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Ultrasonic cavitation for disruption of microalgae
Abstract
Challenges with mid-stream fractionation steps in proposed microalgae biofuel pathways arise from the typically dilute cell density in growth media, micron scale cell sizes, and often durable cell walls. For microalgae to be a sustainable source of biofuels and co-products, efficient fractionation by some method will be necessary. This study evaluates ultrasonic cell disruption as a processing step that fractionates microalgae. A range of species types with different sizes and cell wall compositions were treated. The initial seconds of sonication offered the most significant disruption, even for the more durable Nannochloropsis cells. Following this initial period, diminishing effectiveness was attributed, by acoustic measurements, to attenuation of the ultrasound in the ensuing cloud of cavitating bubbles. At longer exposure times, differences between species were more pronounced. Processing higher concentrations of Isochrysis slowed cell disintegration only marginally, making the expenditure of energy more worthwhile.
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... chlorophyll a fluorescence density (an indirect indicator of cell disruption) and the lipid fluorescence density of Scenedesmus dimorphus and Nannochloropsis oculata increased significantly under both high frequency (3.2 MHz) and low frequency (20 kHz) ultrasonic treatment, revealing efficient cell disruption and lipid releasing caused by ultrasonic treatment [57]. Conventionally, low ultrasound frequencies in the range of 20-40 kHz were most commonly used in the process of microalgal bioproducts extraction [48,55,[58][59][60][61][62]. Specially, for susceptive microalgae with thin cell walls, low-frequency ultrasound is highly effective towards cell disruption. ...
... Several studies have been performed to understand the relationship between ultrasound intensity and other extraction parameters. Greenly and Tester [60] studied the extraction kinetics and found that high intensity (2.5 W/mL) and low frequency (20 kHz) ultrasound offered the most significant cell disruption at the initial 2-5 s of sonication. A maximum power input of 2.2 KW was applied on Schizochitrium limacinum and Chlamydomonas reinhardtii [55]. ...
... The time that intact cells were halved was 2 s and 1 min for the two strains, respectively. Attenuation of the sound wave by the local field of cavitating bubbles was mostly likely the reason of the slowing down of cell breakage after the initial few seconds [60]. However, a long sonication exposure period could result in release of free radical, oxidation of lipids and accumulation of heat generated. ...
Microalgae are a promising feedstock for the production of biofuels, nutraceuticals, pharmaceuticals and cosmetics, due to their superior capability of converting solar energy and CO2 into lipids, proteins, and other valuable bioactive compounds. To facilitate the release of these important biomolecules from microalgae, effective cell disruption is usually necessary, where the use of ultrasound has gained tremendous interests as an alternative to traditional methods. This review not only summarizes the mechanisms of and operation parameters affecting cell disruption, but also takes an insight into measuring techniques, synergistic integration with other disruption methods, and challenges of ultrasonication for microalgal biorefining. Optimal conditions including ultrasonic frequency, intensity, and duration, and liquid viscosity and sonochemical reactor are the key factors for maximizing the disruption and extraction efficiency. A combination of ultrasound with other disruption methods such as ozonation, microwave, homogenization, enzymatic lysis, and solvents facilitates cell disruption and release of target compounds, thus provides powerful solutions to commercial scale-up of ultrasound extraction for microalgal biorefining. It is concluded that ultrasonication is a sustainable “green” process, but more research and work are needed to upscale this process without sacrificing performance or consuming more energy.
... Although a bilinear equation model has been proposed to fit the relationship between cell rupture and energy consumption, the cell disruption is not a first-order process with ultrasonic energy inputs, which depend on the treated algal species and ultrasonic parameters. 5,16,31 In order to upgrade ultrasonic energy efficiency, the correlation between cell disruption and energy inputs needs to be analyzed quantitatively. ...
... 4,47 Another important cause might be that "the ensuing cloud of cavitating bubbles" around the ultrasonic transducers (generally probetype) diffused and dispersed the acoustic energy, resulting in an attenuation of the ultrasonic energy. 31 The acoustic energy consumption is algal species specific due to their unique resistances to sonication. 48 In addition, the energy demand to collapse a given algal species is also impacted by the variations in conversion efficiencies of different ultrasonic transducers from acoustic power into cavitation or free radical force. ...
... and plotted ( Figure 6B,C). 31 In addition, a linear equation model was also evaluated for cell disruption as follows. 12 ...
Ultrasound has been regarded as an environmental friendly technology to utilize microalgae biomass and control algal blooms. In this study, four quantitative techniques, including cell counting, optical density of algal suspension, pigments release, and protein release, were performed on three species of microalgae (M. aeruginosa, C. pyrenoidosa, and C. reinhardtii) to develop effective techniques for rapid monitoring of cell disruption and to optimize the acoustic energy efficiency. Results showed optical density of algal suspensions was not an optimal indicator to monitor cell disruption, although it is a common technique for determining cell concentration in microbial cultures. Instead, an accurate and reliable technique was to determine the release of intracellular pigments (absorbance peaks of supernatant) for indicating cell rupture. The protein released during sonication could also be a useful indicator if it is the component of interest. A fitted power functional model showed a strong relationship between cell disruption and energy consumption (R² > 0.87). This model could provide an effective approach to directly compare the energy efficiency of ultrasound in different systems or with varying microalgae species. This study provides valuable information for microalgae utilization and the treatment of algal blooms by ultrasound, so as to achieve energy conservation and environmental safety.
... The frequencies at which ultrasonic devices emit the acoustic waves also differ. Most studies are using the piezoelectric transducers with excitation frequency 20 kHz [47,48]. However, researchers use also other frequencies, up to the 3.2 MHz [49], which is the highest used frequency reported in this review paper. ...
... Halim et al. [162] determined an open-down parabolic relationship between cell destruction and initial concentration. On the other hand, Greenly and Tester [48] showed that concentration does not play an important role but postulated that the volume of the sample may be important for cavitation efficiency. They determined that in the first few seconds the breakage of Chlamydomonas sp. cells is the highest. ...
... For example, Chlamydomonas sp. and Dunaliella salina which have a thin and irregular cell wall, respectively, were both destructed to a high degree with all AC frequencies investigated. Greenly and Tester [48] observed that Nannochloropsis oculate, which has a robust cell wall, is the most resilient of the species tested. The only microalgae that did not seem to be affected by cavitation were Chlorella kessleri and Chlorococcum sp. ...
A sudden decrease in pressure triggers the formation of vapour and gas bubbles inside a liquid medium (also called cavitation). This leads to many (key) engineering problems: material loss, noise, and vibration of hydraulic machinery. On the other hand, cavitation is a potentially useful phenomenon: the extreme conditions are increasingly used for a wide variety of applications such as surface cleaning, enhanced chemistry, and wastewater treatment (bacteria eradication and virus inactivation). Despite this significant progress, a large gap persists between the understanding of the mechanisms that contribute to the effects of cavitation and its application. Although engineers are already commercializing devices that employ cavitation, we are still not able to answer the fundamental question: What precisely are the mechanisms how bubbles can clean, disinfect, kill bacteria and enhance chemical activity? The present paper is a thorough review of the recent (from 2005 onward) work done in the fields of cavitation-assisted microorganism's destruction and aims to serve as a foundation to build on in the next years.
... The mechanisms of US-induced disruption of microalgae species were also studied intensively (Gerde et al., 2012;Greenly and Tester, 2015;Halim et al., 2013;Ma et al., 2014). It was demonstrated that in US process, the microalgal cells can be ruptured by shock waves (Ma et al., 2014). ...
... In addition, the impact of US-treatment on microalgae species with different sizes and cell wall compositions was studied (Greenly and Tester, 2015). It was demonstrated that the most significant disruption was observed in the initial period of sonication and at longer exposure times. ...
... In general, sonication promoted the formation of smaller liposomes with a lower PDI, in agreement with that previously reported by other authors for this method, which produces homogeneous dispersions of nanometric liposomes [18,26,28]. The sonication effects are based on the cavitation of the bubbles, which provokes a localised, short-lived pressure increase, as well as microstreaming effects and shock waves that rupture lipid vesicles and promote the formation of more homogeneous systems [29]. A linear decrease in the particle size and polydispersity of liposomes as a result of increasing the time and intensity of sonication has previously been reported [18,26]. ...
... This fact demonstrates the good integration of this phenolic compound in P-PVA matrix, without visible dispersed droplets, while the F-PVA films presented a clear phase separation. This was attributed to the formation of Lewis adducts between the phenolic compound and the negatively charged chains of P-PVA, as previously described [28,29]. Nevertheless, the incorporation of carvacrol-free liposomes into P-PVA and F-PVA matrices led to heterogeneous matrices that exhibited a dispersed phase of altered liposomes (Figure 3c,d, respectively). ...
Lecithins of different origins and compositions were used for the liposomal encapsulation of carvacrol within the framework of the development of active films for food packaging. Liposomes were incorporated into aqueous polymeric solutions from fully (F) and partially (P) hydrolysed Poly (vinyl alcohol) (PVA) to obtain the films by casting. The particle size distribution and ζ-potential of the liposomal suspensions, as well as their stability over time, were evaluated. Liposomal stability during film formation was analysed through the carvacrol retention in the dried film and the film microstructure. Subtle variations in the size distributions of liposomes from different lecithins were observed. However, the absolute values of the ζ-potential were higher (−52, −57 mV) for soy lecithin (SL) liposomes, followed by those of soy lecithin enriched with phosphatidylcholine (SL-PC) (−43, −50 mV) and sunflower lecithin (SFL) (−33, −38 mV). No significant changes in the liposomal properties were observed during the study period. Lyotropic mesomorphism of lipid associations and carvacrol leakage occurred to differing extents during the film drying step, depending on the membrane lipid composition and surface charge. Liposomes obtained with SL-PC were the most effective at maintaining the stability of carvacrol emulsion during film formation, which led to the greatest carvacrol retention in the films, whereas SFL gave rise to the least stable system and the highest carvacrol losses. P-PVA was less sensitive to the emulsion destabilisation due to its greater bonding capacity with carvacrol. Therefore, P-PVA with carvacrol-loaded SL-PC liposomes has great potential to produce active films for food packaging applications.
