This book explores intensification of the activated sludge process on the assumption that nitrification is a performance requirement, and that maintaining robust nitrification is a constraint on rated capacity. Capacity can be defined as the flow, load or population equivalent that can be treated. Rated capacity refers to how much is “allowed” to be treated, either by the environmental regulator or, if one exists, in a process performance warranty. Capacity is used as the fundamental metric of “quantity”. While the trend in the industry is towards ever more stringent effluent “quality” requirements at the discharge end of the plant, it has rather unsurprisingly led to derating of the “quantity” that can be received at the front end. Capacity Rated capacity