Yeast surfactant cleans up heavy metals

A NATURAL biosurfactant produced by a species of yeast could be useful for the removal of heavy metal contamination from soil and wastewater, according to researchers in Brazil.

Heavy metals such as lead, zinc and cadmium are common pollutants in industrial areas with lots of metal-working, mining or smelting activity, and remediating such sites can be difficult. Conventional methods, which use acid treatments, metal chelating agents, and chemical surfactants are not always entirely effective and can be toxic to the environment.

Leonie Sarubbo, from the Universidade Católica de Pernambuco, and her team, had previously discovered that the biosurfactant produced by the yeast Candida sphaerica was effective at cleaning up organic pollutants such as motor oil, and decided to test it on heavy metals. The biosurfactant is anionic, and can therefore bind with the positively-charged metal ions, and in addition, it is a natural product which is non-toxic to the environment and can biodegrade easily.

The team used two types of industrial waste as substrates to produce the biosurfactants – groundnut oil refinery residue and corn steep liquor, providing a source of lipids and sugars respectively. They incubated the yeast cells with the substrates at 28?C for 144 h, before isolating the biosurfactant through a combination of centrifugation, acidification and washing with methanol. The biosurfactant was tested on samples of soil obtained from an automotive battery industrial area, containing iron, lead and zinc.

Sarrubbo and the team found that fresh biosurfactant could remove 95% of iron, 90% of zinc and 79% of lead. Once treated to precipitate the heavy metals, recycled biosurfactant could remove 70% of iron, 62% of zinc and 45% of lead. The extraction levels are higher than for the conventional, and more dangerous agents HCl and NaOH.

The researchers say that the biosurfactants could be used with other conventional remediation techniques such as soil extraction and thermal treatment. The next step will be to investigate the effects of other factors, such as of soil composition, metal distribution and the presence of other contaminants.

Process Safety and Environmental Protection DOI: 10.1016/j.psep.2016.05.010