It’s not often publicly remarked upon, but the emphasis on biofuel capacity in the United States has a bit of an international political component to it. American farms exported well over 100,000 metric tons of corn and oilseed in 2010. Some major portion of that production was sent to oil-rich areas which are short on food. The E85 boondoggle can be viewed as a simple declaration to those nations: we can burn your food in our cars, but you can’t eat your oil.
America’s pretty good at producing another item besides food, however, and if early research is any indication, it could be used to run a significant portion of the nation’s car and truck fleet.
According to an article in Chemical & Engineering News, a new process developed by a team led by South Korean scientist Eilhann Kwon makes it easier to extract lipids from… well, you know:
Kwon and his colleagues found a cheaper feedstock for biodiesel production: sewage sludge, the semisolid material left over from wastewater treatment. This sludge is a rich source of lipids, the starting material for biodiesel. Most of sludge’s lipids come from bacteria living in it.
Kwon and his team used n-hexane to extract lipids from sludge pellets from a wastewater treatment plant in Suwon-City, South Korea. Compared to published yields of lipids from soybeans, the sludge produced 2,200 times more lipids per gram of feedstock. Sewage sludge is also a cheaper lipid source than soybeans, Kwon says. Each liter of lipids that the researchers extracted from sludge cost $0.03, while previously published data shows each liter from soybeans costs $0.80.
However, impurities including free fatty acids in the lipids extracted from sewage sludge would interfere with the conventional catalytic process for making biodiesel. So Kwon’s team developed a noncatalytic method that would work in the presence of free fatty acids and other impurities in the feedstock…
To test their idea, the team continuously fed methanol and the extracted sludge lipids into a reactor containing porous activated alumina and heated the reactor to 380 °C. Adding carbon dioxide to the reactor improved the reaction’s yield. The researchers’ method converted about 98% of the sludge lipids to biodiesel.
And there you have it. There’s nothing new about the idea of converting sewage sludge to energy: see this article for an early set of ideas on the topic. Furthermore, sewage sludge already has a cash value: you may be eating some of it right now. This new process maximizes the biofuel return, however, and makes it an attractive choice for future energy.
Will the day come when solar-powered home centrifuges generate biofuel from every toilet in the household? Well, it’s certainly no less likely to happen than, say, a national power infrastructure that would allow everyone in America to charge their Volt or Leaf on 220volt juice without browning-out the whole country every evening.