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. © 2015 Elsevier Ltd. All rights reserved.