Lipid-extracted Algae Research Articles

Activated carbon production from algal biochar: Chemical activation and feasibility analysis

Chemical activation was employed to convert algal biochar obtained from hydrothermal carbonization of lipid-extracted algae (LEA) to activated carbon. Potassium hydroxide, previously utilized on cellulosic biomass but not on algal biomass, was employed as activating agent and the impact of the activation conditions, namely temperature, activation time, and amount of activating agent, were investigated. The yield of activated carbon from biochar ranged from 28 % to 52% and decreased as the temperature was raised from 400 to 600 °C, the residence time from 30 to 60 min, and the KOH/biochar mass ratio from 0.25 to 1.0. In contrast, surface area increased by 2.1-fold when the activation temperature was raised to 600 °C and by 1.5-fold when the KOH: biochar ratio was raised to 1.0. Maximum BET surface area of 847 m2/g was achieved at 600 °C after 30 min at a mass ratio of 1:1. The integrated hydrothermal carbonization and activation process of LEA was simulated in Aspen Plus® and the technoeconomic feasibility was assessed based on our experimental data at 1,000 and 10,000 acres of cultivation area. For the latter, net present value analysis determined a minimum selling price of $2,200/ton for algal activated carbon with a financial breakeven achieved in 3.5 years. This is cost-competitive with the current price of commercial fossil-derived activated carbon, which is $1,543-$2,645/ton. Sensitivity analysis showed that the minimum selling price is significantly affected by algal biomass yield during cultivation and is more sensitive to the operating expenses than to the capital investment.

Using nitrogen starvation and excess phosphorus for two-stage algae cultivation to improve butanol production of lipid-extracted algae

Lipid-extracted algae (LEA) can be processed via acetone, butanol and ethanol fermentation to produce butanol as an additive to algal biofuel, but direct fermentation was ineffective. In this study, nitrogen and phosphorus regulation for algae cultivation was applied to modify the biochemical composition of algal biomass and hence improve butanol production from LEA. The results show that when nitrogen starvation and excess phosphorus were used during algae cultivation, a significant rise of starch productivity and decline of protein productivity for algal biomass were obtained, which resulted in the highest butanol productivity of 20.16 mg L−1 d−1, a 5.48-fold increase over traditional one-stage cultivation. Mechanism analysis suggested that nitrogen starvation enhanced lipid and starch contents and reduced protein content, which modified C/N ratio of LEA, prevented acid crash and improved butanol production; excess phosphorus modified amino acid contents of phenylalanine and arginine, which strengthened fluxes directing to butanol generation. Through this investigation, the approach of using nitrogen starvation and excess phosphorus to modify biochemical composition of algal biomass and subsequently improve butanol production of LEA was demonstrated to be applicable.

Combining ABE fermentation and anaerobic digestion to treat with lipid extracted algae for enhanced bioenergy production

As a downstream process output, biobutanol can be produced via acetone, butanol, and ethanol (ABE) fermentation from lipid-extracted algae (LEA), but the leftover residue has not been treated for additional value. In current study, LEA were acid hydrolyzed to extract glucose into the hydrolysate, which was then used for ABE fermentation to produce butanol. In the meantime, anaerobic digestion was performed on the hydrolysis residue to produce methane and release nutrients for algae recultivation. To optimize butanol and methane production, several carbon or nitrogen supplements were applied. The results showed that the hydrolysate produced a high butanol concentration of 8.5 g/L with bean cake supplemented, and the residue co-digested with wastepaper had a higher methane production compared to the direct anaerobic digestion of LEA. The causes of the enhanced performances were discussed. The digestates were reused for algae recultivation and were proved to be effective for algae and oil reproduction. The combined process of ABE fermentation and anaerobic digestion was thus proved a promising technique to treat LEA for economic benefit.

