BIOMAN 2011 WORKSHOP

MiraCosta CollegePresenter: Elmar Schmid, Ph.D.

“Biofuels Production & Analysis”

Session #2 – Algae Cultivation

Microalgae

• Hold great promise for future biofuels and nutriceuticals production.

• Microscopically small photosynthesizing life forms.• Average cell size around 5-10 μm.• Divide very rapidly under

suitable growth conditions. • Doubling times of algae can

be on the order of 8 to 36 hours.

• Have with 2-4% a much higher photosynthesis efficiency than agricultural plants.

Light Reaction

Dark Reaction

Algae

Photosynthesis

Oils

Other value products

Sunlight is emitted radiation or electromagnetic energy.

Electromagnetic energy is transported in rhythmic waves each with characteristic wavelength (λ), frequence (ν) and amplitude (A).

Light travels at a constant speed (c) of 300,000 km/s.

The “nature” of light

A

Full range of electromagnetic wavelengths. Wavelength of visible light reaches from 380nm (or close UV) to 750nm (or near infra-red spectrum). Green algae only use blue and red part of spectrum.

Electromagnetic spectrum

Fresh water in equilibrium with the atmosphere (0.038 vol% CO2) at 15oC contains about 14 μM dissolved CO2.

The KM values for known Rubisco enzymes are in the range between 30-70 μM.

Photosynthesis rate (and biomass production) increases in response to an increase in CO2 concentration.

From: Light & Photosynthesis in Aquatic Ecosystems: John T.O. Kirk; 2. Ed., Cambridge University Press, 1994; with modifications

184 W/m2

32.9 W/m2

9.4 W/m2

2.6 W/m2

Dissolved CO2 in H2O at PST

Rubisco, CO2 Concentration & Algae cultivation

High light intensities reduce the photosynthetic rate and biomass productivity of algae. Critical value of light intensity is between 200-500 μE/m2/s. Mechanism is not known, but build up of (UV) light induced oxygen radicals and other chemically reactive intermediates may destroy key components of algae photosystems.

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Net

Ph

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Anabaena

Chlorella

Light Intensity ( μE/m2/s )

Light compensation point

Maximum specificphotosynthesis rate Photoinhibition

Photooxidation

Each light wave has a clearly defined amount of energy transported and delivered in small energy parcels, called quanta or photons. The Planck equation allows calculation of the energy of a photon (or light quant).

E = Ћ x ν = Ћ x c/λ

Ћ = Planck’s constant = 6.626 x 10-34 J s (or 6.626 x 10-34 W s2).

Light & Energy calculations

The energy delivered by one mol of photons is calculated by multiplying the Planck equation with the Avogadro constant NA (6.023 x 1023).

(2) Emol = NA x һ x c/λ

The unit for equation (2) is called one Einstein or 1 E.

E.g. 1 mol of blue light with a wavelength of 438 nm has an energy of:

2.72 x 105 Ws = 272 kWs = 272 kJ

Solar irradiance is a radiometry term for the power per unit area of electromagnetic radiation at a surface (e.g. algae photobioreactor).

Irradiance due to solar radiation is also called insolation.

Solar irradiance is usually given in Watts per square meter (W/m2) or in micro-Einsteins per square meter per second (μE/m2/s).

Values for solar irradiance depends on the latitude and the season and varies between 1,500 μE/m2/s (330 W/m2) during winter and 6,000 μE/m2/s (1,320 W/m2) during the hot summer months.

Solar irradiance & Algae cultivation

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Latitude ( degrees )

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microE/sqm/s

Influence of latitude on the annual mean solar irradiance intercepted

Graphic©E.Schmid-2010

San Diego

MCC PBR (W/m2)

Hypertrophic water shed with algal bloom

In the 1960s, some lakes in the U.S. and Europe had phosphate levels exceeding 0.6 mg/liter

Uncontrolled algae growth in nature

Controlled algae growth in closed photobioreactor

Taken from the website of Bioprodukte-Prof. Steinberg GmbH, Germany (http://www.bioprodukte-steinberg.de)

CO2

Aeration pump

FlowMeter

Thermostat32W Fluorescent

Light

3-Wayvalve

SterileFilter (0.22μm)

Conical TubePhotobioreactor

AerationTube

Outlet

WaterTank

Lid

Graphic©E.Schmid-2010

MiraCosta Bubble Column Photobioreactor

Educational bubble column photobioreactor work station

Photo©E.Schmid-2010

Important parameter in algae cultivation

Parameter Unit•Optical density (OD) -•Cell count cells/ml•Biomass production g dry/l•Biomass productivity g dry/l/d•Oil content % (w/w)•Oil productivity mg oil/l/d•Photosynthesis rate µmol O2/mg Chl/h•Aeration rate ml (ccm) air/min•Solar irradiance µE/m2/s or W/m2

Cell counting method

• Compound microscope• Prepare hemocytometer• Observe algae at TM 400x• Count cells in 4-16 micro-squares• Calculate cell density (in cells/ml)

Cell density = cell count x DF x 104

DF = Dilution factor

0.1 mm3 (ul)

Mean doubling time “g”

• Growth constant “k”• Mean doubling time “g” = 1/k• Cell count at time t1: N(t1)• Cell count at time t2: N(t2)

N(t) = N0 x e k x t

N(t)

Time tt1 t2

g = 0.301 x t / log N(t2) – log N(t1)

Microalgae growth curve