Algae Culture

Most designs also culture algae via continuous culture, with a constant input of fresh medium containing nitrogen and other micronutrients and continuous harvesting of algal biomass.

From: Comprehensive Biotechnology (Second Edition) , 2011

Biological Production of Hydrogen from Renewable Resources

Zhinan Xu , in Bioprocessing for Value-Added Products from Renewable Resources, 2007

5.5 Photobioreactors

Algae culture biotechnology has evolved recently into a commercially viable sector, with many companies utilizing both open culture systems and controlled closed photobioreactors. For the purpose of biological hydrogen production, it is essential to use enclosed photobioreactors in which monocultures can be maintained for an extended time period, preferably with sunlight as the energy source. The productivity of photobioreactors is light limited, and a high surface-to-volume ratio is a prerequisite for a photobioreactor. Light energy falling on the light-exposed surface, however, is not always used efficiently. Even under low-intensity sunlight, the photochemical efficiencies are low in most photosynthetic organisms, and tend to decrease under high-intensity sunlight. In addition to the truncated Chl antenna size of the photosystems, many engineering tools have been introduced to create an efficient biological process, including rapidly mixing the culture, diluting light and reasonably distributing light. Thus, it is important to meet the above requirements through rational photobioreactor design.

A number of photobioreactors have been developed. Three of the most noteworthy are pneumatically agitated vertical column reactors, tubular reactors, and flat panel reactors. Depending on the reactor type and the operation mode, cells are exposed to different light/dark cycles. When the cycles are in the range of micro or milli seconds, the photosynthetic efficiency (PE) increases and approaches that at low light intensities [81]. However, when they are from several seconds to tens of seconds, there is no improvement and even a decrease in PE has even been reported in comparison to the efficiency under continuous light. The depth of the photic zone depends on the dimensions and operations of the reactor, biomass concentration, and the specific absorption coefficient of the biomass. On the basis of model calculation and empirical data, flat panel reactors and tubular reactors show the highest efficiencies with rational light regimes in these reactors [82]. In addition, gas accumulation and shear stress should be considered carefully in these reactor designs to overcome their limitations to the productivity. Considering the highest efficiencies attained by flat panel reactors and tubular reactors, these two types of photobioreactors are worthwhile to be further discussed.

Flat panel reactors consist of a rectangular transparent box with a depth of only 1–5 cm. The height and width can be varied to some extent, but in practice only panels with a height and width both smaller than 1 m have been studied. The photobioreactor are mixed with air introduced via a perforated tube at the bottom of the reactor. In order to create a high degree of turbulence, 2.8–4.2 L of air per liter of reactor volume per minute has to be provided. Usually the panels are illuminated from one side by direct sunlight and the panels are placed vertically, or inclined versus the sun. Light/dark cycles are short in these reactors, and this is probably the key factor leading to the high PE. A disadvantage of these bioreactors is that the power consumption of aeration is high, although mixing is always necessary in any reactor. As shown in Fig. 3, a flat panel airlift photobioreactor was designed for the cultivation of Chlorella vulgaris [83]. This new design uses flat panels to reduce light path and baffles to induce a regular light cycling of microalgae. The large-scale flat-plate reactor is a rectangular air-lift photobioreactor with a large number of light re-distributing plates fixed a few centimeters from each other. Many scaled-up versions of photobioreactors consist of repeating many of the smaller photobioreactor units, with its practical implications. Since the scaled-up reactor consists of only one unit, it is still practical to sterilize it and only one regulatory unit is needed.

Fig. 3. Flat panel airlift photobioreactor.

