Interference from haloacetamides during the determination of haloacetic acids using gas chromatography

Reduced formation of brominated trihalomethanes during chlorination of bromide-containing waters in the presence of Mn(II)

Manganese(II) (Mn(II)) and bromide (Br-) are common in natural waters. This study investigated the effect of in-situ Mn(II) oxidation and preformed MnOx on the brominated trihalomethane (Br-THM) formation during chlorination of bromide-containing waters. The results showed Br-THM formation could be substantially inhibited by in-situ Mn(II) oxidation, but the addition of preformed MnOx had limited influence on Br-THM formation during chlorination of bromide-containing waters. Analysis of bromine species showed that about 30 % bromine species were incorporated into the MnOx particles and formed MnOx-Br during the in-situ Mn(II) oxidation process. Consequently, the availability of reactive bromine species for the reaction with dissolved organic matter (DOM) reduced, leading to less Br-THM formation. X-ray diffraction (XRD) analysis of in-situ Mn(II) oxidation product indicated the presence of Br- decreased the crystallinity of Mn oxides, verifying the bromine species entered MnOx crystal. However, the adsorptive uptake of bromine species by preformed MnOx was negligible and had no impact on Br-THM formation. Inhibition rate of Mn(II) oxidation on THM formation decreased with increasing specific ultraviolet absorbance (SUVA254) value of filtered water, showing SUVA254 could be a good indicator of DOM competition ability for oxidant with Mn(II). In addition, Excitation/Emission Matrix indicated that Mn(II) could form complexes with humic substances, which might also retard the reaction between humic substances and oxidant to form Br-THMs. This study highlighted the inhibiting effect of in-situ Mn(II) oxidation on Br-THM formation during chlorination of bromide-containing waters.

Recent progress in identification of water disinfection byproducts and opportunities for future research

Numerous disinfection by-products (DBPs) are formed from reactions between disinfectants and organic/inorganic matter during water disinfection. More than seven hundred DBPs that have been identified in disinfected water, only a fraction of which are regulated by drinking water guidelines, including trihalomethanes, haloacetic acids, bromate, and chlorite. Toxicity assessments have demonstrated that the identified DBPs cannot fully explain the overall toxicity of disinfected water; therefore, the identification of unknown DBPs is an important prerequisite to obtain insights for understanding the adverse effects of drinking water disinfection. Herein, we review the progress in identification of unknown DBPs in the recent five years with classifications of halogenated or nonhalogenated, aliphatic or aromatic, followed by specific halogen groups. The concentration and toxicity data of newly identified DBPs are also included. According to the current advances and existing shortcomings, we envisioned future perspectives in this field.

Effects of phosphate addition on the removal of disinfection by-product formation potentials by biological activated carbon filtration

In drinking water treatment plants (DWTPs), the widely used biological activated carbon filters (BACFs), as the last barrier before disinfection, can remove dissolved organic matter (DOM) known as precursors of disinfection by-products (DBPs). Whether phosphate addition can improve water purification and DBP control of BACFs is still controversial. This study investigated short-term and long-term effects of phosphate addition on controlling DBP formation potentials (FPs) by BACFs via column and batch experiments. The BAC columns presented good water purification performance: they removed around 50 % DOM, nearly all fulvic acid-likes and humic acid-likes as well as 5 %-70 % chlor(am)innated THM₄, HAA₉ and HAN₄ FPs (except chloraminated THM₄ FPs)， which was mainly contributed by aerobic bacteria not anoxic bacteria. Phosphate addition within 7-14 days further improved removals of DOM, aromatic organics, fluorescence fractions in DOM as well as HAA₉ and HAN₄ FPs (especially TCAA FP and TCAN FP) to different extent. However, this improvement did not last longer, and removals of DOM, aromatic organics, two fluorescence fractions (soluble microbial byproduct-likes and humic acid-likes) and DBP FPs decreased despite long-term phosphate addition. Oxic and anoxic batch experiments showed that the positive response of water purification to short-term phosphate addition was also mainly attributed to aerobic bacteria and not to anoxic bacteria. For example, the former decreased DOM and DBP FPs, while the latter increased protein- and tryptophan-like substances as well as chloraminated THM₄ FPs. Phosphate addition resulted in EPS increase in anoxic reactors and decrease in oxic reactors. These results indicated that a high dissolved oxygen in BACFs may be helpful for water purification and DBP control. Overall, short-term phosphate addition into phosphorus-limited water is beneficial for BACFs to control DBPs while long-term addition has no effect. Therefore, an intermittent phosphate addition into BACFs is suggested to control DBPs in DWTPs.

