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How Does Filtration Purify Water: Filtration processes across the spectrum

Membrane Filtration Spectrum Infographic

Clean water is essential for all living things. Humans, animals, and plants all need clean water to live — which is why water filtration is a massive industry today. Whether you’re watering crops on a large farm, pumping ballast water at a foreign port, or simply getting a glass of water from your refrigerator, you are likely to be using water that’s gone through some form of filtration.

As the name suggests, filtration “filters out” harmful substances from our water, making it debris-free and usable in commercial systems. But how exactly does this process work? The answer depends on the type of filtration system you use.

Why Water Filtration Matters

Before we can discuss how filtration purifies our water, it is first important to understand why we filter water at all. According to the United States Geological Survey (USGS), water is a “universal solvent” — in other words, it can easily dissolve a great number of other substances.

While water solvency makes it an effective cleaning tool, it also makes it easy for contaminants to combine with the water itself. Debris, bacteria, and microorganisms can make themselves at home, and this can cause real harm to plants and animals who are exposed to contaminated water.

Membrane Filtration Spectrum Infographic
This membrane filtration spectrum chart shows the process of separation for various materials at increasingly smaller sizes.

Filters are necessary to protect your system from any debris or other contaminants in your water. If particles manage to get into a system, the equipment can suffer from buildup, clogging, and a host of other issues that can shorten the lifespan of the machines. In fact, these risks are so great that many organizations also implement a prefiltration stage. Systems that use ultrafiltration, for example, often use prefiltration to keep out larger particles and protect their primary filter from clogs or other damage.

For people working in industries like agriculture, water treatment, desalination, and much more, having clean water is vital to keeping your customers healthy and your business thriving. Therefore, these industries must rely on filtration to keep their water in safe and healthy conditions.

How Filtration Helps

Simply put, filtration removes the impurities from water, nearly eliminating the risk from any debris or particles that might have been present. This results in filtered water that is cleaner and purer than in its original state, making it safe for use in ballast tanks, industrial systems, and much more.

Filtered water can help prevent contamination of other things. For example, farmers use filtered water to prevent chemicals or bacteria from changing the pH levels in their soil. pH balance is a key component in growing various crops, and therefore farmers cannot have unexpected contaminants changing their soil composition.

Similarly, filtration is necessary for cargo ships that plan to dump ballast water at their next port. The ocean is a wide and varied ecosystem, and microorganisms from one area could drastically alter the ecosystem in another place. Filtering ballast water before dumping it at a port will prevent animals or bacteria from entering a new part of the ocean and drastically altering its biodiversity.

Ultimately, any industry that uses water to run their business can benefit from filtering their water before use. Investing in filtration will result in cleaner and safer water for everyone.

How Filtration Works

Water filtration has been a part of society since 500 B.C.E. when the Greek scientist Hippocrates developed a cloth filter for purifying water. Since that time, humans have developed and tested countless filtration methods for their water, from boiling it under the hot sun to using charcoal to chlorine to kill microorganisms.

But how does filtration work today? Some of the earliest filtration methods (like charcoal filters) are still used in some capacity. However, modern technology has opened the door to a wide range of different filtration methods. The most common filtration systems are:

  • Particle Filtration (two types are discussed below)
  • Membrane Filtration
  • Reverse Osmosis

Particle Filters

Screen Filters

One of the most common types of water filtration system is a screen-based filter. The vast majority of all commercial and industrial filtration systems first start with a screen to filter out as much suspended material as possible, before heading to treatment or use.UF and RO pre filtration

Screen filters use a mesh screen (usually made from polyester or stainless steel) to trap dirt, sediment, and other debris that might be in the water.

Screen filters were one of the earliest filtration tools developed by mankind, and they remain a highly effective method for purifying water even today. However, it is important to note that screen filters have one major drawback: they’re a flat, 2-D system. The standard screen filter doesn’t have any depth, and that means that the screen can become clogged very easily. Many get around this issue by regularly cleaning the filter – either by removing and cleaning it routinely or by using a self-cleaning system that removes debris automatically and keeps the screen fully functional throughout its life cycle.

There are different levels of screen filters that use varying sizes of mesh, which allows you to determine how many particles your filter captures. Additionally, some manufacturers, including Filtersafe, have created multi-layered screens, which capture a greater number of contaminants as the water moves through them. These tools make removing sediment, sand, and microorganisms a quick and painless process, thereby making it easier to have clean and pure water for your business.

