Evaluation of the Efficacy of a Radial Flow Settler for Aquaculture Wastewater Treatment

Aquaculture effluents contains solids, such as uneaten feed and feces, that need to be removed as earlier as possible to avoid water quality depletion. The aim of this study was to evaluate the efficacy of a customized device layout of the radial flow settler (RFS). The prototype was designed according to the existent literature and commercially available products. The experimental phase lasted four months starting from June 2020 and was conducted in a land-based aquaculture farm in Orbetello (Grosseto, Italy). The RFS received a part of the outlet flow from one of the rearing ponds of the farm. The inlet flow was set at 2 Ls-1. Samples of inlet and outlet water and sediments were collected on a monthly basis to evaluate the suspended solids content through gravimetric and filtration methods and the concentration of phosphorous, nitrogen, ammonium, nitrite, and nitrate. The results suggest that the designed device complied with the intended use. Moreover, the functioning of the RFS required a modest hydraulic load (15–20 cm) and therefore low energy requirement. However, a cover on the device to prevent algal blooming is necessary. The gravimetric methods used did not allow a correct evaluation of the amount of sediments as a difference between inlet and outlet, since the error of the method exceeded the difference between the solids content in the inlet and outlet water. However, a sedimentation efficiency of 15–30% was observed through the filtration of the sedimented material, together with a reduction of the P and N contents.