Flue Gas Desulfurization Wastewater 

Mitigation

Sponsored by Progress Energy

Team Crystal Clear

August 2009 – May 2010

Integrated Product and Process Design Program

University of Florida

Gainesville, FL

Executive Sponsor

Paul Crimi

Liason Engineers

Joe Estrada

David Fitzgerald

John Holler

Danny Johnson

Doug Yowell

Team Members

Ani Abraham

Diandra Anwar 

Michael Bachman 

Andrew Claus 

Priyahita Hrenko

Nickolas Nehama 

Leighton Walker

Travis Watson

Faculty Coach

Dr. Spyros Svoronos
Flue Gas Desulfurization Wastewater Mitigation ii Crystal Clear, University of Florida IPPD

Table of Contents

Executive Summary............................................................................5

Introduction.......................................................................................6

Introduction to Flue Gas Desulfurization..................................................................................................6

Electrocoagulation .............................................................................8

Background ...............................................................................................................................................8

Procedure..................................................................................................................................................8

Results.....................................................................................................................................................10

Water Softening...............................................................................11

Background .............................................................................................................................................11

Procedure................................................................................................................................................11

Results.....................................................................................................................................................11

Conclusions......................................................................................14

Recommendations...........................................................................15

Appendix I: Water Analysis ..............................................................17

Introduction to Inductively Coupled Plasma Optical Emission Spectroscopy ........................................17

ICP-OES Procedure and Analysis.............................................................................................................18

Appendix II: Zero Liquid Discharge....................................................20

Introduction to Zero Liquid Discharge ....................................................................................................20

Benefits of Zero Liquid Discharge ...........................................................................................................21

Alternative Low Temperature Zero Liquid Discharge.............................................................................21

The First Step: Softening.........................................................................................................................22

Attempted Continuation of Zero Liquid Discharge.................................................................................22

Appendix III: Water Softening ..........................................................24

Background on Water Softening.............................................................................................................24
Flue Gas Desulfurization Wastewater Mitigation iii Crystal Clear, University of Florida IPPD

Water Softening by Chemical Reagents..................................................................................................24

Methods Used for Water Softening........................................................................................................24

Method 1: sodium hydroxide and soda ash........................................................................................25

Method 2: lime and soda ash..............................................................................................................25

Method 3: hydrochloric acid, sodium hydroxide, and soda ash.........................................................25

Method 4: hydrochloric acid, sodium hydroxide, and less soda ash..................................................25

Method 5: hydrochloric acid and sodium hydroxide..........................................................................25

Results of Water Softening Methods......................................................................................................25

Method 1: sodium hydroxide and soda ash........................................................................................26

Method 2: lime and soda ash..............................................................................................................26

Methods 3 and 4: hydrochloric acid, sodium hydroxide, and soda ash .............................................27

Method 5: hydrochloric acid and sodium hydroxide..........................................................................27

Summary of Softening Results............................................................................................................27

Solid waste produced and Cost of Chemical Reagents (pre-treatment) ................................................27

Water softening after electrocoagulation (post-treatment)..................................................................28

Method 6: sodium hydroxide and soda ash (based on method 1).....................................................28

Appendix IV: Ion Exchange ...............................................................29

The Principles of Ion Exchange ...............................................................................................................29

Resin Selection........................................................................................................................................29

Design of Experiments............................................................................................................................30

Experimental Procedure .........................................................................................................................30

Sequential ...........................................................................................................................................30

Mixed ....................................................................................................................................................1

Ion Exchange Experimentation and Results..............................................................................................1

Resin Cost Analysis..................................................................................................................................33

Appendix V: Electrocoagulation........................................................34

Introduction ............................................................................................................................................34

Electrocoagulation Setups ......................................................................................................................34

Aluminum Plates and Plexiglas Spacer ...............................................................................................34

Graphite Plates and Rubber Spacer....................................................................................................35
Flue Gas Desulfurization Wastewater Mitigation iv Crystal Clear, University of Florida IPPD

Aluminum Plates and Rubber Spacer..................................................................................................37

Aluminum Plates and Rubber Spacer with Welded Tube...................................................................38

Aluminum Plates and Rubber Spacer with Welded Tube with Pre-Softened Wastewater................39

Additional Power Source Testing............................................................................................................41

References.......................................................................................43
Flue Gas Desulfurization Wastewater Mitigation 5 of 43 Crystal Clear, University of Florida IPPD

EXECUTIVE SUMMARY

In order to comply with environmental standards, the Progress Energy (PE) power plant in 

Crystal River, FL, is in the process of installing a flue gas desulfurization (FGD) system on the 

coal-burning Units 4 and 5. Based on industry knowledge and similar systems at their plant in 

Roxboro, NC, PE is expecting the wastewater stream from this process to have contaminants in 

concentrations that exceed the groundwater discharge limits as set forth and enforced by the 

Florida Department of Environmental Protection (FDEP). Consequently, PE has partnered with 

the University of Florida (UF) Integrated Product & Process Design (IPPD) program to 

investigate the potential contaminants and methods of removal. The IPPD team Crystal Clear 

(CC) worked on this task from Fall 2009 through Spring 2010. This is a comprehensive report of 

the work, findings, and recommendations of the team.

The first task, as outlined by PE and in order to best develop remediation techniques, was the 

determination of the contaminants that would be present in the wastewater. Because the 

system in Crystal River was not fully operational at any point during the project, all analyses and 

tests were performed with raw FGD wastewater from Roxboro due to the similarities of the 

systems at both sites. Water contaminant analyses were performed by the team using 

Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) on the UF campus, due to 

both cost and time considerations while maintaining acceptable analysis standards.

A wide variety of potential solutions were researched at a low level and their merits discussed 

and evaluated. Three methods were jointly agreed upon by PE and CC to be further 

investigated: Electrocoagulation (EC), Ion Exchange (IX), and Zero Liquid Discharge (ZLD). After 

initial tests, it was found that selenium was the most difficult to remove out of the tested 

contaminants pertinent to FDEP requirements.

After much research and many tests, involving multiple experimental designs and processes, a 

final option was discovered that effectively removes selenium as well as all other tested 

contaminants to meet discharge limits. This involves using a combination of EC and water 

softening, a subproject from ZLD, and provides a viable alternative to the expensive bioreactor 

process currently utilized at Roxboro. EC alone effectively removes selenium to below discharge 

limits, but in the process it adds a considerable amount of aluminum and other contaminants to 

concentrations above the discharge requirements. Water softening as a post-treatment 

effectively removes the aluminum and other contaminants of interest to levels below the FDEP 

requirements.

This project has developed a basic process which, on a laboratory scale, has been proven to 

meet FDEP discharge limits for all tested contaminants of interest from the Roxboro FGD 

wastewater. Further testing and experimentation is needed to test the scalability of this 

process into an industrial system, as well as its effectiveness on other contaminants outlined by 

the FDEP that were outside of the scope of this project. Additionally, when available, testing 

needs to be conducted with actual FGD wastewater from the Crystal River site, though the 

results are expected to be similar.
Flue Gas Desulfurization Wastewater Mitigation 6 of 43 Crystal Clear, University of Florida IPPD

INTRODUCTION

Due to the complex matrix of contaminants present in the wastewater downstream of flue gas 

desulfurization processes, one simple method of wastewater mitigation is not enough. Based 

on the findings of experimental tests done on a sample of FGD wastewater supplied by Progress 

Energy, Crystal Clear has found that a combination of EC of pH-treated FGD wastewater 

followed by softening is an effective combination of methods. The level of tested contaminants 

following this combination has been confirmed to be below the FDEP limits for discharge into 

the groundwater at Crystal River.

EC is the first step in the removal of selenium from the FGD wastewater. However, this method 

also adds excess levels of certain metals such as iron, manganese, and aluminum. Therefore, EC 

is followed with a chemical based softening method to remove the added and remaining 

contaminants.

Introduction to Flue Gas Desulfurization

In order to reduce the amount of sulfur dioxide that is released to the air, a wet FGD system has 

been installed at the PE power plant in Crystal River, FL. Sulfur dioxide needs to be removed 

from the air waste stream in order to comply with federal and state regulations. The wet FGD 

system in place at Crystal River utilizes a limestone-slurry absorption unit.

Sulfur dioxide (SO2) is removed from the air through water absorption. Sulfur dioxide dissolves 

into water as sulfurous acid (H2SO3). As acid concentrations increase sulfur dioxide removal 

decreases. To reduce the acidity limestone is dissolved in the FGD water. The calcium carbonate 

(CaCO3) and magnesium carbonate (MgCO3) found in limestone reacts with the sulfurous acid 

creating calcium sulfite (CaSO3), magnesium sulfite (MgSO3), water, and carbon dioxide. Forced 

oxidation of the calcium sulfite produces calcium sulfate (CaSO4), which is later processed to 

make calcium sulfate dihydrate (CaSO4•2H20), or gypsum. After the calcium sulfate is extracted 

for gypsum production, the remaining solution is recycled back to the absorber to collect more 

sulfur dioxide.

Sulfur dioxide absorption SO2(g) + H20(l) → 2H+

(aq) + SO3

-2

(aq)

Limestone dissolution CaCO3(s) + H2O(l) → Ca+2

(aq) + CO3

-2

(aq) + H2O 

Limestone neutralization CaCO3(s) + 2H+

(aq) + SO3

-2

(aq) → CaSO3(s) + H2O(l) + CO2(g)

Forced Oxidation CaSO3(s) + H2O(l) → Ca+2

(aq) + SO3

-2

(aq) + 1⁄2O2 → CaSO4(s)

Overall reaction CaCO3(s) + SO2(g) + 1⁄2O2 → CaSO4(s) + CO2(g)
Flue Gas Desulfurization Wastewater Mitigation 7 of 43 Crystal Clear, University of Florida IPPD

FGD wastewater is a product of flue gas desulfurization. Once the chloride levels become 

excessively high, the FGD water becomes corrosive and must be blown down to maintain the 

integrity of the system. This blowdown is FGD wastewater. It contains high levels of calcium, 

and magnesium with trace amounts of various heavy metals. Although these are only present in 

relatively small amounts, many of them are over the discharge limits set forth by the FDEP. In 

order to discharge this water into the environment, effective treatment options must be 

explored. 
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ELECTROCOAGULATION

Background

EC, in terms of wastewater mitigation, is a technique in which water is run between oppositely 

charged plates. An electrical current is applied to the plates to create a voltage drop between 

the plates which produces a pH change in the wastewater between the plates. The electrode 

plates provide a cathode and anode surface for the ions in the wastewater to coagulate and 

precipitate for removal. The exact mechanism of this pH change and ion precipitation has yet to 

be explained by experts in the field, but EC has been proven successful in removing some 

contaminants from wastewater. No exact, successful design specifications were available, so 

several sources were consulted prior to conducting any testing to form a basis upon which to 

begin research (Yilmaz, Boncukcuoğlu, Kocakerim, & Keskinler, 2005) (Emamjomeh & 

Muttucumaru, 2009) (Powell, Apparatus for Electrocoagulation of Liquids, 2000) (Powell, 

Method for Electrocoagulation of Liquids, 2002).

