Separation Of Microalgae Research Articles

Microalgae separation in MP-PVC contaminated wastewater using plant-based coagulant over different extraction methods in Bauru, Brazil

This study investigates the effectiveness of coagulation-flocculation and sedimentation (CFS) for separating microalgae, focusing on the use of various Moringa oleifera extracts as natural coagulants. We examined photobioreactor effluent (PBR) both with and without microplastic PVC (MP-PVC) contamination, referred to as PBR R2 and PBR R1, respectively. Utilising response surface methodology, we identified optimal conditions for the removal of microalgae and MP-PVC. Validation tests demonstrated that the aqueous extract of delipidated Moringa oleifera powder (AEDMOP) achieved high removal efficiencies, with coagulant dosages of 630 mg L−1 for PBR R1 and 625 mg L−1 for PBR R2. Both conditions showed microalgae removal efficiencies exceeding 83% for turbidity, colour, OD540 nm, OD680 nm, and OD750 nm, and 63% for OD254 nm. Interestingly, the optimised conditions for PBR R2 required slightly less coagulant, likely due to the additional particulate matter from MP-PVC. While extracellular polymeric substances (EPS) exhibited a marginal effect on flocculation, further investigation into their role in CFS is necessary. Our findings highlight the potential of AEDMOP for efficient microalgae separation, even in the presence of microplastics.

Optimization of synthesis of cationic starches for wastewater sludge and microalgae separation

The implementation of stricter water protection legislation requires the development of novel environmentally friendly water treatment materials. A new method for the preparation of water soluble cationic starch flocculants using potato starch, 3-chloro-2-hydroxypropyltrimethylammonium chloride and CaO additive was developed and surface response methodology was successfully utilized for the optimization of degree of substitution in the cationization of potato starch with and without CaO additive. Based on the results of destabilization studies of model kaolin, wastewater sludge, and microalgae dispersion systems, optimized conditions ware proposed for obtaining an efficient, soluble, and biodegradable cationic starch flocculant with optimal structure. The duration of starch etherification reaction was reduced to <12 h to obtain soluble cationic starch derivatives with a degree of substitution of quaternary ammonium groups of 0.25, which retained the granular structure during synthesis. An efficient flocculation technology using anionic polymer and high content of biodegradable cationic flocculant was proposed. The highly efficient flocculation of microalgae suspensions using developed cationic starch derivative with the degree of substitution of cationic groups of 0.25 has been also achieved. The developed environmentally friendly cationic starches with tailored flocculation properties proofed to have a great potential in various water cleaning and separation technologies with prospects in wastewater treatment, agriculture or energy sectors.

Optimization and development of denser Chlorella vulgaris microalgae granules for easy harvesting via self-flocculation

Microalgae is widely utilized in water purification technology, biofuel production as well as in the synthesis of biopolymers. However, the separation of microalgae from its growth medium is the major issue that restricts the harvesting processes due to microalgae's lower density. In this study, the effect of environmental factors on microalgae granules development was investigated. Results from response surface methodology (RSM) revealed that maximum growth rate and biomass productivity were obtained at a photoperiod of 23.9 h, aeration rates of 2.4 L/min, inoculum concentration of 11 % and pH 6 respectively. The mixed liquor volatile suspended solids (MLVSS) value of the initial seed microalgae increased from 50 mg/L to 2978 mg/L after 70 days of cultivation. Microalgae productivity in this study is approximately 2 times faster than the standard suspension growing method. The microalgae settleability was significantly enhanced, as indicated by a major reduction in the sludge volume index (SVI30) from an initial value of >3000 to 58.51 mL/g, accompanied by an increase in settling velocity from virtually 0 to 19.2 cm/h and total harvesting time of 15 min. After 70 days of operation, smoothly settled, compact algal granules with largest sizes of 1.90 mm were obtained.

