Coffee is one of the most popular beverages in the world. Though some people cannot stand it, others need it to function properly. Some like it black and strong, others can only tolerate it with milk and sugar. But no matter how you like your cuppa, making it will always leave you with leftover coffee grounds. Some companies make products or floor covering out of these grounds. They are also used to make biofuel, animal food, or you can just use them as compost (they are excellent to grow mushrooms on). Researchers from the Istituto Italiano di Tecnologia (IIT) in Genoa have developed foam made from coffee grounds that can purify water from dangerous heavy metals, such as lead and mercury.

It was already known that powder made from coffee grounds can be used to rid water of harmful heavy metals, but then you need to filter the water. The foam, which works as a filter, kills two birds with one stone.

Once the coffee grounds have been used – the inventors are Italian, after all – they are dried and ground to an even finer powder. This is then mixed with silicone elastomer and sugar, until it hardens. The mixture is then dipped into water, so that the sugar melts away and a foam-like material is left. The amount of silicone (40 per cent) is so low that the sponge is entirely biodegradable.

When a piece of foam is put into heavy metal-contaminated water over a period of 30 hours, the coffee sponge sucks up almost all the metal. After use, the sponge can be washed and reused without losing quality, or thrown away.

The sponge is most effective in non-moving water, taking out 99 per cent of the metals, as opposed to 60 to 70 per cent in running water. Harmless organic matter can pass through the foam.

The foam could help clean contaminated water, and thus help reduce things like lead poisoning and Minamata disease, which is caused by mercury. So you can take another cup of coffee without feeling guilty; the grounds might save a life, after all.

Photos material: IIT