Potential of Wastewater Grown Algae for Biodiesel Production and CO2 Sequestration

In response to a growing fear surrounding increasing levels of CO2 in the atmosphere and rapidly dwindling supplies of traditional oil as a source of energy, A. Fulke et al. investigated the CO2 sequestration rate (as a source of CO2 mitigation), the biomass creation (as a source of biofuel), and lipid composition of algae used in the wastewater stabilization ponds of industrial wastewater treatment plants. The green algae species of the algae they found naturally occurring in the wastewater stabilization ponds have a lipid structure equivalent to vegetable oil currently used to produce biodiesel. In the two most dominant algal classes Chlorophyceae and Cyanophyceae, they found four distinct species (Scenedesmus dimorphus, Scenedesmus incrassatulus, Chroococcus sp. and Chlorella sp.) currently being globally explored as sources of biodiesel. They isolated and cultured samples of these four species and examined the biomass concentration, lipid content, and CO2 fixation rates, finding that the samples where all four of these species were present (as opposed to each species cultured alone) had a biomass concentration (g L-1) and lipid content (g g-1) nearly twice as high as any alone, and a CO2 fixation rate (g L-1d-1) at least double individual species cultivations. They concluded that industrial wastewater could support a diverse culture of algal species capable of being used as a source of biodiesel. —Allison Kerley

Fulke, A., Chambhare, K., Sangolkar, L., Giripunje, M., Krishnamurthi, K., Juwarkar, A., Chakrabarti, T., 2013. Potential of wastewater grown algae for biodiesel production and CO2 sequestration. African Journal of Biotechnology 12, 2939–2948.

                  Fulke et al. collected samples of water from ten different locations in the wastewater stabilization pond at a currently active vehicle manufacturing plant in the western Maharashtra region in India. They found 27 species of Chlorophyceae, 16 species of Cyanophycea, 14 species of Bacillariophyceae, 4 species of Euglenophyceae and 4 species of Chrysophyceae in the wastewater, with a Shannon-Wiener Diversity Index range from 2.91 to 3.66. They used the Nile Red staining method to determine the lipid content and to identify the intracellular lipid content (used in the creation of biodiesel). Four of the algae species found (Scenedesmus dimorphus, Scenedesmus incrassatulus, Chroococcus sp. and Chlorella sp). are currently being globally explored as potential sources of biodiesel, so Fulke et al. chose to further investigate the lipid content and biomass creation during stress and no-stress scenarios. They cultivated each of the species individually in the lab over 14 days, each in a culture with abundant nutrients and in a culture with limited nutrients. They found that upon nutrient depletion, the algae produce more lipids which get trapped within the cell. Cells with a higher lipid concentration are more favorable for biodiesel creation.

Hydrophobic Amino Acids as a New Class of Kinetic Inhibitors for Gas Hydrate Formation

Sa et al. investigated the effects of amino acids as Kinetic Hydrate Inhibiters (KHIs) on the initial formation, the continued growth, and the structure of hydrate blockages in natural gas and oil pipelines. They found that hydrophobic amino acids were more effective KHIs than the more commonly used polyvinyl pyrrolidone (PVP). It was also observed that in general, amino acids with shorter alkyl chains were more effective KHIs than those with longer alkyl chains, with glycine and L-alanine being the most effective KHIs. Examining how various KHI’s impacted the rate of growth of hydrate blockages, it was found that both PVP and glycine as KHIs caused a decrease in the rate of formation of the hydrogen blockage. When comparing amino acids with varying alkyl chain lengths, it was observed that as the length of the alkyl chain increased, its ability to act as an effective KHI decreased. It was found that the crystal structure of hydrates formed did not change in the presence of the amino acid KHIs. However, it was found that all amino acids, regardless of their hydrophobicity, were effective in inhibiting hydrate blockages once the blockages had begun to form, as seen by the increased number of ice crystals in the hydrate in the presence of glycine.—Allison Kerley

Sa, J., Kwak, G., Lee, B., Park, D., Han, K., Lee, K., 2013. Hydrophobic amino acids as a new class of kinetic inhibitors for gas hydrate formation. Scientific Reports 3, 2428.

                  Using nucleation kinetics measurements to observe the onset of hydrate blockage formation, Sa et al. examined the effects of different amino acids and PVP on hydrate formation in fresh water and memory water. The “memory effect” of memory water is a phenomenon in which hydrates form more easily in gas and water that has formed hydrates in the past. While PVP did not display any effect on the inhibition of hydrates, glycine (at an increased concentration of 1.0% mol) slowed the formation of hydrates.
                  Synchrotron powder X-ray diffraction (PXRD) was used to identify the structure of the hydrate blockages, enabling Sa et al. to determine whether KHIs affected the structural makeup of hydrate blockages. It was found that in the presence of glycine, hydrate blockages displayed more ice crystals, which was attributed to water molecules freezing instead of forming hydrates.

Allison Kerley

Recyclable Organic Solar Cells on Cellulose Nanocrystal Substrates

Flexible recyclable solar cells are the most recent addition to solar cell research, and have the potential to lower the costs of solar cells while eliminating the need for the petroleum-based components of traditional solar cells. Zhou et al.(2013) studied the power conversion efficiency, the rectification in the absence of light, and the recyclability of polymer solar cells created with cellulose nanocrystal (CNC) substrates. CNC’s are extracted from plant fibers, and are more environmentally attractive due to their ability to be recycled than their petroleum-based counterparts. Zhou et al. found the power conversion efficiency (PCE) of solar cells on CNC substrates to be noticeably higher than previous attempts at solar cells on paper-like substrates. The CNC substrates and solar cells were also found to be separable when dispersed in distilled water at room temperature, allowing for the various components to recovered and recycled.
 —Allison Kerley
Zhou, Yinhua, Fuentes-Hernandez, Canek, Kahn, Talha M., Liu, Jen-Chieh, Hsu, James, Shim, Jae Won, Dindar, Amir, Youngblood, Jeffrey P., Moon, Robert J., Kippelen, Bernard. 2013. Recyclable organic solar cells on cellulose nanocrystal substrates. Scientific Reports 3, 1536

                  Zhou et al. found their CNC substrate-based solar cells to have a 2.7% PCE; they attribute the low PCE to both the limited transmittance of the thin Ag layer which served as the bottom electrode and to the uneven and random distribution of the CNC in the clear CNC film. The CNC film is desired to be as transparent as possible, while intensifying the light onto the detector. However, the inconsistencies in the spread of the CNC’s (which are only a few hundred nanometers long) cause scattering of the light, lowering the intensity of the light hitting the detector. The efficiency of the solar cell is determined by the intensity of the light hitting the detector, and the transmittances of CNC substrates were found to be lower than that of glass.
                  The other piece of the study conducted by Zhou et al. examined the recyclability potential of the CNC substrate solar cells they created. It was found that the CNC substrate solar cells could be separated into their major components (substrate, organic and inorganic materials) by immersing them in distilled water at room temperature and running the solution through several simple filtering processes. Immersing the solar cell in water disintegrates the CNC substrate, allowing the solid wastes to be filtered out with a simple paper filter. The photoactive layer could then be separated from the electrodes by rinsing the solid wastes over filter paper using chlorobenzene, leaving the materials which acted as electrodes behind.

                  Zhou et al. theorize that the CNC substrate could be tweaked and modified to decrease the scattering of the light, increasing the PCE of the solar cell. In addition, they propose that using a different or modified material for the bottom electrode would increase the transmittance.