Microalgal Harvesting Research Articles

Surfactant-Mediated Microalgal Flocculation: Process Efficiency and Kinetic Modelling.

Microalgae are a valuable source of lipids, proteins, and pigments, but there are challenges in large-scale production, especially in harvesting. Existing methods lack proven efficacy and cost-effectiveness. However, flocculation, an energy-efficient technique, is emerging as a promising solution. Integrating surfactants enhances microalgal harvesting and disruption simultaneously, reducing processing costs. This study investigated cetyltrimethylammonium bromide (CTAB), dodecyltrimethylammonium bromide (DTAB), and sodium dodecyl sulphate (SDS) for harvesting Tetraselmis sp. strains (75LG and 46NLG). CTAB exhibits superior results, with 88% harvesting efficiency at 1500 and 2000 mg L-1 for 75LG and 46NLG, respectively, for 60 min of sedimentation-thus being able to reduce the operating time. Beyond evaluating harvesting efficiency, our study explored the kinetics of the process; the modified Gompertz model led to the best fit. Furthermore, the largest kinetic constants were observed with CTAB, thus highlighting its efficacy in optimising the microalgal harvesting process. With the incorporation of the suggested enhancements, which should be addressed in future work, CTAB could hold the potential to optimise microalgal harvesting for cost-effective and sustainable large-scale production, eventually unlocking the commercial potential of microalgae for biodiesel production.

Environmental impact assessment via life cycle analysis on ultrafiltration membrane fabricated from polyethylene terephthalate waste to treat microalgal cultivation wastewater for reusability

The current study had conducted the life cycle analysis (LCA) to assess the environmental impact of microalgal wastewater treatment via an integrated membrane bioreactor. The functional unit selected for this analysis was 1 kg of treated microalgal wastewater with contaminants eliminated by ultrafiltration membrane fabricated from recycled polyethylene terephthalate waste. Meanwhile, the applied system boundary in this study was distinguished based on two scenarios, namely, cradle-to-gate encompassed wastewater treatment only and cradle-to-cradle which included the reutilization of treated wastewater to cultivate microalgae again. The environmental impacts and hotspots associated with the different stages of the wastewater treatment process had clearly elucidated that membrane treatment had ensued the highest impact, followed by microalgal harvesting, and finally cultivation. Among the environmental impact categories, water-related impact was found to be prominent in the following series: freshwater ecotoxicity, freshwater eutrophication and marine ecotoxicity. Notably, the key performance indicator of all environmental impact, i.e., the global warming potential was found to be very much lower at 2.94 × 10−4 kg CO2 eq as opposed to other literatures reported on the LCA of wastewater treatments using membranes. Overall, this study had proffered insights into the environmental impact of microalgal wastewater treatment and its stimulus for sustainable wastewater management. The findings of this study can be instrumental in making informed decision for optimizing microalgal wastewater treatment and reutilization assisted by membrane technology with an ultimate goal of enhancing sustainability.

A step towards more eco-friendly and efficient microalgal harvesting: Inducing flocculation in the non-naturally flocculating strain Chlorella vulgaris (13-1) without chemical additives

Flocculation is often regarded as a cost-effective and reliable method for microalgal harvesting. However, the traditional method often requires the addition of chemical agents to induce flocculation. This carries certain disadvantages including the chemical contamination of the biomass and the subsequent need to remove the flocculants from the medium. To address these issues, this study aimed to induce flocculation in a naturally non-flocculating strain (Chlorella vulgaris 13-1) without resorting to chemical additives, with the ultimate goal of increasing harvesting efficiency. Scanning electron microscopy showed that Scotelliopsis reticulata UFA-2, a naturally flocculating strain, produces extracellular polymeric substances (EPS) whereas 13-1 does not. As a result, two methods were used to induce flocculation in 13-1: co-cultivation of UFA-2 and 13-1, and insertion of EPS produced by UFA-2 into the growth medium of 13-1. The co-cultivation of 13-1 with UFA-2 significantly increased the flocculation efficiency compared to that of 13-1 alone (30 % higher flocculation efficiency after one hour of settling and 52 % higher after three hours of settling). Alternatively, the insertion of dry tightly-bound (TB) UFA-2 EPS into 13-1 cultures also improved flocculation efficiency (by 19 % compared to the control), while addition of soluble or loosely-bound (LB) EPS was less efficient (less than 1 % and 10 %, respectively). FTIR results showed that the composition of TB-EPS was different to that of LB and soluble EPS. TB-EPS contained higher proportions of proteins and different types of carbohydrates, potentially contributing to its increased efficacy in inducing flocculation in microalgae.

