2018 Technical Supplement

Issue 8

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

Fall 2018

Filming Amine Use in Multi-Metal Hot Water Systems Key Considerations in Selecting Deposit Control Polymers in Industrial Water Treatment Novel Biocide Blend Delivers Improved Microbial Control in Industrial Water Systems Real-World Experiences With a Plant-Based Alternative to Chemical Treatment in Cooling Water Systems

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Cover Sphagnum moss, istock.com

Issue 8

Fall 2018

Spotlight

Filming Amine Use in Multi-Metal Hot Water Systems.......................................................8

Novel Biocide Blend Delivers Improved Microbial Control in Industrial Water Systems.........22

Real-World Experiences With a Plant-Based Alternative to Chemical Treatment in Cooling Water Systems...............................................14

Key Considerations in Selecting Deposit Control Polymers in Industrial Water Treatment....................32

Nathan Hardy and Jim Lukanich, CWT, US Water Services, Inc. In recent years, there has been growing interest and use of filming amines in a variety of water treatment applications. Although filming amines have been used for decades in various corrosion inhibition applications, their use as primary corrosion inhibitors in heating and cooling water applications has been limited. The increased use of aluminum heat exchangers in hot water hydronic systems has presented significant challenges for water treatment professionals. The ability to provide multi-metal corrosion inhibition while operating under the typical manufacturer’s specified pH range (8.0–8.5) has been shown to be difficult with traditional treatments.

This paper describes work conducted in the laboratory and pilot circulating hot water systems comparing the performance of a filming amine blend to other traditional treatments, such as nitrite. Studies were performed in the pH range recommended for aluminum heat exchangers and in the higher range (8.5–9.5) consistent with traditional treatments. Results show the filming amine blend provided equal or better corrosion inhibition in all pH ranges tested compared to traditional inhibitors in the study.

Jeffrey Kramer, Ph.D., BWA Water Additives The failure to control microbial growth in industrial water systems can lead to a loss of efficiency, enhanced corrosion, and potential health risks.

Nonoxidizing biocides play a critical role in controlling microbial growth in industrial water systems. A wide variety of nonoxidizing biocides are available to the water treatment professional; however, they are not always effective due to a narrow spectrum of biocidal efficacy, slow speed of kill, or compatibility issues. Safety and handling issues is also a concern with certain nonoxidizing biocides. Obviously, there is a need in the industrial water treatment industry for a nonoxidizing biocide that overcomes the limitations of currently available nonoxidizing biocides. We report here on the novel combination of two biocidal actives—the potent bactericide 2-bromo-2-nitropropane-1,3-diol (BNPD) and the algicide didecyl dimethyl ammonium chloride—into one product. This combination results in a fast-acting, broad-spectrum, nonoxidizing biocide with excellent compatibility with scale and corrosion inhibitors, and fluorescent tracers. Comparative efficacy studies and field trial data have demonstrated the superior cost effectiveness of this new biocide. The results of these evaluations are discussed, and treatment recommendations are presented.

Steve Chewning, CWT, Southeastern Laboratories, Inc. Companies adopting sustainable business practices understand that they are most successful when economic and environmental benefits align.

Many companies are now positioning their business on a platform of sustainable development that visibly proclaims what they stand for and how they are contributing to their own and their customers’ sustainability goals.

To be successful in today’s market, water treatment service companies will need to be able to offer greener alternatives to supplement or replace their conventional chemical treatment programs. One such alternative is a treatment process that uses the leaves from a particular species of sphagnum moss that grows naturally in New Zealand and along the US–Canadian border. Water that flows from sphagnum moss bogs is among the most pure and pristine in nature due to the plant's ability to absorb contaminants, clarify the water, and, most importantly, suppress bacterial activity.

Emily R. Clark, The Lubrizol Corporation The buildup of deposits in boilers and cooling towers is a persistent problem that can lead to decreased efficiency, overheating, unscheduled shutdown time, and costly maintenance. As steam is generated by a boiler or water evaporating from a cooling tower, dissolved minerals are left behind.

More water is added to make up for the evaporation loss, resulting in more deposition of minerals (e.g., CaCO3, CaSO4, Ca3(PO4)2), corrosion products (e.g., Fe2O3), particulate matter, and microbiological mass. These deposits accumulate in low circulation areas, becoming immobilized and building up on heat exchanger surfaces. Once a scale layer is formed, it will continue to get thicker unless treated, eventually blocking flow and decreasing productivity. Therefore, an effective water treatment program must control scale, corrosion, particulates, and biological growth.

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

2018–2019 AWT Board of Directors President

David Wagenfuhr, LEED OPM

Calendar of Events Association Events 2019 Technical Training West

East

February 27–March 2, 2019 DoubleTree San Diego–Mission Valley San Diego, California

President-Elect

Thomas Branvold, CWT

Secretary

Michael Bourgeois, CWT

March 27–30, 2019 Hotel Annapolis Annapolis, Maryland

2019 Annual Convention & Exposition

Treasurer

September 11–14, 2019 Palm Springs Convention Center and Renaissance Hotel Palm Springs, California

Matt Jensen, CWT

Immediate Past President

Marc Vermeulen, CWT

Directors

Steven Hallier, CWT Stephanie Keck, CWT Andy Kruck, CWT Bonnee Randall

2020 Annual Convention & Exposition

Ex-Officio Supplier Representative

September 30–October 3, 2020 Louisville Convention Center and Omni Hotel Louisville, Kentucky

Past Presidents

2021 Annual Convention & Exposition

Garrett S. Garcia

Jack Altschuler John Baum, CWT R. Trace Blackmore, CWT, LEED AP D.C. “Chuck” Brandvold, CWT Brent W. Chettle, CWT Dennis Clayton Bernadette Combs, CWT, LEED AP Matt Copthorne, CWT James R. Datesh John E. Davies, CWT Jay Farmerie, CWT Gary Glenna Charles D. Hamrick Jr., CWT Joseph M. Hannigan Jr., CWT

Mark R. Juhl Brian Jutzi, CWT Bruce T. Ketrick Jr., CWT Bruce T. Ketrick Sr., CWT Ron Knestaut Robert D. Lee, CWT Mark T. Lewis, CWT Steven MacCarthy, CWT Anthony J. McNamara, CWT James Mulloy Alfred Nickels Scott W. Olson, CWT William E. Pearson II, CWT William C. Smith Marc Vermeulen, CWT Casey Walton, B.Ch.E, CWT Larry A. Webb

Staff

Executive Director

Heidi J. Zimmerman, CAE

Deputy Executive Director

Sara L. Wood, MBA, CAE

Senior Member Services Manager

September 22–25, 2021 Providence Convention Center and Omni Hotel Providence, Rhode Island

2022 Annual Convention & Exposition September 21–24, 2022 Vancouver Convention Centre Vancouver, Canada

2023 Annual Convention & Exposition

October 4–7, 2023 Amway Grand Hotel and Grand Rapids Convention Center Grand Rapids, Michigan 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.

Second Tuesday of each month

Angela Pike

11:00 am

Legislative/Regulatory Committee

2:30 pm

Convention Committee

Second Wednesday of each month

11:00 am

Business Resources Committee

Second Friday of each month

9:00 am

Pretreatment Subcommittee

Kristen Jones, CMP

10:00 am

Special Projects Subcommittee

Exhibits and Sponsorship Manager

11:00 am

Cooling Subcommittee

9:00 am

Certification Committee

3:30 pm

Young Professionals Task Force

Third Tuesday of each month

3:00 pm

Education Committee

Third Friday of each month

9:00 am

Boiler Subcommittee

10:00 am

Technical Committee

11:00 am

Wastewater Subcommittee

Vice President, Meetings

Grace L. Jan, CMP, CAE

Meetings Manager

Morgan Prior

Meetings Manager

Barbara Bienkowski, CMP

Marketing Director

Julie Hill

Third Monday of each month

Website Manager

Jeyin Lee

Production Manager

Jennifer Olivares

Technical Writer/Copy Editor Lynne Agoston

Marketing Coordinator

Tawana Jacobs

Quarterly (call for meeting dates)

Accountant

Dawn Rosenfeld

The Analyst Staff Publisher

Heidi J. Zimmerman, CAE

Managing Editor

Lynne Agoston

Production Manager

Jennifer Olivares

Advertising Sales

Heather Prichard, advertising@awt.org

The Analyst is published quarterly as the official publication of the Association of Water Technologies. Copyright 2018 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: 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.

Other Industry Events • • • • • • •

USGBC, GreenBuild, November 14–16, Chicago, Illinois ASHRAE, Winter Meeting, January 12–16, 2019, Atlanta, Georgia BOMA, Winter Business Meeting, January 18–21, 2019, Miami, Florida CTI, Annual Conference, February 5–9, 2019, New Orleans, Louisiana ASHE, PDC Summit, March 17–20, 2019, Phoenix, Arizona NACE, Corrosion Conference & Expo, March 24–28, 2019, Nashville, Tennessee ACS, Spring National Meeting & Expo, March 31–April 4, 2019, Orlando, Florida

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President’s Message

By David Wagenfuhr, LEED OPM

AWT produces this Technology Supplement every year to provide our members with access to great resources. In addition to this resource, if you haven’t already, be sure to check out The Exchange, our new online community for sharing ideas, asking questions, lending expertise, and networking with peers. The community features a discussion forum as well as a library for sharing documents, resources, links, and more. Be sure to check it out.

Included in this Technology Supplement are several articles about water treatment, including filming amines, deposit control polymers, biocides, and a plant-based alternative to chemical treatment.

