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1 Microalgae Grown in Photobioreactors for Mass Production of Biofuel

2 Need for Sustainable Energy The Price of Energy is Going UP Oil reserves are depleting World demand for energy is increasing Economic Stability/National Security Not good to have energy dependence on foreign countries Global Warming Fossil fuels release greenhouse gases

3 Why focus on Biodiesel? Ease of Implementation Diesel engines require little modification Many homes currently use oil for heat Less Fuel Would be Needed than Ethanol Has a 56.25% higher energy content Diesel engines are more efficient than spark-plug plug

4 Oil Yield Comparison Crop Oil yield (L/ha) Land area needed (M ha) a Percent of existing US cropping area a Corn Soybean Canola Jatropha Coconut Oil palm Microalgae b Microalgae c ,900 58, a For meeting 50% of all transport fuel needs of the United States. b 70% oil (by wt) in biomass. c 30% oil (by wt) in biomass

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6 ngmarkets.com/biodi esel/default.asp

7 Advantages of Algae High Quality Biodiesel Cold filter plugging point comparable to #2 diesel 2 No Phosphatides,, as in biodiesel from plants 3 Can capture CO 2 from exhaust streams Less Land is Required More biomass is obtained Contains higher concentrations of lipids than terrestrial plants

8 Oil Content of Some Microalgae 5 Microalga Oil content (% dry wt) Botryococcus braunii Chlorella sp Crypthecodinium cohnii 20 Cylindrotheca sp Dunaliella primolecta 23 Isochrysis sp Monallanthus salina >20 Nannochloris sp Nannochloropsis sp Neochloris oleoabundans Nitzschia sp Phaeodactylum tricornutum Schizochytrium sp Tetraselmis sueica 15 23

9 Algae Production Methods Raceway Ponds Open system, used for production of algae for health food Photobioreactors Maximize algae growth with controlled conditions

10 Photobioreactor Variations

11 Maximize the Biomass Production Rate, g/l-d Equal to the product of the dilution rate and effluent biomass concentration. Defined as the ratio of the incoming flow rate to the reactor volume Dilution rate is equal to the specific growth rate at steady state

12 Specific Growth Rate Defined as the increase in cell mass per unit time per unit cell mass. May be determined empirically by: specific growth rate = [μ]= Ln (N2 / N1) / (t2 - t1) Where N1 and N2 = biomass at time1 (t1) and time2 (t2) respectively; Levasseur et al (1993).10 Its units are inverse hours. May be modeled as a function of solar irradiance and the maximum specific growth rate. Practical Model: μ = μ max *I av /(I k + I av ) Where Iav is the average irradiance inside the reactor and Ik is an organism-specific specific constant.

13 Design Considerations Effects of Solar Irradiance Solar inhibition Mass Transfer of Gases Through Fluid CO 2 supply and O 2 removal Cell Damage from Shear Stress For high flow rates Nutrient Addition, ph and Temperature Control

14 Solar Irradiance and Inhibition Dissolved Oxygen is directly related to photosynthetic activity. Photoinhibition causes decline in photosynthetic activity at midday.

15 Solution to Photoinhibition Increase cycle frequency of fluid between dark and light zones. Cycle frequency is increased by increasing the fluid velocity.

16 CO 2 Bubbling - Mass Transfer Carbon dioxide needs to be added continuously CO 2 can be consumed at a rate of 26 g CO 2 /m 3 -h Oxygen produced during photosynthesis needs to be removed. High oxygen concentration inhibits growth Photooxidation can damage cells Influence of the oxygen molar fraction in the injected gas on: (a) the steady-state biomass concentration; and (b) the photosynthetic activity (i.e. the volumetric oxygen generation rate) in indoor cultures. The dilution rate and the irradiance level were h 1 and 300 μe m 2 s 1, respectively. 1

17 CO 2 Bubbling Effect of Fluid Velocity Superficial fluid velocity is related to gas velocity and bubble diameter Cycling frequency between light and dark zones is dependent on fluid velocity Shearing damage to cells results from increased radial velocity High radial velocity decreases length of micro-eddies So does increasing the tube diameter

18 Nutrient Addition, ph and Temperature Control Algae require nitrogen and phosphorous Ammonia is the preferred nitrogen source Conjunction with WWTP Optimal ph is between 7.5 and 8.5 Nutrient addition increases ph Sufficient CO 2 must be added to keep the ph from increasing too much Optimal temperature is between 20 and 30C Maintained with heat exchangers and cooling water Especially important at night to reduce losses due to respiration

19 Converting Algae to Fuel Transesterification Most common method of converting vegetable oil to biodiesel Requires the algal suspension first be harvested, dried, and pressed for oil

20 Converting Algae to Fuel Thermochemical Liquefaction Can be applied directly to algal suspension Uses high temperature and pressurized nitrogen to evaporate water CH 2 Cl 2 Catalyst Separates Biodiesel

21 Thermochemical Liquefaction of B. braunii Heating energy for liquefaction: 6.69 MJ/kg For a biomass concentration of 0.5 g/l produced from raceway ponds Heating value of oil produced: 45.9 MJ/kg Concentration in photobioreactors: 6.6g/L Much less energy required on kg basis

22 Achieved Rates of Productivity for P. tricornutum Volume L U L m/s D, h -1 I wm C b, g/l P b, g/l-d ν, Hz Source

23 Energy Yield Maximum tube length = 80 m Maximum tube diameter = 0.1 m So maximum volume of single reactor = L = m 3 Assume oil production rate = 2 g/l-d * 50% oil content = 1 g/l-d = 1 kg/m 3 -d If 270 tubes can fit on one acre, than 62,000 kg of oil/acre could be produced. Or (density = kg/l) 71,759 L = 19,136 gal/acre

24 Wow!! Almost 20,000 gallons/acre of oil that may potentially be produced with current technology With thermochemical liquefaction, the energy required to extract oil is minimal Main Constraint: Huge Capital Investment reactor tubes, water pumps, gas pumps, autoclave for liquefaction. Economies of Scale How long before oil production pays for infrastructure investment?