[Show abstract][Hide abstract] ABSTRACT: The combination of low-dose ozone with ultraviolet (UV) irradiation should be an option to give benefit to disinfection and reduce drawbacks of UV and ozone disinfection. However, less is known about the disinfection performance of UV and ozone (UV/ozone) coexposure and sequential UV-followed-by-ozone (UV-ozone) and ozone-followed-by-UV (ozone-UV) exposures. In this study, inactivation of E. coli and bacteriophage MS2 by UV, ozone, UV/ozone coexposure, and sequential UV-ozone and ozone-UV exposures was investigated and compared. Synergistic effects of 0.5–0.9 log kill on E. coli inactivation, including increases in the rate and efficiency, were observed after the UV/ozone coexposure at ozone concentrations as low as 0.05 mg·L−1 in ultrapure water. The coexposure with 0.02-mg·L−1 ozone did not enhance the inactivation but repressed E. coli photoreactivation. Little enhancement on E. coli inactivation was found after the sequential UV-ozone or ozone-UV exposures. The synergistic effect on MS2 inactivation was less significant after the UV/ozone coexposure, and more significant after the sequential ozone-UV and UV-ozone exposures, which was 0.2 log kill for the former and 0.8 log kill for the latter two processes, at ozone dose of 0.1 mg·L−1 and UV dose of 8.55 mJ·cm−2 in ultrapure water. The synergistic effects on disinfection were also observed in tap water. These results show that the combination of UV and low-dose ozone is a promising technology for securing microbiological quality of water.
Frontiers of Environmental Science & Engineering. 08/2014; 8(4).
[Show abstract][Hide abstract] ABSTRACT: An electrospray ionization-tandem mass spectrometry (ESI-tqMS) method was developed to identify the location of chlorine substitution during the chlorination of model organic compounds. The chlorine substitution in the aliphatic part and that in the benzene ring of an organic molecule can be differentiated by their corresponding ranges of optimum collision energies, 5-7 eV and over 15 eV, respectively, in the precursor ion scan of m/z 35. The method was applied to predict the structures of intermediates and reveal the transformation pathways during the chlorination of 4-amino-2-chlorobenzoic acid and phenylalanine as a function of reaction time and the chlorine-to-precursor ratio. In the case of phenylalanine, chlorine was found to replace one hydrogen atom attached to the aliphatic nitrogen; in the case of 4-amino-2-chlorobenzoic acid, chlorine was found to replace the hydrogen atoms attached to the aromatic rings.
[Show abstract][Hide abstract] ABSTRACT: The UV/free chlorine process forms reactive species such as hydroxyl radicals (HO•), chlorine atoms (Cl•), Cl2•- and O•-. The specific roles of these reactive species in aqueous micropollutant degradation in the UV/chlorine process under different conditions were investigated using a steady-state kinetic model. Benzoic acid (BA) was chosen as the model micropollutant. The steady-state kinetic model developed fitted the experimental data well. The results showed that HO• and Cl• contributed substantially to BA degradation, while the roles of the other reactive species such as Cl2•- and O•- were negligible. The overall degradation rate of BA decreased as the pH increased from 6 to 9. In particular, the relative contributions of HO• and Cl• to the degradation changed from 34.7% and 65.3% respectively at pH 6 to 37.9% and 62% respectively at pH 9 under the conditions evaluated. Their relative contributions also changed slightly with variations in chlorine dosage, BA concentration and chloride concentration. The scavenging effect of natural organic matter (NOM) on Cl• was relatively small compared to that on HO•, while bicarbonate preferentially reduced the contribution of Cl•. This study is the first to demonstrate the contributions of different reactive species to the micropollutant degradation in the UV/chlorine system under environmentally relevant conditions.
