This book compares the process of denitrification/anaerobic digestion/nitrification for the simultaneous removal of nitrogen and carbon from organic loaded effluents. In the first type of process, nitrification and denitrification simultaneously take place in the same reactor (SND). In the second type of process, there is one hybrid reactor with internal recycle, in which denitrification and anaerobic digestion take place, followed by one aerobic reactor where nitrification occurs with recycle to the anoxic/anaerobic stage. This book analyses the different factors that affect both processes, such as: (1) Dissolved oxygen (DO), (2) Carbon and nitrogen ratio in the influent (C/N), (3) Hydraulic residence time (TRH), (4) Effect of the recycle ratio, and (5) Effect of the presence of salt (NaCl) in the influent.