... [5][6][7] Unlike the use of terrestrial oil crops, however, the proposed microalgae biofuel pathways face the following challenges: diluted cell concentration in growth media, micron-scale cell size, and particularly durable cell walls. [8] These walls are typically trilayered and composed of various components, which mainly include cellulose, uronic acid, mannose, xylan or tri-laminar layers of algaenan (a polyaldehyde network), and minerals. [9,10] In addition, a great number of hydroxyproline-rich and glycine-rich glycoproteins, which are generally found in the wall complexes, are arranged into the interlocking fibrillar elements. ...
... Microalgae generally possess durable cell walls that are strongly resistant to the ultrasonic disruption process. [8] The bottleneck of algae lysis may be the hydrogenbond-rich cellulose in cell walls. [19] In the present study, the prominent achievement in lysis efficiency gained by H 2 O 2 -aided ultrasonic pretreatment suggested that it might effectively degrade or alter the cellulosic structure or cellulose hydrogen bond network in walls via producing sufficient hydroxyl radicals. ...
In this work, Chlorella pyrenoidosa was chosen as model microalgae, and several pretreatments, including hydroxyl-peroxide-aided ultrasonic pretreatments and mono-ultrasonication (US), were used to rupture the microalgal cells for extracting cellular inclusion. The disruption efficiency and the energy consumption of each technique were estimated through measuring the amount of released protein from cells and the microscopic images after pretreatment. Results showed that the combined pretreatments obtained a much higher lysis efficiency than did the US (over twofold). However, the concentration of H2O2 used (ranging from 0.1 to 5 mM) failed to influence the lysis efficiency significantly (P < 0.05). Additionally, the acoustic energy efficiency was increased with the initial cell concentration treated, but the coefficient of utilization of algal biomass was decreased significantly. Therefore, an ideal initial cell concentration (13.4 × 10⁷ cells/mL) was gained in terms of the higher coefficient of utilization of algal biomass. This research suggested that a synergistic technique could be an effective pretreatment for microalgal cell disruption and downstream comprehensive utilization. © 2017 Curtin University of Technology and John Wiley & Sons, Ltd.
... The difference in cell shape (filamentous/non-filamentous) was considered as one of the probable reasons for the different levels of susceptibility to sonication. In addition, Greenly and Tester (2015) suggested that cell size and wall composition might have a significant impact on cell lysis efficiency. However, it was difficult to find out which of these properties were the valid and working factors when numerous variables (different properties) were present synchronously in the treated strains. ...
... Furthermore, even if numerous biological features were included (meaning that all of these algae here were taken into account except for PCC 7942 due to the reasons mentioned above), cell disruption was still positive correlated to cell size (r > 0.89, P < 0.05) (Fig. 8). This is in agreement with the report conducted by Greenly and Tester (2015), who demonstrated that Nannochloropsis oculata (CCMP 525), a 2-μm marine green alga, was more indestructible than the other bigger microalgae. ...
Ultrasonication has drawn an increasing attention as one of cell disruption methods for extracting cellular compounds or controlling algal blooms. However, the effects of biological and physical properties of microalgae on cell disruption were not well understood. In this work, cell disruption of six microalgae, namely, Chlamydomonas reinhardtii, Chlorella pyrenoidosa, Microcystis aeruginosa (three strains: PCC 7806, FACHB 469, and FACHB 1343), and Synechococcus elongatus, was compared mutually based on their characteristics induced by a low-frequency ultrasound (35 kHz, 0.043 W mL⁻¹). Results showed that the most sensitive strain was C. reinhardtii which has a hydroxyproline-rich-glycoproteins cell wall and a larger cell size (normally 10 μm in diameter). More than 80% of the cells of C. reinhardtii were ruptured after sonication for 5 min. In comparison, C. pyrenoidosa, a cellulose-rich-wall algal species with a medium size of 4–6 μm, and M. aeruginosa FACHB 1343, a peptidoglycan-wall species with a smaller average size of 2.3 μm, were highly resistant to ultrasound. Only 7.5 and 7.7% of cell disruption were achieved for C. pyrenoidosa and M. aeruginosa FACHB 1343, respectively, when they were sonicated for 60 min. Declumping effect was dominant in these strains. This suggested that cellulose-rich-wall algal species might be much more resistant than hydroxyproline-rich glycoproteins, and peptidoglycan-wall species to sonication. It also revealed that the larger cell size was more susceptible to sonication the cell would be. This research provides useful insights into choosing the low-cost microalgae for extraction or controlling specific microalgal blooms in water systems using ultrasound.
... As remarkable antioxidisability, astaxanthin exhibits the excellent capability for therapeutic and functional applications. The use of astaxanthin as a nutritional supplement has been rapidly growing in foods, feeds and pharmaceuticals (Greenly & Tester, 2015). For quick extraction of this valuable compound, there is a dire need to develop/explore the novel techniques that have minimal effect on the compound with higher extraction efficiency. ...
... As PEF, US treatment requires more energy utilisation and consumption for the cell wall breakage while the extractable astaxanthin was reached to 11.79%. Recently, US treatment has been extensively studied and employed for cell wall disruption to enhance the lipid recovery from N. oculata, C. minutissima, Arthrospira platensis and Porphyridim cruentum Greenly & Tester, 2015). It has been demonstrated that US treatment has the excellent cell disintegration capability and impressive lipid recovery rate from microalgae. ...
The efficiency of various techniques pulsed electric field (PEF), ultrasound (US), high pressure microfluidization (HPMF), hydrochloric acid (HCl) and ionic liquids (ILs) for cell wall disruption in astaxanthin extraction from Haematococcus pluvialis was compared. The results indicated that ILs, HCl and HPMF treatment were shown the most efficient for cell disruption with more than 80 % astaxanthin recovery. While the cell wall integrity of H. pluvialis cyst cell were less affected by US and PEF treatment. It was found that imidazolium-based ILs showed the greater potential for cell disruption than pyridinium-based and ammonium-based ILs. Among all the ILs examined, 1-butyl-3-methylimidazolium chloride ([Bmim] Cl) exhibited efficient cell disruption and capability of astaxanthin recovery at mild condition (pretreatment with 40 % IL aqueous solution at 40 °C, followed by extraction with methanol at 50 °C) without extensive energy consumption and special facility requirement. In addition, recyclability of ILs was excellent.
... When analyzing DNA purity at wavelength 260/230 nm, there was no significant difference between the two protocols (0.07 ± 0.04 vs. 0.68 ± 0.50; p < 0.01). Concerning DNA quantification, there was a significant difference (20.75 ng/L ± 11.74 ng/L vs. 37.01 ng/L ± 36.91 ng/L; p < 0.01) between the protocols used in the analysis. ...
... Among them, the one that obtained the shortest execution time, lowest cost, and the best results were the in-house protocol, as our results also demonstrated. The analyses by Liu et al. (2013), 36 Greenly, and Tester (2015) 37 showed that the use of ultrasound allows cell walls to be cleaved by shock waves, created by rapid changes in pressure caused by sonication. The study by Granger et al. (2004) 15 reported that the use of sonication improved mycobacterial DNA by removing background bacteria and other cells. ...
Tuberculosis (TB) is one of the infectious diseases with high mortality in the world. DNA amplification techniques have been used to overcome barriers to the diagnosis of this disease. However, the success of these methodologies is highly dependent on the DNA obtained from the sample. This study was carried out to verify whether the DNA extracted by sonication (in house method) could yield suitable DNA for amplification by real-time PCR (qPCR). Sixty sputum samples were submitted to DNA extraction using sonication compared to a commercial method (Detect-TB kit, Labtest/MG-Brazil). All DNA samples were amplified by qPCR for IS6110 region (IS6110-qPCR/SYBR Green assay). Out of 60 samples, 40 were positive for TB; of these, all had positive results when extracted by sonication (100%) and 80% when extracted by the commercial method. The limit of detection (LOD) of Mycobacterium tuberculosis (H37Rv strain) by qPCR was 14 CFU/mL when the DNA was extracted by sonication, compared to countless colonies when extracted by commercial kit. In conclusion, the sonication protocol (without purification step) proved to be a simple, fast, and suitable method for obtaining DNA for use in qPCR from sputum samples.
... This high yield attained was a consequence of the highly acidic extraction-reaction medium used in the DP process that promotes significant cell disruption [41]. According to literature [42,43], N. gaditana has a robust cell wall. However, the freeze-drying process to which the biomass was subjected previous FAEE production via DP most probably caused a cell wall breakage, which allowed the release of the lipids to the reaction medium. ...
... for DP using I. galbana, which were similar to the ones obtained with N. gaditana. Both microalgae present a robust cell wall, although the one of I. galbana is weaker [42,43]. In fact, the results confirmed the relatively weak cell wall of both microalgae utilised in this study, because of the freeze-drying treatment, which promote cell wall disruption and the release of their lipid content for their reaction, favouring contact between the catalyst and ethanol, and the lipids of these species. ...
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The integrated production of biodiesel and biogas has been explored by using N. gaditana, I. galbana and A. platensis as substrate. Three fatty acid ethyl ester (FAEE) production approaches were assessed, namely an indirect process with previously extracted lipids (IPPEL), an indirect process with extracted lipids as free fatty acids (IPELFFA) and a direct process (DP) without a previous lipid extraction stage. Besides de FAEE production, these approaches are considered as pre-treatments of the microbial biomasses evaluated in this study with the objective of increasing the methane yield during the anaerobic digestion. Biogas yields of the residues generated under the three FAEE production methodologies were compared to the biogas yield of the raw feedstock. In all cases, the biodiesel and biogas yields were higher after the FAEE production process from the previously extracted lipids as free fatty acids (IPELFFA). Therefore, this constitutes an interesting and promising route in the joint production of biodiesel and biogas.