This research revealed that aluminum and iron sacrificial electrodes should provide the best 

removal of metals in wastewater. To do so, an electrical power source is connected to the 

electrode plates. At the positive terminal (anode), wastewater reacts with the plate and slowly 

corrodes the metal introducing metal ions which interact with the contaminants, possibly 

causing co-precipitation. At the negative terminal (cathode), precipitates deposit and can be 

scraped for removal. The waste stream also contains coagulated, precipitated material.

Procedure

Experimental testing yielded that the best setup for EC was two aluminum plates separated 

with a U-shaped rubber spacer. The spacer is along the left and right sides as well as the 

bottom, leaving the top open for relief of gas produced during the process. Filtered 

wastewater at pH 8 was pumped through a small Tygon tube using a peristaltic pump into the 

bottom through a hole in the rubber space. The exit was a hole drilled into the cathode near 

the top with an angularly cut aluminum pipe welded in place around it (see Figure 1). The pH of 

8 for the input water was chosen because it minimizes the contribution of solids from the 

electrodes (Yilmaz, Boncukcuoğlu, Kocakerim, & Keskinler, 2005). The power source for the 

experiment was six 6 volt batteries in two parallel series of three batteries each, producing 12 

volts.
Flue Gas Desulfurization Wastewater Mitigation 9 of 43 Crystal Clear, University of Florida IPPD

Figure 1: The final electrocoagulation experimental setup.
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Results

Table 1 below shows the results of the EC tests. For every analyte two detection wavelengths 

were used (see Appendix I: Water Analysis) and the table presents the results for both 

wavelengths. Green cells are indicative of meeting the discharge limits while red cells do not 

meet the requirements. Calcium and magnesium do not have specific value limitations, but 

instead are dependent on a total water hardness measurement that is outside the scope of this 

project. Cells with BDL mean that the numbers from the analysis were below the detection 

limit, with the value given in parenthesis. All detection limits were below the discharge limits, 

so values that are BDL meet the discharge requirements (except for arsenic, where the 

detection limit is the discharge limit).

Table 1: ICP-OES analysis of EC treated wastewater

Analyte

ICP-OES 

Detection 

Limit (ppm)

Discharge 

Limits 

(ppm)

Raw (ppm) EC Sample 1 

(ppm)

EC Sample 2 

(ppm)

Ag 0.0009 0.1 0.006 0.006 BDL (0.000)

Ag 0.0009 0.1 0.015 BDL (0.000) BDL (0.000)

Al 0.003 1.5 0.071 528.200 533.900

Al 0.003 1.5 BDL (0.000) 1066.000 1080.000

Ca 0.00002 --- 2179.667 120.700 131.600

Ca 0.00002 --- 2181.000 109.200 117.900

Fe 0.002 0.3 0.014 6.453 6.928

Fe 0.002 0.3 0.012 6.357 6.810

Mg 0.00007 --- 532.667 21.190 23.330

Mg 0.00007 --- 534.333 20.430 22.560

Mn 0.0004 0.1 1.508 25.880 26.520

Mn 0.0004 0.1 1.490 25.720 26.380

Se 0.05 0.071 1.580 0.092 BDL (0.022)

Se 0.05 0.071 BDL (0.000) BDL (0.000) BDL (0.000)
Flue Gas Desulfurization Wastewater Mitigation 11 of 43 Crystal Clear, University of Florida IPPD

WATER SOFTENING

Background

As shown above, EC can effectively remove selenium ions along with some calcium, 

magnesium, and silver ions from FGD wastewater. However, EC adds aluminum, iron, and 

manganese ions to the water during the process, perhaps even as part of the mechanism by 

which it works. Research and experimentation with water softening techniques demonstrated 

that they can remove aluminum, iron, and manganese ions as well as calcium and magnesium 

ions from raw FGD wastewater (see Appendix III: Water Softening). Therefore, water softening 

was considered a plausible post EC treatment method to remove both the remaining 

contaminants as well as those added/increased by EC.

Procedure

Given the highly increased concentrations of aluminum from the EC, it is important that the 

softening method used removes it. Aluminum hydroxide, the molecule most likely to 

precipitate from the solution via softening with sodium hydroxide and soda ash, has the lowest 

solubility between pH 4 and pH 9.5 (Emilia Andersson, 2001). An experiment was conducted 

with a known solution of aluminum chloride hexahydrate (aluminum chloride being the most 

likely molecule in the EC wastewater) to determine the exact pH at which a good precipitate 

would be produced through the addition of sodium hydroxide. Sodium hydroxide was slowly 

added until a white precipitate formed, at a pH of 7.445. Sodium hydroxide was further added 

without additional effect. However, it was found that at pH of 9 or above, the aluminum 

hydroxide precipitate began to dissolve back into solution. The softening process established by 

earlier tests requires the pH to be raised to 12.22 via sodium hydroxide. Consequently, with the 

new higher aluminum concentration an intermediate step was added.

Sodium hydroxide would be added to the post-EC wastewater to raise the pH from 5 to about 

7.445. At this point, the sample would be centrifuged to remove the precipitate that was 

formed. Then the remaining supernatant would be subjected to the water softening method 1 

of adding more sodium hydroxide to a pH of 12.22 and then soda ash to a pH of 12.32 (see 

Method 1: sodium hydroxide and soda ash for more information).

Results

Sodium hydroxide was added to the post-EC water until a pH of 7.372 was reached, at which 

point a white precipitate was formed as expected. The precipitate was removed via centrifuge 

and the supernatant was treated with additional sodium hydroxide to a pH of 12.214. The 

solution was slightly hazy, but without an obvious precipitate as previously experienced during 

softening experimentation. Soda ash was added and the pH actually decreased to 12.065, but 
Flue Gas Desulfurization Wastewater Mitigation 12 of 43 Crystal Clear, University of Florida IPPD

then began to rise until it reached 12.244 at which point additional soda ash did not affect the 

pH (see Table 2). At this point, a brownish-white precipitate formed. 

The brownish-white precipitate was removed using a centrifuge and a clear solution was 

obtained. This solution was analyzed using ICP-OES and the results can be seen in Table 2. 

Table 2: Change in pH with addition of soda ash

Batch # Amount of Soda 

Ash added (g)

pH after 

each batch

1 0.0124 12.189

2 0.0144 12.071

3 0.0315 12.065

4 0.0496 12.135

5 0.0447 12.159

6 0.0847 12.196

7 0.2343 12.244

8 0.0695 12.244

TOTAL 0.5411

This combined, multi-step process of EC followed by two-step water softening successfully 

removes all of the contaminants measured to levels below the discharge requirements set forth 

by the FDEP. A summary of the ICP-OES detection limits, FDEP discharge limits, raw wastewater 

contaminants, and then the results of this combined process (in triplicate tests) can be seen in 

Table 3. The sample of the combined process was analyzed three times to ensure validity of the 

testing. The tests had similar values and all were within the discharge limits. Green cells are 

indicative of meeting the discharge limits while red cells do not meet the requirements. Cells 

with BDL mean that the numbers from the analysis were below the detection limit, with the 

value given in parenthesis. All detection limits were below the discharge limits, so values that 

are BDL meet the discharge requirements (except for arsenic, where the detection limit is the 

discharge limit). 
Flue Gas Desulfurization Wastewater Mitigation 13 of 43 Crystal Clear, University of Florida IPPD

Table 3: Detection limits, discharge Limits, raw wastewater concentrations, and combined process (EC & softening) results

Analyte

ICP-OES 

Detection 

Limit (ppm)

Discharge 

Limits 

(ppm)

Raw (ppm)

EC and 

Softening 1 

(ppm)

EC and 

Softening 2 

(ppm)

EC and 

Softening 3 

(ppm)

Ag 0.0009 0.1 0.006 0.005 0.004 0.003

Ag 0.0009 0.1 0.015 0.005 0.004 0.004

Al 0.003 1.5 0.071 0.404 0.409 0.419

Al 0.003 1.5 BDL (0.000) 0.407 0.410 0.411

As 0.05 0.05 BDL (0.000) BDL (0.032) BDL (0.032) BDL (0.000)

As 0.05 0.05 BDL (0.000) BDL (0.000) BDL (0.022) BDL (0.000)

Ca 0.00002 --- 2179.667 0.801 0.864 0.889

Ca 0.00002 --- 2181.000 0.810 0.880 0.908

Fe 0.002 0.3 0.014 0.037 0.025 0.023

Fe 0.002 0.3 0.012 0.035 0.026 0.023

Mg 0.00007 --- 532.667 0.157 0.170 0.175

Mg 0.00007 --- 534.333 0.155 0.166 0.186

Mn 0.0004 0.1 1.508 0.012 0.011 0.012

Mn 0.0004 0.1 1.490 0.022 0.021 0.023

Se 0.05 0.071 1.580 BDL (0.038) BDL (0.033) BDL (0.044)

Se 0.05 0.071 BDL (0.000) BDL (0.000) BDL (0.000) BDL (0.000)
Flue Gas Desulfurization Wastewater Mitigation 14 of 43 Crystal Clear, University of Florida IPPD

CONCLUSIONS

The above recommended and tested combined process is an effective water treatment tool for 

FGD wastewater. Testing was not done on all contaminants restricted for discharge by the 

FDEP, but for all contaminants tested the process is successful. The most difficult to remove 

contaminant, selenium, could be successfully brought within the discharge limits. While the 

data in Appendix V shows that EC alone could reduce the levels of selenium to within the limits, 

the process contributed other materials which were then above the discharge requirements. 

