Wet Microalgal Research Articles

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.

Optimization of biodiesel production from wet microalgal biomass by direct transesterification using the surface response methodology

Abstract The production of fatty acid methyl esters (FAMEs, biodiesel) was optimized from wet Nannochloropsis gaditana microalgal biomass (81.8 wt% water and 28.1 wt% saponifiable lipids, SLs, from the dry biomass). FAME production was carried out by direct acid-catalyzed methylation of the SLs from the microalgal biomass and FAME extraction with hexane. A three-variable, three-level Box-Behnken design (BBD) was applied to optimize the sulphuric acid (catalyst) concentration, the methanol/SL ratio and the hexane/SL ratio. The best FAME yield was obtained with a methanol/SL ratio of 254 mL/g, a sulphuric acid concentration of 3.7% (v/v) and a hexane/SL ratio of 107.7 mL/g at 100 °C and for 105 min. Under these conditions, 100% of the SLs were transformed into FAMEs. Finally, the FAME purity was increased from 78.7 to 86.8 wt% using an adsorption treatment with bentonite.

Direct saponification of wet microalgae by methanolic potassium hydroxide using acetone as co-solvent

The fatty acids of microalgae are promising source of biodiesel and omega-3 fatty acids. The objective of this study is extraction of fatty acids from wet Dunaliela salina by direct saponification using methanolic potassium hydroxide and a suitable co-solvent. The study identified acetone as an efficient co-solvent for saponification of wet microalgal biomass by methanolic potassium hydroxide. The presence of acetone in methanolic KOH saponification produced 24% more fatty acid than its absence. Further optimization of concentration of acetone (80% v/v), concentration of potassium hydroxide (0.1% v/v) and solvent-dry biomass ratio (75:1) resulted in a maximum yield of 98% fatty acid. The proposed acetone assisted saponification of wet microalgal biomass could serve as an energy efficient route for fatty acid production since the reaction happens under room temperature and normal atmospheric pressure without any cell lysis or drying the biomass.

Subcritical n-hexane/isopropanol extraction of lipid from wet microalgal pastes of Scenedesmus obliquus.

Subcritical co-solvents of n-hexane/isopropanol were primarily utilized to extract lipid from wet microalgal pastes of Scenedesmus obliquus. The effects of key operational parameters were investigated, and the optimal parameters were obtained: solvent ratio of n-hexane to isopropanol was 3:2 (V:V), phase ratio of co-solvents to microalgal biomass was 35:1 (mL:g), reactor stirring speed was 900rpm, extraction time was 60min. Additional pretreatment with acid, ultrasonic and microwave as well as enhanced subcritical pressure/heating treatments were also applied to further study their effects on lipid extraction. The results showed that the lipid recovery rate with acid pretreatment was 8.6 and 6.2% higher than ultrasonic and microwave pretreatment; the optimum enhanced subcritical condition was 55°C with atmospheric pressure. Under optimal operating conditions, the lipid and FAME yield were 13.5 and 7.2%, which was 82.6 and 135.1% higher than the traditional method. The results indicated that the subcritical n-hexane/isopropanol extraction process had promising application potential.

Optimization of the transesterification reaction of microalgal Monoraphidium sp

Abstract This study optimized biodiesel production by Monoraphidium sp. in terms of fatty acid methyl ester (FAME) yield by varying four variables (volume of methanol, reaction temperature, reaction time, and ultrasound power) using a Box-Behnken design (BBD). Within the experimental range, the volume of methanol was found to be the most important factor, having a positive influence on the FAME yield. The test variables affected the FAME yield, and the optimal condition varied between alkali- and acid-catalyzed transesterification. Both types of transesterification reaction occurred at their optimal catalyst concentrations, 0.5% NaOH and 2% H2SO4, respectively, for both dry and wet microalgal biomass. The FAME yield with the acid-catalyzed reaction was better than that with the alkali-catalyzed reaction. The combined alkali-and-acid-catalyzed transesterification reactions enhanced the FAME yield. The microalgae produced fatty acids, comprising mainly palmitic acid (C16:0), oleic acid (C18:1), linoleic acid (C18:2), and linolenic acid (C18:3), with palmitic acid (C16:0) and linoleic acid (C18:2) being the most abundant.

