Microalgal Cell Disruption Research Articles

Active extracellular substances of Bacillus thuringiensis ITRI-G1 induce microalgae self-disruption for microalgal biofuel.

Microalgal cultures are a clean and sustainable means to use solar energy for CO2 fixation and fuel production. Microalgae grow efficiently and are rich in oil, but recovering that oil is typically expensive and consumes much energy. Therefore, effective and low-cost techniques for microalgal disruption and oil or lipid extraction are required by the algal biofuel industry. This study introduces a novel technique that uses active extracellular substances to induce microalgal cell disruption. A bacterium indigenous to Taiwan, Bacillus thuringiensis, was used to produce the active extracellular substances, which were volatile compounds with high thermal stability. Approximately 74% of fresh microalgal cells were disrupted after a 12-h treatment with the active extracellular substances. Algal lipid extraction efficiency was improved and the oil extraction time was decreased by approximately 37.5% compared with the control treatment. The substances effectively disrupted fresh microalgal cells but not dehydrated microalgal cells. An analysis of microalgal DNA from fresh cells after disruption treatment demonstrated typical DNA laddering, indicating that disruption may have resulted from programmed cell death. This study revealed that biological treatments are environmentally friendly methods for increasing microalgal lipid extraction efficiency, and introduced a microalgal cell self-disruption mechanism.

Extractive disruption process integration using ultrasonication and an aqueous two-phase system for protein recovery from Chlorella sorokiniana.

Microalgae emerge as the most promising protein sources for aquaculture industry. However, the commercial proteins production at low cost remains a challenge. The process of harnessing microalgal proteins involves several steps such as cell disruption, isolation and extraction. The discrete processes are generally complicated, time-consuming and costly. To date, the notion of integrating microalgal cell disruption and proteins recovery process into one step is yet to explore. Hence, this study aimed to investigate the feasibility of applying methanol/potassium ATPS in the integrated process for proteins recovery from Chlorella sorokiniana. Parameters such as salt types, salt concentrations, methanol concentrations, NaCl addition were optimized. The possibility of upscaling and the effectiveness of recycling the phase components were also studied. The results showed that ATPS formed by 30% (w/w) K3PO4 and 20% (w/w) methanol with 3% (w/w) NaCl addition was optimum for proteins recovery. In this system, the partition coefficient and yield were 7.28 and 84.23%, respectively. There were no significant differences in the partition coefficient and yield when the integrated process was upscaled to 100-fold. The recovered phase components can still be recycled effectively at fifth cycle. In conclusions, this method is simple, rapid, environmental friendly and could be implemented at large scale.

Nickel oxide nanoparticle-based method for simultaneous harvesting and disruption of microalgal cells

Microalgae biodiesel is considered one of the most promising renewable fuels. However, the high cost of the downstream process is a major barrier to large-scale microalgal lipid production. In this study, a novel approach based on nickel oxide nanoparticles (NiO NPs) was developed and its effectiveness for simultaneous harvesting and cell disruption in microalgal lipid production was determined. NiO NPs exhibited a microalgal harvesting efficiency of 98.75% in 1min at pH 7. Moreover, after treating with NiO NPs for 96h, the lipid extraction efficiency of microalgae (with 80% water content) reached 91.08% and was 208.37% compared to that without NiO treatment. This approach is simple and does not necessitate drying; furthermore, no equipment with high energy consumption was required.

