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The following was a comment provided at one of the blog posts on ethanol I read recently. While I’m no expert on the heterotrophic processes, the arguments here really sound interesting;
The Advantages of Heterotrophic Algae Grown at Corn Ethanol Refineries
Heterotrophic algae does not require sunlight, but the tradeoff is you have to feed it some kind of sugar. Initially, that sounds inefficient. Why expend the cost of sugar, when you can grow algae in sunlight for free. Look a little deeper, and here are the advantages of growing heterotrophic algae in the dark: (1) By growing algae in the dark, the process is simplified. Otherwise, you have to get the algae exposed to the light, or get the light to the algae. That takes up solar surface area, which translates into large land masses. (2) Because the algae can be grown in the dark in tanks, it can be grown anywhere, with a minimum footprint. (3) Heterotrophic algae, grown in nutrient rich water, becomes many times more concentrated, at a hyper fast growth rate.
HETEROTROPHIC algae grows in the dark, and multiplies rapidly when fed sugars or local biomass cellulose converted to sugars. Beside Solazyme, this technology is also being developed by East Kentucky University and General Atomics, working together. They are leveraging local biomass sugars by feeding it to heterotrophic algae grown in vats. Researchers claim that heterotrophic algae can reach densities in the dark that are 1,000 times higher than strains of photo-autotrophic algae that must be grown in the light.
Heterotrophic algae can be grown in the dark in tanks, using very little land. Tanks can be stacked a hundred feet underground, or stack them a hundred feet high above ground. Stack them in a high rise. Grow it in gray water in your basement, on your roof, under your backyard, or under a parking lot, using no additional land. Grow it on a barge.
Take local sugars derived from biomass, corn or sweet sorghum, or food and paper waste, or sewage, or what have you. And leverage the sugars to multiply the algae many times. That is going to be your massive source of feedstock for ethanol, biodiesel, feed, fertilizer, or for whatever you want to make.
Corn ethanol refineries have readily available waste heat, CO2 waste, nutrient rich waste water effluent, and corn sugars. This is a perfect match for growing heterotrophic algae. Why take corn sugar and feed it to algae? Because you multiply the feedstock many times in a short period of time, onsite. It’s conceivable that you could combine a tablespoon full of live algae with a pound of corn sugar, and bubble CO2 waste through a medium of nutrient rich waste water effluent, keep it warm with waste heat, and get a return of 20 pounds of algae or more within 48 hours.
Take all the corn sugar that is now going straight to 10 billion gallons ethanol, and instead, feed it to heterotrophic algae in tanks. At only 20X, that would yield upwards of 200 billion gallons of ethanol per year in the U. S. alone.
Out of tens of thousands of strains of algae, thirty two types of heterotrophic algae have been identified thus far. Some are high in starch. Some are high in oil. Some are high in proteins. Depending on what you want to produce, you would select your strain accordingly. And after your primary product has been taken from the feedstock, you would also make value added products from the remaining materials. Grow a high starch variety of algae ideal for ethanol production. Grow a variety of algae ideal for oil production, or high protein feed production, or fertilizer production. Since corn ethanol plants already produce distillers grains and supply the livestock industry, they would now have a second high protein feed product to market alongside.
We now have 172 corn ethanol refineries, which form a viable framework for a much bigger biofuel and feed industry yet to come.
Well, I guess I have one big question for those who think heterotrophic growth method is great. Whatever be the X (10X, 20X) whatever, if the algae are growing to derive most of their energy from sugar (non-photosynthetic sources), you will need almost as much sugar or more as the energy generated ultimately from ethanol (if the only energy sources are sugar, nutrients, CO2 and some warmth). The following sentence sounds too good to be true: “It’s conceivable that you could combine a tablespoon full of live algae with a pound of corn sugar, and bubble CO2 waste through a medium of nutrient rich waste water effluent, keep it warm with waste heat, and get a return of 20 pounds of algae or more within 48 hours.” How does it produce 20X mass from just less than 2X of sugar + initial amount algae? Are the rest 18+ pounds derived from CO2 and nutrients? In that case, we are going to need a lot of nutrients and CO2, and both have costs attached.
I need to dig deeper into the economics of heterotrophic growth, but the comment has surely tickled my interest. I doubt the numbers are as good as those presented at the comments, but let me first do more research on this.
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