Probing the reduction of adhesion forces between biofilms and anti-biofouling filtration membrane surfaces using FluidFM technology.

Biofouling is a persistent problem in many sectors (healthcare, medicine, marine, and membrane filtration processes). To control the biofouling of surfaces, it is essential to overcome or reduce the adhesion forces between biofilms and surfaces. To access and understand the molecular basis of these interactions, atomic force microscopy (AFM) is a well-suited technology that can measure adhesion forces at the piconewton level. However, AFM-based existing methods only probe interactions between individual cells and surfaces, which is not representative of realistic conditions given that bacteria mainly exist in biofilms. We develop here an original method using FluidFM, a combination of AFM and microfluidics, to probe the adhesion forces between biofilms and filtration membranes modified with an anti-biofouling agent, vanillin. This strategy involves i) growing bacterial biofilms on micrometer-sized polystyrene beads, ii) aspirating these biofilm beads at the aperture of microfluidic cantilevers and iii) using them as probes in force spectroscopy experiments. The results obtained first showed that COOH-functionalized polystyrene beads are more suitable for bacterial growth, and that biofilms obtained after 3 h of incubation could be used with FluidFM. Then, biofilm-scale force spectroscopy experiments showed a significant decrease in adhesion forces, adhesion work, and adhesion events after membrane modification, demonstrating the potential of vanillin-coated membranes to reduce biofouling. In addition, the comparison between results at the individual cell and biofilm scales highlighted the complexity of polymeric matrix unbinding and/or unfolding in the biofilm, showing that individual cells behave differently from biofilms. Overall, this method could have implications in the fields of materials science, chemical engineering, health, and the environment.

Assessing suspension and infectivity times of virus-loaded aerosols involved in airborne transmission.

Airborne transmission occurs through droplet-mediated transport of viruses following the expulsion of an aerosol by an infected host. Transmission efficiency results from the interplay between virus survival in the drying droplet and droplet suspension time in the air, controlled by the coupling between water evaporation and droplet sedimentation. Furthermore, droplets are made of a respiratory fluid and thus, display a complex composition consisting of water and nonvolatile solutes. Here, we quantify the impact of this complex composition on the different phenomena underlying transmission. Solutes lead to a nonideal thermodynamic behavior, which sets an equilibrium droplet size that is independent of relative humidity. In contrast, solutes do not significantly hinder transport due to their low initial concentration. Realistic suspension times are computed and increase with increasing relative humidity or decreasing temperature. By uncoupling drying and suspended stages, we observe that enveloped viruses may remain infectious for hours in dried droplets. However, their infectivity decreases with increasing relative humidity or temperature after dozens of minutes. Examining expelled droplet size distributions in the light of these results leads to distinguishing two aerosols. Most droplets measure between 0 and 40 µm and compose an aerosol that remains suspended for hours. Its transmission efficiency is controlled by infectivity, which decreases with increasing humidity and temperature. Larger droplets form an aerosol that only remains suspended for minutes but corresponds to a much larger volume and thus, viral load. Its transmission efficiency is controlled by droplet suspension time, which decreases with increasing humidity and decreasing temperature.

Development of double porous poly (ε - caprolactone)/chitosan polymer as tissue engineering scaffold.

Polymer blend made from poly(ε - caprolactone)/chitosan (PCL/CHT) offers interesting opportunities for biological applications. The paper presents a new way to fabricate PCL/CHT double-porosity (macrovoids with interconnected microporosity) membrane materials from a chemical optimization of the solvent and non-solvent phases and from a modified phase inversion technique. By varying the PCL/CHT proportion, it is shown that it is possible to improve the chemical and physical properties of the CHT carbohydrate polymer. The PCL/CHT membranes are fully characterized in term of physico-chemical properties (ATR-FTIR, XRD and DSC) to understand the miscibility of the two-polymer blend. Morphological characterization by SEM shows that by increasing CHT wt% in the blend, the size of the macrovoids was increasing. Rapid enzymatic degradation of PCL from all the blend was found by using lipase (from P. cepacia). The mechanisms at the origin of the morphological structuration of the material is also discussed. To test the ability to operate these materials as small diameter vascular scaffolds, cell culture with human umbilical vein endothelial cells (HUVECs) were carried out on the membrane and the results analyzed with laser scanning confocal microscopy (LSCM). Data suggest that the blend membrane with higher concentration of CHT polymer wt% have suitable properties that promote high number of cells on the surface by maintaining cellular cytoskeleton integrity within 3 days. The blend membrane with a double porous morphology could be potentially applicable in future for small diameter vascular graft application. The surface macrovoids (20-90 µm) could be useful for three-dimensional cellular adhesion and proliferation and interconnected microporous spongy network (7-20 µm) is expected to transfer essential nutrients, oxygen, growth factor between the macrovoids and the supernatant.

