Stormwater (rainwater that falls on hard areas such as roads) washes away heavy metal ions that pollute the water bodies. Textiles covered with fungal biomass can be flexible and cost-efficient solution for purification.
After a dry spell, the rain begins to fall. It strikes down the swirling dust on the roads and washes it away, pulling chrome released from the crash barriers with it. Leaching out copper. Zink and lead from the traffic.
The runnels join into streams, where the heavy metal concentrations suddenly spike. But after a while, they drop back to normal again; the bottom of the stream is lined with a fabric covered with fungi, that form an active surface where chemical reactions pull the heavy metal ions from the water and bind them.
Inspired by the Indonesian cuisine
”The fungus is used in Indonesian cooking”, says Nils-Krister Persson at WaterWeave, associate professor and Research Manager at the Smart Textiles Technology Lab.
”There is a dish in Indonesia called tempeh – soy beans that are fermented with an edible mould – and that is the fungus we are using. Obviously, we want a non-toxic material.” WaterWeave grows the fungus on a textile surface, woven in the natural material jute. The real innovation is the combination of textile and biotech:
”It is well known that fungi can absorb metals; from time to time, alarming levels of heavy metals in edible mushrooms are reported. We could probably do what we do with penny bun or common mushrooms too, although we have not tried that. But I have never heard of anyone else putting fungus on a fabric”, Nils-Krister Persson says.
”If we used free-flowing fungi, we would have to come up with some way of recovering them; we want to immobilize them on the surface of the fabric. Since the material is rather fluffy, we also get a large active surface and a lot of chemical reactions”.
An artificial, removable wetland
Thanks to the fabric, large surfaces can be covered cheaply. It also makes the solution portable; the fabric can be rolled up and transported to the site in need of treatment, and then removed again once the purification is finished or the material is saturated. The metals can then be disposed of in a controlled fashion.
”There a many different textile constructions, and we have found that the waffle weave texture works well. It is used in kitchen towels, for instance, and gives more surface area for absorption than a flat surface. Most importantly, the material has to be low-cost and simple to manufacture. Jute is used quite a lot in so-called geotextiles too, which for example are dug down in the ground to separate soils”, Nils-Krister Persson says.
The purification is not a filtering process. The water only has to get into contact with the active surface, where all the chemical reactions are taking place. This means that the technology works with both still and streaming waters.
”You can compare it to an artificial wetland. The contaminated water runs alongside the fabric, and it may take some distance to achieve purification. The process is called biosorption; some biomaterials are capable of concentrating other substances that are present in the water – in this case, heavy metal ions”, Nils-Krister Persson explains. When the fabric is deployed, the fungi are not alive. There are two reasons: first, the company wants to avoid spreading a living, foreign species. Second, the destruction improves the surface chemistry and absorbtion capacity.
”Using the fungus’s own metabolism would be another option – but that is not what we are doing here. This is all about surface structures in the fungal biomass: there is a carboxylic acid group there that absorbs heavy metals”, Nils-Krister Persson says.
A good-enough-solution to purify stormwater
The fabric-based solution from WaterWeave can remove a wide spectrum of heavy metals, for example copper, lead, chrome and cadmium. The efficiency of the uptake of each metal depends on a number of factors, such as the species of fungus and the pH of the water. But the goal is not to eliminate every trace of contaminants.
”The water will not be a hundred percent purified and we are not trying to produce drinking water. Nevertheless, it gives a substantial improvement over untreated water. You could call it a very affordable good-enough-solution: it is meant to be cheap and nature-like, just slightly better”, Nils-Krister Persson says.
WaterWeave imagines the fabrics deployed in the vicinity of landfills, or along highways to capture contaminants close to the source. The primary application is stormwater purification. Stormwater that flows over sealed surfaces in cities is not easily managed, and there are so few technologies available to handle the run-offs that municipalities and property owners have difficulty following the European regulations (read more in the article “Efficient floating filter for storm water purification“).
”But this is something that works. We are not quite in the commercial phase yet, but in the last couple of years we have moved from pure research to performing a lot of tests with customers. We are working with municipalities in the west of Sweden, trying the product in the field and finding out how to handle it in practice”, Nils-Krister Persson says.
Given the current lack of technology, fungal purification could likely do a lot for the environment. How much is strangely difficult to tell, though:
”Consider a city area somewhere. How much heavy metal run-off is there per year? Actually, nobody knows. Maybe there are one-off measures at certain industries or landfills, where there are continous measurements. But cities and municipalities generally have no data to provide a bigger picture. The differences in emission levels over time is huge, too”, Nils-Krister Persson explains.
For the time being, WaterWeave’s agenda is all about finding an efficient way of scaling up the production. One of the things being considered is whether waste flows from the food industry could be a valuable feedstock to grow the fungus from. Meanwhile, Nils-Krister Persson is also busy leading the Smart Textiles Technology Lab at the University of Borås. The innovation lab serves as a link between business and research, with one leg in the academic world, the other in industry.
”We have a broad range of projects in technical textiles, such as conducting non-metal fibers. We are doing research, but in close coordination with businesses. Most of the companies that approach us are not from the textile industry; everyone from the steel industry to construction companies have learned that textile materials and processes have the ability to solve a variety of technical problems in their respective fields. We are not helping Swedish textile industry there, we are helping all of Swedish industry”, Nils-Krister Persson concludes.
The article was published in December 2018.