2023 Tech Supplement

1300 Piccard Drive, Suite LL 14 • Rockville, MD 20850

Fall 2023

Use of IX and Iron Oxide Media for Selective Removal of Selenium, Heavy Metals, and Arsenic from Water and Waste Streams Electrochemical Destruction of PFOA and PFOS in High-Salinity Water Can a Micro-Adsorbent Material and Ceramic Filtration Treatment Successfully Remove PFAS? What Would Fail First if We Did Not Feed Treatment Chemicals to a Steam System?

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Cover Ion exchange treatment system for removing PFAS from drinking water at the Security (Colorado) Water District treatment plant.

Photo courtesy of Mike Henley, MD Henley & Associates

Fall 2023

Technical Supplement 2023

Table of Contents 4

Calendar of Events

5

Letter From the Editor

7

Supplement Introduction: Emerging Treatment Challenges and Water Business Opportunities

Heather Rigby, Managing Editor

Mike Henley, Technical Editor – the Analyst

10 Use of IX and Iron Oxide Media for Selective Removal of Selenium, Heavy Metals, and Arsenic from Water and Waste Streams Zhendong Liu, PhD; Wilson Nova Ruiz; and Firuza Mir, LANXESS Corp.

Kresimir Ljubetic, PhD; H.C. Lian, PhD; and David Kratochvil, PhD, BQE Water

Selenium, heavy metals, and arsenic are often contaminants of concern in wastewater from mining, oil and gas, waste incineration, coal-fired power plants, agriculture, metal plating activities and landfill leaching. They are also present naturally in some groundwaters in certain geological formations. In the U.S., government regulatory agencies have published maximum contaminant levels (MCL) for these species in industrial effluents and drinking water.

20 Electrochemical Destruction of PFOA and PFOS in High-Salinity Water Orren D. Schneider, PhD, Pe; José Alvarez, PhD; and Elisabeth Christ, Aclarity Inc.

In the last several decades, the presence of PFAS has become ubiquitous in the environment. They are widely used in many industries because of their exceptional properties, including thermal, chemical, and biological stability. As such, they are used in products including firefighting foams, coatings on food containers, stain-resistant coatings on fabrics, and other applications. While these properties make this class of compounds very attractive, they also render them very difficult to remove by conventional water treatment processes, and then once removed, they are nearly impossible to degrade. Because of this, they have earned the moniker of “Forever Chemicals.”

32 Can a Micro-Adsorbent Material and Ceramic Filtration Treatment Successfully Remove PFAS? Terence K. Reid, Aqua-Aerobic Systems Inc., and Joseph Quinnan, Arcadis

There are many technologies that target PFAS removal through adsorption, separation or destruction methods.

Each technology differs in their relative removal efficiencies, energy requirements, waste products and operational requirements. PFAS removal from contaminated water presents challenges due to the vast number of species that have different physical and chemical properties. The hydrophobic, lipophobic and surfactant properties that make PFAS highly useful in commercial products make them equally difficult to remove from water.

39 What Would Fail First if We Did Not Feed Treatment Chemicals to a Steam System?

Chris Golden, Taylor Technologies

Sometimes it is hard to explain to facilities that spending money on water treatment chemicals is vital to protect boiler equipment and production rates in manufacturing plants. These "unbelievers" could be susceptible to other treatment technologies or simply cutting budgets for this important service. So how can you make it clear that it is necessary?

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1300 Piccard Drive, Suite LL 14 Rockville, MD 20850 (301) 740-1421 • (301) 990-9771 (fax) www.awt.org

2024 AWT Board of Directors President

Noah Baskin

President-Elect

John D. Caloritis, CWT

Secretary

Kyle Rossi, CWT

Treasurer

Craig Bodenmiller, CWT

Immediate Past President

Steve Hallier, CWT

Directors

Tammy Faber, MBA Michelle Lunn Derrick Vandenberg, CWT Greg Gehrke

Ex-Officio Supplier Representative

Pam Simmons

Past Presidents

Fred Shurtz Matt Jensen, CWT Jack Altschuler Mark R. Juhl John Baum, CWT Brian Jutzi, CWT R. Trace Blackmore, CWT, Bruce T. Ketrick Jr., CWT LEED AP Bruce T. Ketrick Sr., CWT Michael Bourgeois, CWT Ron Knestaut D.C. “Chuck” Brandvold, CWT Robert D. Lee, CWT Thomas Brandvold, CWT Mark T. Lewis, CWT Brent W. Chettle, CWT Steven MacCarthy, CWT Dennis Clayton Anthony J. McNamara, CWT Bernadette Combs, CWT, James Mulloy LEED AP Alfred Nickels Matt Copthorne, CWT Scott W. Olson, CWT James R. Datesh William E. Pearson II, CWT John E. Davies, CWT William C. Smith Jay Farmerie, CWT Marc Vermeulen, CWT Gary Glenna David Wagenfuhr Charles D. Hamrick Jr., CWT Casey Walton, B.Ch.E, CWT Joseph M. Hannigan Jr., CWT Larry A. Webb

Staff

Executive Director

Denise Jackson

Deputy Executive Director

Sara L. Wood, MBA, CAE

Member Services Director

Angela Pike

Senior Vice President, Meetings

Tina Schneider, CMP

Calendar of Events Association Events 2024 Technical Training Seminars (West) March 6-9, 2024 Embassy Suites Dallas – Frisco Convention Hotel Frisco, Texas

2024 Technical Training Seminar (East)

April 17-20, 2024 Cleveland Marriott Downtown at Key Tower Cleveland, Ohio

2024 Annual Convention and Exposition September 10–13, 2024 Louisville Convention Center and Omni Louisville Louisville, Kentucky

2025 Technical Training Seminars (West) February 25–28, 2025 Doubletree Mission Valley San Diego, California

2025 Technical Training Seminars (East)

TBD

2025 Annual Convention and Exposition

November 12–15, 2025 The Broadmoor Hotel Colorado Spring, Colorado

2026 Annual Convention and Exposition September 16–19, 2026 Oklahoma Convention Center and Omni Hotel Oklahoma City, Oklahoma

2027 Annual Convention and Exposition September 8–11, 2027 Cleveland Convention Center Cleveland, Ohio

Also, please note that the following AWT committees meet on a monthly basis.

All times shown are Eastern Time. To become active in one of these committees, please contact us at (301) 740-1421.

Account Executive

Matt Coffindaffer, CAE

Meeting Coordinator

Caroline Bentley

Meeting Planner

Tim Foley

Exhibits and Sponsorship Manager

Jessica Martin

Director of Marketing

Melissa Graham, MBA

Marketing Manager

Mary Claire Gordon

Editorial Services Manager

Heather Rigby

Production Manager

Jansen Vera

Director of Accounting Services

Dawn Rosenfeld

The Analyst Staff Publisher

Second Tuesday of each month, 11:00 am—Legislative/Regulatory Committee Second Tuesday of each month, 2:30 pm—Convention Committee Second Wednesday of each month, 11:00 am—Business Resources Committee Second Friday of each month, Noon—Pretreatment Subcommittee Second Friday of each month, 10:00 am—Special Projects Subcommittee Second Friday of each month, 11:00 am—Cooling Subcommittee Third Monday of each month, 10:00 am—Certification Committee Third Monday of each month, 3:30 pm—Young Professionals Task Force Third Monday of each month, 3:00 pm—Education Committee Third Friday of each month, Noon—Boiler Subcommittee Third Friday of every other month, 10:00 am—Technical Committee Third Friday of each month, (call for meeting dates), 11:00 am—Wastewater Subcommittee Fourth Friday of each month, 1:00 pm—Education Resources Committee

Denise Jackson

Other Industry Events

Heather Rigby, hrigby@msp-amc.com

RETA, Annual Convention, November 13–16, 2023, Jacksonville, Florida Cooling Technology Institute, February 4-8, 2024, Houston, Texas WateReuse Association, March 11–14, 2024, Denver, Colorado ABMA Boiler Technology Conference & Expo, May 1–3, 2024, Aurora, Colorado Electric Utility Chemistry Workshop, June 7–9, 2024 Champaign, Illinois

Managing Editor

Production Manager

Jansen Vera

Technical Editor

Michael Henley, mdhenleywater@gmail.com

Advertising Sales Manager Carol Nettles, carol@awt.org

The Analyst is published quarterly as the official publication of the Association of Water Technologies. Copyright 2023 by the Association of Water Technologies. Materials may not be reproduced without written permission. Contents of the articles are the sole opinions of the author and do not necessarily express the policies and opinions of the publisher, editor or AWT. Authors are responsible for ensuring that the articles are properly released for classification and proprietary information. All advertising will be subject to publisher’s approval, and advertisers will agree to indemnify and relieve publisher of loss or claims resulting from advertising contents. Editorial material in the Analyst may be reproduced in whole or part with prior written permission. Request permission by writing to: Managing Editor, the Analyst, 1300 Piccard Drive, Suite LL 14, Rockville, MD 20850, USA. Annual subscription rate is $100 per year in the U.S. (4 issues). Please add $25 for Canada and Mexico. International subscriptions are $200 in U.S. funds.

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Letter From the Editor

Heather Rigby, Editorial Services Manager

Some of us know exactly what we want to be when we grow up, and we follow that path with the kind of determination that hero stories are written about. I am not “some of us.” When I was a little girl, I wanted to be a ballerina, a teacher, and I think there was even a time where I thought astronaut could be a realistic career path for me. Thankfully, around sophomore year of high school, I realized how much I love working with words—that didn’t stop me from flirting with a biology degree in college.

That came with tutoring other students one-on-one and doing regular supplemental instruction sessions in anatomy, physiology, and microbiology. I recently found the pamphlet I created for an assignment that gives a brief overview of Legionella (including the “fun fact” that it is a TV star, having appeared on House). My first real introduction to the world of water treatment came while doing that project.

Some of our AWT members grew up with the water treatment industry as a family business, and they knew they would follow in their father’s or another family member’s footsteps.

Others may not have discovered it until college (like me) or even later in their careers. A true strength of AWT is the willingness to support the membership regardless of how they came to the field, where they are in their career, or what area of expertise they specialize in. There are resources to meet a variety of needs and interests!

This supplement is one such resource. It covers a couple of technology-related topics, and whether you are a “technology person” or not, there is bound to be something interesting within these pages to capture your attention. Our technical editor, Mike Henley, gives an overview of the content in his introduction. On behalf of both of us, and the rest of the AWT team, I want to thank you for being a part of—and the reason for—everything we do here.

I may not have gone on to get that biology degree (in the end, it was an English degree), but I have been thrilled to be able to combine my loves of the written word, education, and science through my work here on the Analyst.

Sincerely, Heather Rigby

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The third edition of AWT’s TR&TM is now available for purchase!

It has been reviewed and updated to include current technology and recent developments, with an all-new chapter covering even more water treatment topics.

Stay up to date on: • • • • • • • •

General Water Treatment Concepts Pretreatment Boiler Water Cooling Water Regulations Wastewater Potable Water And Other Water Treatment Applications

To order your copy, visit the AWT Bookstore at www.awt.org/awt-bookstore.

For more information, contact Angela Pike at apike@awt.org or (240) 404-6477.

Emerging Treatment Challenges and Water Business Opportunities

By Mike Henley, Technical Editor

of PFAS: PFOA (perfluorooctanoic acid) and PFOS (perfluorooctanesulfonic acid) of 4 parts per trillion (ppt) (4.0 nanograms per liter (ng/L). (In contrast, the EPA-recommended HAL in 2016 was 70 ppt for PFOA and PFOS.) The agency also is proposing limits on any water mixture containing one or more of these chemicals PFNA, PFHxS, PFBS and/or GenX chemicals. At publication time, the agency has not issued a final rule, but many in the environmental and water treatment community expect the agency will issue an enforceable MCL by even sometime in 2024.

Puzzles. Normally, this word conjures the idea of a table with a box full of hundreds or even thousands of pieces that a patient person is working to fit together. The reward is the success of figuring out the placement of pieces and the resulting picture they form.

In this supplement, we focus on two challenges water treaters face in three of the four technical articles—the selective removal of ionic contaminants from water, and, a new issue water treaters are facing, the removal of perand polyfluoroalkyl substances (PFAS) from water. The fourth article focuses on the treatment of boiler water and the consequences one might face ignoring proper treatment guidelines.

There have been no steps taken yet, but many also expect that after the EPA sets enforceable MCLs for some PFAS chemicals in drinking water, that ultimately the agency will move to regulate PFAS in wastewater effluent. On both ends of the water treatment spectrum, there are some who question if the low level of the proposed limits is realistic. Some see the proposals as placing unsustainable financial burdens on smaller water districts. Another criticism is that there are no on-line monitoring technologies that offer immediate results and that the current practice of sending water samples to labs is expensive and it can take literally weeks to learn if a treatment system is or is not removing the PFAS contaminants. It should be noted that there are monitoring technologies available for in-house measurement of PFAS. However, they are not cheap and can cost several hundred thousand dollars.

Background

While it is simplistic to liken water treatment to puzzles, an activity used to pass time and for enjoyment, there are some common characteristics. For example, in Colorado Springs, Colorado, the Colorado Springs Utility faces the relatively simple task of running its water through a coagulation/flocculation process, followed by filtration and chlorination. Conversely, the nearby water utilities in Security, Widefield, Fountain, and Stratmoor Hills are forced to treat their raw water through ion exchange (IX) to remove PFAS contaminants, which are also known as the “forever chemicals.” The difference? The water chemistry and the standards set for drinking water by the U.S. Environmental Protection Agency (EPA) impact if the treatment practices are “routine” with few extra steps, or if they are more complicated.

