Low hydraulic retention time (HRT) and high sludge retention time (SRT)

High bed costs

low sludge production

Requires high concentration of dissolved oxygen in biofilm reactors for denitrification

high resistant to toxic materials

constant active biological biomass

Congestion problems in the fixed beds

Low sensitivity to temperature and amount of sludge production

nitrification in low temperature

Removal of high amount of nutrients

Nitrification and denitrification can simultaneously occur on both exterior and interior sides of a biofilm