Due to significant lipid and carbohydrate production as well as other useful properties such as high production of useful biomolecular substrates (e.g., lipids) and the ability to grow using non-potable water sources, algae are being explored as a potential high-yield feedstock for biofuels production. In both natural and engineered systems, algae can be exposed to a variety of environmental conditions that affect growth rate and cellular composition. With respect to the latter, the amount of carbon fixed in lipids and carbohydrates (e.g., starch) is highly influenced by environmental factors and nutrient availability. Understanding synergistic interactions between multiple environmental variables and nutritional factors is required to develop sustainable high productivity bioalgae systems, which are essential for commercial biofuel production. This article reviews the effects of environmental factors (i.e., temperature, light and pH) and nutrient availability (e.g., carbon, nitrogen, phosphorus, potassium, and trace metals) as well as cross-interactions on the biochemical composition of algae with a special focus on carbon fixation and partitioning of carbon from a biofuels perspective.

Background, aim, and scope Algae biomass has great promise as a sustainable alternative to conventional transportation fuels. In this study, a well-to-pump life cycle assessment (LCA) was performed to investigate the overall sustainability and net energy balance of an algal biodiesel process. The goal of this LCA was to provide baseline information for the algae biodiesel process. Materials and methods The functional unit was 1,000 MJ of energy from algal biodiesel using existing technology. Systematic boundary identification was performed using relative mass, energy, and economic value method using a 5% cutoff value. Primary data for this study were obtained from The USLCI database and the Greenhouse Gases, Regulated Emissions and Energy use in Transportation model. Carbohydrates in coproducts from algae biodiesel production were assumed to displace corn as a feedstock for ethanol production.Results and discussion For every 24 kg of algal biodiesel produced (1,000 MJ algae biodiesel), 34 kg coproducts are also produced. Total energy input without solar drying is 3,292 and 6,194 MJ for the process Electronic supplementary material The online version of this article (with filter press and centrifuge as the initial filtering step, respectively. Net CO 2 emissions are −20.9 and 135.7 kg/functional unit for a process utilizing a filter press and centrifuge, respectively. In addition to the −13.96 kg of total air emissions per functional unit, 18.6 kg of waterborne wastes, 0.28 kg of solid waste, and 5.54 Bq are emitted. The largest energy input (89%) is in the natural gas drying of the algal cake. Although net energy for both filter press and centrifuge processes are −6,670 and −3,778 MJ/functional unit, respectively, CO 2 emissions are positive for the centrifuge process while they are negative for the filter press process. Additionally, 20.4 m 3 of wastewater per functional unit is lost from the growth ponds during the 4-day growth cycle due to evaporation. Conclusions and recommendations This LCA has quantified one major obstacle in algae technology: the need to efficiently process the algae into its usable components. Thermal dewatering of algae requires high amounts of fossil fuel derived energy (3,556 kJ/kg of water removed) and consequently presents an opportunity for significant reduction in energy use. The potential of green algae as a fuel source is not a new idea; however, this LCA and other sources clearly show a need for new technologies to make algae biofuels a sustainable, commercial reality.

BackgroundWhile advantages of biofuel have been widely reported, studies also highlight the challenges in large scale production of biofuel. Cost of ethanol and process energy use in cellulosic ethanol plants are dependent on technologies used for conversion of feedstock. Process modeling can aid in identifying techno-economic bottlenecks in a production process. A comprehensive techno-economic analysis was performed for conversion of cellulosic feedstock to ethanol using some of the common pretreatment technologies: dilute acid, dilute alkali, hot water and steam explosion. Detailed process models incorporating feedstock handling, pretreatment, simultaneous saccharification and co-fermentation, ethanol recovery and downstream processing were developed using SuperPro Designer. Tall Fescue (Festuca arundinacea Schreb) was used as a model feedstock.ResultsProjected ethanol yields were 252.62, 255.80, 255.27 and 230.23 L/dry metric ton biomass for conversion process using dilute acid, dilute alkali, hot water and steam explosion pretreatment technologies respectively. Price of feedstock and cellulose enzymes were assumed as $50/metric ton and 0.517/kg broth (10% protein in broth, 600 FPU/g protein) respectively. Capital cost of ethanol plants processing 250,000 metric tons of feedstock/year was $1.92, $1.73, $1.72 and $1.70/L ethanol for process using dilute acid, dilute alkali, hot water and steam explosion pretreatment respectively. Ethanol production cost of $0.83, $0.88, $0.81 and $0.85/L ethanol was estimated for production process using dilute acid, dilute alkali, hot water and steam explosion pretreatment respectively. Water use in the production process using dilute acid, dilute alkali, hot water and steam explosion pretreatment was estimated 5.96, 6.07, 5.84 and 4.36 kg/L ethanol respectively.ConclusionsEthanol price and energy use were highly dependent on process conditions used in the ethanol production plant. Potential for significant ethanol cost reductions exist in increasing pentose fermentation efficiency and reducing biomass and enzyme costs. The results demonstrated the importance of addressing the tradeoffs in capital costs, pretreatment and downstream processing technologies.

Cereal Chem. 83(5):455-459New corn fractionation technologies that produce higher value coproducts from dry-grind processing have been developed. Wet fractionation technologies involve a short soaking of corn followed by milling to recover germ and pericarp fiber in an aqueous medium before fermentation of degermed defibered slurry. In dry fractionation technologies, a dry degerm defiber (3D) process (similar to conventional corn dry-milling) is used to separate germ and pericarp fiber before fermentation of the endosperm fraction. The effect of dry and wet fractionation technologies on the fermentation rates and ethanol yields were studied and compared with the conventional dry-grind process. The wet process had the highest fermentation rate. The endosperm fraction obtained from 3D process had lowest fermentation rate and highest residual sugars at the end of fermentation. Strategies to improve the fermentation characteristics of endosperm fraction from 3D process were evaluated using two saccharification and fermentation processes. The endosperm fraction obtained from 3D process was liquefied by enzymatic hydrolysis and fermented using either separate saccharification (SS) and fermentation or simultaneous saccharification and fermentation (SSF). Corn germ soak water and B-vitamins were added during fermentation to study the effect of micronutrient addition. Ethanol and sugar profiles were measured using HPLC. The endosperm fraction fermented using SSF produced higher ethanol yields than SS. Addition of B-vitamins and germ soak water during SSF improved fermentation of 3D process and resulted in 2.6 and 2.3% (v/v) higher ethanol concentrations and fermentation rates compared with 3D process treatment with no addition of micronutrients.

injections, nine of ten animals regained fertility, but the time taken for this depended upon the rate of decline of antibody titres. Re-boosting these monkeys with 100 \ g=m\ g oFSH after confirming that recovery had occurred revealed prompt increases in antibody titres followed once again by onset of oligo-azoospermia and infertility, underscoring the specificity of immunization effect. The immunized monkeys, apart from being acutely oligospermic, ejaculated spermatozoa that were markedly deficient in key acrosomal enzymes, such as acrosin and hyaluronidase, and motility as well as in their ability to penetrate a gel in vitro, suggesting that the infertility observed was due to gross reductions in the numbers of spermatozoa that could effectively interact with the oocyte and cause successful fertilization.