Links to Products for City Water Treatment

Products that Deal with Water Hardness


The pages below contain information about the three leading types of hardness treatment for city water.


Conventional Water Softeners

TAC, Template Assisted Crystallization. (ScaleNet, also known as OneFlow)




Whole House Filtration Units

Compact Whole House Filters (Cartridge Style).  Multi-Filter Versions of Compact Whole House Filters.  (See links to other items in this series at the bottom of the article.)

Tank Style Backwashing Filters for Chlorine or Chloramines (See Carbon and Catalytic Carbon units.)

Drinking Water Units

Reverse Osmosis Units  (Black and White)

Simple Undersink Filters — No faucet needed. Filtered water is dispensed through cold water side of the standard sink faucet.

Undersink Filters  (Black and White Series)  — Filters with their own faucet for filtered water.


More information?  Please call 888 382 3814.




Putting Ourselves in Our Place: What If We All Sat in the Ocean at Once?

Editor’s Note:  Probably this is something you’ve wondered about. If everyone on earth decided to go swimming in the ocean at the same time, would there be room for all of us? And would the water spill out of the world’s oceans causing devastating flooding?  To put our minds at ease, here’s the answer from the Curious Kids section of at The Conversation website. 

You can think about the oceans as a gigantic bathtub. More than 70% of the Earth’s surface is ocean, giving this bathtub an area of about 140 million square miles. To figure out how much the water will rise, we need to know the volume of people sitting in it and divide it by this ocean area.

Currently, there are almost 8 billion people on Earth. Human beings come in all sizes, from tiny babies to large adults. Let’s assume the average size is 5 feet tall – a bit bigger than a child – with an average volume of 10 cubic feet. Only half of each person’s body would be submerged when they sit down, so only 5 cubic feet adds to the water level. With 8 billion people total, you can calculate 5 x 8 billion which gives a whopping 40 billion cubic feet that would be added to the oceans.

But remember, this volume would be spread over the vast area of the oceans. Using the same bathtub math as before, we divide the 40 billion cubic feet of volume over the 140 million square miles of ocean.

The answer? The total rise in sea level would be about 0.00012 of an inch, or less than 1/1000th of an inch. If everyone completely submerged themselves, this would double the answer to 0.00024 inches, which is still only about the width of a human hair.

It turns out the oceans are enormous – and humans are just a drop in the bucket.

Source: The Conversation.

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We All Do It, But Is It Actually Safe to Reuse Plastic Water Bottles?

by Eva Hamrud, Metafact

21 MARCH 2021


Every minute about 1 million plastic drinking bottles are purchased, creating huge amounts of waste, which mostly ends up in landfills. Today, many people reuse their water bottles by refilling them. This avoids having to repeatedly buy new bottles, saving money, and reducing the amount of plastic waste.However, these bottles are designed to only be used once, so some people are concerned about where it is actually safe to reuse them. We asked eight experts ‘Is it safe to reuse plastic water bottles?’ and the consensus was 75 percent ‘likely’.What are water bottles made of?Plastic water bottles vary in their material, but most single-use bottles are made of PET – polyethylene terephthalate. PET is a clear, lightweight plastic used for packaging of many foods and drinks.It is approved as safe for contact with food and drink in many parts of the world, including the USA and European Union.


Can leaching chemicals from the plastic give you cancer?

Many online articles claim that reusing water bottles can lead to cancer due to certain chemicals being released from the plastic.One chemical that many people are concerned about is BPA, bisphenol A. BPA may disrupt the endocrine system, potentially causing issues related to reproduction and metabolism. BPA is not used to make PET bottles but can be found in other, more rigid plastics like polycarbonate. Despite this, one study has found very low concentrations (5 ng/L) of BPA in PET-bottled water. Two other studies did not find this chemical, so this finding is inconclusive. A different chemical, antimony, is used as a catalyst for PET production. Antimony is not considered a carcinogen when ingested but can cause vomiting and diarrhea.A 2008 study tested the levels of leached antimony in commercially available bottled waters. They did find that leaching occurred gradually over time, but the amounts were much lower than what is considered dangerous. The concentration at which antimony becomes dangerous is around 6 ppb (parts per billion). The study found that antimony concentrations started at 0.195 ppb and rose to 0.226 ppb after three months at 22 degrees Celsius (71 °F).Antimony is not the only chemical that has been studied in bottled water, a whole range of chemicals from plasticizers to metals have been researched. These studies have found that there are some chemicals, like antimony, that leach into bottled water. As of yet, there is no evidence that these pose a risk to human health.


Is leaving your water bottle in the Sun safe?

There are some concerns that the chemical leaching described above happens more frequently at higher temperatures, meaning that leaving your water bottle in the car on a hot day could be dangerous. The 2008 study on antimony levels did indeed find increased leaching at higher temperatures. When water bottles were left at 60 °C (140 °F) it took them 176 days to rise above the threshold of 6 ppb, whilst at 80 °C this only took 1.3 days. These temperatures are very high, so this is likely to only be a problem if you live in a very hot place and regularly leave your water bottle in the Sun to heat up.


