Experimental study on sewage collection and related performance of square arc angle aquaculture tank

The key to efficient operation of RAS is maintaining good water quality in the aquaculture tank. To improve the hydrodynamics and self-cleaning property in the tank, a reduced physical experimental model was constructed according to the geometric scale of 1:8 of the actual square arc angle aquaculture tank in RAS. The influence of the variation of different parameters including inlet layout mode, inflow angle (α), and diameter to depth ratio (L/H) on the hydrodynamics and sewage collection characteristics was systematically evaluated and analyzed through physical model experiments. The results indicate that the velocity distribution influences greatly the distribution and discharge efficiency of sewage and the sewage sedimentation area highly overlaps with the low-velocity area in the tank. The inlet layout mode of single inlet set at arc wall and inflow angle of 45° which are the preferred design parameters improve significantly the velocity distribution and sewage discharge efficiency in the tank. In addition, the discharge efficiency of solid particles in the aquaculture tank increases with the decrease of the diameter to depth ratio. When L/H = 2:1 3:1, the sewage discharge effect is the best; when L/H = 3.5:1 4.5:1, the sewage discharge effect is relatively good; when L/H = 5:1 7:1, the sewage discharge effect is greatly weakened. The present study provides a basis for further improving the design of the inlet mode, inflow angle, and diameter to depth ratio of aquaculture tanks.