Try:

Carmago et al (2005) 'Hydrodynamic analysis of an anaerobic sequencing batch biofilm reactor with liquid-phase external circulation' INCI v.30 n.4 Caracas sep. 2005http://www.scielo.org.ve/scielo.php?pid=S0378-18442005000400002&script=sci_arttext 

Dear friend,

From a hydraulic residence time perspective, SBR behaves as a batch reactor with a residence time shich is defined  and fixed by the selected cyclic operation, i.e. fill time, reactime time, etc. Consequently it has no residence time distribution.

I would suggest you to get hold of the two technical reports published by IWA for a clearer image of the SBR process; the second one was prepared by me together with, N. Artan at ITU.

Dear Ernest O Nnadi and Derin Orhon

Thank you for your feedback. I will have a look at the suggested papers.