Wet Microalgal Biomass Research Articles

Systematic solvent selection enables the fractionation of wet microalgal biomass

Wet microalgal biomass was recently proposed as a feedstock to circumvent the energy-intensive drying step in biorefineries. However, solvents commonly applied to extract valuable target compounds from dried biomass are usually less effective when applied on wet biomass. In the present study, we investigated the potential of systematic solvent selection to increase pigment and lipid yields for the extraction of wet Phaeodactylum tricornutum biomass. The solvent selection was guided by a large-scale computational screening approach. Experiments revealed, that 2-butanol – a non-toxic, partially water-miscible solvent – extracted 99.4 wt% of lipids and 82.6 wt% of carotenoids from wet biomass. By using only 2-butanol and water as benign solvents, we developed a biorefinery approach that effectively fractionates wet microalgal biomass under ambient conditions into proteins, carbohydrates, carotenoids and lipids without the need for energy-intensive biomass drying.

Glucose Conversion for Biobutanol Production from Fresh Chlorella sorokiniana via Direct Enzymatic Hydrolysis

Microalgae, which accumulate considerable carbohydrates, are a potential source of glucose for biofuel fermentation. In this study, we investigated the enzymatic hydrolysis efficiency of wet microalgal biomass compared with freeze-dried and oven-dried biomasses, both with and without an acidic pretreatment. With the dilute sulfuric acid pretreatment followed by amy (α-amylase and amyloglucosidase) and cellulase hydrolysis, approximately 95.4% of the glucose was recovered; however, 88.5% was released by the pretreatment with 2% (w/v) sulfuric acid, which indicates the potential of the acids for direct saccharification process. There were no considerable differences in the glucose yields among the three kinds of materials. In the direct amy hydrolysis without any pretreatment, a 78.7% glucose yield was obtained, and the addition of cellulase had no significant effect on the hydrolysis to glucose. Compared with the oven-dried biomass, the wet biomass produced a substantially higher glucose yield, which is possibly because the cross-linked cells of the oven-dried biomass prevented the accessibility of the enzymes. According to the results, the fresh microalgal biomass without cell disruption can be directly used for enzymatic hydrolysis to produce glucose. The enzymatic hydrolysate of the wet microalgal biomass was successfully used for acetone–butanol–ethanol (ABE) fermentation, which produced 7.2 g/L of ABE, indicating the application potential of wet microalgae in the bioalcohol fuel fermentation process.

Microalgal Feedstock for Biofuel Production: Recent Advances, Challenges, and Future Perspective

Globally, nations are trying to address environmental issues such as global warming and climate change, along with the burden of declining fossil fuel reserves. Furthermore, countries aim to reach zero carbon emissions within the existing and rising global energy crisis. Therefore, bio-based alternative sustainable feedstocks are being explored for producing bioenergy. One such renewable energy resource is microalgae; these are photosynthetic microorganisms that grow on non-arable land, in extreme climatic conditions, and have the ability to thrive even in sea and wastewater. Microalgae have high photosynthetic efficiencies and biomass productivity compared to other terrestrial plants. Whole microalgae biomass or their extracted metabolites can be converted to various biofuels such as bioethanol, biodiesel, biocrude oil, pyrolytic bio-oil, biomethane, biohydrogen, and bio jet fuel. However, several challenges still exist before faster and broader commercial application of microalgae as a sustainable bioenergy feedstock for biofuel production. Selection of appropriate microalgal strains, development of biomass pre-concentrating techniques, and utilization of wet microalgal biomass for biofuel production, coupled with an integrated biorefinery approach for producing value-added products, could improve the environmental sustainability and economic viability of microalgal biofuel. This article will review the current status of research on microalgal biofuels and their future perspective.

