Yuefeng F. Xie

Analyzing haloacetic acids using gas chromatography/mass spectrometry

Haloacetic acids (HAAs) are a group of disinfection by-products formed in chlorinated water. Due to their potential health effects and widespread occurrences, HAAs are regulated in drinking water in the United States under a promulgated regulation. To better control the formation of HAAs in drinking water, a reliable and accurate analytical method is needed for HAA monitoring. In the present study, a liquid-liquid microextraction, acidic methanol derivatization, and gas chromatography/mass spectrometry (GC/MS) detection method was developed for determining HAAs and dalapon in drinking water. The newly developed method is capable of analyzing all nine HAAs and dalapon at microgram/l levels. The method performance, including the method detection limit (MDL) and spiking recovery, was evaluated. In comparison to EPA Method 552.2, which uses gas chromatography/electron capture detection (GC/ECD), this GC/MS method gave cleaner baselines and had few interfering peaks. For each of all nine HAAs and dalapon, the MDL was less than 1 microgram/l and the spiking recovery ranged from 73 to 165%. Using the GC/MS method, the run time could also be significantly reduced without compromising the analytical results. Further study is needed to fine-tune this GC/MS based analytical method, especially in the detection of brominated trihaloacetic acids and monochloroacetic acid.

Enhanced performance of crumb rubber filtration for ballast water treatment.

Waste-tire-derived crumb rubber was utilized as filter media to develop an efficient filter for ballast water treatment. In this study, the effects of coagulation, pressure filtration and dual-media (gravity) filtration on the performance of the crumb rubber filtration were investigated. The removal efficiencies of turbidity, phytoplankton and zooplankton, and head loss development were monitored during the filtration process. The addition of a coagulant enhanced the removal efficiencies of all targeted matter, but resulted in substantial increase of head loss. Pressure filtration increased filtration rates to 220 m(3)h(-1)m(-2) for 8-h operation and improved the zooplankton removal. Dual-media (crumb rubber/sand) gravity filtration also improved the removal efficiencies of phytoplankton and zooplankton over mono-media gravity crumb rubber filtration. However, these filtration techniques alone did not meet the criteria for removing indigenous organisms from ballast water. A combination of filtration and disinfection is suggested for future studies.

Association between haloacetic acid degradation and heterotrophic bacteria in water distribution systems.

The occurrences of trihalomethanes (THMs), haloacetic acids (HAAs) and heterotrophic bacteria were monitored in five small water systems over a nine-month period to investigate the association between HAA degradation and heterotrophic bacteria populations. The sampling sites were chosen to cover the entire distribution network for each system. An inverse association between heterotrophic bacteria and HAA concentrations was found at some locations where chlorine residuals were around or less than 0.3mgL(-1). At other sample locations, where chlorine residuals were higher (over 0.7mgL(-1)), no HAA reduction was observed. A high heterotrophic bacteria count accompanied with a low chlorine residual could be used as an indicator for HAA degradation in distribution systems.

Effects of ozonation on disinfection byproduct formation and speciation during subsequent chlorination

Ozone has been widely used for drinking water treatment recently. This study was conducted to investigate the effect of dosing ozone on the formation potentials and speciation of disinfection by-products (DBPs, brominated DBPs in particular) during subsequent chlorination. Trihalomethanes (THMs), trihaloacetic acids (THAAs), dihaloacetic acids (DHAAs), dihaloacetonitriles (DHANs), chloral hydrate (CH)and trichloronitromethane (TCNM) were included. The results showed that the yields of THMs, THAAs and DHAAs reached the maxima at 1.83, 0.65 and 0.56 μM, respectively, corresponding to an ozone dose approximately at 2 mg L(-1). The formation potentials of CH and TCNM increased, while that of DHAN decreased, with the increase of ozone dose up to 6 mg L(-1). The bromide incorporation factor values of THMs, THAAs, DHAAs and DHANs increased from 0.62, 0.37, 0.45 and 0.39 at O3=0 mg L(-1) to 0.89, 0.65, 0.62 and 0.89 at O3=6 mg L(-1), respectively. It indicated that the use of ozone as a primary disinfectant may cause a shift to more brominated DBPs during subsequent chlorination, and the shift may be more evident with increased ozone dose. The total percentage of brominated DBPs (as bromide) reached the maximum value of 55% at 2 mg L(-1) ozone dose.

Formation of disinfection by-products: Effect of temperature and kinetic modeling

The temperature of drinking water fluctuates naturally in water distribution systems as well as often deliberately heated for household or public uses. In this study, the temperature effect on the formation of disinfection by-products (DBPs) was investigated by monitoring the temporal variations of twenty-one DBPs during the chlorination of a humic precursors-containing water at different temperatures. It was found that chloroform, DCAA, TCAA, DCAN and CH were detected at the considerable level of tens of μg L(-1). The three regulated DBPs (chloroform, DCAA and TCAA) were found increasing with both contact time and water temperature, while the five typical emerging DBPs (DCAN, CH, TCNM 1,1-DCPN and 1,1,1-TCPN) revealed the significant auto-decomposition in addition to the initial growth in the first few hours. Increasing water temperature could enhance the formation rates of all the eight detected DBPs and the decomposition rates of the five emerging DBPs. Further, a kinetic model was developed for the simulation of DBP formation. The validity and universality of the model were verified by its excellent correlation with the detected values of each DBP species at various temperatures. The formation rates of 1,1-DCPN and 1,1,1-TCPN, and the decomposition rate of 1,1,1-TCPN were faster as compared to the other DBPs. And the formation reaction activation energies of CH, DCAN and 1,1-DCPN were relatively large, indicating that their occurrence levels in the finished water were more susceptible to temperature variations.

