Nutrient bioremediation efficiency of bacterial biofilms and plant based biofilters in a recirculating common carp (Cyprinus carpio L.) culture system

The study aimed to evaluate and compare the nutrient cycling efficiencies of bacterial biofilms of a moving-bed filter and three aquatic plants (Lemna minor, Hygroryza aristata and Phyllanthus fluitans) as biological filters in recirculating aquaculture systems (RASs). The nutrient cycling capacities were tested in 12 independent RASs used for culturing common carp (Cyprinus carpio L.) in greenhouse conditions. The efficiencies were determined by comparing fish survival and growth performance, water quality parameters and removal rates of NH4-N, NO₂-N, NO₃-N, PO43-P and TP among biofilters. All biofilter types were efficient in maintaining water quality parameters, removing nutrients and providing an acceptable environment for fish growth and survival. However, the bacterial biofilm filter had the highest removal efficiencies of NH4-N and NO₂-N than those of the other filters; while H. aristata and L. minor filters had higher removal efficiencies of NO₃-N and PO43-P than those of P. fluitans and bacterial biofilm filters. The bacterial biofilm filter had a higher ability to deal with higher concentrations of NH4-N and NO₂-N; whereas plant based filters were more effective in maintaining NO3-N concentrations. Nutrient uptake capacities of selected plants differ and are strongly influenced by the growth rate of plants. The present study suggests that plant based filters in this filtration technique could be beneficial in removing nutrient overload in RASs, adding harvestable product and reducing the overall cost of RASs; whereas bacterial biofilm filter is a superior filter in maintaining ammonium and nitrite concentrations in RASs.