Residential Chlorine Cartridge Filters



Cartridge-style whole house filters for city water have many advantages.  They install easily without need for a drain connection and electricity, they are compact and can be wall mounted, and they are very effective.

Below are specially priced cartridge-style whole house  filters designed for city homes whose water supplier uses chlorine (rather than chloramine). All use the exceptional Pentek Radial Flow Carbon Filter.  This unique cartridge offers long life, excellent taste/odor performance, and almost no pressure loss.  The radial flow granular style of the RFC20BB restricts flow less than 1 psi at 4 gallons per minute, a fraction of the pressure drop from comparable carbon block filters.  The filter uses powdered carbon that is held in place by a uniquely designed cartridge that eliminates the need for the plastic binders used in carbon block filters.

These units cost a bit more than our standard carbon block whole house units, but their free-flowing performance makes them worth the added expense.

The package systems we’ve put together include a filter wrench, housings, extra O Rings,  brackets, and cartridges.  All housings have 1″ ports (3/4″ or 1.5″ available upon request).  All housings, both 20″ and 10″,  are tough, reliable Pentek “Big Blue.”  All housing packages include mounting screws, heavy duty metal brackets, and one extra housing O Ring.

These systems are designed for parallel installation for larger homes to assure minimal pressure drop and optimal chenical/chlorine performance. See the reference pages listed below for installation pictures. Note that all carbon filters are 20″ and all sediment filters are 10″. The housing caps and brackets are identical for easy installation.

Whole house cartridge filters offer many advantages as compared with tank-style filters.  They install easily (no drain connection and no electricity needed). They are reliable, simple, easily serviced units with a very long lifespan. As compared with backwashing filters, these compact whole house carbon units save hundreds of gallons of water per year because no backwash is needed.

The RFC20 is a NSF-42 certified cartridge with a manufacturer’s rating for 70,000 gallons of chlorine removal @ 4 gpm. PSI drop at 4 gpm is only 0.9 psi.



Price (shipping to lower-48 addresses included)

System 1. One 4.5″ X 10″ 5 micron sediment filter plus one 4.5″ X 20″ carbon filter.Homes with 1 to 3 people. Flow rates to 5 gpm.$314.00
System 2. One 4.5″ X 10″ 5 micron sediment filter plus two 4.5″ X 20″ Chloramine Filters installed in parallel.Homes with up to 5 people. Flow rates to 10 gpm.$526.00
System 3. One 4.5″ X 10″ 5 micron sediment filter plus three 4.5″ X 20″ Chloramine Filters installed in parallel.Homes with up to 8 people. Flow rates to 15 gpm.$743.00

 wh101_306Basic 20″ Big Blue Housing


Multi-filter installation. Water passes through sediment filter on the left, then splits to pass through two carbon filters.  (The sediment filter is a 10″ cartridge and the two carbon filters are 20″.)

See also:

High Performance Cartridge-Style Chloramine Filters.  (This is the chloramine version of the products on this page. Chloramine reduction requires specialty carbon and in general needs a slower flow rate or greater filter capacity than chlorine reduction.)

Compact Whole House Filters.

More Multi-Filter Installation Pictures.

General Installation Instructions for Compact Whole House Filters.

U.S. drinking water widely contaminated with ‘forever chemicals’: environment watchdog


By Timothy Gardner

The contamination of U.S. drinking water with man-made “forever chemicals” is far worse than previously estimated with some of the highest levels found in Miami, Philadelphia and New Orleans, said a report on Wednesday by an environmental watchdog group.

The chemicals, resistant to breaking down in the environment, are known as perfluoroalkyl substances, or PFAS. Some have been linked to cancers, liver damage, low birth weight and other health problems.

The findings  by the Environmental Working Group (EWG) show the group’s previous estimate in 2018, based on unpublished U.S. Environmental Protection Agency (EPA) data, that 110 million Americans may be contaminated with PFAS, could be far too low.

“It’s nearly impossible to avoid contaminated drinking water from these chemicals,” said David Andrews, a senior scientist at EWG and co-author of the report.

