Ultrafiltration Vs Reverse Osmosis


New technologies in water filtration can get a little confusing in that some remove this and some remove that and others remove too many important parts like minerals that are normally contained in water which are healthy and then need to replace. The new technologies that are being used these days are (UF) Ultrafiltration and (RO) Reverse Osmosis which are being used in large and small portable water filters systems. They both work outstanding but what is one better than the other.  Whats is the difference between Ultrafiltration and Reverse Osmosis?

  • Reverse osmosis (RO) eliminates the majority of the dissolved minerals in the water. Making drinking water pure & free from minerals, salts, & total dissolved solids (TDS).
  • Ultrafiltration (UF) -won’t eliminate Total Dissolved Solids (TDS) or salts. It only filters out solid particulate matter, but it does so on a microscopic level.

Clean Drinking Water is the most important part of a healthy household that you can ensure for your family with a little bit of knowledge. What you need and who to listen to could be a game-changer. What contaminates are in dissolved nature and which ones aren’t?

Ultrafiltration Pore Size

UF or Ultrafiltration is a separation process using membranes with pore sizes in the range of 0.1 to 0.001 micron. Typically, ultrafiltration will remove high molecular-weight substances, colloidal materials, and organic and inorganic polymeric molecules. Low molecular-weight organics and ions such as sodium, calcium, magnesium chloride, and sulfate are not removed. This means that the smallest of particles are removed from the water but mineral such calcium and sodium that are low in weight are left.

Many people prefer this type of filtration because minerals that are healthy for you and are beneficial are left behind. Ultrafiltration membrane filtration (UF) is a low-pressure membrane process for water treatment that is designed to remove turbidity causing particles including those comprised of suspended solids, bacteria, colloidal matter, and proteins.

The UF membrane is a super-fine filter that Reduces particles 5,000 times smaller than a human hair. Ultrafiltration gives a 90-100% reduction in these contaminants. While UF can’t reduce some organics, a .05 micron carbon block prefilter can sometimes be added to a system to reduce chlorine taste and odor, lead, cysts, volatile organic compounds (VOCs), and metallic trace elements (MTE). A UF membrane lasts about two years. Ultrafiltration can remove bacteria, protozoa, and even some viruses from water.

Ultrafiltration (UF) is a type of membrane filtration in which hydrostatic pressure forces a liquid against a semipermeable membrane. A semipermeable membrane is a thin layer of material capable of separating substances when a driving force is applied across the membrane. Like this unit Dvluck Class 5 ultrafiltration Machine Sink Water Filter System with Chrome Faucet Filter Cartridges High Capacity Extra Long Life

There are 2 Types of Ultrafiltration

Point of Use Ultrafiltration Systems– These systems are normally installed under the counter water filtration systems.

Point of Entry Ultrafiltration Systems-These is typically used to run water for applications that do not require water filtered down to fine levels. This is found in Whole House Filters.

Both of these water treatment systems do the same thing but at different levels.  Both systems mechanically filter particulate as far down to 0.025 microns under the sink. The water that is consumed for drinking or cooking runs through a special tap where it’s treated by the system.

Microfiltration and Ultrafiltration are basically the same both of these filters of these separate based on size exclusion or particle capture according to the pore size on the filter. A general rule for choice of pore size in a UF system is to use a membrane with a pore size one-tenth that of the particle size to be separated. This limits the number of smaller particles entering the pores and adsorbing to the pore surface. Instead, they block the entrance to the pores allowing simple adjustments of cross-flow velocity to dislodge them.

The distinction in pore size and the types of particles removed means that each type of filter serves a particular purpose. Ultrafiltration is preferred because it wastes less water to the drain than Reverse Osmosis or won’t filter out minerals like RO filtering systems. Some Benefits of Ultrafiltration include:

  • The system operates at a low pressure
  • Removes bacteria and viruses
  • Keeps essential minerals in the water
  • Installs quickly and easily
  • Does not generate  much wastewater
  • Can be periodically back washed and air scoured to improve performance
  • Low fouling membrane modules
  • Excellent filtration performance with high flux
  • High chemical resistance and temperature tolerance for effective membrane cleaning
  • Very fine nominal pore diameter (0.02 µm)
  • The high removal efficiency of bacteria & viruses
  • Dead-end or concentrate bleed flow capabilities

What Is Reverse Osmosis

 

Reverse osmosis (RO) is a special type of filtration that uses a semi-permeable, thin membrane with pores small enough to pass pure water through while rejecting larger molecules such as dissolved salts (ions) and other impurities such as bacteria. RO systems can operate continuously with pressure and are used to produce highly purified water for drinking water systems, industrial boilers, food and beverage processing, cosmetics, pharmaceutical production, seawater desalination, and many other different applications.

​Industries today rely on a continuous supply of high purity water to achieve their mission. The high purity water is often produced on-site, starting with raw water or a municipal supply and removing from it various impurities, including biologicals, gases, suspended solids, and, most commonly, dissolved solids. Reverse osmosis is often part of a complete treatment system that includes pre-pretreatment and sometimes post-treatment polishing by ion exchange.

