SANITARY SIGNIFICANCE OF INCREASES IN
FECAL COLIFORM COUNTS ACROSS A
CATFISH AQUACULTURE SYSTEM
Daryl W. Bennett, Civil/Environmental Engineer
Pape-Dawson Consulting Engineers
San Antonio, Texas 78217
John A. Gordon, Professor
Department of Civil Engineering
Tennessee Technological University
Cookeville, Tennessee 38501
In 1971 the Tennessee Valley Authority (TVA), in cooperation with private industry,
began a research program to determine the feasibility of raising catfish at high densities
in raceways using waste heat from steam-powered electric generating plants. A pilot-scale
raceway facility was constructed at the TVA Gallatin Steam Plant near Gallatin, Tennessee.
The Gallatin Steam Plant draws its cooling water from Old Hickory Lake, raises the temperature of the water about 5 C above the ambient, and then discharges the water into a canal
for flow back to the lake.
The pilot catfish facility is located on the banks of this canal, immediately downstream
of the steam plant, and about 40 feet above the surface of the water in the canal. Water is
drawn from the canal by three 1000-gpm pumps and is used by the facility on a once-
through basis.
The facility uses ten concrete raceways covered by an open-sided building. Each raceway is 4 ft wide by 50 ft long, and has 680 ft3 of effective growing space. The raceways
may be divided into four equivalent sections by metal screens to equalize fish distribution.
To remove, unconsumed food and waste, the raceways are flushed on a daily basis by drawing water from the bottom of the raceway under increased hydraulic head.
The effluents from all raceways empty into a common channel, which empties into a
sedimentation pond. The pond has a hydraulic retention time of about 0.5 hr, and allows
such solids as unused food and fecal wastes to settle out. Effluent is collected by weirs at
the end of the pond and discharged back into the cooling water canal.
In 1973 and 1974 TVA [1,2] conducted wastewater characterization studies of the
raceway effluents. These studies evaluated settleable solids, suspended solids, biochemical
oxygen demand (BOD), chemical oxygen demand (COD), total and soluble phosphates,
ammonia nitrogen, organic nitrogen, nitrite plus nitrate nitrogen, and fecal coliform
bacteria. Organic compounds, solids, ammonia and phosphorus were determined to be the
main pollutants from the high-density catfish cultures, but fecal coliform counts also increased considerably from the upstream to the downstream ends of the raceways. Increases
were observed as high as five orders of magnitude.
Because these organisms indicate the potential presence of organisms pathogenic to man,
it was desirable to determine the realistic health impact of these bacterial increases, both
for catfish aquaculture systems in general and for the Gallatin facility in particular, when
the organisms had reproduced in an aquaculture system in the absence of human waste
inputs. We sought to ascertain this impact by pursuing the following research goals:
1. determine the source of the fecal conforms;
2. monitor indicator organism increases across the system;