Site Visit Notes: Progress Energy Carolinas’ 

Roxboro Steam Electric Plant (March 11, 2008) 

EPA conducted a site visit at Progress Energy Carolinas’ Roxboro Steam Electric Plant located 

in Semora, NC on Tuesday, March 11, 2008 to learn about the operations at the plant, 

specifically the FGD wastewater treatment system. Table 1, located at the end of this summary, 

identifies the site visit participants. 

This summary describes the information collected during the site visit and the pre-site visit 

phone call, which was held on February 5, 2008. 

Plant Overview 

• Roxboro operates four generating units at the power plant. It is a baseload plant, 

generating a total of 2,557 MW. The table below contains some general 

information about the units. 

Unit 

Installation 

Date 

Capacity 

(MW) 

Particulate 

Control NOx Control SO2 Control 

1 1966 410 Cold-side 

ESP 

SCR; lowNOx burner Wet FGD planned 

for 12/2008 

2 1968 657 Cold-side 

ESP 

SCR; lowNOx burner Wet FGD – 4/2007 

3 1973 745 Cold-side 

ESP 

SCR; lowNOx burner Wet FGD planned 

for 5/2008 

4 1980 745 Hot-side 

ESP 

SCR; lowNOx burner Wet FGD – 12/2007 

• The North Carolina Power Agency owns 16.7% of Unit 4. 

• In 1995, Roxboro began working on an upgrade to the boilers to install low-NOx 

burners to reduce the amount of NOx generated in the boilers. According to 

Roxboro personnel, this installation resulted in a 50 – 65% reduction in NOx. 

• In 2001, Roxboro began installing SCRs to all four units. The final SCR began 

operating in 2005. According to Roxboro personnel, the SCR installation 

achieves an additional 80 – 90% reduction in NOx. The SCRs are scheduled to 

operate year-round. 

• Roxboro burns eastern bituminous coal in all four units. Roxboro stated that they 

are currently burning coal with a sulfur content of 1.6 to 2.0 lbs sulfur/MBTU 

(0.69-1.11 percent sulfur). Roxboro stated that they plan to increase the sulfur 

content of the coal as the scrubbers continue to operate and as they bring 

additional scrubbers on line. Roxboro stated they are evaluating the optimum 

sulfur content that can be used in the boilers. Roxboro noted that there can be 
slag issues in the boiler when burning higher sulfur coal. Roxboro is currently 

only increasing the sulfur content of the coal for Unit 4. 

• Roxboro stated that they burn approximately 6 to 7 million tons of coal per year. 

Roxboro stores a 35-day supply of coal on site for units 1, 2, and 3, and a 28-day 

supply of coal for Unit 4. 

• Coal pile runoff is collected in a settling pond and the overflow from the pond is 

discharged directly to Hyco Lake. 

• Units 1 and 2 have once-through cooling systems that withdraw and discharge to 

Hyco Lake. Unit 3 has a once-through and a cooling tower system. However, the 

Unit 3 cooling tower is a once-through cooling tower (helper tower) that is 

operated seasonally (May 1 – October 15). The plant operates the Unit 3 oncethrough cooling system for the rest of the year. Unit 4 has a recirculated cooling 

tower system that is operated year round. 

• Roxboro has 255 employees. 

Ash Handling

• Roxboro stated that they have the capability to handle fly ash with a wet system, 

but they predominantly operate a dry fly ash handling system (about 95% of the 

time). When the plant uses the wet sluice system, they typically operate it for less 

than a day; however, if there is an extended maintenance outage, they could 

operate it for a week. When the wet fly ash handling system is used, the sluice 

water is transferred to the ash pond. 

• Roxboro stated that they converted to a dry fly ash handling system in the 1980s 

because the fly ash sluice was causing selenium toxicity issues in Hyco Lake. 

Roxboro stated that they are still monitoring the selenium levels in the lake. 

Roxboro stated that the plant spent approximately $20 million to convert all four 

units to a dry fly ash system. 

• The plant stores the fly ash in silos and sells approximately one-third of the 

amount generated for use in concrete manufacturing. Any fly ash that is not sold 

is sent to an on-site landfill. 

• Roxboro handles the bottom ash at the plant with a wet sluicing system. Roxboro 

uses intake water from Hyco Lake as the source water for bottom ash sluicing for 

Units 1, 2, and 3. Roxboro uses the Unit 4 cooling tower blowdown as the source 

for bottom ash sluicing for Unit 4. 

• Roxboro stated that all of the bottom ash sluice water is sent directly to the ash 

pond. 