What about microplastics?

Microplastics are small pieces of plastic. They are found almost everywhere, including in our drinking water. In fact, a study found that 93 percent of freshly opened plastic water bottles contained some microplastic contamination. The WHO looked into the potential dangers of microplastics, but based on current data they have concluded that they do not pose a significant threat to human health. Interestingly, Dr Umar Abdulmutalib from the University of Surrey says, “Newly released plastic bottles might contain more microplastics compared to the used ones”. Dr Marek Cuhra from the Institute of Marine Research in Norway also thinks that “drinking water out of a used and washed bottle should be safer than a brand-new bottle”. His group found that water fleas grew and reproduced better in plastic tubes that had been washed with warm water than in new plastic containers.


Are there any other risks?

There is one widely-accepted risk of reusing a disposable plastic water bottle, but this is not chemicals – it’s contamination. As these bottles are not made for durability, they can get easily damaged and crack. Dr Jill Bartolotta says, “The plastic used to make bottles is very thin and consequently subject to cracking due to a weaker structure. These cracks can harbor bacteria.” Contamination is particularly likely if the inside of the bottle is damp. Bacteria can grow very fast in bottled water, one study found an increase from 1 colony per ml to 38,000 colonies per ml in 48 hours when the bottle was kept at 37 °C.


The takeaway:

Of the eight experts, six answered that it is likely that it is safe to reuse plastic water bottles. Studies of chemical leaching and microplastics have found that these occur at very low levels and are unlikely to pose serious health threats, unless bottles are repeatedly exposed to very high temperatures. The more likely risk is that of contamination, so if you do reuse a water bottle – remember to wash it regularly.

Reprinted from Science Alert.

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Converting your Black and White Countertop RO Unit (Style A) to a Standard 3-stage Black and White Reverse Osmosis Unit


The Finished Product


These instructions apply only to Pure Water Products’ standard style A Countertop Reverse Osmosis Unit.  The parts and instructions do not apply to other products.


In addition to the Black and White Style A RO Unit,  here’s what you’ll need:

Our Conversion Kit.  Part Number RP105.  The Kit costs $175 and includes everything you will need.

1  ta005 Storage Tank.

1 jg011 1/4″ tee.

1  jg014 Tank Valve.

1  rc300 Auto Shutoff Valve.

1  rc200 ASO-Membrane Clip

2  rc001 JG Check Valves

1  rc100 Drain Saddle Kit

1  iv100 or iv103 Inlet Kit

1  lf700 Pro-Flo Faucet

5  tb001 Five feet of 1/4″ tubing.



Here’s how you do it

Converting your Black and White Countertop RO to Undersink


1. Install the faucet and inlet kits. When conversion is complete and you install the unit, you will plug the inlet tube into the black (left) housing and the faucet tube into the right (white).

2. Mount the shutoff valve in its clip on top of the RO membrane with the IN/OUT side of the valve facing the capped end of the membrane housing (the end that has only one tube).

3. Remove the tube from the fitting on the membrane cap and install it into the IN port of the shutoff valve.  Run a new tube from the OUT port to the recently vacated fitting in the membrane housing cap.

4. On the other end of the membrane, remove the tube from the Permeate fitting (the one that isn’t the drain) and replace it with a short tube that connects it to the nearest TANK port of the shutoff valve.  Insert a check valve into the new tube between the membrane and the shutoff valve with the arrow pointing toward the shutoff valve.

5. Loop the tube you removed from the Permeate port of the membrane back and insert it into the remaining empty port of the shutoff valve.  (The other end remains connected to the back port of the white postfilter housing.)  At any convenient place in this tube, insert the tee to connect the tank to the unit.

6. Install the shutoff valve onto the top of the storage tank, then use a single tube to connect the tank valve to the tee that you installed in step 5.

7. Install the drain saddle following instructions in the kit and connect the existing RO drain tube to the fitting in the drain saddle.  Install the remaining check valve between the drain line flow restrictor and the drain saddle with the arrow pointing toward the drain saddle.

Refer to the picture at the top of this article as a model, and don’t hesitate to call or email us if you hit a snag.

Pure Water Products

888 382 3814





Boil Water Alerts

Posted February 19th, 2021

Boil Water Orders Are Increasing

What This Means to Residential Water Users

by Gene Franks


“Boil water” alerts are issued by water suppliers when the safety of the water they deliver is in question. The standard instruction is that water should be brought to a rolling boil for at least one minute (longer at higher altitudes) to kill waterborne pathogens.

Formerly, government agencies tracked boil water alerts in the US as public information, but as the number of alerts has increased dramatically in recent times record keeping is no longer done. In the absence of such information, Dr. Kelly Reynolds of the University of Arizona recently used a Google News search to identify boil water alerts across the US for a two-week period in August 2013. Dr. Reynolds found 29 alerts during the period.

