Adam J. Dassey

Harvesting economics and strategies using centrifugation for cost effective separation of microalgae cells for biodiesel applications.

Inefficient or energy-intensive microalgal harvesting strategies for biodiesel production have been a major setback in the microalgae industry. Harvesting by centrifugation is generally characterized by high capture efficiency (>90%) under low flow rates and high energy consumption. However, results from the present study demonstrated that by increasing the flow rates (>1L/min), the lower capture efficiencies (<90%) can be offset by the larger volumes of culture water processed through the centrifuge, resulting in net lower energy consumption. Energy consumption was reduced by 82% when only 28.5% of the incoming algal biomass was harvested at a rate of 18 L/min by centrifugation. Harvesting algal species with a high lipid content and high culture density could see harvesting costs of

Improving protein crystal quality by selective removal of a Ca2+-dependent membrane-insertion loop

0.864/L oil using the low efficiency/high flow rate centrifugation strategy as opposed to

Reducing electrocoagulation harvesting costs for practical microalgal biodiesel production

4.52/L oil using numbers provided by the Department of Energy for centrifugation harvesting.

A covalent linker allows for membrane targeting of an oxylipin biosynthetic complex.

Lipoxygenases (LOXs) catalyze the regiospecific and stereospecific dioxygenation of polyunsaturated membrane-embedded fatty acids. A Ca(2+)-dependent membrane-binding function was localized to the amino-terminal C2-like domain of 8R-lipoxygenase (8R-LOX) from the soft coral Plexaura homomalla. The 3.2 A crystal structure of 8R-LOX and spectroscopic data suggested that Ca(2+) stabilizes two membrane-insertion loops. Analysis of the protein packing contacts in the crystal lattice indicated that the conformation of one of the two loops complicated efforts to improve the resolution of the X-ray data. A deletion mutant of 8R-LOX in which the corresponding membrane-insertion loop is absent (Delta41-45:GSLOX) was engineered. Removal of the membrane-insertion loop dramatically increases the protein yield from bacterial cultures and the quality of the crystals obtained, resulting in a better than 1 A improvement in the resolution of the diffraction data.

Evaluating coagulation pretreatment on poultry processing wastewater for dissolved air flotation.

Electrocoagulation has shown potential to be a primary microalgae harvesting technique for biodiesel production. However, methods to reduce energy and electrode costs are still necessary for practical application. Electrocoagulation tests were conducted on Nannochloris sp. and Dunaliella sp. using perforated aluminium and iron electrodes under various charge densities. Aluminium electrodes were shown to be more efficient than iron electrodes when harvesting both algal species. Despite the lower harvesting efficiency, however, the iron electrodes were more energy and cost efficient. Operational costs of less than

Cost Analysis of Microalgal Harvesting for Biofuel Production

0.03/L oil were achieved when harvesting Nannochloris sp. with iron electrodes at 35% harvest efficiency, whereas aluminium electrodes cost

An analysis of energy consumption for algal biodiesel production: Comparing the literature with current estimates

0.75/L oil with 42% harvesting efficiency. Increasing the harvesting efficiencies for both aluminium and iron electrodes also increased the overall cost per litre of oil, therefore lower harvesting efficiencies with lower energy inputs was recommended. Also, increasing the culturing salinity to 2 ppt sodium chloride for freshwater Nannochloris sp. was determined practical to improve the electrocoagulation energy efficiency despite a 25% reduction in cell growth.

Optimizing the Air Dissolution Parameters in an Unpacked Dissolved Air Flotation System

A naturally occurring bifunctional protein from Plexaura homomalla links sequential catalytic activities in an oxylipin biosynthetic pathway. The C-terminal lipoxygenase (LOX) portion of the molecule catalyzes the transformation of arachidonic acid (AA) to the corresponding 8 R-hydroperoxide, and the N-terminal allene oxide synthase (AOS) domain promotes the conversion of the hydroperoxide intermediate to the product allene oxide (AO). Small-angle X-ray scattering data indicate that in the absence of a covalent linkage the two catalytic domains that transform AA to AO associate to form a complex that recapitulates the structure of the bifunctional protein. The SAXS data also support a model for LOX and AOS domain orientation in the fusion protein inferred from a low-resolution crystal structure. However, results of membrane binding experiments indicate that covalent linkage of the domains is required for Ca (2+)-dependent membrane targeting of the sequential activities, despite the noncovalent domain association. Furthermore, membrane targeting is accompanied by a conformational change as monitored by specific proteolysis of the linker that joins the AOS and LOX domains. Our data are consistent with a model in which Ca (2+)-dependent membrane binding relieves the noncovalent interactions between the AOS and LOX domains and suggests that the C2-like domain of LOX mediates both protein-protein and protein-membrane interactions.

Assessing Feedstocks and Catalysts for Production of Bio-Oils from Hydrothermal Liquefaction

Eleven metal coagulants and one polyelectrolyte were assessed for their suitability in assisting a dissolved air flotation (DAF) system aimed at treating poultry processing wastewater. Preliminary jar tests determined that a combination of 800 mg/L of FeCl3 (ferric chloride) and 900 mg/L of Floccin 1115 would provide the best treatment by removing at least 98% of the total suspended solids (TSS) and 97% of the volatile suspended solids (VSS), while providing a 97% increase in water clarity. Final flotation tests suggested that the flocculated particles could be carried to the surface with 40% recycle ratio of the DAF. The resulting supernatant indicated 94.7% increase in clarity (± 1.4%), 97.3% reduction in TSS (± 0.5%), 96.6% reduction in VSS (±1.1%), 91% reduction in chemical oxygen demand (COD), and nearly 100% removal of fats, oils, and greases (FOGs). Despite the high removal efficiencies, flotation was found not to be critically necessary for treatment because the high concentration of coagulants caused settling of the flocs to occur just as rapidly. Potential coagulant overdosing is suspected at the higher end of the tested coagulant concentrations due to limited alkalinity in the wastewater. However, lack of residual metal (coagulant) ions in water may be linked to reactions leading to phosphate precipitation. The exact effect of the competing phosphate reaction on treatment efficiency is not clearly evident from this present study.

Catalytic cracking of tars from biomass gasification

A challenge for alternative energy has been the development of a liquid alternative to petroleum, which dominates the country’s transportation sector. One feedstock that has potential in biodiesel production is microalgae, eukaryotic oxygenic photosynthetic microorganisms. With some species containing lipid contents as high as 70% of the cell’s biomass, microalgae could potentially produce over 15,000 gal/acre of biodiesel per year in a raceway system as compared to soybean which is capable of only 47 gal/acre per year. However, it has been noted that many microalgae predictions tend to be vastly overestimated. Variations in location, technique, and species will impact algal production and the extraction of lipids. Limited algal production will then require greater energy usage to accommodate the lack of oils produced. Given the relatively low biomass concentration obtainable in microalgal cultivation systems and the small size of microalgal cells, costs and energy consumption for biomass harvesting are significant concerns that need to be addressed properly. Using centrifugation, the authors determined that at higher flow rates, the lower capture efficiencies were offset by the larger volumes of culture processed and lower energy consumption. Energy consumption was reduced by 82% when harvesting was reduced to 28.5% efficacy. Culturing algal species with high lipid content and culture density could see harvesting costs drop to