Disinfection byproducts in drinking water and regulatory compliance: A critical review

Disinfection by-products (DBPs) are regulated in drinking water in a number of countries. This critical review focuses on the issues associated with DBP regulatory compliance, including methods for DBP analysis, occurrence levels, the regulation comparison among various countries, DBP compliance strategies, and emerging DBPs. The regulation comparison between China and the United States (US) indicated that the DBP regulations in China are more stringent based on the number of regulated compounds and maximum levels. The comparison assessment using the Information Collection Rule (ICR) database indicated that the compliance rate of 500 large US water plants under the China regulations is much lower than that under the US regulations (e.g. 62.2% versus 89.6% for total trihalomethanes). Precursor removal and alternative disinfectants are common practices for DBP regulatory compliance. DBP removal after formation, including air stripping for trihalomethane removal and biodegradation for haloacetic acid removal, have gained more acceptance in DBP control. Formation of emerging DBPs, including iodinated DBPs and nitrogenous DBPs, is one of unintended consequences of precursor removal and alternative disinfection. At much lower levels than carbonaceous DBPs, however, emerging DBPs have posed higher health risks.

Characterization of soluble microbial products as precursors of disinfection byproducts in drinking water supply.

Water pollution by wastewater discharge can cause the problem of disinfection byproducts (DBPs) in drinking water supply. In this study, DBP formation characteristics of soluble microbial products (SMPs) as the main products of wastewater organic biodegradation were investigated. The results show that SMPs can act as DBP precursors in simulated wastewater biodegradation process. Under the experimental conditions, stabilized SMPs had DBPFP (DBP formation potential) yield of around 5.6 μmol mmol(-1)-DOC (dissolved organic carbon) and DBP speciation profile different from that of the conventional precursor, natural organic matter (NOM). SMPs contained polysaccharides, proteins, and humic-like substances, and the latter two groups can act as reactive DBP precursors. SMP fraction with molecular weight of <1 kDa accounted for 85% of the organic carbon and 65% of the DBP formation. As small SMP molecules are more difficult to remove by conventional water treatment processes, more efforts are needed to control wastewater-derived DBP problem in water resource management.

Formation of Ketoacids in Ozonated Drinking Water

Three ketoacids; glyoxylic acid, pyruvic acid and ketomalonic acid, were identified in ozonated drinking waters and fulvic acid solutions using gas chromatography-mass spectrometry. It was found that the concentrations of ketoacids were much higher than those of aldehydes in ozonated waters. The significance of ketoacids in finished drinking waters is discussed.

Effect of dissolved oxygen concentration on iron efficiency: Removal of three chloroacetic acids

The monochloroacetic, dichloroacetic and trichloroacetic acid (MCAA, DCAA and TCAA) removed by metallic iron under controlled dissolved oxygen conditions (0, 0.75, 1.52, 2.59, 3.47 or 7.09 mg/L DO) was investigated in well-mixed batch systems. The removal of CAAs increased first and then decreased with increasing DO concentration. Compared with anoxic condition, the reduction of MCAA and DCAA was substantially enhanced in the presence of O2, while TCAA reduction was significantly inhibited above 2.59 mg/L. The 1.52 mg/L DO was optimum for the formation of final product, acetic acid. Chlorine mass balances were 69-102%, and carbon mass balances were 92-105%. With sufficient mass transfer from bulk to the particle surface, the degradation of CAAs was limited by their reduction or migration rate within iron particles, which were dependent on the change of reducing agents and corrosion coatings. Under anoxic conditions, the reduction of CAAs was mainly inhibited by the available reducing agents in the conductive layer. Under low oxic conditions, the increasing reducing agents and thin lepidocrocite layer were favorable for CAA dechlorination. Under high oxic conditions, the redundant oxygen competing for reducing agents and significant lepidocrocite growth became the major restricting factors. Various CAA removal mechanisms could be potentially applied to explaining the effect of DO concentration on iron efficiency for contaminant reduction in water and wastewater treatment.

Effects of organic fractions on the formation and control of N-nitrosamine precursors during conventional drinking water treatment processes

Knowledge of N-nitrosamine precursors from dissolved organic matter (DOM) is important for water professionals to better control N-nitrosamine formation. The characterization of DOM from the Luan River in Northern China was conducted using Amberlite XAD resins and ultra-filtration methods. N-nitrosamine formation potentials were investigated for various DOM fractions. The removal of the DOM during water treatment were evaluated using dissolved organic carbon (DOC) and ultraviolet absorbance at 254 nm (UV254) bulk parameters as well as size exclusion chromatography and fluorescence spectroscopy. The results indicated that the XAD-4 hydrophilic fraction, with normalized yields of N-nitrosodimethylamine (NDMA), N-nitrosopyrrolidine (NPYR), N-nitrosomorpholine (NMOR), and N-nitrosopiperidine (NPIP) of 27.2, 5.2, 5.9, and 6.1 ng/mg-DOC, respectively, tended to form more N-nitrosamines than the hydrophobic and the transphilic fractions. The DOM fraction with a molecular weight (MW) below 1 kDa, with normalized yields of NDMA, NPYR, NMOR, and NPIP of 39.6, 8.1, 14.7, and 3.3 ng/mg-DOC, respectively, tended to form more N-nitrosamines than those with a higher MW. The limited removal of the hydrophilic fraction and the lower MW DOM faction during conventional water treatment processes suggests that the process may not effectively remove the nitrosamine precursors.