Efficiency of pumpkin (Cucurbita pepo), sweet wormwood (Artemisia annua) and amaranth (Amaranthus dubius) in removing nutrients from a smallscale recirculating aquaponic system

In aquaponic systems, plants absorb dissolved nutrients from aquaculture wastewater for their growth. The removal of nutrients allows reuse of water and minimises wastewater discharge to the surrounding environment. This study evaluated the relative nutrient removal efficiencies of three plant species and the performance of Nile tilapia (Oreochromis niloticus) in a small-scale aquaponic system. Three aquaponic systems were assigned as treatments PU (pumpkin), SW (sweet wormwood) and AM (amaranth). Physical-chemical water quality parameters were measured in the fish tanks as well as hydroponic inlets and outlets. Fish sampling was done every 2 weeks for 60 days. Results showed significantly (p < 0.05) lower nutrient concentrations in the hydroponic outlets than the inlets. There was no significant difference in nutrient removal efficiency of the plants (p > 0.05) for all the tested nutrients except for phosphorus. Phosphorus removal was substantially high in PU (75.5 +/- 16.8%) than SW (47.36 +/- 14.5%) and AM (40.72 +/- 13.2%). In addition, the SW system had better (p < 0.05) relative growth rate (0.06 +/- 0.00) than that of PU (0.05 +/- 0.00) and AM (0.05 +/- 0.00). Nitrogen and phosphorus content in plant tissues was significantly high (p < 0.05) in SW and PU plants respectively. Water quality parameters had a significant influence on the growth of fish (p < 0.05). The growth of fish was not different (p > 0.05) in the three treatments. The findings indicate that the tested plants can reduce nutrients in aquaculture discharge water.