Challenges and Business Opportunities No matter one’s viewpoint, there is no argument that these moves on the regulatory front will have two outcomes—a new puzzle piece to fit into the picture of successful water treatment, and the creation of new business opportunities.

Now, in the case of PFAS, the EPA is moving toward setting enforceable maximum contaminant levels (MCLs). In recent years, water utilities have been tracking PFAS-related contaminants, but any action has focused on health advisory levels (HAL) that are not enforceable like MCLs. In March 2023, the EPA issued a proposal for an enforceable MCL for two types

At the treatment end, end users and their service providers will be faced with adding one or more 7

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Supplement Introduction: Emerging Treatment Challenges and Water Business Opportunities continued

additional treatment steps to remove PFAS. Granular activated carbon (GAC) has been used to successfully to remove PFAS. However, at high PFAS, the GAC exhausts sooner and must be changed out more frequently, making it a more expensive option. The metro Colorado Springs water utilities mentioned earlier found that to be the case. IX resins for PFAS removal were then selected because they would last longer before resin replacement was necessary.

The problem the four districts faced was that their common source for much of their raw water, the Widefield Aquifer, had been contaminated with PFAS by runoff from firefighting foam used by a local Air Force base. In this instance, the Air Force accepted responsibility and helped fund treatment systems that originally relied on GAC. But the water utilities found that the PFAS levels above 70 ppt (in some cases much higher) exhausted the GAC, forcing frequent replacement. In this case, the Air Force was willing to switch to IX.

be. For AWT members, the two above areas can present opportunities—even on a smaller scale.

Fall Supplement Articles

Here are brief highlights of the four technical articles in this supplement: One article by Liu, et al. focuses on the selective removal of ionic contaminants by IX and iron oxide media. The article focuses on the use of these treatments for removing selenium, heavy metals, and arsenic from water and waste streams.

Schneider, Alvarez, and Christ write about a new electrochemical oxidation technology that can be used for the destruction of PFOA and PFOS in high-salinity water. One of the challenges in PFAS treatment is the potential that in the future that the EPA will change PFAS contaminants to hazardous waste status, which would mean that exhausted GAC and IX would require hazardous waste disposal methods, which would increase their cost. The alternative is to use a technology that destroys the PFAS during treatment. Hence, the interest in this technology.

Whenever there is a water But there can be other options. treatment challenge, it For example, the use of GAC and IX together. There are also offers a potential business instances where a source water opportunity. could contain another kind of ionic contaminant, for instance selenium, arsenic, nitrate, or sulfate. In those cases, the other contaminant might impact the system technologies, and require the addition of an absorbent material or an ion-selective IX resin ahead of the PFAS treatment. These are all parts of the water “puzzle” that the treatment professional must work through when designing the water system.

The article by Reid and Quinnan looks a technology for the removal of PFOS and PFOA that uses a microabsorbent slurry that is placed in a sorbent reactor for the removal of PFOS and PFOA from raw water. A part of the process also involves the use of a filtration treatment.

Opportunity?

The fourth article by Golden examines the topic of what would fail if one did not feed treatment chemicals to a steam system. Issues he examines include tube pitting, corrosion, and scaling.

Whenever there is a water treatment challenge, it offers a potential business opportunity. In the case of PFAS, or the removal of other specific contaminants, service companies can help by finding treatment chemicals, absorbents, or equipment technologies that can remove contaminants like arsenic nitrates, lead, and others.

If not already in a provider’s technology toolbox, then such options can be added, or made available on an as-needed basis. An interesting facet of the water industry is how fluid (no pun intended) the business can 8

the ANALYST Technology Supplement 2023

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Use of IX and Iron Oxide Media for Selective Removal of Selenium, Heavy Metals, and Arsenic from Water and Waste Streams Zhendong Liu, PhD, Wilson Nova Ruiz, and Firuza Mir, LANXESS Corp.

Kresimir Ljubetic, PhD, H.C. Lian, PhD, and David Kratochvil, PhD, BQE Water

Selenium, heavy metals, and arsenic are often contaminants of concern in wastewater from mining, oil and gas, waste incineration, coal-fired power plants, agriculture, metal plating activities and landfill leaching.

They are also present naturally in some groundwaters in certain geological formations. In the U.S., government regulatory agencies have published maximum contaminant levels (MCL) for these species in industrial effluents and drinking water.

For instance, EPA 40 CFR Part 423 (issued by the U.S. Environmental Protection Agency [EPA]) states that the average of daily values for 30 consecutive days in the steam electric power generating effluent shall not exceed 29 parts per billion (ppb), 34 parts per trillion (ppt) and 8 ppb for selenium (Se), mercury (Hg), and arsenic (As), respectively (1). According to EPA 40 CFR Part 444, the maximum monthly average for arsenic, cadmium, copper, lead, mercury, and zinc in waste combustors effluent are 72 ppb, 26 ppb, 14 ppb, 32 ppb, 1.3 ppb, and 10

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Use of IX and Iron Oxide Media for Selective Removal of Selenium, Heavy Metals, and Arsenic from Water and Waste Streams

54 ppb, respectively (2). For drinking water, the MCL of selenium, mercury, cadmium, lead, and arsenic are 50 ppb, 2 ppb, 5 ppb, 15 ppb (action level), and 10 ppb, respectively (3).

Historically, conventional techniques such as biological treatment, precipitation/co-precipitation, solvent extraction, and membrane filtration are used to remove these species, but these treatment technologies all tend to generate large amounts of secondary wastes in the forms of biological residues, sludge, and/or reverse osmosis (RO) concentrate. Biological treatment and precipitation methods can be used as primary approaches to remove high-level influent contaminants but are not capable of reducing these contaminants to concentrations necessary for meeting environmental compliance.

RO membrane could achieve very low levels of the contaminant species in effluent but it requires expensive capital equipment, a larger footprint, higher energy costs, and generates large volumes of waste for further treatment (4). Although these traditional methods have many disadvantages and limitations, industry has been implementing them because there were no commercially available alternatives to meet the regulatory requirements. Therefore, there is a pressing need to find ways to remove these trace contaminants with economically feasible solutions.

Recently, ion exchange (IX) resins and other adsorption media have been increasingly used in removing trace contaminant ions. These approaches offer the advantages of high selectivity, a smaller footprint (meaning lower capital costs), low effluent discharge concentration, continuous operation, the ability to handle a wide range of temperature and feed variations, low waste generation, and sometimes the ability to recycle the valuable materials by elution and further processing.

IX is ideal for treating large volume effluents with low ppb levels of contaminants. This article discusses the capability and viability of using IX resin and media adsorption technology for removing selenium, heavy metals, and arsenic from water and wastewater.

(oxidation reduction) potentials, it can be present as Se (valence 0), selenite (HSeO3-) (valence IV), or selenate (SeO42-) (valence VI) in most wastewaters, as depicted in the Pourbaix Diagram shown in Figure 1 (5).

Depending on the specific predominant species in the water, different adsorption media can be applied. For example, iron oxide media can be used to preferentially remove Se (IV), while a strong basic anionic resin is more effective for Se (VI) removal.

Iron oxide (hydroxide) media. Both selenite (IV) and selenate (VI) can be irreversibly adsorbed by iron hydroxide and Goethite as inner-sphere complexation, as evidenced by the decreasing zeta potential and point of zero charge (PZC) of media. FTIR (Fourier transform infrared) spectra showed selenite forms a bridging bidentate complex on goethite. Selenite exhibited much greater adsorption than selenate (6), probably due to the steric hinderance of the larger selenate molecule.

Figure 2 shows Rapid Small Scale Column Test (RSSCT) data of the selenium removal from a refinery wastewater by an iron oxide media A. The test water had a slightly above neutral pH (pH 7.8) and an oxidation/ reduction potential that ensured selenite (IV) was the predominant species. The media was crushed from 1.3 millimeters (mm) to about 0.13 mm average particle diameter, and the test was run with a simulated 3.5 Figure 1: Potential–pH equilibrium diagram for the system selenium-water, at 25°C. Source: Reference 5

Selenium Removal

Selenium is a multi-valence element that can exist in soil and water in different oxidation states. In the common pH range (5 to 9) and ambient REDOX 11

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Use of IX and Iron Oxide Media for Selective Removal of Selenium, Heavy Metals, and Arsenic from Water and Waste Streams continued

minute (min) empty bed contact time (EBCT), based on a proportional diffusivity model. At 20 ppb Se breakthrough point, the throughput was about 33,000 bed volumes (BV) (7). The hump in the effluent selenium level between 5,000 and 12,000 BV was most likely due to a restriction in flow. Some biological growth was observed on the pump suction tubing immersed in the drums during that time. It may have caused the flow restriction. This restriction was then rectified by conducting a quick backwash to break up the bed.

nitrate, and chloride) if using IX resin as the adsorbing media. The high oxidation state can be achieved by sufficient aeration (exposure to oxygen) or adding a strong oxidizer (e.g., chlorine).

Figure 4: Selenium removal from a mine wastewater by an SBA resin.

Figure 2: Selenium removal from a refinery wastewater by a proprietary iron oxide media.

IX resin. Under normal wastewater conditions, selenium often exists as one of the anion species HSeO3-, SeO32or SeO42-, which can be captured by a strongly basic anion (SBA) due to the electrostatic attraction as shown by an example in Figure 3. However, studies have shown that selenate had much higher selectivity than selenite on SBA resin (8). The selectivity among common anions on an SBA resin is shown here: Se042- > SO42- > NO 3- > Br- > HPO42- > SeO 32- > NO 2- > Cl - > F Figure 3: Ion exchange between selenate and an SBA resin.

Therefore, it is advised to keep the predominant selenium species as Se (VI) in wastewater to ensure its higher selectivity over other common anions (e.g., sulfate, 12

The effectiveness of selenate removal can be seen from a pilot case study to treat a Canadian mine water in Figure 4. By using an SBA resin, effluent Se could be reduced from 120 to 320 ppb down to <1 ppb (9). The high selectivity to selenate is very important as the mine wastewater contains up to 3 grams per liter (g/L) total dissolved solids (TDS) with high concentrations of competing anions.

Moreover, this pilot study also demonstrated a unique IX and electrochemical technologyB for selenium removal and waste recycling. After regenerating the exhausted IX resin, the eluant was conveniently further processed by electrochemical reduction to recover Se as a valuable byproduct, while the brine solution was recycled back to regenerate the resin (9). The process flow is presented in Figure 5. The ability to recycle selenium and brine regenerant has great economic, environmental and ecological significance. the ANALYST Technology Supplement 2023

Use of IX and Iron Oxide Media for Selective Removal of Selenium, Heavy Metals, and Arsenic from Water and Waste Streams continued

Figure 5: Selenium removal and recovery block flow diagram

Heavy Metal Removal

Heavy metals in industrial wastewater and municipal water typically include mercury, lead, copper, cadmium, zinc, chromium, nickel, and manganese.

For influents with lower metal content (e.g., <10 parts per million [ppm]), IX is the preferred treatment technology to achieve very low metal discharge levels.

Depending on target metal species, the IX resin could be a chelating resin with thiourea, iminodiacetic acid (IDA), aminomethylphosphonic acid (AMPA) or bispicolylamine functional groups, or a basic anionic resin if the metal species are in the form of anionic complexes.

The regular cationic resins are normally not effective towards these heavy metal ions due to their unfavorable selectivity compared to the much higher levels of common hardness ions (calcium and magnesium) presented in the matrix. While the thiourea-based resin is more specific to mercury and precious noble metals, the other types of chelating resins are effective for a broad range of heavy metals. Among them, the IDA-based chelating resin can remove nearly all types of heavy metals, with great selectivity over common hardness ions in water. A typical chelating IX resin with iminodiacetate functional group is shown in Figure 6.

Figure 6: Iminodiacetate-based chelating resin for heavy metal removal.

H2 C

N H 2C

H2 C

COO

COO

Na

Na

The selectivity among common metal ions on an IDA chelating resin is shown here: Fe3+ > Cu2+ > Hg 2+ > Pb2+ > Ni2+ > Zn2+ > Cd2+ > Co2+ > Fe 2+ > Mn2+>>Ca2+ > Mg 2+ Figure 7 shows a treatment scheme to remove mercury and other heavy metals from incineration flue gas scrubber wastewater. The flue gas is first contacted with hydrochloric (HCl) acid followed by an alkaline to precipitate out most of the metals. The mercury-selective thiourea resin was used to capture and reduce mercury to less than 10 ppb, while another IDA chelating resin was employed to remove all other heavy metals from the supernatant water after precipitation.

The performance of the IDA chelating resin in removing heavy metals after the mercury removal step was given

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in Figure 8. The influent water has about 140 g/L sodium chloride (NaCl) after the sodium hydroxide (NaOH) neutralization step. The data shows the IDA-based chelating resin was able to reduce multiple heavy metals to 10 ppb or below in a highly concentrated brine.

In another study as shown in Figure 9, a wastewater stream has 3.1 ppm copper (Cu), 3.1 ppm nickel (Ni), 3.1 ppm zinc (Zn, 5.7 ppm lead (Pb), and 6.1 ppm cadmium (Cd) in 10 g/L calcium chloride (CaCl 2) at pH 6.0. The water was fed through an IX resin column loaded with an IDA chelating resin at 10 BV/hour (hr) at 20°C. All metals were removed down to low-ppb levels with clearly differentiated breakthrough points, reflecting the selectivity among these heavy metal ions. copper broke through much later than Cd, due to its significantly higher affinity to the IDA resin.

