During Secondary Aerobic Wastewater Treatment, Some of the Activated Sludge

Multiple Choice

During secondary aerobic wastewater treatment, some of the activated sludge goes ________ while the rest goes ________.

A) back to the aerator / to the anoxic sludge digester
B) back to the primary system / to the aerator
C) to the anoxic digester / back to the primary system
D) back to the primary system / to the tertiary digester