Harvesting of microalgae by bio-flocculation
TL;DR: This method is as easy and effective as chemical flocculation which is applied at industrial scale, however in contrast it is sustainable and cost-effective as no costs are involved for pre-treatment of the biomass for oil extraction and forPre- treatment of the medium before it can be re-used.
Abstract: The high-energy input for harvesting biomass makes current commercial microalgal biodiesel production economically unfeasible. A novel harvesting method is presented as a cost and energy efficient alternative: the bio-flocculation by using one flocculating microalga to concentrate the non-flocculating microalga of interest. Three flocculating microalgae, tested for harvesting of microalgae from different habitats, improved the sedimentation rate of the accompanying microalga and increased the recovery of biomass. The advantages of this method are that no addition of chemical flocculants is required and that similar cultivation conditions can be used for the flocculating microalgae as for the microalgae of interest that accumulate lipids. This method is as easy and effective as chemical flocculation which is applied at industrial scale, however in contrast it is sustainable and cost-effective as no costs are involved for pre-treatment of the biomass for oil extraction and for pre-treatment of the medium before it can be re-used.
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TL;DR: In this article, the main harvesting processes applied to microalgae, presenting the main advantages and disadvantages of each method, to allow the selection of an appropriate procedure to effectively separate microalgal biomass from the culture medium.
Abstract: Research studies on microalgae have increased in the last decades due to the wide range of applications associated to these photosynthetic microorganisms. Microalgae are an important source of oils and other biomolecules that can be used in the production of biofuels and high-valued products. However, the use of microalgae in these green processes is still not economically viable. One of the main costs associated to microalgal production is related to the harvesting process, as it usually accounts for about 20–30% of total cost. Therefore, this review focuses on the main harvesting processes applied to microalgae, presenting the main advantages and disadvantages of each method, to allow the selection of an appropriate procedure to effectively separate microalgal biomass from the culture medium. To reduce the associated costs, it is common to harvest microalgae in a two-step separation: (i) thickening procedures, in which microalgal slurry is concentrated to about 2–7% of total suspended solids; and (ii) dewatering procedures, which result in the concentration of microalgal slurry to 15–25% of total suspended solids. Selection of the adequate harvesting methods depends on the characteristics of the target microorganism and also on the type and value of the end product.
725 citations
TL;DR: This review aims to collate and present an overview of current harvesting, oil extraction and biofuels production technologies from microalgae, and discusses the various biodiesel production techniques in the later sections.
Abstract: Microalgae are receiving increasing attention worldwide as an alternative and renewable source for energy production. Through various conversion processes, microalgae can be used to produce many different kinds of biofuels, which include biodiesel, bio-syngas, bio-oil, bio-ethanol, and bio-hydrogen. However, large scale production of microalgal biofuels, via many available conversion techniques, faces a number of technical challenges which have made the current growth and development of the algal biofuel industry economically unviable. Therefore, in addition to algae culture and growth, it is also essential to develop cost-effective technologies for efficient biomass harvesting, lipid extraction and biofuels production. This review aims to collate and present an overview of current harvesting, oil extraction and biofuels production technologies from microalgae. Since much of the current studies on oil extraction are focused on biodiesel production from microalga, this study, apart from discussing the various biodiesel production techniques in the later sections, has also done a detailed discussion on the production techniques of other biofuels.
497 citations
TL;DR: A review of micro-algal biofuel production potential and possible ways to put it into practice can be found in this article, with particular emphasis on Scenedesmus obliquus, a type of algae that can efficiently convert sunlight, water and CO2 into a variety of products suitable for renewable energy applications.
Abstract: The rapid growth of human population has led to mounting energy demands, which is projected to increase by 50% or more by 2030. The natural petroleum can not catch-up the current consumption rate, which is already reported to be 105 times faster than nature can create. Besides, the use of fossil fuels is devastating to our environment through greenhouse gas emissions and consequent global warming. Therefore, the search for ‘clean’ energy has become the most overwhelming challenges. Currently, several alternatives are being studied and implemented. Biofuels, fuels from living organisms, provide environmental benefits, since their use leads to a decrease in the harmful emissions of CO2 and hydrocarbons and, to the elimination of SOx emissions, with a consequent decrease in the greenhouse effects. Unfortunately, the present biofuel projections are based on feed-stocks that are also food commodities and resources suitable for conventional agriculture. One possibility to overcome the problem is the cultivation of micro-algae and switching to third generation biofuels, which seem to be a promising source since algae are able to efficiently convert sunlight, water, and CO2 into a variety of products suitable for renewable energy applications. Therefore, this review is intended to recapitulate current works on micro-algal biofuel production potential and discuss possible ways to put it into practice. This review starts by highlighting the advantages and various forms of micro-algal biofuels. Some of the micro-algal species proved to be suitable for biofuel production so far are considered, with particular emphasis on Scenedesmus obliquus. The recent attempts and achievements in improving the economies of production through genetic and metabolic engineering of micro-algal strains are also addressed. Other potential applications such as wastewater treatment and CO2 mitigation that can be coupled with biofuel production are described. Finally, the promises and challenges of algae to biofuel industry are uncovered.
