Complex sentence: Approximately 95% of the surface area is thus alternately immerged in waste water in then exposed to the atmosphere above the liquid under normal operating conditions; carbonaceous substrate is removed in the initial stage of RBC.
Split into simpler sentences: Approximately 95% of the surface area is thus alternately submerged in waste water and then exposed to the atmosphere above the liquid. Carbonaceous substrate is removed in the initial stage of RBC.