Membrane Autopsy Services

A bubble test is performed in order to determine the mechanical integrity of the membrane. While the membrane is completely submerged in water, 3-5psi of air pressure is introduced into the permeate tube. The element is then monitored for escaping air bubbles which would indicate  mechanical damage to the membrane.

Examination of the shipping container for damage incurred during shipment. Examination of the external construction of the element, including the fiberglass shell, ATD’s, and brine seal, for damage incurred during operation and/or shipping. Examination of the feed and concentrate ends of the element before and after removal of the ATD’s. Examination of each individual membrane sheet for evidence of channeling, fouling, pouching, delamination and/or manufacturer defects.  Examination of membrane permeate spacer (Tricot).

Samples collected from the membrane surface are tested for solubility in concentrated acid and caustic solutions. The LOI residue, which is the inorganic portion of the foulant once the organics had been volatilized, is also tested for solubility in concentrated acid and caustic solutions.  Information can be gathered about the nature of the foulant based on its solubility or dispersibility in different chemicals, and the resulting color of the solution.  Effervescence in the presence of acid usually indicates the presence of carbonate salts such as calcium carbonate.

Cell testing is performed in order to determine the performance of the membrane. Samples of the membrane are collected from the element and tested using the testing conditions that are specified by the manufacturer. Salt rejection and flux measurements are then compared with the manufacturer’s specifications and with wet test data when available.

In this test, a Rhodamine dye solution is applied under pressure to the feed side of the membrane sheet.  If the membrane is damaged, the dye color will penetrate to the permeate side of the membrane.  The pattern of dye penetration can be used to determine whether the nature of the membrane damage is chemical or mechanical.

This test is performed to determine whether the membrane surface has been oxidized by a halogen, such as Chlorine or Bromine.  It is standard procedure to perform a Fujiwara test on a membrane that fails the dye test or shows other indications of microstructural damage.

The foulant surface density is used to quantify the extent of fouling and/or scaling on the membrane surface by calculating the ratio of foulant mass to the surface area from which it was collected. The calculation is performed on the foulant upon collection, and again after dehydration at 105°C.

A Loss on Ignition (LOI) test is performed to determine the organic/inorganic content of the foulant. The percentages of moisture, organics and inorganics are then calculated based on the loss of mass.

This test is performed to determine the presence of humic and fulvic acids in the membrane foulant. Humic and fulvic acids are produced from the biodegredation of plant matter and, when present in the water, can foul the membrane.  The membrane foulant is added to a high pH solution in order dissolve any organic materials that are present, and filtered to remove any insoluble matter.   The pH of the filtrate is then lowered to precipitate dissolved organics.  The soluble and insoluble organics are identified based on color.

Tensile strength and elongation tests are performed on hollow fiber membranes to determine their strength and ductility.

Contact angle testing is used to determine the hydrophobicity of a membrane. Higher contact angles are directly correlated with a more hydrophobic surface. Membranes are less prone to biological fouling and have better productivity when they are less hydrophobic.  Certain foulants can make the membrane surface more hydrophobic.

Scanning Electron Microscopy (SEM) analysis is used to determine the topography and morphology of a sample. The SEM shows very detailed 3-dimensional images at much higher magnification than an optical microscope.

Energy Dispersive X-ray Spectroscopy (EDS) analysis is generally performed together with electron microscopy to identify and quantify the elemental composition of a sample surface. The sample material is bombarded with electrons from an SEM which produce X-rays. The produced X-rays are then measured by an X-ray dispersive spectrometer. Every chemical element has its own characteristic wavelength by which it can be identified.

Prismatic Elemental Delineation® (PED) 
Prismatic Elemental Delineation® (PED) uses a Scanning Electron Microscope (SEM) and an Energy Dispersive X-Ray Spectrometry detector (EDS) to identify individual chemical elements embedded on membranes.

PED is a result of X-rays that are released from elements when bombarded by an electron beam from the SEM, producing high-resolution mapped data images. Each image is then color-coded creating a visual map of the inorganic elements. The process allows for easier identification of membrane contaminates through a visual elemental isolation procedure.

Superimposed Elemental Imaging – SEI^®

Our imaging services will help you identify the exact nature of foulants on your membranes, so we can provide you with recommendations for effective cleaning and prevention.

Superimposed Elemental Imaging – SEI^® is an x-ray excitation spectrum based analysis with corresponding layered images showing the composition of specific inorganic particles. The process is used as a part of an autopsy and analysis for the determination of scales and foulants within a membrane system.

The use of this technique for membrane autopsies was pioneered in 2009 by American Water Chemicals in combination with Prismatic Elemental Delineation^® (PED)

Optical Microscopy

Live mounts are performed directly on the foulant to identify the types of microorganisms present and to differentiate between biological fouling due to bacteria, fungae or algae.  Gram staining tests are performed on cultures grown from samples of the foulant. The samples are flame dried, stained and analyzed under an optical microscope to determine if bacteria are Gram-positive or Gram-negative. Gram-negative bacteria have an outer membrane that makes them more resistant to detergents and biocides.

Biological Activity Reaction Test (BART)

A biological activity reaction test, or BART, is an effective method for monitoring the population size and activity of specific groups of bacteria. A BART test usually takes 2 to 8 days of incubation at room temperature. The BART bio-detector takes advantage of microorganisms individual interests to reveal their identity and population. Different microorganisms like to grow at different heights in a column of water to which nutrients are added. Aerobic organisms grow around the ball and anaerobic organisms will grow deep down in the water column. Results are determined by noting the rate of change of color of the test as microorganisms at the bottom of the water column consume the nutrients. Different organisms are encouraged to grow with different nutrients on the bottom of the tube.

Iron related bacteria (IRB), slime forming bacteria, sulfate reducing bacteria (SRB), heterotrophic aerobic bacteria (HAB), and denitrifying bacteria tests are performed. When the BART tests are performed on biofilm rather than water samples, the population counts are only used comparatively to determine the most dominant types of bacteria.

XRD: X-Ray Diffraction

X-Ray Diffraction (XRD) analysis is a technique used to characterize crystallographic structure, and grain size of a sample. The unknown material can be identified by comparing its crystal structure to that of an established data base. XRD can also be used to identify the presence of multiple phases where different crystalline compounds coexist.

X-ray diffraction techniques are non-destructive analytical techniques which reveal information about the crystal structure, chemical composition, and physical properties of materials and thin films. These techniques are based on observing the intensity of an X-ray beam hitting a sample as a function of incident and scattered angle, polarization, and wavelength or energy. X-ray scattering is different from X-ray diffraction.

FTIR: Fourier Transform Infrared Spectrometer

In the membrane autopsy process, the FTIR is a powerful tool for identifying types of chemical bonds (functional groups).  The wavelength of light absorbed is characteristic to the chemical bond.  The tested material can be identified by comparing its spectrum to the spectra of documented compounds in the database.

Fourier transform infrared spectroscopy (FTIR) is used to obtain an infrared spectrum of absorption, emission, photo-conductivity scattering of a solid, liquid or gas. An FTIR spectrometer simultaneously collects spectral data in a wide spectral range.