 The other method is to produce an oxygen gradient within the bio floc.The DO concentration remains high in the outside rings of the floc where nitrification occurs but low in the inner rings of the floc where denitrification occurs.This method is dependent on the floc size and characteristics; however controlling flocs is not well understood and is an active field of study

Typically, SNdN has slower ammonia and nitrate utilization rates as compared to separate basin designs because only a fraction of the total biomass is participating in either the nitrification or the denitrification steps.