Algae in the waste-to-fuel cycle

Algae in the waste-to-fuel cycle

May 21, 2015

Corn and algae can work together more efficiently to maximize the energy output of waste streams. Photo: Castalia Group

ohn O’Renick, in this insightful piece from the Portland (Oregon) Tribune, writes about the problems we create from treating waste streams as garbage to be disposed of instead of assets for energy production. He suggests that, by using integrated biotechnologies to extract energy as efficiently as possible at every step from both our waste streams and agricultural products, we would take a long step closer to ending our dependence on fossil fuels, and we’d do a far better job of cleaning up our wastes.

A farmer grows corn. People eat the corn, its highest, best use. The stover – stalks and leaves – is still full of sugars that can be extracted to make ethanol, instead of increasing food prices and world hunger by putting corn in gas tanks. What is left are yeasts that are mostly protein, and only at this point do you feed any of the corn to livestock. The animal manures are mixed with the correct amounts of other farming wastes (like bedding straw) for most efficient gas production, and biodigested on site.

It is more efficient to burn the gas to cook and make hot water and heat well-insulated buildings with 90-plus percent efficient furnaces than it is to burn it in a 30 percent efficient reciprocating engine to make electricity, so put it to its highest, best, most efficient use – which should be a mantra for everything society does.

The solid remnant from the digester is sterile, stink-free fertilizer. The liquid leftovers, combined with the CO₂, (about half the gas produced) could be used to grow algae for biodiesel. Once the oil is extracted from the algae what’s left is carbohydrate and protein – animal feed, fish food, more ethanol, chemical feedstocks – and the algae cleans the water nicely.

People ate the corn. Their wastes, mixed with the right amounts of food waste or shredded lawn and garden debris, go to a biodigester designed to make methane as efficiently as possible, not just to clean sewage. This cleans up three waste streams at once, and produces clean, carbon-neutral, natural natural gas.

If the feedstock could be kept clean of heavy metals, petro products, etc., the solid remnant from the sewage biodigester would be a better soil amendment than when it went in, sterile, and far less odiferous.

If we can’t clean up our sewage, it can be pyrolized – volatiles cooked out to recover liquid hydrocarbons that can be turned into diesel and gasoline (e.g., Fischer-Tropsch process), and the biochar left from that is mostly carbon, so pumping it back down old oil wells would sequester carbon from the atmosphere.

Back on the farm there is still a liquid waste stream, full of nutrients, and about half the gas produced is carbon dioxide. Combine those to grow algae, which nicely cleans up both, and gets another energy cycle out of the CO₂ before releasing it back to the atmosphere. Press the algae for oil for biodiesel, which is a far better fuel than ethanol or methanol or hydrogen or biobutanol or any other biofuel being developed – more energy dense, less volatile, easier to store and transport, non-toxic, and easily cleaned up, when spilled, by harmless bacteria.

The right algae grown in clean feedstocks, once pressed for oil, are mostly carbohydrate and protein, vitamins and minerals – animal feed; or extract the carbs to make more ethanol, and the remnant protein is still animal/fish food. But if the right algae are grown in clean feedstocks, the carbs and proteins and vitamins and minerals left once the fats have been removed are a virtual health food and could end world hunger, almost as a byproduct of developing a clean, sustainable transportation fuel.

And all of this essentially from making the most efficient use of a crop of corn. We should be investing in the technologies that make the most sense.