Make way for mushi!

Artificial wetlands known as "mushi" are being trialled as organic waterway-cleaning devices in the Royal Botanic Gardens in Melbourne, thanks to a unique collaboration between Arup, Studio Edwards and Swinburne University of Technology.

The world-first experiment involves three floating wetlands, constructed in a series of interlocking triangular-shaped modules about 80cm in diameter, that are composed of mycelium (fungi roots) and organic waste.

Arup Environmental Engineer Alex Reily said they were looking for an all-organic alternative to plastic-made floating wetlands.

“We were looking for ways to replace plastic in waterways: floating wetlands are a proven technology to help clean water but the traditional way of producing them, using plastic, creates other contamination issues when it inevitably degrades,” he said.

“The objective was to find an alternative to plastics using organic matter and waste to produce a product which would become a habitat for wildlife and allow the plants to absorb pollutants in the water.”

The foam-like "mushi" structure is planted with native wetland species, creating a habitat for fauna and insects, while underneath the plant roots absorb excess nitrogen and phosphorous from the waterway.

Swinburne researchers Canhui Chen, Daniel Prohasky and research assistant Joshua Salisbury-Carter contributed to the artificial wetland's structural design and fabrication.

“The Swinburne team we were approached by Arup and Studio Edwards because of our previous research in design and fabrication of the mycelium composite,” Chen said.

“The world is facing very significant environmental challenges and the building industry accounts for nearly 40% of the annual emissions. Therefore, we have been working on utilising organic materials that will not harm the environment when the structure’s life cycle is complete.”

Chen said the research team has been investigating mycelium composite due to its robust structure and because it requires little energy to produce, but the re-use of organic waste is also important, too.

“Mycelium requires a substrate to grow it. We use agricultural or industry by-products. We wanted to reuse materials that would otherwise go to waste. We can use sawdust, which is from the timber mill, and other cellular based agricultural waste, such as corn husks,” he said.

“It's both growing a new material while also avoiding further landfill with those left-over organic materials. The objective was to grow the structure, rather than manufacture it.”

Chen said the mycelium digest the organic material, colonising and binding the fibres together, creating the all-organic wetland platform.

“We're creating a little Islands, effectively, that floats. Plants and birds can live on it, so it’s great for habitat, but the root systems of the plants also help to purify the water below,” Chen said.

The research team will be monitoring and assessing the wetland experiment over the next three months.

“I will be examining how the material degenerates in terms of structural capacity, how it deals with the weather," Chen said. "But there will also be monitoring of its effect on bird and frog species too.”

Royal Botanic Gardens Victoria Director and Chief Executive Tim Entwisle said he looks forward to seeing how the experiment unfolds, as it may be of ongoing use to the gardens established waterways.

“I’m always happy to trial environmentally sensitive ways to manage the Gardens, and I look forward to seeing the results,” he said.

"This technology could be a good complement to our working wetlands system, which currently harvests stormwater from surrounding streets.”