Holistic exploitation of pulsed electric field (PEF)-treated and lipid extracted microalgae Auxenochlorella protothecoides, utilizing anaerobic digestion (AD)

This study proposes a cascade processing of the lipid-rich microalgae Auxenochlorella protothecoides. Freshly harvested biomass is pre-concentrated to 100 g/kgsusp and then pretreated using pulsed electric fields (PEF). PEF-treatment, which affects permeability of cells membrane, induces a spontaneous release of microalgal ingredients into the surrounding medium, mostly carbohydrates and micronutrients, which can be recovered. After separation of this aqueous fraction, lipid extraction is performed on the remaining wet pellet using an ethanol-hexane blend. After recovery of those different valuables, it was considered, to convert the rest biomass (cell envelope and most of the other remaining hard- or non-extractable components), to storable energy. Anaerobic digestion (AD) of the remains to biogas was considered to be a promising solution. AD-processes have the charm that unprocessed wet microalgal biomass, as well as wet organic biomass residues from previous extraction steps can be utilized directly without further purification or drying steps. The obtained biogas can then be upgraded to methane for an energetic use.PEF-treated algal biomass showed a 10 % increased methane outcome (467 mLnorm/gVS) compared to the untreated sample. PEF-treated microalgae, subjected to extraction of the aqueous fraction, demonstrated a 23 % increase in methane yield (558 mLnorm/gVS), compared to control. Finally, the biomass, PEF-treated and subjected to extraction of water fraction and lipids, still achieved 41 % of methane potential (205 mLnorm/gVS) during the AD process, compared to the untreated control.Our study demonstrates the feasibility of cascade processing using PEF-treatment. Moreover, all the study was developed keeping in mind industrial requirements. In particular, our downstream approach did not require any drying, the pretreatment required low amount of energy, i.e. 1.5 MJ/kgCDW and the majority of the biomass was valorized. Since all techniques used, especially PEF-pretreatment, can be up-scaled, we believe this approach has great potential for implementation in industry.

Feasibility of Utilizing Wastewaters for Large-Scale Microalgal Cultivation and Biofuel Productions Using Hydrothermal Liquefaction Technique: A Comprehensive Review.

The two major bottlenecks faced during microalgal biofuel production are, (a) higher medium cost for algal cultivation, and (b) cost-intensive and time consuming oil extraction techniques. In an effort to address these issues in the large scale set-ups, this comprehensive review article has been systematically designed and drafted to critically analyze the recent scientific reports that demonstrate the feasibility of microalgae cultivation using wastewaters in outdoor raceway ponds in the first part of the manuscript. The second part describes the possibility of bio-crude oil production directly from wet algal biomass, bypassing the energy intensive and time consuming processes like dewatering, drying and solvents utilization for biodiesel production. It is already known that microalgal drying can alone account for ∼30% of the total production costs of algal biomass to biodiesel. Therefore, this article focuses on bio-crude oil production using the hydrothermal liquefaction (HTL) process that converts the wet microalgal biomass directly to bio-crude in a rapid time period. The main product of the process, i.e., bio-crude oil comprises of C16-C20 hydrocarbons with a reported yield of 50–65 (wt%). Besides elucidating the unique advantages of the HTL technique for the large scale biomass processing, this review article also highlights the major challenges of HTL process such as update, and purification of HTL derived bio-crude oil with special emphasis on deoxygenation, and denitrogenation problems. This state of art review article is a pragmatic analysis of several published reports related to algal crude-oil production using HTL technique and a guide towards a new approach through collaboration of industrial wastewater bioremediation with rapid one-step bio-crude oil production from chlorophycean microalgae.

Microwave-assisted pretreatment of wet microalgal biomass for recovery of biofuel precursors

Pretreatment of microalgal biomass is essential for the maximal recovery of biofuel precursors packed inside the complex microalgal cell wall. In the present work, microwaves were exploited for efficient pretreatment of wet microalgal biomass. A response surface methodology – Box Behnken design (RSM-BBD) was utilized to obtain the optimum conditions for biomass pretreatment, and a mathematical model was devised. Using the designed experimental setup, the optimum conditions were obtained as 5 min of microwave irradiation time, 700 W output power, and 2 gL-1 microalgal biomass concentration. The model was further validated experimentally. The pretreatment results were confirmed qualitatively through microscopic observations and quantitatively in terms of sugar release and lipid extraction. The optimum conditions were found promising to enhance the lipid extraction by 55.32% compared to the untreated condition. Additionally, the present design showed the importance of water as a green solvent for biomass pretreatment under microwave irradiation. Overall, the current attempt facilitates a cost-effective, green methodology for wet microalgal biomass pretreatment in a short duration.