... For the extraction time of 30 min, raising the temperature from 30 • C to 50 • C exhibited an increasing trend in lipid yield (p < 0.05), showing a notable effect of the temperature on this process. Despite the positive The use of ultrasounds has been recognized as an efficient extraction technique to disrupt the cell wall of different microalgae (for example Chlorella vulgaris [20], Schizochytrium limacinum [21], Chlamydomonas reinhardtii [21], Isochrysis galbana [22,23], Desmodesmus sp. [24]. ...
... These results were in contrast with those of Blanco-Llamero et al., who reported a synergic effect when different hydrolytic enzymes were used simultaneously for the same microalgae species [26]. The use of ultrasounds has been recognized as an efficient extraction technique to disrupt the cell wall of different microalgae (for example Chlorella vulgaris [20], Schizochytrium limacinum [21], Chlamydomonas reinhardtii [21], Isochrysis galbana [22,23], Desmodesmus sp. [24]. ...
Microalgae are alternatives and sustainable sources of omega-3 long chain-polyunsaturated fatty acids (LC-PUFA). However, the eco-friendly extraction of these bioactives remains unexplored. In this work, the use of enzyme-based methods in combination with ultrasounds was evaluated as green approaches to extract the omega-3 lipids from Nannochloropsis gaditana. Three commercial enzymatic solutions (Viscozyme® L, Celluclast® 1.5 L, and Saczyme®) were investigated, and results were compared with the traditional Folch method. A promising extraction approach was developed by using Saczyme®, achieving a lipid yield of 25.7% ± 0.5, comparable to the traditional method (27.3% ± 0.7) (p > 0.05). Similar omega-3 content was found by GC-MS analysis for both lipid extracts (30.2% ± 2.4 and 29.3% ± 0.8 for the green and the traditional method, respectively), showing that the green approaches did not affect the fatty acid profile. Moreover, the cytotoxic activity of produced lipids was assessed by comparing human colon cancer cells (HCT-116) and epithelial nontumorigenic immortalized cells (HCEC-1CT). Results suggest that the lipid extracts have a selective effect, reducing the viability of the colon carcinoma cells but not the nontumorigenic cells. Thus, this study provides new eco-innovative approaches for extracting the omega-3 LC-PUFA from microalgae with promising biological properties.
... As remarkable antioxidisability, astaxanthin exhibits the excellent capability for therapeutic and functional applications. The use of astaxanthin as a nutritional supplement has been rapidly growing in foods, feeds and pharmaceuticals (Greenly & Tester, 2015). For quick extraction of this valuable compound, there is a dire need to develop/explore the novel techniques that have minimal effect on the compound with higher extraction efficiency. ...
... As PEF, US treatment requires more energy utilisation and consumption for the cell wall breakage while the extractable astaxanthin was reached to 11.79%. Recently, US treatment has been extensively studied and employed for cell wall disruption to enhance the lipid recovery from N. oculata, C. minutissima, Arthrospira platensis and Porphyridim cruentum Greenly & Tester, 2015). It has been demonstrated that US treatment has the excellent cell disintegration capability and impressive lipid recovery rate from microalgae. ...
... As remarkable antioxidisability, astaxanthin exhibits the excellent capability for therapeutic and functional applications. The use of astaxanthin as a nutritional supplement has been rapidly growing in foods, feeds and pharmaceuticals (Greenly & Tester, 2015). For quick extraction of this valuable compound, there is a dire need to develop/explore the novel techniques that have minimal effect on the compound with higher extraction efficiency. ...
... As PEF, US treatment requires more energy utilisation and consumption for the cell wall breakage while the extractable astaxanthin was reached to 11.79%. Recently, US treatment has been extensively studied and employed for cell wall disruption to enhance the lipid recovery from N. oculata, C. minutissima, Arthrospira platensis and Porphyridim cruentum Greenly & Tester, 2015). It has been demonstrated that US treatment has the excellent cell disintegration capability and impressive lipid recovery rate from microalgae. ...
The efficiency of various techniques pulsed electric field (PEF), ultrasound (US), high-pressure microflu-idisation (HPMF), hydrochloric acid (HCl) and ionic liquids (ILs) for cell wall disruption in astaxanthin extraction from Haematococcus pluvialis was compared. The results indicated that ILs, HCl and HPMF treatment were shown the most efficient for cell disruption with more than 80% astaxanthin recovery. While the cell wall integrity of H. pluvialis cyst cell was less affected by US and PEF treatment. It was found that imidazolium-based ILs showed the greater potential for cell disruption than pyridinium-based and ammonium-based ILs. Among all the ILs examined, 1-butyl-3-methylimidazolium chloride ([Bmim] Cl) exhibited efficient cell disruption and capability of astaxanthin recovery at mild condition (pretreat-ment with 40% IL aqueous solution at 40°C, followed by extraction with methanol at 50°C) without extensive energy consumption and special facility requirement. In addition, recyclability of ILs was excellent.
... As a result of reduced pressure, microbubbles are formed in the rarefaction regions and eventually collapse emitting a shock wave. This leads to cytoplasmic disruption splitting the cell bodies open [49,50]. An enhancement in oil yield by 50-500%, along with 10 fold reduction in extraction time can be achieved using ultrasound assisted technology [51,52]. ...
Microalgae have gained widespread interest all over the globe as potential substitutes to petroleum-based fuels. The biodiesel production from microalgae has been investigated intensively with a focus on optimization of various upstream and downstream operations involved in the process. Downstream operations in the production of biodiesel consist of various steps whereof microalgal lipid extraction holds utmost importance for the overall efficiency of the process. The conventional method of extraction involves direct use of organic solvents to extract the intracellular lipids, making the process more time consuming and less eco-friendly. This review describes various modifications that have emerged to the conventional approach of lipid extraction, with a focus on potential biodiesel microalgae strains, namely, Chlorella sp., Nannochloropsis sp., and Scenedesmus sp. Various pre-treatment approaches in conjunction with solvent based extraction namely mechanical, chemical and biological cell disruption along with their comparative efficiencies on the basis of lipid yield, extraction time, energy intake, solvent use, biomass status (dry and wet) and scalability are discussed. The other promising approaches i.e. use of greener solvents, viz. bio-based solvents, supercritical fluids, ionic liquids, and switchable solvents are also reviewed along with the simultaneous extraction, and trans-esterification approach. Further, various challenges and solutions to the lipid extraction processes have also been analysed.
... Power ultrasound of 20-100 kHz frequency is known to be broadly effective in breaking microbial cells (Gao et al. 2014;Iida et al. 2008;Jaeschke et al., 2016). Cell breakage by ultrasound is a result of multiple factors including intense turbulence and pressure changes associated with acoustic cavitation (Doulah 1977;Greenly and Tester, 2015). This work reports an ultrasound-mediated disruption of Pseudomonas putida for the release of ADI. ...
The responses of the ultrasound-mediated disruption of Pseudomonas putida KT2440 were modelled as the function of biomass concentration in the cell suspension; the treatment time of sonication; the duty cycle and the acoustic power of the sonicator. For the experimental data, the response surface (RSM), the artificial neural network (ANN) and the support vector machine (SVM) models were compared for their ability to predict the performance parameters. The satisfactory prediction of the unseen data of the responses implied the proficient generalization capabilities of ANN. The extent of the cell disruption was mainly dependent on the acoustic power and the biomass concentration. The cellmass concentration in the slurry most strongly influenced the ADI and total protein release. Nearly 28 U/mL ADI was released when a biomass concentration of 300 g/L was sonicated for 6 min with an acoustic power of 187.5 W at 40% duty cycle. Cell disruption obeyed first-order kinetics.
... This technique utilizes the shock wave to propagate fluctuations that induce cavitation and mechanoacoustic effects for the cell wall rupturing (Naveena et al., 2015;Mubarak et al., 2015). The microbubbles and reduced pressure eventually collapse the 9. Potentials and challenges in biodiesel production from algaedtechnological outlook emitting shock wave, which leads to the opening up of cells by cytoplasmic disruption (Greenly and Tester, 2015). This method reduces extraction time in tenfold along with 50%e500% in enhancement lipid extraction process. ...
... This method used sonic wave with frequencies around 25 kHz for cell disruption. Evaluation on the effectiveness of high-frequency focused ultrasound (HFFU) in microalgae cell disruption was performed [6]. However, only sonication mean was not enough for cell disruption of microalgae; thus, addition of buffer for cooperation on cell breaking was necessary. ...
This study investigated the condition on microalgae cell disruption method by the combination of ultrasonication and buffer solution. Various buffer solutions have been utilized and the duration of the sonication was also tested. The quantity in term of protein concentration and the quality of the protein product were evaluated. Results showed that Mixed buffer III and Triton x lysis buffer showed the high concentration of protein but low quality. SDS lysis buffer showed high quality protein product but low the concentration of protein. For the study on the effect of sonication duration, the concentration of protein significantly increased when longer duration of sonication was applied and this result was observed during continuous sonication test as well. The concentration of protein was not only the important aspect, but the quality of the protein needs to be satisfied. Thus, it could be suggested that the optimum condition of protein extraction from microalgae needs the combination of the use of buffer solution to ensure high quality product and an appropriate duration of ultrasonication to maximize the quantity of protein.
... With the deepening research of ultrasonic technology, applications of the technology is more and more wide in the washing, processing, medical, biological fields and et al. The cavitation characteristics of ultrasonic is applied in a considerable part of these applications [1][2][3] . Study results show that DF ultrasonic can homogenize the sound field, eliminate the standing wave, accelerate the formation of cavitation bubbles and significantly enhance the effect of cavitation compared with single frequency ultrasonic [4,5] . ...
