Pilot study on water quality regulation in a recirculating aquaculture system with suspended growth bioreactors

In situ suspended growth aquaculture systems for oligotrophic species suffer from excess total suspended solids, low dissolved oxygen, and other associated problems. To address these disadvantages, this study designed and tested a closed recirculating aquaculture system containing 3 pilot-scale suspended growth bioreactors (SGBRs) for the water treatment of pollutants. These SGBRs were designed to control extra carbon addition at carbon/nitrogen ratios of 12, 8, and 4, respectively. It was determined that the culture tanks removed total ammonia nitrogen (TAN) and nitrite (NO2−-N) by nitrification, and the SGBRs removed nitrate (NO3−-N) by denitrification and also soluble reactive phosphate (SRP). Concentrations of NO3−-N and SRP in the effluent decreased, as the controlled carbon/nitrogen ratio of the SGBR increased. When carbon was controlled at a carbon/nitrogen ratio of 12, the influent concentrations of NO3−-N (35.41 ± 1.22 mg·L−1) and SRP (4.60 ± 0.67 mg·L−1) were reduced to 7.70 ± 3.58 mg·L−1 and 0.30 ± 0.16 mg·L−1, respectively. Thus, this proposed system had the ability to control simultaneously TAN, NO2−-N, NO3−-N and SRP. The survival rate of Anguilla marmorata was 98.00 ± 1.41%, with a final stocking density of 56.46 ± 0.51 kg·m−3. We suggest that various adjustments in the carbon/nitrogen ratios of SGBRs can be practically controlled according to the concentrations of pollutants in the culture tanks.