The influence of attached biomass bioreactor types on the denitrification process using a low-pitched
groundwater containing nitrates was studied. Two types of fixed-bed and fluidized-bed biofilm reactors,
equipped with expanded clay granular filler, with a particle size fraction of 2-5 mm were used. The nitrite
and nitrate concentrations in the inflow and outflow of the two bioreactors were analytically determined.
Based on the obtained concentration values, the denitrification rates were calculated, ranging between
1275÷1387 g NO3 N/m3/day in the case of the fixed bioreactor and between 3390÷3867 g NO3 N/m3/day in the case of the fluidized bed bioreactor.