422 citations
TL;DR: A Biorefinery design is presented that integrates the treatment of municipal wastewater with the recovery of oleaginous microalgae with potential for biodiesel production, together with the use of seawater supplemented with anaerobically digested piggery waste for cultivating Arthrospira and producing biogas, biodiesel, hydrogen and other high added value products.
415 citations
TL;DR: Order of suitability of harvesting techniques for various applications has been decided and coagulation and flocculation, centrifugation and filtration were found to be most suitable for considered applications.
351 citations
References
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TL;DR: A review of second generation biodiesel production systems using microalgae can be found in this paper, where the main advantages of second-generation microalgal systems are that they: (1) have a higher photon conversion efficiency (as evidenced by increased biomass yields per hectare): (2) can be harvested batch-wise nearly all-year-round, providing a reliable and continuous supply of oil: (3) can utilize salt and waste water streams, thereby greatly reducing freshwater use: (4) can couple CO2-neutral fuel production with CO2 sequestration: (
Abstract: The use of fossil fuels is now widely accepted as unsustainable due to depleting resources and the accumulation of greenhouse gases in the environment that have already exceeded the “dangerously high” threshold of 450 ppm CO2-e. To achieve environmental and economic sustainability, fuel production processes are required that are not only renewable, but also capable of sequestering atmospheric CO2. Currently, nearly all renewable energy sources (e.g. hydroelectric, solar, wind, tidal, geothermal) target the electricity market, while fuels make up a much larger share of the global energy demand (∼66%). Biofuels are therefore rapidly being developed. Second generation microalgal systems have the advantage that they can produce a wide range of feedstocks for the production of biodiesel, bioethanol, biomethane and biohydrogen. Biodiesel is currently produced from oil synthesized by conventional fuel crops that harvest the sun’s energy and store it as chemical energy. This presents a route for renewable and carbon-neutral fuel production. However, current supplies from oil crops and animal fats account for only approximately 0.3% of the current demand for transport fuels. Increasing biofuel production on arable land could have severe consequences for global food supply. In contrast, producing biodiesel from algae is widely regarded as one of the most efficient ways of generating biofuels and also appears to represent the only current renewable source of oil that could meet the global demand for transport fuels. The main advantages of second generation microalgal systems are that they: (1) Have a higher photon conversion efficiency (as evidenced by increased biomass yields per hectare): (2) Can be harvested batch-wise nearly all-year-round, providing a reliable and continuous supply of oil: (3) Can utilize salt and waste water streams, thereby greatly reducing freshwater use: (4) Can couple CO2-neutral fuel production with CO2 sequestration: (5) Produce non-toxic and highly biodegradable biofuels. Current limitations exist mainly in the harvesting process and in the supply of CO2 for high efficiency production. This review provides a brief overview of second generation biodiesel production systems using microalgae.
2,254 citations
"Harvesting of microalgae by bio-flo..." refers background or methods in this paper
...All of them again require treatment of the medium to be re-used (Schenk et al. 2008)....
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...Commercial microalgal biodiesel production is not economically feasible yet, mainly due to the high-energy inputs required for water pumping, mixing and for harvesting the microalgal biomass combined with large investment costs (Schenk et al. 2008)....
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...Although this is an easy and effective method, this is not an appropriate method for cheap and sustainable harvesting of microalgae in large-scale microalgae production plants because excess cationic flocculant needs to be removed from the medium before it can be re-used and this leads to extra operational costs (Schenk et al. 2008)....
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...…method, this is not an appropriate method for cheap and sustainable harvesting of microalgae in large-scale microalgae production plants because excess cationic flocculant needs to be removed from the medium before it can be re-used and this leads to extra operational costs (Schenk et al. 2008)....
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...Commercial microalgal biodiesel production is not economically feasible yet, mainly due to the high-energy inputs required for water pumping, mixing and for harvesting the microalgal biomass combined with large investment costs (Schenk et al. 2008)....
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TL;DR: Although microalgae are not yet produced at large scale for bulk applications, recent advances—particularly in the methods of systems biology, genetic engineering, and biorefining—present opportunities to develop this process in a sustainable and economical way within the next 10 to 15 years.
Abstract: Microalgae are considered one of the most promising feedstocks for biofuels. The productivity of these photosynthetic microorganisms in converting carbon dioxide into carbon-rich lipids, only a step or two away from biodiesel, greatly exceeds that of agricultural oleaginous crops, without competing for arable land. Worldwide, research and demonstration programs are being carried out to develop the technology needed to expand algal lipid production from a craft to a major industrial process. Although microalgae are not yet produced at large scale for bulk applications, recent advances—particularly in the methods of systems biology, genetic engineering, and biorefining—present opportunities to develop this process in a sustainable and economical way within the next 10 to 15 years.