The chemicals were used in products like Teflon and Scotchguard and in firefighting foam. Some are used in a variety of other products and industrial processes, and their replacements also pose risks.

Of tap water samples taken by EWG from 44 sites in 31 states and Washington D.C., only one location, Meridian, Mississippi, which relies on 700 foot (215 m) deep wells, had no detectable PFAS. Only Seattle and Tuscaloosa, Alabama had levels below 1 part per trillion (PPT), the limit EWG recommends.

In addition, EWG found that on average six to seven PFAS compounds were found at the tested sites, and the effects on health of the mixtures are little understood. “Everyone’s really exposed to a toxic soup of these PFAS chemicals,” Andrews said.

In 34 places where EWG’s tests found PFAS, contamination had not been publicly reported by the EPA or state environmental agencies.

The EPA has known since at least 2001 about the problem of PFAS in drinking water but has so far failed to set an enforceable, nationwide legal limit. The EPA said early last year it would begin the process to set limits on two of the chemicals, PFOA and PFOS.

The EPA said it has helped states and communities address PFAS and that it is working to put limits on the two main chemicals but did not give a timeline.

In 2018 a draft report from an office of the U.S. Department of Health and Human Services said the risk level for exposure to the chemicals should be up to 10 times lower than the 70 PPT threshold the EPA recommends. The White House and the EPA had tried to stop the report from being published.

Source: Reuters report via Yahoo News.

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TAC or Water Softener: Pros and Cons

With the growing popularity of alternatives to conventional water softeners, most notably Template Assisted Crystallization (TAC) systems, residential customers are finding it more difficult to choose a home treatment system for hardness.

Below here are some issues that come up and our comments on them, based both on our direct experience with the products themselves and on discussions we’ve had with customers who use them, In each case, we’re comparing a standard TAC unit to a standard conventional water softener.

Adds salt to water:  The softener works by exchanging salt for calcium and magnesium, so, yes, it adds salt.  TAC does not use salt.

Removes hardness.  Calcium and magnesium are the minerals that cause water to be hard. A softener removes them.  TAC “conditions” them so that they are less offensive; it does not remove hardness, so it really should not be called a softener. There is currently no way to quantify the effect that TAC units have on hardness.

Gives the water a feeling of slickness.  Softener, yes; TAC, no.

Makes soap lather better, thus saving soap.  Softener, yes; TAC, perhaps a little.

Makes plumbing and appliances last longer.  Yes in both cases.

Initial cost comparison. Softeners vary in price, a lot, depending on style and manufacturer.  In general, TAC units cost more than good quality softeners but less than high-end softeners.

Upkeep. Operating Cost.  If the user’s labor is considered, or if the user pays someone to keep the softener cleaned and full of salt, the softener costs more. The single “upkeep” cost for TAC units is media replacement, which is expensive, but it only happens about every third year.  TAC uses no salt, no water for regeneration, no electricity, and has no moving parts that break. TAC is so simple that most users can do the occasional media replacement themselves.

Environmental impact.  TAC uses no water for regeneration and adds nothing to the waste stream. Softeners use considerable amounts of water for regeneration and add salt to the city’s waste stream or the septic tank. Why is this a big deal? Because city water departments are hard-pressed to dispose of the waste water, which usually can’t be used for irrigation because of the salt content. Softeners, by the way, can be regenerated with potassium chloride rather than sodium chloride, which is regarded as more environmentally friendly but which is considerably more expensive than plain old softener salt.

Health issues.  Although we believe that amount of salt added to drinking water by a softener probably has no negative health impact unless you drink outrageous amounts of it, not everyone would agree. The salt can be removed from softened water by an undersink reverse osmosis unit. RO removes salt handily.  TAC adds nothing objectionable to drinking water–at least nothing we know about yet. Softeners add salt and remove calcium and magnesium; TAC units neither add nor remove minerals.

Aesthetics. Some people (usually people who grew up with softened water) like the “slick” feel and the illusion that soap can’t be washed off the skin. Some people (usually people who grew up bathing in hard water) don’t.  TAC units do not affect the water aesthetically. The water feels, smells, tastes, and looks the same as untreated water.