Evaluation of various solvent systems for lipid extraction from wet microalgal biomass and its effects on primary metabolites of lipid-extracted biomass.

Microalgae have tremendous potential to grow rapidly, synthesize, and accumulate lipids, proteins, and carbohydrates. The effects of solvent extraction of lipids on other metabolites such as proteins and carbohydrates in lipid-extracted algal (LEA) biomass are crucial aspects of algal biorefinery approach. An effective and economically feasible algae-based oil industry will depend on the selection of suitable solvent/s for lipid extraction, which has minimal effect on metabolites in lipid-extracted algae. In current study, six solvent systems were employed to extract lipids from dry and wet biomass of Scenedesmus obliquus. To explore the biorefinery concept, dichloromethane/methanol (2:1 v/v) was a suitable solvent for dry biomass; it gave 18.75% lipids (dry cell weight) in whole algal biomass, 32.79% proteins, and 24.73% carbohydrates in LEA biomass. In the case of wet biomass, in order to exploit all three metabolites, isopropanol/hexane (2:1 v/v) is an appropriate solvent system which gave 7.8% lipids (dry cell weight) in whole algal biomass, 20.97% proteins, and 22.87% carbohydrates in LEA biomass. Graphical abstract: Lipid extraction from wet microalgal biomass and biorefianry approach.

New algal lipid extraction procedure using an amphiphilic amine solvent and ionic liquid

Lipid extraction is a key step in microalgal biofuel production. However, economical microalgal biofuel production is limited by the high energy consumption of the extraction process. Therefore, in this study, we employed N-methylcyclohexylamine (MCHA) as a switchable solvent to directly extract a wet microalgal slurry, and an ionic liquid, [C4-mim][PF6] (1-butyl-3-methylimidazolium hexafluorophosphate), was used to recover the extracted algal oil through a simple phase separation method. CO2 was used to trigger the separation of MCHA from [C4-mim][PF6], and MCHA was regenerated by heating and purging with N2. Our extraction procedure differs from conventional solvent extraction, which requires drying algal slurries before extraction. The new extraction procedure adopted in this study can be used to extract wet algal slurries directly and recycle the solvent by using a low-energy consumption method. In addition, water-soluble MCHA was investigated for DHA(docosahexaenoic acid) wet algal slurries with 85% water content, and the extraction yield could reach 85% at low stirring speeds (200 rpm). Using [C4-mim][PF6] to separate algal oil from the crude extraction liquid, algal lipid recovery was approximately 77%. In summary, the results showed the feasibility of utilizing MCHA and [C4-mim][PF6] as extracting and separating agents, respectively, for algal oil exaction.

Simultaneous cell disruption and lipid extraction in a microalgal biomass using a nonpolar tertiary amine

A simultaneous cell disruption and lipid extraction method is developed for microalgal biodiesel production using a triethylamine/methanol solvent system. Individually, the pure solvents, i.e. triethylamine and methanol, do not exhibit significant enhancement in lipid extraction, but a 3:7 (v/v) triethylamine/methanol mixture exhibits the highest lipid extraction, corresponding to 150% of the conventional chloroform/methanol (2:1, v/v) solvent extraction. This extraction is equivalent to 92.5% of the total lipids, even when extracted from a wet microalgal biomass with a water content of 80%. The cell surfaces of the microalgae are significantly disrupted without using additional cell disruption reagents and without requiring energy-intensive equipment. The lipid mass transfer coefficient is 1.6 times greater than that of the chloroform/methanol solvent system. It is clearly demonstrated that triethylamine and methanol cooperate well for the cell disruption and lipid extraction.

