Chemosphere 101 (2014) 34–40
Contents lists available at ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
Technical Note
Application of ultrasound and quartz sand for the removal of disinfection byproducts from drinking water Wu Yang a,b, Lili Dong a,b,c, Zhen Luo a,b, Xiaochun Cui a,b, Jiancong Liu a,b, Zhongmou Liu a,b, Mingxin Huo a,b,c,⁄ a b c
State Environmental Protection Key Laboratory of Wetland Ecology and Vegetation Restoration, Northeast Normal University, Changchun 130117, China School of Environment, Northeast Normal University, Changchun 130117, China Key Laboratory of Songliao Aquatic Environment, Ministry of Education, Jilin Architectural and Civil Engineering Institute, Changchun 130118, China
h i g h l i g h t s DBPs with log Kow P 1.97 can be sonodegraded. More chlorine atoms in the DBPs molecular structure seems easier to be adsorbed. All the 12 targeted DBPs can be removed effectively by combined use of US and QS. Part of QS particles were corroded into small particles and play a catalytic role. Enhanced mass transfer rate leading to an improvement of QS adsorption efficiency.
a r t i c l e
i n f o
Article history: Received 4 September 2013 Received in revised form 6 November 2013 Accepted 10 November 2013 Available online 2 December 2013 Keywords: Disinfection byproduct Drinking water Quartz sand Synergistic effect Ultrasound
a b s t r a c t To the best of our knowledge, little information is available on the combined use of ultrasound (US) and quartz sand (QS) in the removal of disinfection byproducts (DBPs) from drinking water. This study investigates the removal efficiency for 12 DBPs from drinking water by 20 kHz sonolytic treatment, QS adsorption, and their combination. Results indicate that DBPs with log Kow 6 1.12 could not be sonolysized; for log Kow P 1.97, more than 20% removal efficiency was observed, but the removal efficiency was unrelated to log Kow. DBPs containing a nitro group are more sensitive to US than those that comprise nitrile, hydrogen, and hydroxyl groups. Among the 12 investigated DBPs, 9 could be adsorbed by QS adsorption. The adsorption efficiency ranged from 12% for 1,1-dichloro-2-propanone to 80% for trichloroacetonitrile. A synergistic effect was found between the US and QS on DBPs removal, and all the 12 DBPs could be effectively removed by the combined use of US and QS. In the presence of US, part of the QS particles were corroded into small particles which play a role in increasing the number of cavitation bubbles and reducing cavitation bubble size and then improve the removal efficiency of DBPs. On the other hand, the presence of US enhances the DBP mass transfer rate to cavitation bubbles and quartz sand. In addition, sonolytic treatment led to a slight decrease of pH, and TOC values decreased under all the three treatment processes. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Although the disinfection of drinking water is key to suppressing microbial activity, a significant risk is associated with the formation of disinfection byproducts (DBPs) through the reactions of the disinfectants with natural organic matter. More than 600 DBPs have been identified since scientists first became aware of DBPs in the early 1970s; many of these DBPs pose risks to human ⁄ Corresponding author at: State Environmental Protection Key Laboratory of Wetland Ecology and Vegetation Restoration, Northeast Normal University, Changchun 130117, China. Tel.: +86 13756478864; fax: +86 431 89165601. E-mail address: [email protected] (M. Huo). 0045-6535/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.chemosphere.2013.11.018
health even at ppb levels (Richardson et al., 2007). Consequently, DBPs, such as THMs and haloacetic acids (HAAs) are regulated by numerous countries and organizations. Continual research has also been conducting over the past decades to satisfy the standards for drinking water quality and minimize health risks. The formation of DBPs can be controlled and minimized by using one, or a combination, of the following approaches: removing DBP precursors prior to disinfection, changing disinfectants, and removing DBPs after disinfection (Kristiana et al., 2011). Among these methods, the removal of DBP precursors is considered more satisfactory (Bond et al., 2011). However, some species tend to remain and retain significant DBP formation potential
W. Yang et al. / Chemosphere 101 (2014) 34–40
even after being treated by coagulation, anion exchange, and activated carbon adsorption (Bond et al., 2011). Significant interest has been gained on the application of advanced oxidation processes, such as O3, UV, and their combination with H2O2, as additional tools for removing DBP precursors and minimizing the formation of regulated DBPs in drinking water (Kleiser and Frimmel, 2000; Toor and Mohseni, 2007; Dotson et al., 2010; Lamsal et al., 2011; Metz et al., 2011; Penru et al., 2012; Yang et al., 2012). Nevertheless, the formation of chloral hydrate (CH), trichloronitromethane (TCNM), and haloketones, which are more toxic than THMs and HAAs, may increase during the subsequent chlorination (Metz et al., 2011; Yang et al., 2012). Alternative disinfectants, such as ClO2, O3, UV, and chloramine can efficiently reduce the formation of THMs and HAAs, but such disinfectant may cause the formation of unregulated DBPs, such as halonitromethanes, haloamides, haloacetonitriles (HANs), and nitrosamines, which pose greater health risks than those of regulated species (Richardson et al., 2007). The application of ultrasound (US) in water and wastewater treatment to degrade organic pollutants has attracted considerable attention since 1990 (Belgiorno et al., 2007; Hamdaoui and Naffrechoux, 2009). According to ‘‘hot spot’’ theory, a widely accepted explanation for sonochemical reactions in the environmental field (Chowdhury and Viraraghavan, 2009), extremely high temperatures (up to 5000 K) and high pressures (about 50 MPa) incur during the collapse of cavitation bubbles, which results in hydroxyl radicals in cavitation bubbles by water dissociation. Under ultrasonic irradiation, aqueous organic compounds can be decomposed via reaction with OH or directly pyrolysised during the collapse of cavitation bubbles. Numerous studies have been conducted to improve ultrasonic efficiency due to its significant advantages, such as safety, cleanliness, and energy conservation without secondary pollution (Gibson et al., 2008; Chowdhury and Viraraghavan, 2009; Matilainen and Sillanpää, 2010; Pang et al., 2011). Among these researches, small semiconductor particles such as titanium dioxide, silica, and alumina were reported to possess catalytic functions that enhance ultrasonic efficiency (Ragaini et al., 2001; Sekiguchi and Saita, 2001; Zouaghi et al., 2011). Adsorption is another well-established technique for removing low concentrations of organic pollutants from potable water, wastewater, and aqueous solutions (Hamdaoui and Naffrechoux, 2009). Aside from being the most widely used filter media in water plants in China, quartz sand (QS) is also used as a sorbent for removing organic pollutants from water (Liu et al., 2011a,b). Liu et al. (2011b) studied the effects of using three sorbents on removing organic pollutants in drinking water and found that QS can effectively remove 16 out of 36 organic pollutant species. By contrast, activated carbon can remove only 10 species. The authors also found that organic pollutants with low concentrations can be completely removed by QS adsorption. Using US technology to remove DBPs in drinking water has been studied for few years. Shemer and Narkis (2005) studied the ultrasonic degradation of aqueous THMs with an initial concentration of 10 mg L1. However, their results were not of representative significance as the chlorinated drinking water typically consists of a mixture of DBPs with low concentrations. Guo et al. (2006) investigated the ultrasonic removal efficiency of DBP mixtures with very low initial concentration (3.19–15.79 lg L1) in chlorinated drinking water, but only THMs were concerned. In addition, no information is available on the use of QS for the removal of DBPs from drinking water. In this study, therefore, we investigated the removal efficiency for 12 DBPs with low concentrations in drinking water by conducting through sonolytic treatment, QS adsorption, and their combination. The synergistic effect was also discussed.
