Frontiers | Overview of Carbon Capture Technology: Microalgal Biorefinery Concept and State-of-the-Art - 1 views
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The impending danger of climate change and pollution can now be seen on the world panorama. The concentration of CO2, the most important Green House Gas (GHG), has reached to formidable levels.
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Sean Nash on 05 Jun 24OK: Is it an important field of study? Check. Is it timely? Check. Is it feasible? Let's see...
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(iii) microalgae cultivation
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Furthermore, microalgae can be fed with notorious waste gasses such as CO2 and NOx, SOx from flue gas, inorganic and organic carbon, N, P and other pollutants from agricultural, industrial and sewage wastewater sources so as to provide us with opportunities to transform them into bioenergy, valuable products and forms that cause least harm to the environment
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OK, so... you could likely create a biofuel from algae produced via the insertion of CO2 into a bioreactor system (perhaps even test the one you have vs. a creation fo your own to maximize growth with a more powerful set of lights and extensive tubing). Right off the top of my head, I know we can easily access commercial CO2 canisters that are used in aquarium setups to boost plant growth. Fluval makes such canisters. You would have to find out the volume/mass of CO2 contained in one. You'd have to be less concerned with toxins of you are able to choose a different algae for this capture vs. the rather toxic species you worked with last year.
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The uncomplicated cellular structures and rapid growth of microalgae endow them with CO2 fixation efficiency as higher as 10–50 folds than terrestrial plants
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Recently, many research studies have come up showing the positive impact of growing microalgae under high concentrations of Ci in the form of pure gaseous CO2, real or simulated flue gas, or soluble carbonate (bicarbonate), reporting increased carbon bio-fixation and biomass productivity
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How does the carbon concentration of such things as flue gas (from industry) compare to the levels in a commercially-available CO2 canister? I'm assuming those are lower, but that's OK. You would just need to be able to do the math to compare the ratios. Also, there is nothing that says you couldn't perhaps use multiple canisters to boost the CO2 levels assuming they could survive in whatever concentration you're feeding them with. It does acidify water.
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Despite such remarkable potential, the production of microalgae for low-value bulk products, such as proteins for food/feed applications, fatty acids for nutraceuticals or bulk products such as biofuels, is heretofore, not economically feasible
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So... this asserts that biofuel production (which would already be better than using human food crops such as corn) is not economically feasible. Let's find out WHY it isn't. What do the numbers look like? What is missing? Is there a way to engineer a process that boosts economic feasibility through some innovation?
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The microalgal biomass majorly constituted of lipids (7–23%), proteins (6–71%) and carbohydrates (5–64%), depending upon the microalgal specie and culture conditions
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Start searching for data on the differences of these compounds in algal cultures of various species. Finding the right species in terms of the components produced (though perhaps your process will boost these numbers in some way- verified by testing at a local lab). I would query perplexity to find papers that outline what components are produced by what species.... then you can compare that to the ease of culture of different species.
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Biofuels from microalgae, production system, conversion technologies, life cycle analyses have been extensively reviewed, hence detailed description is not presented in this review.
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This clearly suggests that a TON of work has been done in these areas. The negative? -> Harder to find original work, the positive -> here is a TON of search terms to build up your background knowledge on primary research in these areas. The real creativity in science often stems from finding a unique wrinkle that is embedded in extensive work.
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the lipid content of common microalgae such as Chlorella, Dunaliella, Isochrysis, Nannochloris, Nannochloropsis, Neochloris, Phaeodactylum, Porphyridium, and Schizochytrium, varies between 20 and 50% of cell dry weight
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can be augmented to higher levels by manipulating environmental and other growth factors, process optimization and genetic modifications of the production strain. Nitrogen starvation and salinity stress are known to induce an increase in TAG (triacylglycerol) accumulation and relative content of oleic acid in most of the microalgal species
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C14:0, C16:0, C18:1, C18:2, and C18:3 fatty acids, yet the relative composition varies from species to species
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The lipids can be converted into FAMEs (fatty acid methyl esters) via transesterification for biodiesel production.