Installation.  The TAC unit is easier to install. The softener needs electricity and a drain connection.  TAC needs neither. The softener has a control valve to program and a startup procedure to follow; TAC units require no programming or setup.

Pre-treatment — A sediment filter is essential in front of the TAC unit and is usually a good idea in front of a softener. In general, softeners are tougher and require less protection. Softeners actually remove small amounts of iron and manganese, but TAC units must be protected  from them by pre-treatment. Likewise, TAC units are very sensitive to copper and have to be protected from new copper piping by remaining in by-pass mode until new copper piping is seasoned. Both softeners and TAC units last longer with pre-treatment for chlorine or chloramine  in city water, but this is not essential.


 The conventional softener in the picture consists of the tall resin tank, the control valve on top, and the brine tank where salt to regenerate the resin is stored.  TAC units have only the tall tank and the top valve does not require electricity. No brine tank is needed. 

Dark Waters: Water Contaminants in the Movies



A highly promoted movie called Dark Waters came out in late November 2019. It stars Mark Ruffalo and tells the story of Cincinnati lawyer Rob Bilott and his dozen-year battle against the centuries-old American chemical company, DuPont.  From an effort to gain justice for a single client whose livestock were poisoned by Dupont’s chemical PFOA, Bilott’s efforts resulted in large class-action settlements for hundreds of injured parties. Ruffalo, who is known as an environmental activist as well as an actor, produced the film as well as starring in it. Other top actors featured are Anne Hathaway and Tim Robbins.

Dark Waters joins other important movies that brought significant water contaminants to public attention. The stories of all are similar. They feature an individual who takes on a powerful company that seems to be above the law.  The best known of these is Erin Brockovich, starring Julia Roberts, which tells the story of the hexavalent chromium (aka chromium-6) poisoning of the water in Hinkley, CA by Pacific Gas and Electric. A lesser known but equally compelling story is that of the TCE poisoning of the wells that supplied Woburn, MA by the W.R. Grace company. The incident inspired an outstanding book by Jonathan Harr that in turn inspired the 1998 movie A Civil Action, starring John Travolta and Robert Duvall. (The book was better than the movie, but both deserve your attention.)

Why Don’t Tiny EOT (End of Tap) Filters Work As Well As Standard Filters? Well, Because They Are Tiny

Most of the bad publicity (“filters don’t work”) that resulted from poor performance on tests done on lead filters supplied to homeowners in Flint and Newark ignored the fact that the filters provided were novelty-sized units meant for off-the-shelf purchase. They could not be expected to “work” as well as full-sized filters actually designed for long-term  use in homes.

Here is sizing information from the manufacturer of MetSorb®, a heavy metal removal medium that is added to carbon block filters to give them lead-removal capacity.


A nominal 10 – inch carbon block, standard for most countertop and undercounter applications, will provide more overall volume and more functional media than the 2 to 2-1/2 inch blocks typically used in end-of-tap (EOT) applications. For example, a nominal 10 – inch carbon block can easily perform for 1000 gallons or more of contaminant reduction, while the smaller EOT blocks are rated at several hundred gallons.

The larger block design also gives longer contact times (EBCT or Empty Bed Contact Time) for better contaminant reduction. For example, a nominal 10 – inch block will provide an EBCT of 10 -15 seconds, while a typical 21/2 inch EOT block gives only 3 seconds EBCT. Devices designed for slower flow rates, e.g., 0.5 gpm (gallons per minute) versus 1.0 gpm will provide longer contact times and better percentage contaminant reduction.


This 10″ carbon block fits standard sized countertop and undersink filters and provides 2500 gallons of lead-free water at 0.75 gallons per minute.   

President Trump Addresses Water Conservation

At a December 16, 2019 meeting of small business leaders at the White House, President Donald Trump talked at length about water and energy conservation, saying the Environmental Protection Agency is looking into restrictions in part because people are flushing their toilets 10 to 15 times instead of once and are therefore using more water.