The high-removal efficiency and throughputs of these heavy metal ions in the concentrated CaCl 2 solution demonstrated their excellent selectivity over common hardness ions in the water matrix.

Figure 7: A process flow for mercury and other heavy metal removal from an incineration plant wastewater after acid/alkaline scrubbers.

Figure 8: Heavy metal removal by an IDA-based chelating resin after the alkaline scrubber in Figure 7.

NaCl = 140g/liter Specific flow rate: 10 BV/hr Operation: Lead (first filter)/Lag (second filter)

Figure 9: Copper, nickel, zinc, lead and cadmium removal by an IDA-based chelating resin in 10g/L CaCl2.

In a low-ionic strength water system (e.g., the municipal water near neutral pH), the IDA-based 14

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Use of IX and Iron Oxide Media for Selective Removal of Selenium, Heavy Metals, and Arsenic from Water and Waste Streams continued

chelating resin was able to remove nickel ion from 100 ppb to less than 5 ppb with a very high throughput of 120,000 BVs, as illustrated in Figure 10. The two-step lead/lag IX resin process used a high flow rate of 70 BV/hr, indicating fast ionic removal kinetics of the IDA resin towards heavy metal ions such as nickel (10).

Figure 11: Potential–pH equilibrium diagram for the system arsenic–water, at 25°C. Source: Reference 5.

Figure 10: Nickel removal by an IDA-based chelating resin in a low ionic strength water treatment system. Source: Reference 10.

Removal of arsenic from natural or industrial wastewater can be achieved by coagulation-flocculation, membrane filtration, adsorption, and ion exchange. Comparably, the adsorption method is the most widely used technique for arsenic removal due to its high arsenic removal efficiency, easy operation and handling, cost-effectiveness, and no sludge production (11). For arsenic adsorption onto an inorganic media (e.g., iron oxide or hydroxide), the higher-oxidation state arsenate (V) is much more favored than the lower-oxidization state arsenite (III).

Arsenic Removal

Arsenic is highly toxic to humans, animals, and aquatic life. It is released into environment from multiple sources, including natural minerals, geological formations, electronics, agriculture, metallurgy, and medicine. Similar to selenium, arsenic is present in wastewater in various forms with different oxidation states, as shown in Figure 11 (5). In natural water and most wastewater conditions, arsenic primarily exists in two forms: arsenite (III) and arsenate (V).

If arsenic pre-exists in the reduced form, it is important to pretreat the influent water with oxidizers to convert it

Figure 12: Adsorption of arsenate onto iron oxide/hydroxide.

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Use of IX and Iron Oxide Media for Selective Removal of Selenium, Heavy Metals, and Arsenic from Water and Waste Streams continued

to arsenate. The interaction between iron oxide/hydroxide with arsenate is irreversible and strong. Therefore, the exhausted media meets leaching criteria testing, and can be disposed directly in a landfill without concerns of future leach-out. A schematic diagram (Figure 12) illustrates the interaction between iron oxide-hydroxide (Fe-OOH) and dihydrogen arsenate (H 2AsO4-).

In order to gain further savings, part of the influent water could be split as a bypass, then recombined with the treated water in the early runs. The final effluent would still meet the MCL requirement.

Figure 13: Arsenic removal by a proprietary iron oxide media in lead/lag operation.

To ensure effective adsorption and high throughput of arsenic on iron oxide/hydroxide media, the requirements of pH, competing/fouling species, and suggested operating parameters are outlined in Table A. Table A: Recommended Conditions for Arsenic Removal by Iron Oxide/Hydroxide Media Operating Parameters

Recommendation for Optimum Arsenic Removal

pH

6.5-8.2

Silica

< 30 ppm

Phosphate

< 300 ppb

Sulfate

< 100 ppm

Manganese

< 50 ppb

Ferric ion

< 300 ppb

Total Suspended Solids

< 5 ppm

Specific flow rate

10-20 BV/hr

Empty bed contact time (EBCT)

3-6 min

Pressure drop

< 10 psi (0.7 bar)

Figure 14: Effect of chlorine on arsenic removal by a proprietary iron oxide media.

The silica requirement is important since silica can significantly foul the iron oxide/hydroxide media by forming a dense polymeric coating on the particle surface, rendering the particle unable to continue adsorbing arsenic.

Figure 13 shows the throughput of a lead/lag operation for arsenic removal by using a proprietary iron oxide/ hydroxide media A. The media was able to reduce the influent arsenic concentration from 50 to 80 ppb down to 1 ppb or below. After breakthrough on the lead vessel at around 39,180 BV, the operation continued because the lag vessel served as a polisher to keep the arsenic in effluent below 10 ppb.

In another EPA case study, the importance of arsenic pre-oxidation was highlighted in Figure 14 with a proprietary iron oxide (hydroxide) media. The As species in the feed water was comprised of 87% As (III).

Originally, chlorine dosing was located after the iron oxide vessel. The effluent arsenic gradually increased during the early runs. At 25,000 BV, the chlorine dosage location was placed before the iron oxide vessel. The data shows there was an instant reduction in effluent arsenic concentration due to a change of the oxidation state of arsenic from valence III to V. This dramatically improved the arsenic removal efficiency (13).

When the lag vessel finally reached breakthrough at 52,150 BV, it was switched to as a lead vessel, and the original lead vessel became the lag vessel after its media was changed out. Such operation maximized the service life of the media while still producing quality water (12).

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Simultaneous Removal of Selenium, Heavy Metals, and Arsenic

References

When the levels of heavy metals and the contaminants are in trace levels, iron oxide media can be used to remove all the contaminant species together. Figure 15 illustrates the removal efficiency of the contaminant species in a drinking water sample by two proprietary iron oxide media. These two iron oxide materials were capable of reducing most of the contaminant species from about 100 ppb to 1 ppb or below at a 20 BV/hr flow rate. For instance, the selenium (IV) concentration was reduced from 91 ppb to 200 ppt. The mercury levels were reduced from 85 ppb to 30 ppt, while the lead levels changed from 180 ppb to 500 ppt. In these three cases, there was a more than 200 times reduction. The exact mechanism for heavy metal removal by iron oxide is not clear, but was suspected to be related to surface complexation, surface precipitation or ion exchange (14).

1. EPA (2020). “Steam Electric Power Generating Effluent Guidelines,” EPA 40 CFR Part 423, U.S. Environmental Protection Agency, Washington, D.C. 2. EPA (2000), "Waste Combustors Effluent Guidelines,” EPA 40 CFR Part 444, U.S. Environmental Protection Agency, Washington, D.C. 3. EPA (2022). National Primary Drinking Water Regulations, U.S. Environmental Protection Agency, Office of Water, Washington, D.C. 4. Littlejohn, P.; Mohammadi, F.O.; Kratochvil, D. (2017). “Advancement in Non-Biological Selenium Removal Treatment Systems – Results of Continuous Pilot Scale Operations,” presented at Water Environment Federation’s Technical Exhibition and Conference.

5. Pourbaix, M. (1974). Atlas of Electrochemical Equilibria in Aqueous Solutions, National Association of Corrosion Engineers, Houston, Texas (2nd English edition).

6.

Su, C.; Suarez, D. (2000), “Selenate and Selenite Sorption on Iron Oxides: An Infrared and Electrophoretic Study,” Soil Science Society of America Journal 64, pp. 101-111.

7. De Nora Water Technologies (2010), Pilot Trial Report.

8. Boegel, J.; Clifford, D. (1986). “Selenium Oxidation and Removal by Ion Exchange,” EPA/600/S2-86/031, U.S. Environmental Protection Agency, Washington, D.C. 9. Mohammadi, F.0.; Littlejohn, P.; Kratochvil, D. (2016), >Selen-IXTM: Ion Exchange and Electrochemistry at Work to Cost-Effectively Remove Selenium for Mine-Impacted Waters to Ultra-Low Concentrations, XXVIII International Mineral Processing Congress, Québec City, Canada.

10. Stetter. U.; Dördelmann, O. (2005). Presentation at IWW Mühlheim a.d.R. (IWW Water Center, Muelheim an der Ruhr, Germany).

11. Nicomel, N.; Leus, K.; Folens, K.; Van Der Voort, P.; Laing, G. (December 2015).

“Technologies for Arsenic Removal from Water: Current Status and Future Perspectives,” International Journal of Environmental Research and Public Health 13(1), pp. 13, 62, ijerph13010062, doi: 10.3390/ijerph13010062, PMID: 26703687; PMCID: PMC4730453.

Figure 15: Selenium, heavy metal ions and arsenic removal from drinking water by two proprietary iron oxide media.

12. EPA (2008A). “Arsenic Removal from Drinking Water by Adsorptive Media Report,” U.S. EPA Demonstration Project at Rimrock, Arizona, Final Performance Evaluation, U.S. Environmental Protection Agency, Washington, D.C. 13. EPA (2008B). “Arsenic Removal from Drinking Water by Adsorptive Media Report,” U.S. EPA Demonstration Project at Brown City, Michigan, Final Performance Evaluation, U.S. Environmental Protection Agency, Washington, D.C. 14. Patoczka, J.; Johnson, R.; Scheri, J. (1998). “Trace Heavy Metals Removal with Ferric Chloride,” presentation at the Water Environment Federation Industrial Wastes Technical Conference.

Endnotes A. The iron oxide media mentioned in the text for arsenic removal is Bayoxide® E33, a treatment product manufactured by LANXESS AG, Cologne, Germany.

B. The unique IX and electrochemical technology for selenium removal mentioned in the text is Selen-IX™, which has been developed by BQE Water Inc., which is based in Vancouver, BC, Canada.

Summary

IX resins and iron oxide/hydroxide media have shown the ability to reduce selenium, heavy metal ions and arsenic levels down to low-ppb concentration levels. SBA resin can remove selenium to trace or non-detect levels from a mining water, and the resin operation was made selfsustainable with regenerant recycle and waste product recovery. Chelating IX resins have been found very effective in removing heavy metal ions from industrial wastewater and municipal streams. Iron oxide/hydroxide media showed very promising results in removing trace level arsenic and other contaminant species.

17

Zhendong Liu earned a PhD in materials science and mineral engineering from University of California at Berkeley in 2001, and an MBA from University of Delaware in 2010. He has authored 20 peer-reviewed journal articles and holds 22 granted U.S. patents. He has more than 20 years’ experience in specialty chemical industry. Dr. Liu is currently employed by LANXESS Corp. as the head of the technical service and business development for its Liquid Purification Technologies business in the Americas. He can be reached at zhendong.liu@lanxess.com.

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Use of IX and Iron Oxide Media for Selective Removal of Selenium, Heavy Metals, and Arsenic from Water and Waste Streams continued

Wilson Nova Ruiz is the specialized processing manager at LANXESS. He has 25 years’ experience in the chemical industry business management in South, Central, and North America. Mr. Ruiz has been with LANXESS for 20 years and has worked in two different business units as a regional business manager. His professional background includes water treatment, industrial preservatives, CASE, metal working fluids, construction materials, mining, hydrometallurgy, chlor-alkali, catalysis, and oil & gas. Mr. Ruiz holds a bachelor’s degree from Universidad Nacional de Colombia in chemical engineering and a masters degree in finance from the Universitario de Posgrado in Spain. He has lived in Pittsburgh, Pennsylvania, since 2011. Mr. Ruiz may be contacted at wilson.nova@lanxess.com.

Firuza Mir is the regional head for the AMS Region and has been a member of the global management team for Lanxess’ Liquid Purification Technologies business unit since 2009. (LANXESS’ industrial chemicals business was once a part of Bayer AG, prior to a business restructuring by Bayer.) She began her career in 1995 with Bayer India as a divisional and marketing services manager for the Animal Health and Environmental Services Division. She later joined Bayer’s corporate management team as head of corporate controlling and strategic development for Bayer India. In 2000, she moved to Canada as the controller for the Chemicals and Polymers Division, and later was promoted as the vice president and general manager of Bayer Chemicals. In July 2004, she came to the U.S. as president and general manager of LANXESS Corp. for North American operations of the firm’s Textile Processing Chemicals business unit. Later, in 2009, Ms. Mir took on her current position. Ms. Mir holds a finance degree from the University of Bombay and an MBA from NMINS both in finance and marketing. She is married and has two sons. Ms. Mir can be contacted at firuza.mir@lanxess.com.

He was previously a process engineer in the company’s Santiago, Chile, office. Dr. Liubetic received his doctorate in materials engineering from the University of British Columbia and his masters in extractive metallurgy from the University of Santiago. He may be contacted at kljubetic@bqewater.com.

H.C. Liang, PhD, PChem, is director of water studies at BQE Water. Dr. Liang has more than 15 years of experience in process chemistry and the engineering of water and wastewater treatment processes for mining and other industrial sectors. At BQE Water, he leads in areas related to water management, treatment, risk assessments, permitting, and engagement with local communities and regulatory agencies. He is a registered professional chemist in British Columbia and received his doctorate in inorganic chemistry from the University of Illinois at Urbana-Champaign and his masters in environmental engineering from Johns Hopkins University. Dr. Liang can be contacted at hliang@bqewater.com.

David Kratochvil, PhD, Peng, is president and CEO of BQE Water. He has more than 20 years of experience in the treatment and management of water in the mining, metallurgical processing, metal smelting, and refining industries.

Under his technical leadership, BQE Water has developed and commercialized four treatment technologies for use in the mining industry. Dr. Kratochvil is a registered professional engineer in British Columbia and received his doctorate in chemical engineering from McGill University in Montreal.

