Chii Shang

The roles of reactive species in micropollutant degradation in the UV/free chlorine system.

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.

Formation of carbonaceous and nitrogenous disinfection by-products from the chlorination of Microcystis aeruginosa.

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).

Bromate formation from bromide oxidation by the UV/persulfate process

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.

Nitrogenous disinfection byproducts formation and nitrogen origin exploration during chloramination of nitrogenous organic compounds

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.

ATR-FTIR and XPS study on the structure of complexes formed upon the adsorption of simple organic acids on aluminum hydroxide

Information on the binding of organic ligands to metal (hydr)oxide surfaces is useful for understanding the adsorption behaviour of natural organic matter on metal (hydr)oxide. In this study, benzoate and salicylate were employed as the model organic ligands and aluminum hydroxide as the metal hydroxide. The attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra revealed that the ligands benzoate and salicylate do coordinate directly with the surface of hydrous aluminum hydroxide, thereby forming inner-sphere surface complexes. It is concluded that when the initial pH is acidic or neutral, monodentate and bridging complexes are to be formed between benzoate and aluminum hydroxide while bridging complexes predominate when the initial pH is alkalic. Monodentate and bridging complexes can be formed at pH 5 while precipitate and bridging complexes are formed at pH 7 when salicylate anions are adsorbed on aluminum hydroxide. The X-ray photoelectron (XP) spectra demonstrated the variation of C 1s binding energy in the salicyate and phenolic groups before and after adsorption. It implied that the benzoate ligands are adsorbed through the complexation between carboxylate moieties and the aluminum hydroxide surface, while both carboxylate group and phenolic group are involved in the complexation reaction when salicylate is adsorbed onto aluminum hydroxide. The information offered by the XPS confirmed the findings obtained with ATR-FTIR.

Correlations between organic matter properties and DBP formation during chloramination.

Characteristics, including fluorescence intensity and specific UV absorbance (SUVA), of 16 organic matter (OM) fractions isolated from four OM samples plus a standard were analyzed and correlated with their specific disinfection by-product (DBP) and total organic halogen (TOX) formation after chloramination. These isolates were obtained from various water sources by using XAD-8/4 resins. Chloramination was achieved by adding 20mg/L monochloramine to a solution containing one OM isolate at 5mg/L DOC and buffered at pH 7.5 for 7 days. The fluorescence regional integration (FRI) method was used to analyze the fluorescence intensity data obtained from excitation-emission matrix (EEM) fluorescence spectroscopy, in which the EEM figure was divided into five regions and a normalized fluorescence volume was calculated. The cumulative normalized EEM volumes at regions II and IV (Phi(II+IV,)(n)) showed linear relationships with the yields of dichloroacetic acid (DCAA) (R(2)=0.60), chloroform (R(2)=0.42), dichloroacetonitrile (DCAN) (R(2)=0.53), and TOX (R(2)=0.63). The SUVA values were found to have linear relationships with the yields of DCAA (R(2)=0.82), chloroform (R(2)=0.73), DCAN (R(2)=0.88) and TOX (R(2)=0.80), but not with the yields of cyanogen chloride (CNCl) and chloropicrin (CP). A modified model is proposed to simplify the reactions involving chloramination of OM fractions. FTIR spectra of OM before and after chloramination partially confirmed that ketone groups were reactive with monochloramine.

Quantification of fullerene aggregate nC60 in wastewater by high-performance liquid chromatography with UV–vis spectroscopic and mass spectrometric detection

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.

Effect of Reductive Property of Activated Carbon on Total Organic Halogen Analysis

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.

PPCP degradation by UV/chlorine treatment and its impact on DBP formation potential in real waters

The ultraviolet/chlorine (UV/chlorine) water purification process was evaluated for its ability to degrade the residues of pharmaceuticals and personal care products (PPCPs) commonly found in drinking water sources. The disinfection byproducts (DBPs) formed after post-chlorination were documented. The performance of the UV/chlorine process was compared with that of the UV/hydrogen peroxide (UV/H2O2) process in treating three types of sand-filtered natural water. Except caffeine and carbamazepine residues, the UV/chlorine process was found to be 59-99% effective for feed water with a high level of dissolved organic carbon and alkalinity, and 27-92% effective for water with a high ammonia content. Both chlorine radicals and hydroxyl radicals were found to contribute to the observed PPCP degradation. The removal efficiencies of chlorine- and UV-resistant PPCPs such as carbamazepine and caffeine were 2-3 times greater than in the UV/H2O2 process in waters not enriched with ammonia. UV/chlorine treatment slightly enhanced the formation chloral hydrate (CH), haloketone (HK) and trichloronitromethane (TCNM). It reduced haloacetonitrile (HAN) formation during the post-chlorination in comparison with the UV/H2O2 process. In waters with high concentrations of ammonia, the UV/chlorine process was only 5-7% more effective than the UV/H2O2 process, and it formed slightly more THMs, HKs and TCNM along with reduced formation of CH and HAN. The UV/chlorine process is thus recommended as a good alternative to UV/H2O2 treatment for its superior PPCP removal without significantly enhancing DBP formation.

Chlorination of pure bacterial cultures in aqueous solution

The fate and distribution of chlorine in aqueous solutions containing four pure bacterial cultures was studied. Solutions were subjected to chlorination at different initial free chlorine concentrations. Resulting concentrations of residual chlorine were determined by both DPD/FAS titration and membrane introduction mass spectrometry (MIMS). In all cases, false-positive breakpoint chlorination curves, probably attributable to the formation of chloroorganic-N compounds, were observed by DPD/FAS titration, while little or no inorganic residual chloramine was found by MIMS. Free chlorine was observed in similar quantities by both methods after chlorine demand by bacterial cellular materials in solution was satisfied. These results indicated the residual chloramines existed in the form of organic chloramines; these compounds are generally recognized as being poor antimicrobial agents. Further investigation confirmed that the bacterial cells were the source of organic-N compounds. The kinetics of chlorination of pure bacterial suspensions was also studied. The pattern of residual chlorine decay following chlorination of the bacterial suspensions indicated rapid initial free chlorine consumption, followed by slow free chlorine consumption, with trace quantities of inorganic chloramine being formed.