This is great information for water treatment professionals. The articles in this Technology Supplement are provided to offer you tips, advice, and knowledge that will help you and your business succeed. We hope you find this information helpful.

As always, I welcome your feedback and can be reached at president@awt.org.

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Filming Amine Use in Multi-Metal Hot Water Systems Nathan Hardy and Jim Lukanich, CWT, US Water Services, Inc.

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Introduction

Corrosion in industrial and commercial water treatment continues to be a major concern as companies strive to reduce costs while maintaining their assets. The need to protect heat exchange equipment and associated piping is vital in minimizing operational costs and preventing downtime. Traditionally, copper and carbon steel have been the metallurgies of choice for comfort heating and cooling heat exchange equipment. However, aluminum is becoming an increasingly attractive option for heat transfer, as it has a high thermal conductivity relative to its initial capital cost.1 While this is an alluring option, it adds challenges to current water treatment programs. Aluminum is a much more anodic metal than iron and copper, increasing its potential for galvanic corrosion, which can lead to devastating effects. Aluminum is also an amphoteric metal, with its protective oxide film being soluble at both low and high pH. Because of this, aluminum boiler manufacturers often recommend a lower pH range for optimal protection (8–8.5). This places the water treatment professional in a difficult position, as this raises the corrosion potential for carbon steel, which prefers a higher pH (>9.0). For systems containing aluminum heat exchangers, the need to provide corrosion inhibition for all metal surfaces has never been greater.

The de-wetting of the metal surface (Figure 2) inhibits corrosion by preventing dissolved gases and water from reaching the metal surface. This unique inhibition mechanism is becoming increasingly appealing to water treaters as this technology allows the film to be maintained by feeding product at a low residual level. Having a resistant film for corrosion inhibition provides additional leeway for system upsets, or times of suboptimal feeding; unlike neutralizing amines which are quickly consumed by carbonic acid. The application of filming amines can be tightly controlled when combined with a fluorescent tracer and commercially available filming amine residual tests. It should be pointed out that the high affinity between filming amines and the metal surface means they are able to penetrate existing deposits and corrosion debris quite well. When applying FFAs for the first time to systems previously fouled with deposits or corrosion byproducts, it is suggested that one start with a very low dose and gradually increase the levels. This will help to avoid excessive sloughing off, which can cause blockages in small diameter passages or in low-flow areas.

Figure 2. Top: Carbon steel with 10 ppm active FFA for 1 hr; Bottom: No treatment. Treated coupon shows a significant difference in contact angle of water droplets, signifying a hydrophobic surface.

Filming Amines

Filming amines have been around for decades, and in the water treatment space are most often used in steam boiler applications.

While their use as primary corrosion inhibitors has been limited, they are receiving increasing attention in heating and cooling water applications. Film forming amines (FFAs) are being considered for application in both closed and open cooling water systems, as they are biodegradable and leave no hazardous byproducts. FFAs have a strong affinity for metal surfaces, likely due to the partial positive charge on the nitrogen atom as the amine comes into contact with metal surfaces. This attraction is exacerbated by the hydrophobic tail, further pushing the amine away from water and toward the metal surface, leaving a tightly packed film with hydrophobic tails protruding outward.2 Polyamines, which inhibit corrosion in a similar mechanism to monoamines (Figure 1) are often preferred, as they can form a more resilient film. Film formation is a dynamic process where constant attachment/detachment is taking place, the additional secondary amine provides an extra binding site between the FFA and the metal surface.

Figure 1. Illustration of monoamines and diamines preventing water and dissolved gases reaching the metal surface.

Traditional Treatments

Nitrite is one of the most commonly used corrosion inhibitors for closed-loop systems, as it is relatively inexpensive and the chemistry is well understood. Nitrite acts as a mild steel corrosion inhibitor by oxidizing the metal surface to form a protective Fe2O3 film; however, nitrite provides no aluminum protection and can even be aggressive to aluminum surfaces.3 In lower temperature (<140 °F) hot water systems, nitrite can become susceptible to microbiological growth from both nitrifying and denitrifying bacteria. Nitrite reacts with oxidizing microbicides to form nitrate, and therefore, should not be used together. Other disadvantages include its relatively high toxicity and strict discharge regulations.

Molybdate, which can be a bit more costly, is known to provide corrosion protection for both aluminum and mild steel. Unlike nitrite, it is not vulnerable to microbiological degradation but does require the presence of dissolved oxygen to form its protective oxide layer on mild steel. Protection of aluminum with molybdate is most effective in a relatively tight pH range (7.8â&#x20AC;&#x201C;8.3). Above this range, aluminum will become more susceptible to corrosion, and if below, mild steel corrosion rates may not be acceptable.

Silicates are very cost-efficient corrosion inhibitors and are known to exhibit some corrosion protection for all metals. Similar to molybdate, they are not degraded by microorganisms and operate in a similar pH range. While silicates can be used for many applications, they are most commonly used as an adjunct to enhance other treatment programs.

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Filming Amine Use in Multi-Metal Hot Water Systems continued

Figure 5. Picture of cold loop used for testing.

Experimental Methods Hot Closed Loop

Coupon testing was performed using a 10-gal, 3,000-Watt hot water heater; a circulation pump; and a CPVC corrosion coupon rack (Figure 3). Each test run lasted 14 days and was maintained at 160 °F. The circulation pump was able to provide a flow velocity of 1.0ft/sec through the coupon rack. While this is lower than the recommended 3–5ft/s, relative data is still recognized to be valuable and quantifiable. Soft water was used to triple rinse the system prior to each run. The rinse water was circulated for 10 minutes at room temperature. Makeup water for each test was prepared separately and was pumped into the water heater.

Makeup water for all trials remained the same (Table 1).

Table 1. Makeup water for hot closed loop trials.

Soft Water pH

Results 8.2

TH

1.1

CaCO3 (mg/L)

376

CaCO3 (mg/L)

Conductivity p-Alk

m-Alk Cl

SO4

PO4

SiO2

740 0

13

12

1.5 35

Units -

μmhos/cm

CaCO3 (mg/L)

Table 2. Makeup water for closed loop trials.

Makeup pH HCO3 (CaCO3) Cl SO4 LSI RSI

Cl (mg/L)

SO4 (mg/L)

PO4 (mg/L)

SiO2 (mg/L)

Figure 3. Schematic for hot closed loop.

Cold Loop Testing Filming amine technology was also tested for efficacy in open cooling systems using a small circulating water loop with LPR corrosion probes (Figures 4 and 5). Makeup water for each trial was prepared directly in the bulk tank. Water analysis is shown below (Table 2). The entire system was triple rinsed with DI water between each run.

Figure 4. Schematic for cold loop.

Results 8.34 300 200 75 -1.3 10.6

Units mg/L mg/L mg/L -

56.78L of DI water was added to the feed tank prior to salt additions. Salts were left to mix for 30 minutes in bypass loop before treatment addition. After treatment addition, the bypass loop was closed, allowing flow though coupon rack and probes.

Corrosion data was obtained from Cosasco Corrators® located in a coupon rack with a flow rate of 4ft/s.

Results and Discussion Hot Closed Loop

A control trial was run to obtain baseline corrosion data for all metals. A pH of 8.2 was chosen, as it is within the upper limit proposed by some aluminum heat exchanger manufacturers, and it is within the limits recommended by AWT for mild steel protection in multi-metal systems. Multiple trials were then performed with a variety of “traditional” hot closed-loop treatments (Table 3). A nitrite/silicate blend was initially evaluated as a multi-metal corrosion inhibitor (trial 2) at a typical operational pH (9.6) for mild steel protection. While mild steel and copper were well protected, nitrite failed to protect aluminum. Results showed that aluminum protection is not viable with a nitrite program at its native pH, and may even have had an antagonistic effect on the aluminum due to the high corrosion rate. Another traditional chemistry, molybdate/silicate, was tested (trials 3 and 4). Test runs were performed at both the naturally derived pH (9.6) as well as a pH adjusted (8.2) run with citric acid. Results, as expected, clearly indicate this combination to be an effective corrosion inhibitor for all metals tested at the lower pH (8.2).

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While a combination of molybdate and silicate is known to provide aluminum protection, its high performance at pH of 9.6 was unexpected.

Table 4. Corrosion coupons for select trials.

Table 3. Corrosion rates of experimental trials.

Trial # 1 2 3 4 5 6 7 8 9 10

Treatment None NO2/SiO2 MO/SiO2 MO/SiO2 Tannin Tannin

Filming Amine Comp Filming Amine Comp Filming Amine USW Filming Amine USW

Product Dosage mg/L None 1350 as NO2 /30 as SiO2 90 as MO/90 as SiO2 90 as MO/90 as SiO2 4000 (as product) 4000 (as product) 5000 (as product) 1000 (as product) 5000 (as product) 1000 (as product)

Azole System pH None 8.2 Yes 9.6 Yes 9.6 Yes 8.2 None 8.6 Yes 9.0 Yes 8.3 Yes 8.3 Yes 7.8 Yes 8.3

MS 2.31 0.09 0.64 1.08 6.23 2.49 0.49 1.06 0.03 0.15

Cu 0.26 0.15 0.08 0.09 0.35 0.19 0 0.09 0 0

Al 13.18 378.83 0.18 0.19 51.86 93.34 0 13.39 0 0

In addition to traditional treatments, greener chemistries were also evaluated. Trials 5 and 6 included a commercially available tannin product. Both tannin trials with and without an azole adjunct did not perform well relative to the control under the conditions tested. Interestingly, even at a pH of 9.0, mild steel corrosion was higher than the control with a pH of 8.2. The high aluminum corrosion rates can likely be attributed to higher pH and an increase in iron in the bulk water.