Fabrication and characterization of low-cost kaolin based tubular ceramic membrane for microalgal harvesting

Tubular membranes with natural kaolin as a key precursor were fabricated in this study. Membranes with five different compositions were prepared, and the optimized membrane (77% kaolin, 2% boric acid, 2% sodium metasilicate, 4% sodium carbonate, and 15% calcium carbonate) was used to harvest microalgal culture. The pore size, porosity, water permeability, chemical and mechanical strength of the membranes were investigated. An assessment of the cost related to the membrane fabrication was also conducted. The fabricated membranes had porosity of ∼26–47%, a pore diameter of 0.123–0.182 µm, water permeability of 4.2 × 10−8 – 17.1 × 10−8 m3 m−2 s−1 kPa−1, along with good mechanical and chemical strength. The optimized membrane was tested for microfiltration of microalgae Monoraphidium sp. KMC4 with 1.5 g L−1 of initial concentration at a persistent cross-flow rate (1.11 × 10−5 m3 s−1) and various transmembrane pressures (69 kPa - 345 kPa). The separation results yielded an average permeate flux of 1.85 × 10−5 m3 m−2 s−1 at 276 kPa transmembrane pressure. Complete algal cell recovery and substantial nutrient passage (>88%) were observed within the pressure range of 69 kPa to 345 kPa. Fouling mechanism was explained by fitting four distinct pore-blocking models, of which the cake filtration model provided the most accurate fit as compared to the complete, intermediate and standard pore-blocking models. Additionally, the total organic carbon varied in the range of 31.6–63.2 mg L−1. This essentially explained the source of pore blocking.

Effects of the supernatant of Chlorella vulgaris cultivated under different culture modes on lettuce (Lactuca sativa L.) growth.

CO2 capture by microalgae is a feasible strategy to reduce CO2 emissions. However, large amounts of cell-free supernatant will be produced after microalgal harvesting, which may be harmful to the environment if it is disorderly discharged. In this study, Chlorella vulgaris (C. vulgaris) was cultivated under three common cultivation modes (autotrophic culture (AC), heterotrophic culture (HC) and mixotrophic culture (MC)), and the obtained supernatant was used as fertilizer to investigate its effect on the growth of lettuce. The biomass concentration of C. vulgaris cultivated under MC and HC was 3.25 and 2.59 times that of under AC, respectively. The contents of macronutrients in supernatant obtained from AC were higher than those of MC and HC. However, the contents of amino acids and hormones in supernatant obtained from MC and HC were higher than those of AC. The fresh shoot weight, fresh root weight and root length of lettuce treated with supernatant were significantly higher than that of control treatment. In addition, the contents of chlorophyll, soluble sugar and soluble protein in lettuce treated with supernatant were also higher than that of control treatment. However, the contents of nitrate in lettuce treated with supernatant was lower than that of control treatment. These results showed that the supernatant could promote the growth of lettuce and was a potential of fertilizer for crop planting.

