I agree with Leah and Marina ...
Published by Bruno Peeters, managing director at Model Engineering
I agree with Leah and Marina and I would like to add to stop feeding wastewater in the aeration tank for at least 8 hours prior to the planned 12 hour shutdown. This will minimize oxygen demand and decay.
Instead of pure oxygen you could also add nitrate preferably as Ca(NO3)2 with sufficient mixing to supply chemical oxygen to the bacteria.