A commercially available filming amine (trial 7 and 8) product was tested and compared to a newly developed FFA formulation (trials 9 and 10). Both products were initially tested at the upper recommended dosage of 5,000 ppm as product. At this level, there was no indication of copper or aluminum corrosion in the 14-day trial with either formulation. Mild steel rates were well within the accepted limits, all while operating at lower than desirable pH for mild steel protection. The results of trial 9 showed a mild steel corrosion rate of 0.03 MPY at a pH of 7.8, within manufacturer recommended limits. Both filming amine blends were tested at the lower end of the usage range (1,000 ppm).

The commercially available filming amine showed some improvement on mild steel and copper compared to the control but didnâ&#x20AC;&#x2122;t provide aluminum protection at this use level. The results (trial 10) for the newly developed FFA at the lower dose were comparable to the results at the 5,000 ppm dose. Only a slight increase in mild steel corrosion is observed, but it is still within the acceptable limits.

Aluminum corrosion coupons for select trials are shown in Table 4. Trial 3, the molybdate/silicate blend, serves as a benchmark of traditional treatments. Coupons from this trial clearly show a clean aluminum surface in comparison to the control and tannin trials. The improved performance of the filming inhibitor (trial 10) is an indication of how viable this technology is.

Cold Loop

Most available filming amine data comes from hot water or steam-related systems. It has been previously shown that FFA adsorption increases at higher temperatures.4 As filming amine technology is being considered for other applications, a study was conducted to determine viability as a corrosion inhibitor in an open cooling circuit. Figure 6 shows the mild steel corrosion rates with varying doses of filming inhibitor; dose levels are as active filming amine.

Figure 6. LPR corrosion data for MS with varying levels of filming amine.

The relatively aggressive nature of the water used in the test (see Table 2) quickly corroded the LPR electrodes in the control run, reaching 20 MPY in under four hours. A dose of 5 ppm FFA significantly reduced initial corrosion rates as compared to the control. However, the trend still indicates an increasing corrosion rate toward the end of the run. The results indicate the FFA provided some level of protection, but the initial dose was not sufficient to adequately film the entire surface. The 10 ppm dose behaved in a similar manner to the 5 ppm dose up to the 4-hour mark. At this point, a steady decrease in corrosion is observed and indicates there was sufficient FFA present to satisfy the surface demand and form a dense, protective film on the LPR electrodes.

It should be noted that the results of this test only demonstrate the need to satisfy the demand from all the system surfaces in order to achieve adequate corrosion protection. The initial dose and time required to achieve protection will vary, as film formation is heavily dependent on surface area, water volume, and temperature.

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Systems with previous fouling, deposition, or buildup of corrosion byproducts may exhibit significant sloughing and deposit removal.

This will also increase the initial demand of the FFA. Corrosion data was also monitored for several days after the initial 10 ppm dose to determine the film stability (Figure 7).

NaOCl was used to treat the circulating loop and residual Cl2 levels were maintained at 0.2–0.5mg/L. As expected, the filming amine did not appear vulnerable to oxidation at the levels of chlorine applied. Corrosion rates were maintained ~1.5 mpy for six to seven days with only the initial dose. Several amine residual tests were taken over the 11-day period after the initial 10 ppm dose. A rose bengal test method for aliphatic amines was used, measuring absorbance at 560 nm with a Hach DR890 spectrophotometer. Three and a half hours after the application of the initial dose, a sample was tested yielding a residual level of 7.96 mg/L. Another sample was tested at 5.5 hours indicating 5.03 mg/L of FFA remained—nearly a 40% loss.

Figure 7. Extended trial of 10 ppm filming amine initial dose with residual testing.

Summary and Conclusions

Comparative testing of corrosion inhibitors was performed in a circulating hot water pilot system (160 °F) containing copper, mild steel, and aluminum. Efficacy of traditional chemistries, as well as filming chemistries was determined by metal loss over a 14-day test period. Results clearly show the filming amines were the most effective corrosion inhibitors for all metals tested at the pH range (8.0–8.5) recommended for protection of aluminum. Results using a nitrite/silicate blend show the difficulty in protecting mild steel and aluminum simultaneously (trial 2). To effectively protect mild steel, a high pH (9.6) was needed. This consequently resulted in a corrosion rate of 378 mpy for aluminum.

A cold-water circuit was also used to evaluate the film formation characteristics of a film-forming inhibitor blend. The data show that corrosion inhibition begins with the initial dose, and corrosion rates continue to improve over an 8-day period.

There are difficulties encountered when treating multi-metal systems, especially when they contain aluminum components.

The results presented in this paper show FFAs offer an effective corrosion inhibitor alternative to traditional chemistries, with possibilities for use in a variety of water systems, including hot, cold, open, or closed..

References 1

2

3

4

A correlation between residual FFA and corrosion rates can easily be seen in the first few days of testing. Corrosion rates sharply decline as the film begins to form in the first two days. From two to eight corrosion rates remain relatively steady as residual filming amine slowly decreases to <0.2mg/L. At day seven, a residual of 0.06 mg/L was measured without a noticeable increase in corrosion rate. It wasn’t until the final measurement of 0.03 mg/L that a corresponding increase in corrosion was noticeable.

Testing indicates that after initial film formation has occurred, residual levels need to only be maintained at near the detection limit to maintain corrosion inhibition.

M. LaBrosse and D. Erickson, 2017. “Pilot Research to Determine Effective Aluminum Corrosion inhibition”, The Analyst, Summer 2017, 23–27

M. Jack, 2015. “The interaction of a film-forming amine with surfaces of a recirculating experimental water loop”, heatexchangerfouling.com 2015, 112 S. Rey and G. Reggiani, 2005. “Molybdate and Non-Molybdate Options for Closed Systems,” Association of Water Technologies

Pensini, E., 2017. Water Resources and Industry, http://dx.doi.org/10.1016/j. wri.2017.11.001

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Real-World Experiences With a Plant-Based Alternative to Chemical Treatment in Cooling Water Systems Steve Chewning, CWT, Southeastern Laboratories, Inc.

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Companies adopting sustainable business practices understand that they are most successful when economic and environmental benefits align. Many companies are now positioning their business on a platform of sustainable development that visibly proclaims what they stand for and how they are contributing to their own and their customers’ sustainability goals. To be successful in today’s market, water treatment service companies will need to be able to offer greener alternatives to supplement or replace their conventional chemical treatment programs.

One such alternative is a treatment process that uses the leaves from a particular species of sphagnum moss that grows naturally in New Zealand and along the US–Canadian border.

Water that flows from sphagnum moss bogs is among the most pure and pristine in nature due to the plant's ability to absorb contaminants, clarify the water, and, most importantly, suppress bacterial activity.

Sphagnum moss has had various uses for centuries. The Vikings used moss for water and food preservation on their voyages. It was used to make bandages in World War I (before penicillin) due to its greater ability to control infection and absorb fluids compared to cloth bandages. Human bodies 2,000 years old, often referred to as "bog bodies," which are perfectly preserved, have been found in moss bogs around the world. They were preserved due to sphagnum moss's unique ability to suppress bacterial activity that decomposes bodies. “As the sphagnum moss dies, it releases a carbohydrate polymer called sphagnan. It binds nitrogen, halting growth of bacteria and further mummifying the corpse."1 Minnesota-based Creative Water Solutions completed extensive research on sphagnum moss and found that the properties described above are derived from the leaves of the plant and are not dependent on the plant being alive. The company has developed a process for harvesting the leaves and packaging them for application in water systems.

The properties that make this significant in the water treatment industry are: • Its ability to act as a natural water softener, removing impurities such as calcium, magnesium, iron, and other metals that can result in scaling and corrosion problems in water systems. The biomass of the living plant consists mainly of polysaccharides made up of glucose and galacturonic acid units. Galacturonic acid is rich in carboxylic acid groups that give sphagnum its high cation exchange capacity.2 Hydrogen ions are released in the exchange process, effectively neutralizing alkalinity.

• Its ability to break down the organic “binders” that hold deposits together, resulting in cleanup and removal of deposits from system surfaces.

• Its ability to inhibit and remove organic contamination resulting from microbiological activity, which insulates heat transfer surfaces and causes corrosion in water systems. In 15

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a lot of applications, this is proving to be a more efficient approach than chemical treatment, which relies on biocidal agents to kill bacteria that produce the contaminants. Over time, bacteria are able to adapt and protect themselves from these chemical agents but appear to have no immunity from conditions produced by sphagnum moss.

• Break down and remove existing deposits. The following photos are from piping going into a plate and frame heat exchanger on an open air washer system. Years of deposits were removed after three months exposure to moss treated water.

So, what are we seeing in systems where we have implemented moss treatment programs? In evaporative cooling systems, we have been able to: • Run higher cycles of concentration where hardness, alkalinity, and/or pH are limiting factors. The following data is from a cooling tower system switched from chemical treatment to moss. Acid feed was being used to allow operation at 3.3 cycles under chemical treatment. Acid feed was discontinued along with the other chemicals with the start of the moss treatment program. Figure 1 shows hardness values and pH as cycles of concentration were increased. As the moss absorbs hardness ions, it displaces hydrogen ions, effectively neutralizing alkalinity.

Figure 1. Hardness values and pH as cycles of concentration increase.

Sphagnum moss removes surface scale. It appears that the removal of scale is in part due to the resolubilizing of calcium.

Removal of organic “binders” eliminates the “glue” that holds together and starts most mineral deposits.

