PCBs from Water
Carolina Transformer Superfund Site
Background
Years ago, the Carolina Transformer Company (CTC) had an electrical
rebuilding and repair operation on a five-acre site in Fayetteville,
N.C. After 15 years of operation, the company closed in 1982 and
the site was abandoned. During operation, CTC had a storage facility
for transformers and other equipment containing transformer oil
contaminated with PCBs. The oil was not properly managed, stored
or disposed of, and as a result, PCBs made their way into the surrounding
acreage and ground water.
Consequently, in 1989, the North Carolina Environmental Services
Division inspected the abandoned CTC site. The soil and groundwater
contamination was confirmed, and the land was designated an EPA
Superfund site under the Comprehensive Environmental Response, Compensation
and Liability Act (also known as CERCLA or Superfund).
After many years of cleanup assessment, contractor proposals and
red tape, 301 Environmental Services (Fayetteville, N.C.) was awarded
a contract in January 2002 to treat and remove trace PCBs from over
1,500,000 gallons of contaminated water at this site (Figure 2).
The level of PCBs in the water had to be reduced below 0.5 parts
per billion (ppb) to conform with the discharge allowances of the
state of North Carolina to the nearby Cape Fear River.
The Problem
A very low PCB discharge level (0.5 ppb) was required. In addition,
transformer oil and PCBs at very dilute concentrations are extremely
difficult to remove from water. This is especially complicated when
mud, silt and clay are in the mix, which can all act as micro-absorbents
and carry PCBs. Standard flocculation and filtration attempts could
only achieved 70 ppb to 100 ppb PCB levels. The other problem with
these suspended solids is that because of their type and size, they
clog and blind-off filter media very quickly. Large backpressures
develop rapidly, and tiny clay and silt particles carrying PCBs
break up and bypass standard filters that don't capture sub-micron
(<1 micron) particles.
In short, purifying water with trace oil, PCBs and sub-micron particulates
such as silt and clay, is a very difficult and time-consuming endeavor.
Typically impacted water of this type must be transported and treated
off-site ( ex-situ). As an added treatment barrier, meeting discharge
limits of 0.5 ppb on-site has, historically, not been economically
feasible.
To meet this challenge, 301 Environmental asked MYCELX Technologies
Corporation (Gainesville, Ga.) to design a complete pump and treat
separation system to remove the PCBs and purify the water in-situ
for discharge to the Cape Fear River.
The Solution
MYCELX Technologies, the manufacturer of MYCELX HRM (Hydrocarbon
Removal Matrix) cartridge technology that is designed to bond and
separate select hydrocarbons from water, in conjunction with the
developers of a natural coagulant gel (provided by Engineering Sales
Associates of Charlotte, N.C.), were able to develop an effective
and inexpensive in-situ system capable of processing water at 180
gallons per minute (gpm).
The Results
To date, over 1,500,000 gallons of water have been purified to below
detectable limits (BDL) of PCBs (<0.5 ppb) and discharged to
the Cape Fear River easily complying with all aspects of the project's
design parameters.
To produce this success, a combination of four technologies were used:
- Flocculation with select polymer additives (20,000 gallon batches).
- Particle Filtration -- a series of vessels and high efficiency
filter media were used to remove particles to less than 1 micron.
- During the evolution of this project, a filter-aid product
was added to improve the particulate filtration and associated pressure
drops. The product is a natural coagulant gel called Chitosan. As
this gel slowly dissolves, it attracts sub-micron particles, which
agglomerate into larger, stable, easier-to-filter particles. This
technology was very important to the over-all success of the project
due to the type and size of suspended solids (i.e. sub-micron silt,
mud and clay). The gel was implemented after gross particle removal
at 50 microns and before fine particle removal.
- HRM Cartridges have an extremely strong bonding attraction
for select hydrocarbon compounds. Examples of hydrocarbons that
are effectively separated from water at up to 99.9 percent include
oil, grease, gasoline, fuel, kerosene, hexane, benzene, toluene,
chlorinated solvents and PCBs. In this application, the HRM
Cartridges removed the PCBs to below detectable limits (BDL).
It is important to note that HRM Cartridges actively bond to
hydrocarbons without desorption and operate at less than one pound
per square inch (psi) pressure drop up to their saturation point.
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