Rhamnolipids turn sewage into biodiesel

A new study by researchers in China has shown that rhamnolipids can help turn sewage into hydrogen and biodiesel, Chemical & Engineering News (C&EN) reported on 10 February.

Rhamnolipids are surfactants named for their rhamnose sugar groups and fatty acid tails.

Researchers at the Harbin Institute of Technology and the Northeast Agricultural University in Harbin, China, took waste-activated sludge – made from raw sewage treated with oxygen to stabilise its microbe populations – from a treatment plant in Harbin.

After putting the mixture through a sieve to remove large particles, the sludge was heated and – using fermentation – bacteria was left to produce hydrogen. Microalgae was then added to generate lipids for use in biofuel production.

The effects of nine surfactants were also tested on the process, with rhamnolipids creating the best environment for the microalgae and the sludge’s bacteria to generate fuels, C&EN wrote.

The researchers speculated that the rhamnolipids’ hydrophilic and hydrophobic groups reduced the surface tension of the waste-activated sludge and the macromolecules contained within it, the report said. This could have helped break down the waste’s organic matter, making vital nutrients more accessible for the hydrogen-producing bacteria to digest. In addition, the surfactant helped biodiesel output as the microalgae fed on the fermentation solution produced by the bacteria.