Ultra-filtration and Micro-filtration Membrane Autopsies
Ultra-filtration (UF) and micro-filtration (MF) membranes differ significantly from RO membranes both in their applications and their construction and usage.
The first key difference is that UF and MF membranes are constructed of much more robust materials than RO membranes. From a construction perspective, they are frequently made from polymers such polysulfone, polypropylene, cellulose acetate, polyvinylidene fluoride (PVDF) but may also be made from ceramics for higher temperature applications. This leads to a key difference in their application where they are used to remove suspended organic and inorganic materials (such as clays) and are then cleaned using oxidizing agents like hypochlorite.
As a result, UF and MF membranes are often cleaned on a much more frequent basis than RO membranes and can involve rapid chemical cleans such as Chemically Enhanced Backwashing where a dilute chemical solution is flushed through the system to remove deposits. Our low-pressure membrane autopsies thus focus not only on the identification of membrane foulants, but also on their removal, allowing you to restore flux and meet production goals.
Like other membrane processes, UF membranes are susceptible to fouling when particulate matter adheres to the membrane surface. Unchecked, this build-up will eventually decrease water production as well as increasing operating pressures, energy consumption and result in more frequently cleaning.
There are a few different types of fouling that can occur, some are reversible and others are irreversible.
Solids fouling: Suspended solids and colloidal particles can collect on the membrane surface and within its pores, preventing the flow of water through the membrane. They are normally removed during cleaning, but some types may be hard to remove, making the existing cleaning program ineffective.
Biological fouling: Biological contaminants like algae and bacteria are often found in surface water and in MBR systems. These microorganisms can attach themselves to the membrane and begin multiplying and form a film that will prevent water from passing through the membrane.
Scaling: Scaling occurs when minerals precipitate on the membrane surface when they exceed their solubility or are oxidized. Once these minerals crystalize, they can be nearly impossible to remove without specific chemical cleaning.
Filtered water contamination: If either solids or bacteria are detected in the filtrate, this usually indicates a damaged membrane. This can be caused by high temperature, pH, oxidants or physical damage. Unfortunately, once this occurs and water is no longer meeting your specifications, replacement is the generally the only option.
Autopsy options
We have developed several different autopsies to help suite a range of different needs. Our Standard Autopsy identifies the cause of failure and is valuable where there is a suspected issue or as part of a maintenance optimisation. Our Advanced Autopsy identifies cleaning strategies when the existing cleaning program is not working and our Premium Autopsy works to evaluate your whole process including pre-treatment and operational procedures to wholistically improve the operation.
Low Pressure Membrane Analysis
| Test | Importance |
|---|---|
| Physical Inspection | Physical inspection of the membrane tells us a lot. We look for physicaldamage to the membrane as well as the different components of thesystem such as air spargers, membrane potting and seals. Inside themembrane we will also look to fouling materials and density. |
| Membrane integrity – bubble point or pressure decay test | Two types of membrane integrity test are available depending on themembrane format. A pressure decay test measures membrane leaksthrough the loss of pressure over a period of time. A bubble point testmeasures the apparent porosity by measuring the pressure required toforce air through the pores. |
| Fouling and deposit analysis | Fouling on an ultra-filtration membranes can be inorganic (such as clays,iron, aluminium or scale), organic (oils/greases, tannins or Natural OrganicMatter) or biological bacterial slime (extracellular polysaccharide orproteins). We use a mix of analytical techniques to identify and quantifythese deposits to help you eliminate them at the source. |
| Electron microscopy | Electron microscopes allow us to look deeply at the membrane and seewhat kind of fouling layers exist on the membrane and more importantly ifthey have penetrated into the pore structure. An additional X-ray analysisallows us to quantify the elements across the fouling layer to find thefouling causes. |
| Membrane cleaner extraction study | Indentifying the fouling material is the first part in solving a UF problem butknowing how to remove it is even more important. In this study we willscreen up to 10 different cleaners and use different analytical techniques toquantify their effectiveness. |
| Flux recovery cleaning study | The ultimate test of the cleaning is to mimic the cleaning process on site andemonstrate improved flux recovery. We will look at 2-3 conditions usingour inhouse flat-sheet or potted hollow fibre membrane rig. |
| Cleaning procedure review | Current site cleaning procedures will be reviewed against both themanufacturers recommendations and our inhouse experience from acrossthe industry. Improvements and recommendations will be prepared forimplementation on site |
| Plant data review | Reviewing site operational data helps identify if fouling is continual or eventbased and whether cleaning procedures are effective at recovering flux.This is key to understanding if a pre-treatment or cleaning approach is thebest way to bring the plant to optimal performance |
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