Fatty acid methyl ester production from wet microalgal biomass by lipase-catalyzed direct transesterification

The aim of this work was to optimize the production of fatty acid methyl ester (FAME, biodiesel) from wet Nannchloropsis gaditana microalgal biomass by direct enzymatic transesterification. This was done in order to avoid the high cost associated with the prior steps of drying and oil extraction. Saponifiable lipids (SLs) from microalgal biomass were transformed to FAME using the lipase Novozyme 435 (N435) from Candida antarctica as the catalyst, and finally the FAME were extracted with hexane. t-Butanol was used as the reaction medium so as to decrease lipase deactivation and increase mass transfer velocity. A FAME conversion of 99.5% was achieved using wet microalgal biomass homogenized at 140 MPa to enhance cell disruption, a N435:oil mass ratio of 0.32, methanol added in 3 stages to achieve a total of 4.6 cm3 g−1 of oil and 7.1 cm3 g−1 oil of added t-butanol, with a reaction time of 56 h. The FAME conversion decreased to 57% after catalyzing three reactions with the same lipase batch. This work shows the influence of the polar lipids contained in the microalgal biomass both on the reaction velocity and on lipase activity.

Improvement in lipids extraction processes for biodiesel production from wet microalgal pellets grown on diammonium phosphate and sodium bicarbonate combinations

Biomass productivity and growth kinetics for microalgae grown on sodium bicarbonate and diammonium phosphate were investigated. Different carbon and nitrogen ratios have shown different growth rates and biomass productivity and C:N ratio 50:10 as mgL−1 has shown the best production than all. For effective lipids extraction from biomass thermolysis and sonolysis were carried out from wet biomass. Sonolysis at 2.3W intensity for 5min has released 8.58mg at neutral pH. More quantity of lipids was extracted when extraction was made at pH 4 and 10 which resulted 9mg and 9.28mg lipids respectively. Thermal treatment at 100°C for 10min has released 12.82mg lipid at neutral pH. In the same thermolysis at pH 4 and 10 more quantity of lipids was extracted which were 15.16mg and 14.81mg respectively. Finally transesterified lipids were analyzed through GC–MS for FAME composition analysis.

Direct transesterification of wet microalgal biomass for preparation of biodiesel

Most conventional processes for algal biodiesel production involve separate lipid extraction steps or require usage of dry biomass that incurs extra cost and an energy intensive drying step. A novel process that involves dehydration of wet biomass via pretreatment with ethanol followed by direct in situ transesterification into biodiesel was investigated in this study. Under mild esterification at 80°C for 30min, pretreating the wet biomass twice with 3 volumes of ethanol resulted in a nearly four-fold increase of fatty acid ethyl ester (FAEE) yield from 3.04mg to 11.78mg, while increasing the ethanol from 1 volume to 10 volumes resulted in a six fold increase of yield from 3.18 to 18.29mg. The FAEE yield further increased when the esterification reaction was run at higher temperature and longer durations of up to 120°C for 2h. The overall positive impact of the pretreatment step on the final yield was far greater for milder reaction conditions, which makes the process more attractive in terms of economics and energy savings. In addition, it was found that the yield is unaffected by the choice of alcohol, which means methanol and butanol can also be used for the process. Lastly, it was found that the low concentration of water in the FAEE containing spent ethanol meant that both the solvent and sulfuric acid could be reused to further concentrate the quantity of FAEE in the final product mixture.

Direct quantification of fatty acids in wet microalgal and yeast biomass via a rapid in situ fatty acid methyl ester derivatization approach.

Accurate determination of fatty acid contents is routinely required in microalgal and yeast biofuel studies. A method of rapid in situ fatty acid methyl ester (FAME) derivatization directly from wet fresh microalgal and yeast biomass was developed in this study. This method does not require prior solvent extraction or dehydration. FAMEs were prepared with a sequential alkaline hydrolysis (15 min at 85 °C) and acidic esterification (15 min at 85 °C) process. The resulting FAMEs were extracted into n-hexane and analyzed using gas chromatography. The effects of each processing parameter (temperature, reaction time, and water content) upon the lipids quantification in the alkaline hydrolysis step were evaluated with a full factorial design. This method could tolerate water content up to 20% (v/v) in total reaction volume, which equaled up to 1.2 mL of water in biomass slurry (with 0.05-25 mg of fatty acid). There were no significant differences in FAME quantification (p>0.05) between the standard AOAC 991.39 method and the proposed wet in situ FAME preparation method. This fatty acid quantification method is applicable to fresh wet biomass of a wide range of microalgae and yeast species.

