Biostyr Duo is a first-of-its-kind integration of biological aerated filter (BAF) and moving bed biofilm reactor (MBBR) technologies. Wastewater first flows through a dynamic MBBR media layer that provides a large surface area for biofilm growth and treatment. Flow then passes through the Biostyrene media layer, which provides additional fixed-film treatment and filtration as the water flows up through the fixed bed.