Supercritical Water Gasification Of Algae

Diversification of our energy supplies – especially in the transport and electricity generation sectors – is required to meet decarbonisation targets. Algae have been identified as suitable alternative feedstocks for third generation biofuels due to their fast growth rates and non-competitiveness with land for food crops. Hydrothermal processing of algae is an appropriate conversion route as it allows the processing of wet feedstock thus removing the energy penalty of drying. In this study, supercritical water gasification was used for (i) the hydrothermal processing of macroalgae for the production of gaseous fuel – mainly hydrogen and methane – and (ii) the upgrading of the process water from hydrothermal liquefaction of microalgae for hydrogen production for biocrude hydrotreating. The supercritical water gasification (SCWG) of the four macroalgae species investigated (Saccharina latissima, Laminaria digitata, Laminaria hyperborea, and Alaria esculenta) produced a gas that mainly consisted of hydrogen, methane and carbon dioxide. Non-catalytic SCWG resulted in hydrogen yields of 3.3-4.2 mol/kg macroalgae and methane yields of 1.6-3.3 mol/kg macroalgae. Catalytic SCWG (using ruthenium) resulted in hydrogen yields of 7.8-10.2 mol/kg macroalgae and methane yields of 4.7-6.4 mol/kg macroalgae. The yield of hydrogen was approximately three times higher when using sodium hydroxide as catalyst (16.3 mol H2 / kg macroalgae) compared to non-catalysed SCWG of L. hyperborea (5.18 mol H2 / kg macroalgae). The energy recovery (an expression of how much chemical energy of the feedstock is recovered in the desired product following hydrothermal processing) was 83% when sodium hydroxide was used as a catalyst, compared to 52% for the non-catalytic SCWG of L. hyperborea. The yield of methane was approximately 2.5 times higher (9.0 mol CH4 kg 1macroalgae) when using ruthenium catalyst compared to the non-catalysed experiment (3.36 mol CH4 / kg macroalgae) and the energy recovery increased by 22% to 74%. The selectivity of methane or hydrogen production during the SCWG of macroalgae can be controlled using ruthenium or sodium hydroxide respectively. Longer hold times and increased reaction temperature favoured methane production when using ruthenium. An increase in catalyst loading had no significant effect on the methane yield. Higher hydrogen yields were obtained through using higher concentrations of sodium hydroxide, lower algal feed concentration and shorter hold times (30 min). Increasing reaction times (>30 min) with a base catalyst (sodium hydroxide) decreased the hydrogen yield. Overall energy recovery was highest at the lowest feed concentrations; 90.5% using ruthenium and 111% using sodium hydroxide. The process waters from the hydrothermal liquefaction (HTL) of microalgae (Chlorella, Pseudochoricystis, and Spirulina) were gasified under supercritical water conditions to maximise hydrogen production. Hydrogen yields ranged from 0.18-0.29 g H2 / g biocrude from SCWG of the process water of HTL along with near complete gasification of the organics (~98%). Compared to the hydrogen requirements for hydrotreating algal biocrude (~0.05 g H2 / g biocrude), excess hydrogen can be produced from upgrading the process water through SCWG. The results indicate that process waters following SCWG are still rich in nutrients that can be recycled for algal cultivation

Techno-Economic and Life Cycle Assessment of Hydrothermal Processing of Microalgae for Biofuels and Co-Product Generation

