ELIMINATION OF NITROGEN IN 2 FLOODED AND STATICALLY PACKED-BED BIOFILTERS WITH AEROBIC AND ANAEROBIC MICROSITES

Nitrogen removal efficiency was studied in a biofilter system consisting of two flooded, statically packed bed biofilters (reactors A and B) with aerobic and anaerobic microsites. During the experimental period the reactors were integrated into a quasi-closed recirculated fish culture system. In two experiments the degradation efficiency of dissolved oxidized nitrogen compounds (NOx-N = N-2(-)-N+NO3--N) was measured with and without oxygen supply. The oxygenation system consisted of silicone membranes integrated into the filter-bed and supplied with technical oxygen. The carbon source during the experimental period was methanol. The efficiency of NOx-N removal for reactor A (without oxygenation) was 55%. With oxygenation, degradation efficiency of reactor A increased to a maximum of 86%. The maximum NOx-N degradation efficiency of both biofilters (reactors A and B) reached 97% when connected in series. Shifting of the bacterial populations as well as a linkage of the nitrogen transformations in the aerated and unaerated microsites are discussed as possible reasons for the higher nitrogen removal rates.