Intensified green production of astaxanthin from Haematococcus pluvialis

The objectives of this study were to evaluate bioethanol wastewater streams (thin stillage, process condensate and scrubber/dryer samples) as potential ‘green’ media to culture microalgae Haematococcus pluvialis, and to assess the effectiveness of ultrasound in microalgal cell disruption and astaxanthin extraction. H. pluvialis was cultured in wastewater dilutions (20–80 times) and formulations. Astaxanthin was extracted using ultrasound with cell-disrupting chemicals (acetic acid, citric acid, hydrogen peroxide and sodium hydroxide) and astaxanthin extracting solvents (acetone, ethanol and methanol) at different extraction durations (5–35min). The results demonstrated that 60 times as the optimum dilution factor of thin stillage for microalgal growth, and a formulation known as GroAst media (60% of 60 times diluted thin stillage, and 40% of process condensate) was proposed as the best media for astaxanthin production: 0.634±0.009mg/ml cyst density, a 10.5% improvement over standard media. Astaxanthin extraction using ultrasound intensified the process in terms of short extraction time (25min), less chemical consumption (2M NaOH), usage of GRAS solvent (methanol), high efficiency in cell disruption, high extraction yield (80.6±0.9%), and suitability to extract thermolabile astaxanthin.

Polymer-enhanced enzymatic microalgal cell disruption for lipid and sugar recovery

Enzymatic cell disruption is a promising, highly energy-efficient technology for recovery of cellular compounds from microalgal cells, but it has not been applied at large scale because of its low cost-efficiency. In this work, we present a novel and highly efficient approach to enhance enzymatic disruption of Chlorella protothecoides cell walls to recover the lipid contents and cell wall compositional sugars. When thermoresponsive polymers, such as poly-(N-isopropylacrylimide-co-allylamine), were mixed with microalgal cell suspensions, cell disruption was increased from 22 to 68%, with equivalent increases in lipid recovery. The use of thermoresponsive polymers allows for simple and efficient separation of polymers after product recovery for reuse in subsequent batches. The highest cell disruption and associated lipid yield reached about 68% and 59%, respectively, which was achieved using 10mol-% amine copolymers with a loading of 0.05g/g algal biomass dry weight (BDW). During this process, about 50% of dry algal cell wall was converted to reducing sugars. Furthermore, we found that copolymers were able to disrupt algal cells in the absence of enzyme. Polymer loadings of 0.1g/gBDW led to the highest cell disruption and lipid recovery for 6h contact time reaching 32% and 30%, respectively. A quantitative and morphological analysis on polymer-enhanced microalgal cell disruption is presented, indicating that the polymer may function by stressing and breaking the cell wall and/or protecting enzyme from denaturation.

Disruption of thermo-tolerant Desmodesmus sp. F51 in high pressure homogenization as a prelude to carotenoids extraction

Six methods for microalgal cell disruption were compared for the optimization of carotenoids extraction from the lutein-rich thermo-tolerant microalga Desmodesmus sp. F51. Among them, both bead-beating and high pressure homogenization (HPH) were found to have potential to disrupt Desmodesmus sp. F51 cells with high efficiency, but this study focused only on HPH treatment. Effects of homogenization pressure, cycle number and cell density on cell disruption efficiency were investigated. The degree of cell disruption increased with increasing high homogenization pressure (10–40kpsi) and cycle number (1–4). Cell density in the range of 2.0–90g/L did not affect the performance of cell disruption process, while a higher specific energy consumption arised when using a lower cell concentration. The HPLC analysis showed that the main carotenoids present in Desmodesmus sp. F51 were neoxanthin, violaxanthin, lutein, α-carotene and β-carotene. Moreover, the developed HPH model could well describe the cell disruption behavior at various high homogenization pressures (10–40 kpsi) and cycle numbers (1–4). The obtained parameters indicate that homogenization pressure is a more significant factor than cycle number in achieving high cell disruption efficiency.

Three-Dimensional Simulation of Ultrasound-Induced Microalgal Cell Disruption.

The three-dimensional distribution (x, y, and z) of ultrasound-induced microalgal cell disruption in a sonochemical reactor was predicted by solving the Helmholtz equation using a three-dimensional acoustic module in the COMSOL Multiphysics software. The simulated local ultrasound pressure at any given location (x, y, and z) was found to correlate with cell disruption of a freshwater alga, Scenedesmus dimorphus, represented by the change of algal cell particle/debris concentration, chlorophyll-a fluorescence density (CAFD), and Nile red stained lipid fluorescence density (LFD), which was also validated by the model reaction of potassium iodide oxidation (the Weissler reaction). Furthermore, the effect of ultrasound power intensity and processing duration on algal cell disruption was examined to address the limitation of the model.