[Show abstract][Hide abstract] ABSTRACT: This study examined the removal of nC60 from wastewater by alum-enhanced primary treatment at different pH levels and alum dosages and identified wastewater characteristics affecting the removal. The efficiency of the removal depended on the alum dosage, pH, alkalinity, and the concentrations of suspended solids, sewage organic matter and salinity. Alum dosage and pH influenced the removal efficiency by changing the hydrolyzed aluminum species distribution at acidic and near neutral pH levels. At pH 9–10, nC60 removal was associated with the formation of magnesium (or calcium) carbonate or hydroxide precipitates. Alkalinity dramatically enhanced the nC60 removal efficiency (by up to 71%) through the formation of sodium aluminum hydroxycarbonate precipitates. Increasing the concentration of suspended solids enhanced the nC60 removal efficiency by up to 46% at 25 mg/L of alum as the solids act as adsorbents and the nuclei around which flocs can grow. Increasing the concentration of sewage organic matter decreased the nC60 removal efficiency (by 17% or less) while salinity improved it, albeit only slightly so. The results of this study demonstrate that nC60 can be effectively removed from wastewater by the alum-based chemically enhanced primary treatment process under appropriate conditions and better removal can be achieved by increasing alum dosage.
Separation and Purification Technology 09/2013; 116:61–66. · 2.89 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study explored the mechanisms for nC60 removal in pure water and filtered saline wastewater by the alum coagulation-flocculation-sedimentation process through analyzing the hydrolyzed aluminum species and exploring the complexation of nC60 with aluminum hydroxide precipitates. Sweep flocculation (enmeshment and adsorption) with Alc is the most dominant mechanism contributing to the nC60 removal in pure water. In filtered saline wastewater, hetero-precipitation of Alb with nC60, colloids, and dissolved solids also contributes to the nC60 removal. Alkalinity affected the nC60 removal by changing the hydrolyzed aluminum species distributions. XPS, FTIR, and SEM evidences suggest that the enmeshment and adsorption of nC60 onto the aluminum hydroxide precipitates can be described as the inner-sphere complexation. Based on the above observations, conceptual models for nC60 removal by the alum coagulation-flocculation-sedimentation process in the different water matrices are proposed.
Journal of Colloid and Interface Science 08/2013; · 3.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The response trends of biochemical oxygen demand (BOD) and organic strength after the chlorination/dechlorination process were explored through a 2-year, 5-month chemically enhanced primary treatment (CEPT) effluent onsite monitoring program and a 2-month laboratory-scale study. The monitoring results showed that better instantaneous mixing at the chlorine injection point reduced the effect of chlorination/dechlorination on the 5-day BOD levels. The laboratory study results demonstrated that chlorination did not change the particle size distribution, dissolved organic carbon, or chemical oxygen demand of the organic content of the effluent. Nevertheless, chlorination/dechlorination strongly affected the BOD measurement when nitrification was inhibited by changing bioactivity/biodegradation rates.
Water Science & Technology 07/2013; 68(2):380-6. · 1.10 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Halonitromethanes (HNMs) are one of the most toxic groups of disinfection by-products. The pH-dependent degradation kinetics and pathways of four HNMs, namely bromonitromethane (BNM), dichloronitromethane (DCNM), dibromonitromethane (DBNM) and trichloronitromethane (TCNM), by ultraviolet (UV) photolysis at 254 nm were studied at pH 3-9. The UV photolysis in a dilute aqueous solution followed first-order kinetics. The photolysis rates of all four HNMs were low at pH 3-5, while that of TCNM was low at all pHs tested. Nevertheless, the photolysis rates of BNM, DCNM and DBNM increased with increasing pH, showing sharp increases as the pH neared their pK(a) values. The increases were correlated with their pH-dependent molar absorptivities, which were determined by the sizes of their deprotonated fractions. Homolysis was likely to be the major photolysis pathway for all four HNMs to produce halides, nitrite and nitrate at acidic pHs when the HNMs were not deprotonated. At high pHs, however, the conjugation systems of the deprotonated mono- and di-HNMs made heterolysis possibly the dominant pathway for the formation of carbon dioxide, nitrite and halides as major products for di-HNMs, and the formation of nitrite, halides and other unknown organics for mono-HNMs. The UV energy required for a 50% degradation of deprotonated HNMs in the real water sample was similar to that needed in UV disinfection processes, suggesting the effectiveness of UV photolysis in controlling HNMs that form conjugation systems at neutral to alkaline pHs.