Microalgal harvesting for biofuels – Options and associated operational costs

Microalgae are a source of a range of natural products, including biofuels, but financial and technical limitations can make large-scale production challenging to commercialize. A significant limitation is the practical and economical bulk harvesting of microalgae from the cultivation medium. Based on chemical and energy demands, common harvesting processes can have high costs due to microalgae having a similar specific gravity as their medium, negative surface charges and significant variability between strains.Determining the cost-effectiveness of harvesting methods is complicated as many publications commonly quote harvesting as costing 20–30 % of the operational cost, regardless of the method of biomass production (e.g., open ponds, bioreactors, etc.) or the harvesting method selected. This non-specific statement does not reflect that specific harvesting methods will have different operational costs. This paper aims to provide a more accurate, method-specific cost analysis of the harvesting stage operating costs to help in the economic analysis of microalgae production systems.The four primary harvesting mechanisms currently used, centrifugation, flocculation, flotation, and filtration, are assessed for their energy and chemical consumption. Centrifugation, flocculation, flotation, and filtration had an average biomass recovery of 92 %, 95 %, 92 % and 91 % and an energy requirement range of 1–8 kWh m−3, 0.1–6.7 kWh m−3, 0.015–7.6 kWh m−3 and 0.1–5.9 kWh m−3, respectively. Furthermore, the operational costs, based on energy requirements and the use of flocculants, were 0.448–1.086 USD m−3, 0.014–16.65 USD m−3, 0.08–31.3 USD m−3 and 0.013–0.791 USD m−3, respectively. Finally, the biomass production costs were calculated as ranging between 0.02–0.177 USD kg−1, 0.006–35.05 USD kg−1, 0.169–26.95 USD kg−1 and 0.02–3.00 USD kg−1 for centrifugation, flocculation, flotation, and filtration microalgae harvesting technologies, respectively.

N-acyl homoserine lactone mediating initial adhesion of microalgal biofilm formation

While pioneering methods have demonstrated that bacterial N-acyl homoserine lactone (AHL) signaling molecules can influence the growth and self-aggregation of suspended microalgae, whether AHLs can affect the initial adhesion to a carrier has remained an open question. Here we revealed that the microalgae exhibited different adhesion potential under AHL mediation, where the performance was affiliated to both AHL types and concentrations. The result can be well explained by the interaction energy theory, where the energy barrier between the carriers and the cells varied due to AHL mediation. Depth analyses revealed that AHL acted through modifying the properties of the surface electron donor of the cells, which were dependent upon three major components, i.e., extracellular protein (PN) secretion, the PN secondary structure, and the PN amino acid composition. These findings expand the known diversity of AHLs mediation on microalgal initial adhesion and metabolisms, which may interface with other major cycles and become helpful to theoretically guide the application of AHLs in microalgal culture and harvesting.

Reclamation of Nutrient Solution from Membrane-Based Microalgal Harvesting Processes for Cultivation of Vegetables in Hydroponic Systems

This study investigates membrane-based microalgal harvesting processes for simultaneously concentrating microalgal cells and reclaiming liquid nutrients for cultivating vegetables in hydroponic systems. During both gravity-driven (with microfiltration and ultrafiltration membranes) and crossflow (with microfiltration membranes) filtration, it was found that cake layer fouling was predominant, regardless of microalgal solution properties, membrane type, and filtration condition. Although the gravity-driven membrane process offered lower operation cost, the water productivity was limited due to its lower fluxes (<1 L/m2h). During crossflow microfiltration of the microalgal solutions, increasing periodic water (50 °C) flushing frequency helped in alleviating both irreversible fouling and cake fouling development, especially with an extending filtration cycle. Under the same water productivity condition, optimal periodic water flushing (50 °C, 5 min duration per 15 min filtration) displayed more effectiveness in cake fouling control compared to periodic ultrasonication (60 s per 15 min filtration). As the collected permeate contained phosphorus and nitrogen, it was utilized as a potential cultivation solution to grow lettuce and basil in hydroponic systems. Both plants cultivated with the permeate grew slower than those with the commercial fertilizer solution, possibly associated with the lack of some essential microelements and possible uptake of certain heavy metals. The targeted hazard quotient (THQ) values of all examined heavy metals in the edible part (stem and leaves) of basil and lettuce were 0.79 and 1.58, respectively, and comparable to those with the fertilizer solution (0.81 for basil and 1.35 for lettuce). This implies that the basil cultivated with the reclaimed microalgal nutrient solution did not pose a potential adverse health effect on human consumption.

