Description of three biological wastewater treatment processes, activated sludge, MBBR (moving bed biofilm reactor), and MBR (membrane bioreactor). Each of these processes is described and discussed in turn. For each of them there is background information about the process, a general description of the process, and description of the process design calculations for that process along with examples illustrating those calculations. Use of spreadsheets for the calculations is covered also, including numerous screenshots of spreadsheets set up to make the various calculations discussed in the book.