Respirometric needs of heterotrophic populations developed in an immersed membrane bioreactor working in sequenced aeration

The aim of this work is first to determine the respirometric needs of heterotrophic populations developed in a submerged membrane bioreactor (MBR) working in sequenced aeration (BIOSEP ® process). The oxygen needs were quantified in known conditions of substrate nature and concentration. The respirometric parameters were measured in a particular system, called Respir’Eaux. Samples of the biological suspension were taken from the BIOSEP ® process and introduced into the Respir’Eaux in which the oxygen supply was controlled. First experiments, carried out without any substrate addition, showed that: (i) endogenous needs remained approximately constant during the 5 months of study, showing an apparent stability of the culture; (ii) exogenous needs were very variable, supposedly because the culture was subjected to very variable biodegradable substrate material flows. With the aim of better underlining the importance of the nature and the concentration of the available substrate, experiments were performed from biomass samples subjected to the addition of specific nutrients (acetate and calibrated fractions of municipal wastewater). The results showed that: (i) oxygen needs depend directly on the nature and the quantity of added substrate; (ii) oxygen needs depend on the acclimation of the micro-organisms to the added substrate; (iii) in the experimental conditions investigated, oxygen needs demonstrate the complete oxidation of the soluble organic fraction of the wastewater by the MBR suspension, although this part may contain recalcitrant compounds for conventional biological culture.