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

A comprehensive review on versatile microalga Tetraselmis: Potentials applications in wastewater remediation and bulk chemical production

Microalgae are considered sustainable resources for the production of biofuel, feed, and bioactive compounds. Among various microalgal genera, the Tetraselmis genus, containing predominantly marine microalgal species with wide tolerance to salinity and temperature, has a high potential for large-scale commercialization. Until now, Tetraselmis sp. are exploited at smaller levels for aquaculture hatcheries and bivalve production. However, its prolific growth rate leads to promising areal productivity and energy-dense biomass, so it is considered a viable source of third-generation biofuel. Also, microbial pathogens and contaminants are not generally associated with Tetraselmis sp. in outdoor conditions due to faster growth as well as dominance in the culture. Numerous studies revealed that the metabolite compositions of Tetraselmis could be altered favorably by changing the growth conditions, taking advantage of its acclimatization or adaptation ability in different conditions. Furthermore, the biorefinery approach produces multiple fractions that can be successfully upgraded into various value-added products along with biofuel. Overall, Tetraselmis sp. could be considered a potential strain for further algal biorefinery development under the circular bioeconomy framework. In this aspect, this review discusses the recent advancements in the cultivation and harvesting of Tetraselmis sp. for wider application in different sectors. Furthermore, this review highlights the key challenges associated with large-scale cultivation, biomass harvesting, and commercial applications for Tetraselmis sp.

Biobutanol production from underutilized substrates using Clostridium: Unlocking untapped potential for sustainable energy development

The increasing demand for sustainable energy has brought biobutanol as a potential substitute for fossil fuels. The Clostridium genus is deemed essential for biobutanol synthesis due to its capability to utilize various substrates. However, challenges in maintaining fermentation continuity and achieving commercialization persist due to existing barriers, including butanol toxicity to Clostridium, low substrate utilization rates, and high production costs. Proper substrate selection significantly impacts fermentation efficiency, final product quality, and economic feasibility in Clostridium biobutanol production. This review examines underutilized substrates for biobutanol production by Clostridium, which offer opportunities for environmental sustainability and a green economy. Extensive research on Clostridium, focusing on strain development and genetic engineering, is essential to enhance biobutanol production. Additionally, critical suggestions for optimizing substrate selection to enhance Clostridium biobutanol production efficiency are also provided in this review. In the future, cost reduction and advancements in biotechnology may make biobutanol a viable alternative to fossil fuels.

Employing Atomic Force Microscopy (AFM) for Microscale Investigation of Interfaces and Interactions in Membrane Fouling Processes: New Perspectives and Prospects

Membrane fouling presents a significant challenge in the treatment of wastewater. Several detection methods have been used to interpret membrane fouling processes. Compared with other analysis and detection methods, atomic force microscopy (AFM) is widely used because of its advantages in liquid-phase in situ 3D imaging, ability to measure interactive forces, and mild testing conditions. Although AFM has been widely used in the study of membrane fouling, the current literature has not fully explored its potential. This review aims to uncover and provide a new perspective on the application of AFM technology in future studies on membrane fouling. Initially, a rigorous review was conducted on the morphology, roughness, and interaction forces of AFM in situ characterization of membranes and foulants. Then, the application of AFM in the process of changing membrane fouling factors was reviewed based on its in situ measurement capability, and it was found that changes in ionic conditions, pH, voltage, and even time can cause changes in membrane fouling morphology and forces. Existing membrane fouling models are then discussed, and the role of AFM in predicting and testing these models is presented. Finally, the potential of the improved AFM techniques to be applied in the field of membrane fouling has been underestimated. In this paper, we have fully elucidated the potentials of the improved AFM techniques to be applied in the process of membrane fouling, and we have presented the current challenges and the directions for the future development in an attempt to provide new insights into this field.

