As previous answers, I know ...
Published by Michael Martin, Deputy Asset & Technical DIrector at SUEZ International
As previous answers, I know GPS-X and Biowin softwares but no excel spreadsheet (we have some within Suez but confidential). I would say that the MBR design is complex due to the different design parameters depending on the membrane supplier (filtration capacity and hydraulic limit, max MLSS in membrane boxes, RAS requirements, scouring aeration, etc). Also the design will depend on the raw water quality and the effluent quality to reach (C+N+DN, etc).
Regards