JOURNAL OF ENVIRONMENTAL PROTECTION SCIENCE (2008), Vol. 2, pp. 81 – 86. Performance of Batch Stirred Tank Bioreactor and Internal Loop Airlift Bioreactor in Degrading Phenol using Pseudomonas spp.-A Comparative Study Pichiah SARAVANAN a , Kannan PAKSHIRAJAN b , Prabirkumar SAHA a, * a Department of Chemical Engineering, Indian Institute of Technology Guwahati, Assam-781039, India; b Department of Biotechnology, Indian Institute of Technology Guwahati, Assam-781039, India __________________________________________________________________________________ Abstract Performance of two bioreactors namely batch stirred tank reactor (BSTR) and internal loop airlift reactor (ILALR) was evaluated in degrading phenol using Pseudomonas spp. and compared. A mixed culture of microorganisms, isolated from a sewage treatment plant, has been used to study the phenol degradation and culture growth kinetics. The BSTR took a maximum of 8 days to degrade the phenol completely with maximum initial concentration of 400 mgl -1 ; where as ILALR took only 47 h to degrade phenol with a maximum initial concentration 600 mgl -1 . The rate of culture growth and phenol degradation expressed in terms of specific growth rate μ and specific degradation rate q respectively and calculated at various concentrations of phenol, demonstrated substrate inhibition behaviour. The biokinetic parameters were evaluated by fitting the experimental data to Haldane deterministic model. Based on the findings obtained in the study, the mixed microbial culture showed a better potential in degrading phenol in an ILALR than BSTR. Keywords: Batch stirred tank reactor; internal loop airlift reactor; biodegradation; phenol; substrate inhibition JEPS (2008), Vol. 2, pp. 81 – 86. __________________________________________________________________________________ Introduction Synthetic organic chemicals like phenols and their derivatives lead to serious environmental contamination because of their toxicity towards aquatic biota. Various industries such as pulp and paper mills, herbicides and fungicides production etc, contribute phenols in their aqueous effluents [1,2,3]. The growing concern for aquatic contamination in the environment has led to quest for better wastewater treatment methods. Among the available treatment methods for phenolics in wastewater, microbe- based degradation of phenols appears to be more promising [4,5,6]. Aerobic degradation of phenol using pure microbial cultures has been studied extensively in batch shake flask [3,4,5,6]. However, aerobic degradation with a mixed culture consortium degrades phenol completely and does not leave any hazardous residues in … the process. However, the successful applications of biological method for wastewater treatment often rely on the type of reactor system employed. For example, biological treatment of phenolics in conventional activated sludge seldom fails to achieve high efficiency in removing recalcitrant due to their toxic nature. In late 70s, batch stirred tank bioreactors were employed for such treatment application owing to their simplicity in construction and operation [7]. But in recent years, airlift bioreactors (generally employed for fermentation) have become popular for same purpose. The major advantage of airlift bioreactors is that they do not need any mechanical agitation. It requires only aeration which serves both as oxygen supply as well as mixing with low energy input for its operation [7]. In general, an internal loop airlift reactor is essentially a bubble column with a baffle or a draught tube separating the rising fluid from the sinking fluid. It is *To whom all correspondence should be addressed: Tel/Fax: +91.361.2582257; E-mail: p.saha@iith.ernet.in (Prabirkumar SAHA) 81