Storage of substrate mixtures under dynamic conditions in anoxic or aerobic environments

In spite of the fact that in most activatedslud ge plants substrate complex mixtures are removedund er alternating anoxic and aerobic conditions, most studies on the dynamic response of biomass are limited to feeding a single substrate (acetate or glucose) under a single redox condition (aerobic or anoxic). In this study, the dynamic response of biomass in a sequencing batch reactor is described in terms of substrate removal and related storage as internal polymers, as functions of single or simultaneous feedof several substrates (acetate, glucose, glutamic acidandethanol) andof anoxic vs. aerobic conditions. Under anoxic conditions, the four substrates were simultaneously removed at a significantly greater nitrate removal rate than when single substrates were present, so showing that the simultaneous removal was partially due to independent metabolic activities. On the other hand, the removal of every substrate was affected (positively or negatively) by the presence of the others, demonstrating that the substrates can be also used by the same metabolism. As an exception, acetate removal was not affectedby the presence of other substrates. As for the comparison of aerobic and anoxic conditions, the acetate uptake rate almost doubled moving from anoxic to aerobic conditions, whereas other substrates were only slightly affected. This difference was probably due to the additional presence of aerobic denitrification, which was much more important for acetate. This also confirmed that acetate removal was independent from other substrates. In all cases, storage was the main mechanism of solids formation, so confirming the general importance of such phenomenon under dynamic conditions, independently from feed complexity and redox conditions.