Comparison of biofloc formation from microalgal cultivation by auto- and bacteria-associated types of flocculation

Microalgal harvesting has still been a challenge to investigators who take their investiment into microalgal production. The cost for microalgal downstream processing is as high as 20% of the total production of biodiesel. Among hundreds of curent methods of biomass harvesting, autoflocculation and bacteria-based aggregation are still being researched and applied in large-scale producuion. This study implemented a comparison of how microalgal cells aggregate large bioflocs according to two types of flocculation. The microalgal autoflocculation was implemented by adding Ca2+ or Mg2+ with an increase of pH to 11, resulting in cell biomass of 13.7 or 15.5 mg/l, respectively. Meanwhile, the bioflocculation under the support of Bacillus subtilis MT300405 and Escherichia coli ATCC 85922 could produce large bioflocs with a cell biomass of 1.5 times higher than the autoflocculation case without the influence of pH. Moreover, images from scanning electron microscopy indicated differences between two types of flocculation. With the presence of bacteria, microalgal cells were more tightly bound by a membrane or a layer of extracellular polimeric substance, inducing to form large bioflocs. This was not found under autoflocculation.

Enhanced growth and auto-flocculation of Scenedesmus quadricauda in anaerobic digestate using high light intensity and nanosilica: A biomineralization-inspired strategy

Coupling municipal anaerobic digestate (MAD) treatments with microalgal cultivation can concomitantly achieve nutrient removal and microalgal bioenergy production. However, the high cost caused by dilution water and microalgal harvesting is a great challenge. In this study, Scenedesmus quadricauda was screened as the most appropriate algae strain due to its potential for growth and auto-flocculation, and the MAD diluted 5-fold with WWTP effluent was demonstrated as an ideal medium for S. quadricauda growth. Moreover, inspired by naturally generated silica shells of diatoms, a low-cost and biomimetic auto-flocculation strategy that combined high light intensity induction and microalgal silicification was proposed to accelerate the auto-flocculation process. Compared with low light intensity groups, this strategy imparted diatom-like features to S. quadricauda cells, and contributed to 3.07-fold higher auto-flocculation efficiency within 30 min. It was attributed to the fact that the high light intensity of 150 μmol·m − 2·s − 1 stimulated the extracellular polymeric substances (EPS) secretion and induced the variation in property and composition of EPS, especially the protein secondary structures, which allowed silica nanoparticles to spontaneously attach onto S. quadricauda cells in the presence of viscous EPS. Furthermore, this strategy significantly increased microalgal biomass yield to a dry weight of 1.37 g·L − 1, accompanied by 93.78%, 96.39% and 91.36% removals of NH4+-N, TP, and COD, respectively. The productivity of valuable by-products, including lipid, carbohydrate, protein, and pigment, reached 56.30, 101.35, 30.39 and 11.28 mg·L − 1·d − 1, respectively. Overall, this study supplies a novel approach for low-cost microalgal bioenergy production from MAD and energy-efficient microalgae harvest by auto-flocculation.

Sustainable Microalgal Harvesting Process Applying Opuntia cochenillifera: Process Parameters Optimization

Microalgae harvesting by coagulation can use coagulant agents such as alum, synthetic polymers or biocoagulants. Biocoagulants have attracted the attention of researchers because they are natural, biodegradable, and promote high microalgal harvesting efficiencies. This study aims to optimize the harvesting of Chlorella vulgaris based on the dosage of the Opuntia cochenillifera extract and the choice of eluent for biopolymer extraction. The outdoor cultivation of C. vulgaris achieved a specific growth rate of 0.455 d−1 and a maximum biomass concentration of 1.28 gDW L−1. In order to harvest the microalgal biomass, the polymer present in the mucilage of O. cochenillifera was extracted using NaOH and HCl. Coagulation and sedimentation assays were performed with different coagulant dosages: 3.5, 5.9, and 8.2 g L−1. The maximum harvesting efficiencies using the acid and alkaline extract coagulant solutions were 80.8% and 99.5%, respectively, with a dosage of 3.5 g L−1. According to the results, the C. vulgaris biomass can be harvested with the mucilage from O. cochenillifera in acid and alkaline eluents. The application of this biocoagulant constitutes a sustainable solution for microalgal harvesting.

