► Effective SMT degradation can be achieved by UV/persulfate oxidation treatment. ► The degradation rate and mineralization degree of SMT were influenced by the S2O82- dose and pH. ► Mass ...spectrometry was applied for identification of intermediates and products. ► Degradation mechanisms were proposed according to the results of LC–MS analysis.
Ultraviolet light (UV)/persulfate (S2O82-) oxidation of a pharmaceutically active compound, sulfamethazine (SMT), was studied in a stainless steel photo-reactor. During the treatment, UV photolytic S2O82- activation to produce highly reactive sulfate radicals (SO4-) to decompose SMT in water. The treatment was advantageous over direct photolysis or persulfate oxidation alone and UV/H2O2 oxidation, suggesting that SO4- is a very effective agent to remove SMT from water. Under the experimental conditions, the SMT degradation exhibited a pseudo-first-order reaction pattern. The degradation rate was influenced by the S2O82- dose and solution pH. Typically, a high persulfate dose could achieve a high SMT removal. In contrast, both the highest SMT degradation rate and the lowest mineralization degree were observed at pH 6.5, while the highest mineralization extent was accomplished at pH 11. The complex pH effect may be associated with the fact that the total radical concentration and fractions of the different radicals were varied with pH. Finally, the major SMT degradation products were identified, and the primary reaction pathways were proposed. This study demonstrated that UV/persulfate is a viable option for controlling SMT pollution in water.
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•Removal efficiency of iopamidol followed the order of UV/Cl2 > UV/H2O2 > .•UV/NH2Cl > UV/ClO2 > UV.•EE/O of iopamidol degradation followed the trend of ...UV/ClO2 > UV > UV/NH2Cl > UV/H2O2 > UV/Cl2.•The pH behaviors of UV-based AOPs upon iopamidol in 5–9 exhibited quite differently.•UV/Cl2 and UV/NH2Cl enhanced classical DBPs and I-THMs while UV/ClO2 and UV/H2O2 exhibited elimination effect.•The risk ranking of DBPs-related toxicity was UV/NH2Cl > UV/Cl2 > UV > UV/H2O2 > UV/ClO2.
The UV-induced advanced oxidation processes (AOPs, including UV/Cl2, UV/NH2Cl, UV/ClO2 and UV/H2O2) degradation kinetics and energy requirements of iopamidol as well as DBPs-related toxicity in sequential disinfection were compared in this study. The photodegradation of iopamidol in these processes can be well described by pseudo-first-order model and the removal efficiency ranked in descending order of UV/Cl2 > UV/H2O2 > UV/NH2Cl > UV/ClO2 > UV. The synergistic effects could be attributed to diverse radical species generated in each system. Influencing factors of oxidant dosage, UV intensity, solution pH and water matrixes (Cl−, NH4+ and nature organic matter) were evaluated in detail. Higher oxidant dosages and greater UV intensities led to bigger pseudo-first-order rate constants (Kobs) in these processes, but the pH behaviors exhibited quite differently. The presence of Cl−, NH4+ and nature organic matter posed different effects on the degradation rate. The parameter of electrical energy per order (EE/O) was adopted to evaluate the energy requirements of the tested systems and it followed the trend of UV/ClO2 > UV > UV/NH2Cl > UV/H2O2 > UV/Cl2. Pretreatment of iopamidol by UV/Cl2 and UV/NH2Cl clearly enhanced the production of classical disinfection by-products (DBPs) and iodo-trihalomethanes (I-THMs) during subsequent oxidation while UV/ClO2 and UV/H2O2 exhibited almost elimination effect. From the perspective of weighted water toxicity, the risk ranking was UV/NH2Cl > UV/Cl2 > UV > UV/H2O2 > UV/ClO2. Among the discussed UV-driven AOPs, UV/Cl2 was proved to be the most cost-effective one for iopamidol removal while UV/ClO2 displayed overwhelming advantages in regulating the water toxicity associated with DBPs, especially I-THMs. The present results could provide some insights into the application of UV-activated AOPs technologies in tradeoffs between cost-effectiveness assessment and DBPs-related toxicity control of the disinfected waters containing iopamidol.
