001. Carrillo-Reyes, J., Barragán-Trinidad, M and Buitrón, G. Laboratory for Research on Advanced Processes for Water Treatment, Unidad Académica Juriquilla, Instituto de Ingeniería, Universidad Nacional Autónoma de México, Blvd. Juriquilla 3001, Querétaro 76230, Mexico. Biological pretreatments of microalgal biomass for gaseous biofuel production and the potential use of rumen microorganisms: A review. Algal Research, 2016, Vol. 18, Page: 341 – 351.

      Pretreatments to break down complex biopolymers in microalgae cells are a key process in the production of gaseous biofuels (methane and hydrogen) from such biomass. Biological pretreatment implies cell degradation by purified enzymes; enzymatic cocktails or by microorganisms with enzymatic activity capable of hydrolyzing the microalgae cell wall. This review presents relevant results using those methods that are less energy intensive and, in some cases, more specific than other strategies, such as chemical and physical pretreatments. Enzymatic pretreatments are specific and efficient, with cellulase, hemicellulase, pectinase, protease and amylase being the most explored enzymes. For biomass pretreatment, enzymatic cocktails have been more effective than single enzymes, as it is more feasible to obtain enzymatic extracts of one or more hydrolytic microorganisms than their purified enzymes. The potential use of hydrolytic cultures for cell disruption to breakdown complex biopolymers has been demonstrated. Their use is less specific than that of enzymatic extracts, but more cost-effective. Pure cultures of hydrolytic bacteria, most of which have carbohydrase activities, have increased the biofuel conversion efficiency from microalgae and from bacterial consortia. The use of natural microbial consortia with hydrolytic activities, such as ruminal microorganisms, represents a potential pretreatment for microalgae. In this review, common hydrolytic activities are highlighted and compared, and the use of ruminal microorganisms as a cell disruption strategy is discussed. Understanding the operational conditions applied to natural consortia, such as ruminal microorganisms, will favor a suitable system for microalgae cell disruption that may increase the biological hydrogen and methane recovery from microalgae.

Keywords: Cell disruption; Ruminal microorganisms; Microalgae; Hydrolytic cultures.

002. Fuentes, J. L., Garbayo, I., Cuaresma, M., Montero, Z., González-del-Valle, M and Vílchez, C. Algal Biotechnology Group, Ciderta and Faculty of Sciences, University of Huelva and Marine International Campus of Excellence (CEIMAR), Huelva 21007, Spain. Impact of Microalgae-Bacteria Interactions on the Production of Algal Biomass and Associated Compounds. Marine drugs, 2016, Vol. 14 (5), Page: 100.

      A greater insight on the control of the interactions between microalgae and other microorganisms, particularly bacteria, should be useful for enhancing the efficiency of microalgal biomass production and associated valuable compounds. Little attention has been paid to the controlled utilization of microalgae-bacteria consortia. However, the studies of microalgal-bacterial interactions have revealed a significant impact of the mutualistic or parasitic relationships on algal growth. The algal growth, for instance, has been shown to be enhanced by growth promoting factors produced by bacteria, such as indole-3-acetic acid. Vitamin B12 produced by bacteria in algal cultures and bacterial siderophores are also known to be involved in promoting faster microalgal growth. More interestingly, enhancement in the intracellular levels of carbohydrates, lipids and pigments of microalgae coupled with algal growth stimulation has also been reported. In this sense, massive algal production might occur in the presence of bacteria, and microalgae-bacteria interactions can be beneficial to the massive production of microalgae and algal products. This manuscript reviews the recent knowledge on the impact of the microalgae-bacteria interactions on the production of microalgae and accumulation of valuable compounds, with an emphasis on algal species having application in aquaculture.

Keywords: microalgae; microalgae-bacteria interactions; microalgae production; aquaculture.

003. Voloshin, R. A., Rodionova, M. V., Zharmukhamedov, S. K., Veziroglu, T. N and Allakhverdiev, S. I. Controlled Photobiosynthesis Laboratory, Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya Street 35, Moscow 127276, Russia. Review: Biofuel production from plant and algal biomass. International Journal of Hydrogen Energy, 2016, Vol. 41 (39), Page: 17257 – 17273.

      Biofuels are the promising alternative to exhaustible, environmentally unsafe fossil fuels. Algal biomass is attractive raw for biofuel production. Its cultivation does not compete for cropland with agricultural growing of food crop for biofuel and does not require complex treatment methods in comparison with lignocellulose-enriched biomass. Many microalgae are mixotrophs, so they can be used as energy source and as sewage purifier simultaneously. One of the main steps for algal biofuel fabrication is the cultivation of biomass. Photobioreactors and open-air systems are used for this purpose. While former ones allow the careful cultivation control, the latter ones are cheaper and simpler. Biomass conversion processes may be divided to the thermochemical, chemical, biochemical methods and direct combustion. For biodiesel production, triglyceride-enriched biomass undergoes transetherification. For bioalcohol production, biomass is subjected to fermentation. There are three methods of biohydrogen production in the microalgal cells: direct biophotolysis, indirect biophotolysis, fermentation.

Keywords: Biofuel; Biomass; Photobioreactor; Biodiesel; Bioalcohol; Biohydrogen.

004. Williams, C. L., Westover, T. L., Emerson, R. M., Tumuluru, J. S and Li, C. Biofuels and Renewable Energy Technology Department, Idaho National Laboratory, Idaho Falls, USA. Sources of Biomass Feedstock Variability and the Potential Impact on Biofuels Production. BioEnergy Research, 2016, Vol. 9 (1), Page: 1 – 14.

      Terrestrial lignocellulosic biomass has the potential to be a carbon neutral and domestic source of fuels and chemicals. However, the innate variability of biomass resources, such as herbaceous and woody materials, and the inconsistency within a single resource due to disparate growth and harvesting conditions, presents challenges for downstream processes which often require materials that are physically and chemically consistent. Intrinsic biomass characteristics, including moisture content, carbohydrate and ash compositions, bulk density, and particle size/shape distributions are highly variable and can impact the economics of transforming biomass into value-added products. For instance, ash content increases by an order of magnitude between woody and herbaceous feedstocks (from ∼0.5 to 5 %, respectively) while lignin content drops by a factor of two (from ∼30 to 15 %, respectively).

Graphical Abstract

      This increase in ash and reduction in lignin leads to biofuel conversion consequences, such as reduced pyrolysis oil yields for herbaceous products as compared to woody material. In this review, the sources of variability for key biomass characteristics are presented for multiple types of biomass. Additionally, this review investigates the major impacts of the variability in biomass composition on four conversion processes: fermentation, hydrothermal liquefaction, pyrolysis, and direct combustion. Finally, future research processes aimed at reducing the detrimental impacts of biomass variability on conversion to fuels and chemicals are proposed.

Keywords: Biomass; Composition; Variability; Conversion; Biochemical; Thermochemical.