Development of enhanced SNAD process in a down-flow packed bed reactor for removal of higher concentrations of NH4–N and COD

• Development of enhanced SNAD using non-acclimatized anammox biomass.
• Enhanced rate of nitrogen removal (2.5 g N/L d) in a down-flow packed bed reactor.
• High-rate COD removal (4.9 g/L d) at 3 h HRT and in DO ≤ 0.35 mg/L.
• No due external addition of alkalinity for ammonia oxidation even @ 2.8 g NH4–N/L d.
• Competitive involvement of anammox (∼50%) and denitrification (∼50%) in N removal.

Enhanced simultaneous partial nitrification, anammox and denitrification (SNAD) process was developed using a 2.4 L down-flow packed bed reactor for removing higher concentrations of ammonia and chemical oxygen demand (COD) (at COD/NH4–N ratio = 1.0) in low dissolved oxygen concentrations (≤0.35 mg/L). SNAD was developed using flocculent type activated sludge sourced from a tannery common effluent treatment plant and the reactor was operated continuously for 122 d at various loading rates with hydraulic retention time (HRT) varied between 12 h and 3 h. The reactor was operated in room temperature and the liquid temperature varied between 28 and 32 °C. The performance of the reactor at 3 h HRT showed enhanced removal rates of NH4–N (2.8 g/L d), total nitrogen (2.5 g/L d) and COD (4.9 g/L d) at ammonia and COD loading rates of 5.4 g/L d. The nitrogen removal was due to the competitive involvement of anammox (∼50%) and denitrification (∼50%) and these processes were confirmed by conducting separate batch experiments. There was no external addition of alkalinity at higher loading rates corresponding to the requirement of oxidation of NH4–N. This study demonstrates SNAD for enhanced rate of removals of NH4–N and COD at high concentrations compared to the reported results in literature and indicates a potential application.