Aqua Clear provides membrane autopsy services to help customers determine cause of failure or fouling of membranes, cleaning recommendations, or ascertain if damage is present in a membrane. We perform autopsies on reverse osmosis membranes, ultra-filtration modules, nano-filtration membranes, cartridge filters and many more. Our team of water industry experts will use the analysis to determine proper implementation of chemical treatment and preventative measures for the future. For more information and more detailed descriptions of our analytical tests and capabilities, click on the link below or contact one of our Aqua Clear water treatment specialists.
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Why Perform a Membrane Autopsy?
It is well known that Reverse Osmosis (RO) membranes reject high percentages of suspended and dissolved solids in water. Because of this trait, RO membranes eventually experience fouling. Implementation of proper pretreatment equipment and chemistry to create good feed water quality may significantly extend membrane life; however, membrane fouling will still inevitably occur. When membrane fouling happens in an RO system, a membrane autopsy can be performed to gain insight on the type of fouling present and how to manage and prevent the problem from occurring in the future.
A membrane autopsy should be performed if a site is experiencing fouling and has not yet come up with a proven cleaning regimen that is targeted specifically for the type of fouling involved. Generic cleaners often do not do an adequate job of returning membrane performance to the manufacturer’s specifications. Additionally, since generic cleaners are not buffered, they may have cleaning pH outside of the manufacturer’s specified range, which in turn causes irreversible pH hydrolysis damage to the membrane. Performing an autopsy allows a specialized cleaning regimen to be identified to restore remaining RO membranes in the system and fouling events in the future.
Membrane autopsies are also commonly used as routine maintenance by water treatment operators. Due to the nature of water filtration, and water’s properties as an excellent solvent, fouling can be subject to change over time. Seasonal changes such as variations in temperature to feed water sources due to rainfall can have a dramatic effect on the type of fouling deposition that occurs in a membrane system. A membrane autopsy may also be needed if a cleaning regimen becomes less and less effective over time. This may be due to changing feed water or a distinct fouling event (e.g. bio-fouling, scaling), where a previously used cleaning regimen may not be as effective at restoring membrane performance.
Fouling can also vary within a system based on position of the membranes. Lead membranes experience the highest concentrations of suspended solids, while the lag membranes experience the highest concentrations of dissolved sparingly soluble salts, which are more likely to precipitate and cause scaling. For this reason, it is often beneficial to perform a membrane autopsy from a lead and tail position in an RO system, as the membrane foulant compositions may completely contrast from one another.
Membrane autopsies are also a useful analytical tool for testing the efficacy of new implementation of pretreatment chemicals (e.g. coagulant, antiscalant) prior to an RO in a pilot study. Autopsies of RO membranes after a pilot study period can help gain useful information about the effectiveness of chemical addition and can help operators to dial in maximum recovery without fouling or scaling.
How Aqua Clear performs a Membrane Autopsy:
When a membrane arrives onsite at Aqua Clear for autopsy, pictures are taken of the exterior and observations are documented. The element is then promptly weighed. Element weight is typically a quick indicator on the severity of fouling. After the element is weighed, it is put into a vessel to be tested for initial performance parameters. Normalized data (flux, salt rejection, differential pressure) is collected and compared to the manufacturer’s specifications to judge how well the element performs.
After the wet test, the element is subjected to a vacuum integrity test. This test is designed to determine if any mechanical leaks are present in the internal components of the element. If vacuum pressure is lost, the element is likely to have experienced damage to its internal components, which is subsequently detrimental to overall salt rejection performance.Aqua Clear performs analysis on the foulant material by determining its total organic content by loss on ignition methods. This helps determine how much of the foulant is contributed by organic fouling. A microbiological analysis is carried out on the foulant material to test for the presence of bacteria, fungi and other microbes.
After the integrity test, the element is cut open for an internal inspection. The membrane components are examined for fouling and signs of physical damage. Acid testing is performed in this step, which checks for the presence of carbonates or metals by chemical reaction. Samples of the foulant material and fouled membrane flat sheet are then collected for further analysis. Additionally, flat sheet samples will be harvested for cell testing and a cleaning study to determine the most effective cleaning regimen to remove the foulant material.
Aqua Clear performs analysis on the foulant material by determining its total organic content by loss on ignition methods. This helps determine how much of the foulant is contributed by organic fouling. A microbiological analysis is carried out on the foulant material to test for the presence of bacteria, fungi and other microbes.
Scanning Electron Microscopy (SEM) is then performed on the fouled membrane samples to get high resolution topographical images of the foulant material. SEM imaging produces high quality monochromatic images in very large magnifications (100 to 20,000x). This imaging shows fine details of the texture or crystal structure of the foulant material. Energy Dispersive X-Ray Spectroscopy (EDS) is also performed on the fouled membrane surfaces. This technique reveals the elemental composition of the foulant sample and gives percentages of each element present.
Aqua Clear then analyzes the foulant on the membrane surface using element mapping. Element mapping is a technique that provides a spatial distribution of elements present within the foulant material on the membrane surface by combining a high-resolution SEM image with collected EDS data. Element mapping software designates a color for an element which is in turn shown on the SEM image. Intensity of color correlates with the concentration of the element in that area. This technique helps to map out exactly the type of foulant complex and can even show contrasting layers of fouling, which makes element mapping a very useful analytical technique for identifying any underlying causes of fouling issues.
The next step in Aqua Clear’s membrane autopsy analysis is the determination of whether damage occurred in the membrane, and if the associated damage is physical or chemical. Polyamide composite RO membranes can be damaged by deposition of abrasive particles and scale. It is also well known that polyamides are intolerable to commonly used water treatment oxidants such as halogens, peroxides and ozone. Aqua Clear’s autopsy for the presence of halogen oxidation via the Fujiwara test. This test is a qualitative test that tests for oxidizing chlorine bonded to the membrane surface. Dye testing can also be a useful tool in revealing the extent and cause of damage to the membrane surface, if the source of damage is not obvious.
Aqua Clear has other ancillary testing services that can be performed to determine cause of fouling when the aforementioned techniques are not enough. Aqua Clear has analytical techniques to help troubleshoot the most difficult feed waters in the industry, such as gray waters. As feed water sources and waste water treatment become more challenging, Aqua Clear has developed techniques to help identify RO incompatible chemical foulants and hydrophobic organics (hydrocarbons).
To determine if our membrane autopsy services or foulant analysis services are needed for your system, contact an Aqua Clear Water Treatment Specialist today.