The degradation of metoprolol (MTP), a β-blocker commonly used for cardiovascular diseases, by UV/chlorine and UV/H2O2 processes was comparatively evaluated. MTP direct photolysis at 254 nm could be ...neglected, but remarkable MTP degradation was observed in both the UV/chlorine and UV/H2O2 systems. Compared with UV/H2O2, UV/chlorine has a more pronounced MTP degradation efficiency. In addition to primary radicals (OH and Cl), secondary radicals (ClO and Cl2–) played a pivotal role in degrading MTP by UV/chlorine process. The relative contributions of hydroxyl radicals (OH) and reactive chlorine species (RCS) in the UV/chlorine system varied at different solution pH values (i.e., the contribution of RCS increased from 57.7% to 75.1% as the pH increased from 6 to 8). The degradation rate rose as the oxidant dosage increased in the UV/chlorine and UV/H2O2 processes. The presence of Cl− slightly affected MTP degradation in both processes, while the existence of HCO3− and HA inhibited MTP degradation to different extents in both processes. In terms of the overall cost of electrical energy, UV/chlorine is more cost efficient than UV/H2O2. The degradation products during the two processes were identified and compared, and the degradation pathways were proposed accordingly. Compared with the direct chlorination of MTP, pre-oxidation with UV/chlorine and UV/H2O2 significantly enhanced the formation of commonly known DBPs. Therefore, when using UV/chlorine and UV/H2O2 in real waters to remove organic pollutants, the possible risk of enhanced DBP formation resulting from the degradation of certain pollutants during post-chlorination should be carefully considered.
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•The degradation of metoprolol by UV/chlorine and UV/H2O2 was compared.•The relative contribution of RCS and OH during UV/chlorine treatment was evaluated.•MTP products were identified, and degradation pathways were proposed.•UV/chlorine and UV/H2O2 pretreatment enhanced DBP formation.•UV/chlorine seems to be more economical than UV/H2O2 in degrading MTP.
•US enhanced heterogeneous activation of PS by nZVI and PRO degradation.•Several key parameters has a profound effect on PRO degradation.•Variations of nZVI before and after use were characterized by ...TEM, XRD, and XPS.•Possible degradation mechanisms of US/nZVI/PS process were suggested.
This study investigated the degradation of propranolol (PRO), a beta (β)-blockers, by nano zero-valent iron (nZVI) activated persulfate (PS) under ultrasonic irradiation. Effects of several critical factors were evaluated, inclusive of PS concentration, nZVI dosage, ultrasound power, initial pH, common anions, and chelating agent on PRO degradation kinetics. Higher PS concentration, nZVI dosage and ultrasound power as well as acidic pH favored the PRO degradation. Conversely, anions and chelating agent took on the inhibitory effect towards PRO degradation to different extents. Furthermore, the variations of morphology and surface composition of nZVI before and after the reaction were characterized by TEM, XRD and XPS. Finally, on the basis of identified degradation intermediates by LC/MS/MS analysis, this work tentatively proposed the degradation pathways. These encouraging results suggest that US/nZVI/PS process is a promising strategy for the treatment of PRO-induced water pollutant.
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•The degradation of SMP in water was accomplished by UV-activated persulfate.•The second-order rate constants of SMP with SO4– and OH were derived.•Degradation pathways based on ...transformation products analysis were proposed.•Impacts of UV/PS treatment on DBP formation during post-chlorination were evaluated.
