT’=kHO*-PNT’+kSO4⋅–PNT’+kSolar-PNT’+krest-PNT’
3.5. Dbps formation during solar/PS pre-oxidation with post chlorine In the drinking water treatment plant, residual PPCPs during peroxidation will react with disinfectants such as chlorine in disinfection process, producing a large number of genotoxic, cytotoxic and carci nogenic disinfection byproducts (DBPs), such as trihalomethanes (THMs) and haloacetic acids (HAA) [31–33]. The (THMs formation during chlorination with or without solar/PS pre-oxidation systems were evaluated (Table.1). In the absence of solar/PS pre-oxidation, the concentration of THMs was determined to be 16.0 μg⋅L-1 at pH 7.0. Among the four monitored THMs, the proportion of trichloromethane (TCM) accounts for the highest of 15.4 μg⋅L-1, followed by bromodi chloromethane (BDCM) of 0.6 μg⋅L-1. For solar/PS pre-oxidation system, the concentration of THMs decreased to 14.7 μg⋅L-1. Among the four THMs, TCM was more prevalent in solar/PS pre-oxidation system, with concentration of 14.1 μg⋅L-1, followed by BDCM of 0.6 μg⋅L-1. The decrease of THMs with solar/PS irradiation at pH 7.0 was due to the decrease of DBPs precursors, such as low-molecule organics, after HO* or SO⋅-4 attack. In addition, the mineralization rate of the system was tested in the study. The mineralization ratios of PNT for solar/PS system
(9)
kHO*-PNT’=kHO*-PNT⋅[HO*]ss
(10)
kobs-SO4⋅-’=kobs-BA’-kobs-HO*’
(11)
kobs-SO4⋅-’=kSO4⋅–BA⋅[SO⋅-4 ]ss
(12)
kSO4⋅–PNT’=kSO4⋅–PNT⋅[SO⋅-4 ]ss
(13) 4
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Fig. 4. Degradation and determination of first-order rate constants of PNT (a), NB (b) and BA (c) with solar/PS under different buffer pHs. Reaction condition: [PNT]0 = [NB]0 = [BA]0 = 1 μM, [PS] = 0.3 mM, 10 mM PBS, pH 5.5, 7.0, and 8.5, T = 25℃, Solar. Table 1 Concentration and toxicity of the THMs detected in this study. Condition
Compound
Concentration (μg/L)
LC50 value (M)
Toxicity
Chlorine
Trichloromethan
15.3
Bromodichloromethane
0.6
Chlorodibromomethane
NA
1.34 × 10-5 4.37 × 10-7 NA
Tribromomethane
NA
Trichloromethan
14.1
Bromodichloromethane
0.6
Chlorodibromomethane
NA
Tribromomethane
NA
9.62 × 10-3 1.15 × 10-2 5.36 × 10-3 3.96 × 10-3 9.62 × 10-3 1.15 × 10-2 5.36 × 10-3 3.96 × 10-3
Solar/PS as preoxidation with post chlorine
Fig. 5. Contribution rates of active components in the degradation of PNT. Reaction condition: [PNT]0 = [NB]0 = [BA]0 = 1 μM, [PS] = 0.3 mM, 10 mM PBS, pH 5.5, 7.0, and 8.5, T = 25℃, Solar.
NA 1.23 × 10-5 4.37 × 10-7 NA NA
DBPs. Fig. S7 showed the effect about frontier electro densities (FED) of the highest occupied molecular orbital (HOMO) on the atoms of PNT. Du et al. [34] proposed that the possible sites of chlorine attack on the ar omatic rings could be predicted by calculating the sum of Hammett
at different pHs were in range of 14.3%-35.6% (Fig. S6) at reaction time of 10 min. Therefore, it was confirmed that intermediates are formed in the reaction, which was consistent with the experimental results of 5
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Separation and Purification Technology 256 (2021) 117851
∑
constant values ( σ) for the substituents present. It was reported that ∑ the site with minimum σ was the most frequently attacked by chlorine [35]. Observing the unsubstituted ortho and meta positions to the phenolic function (sites 1 and 2) of PNT (Fig. S7), the most probable sites of chlorine attack on PNT were the meta to the benzamide (6C–7C) [36]. TCM would probably be formed from the attack of benzene ring [37]. The changes of DBPs cytotoxicity for THMs with or without solar/PS were calculated (Table. 1) according to LC50 and 50% tail DNA values of THMs in this research [38,39]. The calculated cytotoxicity decreased from 1.38 × 10-5 to 1.27 × 10-5 after solar/PS pre-oxidation, as the decreased concentrations of TCM.
Table 2 economic calculation in the Solar system. kobs, min−
pH = 5.5
0.439 ± 0.03 0.425 ± 0.03 0.286 ± 0.02
pH = 7.0 pH = 8.5
1
T, h
V, m3
P, kW
EE/O, kWh/m3/ order
0.087
2.5 × 10-5 2.5 × 10-5 2.5 × 10-5
1.19 × 10-3 1.19 × 10-3 1.19 × 10-3
0.069
0.090 0.134
0.072 0.106
screened, and the mechanism of degradation on PNT with ROS should be figured out in future.
3.6. Economic calculation The efficiency of the solar/PS process in the degradation of PNT was evaluated by electrical energy per order (EE/O), a parameter recom mended by Photochemistry Commission of International Union of Pure and Applied Chemistry (IUPAC). EE/O is defined as the kilowatt-hour (kWh) of electricity required to degrade pollutant of one order of magnitude [40,41]. EE/O = Pt/(60V)
Solar/PS system
CRediT authorship contribution statement Chaoqun Tan: Writing - review & editing, Supervision. Xinchi Jian: Data curation. Haotian Wu: Writing - original draft. Tianyu Sheng: . Kechun Sun: . Haiying Gao: Writing - review & editing.