 (Adapted from [83])

Tubular photobioreactors consist of long transparent tubes with diameters ranging from 3 to 6 cm, and lengths ranging from 10 to 100 m. The culture liquid is pumped through these tubes by means of mechanical or air-lift pumps. The tubes can be positioned on many different ways: in a horizontal plane as straight tubes with a small or large number of U-bends; vertical, coiled as a cylinder or a cone; in a vertical plane, positioned in a fence-like structure using U-bends or connected by manifolds; horizontal or inclined, parallel tubes connected by manifolds; in addition, horizontal tubes can be placed on different reflective surfaces with a certain distance between the tubes. A 0.2-m3 tubular airlift photobioreactor was designed for continuous outdoor culture of the microalge P. tricornutum (Fig. 4) [84]. This design method effectively combines the relevant aspects of external irradiance-dependent cell growth, oxygen accumulation in the solar loop, oxygen removal in the airlift device, and hydrodynamics of the airlift system that determine the flow velocity through the solar receiver. Although tubular reactor design is very diverse, the predominant effect of the specific designs on the light regime is a difference in the photon flux density incident on the reactor surface. In most designs, the shape of light gradient and the cycling of dark/light are similar. The length of the tubes is limited because of accumulation of gas. The way to scale up is to connect a number of tubes via manifolds. One big photobioreactor, which consisted of 25,000 glass tubes with a total surface area of 12,000 m2, was designed and used for the production of Chlorella sp.

Fig. 4. Tubular airlift photobioreactor.

 (Adapted from [84])

A favorable design strategy for the photobioreactor is to separate light collection from biological cultivation [29]. Solar beam irradiation in 'clear sky' areas can be collected and concentrated into optical fibres with lenses or parabolic mirrors. Via the fibres, light can be guided into a large-scale photobioreactor. The design of a photobioreactor with a light redistributing system is a great challenge for process engineers. Various types of bioreactors (stirred-tank reactor, vertical bubble column) were integrated with a large number of glass fibers or a few solid transparent bars (glass or quartz). Recently, one more promising integrated system has been proposed [82]. As shown in Fig. 5, a large number of light redistributing plates are fixed a few centimeters from one another within a rectangular airlift photobioreactor. And these light redistributing plates can be connected to the optical fibers. The predicted problem is how to design light-redistributing plates with uniform radiation across the entire surface. In this system, mixing is provided by air injected between adjacent plates and the culture liquid rises in between. Only the space between the two center plates is not aerated, acting as a downcomer. In this system, the liquid culture volume as a whole is mixed, and this bioreactor is scalable. With the decrease of the production costs of lenses, mirrors, solar tracking devices and optical fibres, this new cultivation strategy is generally applicable.

Fig. 5. A rectangular air-lift photobioreactor with light redistributing plates and external light collection. (A) Cross section vertical plane; (B) Cross section horizontal plane.

 (Adapted from [82])

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RNA Modification

Kai Chen , ... Chuan He , in Methods in Enzymology, 2015

3.1 Reagents, Chemicals, and Enzymes

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Appropriate cell and algae culture medium

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4-Thiouridine (Sigma-Aldrich)

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Glycogen (5   mg/mL; Life Technologies)

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RNasin Plus RNase inhibitor (Promega)

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NaCl (5 M; Sigma-Aldrich)

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Igepal CA-630 (Sigma-Aldrich)

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Affinity-purified anti-m6A rabbit polyclonal antibody (Synaptic Systems)

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200 proof Ethanol (Decon Labs)

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Dynabeads® Protein A (Life Technologies)

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BSA (20   mg/mL; Sigma-Aldrich)

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RNaseKiller solution (5 PRIME)

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Sterile water for RNA work (Fisher Scientific)

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Agencourt AMPure XP beads (Beckman Coulter)

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Sodium acetate (pH 5.2, 3 M; Ambion)

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HEPES (GenScript)

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Tris (Sigma-Aldrich)

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UltraPure EDTA (pH 8.0, 0.5 M; Life Technologies)

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Lithium chloride solution (8 M; Sigma-Aldrich)

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Triton X-100 (Fisher Scientific)

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Potassium chloride (Fisher Scientific)

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Magnesium chloride hexahydrate (Sigma-Aldrich)

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Sodium deoxycholate (Sigma-Aldrich)

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SDS (Fisher Scientific)

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25:24:1 phenol/chloroform/isoamyl alcohol (Sigma-Aldrich)

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Acid:phenol:chloroform, pH 4.5 (with isoamyl alcohol (IAA), 125:24:1, Ambion)

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dNTP mix (10   mM/each, NEB)

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RNase T1 (1000   U/μL, Thermo Fisher)

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Antarctic phosphatase (5   U/μL, NEB)

