An innovative respirometric method to assess the autotrophic active fraction: Application to an alternate oxic–anoxic MBR pilot plant

• Heterotrophic metabolic activity was not affected by the duration of aerated phase.
• The aerated phase increase resulted in a higher autotrophic biomass development.
• A novel respirometric method to estimate the autotrophic active fraction was proposed.
• Microbiological FISH analyses revealed the validity of proposed method.

An innovative respirometric method was applied to evaluate the autotrophic active fraction in an alternate anoxic/oxic membrane bioreactor (MBR) pilot plant. The alternate cycle (AC) produces a complex microbiological environment that allows the development of both autotrophic and heterotrophic species in one reactor. The present study aimed to evaluate autotrophic and heterotrophic active fractions and highlight the effect of different aeration/non aeration ratios in a AC-MBR pilot plant using respirometry. The results outlined that the autotrophic active fraction values were consistent with the nitrification efficiency and FISH analyses, which suggests its usefulness for estimating the nitrifying population. Intermittent aeration did not significantly affect the heterotrophic metabolic activity but significantly affected the autotrophic biomass development. Finally, the heterotrophic active biomass was strongly affected by the wastewater characteristics, whereas the resultant autotrophic biomass was considerably affected by the duration of the aerated phase.

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