The kinetics and mechanisms of the degradation of sulfamethoxypyridazine (SMP) by an ultraviolet-activated persulfate (UV/PS) advanced oxidation process (AOP) and the formation of disinfection byproducts (DBPs) during subsequent chlorination were investigated in this study. The UV/PS process can significantly remove SMP through pseudo-first-order reaction kinetics. In a competitive kinetic experiment, the second-order rate constant of SMP with sulfate radical was determined to be 2.73 × 1010 M−1 s−1, while that with hydroxyl radical was 2.22 × 1010 M−1 s−1. Six major transformation products in SMP degradation were recognized by LC/MS/MS analysis. It was assumed that the degradation pathway of SMP involves the hydroxylation of the aromatic ring, cleavage of the sulfonamide bond, oxidation of the aniline moiety and elimination of SO2. The impacts of persulfate dose, pH, anions (HCO3–, SO42−, and Br−) and humic acid (HA) concentration on SMP degradation efficiency and DBP formation during subsequent chlorination were also examined. SMP degradation was accelerated with increasing persulfate dose, HCO3– and Br- concentration as well as decreasing pH and HA concentration. However, the amount of chloroform (CF) formed was reduced under a higher persulfate dosage and lower pH. In contrast, the amount of dichloroacetonitrile (DCAN) formed was enhanced under a higher persulfate dose and lower pH. Adding HA also increased the formation of both CF and DCAN. While, both HCO3– and SO42– had little effects on the formation of CF and DCAN. The presence of Br– had no significant effects on the bromine incorporation factors (BIFs) of trihalomethanes (THMs) and dihaloacetonitriles (DHANs). Raw water experiments showed that the UV/PS process could destroy SMP in natural water as well as control the formation of DBPs.
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•OH and RCS contributions to ATL degradation during UV/chlorine were investigated.•Effects of several key water quality parameters on ATL degradation were evaluated.•Intermediates and ...disinfection byproducts during ATL decomposition were identified.•The variation of acute toxicity during UV/chlorine process was assessed.
Degradation of atenolol (ATL) was achieved using combination of UV and chlorine treatment (UV/chlorine). Factors affecting ATL degradation, such as pH, chlorine dosage, common anions and natural organic matter (NOM), were systematically studied. ATL degradation could be described by the pseudo-first-order reaction kinetics. Combination of UV-254 nm and 100 μM of chlorine at pH 7 demonstrated 93.5% removal of 10 μM of ATL within 20 min. Radical scavenging tests indicated that both hydroxyl radicals (OH) and reactive chlorine species (RCS) participated in ATL degradation by UV/chlorine. The highest degradation rate was achieved at acidic pH. The contribution of RCS towards ATL degradation elevated as pH value increased. ATL degradation rate constant directly correlated with chlorine dosage in the 0–100 μM range. Scavenging effect of the excess chlorine occurred above 200 μM. HCO3− and NOM presence negatively affected ATL degradation, while Br− had a positive effect. Presence of Cl− had no noticeable impact on ATL degradation. Several ATL degradation pathways were proposed based on analysis of intermediate degradation products obtained using LC/MS/MS technique. Five typical disinfection byproducts including trichloromethane, dichloroacetaldehyde, trichloroacetonitrile, trichloroacetaldehyde and dichloroacetonitrile were detected. Although some intermediate products could potentially be more toxic than ATL, they were very likely further oxidized forming products with lower toxicity. In general, we demonstrated that UV/chlorine AOP is an effective approach to purify ATL contaminated water.
In this study, nano zero-valent iron (nZVI) was utilized to activate persulfate (PS) for the degradation of metoprolol (MTP), a commonly used drug for curing cardiovascular diseases, in water. ...Quenching tests indicated that both the sulfate radical (SO
4
&z.rad;
−
) and hydroxyl radical (&z.rad;OH) contributed to the degradation of MTP, while SO
4
&z.rad;
−
seemed to play a large role under natural pH conditions. Batch tests were conducted to investigate the effects of several influencing factors, such as PS concentration, initial MTP concentration, pH, temperature and common anions, on the degradation performance of MTP. Generally, lower MTP concentration and pH values, and higher PS concentration and temperature favoured MTP degradation. HCO
3
−
, NO
3
−
and SO
4
2−
were found to inhibit MTP degradation, while Cl
−
enhanced MTP degradation. Several corrosion products of nZVI, including Fe
3
O
4
, Fe
2
O
3
and FeSO
4
, were formed during the reaction, which was reflected by the combined XRD and XPS analysis. Degradation pathways of MTP were proposed according to the identified transformation products, and the peak areas of the major products along with the time were also monitored. Finally, the toxicity of the reaction solution was assessed by experiments using
Aliivibrio fischeri
. Overall, it could be concluded that nZVI/PS might be a promising method for the rapid treatment of MTP-caused water pollution.
The influencing factors, mechanism and toxicity of MTP degradation by nZVI activated persulfate were investigated.
