Ødegaard was suggesting ...

Ødegaard was suggesting higher values (if I remember well up to 60%). Anyways I should start with the load of pollutants to remove. Depending on the process you have several parameters to consider (for ex Carbon and oxygen if you are removing nitrogen), from here you see the pollutant load rate (how much gram per m2 of surface per hour) and finally the amount of m2 you need. This means that with the specific surface (surface available for m3) you can see the volume you need of carriers (COST n.1). This volum should be aroud 50%-60% of your reactor, so you can design the reactor (COST n.2). Choose a carbon source if you need it (for ex. in denitrification) (COST n,3) and the aeration rate (for ex Qair = 60% Qwater), so choose the blowers (or the mixer, in denitrification) (COST n4). This is very very basic, there should be also piping, recycling pumps and so on, but it depends on the process scheme you choose