# 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 SvoronosFlue Gas De sulfur ization 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


## Conclusion s
................................ ................................ ...................... 14

Recommendations

................................ ................................ ........... 15
Appendix I: Water Analysis

................................ .............................. 17

Introd uction 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
Attemp ted Continuation of Zero Liquid Discharge

................................ ................................ ................. 22 

## Appendix III: Water Softening

................................ .......................... 24
Background on Water Softening

................................ ................................ ................................ ............. 24Flue Gas De sulfur ization 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

Meth ods 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

Re sin 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

In troduction

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

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

................................ ................................ ............................... 34 Graphite Plates and Rubber Spacer

................................ ................................ ................................ .... 35Flue Gas De sulfur ization 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 Sou rce Testing

................................ ................................ ................................ ............ 41


## References

................................ ................................ ....................... 43Flue Gas Desu lf urization 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 conta minants 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 D esign (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 duri ng 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 Spectro scopy (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 jo intly 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 pertinen t 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 invol ves 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 proce ss 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 require ments.
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 wast ewater from the Crystal River site, though the results are expected to be similar.Flue Gas Desu lf urization 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 m ethods. 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 m ethod 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 red uce 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 (SO 2 ) is removed from the air through water absorption. Sulfur dioxide dissolves into water as sulfurous acid (H 2 SO 3 ). As acid concentrations increas e sulfur dioxide removal decreases. To reduce the acidity limestone is dissolved in the FGD water. The calcium carbonate (CaCO 3 ) and magnesium carbonate (MgCO 3 ) found in limestone reacts with the sulfurous acid creating calcium sulfite (CaSO 3 ), magnesium s ulfite (MgSO 3 ), water, and carbon dioxide. Forced oxidation of the calcium sulfite produces calcium sulfate (CaSO 4 ), which is later processed to make calcium sulfate dihydrate (CaSO 4 • 2H 2 0), or gypsum. After the calcium sulfate is extracted for gypsum produ ction, the remaining solution is recycled back to the absorber to collect more sulfur dioxide.
Sulfur dioxide absorption SO 2(g) + H 2 0 (l) → 2H + (aq) + SO 3 - 2 (aq)

Limestone dissolution CaCO 3(s) + H 2 O (l) → Ca +2 (aq) + CO 3 - 2 (aq) + H 2 O

Limestone neutralization CaCO 3(s) + 2H + (aq) + SO 3 - 2 (aq) → CaSO 3(s) + H 2 O (l) + CO 2(g)

Forced Oxidation CaSO 3(s) + H 2 O (l) → Ca +2 (aq) + SO 3 - 2 (aq) + 1⁄2O 2 → CaSO 4(s)

Overall reaction CaCO 3(s) + SO 2(g) + 1⁄2O 2 → CaSO 4(s) + CO 2(g)Flue Gas Desu lf urization 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 vari ous 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.Flue Gas Desu lf urization Wastewater Mitigation 8 of 43 Crystal Clear, University of Florida IPPD 

## ELECTROC OAGULATION
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 th e 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 expert s 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 begi n 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, a n electrical power source is connected to the electrode plates. At the positive terminal (anode) , wastewater reacts with the plate and slowl y 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, precipi tated 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 pr oduced 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 alumi num 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 Desu lf urization Wastewater Mitigation 9 of 43 Crystal Clear, University of Florida IPPD Figure 1: The final electrocoagulation experimental setup.Flue Gas Desu lf urization Wastewater Mitigation 10 of 43 Crystal Clear, University of Florida IPPD 

### Results

Table 1 below shows the results of the EC tests. For every analyte t wo 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 p arenthesis. 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 a nalysis of EC treate d 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 Desu lf urization 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 F GD wastewater (see Appendix III: Water Softening ). Therefore, water softening

was considered a plausible post EC treatment method to remove both the remaining contami nants 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 solut ion 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 mo lecule 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 furthe r 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 th e 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 s oda 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 precip itate 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, butFlue Gas Desu lf urization 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 cont aminants 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 se en 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 disc harge 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 Desu lf urization Wastewater Mitigation 13 of 43 Crystal Clear, University of Florida IPPD Table 3 : Detection limits, d ischarge Limits, raw wastewater con centrations, 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 Desu lf urization 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 sele nium 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 us e of water softening as a post