Traditional processing methods of algae to biofuels require dewatering after harvesting of the algae before the lipids can be extracted. This is typically the most energy intensive and therefore the most expensive step. Old Dominion University (ODU) has successfully utilized a flash hydrolysis (a kind of hydrothermal) process where proteins are solubilized into the liquid phase of product and the remainder lipid-rich, low nitrogen product is separated into a solid phase. The solid phase (lipid-rich) is then an ideal candidate for biofuel feedstock and the liquid phase, or hydrolysate, can be used for coproducts such as a source of nutrients for new batches of algal cultivation or fertilizer production. The importance of this research lies within the energy conservation associated with the flash hydrolysis process, the quality of the co-products that are generated during the flash hydrolysis process, and the subsequent processing methods utilized to recover the nutrients not directly used for biofuel products. Processes which complement each other in the processing of microalgae to biofuel must be utilized for improving life cycle assessment (LCA) and technoeconomic analysis (TEA) results. These LCA and TEA data are critical for investors in both the public and private sectors. A valuable return on investment must be quantified in order for investors to move forward with advanced biofuels production. A combination of resources are utilized in this dissertation to quantify the LCA and TEA of the hydrothermal processes that are utilized in the ODU Biomass Research Laboratory (BRL) which include Argonne National Laboratory GREET, SuperPro Designer, Aspen Plus, and SimaPro’s Ecoinvent databases. This dissertation evaluates the novel processes researched in the BRL from the microscopic flash hydrolysis process level to a community level macroscopic evaluation. The clarity of how the flash hydrolysis compares with other hydrothermal processes is studied by conducting a LCA comparison. The flash hydrolysis process is then modeled utilizing two different microalgae species with varying cultivation and nutrient extraction properties. The alternate downstream processing methods for recovering preserved nutrients is then modeled for LCA and TEA results in order to quantify how coproduct generation offsets energy costs associated with algae biofuel processing. The final chapter of this dissertation utilizes the LCA and TEA results captured within the preceding assessments to develop a sustainable community model with algae cultivation and downstream processing at the focus of the sustainable community and an ultimate goal of zero net energy and zero waste system boundaries for the community

Holistic Approach in Microalgae Conversion to Bioproducts and Biofuels Through Flash Hydrolysis

In recent years, the demand for renewable energy, mainly biomass has increased. The U.S. Energy Information Administration reported that more than 13.3% of the total energy production in the first seven months of 2017 was produced from a biomass source. Among all biomass resources, microalgae has brought a lot of attention due to their numerous advantages such as higher growth rate and productivity compared with the conventional energy crops, higher energy conversion efficiency by photosynthesis, and less water requirement than terrestrial crops. However, its development is far behind industrial production. Several research efforts across the globe have been concerned with addressing the technical barriers in the commercialization of algae-based sustainable biorefineries. Nutrients cost and management have been highlighted as one of the most significant challenges in algae cultivation and downstream processing. Therefore, any technology advancement that can reduce the energy input to the process, any nutrients recycling that result in reduction of nutrients input or/and production of value-added bioproducts, will enhance the commercialization potential. This study has developed multiple viable pathways to effectively contribute to the algal based industries. Chapter 1, includes an overall introduction through these approaches. In Chapter 2, kinetics of peptides and arginine production from Scenedesmus sp. microalgae through flash hydrolysis (FH) were studied. In chapter 3, the FH process on the Nannochloropsis gaditana as a high-ash marine algae was studied with focus on the biofuels intermediate (BI) characterization and the application of the hydrolysate as a nutrient source for algal cultivation. In chapter 4, two pathways were developed to recover nutrients in the microalgae hydrolysate in the form of value-added bioproducts such as hydroxyapatite and dittmerite. In chapter 5, the effect of reaction time on the phosphate removal from the algae hydrolysate and the chemistry of precipitates minerals were investigated. In chapter 6, the effect of flash hydrolysis process on the lipid extractability of three algal species were investigated. In addition, biocrude yields and composition from hydrothermal liquefaction of raw and biofuels intermediates of Chlorella vulgaris were compared. In chapter 7, several future works and research pathways were recommended by the author of this dissertation

Engineering highly productive cyanobacteria towards carbon negative emissions technologies

Cyanobacteria are a diverse and ecologically important group of photosynthetic prokaryotes that contribute significantly to the global carbon cycle through the capture of CO2 as biomass. Cyanobacterial biotechnology could play a key role in a sustainable bioeconomy through negative emissions technologies (NETs), such as carbon sequestration or bioproduction. However, the primary issues of low productivities and high infrastructure costs currently limit the commercialisation of such applications. The isolation of several fast-growing strains and recent advancements in molecular biology tools now offer promising new avenues for improving yields, including metabolic engineering approaches guided by high-throughput screening and metabolic models. Furthermore, emerging research on engineering coculture communities could help to develop more robust culturing systems to support broader NET applications

