WATER RESEARCH
·
2019
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IF 7.913
Xinran Zhang,Pengfei Ren,Weiguang Li,Yu Lei,Xin Yang,Ernest R. Blatchley
The presence of ammonium (NH 4 + ) in drinking water treatment results in inhibition of disinfection efficiency and formation of nitrogenous disinfection by-products. Our previous study found monochloramine (NH 2 Cl) photolysis under 254 nm UV irradiation can be effective for removal of NH 4 + ; however, the mechanisms of NH 4 + degradation in this process were unknown. The kinetics and fundamental radical chemistry responsible for NH 4 + removal in the UV/NH 2 Cl process were investigated in this study. The results showed that the pseudo first-order rate constant for NH 4 + degradation in the UV/NH 2 Cl process ranged between 3.6 × 10 −4 to 1.8 × 10 −3 s −1 . Solution pH affected radical conversion and a higher NH 4 + degradation efficiency was achieved under acidic conditions. The effects of chloride were limited; however, the presence of either bicarbonate or natural organic matter scavenged radicals and inhibited NH 4 + removal. NH 2 Cl photolysis generated an aminyl radical (NH 2 • ) and a chlorine radical (Cl • ) that further transformed to a chlorine dimer (Cl 2 •- ) and a hydroxyl radical (HO • ). The second-order rate constants for Cl • and Cl 2 •- reacting with NH 4 + were estimated as 2.59 × 10 8 M −1 s −1 and 3.45 × 10 5 M −1 s −1 at pH 3.9, respectively. Cl • , Cl 2 •- , and HO • contributed 95.2%, 3.5%, and 1.3% to NH 4 + removal, respectively, at the condition of 3 mM NH 2 Cl and pH 7.5. Major products included nitrite and nitrate, possibly accompanied by nitrogen-containing gases. This investigation provides insight into the photochemistry of NH 4 + degradation in the UV/NH 2 Cl process and offers an alternative method for drinking water production.
研究领域:
环境科学
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饮用水处理
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产品关联
DOI
PubMed
高影响因子
Journal of Environmental Sciences
·
2022
·
IF 6.796
Shuang Zhang,Yi-Li Lin,Tian-Yang Zhang,Chen-Yan Hu,Zhi Liu,Zheng-Yu Dong,Meng-Yuan Xu,Bin Xu
In this study, the formation of iodinated trihalomethanes (I-THMs) was systematically evaluated and compared for three treatment processes - (i) chlorination, (ii) monochloramine, and (iii) dichloramination - under different pH conditions. The results demonstrated that I-THM formation decreased in the order of monochloramination > dichloramination > chlorination in acidic and neutral pH. However, the generation of I-THMs increased in the dichloramination < chlorination < monochloramination order in alkaline condition. Specifically, the formation of I-THMs increased as pH increased from 5 to 9 during chlorination and monochloramination processes, while the maximum I-THM formation occurred at pH 7 during dichloramination. The discrepancy could be mainly related to the stability of the three chlor (am) ine disinfectants at different pH conditions. Moreover, in order to gain a thorough insight into the mechanisms of I-THM formation during dichloramination, further investigation was conducted on the influencing factors of DOC concentration and Br − /I − molar ratio. I-THM formation exhibited an increasing and then decreasing trend as the concentration of DOC increased from 1 to 7 mg-C/L, while the yield of I-THMs increased with increasing Br − /I − molar ratio from 5:0 to 5:10. During the three processes mentioned above, similar I-THM formation results were also obtained in real water, which indicates that the excessive generation of I-THMs should be paid special attention during the disinfection of iodide-containing water.
