When you hear sewage waste, green roofs is probably not the first thing you think about. Yet it seem that compressed non-recyclable sewage waste, such as used tampons, sanitary pads, and wet wipes, provides an excellent roofing material. Three students won with this idea the BlueCity Circular Challenge in Rotterdam, the Netherlands.

The only thing you should flush down the toilet, aside from your business, is toilet paper, yet a lot of other waste is left behind in the rosters when sewage water is cleaned. 85 per cent of this waste consists of wet wipes, which, despite commonly advertising they are flushable, do not dissolve. Other things flushed all too often are feminine hygiene products such as tampons, and even condoms make their way into the sewer.

Jelle Scharff, Bas van der Leeden, and Anne Korthals, in collaboration with District Water Control Board Schieland and De Krimpenerwaard, had to come up with a sustainable solution for non-recyclable sewage waste, which is otherwise burned.

Because of the enormous amounts of stone and concrete in cities, water is flushed away rather than absorbed, while climate change causes heavier showers and longer periods of drought. Green roofs can help retain water, to reduce the burden on the sewer and save water for drier periods.

Hygiene products often contain super-absorbing polymers, which, although bad for the environment, are designed to absorb a lot of fluid while remaining lightweight. When compressed into panels, this waste creates a perfect base for plants to grow on, for instance to use for green roofs.

The team won 5,000 euros to create a start-up. In the next few months, they will test the effects, before bringing the material to the market.

For other materials that come from the sewer, click here and here.

Photos: Jelle Scharff (via NOS) / Wikimedia / Pxhere