[Show abstract][Hide abstract] ABSTRACT: Nitrogenous disinfection byproducts (N-DBPs) such as haloacetonitriles (HANs) and halonitromethanes (HNMs) are formed during water chlorination. Preozonation is sometimes applied to control trihalomethane (THM) formation, but this may risk promoting the formation of HNMs and HANs. The role of ozone in the formation of HANs and HNMs in natural waters remains unclear. The nitrogen sources involved in HAN and HNM formation during the chloramination of dissolved organic matter (DOM) with and without preozonation were evaluated using 15N-labeled monochloramine. The origin of the nitrogen involved in HAN formation was found to depend on the ratio of dissolved organic carbon to nitrogen. In nitrogen-rich solutions HAN nitrogen was mainly from DOM constituents. The formation of 15N-labeled dichloroacetontrile (DCAN) accounted for approximately 30% of the DCAN produced from all hydrophilic acidic and neutral isolates, which have low carbon to nitrogen ratios, while it reached over 50% for the hydrophobic acidic, basic and neutral isolates with high carbon to nitrogen ratios. Unlabeled trichloronitromethane (TCNM) accounted for over 90% of the total TCNM produced from most of the isolates. The remaining less than 10% of the TCNM was probably generated through an aldehyde pathway. Preozonation reduced DCAN but enhanced the yield of TCNM. The destruction of amino acids and amine structures and subsequent formation of nitro groups by preozonation may help explain the reduced DCAN and increased TCNM formation.
[Show abstract][Hide abstract] ABSTRACT: This study confirmed the physicochemical transformation of aqueous fullerene aggregates (nC(60)) produced via solvent exchange from toluene by chlorine in the dark and under fluorescent light (representing visible light) by comparing the changes in light absorbance at 700 nm and size distribution of nC(60) and characterizing the photochlorination products of nC(60) by XPS, FTIR and TOF-SIMS techniques. The (photo)chlorination of nC(60) was enhanced by increasing the chlorine dosage and the salinity concentration, and the presence of fluorescent light. During (photo)chlorination, nC(60) underwent surface chlorination, hydroxylation and oxidation, and was transformed into products containing carbon-chlorine, epoxy and hydroxyl functional groups. Extensive (photo)chlorination produced products that might not possess the isolated benzenoid ring structure on their cages, although they retained the 60-carbon cage structure. These findings imply the necessity of assessing the fate and toxicity of nC(60) after (photo)chlorination in both engineered and natural environments and demonstrate a simple way to produce new nC(60) derivatives that contain chlorine and oxygen.
[Show abstract][Hide abstract] ABSTRACT: Bromate formation from bromide oxidation by the UV/persulfate process was investigated, along with changes in pH, persulfate dosages, and bromide concentrations in ultrapure water and in bromide-spiked real water. In general, the bromate formation increased with increasing persulfate dosage and bromide concentration. The bromate formation was initiated and primarily driven by sulfate radicals (SO(4)(•-)) and involved the formation of hypobromous acid/hypobromite (HOBr/OBr(-)) as an intermediate and bromate as the final product. Under the test conditions, the rate of the first step driven by SO(4)(•-) is slower than that of the second step. Direct UV photolysis of HOBr/OBr(-) to form bromate and the photolysis of bromate are insignificant. The bromate formation was similar for pH 4-7 but decreased over 90% with increasing pH from 7 to above 9. Less bromate was formed in the real water sample than in ultrapure water, which was primarily attributable to the presence of natural organic matter that reacts with bromine atoms, HOBr/OBr(-) and SO(4)(•-). The extent of bromate formation and degradation of micropollutants are nevertheless coupled processes unless intermediate bromine species are consumed by NOM in real water.