• Inhibit and remove organic contamination associated with microbiological activity in the system. The following data and photos in Figures 2 through 6 are from a trial on a 1,300-ton HVAC cooling tower system. The condenser approach temperature along with the chiller load was logged for the duration of the trial. The approach trended downward, indicating an improvement in heat transfer.

Figure 2. Condenser approach vs. load.

In this case, the plant was able to double cycles of concentration, resulting in an over 60% reduction in tower bleed off to drain– over 5 million gallons of water per year on this system. The need for sulfuric acid feed was also eliminated as the system cycled to a stable pH between 8.7 and 8.8, under their discharge limit of 9.0.

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Real-World Experiences With a Plant-Based Alternative to Chemical Treatment in Cooling Water Systems continued

Figure 3 shows conditions at the start of moss treatment (under chemical treatment).

Figure 4 shows conditions two weeks into moss treatment. There were substantial decreases in ATP levels; total bacteria counts; and iron, copper, and turbidity levels.

Figure 3. Conditions at start of trial (chemical treatment).

Total Bacteria Count 107 CFU/ml ATP–2,610 RLU's Turbidity–28 NTU's Iron–1.69 ppm Copper–0.42 Figure 4. Conditions two weeks into moss treatment.

Total Bacteria Count 102 CFU/ml ATP–126 RLU's Turbidity–2 NTU's Iron–0.02 ppm Copper–0.29

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Figures 5 and 6 depict total bacteria count data and iron and copper levels throughout the trial.

Figure 7. Test data from a chilled water system.

Figure 5. Total bacteria counts.

Figure 6. Iron and copper levels.

Using moss to absorb and remove corrosion byproducts from closed water systems has significant advantages over chemical approaches requiring cleaning, flushing, and re-treating. Moss can also absorb up to 10 times its weight in oil. Moss can be applied using existing bypass feeders or by installing bypass feeders specifically engineered for moss. In open sump systems, specially designed cages can be used.

Corrosion Data

In closed process water systems, we have been able to: â&#x20AC;˘ Remove corrosion byproducts (iron, copper, zinc) as well as absorb oil. Figure 7 shows iron, turbidity, and ATP test data from a chilled water system that was originally treated with a molybdate-based inhibitor system and a microbiocide. This system has an open sump and routinely experiences water loss and oil contamination from the process. The system was converted to moss treatment in June 2017.

Our experience with corrosion control in moss-treated systems has led us to conclude that corrosion control is comparable to chemically treated systems. Although we can often achieve lower general corrosion rates with chemical inhibitor systems, we have fewer issues with microbiologically induced corrosion (MIC) in moss-treated systems. As all water treaters know, MIC is much more destructive to systems than general corrosion. Figure 8 shows data from two cooling tower systems that are representative of the corrosion rates we are measuring with mild steel and copper corrosion coupons.

Figure 8. Data from two cooling tower systems.

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Figure 9 shows a typical water analysis for these cooling tower systems. We operate at an LSI around 1.5.

• More efficient inhibition of organic contaminants in water systems results in better heat transfer, which lowers energy costs and mitigates MIC.

Figure 9. Typical water analysis for cooling tower systems.

• Removal of old deposits leads to improved reliability and efficiency and often extends equipment life.

• Perhaps most significant to users with high sustainability goals, discharged water no longer contains chemicals that are potentially damaging to the environment. This opens up more possibilities for reuse of blowdown water in other processes.

Southeastern Laboratories began working with moss as an alternative to their conventional chemical treatment programs in October 2016. To date we have over 50 clients using moss in their systems. Our goal has been to introduce moss to a variety of water systems allowing us to evaluate and document performance under a wide range of operating conditions. In other words, we have been “testing the limits” of the program.

Our inspections of condenser tube sheets on moss treated systems show results similar to or better than chemical treatment.

In systems that have tube sheet corrosion tubercles, we have seen those being broken down and removed.

So, what does this mean to the end users who are deploying this program in their water systems?

References 1

• Removing cations that limit cycling in evaporative systems translates to water conservation.

2

Europe's Famed Bog Bodies Are Starting to Reveal Their Secrets, Smithsonian Magazine, March 2017.

Spearing, A. M., 1972. Cation-exchange capacity and galacturonic acid content of several species of Sphagnum in Sandy Ridge bog, central New York state.

Bryologist, 75: 154-158.

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the Analyst Technology Supplement 2018

Novel Biocide Blend Delivers Improved Microbial Control in Industrial Water Systems Jeffrey Kramer, Ph.D., BWA Water Additives

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The failure to control microbial growth in industrial water systems can lead to a loss of efficiency, enhanced corrosion, and potential health risks. Nonoxidizing biocides play a critical role in controlling microbial growth in industrial water systems. A wide variety of nonoxidizing biocides are available to the water treatment professional however, they are not always effective due to a narrow spectrum of biocidal efficacy, slow speed of kill, or compatibility issues. Safety and handling issues is also a concern with certain nonoxidizing biocides. Obviously, there is a need in the industrial water treatment industry for a nonoxidizing biocide that overcomes the limitations of currently available nonoxidizing biocides. We report here on the novel combination of two biocidal actives—the potent bactericide 2-bromo-2-nitropropane-1,3-diol (BNPD) and the algicide didecyl dimethyl ammonium chloride—into one product. This combination results in a fast-acting, broad-spectrum, nonoxidizing biocide with excellent compatibility with scale and corrosion inhibitors, and fluorescent tracers. Comparative efficacy studies and field trial data have demonstrated the superior cost effectiveness of this new biocide. The results of these evaluations are discussed, and treatment recommendations are presented.

Introduction

One of the major sources of issues within industrial water systems is the presence and growth of biofouling microorganisms. Microbial-based fouling can reduce the efficiency of these systems and cause damage to the structure directly by impeding the flow of water and indirectly by providing sites for corrosion to occur. In addition, industrial water systems can harbor pathogenic organisms detrimental to human health, specifically Legionella pneumophila. The major organisms that impact cooling towers are typically algae and bacteria, while fungi (yeast and mold) impact cooling towers to a much less extent.1 The most common method of controlling microbial fouling in industrial water systems has been through the use of biocides.

While oxidizing biocides based on bromine and/or chlorine typically form the foundation of a microbial control program, nonoxidizing biocides play an important role in keeping surfaces clean, reducing halogen demand, and controlling problematic microorganisms. While a wide variety of nonoxidizing biocides are available to the water treatment industry, improved methods are required to address efficacy, safety, and economic concerns.

Types of Nonoxidizing Biocides

While nonoxidizing biocides can be divided into categories based on a number of parameters, the most logical way to group them involves their mode of action rather than their specific chemistry. The three categories based on biocidal mechanism are discussed below.

Electrophilic Biocides These biocides react with electron-rich chemical groups. Biocides that act as moderate electrophiles can be divided into aldehyde-based biocides, isothiazolones, and multiple mecha-

nism electrophiles. Aldehyde-based biocides react with cellular nucleophiles, predominately amines, carboxyls, hydroxyls, and sulfhydryls.2 Isothiazolones require movement of the molecules through active transport into the cell in order to be effective, thus making it a relatively slow-acting biocide. Isothiazolones react with sulfhydryl groups of enzymes and proteins.3 If sulfhydryl groups of an enzyme are accessible to isothiazolone, its function is inhibited, thus disrupting important metabolic pathways, such as respiration, causing eventual cell death.

Other biocides, such as dibromonitriloproprionamide (DBNPA) and methylene bisthiocyanate (MBT), are also electrophilic but can also exhibit other mechanisms. For example, MBT can diminish the functionality of metal-containing enzymes within the cell.

The most common aldehyde-based biocide is glutaraldehyde (GA). Glutaraldehyde is an aliphatic di-aldehyde, which functions by cross-linking proteins. Chemically, it functions best at a neutral pH range from 6–8, with activity diminishing with a decrease in pH. Glutaraldehyde is compatible (i.e., retains activity) in the presence of low levels of hydrogen sulfide (H 2S).4 While glutaraldehyde is compatible with H 2S, it is not compatible with ammonia (NH3) and amines. Glutaraldehyde can cause irreversible eye damage and can act as a skin sensitizer, so it should be handled with caution.

Isothiazolones (ISO) are five-member ring compounds containing nitrogen and sulfur. The common biocide is a mixture of two isomers—one chlorinated and the other nonchlorinated. Chemically, it functions across a relatively wide pH range (5.5–9.5), with the best activity seen at the lower end; however, it has been shown to be suitable for use under the more alkaline conditions found in most cooling systems. It is compatible with NH3 but not H 2S. This limits its utility in systems with significant levels of SRBs due to high levels of hydrogen sulfide that these microorganisms produce, which inactivates the isothiazolone, thus necessitating elevated dosages to provide control. Isothiazolone acts as a skin sensitizer and should be handled with caution.

DBNPA is a bromine-containing biocide but is not considered an oxidizing biocide. Although it is fast acting, DBNPA’s chemical stability is controlled by the system pH; DBNPA is increasingly unstable as the pH becomes alkaline, and above pH 8.5, it is generally not feasible to use it. In addition to the pH sensitivity, it is incompatible with both NH3 and H 2S. DBNPA does not typically act as a skin sensitizer.

MBT is another sulfur-containing biocide. While MBT mimics the mechanism of isothiazolone, it also interferes with electron transfer by cytochromes by binding to the iron found in these proteins which makes it somewhat faster acting. Chemically, it loses stability quickly with an increase in pH above 7.5–8.0 with the best activity seen at lower pHs. It is particularly effective against fungi, however its limited water solubility restricts how it can be formulated and used. MBT, as it is a skin sensitizer, should be handled with caution.

