With rapid urbanization, great strains are not only being placed on the production of clean water; there is also an equal, if not, more important need to treat the increasing quantities of wastewaters being produced. With urbanization driving up land prices drastically, it makes good sense to leverage on technologies with smaller plant footprints, like the membrane bioreactor (MBR), as well as to adopt an innovative underground installation of the sewage treatment plant (STP), allowing a non-obnoxious co-existence with nearby residences. Being one of the largest underground STPs, the Jingxi Underground STP in Guangzhou is a 100,000 m3/day MBR-based treatment plant that was commissioned in 2010. The case study described here demonstrates the operational excellence of the STP by illustrating how an optimized internal recirculation for the A2O-MBR process reduced aeration energy demands by 18% while simultaneously improving Total Nitrogen (TN) removal by 24%. Furthermore, the success of a plant trial elucidating conditions that stabilized higher flux operations (to handle surges in water production demands) were also discussed.