Microalgae are autotrophs and CO.sub.2 fixers with great potential to produce biofuels in a sustainable way, however the high cost of biomass production is a challenge. Mixotrophic growth of ...microalgae has been presented as a great alternative to achieve economic sustainability. Thus, the present work reports the energetic characterization of S. platensis biomasses cultivated under autotrophic (A) and mixotrophic conditions using cheese whey waste at different concentrations, 2.5 (M2.5), 5.0 (M5) and 10.0% (M10), in order to analyze the potential production of valuable chemicals and bio-oil by TGA/DTG and Py-GC/MS. The biochemical compositions of the studied biomasses were different due to the influence of different culture mediums. As the whey concentration increased, there was an increase in the carbohydrate content and a decrease in the protein content, which influenced the elemental composition, calorific value, TGA and volatile compounds evaluated by Py-GC/MS at 450°C, 550°C and 650°C. Sample M10 had lower protein content and formed a smaller amount of nitrogenates compounds by pyrolysis at all temperatures evaluated. There was a reduction of 43.8% (450º), 45.6% (550ºC) and 23.8% (650ºC) in the formation of nitrogenates compounds in relation to sample A. Moreover, the temperature also showed a considerable effect in the formation of volatile compounds. The highest yields of nitrogenates compounds, phenols and aromatic and non-aromatic hydrocarbons were observed at 650ºC. The oxygenated, and N and O containing compounds decreased as the temperature increased. Hydrocarbons such as toluene, heptadecane and heneicosane were produced by S.platensis pyrolysis, which makes this biomass attractive for production of high quality bio-oil and valuable chemicals. Therefore, the results showed that it is possible to decrease the formation of nitrogen compounds via manipulation of growth conditions and temperature.
Microalgae have a great potential to produce biofuels, but the cost is still too high mainly due to the biomass production. Mixotrophic cultivation has been pointed as microalgae cultivation mode for ...biomass/bioenergy production with lower cost. The proposals of this work were to cultivate
S. platensis
in autotrophic and mixotrophic medium using molasses as source of organic carbon and investigate the thermal behavior of obtained biomass by means of thermogravimetric analysis and pyrolysis (Py-GC/MS). The kinetics models proposed by Flynn and Wall and model-free kinetic were used to determine the activation energy. These data are important to projection of design, operation and modeling of thermochemical conversion system for microalgae. The use of molasses as supplement in culture medium for the growth of
S. platensis
was a good way to increase the biomass productivity and decrease the protein content. The Flynn–Wall and model-free kinetic methods were adequate to calculate activation energy on the conversion range of 0.20 to 0.80. The activation energies were 168–229 kJ mol
−1
(Flynn and Wall), 177–238 kJ mol
−1
(model-free kinetic) for mixotrophic biomass and 174–220 kJ mol
−1
(Flynn and Wall), 181–229 kJ mol
−1
(model-free kinetic) for autotrophic biomass. The compositions of volatile compounds produced by
S. platensis
biomass pyrolysis were different due to cultivation method that influenced the composition of biomass. Hydrocarbons, oxygenated and nitrogenated compounds were produced with different quantities. The volatile compounds content of phenols, oxygenated and nitrogenated increased and non-aromatic and aromatic hydrocarbons content decreased for pyrolysis of mixotrophic biomass. However, the mixotrophic cultivation has a great influence on the microalgae biomass production and should be a factor considered in thermal degradation project for microalgae.
Microalgae are autotrophs and CO2 fixers with great potential to produce biofuels in a sustainable way, however the high cost of biomass production is a challenge. Mixotrophic growth of microalgae ...has been presented as a great alternative to achieve economic sustainability. Thus, the present work reports the energetic characterization of S. platensis biomasses cultivated under autotrophic (A) and mixotrophic conditions using cheese whey waste at different concentrations, 2.5 (M2.5), 5.0 (M5) and 10.0% (M10), in order to analyze the potential production of valuable chemicals and bio-oil by TGA/DTG and Py-GC/MS. The biochemical compositions of the studied biomasses were different due to the influence of different culture mediums. As the whey concentration increased, there was an increase in the carbohydrate content and a decrease in the protein content, which influenced the elemental composition, calorific value, TGA and volatile compounds evaluated by Py-GC/MS at 450°C, 550°C and 650°C. Sample M10 had lower protein content and formed a smaller amount of nitrogenates compounds by pyrolysis at all temperatures evaluated. There was a reduction of 43.8% (450º), 45.6% (550ºC) and 23.8% (650ºC) in the formation of nitrogenates compounds in relation to sample A. Moreover, the temperature also showed a considerable effect in the formation of volatile compounds. The highest yields of nitrogenates compounds, phenols and aromatic and non-aromatic hydrocarbons were observed at 650ºC. The oxygenated, and N and O containing compounds decreased as the temperature increased. Hydrocarbons such as toluene, heptadecane and heneicosane were produced by S.platensis pyrolysis, which makes this biomass attractive for production of high quality bio-oil and valuable chemicals. Therefore, the results showed that it is possible to decrease the formation of nitrogen compounds via manipulation of growth conditions and temperature.
