| Abstract
| - This paper presents the main results obtained during several years of studies with periodicallyfed biological reactors (sequencing batch reactors, SBRs) from the perspective of wastewatertreatment. Substrate (acetate) removal mechanisms under transient conditions were studiedboth in the SBR and in batch tests, as were their dependence on the applied operating conditionsin the SBR (organic load rate and/or sludge age, feed length, aerobic or anoxic conditions). Themost general evidence was the relevant role of storage (usually representing about 70% of theoverall observed yield) and the negligible role of growth (usually less than 10%) during acetateremoval for all tested conditions. However, when acetate was present for a long enough time,physiological adaptation could occur, and the growth contribution could become more important.The applied operating conditions affected the biomass behavior. In particular, with an increasein the applied organic load rate, the observed yield in the SBR and the acetate removal rate inthe batch tests decreased, whereas with an increase in the feed length (other conditions beingthe same), the relevance of the storage response decreased. The role of dynamic conditions inselecting a floc-forming or filamentous biomass was also investigated. Even though a floc-formingbiomass usually developed, filament growth was also sometimes observed. Thus, the usualassumption that filaments are less able than floc-formers to store the substrate should not beconsidered as an absolute rule. Finally, an empirical kinetic model, including growth and storageboth in parallel and in sequence, was defined and applied to describe and interpret theexperimental results.
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