Candle Filters

Candle filters are another approach for removing fine particles.

Also known as backwashing tubular filters, candle filters are not automatic like many screen filters are, instead of using gravity to produce clean water. Named for its candle-like shape, this filtration system uses a filter cartridge (which is usually made from ceramic or a fine sieve) to filter particles out of the water as it runs through the filter. This system can be an effective way to eliminate sediment, bacteria, and other particles from your water, though most industrial users prefer automatic filtration systems.

Membrane filtration: Micro-, Ultra-, and Nanofiltration

When filtration needs to be done to a much finer degree than particle filters can manage (below 10 microns), membrane filters are the solution (though screen filters are the first step for filtering water, before they pass through membranes). This means that the system uses hydrostatic pressure to force water through a membrane; as the water passes through, any particles or contaminants in the water become trapped, resulting in pure filtered water.

There are three main types of membranous filtration: microfiltration, ultrafiltration, and nanofiltration. While these three types use the same process to filter water, they differ in the size of particles they can trap. The key difference is the size of the pores in each membrane:

  • Microfiltration membranes have a pore size of around 0.1 microns, which means it can catch particles, but not dissolved substances. Microfiltration (MF) membranes developed specifically to solve complex process challenges such as microbial removal, protein fractionation, and pretreatment to other membrane processes. Microfiltration membranes have the most open pore sizes of all polymeric membranes. With a pore size range of 0.1 to 10μm, microfiltration membranes are capable of separating large suspended solids such as colloids, particulates, fat, and bacteria, while allowing sugars, proteins, salts, and low molecular weight molecules pass through the membrane.
  • Ultrafiltration membranes have a pore size of around 0.01 micron, which means it can catch smaller particles and smaller contaminants such as viruses. However, ultrafiltration cannot trap dissolved substances.
  • Nanofiltration membranes have a pore size of 0.001 microns. As one of the smallest pore sizes available (only reverse osmosis membranes are smaller), this filtration type can trap virtually all organic matter, multi-valent salts, and other particles in the water. In addition, nanofiltration membranes are capable of rejecting multivalent salts and larger molecules, while selectively rejecting varying amounts of monovalent salts.


Reverse Osmosis (RO) Filters

The term “osmosis” refers to the phenomenon of a solvent (like water) passing through a semipermeable membrane into a solute or dissolvable substance. When this happens, the water will dissolve and “pick up” some of the solute molecules, resulting in a water-and-solute mixture that is equally concentrated on either side of the membrane.

Reverse osmosis, as the name suggests, reverses this phenomenon – removing particles from a water source through the use of a membrane. This type of filer is most commonly used for desalination in conjunction with a media filtration or ultrafiltration system as a prefilter.

In reverse osmosis, the semipermeable membrane (which is most commonly made of cellulose acetate) does not allow the water to dissolve the solute; instead, it acts as a barrier that keeps material such as minerals or microorganisms from passing through the filtration system. Through this method, you can get purified water that is debris free.

Compared to traditional filtration technologies that rely on a screen or filter to remove particles, reverse osmosis (RO) is a pressure-driven separation process that employs a semipermeable membrane and the principles of crossflow filtration.

Reverse osmosis water treatment provides the finest level of filtration. The RO membrane acts as a barrier to all salts and inorganic molecules, as well as organic molecules with a molecular weight greater than approximately 100 Da (Daltons). It is therefore a highly effective process for removing contaminants such as:

  • Endotoxins/pyrogens.
  • Insecticides/pesticides.
  • Herbicides.
  • Antibiotics.
  • Nitrates.
  • Sugars.
  • Soluble salts.
  • Metal ions.

Get the Best Filtration System for Your Needs

There are a variety of water filtration systems available today, and they each serve a unique purpose. Whether you are purifying water for a water treatment plant, to nourish your crops, or for any other industrial purposes, it is critical to have the right tools at your disposal to do your work effectively – and that means finding the right filtration system for your needs.

And no matter which filtration technology you use for your system, you will need a prefiltration screen to protect and increase your system’s lifespan. A simple prefiltration system will prevent excess wear and tear on your machinery and save you in maintenance costs! Filtersafe has over 30 years of experience in advising and supplying the best system for your needs, helping you protect your systems and reduce costs and downtime. Contact us today to learn how our team can help your facility get cleaner, better water.

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