... Many investigators have used different methods to measure cell disintegration after ultrasonication. These include the diffusion behaviour of proteins and pigments of Chlorella vulgaris in the aqueous phase (Safi et al. 2015), reductions in intact cell counts and reductions in average colony diameters (Halim et al. 2012), counting only intact cells with a haemocytometer (Greenly and Tester 2015), changes in the algal cell concentration, cell size, chlorophyll a fluorescence and Nile Red-stained lipid fluorescence (Wang et al. 2014) and cell disruption efficiency and lipid release (Natarajan et al. 2014). ...
The main objective of this study is to demonstrate the possibilities of using laser light scattering methods, dynamic light scattering and laser Doppler electrophoresis, as suitable methods in investigations of algal production biosystems and biotechnology. This paper highlights the innovative use of the dynamic light scattering (DLS) methods for monitoring the destruction of Parachlorella kessleri cells. Additionally, these results indicate electrophoretic mobility as a new parameter to investigate the effectiveness of cell disruption prior to extraction conducted to optimise the biotechnological processes of recovery of microalgal intracellular metabolites. The efficacy of P. kessleri cell disintegration by ultrasound was determined by measurements of the number of cells with the algal cell reduction (CRns), relative mean hydrodynamic diameter (Rdt) and electrophoretic mobility after applying different lengths of ultrasound exposure to a cell suspension. It was found that stationary-phase cells were the most resistant to the ultrasound treatment, especially at low values of the optical density. Both the relative hydrodynamic diameter and the electrophoretic mobility of cells were correlated statistically significantly with the time of sonication (t) and the algal cell reduction. The relationships allowed estimation of the sonication time needed for total cell disruption.
... The range from 20 kHz to 50 kHz is often considered as the most efficient to induce cavitation [28][29]. But cavitating bubbles attenuate ultrasound transmission [30] and the suitable disruption frequencies depends on the cell's mechanical properties [31]. The process may be employed with wet biomass without the addition of organic solvents but also in addition to solvent extraction. ...
The interest in algae based biofuels has increased over the past few years because of their high potential to reduce the dependence on fossil fuels. Many methods for converting microalgae to biofuel have been proposed in the past; however, an economical and energetically feasible process for algal fuel production has not yet emerged, leading to some disappointment. To get such a process, an integrated microalgal biorefinery approach to obtain a full valorization of each raw microalgae component seems necessary. Moreover, several steps of any microalgal biorefinery model, ranging from species selection, cultivation, harvesting &dewatering and lipids extraction need still improvements to lower the global cost of the process. This review focuses on this latter step. It is shown that the wet route, skipping the drying step preceding the extraction step, seems to be the only way to produce a viable microalgae based biorefinery industry. On the other hand, an efficient cell disruption method, based on scalability, energy consumption, ability to improve lipid accessibility as well as mass transfer must be selected and in this context two promising studies are presented.
... The optimal values of ultrasonic power, reaction time, concentrations of methanol and chloroform in oil to maximize fatty acid methyl ester content and exergy efficiency were evaluated. The mechanism of ultrasonic disruption in suspensions of five strains of microalgae with different sizes and cell wall compositions (including Nannochloropsis sp.) was studied [54]. The most significant cell disruption and a small difference between species were observed during the initial seconds of sonication. ...
Microalgae of Nannochloropsis sp. present valuable source of bio-molecules (pigments, lipids, proteins) that have nutritional potential for the prevention and treatment of human diseases. Moreover, some species of Nannochloropsis are the promising sources of biofuels and excellent candidates for the replacement of classical biofuel crops. This review describes and compares the efficiency of different conventional and novel techniques that can be used for cell disruption and recovery of bio-molecules from Nannochloropsis sp. Classification of different extraction techniques includes chemical, enzymatic, mechanical and other physical methods. The detailed analysis of extraction efficiency assisted by pressure and temperature (subcritical and supercritical fluids, hydrothermal liquefaction), ultrasound, microwaves, and pulsed electric energy (pulsed electric fields and high voltage electrical discharges) is presented. The general discussion includes comparison between techniques, their effectiveness for cell disruption and selectivity of bio-molecules extraction from Nannochloropsis sp. The cost-effectiveness, benefits and limitations of different techniques are also analyzed.
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... Nevertheless, C. zofingiensis possesses rigid cell wall particularly under stress conditions [8] and thus cell disruption is required to facilitate extraction of TAG and astaxanthin from the alga and downstream processes. Many mechanic and non-mechanic disruption methods have been developed and applied to rupture cell walls of various microalgae; the former include bead beating [125], grinding [126], ultrasonication [127], high-pressure homogenization [128] and expeller pressing [129], and the latter include repeated freeze-thaw [130], osmotic shock [131], microwave radiation [132] and enzymatic digestion [133]. These methods should also work for cell wall disruption of C. zofingiensis, though modifications may be needed due to differences in cell wall composition and rigidity between C. zofingiensis and other algae [134]. ...
The algal lipids-based biodiesel, albeit having advantages over plant oils, still remains high in the production cost. Co-production of value-added products with lipids has the potential to add benefits and is thus believed to be a promising strategy to improve the production economics of algal biodiesel. Chromochloris zofingiensis , a unicellular green alga, has been considered as a promising feedstock for biodiesel production because of its robust growth and ability of accumulating high levels of triacylglycerol under multiple trophic conditions. This alga is also able to synthesize high-value keto-carotenoids and has been cited as a candidate producer of astaxanthin, the strongest antioxidant found in nature. The concurrent accumulation of triacylglycerol and astaxanthin enables C. zofingiensis an ideal cell factory for integrated production of the two compounds and has potential to improve algae-based production economics. Furthermore, with the advent of chromosome-level whole genome sequence and genetic tools, C. zofingiensis becomes an emerging model for studying lipid metabolism and carotenogenesis. In this review, we summarize recent progress on the production of triacylglycerol and astaxanthin by C. zofingiensis . We also update our understanding in the distinctive molecular mechanisms underlying lipid metabolism and carotenogenesis, with an emphasis on triacylglycerol and astaxanthin biosynthesis and crosstalk between the two pathways. Furthermore, strategies for trait improvements are discussed regarding triacylglycerol and astaxanthin synthesis in C. zofingiensis .
... The cavitation will burst due to the shear forces and create temporary high pressure on cell wall and weaken the cell walls, resulting in an easy transfer of solvent to cells, whereby the lipid molecules can be released into the bulk medium (Sivaramakrishnan and Incharoensakdi 2017c). Frequencies higher than 20 kHz efficiently weaken the cell wall ensuring the maximum oil extraction efficiency (Greenly and Tester 2015). Moreover, ultrasound indirectly reduces the extraction time and solvent utilization by weakening the cell wall structure (Sivaramakrishnan and Incharoensakdi 2018a). ...
The process development of microalgae oil extraction was optimized in the present study. The ultrasound was used to disrupt the isolated Chlamydomonas sp. cells. Among the various solvents tested, hexane showed the maximum extraction efficiency. Other extraction parameters such as solvent/algae ratio, temperature, and stirring speed were also optimized and found to be 6:1, 55 °C, and 300 rpm respectively. The extraction kinetics showed a first-order mechanism. After evaluation of thermodynamic parameters, the kinetics were found to be irreversible, endothermic, and spontaneous. The extracted oil was transesterified by stepwise and in situ methods and both methods showed similar results. Energy consumption is very similar for both stepwise and in situ transesterification. The methyl ester was characterized by thermogravimetric analysis (TGA) and the fuel properties were satisfactory when compared with the ASTM standard values. From the results, it is clear that the Chlamydomonas sp. under optimal lipid extraction conditions is a potential feedstock for the production of methyl ester.
... Mechanical pretreatment approach of algal biomass aids in releasing intracellular lipids into the solvent, followed by enhancement of its recovery [15]. One of the most promising mechanical-assisted extraction is ultrasonic extraction that utilizes a sound wave frequency of >20 kHz to propagate the pressure fluctuations that induce cavitation [22,29], which will disrupt the cytoplasm and open the cell bodies, leading the solvent extraction yield to increase. Studies [28,30] on microalgae Chlorella sp. reported that ultrasonic pretreatment can increase the yield of extraction and reduce the extraction time up to more than 15 times, compared to conventional organic extraction. ...
In the last few decades, the energy crisis has been one of the main concerns related to the lack of long-term petroleum-based reserves as primary energy resources. Biodiesel emerged as a promising alternative. Nowadays, it is produced from edible vegetable oil, thereby causing commodity prices and food security disruption. In this case, microalgae serve as a sustainable and renewable feedstock for their fast growth, high lipid content, and CO2 absorbing agent. Five processes are applied on the production of microalgae-based biodiesel, namely cultivation, harvesting, extraction, conversion, and refinement. There is currently limited study on technology selection on industrial-scale technology for oil extraction from Chlorella spp. of microalgae. Therefore, this study aims to review and select the most suitable technology using simple multi-attribute rating technique extended to ranking – multi-criteria decision analysis (SMARTER-MCDA). Preliminary studies showed that conventional organic solvent extraction (COE), ultrasound-assisted extraction (UAE), microwave-assisted extraction (MAE), electric pulse extraction (EPE), supercritical fluid extraction (SFE), and hydrothermal liquefaction (HTL) were the most promising technologies. These technologies required a series of evaluations using SMARTER-MCDA with several criteria, including easy scalability, extraction productivity, energy input, additional compound, and environmental impact. The result ranking showed that MAE technology was selected as the most suitable technology for oil extraction from Chlorella spp.
... During ultrasound treatment, the harsh environment created in the bulk medium can cause temporary high temperature and pressure. Under such conditions, reactive oxygen species (ROS) may be generated and the ROS-derived electrons are utilized for lipid synthesis, thus resulting in high lipid content (Greenly and Tester, 2015). The maximum lipid yield of 1.03 g/L was achieved at 20 W power. ...
