Sam Stade

24 Aug 2012

2010 - Master of Science, Lappeenranta University of Technology, Finland

2011 - Project Researcher, Lappeenranta University of Technology, Finland

2012 - Master of laboratory, Laboratory of Membrane Technology, Lappeenranta University of Technology, Finland

2012 - Doctoral student, Lappeenranta University of Technology, Finland.
Topic: Real-time monitoring of membranes and its applications

Abstract


Real-time monitoring of membrane performance with ultrasonic time-domain reflectometry

Pressure-driven membrane filtration processes have become more common in many industrial applications. Membrane performance as well as their operating costs are the key factors limiting their attraction. Performance can be increased and operating costs decreased with process optimization. However, this kind of process optimization requires very good knowledge on the filtration process and understanding what is happening inside the module in real-time.

In this study novel tools and methods are developed for real-time monitoring of membrane performance. Until now, the research in this study has been focused on the development of a ultrasonic time-domain reflectometry (UTDR) based tool, which can be used for both, measuring of membrane compaction and fouling in real-time. UTDR technique has been successfully used to monitor membrane fouling in real-time also in earlier studies. Due to two improvements in the system developed in this study enables more accurate determination of measurement error than in previous studies have been presented. The first improvement is that the transducer which measures the distance to membrane is implemented inside the filter. Thus, sonic waves are not introduced into the filter chamber through the cover of the cell but straight into feed water and reflections from the interface between the filter cover and feed water are avoided. The second improvement is that a secondary transducer is used for determination of sonic speed, which is needed in calculation of the distance from the primary transducer to the membrane. Sonic speed depends on temperature, pressure and flow conditions prevailing in the filter. Varying of these conditions causes changes in sonic speed during filtration. If sonic speed is not determined but evaluated, the variation of filtration conditions increases measurement error in distance values

At this stage of the research, the UTDR tool has been used in measuring of compaction of different ultrafiltration membranes, which have been manufactured from regenerated cellulose (RC) and polyethersulfone (PES). It has been found that there are crucial differences in compaction tendencies of different membranes. The UTDR results showed that the tested RC membrane compacted clearly more than the tested PES membranes. Based on the scanning electron microscopy (SEM) pictures, the support layer of the RC membrane was clearly compacted. A phenomenon of this kind was not seen with the PES membranes. Compaction caused flux decline for all the tested membranes. However, flux of the RC membrane recovered to some extent while the fluxes of the PES membranes were permanently reduced after the compaction. Furthermore, compaction caused a permanent increase in PEG retentions of the PES membranes while with the RC membranes the retentions were at the similar level before and after the compaction. Thus, the results achieved in this study indicate that the PES membranes could be easily modified with precompaction to increase retention.  On the other hand, the results demonstrate that it is possible to weaken membrane performance permanently by introducing, for instance, the precompaction stage of the process at a too high pressure.

At the next stage of the research real-time monitoring of fouling to achieve information especially on the early-stage of fouling will be the goal. In addition to the developed UTDR tool, also other possible methods will be used in fouling monitoring.