Algae Harvesting Research Articles

TRENDS AND PERFORMANCES OF THE ALGAL BIOFUEL: A BIBLIOMETRIC APPROACH

The paper systematically presents a survey of the literature on algal biofuel by a bibliometric assessment. Based on 10,201 articles extracted from the Science Citation Index Expanded database during 1980–2019, a knowledge-generating system about algal biofuel has been established through analysis of publication performance, social networks, citations analysis and keywords analysis. Annual publication output in algal biofuel research has rapidly increased, particularly over the past decade. “Bioresource Technology” is the most outstanding journal when all analysis indices have been taken into account. The USA ranks 1st with 2,151 publications and has a high supremacy in international research collaborations. Through the analysis of keywords, the research trends of algae biofuel in algae selection, cultivation, harvesting, extraction, conversion and bioproducts are reviewed. The future of algal biofuel is quite promising, however, for its commercial production, several technical challenges like large-scale algal biomass production, cheap harvesting technology, etc. have to be met a-priori.

Robotic algae harvester: A novel method for efficient algae collection

Algae are potential renewable energy source that provides numerous types of biofuels. Traditional methods of algae harvesting involve high electrical energy in the range of 200–5000 watt-hour for collecting per kilogram of algae. Moreover the added chemicals during the harvesting process degrade the algae quality leading to inferior biomass feedstock. Based on a comparative analysis of the various algae harvesting methods, this paper introduce a novel robotic algae harvesting system. The focus was on algae harvesting with less energy consumption and without the use of chemical flocculants. Design dimensions and size of the robotic algae harvesting system were determined based on the size of the raceway pond where algae was harvested without any operational trouble. Two algae collection units were designed using plankton nets of 5 µm which facilitate in the collection of the algae. With torque analysis on the system design, the electrical actuators and power source for the harvester was resolved. A wireless switch control system was designed for controlling the harvester’s locomotion while collecting the algae from the raceway pond. The developed system was tested in a raceway pond where it successfully collected a total of 565.67 g algae in 200 test runs in 1 h and 6 min. The estimated total electrical energy consumed by the robotic algae harvesting system to collect per kilogram of algae was 110.5 watt-hour.

A Review on the Reliability and the Readiness Level of Microalgae-Based Nutrient Recovery Technologies for Secondary Treated Effluent in Municipal Wastewater Treatment Plants

Algae-based wastewater treatment technologies are promising green technologies with huge economical potential and environmental co-benefits. However, despite the immense research, work, and achievement, no publications were found wherein these technologies have been successfully applied in an operational environment for nitrogen and phosphorus removal of secondary treated effluent in municipal wastewater treatment plants. Based on a literature review and targeted comprehensive analysis, the paper seeks to identify the main reasons for this. The reliability (considering inlet wastewater quality variations, operating conditions and process control, algae harvesting method, and produced biomass) as well as the technology readiness level for five types of reactors are discussed. The review shows that the reactors with a higher level of control over the technological parameters are more reliable but algal post-treatment harvesting and additional costs are barriers for their deployment. The least reliable systems continue to be attractive for research due to the non-complex operation and relieved expenditure costs. The rotating biofilm systems are currently undertaking serious development due to their promising features. Among the remaining research gaps and challenges for all the reactor types are the identification of the optimal algal strains, establishment of technological parameters, overcoming seasonal variations in the effluent’s quality, and biomass harvesting.