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2-(thiocyanomethythio) benzothiazole (TCMTB) can be thought of as an aromatic version of MBT. TCMTB has an overall mode of action quite similar to that displayed by MBT and the same issues apply in terms of formulation difficulty.

Also, being a metabolic inhibitor, TCMTB needs to be transported into the cell to be effective making it a relatively slow-acting biocide. TCMTB is primarily a fungicide so it is not widely used in industrial water treatment applications.

of attack allow for a quicker and more extensive kill of microbes in systems. Since different organisms display varying response patterns to biocides, combinations of actives increase the likelihood of being able to attain a better overall kill on the mixed micro-flora present in cooling systems. Some common biocide blends include MBT and TCMTB, ISO and BNPD, ISO and PQ and GA and quaternary ammonium compounds (quat).

MBT/TCMTB as a combination provides acceptable results in systems with a moderate to long half-life and where the pH is neutral to only slightly alkaline. The combination of these two actives also provides for broad-spectrum control, including fungi.

Bronopol or 2-bromo-2-nitro-1,3-propanediol (BNPD) is another nonoxidizing, bromine-containing biocide. BNPD is a metabolic poison that works by reacting with thiol groups inside the cell as well as inhibiting membrane-bound dehydrogenase enzymes. This dual action results in slightly faster biocidal activity than other metabolic poisons, such as isothiazolone, MBT, and TCMTB. This biocide was originally developed as a preservative for cosmetics so it is less hazardous than other biocides but, like all biocides, requires some care when handling.

ISO/BNPD are both metabolic poisons, but their modes of action are sufficiently different that they exhibit synergy. Although BNPD is best suited to only slightly alkaline waters, isothiazolone is able to extend the reach of this blend into the higher pH range typical of the majority of cooling applications.

The blend of ISO/PQ uses an electrophilic metabolic poison combined with a surfaceactive biocide, which provides two very different modes of action. This results in good killing action against both bacteria and algae. Both actives are relatively pH tolerant so this combination gives good killing action over a broad pH range.

Membrane Active/Lytic Biocides Quaternaries are a broad group of membrane active biocides that include both quaternary ammonium and quaternary phosphonium compounds. The amphiphilic structure of these biocides allows for permeation and interaction with the cell wall and membrane. This causes a disruption in the structure and function of the cell membrane. With enough molecules permeating the membrane, the cellular structure becomes quickly compromised. Disruption of the cell membrane can result in osmotic lysis, disruption of membrane-associated metabolism, and loss of intracellular material. Due to their cationic nature, quaternaries have the potential to interact with the common fluorescent tracer pyrenetetrasulfonic acid (PTSA), which can limit their applicability.

The GA/alkyl dimethyl benzyl ammonium chloride (ADBAC) quat blend is another example of an electrophilic and surface-active biocide combination. Both biocides principally interact with the cell membrane, but while the GA utilizes protein cross-linking, the quat binds to negatively charged sites. Since both biocides cause damage to the cell membrane, this combination is relatively fast acting.

Tributyl tetradecyl phosphonium chloride (TTPC) is a quaternary phosphonium-based biocide. TTPC is a broad-spectrum biocide and displays excellent activity against both planktonic and sessile organisms. As a membrane active/lytic biocide, TTPC has a very fast rate of kill and it is not affected by NH3 or H 2S. Being surface active, it has the potential to cause foam, but at typical use concentrations, foaming is low. TTPC is ideally suited to alkaline waters, as its efficacy increases with increasing pH. Polyoxyethylene (dimethylimino) ethylene (dimethylimino) ethylene dichloride (polyquat [PQ ]) is a polymeric quaternary ammonium-based biocide. Polyquat varies from monomeric quaternaries in that its charge is not localized at only one point in the structure, and thus, it resembles a polymer with multiple charge sites. Its mode of action, however, is similar as it binds to anionic locations on the cell wall/membrane, resulting in stresses that can affect the cellâ&#x20AC;&#x2122;s permeability and ultimately lead to its rupture.

Blends of Biocides Combining biocides with different or complementary mechanisms has proven beneficial against many types of microorganisms. The logic behind the use of blends is that multiple pathways

A new blend containing an electrophilic and surface-active biocide combines BNPD and a low molecular weight di-alkyl di-methyl ammonium chloride (DDAC). This combination results in a fast-acting, broad-spectrum biocide. This blend is not a skin sensitizer, so would be safer to handle than GA or ISO, which are classified as strong and extreme skin sensitizers, respectively.5 In addition, it is compatible with the fluorescent tracer pyrenetetrasulfonic acid (PTSA).

Experimental Procedure Biocidal Efficacy Testing Biocide Preparation Stock solutions of biocides were prepared in deionized water immediately prior to use. Stock solutions of all biocides were prepared as weight percent solutions. All biocide concentrations are reported as ppm active ingredient.

Bactericidal Testing

Pseudomonas aeruginosa (ATCC 15442), Enterobacter aerogenes (ATCC 13048), and Staphylococcus aureus (ATCC 6538P) were used in this study. All bacterial cultures were maintained and enumerated on plate count agar. Inoculum was prepared by 24

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Novel Biocide Blend Delivers Improved Microbial Control in Industrial Water Systems continued

removing a small portion of growth from a slant or plate and suspending it in sterile saline. One milliliter of this suspension was spread evenly on the surface of a plate of the appropriate media and incubated overnight at 35 °C. Plates were harvested by adding 10 ml of sterile saline, agitating gently with a sterile loop, and removing the resulting cell suspension with a sterile pipette. The suspension was diluted with sterile saline to produce an inoculum containing approximately 108 colony forming units (CFU)/ml. Then, 0.1 ml of inoculum was added to test tubes containing 10 ml of sterile 0.1M phosphate buffer of the appropriate pH. Biocide was added to the test tubes in an amount calculated to give the desired concentration, and the test tubes were then incubated at the appropriate temperature for the desired contact time. An untreated test tube served as a control.

At the desired times, aliquots were removed from the test tubes, and viable microorganisms were enumerated on the appropriate media by standard pour plating of dilutions made in sterile saline. Plates were incubated for 48 hours at 35 °C. Results were reported as CFU/ml. All bactericidal efficacy tests were conducted at 35 °C (95 °F) and pH 8.5 unless otherwise noted.

Algicidal Testing

Chlorella vulgaris (UTEX 26) and Anabaena cylindrica (UTEX B 1611) were used in this study. Stock cultures were grown in 250 ml flasks containing 100 ml of sterile Allan’s medium. Stock cultures were continuously shaken at 200 rpm at 24 °C with 16 hours of cool white fluorescent light per day for three to four weeks. When good growth was evident, 1 ml of stock culture was transferred to a test tube containing 9 ml of sterile 0.1M phosphate buffer at the appropriate pH to give approximately 106 algal cells per milliliter. Biocide was added to the test tubes in an amount calculated to give the desired concentration, and the test tubes were then incubated at the appropriate temperature for the desired contact time. An untreated test tube served as the control. At the desired times, 1 ml aliquots were removed from the test tubes, and serial 10-fold dilutions were made in test tubes containing sterile Allan’s medium. The test tubes were incubated for three weeks under the same conditions used for the stock cultures, and the number of test tubes showing algae growth was determined. The number of viable algae, reported as cells/ml, equals 10 raised to the number of positive tubes.

For example, if there are six positive tubes, the number of viable algae is 106 cells/ml. All algicidal efficacy tests were conducted at 24 °C (75 °F) and pH 8.5 unless otherwise noted.

Results and Discussion Standardized Protocol

While reviewing published literature for various nonoxidizing biocides, it became obvious that inconsistencies in the protocols would make comparing data pulled from these sources difficult.

Furthermore, the organisms that were tested at times came from pure cultures, mixed cultures, or unidentified mixed flora from

cooling systems. The net result was that there was no objective way to compare the efficacy of different nonoxidizing biocides from the literature alone. Therefore, for this study, the plan was to use a standardized protocol to determine the level of biocide that is required to achieve the specific goal of a: 3 log10 reduction within 3 hours The reasoning behind choosing a 3 log10 reduction is that a fouled (or out of control) cooling tower is considered to have a bacterial population around 106 CFU/ml, and a system considered under control when using nonoxidizing biocides has around 103 CFU/ml or less. In other words, obtaining control from a fouled system represents a 3 log10 change in microbial count.

In this study, the minimum concentration of biocide required to attain control of the “system” or to obtain the 103 CFU/ml population was the goal. The timeframe for biocides to work in a cooling tower is important as well for multiple reasons, including retention times of the system and the half-life of the products being used. Gaining control within the three hour time point was chosen to try and accommodate fast-acting as well as slower-acting biocides within this protocol and is consistent with standard industry methods.6 To mimic the conditions in the majority of cooling systems and in keeping with typical environmental and industry standards, the testing was performed at 35 °C (95 °F) and a pH of 8.5. An additional benefit of this standardized approach is that the data can be expanded further in the future to include new biocides while still retaining comparative validity.

Rather than attempting to use cooling water samples with mixtures of different organisms and the resultant problems related to attempting their culture, the decision was made to use pure cultures of bacteria and algae that would be expected to be present in cooling systems. The variety of organisms utilized in the testing included two Gram-negative bacteria (Pseudomonas aeruginosa and Enterobacter aerogenes), one Gram-positive bacteria (Staphylococcus aureus), and two strains of common algae (Chlorella vulgaris and Anabaena cylindrical, representing green and blue-green types, respectively) typically found in these systems. The Gram-positive organisms were included due to their differences in cellular structure and the impact this would be expected to have on biocide performance.