However, previous research showed that water softening could successfully remove these 

added contaminants under other conditions, so the use of water softening as a post-EC 

treatment process was explored and found successful.
Flue Gas Desulfurization Wastewater Mitigation 15 of 43 Crystal Clear, University of Florida IPPD

RECOMMENDATIONS

While the process outlined above has been proven successful, it was only conducted on a 

laboratory scale. Additionally, it did not include all contaminants regulated by the FDEP for 

groundwater discharge. However it did successfully bring one of the most difficult to treat 

contaminants, selenium, into compliance with the discharge limits. Therefore additional work 

and experimentation is required before the above outlined process can be implemented on an 

industrial scale at the PE Crystal River plant. 

One the major efforts needed to bring this process into full scale production is scaling up the EC 

setup from the current two plate apparatus. The two plate setup was initially chosen to show a 

proof of concept, however this proof of concept took many more iterations and developments 

than initially expected (see Appendix V: Electrocoagulation). Consequently, the two plate setup 

was well suited for the performed experiments, but is not practical for industrial application. 

Water currently is only in contact with one side of each plate, whereas an industrial application 

should have alternating charged plates, allowing for both sides of each plate to be in contact 

with the water. Additionally, the flow rate of the current apparatus is on the scale of milliliters 

per minute, but PE expects a flow rate of approximately 300 gallons per minute. Therefore, it is 

recommended to begin a stepwise scale-up of the design to multiple plates beginning with four 

plates and increasing the number per further results. A setup like this would also allow for the 

needed testing of various flow rates, voltages, and amperages to garner a better understanding 

of the optimal conditions under which to run the EC. Setups with different size and/or number 

of plates should also be constructed to determine the effect of these factors on contaminant 

removal. To effectively do this, a larger and more powerful pump than the peristaltic pump 

used will also be needed.

In conjunction with the physical setup of the EC plates and conditions under which to run them, 

testing and analysis needs to be done on the power supply. As discussed in Appendix V: 

Electrocoagulation, a major issue encountered was sufficient, constant power given the low 

resistance of FGD wastewater. Batteries were effective for some proof-of-concept work, but did 

not provide controllable, repeatable, and/or consistent power. Normal off-the-shelf power 

supplies were found to be inadequate for the demands of the project because they 

automatically reduced power as the resistance decreases as a safety measure. Therefore, a 

specialized power supply needs to be either found or built by the team. Based on the testing 

and information gathered, it is recommended that the power supply be able to safely supply at 

least a constant 2-12 V and 0.1-5 A for more than an hour for a two plate setup. Further work 

and analysis would need to be conducted on the nature of the power requirements for multiple 

plates and/or plates of other dimensions. Inclusion of digital voltage and amperage/power 

meters is a necessity, as well as controls to fine tune the output levels.
Flue Gas Desulfurization Wastewater Mitigation 16 of 43 Crystal Clear, University of Florida IPPD

Additionally, analysis needs to be done on the formation of precipitate and the buildup of it on 

the plates, which became more of a problem as the setup ran longer and at higher currents. 

The more effective EC is at removing contaminants, the more coagulated contaminants will be 

present and will need to be removed. If the flow rate provides a high enough superficial velocity 

across the plates to prevent buildup and remove the solids, this may prove to be less of an 

issue. If not, it needs to be removed by another means in order to allow for continued 

operation of the equipment under the desired conditions with the desired results. Ideas 

discussed, but not investigated, include reversing the polarity of the plates, attaching a shaker 

or vibrator to the plates, using a mechanical scraper, and/or some sort of auger type design for 

the plates themselves.

Simultaneously, additional studies are needed to evaluate this process’s effectiveness on the 

concentrations of all other pertinent contaminants whose discharge is regulated by the FDEP. 

While the ICP-OES is a highly effective tool for measuring many of the contaminants of concern, 

it is not applicable for all contaminants. Mercury proved to be very difficult to analyze due to 

issues with the software/computer crashing and the physical system becoming flooded with 

mercury to the point where it could barely be flushed. While boron concentrations can be 

analyzed by ICP-OES, it requires special flushing procedures using dangerous hydrofluoric acid, 

so another method of analysis may be better. Additionally, testing on contaminants such as 

fluorine and chlorine cannot be done via ICP-OES. It is important to note that more precise and 

accurate versions of ICP do exist, notably mass spectroscopy (ICP-MS), but the cost is 

considerably higher. However, some discharge limits may require the use of such testing. It may 

also be advisable to conduct some tests with equipment such as the ICP-MS to ensure complete 

compliance and gain a better understanding of some of the effects of changes in the process. 
Flue Gas Desulfurization Wastewater Mitigation 17 of 43 Crystal Clear, University of Florida IPPD

APPENDIX I: WATER ANALYSIS

Introduction to Inductively Coupled Plasma Optical Emission Spectroscopy

The analysis of water samples was conducted by inductively coupled plasma optical emission 

spectroscopy (ICP-OES). Element concentrations can be detected because when sufficient 

thermal or electrical energy is available an atom or ion can jump to an unstable energy state. As 

the atom or ion returns to the stable energy state a light spectrum is generated. Optical 

emission spectroscopy is the measurement of this light spectrum. The wavelength of this light is 

specific to the elements present in the sample, and the intensity of the light is proportional to 

the concentration of the specific element. The light intensity is compared to the intensities of 

known standards to determine the concentration in the sample.

The inductively coupled plasma is an argon plasma maintained by the interaction between a 

radio frequency field and ionized argon gas. The radio frequency power induces an oscillating 

magnetic field which stabilizes the plasma to flow through an annular column. At the end of the 

column the plasma expands to its full dimension and here the sample is injected as an aerosol 

into the center of the annulus. This design confines the sample in a chemically inert atmosphere 

where the optically thin emission source then reflexes off mirrors until it reaches refraction slits 

before a detector. The operator must specify the wavelength of expected contaminants in 

order to direct the light emission to the proper refraction slit.

There are two ways to view an ICP-OES emission, radially and axially. The classical ICP-OES 

configuration utilizes radial viewing, allowing for the highest linear relationship between 

intensity and concentration. Axial viewing provides up to 10 times better detection limits than 

radial viewing.

Figure 2: Radial viewing

Figure 3: Axial viewing
Flue Gas Desulfurization Wastewater Mitigation 18 of 43 Crystal Clear, University of Florida IPPD

ICP-OES Procedure and Analysis

The method herein used was a Perkin-Elmer Plasma 3200 ICP-OES, a radial viewing ICP-OES, in 

the Particle Engineering Research Center at UF. A broad spectrum and a mercury standard were 

used for the analysis. These standards were calibrated at 0.1, 1, and 10 ppm. However, often 

contaminant concentrations were above 10 ppm. For these cases, dilutions were used until the 

levels were brought within the range of the calibration standards. This occurred for calcium and 

magnesium on samples without softening, and for aluminum with EC samples. In some cases, 

dilutions could not be made and results were above the known range. However, extrapolation 

could still be used for a good approximation of the actual value. 

For every contaminant of interest two detection wavelengths were chosen; this is why result 

tables list each ion twice with different values, one for each of the two wavelengths. If both the 

wavelengths were giving consistent positive results, then the concentration was determined to 

be the average of these values. The ICP-OES was able to successfully detect silver, aluminum, 

calcium, iron, magnesium, selenium, and manganese in the samples. Arsenic and thallium 

concentrations were below the detection limits of the ICP-OES. Several attempts were made to 

determine mercury concentration. Unfortunately calibrating the mercury standard frequently 

crashed the ICP-OES software, preventing further analysis. One trial was able to obtain mercury 

concentration of raw wastewater. These results gave Hg concentration of 32ppm, but because 

this value is outside the calibration range, it can only be definitively said to be above 10 ppm 

but most likely close to 32ppm.

Although there is some notable variance, ICP-OES results are often very precise. Figure below 

shows the ion concentrations of untreated wastewater samples taken on three separate days 

to help display the variance of the ICP-OES.
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Still deviations may occur from contaminants of a previous sample “lingering” in the ICP-OES. 

Flushing the system with Nanopure water between samples improved the accuracy of the 

results, although one flush proved to not always be sufficient. The accuracy and precision of the 

ICP-OES was regularly tested with Nanopure water and calibration standards.

Figure 4: ICP-OES variation across raw water samples
Flue Gas Desulfurization Wastewater Mitigation 20 of 43 Crystal Clear, University of Florida IPPD

APPENDIX II: ZERO LIQUID DISCHARGE

Introduction to Zero Liquid Discharge

ZLD is a wastewater treatment process that is based around the concept of producing zero 

waste that is liquid. ZLD separates wastewater into a solid waste product and a liquid water 

effluent that is no longer considered waste. The concept and application of ZLD exists in many 

variations and has been applied to a variety of applications in the past. However, the 

application of ZLD to flue gas desulfurization wastewater is a relatively recent development and 

the process has not been standardized for the complex matrix that is FGD wastewater. There 

are some companies offering ZLD for FGD applications, but the first project sites are just coming 

online and little to no information is available about the detailed workings of the processes. 

Additionally, there are some variations on ZLD that may be appropriate for FGD applications 

including partial ZLD (stopping before reaching complete separation of water and waste) and 

low temperature ZLD. The work done during this project focused on regular ZLD as it is the best 

basis for exploring the other variations. Partial ZLD is actually an easier process than complete 

ZLD. Low temperature ZLD is an interesting variation with great potential, but it has not been 

applied to FGD wastewater, only to the production of salt cakes (one of the original applications 

of ZLD in general).

At the most basic, ZLD is a three step process as shown in Figure. The FGD purge water, or blow 

down, with the contaminants is brought to the first stage, a softening system. In the softener 

chemicals are added, react with the dissolved solids, and waste precipitates out of the solution 

readily and easily and can be removed as a sludge. The sludge-free water then proceeds to the 

second stage, an evaporator. Most of the water is boiled off at this stage, the vapor is collected, 

and allowed to condense. The now highly concentrated wastewater stream is then sent to the 

final stage, a crystallizer, which removes all of the water that is still in the waste stream, 

producing water vapor that is condensed and recovered and a solid salt cake for disposal.