Microencapsulation by spray drying of omega-3 lipids extracted from oilseeds and microalgae: Effect on polyunsaturated fatty acid composition

In this work, microencapsulation of omega-3 lipids from sustainable sources, including oilseeds such as Salvia hispanica L., Echium plantagineum L. and Camelina sativa L., microalgal lipids (from Nannochloropsis gaditana) and enzymatically produced fatty acid ethyl esters (FAEEs), was successfully done by spray drying and their outcomes studied. Previous to microencapsulation process, lipid extracts from new omega-3 sources (chia, camelina and echium oilseeds and wet microalgal biomass of Nannochloropsis) were produced using Pressurized Liquid Extraction. The best microencapsulation efficiency was achieved for chia FAEEs (76.9%), while the lowest was obtained for camelina oil (58.8%) and Nannochloropsis gaditana lipids (57.0%) microcapsules, which also showed low emulsion stability. Analysis by GC-MS showed that microencapsulation process did not negatively affect omega-3 fatty acid profile of microencapsulated extracts. The percentage of omega-3 in each used lipid was similar before and after spray drying (no significant differences at 5% level). Under the optimal conditions, produced microcapsules ranged from 1.5 to 30 μm and showed spherical shape and smooth surface without cracks. Thus, the proposed method provides an original approach to produce omega-3 microencapsulated lipid extracts from different nature, with high microencapsulation efficiency and payload, for potential applications in the development of foods enriched in omega-3 fatty acids.

Carbonate assisted lipid extraction and biodiesel production from wet microalgal biomass and recycling waste carbonate for CO2 supply in microalgae cultivation

High cost of microalgal biofuel is caused by all the steps in current technology, including cultivation, harvesting, lipid extraction, biofuel processing and wastewater and waste treatment. This study aims to systematically reduce these costs with one integrated process, in which carbonate is used for cell rupture, lipid extraction and biodiesel processing, and then recycled for CO2 absorption and carbon supply for a new round of algae cultivation. To reach this goal, carbonate-heating treatment with N, N' - dibutylurea which can enhance cell disruption were used for cell-wall breaking of wet Neochloris oleoabundans (UTEX 1185) biomass. Lipid extraction was fulfilled with carbonate/ethanol aqueous two phase extraction method and residual carbonate with wastewater from bottom phase was recycled to absorb CO2 to generate bicarbonate for algal cultivation with fresh medium. Taking into comprehensive consideration of cell disruption efficiency, partition coefficient, and lipid recovery, the condition of cell disruption and lipid extraction was set at 90°C, 100min reaction time, 1:7.5 DBU:H2O (w/w) ratio, 1:3 Na2CO3:H2O (w/w) ratio, and 9% (w/wT) ethanol concentration. The results showed that carbonate-heating treatment of wet N. oleoabundans biomass resulted in up to 90.7% cell disruption efficiency. The lipid recovery rate in carbonate/ethanol system was up to 97.9%, and the final biodiesel production was 1.30 times of that with Soxhlet method. Utilization of the waste broth after CO2 absorption with the content of 4% (v/vT) in the medium for new batch of algae cultivation resulted in biomass concentration of 1.68g/L. The corresponding total fatty acids production was 0.35g/L, which was 1.63 fold of that with fresh medium. This study firstly proved the feasibility of using carbonate for lipid extraction and biodiesel production and recycle waste carbonate for carbon re-supply during algae cultivation.

