TRACKING IMPORTED NITRIFYING BIOMASS IN COLD SEQUENCING BATCH REACTORS USING FISH

Nitrifying seed acclimated to 10 and 20°C were added to two different sequencing batch reactor (SBR) systems. One set of SBRs was operated with a short solids retention time (4 days) while another set was operated with a long SRT (12 days) and an HRT of 8 hours. Neither of the systems were nitrifying before seeding was initiated. Full nitrification was achieved in the SBRs with an SRT of 12 days while NH3-N removal in the reactors with an SRT of 4 d was insignificant despite daily addition of nitrifying seed. FISH analysis showed that the ammonia oxidizing bacterial (AOB) community increased as a result of seeding and correlated well with nitrification rates in the reactors with an SRT of 12 d. AOBs acclimated to 10°C were not washed out of the system after seeding was stopped as indicated by FISH analysis and the continuation of full NH3-N removal. FISH analysis also showed that AOBs did not settle well and were being washed out of the system with the effluent. The proportion of AOBs in the effluent was higher than that in the reactor mixed liquor.