Trends in digital image processing of isolated microalgae by incorporating classification algorithm

Identification of microalgae species is of importance due to the uprising of harmful algae blooms affecting both the aquatic habitat and human health. Despite this occurence, microalgae have been identified as a green biomass and alternative source due to its promising bioactive compounds accumulation that play a significant role in many industrial applications. Recently, microalgae species identification has been conducted through DNA analysis and various microscopy techniques such as light, scanning electron, transmission electron, and atomic force -microscopy. The aforementioned procedures have encouraged researchers to consider alternate ways due to limitations such as costly validation, requiring skilled taxonomists, prolonged analysis, and low accuracy. This review highlights the potential innovations in digital microscopy with the incorporation of both hardware and software that can produce a reliable recognition, detection, enumeration, and real-time acquisition of microalgae species. Several steps such as image acquisition, processing, feature extraction, and selection are discussed, for the purpose of generating high image quality by removing unwanted artifacts and noise from the background. These steps of identification of microalgae species is performed by reliable image classification through machine learning as well as deep learning algorithms such as artificial neural networks, support vector machines, and convolutional neural networks. Overall, this review provides comprehensive insights into numerous possibilities of microalgae image identification, image pre-processing, and machine learning techniques to address the challenges in developing a robust digital classification tool for the future.

Insights into using green and unconventional technologies to recover natural astaxanthin from microbial biomass

Microorganisms such as bacteria, microalgae and fungi, are natural and rich sources of several valuable bioactive antioxidant's compounds, including carotenoids. Among the carotenoids with antioxidant properties, astaxanthin can be highlighted due to its pharmaceutical, feed, food, cosmetic and biotechnological applications. The best-known producers of astaxanthin are yeast and microalgae cells that biosynthesize this pigment intracellularly, requiring efficient and sustainable downstream procedures for its recovery. Conventional multi-step procedures usually involve the consumption of large amounts of volatile organic compounds (VOCs), which are regarded as toxic and hazardous chemicals. Considering these environmental issues, this review is focused on revealing the potential of unconventional extraction procedures [viz., Supercritical Fluid Extraction (SFE), Ultrasound-Assisted Extraction (UAE), Microwave-Assisted Extraction (MAE), High-Pressure Homogenization (HPH)] combined with alternative green solvents (biosolvents, eutectic solvents and ionic liquids) for the recovery of microbial-based astaxanthin from microalgae (such as Haematococcus pluvialis) and yeast (such as Phaffia rhodozyma) cells. The principal advances in the area, process bottlenecks, solvent selection and strategies to improve the recovery of microbial astaxanthin are emphasized. The promising recovery yields using these environmentally friendly procedures in lab-scale are good indications and directions for their effective use in biotechnological processes for the production of commercial feed and food ingredients like astaxanthin.

Short-chain fatty acids resource recovery potential from algal sludge via anaerobic fermentation under various pH values

The harvesting of algal sludge from eutrophic lakes, including the large quantity of organic matters, has the potential to be used as valuable products through the process of resource recovery. This study investigates the fatty acid production potential from algal sludge via anaerobic fermentation under different pH values. The results indicated that the recovery of short-chain fatty acids (SCFAs) was the highest (3269.25 ± 32.89 mg·COD/L) at pH 11 after 7 days of fermentation. The SCFAs concentration at pH value 11 was 6.24, 1.27, 4.90, and 0.53 times higher compared with that at pH value 3, 5, 7, and 9, respectively. The SCFAs production was continually increased from day 1 to day 7 at pH value 7, 9, and 11. Much fewer middle- and long-chain fatty acids were produced compared with SCFAs. Gross. fatty acid production was the highest at pH 11. The concentrations of soluble protein and polysaccharide were the highest at pH 11, implying that the disruption of algal cells could have a high value at pH 11. The polysaccharide concentration was the lowest at pH 7. The fluorescence excitation-emission matrix profile implied that the disruption of algal cells was the greatest at pH 11. Methane production was greatest at pH 7 and 9. Overall, the results of this study revealed that a pH of 11 was optimal for the recovery of SCFAs from algal sludge due to the higher cell disruption, suitable ORP condition for SCFAs production and inhibition of methanogens.

