Interplay of different NOM fouling mechanisms during ultrafiltration for drinking water production

Ultrafiltration is an emerging technology for drinking water production, but a main challenge remains the lack of understanding about fouling. This paper investigates the impact of molecular interactions between different natural organic matter (NOM) compounds on ultrafiltration fouling mechanisms. We performed dead-end filtration experiments with individual and mixed humic acid and alginate (polysaccharide). Alginate showed detrimental, but mostly reversible, flux decline and high solute retention. Our results indicate that this was caused by pore blocking transformed into cake building and weak molecular foulant-membrane and foulant-foulant interactions. In the presence of calcium, aggravated fouling was observed, related to complexation of alginate and its subsequently induced gel formation. With humic acid, more severe irreversible fouling occurred due to humic acid adsorption. Minor adsorption of alginate onto the membrane was also observed, which probably caused the substantial irreversible flux decline. The fouling characteristics in the mixtures reflected a combination of the individual humic acid and alginate experiments and we conclude, that the individual fouling mechanisms mutually influence each other. A model elucidates this interplay of the individual fouling mechanisms via hydrophobic and electrostatic interactions. In our study such an interplay resulted in an alginate cake, or gel in the presence of calcium, which is relatively irreversibly adsorbed onto the membrane by humic acid associations. This study shows the importance of mutual influences between various foulants for improved understanding of fouling phenomena. Furthermore it shows that substances with a minor individual influence might have a large impact in mixed systems such as natural water.     

Mapping bacterial surface population physiology in real-time: infrared spectroscopy of Proteus mirabilis swarm colonies

We mapped the space-time distribution of stationary and swarmer cells within a growing Proteus mirabilis colony by infrared (IR) microspectroscopy. Colony mapping was performed at different positions between the inoculum and the periphery with a discrete microscope-mounted IR sensor, while continuous monitoring at a fixed location over time used an optical fiber based IR-attenuated total reflection (ATR) sensor, or "optrode." Phenotypes within a single P. mirabilis population relied on identification of functional determinants (producing unique spectral signals) that reflect differences in macromolecular composition associated with cell differentiation. Inner swarm colony domains are spectrally homogeneous, having patterns similar to those produced by the inoculum. Outer domains composed of active swarmer cells exhibit spectra distinguishable at multiple wavelengths dominated by polysaccharides. Our real-time observations agree with and extend earlier reports indicating that motile swarmer cells are restricted to a narrow (approximately 3 mm) annulus at the colony edge. This study thus validates the use of an IR optrode for real-time and noninvasive monitoring of biofilms and other bacterial surface populations.     

Electrodialysis for recovering salts from a urine solution containing micropollutants

Electrodialysis was investigated for the separation of micropollutants from nutrients in anthropogenic urine. In a continuously operated process, the nutrients were concentrated up to a factor of 3.2. The concentration factor was limited by water transport across the membrane. Water transport was caused by osmosis and electroosmosis, and a model was developed to describe these phenomena. The removal of several spiked micropollutants was investigated in continuous electrodialysis experiments. Ethinylestradiol was removed completely during the whole operating period. Diclofenac and carbamazepine were initially retained, but limited permeation (5-10%) occurred after longer operating times (90 days). Retentions of propranolol and ibuprofen were also high initially, but substantial breakthroughs occurred during extended operation. Considerable adsorption on the membranes was observed for all compounds. The permeation mechanism of several compounds appears to depend on the adsorbed amount on the membrane, which indicates that partitioning and diffusion mechanisms play an important role in the permeation transport. Partial desorption occurred in leaching experiments with polarity reversal, and almost quantitative desorption was observed after incubation of the membranes with Filter Count Gel Solution. Because environmental concentrations are much lower than the concentrations spiked here, it can be anticipated that operation without significant permeation is possible in practice during extended periods of time.     

Gold supported on carbon nanotubes for the selective oxidation of glycerol

Gold nanoparticles were supported on multi-walled carbon nanotubes (MWCNTs) by different methods and tested in the selective oxidation of glycerol under basic conditions, with the main purpose of evaluating the effect of the preparation technique on the activity and selectivity. The catalytic performances largely depended on the gold crystallite size. The sol immobilization method was the most suitable technique to prepare gold supported on carbon nanotubes. The use of MWCNTs as support for Au nanoparticles resulted in the oxidation of the secondary hydroxyl group, and therefore, a remarkable high dihydroxyacetone selectivity of about 60% is obtained independently of the preparation method used. A possible explanation based on the peculiar characteristics of the support is proposed. It was also concluded that dihydroxyacetone in the final mixture can be stabilized by lowering the pH to about 3.     