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• Roxboro excavates the bottom ash from the ash pond using backhoes and other 

machinery. The bottom ash that is removed is sold for use in concrete 

manufacturing. Roxboro stated that they are removing ash from the pond as 

needed, which is almost every day. 

• The ash pond effluent is discharged to Hyco Lake. Roxboro stated that the ash 

pond retention time is approximately 10 to 11 days. Ash pond effluent is not 

reused within the plant. 

• Prior to discharging the ash pond effluent, Roxboro uses a skimmer to prevent the 

discharge of cenospheres to Hyco Lake. Roxboro has a contractor who collects 

the cenospheres from the pond and hauls them off site. 

FGD System 

• Roxboro stated that the Unit 2 and Unit 4 FGD scrubbers began operation in April 

and December 2007, respectively. The plant expects to begin operating the Unit 3 

and Unit 1 FGD scrubbers in May and December 2008, respectively. (Note: Unit 

3 scrubber began commercial operation on May 6, 2008.) 

• Roxboro stated that they will eventually be capable of adding DBA to the 

scrubbers, but currently only spray nozzles are installed in the scrubbers. 

Therefore, all of the other feed equipment will need to be installed before the 

plant could begin using DBA. 

• Roxboro installed Babcock and Wilcox limestone, forced oxidation, tray-tower 

scrubbers. The scrubbers on Units 2, 3, and 4 have five recirculation pumps and 

three spray levels. The Unit 1 scrubber has three recirculation pumps and two 

spray levels.

• Roxboro uses horizontal ball mills to crush limestone to make the limestone slurry 

that is the sorbent in the scrubbers. 

• Roxboro stated that the design maximum chloride level in the scrubbers is 20,000 

ppm, but the plant is operating the scrubbers at a level less than 10,000 ppm

(typically between 5,000 and 8,000 ppm). Roxboro stated that they think the 

actual maximum chloride level for the scrubber material is around 12,000 ppm,

which is why they are operating at the lower chloride level. Operationally, the 

plant is using a 10,000 ppm setpoint as the maximum allowable level to protect 

metallurgy. Roxboro is currently operating at a lower chloride level to maintain 

sufficient margin to prevent exceeding 10,000 ppm while changing the coal used 

for Unit 4. 

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• Roxboro operates two-stages of hydroclones and a vacuum belt filter to dewater 

the gypsum produced in the scrubbers. Each of the scrubbers has an individual 

set of hydroclones and a vacuum belt filter. The blowdown from the scrubbers is 

continuously sent to the primary hydroclone. The primary hydroclone underflow 

can either be returned to the scrubbers or sent to the vacuum filters for 

dewatering. The primary hydroclone overflow is sent to a holding tank and then 

transferred to the secondary hydroclones. The secondary hydroclone underflow is 

returned to the scrubbers and the secondary hydroclone overflow is transferred to 

the blowdown tanks and then to the FGD settling pond. 

• Roxboro stated that the blowdown from the scrubbers is continuous and the flow 

to the blowdown tanks is continuous. The wastewater from the blowdown tanks 

flows intermittently to the settling pond; however, Roxboro stated that when all of 

the FGD scrubbers are operating, the flow to the settling pond could be 

continuous. 

• The gypsum from the primary hydroclone underflow is washed with service water 

that has been filtered and heated as it is applied to the vacuum filter belts. The 

filtrate and the wash water from the vacuum filter belts is returned to the 

scrubbers or used for the preparation of the limestone slurry. 

• The gypsum from the vacuum filter belts is transferred via a conveyor system to 

an uncovered gypsum storage pad. Based on the design coal for the system, the 

plant estimates that they will produce 600,000 tons of gypsum per year. 

• Roxboro stated that they have a contract in place for a company to buy the 

gypsum from the plant; however, they do not think any transactions have occurred 

yet. Roxboro stated that the buyer is planning to use the gypsum to produce 

wallboard. The gypsum produced by Roxboro must have a chlorides 

concentration less than 100 ppm and less than 10 percent moisture to meet the 

terms of the contract. Roxboro stated that the gypsum buyer plans to build a plant 

next door to the power plant. 

FGD Wastewater Treatment System 

• Roxboro’s FGD wastewater treatment system consists of a settling pond followed 

by an biological treatment system for treatment of nitrogen compounds and 

metals. Wastewater then flows from the bioreactor to the ash pond discharge 

canal, which commingles with the cooling water discharge canal, and is 

discharged to Hyco Lake. 

• Roxboro stated that they have been transferring water to the settling pond since 

the Unit 2 FGD system began operation in April 2007; however, Roxboro only 

began transferring wastewater to the bioreactor on February 27 (two weeks prior 

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to the site visit). According to plant staff, the bioreactor is expected to reach 

steady state operation approximately 2-4 weeks after startup. 

