Monday 29 November 2010

Summary of algae research / proposal

Posted by Stella Kin

I've summarised all the algae biomass growth and oil extraction into one post. I'll condense this into power point bullet points shortly.

What I think we should conisder is putting the money into research as discussed before. Like the start up conceived by Wageningen University, we can invest in a number of areas of research including which algae types can be genetically modified to secrete oil, and what conditions of light, nutrient stress, CO2 levels, photo-bioreactor design etc will optimise oil production. Without the algae to begin with, we won't have definitive figures for yields, but but we can make rough estimates from research from different papers. There is no guarantee of success, but if the start-up is successful, we can approach (or most likely be approached by) private energy/oil companies for investment similar to the Exxon-Synthetic Genomics partnership.

Proposal for a start-up to facilitate the research of growth and oil production of microalage in a photobioreactor

Why microalgae?
Algae (as opposed to other plants) are a natural choice for maximum-yield biofuels because of: 

Biomass growth
  1. They intrinsically offer the greatest flux tolerance and photosynthetic efficiency as a consequence of minimum of internally competitive plant functions,  
  2. enjoy fast reproductive cycles,  
  3. have limited nutrient requirements, requiring only sunlight, water, minerals and carbon dioxide, and
  4.  flexible cultivation conditions 
    • They can be grown under conditions which are unsuitable for conventional crop production, unlike some other first- and second-generation biofuel feedstocks.  
    • They can be cultivated under difficult agro-climatic conditions and are able to produce a wide range of commercially interesting byproducts such as fats, oils, sugars and functional bioactive compounds. 
    • They can readily be exposed to temporal and spectral irradiation distributions and intensities that are not encountered in nature but are optimal for bioproductivity via cleverly crafted photonic systems.
    • They can be cultivated in marine water and waste water, deserts, etc, etc.
The algae biofuels produced are:
  1. non-toxic, contains no sulfur, and is highly biodegradable. 
  2. Bio-oil produced by photosynthetic algae and the resultant biofuel will have molecular structures that are similar to the petroleum and refined products we use today. 
  3. They provide much higher yields of biomass and fuels, 10-100 times higher than comparable energy crops. Algae could yield more than 2000 gallons of fuel per acre per year of production. Approximate yields for other fuel sources are far lower:
    - Palm — 650 gallons per acre per year
    - Sugar cane — 450 gallons per acre per year
    - Corn — 250 gallons per acre per year
    - Soy — 50 gallons per acre per year
Research and potential
  1. Algae used to produce biofuels are highly productive.  As a result, large quantities of algae can be grown quickly, and the process of testing different strains of algae for their fuel-making potential can proceed more rapidly than for other crops with longer life cycles. 
  2. If successful, bio-oils from photosynthetic algae could be used to manufacture a full range of fuels including gasoline, diesel fuel and jet fuel that meet the same specifications as today’s products.
Environmental benefits
  1. Microalgae are capable of fixing CO2 in the atmosphere, thus facilitating the reduction of increasing atmospheric CO2 levels. This provides greenhouse gas mitigation benefits.
  2. Use and cleaning of wastewater 
Which algae? 
Those most widely utilized for current commercial applications belong to the genera Chlamydomonas, Chlorella, Haematococcus, and Dunaliella

Diatoms (brown algae), a group of silicon-rich microalgae, and prokaryotic cyanobacteria also offer substantial opportunities for metabolic engineering and biotechnology.
  • Responsible for 1/5 photosynthesis on earth
  • Fixes 25-30% of global CO2
  • Oil content is 60-70% saturates
  • Theoretical calculation - yield 30,000L (or 200 barrels) of oil h-1 per annum.
  • Photo-oxidative stress and nutrient structure (N, Si) can double or triple the production of oil because of a shift in lipid metabolism from membrane lipid synthesis to storage of neutral lipid
  • Could conceivably be genetically engineered so they secrete the oil they produce rather than store it, and therefore need not to be destroyed to obtain oil
    • eliminates cumbersome and expensive extraction process
    • construction of solar panels/angiosperm leaf to cultivate and extract algae
    • diatoms secreting gasoline (instead of crude oil)
What needs to be done?
  1. Identify diatoms and species with high lipid content, faster growth rate, in low cost ..., thermophilic, survive in hydrocarbon mixture exocytosed, efficient photosynthetic capacity.
  2. Design of new technology to grow and harvest algae, or use current technology - bioreactors?
  3. Genetic modification of algae to secrete oil, produce gasoline, change chlorophyll atennae size, etc.
The first is the kep step as there are thousands of micro-algae types and hundreds of just diatoms. Identifying an algae that fits with the criteria is relatively easy. However each algae will respond differently to varying temperatures, pH, light, as well as photo-oxidative and nutrient stress. The question is which algae in which conditions will maximuse oil yield? And can the algae be genetically modified to secerete it's oil?