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Proteinase K (~   20   mg/mL, Thermo Fisher)

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T4 DNA polymerase (3   U/μL, NEB)

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T4 polynucleotide kinase (10   U/μL, NEB)

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T4 DNA ligase (500   U/μL, NEB)

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Phi29 DNA polymerase (10   U/μL, NEB)

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Lambda exonuclease (5   U/μL, NEB)

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RecJf exonuclease (30   U/μL, NEB)

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Phusion® High-Fidelity PCR Master Mix with HF Buffer (2   ×, NEB)

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Ethylene glycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid tetrasodium salt (Sigma-Aldrich)

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TRIzol reagent (Ambion)

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Chloroform (Fisher Scientific)

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Isopropanol (Fisher Scientific)

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Cultivation techniques

Luisa Fernanda Rios Pinto , ... Marija Tasic , in Microalgae, 2021

3.2.3 Different designs of open systems

Inclined (cascade) systems allow the algae culture to flow down an angled surface of a few 100  m2, be collected in a larger-volume recipient, and pumped back to the top (Borowitzka & Moheimani, 2013). During the day, the culture is continuously recirculated to increase light exposure and promote photosynthesis. They can achieve high production once the shallowest pond stores concentrating biomass cultures.

Thin-layer systems are employed to obtain high microalgal biomass concentrations by using a low-depth culture (<   50   mm) and maximizing light-efficiency (Acién et al., 2017). They consist of inclined platforms, sloping cascades, or near-horizontal raceways with a high S/V ratio (25–50   m−   1), that enables the optimal sun incidence to achieve high productivity, in contrast with other open ponds or raceways. Thin-layer cascades can have more than 100   m−   1  S/V, with biomass productivity and density higher than 30   g   m−   2  d−   1 and 10   g   L−   1, respectively (Grivalský et al., 2019).

Algal turf scrubbers consist of a similar system with a substrate that supports attached growth on a sloped surface, where algae absorb nutrients from the flowing wastewater (Hoffman, Pate, Drennen, & Quinn, 2017). They are simple in design and allow a more natural biomass harvest compared to other systems. Furthermore, they exhibit stable and promising biomass productivity, being one drawback of the high content of ash (Hess et al., 2019).

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Recent Advancements in the Production of Biodiesel from Algae: A Review

P. Nautiyal , ... M.G. Dastidar , in Reference Module in Earth Systems and Environmental Sciences, 2014

Harvesting

The low density, colloidal stability of algae culture, high growth rate, and small size of algae make harvesting of algae quite tedious and cost-intensive step (20–30% of total biofuel production costs). Centrifugation is efficient for low-scale harvesting ( Wijffels and Barbosa, 2010). Sedimentation is also not effective for harvesting as large-sized algae settle down, whereas small-sized do not. Wang et al. (2014a,b) reported that downward-flow inclined gravity settler has 72% algae harvesting efficiency with low capital cost investment. Table 2 lists the recent studies investigating the different technologies for algae harvesting. Magnetic harvesting involves the interaction of magnetic particles with algae cells to form aggregate that is then captured using magnetic force. In flotation, gas or air bubbles adhere to algae cell making them to float. Flocculation is considered better than other traditional methods of harvesting, in which dispersed algae cells are made to form aggregates that can settle down easily with the help of flocculating agent; however, large quantities of chemicals used make the downstream and refining processes difficult for biodiesel production and alter the quality of by-products obtained. Further, in coagulation, algae form suspensions that are stable and possess negative surface charge making precipitation difficult. The negative surface charge of algae cell wall is due to the presence of pectin component in its cell wall. Bioflocculation, using bacteria and fungus, is a chemical-free harvesting of algae. The positively charged fungal hyphae interact with negatively surface charged algae leading to coagulation. However, for bacteria, some surface modification is required for effective coagulation as both algae and bacteria are negatively charged species. This modification can be possible by the treatment of bacteria with polymer coagulants that neutralize the negative surface charge. The membranes used for algae filtration suffer the problem of clogging that requires regular scraping, thus decreasing the harvesting efficiency. Submerged microfilters are effective than conventional filters for harvesting of algae because low-pressure involvement avoids cell breakage with improved yield of target molecules from the cell interior.