“We have a situation where we’re looking very strongly at sinks and showers and other elements of bathrooms, where you turn the faucet on in areas where there’s tremendous amounts of water, where it all flows out to sea because you could never handle it all, and you don’t get any water,” he said.

“They take a shower and water comes dripping out, very quietly dripping out. People are flushing toilets 10 times, 15 times, as opposed to once; they end up using more water. So EPA is looking very strongly at that, at my suggestion.

“You go into a new building, new house, a new home, and they have standards where [you] don’t get water, and you can’t wash your hands practically; there’s so little water,” he added. “And the end result is that you leave the faucet on, and it takes you much longer to wash your hands, and you end up using the same amount of water. So we’re looking very seriously at opening up the standard, and there may be some areas where we go the other route, desert areas, but for the most part, you have states where they have so much water where it comes down — it’s called rain — that they don’t know what to do with it.”

In his comments, the president appeared to be referring to the standards set by the National Energy Policy Act of 1995, federal regulations that stipulated that all newly manufactured toilets had to use a maximum of 1.6 gallons of water per flush, a significant decrease from previous standards.

Just a couple of days earlier, at a NATO conference in Europe, the president blamed ocean trash in US waters on the bad habits of other countries:  “I also see what’s happening with our oceans, where certain countries are dumping unlimited loads of things in it. They float — they tend to float toward the United States. I see that happening, and nobody has ever seen anything like it, and it’s gotten worse.”‘

Sulfur & Groundwater


Gazette’s Introductory Note: The piece below is adapted from an information sheet provided by the non-profit Water Systems Council.  It addresses one of the more confusing topics in water treatment, the “sulfur” or rotten egg smell in well water. Bad smelling water is variously attributed to sulfur, sulfate, or hydrogen sulfide. This document seeks to shed some light on the origin and treatment of bad smelling water. 


What is Sulfur?

Two forms of sulfur are commonly found in drinking water: hydrogen sulfide and sulfate-reducing bacteria. Both forms are nuisances that usually do not pose a health risk at the concentrations found in domestic wells.

Hydrogen sulfide gas occurs naturally in some ground water that contains decaying organic matter, such as wetlands, marshes, swamps, river beds. It may be found in deep or shallow wells. Hydrogen sulfide is often present in wells drilled in shale or sandstone, or near coal or peat deposits or oil fields.

Sulfate is a combination of sulfur and oxygen, and is part of naturally occurring minerals in some soil and rock. The mineral dissolves over time and is released into ground water. Sulfur odor is produced when a non-harmful sulfur-reducing bacteria digests a small amount of the sulfate mineral.


What are the health effects of Sulfur?


The EPA considers sulfur a secondary water contaminant, with no direct threat to human health. Sulfate gives water a bitter taste and can have a laxative effect that may lead to dehydration. Hydrogen sulfide gives water a “rotten egg” odor and taste, and can cause nausea.


Hydrogen sulfide is corrosive to metals such as iron, steel, copper and brass. It can tarnish silverware and discolor copper and brass utensils. Hydrogen sulfide can also cause yellow or black stains on kitchen and bathroom fixtures. Coffee, tea and other beverages made with water containing hydrogen sulfide may be discolored and the appearance and taste of cooked foods can be affected. High concentrations of dissolved hydrogen sulfide also can foul the resin bed of an ion exchange water softener.


How do I test for Sulfur?


Testing for hydrogen sulfide can be difficult because the gas escapes into the atmosphere so quickly. Onsite testing is the most accurate method for determining hydrogen sulfide concentration, especially if the odor is excessive. Hydrogen sulfide concentrations greater than 5 mg/L are more difficult to treat and could require special testing methods to assure accuracy.


Sulfate-reducing bacteria is rarely tested, however testing for sulfate ion (mineral) concentration is. The premise is: if a rotten egg odor is present and the sulfate ion concentration is excessive – greater than 150 mg/L – the odor is created by sulfate-reducing bacteria.


The EPA sets standards for secondary water contaminants based on taste, odor, color, corrosiveness, foaming and staining properties. Hydrogen sulfide is not regulated because any concentration high enough to pose a health hazard will also make the water too unpalatable to drink. The EPA’s secondary limit for sulfate in drinking water is 250 parts per million (ppm).


