Copy of BGY4107 ALGAE FINAL EXAM.pdf

CHAPTER 9: CULTURING MICROALGAE IN OUTDOOR PONDS 1. Introduction Why: Cheaper than closed-photobioreactor Suitable for tropical climate Who: Spirulina platensis Chlorella vulgaris Haematococcus pluvialis Dunaliela salina Phaeodactylum tricornutum What:...

CHAPTER 9: CULTURING MICROALGAE IN OUTDOOR PONDS 1. Introduction Why: Cheaper than closed-photobioreactor Suitable for tropical climate Who: Spirulina platensis Chlorella vulgaris Haematococcus pluvialis Dunaliela salina Phaeodactylum tricornutum What: Shallow, unlined, unmixed pond Deep ponds Circular ponds Raceway ponds How: Factor Advantage Disadvantage Example/explaination Several small ponds Avoid culture Expensive - problem, since not the whole production plant is affected Pond size - - - Climatic condition May only be suitable Include: for a part of the year ➔ Daily and annual temperature range ➔ Annual rainfall ➔ Rainfall pattern ➔ No.of sunny days ➔ Degree of cloud cover Availability and cost - Cost of land may be If the cost are high, of land high raceway pond is  better Source and quality of Largest natural The larger the Natural source of water medium pond, the seawater is desirable greater water lost due to evaporation May contain heavy metals or contaminants Well-mixed, intensive Achieve high - - system cell density Final product If the biomass If the biomass - is for animal is for human feed, then it is consumption, less of a then the concern process must be cleaner 2. Pond-Mixing What: To include turbulent flow in the culture Except D.salina Why: Prevent settling of cell Prevent thermal and oxygen stratification How: In raceway cultures, velocities of 5.0 cm · s-1 are sufficient to eliminate thermal stratification and maintain most species of algae in suspension. However, such a low velocity is difficult to maintain in a large pond because of frictional losses in the channel and the corners and losses due to irregularities of the pond lining material velocities of at least 20 to 30 cm · s-1 Higher energy = higher operational cost 3. Relationship between pond-mixing and depth Algae require light, algae near the surface receive more light, thus if the cell density is high, then most of the light is absorbed in the upper few centimeters of the pond Shallow pond is desirable (uniform light intensity) Paddle wheel create mixing at a velocity suitable for raceway culture  good system, is characterized with a maximum productivity per unit pond area (areal productivity) can be achieved by having a balance of optimizing culture depth for photosynthetic efficiency and enhancing mixing/turbulence without damaging algal cells. 4. RACEWAY POND DESIGN AND CONSTRUCTION Types/Construction Factors Advantage Disadvantage Excavated ponds Cheap sloping walls can lead Less materials to an increase of insect and other contamination Insect easily blown into the pond by wind Constant depth difficult to maintain Above ground concrete Concrete Constant Expensive ponds depth Concrete may wear Suitable unevenly over time for leading to water flow freshwater problem algae Rough (Chlorella) Increased friction, reduced water flow PVC High Inhibit growth of algae longevity Contain phthalic acid esters as plasticing agents (cotain unreacted vinyl chloride) Use of lead to stabilize Algae may accumulate the heavy metal CPE Doesn’t Some black CPE inhibit linings is not approved algae for food in USA growth Difficult to work with Does not cause hazard to human  Carbonator Addition of CO2 may increase algae growth 5. Strain Selection General Characteristics: Biochemical composition Temperature tolerance Resistance to mechanical & physiological stress Example: Spirulina sp. 6. Scale-Up This stage has highest chance of contamination by other algae and bacteria due to dilute inoculum Two ways: - Small laboratory flask cultures - 1 : 10 dilution ratio through successive volumes up to the production pond (for Spirulina this ratio is usually 1 : 5), scale-up from a 20-mL flask culture to a 10,000-m3 raceway production pond can take at least 8 to 9 weeks (additional cost for longer time period) - derive the inoculum from existing culture ponds - only Spirulina and Dunaliela due to their extreme environment, not Chlorella and Haematococcus (need axenic culture) 7. Culture Medium General Characteristics: Crowd requirements of the algae Constituent of the medium that may affect final product quality Cost Uses: Health food and nutraceutical - food grade chemicals used Animal feed - Cheaper industrial grade chemical How: cost of nutrients accounts for 10 to 30% of the total production costs Recycle medium that still contain nutrients to reduce environmental problems with discharging large volumes of nutrient-rich water 8. Pond management 8.1 Control and Management of Contaminants General Contaminants: Bacteria Virus Fungi Other Algae Zooplankton Insects Leaves Airborne material General Management: Operating culture system as a batch culture restarting the culture at regular intervals with fresh, unialgal inoculum (Chlorella & H.pluvialis) Providing conditions that favor the desired species over the contaminating species Allow long-term continuous culture Contaminants Examples of Algae Culture How to Manage Green algae Spirulina - Maintaining the bicarbonate concentrations above 0.2 M and the pH above 10 - Repeated pulses of 1 to 2 mM NH3, followed by 30% dilution of the culture Noncarotenogenic species of D.salina - Maintain high salinity Dunaliella Unicellular green algae Spirulina - Rotifers Monoraphidium and Chlorella Aquatic Insects (Ephydridae, Spirulina - Nettin in situ Corixidae and Chironomidae) - Preharvest screening Brine shrimps (Artemia and D.salina - Netting (raceway) Paraartemia) - 20% (w/v) NaCl or higher (large, unmixed pond) Branchionus Freshwater & marine culture - lowering the pH to  about 3.0 by the addition of acid and allowing the culture to stand at this pH for 1 to 2 hours Amoeba Chlorella or Spirulina - Ammonia treatment flagellate amoeba Fabrea D.salina - Increase salinity salina and some ciliate protozoa 8.2 Culture Monitoring Methods Benefits Regular microscopic examination detect any abnormal morphological changes and the presence of contaminating organisms such as other algae and protozoa Routine test on nutrient concentration Avoid unexpected nutrient deficiency Regular monitoring of changes in pH and O2 early warning system levels pulse amplitude for determining the physiological state of the modulated fluorometry (PAM) algae