Recovery in crossflow membrane MF/UF (permeate:feed)

Hi!

What is a typical ratio of permeate to feed flow in micro-/ultrafiltration with tubular membranes (crossflow 1-3m/s)? So, I am actually looking for the ratio of retentate:permeate or the actual inlet flow circulated in the modules. It will for sure vary from application to application, but I'm interested in different applications anyway. 

In some research papers I read extremely low ratios (10-15%), but I don't think that is realistic in real world....