研究领域:
环境科学
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水处理工程
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DOI
PubMed
高影响因子
SEPARATION AND PURIFICATION TECHNOLOGY
·
2024
·
IF 8.1
Dexin Wu,Feng Yang,Di Zhao,Lulu Zhu,Ruiqi Wang,Jun Hu,Zhimin Qiang,Weiting Yu,Yuanchen Chen
The joint disinfection of monochloramine (MCA) and peroxymonosulfate (PMS) can combine the advantages of both sides; and the iodine-containing micropollutants are widely present in drinking water. For the first time, the conversion of iopamidol (IPM) was investigated in the MCA/PMS system. For IPM degradation, the observed pseudo-first-order rate constant ( k obs ) was 0.0076 min −1 , and the apparent rate constant ( k app ) was 6.14 × 10 −7 μM −2.16 min −1 . The reaction orders for MCA ( m ) and PMS ( n ) were fitted to be 1.14 and 1.02, respectively. The mutual activation of MCA and PMS was a base-catalyzed reaction, which was highly exothermic and thermodynamically favored with a free energy of − 78.74 kcal/mol. It is believed that Cl • and 1 O 2 contributed to IPM degradation. The k obs value was increased by an alkaline pH and the presence of Cl − , while reduced by the existence of NOM, HCO 3 − and NH 4 + . The N in MCA was converted to NH 4 + -N, NO 2 − -N and NO 3 − -N, and 47.0 % of I in IPM was converted to IO 3 − . In the MCA/PMS system, IPM transformation was mainly via amide hydrolysis, deiodination and substitution reaction by reactive species. The study provides an insight into the fate of iodine-containing micropollutants during the joint disinfection of MCA and PMS.
研究领域:
环境科学
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化学工程
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产品关联
DOI
高影响因子
CHEMICAL ENGINEERING JOURNAL
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2020
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IF 10.652
Anhong Cai,Jing Deng,Mengyuan Xu,Tianxin Zhu,Shiqing Zhou,Jun Li,Guofang Wang,Xueyan Li
The combination of UV and monochloramine (UV/NH 2 Cl) was investigated to eliminate tetracycline (TC) in water. The results indicated that TC degradation by UV/NH 2 Cl oxidation far exceeded that by UV photolysis and dark chloramination and these processes well fitted pseudo-first-order kinetics. With the increase of NH 2 Cl dosage, the pseudo-first-order rate constant ( k obs ) value increased linearly during TC chloramination, while the growth rate of k obs presented a gradual downward trend in UV/NH 2 Cl process. TC degradation by UV photolysis, dark chloramination and UV/NH 2 Cl oxidation displayed highly pH-dependent. As solution pH increased from 5.0 to 9.0, the TC removal increased during UV photolysis, while decreased during dark chloramination. For UV/NH 2 Cl process, the TC degradation showed a decreasing trend with increasing pH from 5.0 to 7.0, but further increasing pH to 9.0 presented an increasing trend. Reactive chlorine species acted as the major contributors to TC degradation in pH range of 6.0–8.0. TC degradation was not apparently affected after the introduction of HA and chloride, but was substantially accelerated in the presence of HCO 3 − . The proposed degradation pathways involved the hydroxylation, demethylation, dehydration and chlorine substitution processes. Compared with dark chloramination, the N-Nitrosodimethylamine (NDMA) generation was enhanced during TC oxidation by UV/NH 2 Cl process. The NDMA concentration increased with increasing solution pH from 6.0 to 8.0 and also elevated in the presences of humic acid (HA), nitrite, nitrate and ammonium during TC oxidation by chloramination and UV/NH 2 Cl. The results of acute toxicity test demonstrated that the toxicity of the reacted solution exhibited similar trends during dark chloramination and UV/NH 2 Cl treatment and was found to be obviously higher than UV photolysis.