Osmotic shock pre-treatment of Chaetoceros muelleri wet biomass enhanced solvent-free lipid extraction and biogas production

An integrated system for biodiesel and biogas production for the diatom Chaetoceros muelleri was evaluated. We assessed the suitability of osmotic shock pre-treatment of wet microalgal biomass for lipid extraction and biogas production. Osmotic shock pre-treatment released up to 72% of C. muelleri lipid content. Biogas production of pre-treated and lipid-spent microalgae was evaluated by biomethane potential tests and by operating two continuous anaerobic reactors for 200 days. An improvement of 35% in methane production was observed with the pre-treated microalgae in batch conditions, with a maximum methane yield of 521 mL CH4 g VS−1. The methane yield in the continuous experiments of the pre-treated microalgae fluctuated between 0.3 and 0.7 L CH4 g VS−1, with an average of 0.52 L CH4 g VS−1. No significant differences were observed between the pre-treated microalgae without lipid extraction and lipid-spent microalgae in both batch and continuous conditions. The energy potential for a combined biodiesel-biogas biorefinery has been estimated at 20.5 KJ gVS−1 of harvested microalgae.

New insights to direct conversion of wet microalgae impregnated with ethanol to biodiesel exploiting extraction with supercritical carbon dioxide

Biodiesel production from microalgae is viable but faces scale-up challenges. The main drawbacks in the industrial production of biodiesel are high-water content in the biomass (~80%) and the numbers of process stages involved in its production. Using direct transesterification is taken into account to be a good solution; because lipid-extraction and transesterification processes are completed in one step. This converts wet biomass directly into biodiesel. This study evaluates a single-step, environmentally-friendly method that directly converts wet microalgae into biodiesel directly with the involvement of supercritical carbon dioxide. Carbon dioxide is exploited in a supercritical state to simultaneously extract lipids from algal biomass impregnated with 15 cc ethanol per 1 g dry microalgal and transesterify that extract to generate fatty-acid-ethyl esters. Wet microalgal biomass of Nannochloropsis oculata was used as the biomass feed for this process. Its biodiesel production efficiency is impacted by temperature and water content. Water has a negative effect on productivity at temperatures <150 °C. On the other hand, at temperatures of ~150 °C, biodiesel productivity was not negatively influenced despite high water content. These results suggest that by increasing process temperature, biodiesel can be produced efficaciously from wet microalgae, thereby reducing its production costs.

Green energy from Coelastrella sp. M-60: Bio-nanoparticles mediated whole biomass transesterification for biodiesel production

Application of nanoparticles in microalgal biodiesel production comprise of nanoparticle usage for lipid accumulation, lipid extraction and transesterification process. Conventionally, microalgal biomass/oil are converted into fatty acid methyl esters (FAME) using methanol in the presence of homogeneous acid/base catalysis through transesterification. In this study, bio-nanoparticles were synthesized from bio-waste (seashell) and employed them as heterogeneous catalysts in the direct/whole-cell transesterification of wet microalgal biomass. Bio-nano CaO and bio-nano CaCO3 were characterized by Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and Fourier transform infrared (FT-IR) analyses. Specific surface areas of bio-nano CaCO3 and bio-nano CaO were found to be 73.519 and 19.810 m2/g with an average pore size diameter of 7.141 and 2.348 nm respectively through BET analysis. FT-IR analysis of the synthesized bio-nanoparticles showed similar absorption frequencies as that of bulk counterpart with noticeable differences in absorption at some frequencies. Thus, the present study employs the as-synthesized bio-nanoparticles from waste seashell as heterogeneous catalysts for whole-cell/direct transesterification of N starved Coelastrella sp. M-60 for FAME conversion and compared with (i) conventional acid catalyst and (ii) commercial TiO2 nanocatalyst. The above mentioned direct transesterification reactions had yielded C 16:0 (7.5–22.3%) and C 18:1 (63.2–78%) as the major FAME products. Bio-nano CaCO3 and bio-nano CaO had yielded an average of 1.29 and 1.02 folds increase in FAME proportions respectively than conventional acid catalysis. Hence, this study shows the potential of bio-nanocatalysts for direct transesterifcation of Coelastrella sp. M-60 as a greener approach for biodiesel production.

