Determination of dimethyl selenide and dimethyl sulphide compounds causing off-flavours in bottled mineral waters

Treatability of odorous dioxanes/dioxolanes in source water: How does molecular flexibility and pre-oxidation affect odorant adsorption

Odorous dioxanes and dioxolanes, a class of cyclic acetals often produced as byproducts in polyester resin manufacturing, are problematic in drinking water treatment due to their low odor thresholds and resistance to conventional treatment technology. Our research focuses on the removal of ten dioxane/dioxolane compounds through oxidation and adsorption processes, exploring the key molecular properties that govern the treatmentability. We discovered that both chlorination and permanganate oxidation were largely ineffective at degrading cyclic acetals, achieving less than 20% removal even at high applicable doses. Conversely, powdered activated carbon (PAC) adsorption proved to be a more effective method, with a removal of > 90% at a PAC dosage of 10 mg/L for seven out of ten compounds. The presence of natural organic matter (NOM) reduced PAC adsorbability for all odorants, but the deterioration level substantially varied and mostly affected by structural flexibility as indicated by the number of rotatable bonds. The results of both the experimental investigation and molecular simulation corroborated the hypothesis that more rotatable bonds (from one to three here) are indicative of greater structural flexibility, which in consequence determines the susceptibility of cyclic acetals to NOM competitive adsorption. Increased structural flexibility could facilitate greater entry into silt-like micropores or achieve preferential adsorption sites with more compatible morphology against NOM competition. When pre-oxidation (chlorination and permanganate oxidation) and adsorption were applied sequentially, additional low molecular weight NOM components produced by pre-oxidation resulted in intensified NOM competition and decreased odorant adsorbability. If this combination is inevitably required for algae and odorant control, it would be beneficial to utilize a wise screen for oxidants and a reduced oxidant dose (less than 2 mg/L) to mitigate the deterioration of odorant adsorption. This study elucidates the roles of structural flexibility in influencing the treatability of dioxanes and dioxolanes, extending beyond the solely well-established effects of hydrophobicity. It also presents rational practice guidelines for the combination of pre-oxidation and adsorption in addressing odor incidents associated with dioxane and dioxolane compounds.

Degradation of mixed typical odour gases via non-thermal plasma catalysis

The simultaneous treatment of H₂S and NH₃ typical odours by plasma was investigated and the co-treatment of both was found to have a facilitating effect the conversion. The degradation efficiency and by-product emissions of single plasma technology and plasma co-catalytic two-stage technology were compared and the degradation mechanism was further analyzed. The results show that in the single plasma technology conversion experiment, the conversion rate of the treated odours mixture is higher than that of the treated single odours, and the by-product emissions of SO₂ and NO_x are also reduced due to the reaction of intermediate products and by-products during the reaction process. The absolute removal of the odours mixture is optimal when treating at a gas flow rate of 6 L/min, a voltage of 16 kV and a frequency of 200 Hz. The M(Ce,Cu)-Mn/13X loaded catalyst was synthesized by co-precipitation method. Under the conditions of gas flow rate of 3-7 L/min, the efficiency of H₂S and NH₃ removal and the reduction of by-product emission were ranked as: uncatalyzed > Cu-Mn/13X > Ce-Mn/13X, which proved that Ce-Mn/13X showed better catalytic activity and application value.

Hydrochemical characteristics and identification of pollution ions of the springs in the south of Yanbian City, China

