A high-rate and stable nitrogen removal from reject water in a full-scale two-stage AMX^® system

This paper reports long-term performance of a two-stage AMX^® system with a capacity of 70 m³/d treating actual reject water. An air-lift granulation reactor performed partial nitritation (PN-AGR) at an average nitrogen loading rate (NLR) of 3.1 kgN/m³-d, producing an average effluent NO₂^--N/NH₄⁺-N ratio of 1.04. The average nitrogen removal rate of the system was 3.91 kgN/m³-d following an anaerobic ammonium oxidation (Anammox) stage moving bed biofilm reactor (A-MBBR). Although the total nitrogen concentrations in the reject water fluctuated seasonally, overall nitrogen removal efficiency (NRE) of the two-stage AMX^® system was very stable at over 87%. The two-stage AMX^® system, consisting of a PN-AGR followed by an A-MBBR, operated at a stable NLR of 1.86 kgN/m³-d (1.64 kgN/m³-d including the intermediate tank), which is 1.8 times higher (1.6 times including the intermediate tank) than other commercialized single-stage partial nitritation/Anammox (PN/A) processes (which operate at a NLR of about 1 kgN/m³-d). The PN-AGR was affected by high influent total suspended solids (TSS) loads, but was able to recover within a short period of 4 days, which confirmed that the two-stage PN/A process is resilient to TSS load fluctuations.