•Ultrasonically induced degradation of KET and PCT was investigated for comparison.•Various factors affecting ultrasonic degradation behavior were evaluated.•Degradation pathways in the ultrasonic ...process were proposed.•The toxicity of the reaction solution decreased, as reflected in HUVECs.•Ultrasonic treatment enhanced the formation of TCM and TCNM during postchlorination.
The present study comparatively investigated the ultrasonic degradation of ketoprofen (KET) and paracetamol (PCT) in water. Ultrasonic irradiation at 555 kHz achieved rapid degradation of KET and PCT in water, the removal efficiencies of KET (2.5–80 μM) and PCT (2.5–80 μM) reached 87.7%-100% and 50.6%-86.9%, respectively, after 10 min of reaction under an ultrasonic power of 60 W. The degradation behaviors of both KET and PCT followed the Langmuir-Hinshelwood model. KET was eliminated faster than PCT because of its higher hydrophobicity. Acidic media favored ultrasonic degradation of KET and PCT. Organic compounds in water matrices exerted a great negative effect on the ultrasonic degradation rates of KET and PCT major by competing with target compounds with the generated radicals at the bubble/water interfacial region. The effects of anions were species dependent. The introduction of ClO4− and Cl− enhanced KET and PCT degradation to different extents, while the introduction of HCO3− posed a negative effect on both KET and PCT. KET and PCT degradation are accompanied by the generation of several transform intermediates, as identified via LC/MS/MS analysis, and corresponding reaction pathways have been proposed. A human umbilical vein endothelial cell (HUVEC) toxicity evaluation indicated that ultrasonic treatment was capable of controlling the toxicity of KET or PCT degradation. Of note, the enhanced formation of disinfection byproducts (DBPs), i.e., trichloromethane (TCM) and trichloronitromethane (TCNM), was found due to chlorination after ultrasonic treatment for both KET and PCT.
In this study, the degradation of propranolol (PRO) by UV/persulfate process was systematically investigated. Direct photolysis of PRO was limited due to its low quantum yield, while the PRO ...degradation efficiency can be greatly promoted by the combination of persulfate and UV irradiation. Radical scavenging tests showed that both SO4– and OH contributed to the removal of PRO, with SO4– playing a more important role. The degradation rate of PRO was improved by increasing the persulfate dose and initial solution pH consistent with pseudo-first-order reaction kinetics. The effects of common water constituents were species dependent. HCO3− and Cl− promoted PRO degradation. By contrast, NO3− and HA were found to inhibit PRO degradation. A total of nine degradation products were identified by LC/MS/MS, which mainly derived from the ring-opening attack on the naphthalene group or oxidation of the amino moiety by SO4– and OH. Finally, the toxicity of the reaction mixtures was also assessed using luminescent bacteria Vibrio fischeri, and the results indicated that UV/persulfate is capable of controlling the toxicity of PRO degradation.
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•UV-activated persulfate was applied on PRO oxidation.•Various factors influence PRO degradation to different extent.•Naphthalene ring and amino moiety in PRO molecule were two reactive sites.•UV/persulfate is capable of controlling the toxicity during PRO degradation.
In this study, electrochemically activated peroxymonosulfate (EC/PMS) with a sacrificial iron electrode was used for the removal of chloramphenicol (CAP) from water. Compared to electrolysis alone, ...peroxymonosulfate (PMS) alone, and Fe
2+
/PMS, EC/PMS significantly enhanced the CAP degradation. Various parameters, such as the applied current, electrolyte concentration, and PMS dose, were investigated to optimize the process. In addition, acidic conditions facilitated the CAP degradation. The presence of Cl
−
slightly enhanced the CAP degradation, while both HCO
3
−
and NO
3
−
exhibited an inhibitory effect on the CAP degradation. The floccules were also analyzed after the reaction by XPS and XRD. Quenching experiments indicated that both sulfate radicals (SO
4
●−
) and hydroxyl radicals (•OH) were responsible for the CAP degradation. In addition, the degradation products were identified by LC/TOF/MS, and the degradation pathways were proposed accordingly. These results indicated that EC/PMS is a promising treatment process for the remediation of water polluted by CAP.
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