Chris Dotremont

Alumina and titania multilayer membranes for nanofiltration: preparation, characterization and chemical stability

Abstract The preparation and characterization of porous ceramic multilayer nanofiltration (NF) membranes is described. During preparation, special care was given to each sub-layer that forms a part of the multilayer configuration: the macroporous substrate, the membrane interlayers and the NF toplayers. High-quality macroporous supports are prepared from α-Al 2 O 3 . Three types of colloidal sol–gel derived mesoporous interlayers are considered: Al 2 O 3 , TiO 2 and mixed Al 2 O 3 –TiO 2 . The active NF toplayer is a very thin and fine textured polymeric TiO 2 toplayer. Optimized α-Al 2 O 3 /γ-Al 2 O 3 /anatase and α-Al 2 O 3 /anatase/anatase multilayer configurations show high retentions for relatively small organic molecules (molecular weight cut-off 2 O 3 layers is restricted to mild aqueous media (pH 3–11) or non-aqueous media (organic solvents). For NF applications in aqueous media with a lower or higher pH, the multilayer membrane composed of anatase on a α-Al 2 O 3 support is to be preferred.

Benchmark study on algae harvesting with backwashable submerged flat panel membranes.

The feasibility of algae harvesting with submerged flat panel membranes was investigated as pre-concentration step prior to centrifugation. Polishing of the supernatant coming from the centrifuge was evaluated as well. The effect of membrane polymer (polyvinyl chloride [PVC], polyethersulfone polyvinyl-pyrollidone [PES-PVP], poly vinylidene fluoride [PVDF]), pore size (microfiltration [MF], ultrafiltration [UF]), algae cell concentrations and species were investigated at lab-scale. In addition, backwashing as fouling control was compared to standard relaxation. PVDF was the superior polymer, and UF showed better fouling resistance. Backwashing outperformed relaxation in fouling control. The backwashable membranes allowed up to 300% higher fluxes compared to commercial flat panel benchmark (PVC) membranes. Estimations on energy consumption for membrane filtration followed by centrifugation revealed relatively low values of 0.169 kW h/kg of dry weight of algae compared to 0.5 kW h/kg for algae harvesting via classical centrifuge alone.

A new method of measuring and presenting the membrane fouling potential

The silt density index (SDI) and modified fouling index (MFI) characterisation methods are well known for the evaluation of membrane fouling potential of dispersed particulate matter (suspended solids, colloids) in a feed. The SDI and MFI methods, however, reduce the overall and very complex fouling phenomena into a one number value, on which the interpretation of the fouling potential of the feed is based. Considering such a one number characteristic, a significant amount of information from the fouling measurement (data) is lost. In this paper a concept is introduced in order to preserve such information and supplement the existing indexes. The proposed method measures, processes and presents data in a specific format. To illustrate the concept, some results are shown from measurements on three types of feed. Future systematic research will also include the measurement on some model feeds with, for example, well characterised dispersions for comparison purposes. However, based on the contents of this paper, a discussion on the method could be initiated.

Integrated systems involving membrane distillation and applications

Abstract This chapter describes the applications of membrane distillation (MD), in relation to other processes, as alternative or as integrated processes. The emphasis is on the dominant application of MD, which is seawater desalination. This is discussed for small-scale applications, for pilot-scale and for (semi)commercial-scale operations; a comparison between different systems is made. The results obtained at larger scale show a path for the future and demonstrate the clear potential of MD. The economics of the process, which are related to the energy sources that can be used in a given application, are briefly discussed. Other applications reviewed in this chapter focus on aqueous applications (wastewater in different industries and natural waters) and on the food industry. It is suggested that these may be only the top of the iceberg, and that many new applications will emerge in the decades to come; these may have the most potential when operated as integrated processes in conjunction with other separation processes, as part of an overall strategy of recycling and resource recovery.