35
2. Materials and methods 2.1. Materials Four THMs (chloroform (CF), bromoform (BF), bromodichloromethane (BDCM), and dibromochloromethane (DBCM)) of analytical grade were obtained from Aladdin Industrial, China. EPA 551B mixture (containing trichloroacetonitrile (TCAN), dichloroacetonitrile (DCAN), bromochloroacetonitrile (BCAN), dibromoacetonitrile (DBAN), TCNM, 1,1,1-trichloro-2-propanone (1,1,1-TCP), and 1,1dichloro-2-propanone (1,1-DCP)) and CH of analytical grade were obtained from Sigma Aldrich, USA. Na2SO4, methyl tert-butyl ether (MTBE), and QS with a 100–200 mesh (0.075–0.152 mm) diameter were purchased from Sinopharm Chemical Regency, China. 3. Experimental procedure DBPs mixture stock solution (1.2–2.0 mg mL1 for each component in methanol, except for CH in acetone) was spiked into tap water from the laboratory without any pretreatment to ensure that the spiked DBPs were approximately 200 lg L1 for THMs and 100 lg L1 for the rest. Tap water (200 mL) with spiked DBPs in a glass vessel was used in subsequent experiments. In sonolytic treatment experiments, the US was generated by a 20 kHz ultrasonicator (ZFDY, Zhengjie, China) and transferred into the water sample via an immersible titanium alloy probe (1.6 cm diameter) at a constant electrical power output of 150 W. The probe was immersed approximately 3 cm below the water surface. The sample vessel was placed in a water bath at a constant temperature of 20 ± 0.5 °C during the irradiation period. In QS adsorption experiments, 2 g of QS was immersed into a 200 mL tap water with spiked DBPs. The sample vessel was then placed in a thermostatic magnetic stirrer set at 20 °C and 200 rpm. Experiments with the combined use of US and QS were carried out to evaluate the combination’s removal efficiency for DBPs. The 200 mL tap water with the spiked DBP mixtures and 2 g QS was exposed to 20 kHz US. Samples were withdrawn for GC analysis every 15 min within 60 min for all the three treatments. A digital pH meter (WTW 3310, Germany) and a TOC analyzer (TOC-L CPH, Shimadzu, Japan) were used to monitor pH and TOC values before and after different treatment processes. All the experiments were carried out in duplicate. 3.1. Analytical methods All the 12 DBPs were measured with USEPA Method 551.1 with minor modifications. A 5 mL sample was extracted by using 1.0 mL of MTBE, 3 g of Na2SO4, and 0.2 g of phosphate buffer powder. The sample was then vigorously shaken for 2 min. MTBE extract (0.5 mL) was analyzed with a PerkinElmer Clarus 680 GC equipped with a 30 m DB-5 capillary column and an electron capture detector. The GC temperature program started at 30 °C for 8 min, and was then increased to 110 °C at 20 °C min1, and held for 1 min. The carrier and makeup gas was highly pure (>99.999%) nitrogen at 1.5 and 30.0 mL min1, respectively. The injector and detector temperatures were set at 190 and 210 °C, respectively. External standards were used for quantitative determination. 4. Results and discussion 4.1. Sonodegradation efficiencies and kinetics A solution of the spiked DBP mixture was stirred and maintained at 20 °C. Less than 5% of the DBPs appeared to be lost from
W. Yang et al. / Chemosphere 101 (2014) 34–40
4.2. Classification of DBP sensitivity to US The sonolysis of organic compounds contributes to the pyrolytic decomposition in collapsing cavitation bubbles and to the OH oxidation in bulk solution and interfacial regions (Drijvers et al., 2000). The physicochemical properties of an organic compound influence its kinetic properties and mechanisms under sonolytic destructions (Guo et al., 2006). Hua and Hoffmann (1996) stated that sonolysis is a particularly suitable method for degrading volatile hydrophobic molecules because these compounds are reactive in the largest region of a cavitation bubble. log Kow is one of the most extensively used physicochemical parameters for characterizing the water solubility of an organic compound (Donovan and Pescatore, 2002). Wu and Ondruschka (2005) studied the sonochemical removal of 26 model organic compounds in aqueous solution and found that a higher log Kow results in a higher sonolysis rate. By contrast, our study generated different results, as indicated by the comparison of the log Kow (Table 1) with corresponding kus. Fig. 2 shows that, DBPs with a log Kow 6 1.12 could not undergo sonolysis. Conversely, DBPs with a log Kow P 1.97 exhibited sonodegradation. However, the ks values were unrelated to log Kow. Wu and Ondruschka (2005) studied the sonochemical removal of 26 model organic compounds in aqueous solution and found that the Henry’s Law constant (KH) of a substrate substantially affects the degradation rate; that is, a higher KH leads to a higher sonolysis rate. In the present work, similar relations were not obtained between the kus values and KH. TCAN exhibited a KH of 1.34 106 atm L mol1, which is about 399–2740 times lower than that of THMs, but its kus value was 2.1–6.8 times higher. In the same class of compounds (THMs, HANs), however, a higher KH corresponded to a higher kus value. This finding suggests that KH is a critical parameter that controls the ultrasonic degradation of the same class of sonodegradable compounds, but it is not the dominant factor for different class of compounds. Earlier researches have indicated that compounds with a relatively higher vapor pressure tend to more effectively undergo sonodegradation (Drijvers et al., 2000; Shemer and Narkis, 2005) as indicated by the analysis of the same class of compounds (i.e., THMs, halobenzene). A similar result was found for the THMs and HANs in the present work. However, the comparison of all the sonodegradable targeted compounds did not present the same
0.0
a
ln (C/C0 )
-0.2
-0.4
-0.6 Chloroform Bromodichloromethan Dibromochloromethane Bromoform
-0.8
-1.0 0.0
b
-0.2 -0.4 -0.6
ln (C/C0 )
the solution over the experimental period. Thus, the loss of DBPs due to volatilization and photodecomposition during sonolysis is negligible. This finding is inconsistent with previous work, in which 1,1-DCP and 1,1,1-TCP decomposed in fortified drinking water even at a concentration of 50 lg L1 (Nikolaou et al., 2001). The removal efficiency for THMs with US is shown in Fig. 1a. The sonolysis removal of DBPs was successfully fitted to an integrated first-order kinetic expression. The fitting parameters are listed in Table 1. The results shown in Fig. 1 were obtained by using a mixture of all the investigated DBPs given that the sonication of mixtures only moderately affected sonication decomposition rates (Zhang and Hua, 2000). As shown in Fig. 1a, 20 kHz US degraded all the four THMs even at ppb levels, and more than 20% of these components were removed after 60 min of ultrasonic irradiation. CF (kus = 0.014 min1) was removed faster than BDCM (kus = 0.012 min1) and DBCM (kus = 0.006 min1). BF (kus = 0.004 min1) was the most recalcitrant THM to remove, this finding is consistent with previous works (Shemer and Narkis, 2005; Guo et al., 2006). Only TCAN and TCNM of the other 8 DBPs can be degraded by sonolysis (Fig. 1b and c). The kus value was 0.031 and 0.083 min1 for TCAN and TCNM, respectively. The corresponding 60 min removal efficiencies were 83% and 99% for TCAN and TCNM, respectively.
-0.8 -1.0 -1.2
Trichloroacetonitrile Dichloroacetonitrile Bromochloroacetonitrile Dibromoacetonitrile
-1.4 -1.6 -1.8 0
c
-1 -2
ln (C/C0)
36
-3 Chloral Hydrate Chloropicrin 1,1-Dichloro-2-propanone 1,1,1-Trichloro-2-propanone
-4 -5
0
10
20
30
40
50
60
Time (min) Fig. 1. DBPs removal efficiency by ultrasonic irradiation. Sonication conditions: 200 mL, 20 kHz, 150 W, 20 °C.
results. The vapor pressure increased in the order BF < CDBM < TCNM < BDCM < TCAN < CF, whereas the kus values increased in the order TCNM > TCAN > CF > BDCM > CDBM > BF. Similar to KH, vapor pressure is another critical parameter that controls the ultrasonic degradation of the same class of sonodegradable compounds; however, it is not the dominant factor for different class of compounds. The functional group significantly influences the physicochemical properties of an organic compound. However, little information is available on the effects of the functional group presenting in DBPs on sonodegradation kinetics. The comparison of the kus values of TCNM, TCAN, CH, 1,1,1-TCP, and CF indicates that the functional groups (i.e., k value) were ranked as follows: nitro (kus = 0.083 min1) > nitrile (kus = 0.031 min1) > hydrogen (kus = 0.014 min1) > hydroxyl (kus = 0) carbonyl (kus = 0). This rank indicates that compounds containing a nitro group are more sensitive to US than those that comprise nitrile, hydrogen, and hydroxyl groups. 4.3. DBPs removal by QS adsorption QS has proven to be an efficient sorbent in adsorbing organic pollutants in drinking water (Liu et al., 2011a) and wastewater
37
W. Yang et al. / Chemosphere 101 (2014) 34–40 Table 1 Physical and chemical properties and fitted parameters of the investigated compounds. Vp (kPa)
log Kow
KH (atm L mol1)
kus (min1)
kqs (min1)
qe (lg g1)
kc (min1)
67-66-3
26.26
1.97
3.67 103 (24 °C)
0.014
0.006
49.7
0.046
BDCM
75-27-4
6.67
2.0
2.12 103
0.012
0.010
20.1
0.040
CDBM
124-48-1
0.74
2.16
7.83 104 (20 °C)
0.006
0.024
10.0
0.028
BF
75-25-2
0.72
2.38
5.34 104
0.004
0.027
8.3
0.017
HANs TCAN
545-06-2
7.73
2.09
1.34 106
0.031
0.026
13.3
0.080
DCAN
3018-12-0
0.38
0.29
3.79 106
–
0.021
3.0
0.025
BCAN
83463-62-1
0.12
0.38
1.24 106
–
–
–
0.014
DBAN
3252-43-5
0.04
0.47
4.06 107
–
–
–
0.018
Misc. DBPs TCNM
76-06-2
3.20
2.09
2.05 103
0.083
0.013
10.3
0.16
CH
302-17-0
2.00
0.99
5.71 109
–
–
–
0.016
1,1-DCP
513-88-2
3.60
0.2
6.15 106
–
0.025
0.9
0.017
1,1,1-TCP
918-00-3
0.56
1.12
2.17 106
–
0.017
6.6
0.069
Compound
CAS No.
