Techno-economic assessment for the production of algal fuels and value-added products: opportunities for high-protein microalgae conversion.

BACKGROUND: Microalgae possess numerous advantages for use as a feedstock in producing renewable fuels and products, with techno-economic analysis (TEA) frequently used to highlight the economic potential and technical challenges of utilizing this biomass in a biorefinery context. However, many historical TEA studies have focused on the conversion of biomass with elevated levels of carbohydrates and lipids and lower levels of protein, incurring substantial burdens on the ability to achieve high cultivation productivity rates relative to nutrient-replete, high-protein biomass. Given a strong dependence of algal biomass production costs on cultivation productivity, further TEA assessment is needed to understand the economic potential for utilizing potentially lower-cost but lower-quality, high-protein microalgae for biorefinery conversion. RESULTS: In this work, we conduct rigorous TEA modeling to assess the economic viability of two conceptual technology pathways for processing proteinaceous algae into a suite of fuels and products. One approach, termed mild oxidative treatment and upgrading (MOTU), makes use of a series of thermo-catalytic operations to upgrade solubilized proteins and carbohydrates to hydrocarbon fuels, while another alternative focuses on the biological conversion of those substrates to oxygenated fuels in the form of mixed alcohols (MA). Both pathways rely on the production of polyurethanes from unsaturated fatty acids and valorization of unconverted solids for use as a material for synthesizing bioplastics. The assessment found similar, albeit slightly higher fuel yields and lower costs for the MA pathway, translating to a residual solids selling price of $899/ton for MA versus $1033/ton for MOTU as would be required to support a $2.50/gallon gasoline equivalent (GGE) fuel selling price. A variation of the MA pathway including subsequent upgrading of the mixed alcohols to hydrocarbon fuels (MAU) reflected a required solids selling price of $975/ton. CONCLUSION: The slight advantages observed for the MA pathway are partially attributed to a boundary that stops at oxygenated fuels versus fungible drop-in hydrocarbon fuels through a more complex MOTU configuration, with more comparable results obtained for the MAU scenario. In either case, it was shown that an integrated algal biorefinery can be economical through optimal strategies to utilize and valorize all fractions of the biomass.

Integrated evaluation of cost, emissions, and resource potential for algal biofuels at the national scale.

Costs, emissions, and resource availability were modeled for the production of 5 billion gallons yr(-1) (5 BGY) of renewable diesel in the United States from Chlorella biomass by hydrothermal liquefaction (HTL). The HTL model utilized data from a continuous 1-L reactor including catalytic hydrothermal gasification of the aqueous phase, and catalytic hydrotreatment of the HTL oil. A biophysical algae growth model coupled with weather and pond simulations predicted biomass productivity from experimental growth parameters, allowing site-by-site and temporal prediction of biomass production. The 5 BGY scale required geographically and climatically distributed sites. Even though screening down to 5 BGY significantly reduced spatial and temporal variability, site-to-site, season-to-season, and interannual variations in productivity affected economic and environmental performance. Performance metrics based on annual average or peak productivity were inadequate; temporally and spatially explicit computations allowed more rigorous analysis of these dynamic systems. For example, 3-season operation with a winter shutdown was favored to avoid high greenhouse gas emissions, but economic performance was harmed by underutilized equipment during slow-growth periods. Thus, analysis of algal biofuel pathways must combine spatiotemporal resource assessment, economic analysis, and environmental analysis integrated over many sites when assessing national scale performance.

Permanent grounding of a USAF pilot following photorefractive keratectomy.

INTRODUCTION: Photorefractive keratectomy (PRK) has been extensively studied in the literature and its potential application in aircrew has not gone unnoticed. Complication rates following corneal refractive surgery (CRS), including PRK and laser in-situ keratomileusis (LASIK), remain low, with most patients achieving improved uncorrected visual acuity and reduced spectacle dependence. Overall, predictability, low complication rates, high rate of success, stability, and safety have all been cited as instrumental in the adoption of PRK in aviators. Consequently, the U.S. Air Force (USAF) approved PRK for aviators in August 2000. However, quality of vision outcomes following CRS remain a concern given the unique visual performance requirements in military aircrew, especially in austere operational environments. CASE REPORT: This paper will present a recent case of steroid-induced ocular hypertension that is believed to have precipitated non-arteritic anterior ischemic optic neuropathy (NA-AION) associated with reduced visual performance following PRK that resulted in the first permanent grounding of a USAF pilot following CRS. DISCUSSION: CRS has radically widened the aircrew applicant pool and has decreased spectacle dependence in war-fighters. Despite the low-risk profile of modern CRS, this case demonstrates the potential for poor outcomes from such elective surgery. Understanding these rare, but potentially devastating complications and the unique aeromedical risk factors in aircrew is paramount when considering elective vision-enhancing surgery.