Alerts are issued for a variety of reasons–bad weather, especially flooding, a break in a water main, low system pressure, finding of fecal coliform by testing, system leaks, system maintenance, detection of E. coli or cryptosporidium by routing testing, and general elevated bacteria counts—are the most common.

As pipes and pumps age, and as power outages and incidents of challenging weather become more frequent, it is certain that boil water alerts will become more common.

The boil water strategy for assuring micro-biologically safe water is at best a risky one. We have been conditioned to rely on the safety of our water systems to provide potable water, but this perception of safety is changing. Each time a pipe ruptures or pressure in the pipe goes down, microbes are drawn into the delivery system. A blanket “boil water” warning, even if given on time and received by all concerned, is a haphazard way to assure safety. Studies have shown that both reception of the alert and compliance with its recommendations are far below 100%.

It is certain that we have gone past the time of complete trust in the water delivery system to provide pathogen-free water. Just as more and more people are now relying on home treatment devices to provide chemical-free and more aesthetically pleasing water for drinking, cooking, and bathing, it is logical that “final barrier” devices to assure that water is free of bacteria, viruses and protozoa are becoming more common for city residents.

Fortunately, modern water treatment has developed many alternatives–from very tight filters for drinking water to whole house treatments like ultraviolet. These are certain to become prominent fixtures in US homes. As Dr. Reynolds says, “The inherent, unpredictable nature of the distribution system and the quality maintenance of the distributed water add credence to the need for routine POU [point of use] treatment.”

Reference: Water Conditioning and Purification, Sept., 2013.

Start-up of Katalox Light Backwashing Filter

The following instructions are adapted from the media manufacturer’s start-up instructions.

1. Open the new bag of Katalox-Light media and put into the pressure vessel.  (Use a standard softener funnel, and be sure to cover the top of the riser tube to keep Katalox from going into the tube.)

2. With water off, or the filter in bypass, put the control valve into “backwash” position. Fill up the pressure vessel slowly with fresh water from bottom to the top with the control valve in backwash mode.  (The control valve can be unplugged to keep it in backwash as long as needed.)

3. Turn on the water completely and backwash the media for a minimum of 20 minutes.

4. After the backwash is complete perform a rapid rinse for for at least 5 minutes.

PFAS and Covid-19

Posted January 8th, 2021

PFAS exposure linked with worse COVID-19 outcomes

People who had elevated blood levels of a toxic chemical called perfluorobutanoic acid (PFBA) had an increased risk of a more severe course of COVID-19 than those who did not have elevated levels, according to a new study led by Harvard T.H. Chan School of Public Health. PFBA is part of a class of man-made chemicals known as perfluorinated alkylate substances (PFASs), which have previously been shown to suppress immune function.

The study, published December 31, 2020 in PLOS ONE, was led by Philippe Grandjean, adjunct professor of environmental health.

PFASs have water- and grease-resistant properties and are used in a wide variety of products, including nonstick cookware, waterproof clothing, food packaging, and firefighting foams. PFBA, more than other PFASs, is known to accumulate in the lungs, according to the study.

Researchers looked at PFAS levels in blood samples from 323 Danish individuals infected with the coronavirus. They found that those with higher PFBA levels had higher odds of being hospitalized, winding up in intensive care, and dying than those with lower levels.

The findings suggest that further study is needed to determine whether elevated exposures to other environmental immunotoxicants may worsen COVID-19 outcomes, the authors wrote.

Harvard School of Public Health

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The New Showerhead Standards

Posted December 18th, 2020

In a last-minute rule change, the Trump administration rolls back water-saving standards for showerheads

by Robert Glennon, University of Arizona

Gazette’s Introductory Note: The EPA’s showerhead standard, adopted several years ago as one facet of its WaterSense program, saves an estimated 2900 gallons of water per year per shower head. Dumping the standard for no apparent reason other than the perceived personal convenience of a single selfish individual is merely one of the scores of bizarre events of 2020. The article below will acquaint you with some of the ins and outs of the showerhead rule.

For more than 25 years, Congress has directed U.S. government agencies to set energy and water efficiency standards for many new products. These measures conserve resources and save consumers a lot of money. Until recently, they had bipartisan support.

But President Trump has turned efficiency standards into symbols of intrusive government. His administration has opposed many of these rules, including standards for light bulbs, commercial boilers, portable air conditioners and low-flow toilets. His latest target: showerheads.

The Energy Policy Act of 1992, passed by a Democratic Congress and signed by Republican President George H.W. Bush, set the maximum flow rate for showers at 2.5 gallons per minute. Now the Trump administration has increased that rate, which Trump calls inadequate to wash his “beautiful hair.”

It may sound funny, but it’s not. As someone who writes and teaches about water law and policy, I know that the U.S. water supply is finite and exhaustible. Most Americans take water for granted, but as population growth and climate change exacerbate water shortages, experts increasingly argue that water policy should promote conservation.

When is a showerhead not a showerhead?