Approach to microalgal biodiesel production: Insight review on recent advancements and future outlook

AbstractThe environmental concerns about fossil energy and rising oil prices are regular global phenomena. In such an exigency where fossil fuel sources are dwindling, carbon‐neutral biodiesel derived from microalgae lipid seems to be an important renewable energy resource. In recent years, microalgae have become a lucrative feedstock for economically viability of commercial‐scale biofuel production owing to its high biomass growth and high oil yield compared with other crops. The screening and selection of promising microalgae strain should be based on their fatty acid profile and culture conditions. The laboratory to pilot scale culture of microalgae species requires systematic experimental designs to maximize microalgal growth using open or raceway ponds, closed photo bioreactors and hybrid systems. The pros and cons of each harvesting technique, including filtration, centrifugation, sedimentation and flocculation as well cell disruption by thermal, mechanical, chemical and biological techniques, are deliberated in details. Furthermore, the application of homogeneous, heterogeneous and enzyme catalysts in transesterification processes as well as purification technologies are emphasized to ensure high‐quality biodiesel production as per ASTM norms. Microalgae comprise a potential feedstock and biodiesel synthesis from them requires a series of complex up‐streaming and down‐stream processes which are inherently disadvantageous in technology transfer from laboratory to industrial scale. This review paper is mainly focused on microalgal cultivation, harvesting, oil extraction, biodiesel production and purification technologies, and each vital process is critically reviewed in each step. © 2022 Society of Chemical Industry and John Wiley &amp; Sons, Ltd.

Drop-in biofuels production from microalgae to hydrocarbons: Microalgal cultivation and harvesting, conversion pathways, economics and prospects for aviation

In the last few years, governments all around the world have agreed upon migrating towards carbon-neutral economies as a strategy for restraining the effects of climate change. A major obstacle limiting this achievement is greenhouse gases emissions, for which the aviation sector is a key contributor because of its dependence on fossil fuels. As an alternative, biofuels with similar characteristics to current fossil-fuels and fully compatible with the existing petroleum infrastructure (i.e., drop-in biofuels) are being developed. In this regard, microalgae are a promising feedstock thanks to, among other aspects, their potential for lipid accumulation. This review outlines the development status, opportunities, and challenges of different technologies that are capable of or applicable to transform microalgae into aviation fuels. To this effect, a baseline of the existing jet fuels and the requirements for potential aviation biofuels is initially presented. Then, microalgae production and valorization techniques are discussed with an emphasis on the thermochemical pathways. Finally, an assessment of the present techno-economic feasibility of microalgae-derived aviation fuels is discussed, along with the authors’ point of view on the suitability of these techniques. Further developments are needed to reduce the costs of cultivation and harvesting of microalgae, and a biorefinery approach might improve the economics of the overall process. In addition, while each of the conversion routes described has its advantages and drawbacks, they converge upon the need of optimizing the deoxygenation techniques and the proportion of the suitable type of hydrocarbons that match fuel requirements.

Integrated electrocoagulation-flotation of microalgae to produce Mg-laden microalgal biochar for seeding struvite crystallization

Developing sustainable materials for recovering and recycling nutrients from wastewater is critically needed for nutrients such as phosphorus that have a diminishing supply. Struvite crystallization is emerging as a promising strategy for phosphorus recovery which can be enhanced with seeding through microalgal biochar. The main bottleneck of using microalgae is its high harvesting cost. In this study, an integrated electrocoagulation-flotation (ECF) process is used to recover and at the same time modify the algal surface with magnesium anode and inert carbon cathode. Harvesting efficiency of 98% was achieved with 40.78 mA cm−2, 0.5 cm inter-electrode distance and energy consumption of 4.03 kWh kg−1 in 15 min. The harvested microalgae were pyrolyzed to obtain a yield of 52.90% Mg-laden microalgal biochar. Simultaneously, surface impregnation of 28% magnesium was attained as confirmed by Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Phosphorus recovery and struvite yield of 93.70% and 2.66 g L−1, respectively, were obtained from dosing 1.50 g L−1 Mg-laden microalgal biochar. Comparison of physicochemical characteristics of residual supernatant after microalgal harvesting and struvite recovery showed that the combined use of both the residuals can serve as a sustainable growth medium for microalgae. The overall operating cost of the integrated process was found to be 2.48 USD kg−1 with a total energy consumption of 10.76 kWh kg−1, which was found to be lower than conventional harvesting unit processes such as centrifugation and filtration. This novel approach can help attaining a circular bioeconomy by encompassing nutrient recovery and waste management in an integrated process.

