I’m considering going with a rigid wall bioreactor, single use, but need to be able to scale-up to at least 50L in total volume. What are my options?

For the sake of clarity I’m going to go ahead and assume that by single-use you do not mean glass and by rigid wall you are not looking at bags. That being the case, the only option of which I’m aware is the BioBLU family of bioreactors from Eppendorf which has a working volume that goes from as little as 100mL to as much as 40L.