Evaluation of a new model for the reduction of excess sludge production by ozonation of return activated sludge: what solids COD fraction is affected?

摘要

This paper aims at clarifying the effect of ozone on the RAS solids to model activated sludgensystems equipped with RAS-ozonation processes for the reduction of sludge production. Ancommon hypothesis is that ozone only affects active biomass by promoting cryptic growth. Datanfrom a pilot-scale study were used to test this and two other model extensions to IWA-ASM3. Allnmodel extensions were able to simulate the observed linear reduction in sludge production withnincreasing ozone dose when the MLVSS are kept constant. However, model simulations showednthe inconsistency of the cryptic growth hypothesis with the extent of sludge reduction. Thensecond tested model extensions assumes that ozone affects all the solids fractions (activenbiomass, endogenous residue, and influent inert particulate COD) equally. This extension couldnproperly simulate the observed sludge reduction, but it failed to predict the trends in effluentnBOD5, ATP/VSS, and nitrification rates. A third tested model extension, which performed better,nassumes that biomass is inactivated at a specific rate higher than the specific rate ofntransformation by ozone of the other solids fractions. Finally, the predictions from this modelnextension were most accurate if either (i) the nitrifiers were inactivated at a lower rate thennheterotrophs, (ii) the nitrifiers model parameters (e.g., maximum growth rate) were changed undernozone (i.e., metabolic adaptation, (iii) or both.