(14)
Declaration of Competing Interest
Where P is the total electrical power of the system, t is the operating time and V is the volume of the solution. The quantum yield of the solar system was 1.14 × 10-4 E⋅m− 2⋅s− 1 with calculated electrical power of 1.19 × 10-3 kW. The calculated EE/O were 0.069. 0.072, and 0.106 kWh/m/order at pH 5.5, 7.0 and 8.5, respectively (Table. 2). The elec trical energy per order in the solar/PS system were in range of 0.069 ~ 0.106 kWh/m/order, which were close to the lower range of 0.017 ~ 2.26 kWh/m/order in Guo et al. experiment in the UV254 system [42]. The EE/O results suggest that solar/PS system are more economical in degrading pollutants. Table. 2 To evaluate the degradation performance of PNT in actual water, experiments were conducted in the wastewater influent, effluent, river and tap water samples. Fig.S8 showed the degradation of PNT in different actual water. PNT degradation was totally inhabited in wastewater influent which could be attributed to the existence of various competitive substances [43]. Decomposition of PNT was less than 3% and the kobs of PNT was 4.1 × 10-3 min− 1. Although decom position of PNT in effluent and river was restrained comparing the tap water, PNT were degrade to 80% and 90 within 10 min, respectively. The kobs of PNT was calculated to 1.3 × 10-1 ~ 6.8 × 10-1 min− 1. It indicated that the Solar/PS system had broad application prospects in actual water treatment process. Meanwhile, the EE/O values in matrix from different actual water were measured in range of 0.045 ~ 7.417 kWh/m/order (Table S3), which is close to the results reported by Zhou et al. [44].
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgement This work was financially supported by the National Natural Science Foundation of China (No.52070041, 51608109), China; Natural Science Foundation of Jiangsu Province (No. BK20160675), China; the Priority Academic Program Development of Jiangsu Higher Education In stitutions, the Fundamental Research Funds for the Central Universities, the Research Fund of Key Laboratory of Yangze River Water Environ ment, Ministry of Education (Tongji University), China. In addition, Chaoqun Tan wishes to thank Zhishan Youth Scholar Program Of SEU. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.seppur.2020.117851. References [1] Y. Wang, et al., Competitive adsorption of ppcp and humic substances by carbon nanotube membranes: Effects of coagulation and ppcp properties, Sci. Total Environ. 619 (2018) 352–359. [2] I. Tamura, et al., Contribution of pharmaceuticals and personal care products (ppcps) to whole toxicity of water samples collected in effluent-dominated urban streams, Ecotoxicol. Environ. Saf. 144 (2017) 338–350. [3] A.J. Ebele, M. Abou-Elwafa Abdallah, S. Harrad, Pharmaceuticals and personal care products (ppcps) in the freshwater aquatic environment, Emerging Contaminants 3 (1) (2017) 1–16. [4] D. Simazaki, et al., Occurrence of selected pharmaceuticals at drinking water purification plants in japan and implications for human health, Water Res. 76 (2015) 187–200. [5] B.P. Gumbi, et al., Detection and quantification of acidic drug residues in south african surface water using gas chromatography-mass spectrometry, Chemosphere 168 (2017) 1042–1050. [6] F. Qi, W. Chu, B. Xu, Comparison of phenacetin degradation in aqueous solutions by catalytic ozonation with cufe2o4 and its precursor: Surface properties, intermediates and reaction mechanisms, Chem. Eng. J. 284 (2016) 28–36. [7] A. Borgeat, et al., The effect of nonsteroidal anti-inflammatory drugs on bone healing in humans: A qualitative, systematic review, J. Clin. Anesth. 49 (2018) 92–100. [8] M. Cheng, et al., Hydroxyl radicals based advanced oxidation processes (aops) for remediation of soils contaminated with organic compounds: A review, Chem. Eng. J. 284 (2016) 582–598. [9] E.A. Betterton, M.R. Hoffmann, Kinetics and mechanism of the oxidation of aqueous hydrogen-sulfide by peroxymonosulfate, Environ. Sci. Technol. 24 (12) (1990) 1819–1824.
4. Conclusion The work demonstrated that the degradation of PNT was enhanced by PS in solar irradiation system. The removal of PNT reached 100% within 10 min in pH range of 5.5–8.5. Neutral pH was more beneficial than acidic or alkaline conditions and the kobs of PNT was calculated to 6.4 × 10-1 min− 1 for pH 7.0 because of effect with H+ and HPO24 . The consume ratios of PS were 3%-17% for PNT degradation in Solar/PS system. HO*, SO⋅-4 , and related ROS were produced and responsible for PNT degradation in the system. The contribution of HO*, SO⋅-4 , and related ROS to degrading PNT were 27.4%, 11.0%, and 60.7%, respec tively. The concentration and toxicity of THMs decreased and the mineralization rate of PNT were in range of 14.3%-35.6% with solar/PS pre-oxidation. Moreover, the EE/O values of solar/PS system were in range of 0.069 ~ 0.106 kWh/m/order in pH range of 5.5–8.5. Solar/PS system had broad application prospects in actual water treatment pro cess. Based on the results obtained herein, related ROS should be 6
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