HYDROTHERMAL LIQUEFACTION OF MUNICIPAL WASTEWATER CULTIVATED ALGAE: INCREASING OVERALL SUSTAINABILITY AND VALUE STREAMS OF ALGAL BIOFUELS

The forefront of the 21st century presents ongoing challenges in economics, energy, and environmental remediation, directly correlating with priorities for U.S. national security. Displacing petroleum-derived fuels with clean, affordable renewable fuels represents a solution to increase energy independence while stimulating economic growth and reducing carbon-based emissions. The U.S. government embodied this goal by passing the Energy Independence and Security Act (EISA) in 2007, mandating 36 billion gallons of annual biofuel production by 2022. Algae possess potential to support EISA goals and have been studied for the past 30-50 years as an energy source due to its fast growth rates, noncompetitive nature to food markets, and ability to grow using nutrient waste streams. Algae biofuels have been identified by the National Research Council to have significant sustainability concerns involving water, nutrient, and land use. Utilizing municipal wastewater to cultivate algae provides both water and nutrients needed for growth, partially alleviating these concerns. This dissertation demonstrates a pathway for algae biofuels which increases both sustainability and production of high-value products. Algae are cultivated in pilot-scale open ponds located at the Lawrence Wastewater Treatment Plant (Lawrence, KS) using solely effluent from the secondary clarifier, prior to disinfection and discharge, as both water and nutrient sources. Open ponds were self-inoculated by wastewater effluent and produced a mixed-species culture of various microalgae and macroalgae. Algae cultivation provided further wastewater treatment, removing both nitrogen and phosphorus, which have devastating pollution effects when discharged to natural watersheds, especially in large draining watersheds like the Gulf Coast. Algae demonstrated significant removal of other trace metals such as iron, manganese, barium, aluminum, and zinc. Calcium did not achieve high removal rate but did present a significant portion of algae biomass total weight; wastewater treatment using nitrification requires significant daily additions of buffers, most commonly lime or calcium hydroxide. Accumulation of these ions and metals in wastewater-cultivated algae results in a biomass with substantial amount of inorganic ash content. The cultivated biomass was converted to a carbon-rich biocrude, similar to petroleum crude oil, through a process called hydrothermal liquefaction (abbreviated as HTL), which uses subcritical water (water just below its supercritical point) as the chemical driving force for conversion. Biomass HTL produces four product fractions; liquid biocrude, solids (referred to as biochar), an aqueous product (referred to as aqueous co-product; abbreviated as ACP), and gasses. Many factors contribute to the overall viability of using algae HTL biocrude as a petroleum displacement, particularly yield and quality are important for overall economics and ability to utilize existing refining infrastructure, respectively. The HTL product distribution and quality of wastewater-cultivated algae has been found to be extremely unique with significant advantageous over controlled fertilized growth strategies. Biocrude yields of were typically lower but substantially higher quality with lower oxygen content and higher amounts of direct fuel distillate fractions. This phenomenon is contributed to the fact that large amounts of pure-phase substituted hydroxyapatite (a calcium orthophosphate material) are synthesized in-situ, providing catalytically active sites. Hydroxyapatite (abbreviated HA) is a widely studied material for bone (and dental) tissue regeneration purposes and its acid-base catalytic properties. The specific HA produced during HTL of wastewater-cultivated algae presents unique characteristics for performance and tunability in each respective application, providing novel economic value streams for the production of algal biofuels. The overall work of this dissertation concludes Lawrence Wastewater Treatment Plant could produce 10-18 barrels of crude oil and over 2 metric tons of refined hydroxyapatite per day for the creation of revenue sales. The work within this dissertation encompasses novelty of characterization methods, HTL feedstocks, and identification of high-value products. Overall, efforts to demonstrate the feasibility of a sustainable biofuel strategy resulted in formulating hypotheses which led to novel discoveries in creating high-value heterogeneous catalysts and biomedical materials. The works presented have the potential to produce an overall process capable of selling significant quantities of biofuels as a by-product and not as the main economic generator, laying the foundation of breakthrough technology which can meet and potentially exceed the $3 per gal biofuel target

