Membrane Autopsy

Membrane autopsy can be used as a routine operating tool for membrane plant operators to help assess the performance of their membranes. The objective of a membrane autopsy is to identify if there is any damage at the surface of the membrane, to identify foreign compounds on the membrane surface, and to assess how these compounds affect the membrane operation. The autopsy results can be used to make an informed decision about how best to:
  • Rehabilitate membranes
  • Improve pre-treatment
  • Optimise anti-scale or biocide chemistry
  • Improve the cleaning regimes used by the plant
  • Adjust plant operating conditions

Why perform a membrane autopsy?

Membrane processes all experience performance degradation throughout the life of the membranes. Operating parameters provide an indication of membrane damage, scale or fouling which is causing the performance degredation. Operating parameters, which may change, include feed pressure, normalised pressure drops, normalised permeate flows and permeate quality. There are many mechanisms which cause declined membrane performance including membrane surface and structural damage, ineffective pre-treatment, changes in feedwater quality, inadequate plant design or unsuitable cleaning of the membrane surface. Membrane autopsy is used to determine the specific mechanism causing the change in membrane performance.

Analytical Methods

Opening & Examination Modules are examined with the focus on detecting damage to the membrane and housing. Types of deposit, membrane condition, seals, end caps, potting material (MF), glue lines (RO) are reviewed.
Open and Examine
LOI Loss on Ignition (LOI) is used to quantify the level of organic vs inorganic deposits on the membrane
ICP-AES Surface deposits are dissolved into nitric acid and Inductively Couple Plasma (ICP) - Atomic Emission Spectroscopy (AES) is used to quantify the inorganic constituents on the membrane.
Total Organic Carbon Surface deposits are placed into solution and sonicated. Total Organic Carbon (TOC) is performed on the dissolved and suspended material.
Stereo Microscopy A microscope is used to examine the membrane surface. This is particularly useful for hollow fiber membrane examination.
Stereo Microscopy
SEM-EDS Scanning Electron Microscopy (SEM) is used to examine surface deposits at high resolution and Energy Dispersive X-ray Spectroscopy (EDS) is then used to identify the chemical composition of surface deposits.
Fujiwara For polyamide membranes a Fujiwara Test is completed to determine if the membrane surface has been exposed to halide oxidation, eg. chlorine.
Microbiology Various methods are available for microbiolgical analysis including plate counts, protein quantification, polysaccharide identification, Gram staining and Fluorescent In-Situ Hybridisation (FISH).
FEEM Fluorescence Excitation-Emission Matrix (FEEM) is used to fingerprint the presence of certain types of organic compounds which are soluble including humics, fulvics and proteinaceous.
FTIR Fourier Transform - Infrared Spectroscopy (FTIR) is used for specific material identification and to detect polyamide membrane structural damage caused by chemicals.
NMR Nuclear Magnetic Resonance (NMR) can be used to identify specific organic compounds present as fouling deposits on membrane surfaces.
LC-OCD Liquid Chromatography Organic Carbon Detection (LC-OCD) can be used to categorise the organic material found on membrane surfaces based on the molecular weight of the organic compounds.