Innovative UV-LED polymerised bicontinuous microemulsion coating for membranes with special emphasis on MBRs

Abstract

The main objective of this work is the preparation of polymerisable bicontinuous microemulsion (PBM) coatings applied onto commercial membranes for improving the anti-fouling properties and performance, in terms of water flux and foulants rejection. Microstructured and nanostructured materials obtained by PBM have been widely investigated in the course of the last 30 years. The interest in microemulsion lies mainly in the possibility of dissolving larger amounts of oil and water by using polymerisable and non-polymerisable surfactants. By polymerising the bicontinuous microemulsion it is possible to produce transparent porous polymeric solids [Gan et al. (1995), Gan and Chew (1997)]. This thesis represents the follow-up of the work done by Galiano et al. (2015) and Deowan et al. (2016). Galiano et al. (2015) developed the PBM composition that based on a non-polymerisable surfactant (DTAB) and another polymerisable surfactant (AUTEAB). In their work the PBM was polymerised by redox initiators leading to a process that is very difficult to up-scale for a commercial application. Critical issues were, the polymerisation time (at least 20 minutes), and the reproducibility of the coating. Therefore, it is the aim of this work to develop another polymerisation technique that increases the polymerisation speed and allows the easy reproduction of membranes with defined properties. The polymerisation by photoinitiators excited by UV-light represents a promising possibility for this requirement as it has the potential of decreasing the polymerisation time down to a few seconds. Several photoinitiators were selected for their compatibility with the PBM, and studied for their conversion rate efficiency (section 5.1.5). As there is a wide range of potential UV-light sources available, several technologies are studied for their coating performance (section 5.1.3). Subsequent to that, experiments were done in order to define the ideal photoinitiator type and concentration while polymerising onto glass plates. The coating onto commercial membranes is studied deeply for e.g. different casting knife thickness or ambient temperature (section 5.2.2 As the polymerisation under inert conditions is expected to increase the polymerisation speed, experiments are done, both under inert and non-inert conditions. The final membrane, coated under the optimum conditions, is further characterised for their permeability under different conditions like transmembrane pressure (TMP), model foulant experiments and a fixed volume flow (section 5.2.3). Further characterisation is done by contact angle, SEM, AFM (section 5.2.5 to 5.2.7). The prepared PBM membranes are foreseen to be finally applied for model textile dye wastewater treatment by Membrane BioReactor (MBR) technology. According to the previous results of Deowan et al. (2016) higher permeate quality through increased COD, TOC, dyestuffs removal efficiency and stronger anti-fouling properties are expected. Consequently, lower operation/maintenance costs due to reduced necessary aeration for scouring purposes and reduced membrane cleaning cycles as well as less membrane replacement are of special interest for commercial applications. In the previous work of Deowan et al. (2016) a lab scaled MBR with a single membrane housing was used. As of the biocenosis of the bacteria inside the reactor tank, a comparison of the membrane performance of the PBM and commercial membrane is difficult to achieve. Therefore an existing MBR system was redesigned to allow the simultaneous run of a commercial and a PBM coated membrane (section 4.1). As the revamp requires also additional sensors, the data acquisition needs to be adapted as well. To assure the proper function of the MBR the system was running for long term with two commercial membranes using a model textile wastewater (see 5.3.2). Finally the PBM coated membrane was compared with a commercial one for their performance in the MBR. Initial experiments for the water permeability are done as preparation for future work (see 5.3.3).