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This is key.... can we convert algal lipids into FAMEs in the lab at school with the help of Harkleroad & Tabor? Find out what all chemical processes are involved. My initial gut feeling i that it isn't an terribly prohibitive process considering how simple biodiesel was to produce in the school lab previously.
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Furthermore, the residual de-oiled microalgal biomass can be used for animal feed.
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The resistance of cell wall to enzyme hydrolysis is one of the prime bottleneck in the Anaerobic digestion (AD) process. The overall economic feasibility of the process depends on the factors affecting AD, microalgal strain, biomass pretreatment, and culture methods (Jankowska et al., 2017). Lately, to make the system economically viable and environmentally sustainable, a closed-loop production scheme is being adopted wherein AD effluents are recycled and used as an input in the first step of AD. Jankowska et al. (2017) have presented a detailed review microalgae’s cultivation, harvesting and pretreatment for AD for biogas production.
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This is a fascinating element, and one I know less about. This might be significantly more sophisticated, but that in no way should scare you. Perhaps it isn't that difficult and it would be super fun and challenging to engineer a way to do (or improve) this. (?) However, my initial gut feeling is that working with biogas production would be more difficult than liquid forms.
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Bioethanol The carbohydrate part (mainly glucose, starch, cellulose, and hemicellulose) of the microalgal dry biomass can be used for transforming into bioethanol via fermentation. Although, microalgae accumulate relatively low quantities of sugars, the absence of lignin from microalgal structure makes them advantageous over other feedstock such as corn, sugarcane, and lignocellulosic biomass (Odjadjare et al., 2015; Jambo et al., 2016). Isochrysis galbana, Porphyridium cruentum, Spirogyra sp., Nannochloropsis oculate, Chlorella sp., are mainly exploited microalgae for the production of carbohydrates
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OK, now I'm starting to see where they're going with this specific paper.... they are asserting that you'd have to find a way to separate out all of the components of the produced algal mass to gain value for each component to make it economically feasible. Do you perhaps end up finding that one particular species has both a high lipid profile (for biodiesel) as well as a reasonable carbohydrate profile (for bioethanol)?
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I know less about this... is more of a fermentation process and might be a bit more dangerous that biodiesel production. Not sure, just a gut feeling when keeping in mind the safety forms. Something to bookmark.
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Despite having notable significance, limited number of studies have reported laboratory stage work on the fermentation of microalgae biomass to butanol (Cheng et al., 2015; Gao et al., 2016; Wang et al., 2016).
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Value-Added Products In the context of biorefinery approach, intracellular compounds and metabolites have gained immense importance owing to their high monetary value. Microalgal pigments: chlorophyll a and b, lutein, astaxanthin, β-carotene, phycobilins, C- phycocyanin have found wide application in dyes, cosmetics, food and feed additives, nutraceuticals and pharmaceuticals, as natural colors, bioactive components, anti-oxidants, nutritive and neuro-protective agents (Koller et al., 2014; Begum et al., 2016). Microalgae are also exploited as rich source of amino acids (leucine, asparagine, glutamine, cysteine, arginine, aspartate, alanine, glycine, lysine, and valine), Carbohydrates (β1–3- glucan, amylose, starch, cellulose, and alginates), Vitamins and minerals (vitamin B1, B2, B6, B12, C, and E; biotin, folic acid, magnesium, calcium, phosphate, iodine) that are widely used in Food additives, health supplements and medicine. Microalgae, such as Nannochloropsis, Tetraselmis, and Isochrysis are used for extraction of long chain fatty acids popularly known as the omega fatty acids such as DHA (Docosahexaenoic Acid) and EPA (Eicosapentaenoic Acid), have lately gained prime attention as essential for human brain development and health. Other than these, Microalgae are also used for production of Extracellular Polymeric Substances (EPSs) which have many industrial applications and Polyhydroxyalkanoates (PHAs). PHAs can be used for manufacturing bioplastics that are very sought after because of their biodegradability (Markou and Nerantzis, 2013; Koller et al., 2014).
