Hydrothermal Liquefaction

Algae are an appealing source for bioenergy due to their
high yields relative to terrestrial energy crops. The high cost of
production, however, has prohibited commercialization. Hydrothermal liquefaction is a technology that converts more of the algae into oil than alternative technologies, thereby reducing the amount of expensive pond infrastructure and energy required for cultivation. We incorporate recent experimental results into an analysis that models the economic and life-cycle performance of an algal biorefinery across a range of reaction conditions. Two strategies are explored: one pathway with gasification of the aqueous waste products for onsite energy recovery and another pathway featuring cultivation of Escherichia coli on the aqueous products
and recycling of the biomass back through the reactor for boosted oil yields. We found that the maximum net energy ratio of 1.9 and minimum global warming potential of 1.0 kg CO2e/L-oil occurred with gasification, along with the minimum reaction temperature explored, 250 °C, and reaction times close to 1 h. The optimal economic and occupied land results occurred at a maximum temperature of 400 °C and with the shortest reaction time explored of 5 min. The cost of algal oil at these conditions was $1.64 L-oil−1 (or $263 bbl−1). For the regrowth pathway, the land footprint could be further reduced by 10%, and the optimal cost could be reduced to $1.59 L-oil−1. Forgoing gasification had a significantly detrimental effect on the other two metrics. Given the importance of economics to an algal biorefinery’s operations, this could be a viable option.

KEYWORDS: Algae, Hydrothermal liquefaction, Life cycle assessment, Biofuel, Escherichia coli

Globally, approximately 600–700 million tonnes/yr. of solid waste (SW) and 250–300 million tonnes/yr. of fecal sludge (FS) are not managed in an environmentally safe manner. Conversion of these two waste streams using this ratio (2–3: 1 of SW: FS) to produce biocrude for fossil fuel substitution would act as an integrated waste to
energy approach to address current global crises (GHGs emissions, climate change, and global warming). This study took the opportunity to produce petroleum-like biocrude through co-liquefaction of organic solid waste (OSW) and fecal sludge (FS) and optimized crude production yield and quality by varying feedstock ratios (1:0,
1:3, 1:1, 3:1, and 0:1) and temperature (280–340 ◦C). A higher synergistic effect was observed at feedstock ratio 3:1 (OSW: FS) and 320 ◦C with 52% biocrude yield, of which 64% was lighter-fraction (C < 20). The produced light crude contained 60% ester, 14% heterocyclic, and 12% fuel hydrocarbon fractions and exhibited a heating value of 42.7 MJ/kg, suggesting a potential candidate for petro crude (42–49 MJ/kg) substitution. This energetically feasible process (energy recovery 86% and energy consumption ratio 0.36) would provide a revenue of US$ 467.8 per metric ton of waste feedstock, validating the high economic prospects for a cleaner production pathway.

Abstract Hydrothermal Liquefaction is a thermochemical process that uses heat and pressure to convert biowastes into renewable biocrude oil, simultaneously generating both a metal and phosphorus rich solid phase and a nutrient rich aqueous phase. Eight types of food waste, all collected from a campus dining hall and grouped into lipid-rich, protein-rich, and carbohydrate-rich feedstocks, were processed with conditions ranging from 280-340oC and 10-60 min reaction time. The byproducts for the optimized oil yield conditions were analyzed to elucidate mechanisms by which compounds are concentrated in different phases through their characterization. The differences in elemental and biochemical composition among feedstocks demonstrate considerable gaps in understanding the expected characteristics as a result of several reaction parameters and how to best reuse the materials. This work additionally reviews considerations for subsequent anaerobic digestion and algae cultivation with respect to the nutrients and inhibitory contents of the Hydrothermal Liquefaction Aqueous Phase.

Abstract Over the last decades, microalgae have gained a commendable role in the rising field of biofuel production as they do not compete with food supply, reduce greenhouse gases emission, and mitigate CO2. Specifically, thermochemical processing of microalgae yields products, which can be used both for energy and other industrial purposes, depending on the algal strain, processing method and operative conditions. Algae are converted into various high-value products, including nutraceuticals, colourants, food supplements, char, bio-crude, electricity, heat, transportation fuel, and bio-oil. Therefore, microalgae are believed to be a strategic resource for the upcoming years and their utilization is meaningful for many industrial sectors. In this framework, this review addresses the various thermochemical processing of microalgae to various biofuels and their industrial significance. The obstacles in various thermochemical conversion methods have been critically flagged, in order to enable researchers to choose the optimal method for fuel production. Furthermore, light is shed on cultivation systems to generate rapidly microalgal biomass for thermochemical processing. Eventually, all recent literature advancements concerning microalgae cultivation and thermochemical processing are critically surveyed, and summarized.