Optimization of Algae Residues Gasification: Experimental and Theoretical Approaches

Abstract Gasification is one of the thermochemical pathways of biomass conversion that produces synthesis gas, tar, and char. This study aims to convert algal residues via gasification at different operating conditions; temperature, equivalence ratio, and biomass loading. The study was carried out in 3 steps; (1) testing the outcomes of temperature and loading effects on synthesis gas yield, (2) experimental optimization of gasification via Design Expert, and (3) theoretical optimization of gasification via Aspen Plus simulation. Temperature and equivalence ratio highly influenced synthesis gas composition, while loading demonstrated less effect on the synthesis gas composition. The experimental and simulated gasification outcomes were compared to obtain optimized conditions that produce high H2 and CO yields. The data were validated using root mean square error. The optimized temperature, loading, and equivalence ratio were found for both algal residues that produced 36.38 and 13.28mol% of H2 and CO, respectively for lipid extracted algae (LEA) and 47.99 and 26.05mol% of H2 and CO, respectively for fucoidan extracted seaweeds (FEA). There was a considerable variation between experimental and simulated data due to the simulation and experimental limitations. The average Carbon Conversion Efficiency values were 66.36 and 80.42% for LEA and FES, respectively, denoting that LEA produced less carbon-containing products, while FES produced more carbon-containing products. In conclusion, LEA gasification yielded more H2 while FEA produced more CO.

Hydrothermal Carbonization of Residual Algal Biomass for Production of Hydrochar as a Biobased Metal Adsorbent

Conversion of residual algal biomass to value-added products is essential for enhancing the economics of algae cultivation. Algal hydrochar produced via hydrothermal carbonization of lipid-extracted Picochlorum oculatum is a material rich in oxygen functional groups and carbon (up to 67.3%) and hence a promising candidate for remediation of wastewaters. The hydrothermal carbonization conditions were optimized and the adsorption capacity of the hydrochar was tested for metal removal. By the end of the remediation process, cumulative removal of Al3+, Cu2+, Fe2+, Mg2+, Mn2+, and Pb2+ reached 89, 98, 75, 88, 75, and 100%, respectively. The adsorption of all metals was found to follow pseudo second-order kinetics and the Langmuir isotherm. Overall, when hydrothermal carbonization is applied to lipid-extracted algae, it generates a promising biobased adsorbent with value-added potential in metal remediation.

Beneficial use of the aqueous phase generated during hydrothermal carbonization of algae as nutrient source for algae cultivation

Hydrothermal carbonization converts algal biomass to hydrochar, but also generates a waste aqueous phase rich in nitrogen and other elements that need to be treated before discharge into water bodies. At the same time, cultivation of microalgae requires significant amounts of nutrients, such as nitrogen, phosphorous, and trace metals. Utilization of aqueous phase in algae cultivation can potentially reduce algae production cost, while mitigating waste generation, leading to a circular process that enhances the sustainability of algal biofuels and bioproducts. In the present study, we assessed the potential of aqueous phase generated during hydrothermal carbonization of lipid-extracted algae to support algal biomass and lipid production from Chlorella vulgaris. The aqueous phase was found to contain high concentrations of nitrogen (2.4 g/L), phosphorus (1.75 g/L), organic carbon (20.9 g/L), and trace elements. Among several aqueous phase dilutions in non-sterilized water (2.5–7.5% v/v) tested for algae cultivation, maximum lipid productivity that was 1.7-fold higher than with standard cultivation media was achieved when C. vulgaris was grown in 5% aqueous phase. Time course studies showed significant nutrient removal of 95% nitrate, 60% ammonia, 47% phosphate, and 30% organic carbon by C. vulgaris over the course of a 10-day cultivation. Moreover, when compared with standard media, utilization of the aqueous phase resulted in augmentation of both storage and structural algal lipids that can be used for biofuel and nutraceutical production, respectively. Subsequent bench-top photobioreactor cultivation validated that the aqueous phase is a promising cultivation medium for algal product manufacturing.

Improving the feasibility of aquaculture feed by using microalgae.

The aquaculture industry is an efficient edible protein producer and grows faster than any other food sector. Therefore, it requires enormous amounts of fish feed. Fish feed directly affects the quality of produced fish, potential health benefits, and cost. Fish meal (FM), fis oil (FO), and plant-based supplements, predominantly used in fish feed, face challenges of low availability, low nutritional value, and high cost. The cost associated with aquaculture feed represents 40-75% of aquaculture production cost and one of the key market drivers for the thriving aquaculture industry. Microalgae are a primary producer in aquatic food chains. Microalgae are expanding continuously in renewable energy, pharmaceutical pigment, wastewater treatment, food, and feed industries. Major components of microalgal biomass are proteins with essential amino acids, lipids with polyunsaturated fatty acids (PUFA), carbohydrates, pigments, and other bioactive compounds. Thus, microalgae can be used as an essential, viable, and alternative feed ingredient in aquaculture feed. In recent times, live algae culture, whole algae, and lipid-extracted algae (LEA) have been tested in fish feed for growth, physiological activity, and nutritional value. The present review discusses the potential application of microalgae in aquaculture feed, its mode of application, nutritional value, and possible replacement of conventional feed ingredients, and disadvantages of plant-based feed. The review also focuses on integrated processes such as algae cultivation in aquaculture wastewater, aquaponics systems, challenges, and future prospects of using microalgae in the aquafeed industry.