Rapid determination of 14 odorous compounds in drinking water using gas chromatography-mass spectrometry coupled with headspace solid-phase microextraction pretreatment

A sensitive and effective method was developed for the simultaneous determination of 14 odorous compounds in drinking water using gas chromatography-mass spectrometry (GC-MS) coupled with headspace solid phase microextraction (HS-SPME) pretreatment. The influencing factors including SPME fiber, ionic strength, temperature and time on the pretreatment procedure were evaluated systematically. Under the optimized conditions, 10 mL of the samples added with 1.0 g sodium chloride was extracted by CAR/PDMS fiber at 60 °C for 30 min and then desorbed at 280 °C for 3 min. The analytes achieved good linearity as the mass concentrations were in the range of 0.0020-10.0 μg L^-1 with correlation coefficients higher than 0.9990. The limits of detection (LODs) ranging between 0.2 and 50 ng L^-1 were lower than the olfactory threshold of these studied compounds. Satisfactory recoveries were obtained ranging from 84.8% to 110.6%, and good reproducibility indicated by relative standard deviation (RSD) in the range of 0.50-9.5% was obtained as well. The proposed method was convenient, sensitive and accurate, which was suitable for the routine monitoring 14 odorous compounds in water.

Derivatization-free multi-step extraction for trace haloacetic acids analysis with ion chromatography: Performance and mechanisms

Haloacetic acids (HAAs) are a type of disinfection byproducts commonly found in drinking water with carcinogenic, mutagenic, or teratogenic risks to humans. Currently, the analytical methods of trace HAAs are either labor-intensive or very expensive. We herein propose a facile multiple-step extraction strategy for HAAs analysis with common ion chromatography (IC). This study is based on a fundamental water chemistry principle that HAAs become protonated featuring positive logK_ow values (> 0.34) under pH < pK_a but deprotonated featuring negative logK_ow values (< -2.37) under pH > pK_a. By taking advantage of the species and property switches, HAAs can be extracted and enriched into methyl tert-butyl ether first at pH < 0.5 and then back-extracted into neutral water and enriched again. Equally important, interfering anions in IC chromatogram are eliminated because they have negative logK_ow values. Verification results show that HAAs were enriched by 11.4 times in average while interfering anions were almost eliminated (> 99%). Although similar to USEPA Method 552.3 in method detection limits (0.033-0.246 μg/L), recoveries (70%~110%), and relative standard deviations (< 9.91%), this method took ≤ 70 min to run a batch of samples without derivatization, which takes over 2 h. The methodology may be applicable to other pollutants that also have contrasting K_ow values at different pH.

Dummy template based molecularly imprinted solid-phase microextraction coating for analysis of trace disinfection by-product of 2,6-dichloro-1,4-benzoquinone using high-performance liquid chromatography

Trace disinfection by-products (DBPs) produced during the disinfection of drinking water are potentially carcinogenic, teratogenic and mutagenic, which has aroused much attention recently. In this study, a molecularly imprinted (MIP) solid -phase microextraction (SPME) fiber coating was prepared by an in-situ polymerization method using a dummy template molecule for the analysis of trace 2,6-dichloroindole-1,4-benzoquinone (2,6-DCBQ), a typical DBP. The characterization results suggested that this monolithic SPME fiber under the optimized conditions had the porous structure, large surface area and good thermal stability. Due to the strong structural recognition and molecular interaction between MIP SPME coating and target molecule, it showed good extraction selectivity and capacity to trace 2,6-DCBQ with an imprinting factor of 4.7. Then, coupling with high-performance liquid chromatography (HPLC)-ultraviolet (UV) detection, a sensitive analytical method for trace 2,6-DCBQ in water samples was successfully established with a detection limit down to 2.3 ng/mL. The recoveries of the proposed method were in range of 84.4-122% with the relative standard deviations of 1.0-13% (n = 3). The results showed that this MIP SPME-HPLC-UV method possessed high analytical selectivity and sensitivity for trace 2,6-DCBQ in water, which would benefit the improvement of the practicability of DBPs monitoring and detection methodology.