Separation of microalgae from bacterial contaminants using spiral microchannel in the presence of a chemoattractant

Cell separation using microfluidics has become an effective method to isolate biological contaminants from bodily fluids and cell cultures, such as isolating bacteria contaminants from microalgae cultures and isolating bacteria contaminants from white blood cells. In this study, bacterial cells were used as a model contaminant in microalgae culture in a passive microfluidics device, which relies on hydrodynamic forces to demonstrate the separation of microalgae from bacteria contaminants in U and W-shaped cross-section spiral microchannel fabricated by defocusing CO2 laser ablation. At a flow rate of 0.7 ml/min in the presence of glycine as bacteria chemoattractant, the spiral microfluidics devices with U and W-shaped cross-sections were able to isolate microalgae (Desmodesmus sp.) from bacteria (E. coli) with a high separation efficiency of 92% and 96% respectively. At the same flow rate, in the absence of glycine, the separation efficiency of microalgae for U- and W-shaped cross-sections was 91% and 96%, respectively. It was found that the spiral microchannel device with a W-shaped cross-section with a barrier in the center of the channel showed significantly higher separation efficiency. Spiral microchannel chips with U- or W-shaped cross-sections were easy to fabricate and exhibited high throughput. With these advantages, these devices could be widely applicable to other cell separation applications, such as separating circulating tumor cells from blood.Graphical

Optically induced dielectrophoresis for continuous separation and purification of C. vulgaris and H. pluvialis

Marine microalgae are widely present in the natural environment, exhibiting a significant economic value. However, during the inoculation and cultivation process of microalgae, the introduction of unwanted algae is bound to trigger nutrient competition, leading to a decrease in the growth rate of microalgae and consequently impacting their economic value in production. To address this issue, this study integrates the optically induced dielectrophoresis (ODEP) manipulation technology based on the continuous flow in a microfluidic system. A two-stage cell filter, utilizing two virtual optical spots, is designed and manufactured. Leveraging the size differences between microalgae, continuous separation and purification of mixed samples containing Chlorella vulgaris and Haematococcus pluvialis are achieved within microchannels. Additionally, optimal ODEP manipulation conditions for mixed algal liquid samples, comprising C. vulgaris and H. pluvialis, are demonstrated, including appropriate alternating current voltage (6 V), alternating current frequency (100 kHz), light spot width (40 μm), and sample flow rate (0.9 μl/min). Analysis of mixed liquid samples collected at the chip's outlet reveals a reduction in the proportion of H. pluvialis from 37.5% to 1.2% after separation. In summary, this study proposes an ODEP microfluidic system capable of continuously separating and purifying microalgae with different biological characteristics, showcasing its potential as an alternative to traditional labor-intensive microalgae separation techniques.

Valorization of treated swine wastewater and generated biomass by microalgae: Their effects and salt tolerance mechanisms on wheat seedling growth

The extensive use of mineral fertilizers has a negative impact on the environment, whereas wastewater and microalgal biomass can provide crops with nutrients such as nitrogen, phosphorus, and potassium, and have the potential to be used as a source of fertilizers in circular agriculture. In this study, a step-by-step resource utilization study of algae-containing wastewater generated from microalgae treatment of swine wastewater was carried out. When wheat seedlings were cultivated in the effluent after microalgae separation, the root fresh weight, seedling fresh weight, and total seedling length were increased by 3.44%, 14.45%, and 13.64%, respectively, compared with that of the algae-containing wastewater, and there was no significant difference in seedling fresh weight, total seedling length, maximum quantum yields of PSII photochemistry (Fv/Fm), and performance index (PIABS) from that of the Hogland solution group, which has the potential to be an alternative liquid fertilizer. Under salt stress, microalgae extract increased the contents of GA3, IAA, ABA, and SA in wheat seedlings, antioxidant enzymes maintained high activity, and the PIABS value increased. Low-dose microalgae extract (1 mL/L) increased the root fresh weight, seedling fresh weight, longest seedling length, and total seedling length by 30.73%, 31.28%, 16.43%, and 28.85%, respectively. Algae extract can act as a plant biostimulant to regulate phytohormone levels to attenuate the damage of salt stress and promote growth.