• The design flow rate for the FGD wastewater treatment system is 1,269 gpm (for 

all four units combined). At the time of the visit, the average flow rate through 

the system was 540 gpm (only Units 2 and 4 currently operating). The plant is 

estimating that the total flow rate from all four scrubbers will be approximately 

1,000 gpm; however, the Unit 4 coal change could affect this estimate. 

• Roxboro stated that the settling pond was built specifically for FGD wastewater 

treatment and it has a synthetic liner. Roxboro stated that the pond was built to 

have a 10-year life. At the end of the 10 years, the plant can either build a new 

pond next to the existing one or dredge the settling pond. 

• Roxboro stated that the goal for the settling pond is to reduce the wastewater 

temperature to less than 105o

F and reduce the TSS for optimal operation of the 

bioreactor. Roxboro personnel did not know the target TSS level. 

• Roxboro stated that the plant operates the settling pond below the maximum

capacity so they can hold an additional months worth of wastewater in the pond if 

there is an FGD system upset. The extra capacity allows the plant to avoid 

sending the wastewater through the bioreactor if there are issues with the system. 

Roxboro also stated that the settling pond has an emergency overflow to transfer 

wastewater to the ash pond instead of discharging it to the ash pond discharge 

canal. 

• The bioreactor at Roxboro has four parallel trains that each have two biological 

cells in series. The wastewater enters at the top of the first cell in the series and 

flows downward through activated carbon charcoal material. The charcoal 

material contains microbes to reduce the metals present in the wastewater to their 

elemental state. The effluent from the first cell is pumped to the top of the second 

cell in the series. The effluent from each of the four trains is combined and 

discharged to the ash pond canal. Outfall 010 is an internal monitoring point for 

the FGD effluent prior to it entering the Ash Pond Discharge Canal. Outfall 010 

enters the Ash Pond Discharge Canal downstream of outfall 002 (ash pond 

discharge to the Ash Pond Discharge Canal), but upstream of outfall 003 (Heated 

Water Discharge Canal).

• Each of the four treatment trains is designed for a four-hour retention time (based 

on all four units operating FGDs and all four treatment trains operating). The 

design flow rate through all four trains is 700 gpm (175 gpm each). At the time of 

the visit, each train had an 8 hour retention time. At the time of the visit, Roxboro 

was operating all four bioreactor trains even though only two FGD scrubbers were 

operating. Therefore, each bioreactor train was processing wastewater at 

approximately 50 percent of design flowrate, doubling the retention time. 

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• Roxboro stated that the bioreactor needs to be flushed periodically to remove 

solids from the system. Roxboro estimated that each cell will need to be

backflushed twice per year. The source of water for the blackflush is the FGD 

settling pond and the flow rate is estimated to be 6,280 gpm (per unit). Backflush 

wastewater will be transferred to the flush pond, which is located directly next to 

the settling pond. Roxboro stated that they expect most of the water in the flush 

pond to evaporate, otherwise, if the flush pond overflows, it will flow into the 

settling pond. 

• Three weeks prior to the site visit, there was a breach in the flush pond that 

caused a crack to form in the structure of the pond. The start up and 

commissioning water that had been sent to the flush pond leaked out of the pond 

and into the ash pond. The settling pond also had some leaking issues, but the 

settling pond has not yet breached. Roxboro stated that both of the ponds will 

need to be fixed. At this point, Roxboro is determining the cause the problems

and potential solutions. Roxboro is still sending FGD scrubber purge to the 

settling pond. The plant is also pumping some of the water from the FGD settling 

pond to the ash pond to keep the levels in the settling pond low. 

• Roxboro added one new chem.-tech to the plant staff to oversee bioreactor 

operation. Staff present at the visit suggested that the workload would support 

adding another 0.5 FTE. Total staffing to operate the FGD system (not the 

wastewater treatment portion) is approximately 20 operators. 

FGD Wastewater Treatment System Data 

• Roxboro stated that they have a new permitted outfall (Outfall 010) for the 

effluent from the bioreactor system, prior to commingling in the ash pond 

discharge canal. Roxboro stated that they are required to monitor for beryllium

and mercury weekly and to monitor for antimony, selenium, silver, and vanadium

quarterly. Roxboro stated that the metals do not need to be analyzed using lowlevel methods. 

• Roxboro stated that they plan to collect additional performance samples (e.g., 

FGD purge and FGD settling pond effluent samples); however, they have not 

made final decisions regarding which samples will be collected and the frequency 

of sampling. 

