Effects of HRT on biological nitrogen removal in single-stage autotrophic process

Abstract

An external circulation Sequencing Batch Reactor (ecSBR) was used to study the efficiency of nitrogen removal by autotrophic microbe. With gradually reducing the dissolved oxygen (DO) concentration from 1.2 mg/L to 0.04 mg/L, the single-stage autotrophic biological nitrogen removal (sABNR) process could be operated stably. After removing the aeration, the process could still stay sABNR stably, and the concentration of NH4+-N was 0.9 mg/L in effluent, the rate of nitrate (produced)/NH4+-N (removed) was in the range of 0.12–0.40. The results showed that the concentration of NH4+-N in effluent was 0.8, 0.8 and 9.9 mg/L with the hydraulic retention time (HRT) at 8 h, 6 h and 4 h respectively, the removal efficiency of ammonia were 98.2%, 98.1% and 73.6% respectively. The rate of nitrate (produced)/NH4+-N (consumed) was 0.05 at HRT 6 h, and the nitrogen loading rate (NLR) and nitrogen removal rate (NRR) were 169.7 and 129.7 g/m3/d, the removal efficiency of total nitrogen (TN) was 77.5%. In conclusion the optimal HRT was 6 h instead of 8 h or 4 h enough for ammonia removal without causing energy wastage.