THMs CF
Structure
Vp: Vapor pressure at 25 °C; KH: Henrys law constant at 25 °C; log Kow: Octanol–water partition coefficient; kus: first order kinetic constant for sonodegradation; kqs: first order kinetic constant for quartz sand adoption; qe: the predicated adsotpion capcacity for quartz sand; kc: first order kinetic constant for combined use ultrasound and quartz sand.
38
W. Yang et al. / Chemosphere 101 (2014) 34–40
0.08
-1
kus (min )
0.06
0.04
0.02
0.00 0.0
0.5
1.0
1.5
2.0
2.5
logKow Fig. 2. Relationship between the sonolysis rate constant and octanol–water partition coefficient of the investigated DBPs. Sonication conditions: 200 mL, 20 kHz, 150 W, 20 °C.
6.5
a
6.0 5.5
ln(qe-qt)
5.0 4.5 4.0 Chloroform Bromodichloromethane Dibromochloromethane Bromoform
3.5 3.0 5.0
b
4.5
ln(qe-qt)
4.0 3.5 3.0 Trichloroacetonitrile Dichloroacetonitrile
2.5 2.0
c
4.5 4.0
ln(qe-qt)
3.5 3.0
Fig. 3 and Table 1 show that 9 of the 12 DBPs can be adsorbed by QS to a certain extent. The 60 min adsorption efficiency ranged from 12% for 1,1-DCP to 80% for TCAN. The adsorption kinetics of DBPs onto QS was fitted by the pseudo first-order kinetic model as lnðqe qt Þ ¼ ln qe kqs t (the kinetic constant expressed as kqs). The kqs value ranged from 0.002 min1 for 1,1-DCP to 0.046 min1 for TCAN, and the predicated adsotpion capcacity ranged from 1 lg g1 for 1,1-DCP to 50 lg g1 for CF. As for THMs, more than 30% of all the four THMs could be adsorbed by QS within 60 min. The 60 min adsorption efficiency and adsotpion capcacity increased with the increasing number of chlorine atoms in the molecular structure which follows the order of CF (59%, 50 lg g1) > BDCM (51%, 20 lg g1) > CDBM (38%, 10 lg g1) > BF (33%, 7 lg g1). It is well known that silica is the main component of QS, and the surface siloxane bonds (Si–O) of original silicas may hydrolysis to silanols (Si–OH) (Bambrough et al., 1998; Dou et al., 2011). The silanol groups have very strong polar interactivity which is more sensitive to chlorine atoms than to bromine atoms; thus, higher adsorption efficiency was observed for the component with more chlorine atoms in the molecular structure. QS adsorption was observed only for TCAN and DCAN of the four HANs. As mentioned above, the much higher adsorption efficiency was observed for TCAN than for DCAN because of the presence of more chlorine atoms in TCAN. The 60 min adsorption efficiency was 79% and 23% for TCAN and DCAN, and the corresponding adsorption capacity was 13 and 3 lg g1, respectively. Both BCAN and TBAN did not show adsorption by QS because they are lack of chlorine atoms in their molecular structures. Although the molecular structure of CH has three chlorine atoms, no adsorption efficiency was observed. The adsorption capacity for TCNM, 1,1,1-TCP, and 1,1-DCP were 10, 7, and 1 lg g1, respectively. The corresponding 60 min adsorption efficiencies were 50%, 35%, and 12%, respectively. 4.4. DBPs removal by combined use of US and QS As shown in Fig 4, the DBPs removal efficiency by combined use of US and QS was successfully fitted to an integrated (pseudo) firstorder kinetic expression (the kinetic constant expressed as kc). Fig. 4 and Table 1 show that all the 12 targeted DBPs could be effectively removed by the combined use of US and QS. The 60 min removal efficiency ranged from 51% for BCAN to 100% for TCNM. The kc value ranged from 0.014 to 0.16 min1, respectively. At least 51% of BCAN, DBAN, and CH, which cannot be removed by US and QS, were removed within 60 min with the combined use of US and QS. This finding indicates a synergistic effect between US and QS on DBPs removal—a result that makes the removal of DBPs in drinking water by combined use of US and QS an interesting topic to explore. 4.5. Synergistic effects between US and QS
2.5 2.0 1.5
Chloropicrin 1,1,1-trichloro-2-propanone 1,1-dichloro-2-propanone
1.0 0.5 0
10
20
30
40
50
60
Time (min) Fig. 3. DBPs removal efficiency by QS adsorption. Adsorption conditions: 200 mL, 2 g QS, 200 rpm, 20 °C.
(Liu et al., 2011b). In the present work, 2 g of QS was immersed into a 200 mL DBPs mixture to investigate its adsorption characteristics.
In this study, QS with a 100–200 mesh (0.075–0.152 mm) diameter was used. We determined the mass of QS by weighing the amount of QS passing through a 200 mesh sieve before and after 60 min sonolytic treatment. The mass distribution of the QS with a 100–200 mesh diameter was slightly lower (4–7%) after sonolytic treatment. Correspondingly, the BET surface area increased slightly (from 0.95 to 1.12 m2 g1), which is inconsistent with previous works that activated carbon was used as sorbent (Hamdaoui and Naffrechoux, 2009; Zhao et al., 2011). This finding indicates that part of the QS particles were corroded into small particles (smaller than 200 mesh) under sonolytic treatment. Previous studies have demonstrated that small semiconductor particles (from nm to lm scale), such as titanium dioxide, silica, and alumina, play a
39
W. Yang et al. / Chemosphere 101 (2014) 34–40
7.2
a
-0.5
7.0
-1.0
6.8
-1.5
6.6
pH
ln (C/C0)
0.0
-2.0
6.4
Chloroform Bromodichloromethan Dibromochloromethane Bromoform
-2.5
a
6.2
-3.0 0
6.0
b
b
3.0
-1
TOC (mg/L)
ln (C/C0)
2.8
-2
-3 Trichloroacetonitrile Dichloroacetonitrile Bromochloroacetonitrile Dibromoacetonitrile
-4
2.4 2.2
-5 0
c
2.0
Raw
Sonolytic QS adsorption
US+ QS
Fig. 5. Variations of solution pH (a) and TOC (b) values under different treatment processes.
-1
ln (C/C0)
2.6
-2
-3 Chloral Hydrate Chloropicrin 1,1-Dichloro-2-propanone 1,1,1-Trichloro-2-propanone
-4
-5
0
10
20
30
40
50
60
Time (min) Fig. 4. DBPs removal efficiency by combined use of US and QS. Conditions: 200 mL, 20 kHz US with 150 W output power, 2 g QS, 200 rpm, 20 °C .
catalytic role in promoting ultrasonic efficiency, particularly at low frequency (Ragaini et al., 2001; Sekiguchi and Saita, 2001; Zouaghi et al., 2011). According to these studies, the presence of small particles increases the number of cavitation bubbles and reduces cavitation bubble size. The increase in cavitation bubbles improves the pyrolysis of organic compounds, thereby enhances sonolysis efficiency. All the DBPs that cannot be removed by US expressed a lag phase under the combined treatment. As mentioned in Section 3.2, hydrophilic compounds are indirectly decomposed primarily through their reaction with OH, which is produced during the cavitation process. Lim et al. (2011) found that the majority of OH is scavenged in bubbles at low frequencies (i.e., 20 kHz) and is unavailable in bulk solutions and interfacial regions. However, more available OH can escape from the bubbles and react with organic compounds when the presence of small particles in water solution. A considerable amount of time is needed for US to corrode QS particles into small particles, which play a catalytic role to generate more OH, thus, a lag phase occurred and the competition for OH among DBPs caused a different lag phase. We also investigated DBP adsorption by QS, which was treated by 20 kHz US irradiation. Although a minor change in the BET
surface was found, no significant difference in DBP adsorption efficiency was observed between QS and ultrasonic treated QS (data not shown). This finding indicates that the increased DBP removal efficiency was not attributed to the change of the surface properties of QS. Researches have found that the adsorption efficiency of activated carbon significantly increased under sonolytic treatment even though no BET surface changes was observed (Hamdaoui and Naffrechoux, 2009; Lim et al., 2011). Many scholars have suggested that extreme conditions, such as high-speed micro-jets, high-pressure shock waves, and acoustic vortex micro-streaming, occur during sonolytic treatment (Hamdaoui et al., 2003; Nouri and Hamdaoui, 2007; Chowdhury and Viraraghavan, 2009; Hamdaoui and Naffrechoux, 2009). Thus, the mass transfer improves at bulk solutions and liquid–solid interfaces, thereby enhances adsorption efficiency. Thus, increased QS adsorption efficiency may occur under sonolytic treatment due to the extreme conditions.
