Advective transport of solids from a marine fish-rearing tank using gravity-driven effluent pipelines with various flow regimes

Comprehending how a given water flow hydraulic regime will affect particle settling velocity and particle size after being advectively transported in a gravity-driven effluent pipeline is paramount for the design of any land based rearing system. Suspended solids generated by the punctuated snake-eel Ophichthus remiger were analyzed to characterize the settling velocities and particle size properties. At a particular Reynolds number, hydraulic conditions are characterized as turbulent, transitional, or laminar. Suspended solids were tested for three hydraulic conditions during their advective transport when leaving the rearing tank through gravity-driven hydraulic effluent pipelines. The three hydraulic conditions were defined by the Reynolds number as transitional for 2862 Re, turbulent-1 for 5106 Re, and turbulent-2 for 8304 Re. When increasing water turbulence, while advectively transporting suspended solids produced by punctuated snake-eel O. remiger from the rearing tank to a single effluent pipeline of uniform diameter towards a delivery point, the results showed that suspended solids reduced their settling velocity up to nine times and particle size up to two times. These variations in settling velocities and particle size during advective transport would affect the efficacy of suspended solids removal devices in a given rearing system. As a result, it is recommended that land-based aquaculture systems should consider designing their rearing tank gravity-driven effluent pipelines under transitional or turbulent-1 flow conditions, avoiding the turbulent-2 flow zone.