Comparative Kinetic Studies and Performance Evaluation of Biofilm and Biomass Characteristics of Pseudomonas fluorescens in Degrading Synthetic Phenolic Effluent in Inverse Fluidized Bed Biofilm Reactor S. Sabarunisha Begum 1 * and K. V. Radha 2 ABSTRACT: The bioremediation potential of Pseudomonas fluores- cens was studied in an Inverse Fluidized Bed Biofilm Reactor under batch recirculation conditions using synthetic phenolic effluent of various concentrations (400, 600, 800, 1000 and 1200 mg/l). The performance of the reactor was investigated and the characteristics of biomass and biofilm were determined by evaluating biofilm dry density and thickness, bioparticle density, suspended and attached biomass concentration, chemical oxygen demand and phenol removal efficiency. Biodegradation kinetics had been studied for suspended biomass culture and biofilm systems with respect to its specific growth and substrate consumption rates. Suspended biomass followed substrate inhibition kinetics and the experimental data fitted well with the Haldane model. The degradation kinetic behavior of biofilm revealed that a well adapted biofilm system with effective control of biofilm thickness in an inverse fluidized bed biofilm reactor overcomes substrate inhibition effects by tolerating higher phenol concentration and fitted well to the Monod model. Water Environ. Res., 88, 415 (2016). KEYWORDS: biodegradation, kinetics, biofilm, phenolic compounds, inverse fluidized bed, Pseudomonas fluorescens, substrate inhibition. doi:10.2175/106143016X14504669768417 Introduction Phenol represents a model organic pollutant for the study of biodegradation of recalcitrant compounds; it has been widely studied, resulting in a large amount of data being available (Hill and Robinson, 1975; Sekar et al., 1997; Kumaran and Paruchuri, 1997; Bultron et al., 1998; Kapoor et al., 1998; Hannaford and Kuek, 1999; Peyton, 2002; Lin, 2008). Most of the data available on phenol biodegradation is based on free suspended cultivation of microbial cells (Kumar et al., 2005; Jing Bai et al., 2007). However, the use of immobilized cells or biofilm has proved to be much more efficient because of higher cell concentration per unit volume of the bioreactor, higher cell resistance to the toxic effect of phenol and to variations in temperature and pH, and the higher degree of process robustness in general (Tang and Fan, 1987). Especially promising is the use of natural immobi- lized cells or biofilm. Several different types of biofilm reactors have been studied, including rotating disk bioreactors, fixed bed reactors and three phase fluidized bed bioreactors. The latter are considered superior because of large biofilm support surfaces, appropriate hydrodynamic conditions, high mass transfer rates of both oxygen and substrate and excellent contact between the liquid and solid phases (Schugerl, 1997; Reese et al., 1999; Boumehdi Toumi et al., 2008; Daugulis, 2011). However, one significant problem in practically all types of biofilm reactors, including fluidized-bed reactors, is uncontrolled biofilm growth (Sokol and Korpal, 2004, 2006), which limits the diffusion of oxygen and/or the organic substrate to the deeper layers of the biofilm. The use of the Inverse Fluidized Bed Biofilm Reactor (IFBBR) can overcome this problem (Kryst and Karamanev, 2001; Karamanev, 1996) and maintain constant thickness of biofilm over the entire period of operation. In this work, the behavior of a three phase (solid-liquid-gas) inverse fluidized bed biofilm reactor for biodegradation of synthetic waste water containing phenol of various concentra- tions using indigenous pure culture of Pseudomonas fluorescens was examined. The reactor was designed in order to achieve simple and efficient control of biofilm growth. The character- istics of biomass and biofilm attached to solid particles were determined in IFBBR and found the biodegradation potential of P. fluorescens in degrading synthetic phenol waste of higher concentration range. Kinetic studies were analyzed for suspend- ed biomass and biofilm culture with respect to specific growth rate and specific phenol consumption rate, which have not been discussed in combination in any other earlier studies. The main objectives of the present study are:  To investigate the performance of inverse fluidized bed biofilm reactor (IFBBR) for phenol degradation and to study the biofilm and biomass characteristics of P. fluorescens  To analyze the growth kinetics for suspended biomass and biofilm culture for its substrate inhibition effect with 1 Department of Biotechnology, Rajalakshmi Engineering College, Thandalam, Chennai – 602105, Tamil Nadu, India 2 Department of Chemical Engineering, A C College of Technology, Anna University, Chennai – 600 025, Tamil Nadu, India * Department of Biotechnology, Rajalakshmi Engineering College, Thandalam, Chennai – 602105, Tamil Nadu, India; email: sabarunisha@gmail.com May 2016 415