201706201136_redacted

'. JAMES B. HUNTJR„.:;
GOVERNOR,
5
WAYNE MCDEVITT
SECRETARY
NORTH CAROLINA DEPARTMENT OF
ENVIRONMENT AND NATURAL RESOURCES
FAYETTEVILLE REGIONAL OFFICE
« DIVISION OF WATER QUALITY
May 5, 1999
Mr. Michael Johnson
Environmental Coordinator
DuPont Fluoroproducts
22828 NC 87 Hwy West
Fayetteville, NC 28306
SUBJECT: Installation of "Biomixer”
DuPont WWTP
NPDES Permit No. NC0003573
Bladen County
Dear Mr. Johnson:
This letter is follow-up to several conversations held with David Goodrich,
Supervisor NPDES Unit, and myself concerning the installation of a "Biomixer"
to enhance aeration in the main activated sludge aeration tank. Based on those
conversations and a review of the information provided, you may proceed with
the installation and operation of the unit described.
� Please be advised that all NPDES permit conditions and limitations must
be met during and after the installation of this unit.
1; If you have questions or comments concerning this matter, please do not
hesitate to contact me at 910-486-1541.
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'. JAMES B. HUNTJR„.:;
GOVERNOR,
5
WAYNE MCDEVITT
SECRETARY
NORTH CAROLINA DEPARTMENT OF
ENVIRONMENT AND NATURAL RESOURCES
FAYETTEVILLE REGIONAL OFFICE
« DIVISION OF WATER QUALITY
May 5, 1999
Mr. Michael Johnson
Environmental Coordinator
DuPont Fluoroproducts
22828 NC 87 Hwy West
Fayetteville, NC 28306
SUBJECT: Installation of "Biomixer”
DuPont WWTP
NPDES Permit No. NC0003573
Bladen County
Dear Mr. Johnson:
This letter is follow-up to several conversations held with David Goodrich,
Supervisor NPDES Unit, and myself concerning the installation of a "Biomixer"
to enhance aeration in the main activated sludge aeration tank. Based on those
conversations and a review of the information provided, you may proceed with
the installation and operation of the unit described.
� Please be advised that all NPDES permit conditions and limitations must
be met during and after the installation of this unit.
1; If you have questions or comments concerning this matter, please do not
hesitate to contact me at 910-486-1541.
Sincerely,
Paul E. Rawls
Water Quality Regional Supervisor
PER/bs
cC* David Goodrich, NPDES Unit
DWQ Central Files
FRO File, DuPont
225 GREEN STREET, SUITE 714, FAYETTEVILLE, NORTH CAROLINA 2830 1-504 3
PHONE [phone] FAX [phone]
AN EgUAL OPPORTUNITY /AFFIRMATIVE ACTION EMPLOYER - 509'o RECYCLED/1 O�}'o POST -CONSUMER PAPER
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Sincerely,
Paul E. Rawls
Water Quality Regional Supervisor
PER/bs
cC* David Goodrich, NPDES Unit
DWQ Central Files
FRO File, DuPont
225 GREEN STREET, SUITE 714, FAYETTEVILLE, NORTH CAROLINA 2830 1-504 3
PHONE [phone] FAX [phone]
AN EgUAL OPPORTUNITY /AFFIRMATIVE ACTION EMPLOYER - 509'o RECYCLED/1 O�}'o POST -CONSUMER PAPER

Mr. David Goodrich
NC DENR
Division of Water Quality
Permits &Engineering Unit
P. O. Box 29535
Raleigh, NC 27626-0535
RE: NPDES Permit No. NC0003573
Dear Mr. Goodrich:
DuPont Fluoroproducts
22828 NC 87 HWY W.
FAYETTEVILLE, NC 28306
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This letter is to inform you of a planned change to the DuPont —Fayetteville Works
Wastewater Treatment Plant (WWTP), which will enhance the WWTP's performance by adding
additional oxygen and mixing to our main activated sludge Aeration Tank.
DuPont does not believe that this change requires any approval or authorization by the
Division of Water Quality prior to beginning construction for the following reasons:
1. The referenced NPDES Permit states in Part II Section E(2) that notice must be given to
the Director of any planned alteration if the alteration is a new source, if it could
significantly change the nature or increase the quantity of pollutants, or if it results in a
significant change in the sludge use or disposal practices. The proposed alteration is not,
nor does, any of the above.
2. The referenced NPDES Permit states in Part III Section A that no construction of
wastewater treatment facilities or additions to add to the plant's capacity can begin until
written approval is received from the Department. The proposed alteration does not
constitute a wastewater treatment facility, nor is the capacity of the WWTP being
increased.
However, in case NCDENR believes that your approval is needed prior to DuPont proceeding
with this enhancement, DuPont is providing information about this planned change for your
review.
Currently the DuPont WWTP Aeration Tank uses a diffused air system to oxygenate the
wastewater for the aerobic biodegradation using activated sludge. The planned enhancement is
to install an air injection and mixing .device (Biomixer) into the existing Aeration Tank.
Attachment 1 is a drawing of the Biomixer, which shows it to be a floating platform with an
adjustable submerged rotator assembly that diffuses the air.
To improve the efficiency of the WWTP, DuPont plans on installing the Biomixer in the
front half of the Aeration Tank where it will inject compressed air through rotating, submerged
rotors. This action provides additional dissolved oxygen for the wastewater's activated sludge in
a region of the tank that has a measurable oxygen deficiency, and also mixes the contents of the
tank to ensure a more homogenous mixture.
E. L du Pont de Nemours and Company ®Printed on Recycled Paper
FL -4

Mr. David Goodrich
NCDENR Division of Water Quality
April 21, 1999
The Biomixer will be flotation mounted inside the Aeration Tank, and will be fixed in one
location via a floating walkway and mooring cables. Attachment 2 is a "bird's eye view" of the
equipment layout and shows the location of the Biomixer inside the Aeration Tank. Attachment
3 is a side view of the Biomixer and the floating walkway.
The Biomixer's rotation provides not only mixing of the incoming wastewater, but also
creates ultra -fine air bubbles by shearing off emerging bubbles as they are forming on the rotating
diffusers. These extremely small bubbles increase the oxygen transfer rate. Additionally, the
shearing force also reduces biological growth and build-up that can foul the diffuser.
The depth of the Biomixer's diffusion rotors is adjustable, and allows for variable power
input by adjusting the submergence depth of the diffusers. The greatest submergence depth
requires the greatest power to the air blower to realize the maximum air delivery. Also, the
greater the submergence depth results in a higher dissolved oxygen transfer rate since the
individual air bubbles are in the water for a longer time.
Attachment 4 gives some of the general specifications of the Biomixer (model 400-8545),
including the 85 horsepower motor, the air injection rate of 1,691 CFM, and the fourteen blades
of the rotating section. It should be noted that 75 HP of the 85 HP motor will be used to drive
the air blower of the Biomixer, and the remaining 10 HP will be utilized to rotate the blades
underwater.
Attachment 5 shows the DuPont Specifications for the Biomixer, with the specifics of the
piece of equipment to be used in this enhancement.
Hopefully this information is adequate for NCDENR's needs. Should you require additional
information, or if you have any questions, please contact me at [phone].
Michael E. Johnson
Environmental Coordinator
Attachments
cc: Mr. Paul Rawls, NCDENR Division of Water Quality, Fayetteville