Membrane filtration systems are used in a variety of applications across many industries and verticals. Membrane technology can help you improve quality and reduce manufacturing costs. Although they require little maintenance, they often suffer from membrane fouling.
Membrane fouling can be caused by a variety of factors, including the presence of suspended solids, organic matter and microorganisms in the water. In addition, the temperature and pH of the water also affect the formation of scale.
To solve membrane fouling problems, it is important to understand its causes and effects. There are many ways to prevent membrane fouling and keep filtration systems operating efficiently. You can read more about these in this article.
Membrane filtration systems, including microfiltration (MF), ultrafiltration (UF), reverse osmosis (RO), and nanofiltration (NF), all use semi-permeable membranes to capture particles from liquids. Membrane filtration systems remove contaminant solids from a feed stream, producing a treated stream (filtrate) and a waste stream (retentate). Membrane fouling occurs when contaminants deposit on the membrane surface or in the membrane feed gasket, restricting the flow of liquid through the membrane.
Membrane fouling reduces the ability of the membrane to function properly. Membrane fouling can be a major problem in many industries, including water treatment, food and beverage processing, and pharmaceutical manufacturing.
Membrane fouling is usually classified according to the type of foulants or the location of the fouling.Foulants mainly includes four categories: particulate, organic, inorganic and biological microorganisms fouling.
For the location of fouling, fouling can occur inside or on the membrane surface. Most separation processes based on low-pressure membranes, such as UF and MF, suffer from internal fouling due to adsorption and cloggingof pores. On the other hand, relatively denser and more compact semi-permeable membranes, such as NF and RO, suffer from surface fouling.
Particulate fouling usually results from the continuous deposition of colloidal particles on an initially cleaned surface, where this process may even lead to complete blockage of the fluid cross-section.This is often caused by suspended material and non-biological particles in the feed water.
Organic fouling is defined as the collection of carbon-based materials on filter membranes. Natural organic matter consists of carbon-based compounds commonly found in soil, groundwater, and surface water from the decomposition of plant and animal material.
Inorganic pollution is formed by the deposition of inorganic compounds on the surface of the membrane or in the pores of the membrane. The deposits may be inorganic compounds with low solubility in water or solutes present in large amounts in water.
Biofouling refers to the adhesion and accumulation of microorganisms on solid host materials, accompanied by the formation of biofilms. Once bacteria attach to the membrane, they start to multiple and produce extracellular polymetric substances (EPS) to form a viscous, slimy, hydrated gel.
Membrane fouling is a major problem in many industries, especially those that rely on water filtration. Fouled membranes can lead to decreased yields, increased costs, and a need for more frequent cleaning and maintenance.
There are many causes of membrane fouling, but some of the most common include:
This is one of the most common causes of fouling, especially in water filtration systems. Scale is simply a buildup of minerals on the membrane surface. This can happen when water contains high levels of mineral salts, which can then deposit on the membrane surface.
Another common cause of fouling is biological growth, such as algae or bacteria. This can happen when water is not properly disinfected before it enters the filtration system.
Chemical reactions
Organic and inorganic compounds can react with membranes and foul themphysical.
Particulates, proteins, and other biological matter can accumulate on membranes and block pores.
Microorganisms can grow on membranes and foul them.
Membrane fouling problems may arise gradually or suddenly. In the early days, facilities typically experience symptoms such as rising energy costs and declining membrane flux.
If you notice that your water tastes weird, smells bad, or has a visible film on it, these could be signs that your water film is fouled. Fouling is the buildup of particles on the membrane that can ultimately lead to poor water quality. Or if the following phenomena appear, it means that the membrane is polluted.
Declining water quality is often a sign of membrane fouling. If your membrane-based water treatment system begins to produce low-quality permeate, check the composition of the foulant, which may give you more details about what may be causing the problem. If the foulant is colloidal, you may need to check your pretreatment or install a new pretreatment system. If your membrane exhibits both poor salt rejection and elevated transmembrane pressure, your membrane may be fouling.
When a strange, strong smell is emitted it may be a sign of biological growth on the membrane. In this case, there may be a buildup of slime on the surface of the filter or signs of mold on the end. This can usually be counteracted by adjusting the temperature and possibly adding a fungicide.
Differential pressure refers to the pressure drop between the feed and the concentrate of the semipermeable membrane. When the membrane becomes fouled, the pressure difference across the membrane increases. If the fouling is attached to the membrane, higher pressures are required to produce the target amount of permeate water. When differential pressure increases, your system may have membrane fouling and should be cleaned.
Membrane fouling is sometimes reversible — but not always. This is why it is best to first implement preventive measures to avoid or reduce membrane fouling. The system’s cleaning protocol helps prevent fouling from building up on the membrane. Cleaning cycles should be scheduled monthly or regularly to provide maximum benefit.
Mechanical cleaning involves the use of physical force to loosen contaminants from the membrane and flush them out of the system. Typical methods include vibrating water during cleaning, and back or forward flushing on the brine side, where water or cleaning solution flows through the device at a faster rate or higher pressure than normal service cycles, causing turbulent flow to remove the membrane Dirt on.
Chemical cleaning uses custom formulated cleaners, caustics, acids, antiscalants or dispersants to remove scale and particulate deposits that settle on membrane surfaces. Biocides are also used to remove microorganisms that may contaminate equipment, and cleaning chemicals should be selected based on the type of contaminants present and should be provided with a program that matches the unique reverse osmosis process.
Membrane fouling is a critical issue that reduces permeate flux, requires regular cleaning, and limits further membrane development as fouling hinders its wider application in various processes. Therefore, we must pay attention to this problem and minimize its occurrence.
Brother Filtration has has many years of experience custom-designing and manufacturing membrane filtration systems for a range of industries and applications. We also provide 3 different types of membrane system for our customers, which are UF membrane, RO membrane, and NF membrane.
Brother Filtration is an expert at determining the right membrane treatmentsolutions. Let us help extend your membrane life and improve system performance. Contact us to learn more.