Figure 5: Basic outline of ZLD process
Flue Gas Desulfurization Wastewater Mitigation 21 of 43 Crystal Clear, University of Florida IPPD

Benefits of Zero Liquid Discharge

ZLD offers many benefits over other wastewater processing methods. The first and foremost is 

the future-resistant nature of the waste stream. Local and federal requirements for discharging 

process water have only become more stringent and will continue on this path. These lower 

thresholds require more complex and advanced systems that can continuously and reliably 

produce water that meets these standards. Furthermore, testing must be done to ensure these 

are met and in many cases only very specialized and expensive equipment can accurately and 

precisely detect these levels. Other wastewater processing methods still produce a water 

stream with contaminants levels that are only just below the current standard or detection 

limit. In contrast ZLD theoretically completely separates the contaminants from the water 

stream. Consequently, while testing is still needed to ensure functionality and compliance, no 

change in wastewater discharge requirements will affect the process. New advances in 

detection methods and/or reductions in the discharge limits most likely will not affect facilities 

with ZLD.

With ZLD all of the contaminants that are usually split into two streams, one that just meets the 

environmental discharge requirements and a waste stream, instead exits as a solid. This solid, 

depending on initial contaminants and conditions, may qualify for regular disposal in a normal 

landfill. Standards for hazardous versus non-hazardous solids are less stringent than for water. 

If the cake can pass any required tests, such as leeching, this becomes a viable, cost-effective

disposal method. If this is not possible, the salt cake is still a smaller, easy transportable waste 

product that can be properly disposed or stored more readily than contaminated water and/or 

the waste streams from other processes.

Furthermore, if a partial ZLD process is implemented, it may be possible to use the 

concentrated wastewater stream in conjunction with fly ash. Fly ash naturally needs to be 

watered to keep it in place. Partial ZLD water may be eligible for this purpose depending on the 

setup of the plant/facility and whether the fly ash is stored for disposal or sold/reused. This 

could combine two waste streams, with both benefiting from the other. Partial ZLD should also 

be an easier process to implement that total ZLD.

Alternative Low Temperature Zero Liquid Discharge

As mentioned above, there is a relatively new process variation on ZLD called low temperature 

ZLD. This process is based on the same concept as normal ZLD, but involves a low temperature 

evaporator that is designed to reduce operational and capital costs. The first difference is that 

the process does not call for a softening unit, thus eliminating the cost of chemicals, 

equipment, and a waste stream.

However, the main difference is with the evaporator. As water is evaporated, the total 

concentration of contaminants in the liquid increases. As the concentrations of total dissolved 

solids (TDS) increases, so does the boiling point rise (BPR) of the water. Consequently an 

increasingly higher temperature needs to be achieved to reach the BPR to continue to 

evaporate water, correspondingly requiring more power and thus increasing the operating cost. 
Flue Gas Desulfurization Wastewater Mitigation 22 of 43 Crystal Clear, University of Florida IPPD

This also makes it increasingly difficult to remove highly soluble salts. However, boiling point 

decreases with pressure. Therefore it is possible to boil the water using less energy. The 

decreased pressure counteracts the increase in BPR due to higher concentrations of TDS.

This procedure, while seemingly very viable and attractive, does have some drawbacks. The 

documentation available is very limited and while it explains many aspects, it is does not cover 

everything and only barely covers some very key aspects. Furthermore, no testing has been 

performed outside of laboratory settings (Shaw, 2009).

The First Step: Softening

In regular ZLD, for either total or partial, the first step is to soften the water. Flue gas 

desulfurization wastewater has a high concentration of calcium and magnesium dissolved as 

chloride complexes. Calcium chloride and magnesium chloride are highly soluble salts that are 

also very corrosive due to the high chloride levels. Softening serves two purposes as the first 

step. The first is to change the composition to primarily sodium chloride, which while still very 

soluble, can be easily crystallized out of solution. This also serves to reduce the chloride content 

of the waste stream and thus reduce the corrosiveness of the stream. This means that lower 

cost materials, which would be otherwise affected by high chloride content, can be used.

Given the importance of softening to the ZLD process, it was decided to fully explore water 

softening before moving on in the process. Water softening is covered in more depth in 

Appendix III: Water Softening.

Attempted Continuation of Zero Liquid Discharge

While the majority of the initial focus on ZLD actually turned to water softening and its benefits 

as outlined in Appendix III: Water Softening, an experiment was performed on evaporating and 

then condensing the softened water. Only one experiment was performed and the results were 

very puzzling. A small batch distillation was setup in the laboratory with a water-cooled 

condenser to collect the water vapor. The evaporator flask with the liquid was placed on an 

electric hot plate and heated until rapid boiling was achieved. The end of the condenser was 

open to the atmosphere, due to equipment limitations, but set so as to drip into a funnel and 

then into a vial for later analysis. The water flow and boiling rate were maintained so as to 

ensure that all water vapor was condensing well within the condenser. About half of the liquid 

charged to the evaporator flask was evaporated, condensed, and collected.

Both the liquid left in the evaporator flask and the vapor that was condensed were analyzed via 

ICP-OES. The results showed that the collected condensed vapor was completely contaminated, 

while the liquid left in the evaporator flask was nearly pure. This is against everything that was 

predicted and expected to happen. It must be reiterated that this test was only performed once 

without any duplicates due to time and equipment constraints during the term of the project.

There are a couple of possible explanations for this oddity. One possibility is that the 

contaminants were entrained in tiny water droplets in the water vapor and thus left the 
Flue Gas Desulfurization Wastewater Mitigation 23 of 43 Crystal Clear, University of Florida IPPD

evaporator flask. Another potential cause for this, while not suspected, is that the sample vials 

mislabeled and/or swapped at some point between collection and analysis. Outside of these 

options, neither of which is anything more than speculation, the cause for this odd behavior is 

unknown.
Flue Gas Desulfurization Wastewater Mitigation 24 of 43 Crystal Clear, University of Florida IPPD

APPENDIX III: WATER SOFTENING

Background on Water Softening

Water hardness is determined based on the amount of calcium and magnesium dissolved in it. 

Water that is highly concentrated with calcium and magnesium is known to be very “hard.” 

Therefore, water softening is used as a treatment method to remove calcium and magnesium. 

Distillation or reverse osmosis could be used as alternative methods to remove the calcium and 

magnesium; however, these methods are extremely expensive. 

Water softening is used as the first step in the ZLD process, where the highly concentrated 

calcium and magnesium are removed from the FGD purge stream water. The removal of these 

ions could reduce the energy used in the later steps of the ZLD process, evaporator and 

crystallizer, and help protect the system.

Water Softening by Chemical Reagents

The FGD purge stream water is softened using chemical reagents. The chemical reagents are 

added to the water to precipitate most of the calcium and magnesium ions from the water as 

calcium carbonate and magnesium hydroxide. In the softening process, the calcium and 

magnesium ions are substituted with sodium ions and the water becomes an aqueous solution 

of sodium chloride (Shaw, 2009). The precipitates are collected by settling and the softened 

water is fed into the evaporator which is the second step of the ZLD process.

Several chemicals can be used to remove the calcium and magnesium ions from the FGD purge 

stream water. The chemicals used in this study include sodium hydroxide, hydrochloric acid, 

lime and soda ash. Adding these chemicals in a certain order can remove most of the calcium 

and magnesium ions. Analysis of the FGD purge stream water using ICP-OES showed the 

concentration of each ion present in the water, including heavy metals and other contaminants. 

Chemical softening was shown to remove, in addition to the calcium and magnesium, some of 

the aluminum, iron, silver, manganese, and selenium that is present in the raw wastewater.

Methods Used for Water Softening

From all of the softening experiments conducted using the FGD purge stream water, five 

methods were successful in removing most of the calcium and magnesium ions along with

some of the other contaminants. All samples were analyzed with ICP-OES, as described above, 

before and after each treatment process. 
Flue Gas Desulfurization Wastewater Mitigation 25 of 43 Crystal Clear, University of Florida IPPD

Method 1: sodium hydroxide and soda ash

Sodium hydroxide was added first to the FGD purge stream water until the pH reached 12.22. 

The addition of the sodium hydroxide formed a white precipitate solution. After the solution 

was well mixed, soda ash was added to the solution until it reached pH of 12.32. The addition of 

the soda ash made the solution very milky and more white precipitate was formed.

Method 2: lime and soda ash

Lime was added first to the FGD purge stream water until the pH reached 12.21. The addition of 

the lime formed a white precipitate solution. After the solution was well mixed, soda ash was 

added to the solution until it reached pH of 12.70. The addition of the soda ash made the 

solution very milky and more white precipitate was formed.

Method 3: hydrochloric acid, sodium hydroxide, and soda ash

Hydrochloric acid was added first to the FGD purge stream water until the pH reached 1.11. 

Secondly, sodium hydroxide was added to the FGD purge stream water until the pH reached 

12.21. The addition of the sodium hydroxide formed a white precipitate solution. After the 

solution was well mixed, soda ash was added to the solution until it reached pH of 12.58. The 

addition of the soda ash made the solution very milky and more white precipitate was formed.

Method 4: hydrochloric acid, sodium hydroxide, and less soda ash

This is identical to method 3 except that the amount of soda ash added was decreased 

considerably. After addition of soda ash, pH increased to 12.51.

Method 5: hydrochloric acid and sodium hydroxide

Hydrochloric acid was added first to the FGD purge stream water until the pH reached 1.11. 

Then, sodium hydroxide was added to the FGD purge stream water until the pH reached 12.50. 

The addition of the sodium hydroxide formed a white precipitate solution around pH 12.21. 

Then around pH 12.50, the solution became very milky and more white precipitate was formed.

