The sewage-to-biofuel field is attracting interest from major companies like Waste Management and startups like InfoSpi, which are betting that renewable sewage biodiesel can become competitive with petroleum diesel on price. Now the American Chemical Society has published an article* on sewage biodiesel that bears out this promise. The article estimates a cost of $3.11 to produce a gallon of biodiesel from municipal sewage sludge, compared to $3.00 for petroleum diesel.
The article notes some hurdles to overcome in order to push the price lower. Despite these reservations, considering the potential savings to municipalities in terms of reduced sewage sludge disposal costs, and the savings to the national economy in terms of eliminating the chance of another catastrophe on the scale of the British Petroleum oil spill in the Gulf of Mexico, cost-competitive biodiesel from sewage sludge sure looks sweet.
A Word about Sewage Sludge
Raw sewage sludge is a liquid heavy with suspended solids that have been separated out of sewage during the treatment process. In municipal sludge, the solids are primarily organic matter from you can guess where (industrial sludge from factories is a different cup of tea). Modern sewage treatment plants convert the raw sludge into an inert, processed substance by using bacteria to break down the organic material. The processed sludge can then be dewatered and used as a soil enhancer, similar to any other yard material you might pick up at the local nursery.
Sewage Biodiesel! Errr, Not so Fast
Waste Management is a global industry giant, so its ambitious sewage biofuel project provides some indication that sewage biodiesel has a bright future; likewise for InfoSpi, which has planned a string of sewage-to-biofuel plants in the Southeastern U.S. The American Chemical Society article notes, though, that biodiesel from sewage for the mass market has some serious obstacles to overcome. In addition to developing a cost-effective refining process, other factors include collecting the feedstock (the sludge), ensuring quality control, and addressing regulatory issues involving traces of pharmaceuticals and other contaminants that may occur in municipal sludge.
Sewage to Biodiesel – The Big Picture
In the context of the Gulf oil spill, sewage sludge does have a significant advantage over petroleum as a diesel feedstock. Where harvesting petroleum creates new risk and has caused catastrophic environmental and public health damage with consequent costs, “harvesting” sludge is done for precisely the opposite reason: to reduce risk and prevent harm that can lead to extreme economic burdens. Vast quantities of sludge are already transported out of cities and disposed elsewhere, often at great expense. Sewage biodiesel offers the potential of defraying these costs, so even if biodiesel users pay slightly more at the pump, in the big picture that could be offset by the savings to sewage ratepayers. After all, it’s high time to take a good look at the big picture when comparing the cost of fossil fuels and renewable fuels.
*Note: The author of the article is David M. Kargbo of U.S. EPA Region III. Mr. Kargbo specifies that the article represents his opinion and does not reflect EPA policy.
Image: Biodiesel by Laboratorio en Movimiento on flickr.com.