Aggregate formation affects ultrasonic disruption of microalgal cells

Ultrasonication is a cell disruption process of low energy efficiency. This study dosed K+, Ca2+ and Al3+ to Chlorella vulgaris cultured in Bold’s Basal Medium at 25°C and measured the degree of cell disruption under ultrasonication. Adding these metal ions yielded less negatively charged surfaces of cells, while with the latter two ions large and compact cell aggregates were formed. The degree of cell disruption followed: control=K+>Ca2+>Al3+ samples. Surface charges of cells and microbubbles have minimal effects on the microbubble number in the proximity of the microalgal cells. Conversely, cell aggregates with large size and compact interior resist cell disruption under ultrasonication. Staining tests revealed high diffusional resistance of stains over the aggregate interior. Microbubbles may not be effective generated and collapsed inside the compact aggregates, hence leading to low cell disruption efficiencies. Effective coagulation/flocculation in cell harvesting may lead to adverse effect on subsequent cell disruption efficiency.

Microalgal cell disruption through Fenton reaction: Experiments, modeling and remarks on its effect on the extracted lipids composition

Microalgal cell disruption through Fenton reaction: Experiments, modeling and remarks on its effect on the extracted lipids composition

Modeling bubble dynamics and radical kinetics in ultrasound induced microalgal cell disruption

Microalgal cell disruption induced by acoustic cavitation was simulated through solving the bubble dynamics in an acoustical field and their radial kinetics (chemical kinetics of radical species) occurring in the bubble during its oscillation, as well as calculating the bubble wall pressure at the collapse point. Modeling results indicated that increasing ultrasonic intensity led to a substantial increase in the number of bubbles formed during acoustic cavitation, however, the pressure generated when the bubbles collapsed decreased. Therefore, cumulative collapse pressure (CCP) of bubbles was used to quantify acoustic disruption of a freshwater alga, Scenedesmus dimorphus, and a marine alga, Nannochloropsis oculata and compare with experimental results. The strong correlations between CCP and the intracellular lipid fluorescence density, chlorophyll-a fluorescence density, and cell particle/debris concentration were found, which suggests that the developed models could accurately predict acoustic cell disruption, and can be utilized in the scale up and optimization of the process.

Microalgal cell disruption in a high-power ultrasonic flow system

A 2-kW continuous ultrasonic flow system (UFS) was found effective in the disruption of two microalgal strains: Scenedesmus dimorphus and Nannochloropsis oculata. Compared to the control, cell debris concentration of UFS treatments increased up to 202% for S. dimorphus and 112% for N. oculata. Similarly, Nile red stained lipid fluorescence density (NRSLD) increased up to 59.5% and 56.3% for S. dimorphus and N. oculata, respectively. It was also found that increasing ultrasound intensity improved cell disruption efficiency indicated by up to 54% increase in NRSLFD of the two strains. Increasing sonication-processing time to 3-min resulted in 33.0% increase for S. dimorphus and 45.7% increase for N. oculata in NRSLFD compared to the control. Cell recirculation was found beneficial to cell disruption, however, higher initial cell concentration significantly reduced cell disruption efficiency, indicated by 98.2% decrease in NRSLFD per cell when initial cell concentration increased from 4.25×106 to 1.7×107cells ml−1.

Microalgal cell disruption by hydrodynamic cavitation for the production of biofuels

Cell disruption is an essential pre-treatment for the efficient extraction of many types of intracellular metabolites such as proteins, carbohydrates, DNAs or lipids; but the high process energy requirement becomes an important issue for low valued commodities such as biofuels. Current mechanical cell disruption methods such as high-pressure homogeniser or sonication require energy input in the order of hundreds of MJ kg−1 of the dry mass; in addition, these methods do not have the capacity suitable for biofuel production where daily processing volumes are in order of mega litres. This study investigated hydrodynamic cavitation (HC) as a cell disruption technique, with levels of disruption determined by i) lipids extracted and ii) the chlorophyll released. It was found that for the lipid extraction, HC has a disruption energy requirement of 3 MJ kg−1. This amount of energy requirement is more efficient than sonication by a factor of 10; however, it still represents nearly 13 % of the total energy in the biomass and is too high for the production of biofuels. The cell disruption by HC is essentially periplasmic, i.e. mainly confined to the cell wall and membrane. This result suggests that damage to the outer cell barrier such as the cell wall was sufficient to allow for the diffusion of solvents for lipid extraction.