Sequential extraction of lutein and β‐carotene from wet microalgal biomass

AbstractBACKGROUNDMicroalgae are a promising resource to produce carotenoids for food/feed applications. However, energy‐intensive pre‐treatments such as drying and cell destruction can hinder the sustainability of the process. Direct extraction from wet biomass may reduce energy consumption, but the residual water can reduce the effectiveness of the organic solvents used for the extraction. In this work, the extraction of lutein and β‐carotene from wet untreated microalgal biomass is investigated. The process includes a sequence of successive extraction stages with methanol.RESULTSWe show that the sequential extraction can effectively overcome the reduced extraction efficiency induced by the residual water in the biomass. The biomass was dehydrated during the first extraction stage, which increased the efficiency starting from the second stage. This allowed an extraction yield of &gt;95% to be attained for both lutein and β‐carotene after five extraction stages. A mathematical model was developed by coupling mass balances with a linear equilibrium model, satisfactorily describing the partition of the two carotenoids between the solid and the solvent phase. By fitting the model to the data obtained by the first extraction stage, liquid–solid partition coefficients (Kd) equal to 2.0 × 10−3 and 1.1 × 10−4 were estimated for lutein and β‐carotene, respectively. The Kd of both carotenoids increased to ≈10−2 during the six subsequent extraction stages without water.CONCLUSIONSDirect solvent extraction from wet untreated microalgal biomass is a promising strategy to produce carotenoids. The described model can provide guidelines to design industrial processes. © 2020 Society of Chemical Industry

Fe2O3 nanocatalyst aided transesterification for biodiesel production from lipid-intact wet microalgal biomass: A biorefinery approach

Biodiesel production from non-edible feedstock such as microalgae is gaining importance in present day, as they do not interfere with global food economy in addition to higher photosynthetic efficiency as compared to plants. Fresh water grown Neochloris oleoabundans UTEX 1185 is considered as a potential source for biodiesel production. The present study investigated different direct lipid extraction process from wet microalgal biomass through autoclaving, microwave, and ultrasonication pretreatments. Autoclave treatment showed a higher efficiency for lipid extraction as compared to other two pretreatments. Furthermore, transesterification process was carried out in presence of Fe2O3 catalyst and compared with conventional acid (HCl) and base (NaOH) catalysts. Fe2O3 nanoparticles used were synthesized from extract of Hibiscus rosa-sinensis by green procedure. The synthesized Fe2O3 catalyst played an important role in improving the biodiesel yield up to 81%, which is higher than that obtained with HCl (64%) and NaOH (48%). Thereafter transesterification process parameter like catalyst content, reaction temperature and reaction time were optimized and finally 86% biodiesel yield was obtained. Fatty acid methyl esters (FAME) profile analysis and fuel properties revealed the suitability of algal lipid for biodiesel production. 20.2% w/w of carbohydrate present in lipid extracted microalgal biomass was further converted into biohydrogen by dark fermentation and bioethanol under anaerobic condition using acidogenic mixed consortia and Saccharomyces cerevisiae (INVSC-1), respectively. The life cycle assessment study of the overall process was also done.

Simultaneous extraction and fractionation of omega-3 acylglycerols and glycolipids from wet microalgal biomass of Nannochloropsis gaditana using pressurized liquids