Table 2. Recent studies investigating the techniques of harvesting of algae biomass

Method Technique Algae species Reference
Magnetic harvesting Microwave synthesized iron oxide microparticles C. vulgaris Prochazkova et al., 2013
Silica-coated magnetic particles
Polyethylenimine-coated magnetic nanocomposites		 Various species
C. ellipsoidea 		Cerff et al., 2012
Hu et al., 2013
Flotation Vacuum gas lift Mixed algae culture Barrut et al., 2013
Dispersed ozone Scenedesmus obliquus Cheng et al., 2011
Dispersed air flotation S. obliquus, C. vulgaris Agnes Kurniawati et al., 2014
Cetyltrimethylammonium bromide aided foam flotation Chlorella sp. Coward et al., 2014
Flocculation Nano-chitosan as flocculant Nannochloropsis Farid et al., 2013
Inorganic electrolyte flocculation Nannochloris oculata Garzon-Sanabria et al., 2012
pH-induced autoflocculation Various strains Wu et al., 2012; Nguyen et al., 2014
Fungi pelletization assisted bioflocculation C. vulgaris Zhou et al., 2012
Bacteria assisted bioflocculation C. zofingiensis, S. dimorphus Agbakpe et al., 2014
Chitosan bipolymer Neochloris oleoabundans Beach et al., 2012
Aluminum, zinc and ferric salts C. minutissima Papazi et al., 2010
Ferric chloride induced C. zofingiensis Wyatt et al., 2012
Ammonia induced Various species Chen et al., 2012a,b,c
Cationic guar gum as flocculant Chlorella, Chlamydomonas sp Banerjee et al., 2013
Electroflocculation Tetraselmis sp. Lee et al., 2013a,b,c
Electrochemical using nonsacrificial carbon electrodes C. sorokiniana S. obliquus Misra et al., 2014
Filtration PVC membrane ultrafiltration S. quadricauda Zhang et al., 2010
Submerged microfiltration C. vulgaris Bilad et al., 2012
Submerged flat panel membrane filtration Various species Baerdemaeker et al., 2013
Magnetic induced membrane vibration system C. vulgaris Bilad et al., 2013

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Smart nanosensors for pesticide detection

Rajesh Kumar Saini , ... Anil Kumar Bajpai , in New Pesticides and Soil Sensors, 2017

6.3 Whole Cell Biosensors

Whole cell biosensors use living organisms, such as bacteria, fungi, yeast, algae, and tissue culture cells (from animals or plants) as recognition elements, and detect analytical signals by measuring the general metabolic status (growth inhibition, cell viability, cell respiration or bacterial bioluminescence, and substrate uptake) of such living organisms (Wang et al., 2014). Whole cells have several advantages over enzymes, such as high stability, reduced purification requirements, low cost of preparation, and efficient cofactor regeneration (de Carvalho 2011). They can be classified as microbial biosensors [which may be established by immobilizing microorganisms onto a transducer, adopting chemical and physical approaches, such as cross-linking and entrapment, respectively (Lei et al., 2006)], electrochemical microbial biosensors, and plant tissue– and photosynthesis-based biosensors [use plant tissue or whole cells (e.g., microalgae), chloroplasts or thylakoids, and photosystem II as an attractive alternative to enzymatic biosensors]. Microbial biosensors are able to metabolize a wide range of chemical compounds and avoid expensive protocols of enzyme purification, but they show a slow response in comparison to enzyme biosensors due to slow diffusion of substrate and products through the cell wall. However, this problem can be overcome by permeabilization of the cell (D'Souza, 2001).