Application of filamentous fungi in microalgae-based wastewater remediation for biomass harvesting and utilization: From mechanisms to practical application

The model of microalgae-based wastewater remediation for nutrient recovery and biomass production has been intensively studied, but high cost of biomass harvesting jeopardizes the industrial application of this model. To support the implementation of this model and the sustainable development, this work introduces the use of filamentous fungi in microalgae-based wastewater remediation for biomass harvesting and utilization. First, this work describes the research progresses of co-cultivation of fungi and microalgae and fungi-assisted algae harvesting. Second, mechanisms and key parameters of fungi-assisted microalgae harvesting are discussed. Third, an in-depth discussion of co-cultivating filamentous fungi and microalgae in wastewater for nutrient removal and biomass collection is provided. Fourth, this work introduces some high-value components, which are of importance to the economic benefits and industrial application of harvested algal-fungal biomass, in microalgae and filamentous fungi. By the end of this paper, some problems associated with the co-cultivation of algal-fungal consortia in wastewater and fungi-assisted microalgae harvesting are listed and potential solutions to these problems are proposed. It is expected that this work can help readers understand the achievements in the research of fungi-assisted microalgae and the importance of this novel model to biomass harvesting and utilization.

Application of 1.0-μm macroporous hollow fiber membrane for prevention of membrane fouling and enhancement of permeate flux in algae harvesting

We challenged to introduce macroporous membrane for algae harvesting with a permeate flux of 166 L m−2 d−1 to achieve significant reduction of harvesting cost. Analysis of the dissolved organic matter in the supernatant of cultures of the green alga, Coccomyxa sp. strain Obi, detected a scarce amount of hydrophilic macromolecules, which can be membrane fouling agents. The continuous filtration with a macroporous membrane achieved a 30-fold concentration of algal cells from 800 mg biomass/L to 24,000 mg biomass/L with a harvesting efficiency of 100%. Most of previous studies on the membrane filtration for harvesting microalgae merely utilized microfiltration membranes developed for wastewater treatment. However, the use of a membrane of the largest pore size that microalgal cells cannot seep through will result in slower fouling, higher flux, and a great reduction of harvesting cost.

Encapsulation of Chlamydomonas reinhardtii into a metal-phenolic network

Single-cell encapsulation using metal-phenolic networks (MPNs) is an emerging technique to protect cells from stressors. Until now, the MPN coatings have been only applied to some bacteria, yeast, and mammalian cells. To further demonstrate their versatility, we herein coat Chlamydomonas reinhardtii with the network consisting of tannic acid and iron(III). The encapsulation served as a mechanical barrier, which delayed proliferation of the coated cells. Furthermore, we investigated the adsorption of tannic acid onto the surface of C. reinhardtii and identified the optimum concentration to achieve partial coverage on the algae's surface. Finally, we explored the effect of MPN coating for flocculation-enhanced algae harvesting. Overall, the results demonstrate that the cell encapsulation technique using metal-phenolic networks is applicable to the C. reinhardtii, which is promising for the surface engineering of the green algae for energy harvesting and biomedical applications.

Effects of different pore sizes on membrane fouling and their performance in algae harvesting

Membrane fouling caused by the deposition of algae cells and extracellular organic matter (EOM) is a major challenge for algae filtration. To find a suitable membrane pore size for microalgae harvesting, membranes with different pore sizes (0.03, 0.05 and 0.1 μm) were utilized in algae filtration in this study. The 0.1-μm membrane had the highest reversible fouling and the lowest irreversible fouling, in comparison with 0.03- and 0.05-μm membranes; thus, the 0.1-μm membrane was more suitable for algae harvesting than the 0.03-μm and 0.05-μm membranes. The molecular weight distribution of reversible EOM was primarily under 1 kDa whether irreversible EOM was over 100 kDa. Moreover, the larger the pore size, the more likely it was fouled by low molecular weight organics, regardless of reversible fouling or irreversible fouling. Fluorescence excitation-emission matrix spectra analysis showed that for protein-like and humic/fulvic acid-like substances, protein-like substances were more likely to cause reversible fouling while fulvic acid-like substances were more apt to cause irreversible fouling. The 0.1-μm membrane had better repulsion to fulvic acid-like substances than the 0.03- and 0.05-μm membranes, leading to less irreversible fouling. The results obtained from this study have many microalgae applications. For example, employing membrane technology in microalgae harvesting can help treat rivers and promote ecological restoration. In addition, applying this technique in sewage treatment plants will not only lead to wastewater treatment, but it will also acquire biomass resources.

