Typically the media utilised ...

Typically the media utilised in MBBR systems that I have encountered have a fixed density that allows the media to float and be mobile relative to a balanced amount of energy that is transferred into the process, I am not certain if these shells will change in character and subsequent density the longer they are submerged in the wastewater, changing the dynamics of the process? The plastic media utilised is readily available these days, globally.

Hope this helps