Biochemical Engineering Journal 53 (2011) 266–274 Contents lists available at ScienceDirect Biochemical Engineering Journal journal homepage: www.elsevier.com/locate/bej Oxygen transfer during aerobic biodegradation of pollutants in a dense activated sludge slurry bubble column: Actual volumetric oxygen transfer coefficient and oxygen uptake rate in p-nitrophenol degradation by acclimated waste activated sludge Ryo Mineta a , Zeinab Salehi a , Hidemi Yoshikawa b , Yoshinori Kawase a,∗ a Research Center for Biochemical and Environmental Engineering, Department of Applied Chemistry, Toyo University, Kawagoe, Saitama 350-8585, Japan b Education Support Center of Experiment and Training for Students, Tokyo Institute of Technology, Meguro, Tokyo 152-8550, Japan article info Article history: Received 10 October 2010 Received in revised form 16 November 2010 Accepted 20 November 2010 Available online 2 December 2010 Keywords: Volumetric oxygen transfer coefficient Oxygen uptake rate Aerobic biodegradation Acclimated waste activated sludge Slurry bubble column abstract Volumetric oxygen transfer coefficient and oxygen uptake rate in a dense activated sludge slurry bub- ble column were measured by varying activated sludge concentrations (from 2000 to 8000 mg/L) and/or aeration rates (from 0.3 to 1.5 L min -1 ). They were separately determined by the dynamic methods. The endogenous oxygen uptake rate of the activated sludge was estimated by monitoring the dissolved oxygen concentration change after turning off the air sparging in a stirred tank. The volumetric oxygen transfer coefficient in a dense activated sludge slurry bubble column was determined using the dissolved oxygen concentration profiles and the oxygen uptake rates predetermined from the separate measurements. While the oxygen uptake rate almost linearly increased with increasing the activated sludge concen- tration, the volumetric oxygen transfer coefficient decreased with an increase in the activated sludge concentration. Their empirical correlations were obtained as functions of activated sludge concentration by fitting the experimental data. For the aerobic biodegradation of p-nitrophenol (PNP) by acclimated waste activated sludge, the dynamic models for the dissolved oxygen mass balance and PNP degradation kinetics with the pro- posed correlations for volumetric oxygen transfer coefficient and oxygen uptake rate could successfully simulate the concentration profiles of dissolved oxygen and PNP during the time course of an aerobic biodegradation of PNP. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Aerobic wastewater treatment processes require systems which ensure the adequate oxygen supply while minimizing the power requirement. For the maintenance and growth of micro-organisms, the total oxygen transfer rate must exceed or at least coincide with the total oxygen consumption rate by micro-organisms. There- fore, to maintain sufficient dissolved oxygen concentration is extremely critical for industrial aerobic wastewater treatment and oxygen transfer is an important parameter governing the aero- bic biodegradation of pollutants in wastewater (e.g., [1–3]). Since, however, a few studies have been published on the oxygen trans- fer in dense suspensions of micro-organisms [3–7], the published literature does not yet give complete understanding of oxygen transfer in dense micro-organism suspensions. Pneumatically agi- tated columns, bubble columns and airlift columns, have been ∗ Corresponding author. Tel.: +81 492 39 1377; fax: +81 492 31 1031. E-mail address: ykawase@toyonet.toyo.ac.jp (Y. Kawase). attractive as bioreactors for slurry fermentation systems because of their simple design, satisfactory mixing and efficient oxygen trans- fer [1]. Recently, Germain et al. [8] and Henkel et al. [9] examined the oxygen transfer in membrane bioreactors and measured the volumetric gas–liquid mass transfer coefficient (k L a) in a bubble column with changing biomass concentration and gas flow rate. In their studies, gas–liquid mass transfer rate was found to decrease with increasing biomass concentration. However, both of them did not present quantitative analyses based on mixing and solid sus- pension in a bubble column and correlations for the estimation of the k L a coefficient. Consequently, more systematic investigation of oxygen transfer and oxygen uptake in dense slurry bubble column bioreactors is required. There has been much concern with the environment polluted by enormous quantities of organic and inorganic toxic compounds, which are common constituents of aqueous effluents from indus- tries. The use of mixed cultures having a wider spectrum of metabolic properties has been recommended to prevent the pro- duction of toxic intermediates during biological degradation rather than pure cultures. Furthermore, the waste activated sludge can 1369-703X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.bej.2010.11.006