No fungi were included in this testing due to their minimal presence in typical cooling towers. When they are present, they are normally only a problem in degrading wooden structures, and this type of testing would not have successfully represented efficacy against that specific problem.

Biocidal Efficacy

The biocidal efficacy of several commonly used industrial water treatment nonoxidizing biocides was compared against a variety of microorganisms using the standardized protocol described above. The results are shown in Table 1.

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the Analyst Technology Supplement 2018

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Novel Biocide Blend Delivers Improved Microbial Control in Industrial Water Systems continued

Table 1. Minimal cidal concentration of biocides against bacteria and algae.

In general, the quaternary biocides and biocide blends containing quaternary biocides had the best activity (lowest effective dosages) and the broadest spectrum of activity. One notable exception was PQ , which, although a quaternary, required a significantly higher dosage to be effective against algae compared to bacteria. The requirement for high dosages to be effective against algae was also seen with DBNPA and GA, which indicates that these biocides lack true broad-spectrum activity. Certain biocides such as BNPD, ISO, ISO/BNPD, and MBT/TCMTB were effective against the Gram-negative bacteria but seemed to not perform as well against Gram-positive bacteria. When tested against algae, the quaternary biocides, the quaternary blends, and ISO consistently outperformed the other biocides tested.

Carbamate gave very poor performance across the spectrum of microorganisms tested, even at very high dosage rates. While being notably a fungicide, the results suggest that carbamate

has limited activity against bacteria and algae under conditions typically found in industrial water systems.

The two biocides with the consistently lowest minimal cidal concentrations over the entire range of organisms tested were TTPC and BNPD/DDAC. While TTPC had slightly lower minimal cidal concentrations for algae and Gram-positive bacteria than BNPD/DDAC, it has the disadvantage of interfering with the common fluorescent tracer pyrenetetrasulfonic acid (PTSA). Laboratory testing conducted in a synthetic cooling tower water treated with a phosphate-based scale and corrosion formulation containing PTSA showed that repeated additions of 15 ppm active BNPA/DDAC had only a minor effect on the milliamp (mA) signal from PTSA (Figure 1). Based on this, BNPD/DDAC is not expected to interfere with the monitoring and control of systems using PTSA.

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Figure 1. Effect of BNPD/DDAC on the milliamp signal of PTSA.

Table 2. Monthly Legionella pneumophila serogroup 1 results.

*Note: System had not been treated with the BNPB/DDAC biocide for a week prior to this sample being collected.

It’s important to note that the one positive result of 10 CFU/ml for Legionella pneumophila serogroup 1 occurred after there had been an interruption in the application of the BNPB/DDAC biocide. Once the application of the BNPB/DDAC biocide was resumed, Legionella pneumophila serogroup 1 counts returned to undetectable levels when the next sample was collected two weeks later.

Field Trials

Printed Circuit Board Manufacturer – Midwest USA. A high-tech manufacturer of printed circuit boards was using an oxidizing/nonoxidizing biocide program to treat its evaporative condenser. The program consisted of continuous treatment with BCDMH to give 2 ppm free chlorine and twice weekly additions of 5 ppm active of a quaternary-based biocide. While this treatment program maintained planktonic bacteria at undetectable levels, Legionella pneumophila serogroup 1 was periodically detected during monthly testing of the system. When detected, Legionella pneumophila counts were typically very low (at or slightly above the detection limit of 10 CFU/ml) but their presence in the system was a concern, so an improved treatment was sought.

System

B.A.C. Evaporative Condenser

Volume

1,000 gallons (3.8 m3)

Recirculation rate

100 GPM (378 LPM)

Cycles 4 pH 8.7–8.8

In addition to the improved control of Legionella pneumophila serogroup 1, the combination of BCDMH and the BNPB/ DDAC biocide maintained the basin, distribution nozzles, and condensing tubes free of algae and slime despite intense exposure to sunlight. The BNPB/DDAC biocide did not interfere with the scale and corrosion control program and had no effect on the PTSA tracer used in the system. Based on these results, the BNPB/DDAC biocide continues to be used in this system.

Fish Processing Plant – Western Europe. The cooling tower at this plant was being treated once a week with 3.75 ppm active of isothiazolone. While this treatment program maintained planktonic bacteria at low levels, there were health and safety concerns for workers handling the isothiazolone biocide. As a result, the service company decided to evaluate the BNPB/DDAC biocide as a less hazardous option.

System

Counter flow cooling tower

Volume

2,640 gallons (10 m3)

Recirculation rate

36,984 gal/h (140 m3/h)

Cycles 4

Scale and corrosion control

All organic program based on phosphonates, copolymers, and azole

pH 8.0–8.5

Previous biocide

BCDMH supplemented with a quaternary-based biocide

Previous biocide

Since the recommend practice for Legionella pneumophila control is halogenation, treatment with BCDMH was continued as before, but the quaternary-based biocide was replaced by the new BNPB/DDAC biocide. The BNPB/DDAC biocide was dosed at 12 ppm active twice a week.

After five months of treatment with the BNPB/DDAC biocide, the rate of positive Legionella pneumophila serogroup 1 results was reduced from 44% to 20% (Table 2).

Scale & corrosion control All organic program based on phosphonates, copolymers, and azole Isothiazolone

The isothiazolone biocide was replaced by the BNPB/DDAC biocide which was dosed at 12 ppm active once a week. Treatment with the BNPB/DDAC biocide gave an immediate reduction in planktonic bacteria levels in the tower. Both the level of ATP and viable bacteria count were reduced by an order of magnitude after the first addition of the BNPB/DDAC biocide (Figure 2).

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Figure 2. Planktonic ATP and viable bacteria counts in cooling tower over time.

The BNPB/DDAC biocide successfully maintained these low counts over the next several weeks. In addition to the improved microbiological control, the switch to the BNPB/DDAC biocide did not cause any operational issues due to its low foaming characteristics (see Figure 3). Based on these results, the BNPB/ DDAC biocide continues to be used in this system.

Figure 3. Cooling tower basin after the addition of the BNPD/ DDAC biocide showing minimal foaming.

Conclusions

Membrane active quaternary biocides or blends that contained them had broad-spectrum activity regardless of the microorganism they were tested against—bacteria or algae. They also appeared to function at lower dosages than biocides, which functioned as metabolic inhibitors. This is not surprising since their target is the cell membrane, which is readily accessible. In many cases, a mixture of biocides was more effective than the individual biocides alone, indicating that the combination of different or complimentary biocidal mechanisms is most effective in improving biocidal efficacy. This was especially true for BNPD/ DDAC, which showed improved activity over BNPD alone.

Field trials confirmed the broad-spectrum activity, compatibility, and ease of handling of BNPD/DDAC.

References 1 2

3

4

5

6

Kemmer, F. N., 1988. The Nalco Water Handbook, 2nd Edition.

Eager, R. G., Leder, J., and Theis, A. B., 1986. “Glutaraldehyde: Factors Important for Microbial Efficacy” Third Conference on Progress in Chemical Disinfection, Binghamton, NY.

Winecek, K. M. and Chapman, J. S., 1999. “Water Treatment Biocides: How do They Work and Why Should You Care?” CORROSION 1999, paper no. 308 (Houston, TX: NACE).

Grab, L. A. and Theis, A. B., 1992. “Comparative Biocidal Efficacy vs. Sulfate Reducing Bacteria,” CORROSION 1992, paper no. 184 (Houston, TX: NACE).

Gerberick, G.F., Ryan, C.A., Kern, P.S., Schlatter, H., Dearman, R.J., Kimber, I., Patlewicz, G.Y., and Basketter, D.A., 2005. “Compilation of Historical Local Lymph Node Data for Evaluation of Skin Sensitization Alternative Methods” Dermatitis, Vol 16, No 4.

ASTM Standard E645, 2002a. “Standard Test Method for Efficacy of Microbiocides Used in Cooling Systems” ASTM International, West Conshohocken, PA, 2003, DOI: 10/1520/e0645-02A, www.astm.org.

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Key Considerations in Selecting Deposit Control Polymers in Industrial Water Treatment Emily R. Clark, The Lubrizol Corporation

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The buildup of deposits in boilers and cooling towers is a persistent problem that can lead to decreased efficiency, overheating, unscheduled shutdown time, and costly maintenance. As steam is generated by a boiler or water evaporating from a cooling tower, dissolved minerals are left behind. More water is added to make up for the evaporation loss, resulting in more deposition of minerals (e.g., CaCO3, CaSO4, Ca3(PO4)2), corrosion products (e.g., Fe2O3), particulate matter, and microbiological mass. These deposits accumulate in low circulation areas, becoming immobilized and building up on heat exchanger surfaces. Once a scale layer is formed, it will continue to get thicker unless treated, eventually blocking flow and decreasing productivity. Therefore, an effective water treatment program must control scale, corrosion, particulates, and biological growth.1–3 Scale formation is prevented using compounds that adsorb onto crystal growth sites and inhibit crystal growth and/or alter the crystal morphology. Polyphosphates, phosphonates, and deposit control polymers (DCPs) are commonly used components of industrial water treatment programs. Phosphonates, like those shown in Table 1, are used to sequester metal ions, such as copper, manganese, iron, and zinc, and prevent crystal growth and exhibit some activity in dispersing suspended matter. DCPs function as scale inhibitors, crystal modifiers, and dispersants.

Interaction with the DCPs modifies the precipitated solids and keeps them in suspension, inhibiting their ability to adhere to equipment surfaces.2,4–6 Table 1. Commonly used phosphonates in industrial water treatment.

hours. The initial and final soluble ion content is determined through various spectroscopic methods and percent inhibition determined by comparing samples with and without inhibitor.7 Two other experimental methods involve dynamic scale testing.