Results of Water Softening Methods

Overall, the five methods for softening performed well in removing calcium and magnesium 

ions along with other contaminants such as silver, aluminum, iron, and manganese from the 

FGD purge stream water. However, selenium ions were not removed. All of the ions that were

screened for, with the exception of selenium, met the EPA and FDEP discharge requirements 

after the water softening step. Table 4 shows the results of each of the successful water 

softening methods, except for softening method 5. The numbers in Table 4 refer to 

concentrations of each ion in ppm. 
Flue Gas Desulfurization Wastewater Mitigation 26 of 43 Crystal Clear, University of Florida IPPD

Table 4: ICP-OES analysis of raw waste water and softening methods 1-4

Analyte

ICP-OES 

Detection 

Limit (ppm)

Discharge 

Limits 

(ppm)

Raw

wastewater

(ppm)

Softening 

Method 1 

(ppm)

Softening 

Method 2 

(ppm)

Softening 

Method 3 

(ppm)

Softening 

Method 4 

(ppm)

Ag 0.0009 0.1 0.002 BDL (0.000) BDL (0.000) 0.003 0.002

Ag 0.0009 0.1 0.018 BDL (0.000) BDL (0.000) 0.004 0.003

Al 0.003 1.5 0.014 0.263 0.035 BDL (0.000) BDL (0.000)

Al 0.003 1.5 BDL (0.000) 0.259 0.040 0.004 BDL (0.000)

Ca 0.00002 --- 2054.750 1.222 1.869 0.953 19.400

Ca 0.00002 --- 2043.750 1.218 1.875 0.973 18.800

Fe 0.002 0.3 0.020 0.015 0.016 0.016 0.010

Fe 0.002 0.3 0.021 0.015 0.016 0.017 0.010

Mg 0.00007 --- 485.750 0.211 0.212 0.131 0.098

Mg 0.00007 --- 490.200 0.193 0.200 0.105 0.102

Mn 0.0004 0.1 1.519 BDL (0.000) BDL (0.000) 0.002 0.002

Mn 0.0004 0.1 1.500 0.009 0.016 0.012 0.010

Se 0.05 0.071 1.547 1.720 1.695 0.864 0.828

Se 0.05 0.071 BDL (0.000) 1.102 1.116 0.589 BDL (0.000)

Method 1: sodium hydroxide and soda ash

From Table 4, it is apparent that the first method removed most of the ions except for 

aluminum, iron, and selenium. It is seen from the ICP-OES results that aluminum concentration 

increased significantly. This was due to the fact that an EC sample containing significant amount 

of aluminum was tested immediately before testing this sample. Even with flushing out the 

ICP-OES machine for 10 minutes with Nanopure water, the machine was still flooded with 

aluminum. This caused the machine to produce incorrect concentrations for aluminum. 

However, from experience and understanding the chemistry of the FGD purge stream water, it 

can be confidently applied that that method 1 will perform in the same fashion as methods 3 

and 4.

The iron removal from water by softening is shown to be 50%. However, this is because the 

concentration of iron present in the FGD purge water stream is very low. The concentration of 

iron present in the water after softening is 0.015ppm, which is below the discharge limits. The 

increase shown to the selenium concentration for this method falls into the standard error 

present from analyzing selenium ions on the ICP-OES. However, the most important result from 

this method is that selenium ions were not removed. Furthermore, the selenium ion 

concentration is higher than the discharge limit.

Method 2: lime and soda ash

This method had similar results to method 1. It removed most of the ions except for aluminum, 

iron and selenium. The ICP-OES results showed that the concentration of aluminum increased. 

This was also due to the fact that the ICP-OES machine was flooded with aluminum after 
Flue Gas Desulfurization Wastewater Mitigation 27 of 43 Crystal Clear, University of Florida IPPD

analyzing the EC sample. However, this sample was analyzed after the method 1 sample and in 

between these samples the ICP-OES was flushed with Nanopure water explaining the significant 

difference between the percentages of aluminum added for method 1 compared to method 2. 

The removal of iron by this softening method was similar to that of method 1. Also, as in

method 1, selenium ions were not removed by softening.

Methods 3 and 4: hydrochloric acid, sodium hydroxide, and soda ash

These methods showed good removal for most of the ions except for iron and selenium. 

However, it was possible to remove over 44% of selenium ions. Even with 44% removal, 

selenium concentration was still well above the discharge limits.

Method 5: hydrochloric acid and sodium hydroxide

Method 5 was used as a potential pre-treatment for IX and for this reason its results are shown 

in Table 8 in Appendix IV: Ion Exchange. It was successful in precipitating most of the ions from 

the FGD wastewater, but did not remove much selenium. Furthermore, it required a significant 

amount of chemical reagents compared to the other methods. The results of combining this 

method with IX can be seen in Table 7 and Table 8 of Appendix IV: Ion Exchange.

Summary of Softening Results

In conclusion, water softening with chemical reagents removes most of the ions from the FGD 

purge stream water. This treatment alone cannot remove all of the contaminants present in the 

FGD purge stream water, especially selenium.

Solid waste produced and Cost of Chemical Reagents (pre-treatment)

Table 5 shows the different methods that were considered for water softening. This data was 

obtained assuming a FGD purge stream water flow rate of 300 gallons per minute. Specifically, 

the reagents needed (millions of pounds per year), the cost of the reagents (in millions of 

dollars per year), and the amount of solid waste produced (in millions of pounds per year) were 

examined. After analyzing the data, it is recommended to use method 1 since it will cost the 

least amount of money for the reagents and it produces the least amount of solid waste. All 

costs data was collected using commercially available bulk vendors.
Flue Gas Desulfurization Wastewater Mitigation 28 of 43 Crystal Clear, University of Florida IPPD

Table 5: Cost of reagent need for each method and solid waste produced by each method

Method

Reagents needed

(million lbs/year)

Reagents cost

$ Million/year for each 

method Solid Waste 

Produced 

NaOH HCl (million lbs/year)

Soda 

Ash Lime max price min price

1 2.7 --- 9.9 --- 1.85 1.27 13.58

2 --- --- 27.4 11.8 2.43 2.35 33.10

3 21.0 13.4 10.7 --- 10.03 5.43 26.53

4 21.0 13.4 5.6 --- 9.65 5.05 14.44

5 60.3 28.3 --- --- 26.01 12.86 ---

Water softening after electrocoagulation (post-treatment)

Using water softening as a pre-treatment to EC failed to remove selenium ions. EC using FGD 

purge stream water effectively removed selenium ions along with some calcium, magnesium, 

and silver ions. However, aluminum, iron, and manganese ions were added to the water. 

Therefore, water softening was used as a post-treatment method to remove the remaining 

contaminants. A preliminary experiment was conducted with aluminum chloride hexahydrate 

to determine the pH at which aluminum hydroxide precipitate will form in solution. A known 

amount of aluminum chloride hexahydrate was added to de-ionized water and mixed well. 

After this, sodium hydroxide was slowly added until a white precipitate of aluminum hydroxide 

formed. The pH of the solution calculated after precipitation was 7.445. This helped determine 

the pH at which aluminum hydroxide will precipitate. At a pH of 9 or above, the aluminum 

hydroxide precipitate starts to dissolve back into the solution.

Method 6: sodium hydroxide and soda ash (based on method 1)

This post-treatment was conducted as a two step softening process. The pH of the water after 

EC was estimated to be around 5. In the first step, sodium hydroxide was added to the treated 

water until the pH became 7.372. At this point, a white precipitate, which is likely to be 

aluminum hydroxide, was formed. This white precipitate was then removed and a clear solution 

was left. In the second step, more sodium hydroxide was added to bring the pH up to 12.254. 

When the pH was brought up, the solution became slightly hazy. Then, soda ash was added, 

however the pH started going down until it reached 12.065. More soda ash was added to raise 

the pH again to make sure all the calcium would precipitate out of the water. The final pH of 

the solution was 12.24. At this point, a brownish-white precipitate formed. This was removed 

and a clear solution was obtained.
Flue Gas Desulfurization Wastewater Mitigation 29 of 43 Crystal Clear, University of Florida IPPD

APPENDIX IV: ION EXCHANGE

The Principles of Ion Exchange

IX is the process in which wastewater is ran through a packed bed of charged, ion-coated beads. 

The beads, also known as resins or exchangers, are positively or negatively charged particles in 

which the “clean” exchange ions are attached as shown in Figure . These resins are designed to 

trade out highly soluble ions with ones that can easily precipitate out of solution. Anion resins 

and cation resins can only exchange ions of the same negative or positive charge, respectively. 

Typically, cation resins replace positively-charged ions with Na+, while anion resins exchange Clfor negatively charged ions. While most resins collect a wide variety of constituents, some 

target specific elements such as boron and arsenic. Therefore, in theory it is possible that with 

the correct combination and application of cation and anion exchange resins, all of the heavy 

metals could be removed from the FGD wastewater.

Figure 6: Atomic view of IX

Resins become less effective over time due to increased pollutant loading and must 

occasionally be regenerated. In order to regenerate resins, the beads must soak in solution 

containing a high concentration of the original ion from the resin. Most often, cation resins are 

soaked in a sodium solution, while anion resins are regenerated in chloride solution. Some 

resins have color-changing mechanism built-in so that the user knows when it is time for 

replacement. Still, some resins contain a complex mix of ions that cannot be regenerated and 

must be disposed after use.

Resin Selection

Free resin samples were obtained from the Purolite Company, a leading IX vendor. The focus 

was on highly selective resin samples meant to target specific contaminants because it was 

believed that the high Ca, Mg and Cl concentrations in the raw water would decrease the 

efficiency of the resins. Purolite recommended using three different types of IX resins in series
Flue Gas Desulfurization Wastewater Mitigation 30 of 43 Crystal Clear, University of Florida IPPD

to best treat the FGD wastewater. The three resins provided were the S930, Ferrix A33E and 

S920. The S930 and S920 are cation exchangers meant to target Hg and heavy metals in 

solutions with a high ionic background while the Ferrix A33E is an anion exchanger that targets 

As, Se and other anionic species. Purolite suggested treating the water with the S920 first 

followed by the Ferrix A33E and S930 in series.