Nanofiltration performances after membrane bioreactor for hospital wastewater treatment: Fouling mechanisms and the quantitative link between stable fluxes and the water matrix.

Treatment combining membrane bioreactors (MBR) and nanofiltration (NF) is becoming an emerging wastewater treatment strategy. The combined process is capable of producing high quality water potentially reusable; however, diverse compositions of MBR effluents induce several types and degrees of NF membrane fouling that impacts process productivity. Moreover, since MBR effluent composition for one type of wastewater source is variable depending on the MBR efficiency at different periods, downstream NF membrane fouling types and degrees may consequently change over time. In that context, the present paper aims at developing effective fouling control strategies of NF membrane in the case of the filtration of MBR effluents taken from a MBR system installed in a French hospital. These effluents were filtrated under various transmembrane pressures, and stable fluxes during these filtrations were determined. Several types and degrees of fouling mechanisms were then identified through surface morphology observation and the analysis of chemical compositions of fouled membranes. The diverse flux behaviour was further associated with the fouling mechanisms and foulant compositions. Based on the study of these mechanisms, the quantitative link between stable fluxes and calcium phosphate concentrations in MBR effluents has been established.

Electro-oxidation of organic pollutants by reactive electrochemical membranes.

Electro-oxidation processes are promising options for the removal of organic pollutants from water. The major appeal of these technologies is the possibility to avoid the addition of chemical reagents. However, a major limitation is associated with slow mass transfer that reduces the efficiency and hinders the potential for large-scale application of these technologies. Therefore, improving the reactor configuration is currently one of the most important areas for research and development. The recent development of a reactive electrochemical membrane (REM) as a flow-through electrode has proven to be a breakthrough innovation, leading to both high electrochemically active surface area and convection-enhanced mass transport of pollutants. This review summarizes the current state of the art on REMs for the electro-oxidation of organic compounds by anodic oxidation. Specific focuses on the electroactive surface area, mass transport, reactivity, fouling and stability of REMs are included. Recent advances in the development of sub-stoichiometric titanium oxide REMs as anodes have been made. These electrodes possess high electrical conductivity, reactivity (generation of •OH), chemical/electrochemical stability, and suitable pore structure that allows for efficient mass transport. Further development of REMs strongly relies on the development of materials with suitable physico-chemical characteristics that produce electrodes with efficient mass transport properties, high electroactive surface area, high reactivity and long-term stability.

Mineralization of organic pollutants by anodic oxidation using reactive electrochemical membrane synthesized from carbothermal reduction of TiO2.

Reactive Electrochemical Membrane (REM) prepared from carbothermal reduction of TiO2 is used for the mineralization of biorefractory pollutants during filtration operation. The mixture of Ti4O7 and Ti5O9 Magnéli phases ensures the high reactivity of the membrane for organic compound oxidation through •OH mediated oxidation and direct electron transfer. In cross-flow filtration mode, convection-enhanced mass transport of pollutants can be achieved from the high membrane permeability (3300 LMH bar-1). Mineralization efficiency of oxalic acid, paracetamol and phenol was assessed as regards to current density, transmembrane pressure and feed concentration. Unprecedented high removal rates of total organic carbon and mineralization current efficiency were achieved after a single passage through the REM, e.g. 47 g m-2 h-1 - 72% and 6.7 g m-2 h-1 - 47% for oxalic acid and paracetamol, respectively, at 15 mA cm-2. However, two mechanisms have to be considered for optimization of the process. When the TOC flux is too high with respect to the current density, aromatic compounds polymerize in the REM layer where only direct electron transfer occurs. This phenomenon decreases the oxidation efficiency and/or increases REM fouling. Besides, O2 bubbles sweeping at high permeate flux promotes O2 gas generation, with adverse effect on oxidation efficiency.

Drug residues and endocrine disruptors in drinking water: risk for humans?

The presence of pharmaceuticals and endocrine disruptors in the environment raises many questions about risk to the environment and human health. Environmental exposure has been largely studied, providing to date a realistic picture of the degree of contamination of the environment by pharmaceuticals and hormones. Conversely, little information is available regarding human exposure. NSAIDS, carbamazepine, iodinated contrast media, ß-blockers, antibiotics have been detected in drinking water, mostly in the range of ng/L. it is questioned if such concentrations may affect human health. Currently, no consensus among the scientific community exists on what risk, if any, pharmaceuticals and endocrine disruptors pose to human health. Future European research will focus, on one hand, on genotoxic and cytotoxic anti-cancer drugs and, on the other hand, on the induction of genetic resistance by antibiotics. This review does not aim to give a comprehensive overview of human health risk of drug residues and endocrine disruptors in drinking water but rather highlight important topics of discussion.