New insights into external layers of cyanobacteria and microalgae based on multiscale analysis of AFM force-distance curves

External layers, the outermost structures around cells, perform essential eco-physiological functions to support cyanobacteria and microalgae in aquatic environments. These layers have been recognized as adaptations to turbulence, a ubiquitous and inherent physical process occurring in the environments of most cyanobacteria and microalgae. However, the underlying biophysical mechanism of these layers is still poorly understood. Force measurements were performed directly on the external layers of eight living cyanobacterial and green algal strains in situ using atomic force microscopy (AFM). We developed a wavelet analysis method based on a multiscale decomposition of derivative force-distance curves to quantify the elastic responses of various external layers upon mechanical deformation. Such analysis has the advantages of detecting singularities and distinguishing the biomechanical contributions of each external layer. The elastic modulus of the same type of external layer follows the same statistical distribution. However, the elastic response among different types of external layers is challenged by our method, indicating the heterogeneity of the mechanical properties of inner and outer layers in multilayer strains. This discrepancy was due to the thickness and texture of each external layer, especially the chemical presence of ribose, hydroxyproline and glutamic acid. This study highlights a new way to elucidate more precise information about external layers and provides a biophysical mechanistic explanation for the functioning of the various external layers to protect cyanobacterial and microalgal cells in a turbulent environment.

Microalgae proteins: production, separation, isolation, quantification, and application in food and feed

Many countries have been experienced an increase in protein consumption due to the population growth and adoption of protein-rich dietaries. Unfortunately, conventional-based protein agroindustry is associated with environmental impacts that might aggravate as the humankind increase. Thus, it is important to screen for novel protein sources that are environmentally friendly. Microalgae farming is a promising alternative to couple the anthropic emissions with the production of food and feed. Some microalgae show protein contents two times higher than conventional protein sources. The use of whole microalgae biomass as a protein source in food and feed is simple and well-established. Conversely, the production of microalgae protein supplements and isolates requires the development of feasible and robust processes able to fractionate the microalgae biomass in different value-added products. Since most of the proteins are inside the microalgae cells, several techniques of disruption have been proposed to increase the efficiency to extract them. After the disruption of the microalgae cells, the proteins can be extracted, concentrated, isolated or purified allowing the development of different products. This critical review addresses the current state of the production of microalgae proteins for multifarious applications, and possibilities to concatenate the production of proteins and advanced biofuels.

Current methods to monitor microalgae-nanoparticle interaction and associated effects

Widespread use of nanoparticles for different applications has diffused their presence in the environment, particularly in water. Many studies have been conducted to evaluate their effects on aquatic organisms. Microalgae are at the base of aquatic trophic chains. These organisms which can be benthic or pelagic, meaning that they can enter into interaction with all kinds of particulate materials whatever their density, and constitute an interesting model study. The purpose of this review was to gather more than sixty studies on microalgae exposure to the different nanoparticles that may be present in the aquatic environment. After a brief description of each type of nanoparticle (metals, silica and plastic) commonly used in ecotoxicological studies, techniques to monitor their properties are presented. Then, different effects on microalgae resulting from interaction with nanoparticles are described as well as the parameters and techniques for monitoring them. The impacts described in the literature are primarily shading, ions release, oxidative stress, adsorption, absorption and disruption of microalgae barriers. Several parameters are proposed to monitor effects such as growth, photosynthesis, membrane integrity, biochemical composition variations and gene expression changes. Finally, in the literature, while different impacts of nanoparticles on microalgae have been described, there is no consensus on evidence of nanomaterial toxicity with regard to microalgae. A parallel comparison of different nanoparticle types appears essential in order to prioritize which factors exert the most influence on toxicity in microalgae cultures: size, nature, surface chemistry, concentration or interaction time.

Impact of substrate material on algal biofilm biomass growth

Algae are being grown for wastewater purification and biofuels production. Their growth on a substrate facilitates these uses by allowing facile separation of algae from the water. Here, we compare different materials to determine which would best serve this purpose. A mixed culture of Anabaena and Chlorella was grown on various synthetic and natural fiber fabric substrates in a trough system with recirculating simulated wastewater. Filter materials studied as substrates for algal growth were muslin, olefin, pellon (acrylic), two types of polyester, and two types of nylon. Biomass accumulation on the various filter substrates was recorded at 7, 14, and 28 days. Filters were weighed before and after the growth periods and changes in dry biomass were recorded. Biomass accumulation was significantly affected by the fabric type. Olefin fostered the greatest increase in biomass while nylon and polyester also supported competitive increases in biomass. Pellon showed the smallest biomass increase and muslin decreased in mass due to material disintegration. Other concerns such as abrasion resistance and UV susceptibility are discussed.

