Script draft for algae production... not yet finished

Posted by Stella

Microalgae are one of the planet’s most promising sources of renewable biomass. They exist as unicells, colonies and long filaments, and can grow in a wide variety of conditions – from freshwater to extreme salinity. They are more efficient converters of solar energy than terrestrial plants and take carbon dioxide out of the atmosphere as they grow.

Macroalgae, or seaweeds, are also highly efficient at converting solar energy into biomass and their simple internal structure makes them a better material than land plants for complete biological degradation.

During the ... project, strains algae of characterised by high biomass and high oil yields will be selected for genetic modification. The objective is to genetically engineer micro-algae so that firstly it enhances lipid production rates by increasing the activity of the apprpriate enzyme(acetyl-CoA carboxylase (ACCase), a biotin-containing enzyme that catalyzes an early step in fatty acid biosynthesis, may be involved in the control of this lipid accumulation proces), secondly mutating and photoadapting algal strains to
improve flux tolerance by reducing chlorophyll antenna size, and thirdly secrete oil droplets into the surrounding medium. This could lead to continuous harvesting with clean separation of the oil from the algae.

The Culture Collection of Algae and Protozoa (CCAP) at the Scottish Association for Marine Science (SAMS) holds the largest algal culture collection in Europe, some 2700 strains, from which all suitable candidate strains will be screened.

The algae will be grown in closed bioreactors with light, CO2 and nutrients supplied to optimise biomass growth and oil productivity. Once a suitable genetically engineered strain has been identified, there is the potential to enter into partnership with energy compainies for further investment.

There are three key requirements for biodiesel production:

1. Sustainable production of high-oil-yielding microalgae strains

This is the critical requirement, given that there are 200,000-800,000 estimated algae strains, each with differing optimal growth conditions. Considerable research has already been invested into identifying suitable strains of algae. Those most widely utilized for current commercial applications belong to the genera Chlamydomonas, Chlorella, Haematococcus, and Dunaliella, with an oil content of 25-30%. Diatoms, that is brown algae, have an oil content of 60-70%. The number of potential strains may be narrowed down by applying criteria, such as:

• efficient phosynthetic capacity
• high lipid content, 
• faster growth rate, 
• possibly thermophilic, 
• survive in hydrocarbon mixture exocytosed, 
• possession of a cell membrane so that the oil may be diffused into the surrounding medium, or a mechanism through the cell wall by which oil may be secreted

 
Once a suitable strains have been identified, they can be genetically engineered so that they exocytose their oil droplets. The process is likened to milking cows.

"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."

The milking of algae has been done by solvent extraction methods, e.g. dicholoromethane, that do not kill the cells, but in which they are otherwise passive. Here, we propose altering cells so that they actively secrete their oil droplets.

• The process has already been announced by Synthetic Genomics in partnership with Exxon Mobile.
• 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
• 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.

In addition each algae strain will respond differently to varying temperatures, pH, light, as well as photo-oxidative and nutrient stress. These condions can be calibrated in closed photo-bioreactors

A mixture of air and CO2, is bubbled through the reactor, providing both a source of carbon and mixng the medium. The reactor is surrounded with solar-powered LEDs, so that the outer surface is illuminated with light, while the central core is shaded. Nutrients in the form of nitrogen, phosphorous, and in the case of diatoms, silicon are supplied.

The project can take advantage of the almost daily advancements in algal biotechnology by applying new discoveries to our chosen alage strains.

For example

• Projected annual algal biomass yields could be increased from 1g dry weight m-2 h-1, to 100g. by subjectiong algae to microsecond pulses of intense red light at tens to hundreds of kilohertz. Uses a combination of: ultra-efficient high-flux photovoltaics converting solar energy to electricity, and LEDs then converting electricity to pulsed nominally monochromatic red light (review paper: Spirulina platensis (cyanobacteria).
• In a two-phase cultivation process, that is, 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.
• Only 3 weeks ago researchers at MSU found that when baking soda was added at a particular time in the growing cycle, it more than doubled the amount of oil produced in half the time. The discovery should have broad application. 
• Oscillating microbubbles can boost algae yields by 30 percent, using 18% less energy than standard sparging systems. (20 micrometers versus 1–3-mm diameter for sparging. Microbubbles of CO₂ dissolve faster, keep the suspension well mixed, and also help remove oxygen (which is toxic to algae). (Patented)

2. Extraction of the oil from the algae 

The conventional technique involves evaporation of the watery medium, pressing to squeeze the oil out, and centrifuging to separate the oil from the remnants. The cost is estimated to be as much as 50% of biofuel production. 

By secreting the oil directly into the medium, the extraction process can almost entirely be bypassed. 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.

Solvent is dichloromethane. 

3. Conversion of microalgal oil into biodiesel

The parent oil consists of triglycerides. It then undergoes transesterification, that is, it is reacted with methanol to produce 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.