On Aug. 13, 2020, the Department of Energy’s Office of Energy Efficiency and Renewable Energy issued a Notice of Proposed Rulemaking to amend the existing standard for showerheads. The document’s definition of showerheads exemplified the byzantine logic behind this policy shift.

For example, it provided three images of fixtures with between three and eight heads attached to a single pipe coming out of the wall. So long as none of the individual heads had a flow greater than 2.5 gallons per minute, the measure asserted that each fixture satisfied Congress’ quest for water and energy.showerheadsshowerheads



showerheads showerheads


How can the Energy Department allow shower fixtures with as many as eight heads, each emitting 2.5 gallons per minute? For context, Webster’s dictionary defines a showerhead as a “fixture for directing the spray of water in a bathroom shower.”

But the Trump rule interpreted “showerhead” to mean “an accessory to a supply fitting for spraying water onto a bather.” With this sleight of hand, a congressional rule limiting showerhead flows can be deftly avoided by installing a hydra-headed fixture with multiple “showerheads,” each flowing at 2.5 gallons per minute.


The agency also released a fourth image of a wall fixture with seven nozzles, which the new rule would not subject to the 2.5 gallons per minute maximum. The Energy Department deemed these fixtures a “body spray” rather than a showerhead because they are “usually located” below the bather’s head. (Of course, the person showering may be short, or the plumber may install the fixture high on the shower wall.) Body sprays may have six or eight nozzles with no flow limits.

The sad part of this foolishness is that the Environmental Protection Agency’s WaterSense program, which identifies water-efficient projects and promotes water conservation, has been spectacularly successful, at virtually no cost to consumers or the regulated community. Showers constitute 17% of residential water use. That’s 40 gallons per day for the average family, or 1.2 trillion gallons annually in the United States.

WaterSense fixtures and appliances have saved Americans more than 4.4 trillion gallons of water and US$87 billion in water and energy expenses since the program began in 2006. Low-water-use fixtures – including showerheads, toilets and washing machines – are now the accepted norm across the United States.

Some early products, such as the first high-efficiency toilets, had some hiccups. But that was 20 years ago. Today, notwithstanding President Trump’s declaration that “people are flushing toilets 10 times, 15 times, as opposed to once,” consumers embrace low water-use fixtures because they work well, save money and reduce water and energy consumption.

Tapped out

Today the United States faces serious water problems. Georgia and Florida are fighting a prolonged battle over flows in the Apalachicola River, which the two states share. Excessive groundwater pumping is causing water levels in wells to plummet and springs to dry up. As I explain in my book, “Unquenchable: America’s Water Crisis and What To Do About It,” farmers are competing with cities for water.

COVID-19 has helped to make the affordability of water a national issue. Some rural areas, such as the Navajo Nation, where many people need to haul water to their homes and villages, have higher rates of coronavirus infection. People who have lost their jobs find themselves unable to pay their water bills, which in turn compromises the financial stability of water providers.

Allowing showers to use more water will have several unfortunate consequences for cities across the country. It will increase the amount of water cities must treat; raise the chances of raw sewage overflows at water treatment plants – especially in cities such as Washington, D.C. that combine storm and sewer water; and increase the amount of energy used to pump and treat water.

Disrupting low-flow fixture rules will create special hardships for western cities, such as Los Angeles and Las Vegas, that have struggled with water shortages for decades. Both cities remarkably reduced their total water use between the 1980s and 2020, despite rapid population growth, partly by converting residences to low water-use fixtures.

Water is not just another natural resource. Without it our bodies cease to function, our crops dry up, and our economy grinds to a halt. We can’t make any more water, so it makes sense to use the water we have wisely.


Reprinted from The Conversation.

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Common pipe alloy can form cancer-causing chemical in drinking water

Water disinfectant reacts with chromium in iron pipes to form hexavalent chromium

by Holly Ober


The rusted interior of this water pipe contains chromium that reacts with residual water disinfectants to form carcinogenic hexavalent chromium.


Rusted iron pipes can react with residual disinfectants in drinking water distribution systems to produce carcinogenic hexavalent chromium in drinking water, reports a study by engineers at UC Riverside.

Chromium is a metal that occurs naturally in the soil and groundwater. Trace amounts of trivalent chromium eventually appear in the drinking water and food supply and are thought to have neutral effects on health. Chromium is often added to iron to make it more resistant to corrosion.

Certain chemical reactions can change chromium atoms into a hexavalent form that creates cancer-causing genetic mutations in cells. This carcinogenic form of chromium was at the heart of a lawsuit in California’s Central Valley by Erin Brockovich, which became the subject of an Oscar-winning movie.

Haizhou Liu, a professor of chemical and environmental engineering at the Marlan and Rosemary Bourns College of Engineering who studies water treatment chemistry, had an inkling that some of the chromium found in drinking water might come from chemical reactions between water disinfectants and the chromium in cast iron corrosion scales.

