Biodiesel from Sewage Sludge "Very Close" to Economical

Municipal sewage sludge is a "pre-processed" feedstock for biofuels production. It is relatively concentrated, compared to forestry and agricultural leavings and waste. Sewage is non-edible for most non-politicians and non-attorneys. It would seem to be an ideal feedstock for biofuels -- if only there were not so much oil and other fossil fuels waiting to be used!

Existing technology can produce biodiesel fuel from municipal sewage sludge that is within a few cents a gallon of being competitive with conventional diesel refined from petroleum, according to Dr. David Kargbo, with the US EPA’s Office of Innovation, Environmental Assessment & Innovation Division in Philadelphia, PA. His analysis was published online in the ACS journal Energy & Fuels. Sludge is the solid material left behind from the treatment of sewage at wastewater treatment plants.

...Municipal sewage sludge is gaining traction in the US and around the world as a lipid feedstock for biodiesel production. First, municipal sewage sludge contains significant concentrations of lipids derived from the direct adsorption of lipids onto the sludge. These energy-containing lipids include triglycerides, diglycerides, monoglycerides, phospholipids, and free fatty acids contained in the oils and fats. In addition, microorganisms used in the wastewater treatment process utilize organic and inorganic compounds in the wastewater as a source of energy, carbon, and nutrients. The cell membrane of these microorganisms is a major component of sewage sludge and is composed primarily of phospholipids. It is estimated at 24% to 25% of dry mass of the cell and yields about 7% oil from the dried secondary sludge. Other studies have demonstrated that up to 36.8 wt % of the dry sludge is comprised of fatty acids and steroids. With the fatty acids from sludge predominantly in the range of C10 to C18, these are excellent for the production of biodiesel.

—Kargbo 2010
Other potential benefits of using sludge as a feedstock are:

It’s plentiful. In the US alone, approximately 6.2 million dry metric tons of sludge is produced annually by wastewater treatment facilities.
Sludge management is a formidable environmental challenge. Biodiesel production from sludge as a viable alternative to land disposal could help to solve both energy and environmental problems.
Capacity. Studies show that integrating lipid extraction processes in 50% of all existing municipal wastewater treatment plants in the US and transesterification of the extracted lipids could produce approximately 1.8 billion gallons of biodiesel, which is roughly 0.5% of the yearly national petroleum diesel demand.
However, he notes, sludge biodiesel also faces significant challenges, including:

• Collecting the sludge.

• Maintaining product quality.

• Soap formation and product separation.

• Bioreactor design.

• Pharmaceutical chemicals in sludge.

• Regulatory concerns.

• Economics of biodiesel production.

• Determining how best to collect the different fractions (primary and secondary) and treat them for maximum lipids extraction is a major challenge. To accelerate biodiesel production, cosolvents and high shear mixing have been proposed, he notes, but there is very little information on the cost-effective means of increasing lipid solubility.GCC

The global economy is quite sensitive to any kind of shock. Low economic activity leads to low demand for transportation fuels, leading to low oil prices.

The fact that the Earth is floating in methane of several types, and other fossil fuels, does not help the economic equation -- in terms of making biofuels economical. And yet there may be many special niches where the feedstock for particular biofuel processes can actually lead to economical biofuels production -- fully competitive with existing petro-fuels.

Should that be the case, we should see a growing downward resistance to increases in oil and fossil fuels prices, as technology for making biofuels steadily improves.