Engineered Microbes Created to Clean Biodiesel Waste

Gemma Reguera (Michael Steger, Michigan State Univ.)

21 May 2014. Microbiologists at Michigan State University in East Lansing created a process with two types of genetically-engineered bacteria that work together to clean up the waste water in the production of biodiesel, and generate ethanol as a byproduct. The team led by Michigan State’s Gemma Reguera published its findings online earlier this month in the journal Environmental Science and Technology (paid subscription required).

Biodiesel is made from natural oil feedstocks, such as excess cooking oil, but it produces as well waste water with glycerin — a toxic substance also known as glycerol — that needs to be stored, transported, or processed into less harmful products. This need to deal with glycerol in the waste water adds considerable expense to the production costs of biodiesel. And most current processes for handling the waste glycerol require use of fossil fuels, thus negating some of biodiesel’s environmental benefits.

The process devised by Reguera’s lab uses a microbial electrolysis cell, a type of fuel cell that captures the electrochemical processes of two engineered bacteria. One of the bacteria is a form of Geobacter sulfurreducens, which in its natural state can digest and metabolize organic compounds and metals, as well as generate an electric current. In previous work, Reguera and colleagues engineered the bacterium to boost the electrical conductivity in their nanoscale filaments, which the researchers applied to cleaning up nuclear waste and improving the efficiency of biofuel production.

In this biodiesel clean-up process, Geobacter sulfurreducens are paired with another bacterium in the microbial electrolysis cell, Clostridium cellobioparum, which the researchers engineered to ferment glycerol in the waste water. The fermented glycerol becomes ethanol, along with byproducts that serve as feedstocks for Geobacter bacteria.

“One bacterium ferments the glycerol waste to produce bioethanol, which can be reused to make biodiesel from oil feedstocks,” says Reguera in a university statement.  “Geobacter removes any waste produced during glycerol fermentation to generate electricity. It is a win-win situation.” The electricity in this case is captured in the fuel cells to generate hydrogen, which boosts the efficiency of the fuel cells.

Michigan State filed for a patent on the process with Reguera, and the paper’s co-authors Allison Speers and Jenna Young listed as inventors. In addition, the lab is producing prototype fuel cells, funded by a grant from Michigan’s Translational Research and Commercialization program. The researchers say they’re discussing further commercialization of the process with MBI, a program of the Michigan State Foundation that helps bridge the gap in biotechnology between lab research and industrial scale.

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