Journal of Hazardous Materials 270 (2014) 160–168 Contents lists available at ScienceDirect Journal of Hazardous Materials jo ur nal ho me p ag e: www.elsevier.com/locate/jhazmat New mechanistically based model for predicting reduction of biosolids waste by ozonation of return activated sludge Siavash Isazadeh, Min Feng, Luis Enrique Urbina Rivas, Dominic Frigon ∗ Department of Civil Engineering and Applied Mechanics, McGill University, 817 Sherbrooke Street West, Montreal, QC, Canada H3A 0C3 h i g h l i g h t s • Biomass inactivation followed an exponential decay with increasing ozone doses. • From pure cultures, inactivation did not result in significant COD solubilization. • Ozone dose inactivation thresholds resulted from floc structure modifications. • Modeling description of biomass inactivation during RAS-ozonation was improved. • Model best describing inactivation resulted in best performance predictions. a r t i c l e i n f o Article history: Received 7 October 2013 Received in revised form 18 January 2014 Accepted 29 January 2014 Available online 5 February 2014 Keywords: Ozone Sludge reduction Biomass inactivation COD transformation Modeling ASM3 a b s t r a c t Two pilot-scale activated sludge reactors were operated for 98 days to provide the necessary data to develop and validate a new mathematical model predicting the reduction of biosolids production by ozonation of the return activated sludge (RAS). Three ozone doses were tested during the study. In addi- tion to the pilot-scale study, laboratory-scale experiments were conducted with mixed liquor suspended solids and with pure cultures to parameterize the biomass inactivation process during exposure to ozone. The experiments revealed that biomass inactivation occurred even at the lowest doses, but that it was not associated with extensive COD solubilization. For validation, the model was used to simulate the tempo- ral dynamics of the pilot-scale operational data. Increasing the description accuracy of the inactivation process improved the precision of the model in predicting the operational data. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Biosolids are the inevitable by-products of wastewater treat- ment, and their management imposes an important operational cost and logistic burden on treatment plants. As a result, signifi- cant efforts have been recently dedicated to the development of technologies that minimizes the production of waste biosolids. One promising technology is the ozonation of return activated sludge (RAS), which uses the oxidation capacity of ozone to break down the biomass and non-degradable constituents of mixed liquor volatile suspended solids (MLVSS) in activated sludge, thus making them bioavailable [1–3]. Despite the fact that ozonation has proven to be an effective process, so far the ability to predict the level of RAS- ozonation performance for the reduction of biosolids has remained limited due to the lack of proper quantitative parameterization of ∗ Corresponding author. Tel.: +1 514 398 2475; fax: +1 514 398 7361. E-mail address: dominic.frigon@mcgill.ca (D. Frigon). ozone reactions. In this paper, we propose a model that is capable of solving this problem. Modeling is a reliable tool in predicting the efficiency of ozonation at reducing waste biosolids. Initial models describing RAS-ozonated activated sludge systems, used either global model constants or pseudo-first-order reaction kinetics to parameter- ize the effect of ozonation on active biomass and non-degradable MLVSS fractions [4–6]. However, these models could not easily incorporate changes in influent chemical oxygen demand (COD) fractionations (e.g., variations in non-degradable particulate frac- tions of MLVSS) or variations in operational conditions such as SRT and temperature with ozone effects on biosolids reduction [2]. Fur- thermore, they were incapable of clearly describing the effects of ozone on the biomass, which precludes any direct model predic- tion of the evolution of biological activities in the systems after the installation of new RAS-ozonation units. Building models based on the International Water Association (IWA) consensus Activated Sludge Models (ASM) can overcome these limitations by taking the specific characteristics of a 0304-3894/$ – see front matter © 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jhazmat.2014.01.053