Along with doctoral student Cheng Tan and postdoctoral scholar Sumant Avasarala, Liu obtained segments of two pipes that had been in service for about five and 70 years respectively and induced corrosion on portions. After scraping the rust off, grinding it to a powder, and measuring the amount and types of chromium present, the researchers put the samples in hypochlorous acid, the form of chlorine typically used in municipal drinking water treatment plants and drinking water distribution systems.

Previous experiments had shown that water disinfectants could transform trivalent chromium into toxic hexavalent chromium, but the group was surprised when zerovalent chromium that was detected in the rusted iron pipes transformed more quickly to the toxic form. They followed up with modeling experiments that showed a range of possibilities for how much hexavalent chromium could come out of the tap under real-world conditions. The worst-case scenario occurred in drinking water with high bromide levels.

“These new findings change our traditional wisdom on hexavalent chromium control in drinking water and shine light on the importance of managing the drinking water distribution infrastructure to control toxic substances in tap water,” Liu said.

The paper cautions that as the world’s water crisis intensifies, recycled and desalinated water— both of which tend to contain higher bromide levels—will become more important, highlighting the need to understand and prevent chromium contamination. The paper recommends reduced use of pipes with high levels of chromium alloy and use of a disinfectant less reactive with chromium, such as monochloramine.

The work was supported by a National Science Foundation CAREER Program grant. The paper, “Hexavalent Chromium Release in Drinking Water Distribution Systems: New Insights into Zerovalent Chromium in Iron Corrosion Scales,” is published in Environmental Science and Technology.

Source: UC Riverside News

Gazette note on hexavalent chromium treatment for residential users:  Hexavalent chromium is a drinking water issue. There is little if any dermal uptake during bathing or otherwise using the water. See Systemic uptake of chromium in human volunteers following dermal contact with hexavalent chromium, published by the National Library of Medicine. Sensible home treatment is to treat drinking water with an undersink reverse osmosis unit, which removes hexavalent chromium handily, and to not worry about whole house treatment.

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What Is Activated Carbon?

Editor’s Note: The article below is from TIGG, a company that specializes in manufacturing equipment that uses granular activated carbon (GAC) as filtration media for water purification, environmental remediation, industrial processing and municipal water treatment applications. We’re including it in its entirety as an excellent reference source for the understanding of granular activated carbon and how it works. You’ll find a good discussion of topics like impregnated carbons, reactivation (recycling) of carbon, pH, ash content, carbon hardness, particle size (sieves and Tyler Screen), apparent density, raw materials used, pore structure, activity level, adsorption, chemisorption, and much more.

Carbon Fill

Although the term granular activated carbon is used generically, it can refer to dozens of similar – but not identical- adsorbents. Depending on raw material, method and degree of activation and other factors, activated carbons can perform differently in various applications.

What is Activated Carbon?

Granular Activated Carbons are a very versatile group of adsorbents, with capability for selectively adsorbing thousands of organic, and certain in- organic, materials. From medicinal uses of powdered carbons in ancient Egypt, through charred interiors of whiskey barrels, carbon has been activated and used as an adsorbent for centuries. Granular vapor phase activated carbon media was first widely used in WWI military gas masks and, in the years between World Wars, commercially in solvent recovery systems.

Granular liquid phase activated carbons achieved their first prominent applications following WWI’, in sugar de-colorization and in purification of antibiotics. Today, there are hundreds of applications — if diverse uses under the general heading of environmental control are counted separately, ongoing applications number in the thousands.

Adsorption/Adsorbents/Granular Activated Carbon

Since adsorption is a comparatively specialized technology, a capsule definition of terms may be helpful. Adsorption is a surface phenomenon, in which molecules of adsorbate are attracted and held to the surface of an adsorbent until an equilibrium is reached between adsorbed molecules and those still freely distributed in the carrying gas or liquid. While the atoms within the structure of the adsorbent are attracted in all directions relatively equally, the atoms at the surface exhibit an imbalanced attractive force which the adsorbate molecules help to satisfy. Adsorption can then be understood to occur at any surface, such as window glass or a table top. The characteristic which typifies an adsorbent is the presence of a great amount of surface area; normally via the wall area or slots, capillaries or pores permeating its structure, in a very small volume and unit weight.

The type of adsorption which is dependent primarily on surface attraction, in which factors such as system temperature, pressure, or impurity concentration may shift the adsorption equilibrium, is given the further classification of physical adsorption. The electronic forces (Van der Waal’s forces) responsible for adsorption are related to those which cause like molecules to bind together, producing the phenomena of condensation and surface tension. Conceptually, some prefer the analogy of physical adsorption being like iron particles attracted to, and held by, a magnet. Physical adsorption is the most commonly applied type, but an important sub-classification is chemisorption. Chemisorption refers to a chemical reaction between the adsorbate and the adsorbent , or often reaction with a reagent which may be impregnated on the extensive adsorbent surface (see Impregnated Carbons, below). Thus physical adsorption/desorption retains the chemical nature of the adsorbate, while chemisorption alters it.