Investigation of the disruption of algal biomass with chlorine

BACKGROUND

Algal biofuel has a potential for reducing dependence on fossil fuel while curbing CO₂ emissions. Despite these potential benefits, a scalable, sustainable, and commercially viable system has not yet been developed. One of the key barriers is the lack of viable methods for disrupting algal biomass for the separation and extraction of bioproducts. This study experimentally investigated the feasibility of using chlorine as an agent for algal biomass disruption.

RESULTS

Chlorine was an effective agent for disrupting algal cell, as demonstrated with cell viability and SEM analyses. For disruption studies conducted using algal suspension at 0.02% solids (0.2 g/L), 90% of the algal cells were disrupted in 6 min at 10 mg/L chlorine dose. Moreover, the results demonstrated that the estimated specific energy requirement, specific cost, and GWP for chlorine were lower than those of the existing methods. The energy requirement for chlorine was 3.73 MJ/ kg of dry algae disrupted, while the requirements for the existing methods ranged from 33 to 860 MJ/ kg of dry algae. The GWP for chlorine was 0.3 kg CO₂-eq./kg dry algae, while for the existing methods it varied from 5.9 to 369.8 CO₂-eq./kg dry algae. Despite these advantages, it was observed that residual chlorine reacted with and mineralized the cell contents, which is undesirable.

CONCLUSIONS

Future research efforts must be focused on eliminating or reducing the reaction of residual chlorine with cell contents. If this challenge is addressed, chlorine has a potential to be developed into an energy-efficient, cost-effective, and sustainable method for algal biomass disruption. This will in turn will overcome one of the technical bottlenecks, and ultimately increase algal biofuel production and reduce dependence on fossil fuel and curb CO₂ emissions.

Selective and energy efficient extraction of functional proteins from microalgae for food applications

The use of a single controlled bead milling step of the microalga Tetraselmis suecica resulted in a soluble fraction, rich in functional proteins. This was achieved by fine-tuning the processing time, thereby exploiting the difference in rates of protein and carbohydrate release during milling. Soluble proteins were extracted under mild conditions -room temperature, no addition of chemicals, pH 6.5-, with a yield of 22.5% and a specific energy consumption of 0.6 kWh kg_DW^-1, which is within the recommended minimum energy for an extraction step in a biorefinery process. The resulting protein extract contained 50.4% (DW) of proteins and 26.4% carbohydrates, showed light green color and displayed superior surface activity and gelation behavior compared to whey protein isolate. The proposed process is simple (only one bead milling step), scalable, and allows the mild extraction of functional proteins, making it interesting for industrial applications in the food industry.

Comparative toxicity of nano ZnO and bulk ZnO towards marine algae Tetraselmis suecica and Phaeodactylum tricornutum

The wide use of ZnO nanoparticles in a number of products implies an increasing release into the marine environment, resulting in the need to evaluate the potential effects upon organisms, and particularly phytoplankton, being at the base of the throphic chain. To this aim, dose-response curves for the green alga Tetraselmis suecica and the diatom Phaeodactylum tricornutum derived from the exposure to nano ZnO (100 nm) were evaluated and compared with those obtained for bulk ZnO (200 nm) and ionic zinc. The toxic effects to both algae species were reported as no observable effect concentration (NOEC) of growth inhibition and as 1, 10, and 50% effect concentrations (EC1, EC10, and EC50). The toxicity decreased in the order nano ZnO > Zn²⁺ > bulk ZnO. EC50 values for nano ZnO were 3.91 [3.66-4.14] mg Zn/L towards the green microalgae and 1.09 [0.96-1.57] mg Zn/L towards the diatom, indicating a higher sensitivity of P. tricornutum. The observed diverse effects can be ascribed to the interaction occurring between different algae and ZnO particles. Due to algae motility, ZnO particles were intercepted in different phases of aggregation and sedimentation processes, while algae morphology and size can influence the level of entrapment by NP aggregates.This underlines the need to take into account the peculiarity of the biological system in the assessment of NP toxicity.