Mathematical statistics, correlation analysis, Piper and Gibbs diagrams, and geographic information system- based multi-criteria decision analysis were used to study the hydrochemical characteristics and identification of hydrochemical ions affected by human activities of the springs in the south of Yanbian City, China. Four criteria were selected: land use/land cover, village density, distance to towns, and distance to main roads. The improved entropy method was used to assign weight to each criterion, followed by evaluating the human activities impact index map, which was used to extract the human activities impact index of springs. The correlation coefficient was calculated to identify the hydrochemical parameters affected by human activities. The results show that the main hydrochemical parameters are Ca²⁺ among cations and HCO₃^- among anions. Ca²⁺, Mg²⁺, HCO₃^-, Cl^-, and total dissolved solids (TDS) have a strong correlation and similar spatial distribution, showing a decreasing trend from northwest to southeast. Most hydrochemical parameters show a similar spatial distribution trend. The hydrochemical types of springs are HCO₃-Ca, HCO₃-Ca•Mg, HCO₃-Na•Ca, and HCO₃-Ca. In the study area, Na⁺, K⁺, TFe, Mn²⁺, F^-, PO₄^3-, and oxygen consumption are negligibly affected by human activities, Mg²⁺, HCO₃^-, and Cl^- were slightly affected, and TDS and total hardness (TH) were strongly affected. With a correlation coefficient of 0.913, nitrate exhibited the highest correlation with the human activities impact index; it was significantly affected by human activities. We conclude that nitrate was the most affected by human activities, followed by TH, TDS, and other hydrochemical parameters.

Influence of Selenium Biofortification on the Growth and Bioactive Metabolites of Ganoderma lucidum

Selenium biofortification of edible and medicinal mushrooms is an effective way to produce selenium-enriched food supplements. Ganoderma lucidum is the typical one with excellent biological activity. This study investigated G. lucidum growth and bioactive metabolites alterations during liquid culture with different concentrations of selenite. Low selenium levels did not affect growth and mycelia morphology, whereas high selenium levels negatively influenced growth, dramatically decreased biomass, caused nucleic acid and protein leakage, damaged cell walls and membranes, and resulted in indicators such as degraded cells, a red color, and an unpleasant odor. Through headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) analysis, ten volatile Se compounds were identified in G. lucidum with 200 ppm selenite, which led to an odor change, whereas only three with 50 ppm selenite. SeMet was the major selenoamino acid in the 50 ppm selenite group by high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS), but more MeSeCys was produced with 200 ppm selenite. Polysaccharide yields were promoted and inhibited with 50 and 200 ppm selenite, respectively. These results provide comprehensive insights into the effects of selenite on G. lucidum in liquid culture and are beneficial for functional selenium-enriched mushroom production and improving nutritive values.

Modified Exfoliated Carbon Nanoplatelets as Sorbents for Ammonium from Natural Mineral Waters

In this manuscript an improved sorbent based on modified exfoliated carbon nanoplatelets, applied in the removal of ammonium from aqueous samples, is presented. This sorbent showed better efficiency in comparison with the previous one obtained in our group for ammonium removal, the values of the maximum sorption capacity being improved from 10 to 12.04 mg/g. In terms of kinetics and sorption characteristic parameters, their values were also improved. Based on these results, a sorption mechanism was proposed, taking into account ion-exchange and chemisorption processes at the surface of the oxidized exfoliated carbon nanoplatelets. Future applications for simultaneous removal of other positive charged contaminants from natural waters might be possible.

Beer volatile fingerprinting at different brewing steps

Volatile fingerprints of a lager beer were carried out throughout five brewing steps to characterize the changes encompassing this process. Overall, 60 volatile organic metabolites (VOMs) were identified by headspace solid-phase microextraction followed by gas chromatography mass spectrometry (HS-SPME/GC-MS). Specific profiles were observed at different brewing steps - aldehydes and furans dominate in wort, whereas the aliphatic esters and alcohols predominate in the following steps. Such variations can be assigned to specific VOMs, as 3-methylbutanal (wort), ethyl alcohol and ethyl octanoate (fermentation, maturation and filtration), or ethyl alcohol and isoamyl acetate (final product). These VOMs can influence the beer final flavour. Ethyl alcohol contributes to its strong and pungent smell and taste, while isoamyl acetate adds intense 'fruity' and 'banana' odours. These beer volatile fingerprints constitute a valuable tool to obtain insights on the impact of each brewing step on the final product, being also very useful for certification purposes.

