Transient and long-term effects of bicarbonate on the ANAMMOX process

In this study, the effects of both transient and long-term inorganic carbon (IC) addition on the anaerobic ammonium oxidation (ANAMMOX) process under pseudo-steady-state and substrate inhibitions were analyzed using reactor performance and measures of sludge activity. Compared with the nitrogen removal rate (NRR) of 3.42 kg N m−3 day−1 in the control bioreactor (ICDR) without IC, the peak NRR reached 21.0 kg N m−3 day−1 in the reactor (ICAR) with sufficient IC added. It was revealed that the long-term addition of bicarbonate significantly enhanced the performance of the ANAMMOX reactor. The optimum HCO3 −/TN ratio was considered to be 1.20, which is lower than that in normal conditions. The IC concentration affected biomass activity, and the transient addition or removal of IC to differing sludge media caused a significant loss of activity. Sufficient addition of IC alleviated the inhibition of excess substrates, while the inhibition was aggravated by the IC limitation. The half-maximal (50 %) inhibitory concentrations of substrate for the sludge were 295 mg L−1 NO2 −–N and 361 mg L−1 NH4 +–N with 120 mg L−1 of fixed HCO3 − and 346 mg L−1 NO2 −–N and 456 mg L−1 NH4 +–N with unlimited IC, respectively. Changing the HCO3 −/TN (in milligrams per milligram) ratio resulted in the variation of ANAMMOX stoichiometric ratios. Sludge characterization parameters in the ICDR, including biomass, extracellular polymeric substances, heme C, and so on, were lower than those in ICAR. Filamentous bacteria and spherical bacteria were also observed in the reactor with limited IC.