He can be reached at dkratochvil@bqewater.com.

This paper was originally presented at the International Water Conference® that was conducted Nov. 6-10, 2022, in Orlando, Florida.

Please visit www.eswp.com/water for more information about the conference or how to purchase the paper or proceedings.

Keywords: ARSENIC, DRINKING WATER, HEAVY METALS, ION EXCHANGE, IRON OXIDE MEDIA, IRON HYDROXIDE, SELENIUM, TRACE CONTAMINANTS, WASTEWATER

Kresimir Ljubetic, PhD, is the manager of pilot and laboratory services at BQE Water. He is a chemical engineer with more than 10 years of experience in applied research, hydrometallurgy, and water treatment in the mining sector. At BQE, he oversees piloting and laboratory testing programs.

18

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Electrochemical Destruction of PFOA and PFOS in High-Salinity Water Orren D. Schneider*, PhD, PE, José Alvarez, PhD, Elisabeth Christ, Aclarity, Inc. *Corresponding author

Introduction

compounds very attractive, they also render them very difficult to remove by conventional water treatment processes, and then once removed, they are nearly impossible to degrade. Because of this, they have earned the moniker of “Forever Chemicals.”

In the last several decades, the presence of poly- and perfluorinated alkyl substances (PFAS) has become ubiquitous in the environment. Fluorinated surfactants are widely used in many industries because of their exceptional properties including thermal, chemical, and biological stability (1, 2). As such, they are used in products including firefighting foams, coatings on food containers, stain-resistant coatings on fabrics, and other applications. While these properties make this class of

At publication time, there was no enforceable federal regulation governing these compounds in water. In recent years, the U.S. Environmental Protection Agency (EPA) has asked drinking water utilities to track their 20

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Electrochemical Destruction of PFOA and PFOS in High-Salinity Water

levels based on Health Advisory Limits (HAL), but now the agency is moving toward enforceable limits that would be based around Maximum Contaminant Levels (MCL).

When faced with recalcitrant organic contaminants, the water industry has typically turned towards either to adsorption processes like GAC or IX, or to strong oxidation technologies such as ozone or advanced oxidation processes (AOPs). Removal technologies, in general, do not degrade the compounds in question, but instead merely transfer them to solid phase (GAC or IX resin), which must be regenerated or, in the case of PFAS, be disposed of. While oxidation technologies are used for many recalcitrant organics, for PFAS they have been proven ineffective, because the carbon-fluorine bond is among the strongest found in nature. Even hydroxyl radicals with oxidation potentials of +2.8 volt (V), relative to a standard hydrogen electrode (SHE), cannot break these bonds. Thus, new technologies are required to destroy these compounds.

While the EPA has issued a strategic roadmap to address PFAS including regulations for six compounds, these regulations are still in the proposal stage. The agency has taken some action. In March 2023, the EPA issued a proposal for an enforceable MCL for two types of PFAS: perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) of 4 parts per trillion (4.0 nanograms per liter (ng/L). The agency also is proposing limits on any mixture containing one or more of these chemicals PFNA, PFHxS, PFBS and/or GenX chemicals (hexafluoropropylene oxide dimer acid (HFPO-DA)). While the agency had not issued a final ruling at publication time, many in the environmental and water treatment community expect the agency will issue an enforceable MCL for drinking water soon.

Some individual states have been in the forefront of PFAS regulation. While there are more than 4,000 registered PFAS compounds, the two most commonly detected ones are PFOA and PFOS, which typically make up the bulk of PFAS found in many water samples.

For water systems that do treat for PFAS, the most common processes used are granular activated carbon (GAC) and anion exchange (IX), with a few instances of nanofiltration (NF) or reverse osmosis (RO) (3). While these processes can remove these compounds from the water stream, they merely transfer them to a different matrix (GAC or IX media, or NF/RO/IX brines). These waste streams are then removed from the site and must be further treated prior to disposal. This often requires incineration of the brine or wet media.

One of the more promising destructive technologies for PFAS to emerge in the last five years is electrochemical oxidation (EO). EO involves passing the PFAS-laden water between two electrodes. In electrochemical treatment, the PFAS molecules adsorb to the electrode surfaces, where highly energetic electrons break carbon-fluorine bonds, leading to the production of free fluoride ions and partially defluorinated PFAS radicals (4, 5). These PFAS radicals then desorb into the bulk liquid and undergo chain reactions to destroy more PFAS molecules.

Electrochemical oxidation systems work by two main mechanisms – direct and mediated electrolysis (indirect oxidation) (6, 7) as shown in Figure 1.

Figure 1: Electrochemical oxidation mechanisms. Source: Sires, et al., Reference 6.

At present, these compounds are considered non-hazardous, but a hazardous waste classification would significantly alter the economics of disposal practices such as incineration, landfilling, or deep well injection. Because of this and a desire to remove these chemicals from the environment, technologies are being sought that will allow destruction at the site, rather than merely transferring the problem (and potential liability) to other entities.

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www. my r onl . c om 7604382021

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Conduct i vi t y,Resi st i vi t y,TDS TM ORP/ Fr eeChl or i neEqui val ent( FCE ) pH,Temper at ur e

Electrochemical Destruction of PFOA and PFOS in High-Salinity Water continued

In the indirect mechanism, “traditional” oxidants such as hypochlorite, chlorine dioxide, hydrogen peroxide, ozone, and even hydroxyl radicals are formed in the bulk liquid when salts (especially chloride) or water molecules are electrochemically transformed. This occurs when the standard half-cell potential is exceeded. For instance, chloride ions will be oxidized to chlorine gas (Cl 2) at a potential of +1.36 V, dissolved oxygen in water will be oxidized to ozone at a potential of +2.07 V. These in-situ oxidants are then free to react with the constituents in water, including many organic molecules and inorganics such as reduced nitrogen and sulfur compounds, metals, and others.

The second mechanism is direct oxidation. Here, molecules adsorb to the surface of the electrode and undergo direct electron transfer reactions. Because the molecules must diffuse through a boundary layer and then adsorb to the electrode surface prior to the electron transfer, these reactions are generally slower than indirect oxidation, and the diffusion and adsorption is generally considered the rate limiting step.

While these direct electrolysis reactions are generally slower than the indirect mechanisms, there can be a significant advantage, namely that depending on the material of the electrode, highly energetic electrons can be produced, with potentials greater than that for the liquid-phase oxidants, including ozone or hydroxyl radicals. Each electrode material has a characteristic property known as the overpotential. This refers to the potential, over and above the standard oxidation potential for water (+1.23 V) before oxygen evolution is observed.

For instance, an electrode with an overpotential of 1 V can be operated at an anodic voltage of 2.23 V before water is electrolyzed to hydrogen and oxygen. It is this overpotential that enables formation of in-situ oxidants such as chlorine, ozone, and hydroxyl radicals.

Electrodes with high oxidation overpotentials allow for oxidation of even carbon-fluorine bonds, which are estimated to require in excess of 2.7V to break (8).

of breaking carbon-fluorine (C-F) bonds without splitting water.

Over the past 10 years, numerous papers have appeared in the literature showing the effectiveness of these electrode materials for degrading a variety of PFAS species (4, 8, 10-12). It has been found that the longer chain molecules are more easily degraded than shorter chains and that sulfonates and generally more easily degraded than the carboxylates (12).

Materials and Methods

Water Matrix Synthetic Water Two separate experiments were performed. For both experiments, 16 liters (L) of water were prepared using the same ionic matrix. Reagent grade salts purchased from Sigma Aldrich (calcium chloride and magnesium sulfate) and Spectrum Chemical (sodium chloride [NaCl]) were used. The electrolytic composition of the water included 1,250 milligrams per liter (mg/L) of NaCl, 1,250 mg/L of calcium chloride (CaCl 2), and 1,250 mg/L of magnesium sulfate (MgSO4). These salts were added to distilled, deionized water and allowed to mix overnight to allow for dissolution.

For the experiments, a stock solution of PFAS was created using equal amounts PFOA and PFOS purchased from Sigma Aldrich. The PFAS compounds were first dissolved in water to create a nominal 50 mg/L stock solution. An aliquot of this stock solution was then added to the 16-liters of water along with the salts and allowed to mix overnight. Two different concentrations of PFAS were used in the two experiments. For the first experiment, a lower concentration of PFAS was used, with a nominal total concentration of 5,000 nanograms per liter (ng/L). For the second experiment, a higher concentration of PFAS was used, with a nominal total concentration of 50,000 ng/L. Leachate Landfill leachate collected from a centralized waste treatment (CWT) system near Detroit, Michigan, was tested for destruction of PFOA and PFOS. Typical of many leachates, the water was very high in organics and salts, with a measured specific conductivity of 12.8 microsiemens per centimeter (µS/cm). This water was treated as delivered with addition of any salts.

Two of the commonly used electrodes for degradation of PFAS include boron-doped diamond (BDD) and Magnéli-phase Ti4 O7. Electrodes composed of these materials have overpotentials in excess of +2.5 V (9), enabling them to produce energetic electrons capable 24

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Electrochemical Destruction of PFOA and PFOS in High-Salinity Water continued

Reactor The reactor used for these experiments consisted of a single anode and cathode connected to a power supply.

For this reactor, the anode was a solid cylindrical anode composed of solid elemental titanium with a catalytic coating. The surface area of the anode was 926 square centimeters (cm 2). For the synthetic water tests, the cathode was a titanium mesh annulus, with a 5-mm gap between the electrodes; for the leachate test, the cathode was made of 316 Stainless Steel annulus with a 5-mm gap between the electrodes. A photograph of the reactor system is shown in Figure 2 and photos of the anode and cathodes are given in Figure 3. The electrodes were placed in a 4-inch diameter PVC body with flow guides to introduce and collect the water. The reactor was then placed in a closed-loop apparatus with a pump, valves, and a flowmeter. The wetted materials of the reactor included the electrodes, polyvinyl chloride (PVC) body, PVC piping, nylon hoses, and stainless-steel pump casing and impeller. A high-density polyethylene (HDPE) tank was also used to store the water for recirculation during the experiments.

Figure 2: Photograph of the reactor system.

Figure 3: Photographs of cathodes—stainless steel (left) and titanium mesh (middle), and coated titanium anode (right).

During the experiments, the water was pumped through the reactor at a rate of approximately 3 gallons per minute (gpm); previous work with this reactor has shown that this pumping rate maximizes destruction of compounds, likely though a combination of chemical kinetics and improved mass transport. The water was introduced to the reactor at the bottom and allowed to exit at the top, thereby aiding in removal of any gases evolved by water splitting or mineralization of organic carbon to carbon dioxide. After passing through the reactor, the water was returned to the feed tank and recirculated.

Experimental Conditions

Synthetic Water The water containing the PFAS was recirculated through the reactor for six hours. After the flow was established and stabilized, the power supply was turned on and the timer started. The system was operated in constant voltage mode, with an applied potential of 8 V. At t = 5 minutes and at 2-hour (hr) increments, water samples were collected, and system parameters measured and recorded. Samples were collected in 1-L amber glass bottles and refrigerated. Additional samples were collected in a glass beaker and used to measure pH, temperature, conductivity, oxygen reduction potential (ORP), and oxidant residual.

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Electrochemical Destruction of PFOA and PFOS in High-Salinity Water continued

Leachate The leachate was pumped through the reactor for five hours. As with the synthetic water tests, the system was operated in a constant voltage mode, but with an applied potential of 7.5 V. At t = 5 minutes and at 1-hr increments, water samples were collected, and system parameters measured and recorded. Samples were collected in 1-L amber glass bottles and refrigerated.

Additional samples were collected in a glass beaker and used to measure pH, temperature, conductivity, ORP, and oxidant residual.

Leachate The pH, conductivity, and ORP of the water were measured using the same instruments as described above. Total oxidant residuals were measured using DPD powder pillows and measured using a Hach DR6000 UV/Vis spectrophotometer. Samples were diluted, as needed with distilled water to allow for accurate measurement. The temperature was measured using a digital thermometer. The 1-L water samples were stored in a refrigerator and then shipped, overnight on ice, to Enthalpy Analytical in Wilmington, North Carolina, for analysis of PFOA and PFOS by Liquid Chromatography Tandem Mass Spectrometry (LC/MS/MS) with isotope dilution in matrices other than drinking water (15).

Analyses

Synthetic Water The pH, conductivity, and ORP of the water were measured using an Orion 8157BNUMD ROSS Ultra pH/ATC Triode, an Orion 013005MD Conductivity Cell, and an Orion 9179BNMD OPR/ATC Triode, respectively, combined with an Orion VersaStar Pro meter. The temperature was measured using a digital thermometer. The 1-L water samples were stored in a refrigerator and then shipped, overnight on ice, to Arizona State University. There, sub-samples were collected and analyzed for adsorbable organic fluorine (AOF) and PFAS. Samples for PFAS were sent to Eurofins Laboratory and analyzed for PFAS compounds using EPA Method 533.

Results and Discussion

Synthetic Water Low Concentration Test Concentrations of PFOA and PFOS for the low concentration test are shown in Figure 4. Using these data, a first-order kinetic decay constant was calculated using a linear least-squares fit through the data. For PFOS, the rate constant was calculated as 0.0309 min-1, while the rate constant for PFOA was calculated as 0.0298 min-1. During the course of the experiment, the current averaged 61.2A.