Microalgae are primary producers of eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids in marine environment and so they are considered promising alternative sources of omega-3 long-chain polyunsaturated fatty acids (LC-PUFAs). Nannochloropsis gaditana is an oleaginous cultivated microalga with an important content of triglycerides and polar lipids which include interesting EPA amounts. In this work, new methods using pressurized liquids for simultaneous extraction and fractionation of neutral and polar lipids from wet microalgal biomass are proposed. Pressurized liquid extraction (PLE) using different solvents, combined or not with pre-treatment of the alga with enzymes, allows one to enrich and fractionate neutral and polar lipids such as triacylglycerols, diacylglycerols, monoacylglycerols, free fatty acids and glycolipids. The use of enzymatic pre-treatment did not show a significant increase in the lipid yield, though a different fractionation of the microalgal lipids was achieved. PLE with a single solvent (hexane at 120 °C) rendered a lipid yield of 17.6%, slightly higher than the traditional Folch method (16.9%), but with a less-toxic solvent and faster extraction technique. In addition, PLE with hexane attained a high triacylglycerols fraction (17.2% ± 3.0). The optimal four-step sequential method developed using pressurized liquids reached a good fractionation characterized by a high content of glycolipids (29.2% ± 2.0) and monoacylglycerols (17.3% ± 1.9), with a lipid recovery of 14.0% ± 1.3 for the original biomass. The analysis by GC/MS of fractions obtained with each method and solvent combination, showed a different composition in fatty acids of fractionated neutral and polar lipid species, especially in saturated and omega-3 fatty acids. Therefore, the proposed fast PLE methods allow the simultaneous extraction and fractionation of the neutral and polar lipids of Nannochloropsis gaditana and produce enriched EPA fractions (up to 53%).

Advances in microalgal lipid extraction for biofuel production: a review

AbstractAlgal biomass is an attractive feedstock for sustainable biofuel production because of its high growth rate and the fact that it does not compete with food crops. This review examines progress made in the processing and extraction of microalgal lipids as feedstocks for algae‐derived biofuels. The discussion focuses on lipid extraction processes but also mentions drying, cell disruption, and transesterification processes because of their potential effect on the extraction process, and because of the possibility of performing them simultaneously with extraction. Some of the common themes discussed include the benefits of utilizing wet microalgal biomass, combining process steps (process intensification), and the importance of considering the entire life cycle when assessing the ‘greenness’ of a technology. Lipid extraction technologies will need to be improved for microalgal biofuels to compete effectively with fossil fuels, particularly through the development of energy‐efficient extraction methods and the adaptation of these methods for large‐scale production. © 2018 Society of Chemical Industry and John Wiley &amp; Sons, Ltd

Comparison of extraction techniques for product diversification in a supercritical water gasification-based sugarcane-wet microalgae biorefinery: Thermoeconomic and environmental analysis

This study presents a thermoeconomic and environmental assessment of the extraction of lipids and proteins from wet microalgal biomass in a 3G biorefinery by two different technologies: supercritical fluid extraction (SFE) and low-pressure solvent extraction (LPSE). Simulation tools were used to study a sugarcane biorefinery producing ethanol from sugarcane juice (1G) and bagasse (2G); the microalgal growth in an open pond; and the processing of microalgal biomass into lipids, proteins and synthetic natural gas (SNG). Supercritical water gasification (SCWG) of microalgal biomass enables an increase in biofuel production of 10.2% MJ when no extraction process is considered and of 1.9% MJ when LPSE is considered. The heat demand of the proposed biorefinery with LPSE was increased by 87.8% compared with the demand of the sugarcane biorefinery without microalgal growth and processing. When the SFE process is considered, the heat demand of the overall process increased 3.2 times. SFE for wet microalgae processing is not economically attractive, as it increases the total investment by 71%. The CO2 flow used in the SFE process demonstrated to be a key factor in the thermoeconomic viability of the process. Regarding the wet processing of microalgae prior to SCWG, the best alternative studied was the use of LPSE technology.

Cost-effective biodiesel production from wet microalgal biomass by a novel two-step enzymatic process

In this study, a novel two-step enzymatic process was firstly established to produce microalgae biodiesel using wet Chlorella biomass. In the first hydrolysis step, to reduce energy consumption and effectively disrupt microalgal cell wall, among cellulase, hemicellulase, papain, lysozyme and pectinase, the highest hydrolysis efficiency (67.52%) was obtained by cellulase at pH 5.0 with enzyme dosage of 200 U/g dry biomass at 40 °C for 12 h. In the second transesterification step, compared with liquid CAL-A/B from Candida antarctica and PLA from Aspergillus oryzae, liquid lipase TL from Thermomyces lanuginosus achieved the highest biodiesel conversion at 81.15:1 (v/w) ethanol/g TFAs ratio in 78–83% water content with 100 PLU/g TFAs lipase loading at 25 °C for 48 h. Moreover, similar results were obtained with three Chlorella species by this process. Overall, this two-step enzymatic process was a green, low-energy and efficient method for cost-effective biodiesel production using wet microalgal biomass.