Non-immersed zigzag microalgae biofilm overcoming high turbidity and ammonia of wastewater for muti-pollutants bio-purification

Biological treatment that utilizes microalgae technology has demonstrated outstanding efficacy in the wastewater purification and nutrients recovery. However, the high turbidity of the digested piggery wastewater (DPW) leads to serious light attenuation and the culture mode of suspended microalgae results in a huge landing area. Thus, to overcome light attenuation in DPW, a non-immersed titled zigzag microalgae biofilm was constructed by attaching it onto a porous cotton cloth. As a result, the light could directly irradiate microalgae biofilm that attached on both sides of the cotton cloth, and the microalgal biofilm area was up to 6 m2 per bioreactor landing area. When the non-immersed zigzag microalgae biofilm bioreactor (N-Z-MBP) was used to treat wastewater with an ammonia nitrogen (NH4+-N) concentration of 362 mg L−1, the NH4+-N was completely removed in just 5 days and the maximum growth rate of microalgae biofilm reached 7.02 g m−2 d−1. After 21 days of long-term sequencing batch operation for the N-Z-MBP, the biomass density of the biofilm reached 52 g m−2 and remained at this high value for the next 14 days. Most importantly, during the 35 days’ running, the NH4+ -N maximum removal rate of single batch reached up to 65 mg L−1 d−1 and its concentration in the effluent was always below the discharge standard value (80 mg L−1 form GB18596–2001 of China) and total phosphorus was completely removed in each batch. Furthermore, the biomass concentration of microalgae cells in the effluent of the N-Z-MBP was almost zero, indicating that the non-submerged biofilm achieved in situ separation of microalgae from the wastewater. This work suggests that the N-Z-MBP can effectively purify DPW over a long period, providing a possible strategy to treat wastewater with high ammonia nitrogen and high turbidity.

Ultra-high throughput microfluidic concentrator for harvesting of Tetraselmis sp. (Chlorodendrophyceae, Chlorophyta)

Microalgae are of commercial interest for their ability to produce high-value compounds and their potential to be used as feedstock across numerous industries. The production of algal biomass and other algal-based products involves different upstream and downstream processing steps, including cultivation, harvesting, and extraction. In particular, the harvesting process involves the extraction of a condensed algal slurry from a watery growth medium. This process accounts for 20 to 30 % of the biomass production costs, creating technological and economic barriers. The conventional harvesting methods suffer from high costs, cross-contamination, and low yield. This study explores the use of a microfluidic technique, in particular, the rigid spiral microchannel, for ultra-high-throughput algae harvesting. We have designed a novel spiral channel that enables microalgae separation at high flow rates and spatial resolution, taking advantage of inertial microfluidic principles. The results from trials with surrogate microparticles and algal cells reveal that the microchannel has the potential to operate at 12 mL/min with separation efficiency >99 %. Our inertial microfluidic device operates at high flow rates as a single channel, can be multiplexed, and shows excellent potential for large-scale processing of microalgae cultures. In addition, the lower number of loops provides the system with reduced back pressure, making it more desirable for operation using a range of different pumps. Since the overall cost of microalgae dewatering is substantial at the industrial scale, the design and fabrication of low-cost devices are of great importance, similar to the one we have developed in this study.

The influence of physical floc properties on the separation of marine microalgae via alkaline flocculation followed by dissolved air flotation