AOF was measured using Metrohm combustion ion chromatography (Metrohm, Switzerland) coupled with a 920 absorber module and 930 compact ion chromatography flex system. Extraction of the samples was performed using APU sim sample adsorption unit (Analytikjena, Germany). 100 milliliter (mL) of sample passed through two AOF activated carbon microcolumns (P/N 402-880.614, Analytikjena, Germany) according to the method described elsewhere with slight modification (13). The activated carbon columns were then washed with 10 mL of 0.1% ammonia solution (NH4OH) to remove inorganic F- followed by 30 mL Milli-Q water (18 megaohm per centimeter [MΩ.cm]) to wash away any residual NH4OH (14). Later, both columns were manually transferred into the ceramic boats and sent into the combustion chamber with auto boat drive and burned for 20 min at 1050°C. The off-gas was collected in the absorber module into 10 mL Milli-Q water (18 MΩ.cm) and analyzed with 930 compact ion chromatography. The minimum reporting limit for F- was 2 µg/L. 26

Figure 4: PFAS concentration versus applied power—low concentration test.

Results of AOF analyses are shown in Figure 5. It should be noted that the detection limit for this assay was 2 µg/L and the results at ~550 and 800 watts per hour per gallon (W-hr/gal) applied power were reported as below this detection limit. Therefore, the destruction of the PFAS exceeded 56%.

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Electrochemical Destruction of PFOA and PFOS in High-Salinity Water continued

Figure 5: Plot of adsorbable organic fluorine results—low concentration test.

Figure 6: PFAS concentration versus applied power—high concentration test.

Figure 7: Plot of adsorbable organic fluorine results—high concentration test.

High Concentration Test Concentrations of PFOA and PFOS for the high concentration test are shown in Figure 6. Using these data, a first-order kinetic decay constant was calculated using a linear least-squares fit through the data. For PFOS, the rate constant was calculated as 0.0246 min-1, while the rate constant for PFOA was 0.0240 min-1. During the course of the experiment, the current averaged 55.6A. Results of the AOF analysis is shown in Figure 7. Based on the change in the adsorbable organic fluorine, it is estimated that >93% of the added PFAS was mineralized.

Figure 8: Adsorbable organic fluorine and total PFAS concentration versus applied power—low-concentration test.

For both the high- and low-concentration tests, in addition to the PFOA and PFOS, other PFAS species were also measured, including carboxylic acids (C5-C10) and sulfonic acids (C6-C8). These results are shown in Table A. In general, small amounts of these by-products were detected. While EPA Method 533 measures 25 individual compounds (including PFBA and PFBS), only species with any detectable concentrations are shown in the table.

As shown in Figures 8 and 9, the AOF tracked the sum of all measured PFAS compounds quite closely, especially for the high concentration test.

Figure 9: Adsorbable organic fluorine and total PFAS concentration versus applied power—high-concentration test.

It is interesting to note that after the PFOA and PFOS reached non-detectable levels (2 ng/L) after application of 550 W-hr/gal, these compounds reappeared in the mass spectroscopy scans, possibly due to condensation of these compounds from shorter chains. This phenomenon has been noted in other internal (unpublished) testing using different levels of PFAS and salts. Likewise, for the 27

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Electrochemical Destruction of PFOA and PFOS in High-Salinity Water continued

high concentration test, the adsorbable organic fluorine also increased at the end of the test after non-detectable levels were achieved. Other studies have also reported increases in the concentration of shorter chain compounds after extended treatment (12, 16) supporting information).

A photograph of the leachate before and after treatment is shown in Figure 10.

Figure 10: Photograph of Leachate before (left) and after (right) electrolysis.

It is well established that oxidizable precursor compounds can be transformed into PFAS compounds (17, 18) The presence of higher concentrations of measurable PFAS following the achievement of non-detectable levels suggests that the electrochemical process transformed the initial PFOA and PFOS into small fragments that could act as precursor compounds.

Continuing to treat the water with these compounds led to reformation of compounds measurable by EPA 533. This would suggest that users should be careful to properly select and size electrochemical oxidation systems to maximize PFAS destruction without leading to condensation of PFAS from these smaller fragments.

Leachate

Table B shows rate constant values for these tests along with values extracted from tests previously conducted for customers as well as those collected from various literature sources.

Due to the small volume of water available, only a single timed sample was collected after five hours of recirculation. The initial concentration of PFOA was 1,500 ng/L and the concentration of PFOS was 560 ng/L. The results indicated that 98% of PFOA and >99% of PFOS was removed during the testing. The calculated first order rate constants for these compounds are 0.0131 min-1 for PFOA and 0.0163 min-1 for PFOS.

As seen in Table B, the rate constants reported in this study are in line with those reported by Liu et al. (19) and Lin et al. (16) and are higher than those reported by Wang et al.

(20), but lower than that reported by Wang et al. (12).

Table A: By-Product Formation Carboxylic Acids (ng/L)

Sulfonic Acids (ng/L)

Time (min)

PFPeA [C5]

PFHxA [C6]

PFHpA [C7]

PFOA [C8]

PFNA [C9]

PFDA [C10]

PFHxS [C6]

PFHpS [C7]

6:2 FTS [C8]

PFOS [C8]

0

ND

7

4

2,550

6

19

5.5

13

38.5

3,000

120

ND

ND

ND

73

ND

ND

ND

ND

71

60

240

ND

44

ND

ND

ND

ND

ND

ND

230

ND

360

ND

140

72

140

44

43

ND

ND

330

78

0

2.1

50.5

16

21,500

31.5

87

46

180

66

33,500

120

ND

61

ND

290

ND

ND

ND

ND

56

400

240

ND

89

ND

140

ND

ND

ND

ND

340

190

360

ND

110

ND

130

55

75

ND

ND

700

300

Note: ND = non detect

28

the ANALYST Technology Supplement 2023

Electrochemical Destruction of PFOA and PFOS in High-Salinity Water continued

Conclusions

The results of these tests and a review of available literature demonstrate that EO can destroy PFAS compounds, achieving high degrees of defluorination (>90%). While this has been demonstrated in many other papers, most of these have been performed in labs using model waters. The use of a commercially available reactor is a key step towards commercialization and widespread implementation of this emergent technology.

The decay rates measured during this study are generally within one order of magnitude of those reported by a number of other studies published in the past several years using similar anodes. A comparison of decay rates in a synthetic water with negligible levels of natural organic matter and landfill leachate with very high levels of natural organic matter suggests that this organic matter does not significantly interfere with the destruction of PFAS.

organic molecules and increasing hydrophilicity. This reaction is thereby preventing them from sorbing to the electrodes, or if they have sorbed, the oxidants, possibly in combination with oxygen gas formation at the anode provide for a cleaning mechanism, which frees up adsorption sites for PFAS molecules.

Thus, when applied to high concentration streams that also contain high levels of salts and natural organic matter, EO systems can be cost effective when compared to traditional treatment processes such as GAC or IX, which would be fouled or exhausted by salt and background organics.

At present, for low level PFAS contamination of drinking water, direct electrochemical treatment of the water stream is likely not cost-effective, as GAC and IX are commoditized and are well suited for removing low levels of PFAS. The most likely short-term scenario for implementation of EO for treatment of PFAS in municipal water treatment is through treatment of concentrated waste brines from IX and RO treatment.

However, changes in the regulatory environment could also impact this as a move to classify PFAS as hazardous waste would alter the economics of disposal of spent GAC and IX resins.

As shown in Figure 10, treatment of the leachate resulted in an observable difference in color between the untreated and treated leachate. The change in color likely also represents decreased hydrophobicity of the organics as has been demonstrated in numerous studies with conventional oxidants and natural organic matter (21, 22). Because it is known that PFAS does not react with these traditional oxidants, the authors surmise that the in-situ oxidants are reacting with the background

Table B: Compilation of First Order Rate Constants for PFAS Destruction by Magnéli-phase Ti4O7 Anodes Condition

Water Matrix

Voltage (V)

Current Density (mA/cm2)

PFOA

PFOS

Low C

Synthetic

8.1

66.1

3.0 x 10 -2

3.1 x 10 -2

High C

Synthetic

8.0

60.0

2.4 x 10 -2

2.5 x 10 -2

Customer 1

Leachate

7.5

81.0

1.3 x 10 -2

1.6 x 10 -2

Lin et al. 2018, Reference 16

DI w/20 mM NaClO4

3.7-3.9 (anodic potential)

5

3.4 x 10 -2

1.3 x 10 -2

Sulfate

DI w/40 mM Na2SO4

3-3.5 (anodic potential)

10

3.5 x 10 -2

—-

Nitrate

DI w/60 mM NaNO3

3-3.5 (anodic potential)

10

1.4 x 10 -2

—-

Wang et al. 2020, Reference 12

DI w/100 mM Na2SO4

3-3.5 (anodic potential)

10

—-

4.3 x 10 -1

Wang et al. 2021, Reference 20

IX waste brine

Not reported

10

1.2 x 10 -3

1.9 x 10 -3

Case

This Study

Liu et al. 2019, Reference 19

29

First Order Rate Constant (min-1)

the ANALYST Technology Supplement 2023

Electrochemical Destruction of PFOA and PFOS in High-Salinity Water continued

References

1. Meng P.; Deng, S.; Du, Z.; Wang, B.; Huang, J.; Wang, Y.; Yu, G.; Xing, B. (2017). “Effect of hydro-oleophobic perfluorocarbon chain on interfacial behavior and mechanism of perfluorooctane sulfonate in oil-water mixture,” Scientific Reports, 7:44694.

2. Dorrance, L.R.; Kellogg, S.; Love, A.H. (2017). “What You Should Know about Per- and Polyfluoroalkyl Substances (PFAS) for Environmental Claims,” .

Environmental Claims Journal, 29, pp. 290-304.

3. Tow, E.W.; Ersan, M.S.; Kum, S.; Lee, T.; Speth, T.F.; Owen, C.; Bellona, C.; Frenkel, V.S. (2021). “Managing and Treating Per- and Polyfluoroalkyl Substances (PFAS) in Membrane Concentrates,” AWWA Water Science, 3.

4. Chaplin, B.P. (2014). “Critical Review of Electrochemical Advanced Oxidation Processes for Water Treatment Applications,” Environ. Science: Processes & Impacts, 16, p. 1182.

5. Niu, J.; Lin, H.; Xu, J.; Wu, H.; Li, Y. (2012). “Electrochemical Mineralization of Perfluorocarboxylic Acids (PFCAs) by Ce-Doped Modified Porous Nanocrystalline PbO2 Film Electrode,” Environmental Science & Technology, 46, pp.

10191-10198.

6. irés, I.; Brillas, E.; Oturan, M.A.; Rodrigo, M.A.; Panizza, M. (2014). “Electrochemical Advanced Oxidation Processes: Today and Tomorrow. A Review,” Environmental Science and Pollution Research, 21, pp. 8336-8367.

7. Martínez-Huitle, C.A.; Ferro, S. (2006). “Electrochemical Oxidation of Organic Pollutants for the Wastewater Treatment: Direct and Indirect Processes,” Chemical Society Reviews, 35, pp. 1324-1340.

8. Carter, K.E.; Farrell, J. (2008). “Oxidative Destruction of Perfluorooctane Sulfonate Using Boron-Doped Diamond Film Electrodes,” Environmental Science & Technology, 42, pp. 6111-6115.

9. Comninellis, C.; Kapalka, A.; Malato, S.; Parsons, S.A.; Poulios, I.; Mantzavinos, D. (2008). “Advanced Oxidation Processes for Water Treatment: Advances and Trends for R&D,” Journal of Chemical Technology & Biotechnology, 83, pp. 769-776.

10. Liang S.; Pierce, R. Jr.; Lin, H.; Chiang, S.-Y.; Huang, Q. (2018). “Electrochemical Oxidation of PFOA and PFOS in Concentrated Waste Streams,” Remediation, 28, pp. 127–134.

11. Le, T.X.H; Haflich, H.; Shah, A.D.; Chaplin, B.P. (2019). “Energy-Efficient Electrochemical Oxidation of Perfluoroalkyl Substances Using a Ti4O7-Reactive Electrochemical Membrane Anode,” Environmental Science & Technology Letters, 6, pp. 504-510.

12. Wang, Y.; Pierce, R. Jr.; Shi, H.; Liab, C.; Huang, Q. (2020). “Electrochemical Degradation of Perfluoroalkyl Acids by Titanium Suboxide Anodes,” Environmental Science: Water Research & Technology, 6, pp. 144-152.

13. British Standard and B.I. (2004). “Water Quality—Determination of Adsorbable Organically Bound Halogens (AOX), ISO 9562:2004.

14. Miyake, Y.; Yamashita, N.; Rostkowski, P.; So, M. K.; Taniyasu, S.; Lam, P. K. S.; Kannan, K. (2007). “Determination of Trace Levels of Total Fluorine in Water Using Combustion Ion Chromatography for Fluorine: A Mass Balance Approach to Determine Individual Perfluorinated Chemicals in Water,” Journal of Chromatography A, 1143 (1–2), pp. 98–104.

15. Department of Defense (2019). “Appendix B” in the DoD/DOE Consolidated Quality Systems Manual (QSM) for Environmental Laboratories, Based on ISO/ IEC 17025:2005(E), ISO/IEC 17025:2017(E), and the NELAC Institute (TNI) Standards, Volume 1 (September 2009), DoD Quality Systems Manual Version 5.3 U.S. Department of Defense, Washington, D.C. 16. Lin, H.; Niu, J.; Liang, S.; Wang, C.; Wang, Y.; Jin, F.; Luo, Q.; Huang, Q. (2018).

“Development of Macroporous Magnéli Phase Ti4O7 Ceramic Materials: As an Efficient Anode for Mineralization of Poly- and Perfluoroalkyl Substances,” Chemical Engineering Journal, vol. 354.

