Tuckaseigee, North Carolina: Photo tour by Superintendent Stan Bryson
Hi! I'm Stan Bryson and I'm the Superintendent of the
Tuckaseigee Water and Sewer Authority's Waster Water Treatment
Plant, located in Sylva, North Carolina. I would like to take you on a short tour of
our Class A - Lime Only
Pasteurization System.
We have a 1.5 meter belt filter press. Our cake
solids typically are between 15% and 18% dry solids. The cake is
conveyed to the Lime Only Pasteurization Process System with two screw conveyors.
The screw conveyors provide
a simple means of conveying, while minimizing spillage and cleanup. The screw
conveyors also provide a nice weather tight seal at the wall. This is a feature we
really appreciate in the winter.
The dewatered sludge cake is mixed with high calcium
quicklime in the sludge/lime mixer. Our process permit requires that
we elevate the temperature of the sludge cake to over 158° F. We typically operate
in the 162° to
168° F range.
Our processing permit also requires that we maintain
temperature, above 158° F, for thirty minutes. This requirement applies to
every particle of sewage sludge processed. We added a Pasteurization Vessel in order
to accomplish compliance with this
aspect of the EPA - 503 Regulations. I will come back to this topic at the end of
the tour. The Pasteurization Vessel has a
special belt in the bottom that creeps along at about 4" per minute. The result
is the biosolids stay in the Pasteurization Vessel
for at least thirty minutes before being continuously discharged on to the belt conveyor.
The inclined belt conveyor elevates the finished product to a storage pad.
The end product is stored on a concrete pad. The
belt conveyor discharges into a two sided bunker
that provides two push walls.
The end product is a granular product that is fairly easy
to handle. I use the product myself in my small
farming operation and also on twenty acres of Christmas trees that I grow.
This picture shows the overall system. From right
to left we have the lime silo and transfer screw feeder,
inclined sludge cake screw conveyor, sludge/lime mixer, Pasteurization Vessel, and the
inclined and covered belt conveyor.
The Pasteurization Vessel is the heart of the system. It is necessary to subject the
pathogens to +158° F for
thirty minutes in order to effectively kill the pathogens and comply with EPA - 503.
The Pasteurization Vessel has one temperature probe at the inlet. This tells us the initial temperature.
The discharge end of the Pasteurization Vessel also has a
temperature probe. This lets us know what the
temperature is at the discharge. The Pasteurization Vessel has a belt in the
bottom that operates at a fixed speed.
Therefore, we know that the product has been in the Pasteurization Vessel for at
least thirty minutes before it reaches
the discharge temperature probe. The Pasteurization Vessel is insulated with
2" of ceramic wool and is jacketed.
This insures that the temperature of every particle, the entire mass, is at or above the
indicated temperature.
The inlet and discharge temperature readings are
continuously displayed on the system's control panel. The
temperature readings are recorded through the shift.
The original system was installed with a lime silo,
sludge/lime mixer and belt conveyor. The retention time was going
to be met in the truck. The temperature was to be measured using either the
"bucket" or "sweet spot" testing technique.
The high lime dosage resulted in a powder consistency.
The time/temperature requirement
(158° F for thirty minutes) was to be achieved in the bed of the truck. The
contract called for a performance test.
Three commonly used techniques (bucket, sweet spot and
mass pile) were investigated to monitor and record the
time/temperature relationship that is required to be submitted to show compliance with EPA
- 503.
Data was recorded in the field under actual operating
conditions. The data was logged and the test procedure
was video taped.
Using the bucket method, probes are simultaneously
inserted into several locations within a five gallon bucket.
This technique is often used but data shows temperature ranges of over 40° F within the
bucket, depending on where
the probes are inserted. It is easy to show compliance or non-compliance, depending
upon your persuasion.
Using the mass pile method, eight probes are inserted
into the pile at various locations. The results show a
temperature profile that ranged from a high of 162° F to a low of 110º F. The core
of the pile was hot. The data
collected also recorded, however, the cooling effect due to ambient temperature. On
the day the test was conducted,
the outside air temperature ranged from a morning low of 57º F to an afternoon high of
72º F.
The data from Tuckaseigee was submitted to the EPA, who used it when they attempted to
clarify any
misconceptions, by issuing the revised White House Book. The revised document states
that every particle must meet the time
and temperature requirements outlined in Part 503. The complete published text will
be available in the near future.
Additional information is available from EPA's Jim Smith who can be contacted at (513)
569-7355.
Those interested in viewing the complete Performance Test Report should click here.