Self-assembly of Fe3O4 with natural tannin as composites for microalgal harvesting

Anisotropic structures and size control are attracting extensive attention owing to the effect on magnetic behavior and microalgal harvesting performance. Herein, a natural polymeric tannin was chosen as the shaping ligand to control the self-assembly of tannin-coated Fe3O4 (Fe3O4@tannin) for microalgal magnetic harvesting. Compared to naked Fe3O4, the Fe3O4@tannin presented a smaller hydrodynamic diameter of 287 nm, a larger magnetic saturation of 45.16 emu g−1, and a higher uptake capacity of 589.99 mg biomass per g of Fe3O4@tannin. Kinetic experimental data revealed that the magnetic harvesting followed a pseudo-second-order isotherm and the adsorption isotherm fitted the non-linear Freundlich model. The Fe3O4@tannin showed a good recycling potential with only a 7% decrease in harvesting efficiency after 5 cycles. The modified Deryaguin–Landau–Verwey–Overbeek (DLVO) interaction energies among the particles were used to evaluate the algal aggregation mechanism. Furthermore, the results indicated that the magnetic force contributed to the total interaction energies across a wide range of interaction distances. In situ microscopic observation also confirmed the formation of Fe3O4@tannin-to-algae aggregates, which further combined to form chain clusters and collided with free algal cells in the magnetophoretic process.

Harvesting of Microcystis flos-aquae using dissolved air flotation: The inhibitory effect of carboxyl groups in uronic acid-containing carbohydrates

Harvesting algal biomass reduces nutrient loading in eutrophicated lakes and the protein-rich microalgal biomass could be recycled as feedstocks of feed and fertilizer. Due to the complexity of algogenic organic matter (AOM), the key components and functional groups in AOM that inhibit coagulation-based microalgal harvesting have not been disclosed thus far. This study quantitatively analysed the responsive compositions and functional groups of AOM involved in the dissolved air flotation (DAF) harvesting of M. flos-aquae with 1 × 109 cell L−1 density at coagulation pH 6.2. The results showed that harvesting efficiency dropped drastically from 95.5 ± 0.7% to 43 ± 0.7% in the presence of AOM (26.77 mg L−1) at the coagulant dosage of 0.75 mg L−1 and further deteriorated with increasing AOM concentration. Carbohydrates contributed 81% of the total composition of substances involved in the DAF, while the contribution of protein and humic-like substances were only 18% and 1%, respectively. Stoichiometric analysis of functional groups in carbohydrates, proteins, and humic-like substances using model components revealed that carboxyl groups in uronic acid-containing carbohydrates accounted for 76% of the total reduction in carboxyl groups, which was much higher than that in proteins (23%) and humic-like substances (1%), indicating that carboxyl groups in uronic acids containing carbohydrates were the major inhibitors. A conceptual model of charge competition was proposed to explain the inhibition mechanism of carboxyl functional groups in uronic acid-containing carbohydrates on microalgal DAF. Strategies such as preventing carboxyl deprotonation by pH reduction and employment of sweeping/bridging polymeric coagulants/flocculants were proposed for the to reduce the inhibitory effect of carboxyl functional groups.

Sustainable microalgal biomass valorization to bioenergy: Key challenges and future perspectives

The global trend is shifting toward circular economy systems. It is a sustainable environmental approach that sustains economic growth from the use of resources while minimizing environmental impacts. The multiple industrial use of microalgal biomass has received great attention due to its high content of essential nutrients and elements. Nevertheless, low biomass productivity, unbalanced carbon to nitrogen (C/N) ratio, resistant cellular constituents, and the high cost of microalgal harvesting represent the major obstacles for valorization of algal biomass. In recent years, microalgae biomass has been a candidate as a potential feedstock for different bioenergy generation processes with simultaneous treating wastewater and CO2 capture. An overview of the appealing features and needed advancements is urgently essential for microalgae-derived bioenergy generation. The present review provides a timely outlook and evaluation of biomethane production from microalgal biomass and related challenges. Moreover, the biogas recovery potential from microalgal biomass through different pretreatments and synergistic anaerobic co-digestion (AcoD) with other biowastes are evaluated. In addition, the removal of micropollutants and heavy metals by microalgal cells via adsorption and bioaccumulation in their biomass is discussed. Herein, a comprehensive review is presented about a successive high-throughput for anaerobic digestion (AD) of the microalgal biomass in order to achieve for sustainable energy source. Lastly, the valorization of the digestate from AD of microalgae for agricultural reuse is highlighted.

