While biodiesel provides a cleaner-burning alternative to petroleum diesel, it produces CO₂ and hazardous wastewater during manufacturing, requiring extra steps to achieve sustainability. A diagnostic study led by University of Michigan researchers works to improve a process that captures CO₂ while treating biodiesel wastewater and produces valuable co-products like fuels and green chemicals.

During biodiesel production, fats—like vegetable oils, animal fats or recycled restaurant grease—are transformed into fuel through a process called transesterification. With the help of a catalyst, an alcohol (typically methanol) breaks the bonds in the fat molecules to create glycerol and long, chain-like molecules called fatty acid esters.

The fatty acid esters, which resemble petroleum diesel’s molecular structure, become biodiesel while the glycerol goes into the wastewater as a byproduct. If left untreated, glycerol can pollute natural water resources by depleting oxygen levels, suffocating fish and other organisms.