Stoichiometric variation and loading capacity of a high-loading anammox attached film expanded bed (AAEEB) reactor

[Display omitted] •The AAFEB reactor was successfully operated at high loading rate up to 50 gN/L/d.•Anammox stoichiometric equations changed with the increase of loading rate.•The heme C content had a quantitative relationship with anammox activity.•Long-term operation at high loading rate enhanced the substrate tolerance ability.•The (Food/Microorganism)/SAA ratio should be kept lower than 66 ± 7%. The nitrogen loading rate (NLR) of an anammox attached film expanded bed (AAFEB) reactor was increased from 5.0 to 60.0 gN/L/d. During the stable operational period, the TN removal efficiency maintained at 87.3 ± 2.5%, and a maximum nitrogen removal rate (NRR) of 44.9 ± 0.3 gN/L/d was achieved. Overload resulted in the sharp deterioration of reactor performance, the ratio of (Food/Microorganism)/SAA should be maintained at lower than 66 ± 7% to ensure the stable operation of the AAFEB reactor. New stoichiometric equations for the anammox process under the low NLR condition (5.0 gN/L/d) and the high NLR condition (50.0 gN/L/d) were proposed. The quantitative SAA-cytochrome heme C relationship was established for the first time that providing a simple way for monitoring the reactor performance. Substrate tolerance ability was significantly increased that proving the stability of the AAFEB reactor was continuously enhanced during the stable operational periods.