How Pre-filtration Helps Protect Reverse Osmosis Membranes

Investing in a good-quality water filter system is a brilliant decision if you’re serious about protecting your home from dangerous drinking-water contaminants, preserving the environment, and saving money in the long run. However, reverse osmosis (RO) systems are only as good as the prefiltration systems protecting them.

RO technology is considered the gold standard for water filtration across various industries due to its game-changing performance and reliability. But as sophisticated and powerful as home RO filters are, they can be susceptible to premature, irreparable damage from large particles without adequate prefiltering of the water entering the membranes.

If you have an RO filter installed at home or are considering investing in one, this article explains how prefiltration protects your filter membrane and helps keep your RO system running smoothly for longer. Let’s start by looking at membrane filtration and how it works.

What is membrane filtration, and how does it work?

Membrane filtration is a water treatment process that cleans unfiltered water by forcing it through a porous or semipermeable membrane. This membrane works like a screen door that allows air molecules to pass through while blocking pests and anything larger than the holes in the screen door. In the same way, the filter membrane blocks ions, unwanted molecules, and larger particles in the water from passing through it (depending on the membrane’s pore size) and allows the water molecules to pass through.

The most common membrane options on the market are reverse osmosis (RO) membranes, ultrafiltration (UF) membranes, and nanofiltration (NF) membranes, all of which approach membrane filtration slightly differently.

Reverse osmosis applies pressure to a semipermeable membrane, catching the dissolved inorganic compounds and allowing the water molecules to pass through. It separates the water into two pathways.

Ultrafiltration doesn’t separate the water like a reverse osmosis membrane. It is simply an ultra-fine particulate or sediment filter. With mechanical filtration, particulates down to 0.025 microns cannot pass through the ultrafiltration membrane.

Nano-filtration membrane technology works similarly to reverse osmosis, except the filtration is not as refined.

Why is Prefiltration Important to Your RO Filter Membrane?

RO filter membranes are incredibly delicate. They are susceptible to damage from large particles, microbes, and other contaminants and impurities. That means if the source water entering RO systems is not filtered or “strained” to remove sediment before reaching the membrane, sand, dirt, rust, silt, and other particulates could destroy it or cause expensive damage.

When a membrane is compromised, it can require increased applied pressure, which increases energy costs. Added costs can come from frequent cleaning, chemicals, labor, and downtime. In addition, inadequately prefiltered or un-prefiltered water can cause excessive membrane scaling and fouling, leading to sub-par water production, costly and premature replacements, and unscheduled production downtime. Luckily, optimal prefiltration can help you avoid these situations.

Prefiltration is a vital safety and protective maintenance step to protect your RO membranes. That’s probably why the U.S. Food and Drug Administration (FDA) requires RO prefiltration in the food and beverage industry and processes where water for injection is used, such as pharmaceutical production.

Prefiltration can be applied to each membrane unit or the membrane filtration system. But how exactly does prefiltration help protect the membranes?

Prefiltration protects the filter membrane against membrane scaling and fouling.

Prefiltration is the most crucial part of a smooth-running RO unit – after the RO membranes. This vital process helps prevent scaling and fouling of the membrane, thereby maintaining its performance and efficiency and extending its lifespan.

Membrane fouling is a widespread problem in RO filters. It often begins when unwanted materials in the feedwater precipitate, deposit and accumulate on the membrane surface or membrane pores, gradually blocking the pores and reducing water flow throughout the unit.

RO membrane fouling contaminants can be categorized as:

  • Particulate/Scale (clay, silt, particles, calcium, magnesium, barium, aluminosilicates)
  • Biological/Microbiological (bacteria, slime, algae)
  • Organic (oil, n-Hexane, humic acid, fluvic acid, protein)
  • Other materials (coagulants, detergent, biocides)

The consequences of membrane fouling typically include poor water quality, strong odors, mold, and the buildup of solids along the membrane edges. The ability of prefilters to filter out suspended particulates, colloids, and larger color-causing organics, helps determine the performance and longevity of any RO equipment and, specifically, high-performance units.

Pre-filtration removes bacteria to prevent bio fouling of the membranes.

Bio fouling occurs when microorganisms, plants, algae, or other biological contaminants grow on or in filtration membrane surfaces and pores. These bio-foulants tend to thrive in warm environments with low flow rates. They can attach to the membrane and multiply while releasing a protective substance known as extracellular polymetric substance (EPS).

Collectively, the microorganisms and EPS form a slimy gel layer known as a biofilm. Biofilm has specific chemical properties that make it resistant to standard cleaning methods like back washing or applications of biocides, such as chlorine.

