The membrane is weighed as received to determine the extent of scaling and fouling

The membrane in inspected by externally and internally. The product packaging is inspected for damage in transit and the external components of the element, including the fiberglass shell, ATD’s, and brine seal are inspected for damage incurred during operation. Looking at the feed and concentrate ends of the element before and after removal of the ATD’s allows us to see entrained material and suspended solids. Inspection of each individual membrane sheet is conducted to look for evidence of scaling, fouling, scratching, delamination and/or manufacturer defects.  Inspection of the permeate spacer can give indications of mechanical damage.

Water modelling is a powerful tool to understand not only the fouling present on the membrane but also how it can be managed through operational changes or through chemical cleaning or the use of antiscalants. We use the Proton Software that is the most powerful system available for modelling scale formation and allows us to determine fouling factors for many scale types as well as determine antiscalant dose requirements.

Modelling also gives us the expected ion concentrations in both the permeate and brine to identify problems and compare to field analysis.

A Pressure Decay Test (PDT) is performed to determine the mechanical integrity of the membrane. The membrane has a 30-40 kPa vacuum applied to the permeate tube and the rate at which this pressure decays gives an indication of mechanical damage that would let air through. This test can also be performed on UF/MF membranes depending on the module configuration.

Samples collected from the membrane surface are 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 look at 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 determines whether the membrane surface has been oxidized by a halogen, such as Chlorine or Bromine. 

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.

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 biodegradation of plant matter and, when present in the water, can foul the membrane.

Tensile strength and elongation tests are performed on hollow fiber membranes to determine their strength and ductility. Our autopsies include an elongation at break test standard to look for chemical or pH degradation.

Scanning Electron Microscopy (SEM) analysis is used to investigate at a very low-level fouling present on the membrane surface. The SEM shows very detailed 3-dimensional images at much higher magnification than an optical microscope. This shows us membrane surface damage as well showing us what fouling are present and how they have formed. We combine this with Energy Dispersive Spectroscopy (EDS) to get the elemental composition of the different fouling components.

Energy Dispersive X-ray Spectroscopy (EDS) analysis is 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.

Membrane samples are analysed using a microscope to look at detailed surface fouling. The samples are can also be stained with a range of dyes that allow us to highlight specific foulants. In particular EPS and bacterial slimes.

X-Ray Diffraction (XRD) analysis is a technique used to characterize crystal structure and size of a sample. Its a method to positively identify a fouling mineral and can be used to identify the presence of multiple phases where different crystalline compounds coexist.

XRD is 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.

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.

This analysis gives a quantitative estimate of the concentration of microorganisms such as bacteria, yeast or mould spores in a sample. The count represents the number of colony forming units (cfu) per g (or per ml) of the sample. This uses a nutrient rich agar that promotes bacterial growth along with an indicator that changes colour when the bacteria are present. The agar plates are inoculated and then incubated for 48h at 35C.

Multiple dilutions are conducted until between 30 and 300 colonies can be counted on a single plate. The reported count is the number of colonies counted multiplied by the dilution used for the counted plate

A high TVC count indicates a high concentration of micro-organisms which may indicate bacterial fouling.

Both inorganic and organic fouling materials are extracted from the membrane and then analysed by a range of techniques including Inductively Coupled Plasma (ICP) and Dissolved Organic Carbon (DOC) analysis. This allows us to see what inorganic fouling is present, whether its scale or entrained, as well as how much organic or biological material is present. In combination with other techniques it allows us to break down mixed fouling and understand how best to approach cleaning it.

X-ray Photoelectric Spectroscopy (XPS) is a technique that bombards a membrane sample with x-rays which excites the electrons which in turn emit light that can be analysed to identify not only the elements present but also what form that they are in and what they are bonded to. This can be particularly useful in looking at damage to the active membrane layer caused by hydrolysis of oxidation. We often use this to analyse for halide oxidative damage.

This analysis takes a membrane and tests it under a standardized set of conditions supplied by the manufacturer that are used as a benchmark for their new membranes. By comparing the flux and salt rejection to that of a new membrane we can look for hydrolysis and other damage that can be hard to identify analytically. This also provides a standardized performance result that can help understand if a performance problem is driven by operation conditions or the physical condition of the membrane.