[Show abstract][Hide abstract] ABSTRACT: Fullerenes are set to be produced on an industrial scale in anticipation of their wide applications. This calls for research on their environmental and health impacts. This study investigates and compares the cell toxicity of different aqueous fullerene aggregates. Popular C(60) dispersal methods were used to prepare four types of nC(60) aggregates. These aggregates were tested against the indicator species Escherichia coli (E. coli) AMC 198. With aggregates of around 150 nm in diameter, the THF/nC(60) suspension was very toxic and gave rise to a half maximal effective concentration (EC(50)) of 0.54 mg L(-1) in E. coli. By contrast, the Tol/nC(60) suspension exhibited a cytoprotective role while the Aqu-N(2)/nC(60) and Aqu-O(2)/nC(60) suspensions enhanced the metabolism of E. coli. Although some toxicants, such as THF and THF-peroxide, were introduced into the THF/nC(60) suspension during the dispersion, the toxicity of nC(60) itself cannot be neglected.
[Show abstract][Hide abstract] ABSTRACT: When chlorine is applied before or during UV disinfection of bromide-containing water, interactions between chlorine, bromide and UV light are inevitable. Formation of halogenated organic byproducts was studied during medium-pressure UV (MPUV) and chlorine coexposure of phenol, nitrobenzene and benzoic acid and maleic acid, chosen to represent electron-donating aromatics, electron-withdrawing aromatics, and aliphatic structures in natural organic matter (NOM), respectively. All were evaluated in the presence and absence of bromide. MPUV and chlorine coexposure of phenol produced less total organic halogen (TOX, a collective parameter for halogenated organic byproducts) than chlorination in the dark, and more haloacetic acids instead of halophenols. Increases in TOX were found in the coexposure of nitrobenzene and benzoic acid, but maleic acid was rather inert during coexposure. The presence of bromide increased the formation of brominated TOX but did not significantly affect total TOX formation, in spite of the fact that it reduced hydroxyl radical levels. MPUV and chlorine coexposure of NOM gave a higher differential UV absorbance of NOM and a larger shift to lower molecular weight compounds than chlorination in the dark. However, TOX formation with NOM remained similar to that observed from dark chlorination.
Water Research 12/2011; 45(19):6545-54. · 4.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Total organic bromine (TOBr) is a collective parameter representing all the brominated organic disinfection byproducts (DBPs) in water samples. TOBr can be measured using the adsorption-pyrolysis method according to Standard Method 5320B. This method involves that brominated organic DBPs are separated from inorganic halides and concentrated from aqueous solution by adsorption onto the activated carbon (AC). Previous studies have reported that some commonly known brominated DBPs can partially penetrate through the AC during this adsorption step. In this work, the penetration of polar brominated DBPs through AC and ozone-modified AC was explored with two simulated drinking water samples and one chlorinated wastewater effluent sample. Polar brominated DBPs were selectively detected with a novel precursor ion scan method using electrospray ionization-triple quadrupole mass spectrometry. The results show that 3.4% and 10.4% of polar brominated DBPs (in terms of total ion intensity) in the chlorinated Suwannee River fulvic acid and humic acid samples, respectively, penetrated through the AC, and 19.6% of polar brominated DBPs in the chlorinated secondary wastewater effluent sample penetrated through the AC. The ozone-modification of AC minimized the penetration of polar brominated DBPs during the TOBr analysis.
Journal of Environmental Monitoring 08/2011; 13(10):2851-7. · 2.09 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The frequent occurrence of algal blooms in drinking water reservoirs causes problems to water supply, one of which is the release of algal organic matter in high concentrations to affect drinking water quality. Algal organic matter, including extracellular organic matter (EOM) and intracellular organic matter (IOM), was characterized. The formation of a variety of disinfection by-products (DBPs) in chlorination and chloramination of EOM, IOM and algal cells was evaluated. Natural organic matter (NOM) isolated from Suwannee River was also studied for comparison. EOM and IOM were rich in organic nitrogen, which consisted of high (over 10 kDa) and low (70-1000 Da) molecular weight (MW) organic matter, whilst the MW of organic carbon in EOM and IOM was relatively lower. IOM had a higher fraction of total organic nitrogen, with larger proportions of higher MW and more hydrophobic contents than did EOM. IOM also contained higher fractions of free amino acids but lower fractions of aliphatic amines than did EOM. During chlorination of EOM and IOM, organic chloramines were first formed and then became undetectable after 1 d. Chlorination of EOM and IOM produced more nitrogenous DBPs (N-DBPs) and haloaldehydes and less carbonaceous DBPs (C-DBPs) than did chlorination of NOM. Organic chloramines were found after 3-d chloramination of EOM and IOM. The amounts of N-DBPs and C-DBPs formed from chloramination of EOM or IOM were much less than that from NOM. EOM produced less DBPs (except for trichloronitromethane) than did IOM and algal cells in chlorination and chloramination.
