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Generation of coproducts from nutrients is purported to improve the sustainability of algae-derived transportation fuels by minimizing life cycle impacts and improving economic sustainability. Although algae cultivation produces lipids that is upgraded to drop-in transportation fuel products, life cycle assessment and techno-economic analysis have shown that without coproducts, energy/economic returns are diminishing regardless of processing methods. This study utilizes a combined flash hydrolysis (FH), hydrothermal liquefaction (HTL), and coproduct conversion technology (atmospheric precipitation/AP; hydrothermal mineralization/HTM) to conserve the most recyclable nutrients for coproduct marketability. Six biofuel pathways were developed and compared in terms of “well-to-pump” energy, life cycle greenhouse gas (LC-GHG) emissions, and economic profitability: renewable diesel II (RDII), renewable gasoline (RG), and hydroprocessed renewable jet (HRJ) fuel, each were modeled for AP and HTM coproduct conversion. A functional unit of 1 MJ usable energy was employed. RG showed a promising energy-return-on-investment (EROI) due to multiple coproducts. All models demonstrated favorable EROI (EROI > 1). LC-GHG emissions tie in with EROI such that RG produced the least emissions. HRJ-HTM was determined to be the most profitable model with a profitability index (PI) of 0.75. Sensitivity analyses revealed that dewatering affects EROI and PI significantly. To achieve break-even, gasoline must sell at $4.10/gal, diesel at $5.64/gal, and jet fuel at $3.43/gal. 

The development of algal biorefineries is strongly associated with the nutrient management, particularly phosphorus, which is a limited mineral resource. Flash hydrolysis (FH) has been widely applied to a variety of algae species to fractionate its constituents. This chemical-free, subcritical water technique was used to extract more than 80 wt % of phosphorus available in the Scenedesmus sp. as water-soluble phosphates in the aqueous phase (hydrolysate). The phosphate-rich hydrolysate was subjected to the hydrothermal mineralization (HTM) process at 280 °C and 5–90 min of residence time to mineralize phosphates as allotropes of calcium phosphate such as hydroxyapatite (HAp) and whitlockite (WH). In the current study, the effect of reaction time on phosphate mineralization from the hydrolysate as well as the composition, structure and the morphology of the precipitates were studied. Calcium hydroxide and commercial HAp were used as the mineralizer and seeding material, respectively. More than 97 wt % of phosphate and almost 94 wt % of calcium were removed in the first 5 min of the HTM process. Results revealed that as the HTM reaction time increased, calcium phosphate precipitates transformed from WH to carbonated HAp. The integration of the proposed mineralization process with FH can be a cost-effective pathway to produce sustainable, and high value phosphate-based bioproducts from algae. The application of HAp includes biomedical applications such as synthetic bone and implant filling, drug delivery, chromatography, corrosion resistance materials, catalytic activities and fertilizers.