The present study demonstrated the effect of ultrasound treatment on biomass, lipid and total lipid production of Scenedesmus sp. The microalga used in this study was treated with different ultrasonic power (0–50 W), ultrasonic time interval (0–5 s) and time (0–10 min). The significant improvement on biomass and lipid content was achieved at 20 W ultrasonic power, 2 s ultrasonic time interval and 4 min ultrasound. The overall lipid production was increased from 0.76 to 1.31 g/L under optimized ultrasonic conditions. On other hand, the Chl-a, carotenoid contents and oxygen evolution rate were also increased after the ultrasonic treatment with subsequent improvement in the efficiency of light capturing capacity, defense mechanism and oxygen evolution rate of cells leading to enhanced biomass and lipid production. The optimized ultrasound treatment enabled Scenedesmus sp. to increase its biomass, lipid and total lipid production. Hence proper ultrasound treatment on microalgae is an effective method improve the biomass and lipid content considerably.
... A classic example of grinding in biosciences is the use of mortar and pestle [6], which is nowadays optimized with the use of liquid nitrogen (when allowed by the sample). Cells walls can also be disrupted by the shock waves created by rapid changes in pressure elicited by sonication or cavitation [16][17][18]. Other mechanical tools available for cell disruption are shearing, which use a tangential force to make a hole in the cell [6], and bead beating, which uses different glass or steel beads to rupture tough cell wall as mentioned by Bunge et al. [19]. ...
Nucleic acid extraction (NAE) plays a vital role in molecular biology as the primary step for many downstream applications. Many modifications have been introduced to the original 1869 method. Modern processes are categorized into chemical or mechanical, each with peculiarities that influence their use, especially in point-of-care diagnostics (POC-Dx). POC-Dx is a new approach aiming to replace sophisticated analytical machinery with microanalytical systems, able to be used near the patient, at the point of care or point of need . Although notable efforts have been made, a simple and effective extraction method is still a major challenge for widespread use of POC-Dx. In this review, we dissected the working principle of each of the most common NAE methods, overviewing their advantages and disadvantages, as well their potential for integration in POC-Dx systems. At present, it seems difficult, if not impossible, to establish a procedure which can be universally applied to POC-Dx. We also discuss the effects of the NAE chemicals upon the main plastic polymers used to mass produce POC-Dx systems. We end our review discussing the limitations and challenges that should guide the quest for an efficient extraction method that can be integrated in a POC-Dx system.
... An ideal cell disruption technique should have high disruption efficiency for the complete release of bioproducts, while requiring relatively mild pH/temperature conditions to inflict minimal degradation/side reactions with the targeted compounds and maintaining a low energy footprint and process cost. To this end, several cell disruption techniques have been investigated to break the cell walls of microalgae such as bead milling (Agboola et al., 2019;Postma et al., 2015), ultrasonication (Greenly and Tester, 2015;Tan et al., 2018), microwave radiation (Kapoore et al., 2018), enzymatic treatment (Bai et al., 2017), and high-pressure homogenization (de Carvalho et al., 2020). In this chapter, both existing (e.g., ultrasonication, alkali treatments, and enzymatic methods) and novel techniques (i.e., germination, autolysis, and viral infection) for microalgae cell rupture will be reviewed ( Fig. 11.1). the microcrystalline structure of the cellulosic cell walls to conduct a process similar to mercerization (Safi et al., 2014). ...
Microalgae have been widely exploited as a sustainable feedstock of valuable bioactives for the biofuel, pharmaceuticals, and food industries. Most of these high-value components, however, are trapped inside thick and resistant cell walls. Technologies for cell wall disruption therefore need to be investigated, serving as a key step to facilitate the recoveries of target products for industrial manufacture. This chapter will review the operating principles of standard technologies used for microalgae cell disruption, including chemical, mechanical (e.g., bead milling, ultrasonication, and high-pressure homogenization), and enzymatic treatments. In addition, novel techniques such as autolysis, germination, and viral infection will also be reviewed and compared to standard methods. We will then evaluate the application of the above technologies to different microalgae species as well as the correlation between cell wall characteristics and extent of cell disruption. Finally, the chapter will examine the scalability of different cell disruption technologies through discussion of cost requirements and examination of their specific energy consumption.
... It should be noted that SE was adjusted by extending the sonication time to the sample. This phenomenon was simply caused by the lag of dissolved gas to form microbubbles in water, which would oscillate and burst to create the shear force in cavitation/expansion cycle [45]. The fact that the dissolved air in liquid medium is driven off over time suggests that a too long sonication period will guarantee a diminishing return on plant cell destruction and the effectiveness of sonication. ...
Biogas from the fast growing crop, Pennisetum purpureum, has received considerable attention in Southeast Asia since wastewater and bio-waste materials are almost completely utilized. To overcome slow hydrolysis, a rate-limiting step in anaerobic digestion of lignocellulosic biomass, superior microorganism culture, size reduction, and sonication pretreatment were co-applied. In the first experiment, the selection of anaerobic microbial culture to be used in digestion, so-called inoculum, was carried out. Specific anaerobic activities for hydrolysis and methanogenesis of sludge from different sources, a slurry digester of cattle farm (CF) and a wastewater digester of rubber latex factory (RL) were assessed. Results revealed a remarkable synergistic capability in the combined sludge, adding 10% and 49% to the overall biomethanation efficiency over the individual CF and RL sludges. In the second part, interactive effects of size reduction and sonication intensity were studied. Biomethanation efficiency as methane yield increased by 62% by size and 115% by sonication variation, but when optimally combined an additional gain of 40% was recorded. The regression model generated could estimate the energy yield increase as a function of size and sonication intensity with a satisfactory statistical precision R2 of 0.945.
... From this raw ma terial, biodiesel is produced using the conventional technolo gy -etherification of vegetable oils [9]. The product yield in each of these technological processes is limited to a certain extent by the level of homogenisation, i.e. decomposition of raw biomass [10] (bluegreen algae), or, elsewise, openness to mass exchange of the biomass localized inside the cellular membrane of a cyanobacterium. The outer membrane of these bacteria is resistant to external influences, which conditions low intensity of processes and synthesis of biogas, and to ex traction of lipids [11]. ...
... Nucleic acid extraction is the process of separating different forms of DNA and RNA from other biological macromolecules using a specific sequence of biochemical and biophysical methods (Busa et al., 2016). The first protocol for the isolation and purification of nucleic acids was developed by Johannes Friedrich Miescher in 1869 (Greenly et al., 2015). The process of nucleic acid extraction is a fundamentally important step in modern molecular genetic studies, such as polymerase chain reaction (PCR), sequencing, restriction analysis, molecular hybridization, etc (Ali et al., 2017;Akshara, 2018). ...
The article presents the results of evaluating commercial methods for extracting nucleic acids from pig intestinal tissues for the diagnosis of PED. The study was based on samples of small intestine tissues and faeces from 3–5 day old pigs which died from PED. Nucleic acid extraction was performed using commercial kits with different nucleic acid separation strategies based on: silicon-sorbent; silicate membrane fixed in a microcentrifuge column and magnetic balls. The studies were conducted in two stages. The first was a comparison of the results of the amplification of the obtained nucleic acid extracts from the homogenate of the intestines of piglets by using the above-mentioned commercial kits for the extraction of nucleic acids. For this purpose, samples of homogenate were used which in weight corresponded to the guideline for the application of the test kits. The second step was directed to determining the efficiency of extraction of DNA and RNA from homogenate samples with a weight of 10, 50, 100 and 200 mg. Determination of the optimal methodological strategy of nucleic acid extraction for the diagnosis of porcine epidemic diarrhea by PCR has been investigated. The results of the PCR studies of RNA of the PED virus and a unique pig DNA fragment indicate that the extraction of nucleic acids by commercial kits has different levels of efficiency and depends on different factors. According to the research, it was found that the most important of them are the adsorption capacity of the solid-phase sorbent, its configuration and nature, which binds RNA and DNA molecules, the type of sample from which extraction takes place, its volume, or the tissue mass used for extraction. Based on the obtained results, it has been found that the most effective PED virus RNA extraction is by “ArtBioTech”, “Bio Extract Column”, and “Viral DNA/RNA Extraction Kit”, and pig genomic DNA extraction by the “ArtBioTech” and “Viral DNA / RNA extraction Kit”.
... The robust structure of the trilaminar cell wall of H. pluvialis makes this microalga remarkably resistant to physical and chemical cell disruptions and complicates the extraction process of astaxanthin from these cyst cells. Cell disruption techniques such as ionic liquids (IL), hydrochloric acid (HCl), ultrasound, high-pressure homogenisation and different multi-enzyme (ME) treatments have been previously applied to facilitate the extraction of astaxanthin (Greenly & Tester, 2015). Among these techniques, chemical cell wall breakdown techniques (IL, HCl and ME) exhibit a great potential for cell wall disruption and high-efficiency astaxanthin extraction. ...
The robust cell wall structure of Heamatococcus pluvialis (H. pluvialis) consists of polysaccharides and tough non‐hydrolysable sporopollenins, which makes it difficult to extract superpotent antioxidant, astaxanthin from these cells. Therefore, breakdown of cell wall is a key step in the overall process of astaxanthin recovery. In this study, the mechanism of three well‐established chemical techniques for cell disruption of H. pluvialis cysts [ionic liquids (IL), hydrochloric acid (HCl), and multiple enzymes (multi‐enzyme, ME)] on deconstruction of the cyst cell wall of H. pluvialis was explored and characterized by Fourier transform infrared spectroscopy (FTIR), X‐Ray diffraction (XRD), nuclear magnetic resonance (NMR), and gas chromatography‐mass spectrometry (GC‐MS) analyses. The results demonstrated that the three cell wall breakdown techniques exhibited high extraction efficacies for the recovery of astaxanthin from H. pluvialis [IL (86.71±2.06 %), HCl (80.52±2.28%) and ME (71.08±2.49%)]. However, their performances on disrupting the trilayered cell walls of H. pluvialis were significantly different, which were confirmed by distinct morphologies of the treated cell walls visualized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Meanwhile, the results of FTIR confirmed that, to some extent, cellulose, hemicellulose, and lignin in the cell walls were hydrolyzed by HCl, IL, and ME treatments. However, ME exhibited a less hydrolytic effect on lignin than HCl and IL. Moreover, XRD and NMR analyses implied that the amorphous region of cell wall was susceptible to hydrolysis/breakdown by the three techniques.