- EC treatment process was explored and found successful.Flue Gas Desu lf urization 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 contamin ants 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 t he 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 sho uld 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 gall ons 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 r ates, 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

remova l. 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 powe r supply. As discussed in Appendix V: Electrocoagulation , a major issue encountered was sufficient, constant power given the low resistance of FGD wastewater. Batteri es 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 Desu lf urization 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 a nd 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 re move 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 a nd 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 Desu lf urization 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 st ate. 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 inten sity 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 ful l 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 viewingFlue Gas Desu lf urization 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 cali brated 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 inter est 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 b e 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 attem pts 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.Flue Gas Desu lf urization Wastewater Mitigation 19 of 43 Crystal Clear, University of Florida IPPD S till deviations may occur from contaminants of a previous sample “lingering” in the ICP

- OES. Flushing the system with N anopure water between samples improve d the accuracy of the results , although one flush proved to not always be sufficient. The accuracy and precision of the ICP

- OES w as regularly tested with Nanopure water and calibration standards. Figure 4: I CP

- OES variation a cross raw w ater s amplesFlue Gas Desu lf urization Wastewater Mitigation 20 of 43 Crystal Clear, University of Florida IPPD 

## APPENDIX II : ZERO LIQUID DISCHA RGE
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 exi sts 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 var iations 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 fo r 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 contamin ants 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 wate r 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 processFlue Gas Desu lf urization Wastewater Mitigation 21 of 43 Crystal Clear, University of Florida IPPD 

### Benefits of Zero Liquid Discharge

ZLD offers many benefits over other wastewater process ing 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
st ream. 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 n ot 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 contaminant s 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 part ial 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 o f 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 Tempera ture 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 oper ational 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 t he BPR to continue to evaporate water, correspondingly requiring more power and thus increasing the operating cost.Flue Gas Desu lf urization 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 po ssible 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 ver y 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, fo r 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 a re 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 a lso 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 s o 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 e vaporator 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 theFlue Gas Desu lf urization 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 Desu lf urization 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 protec t the system.



### Water S oftening by C hemical R eagents

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 ma gnesium 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 contami nants. 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 U sed for W ater S oftening

From all of the softening experime nts 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 tre atment process

.Flue Gas Desu lf urization Wastewater Mitigation 25 of 43 Crystal Clear, University of Florida IPPD Method 1: sodium hydroxide and soda ash
Sodium hydroxide wa s added first to the FGD purge stream water until the pH reached 12.22. The addition of the sodium hydroxide formed a white precipitat e solution. After the solution was well mixed, soda ash wa s added to the solution until it reached pH of 12.32. T he addition of the soda ash made the solution very milky an d more white precipitate wa s formed.

Method 2: lime and soda ash

Lime wa s added first to the FGD purge stream water until the pH r eached 12.21. The addition of the lime formed a white precipitat e solution. After the solution wa s well mixed, soda a sh wa s added to the solution until it reached pH of 12.70. The addition of the soda ash mad e the solution very mi lky and more white precipitate wa s formed.
Method 3: hydrochloric acid, sodium hydroxide, and soda ash
Hydrochloric acid wa s added first to the FGD purge stream water until the pH reached 1.11. Secondly, sodium hydroxide wa s added to the FGD purge stream water until the pH r eached 12.21. The addition of the sodium hydroxide formed a white precipitat e solution. After the solution was well mixed, soda ash wa s added to the solution until it reached pH of 12.58. The addition of the soda ash ma d e the solution very mi lky and more w hite precipitate wa s 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: h ydrochloric acid and sodium hydroxide
Hydrochloric acid wa s added first to the FGD purge stream water until the pH reached 1.11. Then, sodium hydroxide wa s 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 we re 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 method s , except for softening method 5. The numbers in Table 4 refer to concentrations of each ion in ppm.Flue Gas Desu lf urization 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 m achine 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 lo w. 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 I CP

- 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 afterFlue Gas Desu lf urization Wastewater Mitigation 27 of 43 Crystal Clear, University of Florida IPPD analyzing the EC sample. Howeve r, this sample was analyzed after the method 1 sample and in between these samples the ICP

- OES was flushed with Nano pure 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 th at of method 1

. Also, as in method 1, selenium ion s were not removed by softening.
Methods 3 and 4: hydrochloric acid, sodium hydroxide, and soda ash

Th ese method s showed good removal for most of the ions exc ept for iron and selenium. However, it was possible to remove over 4 4 % of selenium ions. Even with 4 4 % removal, selenium concentration w as still well above the discharge limits.
Method 5: hydrochloric acid and sodium hydroxide

M ethod 5 was used as a potent ial 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 waste water , but did not remove much selenium. Furthermore, it required a significant amount of chemical reagents compared to the other methods. The result s 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 con taminants 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 dolla rs 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 Desu lf urization Wastewater Mitigation 28 of 43 Crystal Clear, University of Florida IPPD Table 5 : Cost of r eagent n eed for e ach m ethod an d solid waste produced by each m ethod

Method Reagents needed (million lbs/year) Reagents cost $ Million/year for each method Solid Waste Produced (million lbs/year) NaOH HCl 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 precipi tation 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)

Th is 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, wh ich 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 sli ghtly 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 Desu lf urization 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 throu gh 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 Cl for negatively charged ions. While most resins collect a wide variety of constituents, some target specific elements such as boron and arsenic. Therefore, in theory i t 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 pol lutant 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 r esins are regenerated in chloride solution. Some resins have color

- changing mechanism built

- in so that the user knows when it i s time for replacement. Still, some resins contain a complex mix of ions that cannot be regenerated and must be disposed after us e.