Hydrothermal gasification of Scenedesmus obliquus and its derivatives: a thermodynamic study using Aspen Plus

AbstractThis study presents the simulation of hydrothermal gasification (HTG) of Scenedesmus obliquus microalgae and their derivatives using Aspen Plus V11. The effect of operating parameters such as temperature, pressure, and biomass concentration on the yield and composition of gaseous products using whole algae, lipid, and lipid extracted algae (LEA) as feedstocks was examined. The results showed that reaction pressure exhibited minimal impact whereas temperature, biomass concentration, and feedstock composition had significant effects on the composition of gaseous products. It was also found that a low temperature (400 °C) and biomass concentration of 40 wt% favored the production of methane‐rich gas. In contrast, high temperature (700 °C) and low biomass concentration (10 wt%) favored hydrogen‐rich gas production in all the three feedstocks considered. The highest mole fraction achieved for CH4 was 53.45, 61.70, and 52.20 mol%, which corresponded to a CH4 yield of 31.14, 56.90, and 30.15 mmol g−1 for whole algae, lipid, and LEA respectively. For H2 rich gas production, the highest mole fractions achieved were 55.77, 52.29, and 55.34 mol%, which correspond to H2 yields of 75.44, 105.51, and 73.49 mmol g−1 for whole algae, lipids, and LEA, respectively. The ranking order for the yield and lower heating value of the product gas from the HTG process is lipid > whole algae > LEA. This study has shown that hydrogen‐rich and methane‐rich gas can be produced from the hydrothermal gasification of microalgae as a function of the reaction conditions and feedstock composition. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd

Techno-economic analysis of biodiesel production over lipid extracted algae derived catalyst

The utilization of algal biomass residue after lipid extraction for other purposes can lead to maximum usage of algal biomass and economically beneficial microalgal biodiesel technology. In this study, the performance and economic potential of the conversion of Scenedesmus sp. lipids to biodiesel over lipid extracted algae (LEA) derived catalysts were investigated. The lipid extracted algae (LEA) derived catalysts (Ni/C and Ni/Fe3O4-C) were synthesized by impregnation technique and characterized using different analytical tools. The biodiesel conversion of 96.43%, 98.5% and 95.12% was achieved using biochar (C), Ni/C, and Ni/Fe3O4-C respectively under the following conditions: reaction time (4 h), temperature (60 °C), methanol to oil molar ratio (30:1) and catalyst dosage (15% w/w of oil). The findings from this study have shown that the use of lipid extracted algae derived catalysts reduced the unit production cost of microalgal biodiesel from 2.03 $/kg to (1.70–1.74 $/kg) when compared to homogeneous catalyst. Among the lipid extracted algae derived catalysts, the use of Ni/C catalyst gave the lowest unit production cost (1.70 $/kg) for biodiesel production from microalgae. The recyclability potential of the LEA derived catalysts could improve the economic viability of the process. The payback period in the range of 1.32 yr–5.57 yr obtained using LEA derived catalysts was below the lifespan of the project (10 years), suggesting that the proposed microalgal biodiesel production is economically feasible.

Recycling of Lipid-extracted Algae Cell Residue for Microorganisms Cultivation and Bioenergy Production

Recycling of Lipid-extracted Algae Cell Residue for Microorganisms Cultivation and Bioenergy Production

Application of Jerusalem artichoke and lipid-extracted algae hydrolysate for docosahexaenoic acid production by Aurantiochytrium sp. KRS101