研究领域:
环境科学
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水处理工程
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毒理学
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DOI
高影响因子
SCIENCE OF THE TOTAL ENVIRONMENT
·
2020
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IF 6.551
Nan Huang,Wen-Long Wang,Zi-Bin Xu,Bei Ye,Zi-Fan Liang,Min-Yong Lee,Qian-Yuan Wu,Hong-Ying Hu
In this study, it was found that monochloramine induced the formation of reactive species during ozonation of chloromethylisothiazolinone (CMIT). CMIT was found recalcitrant to chloramine. However, chloramine promoted the degradation of CMIT by ozonation significantly. Hydroxyl radicals contributed most to CMIT degradation (87%) during ozone/chloramine synergistic oxidation process (SOP). The hydroxyl radical exposure during ozone/chloramine SOP was around 7.9 times higher than that of ozonation process. The hydroxyl radical yield of ozone/chloramine SOP was estimated to be 32%. The reaction mechanisms between ozone and chloramine were postulated to include the oxygen transfer reaction to form singlet oxygen, and the formation of hydroxyl radical by the insertion pathway or electron transfer pathway. Chloramine dosage and pH are essential influencing factors. The degradation of CMIT increased from 41% to 74% with increasing chloramine dosage (0–20 μM), and then decreased to 65% when chloramine dosage continually increased to 40 μM. Ozone/chloramine SOP showed better performance at acidic or neutral conditions than basic condition. Based on the intermediates identified, the degradation pathway of CMIT during ozone/chloramine SOP included the oxidation of sulfur atom and the substitution of chlorine group by hydroxyl group. The oxidation of sulfur atom induced lower toxicities of transformation products . The toxicities of hydroxylation products were lower to fish and algae, but higher to daphnia. Based on the GC-ECD results, only trichloromethane (1.94 μg/L) was detected after ozone/chloramine SOP, accounting for 0.17% (μM/μM) of the CMIT removal.
研究领域:
环境科学
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毒理学
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水处理技术
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产品关联
DOI
PubMed
高影响因子
CHEMOSPHERE
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2020
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IF 5.778
Tianxin Zhu,Jing Deng,Mengyuan Xu,Anhong Cai,Cheng Ye,Jun Li,Xueyan Li,Qiongsong Li
The degradation of N,N -diethyl- meta -toluamide (DEET) in aqueous solution by the UV/monochloramine (UV/NH 2 Cl) process was examined systematically in this study. DEET was resistant to UV photolysis and chloramination, while the synchronous combination of UV irradiation and NH 2 Cl can effectively eliminate DEET, which was caused by the generation of hydroxyl radicals and reactive chlorine species. The former played the critical role in DEET degradation, while the contribution of the latter can be ignored. Under all investigated experimental conditions, DEET degradation in the UV/NH 2 Cl process followed the pseudo-first-order kinetic model. The water quality parameters exerted the complicated impact. Reducing solution pH and raising water temperature both favored the DEET removal. The presence of sulfate, humic acid and fulvic acid accelerated the degradation, while the introduction of bicarbonate and high-concentration chloride retarded the removal. The plausible degradation pathways of DEET in the UV/NH 2 Cl process were proposed through the combination of QTOF/MS analysis and DFT calculation, and mainly involved in the cleavage of C–N bond, dealkylation, mono- and polyhydroxylation. The acute toxicity of reacted solution underwent a trend of first increasing and then decreasing with the prolonged irradiation time, which can be well illustrated by quantitative structure-activity relationship analysis. Electrical energy per order was employed to determine the energy consumption and the optimal conditions were determined as UV fluence of 369.9–493.2 mJ cm −2 and NH 2 Cl dosage of 5–20 mg L −1 .
