Abstract
The stability of single partial nitritation and anammox (SPNA) granular system at different nitrogen loads was evaluated in two laboratory-scale continuous stirred tank reactor (CSTR) reactors (R1with lower influent ammonium concentration, R2 with higher concentration). The effects of different transient substrate shock (50 mg N/L and 100 mg N/L) on the bacteria population structure, nitrogen removal and granular sludge properties of the system were studied. Results showed that R1 had a better resilience, and the average removal efficiencies of TN and ammonium can recover to 66.5 % and 73.9 % after two shocks, while nitrogen performance of R2 deteriorated. The inhibition of free nitrous acid (FNA) to functional bacteria was the key factor influencing reactor performance. When FNA concentration exceeded 2 μg/L, FNA/MLVSS > 1.5 μg/g VSS, the inhibition was irreversible. Moreover, excessive substrate shock changed extracellular polymeric substances (EPS) production and composition, which led to granules disintegration. The formation and disintegration mechanism of SPNA micro-granules were also investigated.
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