Flocculation achieved by raising the pH, termed alkaline flocculation is a sustainable way of inducing flocculation in marine microalgae. Flocs formed post-alkaline flocculation have the potential to be harvested via dissolved air flotation (DAF) or sedimentation. While DAF results in faster separation and biomass with a higher solids content compared to sedimentation, it has not been tested in saline environments, particularly when combined with alkaline flocculation. DAF processes, like most separation techniques, are heavily dependent on physical floc properties. In this study, the impact of alkaline floc properties on the performance of DAF versus sedimentation was evaluated to harvest marine Nannochloropsis oculata, benchmarking against the well-studied ferric chloride flocculation. This was followed by the use of the DAF white-water model to illustrate how alkaline and ferric floc properties impact bubble-particle attachment and DAF separation efficiencies. Alkaline flocs were smaller (peakmax < 300 μm; majority flocs 130–470 μm), stronger (~70 % strength factor) and more compact (scattering exponent > 2.30) compared to ferric flocs which were larger (peakmax ~ 1700 μm; >65 % of flocs >1000 μm), relatively weaker (<40 % strength factor), less compact (scattering exponent 1.49–2.30). However, as both flocs were hydrophilic, sedimentation yielded ~15 % greater efficiency than DAF. Stoke's Law suggested that sedimentation benefited due to alkaline floc compactness and large sizes of ferric flocs. Nonetheless, maximum separation efficiencies of ~80–85 % were still obtained via the DAF process. From the white-water model, bubble-floc attachment efficiency of alkaline flocs (0.01–0.001 %) was observed to be at least an order of magnitude greater than ferric flocs (0.001–0.0001 %) despite both methods resulting in comparable DAF separation efficiencies. For alkaline flocs, elevated bubble-floc attachment efficiency compensated low hydrophilicity; for ferric flocs, low bubble-floc attachment was compensated by large floc sizes. Overall, it is suggested that the determination of floc properties post-coagulation-flocculation could be used to optimise separation processes.

N-rich porous triazine based organic polymer composed with magnetic for high-efficiency removal of blue-green microalgae from wastewater

In the last decades, there has been a growing interest in microalgae due to its broad application scope. Therefore, finding a cost-effective, high yield solution for harvest. In this study, the effectiveness of a new N-rich porous triazine based organic polymer (TrzPOP) was synthesized by the reaction between cyanuric chloride and diethylenetriamine in anhydrous 1,4-dioxane. The TrzPOP is showed high BET surface area (790 m2g−1) and pore volume 1.3 cc g−1 for removal of blue-green microalgae. The results demonstrated that the TrzPOP had a positive zeta potential in neutral pH and harvesting efficiency (HE) of microalgae (1.8 g/L) with above 98 % at a dose of 30 mg/L of it. To reusability and easy separation from the wastewater TrzPOP nanoparticles were functionalized by Fe3O4@SiO2, which results show that the synthesized Fe3O4@SiO2-TrzPOP nanocomposite has a positive zeta potential in acidic pH. The magnetic removal blue-green microalgae (1.8 g/L) at a dose of 40 mg/L of nanocomposite in acidic medium was as same as harvesting efficiency of TrzPOP. The collecting procedure significantly enhanced and less than 2.0 % of microalgae cells were left after just 1 min complete separation of microalgae from paramagnetic functionalized nanoparticles were enabled through the ultrasonic method and Fe3O4@SiO2- TrzPOP was recycled up to five times successfully.

Bubble functionalization in flotation process improve microalgae harvesting

Microalgae are a promising resource for biofuel production, although the lack of effective harvesting techniques limits their industrial use. In this context, flotation, and in particular dissolved air flotation (DAF), is an interesting separation technique that could drastically reduce harvesting costs and make biofuel-production systems more economically viable. But because of the repulsive interaction between cells and bubbles in water, the efficiency of this technique can be limited. To solve this problem, we propose here an original DAF process where bubbles are functionalized with a bio-sourced polymer able to specifically bind to the surface of cells, chitosan. In a first part, we modify chitosan by adding hydrophobic groups on its backbone to obtain an amphiphilic molecule, PO-chitosan, able to assemble at the surface of bubbles. Then, using a recently developed technique based on atomic force microscopy (AFM) combined with microfluidics, we probe the interactions between PO-chitosan coated bubbles and cells at the molecular scale; results show an enhanced adhesion of functionalized bubbles to cells (from 3.5 to 12.8 nN) that is pH-dependent. Separation efficiencies obtained in flotation experiments with functionalized bubbles are in line with AFM data, and a microalgae separation efficiency of approximately 60% could be reached in a single step. In addition, we also found that PO-chitosan could be used efficiently as a flocculant (nearly 100% of cells removed), and in this case AFM experiments revealed that the flocculation mechanism is based on hydrophobic interactions between cells and PO-chitosan. Altogether, this comprehensive study shows the interest of PO-chitosan to harvest cells in flotation or flocculation/flotation processes.