Exposure to Dimethyl Selenide (DMSe)-Derived Secondary Organic Aerosol Alters Transcriptomic Profiles in Human Airway Epithelial Cells

Dimethyl selenide (DMSe) is one of the major volatile organoselenium compounds released from aquatic and terrestrial environments through microbial transformation and plant metabolism. The detailed processes of DMSe leading to secondary organic aerosol (SOA) formation and the pulmonary health effects induced by inhalation of DMSe-derived SOA remain largely unknown. In this study, we characterized the chemical composition and formation yields of SOA produced from the oxidation of DMSe with OH radicals and O₃ in controlled chamber experiments. Further, we profiled the transcriptome-wide gene expression changes in human airway epithelial cells (BEAS-2B) after exposure to DMSe-derived SOA. Our analyses indicated a significantly higher SOA yield resulting from the OH-initiated oxidation of DMSe. The oxidative potential of DMSe-derived SOA, as measured by the dithiothreitol (DTT) assay, suggested the presence of oxidizing moieties in DMSe-derived SOA at levels higher than typical ambient aerosols. Utilizing RNA sequencing (RNA-Seq) techniques, gene expression profiling followed by pathway enrichment analysis revealed several major biological pathways perturbed by DMSe-derived SOA, including elevated genotoxicity, DNA damage, and p53-mediated stress responses, as well as downregulated cholesterol biosynthesis, glycolysis, and interleukin IL-4/IL-13 signaling. This study highlights the significance of DMSe-derived SOA as a stressor in human airway epithelial cells.

Kinetic and mechanistic aspects of selenite oxidation by chlorine, bromine, monochloramine, ozone, permanganate, and hydrogen peroxide

Selenium (mainly in the forms of selenite (Se(IV)) and selenate (Se(VI)) is a regulated drinking water contaminant, but there is little information on the kinetics and mechanisms of Se(IV) oxidation during water treatment. Species-specific and apparent second-order rate constants for the oxidation of Se(IV) at pH 7.0 were determined in buffered solutions and they decrease in the order bromine (5.8 ± 0.3 × 10³ M^-1 s^-1) > ozone (O₃, 513.4 ± 10.0 M^-1 s^-1) > chlorine (61.0 ± 3.6 M^-1 s^-1) > permanganate (2.1 ± 0.1 M^-1 s^-1), monochloramine (NH₂Cl, (1.3 ± 0.1) × 10^-3 M^-1 s^-1), and hydrogen peroxide (H₂O₂, (2.3 ± 0.1) × 10^-5 M^-1 s^-1). The reaction stoichiometries for the reactions of Se(IV) with bromine, O₃, chlorine, NH₂Cl, and H₂O₂ are 1:1. For Mn(VII), the stoichiometries varied with pH and were 5:2, 3:2, and 1:2 for acidic, neutral, and alkaline conditions, respectively. Based on the reaction orders and stoichiometries, the corresponding Se(IV) oxidation mechanisms for various oxidants are discussed. The role of bromide for Se(IV) oxidation was also investigated during chlorination and ozonation of Se(IV)-containing water. During chlorination, bromide-catalysis enhances the rate of the oxidation of Se(IV) to Se(VI) from 50% to nearly 90% with bromide concentrations of 50 μg L^-1 and 200 μg L^-1, respectively, at pH 7.0 and a chlorine dose of 2.0 mg L^-1 (within 15 min). During ozonation, bromide had no effect on Se(IV) oxidation. Based on the determined second order rate constants, the oxidation of Se(IV) by chlorine and ozone were successfully predicted in a natural water by a kinetic model. The second order rate constants for the same oxidants were also investigated and/or evaluated for other related anions, such as arsenite (As(III)) and sulfite (S(IV)). They decreased in the order S(IV) > As(III) > Se(IV).

Occurrence of swampy/septic odor and possible odorants in source and finished drinking water of major cities across China