17. Al Amin, Md.; Luo, Y.; Nolan, A.; Robinson, F.; Niu, J.; Warner, S.; Liu, Y.; Dharmarajan, R.; Mallavarapu, M.; Naidu, R.; Fang. C. (December 2021). “Total Oxidizable Precursor Assay Towards Selective Detection of PFAS in AFFF,” Journal of Cleaner Production, vol. 328, 129568.

18. 18. Kaiser, A-M.; Saracevic, E.; Schaar, H.P.; Weiss, S.; Hornek-Gausterer. R. (2021). “Ozone as Oxidizing Agent for the Total Oxidizable Precursor (TOP) Assay and as a Preceding Step for Activated Carbon Treatments Concerning per- and Polyfluoroalkyl Substance Removal,” Journal of Environmental Management, 300, 113692.

19. Liu, G; Zhou, H.; Teng, J.; You, S. (2019). “Electrochemical Degradation of Perfluorooctanoic Acid by Macro-Porous Titanium Suboxide Anode in the Presence of Sulfate,” Chemical Engineering Journal, pp.7-14.

20. Wang, L.; Nickelsen, M.; Chiang, S.-Y.; Wang, S.W.Y.; Liang, S.; Mora, R.; Fontanez, R.; Anderson, H.; Huang, Q. (2021). “Treatment of Perfluoroalkyl Acids in Concentrated Wastes from Regeneration of Spent Ion Exchange Resin

by Electrochemical Oxidation Using Magnéli phase Ti4O7 Anode,” Chemical Engineering Journal Advances, 5, 100078.

21. Jung, C.; Deng, Y.; Zhao, R.; Torrens, K. (2017). “Chemical Oxidation for Mitigation of UV-Quenching Substances (UVQS) from Municipal Landfill Leachate: Fenton Process versus Ozonation,” Water Research, vol. 108, pp. 260-270.

22. Bose, P.; Bezbarua, B.K.; Reckhow. D.A. (1994). “Effect of Ozonation on Some Physical and Chemical Properties of Aquatic Natural Organic Matter,” Ozone Science and Engineering 16(2).

30

Orren Schneider, PhD, is the chief science officer of Aclarity Inc., which designs electrochemical systems for the degradation of PFAS and other contaminants. He has over 35 years of experience; previously he had worked for American Water as the manager, Water Technology in the R&D team. Dr. Schneider has primary expertise in evaluation and implementation of advanced water treatment technologies, including coagulation/clarification/filtration, oxidation/disinfection, algae control, adsorption, and membrane technologies. He holds a BS in chemical engineering from Cornell University, and an MS and PhD in environmental engineering from the University of Massachusetts at Amherst. He may be contacted at orren.schneider@aclaritywater.com.

José R. Alvarez, PhD, PE., was employed at Aclarity when this paper was written. He currently is a project technical lead at CDM Smith with 24 years of experience in the water industry.

His technical expertise includes design of water and water reclamation systems. He holds a doctorate in civil engineering from Worcester Polytechnic Institute and received his MSc in environmental engineering from the Universidad Nacional de Colombia.

Elisabeth Christ holds bachelor’s degrees in environmental engineering and society, and technology & policy from Worcester Polytechnic Institute. She joined Aclarity in 2021 and focuses on bench scale design, maintenance and product development for electrochemical oxidation reactors. She is a member of the New England Water Environment Association.

This paper was originally presented at the International Water Conference® that was conducted Nov. 6-10, 2022, in Orlando, Florida.

Please visit www.eswp.com/water for more information about the conference or how to purchase the paper or proceedings.

Keywords: DESTRUCTIVE TECHNOLOGY, ELECTROCHEMICAL, EPA, HAZARDOUS WASTE, OXIDATION, PFAS

the ANALYST Technology Supplement 2023

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Can a Micro-Adsorbent Material and Ceramic Filtration Treatment Successfully Remove PFAS? Terence K. Reid (Aqua-Aerobic Systems, Inc.) and Joseph Quinnan (Arcadis)

Background

The Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) was enacted by more than four decades ago to address releases of hazardous substances that could endanger public health or the environment. Through taxing the chemical and petroleum industries, this law established liability for responsible parties and funding for cleanup when such parties could not be identified or no longer existed. CERCLA was subsequently amended by the Superfund Amendments and Reauthorization Act (SARA) (1) in response to the complexities associated with remedies, enforcement and innovative technological approaches to remediation.

32

While CERCLA/SARA attempted to stress a “polluter pays” concept (2), it couldn’t comprehend the recalcitrant and ubiquitous attributes we currently face with so called “forever chemicals”, or per- and polyfluoroalkyl substances (PFAS). Aqueous film-forming foam (AFFF) has saved countless lives over the years yet has threatened the health of many more. As of October 1, 2023, the U.S. Department of Defense (DoD) will no longer purchase AFFF that exceeds 1 ppb PFAS, with complete elimination of PFAS one year later (3). However, the DoD continues to address over 700 U.S. military sites with known or suspected PFAS legacy discharges. The DoD’s Environmental Security Technology Certification Program (ESTCP) is a major initiative to identify the ANALYST Technology Supplement 2023

Can a Micro-Adsorbent Material and Ceramic Filtration Treatment Successfully Remove PFAS?

and demonstrate the most promising and innovative technologies to resolve the most urgent environmental threats, with PFAS being a primary focus.

High-pressure membranes such as reverse osmosis (RO) and nanofiltration (NF) are highly effective methods to remove PFAS, but often require significant pretreatment, high energy input, and increased capital and operational costs. Further, high-pressure membranes simply concentrate the PFAS into a waste stream that can be 10 to 20% of the design flow.

A recently completed ESTCP project demonstrated exceptionally high removal capacities using an advanced sub-micron micro-adsorbent and ceramic filtration technology to adsorb and separate PFAS from two different water matrices. One PFAS treatment system A exhibited broad-spectrum PFAS removals from AFFF impacted surface water at the Horsham Air Guard Station (Horsham) and from groundwater at the Willow Grove Naval Air Station (Willow Grove) over a two-year study (4).

Granular activated carbon (GAC) has been the most common approach to remove PFAS from water, relying on hydrophobic interactions to adsorb the contaminants.

GAC offers benefits in ease of operation and initial capital costs but suffers from non-selectivity that results in reduced sorbability of short-chained PFAS compounds. Higher levels of comingled DOM and suspended solids can compete for adsorption sites and can cause potential media biofouling, resulting in early breakthrough and premature media replacement. The high costs associated with frequent GAC replacements can be reduced by reactivation if the site is reasonably near such reactivation facilities.

Introduction

There are many technologies that target PFAS removal through adsorption, separation or destruction methods.

Each technology differs in their relative removal efficiencies, energy requirements, waste products and operational requirements. PFAS removal from contaminated water presents challenges due to the vast number of species that have different physical and chemical properties. The hydrophobic, lipophobic and surfactant properties that make PFAS highly useful in commercial products make them equally difficult to remove from water.

Ion exchange (IX) is another popular option, relying on both hydrophobic and electrostatic interactions to remove PFAS (12, 13) IX resins can provide higher sorption capacities and excellent removal of anionic short-chained PFAS compared with GAC, but are relatively ineffective at removing neutral PFAS subgroups (8, 12). Certain IX resins are designed for regeneration, but at a higher capital cost due to complicated equipment layouts, flow schemes, and chemical handling. Single-use IX resins are most commonly used, but can be subject to scaling, biofouling and sediment loading, thereby reducing the replacement interval. In many cases, pre-treatment using GAC or zeolite filters are used in conjunction with IX resins.

The PFAS family of compounds can exist in a class as either polymeric or as non-polymers, with non-polymers further divided in to per- and polyfluoroalkyl substances subclasses. Many of these compounds exist as potential precursors, which can be transformed in situ, during transport or treatment into a smaller PFAS compound. The primary compounds of interest include perfluoroalkyl acids (PFAAs), which undergo no further degradation and are often referred to as terminal PFAS compounds. The two PFAA subgroups include carboxylic and sulfonic acids, which respond differently to treatment methods.

Co-contaminants present added difficulties due to interferences with separation, adsorption and thermal, electrical and chemical oxidation efficiencies. Dissolved organic matter (DOM), sediments and metal ions can present challenges to remediation efforts (5-7).

Difficulties can include partial removal, fouling, increased energy demand, lack of scalability and potential transformation to short-chained intermediates (8-11).

33

This study evaluated a carbon-based, micro-adsorbent coupled with a low-pressure system to adsorb and remove PFAS as well as suspended solids and other comingled DOM. The media presents a significantly higher effective surface area due to a mean particle diameter of about 1 micrometer (µm). The small particle size permits media suspension in a slurry that results in rapid kinetics and higher specific adsorption capacities (SACs) that are about 400 times higher than GAC (14).

Methodology

The demonstration study’s objectives were to confirm the technology’s capability of achieving a 40 nanograms per the ANALYST Technology Supplement 2023

Can a Micro-Adsorbent Material and Ceramic Filtration Treatment Successfully Remove PFAS? continued

liter (ng/L) sum of the Third Unregulated Contaminant Monitoring Rule (UCMR3) compounds, including PFOS, PFOA, PFNA, PFHxS, PFHpA and PFBS. This target was selected in anticipation of EPA maximum contaminant levels (MCLs) falling significantly below the 70 ng/L combined PFOA and PFOS health advisory levels that existed at the time of the research.

System operation. The process flow schematic (Figure 1) illustrates the technology’s operation. Raw water is pumped (1) and screened (2) prior to the introduction to the sorbent reactor (4). Micro-adsorbent material (3) is initially pumped into the sorbent reactor to reach the target slurry concentration. The slurry is pumped (5) through the ceramic separator (6) and returned to the reactor in a crossflow hydraulic flow path. The sorbent is maintained in the closed-loop reactor for a short interval of one to two weeks before replacement.

As flow enters the system, it displaces filtered, PFASfree water through the membrane and is collected in a filtrate tank (7). The system does not generate backwash in the one to two-week period as the membrane system is cleaned using a brief back-pulse using filtrate and a pump (8). The filtrate used in the back-pulse operation is discharged into the sorption reactor and retreated.

system by a factor of 3 to 5 times with a final slurry concentration of about 80 to 100 grams per liter (g/L).

The slurry is then removed to off-line gravity thickening, where it is further concentrated by another 2 to 3 times, with a final disposal concentration of 200 to 250 g/L. Typical operation will produce approximately 40 to 80 gallons of waste solids for each 1 million gallons of water treated.

Surface Water at the Horsham Air Guard Station

Storm events dramatically changed the water surface and sediment loading in Horsham Outfall No. 9. A floating, submersible pump was used to draw water during both dry and wet weather conditions and through a coarse (2.3 millimeter [mm]) screen. Baseline turbidity was typically between 2 and 4 Nephelometric Turbidity Units (NTU), but often exceeded 100 NTU due to wind and rain events (Figure 2).

Figure 2: Horsham AGS outfall during dry weather (left) and wet weather (right) conditions.

Figure 1: Process Flow Diagram for the treatment system used at Horsham AGS and Willow Grove.

Waste minimization. The short detention, highadsorption capacity and frequent replacement interval results in media replacement that is only 1 to 2% of that required for GAC on a dry mass basis. As a slurry, the media replacement can be automated using pumps, valves and controls. At time of replacement, the feed pump (1) is stopped briefly while the system continues to produce filtrate. The sorbent reactor level is reduced, and the sorbent slurry is concentrated using the membrane 34

Effluent from the system was virtually free of suspended solids, which increased rapidly within the sorption reactor and interfered with PFAS removal. An automatic backwashing filter was installed to remove high sediment levels prior to the adsorption process. A 5-µm cloth media filter provided effective pretreatment and was able to reduce turbidity from values from 30 to 90 NTU to levels of 2 to 4 NTU (Figure 3). While the pre-treatment filter effectively removed sediment, it had little effect on raw PFAS concentrations.

A series of 26 individual trials were conducted over a nine-month period that evaluated sorbent reactor the ANALYST Technology Supplement 2023

Can a Micro-Adsorbent Material and Ceramic Filtration Treatment Successfully Remove PFAS? continued

Figure 3: Influent and effluent turbidity using cloth media filtration prior to the PFAS treatment systemA .

Figure 5: Dual stage PFAS removal systemA performance at Horsham (values listed at 3 ng/L reflect the test method’s limit of quantification).

concentrations from 5 to 50 g/L and detention times from 5 to 60 minutes (min). The two-train system was operated in both series and parallel modes. DOM typically ranged from 2 to 4 mg/L with particulate concentrations spiking with the increased sediment loadings. Table A illustrates the influent concentrations of the targeted PFAS compounds encountered throughout the study.

on identifying the adsorption capacity at the targeted breakthrough threshold. The latter portion of testing was conducted in a two-stage (or series) configuration using a lead-lag arrangement in which the effluent from the first stage fed the second stage system. This was important to understand, as typical PFAS treatment systems include two or more treatment systems in series, often with two different technologies used (e.g., GAC followed by IX).

Single-stage testing proved to be highly effective at a time-dependent sorbent level of 300 g-min/L and was able to meet the 40 ng/L combined UCMR3 compound list at a specific adsorption capacity of 125 micrograms (µg) PFAS removed per gram of sorbent (Figure 4). The sorbent’s capacity to remove PFAS is dependent upon the targeted effluent objective, with higher effluent values offering more longevity in media performance. For example, a higher 300 ng/L effluent target for combined UCMR3 compounds resulted in more than 250 µg PFAS removed per gram of sorbent from a 9,000 ng/L influent over the replacement interval.

