Monday, May 2, 2011
Grand Ballroom C-D, 2nd fl (Sheraton Seattle)
The cost of cellulase enzymes is one of the major bottlenecks on the economics of cellulosic ethanol. Enzyme production can be carried out using submerged (SmF) or solid-state fermentation (SSF). Each process has different advantages and disadvantages. In this study, we are evaluating celullase production in a combined fermentation process, which aggregates the advantages of SSF and SmF in one equipment, a pneumatic bioreactor. Due to the difficulties in measuring cellular biomass in the presence of solids, we developed a methodology for indirect quantification of this biomass. The cultivation of Aspergillus niger was initiated as SSF using sugar cane bagasse as solid substrate and a liquid medium containing glucose was added after 24h of growth. Samples were collected during 72h and the glucose consumed was quantified. Experiments in liquid medium in the absence of bagasse were conducted in parallel for the determination of the growth kinetic parameters by measuring both variations on glucose and biomass during the cultivation. The software Anabio 1.2 was used to simulate a simple unstructured model. The simulations showed that the growth followed the Contois model, with μmax of 0,034h-1, Yx/s of 0,297g/g and death constant of 0,005h-1. The model parameters were used to simulate the profile of glucose consumption and generate the simulated profile of cellular growth in the medium containing solids. The developed methodology for indirect quantification of biomass showed to be reliable, since the proposed model fitted very well to experimental data and only one parameter needed to be adjusted.