Feeding strategy for single-stage deammonification to treat moderate-strength ammonium under low free ammonia conditions

Single-stage deammonification (SSD) processes have been successfully operated using the step-feeding strategy to treat high-strength NH4+ (>300 mg/L), but often failed to treat moderate-strength NH4+ (100-300 mg/L). Because it is hard to maintain the free ammonia (FA) above 1 mg/L, which is a concentration in which the activity of NO2- oxidizing bac-teria (NOB) can be selectively suppressed. In this study, to evaluate the effectiveness of the step-feeding strategy on the long-term stability of treating moderate-strength NH4+, two SSD sequential-batch reactors (SBRs) were operated under one-step feeding and multi-step feeding strategies. The one-step feeding SBR achieved a higher nitrogen removal effi-ciency (86 %), nitrogen removal rate (0.61 kg/m3/d), and COD removal efficiency (95 %) than the multi-step feeding SBR (73 %, 0.39 kg/m3/d, and 95 %, respectively). This means the appropriate FA to selectively suppress NOB activity was successfully maintained in the one-step feeding SBR (FA > 1 mg/L). Therefore, it the necessary to apply a step feed strategy that can be maintained above FA (1 mg/L) from the start-up of operation to treat moderate-strength NH4 (+).

Automated summary

Single-stage deammonification (SSD) processes have been successful in treating high-strength NH4+ (>300 mg/L) using the step-feeding strategy, but struggle to treat moderate-strength NH4+ (100-300 mg/L). This study evaluated the effectiveness of the step-feeding strategy on the long-term stability of treating moderate-strength NH4+ using two SSD sequential-batch reactors (SBRs). The results showed that the one-step feeding SBR achieved higher nitrogen and COD removal efficiency compared to the multi-step feeding SBR, indicating the importance of maintaining an appropriate FA level to selectively suppress NOB activity throughout the operation.