Separation of microalgae cells in a microfluidic chip based on AC Dielectrophoresis

AbstractBACKGROUNDMicroalgae is an important natural resource with extensive applications in various fields, such as health products, animal feed, biopharmaceuticals, and clean energy. However, before the research and utilization of microalgae resources, the microalgae cells of interest must be separated from hybrid strains and bacteria. The traditional method of microalgae separation requires manual labor under the microscope that is time‐consuming and labor‐intensive.RESULTSHerein, a novel microalgae cell separation method based on the dielectrophoresis (DEP) technique was proposed. A unique DEP separation chip with a 3D electrode was designed. Chlorella and Closterium were used as the experimental samples to verify the effectiveness of the proposed method because they have similar volumes and very different electrical properties. Within a certain frequency range, Chlorella suffers from negative dielectrophoresis (nDEP) force and Closterium suffers from positive dielectrophoresis (pDEP) force, so their separation can be achieved. The separation efficiency exceeded 90%. In addition, the DEP response of the Chlorella and Closterium were studied, and the DEP spectra of the two microalgae cells were obtained. Moreover, the effects of DEP force on cell viability under different voltages and frequencies were experimentally analyzed.CONCLUSIONThese findings will contribute to DEP technology, to the portable and harmless separation of microalgae, and to research on the dielectric properties of microalgae cells. © 2022 Society of Chemical Industry (SCI).

Uses of electro-coagulation-flocculation (ECF) for the pre-concentration of microalgae biomass

The separation of microalgae biomass from diluted cultures found in large-scale production systems is a major challenge for microalgae-related processes. Conventional methods use centrifugation but it requires too much energy (1 kWh/m3), the combination with previous pre-concentration operations such as settling or flotation is needed to reduce this energy consumption. However, both settling and flotation of microalgae biomass require the addition of chemical coagulants/flocculants, thus contaminating the biomass. This work explores the potential use of Electro-Coagulation-Flocculation (ECF) as a method for the pre-concentration of microalgae biomass. Thus, the recovery of freshwater microalgae Scenedesmus almeriensis was studied, both in batch and continuous mode, using this technique to optimize the operating conditions. Data from batch experiments show as a minimum conductivity of 5 mS∙cm−1 is required, the electrical potential of 12 V and current density of 18 mA∙cm−2 allowing for the recovery of 90 % of the biomass, while the biomass recovery increases up to 99 % when increasing the current density to 23 mA∙cm−2. The efficiency of the process increases when increasing the biomass concentration, thus energy consumption reduces by half from 1.0 to 0.5 kWh∙Kg−1 when the biomass concentration increases from 2.8 to 5.0 g∙L−1. To optimize the performance of the system experiments were performed in continuous mode maintaining the voltage and current density at 12 V and 47 mA∙cm−2 respectively, but modifying the flow rate and biomass concentration provided to the electrocoagulation chamber. Data shows as the optimal residence time is 15 s whereas the energy consumption reduces from 3.2 to 0.58 kWh∙Kg−1 when increasing the biomass concentration from 0.75 to 4.20 g∙L−1. Results confirm the reliability of this method for the pre-concentration of microalgae biomass, it being a fast process consuming reasonable energy. Further optimization of the electrocoagulation chamber and electrical conditions will improve the efficiency of this system for further commercial processes while keeping its major advantages of non-contaminating the biomass and allowing to achieve high biomass recovery values in short times.

Immobilization Method to Separate Microalgae Biomass for Fatty Acid Methyl Ester Production

AbstractAn immobilization method for simplified separation of cultured cells and their products from the growth media was developed. The growth rates of both immobilized and free cells of the microalga Chlorella vulgaris were compared. The free and immobilized cells reached nearly identical cell densities. The reported immobilization strategy uses a combination of matrices (sodium alginate (SA), calcium alginate (CA), and sodium carboxymethyl cellulose (CMC)) at different matrix/microalgae volumetric ratios of 0.3:1 and 1:1. The microalgae in the SACACMC/Mc (0.3:1) beads achieved the highest cell density. The cells immobilized in SACACMC/Mc (0.3:1) gave the highest lipid yield, as compared to the cells immobilized in SA. Pore size and membrane thickness analysis as well as surface images of SACACMC/Mc (0.3:1) showed that the mixed matrix had a unique structure favoring lipid production.