Integration of Algal Biofuel Production with Municipal Wastewater Treatment: a Review

The integration of algae-based wastewater treatment and biofuel production has been of growing research interest in recent years. This article reviewed recent researches in algae biofuel production and the integration of algal wastewater treatment and biofuel production. The methods to algal biofuel production, biofuel productivity, and removal rate of treated municipal wastewater were summarized in this review. Chlorella is largely used, especially in biodiesel and bioethanol production. Spirulina is more often used to produce biogas. The removal rate of NH4+-N can be high in this integration. The most common biofuel products in this integration are biomethane and lipid. Traces of the integration are numerous on laboratory basis and limited in commercial use for now. The barrier to apply it from lab to commercial use may include a high cost during algae harvesting as well as land use and availability. Possible solutions and research gaps are outlined in this article.

Metal residues in macroalgae feedstock and implications for microbial fermentation

Macroalgae cultivation shows potential for the application as emerging feedstock for microbial fermentation to produce biochemicals. However, metal residues in macroalgae might affect the fermentation capacity of relevant microorganisms. This aspect is currently not considered when selecting macroalgae and microorganism species for microbial fermentation. To consider this aspect for selecting viable macroalgae and microorganism species, we link metal exposure in bioreactors from macroalgae residues to ecotoxicological test results for relevant microorganisms. Our results indicate that estimated bioreactor concentrations for most metals are below microorganism effect levels. For copper and hexavalent chromium, however, reactor concentrations might exceed relevant effect levels for at least some considered microorganism species. Adjusting water hardness in the bioreactor as well as selecting algae harvest location and macroalgae species might minimize metal exposure to fermenting microorganisms, in support of optimizing the biorefining process for biochemical production.

Water toxicity in reservoirs after freshwater algae harvest

Blooms of microalgae and cyanobacteria increase every year, presenting great problems for the environment. Finding a way of harvesting these microalgae could be useful for water governance. Furthermore, the method should not cause cell lysis and should thus avoiding discharging toxins into the water. Three reservoirs were studied, two of them with eutrophication problems (As Conchas and A Baxe) and another (Salas) with no such problems. Three different harvesting methods were studied; electroflocculation (EF) with the application time being varied; centrifugation, with application times and speeds being varied; and finally, natural sedimentation. The highest efficiency was obtained in the culture from A Baxe, which had a higher initial absorbance value (1.664), using EF (90.64% for an application time of 2 min and 30 s) and centrifugation at 4000 rpm (92.25% for2 minutes, 92.73% for 5 min). Electrofloculation can obtain up to 84% more biomass than natural sedimentation alone. Sample toxicity was studied before and after harvesting using Microcystest and found to be higher after harvesting. It was observed that for the same sample, the higher the yield was the greater the toxicity was. For the A Baxe culture with an application time of 2 min, a speed of 2000 rpm and a yield of 87.02%, a toxicity figure of 0.94 μg/L was obtained, while for a speed of 4000 rpm the yield was 92.25% and the toxicity was 1.05 μg/L. The toxicity limit set by the World Health Organization (WHO) is 1 μg/L, and this small difference seems to be key. With these results, this study concludes that chlorophyll levels may interfere with the test used. Future tests or analyses should be developed so as to avoid such interference, which may alter the toxin values. Electroflocculation seems to be a promising method since it does not cause the lysis of Microcystis aeruginosa, whereas the centrifugation method could give problems. Finally, it is worth highlighting the importance of performing toxin measurements after harvesting the microalgae to check that the method is viable in natural ecosystems.

