Sabine Sané, a doctoral student in the Department of Microsystems Engineering (IMTEK) at the University of Freiburg, has developed a concept that shows how micropollutants can be degraded in wastewater and how the latter can serve as a valuable source of raw materials. She is one of four researchers who have been awarded the 2014 Huber Technology Prize “Future Water” with a purse of 10,000 euros. Her concept is based on an enzyme that is secreted by the turkey tail fungus Trametes versicolor. This enzyme, known as laccase, has been shown to efficiently degrade pollutants and increase the performance of biofuel cells.
Wastewater contains a wide range of pollutants, including heavy metals, synthetic organic compounds, viruses and bacteria. Micropollutants are pollutants that occur in concentrations of less than a few micogrammes per litre. Technological progress has improved the detection of such small concentrations of substances. “The degradation of micropollutants has not previously been an issue, particularly because technologies that can detect them have only recently become available,” says Sané, doctoral student in the IMTEK’s Bioelectrochemical Systems research group.
Drug residues or hormones from private households are among those compounds that wastewater plants are unable to degrade. “Many women take hormone-based contraceptives, which are partially excreted with urine,” says Sané. Ibuprofen and diclofenac are synthetic chemicals that cannot be broken down, and instead accumulate in the ecosystem. The same thing happens with X-ray contrast agents used in hospitals and antibiotics used in industrial livestock farming.
Compounds that cannot be broken down in wastewater plants accumulate in aquatic ecosystems, and threshold limits need to be put in place in order to reduce the negative effects on the environment. Antidepressant drugs are known to impact the metabolism and behaviour of fish: it makes them more aggressive rather than happier. Oestrogens have been shown to render fish infertile.
However, a fungus known as Trametes versicolor or turkey tail fungus has been shown to change the situation. This particular fungus is a polypore fungus commonly found on European beech. The fungus degrades fallen trees and is also able to break down lignin. These processes are achieved by the fungal enzyme laccase, which catalyses the oxidation of aromatic compounds concomitantly with the reduction of oxygen to water. The enzyme is extremely stable and withstands high temperatures and solvents. The fungus has been used in research for a number of years, and can be cultivated in a similar way to bacteria.
The fungal laccase enzyme can be used to break down pollutants into their constituents. “Laccase oxidises micropollutants and is far from selective,” says Sané. “It is completely non-specific and can use all kinds of substrates.” Compared to ozone or activated charcoal for the treatment of wastewater, the fungus appears to be the smarter alternative. Activated charcoal is produced from carbonaceous materials and needs to be disposed of after use; the method involving ozone consumes a lot of energy and requires trained personnel to deal with the large number of dangerous products generated. Nevertheless, the production of laccase tends to be rather expensive as it needs to be expressed in and isolated from microorganisms.
Sané’s project therefore involved looking for a cheaper way to produce laccase. She decided to use the crude culture supernatant without further treatment. “When the fungus is grown on a liquid nutrient culture, it floats on top of it just like mould on apple juice.” In this case, Trametes appears to secrete more than just laccase. “The fungus secretes the entire enzyme complex into the liquid medium and we are using the crude supernatant for the degradation of pollutants without further purification.”
This is only part of the concept for which Sané and three other up-and-coming scientists were recently awarded the 2014 Huber Technology Prize: Future Water for projects involving “Energy and Resources from Wastewater”. The objective of this new prize is to encourage up-and-coming scientists to develop concepts that contribute to protecting the environment and saving resources. The second part of Sané’s concept foresees the use of the fungus for improving the performance of a hybrid microbial-enzymatic fuel cell.
Department of Microsystems Engineering - IMTEK
University of Freiburg
Tel.: +49 (0)761 / 203-73262