... Ultrasound assisted extraction is a suitable technology for deriving antibacterial compounds from algae, as it obviates the need for high temperatures, toxic solvents, and prolonged extraction times. It also fractionates the hardy, complex cell walls of algae [106]. ...
The marine environment is home to a taxonomically diverse ecosystem. Organisms such as algae, molluscs, sponges, corals, and tunicates have evolved to survive the high concentrations of infectious and surface-fouling bacteria that are indigenous to ocean waters. Both macroalgae (seaweeds) and microalgae (diatoms) contain pharmacologically active compounds such as phlorotannins, fatty acids, polysaccharides, peptides, and terpenes which combat bacterial invasion. The resistance of pathogenic bacteria to existing antibiotics has become a global epidemic. Marine algae derivatives have shown promise as candidates in novel, antibacterial drug discovery. The efficacy of these compounds, their mechanism of action, applications as antibiotics, disinfectants, and inhibitors of foodborne pathogenic and spoilage bacteria are reviewed in this article.
... The sample is frozen by immersing it in liquid nitrogen before the grinding process Zheng et al. (2011) Ultrasonication Cells are ruptured by the cavitation that is formed due to the high-frequency sound waves. Adam et al. (2012), Greenly and Tester (2015) and Neto et al. (2013) Hydrodynamic cavitation Cells are broken by the cavitation that is generated by the rapid change in pressure and Lee and Han (2015) Screw expeller pressing A high volume of dried cells is crushed when they are compressed through a caged barrellike cavity. This method allows for direct oil extraction (2012) and Samorì et al. (2010) Conventional lipid extraction technology relies on the use of organic solvents to interact with the neutral lipid molecules (Grima et al. 2013). ...
Microalgae are feedstocks for production of carbon-neutral biofuels. Efforts have been performed to market microalgae biofuels, yet the production of microalgae biofuel remains a challenge due to the high production cost and low product yield. In particular, lipid extraction is a critical step to be optimized. Here, we review lipid extraction technologies and cell lysis strategies. Extraction techniques involve solvents such as organic solvents, supercritical fluids, ionic liquids, deep eutectic solvents and switchable solvents. Advantages and shortcomings of solvents are discussed. Besides, strategies have been designed to reduce power costs by integration of unit operations in downstream processing. We present single-step processes for simultaneous cell lysis and lipid extraction, such as ultrasound-, microwave-, bead-beating-, surfactant- and pulsed electric field-assisted extractions. The lipid extraction yield is enhanced by incorporating cell disruption into the lipid extraction process.
... The mechanism of US disruption in suspensions of five strains of microalgae (including Chlamydomonas reinhardtii (wild type and mutant strain), Thalassiosira pseudonana, Isochrysis galbana, Nannochloropsis oculata) with different sizes and cell wall compositions was studied (Greenly and Tester, 2015). The most significant cell disruption and a small difference between species were observed during the initial seconds of US. ...
This research work focuses on extraction and fractionation of bio-molecules from microalgae using physical treatments: pulsed electric fields (PEF), high voltage electrical discharges (HVED) and ultrasonication (US) techniques. In this study, three microalgae species Nannochloropsis sp., Phaeodactylum tricornutum (P. tricornutum) and Parachlorella kessleri (P. kessleri) were investigated. These species have different cell shapes, structure and intracellular contents. The effects of tested techniques on extraction of bio-molecules have been highlighted in a quantitative and qualitative analysis by evaluating the ionic components, carbohydrates, proteins, pigments and lipids. A comparative study of physical treatments (PEF, HVED and US) at the equivalent energy input for release of intracellular bio-molecules from three microalgal species allowed us to better understand the different disintegration mechanisms. For each microalga at the same energy consumption, the HVED treatment proved to be the most efficient for extraction of carbohydrates, while the US treatment for extraction of proteins and pigments. In general, the smallest efficiency was observed for the PEF treatment. However, the highest selectivity towards carbohydrates can be obtained using the mild PEF or HVED technique. The preliminary physical treatments (PEF, HVED or US) of more concentrated suspensions followed by high pressure homogenization (HPH) of diluted suspensions allowed improving the extraction efficiency and decreasing the total energy consumption. The physical pretreatments permit to reduce the mechanical pressure of the HPH and number of passes, to reach the same extraction yield. For the maximum valorisation of microalgal biomass, extraction procedure assisted by HVED treatment (40 kV/cm, 1-8 ms) followed by aqueous and non-aqueous extraction steps seems to be useful for selective extraction and fractionation of different bio-molecules from microalgae. The significant effects of HVED pre-treatment on organic solvent extraction of pigments (chlorophylls, carotenoids) and lipids were also observed.
... The cavitation is characterized by the violent collapse of bubbles in an alternating pressure field. Cavitation bubbles in the aqueous suspension of algae produce severe and localized short-term pressure increases as well as microstreaming effects (movement of liquid around gas bubbles formed by cavitation) and shock waves that promote the rupture of algae cells [19]. Some authors have reported the use of UAE in the extraction of phycobiliproteins from different species of microalgae [20][21][22][23]. ...
A new method that combines ultrasonic assisted extraction (UAE) with ionic liquids (ILs) was proposed to extract phycobiliproteins from the microalgae Spirulina (Arthrospira) platensis. Extraction of the pigments was carried out in an ultrasonic bath at 25 °C and at a frequency of 25 kHz. The effects of pH and solvent:biomass ratio were evaluated through a central rotational composite design and response surface methodology were used to determine the best extraction conditions. Solvents used were protic ionic liquids (PILs) 2-hydroxy ethylammonium acetate (2-HEAA), 2-hydroxy ethylammonium formate (2-HEAF), their equimolar mixture (2-HEAA+2-HEAF) (1:1 v/v) and the commercial ionic liquid, 1-butyl-3-methylimidazolium chloride [Bmim][Cl] and sodium phosphate buffer (0.1 M) as a control. Results showed that the PILs were able to extract the phycobiliproteins from microalgae. The pH was the most significant variable. Solvent:biomass ratio was also significant in the extraction process. The highest concentrations of phycobiliproteins were observed using 2-HEAA +2-HEAF as solvent at pH 6.50 and solvent:biomass ratio 7.93 mL·g⁻¹ within 30 min of extraction. Allophycocyanin was the pigment extracted in greater quantity (6.34 mg·g⁻¹), followed by phycocyanin (5.95 mg·g⁻¹) and phycoerythrin (2.62 mg·g⁻¹). Scanning electron microscopy (SEM) revealed that the ultrasound affect the cellular structure of the microalgae.
... The cavitation is the main phenomenon that is characterized by the violent collapse of bubbles in an alternating pressure field. Cavitation bubbles in the aqueous suspension of microalgae cells produce severe and localized short-term pressure increase as well as micro-streaming effects (movement of liquid around gas bubbles formed by cavitation) and shock waves that promote the rupture of microalgae cells (Greenly and Tester 2015). ...
Microalgal biomasses (MAB) is the most abundant source of various natural value-added biomolecules and bioactive compounds (BACs), therefore, considered as the best promising feedstock for the food and pharmaceutical industries. Microalgae-based BACs such as carotenoids, peptide molecules, phycocyanins, polyphenols, and polyunsaturated fatty acids (PUFAs) have significant application as functional ingredients in the pharmaceutical and nutraceutical industries. Due to the awareness of the consumers about the nutraceuticals in combating the occurrence of lifestyle and chronic diseases, the demands for the algal-based nutraceuticals have recently increased by several folds. Microalgae pigments, such as phycobiliproteins, chlorophylls, and carotenoids, have enormous possibilities for commercialization due to its therapeutic activities, which include antimicrobial, antioxidant, anti-inflammatory, antiproliferative, and anti-atherogenic activities. As per the estimates, the nutraceuticals market would cross about $278.96 billion by the end of 2021. Similarly, microalgae-based polyunsaturated fatty acids (PUFAs) such as eicosapentaenoic acid, EPA, docosahexaenoic acid, arachidonic acid, etc. are also an important commercial product, and its global market is around USD 9.0 billion/Year. This chapter provides a comprehensive overview of bioactive compounds of microalgae and its pharmaceutical and nutraceutical properties. Various strategies used for the profitable production of microalgae biomass and extraction of bioactive compounds from algal biomass are discussed in detail. The commercial potential of algae BACs, associated safety, and regulatory issues are also discussed.
... Current cell disruption methods include mechanical and non-mechanical techniques. Mechanical techniques destroy the cell wall using non-specific solid and liquid shear forces or energy transfer through heating and waves (Günerken et al., 2015), which include compression, high-pressure homogenization (HPH) (Park et al., 2015), ultrasonic bath (Greenly and Tester, 2015), autoclave (Lee et al., 2010), bead mill, microwave and magnetic stirring (Cravotto et al., 2008;Virot et al., 2008); while non-mechanical techniques include chemical lysing using enzymes or chemical agents and osmotic shock (Demuez et al., 2015;Harun et al., 2011). Selective interactions between chemical agents (enzymes, antibiotics, chelating agents, chaotropes, detergents, hypochlorite, acids and alkali) and the cell wall or membrane are designed to facilitate biolipid leaching (Günerken et al., 2015). ...
