Studies on Performance Characteristics of Diverging – Converging Fluidized Bed Biofilm Reactor with Special Reference to Lactic Acid Synthesis from Molasses and Cheese Whey

Abstract

Attempts have been made to study the synthesis of lactic acid by microbial fermentation of molasses and cheese whey permeate in a fluidized bed bioreactor of diverging – converging geometry. The reactor core consists of support particles (polymer beads) each surrounded by a thin film of microbial solution (Enterococcus Faecalis culture in case of molasses and a culture of Lactobacillus helveticus in case of cheese whey permeate) and these particle – biofilm aggregates remain fluidized in the ascending stream of the feed solution. The core is composed of three segments each of length LS and the feed solution is admitted from the bottom at the minimum cross – section. The angle of convergence / divergence is maintained constant at 50 throughout the length of the column. The performance of the bioreactor is analysed mathematically by developing a simulation model that assumes dispersed flow through the reactor, with continuous change of superficial fluid velocity along the length (height) of the reactor column. The performance equations are solved using a specially developed numerical algorithm NUMCM that involves a modified form of Runge – Kutta method. Solution using line successive over – relaxation (SOR) method has also been attempted. Extensive experimental data have also been collected using a laboratory bioreactor of proposed geometry. Excellent agreement has been observed between results computed using the software package developed and the experimental data compiled (maximum deviation = ∓ 10%). It has also been observed that the bioreactor of proposed design provides distinctly superior performance (provides 20 to 25 % higher fractional conversion of substrate) when operating at the same feed flow rate and feed inlet concentration as compared to a conventional fluidized bed of same reactor volume.
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