Water Research 12/2010; 44(20):5897-906. · 4.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A collective parameter and a toxicity indicator for all the halogenated organic disinfection byproducts in a water sample is total organic halogen (TOX), which can be differentiated as total organic chlorine (TOCl), total organic bromine (TOBr) and total organic iodine. The TOX method involves concentration of organic halogens from water by adsorption onto activated carbon (AC). A previous study showed that a portion of TOCl can be reduced to chloride during the adsorption procedure, which can be minimized by ozonation of the AC. In this study, a portion of TOBr was sometimes found to be reduced by AC to bromide, and the reduction was generally less than that of corresponding TOCl. The results suggested that around 10% of brominated Suwannee River fulvic acid was reduced to bromide. However, some brominated amino compounds (especially glycylglycine, phenylalanine, and cytosine) were found to be more reactive with the AC. For the iodinated compounds studied, the reduction to iodide was not significant. The method for the TOBr measurement was improved by using ozonated AC when reduction occurred on the original AC. The improved method was also evaluated on treated wastewater and swimming pool water samples.
Water Research 10/2010; 45(3):1229-37. · 4.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Mechanisms contributing to the adsorption of natural organic matter (NOM) on surfactant-modified iron oxide-coated sand (IOCS) were explored by microscopic surface characterization techniques and adsorption tests. Electrostatic interactions that were thought to be from the positively charged, surface-coated surfactant, hexadecyltrimethyl ammonium (HDTMA), seemed to be unimportant, likely because the outward-pointing tail groups of the surface-coated HDTMA monolayers hindered the interactions. Improved hydrophobic interactions followed by ligand exchange are believed to be the dominant mechanisms. Atomic force microscopy (AFM) force analysis with chemically modified tips was used to explore the adsorption mechanisms between NOM and IOCS, where an iron oxide-coated mica surface was utilized as a substitute for the IOCS surface. It demonstrates the changes of pull-on forces and the increases in hydrophobic interactions from the modification of IOCS with HDTMA.
Water Research 04/2010; 44(12):3651-8. · 4.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper evaluates the performance of liquid-liquid extraction (LLE) and solid phase extraction (SPE) in separating and concentrating aqueous fullerene (nC(60)) from wastewater and compares UV-vis spectroscopy and mass spectrometry for the quantification of C(60). LLE was suitable for multiple wastewater matrices, while SPE required filtration or reclaimed wastewater and secondary effluent of less suspended solids. Calibration curves plotted as peak areas of UV absorbance at 332 nm against spiked nC(60) concentrations showed good linearity over a range of 20-200 microg L(-1) after 10-fold concentration by LLE, but only over the range of 0.8-2 microg L(-1) for reclaimed wastewater and 0.8-4 microg L(-1) for secondary effluent after 1000-fold concentration by SPE. Recoveries of nC(60) by LLE were in the range of 89-94% with a standard deviation (SD) not more than 2% and recoveries of nC(60) by SPE were much lower, only 18% for reclaimed wastewater and 9% for secondary effluent. The method detection limits (MDLs) of LLE with UV-vis spectroscopy were 3-4 microg L(-1) for six water matrices and the MDLs of SPE with UV-vis spectroscopy were 0.42 microg L(-1) for reclaimed wastewater and 0.64 microg L(-1) for secondary effluent. UV-vis spectroscopy and mass spectrometry gave similar sensitivity. With LLE, mass spectrometry offered a small linear range of 20-60 microg L(-1), but it provided specificity based on the mass-to-charge ratios (m/z) of the molecular ions. This paper demonstrates the feasibility of the combination of different extraction and detection methods to quantify nC(60) in engineered wastewater matrices.
