Various technologies are used to aerate activated sludge processes, including Biological Nutrient Removal (BNR) and Enhanced Nutrient Removal (ENR) processes. Various aeration options currently used, available, and evolving for activated sludge, BNR, and ENR processes will be covered in this course. Specifically, types of aeration diffusers (mechanical, fine bubble, and membranes) and blowers (positive, multistage, single stage, and high speed) will be addressed. The influence of MCRT and MLSS will also be addressed as to the efficiency, ease (or difficulty) and cost of aeration. Airflow rate requirements and their calculations will be discussed in depth. Diffuser fouling and scaling issues will be discussed. Finally, helpful operating hints will be provided based on experiences from operating facilities.