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Although many have reported successful utilization of microalgal biomass for the production of bioproducts within a biorefinery framework, the economic feasibility is unrealized and the microalgae biorefinery is way much expensive (’t Lam et al., 2017; Zhou et al., 2017). To attain feasibility and sustainability, both upstream processing (USP) and downstream processing (DSP) need to be efficiently simplified and integrated. The efficiency of the USP is determined by microalgal strain selection, nutrient supply (CO2, N, and P) and culture conditions (temperature, light intensity) (Vanthoor-Koopmans et al., 2013). Whereas, the constraints at the DSP level are mainly characterized by harvesting, cell disruption, and extraction methods. DSP, specifically harvesting accounts for 20–40% of the total production costs and for a multi-product biorefinery, the cost increases to 50–60% (’t Lam et al., 2017).
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high throughput screening techniques like 96-well microplate swivel system (M96SS) have made processing upto 768 microalgal samples at the same time, possible
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mixed diverse community of microalgae, dominated by Desmodesmus spp., could be adapted over a time of many months to survive in 100% flue gas from an unfiltered coal-fired power plant containing 11% CO2
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Besides stress manipulation and acclimatization, desirable traits of the microalgal strains can be effectively improved by genetic and metabolic engineering/synthetic biology. Lately, genome editing tools such as Clustered Regularly Interspaced Short Palindromic Repeats – CRISPR associated protein 9 (CRISPR-Cas9) and Transcription Activator-Like (TAL) Effector Nucleases (TALEN) are being used in microalgal gene alterations. Moreover, gene-interfering tools, such as CRISPR-dCas9, micro RNA (miRNA), and silence RNA (siRNA) are being explored to alter the gene expression unlike gene modification.
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Large scale microalgal cultivation and nutrient supply pose huge economic burden. In this context emphasis is being laid on biofilm based attached cultivation rather than aqua-suspend methods that have massive water requirement, low biomass productivity, energy intensive and cannot be easily scaled up
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So... the scale is the problem. Methods of growing suspended in water are all I have been thinking of.... even engineering some crazy method of networks of fine, clear tubes full of algae, etc... here they're saying this is a massive challenge and requires a big industrial output to make it economically feasible. The good and the bad? The bad is that you could do a ton fo work that in the end isn't economically feasible for real world use. The good is that optimizing some stage or element of the process could potentially change this calculaton.
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Centrifugation is the most efficient (>95% efficiency) method for harvesting microalgae
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Flocculation is a low-cost alternative. Cationic chemical flocculants and polymeric flocculants are generally used (Brennan and Owende, 2010), but can negatively affect the toxicity of the biomass and output water (Ryan, 2009). Zhou et al. (2012) reported a novel fungi assisted bioflocculation technique, in which a filamentous fungal spores were added to the algal culture under optimized conditions and the pellets were formed after 2 days that can be harvested by simple filtration. Attached culture can also make harvesting simple (Wang et al., 2017).
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This whole topic you have stumbled upon (bioengineering of algae as ultimately a way to sequester carbon in an economically-feasible way) is massive in terms of complexity of the entire system. But, subsystems are less complex and more ripe for digging into. The key thing is that this has to be interesting enough to you.... that you are willing to understand ALL of the moving parts so that you would know how your component of the puzzle fits into the broader scope of the work. It is super interesting to me and I do think there are a million variables to choose form here.... once you decide IF this is worth pouring your heart into... it is time to read read read!
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Microalgae based carbon capture technologies are certainly promising but their successful implementation is still to be realized.
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But, the prospects of successful commercial deployment lie in unsophisticated innovations in DSP, particularly harvesting, cell disruption and extraction, which can actually cut down the costs at a biorefinery level, along with process integration.
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. Recent technoeconomic analyses and life-cycle assessments of microalgae-based production systems have suggested that the only possible way for scaling up the production is to completely use the biomass in an integrated biorefinery set-up wherein every valuable component is extracted, processed and valorized.
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The temperature of the planet has risen by 0.85°C from 1880 to 2012 and it has been forecasted that by the end of this century
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CO2 capture is done from large point sources such as power plants and cement manufacturing plants. The separation and capture of CO2 from other exhaust components is usually done via following methods: (i) chemical absorption; (ii) physical adsorption; (iii) membrane separation; and (iv) cryogenic distillation (Figueroa et al., 2008; Pires et al., 2011, 2012).