Under dynamic conditions, the water is pumped through metal tubing to simulate the agitated conditions of a boiler or cooling tower. The dynamic scale testing rig (DSTR) is designed to evaluate corrosion and scale control by controlling water temperature and pH as it flows through and around various metal alloys.

Inhibitor performance is evaluated by spectroscopic methods, calculating corrosion rates, and visually inspecting for scale formation.8 The dynamic scale loop (DSL) pumps water through a temperature- and pressure-regulated metal capillary sample loop and monitors the difference in pressure before and after passing through the loop. As scale builds, pressure increases.

Why Polymers?

Phosphorous-based compounds, like those shown in Table 1, are broadly effective in water treatment programs to control mild steel corrosion and inhibit calcium carbonate (CaCO3) scale.

They are key components in all-organic industrial water treatment programs, but under high stress conditions (e.g., high pH, temperature), they can react stoichiometrically, with Ca 2+ creating a Ca-phosphonate salt that may precipitate out of solution.9 The tolerance of phosphonate to calcium ions is the minimum concentration of phosphonate at a given pH, temperature, and ion concentration necessary to cause precipitation of phosphonate. The calcium tolerance of three phosphonates from Table 1 per 250 mg/L calcium ion at 45 °C are as follows:10 PBTC (73 mg/L) > ATMP (13.5 mg/L) > HEDP (7.5 mg/L)

Water treatment formulations can incorporate one or multiple methods of scale inhibition, relying on synergistic components to effectively control corrosion, scaling, and microbiological fouling in the industrial water system. Several factors need to be considered when developing a treatment plan, including component performance, cost, and stability; operating costs of using multiple methods; and field experience.

There are multiple types of experimental methods for investigating scale formation. Most of the results reviewed in this paper were acquired through static bottle testing (SBT). SBT keeps water at a consistent temperature, without agitation, for several

Ca-phosphonate salt formation alone can cause problems, but the situation is exacerbated as depletion of the phosphonate inhibitor allows CaCO3 scale to form. Continuous and effective system performance requires a treatment program that keeps phosphonates in solution and available to prevent precipitation and deposition. The addition of DCPs can extend the calcium tolerance of phosphonates, control calcium phosphate and the formation of other types of scale (e.g., CaCO3, SrSO4, CaF 2), and disperse suspended solids in the recirculating water, minimizing potential deposition on system surfaces.11 The monomer structure(s) and molecular weight of each DCP provides insight on its performance against scale and corrosion.

Homopolymers comprise a single repeating unit, copolymers – 2 repeating units, terpolymers – 3 repeating units, etc.

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Table 2. Common deposit control polymers used in industrial water treatment.

Specific types of scale will respond better to certain functional groups. For example, acrylic acid based terpolymers inhibit calcium phosphonate better than acrylic or maleic acid homopolymers. Polysulfonic acid homopolymers are more tolerant to calcium than both PAA and PMA homopolymers, but combining sulfonic and acrylic acid into a copolymer extends calcium tolerance compared to the three homopolymers.10 PAA, PMAA, and other DCPs dominated by carboxyl groups exhibit excellent CaCO3, calcium sulfate, and calcium fluoride inhibition, while DCPs with larger, hydrophobic, and strong acid groups perform better as calcium phosphate scale inhibitors and suspended solids dispersants.12 Among PAA homopolymers, as MW decreases, calcium tolerance and CaCO3 inhibition increases. The opposite phenomenon is seen in strontium sulfate scale; as MW increases, scale inhibition decreases (Figure 1). PAA inhibition of calcium phosphate and calcium sulfate is also MW dependent but reaches threshold inhibition at ~2k; increasing the MW above 2k does not improve performance.

Figure 1. Representation of PAA performance vs. MW for Ca ion tolerance, and CaCO3 and SrSO4 scale inhibition.

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MW differences for similar composition polymers can contribute to performance differences, as lower MW polymers generally adsorb faster than the high MW polymers due to steric hinderance.6,11,13 Investigations into the relationship between MW and inhibition have revealed that optimum MW is dependent on the polymer composition and targeted scale.

or phosphate inhibitor by controlling the thickness of the film on metal surfaces in addition to controlling calcium phosphate and phosphonate precipitation. At the same time, since the DCP is working to control both CaCO3 and phosphorous-based scale, higher doses are often required for overall scale inhibition. Sulfonic acid terpolymers have the excellent Ca 2+ tolerance and can be blended with carboxylic acid-based phosphonates or low MW PAAs for synergistic water treatment.3,8,10

In general, solvent-polymerized PAAs provide somewhat better performance than water-polymerized PAAs. This is attributed to distinctive end groups and branching not seen in water-polymerized PAA or other polymers. This relationship between MW and synthesis conditions of homopolymers is depicted in Table 3.

Thermal Degradation

Further investigation has shown that sulfonated terpolymers perform better as overall scale inhibitors at lower doses compared to homo- or copolymers. Blends of the PAAs and poly(AA/SA/ SS) inhibit scale characteristics of each polymer individually, providing a synergistic effect on scale inhibition and material dispersion.3,6,11 Table 3. Ranking of homopolymer performance against CaCO3 scale.4

Maintaining the correct dosage of scale inhibitor(s) can also play a key role in preventing deposit formation. Small doses of DCPs can be very effective in controlling scale, as only 3–5% of a carbonate scale crystal needs to be covered by polymer for complete inhibition. This is compared to 16% coverage required with phosphonate inhibitors.2 In general, increasing the dosage increases the inhibition; however, at some point, the dosage reaches critical value and the inhibition rate plateaus. One study found that 5 ppm of copolymer was sufficient to inhibit >90% CaSO4 scale, and any increase in dosage resulted in a decrease in inhibition. However, 7.5 ppm was needed to reach threshold inhibition of CaCO3, and as much as 40 ppm was needed to inhibit >70% of strontium and barium sulfate scale.3,6,13,14 Polymer dosage is critical to inhibition performance, and the best way to determine optimal dosage is through experimentation with the water being treated.

High stress often equates to high temperatures, which is when degradation of the scale inhibitor(s) becomes a key concern. In general, degradation rates increase with increasing temperature, but rates are also affected by pH, inhibitor dose, and exposure time. All polymers when subjected to stress conditions (up to 250 °C for 20 hr at pH 10.5) undergo some degradation or compositional changes. The extent of the degradation is dependent on polymer composition. Homopolymers experience less degradation and fewer structural changes at elevated temperatures than co- or terpolymers, with acrylic acid outperforming maleic acid homopolymers. Analytical characterization of polyacrylic acid (PAA), polymethylacrylic acid (PMAA), and polymaleic acid (PMA) polymers commonly used in boiler applications show that while all three homopolymers underwent some molecular weight loss indicative of degradation, PAA and PMAA had minimal performance changes in preventing CaCO3 scale (Figure 2). PMA, however, suffered a substantial loss in performance, as it inhibited twice as much scale before thermal stress than it did after.4,5,15 Figure 2. CaCO3 inhibition by homopolymers vs. thermal stress.

A graphic representation of the effect of thermal stress on CaCO3 inhibition by homopolymers.15

High Stress Conditions

As previously mentioned, phosphonates are effective scale inhibitors, but as Ca 2+ concentration increases, the risk of Ca-phosphonate and calcium phosphate formation also increases. Investigations into CaCO3 inhibitors have found that phosphonate and polymer scale used individually inhibit < 80% CaCO3 scale when dosed at 30 ppm in 180x calcite saturation. The phosphonate efficacy in high Ca 2+ water is predicated on the polymer inhibitor. In studies that combined polymer with PBTC or HEDP, greater than 90% inhibition of CaCO3 was seen under similar conditions at 40 ppm.1 The polymer works with the phosphonate

Solvent-polymerized PAAs (PAA-S) outperform water-polymerized PAAs (PAA-W) of the same MW. PAAs with a lower MW of 2k are better CaCO3 inhibitors than their 5k counterparts, regardless of the thermal stress conditions. PMA performance is most affected by thermal stress; there was a sharp decrease in percent inhibition as the temperature was increased from 23 °C to 250 °C.

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The pathway of DCP degradation during thermal stress is still being investigated. Figure 3 illustrates possible degradation routes in a poly(AA/SA) copolymer.

Figure 4. CaCO3 inhibition by various DCPs as a function of dose.6

Figure 3. Pathways for thermal degradation of an acrylic and sulfonic acid copolymer. (A) Scission of backbone (B) Decarboxylation (C) Hydrolysis of pedent and/or end groups.5

Relatively small MW losses are evident in lower MW PAAs, suggesting minimal scission of the polymer backbone. Homopolymers suffer less damage due to thermal degradation, losing < 8% MW at 250 °C, compared to > 10% loss in co- or terpolymers at ≥ 200 °C.4 When comparing homopolymers, it is important to recognize differences between the synthesis and composition. PMA is made under different polymerization conditions; is structurally dissimilar, with two carboxyl groups on adjacent carbon atoms compared to only one carboxyl group present in the PAAs; and its MW is much lower than other homopolymers. PMA is not as thermally stable as either the PAAs or PMAAs and may follow a different route or multiple routes of degradation.

Calcium Carbonate

Calcium carbonate is one of the most frequently encountered scales in industrial water treatment and has been the focus of many DCP performance studies. Most minerals are less soluble as the temperature decreases; calcium carbonate is an exception, and its formation is exacerbated by low pressure and high pH. Low pH, controlled by acid feed treatment, is an effective means to control calcium carbonate scale, but there are safety and corrosion drawbacks of acid addition.

