Aqueous ozonation of furans:Kinetics and transformation mechanisms leading to the formation of α,β-unsaturated dicarbonyl compounds

Despite the widespread occurrence of furan moieties in synthetic and natural compounds, their fate in aqueous ozonation has not been investigated in detail. Reaction rate constants of seven commonly used furans with ozone were measured and ranged from kO3 = 8.5 × 104 to 3.2 × 106 M−1 s−1, depending on the type and position of furan ring substituents. Transformation product analysis of the reaction of furans with ozone focusing on the formation of toxic organic electrophiles using a novel amino acid reactivity assay revealed the formation of α,β-unsaturated dicarbonyl compounds, 2-butene-1,4-dial (BDA) and its substituted analogues (BDA-Rs). Their formation can be attributed to ozone attack at the reactive α-C position leading to furan ring opening. The molar yields of α,β-unsaturated dicarbonyl compounds varied with the applied ozone concentration reaching maximum values of 7% for 2-furoic acid. The identified α,β-unsaturated dicarbonyls are well-known toxicophores that are also formed by enzymatic oxidation of furans in the human body. In addition to providing data on kinetics, transformation product analysis and proposed reaction mechanisms for the ozonation of furans, this study raises concern about the presence of α,β-unsaturated dicarbonyl compounds in water treatment and the resulting effects on human and environmental health.</p

Effect of Solution pH on the Dual Role of Dissolved Organic Matter in Sensitized Pollutant Photooxidation

[Image: see text] Dissolved organic matter (DOM) has a dual role in indirect phototransformations of aquatic contaminants by acting both as a photosensitizer and an inhibitor. Herein, the pH dependence of the inhibitory effect of DOM and the underlying mechanisms were studied in more than 400 kinetic irradiation experiments over the pH range of 6–11. Experiments employed various combinations of one of three DOM isolates, one of two model photosensitizers, the model antioxidant phenol, and one of nine target compounds (TCs), comprising several aromatic amines, in particular anilines and sulfonamides, and 4-cyanophenol. Using model photosensitizers without antioxidants, the phototransformation of most TCs increased with increasing pH, even for TCs for which pH did not affect speciation. This trend was attributed to pH-dependent formation yields of TC-derived radicals and their re-formation to the parent TC. Analogous trends were observed with DOM as a photosensitizer. Comparison of model and DOM photosensitizer data sets showed increasing inhibitory effects of DOM on TC phototransformation kinetics with increasing pH. In systems with anilines as a TC and phenol as a model antioxidant, pH trends of the inhibitory effect could be rationalized based on the reduction potential difference (ΔE(red)) of phenoxyl/phenol and anilinyl/aniline couples. Our results indicate that the light-induced transformation of aromatic amines in the aquatic environment is governed by the pH-dependent inhibitory effects of antioxidant phenolic moieties of DOM and pH-dependent processes related to the formation of amine oxidation intermediates

Simplified in-situ tailoring of cross-linked self-doped sulfonated polyaniline (S-PANI) membranes for nanofiltration applications

Sulfonated polyaniline (S-PANI) membranes could have wide-ranging applications due to their electrical tunability, antifouling behaviour and chlorine resistance. However, S-PANI membranes below the ultrafiltration (UF) separation range have not been successfully established. This study presents a scalable approach to produce the first in-situ cross-linked S-PANI membranes at nanofiltration (NF) range. S-PANI membranes were produced by non-solvent induced phase separation (NIPS). The presence of sulfonic groups as polymer cross-linking anchors and controlling the coagulation bath's acidic strength resulted in instant stabilisation of the selective layer, which hindered the solvent/non-solvent exchange rate. This enabled the production of a tailored membrane morphology with a dense skin layer, suppressed macro-voids, reduced porosity, enhanced tensile strength, increased hydrophilicity and solvent stability. S-PANI membranes cast in 3 M HCl(aq) with MWCO≈680 g mol−1 (sucrose octa-acetate) showed a rejection of 99 % for PEG 1000 g mol−1 and 91–100 % for dye solution (MW range of 320–1017 g mol−1) compared to 34 % and 74–85 % rejection for a commercial fluoropolymer membrane (nominal MWCO 1000 g mol−1), respectively. The reported approach is simple and can be applied to design new classes of cross-linked solvent stable S-PANI NF membranes

Photoinactivation of Eight Health-Relevant Bacterial Species: Determining the Importance of the Exogenous Indirect Mechanism

It is presently unknown to what extent the endogenous direct, endogenous indirect, and exogenous indirect mechanisms contribute to bacterial photoinactivation in natural surface waters. In this study, we investigated the importance of the exogenous indirect mechanism by conducting photoinactivation experiments with eight health-relevant bacterial species (<i>Bacteroides thetaiotaomicron, Campylobacter jejuni</i>, <i>Enterococcus faecalis</i>, <i>Escherichia coli</i> K12, <i>E. coli</i> O157:H7, <i>Salmonella enterica</i> serovar Typhimurium LT2, <i>Staphylococcus aureus</i>, and <i>Streptococcus bovis</i>). We used three synthetic photosensitizers (methylene blue, rose bengal, and nitrite) and two model natural photosensitizers (Suwannee River natural organic matter and dissolved organic matter isolated from a wastewater treatment wetland) that generated singlet oxygen and hydroxyl radical. <i>B. thetaiotaomicron</i> had larger first order rate constants than all other organisms under all conditions tested. The presence of the synthetic photosensitizers generally enhanced photoinactivation of Gram-positive facultative anaerobes (<i>Ent. faecalis</i>, <i>Staph. aureus</i>, and <i>Strep. bovis</i>). Among Gram-negative bacteria, only methylene blue with <i>E. coli</i> K12 and rose bengal with <i>C. jejuni</i> showed an enhancing effect. The presence of model natural photosensitizers either reduced or did not affect photoinactivation rate constants. Our findings highlight the importance of the cellular membrane and photosensitizer properties in modulating the contribution of the exogenous indirect mechanism to the overall bacterial photoinactivation