Industrial prospective of bio-fuel production from Algae harvesting: A Review

Commercializing of algal bio-fuel is the major challenge due to proficient harvesting in current scenario. Several species of the algae contain a high concentration of lipids and necessitate simple cultivation methods than usual crops for the conversion of bio-fuels. Algae have the capability to make many biofuels such as bioethanol, biodiesel, bio-hydrogen, etc. Algae bio mass have potential in terms of ‘energy’, but there is challenge in having a feasible balanced energy in algae bio-fuel development operations. Extra challenges of algal harvesting appear from the minute structure of algal cell, comparison of density in the algal cells to the augmentation medium, the pessimistic surface indict on the algal and micro-algae enlargement process which necessitate numerous harvesting compared to the earthbound plants. Centrifugation sedimentation, flotation, filtration and flocculation or a blend of these are main methods of algal harvesting. This paper reviews different methods of harvesting of algae & potential growth of algal biofuel.

Bioinspired synthesis of zinc oxide nano-flowers: A surface enhanced antibacterial and harvesting efficiency

Despite of broad range application, the cost effective, highly stable and reproduceable synthesis of ZnO is needed, especially which can make it biosafe as well. Here, a unique bioinspired synthesis of ZnO nanoflowers (NFs) has been introduced using Withania coagulans extract as reducing agent. Different molar concentrations were assessed to counter the effect of structural, morphological, antibacterial activity and high efficiency of algae harvesting. The UV-spectroscopy authenticates the synthesis of ZnO NFs having Wurtzite hexagonal structure with the size in the range of 360–550 nm. While surface analysis revealed the presence of stabilizing agent like phenolic, amine, etc. on surface of ZnO NFs. These perineum ZnO NFs exhibited a stronger antibacterial with Gram-positive bacteria Staphylococcus aureus as compare to Gram-negative bacteria Pseudomonas aeruginosa and greater harvesting efficiency up to 94% on the account of greater surface area and unique surface chemistry, thus leading a new horizon of more efficient and effective applications for ethanol production.

An Innovative Low-Cost Equipment for Electro-Concentration of Microalgal Biomass

Microalgal harvesting is one of the most challenging processes in the development of algal research and development. Several methods, such as centrifugation, flocculation and filtration, are available at the laboratory scale. However, the requirement for expensive pieces of equipment and the possibility of biomass contamination are recurring gaps that hinder the development of microalgae R&D (research and development) in different parts of the world. Recently, electroflotation has been proved to be a suitable method for the harvesting of different species of microalgae and cyanobacteria. To this day, there are no companies that sell laboratory-scale electroflotation equipment; this is mainly due to the gap in the knowledge of which factors (time, mixing rate, number of electrodes and others) will affect the efficiency of concentration without reducing the biomass quality. This paper aims to build an innovative, low-cost electroflotation system for under 300 USD (United States dollar) with cheap and resistant materials. To achieve our goal, we tested the interaction of three variables (time, mixing rate and amount of electrodes). Results showed that an efficiency closer to 100% could be achieved in under 20 min using > 10 electrodes and 150 rpm (round per minute). We hope this innovative approach can be used by different researchers to improve our knowledge of the concentration and harvesting of algae and cyanobacteria.

Sustainable Cost-Effective Microalgae Harvesting Strategies for the Production of Biofuel and Oleochemicals

Microalgae have been explored for sustainable production of biofuel and chemicals. Microalgae is promising feed stock for the production of several oleochemicals. It has the ability to utilize a variety of low cost feed stocks, accumulated large quantities of lipids and variety of value added products in their biomass. One of the major obstacles associated with the conversion of algae into value-added products is harvesting. The harvesting of algae is the most problematic area due to its low sedimentation rate, low biomass concentration, and high capital costs. Harvesting of algae is carried out by different physical, chemical, mechanical, biological, and electrolytic methods such as sedimentation, centrifugation, microstraining, dissolved air flotation, electrolytic flotation, chemical flocculation, bioflocculation, autoflocculation, Filtration. This review highlights the various methods of microalgae harvesting with advantages and future perspective of sustainable and cost-effective harvesting of microalgae.