The surface phenomenon of adsorption may now be contrasted with apsorption, in which one material intermingles with the physical structure of the other; for example, phenol dissolving into fibers of cellulose acetate (absorption) versus being adhered by surface attraction to the outer layer of the fibers (adsorption).

Granular Activated Carbon (activated charcoal) is an adsorbent derived from carbonaceous raw material, in which thermal or chemical means have been used to remove most of the volatile non-carbon constituents and a portion of the original carbon content, yielding a structure with high surface area. The resulting carbon structure may be a relatively regular network of carbon atoms derived from the cellular arrangement of the raw material, or it may be an irregular mass of crystallite platelets, but in either event the structure will be laced with openings to appear, under electron micrographic magnification, as a sponge like structure. The carbon surface is characteristically non-polar, that is, it is essentially electrically neutral. This non-polarity gives the activated carbon surface high affinity for comparatively non-polar adsorbates, including most organics. As an adsorbent, activated carbon is this respect contrasts with polar desiccating adsorbents such as silica gel and activated alumina. Granular Activated carbon will show limited affinity for water via capillary condensation, but not the surface attraction for water of a desiccant.

Activity Level

Activity level is often expressed as total surface area per unit weight, usually in square meters per gram. This total exposed surface will typically be in the range of 600-1200 m2/g. Toward the higher end of this range, one might better visualize one pound, about a quart in volume, of granular activated carbon with a total surface area of 125 acres.

To be useful in adsorption, surface area must be present in openings large enough to admit the adsorbate molecule(s). To provide some guidance on this topic, and for quality control purposes, the carbon industry has developed additional standardized vapor and liquid adsorption tests, using adsorbates of varying molecular size and chemical nature such as iodine, phenol, methylene blue, carbon tetrachloride, benzene and the color in standard black strap molasses. However activity level is measured, it is most meaningful when considered with additional characteristics described in the following sections.

Pore Structure

While openings into the carbon structure may be of various shapes, the term “pore,” implying a cylindrical opening, is widely used. A description of the minute distances between walls of these pores, normally expressed as a function of the total surface area or total pore volume presented by pores of various “diameters,” is the pore structure curve. The following sketches show some sample pore structure curves and what approximate pore shapes are described by the curves. Please note that the average pore shape depicted is derived from a summation of pores of various sizes and shapes. Thus no pore within the activated carbon is likely to have precisely the average shape, but the granular activated carbon overall will often perform as if all its surface area were in pores of that shape.

The smallest diameter pores make up the micropore structure, and are the highest adsorption energy sites. Microporosity is helpful in adsorbing lower molecular weight, lower boiling point organic vapors, as well as in removing trace organics in water to non-detectable levels. Larger pore openings make up the macroporosity, which is useful in adsorbing very large molecules and aggregates of molecules, such as “color bodies” in raw sugar solutions. Another important function of the macropore structure is in assisting diffusion of fluids to adsorption sites in the interior of the carbon particle.

Given the above, pore structure. (1) would be effective in adsorbing high volatility solvents, for certain types of odor control, and in removing trace organics from water; the latter with the liability of marginal diffusion characteristics. Pore structures along the lines of. (2) offer a good balance of selectivity for molecules of various sizes, ability to reduce vaporous and liquid contamination to ultra low levels, and good diffusion characteristics. Structure (3) would allow excellent diffusion and can accommodate very large molecular sizes, but has little micro- pore structure and would have very poor retentivity for most organics.

Raw Material

Granular activated carbon can be produced from various carbonaceous raw materials, each of which will impart typical qualities to the finished product. Commercial grades are normally prepared from coconut and other nut shells, bituminous and lignite coals, petroleum coke, and sawdust, bark and Other wood products. In general, nut shells and petroleum cokes will produce very hard carbons with a pore structure characterized by.(1) above, coals a (2) type structure in comparatively hard carbons, and wood (3) structure in carbons lacking great crush and abrasion resistance. It should be emphasized that specific production techniques may yield carbons that depart from the norm of a given raw material.

Apparent Density

The solid, or skeletal, density of most activated carbons will range between 2.0-2.1 g/cc, or about 125-130 lbs/cubic foot. However, this would describe a material with essentially no surface area and no adsorptive capacity. For GAC, a much more practical density is the apparent density (A.D.), or mass of a given volume of adsorbent particles. This density will be significantly lower than the solid density, due to the presence of pores within particles, and void space between particles. In most commercial GACs, the A.D. variation is between 0.4- 0.5 g/cc, or between 25-31 lbs/cubic foot.

Since granular activated carbons are used in adsorbers of fixed volume, apparent density values can be used to calculate volume activity, which may help determine the work capacity of an adsorber with alternative carbon loadings. For example, assume that carbon A adsorbs iodine to produce a standardized Iodine Number of 1100 mg/g., and has an A.D. of 0.4 g/cc Carbon B has an Iodine Number of 950 mg/g and an A.D. of 0.5 g/cc. Multiplying the A.D. by the weight basis activity value, carbon A has a volume iodine capacity of 440 mg/cc while carbon B has a value of 475 mg/cc. Therefore, carbon B, which has lower activity, might actually do more work and therefore have a longer service life than carbon A of an equal volume. If the price of carbon B permitted filling a given adsorber with the greater weight required, it could thus be the most economical of these adsorbents on a net cost basis.