Swampy/septic odors are one of the most important odor types in drinking water. However, few studies have specifically focused on it compared to the extensive reported musty/earthy odor problems, even though the former is much more offensive. In this study, an investigation covering the odor characteristics, algal distribution and possible odorants contributing to swampy/septic odor, including dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS), diisopropyl sulfide (DIPS), dipropyl sulfide (DPS), dibutyl sulfide (DBS), 2-methylisoborneol (2-MIB) and geosmin (GSM), was performed in source and finished water of 56 drinking water treatment plants (DWTPs) in 31 cities across China. While the musty/earthy and swampy/septic odors were dominant odor descriptors, the river source water exhibited a higher proportion of swampy/septic odor (38.5%) compared to much higher detection rate of musty/earthy odor (50.0%) in the lake/reservoir source water. The occurrence of swampy/septic odor, which was much easier to remove by conventional drinking water treatment processes compared to musty/earthy odors, was decreased by 62.9% and 46.3% in river and lake/reservoir source water respectively. Statistical analysis showed that thioethers might be responsible for the swampy/septic odor in source water (R² = 0.75, p < 0.05). Specifically, two thioethers, DMDS and DMTS were detected, and other thioethers were not found in all water samples. DMDS was predominant with a maximum odor activity value (OAV) of 2.0 in source water and 1.3 in finished water. The distribution of the thioethers exhibited a marked regional characteristics with higher concentrations being detected in the east and south parts of China. The high concentrations of thioethers in lake/reservoir source water samples could be partly interpreted as the bloom of the cyanobacteria. This study provides basic information for swampy/septic odor occurrence in drinking water and will be helpful for further water quality management in water industry in China.

The synergistic effect of Selenium (selenite, -SeO32-) dose and irradiance intensity in Chlorella cultures

Microalgae are able to metabolize inorganic selenium (Se) to organic forms (e.g. Se-proteins); nevertheless at certain Se concentration culture growth is inhibited. The aim of this work was to confirm the hypothesis that the limit of Se tolerance in Chlorella cultures is related to photosynthetic performance, i.e. depends on light intensity. We studied the relation between the dose and irradiance to find the range of Se tolerance in laboratory and outdoor cultures. At low irradiance (250 µmol photons m⁻² s⁻¹), the daily dose of Se below 8.5 mg per g of biomass (<20 µM) partially stimulated the photosynthetic activity (relative electron transport rate) and growth of Chlorella cultures (biomass density of ~1.5 g DW L⁻¹) compared to the control (no Se added). It was accompanied by substantial Se incorporation to microalgae biomass (~0.5 mg Se g⁻¹ DW). When the Se daily dose and level of irradiance were doubled (16 mg Se g⁻¹ DW; 500 µmol photons m⁻² s⁻¹), the photosynthetic activity and growth were stimulated for several days and ample incorporation of Se to biomass (7.1 mg g⁻¹ DW) was observed. Yet, the same Se daily dose under increased irradiance (750 µmol photons m⁻² s⁻¹) caused the synergistic effect manifested by significant inhibition of photosynthesis, growth and lowered Se incorporation to biomass. In the present experiments Chl fluorescence techniques were used to monitor photosynthetic activity for determination of optimal Se doses in order to achieve efficient incorporation without substantial inhibition of microalgae growth when producing Se-enriched biomass.

Development of the MOOSY4 eNose IoT for Sulphur-Based VOC Water Pollution Detection

In this paper, we describe a new low-cost and portable electronic nose instrument, the Multisensory Odor Olfactory System MOOSY4. This prototype is based on only four metal oxide semiconductor (MOS) gas sensors suitable for IoT technology. The system architecture consists of four stages: data acquisition, data storage, data processing, and user interfacing. The designed eNose was tested with experiment for detection of volatile components in water pollution, as a dimethyl disulphide or dimethyl diselenide or sulphur. Therefore, the results provide evidence that odor information can be recognized with around 86% efficiency, detecting smells unwanted in the water and improving the quality control in bottled water factories.

Predicting water filter and bottled water use in Appalachia: a community-scale case study

A questionnaire survey was conducted in order to assess residents' perceptions of water quality for drinking and recreational purposes in a mid-sized city in northcentral West Virginia. Two logistic regression analyses were conducted in order to investigate the factors that influence bottle use and filter use. Results show that 37% of respondents primarily use bottled water and that 58% use a household filter when drinking from the tap. Respondents with lower levels of environmental concern, education levels, and lower organoleptic perceptions were most likely to perceive health risks from tap water consumption, and were most likely to use bottled water. Income, age, and organoleptic perceptions were predictors of water filter use among respondents. Clean water for recreational purposes was not found to be significant with either of these models. Our results demonstrate that bottle use and filter use are explained differently. We argue that more education and better communication about local tap water quality would decrease the use of bottled water. We demonstrate that household filters could be used as an alternative to bottled water.