Membrane Autopsy Facilities
Fouling occurs in all membrane systems and the general operating principle is not how to eliminate fouling but how can it best be managed. This usually occurs in the form of pre-treatment of the feed water, dosing the feed water with chemicals such as acid or base to modify the pH or anti-scalants. Cleaning strategies also form an integral part of fouling management.
Membrane Autopsy is a useful technique for determining causes of fouling events in membrane systems. When conducting an autopsy it is usually on the premise that the fouling management process has failed and the aim of the autopsy is to identify the root cause of the fouling event and provide some recommendation on how to correct or manage it.
The UNESCO Centre for Membrane Science and Technology (CMST) has been providing autopsy services on a commercial basis for over 10 years and has conducted over 60 autopsies with clients ranging from large treatment plants to small industry. Since 200x the centre has been developing an autopsy database which stores information gathered from previous autopsies to be used as reference material for further work, thereby benefiting clients.
The standard autopsy is designed to provide a broad overview of the condition of the membrane element, and determine the type and extent of fouling on the membrane surface.
A standard autopsy includes the following techniques:
- Internal and external visual inspection
- Scanning electron microscopy (SEM) / Energy dispersive x-ray spectroscopy (EDS)
- Dead-end wet testing and comparison with fresh membranes
- Wet testing / Dye integrity testing
- Oxidative / Halide damage testing via the Fujiwara method
- Inductively coupled plasma (ICP) / Optical emission spectroscopy (OES/AES)
- Microbial analysis
- Loss on ignition (LOI) testing
- Fourier transform infrared spectrometry (FTIR)
- X-Ray Diffraction (XRD)
- Total organic carbon (TOC) analysis
When is an Autopsy undertaken?
- When a loss of performance is observed, such as:
- High permeate conductivity/ low rejection
- High TMP
- High ∆P
- Decrease in product flux
- Increased frequency of cleaning
- Other reasons
- End of trials
- To determine the long term effects of cleaning methods
- After an incident or mishap within the system
The Autopsy Process
The autopsy consists of three steps. Prior to conducting the autopsy, initial information is obtained from the supplier of the membrane including:
- Feedwater and system characteristics
- Normalised performance history
The second step is the autopsy itself. Samples are taken, analysed and the results collected. The final step is the analysis and interpretation of results with reference to the initial information.
The results are also compared to and cross-referenced with the autopsy database. The autopsy data is then stored on the database and used as reference material for further work.