Electrochemical microbial biosensors consist of a microbial film sandwiched between a porous cellulose membrane and a gas-permeable membrane, and are widely applied for the determination of biochemical oxygen demand of biodegradable organic pollutants in aqueous samples. They are based on the principle that organic waste diffuses via dialysis membranes, which are further assimilated by the immobilized microbial population, which consequently leads to an increase in the respiration rate of bacteria. Thus, the Clark oxygen electrode detects the sparingly soluble oxygen, which has diffused via an oxygen-permeable Teflon membrane (Liu and Mattiasson, 2002). Potentiometric microbial biosensors that are coated with an immobilized microbial layer make use of ion- or gas-selective electrodes, such as ammonium and pH, and pCO2, respectively. These biosensors record the fluctuations in potential resulting from assimilation of substrates by microbes (Lei et al., 2006). Optical microbial biosensors are used for the detection of pollutants, such as phenols and heavy metals (Su et al., 2011; Lagarde and Jaffrezic-Renault, 2011). Plant tissue– and photosynthesis-based biosensors are low-cost, highly stable, and active lifetime biosensors with high reproducibility. Furthermore, the time-consuming and tedious steps, such as enzyme extraction and purification, are avoided and biosensors find applications in detecting pollutants found in water bodies and other aquatic ecosystems (Campas et al., 2008).

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From the Ancient Tribes to Modern Societies, Microalgae Evolution from a Simple Food to an Alternative Fuel Source

Suphi S. Oncel , ... Giuseppe Torzillo , in Handbook of Marine Microalgae, 2015

5.5 OMEGA (Offshore Membrane Enclosures for Growing Algae)

OMEGA was established by NASA between 2009 and 2012. The system consisted of light-penetrating plastic bag PBRs with specially designed osmosis membranes (Hughes et al., 2014 ). Algae cultures within the bags floating on the water surface used sunlight and nutrients in water to release clean water and oxygen back into the water environment. In other studies, lipids extracted from harvested biomass were used as feedstock for biodiesel and waste biomass was also used as fertilizers. The prototype studies started with 1–2  L of PBRs and scaled up to 110, 1600   L; respectively. The very first findings reported 14.1   ±   1.3   g dry biomass per square meter of PBR surface area per day. The project was not a leading one in terms of innovative algae cultivation, but it established the usefulness of various equipment and apparatus to measure temperature, photosynthetic active radiation, and oxygen–carbon dioxide levels. In addition, the ecological aspects of the floating PBR on the sea surface were also discussed and evaluated (Trent, 2012; Hughes et al., 2014).

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Primary Producer-Consumer Interactionsce

Gary A. Lamberti , ... Catherine M. Pringle , in Methods in Stream Ecology (Second Edition), 2007

C. Optional Methods

The above methods are designed primarily to determine the effects of consumers on benthic producers. However, these approaches can be expanded to assess specific effects of producers on consumer populations as well. For example, the platforms can be used do "culture" algae in a grazer-free condition, and then after returning those periphyton patches to the stream bottom, the rate of grazer colonization and depletion of those patches can be determined (e.g., Lamberti and Resh 1983). The cage method can be used to measure grazer growth rates by determining starting and ending weights of grazers, which can test for grazer competition (e.g., Lamberti et al. 1987b) or facilitation among consumers (Feminella and Resh 1991, Heard and Buchanan 2004). Electric exclosures can accumulate uneaten detritus that then provides resource 'islands' for other consumers unaffected by the electricity.

Grazer manipulations in streams are not limited to the three approaches described above; certain types of grazers can be manipulated effectively using other techniques. For example, densities of certain sedentary or sessile grazers (e.g., fifth-instar hydroptilid caddisflies) can be altered by direct removal of animals from rock surfaces (e.g., McAuliffe 1984, Hart 1985). In another approach, insecticides can be mixed with agar in diffusing substrata to deter some grazers (e.g., chironomid larvae) from colonizing those substrata (Gibeau and Miller 1989, Peterson et al. 1993). However, care must be taken when using insecticides to avoid deleterious effects on nontarget organisms.

