Studies on Synthesis of Lactic Acid from Agricultural and Food Wastes in Downflow Stationary Fixed Film (DSFF) Bioreactors

摘要

Lactic acid is the raw material for the manufacture of bio-plastics such as PLLA (Poly Laevo Lactic Acid). However, since lactic acid synthesis has been so far attempted using glucose or lactose solutions as starting materials, the cost of production of this bioplastic is very high. In this project, attempts have been made to study synthesis of lactic acid in a DSFF bioreactor using molasses and cheese whey permeate as substrates. Fermentation is carried out employing Enterococcus faecalis and Lactobacillus helveticus cultures. The performance characteristics of the bioreactor have been studied at different feed flow rates, different cell mass concentration in the biofilm and at different column dimensions. Based on PFDR approach, the bioreactor has been modelled and a simulation package (CAD software) developed (which is subsequently verified by comparing with typical experimental data). Correlations have also been developed to predict the dependence of fractional substrate conversion attained on feed flow rate (capacity of bio-reactor), bioreactor height/volume and cell mass concentration in biofilm. Though demands a large column height, DSFF bioreactors have been observed to provide substantially large substrate conversion (thereby significantly large lactic acid yield) even at high flow rates (high capacities). Since the raw materials employed are agricultural wastes (molasses) and food wastes (cheese whey), the cost of manufacture shall be quite low and this shall promote economical and large scale production of bio-plastics such as PLLA.