Different technical combinations will be selected according to your inlet water quality and your government's requirements on the treated outlet water quality.
Every country or city has its own emission standard. Almost every plant has customized needs.
Generally, an A/A/O package wastewater treatment plant includes anaerobic tank, anoxic tank, aeration tank, sedimentation tank, sludge tank, and clean water tank. It will be a little different according to the water quantity/flow rate.