The Cause of Inorganic Compounds from Auto-flocculated Algal Solids and Their Effect on the Solid and Biocrude Products of Conventional Hydrothermal Liquefaction

The recent increase in demand for more sustainable and renewable alternatives to both energy and other commercial products has given rise to a modern bioeconomy. With advances in the life sciences, various biomass resources and conversion techniques have been explored to create such products. Often overseen within a bioeconomy, however, is the need for sustainable and renewable means of nutrient recovery, and since 2015 the National Science Foundation, along with several other federal agencies, has invested over $100 million to explore new, innovative processes that are both physical and biological that address the global rise in food, energy, and water. Referred to as the Food, Energy, and Water Nexus, a primary objective of such research is to discover “means of extending resources via methods such as recycling, recovery, and reuse.” Hydrothermal liquefaction (HTL) of algal biomass has been proven to be an effective wet, thermochemical technique for the conversion of biomass to a high quality biocrude oil product. Furthermore, the subcritical water conditions of HTL provide an outstanding environment for the inorganic,0 solid synthesis of high-valued biomaterials and catalysts. The Feedstock to Tailpipe Initiative at the University of Kansas was one of the first to trial HTL on algal solids that were cultivated in wastewater effluent. In addition to an enhanced biocrude product, HTL of wastewater-cultivated algal solids produced a high amount HTL solids unlike several other algal HTL research had previously observed. Further analysis of these HTL solids indicated they were a calcium phosphate material known as hydroxyapatite (HAp), Ca5(PO4)3OH. With a proven proof of concept that HTL of wastewater-cultivated algal solids yields an abundance of HTL solids and an upgraded biocrude product, the major research thrust of this dissertation was to understand the chemical and biological characteristics that created these results. A high ash and calcium content in the wastewater-culitvated algal solids was known to be caused due to the addition of lime, Ca(OH)2, during the wastewater treatment process to control the alkalinity, or buffering capacity, of the wastewater effluent. Thus, Lab- and bench-scale light rack tanks and raceway ponds, respectively, were utilized to grow Chlorella kessleri in BG-11 media with augmented calcium concentrations. All algal cultivation and harvesting were overseen by the collaborating environmental engineers. Algal solid characterization was divided amongst the collaborators and primary author while all HTL reactions and extractions were overseen by the primary author. A majority of the HTL products were also characterized by the primary author with additional analysis and experimentation performed by the collaborator. Light rack experiments aided in discovering the cause for high ash or inorganic capture within the algal solids. Auto-flocculation is an effective dewatering technique that utilizes external coagulants that causes microalgae to flocculate and condense at the bottom of the growth tanks. An increase in pH of 10 or 11 causes solids to precipitate from algal growth media and act as natural coagulants for the auto-flocculation of algal solids. These precipitated solids from auto-flocculation are the cause of the high calcium and ash content in the algal solids. X-ray diffraction (XRD) revealed the primary, crystalline structure of auto-flocculated and wastewater-cultivated algal solids was calcite or CaCO3. Algal solids cultivated in the light racks with various Ca:P molar ratios also showed that an increased calcium content causes a nearly 100% recovery of phosphorus in the HTL solid product. Identical P-recovery in the solid-phase was also observed from the previous HTL of wastewater-cultivated algal solids. Thus, auto-flocculation and subsequent HTL of algal solids provides excellent means for sustainable, renewable P-recovery. A uniform HAp or alternative calcium phosphate structure, such as tricalcium phosphate (TCP) Ca3(PO4)2, were not observed in the HTL solids produced from auto-flocculated algal solids that were cultivated in the light racks. Thus, inorganic and biological model compounds were reacted at identical, conventional HTL conditions (350°C for 60 minutes). Calcite and trisodium phosphate, Na3PO4, were the primary inorganic model compounds used to create a uniform calcium phosphate HTL solid. Initial results were unsuccessful and identical XRD patterns of the HTL solids from duplicate reactions were unachievable. However, the addition of silicon dioxide, SiO2, did enhance the intensity of calcium phosphate structures in the XRD patterns of HTL solids both from the inorganic