Microalgae-derived docosahexaenoic acid (DHA) production has been considered an alternative technology to overcome several disadvantages of fish oil-based DHA production. Despite its potential, efficient production methods for DHA have been rarely reported. Accordingly, in this study we investigated the potential application of Jerusalem artichoke and lipid-extracted algae (LEA) hydrolysates as inexpensive sources of carbon and other nutrients for DHA production using Aurantiochytrium sp. KRS101. Response surface methodology (RSM) with central composite design (CCD) was used to determine the maximum point of DHA productivity in the presence of 51.9 g L−1 fructose and 4.9 g L−1 yeast extract. Hydrolysis of 76.6 g L−1 Jerusalem artichoke powder with 0.25 N sulfuric acid at 70 °C yielded the desired concentration of fructose for use as the medium. Cultivation of the microalgae using the Jerusalem artichoke hydrolysate (JAH) and JAH + LEA (JLH-1) resulted in 27.8% and 31.3% improvements in biomass productivity, respectively, compared with the basal medium control. In addition, simultaneous one-step hydrolysis of Jerusalem artichoke and LEA (JLH-2) resulted in 7.2% higher biomass and 47% higher DHA yields than that obtained from hydrolyzing the two components separately (JLH-1). These results suggested that a strategy using JAH combined with LEA could replace expensive nutrient sources and produce efficient and eco-friendly DHA from Aurantiochytrium sp. KRS101.

Optimizing performance of a microbial carbon-capture cell using Box-Behnken design

Performance of a microbial carbon-capture cell (MCC), in which a microbial fuel cell and a photo-bioreactor gets mutually benefitted, is reliant on certain critical factors. In present investigation, Box-Behnken design is adopted to statistically evaluate the effect of influential parameters, namely nitrate concentration in catholyte, photoperiod and concentration of lipid extracted algae (LEA) of mixed culture microalgae in the anodic inoculum, on the performance of MCC. As per validation experiment, based on statistical model prediction, the ideal performance (higher power density and algal productivity) was achieved at LEA concentration, nitrate concentration and photoperiod in a range of 5.3–5.7 g/L, 44−50 mg/L and 10.00–10.67 h, respectively. Furthermore, the accuracy of model predictions was successfully validated by operating a separate MCC, which gave a power density and algal productivity (7.12 ± 0.09 W/m3 and 0.83 ± 0.02 g/L.day) close to the predicted output (7.05 ± 0.13 W/m3 and 0.838 ± 0.019 g/L.day). Box-Behnken design aided in optimizing the influential factors so as to make MCC economical and efficient for scale-up.

Heterotrophic cultivation of Ettlia sp. based on sequential hydrolysis of Helianthus tuberosus and algal residue

Heterotrophic cultivation of microalgae results in substantial productivity but requires significant nutrient input. Alternative sources of major nutrients such as C and N should be carefully selected to make heterotrophic production of microalgal biomass feasible. In this study, Helianthus tuberosus and lipid-extracted algae (LEA) were hydrolyzed with sulfuric acid to grow Ettlia sp. YC001. Hydrolysis of H. tuberosus with 0.3 N of sulfuric acid resulted in fructose yield of 0.51 g g−1 and glucose yield of 0.14 g g−1 at 80 °C in 1 h. Proteolysis of algal residue with 2 N of sulfuric acid resulted in amino acid yield of 0.38 g g−1 at 110 °C in 24 h. To simplify the production of hydrolysates, the hydrolysis conditions were combined to establish a tailored sequential hydrolysis process. Then, simultaneous neutralization and salt removal of the hydrolysates were done with barium hydroxide. Consequently, cultivation of Ettlia sp. with the diluted sequential hydrolysate of H. tuberosus and LEA successfully achieved 5.90 g L−1 d−1 of biomass productivity and 1.42 g L−1 d−1 of lipid productivity with Ettlia sp.

Techno-economic feasibility of algal aquaculture via fish and biodiesel production pathways: A commercial-scale application

The industrialization of integrated algae-aquaculture systems entails appropriate information regarding environmental and economic assessments, field and laboratory analyses, and feasibility studies. Accordingly, Scenedesmus obliquus was cultivated in a raceway pond (300 m3), and the algal biomass was used as a protein source for the growth of Nile tilapia (Oreochromis niloticus). Nile tilapia fish was cultivated in five commercial-scale tanks for 44 weeks, having a productivity of 15–20 kg (live weight)·m−3. Among various algal-based fish meals, the diet containing 7.5% microalgae provided the largest body length (29 cm) and weight (402 g), as well as the optimum growth performance parameters. Scenedesmus obliquus was subjected to lipid extraction, and the defatted biomass was also used as a substitute for fishmeal in diets. Nile tilapia grown using the lipid-extracted algae had improved health status, and the biochemical composition was satisfactory. Further, two scenarios were economically investigated: Case 1, the direct use of algal biomass for fish production, and Case 2, the utilization of algae for biodiesel production followed by the application of residual biomass in fishmeal diets. Based on field experiments and financial information reported in the literature, the two options would offset their initial investment cost within payback periods of 7.5 and 6.8 yr, respectively.

