Sludge reduction by ozone: Insights and modeling of the dose-response effects.

Applying ozone to the return flow in an activated sludge (AS) process is a way for reducing the residual solids production. To be able to extend the activated sludge models to the ozone-AS process, adequate prediction of the tri-atoms effects on the particulate COD fractions is needed. In this study, the biomass inactivation, COD mineralization, and solids dissolution were quantified in batch tests and dose-response models were developed as a function of the reacted ozone doses (ROD). Three kinds of model-sludge were used. S1 was a lab-cultivated synthetic sludge with two components (heterotrophs XH and XP). S2 was a digestate of S1 almost made by the endogenous residues, XP. S3 was from a municipal activated sludge plant. The specific ozone uptake rate (SO3UR, mgO3/gCOD.h) was determined as a tool for characterizing the reactivity of the sludges. SO3UR increased with the XH fraction and decreased with more XP. Biomass inactivation was exponential (e-β.ROD) as a function of the ROD doses. The percentage of solids reduction was predictable through a linear model (CMiner + Ysol ROD), with a fixed part due to mineralization (CMiner) and a variable part from the solubilization process. The parameters of the models, i.e. the inactivation and the dissolution yields (β, 0.008-0.029 (mgO3/mgCODini)-1 vs Ysol, 0.5-2.8 mg CODsol/mgO3) varied in magnitude, depending on the intensity of the scavenging reactions and potentially the compactness of the flocs for each sludge.