Note to readers, attached is the complete final report for FNE96-121
Mr. Brockway raises catfish and small-mouth bass in a suburban neighborhood. He designed his own aquaculture system, which is most notable for the small space it occupies, not much more than a corner of his garage, and for being largely self-contained as far as water is concerned. He recirculates water from the fish tanks through a series of settling tanks and filters, and past ultra-violet lights to inhibit algal growth. He daily monitors a number of parameters, including oxygen, ammonia, and nitrite concentrations, pH, suspended solids, and water hardness, to assure an environment that will support his fish. His SARE project involved installation of a biofilter, to deal with nitrogen accumulations from fish excretions.
The biofilter consists of a 55-gallon plastic barrel filled with plastic balls. Water from the system is sprayed over the top at a rate that can be varied from 9 to 35 gallons per minute, and trickles through and out the bottom, and into a settling tank. Mr. Brockway seeded the filter with two kinds of bacteria—Nitrosomonas, which oxidizes ammonia to nitrite, and Nitrobacter, which oxidizes nitrite to nitrate. Elsewhere in the system an anaerobic biofilter reduces the nitrate to gaseous forms of N, which escape into the atmosphere.
From time to time, when the mass of the bacterial colony grows inconveniently large, Mr. Brockway raises the water level in the biofilter. This dislodges the material, which passes through to the settling tank. There he scoops it out, and most of it winds up as compost in his garden.
Mr. Brockway reports that the system works well. He has not done an economic analysis, but guesses that his costs amount to 80 or 90 cents per pound of fish. By way of comparison catfish retails in his area for $3 to $7 per pound, with the higher price in the winter.