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Astaxanthin production from Haematococcus pluvialis by using illuminated photobioreactor

Yiu-Hang Ho , ... Ambati Ranga Rao , in Global Perspectives on Astaxanthin, 2021

3.5 Hydrodynamic and mass transfer in the photobioreactors

H. pluvialis can achieve an effective growth rate inside the PBRs together with optimum culture condition, for example light input, nutrients, pH, temperature, CO2 supply, etc. Moreover the nutrients available in PBRs are significantly affected by the aeration rate, gas holdup, and mixing for the algal culture. Besides, dissolve oxygen will be accumulated in alga cultures due to the oxygen production in photosynthetic reactions. If excessive oxygen is present inside culture, the photosynthesis rate may be suppressed [45]. Generally the productivity of the PBRs depends on the hydrodynamic and mass transfer [46]. Efficient mixing helps to reduce the dissolved oxygen inside the cultures and provide good mass transfer of oxygen and CO2 in the culture system, simultaneously improve the heat transfer [47]. Hence the design of the PBR needs to evaluate several parameters, such as gas holdup, liquid volume, mass transfer coefficient (k L a), and mixing time.

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Design and Operating Guide for Aquaculture Seawater Systems - Second Edition

In Developments in Aquaculture and Fisheries Science, 2002

15.5 Algae

Another interesting process for nutrient removal involves polyculture with marine algae. This includes both phytoplankton and macrophytes or seaweeds. Although there exist considerable data about the nutrient uptake properties of mass phytoplankton cultures, their microscopic characteristics make them difficult, in most cases clearly impractical, to separate from process water. Seaweeds are much easier to handle and very effective in removing nutrients from seawater. Since many seaweeds have high value for industrial, pharmaceutical and food additives, there are considerable data available on seaweed physiology but a great deal less on seaweed culture systems. Maintaining and operating algae cultures can require considerable time and effort. Unless the seaweeds are of direct interest, such as for educational or research purposes, they are not likely to be worth the trouble. Seaweeds need light, although too much can be inhibiting, a carbon source, substrate for attachment (sometimes), nutrients, trace materials and some water current. Algae cultures by themselves tend to drive the pH of the system to basic, while the animal wastes are acidic. With care a good pH balance is possible. One problem is that biological activity in recycling systems and some of the processing equipment tend to deplete essential trace materials that might be needed by the seaweeds. It is quite possible that there are a number of trace materials whose importance is not yet recognized. The addition of a seawater makeup flow will substantially reduce these risks. Sizing of the seaweed unit will depend on the animal biomass and their waste products. However, seaweeds are tolerant to wide variations in nutrient concentrations. Sizing data, design considerations and a bibliography can be found in Huguenin (1976b). While seaweeds can be effective in water treatment and can also be cultured for their extracts, optimizing for the two objectives produces different systems and modes of operation. Under many conditions, the seaweed unit may require an area comparable to that for the animal culture and may result in large heat gains or losses to the system. These can be major disadvantages.

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Vegetal Production

Philippe Girardon , ... Eric Schmitt , in Gases in Agro-Food Processes, 2019

6.2.4.11 Conclusion

So much work has been done so far to understand the mechanism of absorption and use of various gases by microalgae, and especially the flue gas ones. By that way, microalgae are fully entering into a new business model, the circular economy, where algae should be grown industrially in a very large scale in a profitable way while using a massive quantity of flue gas with a beneficial environmental impact. Hence, the issue about gas transportation for making that algae cultivation concept true. The new business model should be based on a solid, win-win, and durable industrial partnership between a large-scale algae producer and an industrial plant wanting to get rid of its gas for various reasons. Worldwide, very rare microalgae producers have already installed their algae culture plant aside to an industrial flue gas producer; Algae Natural Food from Riquewihr, France, has done it since 2014 by setting up its Spirulina cultivation facilities next to a malting plant in Strasbourg, France, that produces malt for the beer industry from barley. In that business model, Algae Natural Food uses not only the rinsing water from barley as the liquid base to cultivate Spirulina inside, saving hundreds of cubic meters of fresh water, but also it uses calorific energy that the malting plant produces to keep the right cultivation temperature, especially during winter, and of course the CO 2 gas coming from the respiration of barley during the germination into malt process. The short distance between the algae cultivation platform and the malting plant enables getting a low CAPEX and OPEX for production microalgae, and consequently offers an attractive selling price for the food and feed industries.

Reusing byproducts of plants such as flue gases in order to restart new primary biological productions as microalgae not only permits industrially acting in an economically friendly way, but also significantly decreases production costs and opens new markets. The circular economy fully applies here and is now a reality for producing microalgae that way, and will develop for the next generations to come.

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