Cultivation of different microalgae with pentose as carbon source and the effects on the carbohydrate content.

In the search for alternative carbon sources for microalgae cultivation, pentoses can be considered interesting alternatives since the most abundant global source of renewable biomass is lignocellulosic waste, which contains significant quantities of pentoses. However, the use of pentoses (C5) in the cultivation of microalgae is still not widely studied and only recently the first metabolic pathway for pentose absorption in microalgae was proposed. So, the objective of this work was to evaluate if the use of pentoses affects the growth and carbohydrates content of Chlorella minutissima, Chlorella vulgaris, Chlorella homosphaera and Dunaliella salina. The kinetic parameters, carbohydrate and protein content and the theoretical potential for ethanol production were estimated for all strains. The highest cellular concentrations (1.25 g L-1) were obtained for D. salina with 5% of pentoses. The addition of pentoses leads to high levels of carbohydrates for C. minutissima (58.6%) cultured with 5% of pentoses, and from this biomass, it is possible to determine a theoretical production of ethanol of 38 mL per 100 g of biomass. The pentoses affect the growth and the biomass composition of the studied strains, generating biomass with potential use for bioethanol production.

Pentoses Used in Cultures of Synechococcus nidulans and Spirulina paracas: Evaluation of Effects in Growth and in Content of Proteins and Carbohydrates

Abstract The biological assimilation of the sugars present in lignocellulosic residues has gained prominence since these residues are the most abundant and economic residues in nature. Thus, the objective of this work was to determine whether the use of D-xylose and L-arabinose as sources of carbon in Synechococcus nidulans and Spirulina paracas cultures affects the growth and production of proteins and carbohydrates. Kinetic growth parameters, pentose consumption, protein content and carbohydrates were evaluated. Synechococcus nidulans and Spirulina paracas consumed all concentrations of pentose used. The highest cellular concentration (1.37 g.L-1) and the highest protein productivity (54 mg.L-1.d-1) were obtained for Spirulina paracas, which was submitted to the addition of 38.33 mg.L-1 D-xylose and 1.79 mg.L-1 L-arabinose. The use of pentose promoted the accumulation of proteins for the studied microalgae. This is one of the first works to report protein bioaccumulation as a result of pentose addition.

Dynamics and control strategies for a butanol fermentation process.

In this work, mathematical modeling was employed to assess the dynamic behavior of the flash fermentation process for the production of butanol. This process consists of three interconnected units as follows: fermentor, cell retention system (tangential microfiltration), and vacuum flash vessel (responsible for the continuous recovery of butanol from the broth). Based on the study of the dynamics of the process, suitable feedback control strategies [single input/single output (SISO) and multiple input/multiple output (MIMO)] were elaborated to deal with disturbances related to the process. The regulatory control consisted of keeping sugar and/or butanol concentrations in the fermentor constant in the face of disturbances in the feed substrate concentration. Another objective was the maintenance of the proper operation of the flash tank (maintenance of the thermodynamic equilibrium of the liquid and vapor phases) considering that oscillations in the temperature in the tank are expected. The servo control consisted of changes in concentration set points. The performance of an advanced controller, the dynamic matrix control, and the classical proportional-integral controller was evaluated. Both controllers were able to regulate the operating conditions in order to accommodate the perturbations with the lowest possible alterations in the process outputs. However, the performance of the PI controller was superior because it showed quicker responses without oscillations.