Coagulant derived from waste biogenic material for sustainable algae biomass harvesting

Highly efficient and sustainable algae harvesting that produced biomass with enhanced characteristics and reusable culture medium were developed from the use of coagulant derived from the waste shell of Gastropod. Thermally treated Gastropod shell samples were screened for the algal cell harvesting efficiency (%) and the underlying mechanism was elucidated from the hydrodynamic equilibrium data and scanning electron microscopic analysis. The floc strength, settling rate parameters, settleability, and filterability were determined and compared with the flocs obtained from the pH induced autocoagulation system. The values of floc settling rate and the sludge volume index (mL/g) showed that the flocs obtained from the Gastropod shell system (rate constant = 1.945 L·mol−1·s−1) settled faster and more compacted than those from the pH induced system (rate constant = 0.2155 (L·mol−1·s−1). Both the growing and harvested flocs from the Gastropod shell system had better strength and breakage factors (>90%) than the pH induced system. The proximate and elemental compositions of the biomass from the Gastropod shell system were comparable with those from centrifugation and pH induced systems. Both the separated culture medium and the harvested algae biomass were successfully reused, in separate systems, to cultivate fresh algae. This indicated the non-toxic effects of the coagulants on both the culture medium and the algae harvested biomass.

Global dynamics of a cell quota-based model of light-dependent algae growth in a chemostat

A chemostat is a widely used laboratory and industrial scale equipment for continuous culture of microalgae and other microorganisms under controlled conditions. Being a photosynthetic organism, light and other nutrients are growth limiting for all microalgal species, and thus optimization of external conditions is necessary to maximize algae harvest at a commercial scale. In this study, we mechanistically formulate a cell quota-based, light-dependent model of algae growth in a chemostat and study various mathematical properties of the model, in addition to exploration of the parameter space for obtaining guidelines on biomass growth optimization.

Assessing Domestic Wastewater Effluent with a Battery of Bioassays after Treatment with a Specific Consortium of Microalgae and Different Flocculation Methods

Wastewater stabilization ponds (WSP) are a common method to treat wastewater before release. The purpose of the current study was to find the most inexpensive coagulation and flocculation reagents to use during harvesting of WSP algae from effluent so that water without algae can be generated for irrigation purposes. In the study, the toxicity of effluent from the algae-based WSP system after treatment with alum and chitosan was investigated. The chemical composition of the resultant supernatants was tested in conjunction with a battery of bioassays (Daphnia magna, Allium cepa, Lactuca sativa and Triticum aestivum). The bioindicator organisms were exposed to varying concentrations of the supernatant resulting from harvesting the algae biomass with chitosan (0.368 g/L chitosan) and aluminium sulphate (9.96 g/L powder). Alum was lethal to D. magna, while chitosan did not seem to affect the Daphnia test specimens. Undiluted chitosan supernatant and 100% alum resulted in minimal inhibition of the rate of T. aestivum seed germination, while both resulted in significant inhibition of the L. sativa seed germination rates. Similarly, minimal effects were found for the root growth in T. aestivum, with significant root growth inhibition observed in L. sativa and A. cepa. In A. cepa, clear differences were observed in the inhibition of root growth when the two reagents were compared. The alum and chitosan supernatants had a total carbon, iron and sulphate concentration of 327.78 mg/L, 0.12 mg/L and 68.44 mg/L and 182.04 mg/L, 0.16 mg/L and 166.80 mg/L, respectively. Based on the test specimens’ response, chitosan as flocculation method was less toxic when compared with alum coagulation, even though both algae harvesting methods changed the chemical composition of the algae-treated water.

Evaluation of Microbial Load, Formation of Odorous Metabolites and Lipid Stability during Wet Preservation of Nannochloropsis gaditana Concentrates

