Efficient production of fatty acid methyl esters by a wastewater-isolated microalgae-yeast co-culture.

Improving the competitiveness of biodiesel production by microalgae cultures requires the application of several strategies to obtain a high content of lipids, rapid biomass growth and a capacity to adapt to different kinds of environment, with the aim of using non-renewable nutrient sources. Therefore, the use of an individual indigenous microalgae strain or a consortium from natural or anthropogenic sites is now considered an alternative for biofuel production. This study examined the temporal behaviour of secondary metabolites produced by a native microalgae and yeast consortium isolated from wastewater, which was characterized by a genetic identification method based on the MiSeq system. The predominant species in the consortium was Scenedesmus obliquus, representing 68% of the organisms. In addition, the consortium contained a number of yeast species, including Candida pimensis (43%), Arthroderma vanbreuseghemii (23%), Diaporthe aspalathi/Diaporthe meridionalis (25%) and Hericium americanum (3%). This indigenous co-culture of microalgae and yeast showed biomass productivity of 0.06 g l-1 day-1, with a content of 30% (w/w) carbohydrates, 4% (w/w) proteins and 55% (w/w) lipids. Transesterification of the extracted lipids produced fatty acid methyl esters (FAMEs), which were analysed by gas chromatography (GC). The FAMEs included methyl pentadecanoate (1.90%), cis-10-pentanedecanoic acid methyl ester (1.36%), methyl palmitate (2.64%), methyl palmitoleate (21.36%), methyl oleate (64.95%), methyl linolenate (3.83%) and methyl linolelaidate (3.95%). This composition was relevant for biodiesel production based on the co-culture of indigenous microalgae and yeast consortia.

Development of a green one-step neutralization process for valorization of crude glycerol obtained from biodiesel.

Biodiesel production from the transesterification of triglycerides produces crude glycerol as a by-product with a percentage of glycerol typically 20-80% (w/w) depending on the specific conditions of the transesterification process. This crude glycerol requires further purification in order to achieve commercial value and to increase the profitability of biodiesel production. For this reason, the main objective of this work was to obtain glycerol with a purity greater than 90% (w/w) starting from water-free crude glycerine as obtained from the IPN-GBD-1000® transesterification process and treating it via single-step neutralization according to green chemistry principles. For this purpose, sulphuric (H2SO4) and citric (C6H8O7) acids were evaluated as neutralizers by adding dilute acid solutions to crude glycerine under mild conditions. The physicochemical characterization of both crude and purified glycerol was carried out by means of infrared spectroscopy (FTIR), 1H and 13C nuclear magnetic resonance (NMR) and thermogravimetric analysis (TGA). The results indicated that the neutralization method herein developed allowed the obtaining of glycerol with purities of 98.5% and 84.37% (w/w) and treatment efficiencies of 98.5% and 46.7% for sulphuric and citric acid treatments, respectively. In addition, the environmental viability of the sulphuric acid process was evaluated through the calculation of green metrics such as environmental factor, water factor and mass intensity, through which significant environmental advantages were confirmed. The one-step neutralization process reported herein generates zero waste when sulphuric acid is used; it also decreases the water consumption 17-fold and reduces 3-fold the use of raw materials per mass unit of purified glycerol compared to the conventional acidification-neutralization process.

Adsorption of zwitterionic surfactant on limestone measured with high-performance liquid chromatography: micelle-vesicle influence.

Herein is presented a new methodology to determine the static adsorption of a zwitterionic surfactant on limestone in three different aqueous media [high-performance liquid chromatography (HPLC) water, seawater, and connate water] with the use of HPLC at room temperature and 70 °C. The results showed that, in both HPLC water and seawater, the surfactant adsorption followed a monolayer Langmuir tendency. In contrast, for connate water, the surfactant presented a new adsorption profile, characterized by two regions: (i) At surfactant concentrations below 1500 mg L(-1), an increase of adsorption is observed as the amount of divalent cations increases in the aqueous media. (ii) At surfactant concentrations above 1500 mg L(-1), the adsorption decreases because the equilibrium, monomer ⇆ micelle ⇆ vesicle, is shifted to the formation of vesicles, giving as a result a decrease in the concentration of monomers, thus reducing the interaction between the surfactant and the rock, and therefore, lower adsorption values were obtained. The behavior of the surfactant adsorption under different concentrations of divalent cations was well-described by the use of a new modified Langmuir model: (dΓ/dt)ads = k(ads)c(Γ∞ - Γ) - k(cmc)(c - c(cmc))(n)ΓH(c - c(cmc)). It was also observed that, as the temperature increases, the adsorption is reduced because of the exothermic nature of the adsorption processes.