Fe3O4-PEI Nanocomposites for Magnetic Harvesting of Chlorella vulgaris, Chlorella ellipsoidea, Microcystis aeruginosa, and Auxenochlorella protothecoides.

Magnetic separation of microalgae using magnetite is a promising harvesting method as it is fast, reliable, low cost, energy-efficient, and environmentally friendly. In the present work, magnetic harvesting of three green algae (Chlorella vulgaris, Chlorella ellipsoidea, and Auxenochlorella protothecoides) and one cyanobacteria (Microcystis aeruginosa) has been studied. The biomass was flushed with clean air using a 0.22 μm filter and fed CO2 for accelerated growth and faster reach of the exponential growth phase. The microalgae were harvested with magnetite nanoparticles. The nanoparticles were prepared by controlled co-precipitation of Fe2+ and Fe3+ cations in ammonia at room temperature. Subsequently, the prepared Fe3O4 nanoparticles were coated with polyethyleneimine (PEI). The prepared materials were characterized by high-resolution transmission electron microscopy, X-ray diffraction, magnetometry, and zeta potential measurements. The prepared nanomaterials were used for magnetic harvesting of microalgae. The highest harvesting efficiencies were found for PEI-coated Fe3O4. The efficiency was pH-dependent. Higher harvesting efficiencies, up to 99%, were obtained in acidic solutions. The results show that magnetic harvesting can be significantly enhanced by PEI coating, as it increases the positive electrical charge of the nanoparticles. Most importantly, the flocculants can be prepared at room temperature, thereby reducing the production costs.

Separation of Microalgae by a Dynamic Bed of Magnetite-Containing Gel in the Application of a Magnetic Field

Microalgae are now known as potential microorganisms in the production of chemicals, fuel, and food. Since microalgae live in the sea and the river, they need to be harvested and separated and cultured for further usage. In this study, to separate microalgae, a bed of magnetite-containing gel (Mag gel, 190 µm) was packed in the column by the application of a magnetic field for the separative elution of injected microalgae (including mainly four species), cultured at Saga University in Japan. The applied magnetic field was set at a constant and dynamic-convex manner. At a constant magnetic field of 0.4–1.1 T, the elution percentage of the microalgae at less than 5 µm was 30–50%. At 1.1 T, the larger-sized microalgae were eluted at a percentage of 20%, resulting in the structural change of the bed by the applied magnetic field. In a convex-like change of the magnetic field at 1.1 T ⇄ 0.4 T, the smaller-sized microalgae were selectively eluted, whereas at 1.1 T ⇄ 0.8 T, the larger-sized microalgae were eluted. Dynamic convex-like changes by the magnetic field selectively eluted the microalgae, leading to the separation and the extraction of potential microalgae.

Performance enhancement and fouling alleviation by controlling transmembrane pressure in a vibration membrane system for algae separation

Although transmembrane pressure (TMP) has proven to be a significant factor in the separation of microalgae by the vibration membrane process, there is a lack of systematic research on this factor. This study introduced a multi-angle insight by analyzing hydrodynamic interaction acting on algae, compressibility of the cake layer, and quantitative evaluation of the membrane fouling performance to assess the relationship between TMPs and membrane fouling in the vibration membrane system. Supported by a collision-attachment model which illustrated the algae/membrane hydrodynamic interactions under different TMPs, the critical point in TMP was confirmed as at or beyond which membrane fouling became serious. Then, after analyzing the main membrane fouling indicators of polysaccharides and proteins, the results demonstrated that TMP had a greater effect on reversible fouling. Furthermore, using the theory of algae deposition, the study verified that the increase of TMP would lead to a greater compressibility of the cake layer, and the operation at the critical point could cause more serious membrane fouling. Finally, energy consumption and the technique for order preference by similarity to ideal solution combined with grey relational analysis (TOPSIS-GRA) could quantitatively evaluate membrane fouling performance, and the results showed that a lower TMP, especially below the critical point, was a good choice for sustainable control of membrane fouling. Over all, this insight into TMP elucidated the importance of employing lower TMP during the algae separation process under specific vibration conditions, providing a theoretical basis for the selection of TMP. • The collision-attachment model was applied to explore the critical point in TMP. • The analysis of membrane fouling indicators demonstrated TMP exhibited a greater effect on reversible fouling. • The theory of algae deposition was used to verify a higher TMP led to a greater compressibility of the cake layer. • Quantitative assessment methods were applied to confirm operation below a critical point was economical and effective.

