The application of tertiary anammox biofilter for energy-efficient short-cut nitrogen removal

BKT’s BioFiltration (BBF) is an up-flow biological aerated filter (BAF) system that uses expanded polypropylene (EPP) media for maximizing biomass growth and particle filtration. Coincidently, total inorganic nitrogen (TIN) loss (25~30%) was observed in a nitrifying BBF pilot system (V=330L) from a non-nitrified secondary effluent of a high purity oxygen activated sludge (HPOAS) system. Distinctive red granules were coincidently discovered at the BBF backwash holding tank. The anammox bacteria (AnAOB) population at the BBF backwash was confirmed based on quantitative PCR and clone library targeting 16S rRNA genes. The anammox biofiltration (AMX BBF) pilot was operated with nitrite-amended secondary effluent (NH4-N=37.9±2.2 mg N/L, NO2-N=50.2±13.3 mg N/L) under anaerobic condition. Within 40 days of AMX BBF, nitrogen removal rate (NRR) and % N removal have exponentially increased up to 1.5 kg N/m3/d, and 90% TIN removal, respectively. Increased N loading (at 20 min. empty bed contact time: EBCT) resulted in up to 5.4 kg N /m3/d of NRR. 0.12 day-1 of maximum AnAOB growth rate (μmax) was determined, which corresponded 5.8 days of doubling time. The results so far allowed us to provide an insight into the feasibility of an energy-efficient anammox bio-filtration at the mainstream with non-nitrified secondary effluent. In addition, a low effluent turbidity from AMX BBF would enable to reduce the additional cost for post treatment while implemented in water reuse.