As previously mentioned, MW and composition are key factors in predicting DCP performance. Studies have shown that higher carboxyl content and lower MW polymers perform well as CaCO3 scale inhibition. This relationship is illustrated in Figure 4 below. Poly(AA/SA/SS) terpolymers inhibit less CaCO3 compared to PAA homopolymers. This is due to the greater amount and accessibility of the carboxylate groups on PAA compared to the P(AA/SA/SS).

The same phenomenon is seen with phosphonates, as PBTC, which has a carboxylate group, outperforms both ATMP and HEDP in inhibiting CaCO3. Under thermal stress, sulfonic acid polymer performance improves, most likely due to the hydrolysis of the sulfonic acid, which in turn increases the carboxyl content of the polymer. PMA, which loses carboxyl content during thermal stress is a poor inhibitor of CaCO3 scale compared to PAAs at temperatures above 150 °C.6

Results were obtained from SBT at 66 °C for 24 hrs. P(AA/SA/ SS) terpolymer (TP) performance, represented by the triangles, is not an effective CaCO3 inhibitor when compared to the PAA homopolymers. The performance of PAA + TP (circles) lags but loosely parallels PAA-only performance.

With the addition of phosphonates to industrial water systems, the induction time of CaCO3 formation is delayed, and the rate of CaCO3 precipitation decreases by a factor of ≥ 5 when the phosphonate concentration increases from 5 to 40 mg/L. While terpolymer performance is inferior to that of the PAAs in inhibiting CaCO3 scale, a 3:1 blend of PBTC and sulfonic acid terpolymer outperformed other combinations of polymer and phosphonate in high stress conditions due to the inhibition abilities of the combined functional groups.4,6,16

Calcium Phosphate

Calcium phosphate deposits can occur on heat exchanger and reverse osmosis membrane surfaces, and an increase in the phosphate concentrations in lakes and rivers compounds the necessity for effective scale inhibition. Like CaCO3, calcium phosphate forms more readily under stressed conditions when phosphorous-based scale inhibitors are more likely to react with calcium and precipitate out of solution. The addition of DCPs to a water treatment program can improve calcium phosphate inhibition.

It is generally known that homopolymers are not good inhibitors for calcium phosphate scale. Studies have shown that PAAs offer < 20% inhibition when dosing at greater than 15 ppm. It has also been established in the previous section that the same PAAs that poorly inhibit calcium phosphate also excel at inhibiting calcium carbonate. The benefit to introducing sulfonic acid functional groups is a significant increase in the performance of DCPs at low doses. Remarkably, co- and terpolymers containing a blend of functional groups of different ionic charge are more effective calcium phosphate and calcium phosphonate inhibitors (Figure 5).17 The use of poly(SA/AA) copolymers increases the calcium phosphate inhibition to 50% at 15 ppm. Terpolymers containing a blend of acrylic acid, sulfonic acid, and sulfonated styrene improve inhibition to > 90% at the same dose.3,6,10 36

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Figure 5. Calcium phosphate inhibition by DCPs as a function of dose.

Results were obtained from SBT at 70 °C for 24 hrs. Poly(AA/ SA/SS) outperforms the P(AA/SA) copolymers, followed closely by a terpolymer with a non-ionic functional group. Lowering the MW of the P(AA/SA) copolymer lowers its inhibition performance, possibly due to the decreased amount of available SA groups.18

Under mild conditions, Poly(AA/SA/SS) significantly outperforms other homo- and copolymers, offering > 70% iron oxide dispersion at a relatively small dose of 1 ppm (Figure 6).6 The excellent performance of the terpolymer is likely due to the electrostatic interactions of the sulfonated groups with the negative charge of iron oxide. There is also evidence that the sulfonated co- and terpolymers have a stronger influence on the iron oxide particle size in solution.19 As with most scale inhibition studies, lowering the DCP dose lowers performance. Less than 50% iron oxide is dispersed at 0.25 ppm poly(AA/SA/SS). In general, the addition of suspended matter to recirculating water antagonizes DCP performance. Higher doses are necessary to achieve scale inhibition and dispersion.8,19 Figure 6. Graphic representation of iron oxide dispersion by various DCPs at 1 ppm as a function of time. P(AA/SA/SS) terpolymer clearly outperforms both solvent and water-polymerized PAAs, reaching a threshold dispersion of ~80% after 3 hours.6

Iron Oxide Dispersion

The mechanism for DCPs in industrial water treatment applications includes preventing deposition of suspended matter, such as iron oxide, by adsorbing onto the surface of the particles and dispersing the particulates throughout the solution, preventing them from settling on metal surfaces. The most commonly encountered iron oxides in industrial water applications—hematite and magnetite—are often the result of equipment corrosion or precipitation of soluble iron. DCPs of varying functional groups and MWs have been the subject of multiple experiments to stabilize iron oxide in solution.

Table 4. Ranking of common DCPs as iron oxide dispersants.

Conclusion

Based on the performance data reviewed within, deposit control polymers could be a critical addition to any industrial water treatment program, whether added independently or paired with a polyphosphate or phosphonate inhibitor. A wide range of homopolymers, copolymers, and terpolymers are available for mineral scale inhibition (e.g., CaCO3, Ca-phosphate), crystal modification, and particle dispersion (e.g., iron oxide). In brief, low MW solvent-polymerized PAAs outperform other DCPs at inhibiting CaCO3 scale, while P(AA/SA/SS) terpolymers are industry mainstays, inhibiting several types of scale and dispersing suspended matter. Selecting the ideal DCP or combination of DCPs depends on the functional groups, MW, water content, and treatment conditions.

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References 1

2

3

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L. A. Perez, G. E. Geiger and C. R. Ascolese, 2010. "Design and Applications of Cooling Water Treatment Programs," in The Science and Technology of Industrial Water Treatment, New York, CRC Press, pp. 113-128.

M. A. Kelland, 2014. "Scale Control," in Production Chemicals for the Oil and Gas Industry, Boca Raton, CRC Press, pp. 51-109.

Z. Amjad, J. Pugh, J. Zibrida and R. W. Zuhl, 1996. "Polymer Performance in Cooling Water: The Influence of Process Variables," Paper No. 160, CORROSION/96, NACE International, Denver, CO.

Z. Amjad and R. W. Zuhl, 2013. "The Impact of Thermal Stress on Deposit Control Polymer Performance," Association of Water Technologies, Uncasville, CT.

Z. Amjad, R. Zuhl and J. Zibrida, 2015. "Deposit Control Polymer Selection Criteria for High-Temperature Applications: Part 1-Polymer Characterizations," the Analyst, vol. 22, no. 3, pp. 40-46.

Z. Amjad and R. W. Zuhl, 2012. "Water Treater Deposit Control Polymer Evaluation Criteria and Considerations," Association of Water Technologies, Palm Springs, FL.

R. W. Zuhl and Z. Amjad, 1993. "The Role of Polymers in Water Treatment Applications and Criteria for Comparing Alternatives," Association of Water Technologies, Las Vegas, NV.

L. Z. Perez, Z. Amjad and R. W. Zuhl, 2017. "Stressed Alkaline Cooling Water Deposit Control: High Temperature, Suspended Solids, and Iron Impacts," Paper No. 9422, CORROSION/2017, NACE International, New Orleans, LA. W. F. Masler and Z. Amjad, 1988. "Advances in the Control of Calcium Phosphonate with a Novel Polymeric Inhibitor," CORROSION/88, NACE International, Houston, TX.

Z. Amjad, R. Zuhl and J. F. Zibrida, 2004. "The Use of Polymers to Improve Control of Calcium Phosphonate and Calcium Carbonate in High Stressed Cooling Water Systems," Association of Water Technologies, Nashville, TN.

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R. W. Zuhl and Z. Amjad, 2010. "Scale and Deposit Control Polymers for Industrial Water Treatment," in The Science and Technology of Industrial Water Treatment, New York, CRC Press, pp. 81-104.

Z. Amjad, R. W. Zuhl and J. F. Zibrida, 2014. "Deposit Control Polymer Selection Criteria for High Temperature Applications," Association of Water Technologies, Fort Worth, TX.

Z. Amjad and J. McFarland, 2017. "Polymer Evaluations as Strontium Sulfate Precipitation Inhibitors for Industrial Systems,â&#x20AC;? Association of Water Technologies, Grand Rapids, MI.

H. Luo, D. Chen, X. Yang, X. Zhao, H. Feng, M. Li and J. Wang, 2015. "Synthesis and Performance of a Polymeric Scale Inhibitor for Oilfiled Applications," J. Petrol Explor Prod Technol, vol. 5, pp. 177-187.

Z. Amjad and R. W. Zuhl, 2015. "Thermal Stress Effects on Deposit Control Polymers," Materials Performance, vol. 54, no. 9, pp. 54-58.

R. H. Ashcroft, 1985. "Scale Inhibition Under Harsh Conditions by 2-Phosphobutane 1,2,4-tricarboxylic acid," CORROSION/85, NACE International, Houston, TX.

E. B. Smyk, J. E. Hoots, K. P. Fivizzani and K. E. Fulks, 1988. "The Design and Application of Polymers in Cooling Water Programs," CORROSION/88, NACE International, Houston, TX.

L. Perez, Z. Amjad and R. W. Zuhl, 2015. "Deposit Control Polymers for Stressed Phosphate-Based Cooling Water Systems," Association of Water Technologies, Nashville, TN. S. G. Rokidi, P. G. Koutsoukos, L. A. Perez, Z. Amjad and R. W. Zuhl, 2016.

"Iron Oxide Colloidal Suspension Stabilization by Polymeric Disperants," CORROSION, NACE International, Vancouver, BC.

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