Effects of extracellular organic matter on chitosan coagulation-microfiltration harvesting of Microcystis flos-aquae

Extracellular organic matter (EOM) is considered an important cause of membrane fouling when harvesting Microcystis cells using filtration technology. Coagulation pre-treatment has increasingly been applied as an effective method to alleviate membrane fouling. However, the effects and mechanisms of EOM on coagulation-microfiltration of Microcystis cells remain unclear. This study investigated the coagulation-microfiltration performance of EOM-free and EOM-containing Microcystis flos-aquae and explored the effect mechanisms of EOM from the perspective of floc characteristics and deposited algal cake structure. The results showed that the presence of EOM decreased the average flux from 4256.4 L/(m2·h) to 3378.4 L/(m2·h) at the optimal chitosan dosage of 15.11 mg/g. Electrostatic adsorption and/or bridging between carboxyl and amino/hydroxyl groups in EOM and chitosan resulted in a loose floc structure and high compressibility of the cake layer, thus reducing the filtration performance. In addition, interception of EOM in the cake layer contributed to membrane fouling during coagulation-microfiltration. These results revealed the mechanism by which EOM hinders coagulation-filtration performance, which would be helpful for the development of efficient coagulation-filtration-based microalgal harvesting techniques.

Optimization of Chlorella Culture Conditions with Response Surface Methodology to Increase Biomass

Microalgae is gaining popularity as a major ingredient in nutrition supplements. To mass cultivate, it is imperative to improve the biomass yield hence optimization of cultures conditions becomes paramount. In this work, an attempt has been made to optimize the microalgal production using response surface methodology (RSM) and validate further the optimized parameters. The optimum conditions for the cultivation of Chlorella sp. KPU016 under optimized nutrient conditions were pH 8.2, the light intensity of 3100 lx, glycerol 1.44 g.L-1 (under pre-set conditions of 12 h lighting, the temperature at 27±1°C. With these RSM-driven optimum conditions, the yield of microalgal biomass achieved was 282.50 mg.L-1. For larger-scale microalgal harvesting, the validated optimal conditions can be inferred as the best for enhanced microalgal production. The isolate was partially sequenced and submitted to the NCBI database and the GenBank accession number is MZ348364.

Bioflocculation of Euglena gracilis via direct application of fungal filaments: a rapid harvesting method

The high cost and environmental impact of traditional microalgal harvesting methods limit commercialization of microalgal biomass. Fungal bioflocculation of microalgae is a promising low-cost, eco-friendly method but the range of fungal and microalgal species tested to date is narrow. Here, eight non-pathogenic, filamentous fungi were screened for their ability to self-pelletize and flocculate Euglena gracilis (ca.50 µm motile microalga) in suspension. Self-pelletization was tested under various rotational speeds, and species which formed pellets (Ø > 0.5 cm) were selected for harvesting tests. Filaments of each species were combined with E. gracilis at various ratios based on dry weight. Harvesting efficiency was determined by measuring the change in cell counts over time, and settling of the flocs was evaluated by batch settling tests. Three fungal species, Ganoderma lucidum, Pleurotus ostreatus, and Penicillium restrictum, were able to reliably flocculate and harvest 62–75% of the microalgae while leaving it unharmed. The results demonstrated that self-pelletization, harvesting, and settling were dependent on the fungal species. The fungi to algae ratio also had significant but contrasting effects on harvesting and settling. In balancing the needs to both harvest and settle the biomass, the optimal fungi to algae ratio was 1:2. The application of fungal filaments to microalgae in suspension produced readily settling flocs and was less time-consuming than other commonly used methods. This method is especially attractive for harvesting microalgal biomass for low-value products where speed, low cost, and cell integrity is vital.