Christel Causserand

Cyclophosphamide removal from water by nanofiltration and reverse osmosis membrane

The rejection of cyclophosphamide (CP) by nanofiltration (NF) and reverse osmosis (RO) membranes from ultrapure (Milli-Q) water and membrane bioreactor (MBR) effluent was investigated. Lyophilization-extraction and detection methods were first developed for CP analysis in different water matrices. Experimental results showed that the RO membrane provided excellent rejection (>90%) under all operating conditions. Conversely, efficiency of CP rejection by NF membrane was poor: in the range of 20-40% from Milli-Q water and around 60% from MBR effluent. Trans-membrane pressure, initial CP concentration and ionic strength of the feed solution had almost no effect on CP retention by NF. On the other hand, the water matrix proved to have a great influence: CP rejection rate by NF was clearly enhanced when MBR effluent was used as the background solution. Membrane fouling and interactions between the CP and water matrix appeared to contribute to the higher rejection of CP.

Study of the effects of defects in ultrafiltration membranes on the water flux and the molecular weight cut-off

Abstract The aim of this study was to evaluate how defects in a membrane surface can affect the molecular weight cut-off (MWCO) and the membrane permeability as they are traditionally defined. These two parameters are important criteria for the selection of ultrafiltration membranes with regard to efficiency and rejection of dissolved and particulate substances and especially disinfective retention. Tests were conducted with a flat-sheet membrane with an effective filtration area of 1.45×10−3 m−2. Dead-end filtration experiments were performed with various feed solutions: pure water to measure the hydraulic permeability, a mixture of dextrans to determine the apparent MWCO and protein solutions. This was done before and after the membrane integrity was altered by perforating its surface with a sharp tip.

Formation of bacterial streamers during filtration in microfluidic systems

Bacterial behavior during filtration is complex and is influenced by numerous factors. The aim of this paper is to report on experiments designed to make progress in the understanding of bacterial transfer in filters and membranes. Polydimethylsiloxane (PDMS) microsystems were built to allow direct dynamic observation of bacterial transfer across different microchannel geometries mimicking filtration processes. When filtering Escherichia coli suspensions in such devices, the bacteria accumulated in the downstream zone of the filter forming long streamers undulating in the flow. Confocal microscopy and 3D reconstruction of streamers showed how the streamers are connected to the filter and how they form in the stream. Streamer development was found to be influenced by the flow configuration and the presence of connections or tortuosity between channels. Experiments showed that streamer formation was greatest in a filtration system composed of staggered arrays of squares 10 μm apart.

Effects of sodium hypochlorite exposure mode on PES/PVP ultrafiltration membrane degradation.

Drinking water production plants using membrane filtration processes report membrane failure issues. According to the literature, membrane degradation is often induced by exposure to sodium hypochlorite, an oxidant widely used during in-place cleanings. The present study focused on quantifying the effect of membrane exposure mode to hypochlorite on properties modifications of a PES/PVP ultrafiltration membrane widely used for drinking water production. For this purpose effects of sodium hypochlorite concentration, contact duration and exposure mode (static or dynamic) were investigated. The pH of the hypochlorite solution was set to 8 as it was demonstrated in numerous previous works that the pH range 7-8 leads to the most severe modification in the membrane characteristics. Membrane degradation was monitored at molecular scale by attenuated total reflectance infrared spectroscopy and at macroscopic scale by pure water permeability and elongation at break measurements. The results obtained in static (soaking) and dynamic (filtration and filtration/backwashing cycles) hypochlorite exposure modes indicated that PES/PVP membrane degradation progress was predominantly governed by hypochlorite oxidation rate. In the tested conditions, mechanical stress (pressure differentials) did not significantly contribute to membrane ageing. The correlation between molecular and macroscopic characterizations demonstrated that PVP degradation is responsible for the membrane integrity loss. A linear relationship between the loss of ductility of the membrane and the progress of the PVP degradation was obtained whatever the exposure mode. Thanks to experiments conducted at various hypochlorite concentrations and exposure durations, the hypochlorite dose parameter (hypochlorite concentration times contact time), widely used in the literature, was demonstrated to be inappropriate to describe the degradation rate: the hypochlorite concentration impact was shown to be dominating the exposure times one on the degradation rate.

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.

Feasibility of Micropollutants Treatment by Coupling Nanofiltration and Electrochemical Oxidation: Case of Hospital Wastewater

Abstract In spite of good performances of the membrane bioreactor (MBR) process, permeate from it can still contain refractory pollutants that have to be removed before water reuse or discharge. The present study is an attempt to combine the advantages of two well-known technologies, which are nanofiltration (NF) and electrochemical oxidation (EO) to treat MBR effluent from hospital wastewater. The concept is based on a preconcentration of micropollutants with a reduction of the wastewater volume by NF and treatment of the NF retentate by oxidation. During filtration process the rejection of ciprofloxacin, as a target molecule, reached beyond 97%. Then the NF retentate was treated by EO using a boron-doped diamond anode (BDD). Galvanostatic electrolyses showed that this anode is efficient to mineralize not only ciprofloxacin but also all the micropollutants and organics contained in MBR effluent. The results demonstrated that rapid mineralization occurred: the removal of total organic carbon and chemical oxygen demand (COD) reached 97% and 100%, respectively, in our conditions in 300 min maximum. The specific energy consumption for the total removal of COD was calculated to be 50 kW h kg˗1 COD.

Effects of Ionic Strength on Bacteriophage MS2 Behavior and Their Implications for the Assessment of Virus Retention by Ultrafiltration Membranes

Bacteriophage MS2 is widely used as a surrogate to estimate pathogenic virus elimination by membrane filtration processes used in water treatment. Given that this water technology may be conducted with different types of waters, we focused on investigating the effects of ionic strength on MS2 behavior. For this, MS2 was analyzed suspended in solutions of various ionic strengths, firstly in a batch experiment and secondly during membrane ultrafiltration, and quantified using (i) quantitative RT-PCR (qRT-PCR), which detects the total number of viral genomes, (ii) qRT-PCR without the RNA extraction step, which reflects only particles with a broken capsid (free RNA), and (iii) the Plaque Forming Unit (PFU) method, which detects only infectious viruses. At the beginning of the batch experiments in solutions containing low amounts of salts, a loss of MS2 infectivity (90%) and broken particles (20%) were observed; these proportions did not change during filtration. In contrast, in high ionic strength solutions, bacteriophages kept their biological activity in static conditions but they quickly lost their infectivity during the filtration process. Increasing the ionic strength decreased both the inactivation and the capsid breakup in the feed suspension, and increased the loss of infectivity in filtration retentate, while the amount of MS2 genomes was identical in both experiments. In conclusion, ionic strength effects on MS2 behavior may significantly distort the results of membrane filtration processes and therefore the combination of classical and molecular methods used here is useful for an effective validation of the retention efficiency of ultrafiltration membranes.

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.