Step 2: Modification of current bioreactor designs

Photobioreactor supplies light, CO2, nutrients, mixing and optimal culture density

The light in an aerated vertical column can be supplied by light redistribution plates (solar powered), LEDs (possibly solar powered) or even optical fibres


Adv: High mass transfer, good mixing with low shear stress, low energy consumption, high potentials for scalability, easy to sterilize, readily tempered, good for immobilization of algae, reduced photoinhibition and photo-oxidation
Disadv: Small illumination surface area, their construction requires sophisticated materials, shear stress to algal cultures, decrease of illumination surface area upon scale-up
 

Light
One of the limiting factors is in fact light. Diatoms flourish at low light levels. Above a certain value of light intensity, a further increase in light level actually reduces the biomass growth rate (see figure) – photoinhibition at light intensities only slightly greater than the light level at which the specific growth rate peaks.


One solution advocated is irradiating the algae with microsecond pulses of intense red light at tens to hundreds of kilohertz. Through turbulence, the algae are therefore cycled through light and dark zones at high frequency, allowing an increase in the algae's flux tolerance to light. Projected annual algal biomass yields could be increased from 1g dry weight m-2 h-1, to 100g.

Photosynthesis driven with pure red light is 5 times more efficient than with full-spectrum sunlight. It could involve a combination of: (a) Ultra-efficient high-flux photovoltaics converting solar energy to electricity, and (b) LEDs then converting electricity to pulsed nominally monochromatic red light
Photovoltaic-LED combination can transform solar radiation into pulsed red light at conversion efficiencies of ∼20% with commercially available components

Effect of nutrient deprivation
Under nutrient sufficient and deficient conditions, for specific strains, lipid productivity increased from 117 mg/L/day in nutrient sufficient media (with an average biomass productivity of 0.36 g/L/day and 32% lipid content) to 204 mg/L/day (with an average biomass productivity of 0.30 g/L/day and more than 60% final lipid content) in nitrogen deprived media. 

In a two-phase cultivation process (a nutrient sufficient phase to produce the inoculum followed by a nitrogen deprived phase to boost lipid synthesis) the oil production potential could be projected to be more than 90 kg per hectare per day. 

CO2
When added at a particular time in the growing cycle, baking soda more than doubled the amount of oil produced in half the time in three different types of algae. If growers can produce oil faster, they can reduce the opportunity for contamination to ruin the product. The three types of algae used in the study were not closely related, so the discovery should have broad application. (11 November 2010) 

Mixing using microbubbles
Airlift bioreactor usesing oscillating microbubbles can boost algae yields by 30 percent. It uses 18% less energy than standard sparging systems. The generator improves the performance of air-lift loop bioreactors (ALBs) by producing smaller bubbles, around 20 micrometers versus 1–3-mm diameter for sparging. Produces 30% more algae than one fed with conventionally produced bubbles. Microbubbles of CO2 dissolve faster, keep the suspension well mixed, and also help remove oxygen (which is toxic to algae). (Patented)

Step 3: Genetic modification to secrete oil
"We do not harvest milk from cows by grinding them up and extracting the milk. Instead, we let them secrete the milk at their own pace, and selectively breed cattle and alter their environment to maximize the rate of milk secretion.266–269 We do not simultaneously attempt to maximize their rate of reproduction. Perhaps we could do the same with diatoms. The milking of algae has been done by solvent extraction methods that do not kill the cells,270,271 but in which they are otherwise passive. Here, we propose altering cells so that they actively secrete their oil droplets."
It may be possible to genetically engineer diatoms so that they exocytose their oil droplets. This could lead to continuous harvesting with clean separation of the oil from the diatoms, provided by the diatoms themselves.

