Performance of nitrogen removal in attached growth reactors with different carriers

Two waste materials, concrete and sponge, were used as biomass carriers in the attached growth reactor in a nitrogen wastewater treatment system. The nitrogen removal performance was compared to a control reactor using commercial carrier material. The highest nitrogen removal efficiency, 87%, was found in the sponge reactor, with the concrete reactor showing 82% efficiency ahead of the commercial reactor of 76%. A thick biofilm developed on the fiber of the sponge carrier, with the biomass increasing from 270 g-VSS/m3-carrier to 1,000 g-VSS/m3-carrier. For the concrete carrier, biomass was observed on the concrete cracks and also as a biofilm on the surface. The maximal biomass was 630 g-VSS/m3-carrier. The content of the biomass agglomerated in the commercial carrier was 310 g-VSS/m3-carrier. Nitrification and denitrification simultaneously occurred to remove nitrogen in the sponge and the commercial carrier reactor. However, in the concrete reactor, nitrification mainly occurred during the aeration phase and denitrification occurred in the non-aeration phase. These results demonstrate that the sponge was the best carrier, with high nitrogen removal efficiency, dense biomass and tolerance to shock loading. The simplicity inherent in the system design together with good performance make it suitable for use in wastewater treatment systems.