[Show abstract][Hide abstract] ABSTRACT: Formation of carbonaceous disinfection by-products (C-DBPs), including trihalomethanes (THMs), haloacetic acids (HAAs), haloketones (HKs), chloral hydrate (CH), and nitrogenous disinfection by-products (N-DBPs), including haloacetonitriles (HANs) and trichloronitromethane (TCNM) from chlorination of Microcystis aeruginosa, a blue-green algae, under different conditions was investigated. Factors evaluated include contact time, chlorine dosages, pH, temperature, ammonia concentrations and algae growth stages. Increased reaction time, chlorine dosage and temperature improved the formation of the relatively stable C-DBPs (e.g., THM, HAA, and CH) and TCNM. Formation of dichloroacetonitrile (DCAN) followed an increasing and then decreasing pattern with prolonged reaction time and increased chlorine dosages. pH affected DBP formation differently, with THM increasing, HKs decreasing, and other DBPs having maximum concentrations at certain pH values. The addition of ammonia significantly reduced the formation of most DBPs, but TCNM formation was not affected and 1,1-dichloropropanone (1,1-DCP) formation was higher with the addition of ammonia. Most DBPs increased as the growth period of algal cells increased. Chlorination of algal cells of higher organic nitrogen content generated higher concentrations of N-DBPs (e.g., HANs and TCNM) and CH, comparable DCAA concentration but much lower concentrations of other C-DBPs (e.g., THM, TCAA and HKs) than did natural organic matter (NOM).
Water Research 03/2010; 44(6):1934-40. · 4.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Formation of nitrogenous disinfection by-products (N-DBPs) of cyanogen chloride (CNCl), dichloroacetonitrile (DCAN) and chloropicrin was evaluated during chloramination of several selected groups of nitrogenous organic (organic-N) compounds, including alpha-amino acids, amines, dipeptides, purines, and pyrimidines, The intermediates generated, reaction pathways, and nitrogen origin in N-DBPs were explored as well. CNCl was observed in chloramination of all tested organic-N compounds, with glycine giving the highest yields. DCAN was formed during chloramination of glutamic acid, cytosine, cysteine, and tryptophan. Chloramination of most organic-N compounds except for cysteine and glutamic acid generated chloropicrin. Aldehydes and nitriles were identified as the intermediates by negative mode electrospray ionization mass spectrometry during reactions of NH(2)Cl and organic-N compounds. Labeled (15)N-monochloramine ((15)NH(2)Cl) techniques showed that nitrogen in N-DBPs may originate from both NH(2)Cl and organic-N compounds and the nitrogen partition percentages vary as functions of reactants and pH.
Water Research 02/2010; 44(9):2691-702. · 4.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Total organic halogen (TOX) is a collective parameter and a toxicity indicator for all the halogenated organic disinfection byproducts (DBPs) in a water sample. TOX can be measured with the adsorption-pyrolysis method based on Standard Method 5320B. This method involves concentration of organic halogens from water by adsorption onto activated carbon (AC) and removal of inorganic halides present on the AC by competitive displacement by nitrate ions. Since AC can also act as a reductant, this work studied whether the reduction of chlorinated DBPs by AC occurs during the TOX measurement, to what extent the reduction affects the measurement of TOX, what type of chlorinated DBPs can be reduced by AC, and whether the method for the TOX measurement can be improved. Initially, chlorinated Suwannee River fulvic acid samples were prepared and pretreated with precipitation/dialysis/ultrafiltration to minimize the chloride levels in the samples. It was found that the fractions of TOX in the precipitated, dialyzed, and ultrafiltered samples that were reduced by AC in 5 min were around 13%, 20% and 24%, respectively. The formation of some N-chloroamino compounds and their reactivity with AC were examined. The results indicate that organic chloramines are one type of DBPs in TOX that could be reduced by AC. It was demonstrated that slight oxidation of AC with ozone basically inhibited its reduction for TOX and meanwhile maintained its adsorption capacity for TOX.
Environmental Science and Technology 02/2010; 44(6):2105-11. · 5.48 Impact Factor