Dioxanes and dioxolanes in source waters: Occurrence, odor thresholds and behavior through upgraded conventional and advanced processes in a drinking water treatment plant.

Over the last years, the human probable carcinogen 1,4-dioxane and alkyl-1,3-dioxanes and dioxolanes have been detected and identified as the cause of several pollution episodes in the Llobregat River (Catalonia, NE Spain) and its aquifer. It is an issue of major concern to study these compounds which are released to the environment by resin manufacturing plants' spills and wastewater discharges spread along rivers and reach drinking water treatment plants (DWTPs) in order to protect the environment and public health. In this study four seasonal sampling campaigns were carried out over a year to determine the removal efficiency of the dioxanes and dioxolanes at each step of a DWTP including ozonation, granular activated carbon filters, ultrafiltration and reverse osmosis step's treatments. Additionally, a weekly sampling monitoring of 1,4-dioxane and alkyl-1,3-dioxanes and dioxolanes in raw water, groundwater and finished water was performed at a DWTP over more than two years. Aqueous odor concentration thresholds (OTCs) were established by the three-alternative forced choice method (3-AFC). Following a previous published methodology, samples were analyzed and results showed that the advanced treatment (Ultrafiltration followed by reverse osmosis) line removes more efficiently 1,4-dioxane, alkyl dioxanes and dioxolanes (80 ±â€¯6% for 1,4-dioxane, 97 ±â€¯7% for 5,5-DMD and 100 ±â€¯0% for 2,5,5-TMD) than the upgraded conventional treatment line (ozonation followed by granular activated carbon filters) (-12 ±â€¯50%, 25 ±â€¯62% and 50 ±â€¯51% respectively), where some desorption processes were eventually observed. From the monitoring study, results suggest that the presence of 1,4-dioxane is not only due to spills, but also from other sources of contamination. Whereas dioxolanes almost completely disappeared in time, 1,4-dioxane's concentrations remained low and fluctuant. A background concentration of 1,4-dioxane in surface waters (∼1 µg/L) has been determined with a relevant concentration up to 11.6 µg/L of 1,4-dioxane in groundwater. The perception values for some of the studied compounds were extremely low (few ng/L only), which confirms the relevancy of this group of compounds as malodorous agents in waters.

Simultaneous determination of the potential carcinogen 1,4-dioxane and malodorous alkyl-1,3-dioxanes and alkyl-1,3-dioxolanes in environmental waters by solid-phase extraction and gas chromatography tandem mass spectrometry.

1,4-dioxane is a synthetic industrial solvent used in various industrial processes, and it is a probable human carcinogen whose presence in the aquatic environment is frequently reported. Alkyl-1,3-dioxanes and alkyl-1,3-dioxolanes are compounds that have been identified as causing several odor episodes in waters over the last years, with the result of downtime of drinking water treatment plants. According to published studies, some of these episodes may be caused either by resins synthesis processes, or by industrial residues added to dehydrated sludge in wastewater treatment plants (WWTPs) in order to increase biogas production efficiency. Analytical methods based on closed loop stripping analysis (CLSA) are routinely used when taste and odor events appear, but this technique has demonstrated to be unsuitable to determine 1,4-dioxane at trace levels. In this context, drinking water companies tend to focus on determining odorous compounds, but not on those compounds that are potentially harmful. The suitability of a SPE method and further analysis by GC/MS-MS to simultaneously determine 1,4-dioxane and alkyl-1,3-dioxanes and dioxolanes has been demonstrated. Recoveries in surface waters spiked at 25ng/L ranged from 76% to 105%, whereas method quantification limits (MQLs) varied from 0.7 to 26ng/L for dioxanes, and dioxolanes and 50ng/L for 1,4-dioxane. Uncertainties were evaluated at two different concentrations, 0.02µg/L and 0.4µg/L, with values of 25% for 1,4-dioxane, and of 16-28% for alkyl-1,3-dioxanes and alkyl-1,3-dioxolanes for the later. The methodology has been successfully applied to samples from the aquifer of the Llobregat River (NE. Spain).

Odor Events in Surface and Treated Water: The Case of 1,3-Dioxane Related Compounds.

A study has been carried out to identify the origin of the odorous compounds at trace levels detected in surface waters and in Barcelona's tap water (NE Spain) which caused consumer complaints. The malodorous compounds were 2,5,5-trimethyl-1,3-dioxane (TMD) and 2-ethyl-5,5-dimethyl-1,3-dioxane (2EDD) which impart a distinctive sickening or olive-oil odor to drinking water at low ng/L levels. Flavor profile analysis (FPA) or threshold odor number (TON) were used for organoleptic purposes. Levels up to 749 ng/L for TMD and 658 ng/L for 2EDD were measured at the entrance of the drinking water treatment plant. Three wastewater treatment plants (WWTPs) using industrial byproducts coming from resin manufacturing plants to promote codigestion were found to be the origin of the event. Corrective measures were applied, including the prohibition to use these byproducts for codigestion in the WWTPs involved. A similar event was already recorded in the same area 20 years ago.