How Does Reverse Osmosis Work

The heart of Reverse Osmosis filter is an Osmosis membrane. It divides a canister or area into 2 pressure zones. You have a differential pressure about a semi-permeable membrane. This membrane has very tiny holes. These holes are so small so except for water and a few of the gases rejecting larger particles like dissolved salts and impurities like bacteria. Some advantages are:

  • Simple to operate
  • Does not require any hazardous chemicals to operate it
  • Energy-efficient, especially when used instead of distillation to produce high-purity water
  • The design allows for easy installation
  • It reduces water and sewage cost
  • Can be integrated with other membrane systems

Reverse Osmosis operates by reversing the principals of Osmosis which is the natural tendency of water containing salts to flow through a membrane with higher salt concentration. This natural process is found all through nature. Plants use Osmosis to absorb water and nutrients from the soil.

In the human body, and in animals, kidneys use osmosis to absorb water from the blood. In the mechanical process of Osmosis 75% of the raw feedwater is purified. In applications in which water conservation is important, 85% of the raw feedwater is purified.

The Reverse Osmosis system uses Cross filtration where the solution crosses the filter with two outlets: the filtered water goes one way and the contaminated water goes another way. this keeps contaminants from building up, Cross-flow filtration allows water to sweep away the contaminant buildup and add enough turbulence to keep the membrane surface clean. like this unit iSpring RCS5T 500GPD Commercial Tankless Reverse Osmosis RO Water Filter System with 1:1 Drain Ratio

 Reversed Osmosis Benefits

Ultrafiltration Filters work like many other types of sediment filters. Ultrafiltration is a water treatment process that uses a hollow fiber or a sheet membrane to mechanically filter water containing a very small suspended particulate that is bigger than 0.025 microns.

  • It will also get rid of things like viruses or living organisms. This is because bacteria are solids and larger than 0.025 microns and are able to be taken out by the filter.
  • It won’t be able to take out dissolved minerals that a Reversed Osmosis will.

Ultrafiltration systems normally are attached and work with Carbon Filtration that should be replaced every year or so depending on their rating and sometimes when the flowrate starts to noticeably decrease.  Ultrafiltration is a mechanical filter that takes out particulate. The rating for the filter is dependent on the pore size of the filter. The Ultrafiltration Filter no matter how small the pore size will be able to take out Dissolved Solids that an RO or Reverse Osmosis Filter can.  

When considering filter size, look for an absolute (the largest hole), not a nominal (the average hole), rating. EPA and CDC recommend an absolute one-micron filter (or one labeled for cyst removal) to remove Cryptosporidium.

Some Contaminants can be filtered by size microns     

  • Giardia lamblia – 8 to 12
  • Cryptosporidium parvum  4 to 6 microns
  • Bacteria (such as E. coli and
    salmonella) – 0.2 to 4 microns
  • Viruses – 0.004 to 0.1 microns
  • Giardia and Cryptosporidium-distillation, reverse osmosis, absolute one-micron filters, ultraviolet light, and filters certified for cyst removal.

 

What Contaminants can’t be filtered out:

  • Lead – distillation, reverse osmosis, and some carbon filters.
  • Nitrates – distillation, reverse
    osmosis or ion exchange.
  • Salts
  • Flouride
  • Sulfates
  • Pesticides – some carbon filters.
  • Radium – ion exchange, distillation or reverse osmosis.
  • Radon – activated carbon
  • Calcium-Reversed Osmosis
  • Arsenic-Reversed Osmosis, some carbon filters

Ultrafiltration:

  • can filter can typically filter 1 gallon of water in a minute
  • Produces no wastewater
  • Can operate smoothly under pressure

Reverse Osmosis:

  • Requires a storage tank because of slow filtering speeds
  • Converts 4 out of every 5 gallons into wastewater
  • Needs minimum a minimum of 50 psi to function properly

Some people use a Home Water Treatment filter just to improve taste and to remove lead that is found in plumbing pipes in houses. These filters can cost $20.00 dollars to more elaborate systems using Reverse Osmosis that be hundreds of dollars. All water used for drinking should be expected to contain some contaminants but at low enough level that they won’t hurt the person consuming them. As long as the water contains less than what EPA says are safe standards then there should be nothing to worry about.

Reverse Osmosis Units: Reverse osmosis units force water through a semi-permeable membrane under pressure, leaving contaminants behind. Reverse osmosis units use approximately three times as much water as they treat, but they are effective in eliminating all disease-causing organisms and most chemical contaminants.

  • Use a point-of-use filter end-of-tap, under sink filters that remove particles one micrometer or less in diameter
  • Filters that use reverse osmosis, those labeled as “absolute one-micron filters,” or those labeled as certified by an American National Standards Institute (ANSI)
  • Accredited organization to ANSI/NSF Standard 53 for “Cyst Removal” provide the greatest assurance of removing Cryptosporidium
  • Make sure to follow the Manufacturer’s instruction for changing filters.

 

  JimGalloway Author/Editor

 

 

References:

EPA -Home Drinking Water Filtration Fact Sheet

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