Practical applications of low-pressure hydrocyclone (LPH) for feed waste and fecal solid removal in a recirculating aquaculture system

•Separation performance for the low-pressure hydrocyclone (LPH) was determined for the feed waste and fecal solids from common carp and Nile tilapia.•Maximum separation efficiencies were shown at the lower inflow rate under 600 mls−1.•The LPH can treat wide size range of solids in recirculation aquaculture systems.

In this work, the practical application of a low-pressure hydrocyclone was examined for feed waste and fecal solid removal for common carp (27 ± 3.1 g, average ± SD) and Nile tilapia (33 ± 3.4 g, average ± SD) in a recirculating aquaculture system. The dimensions of the low-pressure hydrocyclone included an inflow diameter of 30 mm, a cylinder length of 575 mm, an overflow diameter of 60 mm, an underflow diameter of 50 mm, a cylinder diameter of 335 mm and a cone angle of 68°. The different operating conditions tested were inflow rates of 400, 600, 800 and 1000 ml s−1, and underflow rates of 25%, 25%, 20% and 10% of the inflow rates, respectively. Feed waste totals of 4.1 to 4.8% and 3.6 to 4.0% of the feed intake were produced by the common carp and Nile tilapia, respectively. The maximum separation efficiency (Et) for the feed waste from the common carp was 71% at an inflow rate of 600 ml s−1 with an underflow rate of 25% of the inflow rate. The maximum separation efficiency for the feed waste from the tilapia was 59% at an inflow rate of 400 ml s−1 with an underflow rate of 25% of the inflow rate. The fecal solid production estimated from the digestibility was 37.9% and 35.7% of the feed intake for the common carp and Nile tilapia, respectively. The maximum separation efficiency for the feces from the common carp was 60% for an inflow rate of 600 ml s−1 and an underflow rate of 25% of the inflow rate. The maximum separation efficiency for the tilapia feces was 63% at an inflow of 400 ml s−1 with an underflow rate of 25% of the inflow rate. The low-pressure hydrocyclone can be adopted for prefiltration and/or post-filtration for the removal of various sized solids. Furthermore, the solids separated from the underflow can be easily removed for further processing.