Disruption of microalgal cells for lipid extraction through Fenton reaction: Modeling of experiments and remarks on its effect on lipids composition

A novel cell disruption technique, based on the use of Fenton reaction, for the improvement of lipid extraction from microalgae has been recently proposed in the literature. The experimental results have shown that, when disruption is performed under suitable operating conditions, the amount of lipids subsequently extracted from Chlorellavulgaris is greatly increased with respect to the case where no pretreatment was performed. Specifically, the use of Fenton reactant leads to a corresponding increase of the extracted lipids from 6.9 to 17.4%wt/wt. Moreover, it is observed that the treatment provokes a significant improvement of the quality of fatty acids methyl esters (FAMEs) obtained by trans-esterification of extracted lipids. These results, together with the extreme simplicity, low cost and energy consumption of the proposed technique, are very promising in view of its industrial transposition. To this aim, the use of suitable mathematical models might represent a valuable tool to design and control possible industrial size reactors. Along these lines, a simple but exhaustive model to quantitatively describe the effects of contact time and reactants concentration on the amount of lipids extractable from microalgae is proposed in this work. The model takes into account the effect of the OH species on both cell wall breakage and lipid peroxidation phenomena. Model results and experimental data are successfully compared in terms of lipids extracted from wet microalgae previously subjected to the disruption treatment under different operating conditions. Furthermore, the possible chemical physical mechanisms underlying the improvement of FAMES composition, observed after the disruption treatment, is discussed. Finally, potential capabilities of the model to contribute to the industrial scale transposition of the proposed technique are presented.

Microalgal cell disruption via ultrasonic nozzle spraying.

The objective of this study was to understand the effect of operating parameters, including ultrasound amplitude, spraying pressure, nozzle orifice diameter, and initial cell concentration on microalgal cell disruption and lipid extraction in an ultrasonic nozzle spraying system (UNSS). Two algal species including Scenedesmus dimorphus and Nannochloropsis oculata were evaluated. Experimental results demonstrated that the UNSS was effective in the disruption of microalgal cells indicated by significant changes in cell concentration and Nile red-stained lipid fluorescence density between all treatments and the control. It was found that increasing ultrasound amplitude generally enhanced cell disruption and lipid recovery although excessive input energy was not necessary for best results. The effect of spraying pressure and nozzle orifice diameter on cell disruption and lipid recovery was believed to be dependent on the competition between ultrasound-induced cavitation and spraying-generated shear forces. Optimal cell disruption was not always achieved at the highest spraying pressure or biggest nozzle orifice diameter; instead, they appeared at moderate levels depending on the algal strain and specific settings. Increasing initial algal cell concentration significantly reduced cell disruption efficiency. In all UNSS treatments, the effectiveness of cell disruption and lipid recovery was found to be dependent on the algal species treated.

The effects of microalgal cell disruption via FeCl3-based synergistic effect between Fenton-like and Lewis acid reaction for lipid extraction

In this study, crude oil was extracted from Nannochloropsis salina for biodiesel production using FeCl3 as a catalyst. Scanning electron microscopy (SEM) analysis revealed that microalgae cells became wrinkled or burst after reaction. An optimal extraction condition, via the response surface methodology (RSM), was evaluated with respect to FeCl3 concentration (1–3mM), reaction time (30–90min) and temperature (60–100°C). At a condition of FeCl3 of 2mM, 90min, and 87°C, a maximum extraction yield of 213mg/g biomass and a FAME conversion rate of more than 80% were achieved. In light of FeCl3 being a reference coagulant, even for microalgae harvesting, its use for lipid extraction is expected to conceivably reduce the overall cost of microalgae-derived biodiesel production.