Energy efficient bead milling of microalgae: Effect of bead size on disintegration and release of proteins and carbohydrates

The disintegration of three industry relevant algae (Chlorella vulgaris, Neochloris oleoabundans and Tetraselmis suecica) was studied in a lab scale bead mill at different bead sizes (0.3-1mm). Cell disintegration, proteins and carbohydrates released into the water phase followed a first order kinetics. The process is selective towards proteins over carbohydrates during early stages of milling. In general, smaller beads led to higher kinetic rates, with a minimum specific energy consumption of ⩽0.47kWhkg_DW^-1 for 0.3mm beads. After analysis of the stress parameters (stress number and stress intensity), it appears that optimal disintegration and energy usage for all strains occurs in the 0.3-0.4mm range. During the course of bead milling, the native structure of the marker protein Rubisco was retained, confirming the mildness of the disruption process.

Nitrogen deprivation of microalgae: effect on cell size, cell wall thickness, cell strength, and resistance to mechanical disruption

Nitrogen deprivation (N-deprivation) is a proven strategy for inducing triacylglyceride accumulation in microalgae. However, its effect on the physical properties of cells and subsequently on product recovery processes is relatively unknown. In this study, the effect of N-deprivation on the cell size, cell wall thickness, and mechanical strength of three microalgae was investigated. As determined by analysis of micrographs from transmission electron microscopy, the average cell size and cell wall thickness for N-deprived Nannochloropsis sp. and Chlorococcum sp. were ca. 25% greater than the N-replete cells, and 20 and 70% greater, respectively, for N-deprived Chlorella sp. The average Young’s modulus of N-deprived Chlorococcum sp. cells was estimated using atomic force microscopy to be 775 kPa; 30% greater than the N-replete population. Although statistically significant, these microstructural changes did not appear to affect the overall susceptibility of cells to mechanical rupture by high pressure homogenisation. This is important as it suggests that subjecting these microalgae to nitrogen starvation to accumulate lipids does not adversely affect the recovery of intracellular lipids.

2D and 3D Mechanobiology in Human and Nonhuman Systems

Mechanobiology involves the investigation of mechanical forces and their effect on the development, physiology, and pathology of biological systems. The human body has garnered much attention from many groups in the field, as mechanical forces have been shown to influence almost all aspects of human life ranging from breathing to cancer metastasis. Beyond being influential in human systems, mechanical forces have also been shown to impact nonhuman systems such as algae and zebrafish. Studies of nonhuman and human systems at the cellular level have primarily been done in two-dimensional (2D) environments, but most of these systems reside in three-dimensional (3D) environments. Furthermore, outcomes obtained from 3D studies are often quite different than those from 2D studies. We present here an overview of a select group of human and nonhuman systems in 2D and 3D environments. We also highlight mechanobiological approaches and their respective implications for human and nonhuman physiology.

A versatile and economical method for the release of recombinant proteins from Escherichia coli by 1-propanol cell disruption

Release of enhanced green fluorescent protein from Escherichia coli by 1-propanol cell disruption.

Aggregate formation affects ultrasonic disruption of microalgal cells

Ultrasonication is a cell disruption process of low energy efficiency. This study dosed K(+), Ca(2+) and Al(3+) 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(+)>Ca(2+)>Al(3+) 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.