4.6. Variations of pH and TOC under different treatment processes The pH and TOC values of the samples before and after different treatment processes are compared in Fig. 5. As can be seen, the pH values decreased slightly from 7.1 to 6.8 and 6.6 under the treatment of sonolytic and combined use of US and QS, respectively. QS adsorption did not change the solution pH. The decreased pH may be attributed to the formation of acidic intermediates and products in the presence of US (Guo et al., 2006), and the presence of QS may enhance the formation of intermediates and products. It is notable that though pH values decreased, it is still in the acceptable range of drinking water quality (6.5–8.5) in China. The TOC values decreased from 3.1 mg L1 to 2.8, 2.9 and 2.5 mg L1 under the treatment of sonolytic, QS adsorption and the combination of US and QS, respectively. The decreased TOC is larger than the carbon concentrations contributed from the 12
40
W. Yang et al. / Chemosphere 101 (2014) 34–40
DBPs, indicating these treatment processes can also remove other organic compounds presented in drinking water. The lowest TOC was detected under the combination of US and QS also indicating a synergistic effect between US and QS. Acknowledgments The authors wish to thank the Natural Science Foundation of China (51238001 and 51278093) and the Fundamental Research Funds for the Central Universities (11SSXT139) for their financial support. References Bambrough, C.M., Slade, R.C.T., Williams, R.T., 1998. Synthesis of a large pore phenyl-modified mesoporous silica and its characterization by nitrogen and benzene sorption. J. Mater. Chem. 8, 569–571. Belgiorno, V., Rizzo, L., Fatta, D., Rocca, C.D., Lofrano, G., Nikolaou, A., Naddeo, V., Meric, S., 2007. Review on endocrine disrupting-emerging compounds in urban wastewater: occurrence and removal by photocatalysis and ultrasonic irradiation for wastewater reuse. Desalination 215, 166–176. Bond, T., Goslan, E.H., Parsons, S.A., Jefferson, B., 2011. Treatment of disinfection byproduct precursors. Environ. Technol. 32, 1–25. Chowdhury, P., Viraraghavan, T., 2009. Sonochemical degradation of chlorinated organic compounds, phenolic compounds and organic dyes – a review. Sci. Total Environ. 407, 2474–2492. Donovan, S.F., Pescatore, M.C., 2002. Method for measuring the logarithm of the octanol–water partition coefficient by using short octadecyl–poly (vinyl alcohol) high-performance liquid chromatography columns. J. Chromatogr. A 952, 47–61. Dotson, A.D., Keen, V.S., Metz, D., Linden, K.G., 2010. UV/H2O2 treatment of drinking water increases post-chlorination DBP formation. Water Res. 44, 3703–3713. Dou, B., Hu, Q., Li, J., Qiao, S., Hao, Z., 2011. Adsorption performance of VOCs in ordered mesoporous silicas with different pore structures and surface chemistry. J. Hazard. Mater. 186, 1615–1624. Drijvers, D., Van Langenhove, H., Herrygers, V., 2000. Sonolysis of fluoro-, chloro-, bromo- and iodobenzene: a comparative study. Ultrason. Sonochem. 7, 87–95. Gibson, J.H., Yong, D.H.N., Farnood, R.R., Seto, P., 2008. A literature review of ultrasound technology and its application in wastewater disinfection. Water Qual. Res. J. Can. 43, 23–35. Guo, Z., Gu, C., Zheng, Z., Feng, R., Jiang, F., Gao, G., Zheng, Y., 2006. Sonodegradation of halomethane mixtures in chlorinated drinking water. Ultrason. Sonochem. 13, 487–492. Hamdaoui, O., Naffrechoux, E., 2009. Adsorption kinetics of 4-chlorophenol onto granular activated carbon in the presence of high frequency ultrasound. Ultrason. Sonochem. 16, 15–22. Hamdaoui, O., Naffrechoux, E., Tifouti, L., Pétrier, C., 2003. Effects of ultrasound on adsorption–desorption of p-chlorophenol on granular activated carbon. Ultrason. Sonochem. 10, 109–114. Hua, I., Hoffmann, M.R., 1996. Kinetics and mechanism of the sonolytic degradation of CCl4: intermediates and byproducts. Environ. Sci. Technol. 30, 864–871. Kleiser, G., Frimmel, F.H., 2000. Removal of precursors for disinfection by-products (DBPs) — differences between ozone- and OH-radical-induced oxidation. Sci. Total Environ. 256, 1–9.
Kristiana, I., Joll, C., Heitz, A., 2011. Powdered activated carbon coupled with enhanced coagulation for natural organic matter removal and disinfection byproduct control: Application in a Western Australian water treatment plant. Chemosphere 83, 661–667. Lamsal, R., Walsh, M.E., Gagnon, G.A., 2011. Comparison of advanced oxidation processes for the removal of natural organic matter. Water Res. 45, 3263–3269. Lim, M., Son, Y., Khim, J., 2011. Frequency effects on the sonochemical degradation of chlorinated compounds. Ultrason. Sonochem. 18, 460–465. Liu, H., Feng, S., Du, X., Zhang, N., Liu, Y., 2011a. Comparison of three sorbents for organic pollutant removal in drinking water. Energy Procedia 5, 985–990. Liu, J., Wang, X., Fan, B., 2011b. Characteristics of PAHs adsorption on inorganic particles and activated sludge in domestic wastewater treatment. Bioresour. Technol. 102, 5305–5311. Matilainen, A., Sillanpää, M., 2010. Removal of natural organic matter from drinking water by advanced oxidation processes. Chemosphere 80, 351–365. Metz, D.H., Meyer, M., Dotson, A., Beerendonk, E., Dionysiou, D.D., 2011. The effect of UV/H2O2 treatment on disinfection by-product formation potential under simulated distribution system conditions. Water Res. 45, 3969–3980. Nikolaou, A.D., Lekkas, T.D., Kostopoulou, M.N., Golfinopoulos, S.K., 2001. Investigation of the behaviour of haloketones in water samples. Chemosphere 44, 907–912. Nouri, L., Hamdaoui, O., 2007. Ultrasonication-assisted sorption of cadmium from aqueous phase by wheat bran. J. Phys. Chem. A 111, 8456–8463. Pang, Y.L., Abdullah, A.Z., Bhatia, S., 2011. Review on sonochemical methods in the presence of catalysts and chemical additives for treatment of organic pollutants in wastewater. Desalination 277, 1–14. Penru, Y., Guastalli, A.R., Esplugas, S., Baig, S., 2012. Application of UV and UV/H2O2 to seawater: disinfection and natural organic matter removal. J. Photochem. Photobiol., A 233, 40–45. Ragaini, V., Selli, E., Bianchi, C.L., Pirola, C., 2001. Sono-photocatalytic degradation of 2-chlorophenol in water: kinetic and energetic comparison with other techniques. Ultrason. Sonochem. 8, 251–258. Richardson, S.D., Plewa, M.J., Wagner, E.D., Schoeny, R., Demarini, D.M., 2007. Occurrence, genotoxicity, and carcinogenicity of regulated and emerging disinfection by-products in drinking water: a review and roadmap for research. Mutat. Res.-Rev. Mutat. 636, 178–242. Sekiguchi, H., Saita, Y., 2001. Effect of alumina particles on sonolysis degradation of chlorobenzene in aqueous solution. J. Chem. Eng. Jpn. 34, 1045–1048. Shemer, H., Narkis, N., 2005. Sonochemical removal of trihalomethanes from aqueous solutions. Ultrason. Sonochem. 12, 495–499. Toor, R., Mohseni, M., 2007. UV-H2O2 based AOP and its integration with biological activated carbon treatment for DBP reduction in drinking water. Chemosphere 66, 2087–2095. Wu, Z., Ondruschka, B., 2005. Roles of hydrophobicity and volatility of organic substrates on sonolytic kinetics in aqueous solutions. J. Phys. Chem. A 109, 6521–6526. Yang, X., Peng, J., Chen, B., Guo, W., Liang, Y., Liu, W., Liu, L., 2012. Effects of ozone and ozone/peroxide pretreatments on disinfection byproduct formation during subsequent chlorination and chloramination. J. Hazard. Mater. 239–240, 348– 354. Zhang, G., Hua, I., 2000. Ultrasonic degradation of trichloroacetonitrile, chloropicrin and bromobenzene: design factors and matrix effects. Adv. Environ. Res. 4, 219– 224. Zhao, D., Cheng, J., Vecitis, C.D., Hoffmann, M.R., 2011. Sorption of perfluorochemicals to granular activated carbon in the presence of ultrasound. J. Phys. Chem. A 115, 2250–2257. Zouaghi, R., David, B., Suptil, J., Djebbar, K., Boutiti, A., Guittonneau, S., 2011. Sonochemical and sonocatalytic degradation of monolinuron in water. Ultrason. Sonochem. 18, 1107–1112.
