Algal Biotechnology:
Physiology of growth,
and Mass Cultivation,
Photobioreactors
Algae : biology, growth, production
• Algae formal tax. standing, polyphyletic origin, artificial assemblage of
O2 evolving photosynthetic organisms; wide range of growth form; wide
range of growth strategies; wide range of reproduction strategies (vegetative,
asexual, sexual); tolerance of wide range of environmental condition (e.g.
Nutrients, pH, temp., turbidity, O2 & CO2 conc.)
• Aquatic – marine & freshwater – planctonic, bentic, kelps; subaerial;
symbiotic
• Unicellular; colonies; coenobia; filamentous; thalloid
• Nutritional strategies
• Autotrophy (photoautotrophy) – Heterotrophy (osmotrophy, phagotrophy) – mixotrophy
(auxotrophy)
Obligate – Facultative
• Wide range of valuable metabolites – pigments, antioxidants, toxins,
alelopathic metabolites, fatty acids, phenols,
Algae : biology, growth, production
• Environment
– Light (intensity, spectrum, photoperiod)
– absorption, transmision, reflection, scattering,
interference; environmental accessibility
– Temperature
– Substrate & Nutrients
– Sources vs. Requirements
– Environmental stability
– nutrient flow, mechanical condions, stream, randomization
Algae : biology, growth, production
• Nutrient (N,P & CO2, HCO3) accesibility; N2
fixation; motile stage
• Synergistic effects of combinations of chemical
and physical factors
• Photosynthesis
– Structure & function (thylacoid, chloroplast, cell;
pigments – primary, accesory ;
photosystems vs. antena)
– Light reaction (ETR, O2 evolution); Calvin Benson
Bassham Cycle (RuBisCO activity); CCM
Algae : biology, growth, production
• LRC
• Pn max
• Rd
• Ic
• photoinhibition
Methods used for
algal culture growth evaluation
• direct
– fresh/dry mass determination
– counting – number of cells (colonies)
– cell volume, PCV
– protein content
– calorific value
– flow-cytometry & epifluorescence microscopy
• indirect
– turbidity; optical density; pH; CO2, O2 conc.
– chlorophyll content
Culture methods
• Batch cultures – small scale
– common, simple, low cost, closed system, volume-limited
– any flow of nutritions & products
– Erlenmeyer flasks, tubes, Petri dishes
– growth curve phases – lag, acceleration, exponential, retardation,
stationary, decline
Culture methods
• Continuous cultures
– resources are potentially infinite
– cultures are maintained at chosen point on the growth
curve by regulated addition of fresh medium
– air pump – CO2 source, mixing-turbulence
– categories of contin. cult.:
• turbidostat
• chemostat
• cyclostat
• Semi-continuous cultures
– periodic fresh medium addition & harvesting
Mass production of Microalage
• Open ponds
– Lakes and natural ponds
– Inclined systems
– Cirkular ponds
– Raceway ponds
…..
Ideal
dense suspension (cells, colonies, coenobias, fillaments) cultured
at low PAR/cell, high O2 conc. And limits of anorg. C availability
Mass production of Microalage
… then growth depends on interplay of several parameters:
avg. PAR/cell
mixing
gas exchange
temperature
Effective light distribution in suspension
<>
efficiency of light conversion
> effective PBR design
> cell suspension density
> selection (gen modif.) of the culture > small antena
(to reduce excitation presure of PS units under high PAR &
maintain high efficiency of light conversion)
Mass production of Microalage
……
• Photobioreactor
– Tubular photobioreactors
• Serpentine photobioreactors
• Manifold photobioreactors
• Helical photobioreactors
– Flat photobioreactors
• Flat alveolar panels
– Vertical cylinders and sleeves
Biomass growth rate
• growth curve – exponential phase
– doubling time
• Commercial-scale cultures
– volume of cca. 102 – 109 l
– large open ponds, circular ponds with rotating arm,
raceway ponds, large bags, tube system
– factors to be considered:
• biology of alga; the cost of land; labor; energy; water; nutrients; climate (if
outdoors); type of product
• light utilization efficiency (PBR & open ponds, surface-to-volume ratio 20-200
vs 5-10m-1, orientation, inclination); ability to control temp.; hydrodynamic
stress (mixing); oxygen accumulation; ability to maintain culture unialgal or
axenic (photobioreactors vs. open ponds)
-scale up ability
• Harvesting (20-30%cost) – species specific
– Flocculation -↑pH, cationic polymers (Chitosan, Zetag)
– Centrifugation & filtration
• Dehydrating – sun-drying, spray-drying, drum-drying, freeze-drying
• Cell disruption – mechanical (homogenizers, bead mills, ultrasound), chemical
• Product isolation and purification
– Chlorella, Spirulina, Dunaliella, Nannochloropsis
Algae & energy
• Biodiesel
– Algal fatty esters or vegetable oils or animal fats
– "B" factor (biodiesel in fuel)
• Oil Extraction
– 1. Expeller/Press; 2. Hexane solvent oil extraction; 3. Supercritical
Fluid extraction; Enzymatic extraction; Osmotic shock; Ultrasonicassisted
Extraction
• Ethanol from algae
– high carbohydrate content (Sargassum, Glacilaria, Prymnesium
parvum, Euglena gracilis)
• Cultivation of algae for CO2 capture
– can absorb over 2 million tons of Co2 a year per acre
Algae & Men
• macroalgae (commerce - 42 countries)
• food
– Laminaria (China, N.,S.Korea, Japan, Philipines, Chile, Norway,
Indonesia, U.S., India)
– Porphyra, Kappaphycus, Undaria (Wakame), Euchema, Gracilaria,
Caulerpa lentillifera (green caviar)
– Nori (Porphyra yezzoensis) – 13mil. t/y
• microalgae
• carotenoids, pigmenst, proteins, vitamins, …
– Dunaliella, Haematococcus, Arthrospira, Chlorella
– nutraceuticals, pharmaceuticals, animal feed additives, cosmetics, fertilizers
– N2-fixing cyano.-biofertilizers in rice fields
– Wastewater oxidation, bioremediation
• Microalgae – platform for recombinant proteins (e.g. hGH in Chlorela)