Design of Experiments

Two types of bench-scale setups were designed to investigate the ability of the IX resins to 

remove the target metals in the wastewater. This was done in order to determine the optimum 

blend or combination of resins that would remove the metals from the water. The first method 

involved using the IX resins sequentially. This was accomplished by allowing each type of resin 

to react individually with the wastewater in a sequential manner. For the second method, the 

resins were combined in a container and allowed to react with the wastewater at the same 

time. The idea behind the sequential setup was to mimic the effect of having a plug flow 

reactor with the three resins occupying distinct segments. The mixed setup was to simulate the 

actual reaction of a continuously stirred tank reactor or a rapid mix process. The effects of high 

calcium and magnesium content in the FGD wastewater on the performance of the resins were 

also of concern. To investigate this it was also decided that the resins would be tested with raw 

(not pre-softened wastewater) and pre-softened wastewater. Resin concentrations and contact 

times were also varied to determine the optimum conditions for use.

Experimental Procedure

Sequential

One trial for the sequential method was done in triplicate, where the resins were allowed to 

contact the wastewater individually. Contact was made in the following order: S930, Ferrix, and 

S920 as shown in Figure . Each resin type was reacted with the solution for a period of 20 

minutes. A resin concentration of 1 g/L was used for each resin. Prior to contacting the water, 

resins were weighed carefully on an analytical micro-balance and then transferred into labeled 

weigh boats. Samples of non-softened and softened wastewater were transferred to 100 mL

beakers with clean magnetic stirring beads. Beakers were placed on a magnetic stir plate and 

then agitated to ensure good contact between the resins and the wastewater. This procedure 

was performed for both the non-softened and softened wastewater samples. At the end of 

each 20 minute period the resins were separated from the solution by vacuum filtering the 

wastewater with Whatman filter paper (5- 10 μm pore size). The final supernatants were 

transferred into clean, labeled glass vials then sealed and stored at room temperature until 

analysis.
Flue Gas Desulfurization Wastewater Mitigation 31 of 43 Crystal Clear, University of Florida IPPD

Mixed

A few experimental trials at different resin concentrations (1, 5 and 10 g/L) were performed in 

triplicate and the resins (S930, Ferrix and S920) were completely mixed and allowed to contact 

the water at the same time as show in Figure . The first trial involved using 1 g/L resin 

concentration. The respective volumes of non-softened and softened wastewater were 

measured in beakers followed by the addition of the resins. Resins were weighed using a 

analytical micro balance, placed in clean weigh boats and then placed in the beakers. The 

solutions were then agitated on a magnetic stirrer for 20 minutes. At the end of this period, 

resins were separated from the solution using the same filtration procedure outlined in the 

Sequential section above. This same procedure was used for resin concentrations of 5 and 10 

g/L, except with stirring times of 30 minutes instead of 20 minutes. The final supernatant

solutions were transferred into clean, labeled glass vials, which were sealed and stored at room 

temperature until analysis using the ICP-OES.

Ion Exchange Experimentation and Results

After receiving the three IX resins from Purolite, the first goal was to determine if the selected 

resins performed better mixed together or sequentially one after the other. The results of these 

tests can be seen in Table 6. The results in red are above the discharge limits for the Crystal 

River plant. The results in green are below the discharge limits. Calcium and magnesium 

S-930

Filtration Filtration

Ferrix S-920

Figure 7: Schematic of sequential IX process

Figure 8: Schematic of mixed IX process
Flue Gas Desulfurization Wastewater Mitigation 32 of 43 Crystal Clear, University of Florida IPPD

concentrations are not color coded as they do not have direct discharge limits in terms of parts 

per million, however they are important in the general water analysis.

Table 6: ICP-OES analysis of sequential versus mixed IX

Analyte

ICP-OES 

Detection 

Limit (ppm)

Discharge 

Limits 

(ppm)

Raw 

Wastewater

(ppm)

Sequential IX 

(ppm)

Mixed IX 

(ppm)

Ag 0.0009 0.1 0.012 0.013 0.009

Al 0.003 1.5 0.049 0.041 0.035

Ca 0.00002 -- 1739.000 2552.000 1769.000

Fe 0.002 0.3 0.025 0.027 0.029

Mg 0.00007 -- 419.000 578.000 409.000

Mn 0.0004 0.1 1.375 1.145 1.081

Se 0.05 0.071 1.312 1.263 1.289

The results proved that mixed IX performed slightly better than the sequential setup. As a 

result, all further experiments were run using the mixed resin setup. Still, the wastewater 

contained several contaminants over the discharge limits. Since removal was so poor, it was 

hypothesized that the IX resins were being “blinded” by the high concentrations of calcium and 

magnesium. To test this hypothesis, efforts were made to first remove calcium and magnesium 

via chemical softening before testing the effectiveness of the resins to remove the remaining 

contaminants. The results of these tests can be seen in Table 7. As before, those results in red 

are above the discharge limits, while those in green are below the limits.

Table 7: ICP-OES analysis of the effect of water softening on IX

Run 1

(ppm)

Run 2

(ppm)

Run 3

(ppm)

Run 1

(ppm)

Run 2

(ppm)

Run 3

(ppm)

Ag 0.0009 0.1 0.032 0.018 0.004 0.021 0.005 0.004

Al 0.003 1.5 0.050 0.042 0.014 0.022 BDL (0.000) BDL (0.000)

Ca 0.00002 -- 1273.000 1044.500 1048.500 81.550 47.550 44.550

Fe 0.002 0.3 0.154 0.150 0.118 0.137 0.090 0.115

Mg 0.00007 -- 329.500 283.500 273.500 10.450 BDL (0.000) BDL (0.000)

Mn 0.0004 0.1 0.335 0.364 0.199 0.024 0.020 0.015

Se 0.05 0.071 1.295 1.309 0.730 1.644 0.882 BDL (0.017)

Analyte

ICP-OES 

Detection 

Limit (ppm)

Discharge 

Limits 

(ppm)

Without Softening With Softening

The results show that more contaminants were removed through the combined softening and 

IX than through IX alone. It should also be noted that the results shown above without 

softening are better than the initial testing results from sequential versus mixed IX shown in 

Table 6. This is not an anomaly in the resins, but most likely due to general improvement in the 

experimental procedure. However, the one analysis that shows complete removal of selenium 

is attributed to experimental error.

Following the positive results of combining chemical softening with mixed IX, the next step was 

to see if the results could be further improved by increasing the resin concentration. It is 

possible that the removal capability above is limited by the amount of ions available from the 
Flue Gas Desulfurization Wastewater Mitigation 33 of 43 Crystal Clear, University of Florida IPPD

resins for exchange with the contaminants. If this is the case, increasing the concentration of 

resins, and thus the amount of ions available for exchange, may overcome this limitation. 

Consequently, pre-softened wastewater was then used with the Ferrix resin at 5 g/L and 10 g/L 

concentrations. Also a sample of the softening method was taken to determine whether the IX 

resins were responsible for the removal, or if the contaminant removal above was due to the 

softening. The results from these tests can be seen in Table 8. As before, those results in red are 

above the discharge limits, while those in green are below the limits.

Table 8: ICP-OES analysis of of IX with softened water at 5 g/L and 10 g/L versus just softened water

Analyte

ICP-OES 

Detection 

Limit (ppm)

Discharge 

Limits 

(ppm)

Raw

Wastewater

(ppm)

Softened 

Water 

(ppm)

IX 5 g/L

(ppm)

IX 10 g/L

(ppm)

Ag 0.0009 0.1 0.011 0.001 BDL (0.000) BDL (0.000)

Al 0.003 1.5 0.036 0.053 0.251 0.284

Ca 0.00002 -- 2180.333 0.759 6.454 9.219

Fe 0.002 0.3 0.013 0.012 1.097 0.309

Mg 0.00007 -- 533.500 0.025 0.439 0.761

Mn 0.0004 0.1 1.499 0.023 0.153 0.143

Se 0.05 0.071 1.580 1.284 1.032 0.943

The IX resins actually proved to be less effective in this group of experiments. Overall the 

removal was poor compared to other tested methods, and actually increased the 

concentrations of all ions with the exception of selenium. This disproves the above hypothesis, 

but without a deeper understanding of the proprietary composition and reaction(s) of the 

resins, this cannot be explained.

Resin Cost Analysis

Given the above unpromising IX results, it was decided to perform an initial cost estimate of 

using IX resins for the Crystal River plant before any further testing was performed. This 

analysis is performed based on the above described Ferrix A33E resin (current price of $165/ft3) 

which has a density of 47 lb/ft3. The flow rate of the wastewater is 300 gallons per minute with 

a resin concentration of 10 g/L. Based on these specifications, the estimated yearly cost for the 

resins alone is $46.2 million per year. This does not include additional costs for waste removal, 

maintenance, operation, and equipment. The IX resins cannot be regenerated, and thus 

becomes waste. Using the above parameters, the minimum solid waste would be 6580 tons per 

year. Neither the cost nor waste analysis includes the softening step with its own chemical cost 

and waste stream. Based on this preliminary cost analysis, PE and CC jointly decided to cease 

exploring IX as a plausible wastewater treatment method.
Flue Gas Desulfurization Wastewater Mitigation 34 of 43 Crystal Clear, University of Florida IPPD

APPENDIX V: ELECTROCOAGULATION

Introduction

EC, in terms of wastewater mitigation, is a technique in which water is run between oppositely 

charged plates. An electrical current is applied to the plates to create a voltage drop between 

the plates which produces a pH change in the wastewater between the plates. The electrode 

plates provide a cathode and anode surface for the ions in the wastewater to coagulate and 

precipitate for removal. The exact mechanism of this pH change and ion precipitation has yet to 

be explained by experts in the field but the process has been known to successfully remove 

contaminants from wastewater. No exact, successful design specifications were available, so 

several sources were consulted prior to conducting any testing to form a basis upon which to 

begin research (Yilmaz, Boncukcuoğlu, Kocakerim, & Keskinler, 2005) (Emamjomeh & 

Muttucumaru, 2009) (Powell, Apparatus for Electrocoagulation of Liquids, 2000) (Powell, 

Method for Electrocoagulation of Liquids, 2002).

This research showed that aluminum and iron sacrificial electrodes should provide the best 

removal results for metals in wastewater. An electrical power source is then connected to the 

electrode plates. At the positive terminal (anode), wastewater reacts with the plate and slowly 

corrodes the metal introducing metal ions which interact with the contaminants. At the 

negative terminal (cathode), precipitates deposit and can be scraped for removal. The waste 

stream also contains coagulated, precipitated material.

