Background description of MBBR (moving bed biofilm reactor) wastewater treatment process as an attached growth process using plastic carriers on which the biofilm grows. Flow diagrams are shown for BOD removal and for nitrification, including single stage and two stage processes. Discussion of process design calculations, including the surface area loading rate (SALR) and its use to calculate the carrier surface area needed and the MBBR tank volume needed. Example process design calculations are included for a single stage BOD removal MBBR process, a two stage BOD removal MBBR process, a two stage MBBR process for BOD removal and nitrification and for a single stage nitrification MBBR process. Each of the example calculations includes a screenshot of a spreadsheet for carrying out the MBBR process design calculation for that example. The second edition has the design SALR for nitrification stages calculated based on user input values for the design wastewater temperature, reactor D.O. concentration, and target effluent ammonia nitrogen concentration.