Lipid-Extracted Algae as a Soil Amendment Can Increase Soil Salinization and Reduce Forage Growth

Algae as a biodiesel feedstock are more productive per unit area than traditional feedstock options, but currently algae production is not economical without high-value co-products. Lipid-extracted algae (LEA) may be useful as a soil amendment; however, research is needed to determine the feasibility and management strategies required. The objective was to determine salinity-associated effects of LEA as a soil amendment on a range of salt tolerant forages [foxtail millet (Setaria italica L.), pearl millet (Pennisetum glaucum L.), and a sorghum-sudangrass hybrid (Sorghum bicolor L. Moench)]. Forage seed were planted in columns containing sandy clay loam soil amended with the following: (1) control [nitrogen (N) and phosphorus (P) fertilizer added], (2) 1.5% LEA by weight, (3) 3.0% LEA, (4) 1.5% LEA + 1.5% wheat straw (WS), and (5) 1.5% WS (+N, +P). Seedling emergence and total herbage mass (HM) from sequential harvests was determined, along with forage mineral uptake. Soil pH and electrical conductivity (EC) were analyzed after the final harvest. Seedling emergence of pearl millet was negatively affected by LEA application, but not foxtail millet or sorghum-sudangrass. Pearl millet emergence was most reduced in 3.0% LEA treated soil, however, this treatment produced greater HM by the third harvest. Soil pH and EC were greater in 3.0% LEA-treated soil than the control and 1.5% WS treatment. Production of salt tolerant forages such as sorghum-sudangrass is possible in LEA-amended soil; however, with repeated applications soil salinity may reduce productivity and sustainability.

Carbon balance of major volatile fatty acids (VFAs) in recycling algal residue via a VFA-platform for reproduction of algal biomass

The feasibility of a carbon recycling system that transforms algal residue to volatile fatty acids (VFAs) for re-cultivating microalgae was evaluated based on a carbon balance analysis of major VFAs consisting of acetate (HAc), propionate (HPr), and butyrate (HBu). This system largely involves two processes: (i) bioconversion of algal residue to VFAs by anaerobic fermentation, and (ii) cultivation of microalgae using the produced VFAs. The carbon balance for each unit process was examined to assess how much carbon in algal residue can be converted to these major VFAs and then assimilated to microalgae biomass. First, the yield and the profile of VFAs from raw algae (RA) and lipid-extracted algae (LEA) at psychrophilic (15 °C), mesophilic (35 °C), and thermophilic conditions (55 °C) were compared. When digesting the LEA under the thermophilic condition, the highest conversion yield, 0.36 (g carbon in VFAs/g carbon in biomass), with a compositional ratio of 6:1:3 (HAc: HPr: HBu) was obtained. Consumption of VFAs for microalgal growth reached a maximum value of 0.66 (g VFAs assimilated to biomass/g VFAs provided) at the compositional ratio of 6:1:3. Consequently, the maximum total carbon recycling ratio was 23.8% when fermenting LEA at the thermophilic condition. Our findings comprehensively revealed that establishing conditions that convert LEA to higher content of acetate is a decisive factor. It was estimated that around 40% of the total carbon from the LEA can be recovered for the production of algal biomass, when increasing the VFA conversion yield beyond 60% by adopting pretreatment methods.

Effect of water content on [Bmim][HSO4] assisted in-situ transesterification of wet Nannochloropsis oceanica

1-Butyl-3-methylimidazolium hydrogen sulfate ([Bmim][HSO4]) was employed to catalyze the in-situ transesterification of wet Nannochloropsis oceanica. Algal cell wall was dissolved by [Bmim][HSO4] according to TEM analysis of untreated Nannochloropsis sp. cells and lipid extracted algae (LEA). The temperature and time are favorable to biodiesel production in 100–200 °C, time of 0–70 min, with methanol: algae, however, it decreased to 10.64% at time of 90 min. The biodiesel and energy production of [Bmim][HSO4] catalyzed in-situ transesterification varied due to the competition of catalytic property and algal dissolution ability with variation of water content. The catalytic property of [Bmim][HSO4] was the dominate parameter affecting biodiesel production, therefore, total energy production of in-situ transesterification, as a parameter of biodiesel production, was slightly increased from 13.12 kJ to 14.51KJ with water content of wet algae varied from 0 to 15 wt%. However, it decreased to 8.37 at water content of 20 wt% due to the weakened algal dissolution ability, which was proved by the decrease of hydrogen bond acceptor capacity(β) from 0.942858 to 0.942851 in water content of 0–30 wt%. The decomposition of carbohydrates and proteins in IL – water mixtures enhanced biodiesel production according to elemental analysis of LEA.

