I was looking at some papers related to moving bed Biofilm reactor and it says that it can be used both in anoxic and oxic condition. So, I want to know what are the advantages of treatment plants that can work in both anoxic and oxic conditions?
TLDR: Treatment technologies that can function in oxic and anoxic conditions are more flexible and can be applied in more circumstances.
First, I think clearing up some terminology would be helpful. These terms are not super specific, but this is how they are generally used in my experience.
A Treatment plant is a facility which receives wastewater, treats it, and discharges it somewhere. It is not oxic or anoxic, but it has treatment processes which can be oxic or anoxic. Most plants have numerous processes, including both oxic and anoxic (and anaerobic) processes for treatment of different things. A treatment process uses a specific treatment technology or technologies to accomplish its goals. A moving bed biofilm reactor (MBBR) is a specific technology involving suspended media to host biofilm growth.
MBBR tanks can be aerated (oxic conditions) or un-aerated (anoxic conditions) depending on the goals of the treatment process. The fact that the technology can be applied in both kinds of processes doesn't usually* benefit the process itself. It does benefit the manufacturer because their potential market is larger however. This does not mean this is just marketing hype; it serves to clarify for customers the potential applications.
*I say doesn't usually benefit the process, but there are some plants that have "swing" zones that can be operated either oxically or anoxically depending on the influent conditions. I don't know of an MBBR that is operated this way, but I don't see why it couldn't be. In this case, the flexibility helps the plant adapt to the current conditions.
the two processes are used to degrade two different classes of contaminants in the wastewater stream. the oxic/activated sludge process is nearly universal but depending on the discharge regulations, the anoxic process may be required to meet the regs. this means the plant would have to contain both processes.