A waste effluent treatment
system based on microbial mats for black sea bass Centropristis striata
recycled-water mariculture
J. Bender, R. Lee, M. Sheppard, K. Brinkley, P.
Phillips, Y. Yeboah, R.Ch. Wah-2004
Aquacultural Engineering, 31(1-2): 73-82
Abstract:
The objective of this project was to determine if a
low-cost biosolar filter system, based on microbial mats and fluidized sand
filters, could be used for a greenhouse recirculating black sea bass (Centropristis
striata) mariculture project. Microbial mats are stratified microbial
communities, composed of a complex of bacteria and dominated by
photoautotrophic cyanobacteria, which can transform nitrogenous wastes into
cellular protein and rapidly metabolize other fish wastes. The microbial
mats also provided an excess of oxygen for the nitrifying bacteria on the
fluidized sand filters, providing favorable conditions for ammonia removal.
The filter system was altered after it was found that microbial mat surfaces
became covered with fish wastes, which resulted in oxygen-production
decreases and ammonia-concentration increases. The modification included
delivering the fish wastewater under the mats, rather than on the surface,
thus depositing solids beneath the photosynthetic surfaces. Instead of
pellets, live tilapia (Oreochromis sp.) juveniles were used as food
which decreased the amount of solid wastes produced. Water and sludge from
the fish tank were drained by gravity from the bottom of the fish tanks into
the microbial mat trays at a rate of 7 l/min. Stable functioning mats
provided high oxygen levels, supported the nitrifying bacteria and removed
wastes produced by the black sea bass. Oxygen concentrations ranged from 6
to 10 mg/l and total ammonia concentrations remained below 1 mg/l.
During the 9th month there was a steady fish growth, little buildup of
solids and the fish tank remained clear. The mean weights of the 15 fishes
increased from 161±45 to 215±72 g, and to 337±99 g after 2, 4,
and 9 months, respectively.
(Research Center for Science and Technology, Clark
Atlanta University, Atlanta, GA 30314, USA, dick@skio.peachnet.edu)