Contents lists available at ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
Technical Note
Application of ultrasound and quartz sand for the removal of disinfection byproducts from drinking water Wu Yang a,b, Lili Dong a,b,c, Zhen Luo a,b, Xiaochun Cui a,b, Jiancong Liu a,b, Zhongmou Liu a,b, Mingxin Huo a,b,c,⁄ a b c
State Environmental Protection Key Laboratory of Wetland Ecology and Vegetation Restoration, Northeast Normal University, Changchun 130117, China School of Environment, Northeast Normal University, Changchun 130117, China Key Laboratory of Songliao Aquatic Environment, Ministry of Education, Jilin Architectural and Civil Engineering Institute, Changchun 130118, China
h i g h l i g h t s DBPs with log Kow P 1.97 can be sonodegraded. More chlorine atoms in the DBPs molecular structure seems easier to be adsorbed. All the 12 targeted DBPs can be removed effectively by combined use of US and QS. Part of QS particles were corroded into small particles and play a catalytic role. Enhanced mass transfer rate leading to an improvement of QS adsorption efficiency.
a r t i c l e
i n f o
Article history: Received 4 September 2013 Received in revised form 6 November 2013 Accepted 10 November 2013 Available online 2 December 2013 Keywords: Disinfection byproduct Drinking water Quartz sand Synergistic effect Ultrasound
a b s t r a c t To the best of our knowledge, little information is available on the combined use of ultrasound (US) and quartz sand (QS) in the removal of disinfection byproducts (DBPs) from drinking water. This study investigates the removal efficiency for 12 DBPs from drinking water by 20 kHz sonolytic treatment, QS adsorption, and their combination. Results indicate that DBPs with log Kow 6 1.12 could not be sonolysized; for log Kow P 1.97, more than 20% removal efficiency was observed, but the removal efficiency was unrelated to log Kow. DBPs containing a nitro group are more sensitive to US than those that comprise nitrile, hydrogen, and hydroxyl groups. Among the 12 investigated DBPs, 9 could be adsorbed by QS adsorption. The adsorption efficiency ranged from 12% for 1,1-dichloro-2-propanone to 80% for trichloroacetonitrile. A synergistic effect was found between the US and QS on DBPs removal, and all the 12 DBPs could be effectively removed by the combined use of US and QS. In the presence of US, part of the QS particles were corroded into small particles which play a role in increasing the number of cavitation bubbles and reducing cavitation bubble size and then improve the removal efficiency of DBPs. On the other hand, the presence of US enhances the DBP mass transfer rate to cavitation bubbles and quartz sand. In addition, sonolytic treatment led to a slight decrease of pH, and TOC values decreased under all the three treatment processes. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Although the disinfection of drinking water is key to suppressing microbial activity, a significant risk is associated with the formation of disinfection byproducts (DBPs) through the reactions of the disinfectants with natural organic matter. More than 600 DBPs have been identified since scientists first became aware of DBPs in the early 1970s; many of these DBPs pose risks to human ⁄ Corresponding author at: State Environmental Protection Key Laboratory of Wetland Ecology and Vegetation Restoration, Northeast Normal University, Changchun 130117, China. Tel.: +86 13756478864; fax: +86 431 89165601. E-mail address: [email protected] (M. Huo). 0045-6535/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.chemosphere.2013.11.018
health even at ppb levels (Richardson et al., 2007). Consequently, DBPs, such as THMs and haloacetic acids (HAAs) are regulated by numerous countries and organizations. Continual research has also been conducting over the past decades to satisfy the standards for drinking water quality and minimize health risks. The formation of DBPs can be controlled and minimized by using one, or a combination, of the following approaches: removing DBP precursors prior to disinfection, changing disinfectants, and removing DBPs after disinfection (Kristiana et al., 2011). Among these methods, the removal of DBP precursors is considered more satisfactory (Bond et al., 2011). However, some species tend to remain and retain significant DBP formation potential
W. Yang et al. / Chemosphere 101 (2014) 34–40
even after being treated by coagulation, anion exchange, and activated carbon adsorption (Bond et al., 2011). Significant interest has been gained on the application of advanced oxidation processes, such as O3, UV, and their combination with H2O2, as additional tools for removing DBP precursors and minimizing the formation of regulated DBPs in drinking water (Kleiser and Frimmel, 2000; Toor and Mohseni, 2007; Dotson et al., 2010; Lamsal et al., 2011; Metz et al., 2011; Penru et al., 2012; Yang et al., 2012). Nevertheless, the formation of chloral hydrate (CH), trichloronitromethane (TCNM), and haloketones, which are more toxic than THMs and HAAs, may increase during the subsequent chlorination (Metz et al., 2011; Yang et al., 2012). Alternative disinfectants, such as ClO2, O3, UV, and chloramine can efficiently reduce the formation of THMs and HAAs, but such disinfectant may cause the formation of unregulated DBPs, such as halonitromethanes, haloamides, haloacetonitriles (HANs), and nitrosamines, which pose greater health risks than those of regulated species (Richardson et al., 2007). The application of ultrasound (US) in water and wastewater treatment to degrade organic pollutants has attracted considerable attention since 1990 (Belgiorno et al., 2007; Hamdaoui and Naffrechoux, 2009). According to ‘‘hot spot’’ theory, a widely accepted explanation for sonochemical reactions in the environmental field (Chowdhury and Viraraghavan, 2009), extremely high temperatures (up to 5000 K) and high pressures (about 50 MPa) incur during the collapse of cavitation bubbles, which results in hydroxyl radicals in cavitation bubbles by water dissociation. Under ultrasonic irradiation, aqueous organic compounds can be decomposed via reaction with OH or directly pyrolysised during the collapse of cavitation bubbles. Numerous studies have been conducted to improve ultrasonic efficiency due to its significant advantages, such as safety, cleanliness, and energy conservation without secondary pollution (Gibson et al., 2008; Chowdhury and Viraraghavan, 2009; Matilainen and Sillanpää, 2010; Pang et al., 2011). Among these researches, small semiconductor particles such as titanium dioxide, silica, and alumina were reported to possess catalytic functions that enhance ultrasonic efficiency (Ragaini et al., 2001; Sekiguchi and Saita, 2001; Zouaghi et al., 2011). Adsorption is another well-established technique for removing low concentrations of organic pollutants from potable water, wastewater, and aqueous solutions (Hamdaoui and Naffrechoux, 2009). Aside from being the most widely used filter media in water plants in China, quartz sand (QS) is also used as a sorbent for removing organic pollutants from water (Liu et al., 2011a,b). Liu et al. (2011b) studied the effects of using three sorbents on removing organic pollutants in drinking water and found that QS can effectively remove 16 out of 36 organic pollutant species. By contrast, activated carbon can remove only 10 species. The authors also found that organic pollutants with low concentrations can be completely removed by QS adsorption. Using US technology to remove DBPs in drinking water has been studied for few years. Shemer and Narkis (2005) studied the ultrasonic degradation of aqueous THMs with an initial concentration of 10 mg L1. However, their results were not of representative significance as the chlorinated drinking water typically consists of a mixture of DBPs with low concentrations. Guo et al. (2006) investigated the ultrasonic removal efficiency of DBP mixtures with very low initial concentration (3.19–15.79 lg L1) in chlorinated drinking water, but only THMs were concerned. In addition, no information is available on the use of QS for the removal of DBPs from drinking water. In this study, therefore, we investigated the removal efficiency for 12 DBPs with low concentrations in drinking water by conducting through sonolytic treatment, QS adsorption, and their combination. The synergistic effect was also discussed.
