A bed of MBBR media generally consists of thousands of tiny pieces that suspend themselves throughout a wastewater treatment tank, typically taking up about 50% to 70% of the available space. Their design makes them optimal for hosting beneficial bacteria and promoting their growth. Many types of MBBR media resemble wheel-shaped pasta, with the spokes of the wheel providing valuable surface area for bacterial growth. Others are thin, coin-shaped discs or squares. http://www.bioetp.net/