What are the treatments for Sulfur in drinking water?


Treatment options depend on the form (whether hydrogen sulfide or sulfate-reducing bacteria) and quantities of the “rotten egg odor-producing” contaminants. Hydrogen sulfide treatment is with chlorination or aeration followed by filtration. Often, treatment for hydrogen sulfide is the same as for iron and manganese, allowing the removal of all three contaminants in one process.


Most water heater anode rods contain some sulfate so, in the presence of sulfate-reducing bacteria, a rotten egg odor is created in the hot water only. If this occurs, the first course of action is to replace the anode rod with an aluminum-based rod which limits the sulfate and therefore stops the odor.


Sulfate-reducing bacteria is treated with continuous chlorination. Removing sulfate mineral is difficult and usually not feasible, so chlorination kills the bacteria instead. The chlorination process involves a chemical feed pump system that injects a chlorine solution into the inlet of a retention tank that must be installed in the house piping. The retention tank must hold enough water to provide a 20-minute time period for the chlorine to react with the bacteria. The capacity needed for the retention tank can be calculated by multiplying the well pump output times 20. A continuous chlorine residual of 1.0 mg/L is required at the outlet of the retention tank to assure the bacteria were destroyed. Since chlorine can be combined with natural organic matter, it’s always recommended that an activated carbon filter be installed after the retention tank to remove the chlorine.


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 Testing for ORP with Potassium Permanganate

Editor’s Note: The instructions below, which we’ve modified a bit, were prepared by the original manufacturer of Filox-R iron removal media. The purpose is to provide a quick and easy way to determine if your water can be treated by standard manganese dioxide-based iron filter media like Filox without the use of additional oxidizers like chlorine, air, ozone, hydrogen peroxide or potassium permanganate. 


Oxidation Reduction Potential (ORP) can be the most important factor to take into consideration in certain waters. Highly reducing waters may cause premature exhaustion or even destruction of the Filox-R bed.


Precautions can be taken prior to installation that can prevent ORP problems. Use one of the screening tests and follow the instructions below if the subject water has reducing properties that will require additional oxidants. 


 The Simple Test


Mix 1.75 ounces (50 grams) water with 0.75 ounces (22 grams) of potassium permanganate crystals. Then take 2 drops of the mixture and stir into a fresh ¼ gallon (1 liter) sample of the subject water. Let the subject water stand for 15 minutes. If the pink color remains, Filox-R can be installed without additional oxidants. If the pink color disappears, additional oxidants will be needed for Filox-R to function properly.


The ORP Test with a Meter


Note: Must use a calibrated ORP meter. Any reading that is above a negative 170 millivolts indicates that Filox-R can be used effectively without additional oxidants. Any reading falling below a negative 170 millivolts indicates that additional oxidants will be required.


The amount of oxidant required for proper installation can be determined by measuring the amount of oxidant added to a specific volume of subject water until the solution remains pink or the meter reads at negative 170 millivolts or above. An extrapolation can then be made to determine the correct feed rate for the oxidant with respect to the subject water flow rate. Once installed, sample the solution after the injector and mixer and repeat the above test to confirm that the feed rate is correct.


How to Pick the Best Filter Cartridge

The “best” water filter cartridge is not necessarily the one that removes most contaminants or the one that treats the most gallons of water or the one that has the least pressure drop. The best for you is the one that does what is needed in your application.

This article makes some generalizations about water filter cartridges to help clarify what performance information provided by manufacturers means to the filter customer. We’re using “whole house” carbon filter cartridges, 4.5″ X 20″, treating chlorine and chloramine, to illustrate, but the principles apply as well to other filters, like sediment filters and “media” cartridges that are intended for problems like iron, turbidity, lead,  and nitrate reduction.

In general terms, the more tightly the filter media is packed together, the more effective the filter is at removing contaminants, but the more it restricts the flow of water through it and the more likely it is to become clogged by particles. The looser the media is packed, the less effective the filter is at contaminant removal, but the less it restricts the flow of water and the less likely it is to be clogged. Tighter means more effective performance but greater pressure loss.