Development of Carbon-Based Solid Acid Catalysts Using a Lipid-Extracted Alga, Dunaliella tertiolecta, for Esterification.

Novel carbon-based solid acid catalysts were synthesized through a sustainable route from lipid-extracted microalgal residue of Dunaliella tertiolecta, for biodiesel production. Two carbon-based solid acid catalysts were prepared by surface modification of bio-char with sulfuric acid (H₂SO₄) and sulfuryl chloride (SO₂Cl₂), respectively. The treated catalysts were characterized and their catalytic activities were evaluated by esterification of oleic acid. The esterification catalytic activity of the SO₂Cl₂-treated bio-char was higher (11.5 mmol Prod.∙h⁻¹∙g Cat. ⁻¹) than that of commercial catalyst silica-supported Nafion SAC-13 (2.3 mmol Prod.∙h⁻¹∙g Cat. ⁻¹) and H₂SO₄-treated bio-char (5.7 mmol Prod.∙h⁻¹∙g Cat. ⁻¹). Reusability of the catalysts was examined. The catalytic activity of the SO₂Cl₂-modified catalyst was sustained from the second run after the initial activity dropped after the first run and kept the same activity until the fifth run. It was higher than that of first-used Nafion. These experimental results demonstrate that catalysts from lipid-extracted algae have great potential for the economic and environment-friendly production of biodiesel.

An Assessment of Gasification of Lipid-Extracted Algae by Thermodynamic Simulation

Thermodynamic simulation of gasification of Nannochloropsis gaditana (after lipid extraction and before lipid extraction) over a wide range of temperatures (800 – 1400 oC) was performed in this study. The reactor temperature variation with respect to the O2 to fuel ratio and the syngas composition with temperature were evaluated for gasification performance. The results showed the H2/CO ratio for lipid-extracted algae (LEA) was very similar to the gasification behavior of raw algae (RA) before lipid extraction. Only a slight variation was observed for the lower heating value (9.2 MJ/Nm3 for RA and 8.9 MJ/Nm3 for LEA at 1000 oC) of the syngas from the two feedstocks. The H2/CO ratio for both RA and LEA remained almost the same over the range of temperatures (800-1400 oC) under consideration. The cold gas efficiency was found between 82 % to 75 % for RA and 75 % to 69 % for LEA at 1000 oC and 1400 oC respectively. As the overall gasification performance did not degrade significantly after extraction of lipid from algae, the LEA holds remarkable potential as a gasification feedstock in a biorefinery set up.Journal of Chemical Engineering, Vol. 30, No. 1, 2017: 59-63

Hydrothermal Conversion of Lipid-Extracted Microalgae Hydrolysate in the Presence of Isopropanol and Steel Furnace Residues

PurposeMicroalgae have a high potential as a feedstock for the production of biofuels, either indirectly, through the extraction of lipids, which can be transformed into biodiesel, or directly via whole cell conversion using hydrothermal liquefaction (HTL). Both approaches have disadvantages, due to the high cost of cultivating microalgae with sufficient lipid content (>40%), while the whole cell conversion produces low quality oils, which require significant further upgrading. This work investigated the possibility of realising the benefits of both processes, by studying the liquefaction reaction of a lipid-extracted algae hydrolysate.MethodsIn order to enhance oil yields, the reaction was conducted in the presence of varying loadings of iso-propyl alcohol (IPA) and applied two waste steel furnace residues as potential liquefaction catalysts.ResultsPrimarily, The lipid extraction process needs to be optimized to reduce the amount of acid contaminant within the liquefaction medium. For the HTL process, the addition of 50 vol% IPA resulted in remarkably high oil yields of up to 60.2 wt% on an organic basis, whereas the two furnace residues had no positive effect on the product distribution, and instead favoured the formation of solid reaction products. Nevertheless, the results suggested that the presence of iron potentially reduced the nitrogen and oxygen content of the bio-oil.ConclusionsAs such, HTL is a suitable method for valorising lipid-extracted algal biomass, where the bio-oil yields can be enhanced substantially by using IPA in conjunction with the water.