### Resin Selection

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

. The focus was on h ighly 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 seriesFlue Gas Desu lf urization 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 F errix 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 combinati on 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 meth od
, 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 s etup 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 wa s also decided that the resins woul d 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 tr ial for the sequential method was done in triplicate , where the resins were allowed to contact the waste water individually. Contact was made in the following order: S 930, Ferrix , and S 920 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 agit ated 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 t he wastewater with W h atman 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 Desu lf urization 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 (S 930, Ferrix and S920) were completely mixed and allowed to contact the water at the same time as show in Figur e . 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 us ing 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 P urolite, the first goal was to determine if the selected resins performed better mi xed together or seq uentially 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

- 9 2 0

Figure 7 : Schematic of s equential I X p rocess

Figure 8 : Schematic of mixed IX p rocessFlue Gas Desu lf urization 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 bett er than the sequential setup. As a result
, all further experiments were run using the mixed resin setup

. Still
, the w astewater 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 mag nesium 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 res ults 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 sh own 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
p ossible that the removal capability above is limited by the amount of ions available from theFlue Gas Desu lf urization 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 ov ercome this limitation. Consequently, p re

- softened wastewater was then use d with the F errix resin at 5 g/L and 10 g/L concentrations

. Also a sample of the softening meth od 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 resin s actually proved to be less effective in this group of experime nt s. 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/ft 3 ) which has a density of 47 lb/ft 3 . The flow rate of the wastewater is 300 gallons per minute with a resin concentration of 10 g/L. Based on these specifi cations, 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 explo ring IX as a plausible wastewater treatment method.Flue Gas Desu lf urization 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 t he 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 electr odes 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 Sp acer
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 t hrough 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 wat er 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 leak s in the seals . Once th is happened , the pla tesFlue Gas Desu lf urization 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 unkn own content of the scrap aluminum electrodes and a lack of comprehensive analysis technique s 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 r esults 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 w ater u sing scrap aluminum plates and Plexiglas s pacer

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 EC Raw Water 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 a ddition 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 meta l 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 delive rs 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 cavityFlue Gas Desu lf urization 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, signi ficant 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 wa s 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 a nalysis of EC w ater u sing g raphite plates and rubber s pacer

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 t he previous aluminum plat es . While there were fewer contaminants added by the inert graphite plates, the low selenium removal results discourage d 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 co

precipitation with the aluminum hydroxide, which would explain the lack of selenium removal by use of graphite plates (Castaldi, Behrens, & Harg rove Jr., 2001)

.Flue Gas Desu lf urization 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 pre vious 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 batter ies 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 ove r load. 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 t he 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 u sing n ew aluminum p lates and r ubber s pacer

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 failu re 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 Desu lf urization 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 test ing 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 DuplicateFlue Gas Desu lf urization Wastewater Mitigation 39 of 43 Crystal Clear, University of Florida IPPD Table 10 : Voltage drop over the course of the p H 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 r educed 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 sacr ificial 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 silv er 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 wa s 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 w ith 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 ne ed for sacrificial electrode replacement, the use pre

softened 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 t o produce less solid waste.
These experiments were run using the same aluminum plate with welded exit tube and U

shaped 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 leastFlue Gas Desu lf urization 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 pre

softened water at p H 8 and p H 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 p H 8 pre

softened 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 th e 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 the se results that pre

- softening the wastewater considerably decreased selenium removal

. A luminum 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 rawFlue Gas Desu lf urization 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 conduct ed . 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 pa rallel 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 Desu lf urization Wastewater Mitigation 42 of 43 Crystal Clear, University of Florida IPPD Table 15 : Voltage and current f luctuations during the f our t rials

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 r esistances and p ower c alculated b ased on the v oltage and current r eadings
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 Desu lf urization Wastewater Mitigation 43 of 43 Crystal Clear, University of Florida IPPD 

## R EFERENCES

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 process es. 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. Jour nal of Hazardous Materials , 160

- 165.