35
2. Materials and methods 2.1. Materials Four THMs (chloroform (CF), bromoform (BF), bromodichloromethane (BDCM), and dibromochloromethane (DBCM)) of analytical grade were obtained from Aladdin Industrial, China. EPA 551B mixture (containing trichloroacetonitrile (TCAN), dichloroacetonitrile (DCAN), bromochloroacetonitrile (BCAN), dibromoacetonitrile (DBAN), TCNM, 1,1,1-trichloro-2-propanone (1,1,1-TCP), and 1,1dichloro-2-propanone (1,1-DCP)) and CH of analytical grade were obtained from Sigma Aldrich, USA. Na2SO4, methyl tert-butyl ether (MTBE), and QS with a 100–200 mesh (0.075–0.152 mm) diameter were purchased from Sinopharm Chemical Regency, China. 3. Experimental procedure DBPs mixture stock solution (1.2–2.0 mg mL1 for each component in methanol, except for CH in acetone) was spiked into tap water from the laboratory without any pretreatment to ensure that the spiked DBPs were approximately 200 lg L1 for THMs and 100 lg L1 for the rest. Tap water (200 mL) with spiked DBPs in a glass vessel was used in subsequent experiments. In sonolytic treatment experiments, the US was generated by a 20 kHz ultrasonicator (ZFDY, Zhengjie, China) and transferred into the water sample via an immersible titanium alloy probe (1.6 cm diameter) at a constant electrical power output of 150 W. The probe was immersed approximately 3 cm below the water surface. The sample vessel was placed in a water bath at a constant temperature of 20 ± 0.5 °C during the irradiation period. In QS adsorption experiments, 2 g of QS was immersed into a 200 mL tap water with spiked DBPs. The sample vessel was then placed in a thermostatic magnetic stirrer set at 20 °C and 200 rpm. Experiments with the combined use of US and QS were carried out to evaluate the combination’s removal efficiency for DBPs. The 200 mL tap water with the spiked DBP mixtures and 2 g QS was exposed to 20 kHz US. Samples were withdrawn for GC analysis every 15 min within 60 min for all the three treatments. A digital pH meter (WTW 3310, Germany) and a TOC analyzer (TOC-L CPH, Shimadzu, Japan) were used to monitor pH and TOC values before and after different treatment processes. All the experiments were carried out in duplicate. 3.1. Analytical methods All the 12 DBPs were measured with USEPA Method 551.1 with minor modifications. A 5 mL sample was extracted by using 1.0 mL of MTBE, 3 g of Na2SO4, and 0.2 g of phosphate buffer powder. The sample was then vigorously shaken for 2 min. MTBE extract (0.5 mL) was analyzed with a PerkinElmer Clarus 680 GC equipped with a 30 m DB-5 capillary column and an electron capture detector. The GC temperature program started at 30 °C for 8 min, and was then increased to 110 °C at 20 °C min1, and held for 1 min. The carrier and makeup gas was highly pure (>99.999%) nitrogen at 1.5 and 30.0 mL min1, respectively. The injector and detector temperatures were set at 190 and 210 °C, respectively. External standards were used for quantitative determination. 4. Results and discussion 4.1. Sonodegradation efficiencies and kinetics A solution of the spiked DBP mixture was stirred and maintained at 20 °C. Less than 5% of the DBPs appeared to be lost from
W. Yang et al. / Chemosphere 101 (2014) 34–40
4.2. Classification of DBP sensitivity to US The sonolysis of organic compounds contributes to the pyrolytic decomposition in collapsing cavitation bubbles and to the OH oxidation in bulk solution and interfacial regions (Drijvers et al., 2000). The physicochemical properties of an organic compound influence its kinetic properties and mechanisms under sonolytic destructions (Guo et al., 2006). Hua and Hoffmann (1996) stated that sonolysis is a particularly suitable method for degrading volatile hydrophobic molecules because these compounds are reactive in the largest region of a cavitation bubble. log Kow is one of the most extensively used physicochemical parameters for characterizing the water solubility of an organic compound (Donovan and Pescatore, 2002). Wu and Ondruschka (2005) studied the sonochemical removal of 26 model organic compounds in aqueous solution and found that a higher log Kow results in a higher sonolysis rate. By contrast, our study generated different results, as indicated by the comparison of the log Kow (Table 1) with corresponding kus. Fig. 2 shows that, DBPs with a log Kow 6 1.12 could not undergo sonolysis. Conversely, DBPs with a log Kow P 1.97 exhibited sonodegradation. However, the ks values were unrelated to log Kow. Wu and Ondruschka (2005) studied the sonochemical removal of 26 model organic compounds in aqueous solution and found that the Henry’s Law constant (KH) of a substrate substantially affects the degradation rate; that is, a higher KH leads to a higher sonolysis rate. In the present work, similar relations were not obtained between the kus values and KH. TCAN exhibited a KH of 1.34 106 atm L mol1, which is about 399–2740 times lower than that of THMs, but its kus value was 2.1–6.8 times higher. In the same class of compounds (THMs, HANs), however, a higher KH corresponded to a higher kus value. This finding suggests that KH is a critical parameter that controls the ultrasonic degradation of the same class of sonodegradable compounds, but it is not the dominant factor for different class of compounds. Earlier researches have indicated that compounds with a relatively higher vapor pressure tend to more effectively undergo sonodegradation (Drijvers et al., 2000; Shemer and Narkis, 2005) as indicated by the analysis of the same class of compounds (i.e., THMs, halobenzene). A similar result was found for the THMs and HANs in the present work. However, the comparison of all the sonodegradable targeted compounds did not present the same
0.0
a
ln (C/C0 )
-0.2
-0.4
-0.6 Chloroform Bromodichloromethan Dibromochloromethane Bromoform
-0.8
-1.0 0.0
b
-0.2 -0.4 -0.6
ln (C/C0 )
the solution over the experimental period. Thus, the loss of DBPs due to volatilization and photodecomposition during sonolysis is negligible. This finding is inconsistent with previous work, in which 1,1-DCP and 1,1,1-TCP decomposed in fortified drinking water even at a concentration of 50 lg L1 (Nikolaou et al., 2001). The removal efficiency for THMs with US is shown in Fig. 1a. The sonolysis removal of DBPs was successfully fitted to an integrated first-order kinetic expression. The fitting parameters are listed in Table 1. The results shown in Fig. 1 were obtained by using a mixture of all the investigated DBPs given that the sonication of mixtures only moderately affected sonication decomposition rates (Zhang and Hua, 2000). As shown in Fig. 1a, 20 kHz US degraded all the four THMs even at ppb levels, and more than 20% of these components were removed after 60 min of ultrasonic irradiation. CF (kus = 0.014 min1) was removed faster than BDCM (kus = 0.012 min1) and DBCM (kus = 0.006 min1). BF (kus = 0.004 min1) was the most recalcitrant THM to remove, this finding is consistent with previous works (Shemer and Narkis, 2005; Guo et al., 2006). Only TCAN and TCNM of the other 8 DBPs can be degraded by sonolysis (Fig. 1b and c). The kus value was 0.031 and 0.083 min1 for TCAN and TCNM, respectively. The corresponding 60 min removal efficiencies were 83% and 99% for TCAN and TCNM, respectively.
-0.8 -1.0 -1.2
Trichloroacetonitrile Dichloroacetonitrile Bromochloroacetonitrile Dibromoacetonitrile
-1.4 -1.6 -1.8 0
c
-1 -2
ln (C/C0)
36
-3 Chloral Hydrate Chloropicrin 1,1-Dichloro-2-propanone 1,1,1-Trichloro-2-propanone
-4 -5
0
10
20
30
40
50
60
Time (min) Fig. 1. DBPs removal efficiency by ultrasonic irradiation. Sonication conditions: 200 mL, 20 kHz, 150 W, 20 °C.
results. The vapor pressure increased in the order BF < CDBM < TCNM < BDCM < TCAN < CF, whereas the kus values increased in the order TCNM > TCAN > CF > BDCM > CDBM > BF. Similar to KH, vapor pressure is another critical parameter that controls the ultrasonic degradation of the same class of sonodegradable compounds; however, it is not the dominant factor for different class of compounds. The functional group significantly influences the physicochemical properties of an organic compound. However, little information is available on the effects of the functional group presenting in DBPs on sonodegradation kinetics. The comparison of the kus values of TCNM, TCAN, CH, 1,1,1-TCP, and CF indicates that the functional groups (i.e., k value) were ranked as follows: nitro (kus = 0.083 min1) > nitrile (kus = 0.031 min1) > hydrogen (kus = 0.014 min1) > hydroxyl (kus = 0) carbonyl (kus = 0). This rank indicates that compounds containing a nitro group are more sensitive to US than those that comprise nitrile, hydrogen, and hydroxyl groups. 4.3. DBPs removal by QS adsorption QS has proven to be an efficient sorbent in adsorbing organic pollutants in drinking water (Liu et al., 2011a) and wastewater
37
W. Yang et al. / Chemosphere 101 (2014) 34–40 Table 1 Physical and chemical properties and fitted parameters of the investigated compounds. Vp (kPa)
log Kow
KH (atm L mol1)
kus (min1)
kqs (min1)
qe (lg g1)
kc (min1)
67-66-3
26.26
1.97
3.67 103 (24 °C)
0.014
0.006
49.7
0.046
BDCM
75-27-4
6.67
2.0
2.12 103
0.012
0.010
20.1
0.040
CDBM
124-48-1
0.74
2.16
7.83 104 (20 °C)
0.006
0.024
10.0
0.028
BF
75-25-2
0.72
2.38
5.34 104
0.004
0.027
8.3
0.017
HANs TCAN
545-06-2
7.73
2.09
1.34 106
0.031
0.026
13.3
0.080
DCAN
3018-12-0
0.38
0.29
3.79 106
–
0.021
3.0
0.025
BCAN
83463-62-1
0.12
0.38
1.24 106
–
–
–
0.014
DBAN
3252-43-5
0.04
0.47
4.06 107
–
–
–
0.018
Misc. DBPs TCNM
76-06-2
3.20
2.09
2.05 103
0.083
0.013
10.3
0.16
CH
302-17-0
2.00
0.99
5.71 109
–
–
–
0.016
1,1-DCP
513-88-2
3.60
0.2
6.15 106
–
0.025
0.9
0.017
1,1,1-TCP
918-00-3
0.56
1.12
2.17 106
–
0.017
6.6
0.069
Compound
CAS No.