Ultrasonic intensification as a tool for enhanced microbial biofuel yields

Ultrasonication has recently received attention as a novel bioprocessing tool for process intensification in many areas of downstream processing. Ultrasonic intensification (periodic ultrasonic treatment during the fermentation process) can result in a more effective homogenization of biomass and faster energy and mass transfer to biomass over short time periods which can result in enhanced microbial growth. Ultrasonic intensification can allow the rapid selective extraction of specific biomass components and can enhance product yields which can be of economic benefit. This review focuses on the role of ultrasonication in the extraction and yield enhancement of compounds from various microbial sources, specifically algal and cyanobacterial biomass with a focus on the production of biofuels. The operating principles associated with the process of ultrasonication and the influence of various operating conditions including ultrasonic frequency, power intensity, ultrasonic duration, reactor designs and kinetics applied for ultrasonic intensification are also described.

Lutein production from biomass: marigold flowers versus microalgae

Microalgae have faster growth rates and more free lutein than marigold flowers, the current source of lutein. However, no commercial lutein production uses microalgae. This review compares lutein content, cultivation, harvesting, cell disruption, and extraction stages of lutein production using marigold flowers and those using microalgae as feedstock. The lutein production rate of microalgae is 3-6 times higher than that of marigold flowers. To produce 1 kg of pure lutein, marigolds need more land and water, but require less nutrients (N, P, K) and less energy than microalgae. Since lutein is tightly bound in microalgae and microalgae are small, cell disruption and subsequent extraction stages consume a considerable amount of energy. Research and development of affordable lutein production from microalgae are discussed.

Microalgal drying and cell disruption--recent advances

Production of intracellular metabolites or biofuels from algae involves various processing steps, and extensive work on laboratory- and pilot-scale algae cultivation, harvesting and processing has been reported. As algal drying and cell disruption are integral processes of the unit operations, this review examines recent advances in algal drying and disruption for nutrition or biofuel production. Challenges and prospects of the processing are also outlined. Engineering improvements in addressing the challenges of energy efficiency and cost-effective and rigorous techno-economic analyses for a clearer prospect comparison between different processing methods are highlighted. Holistic life cycle assessments need to be conducted in assessing the energy balance and the potential environmental impacts of algal processing. The review aims to provide useful information for future development of efficient and commercially viable algal food products and biofuels production.

Cell disruption for microalgae biorefineries

Microalgae are a potential source for various valuable chemicals for commercial applications ranging from nutraceuticals to fuels. Objective in a biorefinery is to utilize biomass ingredients efficiently similarly to petroleum refineries in which oil is fractionated in fuels and a variety of products with higher value. Downstream processes in microalgae biorefineries consist of different steps whereof cell disruption is the most crucial part. To maintain the functionality of algae biochemicals during cell disruption while obtaining high disruption yields is an important challenge. Despite this need, studies on mild disruption of microalgae cells are limited. This review article focuses on the evaluation of conventional and emerging cell disruption technologies, and a comparison thereof with respect to their potential for the future microalgae biorefineries. The discussed techniques are bead milling, high pressure homogenization, high speed homogenization, ultrasonication, microwave treatment, pulsed electric field treatment, non-mechanical cell disruption and some emerging technologies.

Pre-treatment options for halophytic microalgae and associated methane production

Methane production from lipid extracted, pre-treated disrupted and non-pretreated Tetraselmis spp. microalgae was investigated. The results demonstrated that 122 mL per g VS methane was produced for the lipid extracted Tetraselmis spp., demonstrating that lipid free Tetraselmis can be effectively digested in an anaerobic environment. A total of 252 mL per g VS and 248 mL per g VS of methane was reported for non-disrupted and pre-treated disrupted Tetraselmis sp. respectively. It was also observed that the microbial community caused cell lysis of Tetraselmis spp. during the anaerobic digestion process. Cell lyses can offer a direct conversion pathway of intact Tetraselmis spp. for energy production, thus negating the need for pre-treatment.

Algal cell disruption using microbubbles to localize ultrasonic energy

Microbubbles were added to an algal solution with the goal of improving cell disruption efficiency and the net energy balance for algal biofuel production. Experimental results showed that disruption increases with increasing peak rarefaction ultrasound pressure over the range studied: 1.90 to 3.07 MPa. Additionally, ultrasound cell disruption increased by up to 58% by adding microbubbles, with peak disruption occurring in the range of 10(8)microbubbles/ml. The localization of energy in space and time provided by the bubbles improve efficiency: energy requirements for such a process were estimated to be one-fourth of the available heat of combustion of algal biomass and one-fifth of currently used cell disruption methods. This increase in energy efficiency could make microbubble enhanced ultrasound viable for bioenergy applications and is expected to integrate well with current cell harvesting methods based upon dissolved air flotation.