The series operation of the PFAS removal system proved to be quite effective at reducing all UCMR3 compound concentrations to desired levels within the defined replacement period. Figure 6 illustrates the staged performance when the technology was used in series.

Most of the initial testing evaluated the PFAS treatment technologyA in a one-stage operation, with a focus

Rapid, small-scale column testing (RSST) was performed using GAC and compared with the microadsorbent used in the PFAS treatment system A. The data in Table B reflects the adsorption capacity reached at a 10% breakthrough concentration for both media types.

Consistent with prior studies (14), the micro-adsorbent proved to be several orders of magnitude more effective in removing most compounds. More importantly, the GAC was unable to reach the 40 ng/L combined

Table A: Horsham AGS Influent Composition Statistic

Total Measured

UCMR3

PFOS

PFOA

PFNA

PFHxS

PFHpA

PFBS

Count

101

101

101

101

101

101

101

101

Maximum

18,213

12,259

10,032

602

14

2,399

203

395

Upper Quartile

11,943

8,743

6,138

456

14

1,750

144

297

Media

10,510

7,597

5,103

381

11

1,603

133

269

Mean

9,842

7,109

4,880

367

12

1,498

123

240

Lower Quartile

7,815

5,513

3,695

298

11

1,093

96

178

Minimum

2,108

1,641

1,237

79

7

262

1

20

Standard Deviation

3,171

2,307

1,773

117

2

508

40

82

35

the ANALYST Technology Supplement 2023

Can a Micro-Adsorbent Material and Ceramic Filtration Treatment Successfully Remove PFAS? continued

UCMR3 target during the RSSCT evaluation, whereas the PFAS-removal treatment approach A was successful in the pilot testing.

UCMR3 compounds comprised a higher fraction (84%) of the total PFAS measured. Similarly, combined PFOA and PFOS made up 85% of the UCMR3 compounds (Table C).

Groundwater at the Willow Grove Naval Air Station

A series of ten individual trials were completed evaluating both single- and dual-staged treatment.

With total organic carbon (TOC) levels below 1 mg/L, adsorption capacities were significantly higher than recorded on the previous surface water. With PFAS values often exceeding 40,000 ng/L, the system was unable to meet the 40 ng/L combined UCMR3 target within the designed replacement interval. However, the system was able to attain the prevailing 70 ng/L EPA HAL at an adsorption capacity exceeding 4,000 µg PFAS removed per gram of sorbent (Figure 7). Further, capacities approached 7,000 µg/g while realizing more than 95% removal of the UCMR3 compounds.

Phase two of the program included similar testing at the nearby Willow Grove NAS facility. Unlike the prior testing, this effort evaluated the PFAS treatment technologyA on groundwater that contained no measurable solids but contained significantly higher PFAS levels. Figure 6 shows the pilot test equipment used at Willow Grove.

Figure 6: Dual-system PFAS treatment A pilot system at Willow Grove NAS.

Figure 7. PFAS Removal with a single stage systemA at Willow Grove.

Table B: Comparative Adsorption Capacities (µg PFAS removed per gram of sorbent) Test

PFOA + PFOS UCMR3

PFOS

PFOA

PFHXS

PFHPA

PFBS

GAC

0.6

2.1

0.7

0.1

0.7

0.1

0.1

PFOS Removal System

>431

578

>543

31

124

4.7

4.0

Table C: Willow Grove NAS Influent Composition Statistics

Total Measured

UCMR3

PFOS

PFOA

PFNA

PFHxS

PFHpA

PFBS

Count

63

63

63

63

NA

63

63

63

Maximum

58,426

49,392

39,429

3,300

NA

6,245

410

990

Upper Quartile

44,801

37,814

30,383

2,230

NA

4,733

301

836

Median

39,840

33,469

26,000

1,937

NA

4,244

276

719

Mean

40,859

34,291

27,191

2,090

NA

3,987

289

734

Lower Quartile

35,623

29,796

23,000

1,788

NA

3,623

252

645

Minimum

31,690

25,616

19,175

1,633

NA

2,092

232

489

Std. Dev.

6,283

5,636

4,948

427

NA

1,081

47

123

36

the ANALYST Technology Supplement 2023

Can a Micro-Adsorbent Material and Ceramic Filtration Treatment Successfully Remove PFAS? continued

exist. Factors, including PFAS species, concentration, co-contaminants, water quality characteristics, site infrastructure, effluent limits, and economic considerations will influence the technologies that are most suitable for any individual circumstance.

The first stage in the PFAS treatment A is responsible for the majority of the overall PFAS removal, but also removes TOC with higher molecular weights and particulates from the raw water. The resulting filtrate is exceptionally clean and ideally conditioned for second-stage adsorption of shorter-chained constituents (i.e., C4 and C6 PFAS). Two-stage testing proved to be successful in reaching the 40 ng/L combined UCMR3 target (Figure 8).

GAC, IX resins, or a combination of the two are currently the most common approaches for removing PFAS from water and wastewater. Emerging regulatory pressures are impacting the technology landscape as responsible parties seek effective, resilient and economically viable solutions. Removal technologies such as high-pressure membranes and foam fractionation, as well as destructive solutions like supercritical or electrochemical water oxidation can positively remove PFAS but may not be affordable or scalable in all cases. There exists an increasing need for alternative treatment solutions to solve these problems in both an environmentally and fiscally responsible way.

Figure 8: Dual-stage PFAS-removal systemA performance at Willow Grove (values listed at 1 ng/L reflect the test method’s limit of quantification).

The PFAS-removal system A provides an alternative approach for cost-effective and reliable PFAS removal.

With adsorption capacities more than 400 times greater than conventional adsorbents like GAC, media costs and disposal requirements can be lowered. The use of low-pressure, ceramic membranes to separate the sorbent from treated water results in exceptional quality effluent that is compliant with emerging drinking water standards. Requirements for media replacement are simplified with the automated slurry control via pumps and valves. Weekly or bi-weekly spent media replacement reduces costs, labor and minimizes downtime events.

The adsorption capacity remained high in two-stage operation with values exceeding 2,000 µg PFAS per gram of sorbent at the 27 ng/L effluent. Another notable difference from GAC was the system’s ability to achieve significant removals of the C4 PFBS compound, particularly in the second stage of treatment. The effluent target during the testing was selected at 40 ng/L for the combined UCMR3 compounds, but the system performance closely aligned with the EPA Maximum Contaminant Levels (MCLs) proposed in the National Primary Drinking Water Regulation (NPDWR) for six PFAS compounds. In the proposed rule, effluent discharge limits for PFOA and PFOS would be regulated to 4 ng/L each (15).

More importantly, frequent adsorbent replenishment assures stable performance and avoids issues related to biological growth, solids build-up or media scaling.

Unlike typical RSSCTs, scalable piloting of this technology can be completed in a short time with unmodified, production-quality sorbent and filtration operation. As the complexities with PFAS removal are unique to each situation, piloting is essential to understand the long-term operational costs. It is equally critical to evaluate different alternatives to identify the treatment technology that best fits the given needs.

Summary and Implications

Depending on the source and classification criteria, anywhere from 4,000 to more than 14,000 unique PFAS compounds have been identified, all of which have been designed with chemical properties that make removal from water challenging. It follows that universally effective removal technology does not 37

the ANALYST Technology Supplement 2023

Can a Micro-Adsorbent Material and Ceramic Filtration Treatment Successfully Remove PFAS? continued

References

Abbreviations

1. EPA (April 10, 2023). “The Superfund Amendments and Reauthorization Act (SARA),” https://www.epa.gov/superfund/superfund-amendments-and-reauthorization-act-sara.

2. Moore, Sen. Shelley. (September 12, 2023). “Addressing America’s PFAS Issue Cannot Wait Forever,” – Roll Call, accessible at https://rollcall.com/2023/09/12/ addressing-americas-pfas-issue-cannot-wait-forever.

3. Cramer, P. (February 2022). “Briefing to Congress on Aqueous Film Forming Foam (AFFF) Replacements and Alternatives,” accessible at https://media. defense.gov/2022/Apr/05/2002970013/-1/-1/0/AFFF-TECHNOLOGIES-REPLACEMENT-AND-ALTERNATIVES-BRIEFING-FEB-2022.PDF 4. Quinnan, J.; Reid, T.; Pulikkal, V.; Bellona, C. (December 2022). “Improved longevity and selectivity of pfas groundwater treatment using sub-micron powdered activated carbon (SPAC) and ceramic membrane filtration (CMF),” ESTCP Project ER19-5181 Final Report. ER19-5181 Final Report.pdf (amazonaws.com).

5. Dixit, F.; Barbeau, B.; Mostafavi, S.G.; Mohseni, M. (September 2020). “Removal of Legacy PFAS and Other Fluorotelomers: Optimized Regeneration Strategies in DOM-Rich Waters,” Water Research, 183, accessible at https://doi. org/10.1016/j.watres.2020.116098 “, 183. https://doi.org/10.1016/j. watres.2020.116098.

6. hong Vo, H.N.; Ngo, H.H.; Guo, W.; Hong Nguyen, T.M.; Li, J.; Liang, H.; Deng, L.; Chen, Z., Hang Nguyen, T.A. (2020). “Poly‐and perfluoroalkyl substances in water and wastewater: A comprehensive review from sources to remediation,” Journal of Water Process Engineering, 36, available at 101393HYPERLINK “https://doi.org/10.1016/j.jwpe.2020.101393”. https://doi.org/10.1016/j. jwpe.2020.101393.

7. Naidu, R.; Nadebaum, P.; Fang, C.; Cousins, I.; Pennell, K.; Conder, J.; Newell, C.J.; Longpré, D.; Warner, S.; Crosbie, N.D.; Surapaneni, A.; Bekele, D.; Spiese, R.; Bradshaw, T.; Slee, D.; Liu, Y.; Qi, F.; Mallavarapu, M.; Duan, L.; Nathanail, P. (2020). :Per- and poly-fluoroalkyl substances (PFAS): Current status and research needs,” Environmental Technology & Innovation, 19 accessible at https://doi. org/10.1016/j.eti.2020.100915.

8. Crone, B.C.; Speth, T.F.; Wahman, D.G.; Smith, S.J.; Abulikemu, G.; Kleiner, E.J.; Pressman, J.G. (2019). “Occurrence of Per- and Polyfluoroalkyl Substances (PFAS) in Source Water and their Treatment in Drinking Water,” Critical Reviews in Environmental Science and Technology 49(24), pp. 2359-2396, accessible at https://doi.org/10.1080/10643389.2019.1614848.

9. Vu, C.T.; Wu, T. (2022). “Recent progress in adsorptive removal of per- and poly-fluoroalkyl substances (PFAS) from water/wastewater,” Critical Reviews in Environmental Science and Technology52(1), pp. 90-129, https://doi.org/10.1080/10 643389.2020.1816125.

10. Appleman, T.D.; Higgins, C.P.; Quinones, O.; Vanderford, B.J.; Kolstad, C.; Zeigler-Holady, J.C.; Dickenson, E.R. (2014). “Treatment of poly- and perfluoroalkyl substances in U.S. full-scale water treatment systems,” Water Research, 51, pp. 246-55.

11. Rahman, M.F.; Peldszus, S.; Anderson, W.B. (2014). “Behaviour and fate of perfluoroalkyl and polyfluoroalkyl substances (PFASs) in drinking water treatment: A review,” Water Research, 50, pp. 318-340, ISSN 0043-1354, accessible at https://doi.org/10.1016/j.watres.2013.10.045”, https://doi. org/10.1016/j.watres.2013.10.045.

12. McCleaf, P.; Englund, S.; Ostlund, A.; Lindegren, K;, Wiberg, K.; Ahrens, L. (2017). “Removal Efficiency of Multiple Poly- and Perfluoroalkyl Substances (PFASs) in Drinking Water Using Granular Activated Carbon (GAC) and Anion Exchange (AE) Column Tests,” Water Research, 120, pp. 77-87, accessible at https://doi.org/10.1016/j.watres.2017.04.057.

13. del Moral, L.L.; Choi, Y.J.; Boyer, T.H. ( July 2020). “Comparative removal of Suwannee River natural organic matter and perfluoroalkyl acids by anion exchange: Impact of polymer composition and mobile counterion,” Water Research, 178, accessible at https://doi.org/10.1016/j.watres.2020.115846”, 178, 115846. https://doi.org/10.1016/j.watres.2020.115846.

14. Murray, C.C.; Vatankhah, H.; McDonough, C.A.; Nickerson, A., Hedtke, T.T.; Cath, T.Y.; Higgins, C.P.; Bellona, C.L. (2019). “Removal of per- and polyfluoroalkyl substances using super-fine powder activated carbon and ceramic membrane filtration,.” Journal of Hazardous Materials, 366, pp. 160-168, accessible at https:// doi.org/10.1016/j.jhazmat.2018.11.050.

15. US EPA (March 14, 2023). “Per- and Polyfluoroalkyl Substances (PFAS) Proposed PFAS National Primary Drinking Water Regulation.” https://www.epa.gov/ ground-water-and-drinking-water/national-primary-drinking-water-regulations

PFOS–Perfluorooctanesulfonic acid PFOS–Perfluorooctanoic acid PFNA–Perfluorononanoic acid PFHxS–Perfluorohexanesulfonic acid PFHpA– Perfluoroheptanoic acid PFBS–Perfluorobutanesulfonic acid

Terence Reid is the director of research and development for Aqua-Aerobic Systems, Inc. He is responsible for overseeing developmental activities focused on new product design and product enhancement in biological treatment, filtration and membrane technologies. Mr. Reid holds a number of patents in activated sludge, filtration, software control methods and PFAS removal. He holds a bachelor’s degree in civil and environmental engineering from the University of Wisconsin-Madison and a master’s degree in product design and development from Northwestern University. Mr. Reid is a licensed professional engineer registered in the state of Illinois. Mr. Reid can be contacted at treid@aqua-aerobic.com.