Since standard activity tests are run with oven dried carbon, it will be immediately apparent why high A.D. values that reflect added moisture will not produce the benefit illustrated above. Similarly, high densities due to significantly low activity levels, or ash or inactive char residue from reactivation, or any non-carbon adulterants will not normally benefit service life nor the adsorbent’s capability to produce highly purified fluids.

Particle Size

The size of most granular activated carbons is given by the U.S. Sieve range that will include the majority of the particles in a distribution of sizes. Typically the range will cover 85-95% of the total product, with a few percent slightly larger and smaller sizes permitted by specification. A similar approach is occasionally used with Tyler Screen or other screen sizes. Pelletized carbon, although not truly granular, often is described by the sieve range method, or by diameter of the pellets.

Common vapor phase U.S. Sieve size ranges are 4×6, 4×8, 4×1 0, 6×16 and 12×30. Liquid phase granular activated carbons are usually somewhat smaller, with 8×30, 12×20, 12×40 and 20×50 being common. Detailed sieve descriptions are found in engineering handbooks, so only a few representative sizes are given here:

Since impurity removal requires the diffusion of adsorbate into the intra particle structure, the rate of adsorption will increase as the particle size decreases. As fluid flows through an adsorber, increased rate of adsorption will require less adsorbent bed depth and contact time for the region in which the adsorbate is being removed. This functional adsorption region is termed the adsorption wave front or ~ transfer zone. However, with any given fluid, decreasing particle size carries the liability of increasing flow resistance or pressure drop. In practice, particle sizes are selected to produce a reasonable balance between the competitive benefits of rapid rate of adsorption and effective removal, versus the liabilities of increased flow resistance and attendant higher pumping costs.


Hardness and abrasion resistance are generally beneficial in all granular activated carbons, although their operational usefulness can vary greatly. Within common adsorber designs and operating ranges, all commercial granular activated carbons can withstand their own weight and the pressure effects induced by fluid flow. Thus in systems in which the granular activated carbons will be used once or handled very infrequently, hardness characteristics may be of little or no import. Conversely, if the carbon will be subject to frequent handling for a regeneration step, is subjected to thermal excursions by regeneration in place, or must resist excessive vibration, hardness may become quite important. For example, fines (dust) from handling a soft carbon in a system using thermal reactivation may double or treble the losses in the reactivation furnace itself. In solvent recovery systems using steaming cycles for regeneration, carbons that fracture easily can frequently raise pressure drop enough to require that the adsorbent be re-screened and replenished, or replaced.

In evaluating hardness numbers, it should be remembered that the granular activated carbons hardness test has no relation to the hardness scales used for plastics, metals or minerals. A carbon, of 98 hardness, is appreciably harder than one of 80, but even harder materials such as diamond, steel and copper, even though they differ in actual hardness, will all report as 100 on the basis of the granular activated carbons hardness test.


If part of the carbon raw material, ash generally varies between 2-20 weight percent in commercial granular activated carbons. A portion of total ash may be water-soluble, normally a greater amount acid soluble, and the remainder deeper within the skeletal structure of the carbon to be effectively insoluble. Ash from wood and nut shell carbons tends to be rich in alkaline metals, while that from coal largely oxides of aluminum, silicon and iron. For the limited instances in which traces of soluble or reactive ash are objectionable, granular activated carbons pre-washed with water or acids are available, or grades based on certain raw materials may minimize the total ash level or particular ash components.

Natural ash is normally not detrimental to the adsorption process, and standard activity tests report granular activated carbons efficiency including the weight of the ash. However, in certain regenerated granular activated carbons, ash that is a residue of previous uses may block some or all of the micropore structure that is vital for removing organics to ultra low levels. Similarly, if ash is due to previous impregnation for another use, or due to any other adulterant, the carbon performance may be seriously compromised.


Water extracts of activated carbons are used for reporting pH. Untreated coal base carbons are typically close to neutrality, while nutshell and wood carbons are more alkaline. Most untreated GACs vary between pH 6-10, but added acids or alkalis may further extend this range.

In purifying water and aqueous solutions, the pH of the granular activated carbons should be contrasted with the preferred pH of the solution. Most organics are best adsorbed from slightly acid, pH 5-7, solution. However, the beginning pH of the GAC will not influence the pH of the treated solution very long (although adsorbates being removed may alter solution pH).

Impregnated Carbons

High surface area per unit weight or volume can make granular activated carbon an effective substrate for dispensing other materials in a manageable form. Impregnants may be catalysts, or they might be reactive chemicals added to improve the rate of adsorption, selectivity, or capacity for certain adsorbates. Examples of the latter would include carbons with a faster rate of removal for hydrogen sulfide and other acid gases, some with capability to remove ammonia and lighter amines, and some with enhanced capacity for reduction of mercury vapor. Impregnated carbons usually retain 75% or more of the physical adsorption capability of the base carbon, so they are often used for combined physical adsorption and chemisorption. Whether an impregnated granular activated carbon will be cost effective frequently depends on whether a particular adsorbate is the only, or primary, removal candidate.