A novel cell disruption technique to enhance lipid extraction from microalgae

Lipid extraction represents one of the main bottlenecks of the microalgal technology for the production of biofuels. A novel method based on the use of H2O2 with or without FeSO4, to disrupt the cell wall of Chlorella vulgaris and favor the subsequent extraction of lipids from wet biomass, is proposed. Experimental results show that, when disruption is performed under suitable operating conditions, the amount of lipids extracted is significantly increased with respect to the case where a classical approach is applied. Moreover, quality of lipids extracted after disruption seems to be improved in view of their exploitation for producing biofuels.

Selective extraction from microalgae Nannochloropsis sp. using different methods of cell disruption

This work studies the extraction of intracellular components from microalgae Nannochloropsis sp. with application of different cell disruption techniques, including pulsed electric field (PEF) (20kV/cm, 1-4ms, 13.3-53.1kJ/kg), high voltage electrical discharge (HVED) (40kV/cm, 1-4ms, 13.3-53.1kJ/kg), ultrasonication (USN) (200W, 1-8min, 12-96kJ/kg), and high pressure homogenization (HPH) (150MPa, 1-10 passes, 150-1500kJ/kg). The data evidence that electrically based disruption techniques (PEF and HVED) allowed selective extraction of water soluble ionic components and microelements, small molecular weight organic compounds and water soluble proteins. Microscopic and sedimentation stability analyses have shown that microalgae cells in HVED-treated suspension were noticeably agglomerated and could be easily settled in centrifuge. The electrically based disruption techniques were ineffective for delivery of pigments (e.g., chlorophylls or carotenoids) and their extraction required subsequent application of more potent disruption techniques. The obtained data have shown that HPH disruption technique was the most effective; however, this mode required the highest power consumption.

Dynamic microstructures and fractal characterization of cell wall disruption for microwave irradiation-assisted lipid extraction from wet microalgae

To extract lipids from wet microalgae through cell disruption, the effects of microwave treatment on the dynamic cell wall microstructures were investigated. The fractal dimension of raw, untreated microalgal cells was 1.46. The disruption level of microalgal cell walls was enhanced when microwave treatment temperature increased from 80 to 120°C, resulting in an increase in microalgal cell fractal dimension from 1.61 to 1.91. The cell wall thickness and pore diameters in cell walls increased from 0.11 to 0.59 μm and from 0.005 to 0.18 μm, respectively, when microwave treatment time increased from 0 to 20 min. The outer pectin layers of cell walls gradually detached and the porosity of inner cellulose layers increased when microwave treatment time increased to 26 min. The initial point of disruption appeared at the maximum curvature (approximately 1.01×10(7) m(-1)) of cell walls. Numbers of short-chain and saturated lipids increased because of microwave electromagnetic effect.

Quantitative evaluation of the ease of rupture of industrially promising microalgae by high pressure homogenization

The susceptibility to rupture of the microalgae Nannochloropsis sp., Chlorella sp. and Tetraselmis suecica by high pressure homogenization was compared quantitatively to the yeast Saccharomyces cerevisiae. Methods for quantifying cell rupture were investigated including cell counting, turbidity, metabolite release and particle sizing. Cell counting was the only reliable method for quantitative comparisons of all microalgae, with turbidity complicated by agglomeration of cell debris for T. suecica, and measurement of metabolite release affected by degradation occurring for all microalgae after significant rupture. The rupture of all microalgae followed exponential decay as a function of number of passes. The pressure required to achieve rupture of 50% of the cells per pass was determined to be 170, 1070, 1380, and ca. 2000 bar for Tetraselmis sp., Chlorella sp., S. cerevisiae, and Nannochloropsis sp., respectively. These results extend the criteria for selecting microalgae for industrial applications beyond consideration of growth and compositional attributes.