model compounds and previously auto-flocculated algal solids. The largest discovery from the experimentation of model compounds was a technique for measuring inorganic carbon, (CO32-) within a solid sample through thermal gravimetric analysis (TGA). Calcium carbonate degrades between 600-800°C releasing CO2 and resulting in CaO. TGA allows one to measure the mass lost due to CO2, and from stoichiometry, one can determine the initial mass of CaCO3 with less than 1% error. A greater error occurs, however, when applying this technique to measuring the amount of carbonate in algal solids. The additional organic, biomass of algal solids delays the degradation of CO3 within the algal solids. Correlated trends from both TGA-measured carbonate and the theoretical carbonate as determined through water chemistry modeling for the algal solids justified further use TGA method for measuring carbonate. Carbohydrate, lipid, and protein biological compounds were also reacted at conventional HTL conditions both with and without the addition of various, previously observed, inorganic compounds. Nutritional supplement, soy protein was the only biological compound that produced a viable biocrude product for analysis. Despite several combinations of HTL reactions with different biological and inorganic model compounds, substantial changes to the organic biocrude product were not observed with HAp. The lack of success in proving HAp could be acting as a catalyst and cause in-situ biocrude upgrading aids in further determination and exploration for other causes for the enhanced biocrude properties observed from the HTL of auto-flocculated algal solids. The final raceway study was a comprehensive overview for the previous observations and conclusions from the light rack and model compound studies. The larger raceway ponds allowed for ample algal solid production from both N- and P-limited growth media. Furthermore, algal solids were auto-flocculated and harvested at various growth stages to alter both their inorganic composition, in terms of bio-P and solid-P, as well as their biomolecular content. The theory and original hypothesis proposed by the collaboration was the aqueous phosphorus that remains in solution would precipitate as solid, amorphous calcium phosphate. Thus, algal solids cultivated in N-limited media created algal solids with a majority of theoretical solid-P sustained throughout all growth stages while the theoretical amount of solid-P decreased as algal growth accumulated in P-limited media. The hypothesis that amorphous calcium phosphate precipitates from solution was confirmed with the observance of calcium phosphate structures in the algal solid ash. The amount of amorphous calcium phosphate in the algal solids could be further estimated using the previous TGA-method for estimating the carbonate. The balance of calcium not stoichiometrically correlated to the mass of carbonate was assumed to be associated with amorphous calcium phosphate. Similar, correlating trends between the theoretical solid-P, the estimated percent of calcium as calcium phosphate, and the calcium phosphate structure in the algal solids’ ash confirmed the initial hypothesis that amorphous calcium phosphate precipitates and is captured within the algal solids. Uniform calcium phosphate structures in the HTL solids were also produced from algal solids that contained a majority of amorphous calcium phosphate. Thus, the algal growth media and growth stage ultimately decide the final structure of the HTL solids. Finally, the algal growth media and growth stage impacted the biocrude composition as well. A decrease in long chain amides and C20 hydrocarbons that had previously been observed in the biocrude produced by the HTL of wastewater-cultivated algal solids also only appeared from N-limited, stationary-stage, auto-flocculated algal solids cultivated in the raceway. The uniqueness of the results leads to believe that the N-limited, semi-batch cultivation of algal solids from wastewater effluent may be the cause for improvements in the biocrude as opposed to the HTL solids. However, substantial variances were observed in biocrude properties from algal solids cultivated in the same growth media and harvested from the same growth stage with only the inorganic composition varying. Furthermore, biocrude with the highest H/C molar ratio was achieved when complimented with HTL solids with a primarily calcite structure. Thus, it is suggested that future work focus on the impact and role of CaCO3 during the HTL of algal solids

Algae as a Potential Source of Food and Energy in Developing Countries

Algal biomass has large potential for the production of fuels and of value added chemical products. A brief survey of methods for the recovery of the biomass, for its successive transformation, and of the potential targets is here provide