Routine analysis of off-flavor compounds in water at sub-part-per-trillion level by large-volume injection GC/MS with programmable temperature vaporizing inlet

Effective catalytic hydrodechlorination removal of chloroanisole odorants in water using palladium catalyst confined in zeolite Y

Chloroanisoles is a class of odorous pollutants commonly identified in drinking water. In the present study, we confined noble metal palladium (Pd) in the micropores of zeolite Y (ie-Pd@Y) using an ion exchange method, and applied it for the catalytic hydrodechlorination removal of chloroanisoles (represented by 2,4,6-trichloroanisole/TCA) in water. Pd supported on zeolite Y surface (im-Pd/Y, prepared by conventional impregnation method) was used as the benchmarking catalyst. The characterization results revealed that ie-Pd@Y had smaller Pd particle size and higher Pdⁿ⁺/Pd⁰ ratio than im-Pd/Y. The catalytic hydrodechlorination of TCA followed a concerted dechlorination pathway and the Langmuir-Hinshelwood model. The ie-Pd@Y catalysts with different Pd loadings exhibit excellent catalytic activities with more than 95% of TCA removed within 30 min, which is far superior to the im-Pd/Y catalysts (27-70%). Moreover, due to the confinement effect of zeolite Y, ie-Pd@Y displayed enhanced catalytic stability as compared with im-Pd/Y. The initial activity of ie-Pd@Y was more than 20 times higher than that of im-Pd/Y after five reaction cycles. Additionally, with the assistance of sieving effect, ie-Pd@Y displayed much stronger capability against the interference from dissolved organic matter than im-Pd/Y. The present results demonstrate that the confined catalysts ie-Pd@Y can be applied in liquid phase catalytic hydrogenation to effectively eliminate halogenated odorants in waters.

A framework for identifying characteristic odor compounds in municipal wastewater effluent

Municipal wastewater often contains trace amounts of organic compounds that can compromise aesthetics of drinking water and undermine public confidence if a small amount of effluent enters the raw water source of a potable water supply. To efficiently identify compounds responsible for odors in wastewater effluent, an analytical framework consisting of gas chromatography with mass spectrometry (GC-MS) and gas chromatography with olfactometry detection (GC-Olf) coupled with flavor profile analysis (FPA) was used to identify and monitor compounds that could affect the aesthetics of drinking water. After prioritizing odor peaks detected in wastewater effluent by GC-Olf, the odorous components were tentatively identified using retention indices, mass spectra and odor descriptors. Wastewater effluent samples were typically dominated by earthy-musty odors with additional odors in the amine, sulfidic and fragrant categories. 2,4,6-trichloroanisole (246TCA), geosmin and 2-methylisoborneol (2MIB) were the main sources of the earthy/musty odors in wastewater effluent. The other odors were attributable to a suite of compounds, which were detected in some but not all of the wastewater effluents at levels well in excess of their odor thresholds. In most cases, the identities of odorants were confirmed using authentic standards. The fate of these odorous compounds, including 2-pyrrolidone, methylnaphthalenes, vanillin and 5-hydroxyvanillin (5-OH-vanillin), should be considered in future studies of water systems that receive effluent from upstream sources.

Odorous compounds in municipal wastewater effluent and potable water reuse systems

The presence of effluent-derived compounds with low odor thresholds can compromise the aesthetics of drinking water. The potent odorants 2,4,6-trichloroanisole and geosmin dominated the profile of odorous compounds in wastewater effluent with concentrations up to 2 orders of magnitude above their threshold values. Additional odorous compounds (e.g., vanillin, methylnaphthalenes, 2-pyrrolidone) also were identified in wastewater effluent by gas chromatography coupled with mass-spectrometry and olfactometry detection. Full-scale advanced treatment plants equipped with reverse osmosis membranes decreased odorant concentrations considerably, but several compounds were still present at concentrations above their odor thresholds after treatment. Other advanced treatment processes, including ozonation followed by biological activated carbon and UV/H(2)O(2) also removed effluent-derived odorants. However, no single treatment technology alone was able to reduce all odorant concentrations below their odor threshold values. To avoid the presence of odorous compounds in drinking water derived from wastewater effluent, it is necessary to apply multiple barriers during advanced treatment or to dilute wastewater effluent with water from other sources.