Study of the relationship of rheology, morphology and biomass concentration of Trichoderma reesei fermentation

Abstract

Bioethanol produced from cellulosic materials, abundantly found as wastes, appears to be a viable alternative to fossil fuels. Cellulose is a glucose polymer and must undergo a hydrolysis step by cellulase enzymes prior to be used for bioethanol production. In order to make bioethanol more cost competitive, all aspects of the production are being examined, including trying to improve the production of these enzymes using a filamentous microorganism, Trichoderma reesei. Filamentous fungi broth is widely known for being highly viscous, which limits transport properties, thus hindering the production of cellulase. Therefore, the overall objective of this work is to understand the intimate relationship that exists between enzyme production, morphology of microorganism, rheology of the broth and operating conditions. In this work, the rheology of the fermentation broth is examined in order to understand its impact on the other process variables. As a preliminary step, the choice of an appropriate rheological instrument was discussed. Fed-batch fermentation runs were performed in two bioreactors: a stirred tank bioreactor with an agitation speed of 200, 300, 400 and 500 RPM and a reciprocating plate bioreactor agitated at 0.25, 0.50, 0.75 and 1.00 Hz. Herschel-Bulkley equation described relatively well rheological data. The effect of morphology and biomass concentration (X) on the consistency index (K) was studied separately. Biomass reconstitution experiments showed that biomass exponent alpha, in K/Xalpha, remained constant. K/X alpha varied during the course of the fermentation runs, underlying the importance of including a morphological parameter in the prediction of K. Although several morphological parameters were analyzed, K/Xalpha was found to correlate well with the average roundness, when the batch and the fed-batch data were considered separately. Parity plot analysis of the models showed good prediction of the experimental K.