Vortex fluidic mediated direct transesterification of wet microalgae biomass to biodiesel

A bottleneck in the production of biodiesel from microalgae is the dewatering and lipid extraction process which is the dominant energy penalty and cost. A novel biodiesel production platform based on vortex fluidic device (VFD)-assisted direct transesterification (DT) of wet microalgal biomass of Chloroparva pannonica was developed and evaluated. Fatty acid extraction and fatty acid to FAME conversion efficiencies were used at different parameter settings to evaluate performance of the processing technology in confined and continuous mode. A response surface method based on Box-Behnken experimental design was used to determine the effects of water content, the ratio of biomass to methanol and residence time in the VFD. Average extraction efficiencies were 41% and conversion efficiencies >90% with the processing technology showing a broad tolerance to parameter settings. The findings suggest that VFD-assisted DT is a simple and effective way to produce biodiesel directly from wet microalgae biomass at room temperature.

Optimization of the ionic liquid-microwave assisted one-step biodiesel production process from wet microalgal biomass

This study illustrates the influence of ionic liquid (IL)-microwave heating on the direct transesterification (in-situ transesterification) of wet Nannochloropsis sp. biomass to biodiesel. The ionic liquid used was 1-ethyl-3-methylimmidazolium methyl sulphate [EMIM][MeSO4]. Direct transesterification process variables such as the wet algae to methanol ratio, reaction time and methanol to IL ratio influencing the biodiesel production were optimised using response surface methodology (RSM). The results revealed that the maximum biodiesel yield (40.9%) was achieved when the ratio of wet algae to methanol (wt/vol) was kept at 1:4, methanol:IL ratio maintained at 1:0.5 at reaction time of 25 min. The FAMEs composition depicted a high content of unsaturated FAMEs suitable for biodiesel production. The synergetic effect of combining IL-methanol solvent and microwave heating at optimised reaction conditions enabled the production of an incredibly high biodiesel yield per dry biomass of 42.22%.

Easy reuse of magnetic cross-linked enzyme aggregates of lipase B from Candida antarctica to obtain biodiesel from Chlorella vulgaris lipids

In this work, magnetic cross-linked enzyme aggregates (mCLEAs) of CALB (lipase B from Candida antarctica) were prepared and characterized. Moreover, a method for an easy, sustainable and economic extraction of lipids from nitrogen-starved cells of Chlorella vulgaris var L3 was developed. Then, the extracted lipids (oils and free fatty acids, FFAs) were converted to biodiesel using mCLEAs and chemical acid catalysis. Among several lipid extraction methods, saponification was selected given the amount of wet microalgal biomass it can process per unit of time, its low market value, and because it allows for the use of less toxic solvents. A biodiesel conversion of 80.2±4.4% was obtained by chemical catalysis (1h at 100°C) using FFAs and methanol as the alkyl donor. However, a biodiesel conversion of more than 90% (3h at 30°C) was obtained using mCLEAs and methanol. Both chemical and enzymatic catalysts gave biodiesel with similar fatty acid alkyl ester (FAAE) composition. Methanol, at 15% (v/v) or higher concentration, caused a decrease of lipase activity and a concomitant increase in the size of mCLEA aggregates (up to 2μm), as measured by dynamic light scattering (DLS). The magnetic character of the novel biocatalyst permits its easy recovery and reuse, for at least ten consecutive catalytic cycles (retaining 90% of the initial biodiesel conversion), using mild reaction conditions and environmentally-friendly solvents.