研究领域:
环境科学
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化学工程
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毒理学
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产品关联
DOI
PubMed
高影响因子
SCIENCE OF THE TOTAL ENVIRONMENT
·
2021
·
IF 7.963
Xuelin Wang,Xiuwei Ao,Tianyang Zhang,Zifu Li,Ran Cai,Zhongyun Chen,Yonglei Wang,Wenjun Sun
Monochloramine (NH 2 Cl) oxidant combined with a Ultraviolet (UV)-Light-emitting-diode (LED) light source forms a new advanced oxidation process (AOP), which can achieve high-efficiency degradation of carbamazepine (CBZ). The degradation of CBZ displayed pseudo-first-order reaction kinetics (R 2 > 0.98, k CBZ = 0.0043 cm 2 mJ −1 at pH 7). The degradation of CBZ was dependent on UV-LED wavelength, with maximum degradation efficiency observed at 265 nm since it was the lowest wavelength studied among UV-LEDs. Variation in pH across the range, which might be expected under normal environmental conditions (pH 6–8), and the presence of Cl − had no significant effect on the degradation efficiency of CBZ, while the presence of HCO 3 − and natural organic matter (NOM) inhibited degradation. Electron paramagnetic resonance (EPR) experiments detected OH in the system. Probe compounds were used to distinguish the contribution of reactive chlorine species (RCS). It was proved that OH and Cl played major roles and OH was responsible for around 50% of the observed degradation of CBZ. Eight transformative products (TPs) in the degradation process of CBZ were identified, with a generally decreasing toxicity. The concentration of disinfection by-products (DBPs) formed during CBZ degradation was all within limits of WHO and China standard for drinking water . Although the concentration of nitrogen-containing DBPs (N-DBPs) was the lowest, N-DBPs were the main contributors to toxicity, and these would require more attention in practical applications. UV-LED/NH 2 Cl AOP was identified as an effective way to degrade pharmaceutically active compounds.
研究领域:
环境科学
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化学工程
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产品关联
DOI
PubMed
高影响因子
CHEMICAL ENGINEERING JOURNAL
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2021
·
IF 13.273
Huiming Xiang,Naiyun Gao,Xian Lu,Yuanquan Xiang,Wenhai Chu
Ultraviolet combined monochloramine (UV/NH 2 Cl) process is a promising advanced oxidation process (AOP) to remove organic micropollutants effectively through the generation of various reactive species e.g., hydroxyl radicals (HO • ), reactive chlorine species (RCS), and reactive nitrogen species (RNS). This study investigated the kinetics, transformation pathways, DBPs formation, and toxicity alternation in the degradation of sulfamethazine (SMT). Based on the calculation of degradation kinetic models, RNS was proved to be the most important reactive species in the degradation of SMT in UV/NH 2 Cl. The contribution of RNS, HO • and RCS were approximately 56.6%, 38.8%, and 4.5%, respectively. With the NH 2 Cl dosage increased from 100 to 800 µmol L -1 , degradation rate increased from 37% to 73% in 10 min. Significantly alternation was not observed with the changing of pH. Natural organic matter (NOM) remarkably inhibited the degradation rate to 48.6% and 32.8% in the presence of 1 and 2 mg L -1 NOM. Degradation reactions of SMT in UV/NH 2 Cl system primarily comprised of hydroxylation, nitrosation, and ring opening reactions. The total theoretical toxicity of degradation system increased in the first 20 min and decreased eventually. Comparing with UV/free chlorine (UV/Cl 2 ) process, less disinfection by-products (DBPs) generated in UV/NH 2 Cl treatment. Thus, the theoretical toxicity of DBPs formed in UV/NH 2 Cl was much lower than UV/Cl 2 . Within 40 min degradation, the theoretical toxicity value reached maximum at pH 7.1 due to the mass production of dicloroacetonitrile (DCAN). Bromide ions (10 µmol L -1 ) significantly promoted the formation of brominated DBPs especially dibromoacetonitrile (DBAN). This study provided insight into the important role of RNS in the SAs’ transformation in UV/NH 2 Cl process and reference to benefits and disadvantages when selecting the process for disinfection in drinking water treatment.
