Note from the author:
While I am keeping the tone brash and casual for fun reading, I am absolutely committed to scientific accuracy. I am happy to get as technical as necessary to get to the bottom of any issue of interest, including original references, mathematics, etc. Please give me your technical feedback, I will make sure that everything is explained and referenced!
Here are some answers to basic questions many people ask about algae farming:
What are algae?
The algae we are talking about are microscopic, single-celled plants that live suspended in water.
Why are they interesting?
Algae were the first photosynthesizers on the planet, and created the Earth’s oxygen atmosphere billions of years ago. Despite being microscopic, they can routinely be observed from space, as they transform the appearance of entire oceans. Algae generated more than half of the oxygen you now breath, and recycle a comparable fraction of the globe’s carbon dioxide back into biomass, a quantity far exceeding that generated by human beings.
When farmed, they are capable of producing more than 100x oil per acre than the U.S.’s current main oil crop, soybeans. This means that it would be possible to grow enough oil in an area the size of Illinois to make the whole U.S. energy independent.
U.S. petroleum importation: 9,783,000 barrels/day
9,783,000 barrels/day * 42 gallons/barrel * 365 days/year = 150B gallons/year
Assuming we can replace crude with algae oil, and average algae pond yields of 4000 gallons/acre/yr, we’d need 37 million acres of algae to replace the importation of petroleum. This is the area of the state of Illinois, which is less than half the area of New Mexico!
Unlike any other biofuel crop, they do not compete with conventional agriculture, as algae are capable of growing in deserts, or on the surface of the ocean, using salt or waste water. And they can, at the same time, clean waste water and exhaust from power plants, potentially creating a net-positive ecological impact. They can also produce a wide variety of products, potentially unlimited if one considers the possibility of genetically modifying them.
Will they really be able to replace oil?
Probably, no, mainly because no one has figured out how to do it cheaply enough. That said, there are many potential ways to cut the cost of production (and raise profits), but no one has yet publicly demonstrated a clear path. We’ll get into the specifics on individual techniques below.
In any case, we’ll be dealing algae whether we like it or not, as destructive algae blooms are increasing around the world, driven by rising populations, increasing use of fertilizers and phosphate-bearing products around the world, as well as by global warming, and in many places the algae create vast and growing “dead zones” as they decay.
How does one grow algae?
Anyone who has left a container of water alone long enough knows that algae are easy to grow. All one needs is water, sunlight, and carbon dioxide, plus a little fertilizer — the same kind that land plants use (NPK plus micronutrients). To grow a particular strain of algae, though, requires having the correct temperature, acidity, salinity, and mixing, and eliminating parasites, predators, toxins, and competing algae. Under the right circumstances, they will grow very rapidly — even doubling their numbers more than once a day.
How does one harvest algae?
This is one of biggest tricks of algae farming. Even when an algae culture is so thick that its growth is limited by the fact that the light get absorbed by the surface algae and thus can’t reach the deeper one, the culture is still 99.9% water. Thin photobioreactors can reach higher densities, as little as 99% water when optimized. This means that for every unit of algae you harvest, you have to handle between 100 and 1000 units of water. Most currently-operating commercial algae farms use centrifuges to separate the algae from the water. Spinning all this water at high speed amounts to a major expense, both for the machinery itself and electricity to run it — not a show-stopper when making high-value nutraceutical and cosmetic products, but to make low-value products such as fuel economical, alternatives must be found. Common techniques include getting the algae to sink to the bottom, or float to the top, as well as filtration, heating, and electro-kinetic techniques. There are also algae cultivation techniques that “milk” the algae, obtaining products without removing the algae from the water. We’ll be talking about these important issues more later in the blog.
How is algae converted into useful products?
In some cases, once the algae are dried, they are already products — this is true of most nutritional algae. In general, though, purified algae products — e.g., oil — need to be extracted. In laboratories, chemical extraction based on two solvents (e.g. hexane and an alcohol) is generally used, sometimes with a step to disrupt the cell wall first, as otherwise the dissolved lipid has to diffuse through it. The subsequent processing of the oil into fuel products can be done through transesterification to create biodiesel, through techniques that can be carried out in a garage, or it can be dealt with using refinery-type processes of cracking and reforming to make fuels indistinguishable from petro-diesel, gasoline, or jet fuel.