RAS Filter Raceway System

What is a RAS Filter Raceway System?   

A RAS Filter Raceway system is a closed-loop water recirculation/filtration system between one round tank and one filter raceway (as shown in the photo).  The water from the round tank gravity flows to the filter raceway where the filter media traps suspended organic matter (floc, feces, algae, etc) through a series of three chambers before pumping back to the round tank.