Microalgae harvesting and cell disruption: a preliminary evaluation of the technology electroflotation by alternating current.

Some species of microalgae have high productivity and lipid content, which makes them good candidates for biodiesel production. Biomass separation and cell disruption are important steps in biodiesel production from microalgae. In this work, we explored the fundamentals of electroflotation by alternating current (EFAC) with non-consumable electrodes to simultaneously harvest microalgae and disrupt cells from mixed microalgae obtained from waste stabilization ponds. The harvesting efficiency was evaluated using chlorophyll-a and turbidity, which reached removals of 99% and 95%, respectively, during a batch time of 140 min. Cell disruption was evaluated using lipid extraction, and the best results were achieved with a batch time of 140 min, which resulted in a 14% yield. Therefore, EFAC was shown to be an attractive potential technology for simultaneous microalgal harvesting and cell disruption.

Disruption of microalgal cells using high-frequency focused ultrasound

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.

Cationic surfactant-based method for simultaneous harvesting and cell disruption of a microalgal biomass

Microalgae are one of the most promising sustainable energy sources for biodiesel production. However, the high costs of the downstream process are a major bottleneck for commercial-scale production of biodiesel from a microalgal biomass. A novel approach called the cationic surfactant-based harvesting and cell disruption (CSHD) method was studied to determine its effectiveness in simultaneous microalgal biomass harvesting and cell disruption. Using CSHD, the harvesting efficiency reached more than 91% in less than 5 min and 97% in 90 min. Moreover, CSHD exhibited a powerful ability to disrupt the cells; the lipid recovery was increased 133% compared to not using CSHD. CSHD allowed the extraction of up to 100% of the total lipids from a wet microalgal biomass with 80% water content. All of these results were achieved without using energy-intensive equipment. Altogether, our results suggest that CSHD is an energy-efficient technique for the downstream process of microalgal lipid production.

Force and energy requirement for microalgal cell disruption: An atomic force microscope evaluation

Cell disruption is an essential step in the release of cellular contents but mechanical cell disruption processes are highly energy intensive. This energy requirement may become a critical issue for the sustainability of low valued commodities such as microalgal biofuels derived from extracted lipids. By the use of an atomic force microscope (AFM), this study evaluated the force and energy required to indent and disrupt individual cells of the marine microalga, Tetraselmis suecica. It was found that the force and energy required for the indentation and disruption varies according to the location of the cell with the average being 17.43pJ. This amount is the equivalent of 673Jkg−1 of the dry microalgal biomass. In comparison, the most energy efficient mechanical cell disruption process, hydrodynamic cavitation, has specific energy requirement that is approx. 5 orders of magnitude greater than that measured by AFM. The result clearly shows that existing mechanical cell disruption processes are highly energy inefficient and further research and innovation is required for sustainable microalgal biofuels production.

Microalgal cell disruption for biofuel development

The production of alternative fuels from microalgae involves lengthy processing steps. Cell disruption is an integral part of the downstream pool of unit operations as it facilitates the release of intracellular products essential for biofuel production. This study investigated the use of high-pressure homogenization, ultrasonication, bead beating, and sulfuric acid treatment as laboratory-scale disruption methods for microalgal cells. The performance of each cell disruption method was evaluated in terms of two key indicators: reduction in the intact cell count and reduction in the average colony diameter. The microalgal strain, Chlorococcum sp., was used throughout the study. The most effective disruption was obtained using high-pressure homogenization (average disruption = 73.8% of initial intact cells) followed by sulfuric acid treatment (average disruption = 33.2% of initial intact cells) and bead beating (average disruption = 17.5% of initial intact cells). Even though ultrasonication failed to disrupt the microalgal cells under the investigated conditions (average disruption = 4.5% of initial intact cells), it still managed to disintegrate cellular colonies.