• Roxboro stated that although the biological treatment system is only in the startup phase, it has shown good removals for mercury and selenium. Roxboro stated 

that they need to decrease the oxidation-reduction numbers in the system, increase 

the temperature of the wastewater, and increase the flow rate through the system. 

Roxboro thinks that these changes will improve the system performance. 

• Roxboro stated that they are considering using a chemical additive (polymer) in 

the settling pond to improve mercury removals. 

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• Roxboro provided the following results from sampling conducted on March 4, 

2008. The influent sample was collected from a common header entering the 

system and the effluent was collected from the effluent pipes from the two 

operating treatment trains. Please note that this is sampling for the initial start up 

of the system and may not represent long-term results. According to plant staff, 

TSS into the bioreactor (settling pond effluent) is approximately 5 mg/L. 

Roxboro Sampling Results: March 4, 2008 

Analyte Sample 

Influent to the Bio 

System (ug/L) 

Effluent from the 

Bio System (ug/L) 

Percent 

Removal 

(%) 

Mercury 1 0.511 0.023 95.5

2 0.511 <0.019 >96.3

Selenium 1 1840 47 97.4

2 1840 394 78

 

• Because of the leaking issues with the FGD settling pond, the state of North 

Carolina is requiring Roxboro to collect weekly grab samples from the FGD 

wastewater treatment system until 90 days after the problem is fixed. Roxboro 

will be required to sample for a range of metals and other analytes from the 

following five sample locations: 

o FGD purge water, before settling pond; 

o Settling pond effluent (influent to bioreactor); 

o Effluent from bioreactor (this is similar to NPDES outfall 010); 

o Outfall 002 (discharge from ash pond into the Ash Pond Discharge Canal); 

and 

o Outfall 003 (discharge from Heated Water Discharge Canal to Hyco 

Lake). 

• Roxboro will be required to submit a report of the sampling results to the state of 

North Carolina each month. Roxboro agreed to supply Ron Jordan, EPA, with the 

report as well. 

FGD Wastewater Treatment Cost Information 

• EPA stated that they were interested in receiving cost information from Roxboro 

regarding the FGD wastewater treatment system. Roxboro provided the 

following capital cost information: 

o Blowdown line $1.258 million 

o Settling pond $7.571 million 

o Flush pond $2.534 million 

o Bioreactor system $22.43 million 

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• Roxboro stated that they do not have the operating and maintenance costs yet 

because the system is not yet operating. Roxboro did state, that it costs 

approximately $200,000 to inoculate the microbes for the bioreactor, which would 

be a significant expense if the microbes are killed. 

• EPA stated that they would be interested in any projected O&M costs that the 

plant can estimate. 

Progress Energy’s Mayo Plant 

• Progress Energy also operates the Mayo Steam Electric Plant, located in Person 

County, NC. The Mayo plant will soon start operating an FGD scrubber. The 

FGD wastewater treatment system will be similar to the Roxboro treatment 

system (settling pond plus bioreactor), except that Mayo’s bioreactor is designed 

for an 8-hour retention time at full flow, rather than the 4-hour design retention 

time for Roxboro. The FGD wastewater treatment system is scheduled to begin 

operating in spring 2009. 
Table 1. Site Visit Attendees 

Name Organization (Representing) Telephone E-maRobin Bryson Progress Energy (919) 546-3962 robin.bryson@pTom Copolo Progress Energy (336) 597-6193 tom.copolo@pgJodirah Green Progress Energy (336) 598-4068 jodirah.green@Fred Holt Progress Energy (919) 546-5286 fred.holt@pgnmDanny Johnson Progress Energy (919) 546-7724 danny.johnson@Shannon Langley Progress Energy (919) 546-2439 shannon.langleyBilly Milam Progress Energy (336) 597-6284 william.milam@Issa Zarzar Progress Energy (919) 546-3962 issa.zarzar@pgDonna Hill Southern Company (205) 257-5234 dbhill@southerSergei Chernikov North Carolina Department of Environment and Natural Resources (DENR) (919) 387-8044 ext. 594 sergei.chernikoAutumn Hoban North Carolina DENR (919) 791-4247 autumn.hoban@Vicki Webb North Carolina DENR (919) 791-4256 vicki.webb@ncKarrie-Jo Shell EPA/Region 4 (404) 562-9308 shell.karrie-jo@Josh Hall EPA/Office of Water (202) 566-1002 hall.josh@epa.gRon Jordan EPA/Office of Water (202) 566-1003 jordan.ronald@T.J. Finseth ERG (Contractor to EPA) (703) 994-7130 thomas.finseth@