Microalgae are considered as the third generation source of biofuel and an excellent candidate for biofuel production to replace the fossil energy. The use of ultrasonic in producing biodiesel by direct transesterification of Nannochloropsis occulata using KOH as catalyst and methanol as a solvent was investigated. The following condition were determined as an optimum by experimental evaluates:: 1: 15 microalga to methanol (molar ratio); 3% catalyst concentration at temperature 40°C after 30 minute of ultrasonication. The highest yield of biodiesel produced was 30.3%. The main components of methyl ester from Nannochloropsis occulata were palmitic (C16 :0),, oleic (C18:1), stearic (C18;0), arahidic (C20:0) and myristic (C14:0). This stated that the application of ultrasounic for direct transesterificaiton of microalgae effectively reduced the reaction time compared to the reported values of conventional heating systems.
This study investigated the beneficial effects of ultrasonic treatment on the biomass, lipid and protein of the microalgae Anabaena variabilis. The microalgae after 11 days cultivation (initial algae) were treated at the powers of 200, 350 and 500 W for 10 min and then cultured continuously for 3 days (day 12–14). The power of 200 W induced the highest lipid content 37.8% on day 12. The subsequent experiments tested the ultrasonic treatment times of 5, 10, 20 and 40 min at 200 W in the initial algae. The significantly improved lipid content 46.9% and productivity 54.2 mg/L/d were obtained almost 1.46 and 1.86 times more than that of the control algae respectively after 1 day of continuous cultivation at 5 min. The proper ultrasonic treatment showed the feasibility and high efficiency in promoting lipid accumulation without negatively influencing the biomass, fatty acid profiles and protein content.
Spirulina platensis is considered an alternative and excellent source of protein [46–63% dry basis (DB)], having protein levels comparable to meat and soybeans. Thus, it can be considered an adequate ingredient to supply the necessity of this compound in the food industry. Its carbohydrates (8–14% DB) may also be a useful food ingredient or a potential source of bioenergy. Thus, extracting these compounds from the microalgae biomass will maximize its exploitation. Sonication can completely or partially degrade the microalgal cell wall, providing a useful technique to extract the protein and carbohydrate. This study used a sequential strategy of experimental design (fractional factorial design and central composite rotatable design) to evaluate the protein and carbohydrate extraction from S. platensis defatted biomass using ultrasonic waves and mechanical agitation, under alkaline conditions. The optimal conditions for protein and carbohydrate co-extraction were established by selecting and maximizing the variables that significantly influenced the extraction. The optimized percentages recovery from the extraction process yielded 75.76% protein and 41.52% carbohydrate at 33–40 min sonication and 40–55 min agitation. The protein fraction may be further concentrated and purified for use in food formulations, and the carbohydrates may be a useful feedstock for bioethanol production.
This review detailed an in-depth analysis of the scope and approach for the synthesis of biodiesel from microalgae. Biodiesel derived from microalgae has been regarded as a strong substitute for conventional diesel primarily due to their high lipid content and sustainability which have been summarized and validated in this article. There are diverse species of microalgae with varying lipid content which can thrive in different environment. There are various factors which affect the propagation of microalgal cells in addition to the cultivation techniques. The main biomass of microalgae that can be converted to biodiesel is lipid and the lipid content can be further optimized by inducing nutrient and environmental stress to microalgae. Optimising lipid production can lead to lowering the cost of production. The cells of microalgae have to be processed and the lipid extracted has to be transesterified to biodiesel which have been extensively discussed in this review article.
The two-stage cultivation strategy was optimized in this study to simultaneously promote the growth and lipid accumulation of Tetradesmus obliquus. Results showed that the optimal dual-stress conditions were nitrogen concentration at 25 mg N·L⁻¹ and low-frequency ultrasound at 200 Watt, 1 minute, and 8 hours interval. The biomass and lipid content of Tetradesmus obliquus were increased by 32.1% and 44.5%, respectively, comparing to the control, and the lipid productivity reached 86.97 mg⁻¹·L⁻¹·d⁻¹ at the end of the cultivation period. The protein and photosynthetic pigment contents of microalgae decreased by 22.4% and 14.0% under dual stress comparing to the control environment. In addition, dual stress cultivation of microalgae presented higher level of antioxidant capacity to balance to oxidation level in microalgal cells. This study provides a new insight for microalgae growth and lipid accumulation with dual stress stimulation.
The effect of ultrasonication on the cell rupture of marine microalgae Nannochloropsis sp. was studied as a function of the slurry solids concentration and treatment time. The concentrated viscous wet-biomass (~12 to 25% solids concentration) was subjected to ultrasonication (20 kHz) at 3.8 W/mL for up to 5 min. Compared to extraction without cell rupture, sonication led to a significant increase in lipid yield from ~11% to about 70% within 5 min of sonication. The extraction yield was found to decrease with increased solids concentration, with a large decrease between 20% to 25% solids. This is attributed to the increase in viscosity and decrease in speed of sound with increase in solids. The ultrasound attenuation coefficient increased 320-fold as the solids increased from 20 to 25%. Such a large attenuation of ultrasound places a limit of 20% solids to be used for cell rupture by ultrasound. The specific energy requirements per unit mass of extracted lipid were lowest at 20% solids. At lower concentrations energy was wasted heating water, at higher concentrations the lipid yields were reduced due to ultrasound attenuation.
The impacts of sonication on the photosynthetic activity of Synedra sp. (diatom) and its mechanism were investigated for the first time. Three photosynthetic parameters, i.e., effective quantum yield (Φe), initial slope of rapid light curves (α) and maximum relative electron transport rate (rETRmax) were employed to evaluate its photosynthetic activity during sonication for the first time. The results showed that 600 kHz is the optimal frequency for the inhibition of the photosynthetic activity and biomass as the ultrasonic frequencies varied from 100 to 800 kHz. When the photosynthetic activity was inhibited to be not detected by sonication, Φe, α and rETRmax gradually recovered from 0 to 36.4%, 35.2% and 48.3% of that in the blank group, respectively, after 12-day cultivation (no sonication). However, the biomass was still suppressed to 9.2% of that in the blank after the same cultivation. A single time sonication treatment achieved better inhibition efficiency than the multiple times modes when their total sonication time was equal. The inhibition mechanism for the photosynthetic activity of Synedra sp. by sonication can be concluded as follows: at the early stage, the thylakoids membrane expansion and oscillation can lead to the structure damage of thylakoids; subsequently, [rad]OH oxidation is responsible for the chlorophyll-a degradation.
Algal biofuel has been advocated as a sustainable and environmentally friendly renewable energy source. However, intensive chemical usage, high energy consumption, and high operation and maintenance costs associated with current cell disruption methods have been identified as main challenges to cost-effective production of algal biofuel. Viral infection of algae is a natural process that can lyse algal cells under ambient conditions without using chemicals or energy-intensive equipment. This study, for the first time, provides a comprehensive and in-depth evaluation of the feasibility of using viruses to assist algal lipid extraction. Detailed mechanistic studies were conducted to evaluate the impact on mechanical strength of algal cell walls, lipid yield, and lipid distribution when Chlorella sp. were infected by Paramecium bursaria Chlorella virus 1 (PBCV-1). Viral disruption with multiplicity of infection of 10⁻⁸ was able to disrupt concentrated algal biomass completely in six days. Our results indicated that viral disruption significantly reduced the mechanical strength of algal cells. Lipid yield with viral disruption increased more than three times compared to no disruption controls and was similar to that of ultrasonic disruption. Moreover, lipid composition analysis showed that the quality of extracted lipids was not affected by viral infection. The results showed that viral infection is a highly cost-effective technique to promote lipid extraction without extensive energy input and chemicals required by existing disruption methods. The results of this study provided new insights in the development of nature-inspired lipid extraction methods for cost-efficient biofuel production.
The challenges associated with effective cell wall disruption remain an important bottleneck that has restricted efforts to extract astaxanthin from Haematococcus pluvialis. Here, available transcriptomic data and an Agrobacterium tumefaciens-mediated transformation system were used to establish an H. pluvialis strain in which the key cell wall formation-related enzyme α-1,6-mannosyltransferase (HpOCH1) was downregulated in an effort to thin cell walls and thereby simplify the astaxanthin extraction process. The cell wall remodeling activity observed in these HpOch1 knockdown H. pluvialis cells resulted in dramatic reductions in the mannan organization and protective ability of the established cell walls. The cell fragmentation rate increased by 58% in HpOch1⁻ group relative to the control group. Critically, astaxanthin synthesis was not altered in the HpOch1 knockdown cells. Overall, this study highlights a novel technical approach to artificial cell wall thinning, offering a foundation for further efforts to more effectively leverage the astaxanthin resources of H. pluvialis.
Phycobiliproteins are potential molecules for use in various applications. Although phycobiliproteins extraction classical methods are reproducible and show good yields, they are generally time-consuming and require the use of high energy consumption and/or large volumes of solvent. Therefore, it is necessary the development of new eco-friendlier process by extraction techniques, permitting the transfer of the results obtained in laboratory scale for industrial. Then, microwave-assisted extraction using protic ionic liquid as solvent was proposed and optimized to extract phycobiliproteins from Arthrospira platensis in an efficient manner. The protic ionic liquids (PILs): 2-hydroxyethylammonium acetate (2-HEAA), 2-hydroxyethylammonium formate (2-HEAF), their equimolar mixture (2-HEAA + 2-HEAF), and the commercial ionic liquid 1-butyl-3-methylimidazolium chloride [Bmim]Cl were used as solvents, and sodium phosphate buffer as a control and the conditions of extraction were evaluated. The irradiation power was the most significant variable for the extraction process, and it showed a negative effect. The process conducted at 62 W and pH 7.0, using 2-HEAA + 2-HEAF and a solvent: biomass ratio of 10 mL∙g⁻¹, showed the highest phycobiliproteins concentrations. The purity obtained for phycocyanin, allophycocyanin and phycoerythrin were 1.22, 1.03, and 0.71, respectively. The mixture of the PILs (2-HEAA + 2-HEAF) can be reused for three cycles for extraction of allophycocyanin. The extraction of phycobiliproteins using microwave and ionic liquids was efficient and the degree of purity and antioxidant activity achieved allows the application of these pigments in food and cosmetics.