Another generalization that’s true of most cartridges is that the slower the water goes through the filter, the more effectively it treats contaminants, the longer it lasts, and the less water pressure is lost. Conversely, the faster the flow, the poorer the performance, the greater the pressure loss, and the shorter the lifespan of the filter.

The art of selecting a filter, then, is to choose one that’s tight enough to be effective but not so tight that it restricts service flow or stops up easily. It must also be large enough to accommodate the needed service flow rate. Sometimes with cartridge filters to get a larger filter the most practical approach is to install 2 or more filters in parallel.  (See the picture below.)

To see how pressure drop, capacity, and micron size are related, here is a comparison of chlorine treatment figures for  two 4.5″ X 20″ MatriKX carbon blocks, identical except in tightness. (Micron size is the way filter makers state tightness: the lower the micron number, the tighter the filter.)

Two Identical Carbon Block Filters of Different Micron Ratings: Chlorine Reduction

Filter TypeCoconut Shell Carbon BlockCoconut Shell Carbon Block
Micron RatingNominal 5 micronsNominal 1 micron
Chlorine Removal Capacity34,000 gallons @ 7 gpm160,000 gallons @ 7 gpm
Pressure Drop8 psi @ 7 gpm16 psi @ 7 gpm
Current Retail Price$68.00$89.00


The very tight CTO+ would seem like the better value in terms of gallons treated per cost, but it is very unlikely that in residential use such a tight filter would treat 160,000 before it stops up. Also, the excessive pressure drop gets even worse as the filter picks up particulate. Its performance is remarkable, but it probably is not the better choice for whole house residential treatment of chlorine.

The looser CTO has half the pressure drop. Most residential water use is at a rate below 7 gpm, so you can expect the 34K capacity of the CTO to go up. We’ve found the CTO to be an excellent residential filter for water treated with chlorine.

The pair of filters compared below are identical “radial flow” granular filters. Though both are rated at 25 microns, the chloramine filter evidently uses a finer carbon and is therefore a bit more restrictive.  These are very high grade radial flow cartridges, not to be confused with the standard axial flow cartridges that normally use regular-grind (not powdered) carbon and have much lower performance numbers.  (Axial vs. radial explained.)

Similar Radial Flow Granular Carbon Filters: One for Chlorine, the other for Chloramine

Pentek RFC20BB—Chlorine GradePentek CRFC20BB –Chloramine Grade
Filter TypeRadial Flow GAC (powdered)Radial Flow Catalytic GAC (powdered)
Micron Rating25 Microns25 Microns
Chlorine Removal Capacity70,000 gallons @ 4 gpmUnknown
Chloramine Removal CapacityUnknown

10,000 gallons @ 5 gpm

25,000 gallons @ 2.5 gpm

Pressure Drop

0.9 psi @ 4 gpm

2 psi@ 7 gpm

4 psi @ 11 gpm

1 psi @ 2.5 gpm

2.5 psi @ 5 gpm

5 psi @ 7 gpm

Current Retail Price$95.00$168.00


Reducing the flow rate more than doubles the lifespan of the chloramine cartridge. While this ratio doesn’t apply everywhere, as a general rule cutting the flow rate through the filter significantly adds to its life expectancy, adds to its efficiency, and reduces pressure drop. Therefore, running two filters in parallel more than doubles the valve of a single filter. In many cases using multiple filters actually costs less than using one, plus you get lower pressure drop.


 Split installation: each filter gets half the flow rate. Efficiency goes up, pressure drop goes down, and cost goes down.

With a flow rate of 5 gpm, one filter treats 10,000 gallons with a pressure drop of 2.5 psi, but two filters treat 50,000 gallons with a pressure drop of 1 psi. What’s more, operation cost is 1.6 cents per gallon for one filter and 0.66 cents for two.

Flow rate matters!