研究领域:
环境科学
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水处理
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高级氧化工艺
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水中的药物
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毒理学
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产品关联
DOI
高影响因子
WATER RESEARCH
·
2024
·
IF 11.4
Qing Bai,Qian-Yuan Wu,Bei Ye,Yun-Peng Wu,Ju-Won Lee,Min-Yong Lee,Wen-Long Wang
The KrCl* excimer lamp (UV222) is a promising alternative of low-pressure mercury lamp (UV254) for UV-based advanced oxidation processes (UV-AOPs), because it is mercury-free and has high photon energy. But there lacks a comprehensive assessment of UV222-AOPs based on different radicals. Herein, the properties (e.g., oxidant decay and innate radical quantum yield), and micropollutant degradation, were comprehensively studied for representative oxidants (i.e., hydrogen peroxide, persulfate (PDS), monochloramine, and free active chlorine (FAC)) under UV222 irradiation. UV222 outperformed UV254 for the activation of oxidants with 2.6-14.4 times fluence-based kinetic constant ( k F ). The main reason of enhanced activation varied with oxidants: higher UV absorption for H 2 O 2 , higher innate quantum yield for monochloramine and FAC, and both reasons for PDS. Overall, PDS was the optimum oxidant under UV222 for the degradation of 8 representative micropollutants because of effective promotion of radical formation, as confirmed by radical competitive kinetics and modeling simulations. In real water, UV222/PDS still show advantages than UV254/PDS in terms of micropollutant elimination efficacy (3.2-5.3 times) and energy consumption (33.9%-57.6% lower) though it was more inhibited by water constituents via competing for UV222 photons. This study fills gaps in photochemistry knowledge and will facilitate engineering practice of UV222-AOPs.
研究领域:
环境科学
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化学工程
·
光化学
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产品关联
DOI
PubMed
高影响因子
SCIENCE OF THE TOTAL ENVIRONMENT
·
2021
·
IF 7.963
Han Chen,Tao Lin,Xiaoshu Yan,Hang Xu
The formation of haloacetonitriles (HANs) during chlorination after sulfite/ultraviolet (UV) treatment of bromate (BrO 3 − ) in the presence of amino acids (AAs) was investigated. During sulfite/UV treatment, the primary species hydrated electrons (e aq − ) and hydrogen atom radicals (H ) dominated the reduction of BrO 3 − to bromide (Br − ), whereas the sulfite anion radicals (SO 3 − ) and H degraded AAs to produce the intermediates HN=C(CH 3 )–COOH, CH 3 –CH=NH, and CH 3 –C≡N via α‑hydrogen abstraction and NH 2 –hydrogen abstraction mechanisms. During post-chlorination, Br − was converted to HBrO/BrO-, and the HN=C(CH 3 )–COOH, CH 3 –CH=NH, and CH 3 –C≡N groups featured higher bromine utilization factor (BUF) and chlorine utilization factor (CUF) values than AAs, enhancing the formation of dibromoacetonitrile (DBAN) and dichloroacetonitrile (DCAN). The energetic feasibility of the transformation pathway, that is, HN=C(CH 3 )–COOH, CH 3 –CH=NH, and CH 3 –C ≡ N formation via hydrogen abstraction by SO 3 − and H and their further conversion to HANs, was proved by density functional theory calculations, which showed stepwise negative Gibbs free energy changes (ΔG < 0). The effects of pH and water matrices (e.g., HCO 3 − , Cl − , Fe 3+ , and natural organic matter) were comprehensively evaluated. Although 72% of BrO 3 − was removed by sulfite/UV treatment in the presence of AAs, the cytotoxicity index (CTI) and genotoxicity index (GTI) during post-chlorination increased by 213% and 125%, respectively, due to the formation of 24 CX 3 R-type disinfection by-products (DBPs), especially brominated DBPs. Accordingly, more attention should be given to the formation of brominated DBPs during post-chlorination when using sulfite/UV processes to remove BrO 3 − in the presence of AAs. As a solution, using monochloramine instead of chlorine as a disinfectant after the sulfite/UV process could significantly lower the CTI and GTI values by alleviating the formation of brominated DBPs.
研究领域:
环境科学
·
水处理
·
化学工程
·
毒理学
✓ 已验证
产品关联
DOI
PubMed
高影响因子
危险品化学品经营许可证（带存储）