Muna I recall a university ...

Muna

I recall a university professor saying the important thing in life is to know the difference between a salesman's opinion and a consultant's evidence based advise.

There will be many salesman who offer their opinion of the best treatment plant, but the only way to answer your question is to obtain a project specific feasibility study as there will surely be many cost and performance variables that are specific and unique to the project.

For example, the optimum bacteria will not only relate to the process plant size but also operating temperature, one process could favour anearobic bacteria, whilst another will favour aerobic bugs or even worms.  Local civil and environment regulations will also impact on the consultants advise.