Biotechnological application of microalgae cultures at large scale has significant potential in the various fields of biofuels, food and feed, cosmetic, pharmaceutic, environmental remediation and water treatment. Despite this great potential application, industrialisation of microalgae culture and valorisation is still faced with serious remaining challenges in culture scale-up, harvesting and extraction of target molecules. This review presents a general summary of current techniques for harvesting and extraction of biomolecules from microalgae, their relative merits and potential for industrial application. The cell wall composition and its impact on microalgae cell disruption is discussed. Additionally, more recent progress and promising experimental methods and studies are summarised that would allow the reader to further investigate the state of the art. A final survey of energetic assessments of the different techniques is also made. Bead milling and high-pressure homogenisation seem to give clear advantages in terms of target high value compounds extraction from microalgae, with enzyme hydrolysis as a promising emerging technique. Future industrialisation of microalgae for high scale biotechnological processing will require the establishment of universal comparison-standards that would enable easy assessment of one technique against another.
The present study developed an approach using ultrasound stimulation coupled nitrogen and phosphorus stress (UCNP) to enhance the biomass concentration and the lipid production in Desmodesmus intermedius Z8. With the effort, the highest values of lipid content and lipid production of 43.19% and 2.33 g/L were obtained, respectively, which were almost 1.21 and 1.33 folds higher than that of the control group on day 6 under the optimal condition. Furthermore, the mechanisms of physiological response to the UCNP conditions were also investigated. The findings show that multiple intracellular antioxidant enzymes and antioxidants work together in response to oxidative stress to ensure efficient accumulation of microalgae lipid. In addition, under UCNP conditions, the ratios of lipid fractions C16-C18 and the saturated fatty acids (SFA) were increased by 20.28% and 50.29%, respectively, compared to the control group, which were also more in line with the biodiesel material standard. This study suggests that the approach of UCNP is an effective strategy for enhancing the production and quality of lipid in microalgae.
During cavitation, nucleation, growth, and subsequent collapse of microbubbles in a liquid medium result in the generation of high temperature and pressure locally at millions of locations within, and in the immediate vicinity of the collapsing cavity in the sonochemical reactor. These effects have been effectively utilized to promote and intensify various physicochemical transformations in numerous applications in chemical synthesis via reducing the reaction time, increasing the reaction yield, switching of the reaction pathways, and initiation of the chemical reactions due to the formation of reactive free radicals. This chapter highlights various applications and future trends of the cavitation phenomenon involving intensification of various unit operations and processes in water and wastewater, biotechnology, material science, food and beverage, petroleum, textile processing, and other allied industries. For each of the applications, improvement demonstrated by ultrasound and ultrasonic cavitation over the conventional method is presented. The typical challenges in each of these segments are also presented.
The culture medium Aquil has been designed for studying trace metal physiology in algae. We describe recent modifications in the preparation of Aquil and discuss processes that affect its trace metals and their physiological effects. The major changes in Aquil preparation are purification of the Chelex column to avoid contamination by chelating agents, use of alternative sterilization procedures, and increases in the concentration of trace metal buffers. During growth, phytoplankton take up trace metals, thus continuously reducing their concentrations in the medium. Algae can also modify the redox state and degree of organic complexation of trace metals through the direct and indirect activity of cell surface enzymes and the release of metabolites. Illumination of the culture medium necessary to promote photosynthesis also promotes a variety of photochemical reactions that alter the chemistry of the medium and maintain it in a state of disequilibrium. In particular, light absorption by FeEDTA leads to reduction of the iron and oxidation of the EDTA. Rapid reoxidation of Fe (II) leads to a high steady-state inorganic Fe (III) concentration. Slow coordination kinetics with chelating agents contribute to maintaining the disequilibrium conditions promoted by cellular and photochemical processes. Kinetic processes rather than pseudo-equilibrium conditions are now the focus in the study of trace metal-phytoplankton interactions.
The erratic behaviour of cavitational activity exhibited in a sonochemical reactor pose a serious problem in the efficient design and scale-up; thus it becomes important to identify the active and passive zones existing in the reactor so as to enable proper placement of the reaction mixtures for achieving maximum benefits. In the present work mapping of ultrasonic horn has been carried with the help of local pressure measurement using a hydrophone and estimation of amount of liberated iodine using the Weissler reaction and a quantitative relationship has been established. The measured local pressure pulses have been used in the theoretical simulations of the bubble dynamics equations to check the type of cavitation taking place locally and also estimate the possible collapse pressure pulse in terms of maximum bubble size reached during the cavitation phenomena. Relationship has been also established between the observed iodine liberation rates and the maximum bubble size reached. The engineers can easily use these unique relationships in efficient design, as the direct quantification of the secondary effect is possible.
The objective of this study was to evaluate the effectiveness of high-frequency focused ultrasound (HFFU) in microalgal cell disruption. Two microalgal species including Scenedesmus dimorphus and Nannochloropsis oculata were treated by a 3.2-MHz, 40-W focused ultrasound and a 100-W, low-frequency (20kHz) non-focused ultrasound (LFNFU). The results demonstrated that HFFU was effective in the disruption of microalgal cells, indicated by significantly increased lipid fluorescence density, the decrease of cell sizes, and the increase of chlorophyll a fluorescence density after treatments. Compared with LFNFU, HFFU treatment was more energy efficient. The combination of high and low frequency treatments was found to be even more effective than single frequency treatment at the same processing time, indicating that frequency played a critical role in cell disruption. In both HFFU and LFNFU treatments, the effectiveness of cell disruption was found to be dependent on the cell treated.
It is well-established that microalgal-derived biofuels have the potential to make a significant contribution to the US fuel market, due to several unique characteristics inherent to algae. Namely, autotrophic microalgae are capable of achieving very high efficiencies in converting solar energy into biomass and oil relative to terrestrial oilseed crops, while at the same time exhibiting great flexibility in the quality of land and water required for algal cultivation. These characteristics allow for the possibility to produce appreciable amounts of algal biofuels relative to today’s petroleum fuel market, while greatly mitigating “food-versus-fuel” concerns. However, there is a wide lack of public agreement on the near-term economic viability of algal biofuels, due to uncertainties and speculation on process scale-up associated with the nascent stage of the algal biofuel industry.
The Barbier reaction of benzaldehyde, n-heptyl bromide, and lithium was effected under various sonochemical conditions. The rate of formation of 1-phenyloctanol depends strongly on the intensity of the ultrasonic waves and the temperature. For both parameters, an optimum is observed. An unusual variation of rate with temperature is evidenced, which reveals that the reaction is not mass-transport controlled. Electron microscopy examination of the metal shows the very important activation role of the acoustic waves, through the cavitation phenomenon.
The effect of ultrasonic irradiation (up to 3W/cm2 and 1 MHz of frequency) on unicellular algae is experimentally studied. It is unambiguously shown that the damage of the cells and their breakage is to be related to cavitation. The dynamics of the breakage is examined from the point of view of practical application.
Ultrasoniccavitation in liquids gives rise to a sound oscillating field at a frequency one‐half of the ultrasound‐driving frequency. The appearance of such a subharmonic may be used to detect the cavitation. The authors investigate experimentally such a possibility.
The medium Aquil and its variations have been successfully used for trace metal studies of marine phytoplankton (diatoms and dinoflagellates) over the past three years. Here, the recipes, the methods of preparation and the chemical composition of Aquil are presented in detail. To permit complete definition of chemical speciation of the various components as calculated from thermodynamic equilibria, trace element contamination is controlled and the formation of precipitates and adsorbates is avoided. It is established that Aquil is suitable for physiological experiments with a variety of marine phytoplankters representing all major phyla. Modifications of the basic recipe and design of chemically defined media in general are discussed.
A general review is given of the mechanism of rectified diffusion. The equations that describe the threshold acoustic pressure amplitude as well as the growth rate are presented. Simplified versions of the complicated threshold equation are also obtained for two regions that are of particular interest. Graphical representations of the equations for a variety of physical parameters are given as well as a comparison between the available measurements and the theoretical predictions. Finally, some suggested areas of future research in this area are presented.
Algae are an attractive source of biomass energy since they do not compete with food crops and have higher energy yields per area than terrestrial crops. In spite of these advantages, algae cultivation has not yet been compared with conventional crops from a life cycle perspective. In this work, the impacts associated with algae production were determined using a stochastic life cycle model and compared with switchgrass, canola, and corn farming. The results indicate that these conventional crops have lower environmental impacts than algae in energy use, greenhouse gas emissions, and water regardless of cultivation location. Only in total land use and eutrophication potential do algae perform favorably. The large environmental footprint of algae cultivation is driven predominantly by upstream impacts, such as the demand for CO(2) and fertilizer. To reduce these impacts, flue gas and, to a greater extent, wastewater could be used to offset most of the environmental burdens associated with algae. To demonstrate the benefits of algae production coupled with wastewater treatment, the model was expanded to include three different municipal wastewater effluents as sources of nitrogen and phosphorus. Each provided a significant reduction in the burdens of algae cultivation, and the use of source-separated urine was found to make algae more environmentally beneficial than the terrestrial crops.
Ultrasound is used in different domains, and in sonochemistry particularly, for different purposes and in various flow configurations: monophasic, two-phase and polyphasic reactors. In order to optimize and to design sonochemical reactors, it is important to describe the ultrasonic intensity space and time distribution. In addition, it is important to study the different parameters influencing the intensity profiles of the ultrasonic wave. In this work, a thermoelectric probe has been used to measure the ultrasonic intensity. This procedure has shown that the ultrasound propagation is influenced by the presence of cavitation bubbles, the flow regime and the presence of solid particles.
Streaming and other activity around sonically induced bubbles is a cause of damage to living cells.