Joe Quinnan is a senior vice president with Arcadis in Novi, Michigan. He has more than 32 years’ professional experience in environmental consulting. He is co-author of the book Remediation Hydraulics (CRC Press, 2008). He is the technical lead for Arcadis’s PFAS program for the DoD and North American Director of Emerging Contaminants. Mr. Quinnan is currently leading several ESTCP projects and was the principal investigator on the reference study that evaluated micro-adsorbents and ceramic membrane filtration to treat PFAS-impacted water. He has both a master’s and bachelor’s degree in geological engineering from Michigan Technological University. Mr. Quinnan can be contacted at joseph.quinnan@arcadis.com.

Keywords: ACTIVATED CARBON, GROUNDWATER, ION EXCHANGE, PFAS, REVERSE OSMOSIS, SURFACE WATER

Endnote A The PFAS removal system mentioned in the text is the AquaPRS™ PFAS treatment system that has been developed by Aqua-Aerobics.

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What Would Fail First if We Did Not Feed Treatment Chemicals to a Steam System?

Chris Golden, CWT, Taylor Water Technologies LLC

Waiting to recieve access to "Things to Fix"

Sometimes it is hard to explain to facilities that spending money on water treatment chemicals is vital to protect boiler equipment and production rates in manufacturing plants. These “unbelievers” could be susceptible to other treatment technologies or simply cutting budgets for this important service. So how can you make it clear that it is necessary?

would fail first?” The costs associated with the potential outcomes far outweigh the cost of a properly designed program. Understanding and explaining this need may also help your client’s CFO appreciate you! (This may also help you explain to your spouse, family, and friends what you do for a living!) Our industry was built on this!

This article discusses the implications of poor or even non-existent chemical water treatment. “What if the chemicals got turned off? What would happen, and what

I had a cogeneration plant that was installing a backup boiler for when they had outages for the main boiler. The plant manager wanted to use this opportunity to re-train

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What If I Don’t Treat the Boiler?

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What Would Fail First if We Did Not Feed Treatment Chemicals to a Steam System? continued

In addition to a loss in production rates and high repair costs, there are additional costly problems associated with oxygen corrosion in the system: corrosion products. The corrosion products from the oxygen acting in the system, often iron and copper, are transported into the boiler, deposited onto the heat transfer surfaces, and become insulators on the boiler tubes. In turn, heat transfer is reduced, and fuel requirements increase to produce the same amount of steam.

the seasoned operators in the plant. Traditional training would be pretty boring to these veterans, so I wanted to do something different. This situation made me think of the concept, “If you don’t chemically treat steam boiler systems, what would fail first?”

Oxygen Corrosion

Most likely, parts of the system that would fail first would be due to oxygen corrosion. In an untreated system, oxygen is the most dangerous actor. As the temperatures increase in the boiler system, oxygen becomes very aggressive toward mild steel and copper components. The oxygen comes from the make-up water and is partially removed by properly working feedwater heaters and deaerators. However, residual oxygen is highly corrosive to the feedwater piping and, later, the boiler tubes. The metal loss is a pitting type of corrosion and a very early instigator of high maintenance costs.

Even more aggravating are the unplanned production shutdowns for the associated maintenance. Since oxygen is volatile, any residual oxygen within the boiler water can further affect the steam and condensate system equipment. This occurrence promotes oxygen corrosion in the whole system. Figure 1 shows an example of pitting corrosion.

“Dirty boilers” use more fuel, so the additional penalty is much higher fuel costs. As fuel is the highest operational cost item in a boiler system, even a slight efficiency loss can mean big money to a facility. This loss in efficiency is far greater than the cost of proper water treatment. Given enough time, these boiler tubes, fouled with iron and copper, will fail due to overheating. This progression is discussed further in the next section.

Of course, keep in mind that these same problems could also exist within undertreated or poorly serviced systems.

Condensate System Corrosion

Figure 1: An example of pitting corrosion. This photo shows moon craters. Source: S.O’Neil, Bluegrass KESCO INC.

The next problem most likely to affect our boiler system is untreated steam and condensate. Corrosion in the system will lead to system equipment failures, but more importantly, the transport of those corrosion products into the boiler will eventually cause more significant concerns.

Corrosion will occur in the condensate system when carbon dioxide is absorbed into the pure condensate, forming carbonic acid. The source of the carbon dioxide is carbonate alkalinity in the feedwater, which volatilizes in the boiler to form carbon dioxide in the steam. Carbonic acid lowers the condensate pH, causing acid gouging. The metal loss eventually causes leaks in the system, requiring equipment replacement.

The condensate equipment loss may be tolerable, but what is not tolerable is the subsequent corrosion product getting back into the boiler system.

This iron corrosion product enters the boiler where it prefers to deposit, in heat flux areas. These heat flux areas are where we are looking for the heat from

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Scale

the combusted fuel to heat the boiler water. The iron corrosion product is porous and less dense than the original iron on the piping. This lower-density deposit works as an insulator, impeding heat transfer and causing the boiler tube temperature to increase to produce the same amount of steam required. As the boiler tube increases in temperature, its yield strength decreases. Eventually, with enough insulating deposit, the boiler tube’s yield strength will become so low that the boiler tube fails.

The final “poison” to the boiler system is the hardness in the feedwater. Depending on the make-up water’s hardness levels, the hardness scale may compete with condensate corrosion to be considered the second most detrimental factor to the steam boiler system. However, there is usually adequate pretreatment equipment to mechanically reduce hardness coming into the system.

With copper corrosion product, the copper can also deposit on boiler tube surfaces; however, the chances for galvanic corrosion on the boiler tube can be worse than the insulating factor of the copper deposit. Metal loss of the boiler tube around the deposit will progress until the tube fails due to galvanic corrosion. According to reference documents, galvanic corrosion from copper deposits is rare in well-passivated boilers.

For these reasons, you can see why it is essential to properly treat the condensate, checking to be sure it is properly neutralized, and the corrosion product is low.

In systems where neutralizing amines are ineffective, filming amines should be considered to protect the systems. The filming amines also must be monitored to avoid under or overfeeding of treatment chemicals.

Figure 2 is an example of condensate corrosion.

Figure 2: Condensate corrosion examples. These two photos show low-pH corrosion. Source: S.O’Neil, Bluegrass KESCO INC.

Hardness, which enters the boiler system through the make-up water and then into the feedwater, will form scale on the boiler tubes in an undertreated system.

The scale then impedes heat transfer from the fireside to the boiler water, eventually causing the boiler tube to overheat until the metal’s yield strength decreases to the point of failure. However, the timing of this process depends on the amount of hardness in the feedwater.

You may say, “My pretreatment process has a softener or reverse osmosis system on the make-up water, so I don’t have any hardness entering the system.” Even though your pretreatment looks like it measures 0 parts per million (ppm) hardness, some hardness is getting through (at least) on a parts-per-billion (ppb) level.

When testing low-level hardness in any water, you should never report a level of 0 ppm calcium carbonate (CaCO3). Since there is always some hardness in the water, the correct way of reporting the hardness level is <0.1 ppm as CaCO3.* Without internal chemical treatment (like phosphates, phosphonates, chelants, polymers, and tannins), this very low level of hardness will accumulate on the boiler tubes, eventually causing failures. *Note: All test methods have low detection limits.

For hardness tests, it is generally <0.1 ppm. A proper service report should never contain “0” for a test result; it should instead list the method’s lowest detection limit as provided by the test kit manufacturer.

So, if we only treat a system for oxygen and condensate corrosion, eventually, the boiler will fail from scale.

If we have a properly operating pretreatment system, this last failure may take a long time. However, if the pretreatment is prone to periodic upsets, this failure could happen much earlier than expected.

Keep in mind that contamination of hardness into the condensate system will also accelerate this process.

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amine or blend of amines. Amines have varying vaporto-liquid (V:L) ratios, meaning they distribute across a steam system differently. In a simple system, like a boiler with a turbine, an amine with a low V:L ratio (like morpholine ~0.4) could be chosen. However, if the steam system is extensive, an amine with a high V:L ratio should be included (like cyclohexylamine ~4.0). An amine with a moderate V:L ratio (like diethylaminoethanol/DEAE ~1.7) should be used to cover intermediate areas of a steam system. These chemicals are monitored and controlled by testing condensate pH levels across the system, not just at the condensate return. Corrosion product testing (for iron and copper) must also be periodically performed to verify the performance of the chemical program.

Figure 3 shows an example of scaling in a boiler tube.

Figure 3: Scaling in a boiler tube. Source: S.O’Neil, Bluegrass KESCO INC.

Chemical Treatment Quick Overview:

To properly treat the boiler systems to prevent failure, we look for the following:

Oxygen Corrosion First, we make sure the mechanical equipment (feedwater heaters or deaerators) is working properly.

We do that by turning off the chemical oxygen scavengers and testing the feedwater for residual oxygen.

If the mechanical equipment is not performing to specifications, then work needs to be done to investigate the root cause and make corrections.

Filming amines (like octadecylamine) are used in difficult condensate systems where corrosion occurs, especially when oxygen ingress is a problem. Filming amines create a protective barrier on the condensate metal surfaces and do not allow the corrosive condensate to touch the surfaces. These chemicals, too, need to be monitored with effective chemical residual testing and corrosion product testing.

Scale As with any treatment scenario, the program starts with verifying the mechanical pretreatment equipment is performing properly. It is best to test a composite sample taken over time rather than a grab sample taken at the time of the visit. The composite sample should show how the equipment performs during various production cycles (like for a regularly regenerated softener).

Second, treatment chemicals are applied. There are inorganic oxygen scavengers (sulfite compounds) and organic compounds (carbohydrazide, erythorbate, DEHA, and others). The residual levels of the oxygen scavengers need to be regularly tested, especially during service visits.

Condensate System Corrosion The prime mechanical devices to reduce condensate corrosion are the pretreatment strategies of reverse osmosis, dealkalization, and demineralization. These systems remove carbonate alkalinity from the make-up water and must be surveyed regularly to confirm they are working correctly.

Chemical treatment consists of phosphates, phosphonates, chelates, polymers, and tannins. These treatment chemicals have advantages and disadvantages, and selecting the proper chemical is system specific.

Testing for control consists of evaluating the pretreatment system for the mechanical removal of hardness and the boiler water for the proper treatment chemical(s) levels. The feedwater and condensate should also be monitored to confirm there are no other sources of contamination.

Epilogue

Chemical treatment primarily consists of neutralizing amines. It is crucial to select the appropriate individual

How do I make sure the boiler is properly treated?

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In this article, we have discussed the importance of boiler water treatment. Based on that premise, how do you ensure your programs protect the systems? The answer is a proper testing regimen with each service visit.

Proper water treatment saves money, and thorough monitoring assures results. By regularly surveying boiler systems, you’ll have all the tools and experience to pass the “final exam”—the annual boiler inspections!

The foremost concern is oxygen, so performing a test for oxygen scavenger residuals is a must. The results would tell us whether the mechanical and chemical programs are working correctly or not. Low chemical residuals, or high chemical usage rates, would have us looking for the root cause.

Now we know three very good reasons to chemically treat a boiler: To reduce unplanned outages To reduce maintenance costs To reduce fuel costs

An additional protective measure is to test the actual oxygen residual in the boiler feedwater. Testing the oxygen residual with the oxygen scavenger not feeding allows you to evaluate the performance of the pretreatment equipment: feedwater heaters and deaerators. The mechanical removal of the oxygen provided by these pieces of equipment are the prime contributor to lower oxygen levels and chemical demand.

Next, you need to test the condensate. To ensure the treatment program is controlled, you should test pH during every visit and test metals (iron and copper) regularly. High iron and copper levels would indicate the need to evaluate the program and possibly consider a filming amine program.

This paper was presented at the AWT annual conference, which was conducted Oct. 4-6, 2023, in Grand Rapids, Michigan.

Finally, the softener effluent, condensate, and boiler feedwater should be tested for trace hardness. There will be long-term problems if uncontrolled hardness gets into the boiler system. Consider taking composite samples to see what happens over time; grabbing samples during your service visits may not tell you the complete story! Also, be sure your internal treatment chemical (phosphate, chelant, polymer, or tannin) is at the appropriate level.

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Chris Golden, CWT, is the senior director of sales at Taylor Water Technologies, which he joined in 2007. He started in water treatment in 1989. He background includes working with water systems at power stations, food and beverage plants, and manufacturing plants. Mr. Golden received the Ray Baum Award from the AWT for lifetime contributions to the industrial water treatment industry in 2018. He has a bachelor’s degree in chemical engineering from Lehigh University and holds a Certified Water Technologist credential from the AWT. He may be contacted at cgolden@fluidra.com.

Enviromental Safety Technologies

Keywords: BOILERS, BOILER TUBES, CORROSION, MATERIALS OF CONSTRUCTION, MONITORING, OXYGEN, PRETREATMENT, SCALING, TREATMENT CHEMICALS

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QualiChem

22 Myron L Company

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Solugen, Inc.

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44 Walchem Iwaki America Quantrol

Pulsafeeder

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