Reduction of the environmental impacts of the hydropower plant by microalgae cultivation and biodiesel production

Hydropower plants supply their energy needs for electricity generation from rivers or water canals, so these power plants cannot be used for sustainable electricity generation, and the best time to use these power plants is during peak power consumption. These power plants are less polluting in terms of environment than other power plants, but they also have negative environmental effects, such as freshwater eutrophication and water salinity or microalgae. This study focused its attention on microalgae extraction as an environmentally friendly method to reduce water salinity and how they can be used for biodiesel production as an auxiliary fuel to enhance the energy production by hydropower plants. The information of the sample hydroelectric power plant (Gotvand Dam) that was required for the processing and simulation process is stated. The step-by-step simulation is reviewed and the results and optimizations are described. The highest separation of microalgae for 1 min electrolysis with distance of 1 cm between the two electrodes is 90%, which reduces the salt content of the water in which the microalgae is grown by 13%. The maximum separation of salt from water is 19.5%, which is reduced to 9.5% in the centrifuge method. Water salinity reduction to microalgae extraction ratio is 14.45%. The optimal combination of diesel and biodiesel is 80%–20%. As can be seen from the results it is recommended to use microalgae for reducing negative environmental impacts in addition to increasing the power generation capacities of hydropower plants. Also more specific studies on terms of the culture of the microalgae and its individual cultivation methods for hydropower plants beneficial programs should be taken into account and be used by policy makers in the future.

A Tool for Modelling of One- or Two-Step Microalgae Harvesting Processes

Separation of microalgae from aqueous solutions still requires further optimization and knowledge. The tool for modelling of one- or two-step microalgae harvesting technology should provide a way to predict the final concentration of microalgal suspensions. The presented spreadsheet-based tool enables to determine the mass balance of the separation process and other parameters required for the equipment basic design. These parameters are the mass flow rate of individual media, an agent consumption, and the estimation of energy consumption. The tool allows a user to combine different separation processes of various separation efficiencies. A pretreatment by coagulation or flocculation before the separation process can be also included. The applicability of this approach was demonstrated on three cases.

Separation of microalgae using a compacted magnetite-containing gel bed.

Separation of microalgae of various sizes and shapes is an important process that enables subsequent production of useful compounds. Herein, the separation of microalgae was accomplished using a magnetite-containing gel (42μm) packed into a column. An algal suspension was injected into the top of the gel bed, after which water was passed through the column. The pressure generated during the process caused the lower domain of the gel bed to deform, resulting in narrowed gaps between the gel beads. When a suspension of Nannochloropsis sp. (0.0069-0.69gL-1) was loaded and water was passed through the column at an applied pressure of 0.01-0.10MPa, the majority of microalgae were captured within the upper domain of the gel bed, while only 20% were captured within the lower domain. The amount of Nannochloropsis sp. captured was expressed by an ordinary differential equation to determine the capture coefficient, K, and the maximum capture amount, Qmax. As pressure increased, gel gaps narrowed, K increased, and Qmax decreased because of a reduction in the number of effective capture sites upon compaction of the gel. When a mixed suspension of Anabaena sp., Monoraphidium sp., and Desmodesmus sp. (0.069gL-1 each) was injected into the gel bed at an applied pressure of 0.01MPa, only Anabaena sp. was captured at the bottom of the gel bed. This device can be applied for the separation of microalgae in rivers and the sea.