Four new SYBR<Superscript>®</Superscript>Green qPCR screening methods for the detection of Roundup Ready<Superscript>®</Superscript>, LibertyLink<Superscript>®</Superscript>, and CryIAb traits in genetically modified products

SYBR^®Green qPCR methods for the detection of the Roundup Ready^® “CP4-EPSPS”, LibertyLink^® “PAT” and “BAR,” and the Bacillus thuringiensis “CryIAb” traits as present in genetically modified organisms (GMO) were developed. Their specificity, sensitivity, and PCR method efficiency were determined. All methods are specific and generate amplicons of 108, 73, 109, and 69 bp, respectively, for “CP4-EPSPS,” “CryIAb,” “PAT,” and “BAR” targets. They perform well at low target levels and can detect down to 5 copies of their respective targets extracted from a sample. The PCR efficiency of the methods ranges between 91 and 109%. Due to their trait-specific nature, these methods allow an efficient screening between the different GMO. In this way, the number of possible GMO candidates present in a sample can be reduced what results in lower global costs due to limiting of further the number of analytical identification steps. The application of these methods in CoSYPS GMO analysis is illustrated using two GEMMA proficiency test samples and a reference material from the GM rapeseed event RF3. This set of SYBR^®Green qPCR trait-specific methods represents a very interesting novel set of GMO analysis methods allowing cost-effective identification of GM materials in products.     

Oxidation resistance of Ti3AlC2 and Ti3Al0.8Sn0.2C2 MAX phases: A comparison

Ti₃AlC₂ and Ti₃Al_0.8Sn_0.2C₂ MAX phase powders are densified using Spark Plasma Sintering (SPS) technique to obtain dense bulk materials. Oxidation tests are then performed over the temperature range 800°C-1000°C under synthetic air on the two different materials in order to compare their oxidation resistance. It is demonstrated that, in the case of the Ti₃Al_0.8Sn_0.2C₂ solid solution, the oxide layers consist in TiO₂, Al₂O₃, and SnO₂. The presence of Sn atoms in the A planes of the solid solution leads to an easy diffusion of Sn out of the MAX phase which promote the formation of the nonprotective and fast growing SnO₂ oxide. Moreover, the small Al/Ti atom's ratio promotes the growth of a nonprotective rutile-TiO₂ scale as well. In the case of the Ti₃AlC₂ MAX phase, the oxide layer consists in a protective alumina scale; a few TiO₂ grains being observed on the top of the Al₂O₃ layer. The parabolic oxidation rate constants are about 3 orders of magnitude smaller for Ti₃AlC₂ compared to Ti₃Al_0.8Sn_0.2C₂.     

Cationic UV‐curing of epoxidized cardanol derivatives

This paper demonstrates the high reactivity and potentiality of bio‐renewably obtained cardanol‐based epoxy monomers as well as the possibility of tuning the final thermomechanical properties by changing either the epoxy content or the chemical structure of the starting photocurable resin. The reactivity of the cardanol monomers towards the cationic UV‐curing process was investigated by Fourier transform IR analysis and it was shown that a high epoxy group conversion was achieved. Furthermore, the thermomechanical properties were investigated on crosslinked films by means of DSC and dynamic thermomechanical analysis. © 2020 Society of Chemical Industry     

Cobalt‐Catalyzed Reductive Cross‐Coupling Between Benzyl Chlorides and Aryl Halides

A new protocol for the direct reductive cobalt‐catalyzed arylation of benzyl chlorides has been developed in order to form functionalized diarylmethanes. A variety of reactive groups either on the aryl or the benzyl halide was employed. This represents the first cobalt‐catalyzed reductive cross‐coupling which does not require any ligand and pyridine. A reaction pathway is proposed involving a radical benzyl species.

     

Treatment of source-separated urine by a combination of bipolar electrodialysis and a gas transfer membrane.

Urine contains nutrients which can be applied usefully as a fertiliser in agriculture, but the relatively high pH can lead to ammonia evaporation. Electrodialysis with bipolar membranes was combined with an additional mass transfer unit in order to render a product containing ammonium and phosphate at a low pH. In one case, the additional mass transfer unit consisted of bubble columns placed in acid and basic concentrate streams, connected with a circulating gas phase. In the other case, the unit consisted of a gas-filled (hydrophobic) membrane placed in between the circulating acid and basic concentrate streams. The results showed that ammonia was transferred through the gas phase, but also carbonate, which is present in stored urine originating from the hydrolysis of urea. Although the pH in the product stream decreases initially, it rises above pH 7 at longer operation times. This pH increase can be attributed to a combination of proton compensating effects. The use of ammonia-selective membranes for the transfer into the acid concentrate could provide a solution to generate an ammonium phosphate product at low pH and high recoveries.