Electrocoagulation Setups

Aluminum Plates and Plexiglas Spacer

In order to obtain a preliminary idea of the process, the first prototype model was built out of 

scrap aluminum metal plates. The plates were separated with glued Plexiglas spacers (forming a 

“window pane” with strips of Plexiglas on the top, bottom, and sides) and Tygon peristaltic 

tubing was used for the inlet (through the bottom) and outlet (at the top). A simplified batch 

process was used to understand the process better, with future scale-up in mind. The 

windowpane spacer with the tubing running through it was sandwiched by the two electrode 

plates and held together by nylon threaded nuts and bolts. Silicon caulking was used to seal the 

interfaces between Plexiglas and aluminum as well as the inlet and outlet tubing. For operation, 

the metal plates were positioned vertically. 

The design had many flaws as the pressure build-up from gas evolution of the reaction proved 

too large for the caulking. The non-porous surfaces of the Plexiglas and aluminum were not 

suitable for the caulking and were not water tight. A standard power output, Paradyne Pression 

1650 Tri-output Power Supply, was used to supply power to the setup. However, the power 

delivered was not enough given the low resistance of wastewater and the resultant current 

shortages. The voltage of the system could not be raised above 5 V. While pumping raw filtered 

wastewater through the tube and applying current to the plates, solids and pressure quickly 

increased within the cavity and tubing causing leaks in the seals. Once this happened, the plates 
Flue Gas Desulfurization Wastewater Mitigation 35 of 43 Crystal Clear, University of Florida IPPD

were separated and inspected. The applied current indeed caused solid buildup within the 

cavity and corrosion was observed on the anode. Solid build-up resembled white/gray paste 

and was thought to be mostly aluminum hydroxide. However, due to the unknown content of 

the scrap aluminum electrodes and a lack of comprehensive analysis techniques for solid 

products, the actual composition of these plates could not be determined. Liquid from the 

process was collected and filtered for ICP-OES analysis, with results shown in Table 9. Results 

from this experiment were not fully understood. Due to the lack of knowledge about the 

process and the wastewater, the findings could not be fully characterized at the time.

Table 9: ICP-OES analysis of EC water using scrap aluminum plates and Plexiglas spacer

Conc (ppm) % Removal

Ag 0.007 0.016 -128.57

Ag 0.017 0.021 -23.53

Al 0.049 53 -108063.27

Al 0 48 ---

As 0 0 ---

As 0 0 ---

Ca 1739 838.4 51.79

Ca 1738 870.8 49.90

Fe 0.025 0.142 -468.00

Fe 0.024 0.138 -475.00

Mg 413.7 735 -77.66

Mg 424.6 739 -74.05

Se 1.312 0 100.00

Se 0 0 ---

Tl 0 0 ---

Tl 0 0 ---

Mn 1.38 10.9 -689.86

Mn 1.369 10.77 -686.71

Raw Water EC

Conc. (ppm)

Ion

Initial results suggested that EC performed well with selenium removal. There is a level of 

uncertainty in the full removal of selenium due to possible operational error in the ICP-OES. 

Confidence in the removal of selenium needed to be confirmed. However, design changes had 

to be made in order to run a successful experiment for EC.

For other contaminants in the water, EC shows addition of metals into the raw water which was 

to be expected as a byproduct of the process. As previously stated, EC is best used in 

conjunction with other wastewater mitigation techniques.

Graphite Plates and Rubber Spacer

Due to the large amount of metal ions added by the aluminum plates, carbon graphite plates 

were suggested as an alternative. Dr. Mark Orazem of the UF Chemical Engineering 

department, a worldwide electrochemistry expert, suggested using graphite plates as an inert 

electrode which delivers the current and produces the pH change in the wastewater necessary 

for contaminant removal. In order to overcome the leaking problem with the Plexiglas spacers, 

a thick rubber gasket was created with the same windowpane idea to create the cavity 
Flue Gas Desulfurization Wastewater Mitigation 36 of 43 Crystal Clear, University of Florida IPPD

between the electrodes. This removed the need for caulking and also ensured against leakage 

when pressure increased. Inlet and outlet tubing was slightly altered, using one piece of Tygon 

tubing at the inlet and three pieces of Tygon tubing at the outlet. Current shortage and power 

failure with the wastewater was not yet mitigated. The experiment was conducted at the 

highest voltage setting of the original power source, allowing the eventual power loss as part of 

the experiment. As the experiment progressed, significant heat was found to be generated at 

the plates and “sweating” of wastewater through the plates occurred. This was thought to be 

caused by increased porosity of graphite at higher temperatures due to the applied current. 

However, no temperature data was collected to fully investigate this event.

Heavy leakage through the plates ended the experiment early and liquid was again withdrawn 

and collected for analysis with results shown in Table 10. No solid build-up was observed within 

the cavity.

Table 10: ICP-OES analysis of EC water using graphite plates and rubber spacer

Conc (ppm) % removal

Ag 0 0.014 ----

Ag 0.016 0.018 -12.50

Al 0.028 0.091 -225.00

Al 0 0 ----

As 0 0 ----

As 0 0 ----

Ca 2054.75 N/A ----

Ca 2043.75 N/A ----

Fe 0.03 0.134 -346.67

Fe 0.033 0.138 -318.18

Mg 485.75 N/A ----

Mg 490.2 N/A ----

Se 1.532 1.282 16.32

Se 0 0 ----

Tl 0 0 ----

Tl 0 0 ----

Mn 1.425 0.036 97.47

Mn 1.405 0.036 97.44

Raw Water 

Conc. (ppm)

EC

Ion

Graphite plates were clearly not as effective at removing selenium as the previous aluminum 

plates. While there were fewer contaminants added by the inert graphite plates, the low 

selenium removal results discouraged the use of graphite plates for EC. With that in mind, it is 

clear that there are reasons other than merely a pH change responsible for the precipitation 

and coagulation of wastewater contaminants. It is believed that the selenium is removed by coprecipitation with the aluminum hydroxide, which would explain the lack of selenium removal 

by use of graphite plates (Castaldi, Behrens, & Hargrove Jr., 2001).
Flue Gas Desulfurization Wastewater Mitigation 37 of 43 Crystal Clear, University of Florida IPPD

Aluminum Plates and Rubber Spacer

New aluminum plates, with known composition, were purchased in order to gain a better 

understanding of which metal constituent(s) were reacting with the wastewater. An 

experimental setup similar to the previous experiment with graphite plates was utilized. The 

rubber spacer was again used with one inlet Tygon tube and three outlet Tygon tubes. It was 

once again difficult to provide consistent power supply to the plates. This led to the use of two 

6-V batteries in series as a power supply, with the assumption that they would deliver more 

consistent, unregulated power than the original current supplies. The Paradyne power supply 

had an internal safety feature which shuts off the unit when there is a power overload. This was 

caused by the reduced resistance as water filled between the plates. The batteries were 

successful in providing more consistent power, but the experiment failed when the rubber 

gasket blew out from between the plates. Hydrolysis is part of the reaction, and the lack of 

large enough outlet tubing led to a pressure buildup which caused the gasket to blow out. The 

water that could be collected was analyzed and the results are tabulated in Table 11.

Table 11: ICP-OES analysis of EC water using new aluminum plates and rubber spacer

Conc (ppm) % Removal

Ag 0.006 0.002 68.42

Ag 0.015 0.001 ----

Al 0.071 3134 -4413000

Al 0.000 2953 ----

As 0.000 0.042 ----

As 0.000 <0 ----

Ca 2180 1.341 99.94

Ca 2181 1.307 99.94

Fe 0.014 0.023 -68.29

Fe 0.012 0.025 -108.33

Mg 532.7 0.003 ----

Mg 534.3 0.017 ----

Mn 1.508 0.014 99.07

Mn 1.490 0.040 97.31

Se 1.580 1.459 7.66

Se 0.000 0.920 ----

Tl 0.049 0.032 34.69

Tl 0.000 <0 ----

Ion

Raw Water 

Conc. (ppm)

EC

Due to the design flaws of this experiment, a full experimental run could not be completed. 

Gasket failure prematurely ended the experiment and did not generate the desired selenium 

removal results. However, the increased power supply did generate different removal results 

such as increased addition of both aluminum and iron into the electrocoagulated water. Results 

of low concentrations of manganese are contrary to the expected addition from the electrode. 

This may have affected the selenium removal.
Flue Gas Desulfurization Wastewater Mitigation 38 of 43 Crystal Clear, University of Florida IPPD

Aluminum Plates and Rubber Spacer with Welded Tube

In order to mitigate pressure buildup in the cavity, the experimental setup was modified. The 

top portion of the window pane of the rubber gasket was removed, allowing for all excess 

hydrogen gas to be evacuated through the top. To collect the outlet water, a hole was cut at 

the top of the cathode and a one-inch aluminum pipe was welded to the plate. This would allow

water to exit the system by gravity and also eliminate clogging that was occurring in the old 

outlet tubes. Six-volt batteries were again used as a power supply. This time, a total of six 

batteries were used in two parallel series of three batteries each to provide 12 V of power to 

the setup. The testing produced measurable results, seen in Table 12. The voltage drop was also 

recorded during these experiments as seen in Table 13 and Table 14.