THMs CF
Structure
Vp: Vapor pressure at 25 °C; KH: Henrys law constant at 25 °C; log Kow: Octanol–water partition coefficient; kus: first order kinetic constant for sonodegradation; kqs: first order kinetic constant for quartz sand adoption; qe: the predicated adsotpion capcacity for quartz sand; kc: first order kinetic constant for combined use ultrasound and quartz sand.
38
W. Yang et al. / Chemosphere 101 (2014) 34–40
0.08
-1
kus (min )
0.06
0.04
0.02
0.00 0.0
0.5
1.0
1.5
2.0
2.5
logKow Fig. 2. Relationship between the sonolysis rate constant and octanol–water partition coefficient of the investigated DBPs. Sonication conditions: 200 mL, 20 kHz, 150 W, 20 °C.
6.5
a
6.0 5.5
ln(qe-qt)
5.0 4.5 4.0 Chloroform Bromodichloromethane Dibromochloromethane Bromoform
3.5 3.0 5.0
b
4.5
ln(qe-qt)
4.0 3.5 3.0 Trichloroacetonitrile Dichloroacetonitrile
2.5 2.0
c
4.5 4.0
ln(qe-qt)
3.5 3.0
Fig. 3 and Table 1 show that 9 of the 12 DBPs can be adsorbed by QS to a certain extent. The 60 min adsorption efficiency ranged from 12% for 1,1-DCP to 80% for TCAN. The adsorption kinetics of DBPs onto QS was fitted by the pseudo first-order kinetic model as lnðqe qt Þ ¼ ln qe kqs t (the kinetic constant expressed as kqs). The kqs value ranged from 0.002 min1 for 1,1-DCP to 0.046 min1 for TCAN, and the predicated adsotpion capcacity ranged from 1 lg g1 for 1,1-DCP to 50 lg g1 for CF. As for THMs, more than 30% of all the four THMs could be adsorbed by QS within 60 min. The 60 min adsorption efficiency and adsotpion capcacity increased with the increasing number of chlorine atoms in the molecular structure which follows the order of CF (59%, 50 lg g1) > BDCM (51%, 20 lg g1) > CDBM (38%, 10 lg g1) > BF (33%, 7 lg g1). It is well known that silica is the main component of QS, and the surface siloxane bonds (Si–O) of original silicas may hydrolysis to silanols (Si–OH) (Bambrough et al., 1998; Dou et al., 2011). The silanol groups have very strong polar interactivity which is more sensitive to chlorine atoms than to bromine atoms; thus, higher adsorption efficiency was observed for the component with more chlorine atoms in the molecular structure. QS adsorption was observed only for TCAN and DCAN of the four HANs. As mentioned above, the much higher adsorption efficiency was observed for TCAN than for DCAN because of the presence of more chlorine atoms in TCAN. The 60 min adsorption efficiency was 79% and 23% for TCAN and DCAN, and the corresponding adsorption capacity was 13 and 3 lg g1, respectively. Both BCAN and TBAN did not show adsorption by QS because they are lack of chlorine atoms in their molecular structures. Although the molecular structure of CH has three chlorine atoms, no adsorption efficiency was observed. The adsorption capacity for TCNM, 1,1,1-TCP, and 1,1-DCP were 10, 7, and 1 lg g1, respectively. The corresponding 60 min adsorption efficiencies were 50%, 35%, and 12%, respectively. 4.4. DBPs removal by combined use of US and QS As shown in Fig 4, the DBPs removal efficiency by combined use of US and QS was successfully fitted to an integrated (pseudo) firstorder kinetic expression (the kinetic constant expressed as kc). Fig. 4 and Table 1 show that all the 12 targeted DBPs could be effectively removed by the combined use of US and QS. The 60 min removal efficiency ranged from 51% for BCAN to 100% for TCNM. The kc value ranged from 0.014 to 0.16 min1, respectively. At least 51% of BCAN, DBAN, and CH, which cannot be removed by US and QS, were removed within 60 min with the combined use of US and QS. This finding indicates a synergistic effect between US and QS on DBPs removal—a result that makes the removal of DBPs in drinking water by combined use of US and QS an interesting topic to explore. 4.5. Synergistic effects between US and QS
2.5 2.0 1.5
Chloropicrin 1,1,1-trichloro-2-propanone 1,1-dichloro-2-propanone
1.0 0.5 0
10
20
30
40
50
60
Time (min) Fig. 3. DBPs removal efficiency by QS adsorption. Adsorption conditions: 200 mL, 2 g QS, 200 rpm, 20 °C.
(Liu et al., 2011b). In the present work, 2 g of QS was immersed into a 200 mL DBPs mixture to investigate its adsorption characteristics.
In this study, QS with a 100–200 mesh (0.075–0.152 mm) diameter was used. We determined the mass of QS by weighing the amount of QS passing through a 200 mesh sieve before and after 60 min sonolytic treatment. The mass distribution of the QS with a 100–200 mesh diameter was slightly lower (4–7%) after sonolytic treatment. Correspondingly, the BET surface area increased slightly (from 0.95 to 1.12 m2 g1), which is inconsistent with previous works that activated carbon was used as sorbent (Hamdaoui and Naffrechoux, 2009; Zhao et al., 2011). This finding indicates that part of the QS particles were corroded into small particles (smaller than 200 mesh) under sonolytic treatment. Previous studies have demonstrated that small semiconductor particles (from nm to lm scale), such as titanium dioxide, silica, and alumina, play a
39
W. Yang et al. / Chemosphere 101 (2014) 34–40
7.2
a
-0.5
7.0
-1.0
6.8
-1.5
6.6
pH
ln (C/C0)
0.0
-2.0
6.4
Chloroform Bromodichloromethan Dibromochloromethane Bromoform
-2.5
a
6.2
-3.0 0
6.0
b
b
3.0
-1
TOC (mg/L)
ln (C/C0)
2.8
-2
-3 Trichloroacetonitrile Dichloroacetonitrile Bromochloroacetonitrile Dibromoacetonitrile
-4
2.4 2.2
-5 0
c
2.0
Raw
Sonolytic QS adsorption
US+ QS
Fig. 5. Variations of solution pH (a) and TOC (b) values under different treatment processes.
-1
ln (C/C0)
2.6
-2
-3 Chloral Hydrate Chloropicrin 1,1-Dichloro-2-propanone 1,1,1-Trichloro-2-propanone
-4
-5
0
10
20
30
40
50
60
Time (min) Fig. 4. DBPs removal efficiency by combined use of US and QS. Conditions: 200 mL, 20 kHz US with 150 W output power, 2 g QS, 200 rpm, 20 °C .
catalytic role in promoting ultrasonic efficiency, particularly at low frequency (Ragaini et al., 2001; Sekiguchi and Saita, 2001; Zouaghi et al., 2011). According to these studies, the presence of small particles increases the number of cavitation bubbles and reduces cavitation bubble size. The increase in cavitation bubbles improves the pyrolysis of organic compounds, thereby enhances sonolysis efficiency. All the DBPs that cannot be removed by US expressed a lag phase under the combined treatment. As mentioned in Section 3.2, hydrophilic compounds are indirectly decomposed primarily through their reaction with OH, which is produced during the cavitation process. Lim et al. (2011) found that the majority of OH is scavenged in bubbles at low frequencies (i.e., 20 kHz) and is unavailable in bulk solutions and interfacial regions. However, more available OH can escape from the bubbles and react with organic compounds when the presence of small particles in water solution. A considerable amount of time is needed for US to corrode QS particles into small particles, which play a catalytic role to generate more OH, thus, a lag phase occurred and the competition for OH among DBPs caused a different lag phase. We also investigated DBP adsorption by QS, which was treated by 20 kHz US irradiation. Although a minor change in the BET
surface was found, no significant difference in DBP adsorption efficiency was observed between QS and ultrasonic treated QS (data not shown). This finding indicates that the increased DBP removal efficiency was not attributed to the change of the surface properties of QS. Researches have found that the adsorption efficiency of activated carbon significantly increased under sonolytic treatment even though no BET surface changes was observed (Hamdaoui and Naffrechoux, 2009; Lim et al., 2011). Many scholars have suggested that extreme conditions, such as high-speed micro-jets, high-pressure shock waves, and acoustic vortex micro-streaming, occur during sonolytic treatment (Hamdaoui et al., 2003; Nouri and Hamdaoui, 2007; Chowdhury and Viraraghavan, 2009; Hamdaoui and Naffrechoux, 2009). Thus, the mass transfer improves at bulk solutions and liquid–solid interfaces, thereby enhances adsorption efficiency. Thus, increased QS adsorption efficiency may occur under sonolytic treatment due to the extreme conditions.