As explained earlier, carbon activation is frequently carried out in high temperature furnaces, under mildly oxidizing conditions. As the name implies, reactivation refers to using a similar process to volatilize and oxidize the adsorbates on spent carbons. The term reactivation might be contrasted with re-Qeneration, which refers to steaming or other methods to restore a portion of the GAC adsorptive capacity, al- though the terms are commonly interchanged. Reactivation will almost always produce measurable changes in pore structure, due to additional oxidative sculpturing of the carbon surface and, frequently, deposits of residual chars or inorganic materials. In a few cases, reactivated granular activated carbons perform better than or as well as the virgin material, but in many others there may be a defined loss of comparative efficiency or a gradually increasing loss of efficiency. When loss of efficiency is encountered, it is normally most pronounced in the micropore structure, therefore it is most significant operationally when the last traces of contamination must be removed.

Dedicated reactivation, in which a granular activated carbon will be segregated and returned to the same use, tends to be more predictable than employing a reactivated GAC from a different previous use, or a mixture of reactivated granular activated carbons from a variety of previous uses. However, dedicated re- activation is impractical for spent GAC quantities under several tons. The cost effectiveness of reactivated versus virgin carbons can be understood to vary with the performance requirements, the comparative volume service life, and the volume cost of the material (cost per unit weight may be misleading, as reactivated carbons frequently have higher apparent densities). Given the possible variations in reactivated carbons, it will also be understood that a reputable supplier should always specify if virgin or reactivated GAC is being offered.

Quality Assurance

Granular activated carbons quality and uniformity will fundamentally relate to characteristics involving: (1) adsorption capacity and (2) a physical description of the product. The activated carbon industry, often in cooperation with A.S.T.M. and other standards organizations, has developed a series of tests that measure these characteristics. As would be expected, such tests can be used both as production controls and, as published specifications, assurance for prospective buyers.

Not all granular activated carbons manufacturers and distributors publish adsorption specifications. Among those that adhere to specifications, the same precise group of tests may not be used. However, some correlation of values is usually possible as, for example, between the vapor phase carbon tetrachloride test used in the U.S. and the benzene and acetone tests more common in Europe and the Far East.

Among physical tests, the methods to determine moisture, apparent density and particle size or distribution are relatively standard among manufacturers. Hardness or abrasion values may require some interpretation or correlation, as above.

Terms such as “high quality; excellent adsorption characteristics; hard; dense; etc.” are inadequate substitutes for specifications. They offer no guidance for comparison, no assurance of quality, and no confidence of uniformity.

Predicting Performance

Many prospective granular activated carbon users will be considering applications that are unique to some extent. Perhaps the mix of impurities is unusual, or the system conditions or performance required may be new. The uncertainty of these situations has historically been resolved by testing. More recently, vapor and liquid computer-assisted correlative techniques have been developed for use when urgency, lack of test fluids, or costs make tests impractical; or to help establish test protocols that will yield the most useful information. A description of TIGG Corporation’s Adsorption Predictive Technique (APTTM) computer service is available on request.

Experimental granular activated carbons tests include adsorption isotherms and column tests. Isotherms are batch tests which require careful evaluation before eventual GAC performance in continuous adsorbers may be predicted. Column tests may vary from laboratory bench to pilot or semi- commercial scale. Sometimes results of such test are termed “treat-ability studies,” and many useful results have been published. Unfortunately, some published data do not describe the methodology or adsorbents used; others employ test methods or data interpretations that are suspect. Therefore the literature can be a risky basis for determining GAC efficiency, although tests performed and interpreted properly are quite dependable. Major GAC manufacturers, as well as firms such as TIGG Corporation which specialize in GAC equipment, can recommend test procedures and may have small scale adsorbers available.

A very important evaluation caveat is that different GACs have differing efficiencies for different applications. Thus a test, literature search or computer projection based on a particular GAC will not necessarily describe the performance to be anticipated from another GAC.


Readers will appreciate that, while not to be ignored, granular activated carbons price is rarely the leading factor in selecting an adsorbent. GACs of diverse efficiencies, qualities, sources and prices are in the marketplace. Price per pound or per cubic foot should be interpreted in terms of effectiveness. Cost effectiveness, in turn, may relate both to the GAC and the adsorber in which it will be applied, since even the optimum GAC will not overcome a deficient adsorber design. We hope that some of the commentary in this guide will assist in selection of the most cost effective adsorbent.


An overriding factor in outlining the proper granular activated carbons to use, and predicting expected results, is the clearest possible definition of the application. Eventual performance typically reflects the quality of information used for initial technical judgments, and selecting a GAC follows this truism.

Source: Newterra, Ltd.

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