Table 9: ICP-OES analysis of EC water using new aluminum plates with welded tube and new rubber spacer

Conc (ppm) % Removal Conc (ppm) % Removal

Ag 0.006 0.003 52.63 0.010 -57.89

Ag 0.015 0.000 ---- 0.015 ----

Al 0.071 531.1 -747900 86.220 -121300

Al 0.000 1073 ---- 128.700 ----

As 0.000 0.000 ---- 0.000 ----

As 0.000 0.000 ---- 0.000 ----

Ca 2180 126.2 94.21 103.900 95.23

Ca 2181 113.6 94.79 83.790 96.16

Fe 0.014 6.691 -48850 1.745 -12670

Fe 0.012 6.584 -54760 1.711 -14160

Mg 532.7 22.26 95.82 30.250 94.32

Mg 534.3 21.50 95.98 27.790 94.80

Mn 1.508 26.20 -1638 16.580 -999.7

Mn 1.490 26.05 -1649 16.770 -1026

Se 1.580 0.047 97.03 0.006 99.62

Se 0.000 0.000 ---- 0.000 ----

Tl 0.049 0.013 74.49 N/A ----

Tl 0.000 0.000 ---- N/A ----

Ion Raw Water 

Conc. (ppm)

EC New Al Plates Best 

Setup

EC New Al Plates Best 

Setup Duplicate
Flue Gas Desulfurization Wastewater Mitigation 39 of 43 Crystal Clear, University of Florida IPPD

Table 10: Voltage drop over the course of the pH 8 raw 

water experiment

Time (min) Voltage (V)

0 12.00

10 9.00

28 7.38

35 7.20

39 6.29

42 6.07

45 6.20

60 7.30

65 7.47

68 7.60

Table 11: Voltage drop over the course of the pH 8 raw 

water duplicate experiment

Time (min) Voltage (V)

0 10.65

3 8.48

8.5 7.08

14.5 6.80

19.5 6.60

25.5 6.58

32 5.75

39.5 6.05

49 5.17

Results from this experiment confirm the initial selenium removal results from the first 

aluminum plate setup. Most notably, the concentration of selenium was reduced to at most 

0.047 ppm, below the discharge limit of 0.071 ppm. Further analysis showed that this method 

also removed some calcium and magnesium from the raw wastewater, but also added 

significant amounts of aluminum, manganese, and iron from the sacrificial plates. The amount 

of oven-dried solid waste formed during the first experiment was 6.001 grams on the anode 

and 6.054 grams on the cathode.

A duplicated test was performed to confirm the results of this experiment. Results for the 

addition of silver are probably due to operational error of the ICP-OES as the electrodes do not 

have a high composition of silver. Thallium was not included as an analyte of interest in the 

duplicated test. Significantly lower addition of aluminum, iron, and manganese was due to the 

differences in power supplied during this experiment. The primitive, but necessary, battery 

supply does not allow for a precise control of the current, which limits exact control over all 

testing parameters.

Aluminum Plates and Rubber Spacer with Welded Tube with Pre-Softened Wastewater

As EC by nature produces large amounts of solid waste from the reaction, significant 

maintenance must be performed on the plates to ensure consistent results. In an attempt to 

lower solid waste and reduce the need for sacrificial electrode replacement, the use presoftened wastewater was expected to mitigate this problem. Softening removes high levels of 

contaminants other than selenium from the initial raw wastewater. Lower levels of 

contaminants were expected to produce less solid waste.

These experiments were run using the same aluminum plate with welded exit tube and Ushaped rubber spacer. However, instead of using filtered wastewater, pre-softened water at pH 

8 and pH 12.32 were run through the EC setup. The power source for the experiment using the 

water at pH 8 was six 6 volt batteries; two parallel series of three batteries each. The power 

source for the experiment using the water at pH 12.32 was ten 6 volt batteries; two parallel 

series of five batteries each. Results from previous research found that water at pH 8 had least 
Flue Gas Desulfurization Wastewater Mitigation 40 of 43 Crystal Clear, University of Florida IPPD

contribution of solids from the electrode (Yilmaz, Boncukcuoğlu, Kocakerim, & Keskinler, 2005). 

Consequently, the pre-softened water pH was adjusted using both hydrochloric and nitric acids 

for two different experiments. The addition of more ions into the water most likely contributed 

to the observed power loss. The results of these experiments can be seen in Table 15, and the 

voltage changes can be seen in Table 16 and Table 17. Table 12: ICP-OES analysis of EC water using new aluminum plates with welded tube and new rubber spacer with presoftened water at pH 8 and pH 12

Conc (ppm) % Removal Conc (ppm) % Removal

Ag 0.006 0.008 -26.32 0.011 -73.68

Ag 0.015 0.010 34.78 0.013 15.22

Al 0.071 86.22 -121300 86.22 -121300

Al 0.000 128.7 ---- 128.7 ----

As 0.000 0.000 ---- 0.000 ----

As 0.000 0.000 ---- 0.000 ----

Ca 2180 0.530 99.98 0.115 99.99

Ca 2181 0.531 99.98 0.131 99.99

Fe 0.014 0.015 -9.76 0.022 -60.98

Fe 0.012 0.013 -8.33 0.021 -75.00

Mg 532.7 0.056 99.99 0.000 100.0

Mg 534.3 0.059 99.99 0.006 100.0

Se 1.580 1.149 27.28 0.679 57.03

Se 0.000 0.871 ---- 0.582 ----

Tl 0.049 N/A ---- N/A ----

Tl 0.000 N/A ---- N/A ----

Mn 1.508 0.002 99.87 0.007 99.54

Mn 1.490 0.016 98.93 0.028 98.12

Ion

Raw Water 

Conc. (ppm)

EC New Al Plates pH 8 

Softened Water

EC New Al Plates pH 12 

Softened Water

Table 13: Voltage drop over the course of the pH 8 presoftened water experiment

Time (min) Voltage (V)

0 10.3

6 5.2

11 1.053

15 1.028

20 1.065

25 1.015

29 1.005

Table 14: Voltage drop over the course of the pH 12.32 

pre-softened water experiment

Time (min) Voltage (V)

0 11.56

3 5.65

6 4.53

9 3.15

12 2.84

15 2.67

It is clear from these results that pre-softening the wastewater considerably decreased 

selenium removal. Aluminum and iron were added to the water again, however manganese 

was not added and calcium and magnesium were nearly completely removed. It is 

hypothesized that the previously observed almost complete removal of selenium from raw 
Flue Gas Desulfurization Wastewater Mitigation 41 of 43 Crystal Clear, University of Florida IPPD

wastewater is partially due to co-precipitation with calcium and/or magnesium. A further test 

with raw FGD wastewater (results shown in Table 1) confirmed that without pre-softening EC 

does indeed remove selenium to below discharge standards. In total, four different tests have 

yielded almost complete removal of selenium if the water is not pre-softened.

Additional Power Source Testing

Due to the lack of consistent voltage during the course of the experiments and the lack of 

current information, additional testing to determine the effects of different types of water on 

the voltage and current was conducted. Using tap, raw and two samples of raw filtered water, 

four experiments were performed with the entire cavity of the aluminum plates and rubber 

spacer with welded tube setup completely filled, approximately 140 mL. Six 6 volt batteries, in 

the same two parallel series of three batteries each, were connected to the plates and run for 

15 minutes, noting the voltage and current every minute during each experiment, as seen in 

Table 18.
Flue Gas Desulfurization Wastewater Mitigation 42 of 43 Crystal Clear, University of Florida IPPD

Table 15: Voltage and current fluctuations during the four trials

Time (min) Voltage (V) Current (A) Voltage (V) Current (A) Voltage (V) Current (A) Voltage (V) Current (A)

0 12.91 2.13 4.25 7.22 4.50 7.36 4.01 7.76

1 13.54 1.63 3.96 7.07 4.12 7.40 4.00 7.56

2 13.74 1.48 3.26 5.45 3.97 7.37 4.00 7.48

3 13.81 1.41 3.31 5.50 3.92 7.38 4.02 7.45

4 13.82 1.38 3.39 5.55 3.92 7.42 4.11 7.39

5 13.84 1.35 3.50 5.59 4.00 7.40 4.22 7.29

6 13.81 1.35 3.61 5.62 4.11 7.34 4.42 7.16

7 13.81 1.34 0.85 0.24 4.33 7.24 4.71 6.94

8 13.83 1.32 0.922 0.30 4.60 7.08 4.82 6.88

9 13.81 1.31 0.933 0.30 4.74 7.01 4.91 6.79

10 13.75 1.34 0.947 0.30 4.92 6.91 5.10 6.66

11 13.72 1.35 0.960 0.31 5.18 6.75 5.38 6.44

12 13.70 1.34 0.982 0.33 5.54 6.50 5.66 6.23

13 13.71 1.33 1.002 0.34 6.01 6.20 5.84 6.11

14 13.72 1.31 1.023 0.36 6.37 5.90 6.09 5.89

15 13.74 1.28 1.044 0.38 6.74 5.68 6.29 5.74

Tap Water

Raw FGD 

Wastewater

Filtered FGD 

Wastewater Trial 1

Filtered FGD 

Wastewater Trial 2

Table 16: Average resistances and power calculated based on the voltage and current readings

Tap 

Water

Raw FGD 

Wastewater

Filtered FGD 

Wastewater Trial 1

Filtered FGD 

Wastewater Trial 2

Resistance (Ω) 9.839 1.982 0.710 0.723

Power (W) 27.4983 30.685 32.49 33.12

It is clear that the voltage and current decreases are due to the high contaminant concentration 

of the FGD wastewater, as the tap water voltage and current readings were fairly consistent. In 

addition, the FGD wastewater required a higher power supply than the cleaner tap water.
Flue Gas Desulfurization Wastewater Mitigation 43 of 43 Crystal Clear, University of Florida IPPD

REFERENCES

Castaldi, F. J., Behrens, G. P., & Hargrove Jr., O. W. (2001). Patent No. 6,235,204. United States 

of America.

Emamjomeh, M. M., & Muttucumaru, S. (2009). Review of pollutants removed by 

electrocoagulation and electrocoagulation/flotation processes. Journal of Environmental 

Management , 1663-1679.

Emilia Andersson, H. H. (2001). Precipitation of reactive aluminium hydroxide from an acidic 

aluminium sulphate solution by addition of sodium hydroxide. Department of Chemical 

Engineering II, University of Lund, P.O. Box 124, S-22100 Lund, Sweden .

Powell, S. W. (2000). Patent No. 6,139,710. United States of America.

Powell, S. W. (2002). Patent No. 6,488,835. United States of America.

Shaw, W. A. (2009). New Low-Temperature ZLD Process. International Water Conference (pp. 

IWC-09-52). Orlando, FL: Engineer's Society of Western Pennsylvania.

Yilmaz, A. E., Boncukcuoğlu, R., Kocakerim, M. M., & Keskinler, B. (2005). The investigation of 

parameters affecting boron removal by electrocoagulation method. Journal of Hazardous 

Materials , 160-165.