4.6. Variations of pH and TOC under different treatment processes The pH and TOC values of the samples before and after different treatment processes are compared in Fig. 5. As can be seen, the pH values decreased slightly from 7.1 to 6.8 and 6.6 under the treatment of sonolytic and combined use of US and QS, respectively. QS adsorption did not change the solution pH. The decreased pH may be attributed to the formation of acidic intermediates and products in the presence of US (Guo et al., 2006), and the presence of QS may enhance the formation of intermediates and products. It is notable that though pH values decreased, it is still in the acceptable range of drinking water quality (6.5–8.5) in China. The TOC values decreased from 3.1 mg L1 to 2.8, 2.9 and 2.5 mg L1 under the treatment of sonolytic, QS adsorption and the combination of US and QS, respectively. The decreased TOC is larger than the carbon concentrations contributed from the 12
40
W. Yang et al. / Chemosphere 101 (2014) 34–40
DBPs, indicating these treatment processes can also remove other organic compounds presented in drinking water. The lowest TOC was detected under the combination of US and QS also indicating a synergistic effect between US and QS. Acknowledgments The authors wish to thank the Natural Science Foundation of China (51238001 and 51278093) and the Fundamental Research Funds for the Central Universities (11SSXT139) for their financial support. References Bambrough, C.M., Slade, R.C.T., Williams, R.T., 1998. Synthesis of a large pore phenyl-modified mesoporous silica and its characterization by nitrogen and benzene sorption. J. Mater. Chem. 8, 569–571. Belgiorno, V., Rizzo, L., Fatta, D., Rocca, C.D., Lofrano, G., Nikolaou, A., Naddeo, V., Meric, S., 2007. Review on endocrine disrupting-emerging compounds in urban wastewater: occurrence and removal by photocatalysis and ultrasonic irradiation for wastewater reuse. Desalination 215, 166–176. Bond, T., Goslan, E.H., Parsons, S.A., Jefferson, B., 2011. Treatment of disinfection byproduct precursors. Environ. Technol. 32, 1–25. Chowdhury, P., Viraraghavan, T., 2009. Sonochemical degradation of chlorinated organic compounds, phenolic compounds and organic dyes – a review. Sci. Total Environ. 407, 2474–2492. Donovan, S.F., Pescatore, M.C., 2002. Method for measuring the logarithm of the octanol–water partition coefficient by using short octadecyl–poly (vinyl alcohol) high-performance liquid chromatography columns. J. Chromatogr. A 952, 47–61. Dotson, A.D., Keen, V.S., Metz, D., Linden, K.G., 2010. UV/H2O2 treatment of drinking water increases post-chlorination DBP formation. Water Res. 44, 3703–3713. Dou, B., Hu, Q., Li, J., Qiao, S., Hao, Z., 2011. Adsorption performance of VOCs in ordered mesoporous silicas with different pore structures and surface chemistry. J. Hazard. Mater. 186, 1615–1624. Drijvers, D., Van Langenhove, H., Herrygers, V., 2000. Sonolysis of fluoro-, chloro-, bromo- and iodobenzene: a comparative study. Ultrason. Sonochem. 7, 87–95. Gibson, J.H., Yong, D.H.N., Farnood, R.R., Seto, P., 2008. A literature review of ultrasound technology and its application in wastewater disinfection. Water Qual. Res. J. Can. 43, 23–35. Guo, Z., Gu, C., Zheng, Z., Feng, R., Jiang, F., Gao, G., Zheng, Y., 2006. Sonodegradation of halomethane mixtures in chlorinated drinking water. Ultrason. Sonochem. 13, 487–492. Hamdaoui, O., Naffrechoux, E., 2009. Adsorption kinetics of 4-chlorophenol onto granular activated carbon in the presence of high frequency ultrasound. Ultrason. Sonochem. 16, 15–22. Hamdaoui, O., Naffrechoux, E., Tifouti, L., Pétrier, C., 2003. Effects of ultrasound on adsorption–desorption of p-chlorophenol on granular activated carbon. Ultrason. Sonochem. 10, 109–114. Hua, I., Hoffmann, M.R., 1996. Kinetics and mechanism of the sonolytic degradation of CCl4: intermediates and byproducts. Environ. Sci. Technol. 30, 864–871. Kleiser, G., Frimmel, F.H., 2000. Removal of precursors for disinfection by-products (DBPs) — differences between ozone- and OH-radical-induced oxidation. Sci. Total Environ. 256, 1–9.
Kristiana, I., Joll, C., Heitz, A., 2011. Powdered activated carbon coupled with enhanced coagulation for natural organic matter removal and disinfection byproduct control: Application in a Western Australian water treatment plant. Chemosphere 83, 661–667. Lamsal, R., Walsh, M.E., Gagnon, G.A., 2011. Comparison of advanced oxidation processes for the removal of natural organic matter. Water Res. 45, 3263–3269. Lim, M., Son, Y., Khim, J., 2011. Frequency effects on the sonochemical degradation of chlorinated compounds. Ultrason. Sonochem. 18, 460–465. Liu, H., Feng, S., Du, X., Zhang, N., Liu, Y., 2011a. Comparison of three sorbents for organic pollutant removal in drinking water. Energy Procedia 5, 985–990. Liu, J., Wang, X., Fan, B., 2011b. Characteristics of PAHs adsorption on inorganic particles and activated sludge in domestic wastewater treatment. Bioresour. Technol. 102, 5305–5311. Matilainen, A., Sillanpää, M., 2010. Removal of natural organic matter from drinking water by advanced oxidation processes. Chemosphere 80, 351–365. Metz, D.H., Meyer, M., Dotson, A., Beerendonk, E., Dionysiou, D.D., 2011. The effect of UV/H2O2 treatment on disinfection by-product formation potential under simulated distribution system conditions. Water Res. 45, 3969–3980. Nikolaou, A.D., Lekkas, T.D., Kostopoulou, M.N., Golfinopoulos, S.K., 2001. Investigation of the behaviour of haloketones in water samples. Chemosphere 44, 907–912. Nouri, L., Hamdaoui, O., 2007. Ultrasonication-assisted sorption of cadmium from aqueous phase by wheat bran. J. Phys. Chem. A 111, 8456–8463. Pang, Y.L., Abdullah, A.Z., Bhatia, S., 2011. Review on sonochemical methods in the presence of catalysts and chemical additives for treatment of organic pollutants in wastewater. Desalination 277, 1–14. Penru, Y., Guastalli, A.R., Esplugas, S., Baig, S., 2012. Application of UV and UV/H2O2 to seawater: disinfection and natural organic matter removal. J. Photochem. Photobiol., A 233, 40–45. Ragaini, V., Selli, E., Bianchi, C.L., Pirola, C., 2001. Sono-photocatalytic degradation of 2-chlorophenol in water: kinetic and energetic comparison with other techniques. Ultrason. Sonochem. 8, 251–258. Richardson, S.D., Plewa, M.J., Wagner, E.D., Schoeny, R., Demarini, D.M., 2007. Occurrence, genotoxicity, and carcinogenicity of regulated and emerging disinfection by-products in drinking water: a review and roadmap for research. Mutat. Res.-Rev. Mutat. 636, 178–242. Sekiguchi, H., Saita, Y., 2001. Effect of alumina particles on sonolysis degradation of chlorobenzene in aqueous solution. J. Chem. Eng. Jpn. 34, 1045–1048. Shemer, H., Narkis, N., 2005. Sonochemical removal of trihalomethanes from aqueous solutions. Ultrason. Sonochem. 12, 495–499. Toor, R., Mohseni, M., 2007. UV-H2O2 based AOP and its integration with biological activated carbon treatment for DBP reduction in drinking water. Chemosphere 66, 2087–2095. Wu, Z., Ondruschka, B., 2005. Roles of hydrophobicity and volatility of organic substrates on sonolytic kinetics in aqueous solutions. J. Phys. Chem. A 109, 6521–6526. Yang, X., Peng, J., Chen, B., Guo, W., Liang, Y., Liu, W., Liu, L., 2012. Effects of ozone and ozone/peroxide pretreatments on disinfection byproduct formation during subsequent chlorination and chloramination. J. Hazard. Mater. 239–240, 348– 354. Zhang, G., Hua, I., 2000. Ultrasonic degradation of trichloroacetonitrile, chloropicrin and bromobenzene: design factors and matrix effects. Adv. Environ. Res. 4, 219– 224. Zhao, D., Cheng, J., Vecitis, C.D., Hoffmann, M.R., 2011. Sorption of perfluorochemicals to granular activated carbon in the presence of ultrasound. J. Phys. Chem. A 115, 2250–2257. Zouaghi, R., David, B., Suptil, J., Djebbar, K., Boutiti, A., Guittonneau, S., 2011. Sonochemical and sonocatalytic degradation of monolinuron in water. Ultrason. Sonochem. 18, 1107–1112.
