Nutrient removal from aquaculture effluent using settling ponds and filter-feeding species (Amphibalanus amphitrite and Saccostrea cucullata): an in-situ study

The potential application of settling ponds and two fouling filter-feeder species Amphibalanus amphitrite and Saccostrea cucullata to bioremediate semi-intensive shrimp farm effluent through 6 hours residence time was investigated. Settling pond reduced total nitrogen, total phosphorus and chlorophyll a to 80.5%, 77.8% and 94.3% of the initial concentrations (2.47 ± 0.07 mg L-1, 0.154 ± 0.006 mg L-1, and 24.44 ± 2.02 µg L-1), respectively. Amongst S. cucullata, A. amphitrite and combination of both species, oysters showed the highest efficiency in nutrient removal. Total nitrogen, total phosphorus and chlorophyll a diminished respectively to 70.6%, 67.7% and 40.9% of the initial concentrations in oyster treatments. These proportions were respectively 81.5%, 63.2% and 72.4% for ponds contacting barnacles, and 69.3%, 71.2% and 44.9% of the initial amounts in the combination of the two species treatment. Among three different densities used for treatments, medium density of oysters (0.54 oyster per liter) showed comparable effectiveness in nutrients and phytoplankton removal to the high density. Lower ammonia production along with imposing less costs and effort, as well as relatively equal ability; suggest the medium density of S. cucullata as the most suitable choice. Our results suggest that applying settlement ponds, and particularly with filter-feeder species such as S. cucullata, might mitigate the adverse impacts of shrimp wastewater, including coastal eutrophication, on adjacent ecosystems.