It can be challenging to correct bio-fouled membranes. In some cases, they may need replacement. Over time, a bio-fouled membrane will restrict water flow from one side of the membrane to the other, a condition indicated by a more significant differential pressure from the feed to the concentrate, decreased membrane flux, greater pressure-demand, and higher energy costs.

Bacteria range in size from 0.2 to 2 microns in width or diameter and from 1 to 10 microns in length for the non-spherical specie, so a 1-micron prefilter will remove most bacteria and cysts in waters where bio fouling is a concern.

Prefiltration protects the filter membrane from chlorine and other toxic chemicals.

RO membranes aren’t only susceptible to damage from sediment in the source water. These membranes are also vulnerable to free chlorine attack. Chlorine is a potent oxidizing agent, and it attacks the chemical bonds of polymeric membranes, which can lead to a decline in performance due to membrane degradation. Extended exposure to chlorine has been found to affect the membrane’s physical and chemical properties more severely than increases in chlorine concentrations.

Prefiltration reduces the operating expenses of the system.

Proper pre-treatment prevents fouling and scaling of the membranes as well as bio fouling. As a result, you can save money on the operation costs of the system as there’s a decrease in chemicals needed for cleaning. Pre-filtration also lowers the amount of power the RO system consumes and extends the membrane’s life. The better source water is prefiltered, the better it prevents biofilm formation on the RO membrane.

Prefiltration extends the membrane’s lifespan.

An RO membrane that is fully protected from microbes and damaging carbon particles typically lasts up to two years, while one that fouls within a year may indicate substandard or no prefiltration.

How often should you replace your RO membrane filter?

It would be best to replace your RO membrane every two to three years, depending on your water quality. If your RO system is still producing good-quality water after two or three years, you may be able to keep it for up to five years if you feed the RO system with softened water and replace the prefilters on time.

If you have a Springwell RO system installed at home, the SWROMR Membrane Replacement Filter replaces the Reverse Osmosis Membrane (Stage 3) of the RO unit and lasts up to 24 months. This replacement filter is designed and evaluated to provide the same performance and efficiency as the previous one, filtering out a broad range of contaminants in drinking water. Also, it is engineered for the most effortless replacement. You can twist off the old filter and replace it with a new one – no need to disconnect hoses or water lines.

Prefiltration in Springwell RO Filter Systems

Paired with a sediment prefilter and a carbon block prefilter in the same Springwell RO setup, the system effectively removes up to 99% of contaminants that could potentially damage your RO membrane. Prefiltration in Springwell’s Undercounter Reverse Osmosis Systems involves two crucial stages:

Sediment Prefiltration (Stage 1): Once the feedwater enters the system, it goes through a 5-micron sediment filter. This filter removes dirt, sand, silt, debris, rust flakes, and other suspended solid particles the filter’s micron-rated capacity can capture. It also reduces cloudiness in water caused by suspended solids. High concentrations of these solids can cause the water to appear brown, orange, or yellow. This prefiltration stage is crucial because it blocks these undesirable particles that could otherwise damage your RO membrane.

Carbon Prefiltration (Stage 2): At this stage, carbon filtration is used to filter out chlorine, chloramine, herbicides, pesticides, and other potentially toxic chemicals and compounds. This is another vital stage as it removes harsh chemicals from the water that could harm the RO membrane.

Reverse Osmosis (Stage 3): Stage three involves using the RO membrane to filter heavy metals, such as lead, mercury, arsenic, fluoride, iron, aluminum, etc. Thanks to the two earlier prefiltration stages (stages 1 and 2), the RO membrane can work without hindrances and the risk of damage from sediment and toxic chemicals.

Carbon Post-Filtration (Stage 4): Stage 4 is the final stage of the treatment phase. At this stage, a carbon filter removes any contaminants that evaded the first three stages.

With the combined power of prefiltration and reverse osmosis, you reap all the benefits of a healthy, good-working RO membrane – more money in your pockets and, most importantly, immediate access to clean, healthy water for drinking, cooking, washing fruits and vegetables, and more.

For more information on our robust and reliable Under counter Reverse Osmosis Water Filter Systems and the RO replacement filter options available, call us at 800-589-5592.

Final Thoughts

Reverse osmosis is among the most effective and reliable residential water filtration technologies, removing sources of contaminants from drinking water, including heavy metals, toxic chemicals, and even microbes. However, for RO filters to maintain their exceptional performance and reliability, they need a quality prefiltration system to protect the RO membrane.

Prefiltration helps protect the membrane against fouling and scaling, thus preventing potentially expensive damage and extending the membrane’s life. Luckily, our Undercounter Reverse Osmosis Water Filter Systems are designed with a powerful prefiltration system to guard the RO membrane. So, when you purchase one of our RO systems, you can be sure your RO membrane will last longer and continue to help provide clean, healthy, great-tasting water for longer.