Common Problems Of Ultrafiltration System Operations

By Nick Nicholas

Gazette Introductory Note: This article is being reprinted because it presents a concise, easy-to-understand explanation of the ultrafiltration process. It concerns use of UF for wastewater treatment, but the problems it raises–membrane fouling and scaling, waste stream disposal, etc.–apply as well to residential applications. We (Pure Water Products) do not currently offer residential ultrafiltration units for the whole home partly because the issues detailed in the article should be addressed by professionals rather than home owners, our main customers. –Gene Franks.

One facet of technological advancement is attempting to mitigate the more glaring issues that consistently crop up due to the nature of a system process. Of course, even with decades of improvement nothing is infallible. In this article, we will discuss the common issues that can occur using UF filtration systems.

Ultrafiltration is a pressure driven membrane separation technology that is a compact and refined filtration method utilized in drinking water and tertiary wastewater reuse applications. Its semipermeable membrane can remove solids as small as 0.01 microns, including silt and viruses. However, membrane filtration technologies will have problems without proper care for appropriate pretreatment, operation, and maintenance.

UF filter systems are typically affected by three main issues:

Membrane Fouling

UF filtration, like any other membrane separation technology including reverse osmosis, is susceptible to what is known as membrane fouling. In simple terms, fouling is what happens when particulate matter adheres to the surface of a membrane. The unchecked buildup will eventually cause reduced efficiency, a pressure drop, and increased energy consumption.

There are a few different types of fouling that can occur. Each has its own cause as well as some differences in effects. Of these membrane foulants, some are reversible and others are irreversible.


Suspended solids and colloidal particles collect on the surface of the ultrafiltration membrane as well as within its pores, preventing the flow of water through the membrane. This fouling occurs more commonly in applications with high turbidity and suspended solids without appropriate pretreatment.


Membrane scaling is not unlike what happens in pipes that carry water with high concentrations of hardness materials. When the concentration of these dissolved minerals is high enough to surpass the saturation limit of the solvent solution, they begin to precipitate out of solution onto the surface of the membrane. These minerals can crystalize, which makes them nearly impossible to remove without some sort of chemical cleaning or antiscalant pretreatment. Calcium and magnesium are two primary minerals that can cause scaling to occur on the UF filter system’s membranes.


Biological contaminants like algae and microorganisms are often found in surface water sources. Provided with a warm environment and low flow rates, these contaminants will attach themselves to the surface of a membrane and begin multiplying. Over time, they can form a film that will prevent water from passing through the membrane and cause an increase in the trans membrane pressure differential. This increased pressure differential will put more strain on the pumps and increase the amount of energy they draw.

Waste Stream Disposal

This relates to the UF filter concentrate discharge. The filtration system did what it’s supposed to do and you have clean water that you can safely discharge into an outdoor stream without having to pay any environmental regulation fines. Or maybe you are going to reuse it somehow. Regardless of what is going to happen to it, you have this water resource.

However, what about all that contaminants that were removed? Sadly, this concentrate stream didn’t disappear into thin air, never to be dealt with again. Nope. It’s still there, whether it’s stuck to the membrane or sitting in a concentrate waste tank, and something needs to be done about it.

The problem is, you can’t just toss it out the window and call it a day. This reject wastewater is a concentrated form of whatever was in the feedwater. Therefore, in some cases, it may be safe enough to discharge into the environment; however, in others, the facility would be charged a hefty fine if it contains harmful pollutants.

Increased Permeate Contamination

This point is pretty rare for systems that are well maintained and monitored. To reiterate, permeate refers to the water that has been separated from the contaminating solids. It’s the clean water that you get out of this filtration process. Therefore, it’s definitely an issue when you start noticing that the quality of your permeate water is getting worse. Either there are larger solids or bacteria that should have been retained by the membrane contaminating the water.

This decrease in removal efficiency is usually indicative of a compromised membrane. Polymeric membranes can get worn out over time. High temperature or pH levels can degrade them pretty quickly, and without a decent pretreatment regime, rough particles can damage the inner pores of the membrane. To state the obvious, membranes do not work very well if they are full of additional holes (other than their pores of course). And now the system isn’t meeting it’s designed specifications and you have to replace the membrane and recirculate the contaminated permeate.

Source: Water Online.

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