1,712 citations
"Harvesting of microalgae by bio-flo..." refers background in this paper
...For low-value bulk products, both the investment as well as the operational costs should drastically decrease to make commercial production feasible (Wijffels and Barbosa 2010)....
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TL;DR: The importance of lipid productivity as a selection parameter over lipid content and growth rate individually is demonstrated and provides a framework for decision-making and a starting point for further investigation of species selection.
Abstract: Microalgae are a promising alternative source of lipid for biodiesel production. One of the most important decisions is the choice of species to use. High lipid productivity is a key desirable characteristic of a species for biodiesel production. This paper reviews information available in the literature on microalgal growth rates, lipid content and lipid productivities for 55 species of microalgae, including 17 Chlorophyta, 11 Bacillariophyta and five Cyanobacteria as well as other taxa. The data available in the literature are far from complete and rigorous comparison across experiments carried out under different conditions is not possible. However, the collated information provides a framework for decision-making and a starting point for further investigation of species selection. Shortcomings in the current dataset are highlighted. The importance of lipid productivity as a selection parameter over lipid content and growth rate individually is demonstrated.
1,353 citations
Additional excerpts
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Journal Article•
TL;DR: Of the two commercial cationic starch flocculants tested, Greenfloc 120 (used in wastewater treatment) was more efficient than Cargill C*Bond HR 35.849 ( used in paper manufacturing), and measurements of the maximum quantum yield of PSII suggest that GreenFloc 120 cationIC starch was not toxic to Parachlorella.
Abstract: Due to their small size and low concentration in the culture medium, cost-efficient harvesting of microalgae is a major challenge. We evaluated the potential of cationic starch as a flocculant for harvesting microalgae using jar test experiments. Cationic starch was an efficient flocculant for freshwater (Parachlorella, Scenedesmus) but not for marine microalgae (Phaeodactylum, Nannochloropsis). At high cationic starch doses, dispersion restabilization was observed. The required cationic starch dose to induce flocculation increased linearly with the initial algal biomass concentration. Of the two commercial cationic starch flocculants tested, Greenfloc 120 (used in wastewater treatment) was more efficient than Cargill C*Bond HR 35.849 (used in paper manufacturing). For flocculation of Parachlorella using Greenfloc 120, the cationic starch to algal biomass ratio required to flocculate 80% of algal biomass was 0.1. For Scenedesmus, a lower dose was required (ratio 0.03). Flocculation of Parachlorella using Greenfloc 120 was independent of pH in the pH range of 5 to 10. Measurements of the maximum quantum yield of PSII suggest that Greenfloc 120 cationic starch was not toxic to Parachlorella. Cationic starch may be used as an efficient, nontoxic, cost-effective, and widely available flocculant for harvesting microalgal biomass.
306 citations
"Harvesting of microalgae by bio-flo..." refers methods in this paper
...The sedimentation kinetics were measured in cuvettes instead of in conventional jar tests (Vandamme et al. 2010) or recently used cylindrical glass tubes (Papazi et al. 2010)....
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...The sedimentation kinetics were measured in cuvettes instead of in conventional jar tests (Vandamme et al. 2010) or recently used cylindrical glass tubes (Papazi et al....
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TL;DR: In this paper, the potential of cationic starch as a flocculant for harvesting microalgae using jar test experiments was evaluated, and it was shown that the amount of Cationic Starch required to induce flocculation increased linearly with the initial algal biomass concentration.
Abstract: Due to their small size and low concentration in the culture medium, cost-efficient harvesting of microalgae is a major challenge. We evaluated the potential of cationic starch as a flocculant for harvesting microalgae using jar test experiments. Cationic starch was an efficient flocculant for freshwater (Parachlorella, Scenedesmus) but not for marine microalgae (Phaeodactylum, Nannochloropsis). At high cationic starch doses, dispersion restabilization was observed. The required cationic starch dose to induce flocculation increased linearly with the initial algal biomass concentration. Of the two commercial cationic starch flocculants tested, Greenfloc 120 (used in wastewater treatment) was more efficient than Cargill C*Bond HR 35.849 (used in paper manufacturing). For flocculation of Parachlorella using Greenfloc 120, the cationic starch to algal biomass ratio required to flocculate 80% of algal biomass was 0.1. For Scenedesmus, a lower dose was required (ratio 0.03). Flocculation of Parachlorella using Greenfloc 120 was independent of pH in the pH range of 5 to 10. Measurements of the maximum quantum yield of PSII suggest that Greenfloc 120 cationic starch was not toxic to Parachlorella. Cationic starch may be used as an efficient, nontoxic, cost-effective, and widely available flocculant for harvesting microalgal biomass.
296 citations