[Influence of Substrate Exposure Level on ANAMMOX Microbial Activity and Biomass]

Substrate exposure levels are vital for the growth and metabolism of ANAMMOX microorganisms, and their effects on growth characteristics of ANAMMOX sludge during the enrichment process have been rarely reported. Using two continuous flow stirred reactors and the process of a gradually developing nitrogen load, the changes in biomass and activity, as well as nitrogen removal efficiency of the reactors were investigated under high substrate exposure level culture mode (R1:effluent NH₄⁺-N and NO₂^--N concentrations were 40-60 mg·L^-1) and low substrate exposure level culture mode (R2:effluent NH₄⁺-N and NO₂^--N concentrations were 0-20 mg·L^-1). The results showed that the high substrate exposure level culture mode was more beneficial to the improvement of nitrogen removal performance of the ANAMMOX reactor. For comparison, the NLR (nitrogen load rate), which was 0.69 kg·(m³·d)^-1, and the NRR (nitrogen remove rate), which was up to 0.41 kg·(m³·d)^-1, was obtained in the high substrate exposure culture mode. These values were twice as high as those obtained in the low substrate exposure culture mode. Under the culture mode with high substrate exposure level, the sludge concentration (in VSS) and the total gene copy numbers of ANAMMOX reached 1805 mg·L^-1 and 4.81×10¹² copies, respectively, which was conducive to the rapid enrichment of ANAMMOX microorganisms. In the low substrate exposure level culture mode, ANAMMOX sludge was more active,in N/VSS, 0.27 g·(g·d)^-1, which was conducive to the cultivation of ANAMMOX sludge with higher biological activity.