Wet preservation of algae allows us to bridge the time period between algae harvest and processing while avoiding the costs and nutritional losses associated with algae drying. This study aimed to identify suitable storage conditions for the wet preservation of Nannochloropsis gaditana concentrates. The impact of storage temperature, time and the way of closing the storage recipient was evaluated using a full factorial design. The effect of acetic acid addition was tested for one storage condition. Storage temperature was the main factor determining the microbial count and had a vast impact on the formation of odorous metabolites. Storage at 20 °C in closed recipients led to rapid O2 consumption, accumulation of malodorous short-chain fatty acids above their odor thresholds, and the production of H2S and methanethiol. These odorous metabolites were not formed or to a much lower extent during 4 °C and 8 °C storage in closed recipients. Acetic acid supplementation (50 mM) suppressed the formation of short-chain fatty acids during 8 °C storage in unsealed recipients and reduced the aerobic microbial count and the number of yeasts and molds by approximately one log unit after 14 days. Yet, acetic acid addition also induced lipid hydrolysis and decreased chlorophyll levels when algae were stored for more than one week. This study demonstrated that temperature control is needed and that acetic acid addition is a promising approach when N. gaditana concentrates are stored for less than one week.

Algal cells harvesting using cost-effective magnetic nano-particles

Innovative iron-based nanoparticles were synthesized, characterized and tested for the first time for harvesting single and mixed algal culture from real wastewater. The tailor-made magnetic nanoparticles (MNPs; Fe-MNP-I and Fe-MNP-II) achieved a percentage algae harvesting efficiency (%AHE) higher than 95% using a concentration of MNPs (CMNP) of 25 ± 0.3 (std. dev = 0.08) mg.L−1, mixing speed (Mspeed) of 120 ± 2 (std. dev = 0.10) rpm, short contact time (Ct) of 7 ± 0.1 (std. dev = 0.05) min and separation time (SPt) of 3 ± 0.1 (std. dev = 0.09) min. The optimum operational conditions for harvesting of Chlorella vulgaris (C.v) were determined at (CMNP = 40 ± 0.4 (std. dev = 0.5) gMNPs.L−1, SPt = 2.5 ± 0.4 (std. dev = 0.1) min, Mspeed = 145 ± 3 (std. dev = 1.50) rpm and Ct = 5 ± 0.3 (std. dev = 0.10) min using surface response methodology. Langmuir model describes better the adsorption behavior of algae-Fe-MNP-I system, while both Langmuir and Freundlich fit well the adsorption behavior of algae-Fe-MNP-II. The maximum adsorption capacity of Spirulina platensis (SP.PL) (18.27 ± 0.07 (std. dev = 0.19) mgDWC.mgparticles−1) was higher than that for Chlorella vulgaris (C.v) (11.52 ± 0.01 (std. dev = 0.34) mgDWC.mgparticles−1) and mixed algal culture (M.X) (17.20 ± 0.07 (std. dev = 0.54) mgDWC.mgparticles−1) over Fe-MNP-I. Zeta potential measurements revealed that the adsorption mechanism between MNPs and algal strains is controlled by electrostatic interaction. The synthesized MNPs were recycled 10 times using alkaline-ultrasonic regeneration procedure.

Improved Nylon 6,6 Nanofiber Membrane in A Tilted Panel Filtration System for Fouling Control in Microalgae Harvesting.

The competitiveness of algae as biofuel feedstock leads to the growth of membrane filtration as one of promising technologies for algae harvesting. Nanofiber membrane (NFM) was found to be efficient for microalgae harvesting via membrane filtration, but it is highly limited by its weak mechanical strength. The main objective of this study is to enhance the applicability of nylon 6,6 NFM for microalgae filtration by optimizing the operational parameters and applying solvent vapor treatment to improve its mechanical strength. The relaxation period and filtration cycle could be optimized to improve the hydraulic performance. For a cycle of 5 min., relaxation period of ≤2 min shows the highest steady-state permeability of 365 ± 14.14 L m−2 h−1 bar−1, while for 10 min cycle, 3 min. of relaxation period was found optimum that yields permeability of 402 ± 34.47 L m−2 h−1 bar−1. The treated nylon 6,6 NFM was also used to study the effect of aeration rate. It is confirmed that the aeration rate enhances the steady-state performance for both intermittent and continuous mode of aeration. Remarkably, intermittent aeration shows 7% better permeability than the full aeration for all tested condition, which is beneficial for reducing the total energy consumption.