Assessment and comparison of the properties of biodiesel synthesized from three different types of wet microalgal biomass

In recent years, microalgae-based carbon-neutral biofuels (i.e., biodiesel) have gained considerable interest due to high growth rate and higher lipid productivity of microalgae during the whole year, delivering continuous biomass production as compared to vegetable-based feedstocks. Therefore, biodiesel was synthesized from three different microalgal species, namely Tetraselmis sp. (Chlorophyta) and Nannochloropsis oculata and Phaeodactylum tricornutum (Heterokontophyta), and the fuel properties of the biodiesel were analytically determined, unlike most studies which rely on estimates based on the lipid profile of the microalgae. These include density, kinematic viscosity, total and free glycerol, and high heating value (HHV), while cetane number (CN) and cold filter plugging point (CFPP) were estimated based on the fatty acid methyl ester profile of the biodiesel samples instead of the lipid profile of the microalgae. Most biodiesel properties abide by the ASTM D6751 and the EN 14214 specifications, although none of the biodiesel samples met the minimum CN or the maximum content of polyunsaturated fatty acids with ≥4 double bonds as required by the EN 14214 reference value. On the other hand, bomb calorimetric experiments revealed that the heat of combustion of all samples was on the upper limit expected for biodiesel fuels, actually being close to that of petrodiesel. Post-production processing may overcome the aforementioned limitations, enabling the production of biodiesel with high HHV obtained from lipids present in these microalgae.

The role of co-solvents in improving the direct transesterification of wet microalgal biomass under supercritical condition

In this research, direct conversion of wet algal biomass into biodiesel using supercritical methanol was studied. In this process, microalgal lipids simultaneously was extracted and converted to biodiesel under high pressure and temperature conditions without using any catalyst. Several experiments have been performed to optimize the methanol amount and it has been revealed that the best performance was achieved by using methanol/wet biomass ratio of 8:1. The effect of using various co-solvents in increasing the efficiency of the supercritical process was investigated. It has been shown that hexane was the most effective co-solvent and its optimal ratio respect to wet biomass was 6:1. The results indicated that compare to conventional extraction plus transesterification reaction, fatty acid methyl esters (FAMEs) yield was slightly higher in the direct conversion process. Moreover, increasing the moisture content up to 80% has no significant effect on reducing the performance of this process.

Physicochemical characterization of wet microalgal cells disrupted with instant catapult steam explosion for lipid extraction

Instant catapult steam explosion (ICSE) was employed to disrupt wet microalgal cells for efficient lipid extraction. Physicochemical properties of exploded cells were investigated through SEM, TEM, FTIR, and TGA. The exploded cells increased in fractal dimension (1.53–1.65) when preheat time was prolonged from 0min to 5min and in surface pore area when steam pressure was increased. Meanwhile, the exploded cells decreased in mean size (1.69–1.44μm) when the filling ratio of wet microalgal biomass in the preheat chamber decreased (75–12.5%). Flash evaporation and volume expansion exploded the cell walls and released the cytoplasm of the microalgal cells. These phenomena decreased the carbohydrate content and increased the lipid content in the exploded biomass. However, ICSE treatment did not change the lipid compositions in the microalgal cells. Using isopropanol as a cosolvent significantly increased the yield of lipids extracted with hexane from the exploded wet microalgal biomass.

Biodiesel production from wet microalgal biomass by direct transesterification

The aim of this work was to optimize the production of fatty acid methyl esters (FAMEs, biodiesel) from marine Nannochloropsis gaditana wet microalgal biomass (25wt% dry biomass and 11.1wt% saponifiable lipids, SLs, of dry biomass) by direct acid catalyzed methylation of SLs in the microagal biomass and extraction of FAMEs with hexane. The best FAME yield was attainted with a methanol/SL ratio of 171.1mL/g, an acetyl chloride (catalyst) concentration of 5% (v/v), 100°C and a reaction time of 105min. In these conditions 100% of SLs were transformed to FAMEs. Similar yields were obtained at lower temperatures and higher reaction times. The pretreatment of wet biomass by homogenization did not improve the above results. Finally, the FAME purity was increased from 74.5 to 82.7wt% by a treatment of adsorption with bentonite.