Given a wastewater treatment process (a sewage treatment plant), we will look to drive its load to maximize the amount of water sanitized daily or any other time unit. In terms of engineering, we want to improve the performance of a bioprocess. The optimization or optimal control of industrial processes has been the subject of countless general treaties. However, works dedicated to the optimization of bioprocesses are rarer. This book has two parts. The first "Learn to use the Maximum Principle" deals with the simplest possible way to use the basic tool of optimization methods necessary for conditions of optimality. The second deals with examples.