Produção de Hidrogênio e Etanol a partir da alga verde Chlamydomonas reinhardtii

Abstract

The lack of fossil fuels and the climate changes caused by increases on the carbon dioxide in the atmosphere encouraged the use of alternative fuels that do not cause greenhouse gases accumulation. Therefore, the use of biofuels, such as hydrogen (H2), produced from renewable sources stands out. The aim of this work was to evaluate hydrogen and ethanol production by biological routes using 50 mL sealed bioreactor maintained in incubator at 25° C, 12 h photoperiod with luminosity of 2200 lux (30 μE·m-2·s-1). A green alga Chlamydomonas reinhardtii was used. The operational parameters age of inoculum, inoculum density, time of fermentation and the effect of sulfur contents in the culture medium on the biofuels production were investigated. The temperature was also evaluated by a 23 factorial design (I), with three central points was used. The influence of sulfur content into the medium (7, 11.5 e 16 mg of SO4 2-), inoculum density (0.10, 0.15 and 0,20 g/L) and the temperature (25, 30 e 35° C) on the H2 productivity was evaluated. In addition, the behavior of carbon sources such as sodium acetate and milk whey permeate (rich in lactose) on the target-product synthesis was also verified. In this case, sulfur deprived condition and 0.1 g/L of inoculum density were used. To increase the hydrogen production the influence of different carbon sources was also investigated. In this case, 23 factorial design (II) with three central points was also used. Furthermore, the effect of supplementary carbon source (sodium citrate) and sodium acetate, both varying from 0.1 g/L (low level) to 1.9 g/L (high level) and milk whey permeate (1, 1.5 and 2 g/L) using a basal medium with sulfur content of 10 mg SO4 2- and inoculum density of 0.1 g/L were evaluated. To improve hydrogen system production a hybrid configuration using the green algae (C. reinhardtii) and the photosynthetic bacterium (R. capsulatus) was performed. In this step, sulfur deprived and 0.1 g/L inoculum density were fixed. After that, the carbon source at different concentrations (0.1 and 1 g/L) was evaluate. It is important to note the medium offered to PNS bacterium was previously supplemented with malic acid (30mM), permeate (6 g/L) and sodium glutamate(2.54 g/L). Co-cultures of both strains were also performed to biofuels evolution. In these experiments a microorganism contribution range was from 0 to 100%. The results shown that citrate (1.9 g/L) and permeate (2 g/L) strongly increased the hydrogen production (1975.10 μM/L·d). Ethanol was also produced with isolated carbon source was investigated. In the hybrid system, ethanol concentration was 1.3-fold (19,93 g/L) higher at 0.1 g/L of permeate associated to acetate. Finally, to co-culture maintained in RCV medium, ethanol (12,60 g/L) and hydrogen (7.41 μM/L·d) were obtained simultaneously.