Exocytosis of beta-carotene globules has been hypothesized as the mechanism of extraction into the biocompatible hydrophobic liquid dodecane from the unicellular green alga Dunaliella, perhaps accelerated from the natural exocytosis mechanism of this species by the presence of the dodecane. Higher plants have oil secretion glands, and diatoms already exocytose the silica contents of the silicalemma, adhesion and motility proteins, and polysaccharides, so the concept of secretion of oil by diatoms is not far-fetched.

Adapting the bioreactor for oil secretion
A system that is closed except for oil secretion and gas exchange may be able to conserve micronutrients, especially if little or no net growth of cells is occurring. This might solve the productivity gap by getting 10-200 times more oil, compared to oilseed crops.

With at least a boundary layer of water on the diatoms, secreted oil droplets would separate under gravity, rising to the top, forming an unstable emulsion, which should progressively separate. The oil could then be removed, very similar to the cream that rises to the top of milk.


Gasoline production?
Biodiesel refers to a vegetable oil- or animal fat-based diesel fuel consisting of long-chain alkyl (methyl, propyl or ethyl) esters. Biodiesel is typically made by chemically reacting lipids (e.g., vegetable oil, animal fat) with an alcohol. Biodiesel can be used alone, or blended with petrodiesel. However, higher levels of polyunsaturated fatty acids tend to decrease the stability of biodiesel.

The bulk of a typical gasoline consists of hydrocarbons C4-C12.

Hypothesis that some short-chain hydrocarbons are produced during diatom and dinoflagellate lifecycles. Their results suggest that ethane, ethene, propane and propene are produced during the autolysis of some phytoplankton, possibly by the oxidation of polyunsaturated lipids released into their culture medium.

In contrast, isoprene and hexane appear during phytoplankton (of which diatoms are a type) growth and are thus most likely produced either directly by the plankton or through the oxidation of exuded dissolved organic carbon. Studies predict that high concentrations of ethylene are produced in areas with high primary productivity. This is supported by observations of C2-C4 alkanes in ocean surface waters, along with isoprene (C5), also attributed to algae (mostly diatoms), and direct laboratory observation of isoprene production by diatoms.

Biodiesel production

The parent oil consists of triglycerides. It is reacted with methanol (transesterification) producing methyl esters of fatty acids, that are biodiesel, and glycerol.


Yields of methyl esters exceed 98%. The biodiesel is recovered by repeated washing with water to remove glycerol and methanol.

The hydrocarbon mixture is similar to crude petroleum, along with volatile alkane and alkene gases (C2-C5). This conversion allows the generation of a burnable fuel of very high calorific value.

Lipids in diatoms are converted to hydrocarbons:
C50H92O6   =>    CXHY           +        nCO2
    lipids               hydrocarbon          carbon dioxide

From this, it is evident that the direct extraction of diatom lipids is a more-efficient method for obtaining energy than fermentation. This can occur by having solvents such as CH2Cl2 (dichloromethane), through the direct expression of the liquid lipids, or a combination of both methods. The thermochemical liquefaction process often results in a heavy oily or tarry material that is then separated into different fractions by catalytic cracking. As with hydrocarbons derived from other forms of renewable biomass, microalgal diatom lipids can be converted to suitable gasoline and diesel fuels through transesterification.

4 comments:

  1. Heya¡­my very first comment on your site. ,I have been reading your blog for a while and thought I would completely pop in and drop a friendly note. . It is great stuff indeed. I also wanted to ask..is there a way to subscribe to your site via email?








    Research proposal

    ReplyDelete
  2. Hey,
    I like this post... have been searching simple info on biofuels.. and this is so simple and awesome... too helpful...
    Thanks alot...

    ReplyDelete
  3. Nice post…Its really helpful to us…
    Research Proposal

    ReplyDelete
  4. Hi, this is Dr. Sama AlMaarofi. I am highly interested to discuss the possibility of using your research proposal idea to apply for a research grand. If you agree, you will be the main corespondent advisor for the project.
    if you are interested we can discuss this matter in details. please contact me at salmaaro@lakeheadu.ca

    ReplyDelete